Phononic and Photonic Nanostructures

Group Leader: Clivia M. Sotomayor Torres

Publications

2021

  • Antibacterial activity testing methods for hydrophobic patterned surfaces

    Perez-Gavilan A., de Castro J.V., Arana A., Merino S., Retolaza A., Alves S.A., Francone A., Kehagias N., Sotomayor-Torres C.M., Cocina D., Mortera R., Crapanzano S., Pelegrín C.J., Garrigos M.C., Jiménez A., Galindo B., Araque M.C., Dykeman D., Neves N.M., Marimón J.M. Scientific Reports; 11 (1, 6675) 2021. 10.1038/s41598-021-85995-9. IF: 3.998

    One strategy to decrease the incidence of hospital-acquired infections is to avoid the survival of pathogens in the environment by the development of surfaces with antimicrobial activity. To study the antibacterial behaviour of active surfaces, different approaches have been developed of which ISO 22916 is the standard. To assess the performance of different testing methodologies to analyse the antibacterial activity of hydrophobic surface patterned plastics as part of a Horizon 2020 European research project. Four different testing methods were used to study the antibacterial activity of a patterned film, including the ISO 22916 standard, the immersion method, the touch-transfer inoculation method, and the swab inoculation method, this latter developed specifically for this project. The non-realistic test conditions of the ISO 22916 standard showed this method to be non-appropriate in the study of hydrophobic patterned surfaces. The immersion method also showed no differences between patterned films and smooth controls due to the lack of attachment of testing bacteria on both surfaces. The antibacterial activity of films could be demonstrated by the touch-transfer and the swab inoculation methods, that more precisely mimicked the way of high-touch surfaces contamination, and showed to be the best methodologies to test the antibacterial activity of patterned hydrophobic surfaces. A new ISO standard would be desirable as the reference method to study the antibacterial behaviour of patterned surfaces. © 2021, The Author(s).


  • Heat transport control and thermal characterization of low-dimensional materials: A review

    El Sachat A., Alzina F., Sotomayor Torres C.M., Chavez-Angel E. Nanomaterials; 11 (1, 175): 1 - 32. 2021. 10.3390/nano11010175. IF: 4.324

    Heat dissipation and thermal management are central challenges in various areas of science and technology and are critical issues for the majority of nanoelectronic devices. In this review, we focus on experimental advances in thermal characterization and phonon engineering that have drastically increased the understanding of heat transport and demonstrated efficient ways to control heat propagation in nanomaterials. We summarize the latest device-relevant methodologies of phonon engineering in semiconductor nanostructures and 2D materials, including graphene and transition metal dichalcogenides. Then, we review recent advances in thermal characterization techniques, and discuss their main challenges and limitations. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.


  • Injection locking in an optomechanical coherent phonon source

    Arregui G., Colombano M.F., Maire J., Pitanti A., Capuj N.E., Griol A., Martínez A., Sotomayor-Torres C.M., Navarro-Urrios D. Nanophotonics; 10 (2): 1319 - 1327. 2021. 10.1515/nanoph-2020-0592. IF: 7.491

    Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform. © 2021 Guillermo Arregui et al., published by De Gruyter.


  • Layered Nanocomposite 2D-TiO2 with Cu2O Nanoparticles as an Efficient Photocatalyst for 4-Chlorophenol Degradation and Hydrogen Evolution

    Alegría M., Aliaga J., Ballesteros L., Sotomayor-Torres C., González G., Benavente E. Topics in Catalysis; 64 (1-2): 167 - 180. 2021. 10.1007/s11244-020-01360-6. IF: 2.406

    New composites formed by layered hybrid TiO2(stearic acid) (LHTiO2) and, Cu2O nanoparticles were studied as photocatalysts that extend the response range to light visible for the evolution of hydrogen and the degradation of 4-chlorophenol. The results revealed that LHTiO2/Cu2O exhibited a clearly improved photocatalytic degradation, about 5.6 times faster than pristine TiO2, and hydrogen evolution of about 2.7 times higher than the TiO2 anatase. The enhanced photocatalytic activity can be assigned to the properties of the two-dimensional morphology, in sheets-like arrangement of LHTiO2, benefitting from the high exposure of surface, with more active sites available to improve matching with the surfaces of the Cu2O nanocrystals and significant reduction of migration distances of photogenerated carriers. In the photocatalytic degradation, a mechanism Z-scheme is supported, and in the photocatalytic evolution of hydrogen a mechanism type II band alignment is indicated. Photocatalytic reuse tests showed that stability and catalytic activity of LHTiO2/Cu2O were maintained for three cycles. Photoelectrochemical evaluation were performed through measurements of the photocurrent response and electrochemical impedance. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.


  • Optomechanical crystals for spatial sensing of submicron sized particles

    Navarro-Urrios D., Kang E., Xiao P., Colombano M.F., Arregui G., Graczykowski B., Capuj N.E., Sledzinska M., Sotomayor-Torres C.M., Fytas G. Scientific Reports; 11 (1, 7829) 2021. 10.1038/s41598-021-87558-4. IF: 3.998

    Optomechanical crystal cavities (OMC) have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of OMCs operating under ambient conditions as a sensor of submicrometer particles by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region. OMCs have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, viruses and bacteria. © 2021, The Author(s).


  • Quantifying the Robustness of Topological Slow Light

    Arregui G., Gomis-Bresco J., Sotomayor-Torres C.M., Garcia P.D. Physical Review Letters; 126 (2, 027403) 2021. 10.1103/PhysRevLett.126.027403. IF: 8.385

    The backscattering mean free path ζ, the average ballistic propagation length along a waveguide, quantifies the resistance of slow light against unwanted imperfections in the critical dimensions of the nanostructure. This figure of merit determines the crossover between acceptable slow-light transmission affected by minimal scattering losses and a strong backscattering-induced destructive interference when the waveguide length L exceeds ζ. Here, we calculate the backscattering mean free path for a topological photonic waveguide for a specific and determined amount of disorder and, equally relevant, for a fixed value of the group index ng which is the slowdown factor of the group velocity with respect to the speed of light in vacuum. These two figures of merit, ζand ng, should be taken into account when quantifying the robustness of topological and conventional (nontopological) slow-light transport at the nanoscale. Otherwise, any claim on a better performance of topological guided light over a conventional one is not justified. © 2021 American Physical Society.


  • Understanding the molecular basis of 5-ht4 receptor partial agonists through 3d-qsar studies

    Castro-Alvarez A., Chávez-ángel E., Nelson R. International Journal of Molecular Sciences; 22 (7, 3602) 2021. 10.3390/ijms22073602. IF: 4.556

    Alzheimer’s disease (AD) is a neurodegenerative disorder whose prevalence has an incidence in senior citizens. Unfortunately, current pharmacotherapy only offers symptom relief for patients with side effects such as bradycardia, nausea, and vomiting. Therefore, there is a present need to provide other therapeutic alternatives for treatments for these disorders. The 5-HT4 receptor is an attractive therapeutic target since it has a potential role in central and peripheral nervous system disorders such as AD, irritable bowel syndrome, and gastroparesis. Quantitative structure-activity relationship analysis of a series of 62 active compounds in the 5-HT4 receptor was carried out in the present work. The structure-activity relationship was estimated using three-dimensional quantitative structure-activity relationship (3D-QSAR) techniques based on these structures’ field molecular (force and Gaussian field). The best force-field QSAR models achieve a value for the coefficient of determination of the training set of R2 training = 0.821, and for the test set R2 test = 0.667, while for Gaussian-field QSAR the training and the test were R2 training = 0.898 and R2 test = 0.695, respectively. The obtained results were validated using a coefficient of correlation of the leave-one-out cross-validation of Q2LOO = 0.804 and Q2LOO = 0.886 for force-and Gaussian-field QSAR, respectively. Based on these results, novel 5-HT4 partial agonists with potential biological activity (pEC50 8.209– 9.417 for force-field QSAR and 9.111–9.856 for Gaussian-field QSAR) were designed. In addition, for the new analogues, their absorption, distribution, metabolism, excretion, and toxicity properties were also analyzed. The results show that these new derivatives also have reasonable pharmacokinetics and drug-like properties. Our findings suggest novel routes for the design and development of new 5-HT4 partial agonists. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.


2020

  • 2D Phononic Crystals: Progress and Prospects in Hypersound and Thermal Transport Engineering

    Sledzinska M., Graczykowski B., Maire J., Chavez-Angel E., Sotomayor-Torres C.M., Alzina F. Advanced Functional Materials; 30 (8, 1904434) 2020. 10.1002/adfm.201904434. IF: 16.836

    The central concept in phononics is the tuning of the phonon dispersion relation, or phonon engineering, which provides a means of controlling related properties such as group velocity or phonon interactions and, therefore, phonon propagation, in a wide range of frequencies depending on the geometries and sizes of the materials. Phononics exploits the present state of the art in nanofabrication to tailor dispersion relations in the range of GHz for the control of elastic waves/phonons propagation with applications toward new information technology concepts with phonons as state variable. Moreover, phonons provide an adaptable approach for supporting a coherent coupling between different state variables, and the development of nanoscale optomechanical systems during the last decade attests this prospect. The most extended approach to manipulate the phonon dispersion relation is introducing an artificial periodic modulation of the elastic properties, which is referred to as phononic crystal (PnC). Herein, the focus is on the recent experimental achievements in the fabrication and application of 2D PnCs enabling the modification of the dispersion relation of surface and membrane modes, and presenting phononic bandgaps, waveguiding, and confinement in the hypersonic regime. Furthermore, these artificial materials offer the potential of modifying and controlling the heat flow to enable new schemes in thermal management. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • A frequency-domain thermoreflectance method for measuring the thermal boundary conductance of a metal-polymer system

    Sandell S., Maire J., Chavez-Angel E., Sotomayor Torres C.M., He J. Proceedings - 2020 IEEE 8th Electronics System-Integration Technology Conference, ESTC 2020; (9229862) 2020. 10.1109/ESTC48849.2020.9229862. IF: 0.000

    The use of nanostructures in electronic devices has opened up a new field of challenges in thermal management, where standard thermal measurement techniques reach their limits. An especially challenging scenario is related to the thermal transport at interfaces between dissimilar materials. In these interfaces, a considerable thermal resistance arises. As the number of interfaces per area increases, the interface thermal resistance becomes a limiting factor in heat dissipation of the device, impeding the heat flow out of the device. In this work, we describe a contactless, optothermal method for measuring the thermal boundary conductance (TBC) of heterointerfaces, the frequency-domain thermoreflectance (FDTR) method. The method is demonstrated by measuring TBC between gold and polymethyl methacrylate (PMMA). By inserting a nickel nanofilm between gold and PMMA, the TBC increases from 59 MW/m2K to 139 MW/m2K. © 2020 IEEE.


  • Broadband Dynamic Polarization Conversion in Optomechanical Metasurfaces

    Zanotto S., Colombano M., Navarro-Urrios D., Biasiol G., Sotomayor-Torres C.M., Tredicucci A., Pitanti A. Frontiers in Physics; 7 (231) 2020. 10.3389/fphy.2019.00231. IF: 2.638

    Artificial photonic materials, nanofabricated through wavelength-scale engineering, have shown astounding and promising results in harnessing, tuning, and shaping photonic beams. Metamaterials have proven to be often outperforming the natural materials they take inspiration from. In particular, metallic chiral metasurfaces have demonstrated large circular and linear dichroism of light which can be used, for example, for probing different enantiomers of biological molecules. Moreover, the precise control, through designs on demand, of the output polarization state of light impinging on a metasurface, makes this kind of structures particularly relevant for polarization-based telecommunication protocols. The reduced scale of the metasurfaces makes them also appealing for integration with nanomechanical elements, adding new dynamical features to their otherwise static or quasi-static polarization properties. To this end we designed, fabricated and characterized an all-dielectric metasurface on a suspended nanomembrane. Actuating the membrane mechanical motion, we show how the metasurface reflectance response can be modified, according to the spectral region of operation, with a corresponding intensity modulation or polarization conversion. The broad mechanical resonance at atmospheric pressure, centered at about 400 kHz, makes the metasurfaces structure suitable for high-frequency operation, mainly limited by the piezo-actuator controlling the mechanical displacement, which in our experiment reached modulation frequencies exceeding 1.3 MHz. © Copyright © 2020 Zanotto, Colombano, Navarro-Urrios, Biasiol, Sotomayor-Torres, Tredicucci and Pitanti.


  • Enhancement of thermal boundary conductance of metal–polymer system

    Sandell S., Maire J., Chávez-ángel E., Torres C.M.S., Kristiansen H., Zhang Z., He J. Nanomaterials; 10 (4, 670) 2020. 10.3390/nano10040670. IF: 4.324

    In organic electronics, thermal management is a challenge, as most organic materials conduct heat poorly. As these devices become smaller, thermal transport is increasingly limited by organic–inorganic interfaces, for example that between a metal and a polymer. However, the mechanisms of heat transport at these interfaces are not well understood. In this work, we compare three types of metal–polymer interfaces. Polymethyl methacrylate (PMMA) films of different thicknesses (1–15 nm) were spin-coated on silicon substrates and covered with an 80 nm gold film either directly, or over an interface layer of 2 nm of an adhesion promoting metal—either titanium or nickel. We use the frequency-domain thermoreflectance (FDTR) technique to measure the effective thermal conductivity of the polymer film and then extract the metal–polymer thermal boundary conductance (TBC) with a thermal resistance circuit model. We found that the titanium layer increased the TBC by a factor of 2, from 59 × 106 W·m−2·K−1 to 115 × 106 W·m−2·K−1, while the nickel layer increased TBC to 139 × 106 W·m−2·K−1. These results shed light on possible strategies to improve heat transport in organic electronic systems. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.


  • Ferromagnetic Resonance Assisted Optomechanical Magnetometer

    Colombano M.F., Arregui G., Bonell F., Capuj N.E., Chavez-Angel E., Pitanti A., Valenzuela S.O., Sotomayor-Torres C.M., Navarro-Urrios D., Costache M.V. Physical Review Letters; 125 (14, 147201) 2020. 10.1103/PhysRevLett.125.147201. IF: 8.385

    The resonant enhancement of mechanical and optical interaction in optomechanical cavities enables their use as extremely sensitive displacement and force detectors. In this Letter, we demonstrate a hybrid magnetometer that exploits the coupling between the resonant excitation of spin waves in a ferromagnetic insulator and the resonant excitation of the breathing mechanical modes of a glass microsphere deposited on top. The interaction is mediated by magnetostriction in the ferromagnetic material and the consequent mechanical driving of the microsphere. The magnetometer response thus relies on the spectral overlap between the ferromagnetic resonance and the mechanical modes of the sphere, leading to a peak sensitivity of 850 pT Hz-1/2 at 206 MHz when the overlap is maximized. By externally tuning the ferromagnetic resonance frequency with a static magnetic field, we demonstrate sensitivity values at resonance around a few nT Hz-1/2 up to the gigahertz range. Our results show that our hybrid system can be used to build a high-speed sensor of oscillating magnetic fields. © 2020 American Physical Society.


  • Fracturing of Polycrystalline MoS2 Nanofilms

    Marianna Sledzinska, Gil Jumbert, Marcel Placidi, Alois Arrighi, Peng Xiao, Francesc Alzina, Clivia M. Sotomayor Torres Acs Applied Electronic Materials. 2 (4): 1169-1175; 2 (4): 1169 - 1175. 2020. 10.1021/acsaelm.0c00189. IF: 0.000


  • Graphene related materials for thermal management

    Fu Y., Hansson J., Liu Y., Chen S., Zehri A., Samani M.K., Wang N., Ni Y., Zhang Y., Zhang Z.-B., Wang Q., Li M., Lu H., Sledzinska M., Torres C.M.S., Volz S., Balandin A.A., Xu X., Liu J. 2D Materials; 7 (1, 012001) 2020. 10.1088/2053-1583/ab48d9. IF: 7.140

    Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field. © 2019 IOP Publishing Ltd.


  • High-Frequency Mechanical Excitation of a Silicon Nanostring with Piezoelectric Aluminum Nitride Layers

    Pitanti A., Makkonen T., Colombano M.F., Zanotto S., Vicarelli L., Cecchini M., Griol A., Navarro-Urrios D., Sotomayor-Torres C., Martinez A., Ahopelto J. Physical Review Applied; 14 (1, 014054) 2020. 10.1103/PhysRevApplied.14.014054. IF: 4.194

    A strong trend for quantum-based technologies and applications follows the avenue of combining different platforms to exploit their complementary technological and functional advantages. Micro and nanomechanical devices are particularly suitable for hybrid integration due to the ease of fabrication at multiscales and their pervasive coupling with electrons and photons. Here, we report on a nanomechanical technological platform where a silicon chip is combined with an aluminum nitride layer. Exploiting the AlN piezoelectricity, surface acoustic waves (SAWs) are injected in the Si layer where the material has been locally patterned and etched to form a suspended nanostring. Characterizing the nanostring vertical displacement induced by the SAW, we find an external excitation peak efficiency in excess of 500 pm/V at 1-GHz mechanical frequency. Exploiting the long-term expertise in silicon photonic and electronic devices as well as the SAW robustness and versatility, our technological platform represents a candidate for hybrid quantum systems. © 2020 American Physical Society.


  • High-temperature silicon thermal diode and switch

    Kasprzak M., Sledzinska M., Zaleski K., Iatsunskyi I., Alzina F., Volz S., Sotomayor Torres C.M., Graczykowski B. Nano Energy; 78 (105261) 2020. 10.1016/j.nanoen.2020.105261. IF: 16.602

    A thermal rectifier/diode is a nonreciprocal element or system that enables preferential heat transport in one direction. In this work we demonstrate a single-material thermal diode operating at high temperatures. The diode is made of nanostructured silicon membranes exhibiting spatially and temperature-dependent thermal conductivity and, therefore, falling into the category of spatially asymmetric, nonlinear nonreciprocal systems. We used an all-optical state-of-the-art experimental technique to prove rectification along rigorous criteria of the phenomenon. Using sub-milliwatt power we achieve rectification of about 14%. In addition, we demonstrate air-triggered thermal switching and passive cooling. Our findings provide a CMOS-compatible platform for heat rectification and applications in energy harvesting, thermal insulation and cooling, as well as sensing and potentially thermal logic. © 2020 The Authors


  • Ion bombardment induced formation of self-organized wafer-scale GaInP nanopillar assemblies

    Visser D., Jaramillo-Fernandez J., Haddad G., Sotomayor Torres C.M., Anand S. Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics; 38 (1, 012801) 2020. 10.1116/1.5127265. IF: 1.351

    Ion sputtering assisted formation of nanopillars is demonstrated as a wafer-scale, lithography-free fabrication method to obtain high optical quality gallium indium phosphide (GaInP) nanopillars. Compared to binary materials, little has been reported on the formation of self-organized ternary nanostructures. Epitaxial (100) Ga0.51In0.49P layers lattice matched to GaAs were sputtered by nitrogen (N2) ions with relatively low ion beam energies (∼400 eV) to reduce ion bombardment induced damage. The influence of process parameters such as temperature, sputter duration, ion beam energy, and ion beam incidence angle on the pillar formation is investigated. The fabricated GaInP nanopillars have average diameters of ∼75-100 nm, height of ∼220 nm, and average density of ∼2-4 × 108 pillars/cm2. The authors show that the ion beam incidence angle plays an important role in pillar formation and can be used to tune the pillar shape, diameter, and spatial density. Specifically, tapered to near cylindrical pillar profiles together with a reduction in their average diameters are obtained by varying the ion beam incidence angle from 0° to 20°. A tentative model for the GaInP nanopillar formation is proposed based on transmission electron microscopy and chemical mapping analysis. μ-Photoluminescence and μ-Raman measurements indicate a high optical quality of the c-GaInP nanopillars. © 2019 Author(s).


  • Large thermoelectric power variations in epitaxial thin films of layered perovskite GdBaCo2O5.5±δwith a different preferred orientation and strain

    Chatterjee A., Chavez-Angel E., Ballesteros B., Caicedo J.M., Padilla-Pantoja J., Leborán V., Sotomayor Torres C.M., Rivadulla F., Santiso J. Journal of Materials Chemistry A; 8 (38): 19975 - 19983. 2020. 10.1039/d0ta04781c. IF: 11.301

    This work describes the growth of thin epitaxial films of the layered perovskite material GdBaCo2O5.5±δ(GBCO) on different single crystal substrates SrTiO3(STO), (LaAlO3)0.3(Sr2TaAlO6)0.7(LSAT) and LaAlO3(LAO) as an approach to study changes in the thermoelectric properties by means of the induced epitaxial strain. In addition to strain changes, the films grow with considerably different preferred orientations and domain microstructures: GBCO films on STO are purelyc-axis oriented (c⊥) with an average 0.18% in-plane tensile strain; GBCO on LSAT is composed of domains with a mixed orientation (c‖andc⊥) with an average 0.71% in-plane compressive strain; while on LAO it isb-axis oriented (c‖) with an average 0.89% in-plane compressive strain. These differences result in important cell volume changes, as well as in the orthorhombicity of thea-bplane of the GBCO structure, which in turn induce a change in the sign and temperature dependence of the thermopower, while the electrical conductivity remains almost unchanged. In general, compressively strained films show negativeSthermopower (n-type) while tensile strained films show a positiveS(p-type) at low temperatures, probing the adaptive nature of the GdBaCo2O5.5±δcompound. These results point to the spontaneous generation of oxygen vacancies to partially accommodate the epitaxial stress as the main cause for this effect. © The Royal Society of Chemistry 2020.


  • Nanoscale Mapping of Thermal and Mechanical Properties of Bare and Metal-Covered Self-Assembled Block Copolymer Thin Films

    Alexandros El Sachat, Jean Spièce, Charalambos Evangeli, Alexander James Robson, Martin Kreuzer, Maria R. Rodríguez-Laguna, Emigdio Chavez, Marianna Sledzinska, Clivia M. Sotomayor Torres, Oleg V. Kolosov, Francesc Alzina Acs Applied Polymer Materials; 2 (2): 487 - 496. 2020. 10.1021/acsapm.9b00924. IF: 0.000


  • Phonon bridge effect in superlattices of thermoelectric tinisn/hfnisn with controlled interface intermixing

    Heinz S., Angel E.C., Trapp M., Kleebe H.-J., Jakob G. Nanomaterials; 10 (6, 1239): 1 - 12. 2020. 10.3390/nano10061239. IF: 4.324

    The implementation of thermal barriers in thermoelectric materials improves their power conversion rates effectively. For this purpose, material boundaries are utilized and manipulated to affect phonon transmissivity. Specifically, interface intermixing and topography represents a useful but complex parameter for thermal transport modification. This study investigates epitaxial thin film multilayers, so called superlattices (SL), of TiNiSn/HfNiSn, both with pristine and purposefully deteriorated interfaces. High-resolution transmission electron microscopy and X-ray diffractometry are used to characterize their structural properties in detail. A differential 3ω-method probes their thermal resistivity. The thermal resistivity reaches a maximum for an intermediate interface quality and decreases again for higher boundary layer intermixing. For boundaries with the lowest interface quality, the interface thermal resistance is reduced by 23% compared to a pristine SL. While an uptake of diffuse scattering likely explains the initial deterioration of thermal transport, we propose a phonon bridge interpretation for the lowered thermal resistivity of the interfaces beyond a critical intermixing. In this picture, the locally reduced acoustic contrast of the less defined boundary acts as a mediator that promotes phonon transition. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.


  • Properties of nanocrystalline silicon probed by optomechanics

    Navarro-Urrios D., Colombano M.F., Maire J., Chávez-Ángel E., Arregui G., Capuj N.E., Devos A., Griol A., Bellieres L., Martínez A., Grigoras K., Häkkinen T., Saarilahti J., Makkonen T., Sotomayor-Torres C.M., Ahopelto J. Nanophotonics; 9 (16): 4819 - 4829. 2020. 10.1515/nanoph-2020-0489. IF: 7.491

    Nanocrystalline materials exhibit properties that can differ substantially from those of their single crystal counterparts. As such, they provide ways to enhance and optimize their functionality for devices and applications. Here, we report on the optical, mechanical and thermal properties of nanocrystalline silicon probed by means of optomechanical nanobeams to extract information of the dynamics of optical absorption, mechanical losses, heat generation and dissipation. The optomechanical nanobeams are fabricated using nanocrystalline films prepared by annealing amorphous silicon layers at different temperatures. The resulting crystallite sizes and the stress in the films can be controlled by the annealing temperature and time and, consequently, the properties of the films can be tuned relatively freely, as demonstrated here by means of electron microscopy and Raman scattering. We show that the nanocrystallite size and the volume fraction of the grain boundaries play a key role in the dissipation rates through nonlinear optical and thermal processes. Promising optical (13,000) and mechanical (1700) quality factors were found in the optomechanical cavity realized in the nanocrystalline Si resulting from annealing at 950°C. The enhanced absorption and recombination rates via the intragap states and the reduced thermal conductivity boost the potential to exploit these nonlinear effects in applications including Nanoelectromechanical systems (NEMS), phonon lasing and chaos-based devices. © 2020 Daniel Navarro-Urrios et al., published by De Gruyter, Berlin/Boston 2020.


  • Real-time Optical Dimensional Metrology via Diffractometry for Nanofabrication

    Whitworth G.L., Francone A., Sotomayor-Torres C.M., Kehagias N. Scientific Reports; 10 (1, 5371) 2020. 10.1038/s41598-020-61975-3. IF: 3.998

    Surface patterning technologies represent a worldwide growing industry, creating smart surfaces and micro/nanoscale device. The advent of large-area, high-speed imprinting technologies has created an ever-growing need for rapid and non-destructive dimensional metrology techniques to keep pace with the speed of production. Here we present a new real-time optical scatterometry technique, applicable at the mesoscale when optical inspection produces multiple orders of diffraction. We validate this method by inspecting multiple silicon gratings with a variety of structural parameters. These measurements are cross-referenced with FIB, SEM and scanning stylus profilometry. Finally, we measure thermally imprinted structures as a function of imprinting temperature in order to demonstrate the method suitable for in-line quality control in nanoimprint lithography. © 2020, The Author(s).


  • Self-organized synchronization of mechanically coupled resonators based on optomechanics gain-loss balance

    Djorwé P., Pennec Y., Djafari-Rouhani B. Physical Review B; 102 (15, 155410) 2020. 10.1103/PhysRevB.102.155410. IF: 3.575

    We investigate self-organized synchronization in a blue-detuned optomechanical cavity that is mechanically coupled to an undriven mechanical resonator. By controlling the strength of the driving field, we engineer a mechanical gain that balances the losses of the undriven resonator. This gain-loss balance corresponds to the threshold where both coupled mechanical resonators enter simultaneously into self-sustained limit cycle oscillations regime. This leads to rich sets of collective dynamics such as in-phase and out-of-phase synchronizations, depending on the mechanical coupling rate, the frequency mismatch between the resonators, and the external driving strength through the mechanical gain and the optical spring effect. Moreover, we show that the introduction of a quadratic coupling, which results from a quadratically coupling of the optical cavity mode to the mechanical displacement, enhances the in-phase synchronization. This work shows how phonon transfer can optomechanically induce synchronization in a coupled mechanical resonator array and opens up new avenues for phonon processing and novel memories concepts. © 2020 American Physical Society.


  • Thermal transport in nanoporous holey silicon membranes investigated with optically induced transient thermal gratings

    Ryan A. Duncan, Giuseppe Romano, Marianna Sledzinska, Alexei A. Maznev, Jean-Philippe M. Péraud, Olle Hellman, Clivia M. Sotomayor Torres, and Keith A. Nelson Journal of Applied Physics; 128 (235106) 2020. 10.1063/1.5141804.

    In this study, we use transient thermal gratings—a non-contact, laser-based thermal metrology technique with intrinsically high accuracy—to investigate room-temperature phonon-mediated thermal transport in two nanoporous holey silicon membranes with limiting dimensions of 120 nm and 250 nm, respectively. We compare the experimental results with ab initio calculations of phonon-mediated thermal transport according to the phonon Boltzmann transport equation (BTE) using two different computational techniques. We find that the calculations conducted within the Casimir framework, i.e., based on the BTE with the bulk phonon dispersion and diffuse scattering from surfaces, are in quantitative agreement with the experimental data and thus conclude that this framework is adequate for describing phonon-mediated thermal transport in silicon nanostructures with feature sizes of the order of 100 nm.


  • Thermoreflectance techniques and Raman thermometry for thermal property characterization of nanostructures

    Sandell S., Chávez-Ángel E., El Sachat A., He J., Sotomayor Torres C.M., Maire J. Journal of Applied Physics; 128 (13, 131101) 2020. 10.1063/5.0020239. IF: 2.286

    The widespread use of nanostructures and nanomaterials has opened up a whole new realm of challenges in thermal management, but also leads to possibilities for energy conversion, storage, and generation, in addition to numerous other technological applications. At the microscale and below, standard thermal measurement techniques reach their limits, and several novel methods have been developed to overcome these limitations. Among the most recent, contactless photothermal methods have been widely used and have proved their advantages in terms of versatility, temporal and spatial resolution, and even sensitivity in some situations. Among them, thermoreflectance and Raman thermometry have been used to measure the thermal properties from bulk materials to thin films, multilayers, suspended structures, and nanomaterials. This Tutorial presents the principles of these two techniques and some of their most common implementations. It expands to more advanced systems for spatial mapping and for probing of non-Fourier thermal transport. Finally, this paper concludes with discussing the limitations and perspectives of these techniques and future directions in nanoscale thermometry. © 2020 Author(s).


2019

  • A Self-Assembled 2D Thermofunctional Material for Radiative Cooling

    Jaramillo-Fernandez J., Whitworth G.L., Pariente J.A., Blanco A., Garcia P.D., Lopez C., Sotomayor-Torres C.M. Small; 15 (52, 1905290) 2019. 10.1002/smll.201905290. IF: 10.856

    The regulation of temperature is a major energy-consuming process of humankind. Today, around 15% of the global-energy consumption is dedicated to refrigeration and this figure is predicted to triple by 2050, thus linking global warming and cooling needs in a worrying negative feedback-loop. Here, an inexpensive solution is proposed to this challenge based on a single layer of silica microspheres self-assembled on a soda-lime glass. This 2D crystal acts as a visibly translucent thermal-blackbody for above-ambient radiative cooling and can be used to improve the thermal performance of devices that undergo critical heating during operation. The temperature of a silicon wafer is found to be 14 K lower during daytime when covered with the thermal emitter, reaching an average temperature difference of 19 K when the structure is backed with a silver layer. In comparison, the soda-lime glass reference used in the measurements lowers the temperature of the silicon by just 5 K. The cooling power of this simple radiative cooler under direct sunlight is found to be 350 W m−2 when applied to hot surfaces with relative temperatures of 50 K above the ambient. This is crucial to radiatively cool down devices, i.e., solar cells, where an increase in temperature has drastic effects on performance. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Ammonium hexadeca-oxo-heptavanadate microsquares. A new member in the family of the V7O16 mixed-valence nanostructures

    Navas D., Donoso J.P., Magon C., Sotomayor-Torres C.M., Moreno M., Lozano H., Benavente E., González G. New Journal of Chemistry; 43 (45): 17548 - 17556. 2019. 10.1039/c9nj02188d. IF: 3.069

    This paper presents a new mixed valence heptavanadate (NH4)2V7O16, obtained from a two-stage treatment in a single container of ammonium metavanadate with hexadecylamine in an acetic medium. The hydrolysis of the precursor under normal conditions leads to an intermediate, layered hybrid nanocomposite, V2O5/alkylamine, which after an in situ hydrothermal treatment is transformed almost quantitatively into an amine-free microcrystalline phase constituted by perfect square microparticles of (NH4)2V7O16. The analysis of composition, structure and morphology of the product points to a mixed valence vanadium oxide with a high content of V(iv) (approximately 73%). The microsquares have a tetragonal structure similar to that of BaV7O16, as well as to those proposed for the VOx/amine hybrid nanocomposite series: nanotubes, nano urchins and the compound (en)V7O16. The results suggest that all these phases belong to the V7O16 family, but that they differ in the amine content, the degree of reduction and the curvature of the network. The feasibility of obtaining flat nanostructures based on V7O16 without templates, beyond demonstrating the robustness of the structural unit V7O16 in networks with different degrees of reduction and curvatures, clarifies the role of alkylamines in this type of anti-entropic supramolecular process. First, the amine provides a stable platform that allows for an orderly reduction of the network under hydrothermal conditions and, when the medium favours the stability of the V-amine bond, the alkylamine contributes to the driving force that leads to the curving of the V-O network. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.


  • Anderson Photon-Phonon Colocalization in Certain Random Superlattices

    Arregui G., Lanzillotti-Kimura N.D., Sotomayor-Torres C.M., García P.D. Physical Review Letters; 122 (4, 043903) 2019. 10.1103/PhysRevLett.122.043903. IF: 9.227

    Fundamental observations in physics ranging from gravitational wave detection to laser cooling of a nanomechanical oscillator into its quantum ground state rely on the interaction between the optical and the mechanical degrees of freedom. A key parameter to engineer this interaction is the spatial overlap between the two fields, optimized in carefully designed resonators on a case-by-case basis. Disorder is an alternative strategy to confine light and sound at the nanoscale. However, it lacks an a priori mechanism guaranteeing a high degree of colocalization due to the inherently complex nature of the underlying interference processes. Here, we propose a way to address this challenge by using GaAs/AlAs vertical distributed Bragg reflectors with embedded geometrical disorder. Because of a remarkable coincidence in the physical parameters governing light and motion propagation in these two materials, the equations for both longitudinal acoustic waves and normal-incidence light become practically equivalent for excitations of the same wavelength. This guarantees spatial overlap between the electromagnetic and displacement fields of specific photon-phonon pairs, leading to strong light-matter interaction. In particular, a statistical enhancement in the vacuum optomechanical coupling rate, go, is found, making this system a promising candidate to explore Anderson localization of high frequency (∼20 GHz) phonons enabled by cavity optomechanics. The colocalization effect shown here unlocks the access to unexplored localization phenomena and the engineering of light-matter interactions mediated by Anderson-localized states. © 2019 American Physical Society.


  • Coherent generation and detection of acoustic phonons in topological nanocavities

    Arregui G., Ortíz O., Esmann M., Sotomayor-Torres C.M., Gomez-Carbonell C., Mauguin O., Perrin B., Lemaître A., García P.D., Lanzillotti-Kimura N.D. APL Photonics; 4 (3, 030805) 2019. 10.1063/1.5082728. IF: 4.383

    Inspired by concepts developed for fermionic systems in the framework of condensed matter physics, topology and topological states are recently being explored also in bosonic systems. Recently, some of these concepts have been successfully applied to acoustic phonons in nanoscale multilayered systems. The reported demonstration of confined topological phononic modes was based on Raman scattering spectroscopy [M. Esmann et al., Phys. Rev. B 97, 155422 (2018)], yet the resolution did not suffice to determine lifetimes and to identify other acoustic modes in the system. Here, we use time-resolved pump-probe measurements using an asynchronous optical sampling (ASOPS) technique to overcome these resolution limitations. By means of one-dimensional GaAs/AlAs distributed Bragg reflectors (DBRs) used as building blocks, we engineer high frequency (∼200 GHz) topological acoustic interface states. We are able to clearly distinguish confined topological states from stationary band edge modes. The generation/detection scheme reflects the symmetry of the modes directly through the selection rules, evidencing the topological nature of the measured confined state. These experiments enable a new tool in the study of the more complex topology-driven phonon dynamics such as phonon nonlinearities and optomechanical systems with simultaneous confinement of light and sound. © 2019 Author(s).


  • Crossover from ballistic to diffusive thermal transport in suspended graphene membranes

    El Sachat A., Köenemann F., Menges F., Del Corro E., Garrido J.A., Sotomayor Torres C.M., Alzina F., Gotsmann B. 2D Materials; 6 (2, 025034) 2019. 10.1088/2053-1583/ab097d. IF: 7.343

    We report heat transport measurements on suspended single-layer graphene disks with radius of 150-1600 nm using a high-vacuum scanning thermal microscope. The results of this study revealed a radius-dependent thermal contact resistance between tip and graphene, with values between 1.15 and 1.52 × 108 KW-1. The observed scaling of thermal resistance with radius is interpreted in terms of ballistic phonon transport in suspended graphene discs with radius smaller than 775 nm. In larger suspended graphene discs (radius >775 nm), the thermal resistance increases with radius, which is attributed to in-plane heat transport being limited by phonon-phonon resistive scattering processes, which resulted in a transition from ballistic to diffusive thermal transport. In addition, by simultaneously mapping topography and steady-state heat flux signals between a self-heated scanning probe sensor and graphene with 17 nm thermal spatial resolution, we demonstrated that the surface quality of the suspended graphene and its connectivity with the Si/SiO2 substrate play a determining role in thermal transport. Our approach allows the investigation of heat transport in suspended graphene at sub-micrometre length scales and overcomes major limitations of conventional experimental methods usually caused by extrinsic thermal contact resistances, assumptions on the value of the graphene's optical absorbance and limited thermal spatial resolution. © 2019 IOP Publishing Ltd.


  • Defects in nano-imprint lithography line patterns: Computational modelling and measurement accuracy

    Constantoudis V., Whitworth G., Kehagias N., Papavieros G., Sotomoyor Torres C.M., Gogolides E. Proceedings of SPIE - The International Society for Optical Engineering; 10958 (109581K) 2019. 10.1117/12.2523931.

    NIL patterns frequently suffer from the presence of defects such as missing lines or dots which degrade their properties and functionality. Due to their low density and nanosize, the measurement of their fraction is challenging nanometrology trade-off between resolution and measurement range. In this paper, we focus on the use of range-limited SEM images and explore the benefits of a computational modeling approach to simulate the measurement process and estimate the statistics and accuracy of the measurement of missing lines in patterns. The main questions we address have to do with the choice of the parameters available in the measurement process such as the number of acquired images, their magnification defining the lines included in images and the position (overlapped or not) at line pattern. The missing lines can have both uncorrelated and correlated positions in pattern. In the case of positive correlations, the defects are aggregated whereas in the opposite case of negative correlations they are arranged in periodic-like positions. We found that for uncorrelated defects, the critical parameter is the total number of lines included in the measurement process while the image position do not have any impact on the measurement accuracy. On the contrary, when correlations in defect positions are considered, the number of images and the number of lines per image differentiate their effects on the accuracy of the result while the arrangement of images along pattern also plays a crucial role in the measurement process. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.


  • Development of low-melting point molten salts and detection of solid-to-liquid transitions by alternative techniques to DSC

    Rodríguez-Laguna M.D.R., Gómez-Romero P., Sotomayor Torres C.M., Lu M.-C., Chávez-Ángel E. Solar Energy Materials and Solar Cells; 202 (110107) 2019. 10.1016/j.solmat.2019.110107. IF: 6.019

    The ‘Solar salt’ (60% NaNO3-40% KNO3, wt. %) is the most used heat transfer and storage material in high temperature CSP systems. The main drawback is its high melting temperature of 228 °C, which requires extra-energy to keep it in the liquid state and avoid damage to pipes at low temperatures. Multi-component salts are combinations of different cations and anions. The difference in size of the ions hinders the crystallization of the material and provides lower melting temperatures. Multi-component salts are considered in this study to replace simpler combinations, such as binary and ternary eutectic mixtures. Herein, we report on two novel six-component nitrates with a melting temperature of 60–75 °C and a thermal stability up to ~500 °C under a linear heating program in N2 atmosphere. Properties such as the thermal conductivity in solid and molten state, heat capacity and vibrational spectra were evaluated. The study of the thermal behaviour of these materials using differential scanning calorimetry was insufficient, hence alternative and complementary techniques were used, such as: the three-omega technique, optical transmission and Raman spectroscopy. Multi-component salts were found to solidify as amorphous solids even at slow cooling rates and water was found to behave as a catalyst of crystallization. © 2019 Elsevier B.V.


  • Enhanced thermoelectric properties of lightly Nb doped SrTiO3 thin films

    Bhansali S., Khunsin W., Chatterjee A., Santiso J., Abad B., Martin-Gonzalez M., Jakob G., Sotomayor Torres C.M., Chávez-Angel E. Nanoscale Advances; 1 (9): 3647 - 3653. 2019. 10.1039/c9na00361d. IF: 0.000

    Novel thermoelectric materials developed for operation at room temperature must have similar or better performance along with being as ecofriendly as those commercially used, e.g., Bi2Te3, in terms of their toxicity and cost. In this work, we present an in-depth study of the thermoelectric properties of epitaxial Nb-doped strontium titanate (SrTi1-xNbxO3) thin films as a function of (i) doping concentration, (ii) film thickness and (iii) substrate type. The excellent crystal quality was confirmed by high resolution transmission electron microscopy and X-ray diffraction analysis. The thermoelectric properties were measured by the three-omega method (thermal conductivity) and van der Pauw method (electrical resistivity), complemented by Seebeck coefficient measurements. A maximum power factor of 8.9 × 10-3 W m-1 K-2 and a thermoelectric figure of merit of 0.49 were measured at room temperature in 50 nm-thick films grown on lanthanum strontium aluminate. The mechanisms behind this high figure of merit are discussed in terms of a possible two-dimensional electron gas, increase of the effective mass of the electrons, electron filtering and change in strain due to different substrates. The overall enhancement of the thermoelectric properties suggests that SrTi1-xNbxO3 is a very promising n-type candidate for room- to high-temperature applications. © 2019 The Royal Society of Chemistry.


  • Heterostructured 2D ZnO hybrid nanocomposites sensitized with cubic Cu2O nanoparticles for sunlight photocatalysis

    Segovia M., Alegría M., Aliaga J., Celedon S., Ballesteros L., Sotomayor-Torres C., González G., Benavente E. Journal of Materials Science; 54 (21): 13523 - 13536. 2019. 10.1007/s10853-019-03878-x. IF: 3.442

    In this research, we report a series of new heterostructured hybrid 2D ZnO nanocomposites sensitized with Cu2O nanoparticles for sunlight photocatalysis. The Cu2O nanoparticles were synthesized by a surfactant-free method and size reduced by a solvothermal method. 2D ZnO/Cu2O composites were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, reflectance diffuse spectroscopy and Fourier transform infrared. The results showed that the product is a material comprised of layered hybrid 2D ZnO with cubic Cu2O nanoparticles. The photocatalytic activities of the composites were investigated for photodegradation of methylene blue solution as models’ pollutant under sunlight irradiation. The photocatalytic efficiency of a 0.1:1 mixture of Cu2O nanoparticles with 2D ZnO showed that the degradation rate was faster than those of individual ZnO nanocomposites and bulk nanoparticles, respectively. The photocatalytic degradation mechanism studied using specific radical scavengers corroborates the synergy between both semiconductors in the composite and evidences a Z-scheme mechanism to explain the electron transfer. The catalytic reuse tests show that the presence of the ZnO nanocomposite avoids the typical corrosion of Cu2O. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.


  • Impact of the regularization parameter in the mean free path reconstruction method: Nanoscale heat transport and beyond

    Sanchez-Martinez M.-Á., Alzina F., Oyarzo J., Torres C.M.S., Chavez-Angel E. Nanomaterials; 9 (3, 414) 2019. 10.3390/nano9030414. IF: 4.034

    The understanding of the mean free path (MFP) distribution of the energy carriers in materials (e.g., electrons, phonons, magnons, etc.) provides a key physical insight into their transport properties. In this context, MFP spectroscopy has become an important tool to describe the contribution of carriers with different MFP to the total transport phenomenon. In this work, we revise the MFP reconstruction technique and present a study on the impact of the regularization parameter on the MFP distribution of the energy carriers. By using the L-curve criterion, we calculate the optimal mathematical value of the regularization parameter. The effect of the change from the optimal value in the MFP distribution is analyzed in three case studies of heat transport by phonons. These results demonstrate that the choice of the regularization parameter has a large impact on the physical information obtained from the reconstructed accumulation function, and thus cannot be chosen arbitrarily. The approach can be applied to various transport phenomena at the nanoscale involving carriers of different physical nature and behavior. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.


  • Modification of the raman spectra in graphene-based nanofluids and its correlation with thermal properties

    Rodríguez-Laguna M.D.R., Romero P.G., Torres C.M.S., Chavez-Angel E. Nanomaterials; 9 (5, 804) 2019. 10.3390/nano9050804. IF: 4.034

    It is well known that by dispersing nanoparticles in a fluid, the thermal conductivity of the resulting nanofluid tends to increase with the concentration of nanoparticles. However, it is not clear what the mechanism behind this phenomenon is. Raman spectroscopy is a characterization technique connecting the molecular and macroscopic world, and therefore, it can unravel the puzzling effect exerted by the nanomaterial on the fluid. In this work, we report on a comparative study on the thermal conductivity, vibrational spectra and viscosity of graphene nanofluids based on three different amides: N, N-dimethylacetamide (DMAc); N, N-dimethylformamide (DMF); and N-methyl-2-pyrrolidinone (NMP). A set of concentrations of highly stable surfactant-free graphene nanofluids developed in-house was prepared and characterized. A correlation between the modification of the vibrational spectra of the fluids and an increase in their thermal conductivity in the presence of graphene was confirmed. Furthermore, an explanation of the non-modification of the thermal conductivity in graphene-NMP nanofluids is given based on its structure and a peculiar arrangement of the fluid. © 2019, MDPI AG. All rights reserved.


  • NanoElectronics roadmap for Europe: From nanodevices and innovative materials to system integration

    Ahopelto J., Ardila G., Baldi L., Balestra F., Belot D., Fagas G., De Gendt S., Demarchi D., Fernandez-Bolaños M., Holden D., Ionescu A.M., Meneghesso G., Mocuta A., Pfeffer M., Popp R.M., Sangiorgi E., Sotomayor Torres C.M. Solid-State Electronics; 155: 7 - 19. 2019. 10.1016/j.sse.2019.03.014. IF: 1.492

    The NEREID project (“NanoElectronics Roadmap for Europe: Identification and Dissemination”) is dedicated to mapping the future of European Nanoelectronics. NEREID's objective is to develop a medium and long term roadmap for the European nanoelectronics industry, starting from the needs of applications to address societal challenges and leveraging the strengths of the European eco-system. The roadmap will also identify promising novel nanoelectronic technologies, based on the advanced concepts developed by Research Centres and Universities, as well as identification of potential bottlenecks along the innovation (value) chain. Industry applications include Energy, Automotive, Medical/Life Science, Security, loT, Mobile Convergence and Digital Manufacturing. The NEREID roadmap covers Advanced Logic and Connectivity, Functional Diversification (Smart Sensors, Smart Energy and Energy for Autonomous Systems), Beyond-CMOS, Heterogeneous Integration and System Design as well as Equipment, Materials and Manufacturing Science. This article gives an overview of the roadmap's structure and content. © 2019 Elsevier Ltd


  • Nanowire forest of pnictogen-chalcogenide alloys for thermoelectricity

    Singhal D., Paterson J., Ben-Khedim M., Tainoff D., Cagnon L., Richard J., Chavez-Angel E., Fernandez J.J., Sotomayor-Torres C.M., Lacroix D., Bourgault D., Buttard D., Bourgeois O. Nanoscale; 11 (28): 13423 - 13430. 2019. 10.1039/c9nr01566c. IF: 6.970

    Pnictogen and chalcogenide compounds have been seen as high-potential materials for efficient thermoelectric conversion over the past few decades. It is also known that with nanostructuration, the physical properties of these pnictogen-chalcogenide compounds can be further enhanced towards a more efficient heat conversion. Here, we report the reduced thermal conductivity of a large ensemble of Bi2Te3 alloy nanowires (70 nm in diameter) with selenium for n-type and antimony for p-type (Bi2Te3-ySey and Bi2-xSbxTe3 respectively). The nanowire growth was carried out through electrodeposition in nanoporous aluminium oxide templates with high aspect ratios leading to a forest (109 per centimetre square) of nearly identical nanowires. The temperature dependence of thermal conductivity for the nanowire ensembles was acquired through a highly sensitive 3ω measurement technique. The change in the thermal conductivity of nanowires is largely affected by the roughness in addition to the size effect due to enhanced boundary scattering. The major factor that influences the thermal conductivity was found to be the ratio of the rms roughness to the correlation length of the nanowire. With a high Seebeck coefficient and electrical conductivity at room temperature, the overall thermoelectric figure of merit ZT allows the consideration of such forests of nanowires as efficient potential building blocks of future TE devices. © 2019 The Royal Society of Chemistry.


  • On the Enhancement of the Thermal Conductivity of Graphene-Based Nanofluids

    Rodriguez-Laguna M.R., Torres C.M.S., Gomez-Romero P., Chavez-Angel E. Proceedings of the IEEE Conference on Nanotechnology; 2018-July (8626244) 2019. 10.1109/NANO.2018.8626244. IF: 0.000

    Heat transfer fluids have been extensively used in both low-temperature and high temperature applications (e.g. microelectronics cooling and concentrated solar power). However, their low thermal conductivity is still a limit on performance. One way to enhance thermal properties is to disperse nanomaterials, such as graphene flakes in the base fluid. In this work, we have developed highly stable DMAc-graphene nanofluids with enhanced thermal properties. Furthermore, the displacement of several Raman bands as a function of graphene concentration in DMAc suggests that the solvent molecules are able to interact with graphene surfaces strongly. © 2018 IEEE.


  • Subamorphous Thermal Conductivity of Crystalline Half-Heusler Superlattices

    Chavez-Angel E., Reuter N., Komar P., Heinz S., Kolb U., Kleebe H.-J., Jakob G. Nanoscale and Microscale Thermophysical Engineering; 23 (1): 1 - 9. 2019. 10.1080/15567265.2018.1505987. IF: 3.323

    The quest to improve the thermoelectric figure of merit has mainly followed the roadmap of lowering the thermal conductivity while keeping unaltered the power factor of the material. Ideally an electron-crystal phonon-glass system is desired. In this work, we report an extraordinary reduction of the cross-plane thermal conductivity in crystalline (TiNiSn):(HfNiSn) half-Heusler superlattices (SLs). We create SLs with thermal conductivities below the effective amorphous limit, which is kept in a large temperature range (120–300 K). We measured thermal conductivity at room temperature values as low as 0.75 W m −1  K −1 , the lowest thermal conductivity value reported so far for half-Heusler compounds. By changing the deposition conditions, we also demonstrate that the thermal conductivity is highly impacted by the way the single segments of the SL grow. These findings show a huge potential for thermoelectric generators where an extraordinary reduction of the thermal conductivity is required but without losing the crystal quality of the system. © 2018, © 2018 Taylor & Francis.


  • Synchronization of Optomechanical Nanobeams by Mechanical Interaction

    Colombano M.F., Arregui G., Capuj N.E., Pitanti A., Maire J., Griol A., Garrido B., Martinez A., Sotomayor-Torres C.M., Navarro-Urrios D. Physical Review Letters; 123 (1, 017402) 2019. 10.1103/PhysRevLett.123.017402. IF: 9.227

    The synchronization of coupled oscillators is a phenomenon found throughout nature. Mechanical oscillators are paradigmatic examples, but synchronizing their nanoscaled versions is challenging. We report synchronization of the mechanical dynamics of a pair of optomechanical crystal cavities that, in contrast to previous works performed in similar objects, are intercoupled with a mechanical link and support independent optical modes. In this regime they oscillate in antiphase, which is in agreement with the predictions of our numerical model that considers reactive coupling. We also show how to temporarily disable synchronization of the coupled system by actuating one of the cavities with a heating laser, so that both cavities oscillate independently. Our results can be upscaled to more than two cavities and pave the way towards realizing integrated networks of synchronized mechanical oscillators. © 2019 American Physical Society.


  • Thermal conductivity in disordered porous nanomembranes

    Sledzinska M., Graczykowski B., Alzina F., Melia U., Termentzidis K., Lacroix D., Sotomayor Torres C.M. Nanotechnology; 30 (26, 265401) 2019. 10.1088/1361-6528/ab0ecd. IF: 3.399

    In this work we study the effects of disorder on the thermal conductivity of porous 100 nm thick silicon membranes, in which the size, shape and position of the pores were varied randomly. Measurements using two-laser Raman thermometry on both non-patterned and porous membranes revealed more than a 10-fold reduction of the thermal conductivity compared to that of bulk silicon and a six-fold reduction compared to non-patterned membranes for the sample with random pore shapes. Using Monte Carlo methods we solved the Boltzmann transport equation for phonons and compared different possibilities of pore organization and its influence on the thermal conductivity of the samples. The simulations confirmed that the strongest reduction of thermal conductivity is achieved for a distribution of pores with arbitrary shapes that partially overlap. Up to a 15% reduction of the thermal conductivity with respect to the purely circular pores was predicted for a porous membrane with 37% filling fraction. The effect of the pore shape and distribution was further studied. Maps of temperature and heat flux distributions clearly showed that for particular pore placement heat transport can be efficiently blocked and hot spots can be found in narrow channels between pores. These findings have an impact on the fabrication of membrane-based thermoelectric devices, where low thermal conductivity is required. This work shows that for porous membranes with a given filling fraction the thermal conductivity can be further modified by introducing disorder in the shape and placement of the pores. © 2019 IOP Publishing Ltd.


2018

  • All-optical radio-frequency modulation of Anderson-localized modes

    Arregui G., Navarro-Urrios D., Kehagias N., Torres C.M.S., García P.D. Physical Review B; 98 (18, 180202) 2018. 10.1103/PhysRevB.98.180202. IF: 3.813

    All-optical modulation of light relies on exploiting intrinsic material nonlinearities [V. R. Almeida, Nature 431, 1081 (2004)NATUAS0028-083610.1038/nature02921]. However, this optical control is rather challenging due to the weak dependence of the refractive index and absorption coefficients on the concentration of free carriers in standard semiconductors [R. A. Soref and B. R. Bennett, Proc. SPIE 704, 32 (1987)PSISDG0277-786X10.1117/12.937193]. To overcome this limitation, resonant structures with high spatial and spectral confinement are carefully designed to enhance the stored electromagnetic energy, thereby requiring lower excitation power to achieve significant nonlinear effects [K. Nozaki, Nat. Photonics 4, 477 (2010)1749-488510.1038/nphoton.2010.89]. Small mode-volume and high-quality (Q)-factor cavities also offer an efficient coherent control of the light field and the targeted optical properties. Here, we report on optical resonances reaching Q∼105 induced by disorder on photonic/phononic-crystal waveguides. At relatively low excitation powers (below 1mW), these cavities exhibit nonlinear effects leading to periodic (up to ∼35 MHz) oscillations of their resonant wavelength. Our system represents a test bed to study the interplay between structural complexity and material nonlinearities and their impact on localization phenomena and introduces a different functionality to the toolset of disordered photonics. © 2018 American Physical Society.


  • Composites of laminar nanostructured ZnO and VOx-nanotubes hybrid as visible light active photocatalysts

    Benavente E., Navas D., Devis S., Segovia M., Sotomayor-Torres C., González G. Catalysts; 8 (2, 93) 2018. 10.3390/catal8020093. IF: 3.465

    A series of hybrid heterostructured nanocomposites of ZnO with V2O5 nanotubes (VOx-NTs) in different mixing ratios were synthesized, with the aim of reducing the recombination of photoinduced charge carriers and to optimize the absorption of visible light. The study was focused on the use of heterostructured semiconductors that can extend light absorption to the visible range and enhance the photocatalytic performance of ZnO in the degradation of methylene blue as a model pollutant. The addition of VOx-NTs in the synthesis mixture led to a remarkable performance in the degradation of the model dye, with hybrid ZnO (stearic acid)/VOx-NTs at a ratio of 1:0.06 possessing the highest photocatalytic activity, about seven times faster than pristine zinc oxide. Diffuse reflectance spectroscopic measurements and experiments in the presence of different trapping elements allowed us to draw conclusions regarding the band positions and photocatalytic degradation mechanism. The photocatalytic activity measured in three subsequent cycles showed good reusability as no significant loss in efficiency of dye degradation was observed. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.


  • Design of a Multifunctional Nanoengineered PLLA Surface by Maximizing the Synergies between Biochemical and Surface Design Bactericidal Effects

    Nerantzaki M., Kehagias N., Francone A., Fernández A., Sotomayor Torres C.M., Papi R., Choli-Papadopoulou T., Bikiaris D.N. ACS Omega; 3 (2): 1509 - 1521. 2018. 10.1021/acsomega.7b01756. IF: 0.000

    Nanotechnology, the manipulation of matter on atomic, molecular, and supramolecular scales, has become the most appealing strategy for biomedical applications and is of great interest as an approach to preventing microbial risks. In this study, we utilize the antimicrobial performance and the drug-loading ability of novel nanoparticles based on silicon oxide and strontium-substituted hydroxyapatite to develop nanocomposite antimicrobial films based on a poly(l-lactic acid) (PLLA) polymer. We also demonstrate that nanoimprint lithography (NIL), a process adaptable to industrial application, is a feasible fabrication technique to modify the surface of PLLA, to alter its physical properties, and to utilize it for antibacterial applications. Various nanocomposite PLLA films with nanosized (black silicon) and three-dimensional (hierarchical) hybrid domains were fabricated by thermal NIL, and their bactericidal activity against Escherichia coli and Staphylococcus aureus was assessed. Our findings demonstrate that besides hydrophobicity the nanoparticle antibiotic delivery and the surface roughness are essential factors that affect the biofilm formation. © 2018 American Chemical Society.


  • Enhancement photocatalytic activity of the heterojunction of two-dimensional hybrid semiconductors ZnO/V2O5

    Aliaga J., Cifuentes N., González G., Sotomayor-Torres C., Benavente E. Catalysts; 8 (9, 374) 2018. 10.3390/catal8090374. IF: 3.465

    In this work, we report the fabrication of the new heterojunction of two 2D hybrid layered semiconductors—ZnO (stearic acid)/V2O5 (hexadecylamine)—and its behavior in the degradation of aqueous methylene blue under visible light irradiation. The optimal photocatalyst efficiency, reached at a ZnO (stearic acid)/V2O5 (hexadecylamine) ratio of 1:0.25, results in being six times higher than that of pristine zinc oxide. Reusability test shows that after three photocatalysis cycles, no significant changes in either the dye degradation efficiency loss, nor the photocatalyst structure, occur. Visible light photocatalytic performance observed indicates there is synergetic effect between both 2D nanocomposites used in the heterojunction. The visible light absorption enhancement promoted by the narrower bandgap V2O5 based components; an increased photo generated charge separation favored by extensive interface area; and abundance of hydrophobic sites for dye adsorption appear as probable causes of the improved photocatalytic efficiency in this hybrid semiconductors heterojunction. Estimated band-edge positions for both conduction and valence band of semiconductors, together with experiments using specific radical scavengers, allow a plausible photodegradation mechanism. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.


  • Fabrication and replication of re-entrant structures by nanoimprint lithography methods

    Kehagias N., Francone A., Guttmann M., Winkler F., Fernández A., Torres C.M.S. Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics; 36 (6, 06JF01) 2018. 10.1116/1.5048241. IF: 1.314

    In this work, the authors present and demonstrate a simple method to fabricate and mass replicate re-entrant structures. The method consists of the direct imprinting of polymer mushroomlike microstructures produced by a combination of photolithography and nickel up-plating process. In particular, they have studied the conditions to generate highly robust mushroomlike topographies and their topographical impact on the replication process. They discuss all the imprinting conditions suitable to replicate such topographies using both ultraviolet light assisted nanoimprint lithography (UV-NIL) and thermal NIL methods in two polymer films, poly(methyl methacrylate) and polypropylene, and a hybrid (organic-inorganic) UV light curable photoresist, namely, Ormocomp. Re-entrant topographies have been widely studied for liquid/oil repelling and dry adhesive properties, whereas in their experiments, they have proved evidence for their amphiphobic potential. © 2018 Author(s).


  • Heterostructured layered hybrid ZnO/MoS2 nanosheets with enhanced visible light photocatalytic activity

    Benavente E., Durán F., Sotomayor-Torres C., González G. Journal of Physics and Chemistry of Solids; 113: 119 - 124. 2018. 10.1016/j.jpcs.2017.10.027. IF: 2.207

    A series of novel heterostructured hybrid layered ZnO and MoS2 nanosheets composites were successfully prepared with different MoS2 contents. Among all the prepared materials, ZnO/MoS2 (1:0.05) composite showed enhanced photocatalytic activity for methylene blue degradation under direct solar light compared with pristine ZnO. The MoS2 component played a key role for the visible light activity of the composite system at longer wavelengths. The kinetic equations of photocatalytic reaction and possible photocatalytic degradation mechanism were investigated. The results indicated that it belongs to the zero order kinetic and the photogenerated electrons are transferred from hybrid layered ZnO to the MoS2 nanosheets, facilitating an interfacial electron transfer suppressing the recombination of charge carriers during the photocatalytic degradation. © 2017 Elsevier Ltd


  • Impact of the: In situ rise in hydrogen partial pressure on graphene shape evolution during CVD growth of graphene

    Gebeyehu Z.M., Arrighi A., Costache M.V., Sotomayor-Torres C.M., Esplandiu M.J., Valenzuela S.O. RSC Advances; 8 (15): 8234 - 8239. 2018. 10.1039/c7ra13169k. IF: 2.936

    Exposing graphene to a hydrogen post-etching process yields dendritic graphene shapes. Here, we demonstrate that similar dendritic structures can be achieved at long growth times without adding hydrogen externally. These shapes are not a result of a surface diffusion controlled growth but of the competing backward reaction (etching), which dominates the growth dynamics at long times due to an in situ rise in the hydrogen partial pressure. We have performed a systematic study on the growth of graphene as a function of time to identify the onset and gradual evolution of graphene shapes caused by etching and then demonstrated that the etching can be stopped by reducing the flow of hydrogen from the feed. In addition, we have found that the etching rate due to the in situ rise in hydrogen is strongly dependent on the confinement (geometrical confinement) of copper foil. Highly etched graphene with dendritic shapes was observed in unconfined copper foil regions while no etching was found in graphene grown in a confined reaction region. This highlights the effect of the dynamic reactant distribution in activating the in situ etching process during growth, which needs to be counteracted or controlled for large scale growth. © The Royal Society of Chemistry 2018.


  • In-line metrology for roll-to-roll UV assisted nanoimprint lithography using diffractometry

    Kreuzer M., Whitworth G.L., Francone A., Gomis-Bresco J., Kehagias N., Sotomayor-Torres C.M. APL Materials; 6 (5, 058502) 2018. 10.1063/1.5011740. IF: 4.127

    We describe and discuss the optical design of a diffractometer to carry out in-line quality control during roll-to-roll nanoimprinting. The tool measures diffractograms in reflection geometry, through an aspheric lens to gain fast, non-invasive information of any changes to the critical dimensions of target grating structures. A stepwise tapered linear grating with constant period was fabricated in order to detect the variation in grating linewidth through diffractometry. The minimum feature change detected was ∼40 nm to a precision of 10 nm. The diffractometer was then integrated with a roll-to-roll UV assisted nanoimprint lithography machine to gain dynamic measurements in situ. © 2018 Author(s).


  • Integrated 3D hydrogel waveguide out-coupler by step-and-repeat thermal nanoimprint lithography: A promising sensor device for water and pH

    Francone A., Kehoe T., Obieta I., Saez-Martinez V., Bilbao L., Khokhar A.Z., Gadegaard N., Simao C.D., Kehagias N., Sotomayor Torres C.M. Sensors (Switzerland); 18 (10, 3240) 2018. 10.3390/s18103240. IF: 2.475

    Hydrogel materials offer many advantages for chemical and biological sensoring due to their response to a small change in their environment with a related change in volume. Several designs have been outlined in the literature in the specific field of hydrogel-based optical sensors, reporting a large number of steps for their fabrication. In this work we present a three-dimensional, hydrogel-based sensor the structure of which is fabricated in a single step using thermal nanoimprint lithography. The sensor is based on a waveguide with a grating readout section. A specific hydrogel formulation, based on a combination of PEGDMA (Poly(Ethylene Glycol DiMethAcrylate)), NIPAAm (N-IsoPropylAcrylAmide), and AA (Acrylic Acid), was developed. This stimulus-responsive hydrogel is sensitive to pH and to water. Moreover, the hydrogel has been modified to be suitable for fabrication by thermal nanoimprint lithography. Once stimulated, the hydrogel-based sensor changes its topography, which is characterised physically by AFM and SEM, and optically using a specific optical set-up. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.


  • Localized thinning for strain concentration in suspended germanium membranes and optical method for precise thickness measurement

    Vaccaro P.O., Alonso M.I., Garriga M., Gutiérrez J., Peró D., Wagner M.R., Reparaz J.S., Sotomayor Torres C.M., Vidal X., Carter E.A., Lay P.A., Yoshimoto M., Goñi A.R. AIP Advances; 8 (11, 115131) 2018. 10.1063/1.5050674. IF: 1.653

    We deposited Ge layers on (001) Si substrates by molecular beam epitaxy and used them to fabricate suspended membranes with high uniaxial tensile strain. We demonstrate a CMOS-compatible fabrication strategy to increase strain concentration and to eliminate the Ge buffer layer near the Ge/Si hetero-interface deposited at low temperature. This is achieved by a two-steps patterning and selective etching process. First, a bridge and neck shape is patterned in the Ge membrane, then the neck is thinned from both top and bottom sides. Uniaxial tensile strain values higher than 3% were measured by Raman scattering in a Ge membrane of 76 nm thickness. For the challenging thickness measurement on micrometer-size membranes suspended far away from the substrate a characterization method based on pump-and-probe reflectivity measurements was applied, using an asynchronous optical sampling technique. © 2018 Author(s).


  • Mechanisms behind the enhancement of thermal properties of graphene nanofluids

    Rodríguez-Laguna M.R., Castro-Alvarez A., Sledzinska M., Maire J., Costanzo F., Ensing B., Pruneda M., Ordejón P., Sotomayor Torres C.M., Gómez-Romero P., Chávez-Ángel E. Nanoscale; 10 (32): 15402 - 15409. 2018. 10.1039/c8nr02762e. IF: 7.233

    While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π-π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties. © The Royal Society of Chemistry.


  • Nanocrystalline silicon optomechanical cavities

    Navarro-Urrios D., Capuj N.E., Maire J., Colombano M., Jaramillo-Fernandez J., Chavez-Angel E., Martin L.L., Mercadé L., Griol A., Martínez A., Sotomayor-Torres C.M., Ahopelto J. Optics Express; 26 (8): 9829 - 9839. 2018. 10.1364/OE.26.009829. IF: 3.356

    Silicon on insulator photonics has offered a versatile platform for the recent development of integrated optomechanical circuits. However, there are some constraints such as the high cost of the wafers and limitation to a single physical device level. In the present work we investigate nanocrystalline silicon as an alternative material for optomechanical devices. In particular, we demonstrate that optomechanical crystal cavities fabricated of nanocrystalline silicon have optical and mechanical properties enabling non-linear dynamical behaviour and effects such as thermo-optic/free-carrier-dispersion self-pulsing, phonon lasing and chaos, all at low input laser power and with typical frequencies as high as 0.3 GHz. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.


  • Optical modulation of coherent phonon emission in optomechanical cavities

    Maire J., Arregui G., Capuj N.E., Colombano M.F., Griol A., Martinez A., Sotomayor-Torres C.M., Navarro-Urrios D. APL Photonics; 3 (12, 126102) 2018. 10.1063/1.5040061. IF: 0.000

    Optomechanical (OM) structures are well suited to study photon-phonon interactions, and they also turn out to be potential building blocks for phononic circuits and quantum computing. In phononic circuits, in which information is carried and processed by phonons, OM structures could be used as interfaces to photons and electrons thanks to their excellent coupling efficiency. Among the components required for phononic circuits, such structures could be used to create coherent phonon sources and detectors, but more complex functions remain challenging. Here, we propose and demonstrate a way to modulate the coherent phonon emission from OM crystals by a photothermal effect induced by an external laser, effectively creating a phonon switch working at ambient conditions of pressure and temperature and the working speed of which is only limited by the build-up time of the mechanical motion of the OM structure. We additionally demonstrate two other modulation schemes: modulation of harmonics in which the mechanical mode remains active but different harmonics of the optical force are used, and modulation to and from a chaotic regime. Furthermore, due to the local nature of the photothermal effect used here, we expect this method to allow us to selectively modulate the emission of any single cavity on a chip without affecting its surroundings in the absence of mechanical coupling between the structures, which is an important step toward freely controllable networks of OM phonon emitters. © 2018 Author(s).


  • Raman thermometry analysis: Modelling assumptions revisited

    Jaramillo-Fernandez J., Chavez-Angel E., Sotomayor-Torres C.M. Applied Thermal Engineering; 130: 1175 - 1181. 2018. 10.1016/j.applthermaleng.2017.11.033. IF: 3.771

    In Raman thermometry, several assumptions are made to model the heat conduction and to extract the thermal conductivity of the samples from the measured data. In this work, the heat conduction in bulk and mesa-like samples was investigated by numerical simulation and measured by the temperature-induced Raman shift method, to study the range of applicability of these assumptions. The effects of light penetration depth and finite sample size on the accuracy of the thermal conductivity determination were investigated by comparing the results of the finite element method with the usual analytical approximation for bulk samples. We found that the assumptions used in the analytical model can be applied to extract the thermal conductivity in solids if the following conditions are fulfilled: the ratio of light penetration depth to laser spot radius is smaller than 0.5, the ratio of spot radius to sample thickness is smaller than 0.1, and the ratio of spot radius to sample half width is smaller than 0.01. © 2017


2017

  • Angle-Dependent Photoluminescence Spectroscopy of Solution-Processed Organic Semiconducting Nanobelts

    Wang M., Gong Y., Alzina F., Sotomayor Torres C.M., Li H., Zhang Z., He J. Journal of Physical Chemistry C; 121 (22): 12441 - 12446. 2017. 10.1021/acs.jpcc.7b02958. IF: 4.536

    We report an anomalous anisotropy in photoluminescence (PL) from crystalline nanobelt of an organic small-molecule semiconductor, 6,13-dichloropentacene (DCP). Large-area well-aligned DCP nanobelt arrays are readily formed by self-assembly through solution method utilizing the strong anisotropic interactions between molecules. The absorption spectrum of the arrays suggests the formation of both intramolecular exciton and intermolecular exciton. However, the results of angle-dependent PL spectroscopy indicate that the PL arises only from the relaxation of intramolecular exciton, which has an optical transition dipole moment with an angle of 115° with the long-axis of the nanobelts. The angular dependence of PL signals follows a quartic rule (IPL(θ) ∞ cos4(θ - 115)) and agrees well with the optical selection rule of individual DCP molecules. The measured polarization ratio ρ from the individual nanobelts is on average 0.91 ± 0.02, superior to that of prior-art organic semiconductors. These results provide new insights into exciton behavior in 1D π-π stacking organic semiconductors and demonstrate DCP's great potential in the photodetectors and optical switches for large-scale organic optoelectronics. © 2017 American Chemical Society.


  • Characterization of industrial Coolant Fluids and continuous ageing monitoring by wireless node—Enabled fiber optic sensors

    El Sachat A., Meristoudi A., Markos C., Sakellariou A., Papadopoulos A., Katsikas S., Riziotis C. Sensors (Switzerland); 17 (3, 568) 2017. 10.3390/s17030568. IF: 2.677

    Environmentally robust chemical sensors for monitoring industrial processes or infrastructures are lately becoming important devices in industry. Low complexity and wireless enabled characteristics can offer the required flexibility for sensor deployment in adaptable sensing networks for continuous monitoring and management of industrial assets. Here are presented the design, development and operation of a class of low cost photonic sensors for monitoring the ageing process and the operational characteristics of coolant fluids used in an industrial heavy machinery infrastructure. The chemical, physical and spectroscopic characteristics of specific industrial-grade coolant fluids were analyzed along their entire life cycle range, and proper parameters for their efficient monitoring were identified. Based on multimode polymer or silica optical fibers, wide range (3–11) pH sensors were developed by employing sol-gel derived pH sensitive coatings. The performances of the developed sensors were characterized and compared, towards their coolants’ ageing monitoring capability, proving their efficiency in such a demanding application scenario and harsh industrial environment. The operating characteristics of this type of sensors allowed their integration in an autonomous wireless sensing node, thus enabling the future use of the demonstrated platform in wireless sensor networks for a variety of industrial and environmental monitoring applications. © 2017 by the authors. Licensee MDPI, Basel, Switzerland.


  • Design of Hierarchical Surfaces for Tuning Wetting Characteristics

    Fernández A., Francone A., Thamdrup L.H., Johansson A., Bilenberg B., Nielsen T., Guttmann M., Sotomayor Torres C.M., Kehagias N. ACS Applied Materials and Interfaces; 9 (8): 7701 - 7709. 2017. 10.1021/acsami.6b13615. IF: 7.504

    Patterned surfaces with tunable wetting properties are described. A hybrid hierarchical surface realized by combining two different materials exhibits different wetting states, depending on the speed of impingement of the water droplets. Both "lotus" (high contact angle and low adhesion) and "petal" (high contact angle and high adhesion) states were observed on the same surface without the need of any modification of the surface. The great difference between the capillary pressures exerted by the microstructures and nanostructures was the key factor that allowed us to tailor effectively the adhesiveness of the water droplets. Having a low capillary pressure for the microstructures and a high capillary pressure for the nanostructures, we allow to the surface the possibility of being in a lotus state or in a petal state. © 2017 American Chemical Society.


  • Directional elastic wave propagation in high-aspect-ratio photoresist gratings: Liquid infiltration and aging

    Alonso-Redondo E., Gueddida A., Li J., Graczykowski B., Sotomayor Torres C.M., Pennec Y., Yang S., Djafari-Rouhani B., Fytas G. Nanoscale; 9 (8): 2739 - 2747. 2017. 10.1039/c6nr08312a. IF: 7.367

    Determination of the mechanical properties of nanostructured soft materials and their composites in a quantitative manner is of great importance to improve the fidelity in their fabrication and to enable the subsequent reliable utility. Here, we report on the characterization of the elastic and photoelastic parameters of a periodic array of nanowalls (grating) by the non-invasive Brillouin light scattering technique and finite element calculations. The resolved elastic vibrational modes in high and low aspect ratio nanowalls reveal quantitative and qualitative differences related to the two-beam interference lithography fabrication and subsequent aging under ambient conditions. The phononic properties, namely the dispersion relations, can be drastically altered by changing the surrounding material of the nanowalls. Here we demonstrate that liquid infiltration turns the phononic function from a single-direction phonon-guiding to an anisotropic propagation along the two orthogonal directions. The susceptibility of the phononic behavior to the infiltrating liquid can be of unusual benefits, such as sensing and alteration of the materials under confinement. © The Royal Society of Chemistry 2017.


  • Effect of the annealing on the power factor of un-doped cold-pressed SnSe

    Morales Ferreiro J.O., Diaz-Droguett D.E., Celentano D., Reparaz J.S., Sotomayor Torres C.M., Ganguli S., Luo T. Applied Thermal Engineering; 111: 1426 - 1432. 2017. 10.1016/j.applthermaleng.2016.07.198. IF: 3.444

    Tin Selenide (SnSe), a thermoelectric material of the chalcogenide family, has attracted tremendous interest in the past few years due to its unprecedented thermoelectric figure-of-merit, ZT, of 2.6. In this work we have carried out an experimental study of the impact of annealing on the thermoelectric properties of polycrystalline SnSe formed by cold-pressing un-doped SnSe powders with a Hall carrier concentration of 5.37 × 1017 cm−3. The crystalline structure and morphology of the samples are characterized and properties, including electrical conductivity, Seebeck coefficient and thermal conductivity, are measured. It is found that thermal annealing has a large impact on both the microstructure and the thermoelectric properties. Notably, annealing leads to re-alignment of crystalline domains, increase in Seebeck coefficient by a factor of as much as 3, and increase in the electrical conductivity. A peak ZT of 0.11 was achieved at 772 K which is smaller than un-doped polycrystalline SnSe. © 2016 Elsevier Ltd


  • Elastic Properties of Few Nanometers Thick Polycrystalline MoS2 Membranes: A Nondestructive Study

    Graczykowski B., Sledzinska M., Placidi M., Saleta Reig D., Kasprzak M., Alzina F., Sotomayor Torres C.M. Nano Letters; 17 (12): 7647 - 7651. 2017. 10.1021/acs.nanolett.7b03669. IF: 12.712

    The performance gain-oriented nanostructurization has opened a new pathway for tuning mechanical features of solid matter vital for application and maintained performance. Simultaneously, the mechanical evaluation has been pushed down to dimensions way below 1 μm. To date, the most standard technique to study the mechanical properties of suspended 2D materials is based on nanoindentation experiments. In this work, by means of micro-Brillouin light scattering we determine the mechanical properties, that is, Young modulus and residual stress, of polycrystalline few nanometers thick MoS2 membranes in a simple, contact-less, nondestructive manner. The results show huge elastic softening compared to bulk MoS2, which is correlated with the sample morphology and the residual stress. © 2017 American Chemical Society.


  • Hierarchical surfaces for enhanced self-cleaning applications

    Fernández A., Francone A., Thamdrup L.H., Johansson A., Bilenberg B., Nielsen T., Guttmann M., Sotomayor Torres C.M., Kehagias N. Journal of Micromechanics and Microengineering; 27 (4, 045020) 2017. 10.1088/1361-6439/aa62bb. IF: 1.794

    In this study we present a flexible and adaptable fabrication method to create complex hierarchical structures over inherently hydrophobic resist materials. We have tested these surfaces for their superhydrophobic behaviour and successfully verified their self-cleaning properties. The followed approach allow us to design and produce superhydrophobic surfaces in a reproducible manner. We have analysed different combination of hierarchical micro-nanostructures for their application to self-cleaning surfaces. A static contact angle value of 170 with a hysteresis of 4 was achieved without the need of any additional chemical treatment on the fabricated hierarchical structures. Dynamic effects were analysed on these surfaces, obtaining a remarkable self-cleaning effect as well as a good robustness over impacting droplets. © 2017 IOP Publishing Ltd.


  • Mechanical oscillations in lasing microspheres

    Toncelli A., Capuj N.E., Garrido B., Sledzinska M., Sotomayor-Torres C.M., Tredicucci A., Navarro-Urrios D. Journal of Applied Physics; 122 (5, 053101) 2017. 10.1063/1.4997182. IF: 2.068

    We investigate the feasibility of activating coherent mechanical oscillations in lasing microspheres by modulating the laser emission at a mechanical eigenfrequency. To this aim, 1.5%Nd3+:Barium- Titanium-Silicate microspheres with diameters around 50 lm were used as high quality factor (Q>106) whispering gallery mode lasing cavities. We have implemented a pump-and-probe technique in which the pump laser used to excite the Nd3+ ions is focused on a single microsphere with a microscope objective and a probe laser excites a specific optical mode with the evanescent field of a tapered fibre. The studied microspheres show monomode and multi-mode lasing action, which can be modulated in the best case up to 10 MHz. We have optically transduced thermally activated mechanical eigenmodes appearing in the 50-70MHz range, the frequency of which decreases with increasing the size of the microspheres. In a pump-and-probe configuration, we observed modulation of the probe signal up to the maximum pump modulation frequency of our experimental setup, i.e., 20 MHz. This modulation decreases with frequency and is unrelated to lasing emission, pump scattering, or thermal effects. We associate this effect to free-carrier-dispersion induced by multiphoton pump light absorption. On the other hand, we conclude that, in our current experimental conditions, it was not possible to resonantly excite the mechanical modes. Finally, we discuss on how to overcome these limitations by increasing the modulation frequency of the lasing emission and decreasing the frequency of the mechanical eigenmodes displaying a strong degree of optomechanical coupling.


  • Nonlinear dynamics and chaos in an optomechanical beam

    Navarro-Urrios D., Capuj N.E., Colombano M.F., Garciá P.D., Sledzinska M., Alzina F., Griol A., Martínez A., Sotomayor-Torres C.M. Nature Communications; 8 ( 14965) 2017. 10.1038/ncomms14965. IF: 12.124

    Optical nonlinearities, such as thermo-optic mechanisms and free-carrier dispersion, are often considered unwelcome effects in silicon-based resonators and, more specifically, optomechanical cavities, since they affect, for instance, the relative detuning between an optical resonance and the excitation laser. Here, we exploit these nonlinearities and their intercoupling with the mechanical degrees of freedom of a silicon optomechanical nanobeam to unveil a rich set of fundamentally different complex dynamics. By smoothly changing the parameters of the excitation laser we demonstrate accurate control to activate two- A nd four-dimensional limit cycles, a period-doubling route and a six-dimensional chaos. In addition, by scanning the laser parameters in opposite senses we demonstrate bistability and hysteresis between two- A nd four-dimensional limit cycles, between different coherent mechanical states and between four-dimensional limit cycles and chaos. Our findings open new routes towards exploiting silicon-based optomechanical photonic crystals as a versatile building block to be used in neurocomputational networks and for chaos-based applications. © 2017 The Author(s).


  • Optomechanical coupling in the Anderson-localization regime

    García P.D., Bericat-Vadell R., Arregui G., Navarro-Urrios D., Colombano M., Alzina F., Sotomayor-Torres C.M. Physical Review B; 95 (11, 115129) 2017. 10.1103/PhysRevB.95.115129. IF: 3.836

    Optomechanical crystals, purposely designed and fabricated semiconductor nanostructures, are used to enhance the coupling between the electromagnetic field and the mechanical vibrations of matter at the nanoscale. However, in real optomechanical crystals, imperfections open extra channels where the transfer of energy is lost, reducing the optomechanical coupling efficiency. Here, we quantify the role of disorder in a paradigmatic one-dimensional optomechanical crystal with full phononic and photonic band gaps. We show how disorder can be exploited as a resource to enhance the optomechanical coupling beyond engineered structures, thus providing a new tool set for optomechanics. © 2017 American Physical Society.


  • Physics of Quantum Light Emitters in Disordered Photonic Nanostructures

    García P.D., Lodahl P. Annalen der Physik; 2017. 10.1002/andp.201600351. IF: 3.039

    Nanophotonics focuses on the control of light and the interaction with matter by the aid of intricate nanostructures. Typically, a photonic nanostructure is carefully designed for a specific application and any imperfections may reduce its performance, i.e., a thorough investigation of the role of unavoidable fabrication imperfections is essential for any application. However, another approach to nanophotonic applications exists where fabrication disorder is used to induce functionalities by enhancing light-matter interaction. Disorder leads to multiple scattering of light, which is the realm of statistical optics where light propagation requires a statistical description. We review here the recent progress on disordered photonic nanostructures and the potential implications for quantum photonics devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA.


  • Raman antenna effect from exciton-phonon coupling in organic semiconducting nanobelts

    Wang M., Gong Y., Alzina F., Svoboda O., Ballesteros B., Sotomayor Torres C.M., Xiao S., Zhang Z., He J. Nanoscale; 9 (48): 19328 - 19336. 2017. 10.1039/c7nr07212k. IF: 7.367

    The highly anisotropic interactions in organic semiconductors together with the soft character of organic materials lead to strong coupling between nuclear vibrations and exciton dynamics, which potentially results in anomalous electrical, optical and optoelectrical properties. Here, we report on the Raman antenna effect from organic semiconducting nanobelts 6,13-dichloropentacene (DCP), resulting from the coupling of molecular excitons and intramolecular phonons. The highly ordered crystalline structure in DCP nanobelts enables the precise polarization-resolved spectroscopic measurement. The angle-dependent Raman spectroscopy under resonant excitation shows that all Raman modes from the skeletal vibrations of DCP molecule act like a nearly perfect dipole antenna IRaman ∝ cos4(θ - 90), with almost zero (maximum) Raman scattering parallel (perpendicular) to the nanobelt's long-axis. The Raman antenna effect in DCP nanobelt is originated from the coupling between molecular skeletal vibrations and intramolecular exciton and the confinement of intermolecular excitons. It dramatically enhances the Raman polarization ratio (ρ =I∥/I⊥ > 25) and amplifies the anisotropy of the angle-dependent Raman scattering (κRaman = Imax/Imin > 12) of DCP nanobelts. These findings have crucial implications for fundamental understanding on the exciton-phonon coupling and its effects on the optical properties of organic semiconductors. © 2017 The Royal Society of Chemistry.


  • Record Low Thermal Conductivity of Polycrystalline MoS2 Films: Tuning the Thermal Conductivity by Grain Orientation

    Sledzinska M., Quey R., Mortazavi B., Graczykowski B., Placidi M., Saleta Reig D., Navarro-Urrios D., Alzina F., Colombo L., Roche S., Sotomayor Torres C.M. ACS Applied Materials and Interfaces; 9 (43): 37905 - 37911. 2017. 10.1021/acsami.7b08811. IF: 7.504

    We report a record low thermal conductivity in polycrystalline MoS2 obtained for ultrathin films with varying grain sizes and orientations. By optimizing the sulfurization parameters of nanometer-thick Mo layers, five MoS2 films containing a combination of horizontally and vertically oriented grains, with respect to the bulk (001) monocrystal, were grown. From transmission electron microscopy, the average grain size, typically below 10 nm, and proportion of differently oriented grains were extracted. The thermal conductivity of the suspended samples was extracted from a Raman laser-power-dependent study, and the lowest value of thermal conductivity of 0.27 W m-1 K-1, which reaches a similar value as that of Teflon, is obtained in a polycrystalline sample formed by a combination of horizontally and vertically oriented grains in similar proportion. Analysis by means of molecular dynamics and finite element method simulations confirm that such a grain arrangement leads to lower grain boundary conductance. We discuss the possible use of these thermal insulating films in the context of electronics and thermoelectricity. © 2017 American Chemical Society.


  • Self-Assembled Nanofeatures in Complex Three-Dimensional Topographies via Nanoimprint and Block Copolymer Lithography Methods

    Cian Cummins, Dipu Borah, Sozaraj Rasappa, Ramsankar Senthamaraikannan, Claudia Simao, Achille Francone, Nikolaos Kehagias, Clivia M. Sotomayor-Torres, Michael A. Morris ACS Omega; 2 (2): 4417 - 4423. 2017. 10.1021/acsomega.7b00781. IF: 0.000

    Achieving ultrasmall dimensions of materials and retaining high throughput are critical fabrication considerations for nanotechnology use. This article demonstrates an integrated approach for developing isolated sub-20 nm silicon oxide features through combined “top-down” and “bottom-up” methods: nanoimprint lithography (NIL) and block copolymer (BCP) lithography. Although techniques like those demonstrated here have been developed for nanolithographic application in the microelectronics processing industry, similar approaches could be utilized for sensor, fluidic, and optical-based devices. Thus, this article centers on looking at the possibility of generating isolated silica structures on substrates. NIL was used to create intriguing three-dimensional (3-D) polyhedral oligomeric silsesquioxane (POSS) topographical arrays that guided and confined polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) BCP nanofeatures in isolated regions. A cylinder forming PS-b-PDMS BCP system was successfully etched using a one-step etching process to create line-space arrays with a period of 35 nm in confined POSS arrays. We highlight large-area (>6 μm) coverage of line-space arrays in 3-D topographies that could potentially be utilized, for example, in nanofluidic systems. Aligned features for directed self-assembly application are also demonstrated. The high-density, confined silicon oxide nanofeatures in soft lithographic templates over macroscopic areas illustrate the advantages of integrating distinct lithographic methods for attaining discrete features in the deep nanoscale regime.


  • Self-assembled three-dimensional inverted photonic crystals on a photonic chip

    Arpiainen S., Vynck K., Dekker J., Kapulainen M., Khunsin W., Aalto T., Mulot M., Kocher-Oberlehrer G., Zentel R., Torres C.M.S., Cassagne D., Ahopelto J. Physica Status Solidi (A) Applications and Materials Science; 214 (9, 1700039) 2017. 10.1002/pssa.201700039. IF: 1.775

    Three dimensional photonic crystals (PhCs) exhibiting a full photonic band gap have high potential in optical signal processing and detector applications. However, the challenges in the integration of the 3D PhCs into photonic circuits have so far hindered their exploitation in real devices. This article demonstrates the fabrication of 3D PhCs exploiting the capillary directed self-assembly (CDSA) of monodisperse colloidal silica spheres, their inversion to silicon shells, and integration with silicon waveguides. The measured transmission characteristics agree with numerical predictions and provide strong indication of a full photonic band gap in the inverted 3D photonic crystals at wavelengths close to 1.55 μm. Silicon inverted photonic crystal self-assembled into a cavity in a waveguide intersection and the corresponding photonic band structure of the crystal, together with the simulated transmission, reflection, and absorption spectra. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • Synthesis and optical characterization of Er-doped bismuth titanate nanoparticles grown by sol–gel hydrothermal method

    Fuentes S., Muñoz P., Llanos J., Vega M., Martin I.R., Chavez-Angel E. Ceramics International; 43 (4): 3623 - 3630. 2017. 10.1016/j.ceramint.2016.11.200. IF: 2.986

    The Er3+-doped bismuth titanate (Bi4Ti3O12, BIT) nanoparticles were synthesized by a combined sol–gel and hydrothermal method under a partial oxygen pressure of 30 bar. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering. They showed pure and homogeneous spherical BIT nanoparticles with a size below the 30 nm. The incorporation of Er ions showed a strong decrease in the lattice parameters, as well as averaged particle size. The photoluminescence up-conversion (excitation wavelength =1480 nm) showed an enhancement of the infrared emission (980 nm) as Er concentration increased, achieving a maximum for 6% mol, while photoluminescence spectra (excitation wavelength =473 nm) showed a strong green emission (529 and 553 nm) with a maximum at 4% mol. © 2016 Elsevier Ltd and Techna Group S.r.l.


  • Thermal conductivity and air-mediated losses in periodic porous silicon membranes at high temperatures

    Graczykowski B., El Sachat A., Reparaz J.S., Sledzinska M., Wagner M.R., Chavez-Angel E., Wu Y., Volz S., Wu Y., Alzina F., Sotomayor Torres C.M. Nature Communications; 8 (1, 415) 2017. 10.1038/s41467-017-00115-4. IF: 12.124

    Heat conduction in silicon can be effectively engineered by means of sub-micrometre porous thin free-standing membranes. Tunable thermal properties make these structures good candidates for integrated heat management units such as waste heat recovery, rectification or efficient heat dissipation. However, possible applications require detailed thermal characterisation at high temperatures which, up to now, has been an experimental challenge. In this work we use the contactless two-laser Raman thermometry to study heat dissipation in periodic porous membranes at high temperatures via lattice conduction and air-mediated losses. We find the reduction of the thermal conductivity and its temperature dependence closely correlated with the structure feature size. On the basis of two-phonon Raman spectra, we attribute this behaviour to diffuse (incoherent) phonon-boundary scattering. Furthermore, we investigate and quantify the heat dissipation via natural air-mediated cooling, which can be tuned by engineering the porosity. © 2017 The Author(s).


  • Thermal conductivity of epitaxially grown InP: experiment and simulation

    Jaramillo-Fernandez J., Chavez-Angel E., Sanatinia R., Kataria H., Anand S., Lourdudoss S., Sotomayor-Torres C.M. CrystEngComm; 19 (14): 1879 - 1887. 2017. 10.1039/c6ce02642g. IF: 3.474

    The integration of III-V optoelectronic devices on silicon is confronted with the challenge of heat dissipation for reliable and stable operation. A thorough understanding and characterization of thermal transport is paramount for improved designs of, for example, viable III-V light sources on silicon. In this work, the thermal conductivity of heteroepitaxial laterally overgrown InP layers on silicon is experimentally investigated using microRaman thermometry. By examining InP mesa-like structures grown from trenches defined by a SiO2 mask, we found that the thermal conductivity decreases by about one third, compared to the bulk thermal conductivity of InP, with decreasing width from 400 to 250 nm. The high thermal conductivity of InP grown from 400 nm trenches was attributed to the lower defect density as the InP microcrystal becomes thicker. In this case, the thermal transport is dominated by phonon-phonon interactions as in a low defect-density monocrystalline bulk material, whereas for thinner InP layers grown from narrower trenches, the heat transfer is dominated by phonon scattering at the extended defects and InP/SiO2 interface. In addition to the nominally undoped sample, sulfur-doped (1 × 1018 cm−3) InP grown on Si was also studied. For the narrower doped InP microcrystals, the thermal conductivity decreased by a factor of two compared to the bulk value. Sources of errors in the thermal conductivity measurements are discussed. The experimental temperature rise was successfully simulated by the heat diffusion equation using the FEM. © The Royal Society of Chemistry.


  • Thermal transport in epitaxial Si1-xGe x alloy nanowires with varying composition and morphology

    Sachat A.E., Reparaz J.S., Spiece J., Alonso M.I., Goñi A.R., Garriga M., Vaccaro P.O., Wagner M.R., Kolosov O.V., Sotomayor Torres C.M., Alzina F. Nanotechnology; 28 (50, 505704) 2017. 10.1088/1361-6528/aa9497. IF: 3.440

    We report on structural, compositional, and thermal characterization of self-assembled in-plane epitaxial Si1-xGe x alloy nanowires grown by molecular beam epitaxy on Si (001) substrates. The thermal properties were studied by means of scanning thermal microscopy (SThM), while the microstructural characteristics, the spatial distribution of the elemental composition of the alloy nanowires and the sample surface were investigated by transmission electron microscopy and energy dispersive x-ray microanalysis. We provide new insights regarding the morphology of the in-plane nanostructures, their size-dependent gradient chemical composition, and the formation of a 5 nm thick wetting layer on the Si substrate surface. In addition, we directly probe heat transfer between a heated scanning probe sensor and Si1-xGe x alloy nanowires of different morphological characteristics and we quantify their thermal resistance variations. We correlate the variations of the thermal signal to the dependence of the heat spreading with the cross-sectional geometry of the nanowires using finite element method simulations. With this method we determine the thermal conductivity of the nanowires with values in the range of 2-3 W m-1 K-1. These results provide valuable information in growth processes and show the great capability of the SThM technique in ambient environment for nanoscale thermal studies, otherwise not possible using conventional techniques. © 2017 IOP Publishing Ltd.


  • Unveiled electric profiles within hydrogen bonds suggest DNA base pairs with similar bond strengths

    Ruiz-Blanco Y.B., Almeida Y., Sotomayor-Torres C.M., García Y. PLoS ONE; 12 (10, e0185638) 2017. 10.1371/journal.pone.0185638. IF: 2.806

    Electrical forces are the background of all the interactions occurring in biochemical systems. From here and by using a combination of ab-initio and ad-hoc models, we introduce the first description of electric field profiles with intrabond resolution to support a characterization of single bond forces attending to its electrical origin. This fundamental issue has eluded a physical description so far. Our method is applied to describe hydrogen bonds (HB) in DNA base pairs. Numerical results reveal that base pairs in DNA could be equivalent considering HB strength contributions, which challenges previous interpretations of thermodynamic properties of DNA based on the assumption that Adenine/Thymine pairs are weaker than Guanine/Cytosine pairs due to the sole difference in the number of HB. Thus, our methodology provides solid foundations to support the development of extended models intended to go deeper into the molecular mechanisms of DNA functioning. © 2017 Ruiz-Blanco et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


2016

  • A hybrid organic-inorganic layered TiO2 based nanocomposite for sunlight photocatalysis

    Benavente E., Maldonado C., Devis S., Diaz L., Lozano H., Sotomayor-Torres C., González G. RSC Advances; 6 (22): 18538 - 18541. 2016. 10.1039/c5ra26981d. IF: 3.289

    A novel hybrid nanocomposite constituted of single TiO2 nanosheets sandwiched between stearic acid self-assembled monolayers was synthesized and tested in the photodegradation of methylene blue under sunlight. The product showed better photocatalytic performance than anatase under similar conditions, which may be further improved through sensitization with cadmium sulfide. © The Royal Society of Chemistry 2016.


  • Catalytically Doped Semiconductors for Chemical Gas Sensing: Aerogel-Like Aluminum-Containing Zinc Oxide Materials Prepared in the Gas Phase

    Hagedorn K., Li W., Liang Q., Dilger S., Noebels M., Wagner M.R., Reparaz J.S., Dollinger A., Schmedt Auf Der Günne J., Dekorsy T., Schmidt-Mende L., Polarz S. Advanced Functional Materials; 26 (20): 3424 - 3437. 2016. 10.1002/adfm.201505355. IF: 11.382

    Atmospheric contamination with organic compounds is undesired in industry and in society because of odor nuisance or potential toxicity. Resistive gas sensors made of semiconducting metal oxides are effective in the detection of gases even at low concentration. Major drawbacks are low selectivity and missing sensitivity toward a targeted compound. Acetaldehyde is selected due to its high relevance in chemical industry and its toxic character. Considering the similarity between gas-sensing and heterogeneous catalysis (surface reactions, activity, selectivity), it is tempting to transfer concepts. A question of importance is how doping and the resulting change in electronic properties of a metal-oxide support with semiconducting properties alters reactivity of the surfaces and the functionality in gas-sensing and in heterogeneous catalysis. A gas-phase synthesis method is employed for aerogel-like zinc oxide materials with a defined content of aluminum (n-doping), which were then used for the assembly of gas sensors. It is shown that only Al-doped ZnO represents an effective sensor material that is sensitive down to very low concentrations (<350 ppb). The advance in properties relates to a catalytic effect for the doped semiconductor nanomaterial. Doping of a semiconductor nose: Gas-sensors assembled from hollow ZnO aerogels can be made sensitive for new compounds like acetaldehyde via chemical doping with aluminum, which not only leads to effective n-doping but also results in a catalytic effect. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


  • Fabrication of phononic crystals on free-standing silicon membranes

    Sledzinska M., Graczykowski B., Alzina F., Santiso Lopez J., Sotomayor Torres C.M. Microelectronic Engineering; 149: 41 - 45. 2016. 10.1016/j.mee.2015.09.004. IF: 1.277

    Free-standing Si films have been and remain an excellent example to study experimentally the effect of the reduction of the characteristic size on the phonon dispersion relation. A step further in geometrical complexity and, therefore, in increasing the control and manipulation of phonons is achieved by introducing periodicity in the medium to form phononic crystals. Here we report on the development of the fabrication process of large-area, solid-air and solid-solid two-dimensional phononic crystals, directly on free-standing, single crystalline silicon membranes. The patterning of the membranes involved electron-beam lithography and reactive ion etching for holes or metal evaporation and lift-off for pillars. The fabrication was possible due to the external strain induced on the membrane in order to reduce the buckling, which is typically found in large area free-standing structures. As a result, we obtained 250 nm thick structured membranes with patterned areas up to 100 × 100 μm, feature size between 100 and 300 nm and periodicity between 300 and 500 nm. The changes in dispersion relations of hypersonic acoustic phonons due to nanopatterning in free-standing silicon membranes were measured by Brillouin light scattering and the results were compared with numerical calculations by finite elements method. Information on phonon dispersion relation combined with a reliable fabrication process for large-scale structures opens a way for phonon engineering in more complex devices. © 2015 Elsevier B.V. All rights reserved.


  • Finite element analysis of true and pseudo surface acoustic waves in one-dimensional phononic crystals

    Graczykowski B., Alzina F., Gomis-Bresco J., Sotomayor Torres C.M. Journal of Applied Physics; 119 (2, 025308) 2016. 10.1063/1.4939825. IF: 2.101

    In this paper, we report a theoretical investigation of surface acoustic waves propagating in one-dimensional phononic crystal. Using finite element method eigenfrequency and frequency response studies, we develop two model geometries suitable to distinguish true and pseudo (or leaky) surface acoustic waves and determine their propagation through finite size phononic crystals, respectively. The novelty of the first model comes from the application of a surface-like criterion and, additionally, functional damping domain. Exemplary calculated band diagrams show sorted branches of true and pseudo surface acoustic waves and their quantified surface confinement. The second model gives a complementary study of transmission, reflection, and surface-to-bulk losses of Rayleigh surface waves in the case of a phononic crystal with a finite number of periods. Here, we demonstrate that a non-zero transmission within non-radiative band gaps can be carried via leaky modes originating from the coupling of local resonances with propagating waves in the substrate. Finally, we show that the transmission, reflection, and surface-to-bulk losses can be effectively optimised by tuning the geometrical properties of a stripe. © 2016 AIP Publishing LLC.


  • Measurement and modeling of the effective thermal conductivity of sintered silver pastes

    Ordonez-Miranda J., Hermens M., Nikitin I., Kouznetsova V.G., Van Der Sluis O., Ras M.A., Reparaz J.S., Wagner M.R., Sledzinska M., Gomis-Bresco J., Sotomayor Torres C.M., Wunderle B., Volz S. International Journal of Thermal Sciences; 108: 185 - 194. 2016. 10.1109/THERMINIC.2015.7389630. IF: 2.769

    The effective thermal conductivity of sintered porous pastes of silver is modeled through two theoretical methods and measured by means of three experimental techniques. The first model is based on the differential effective medium theory and provides a simple analytical description considering the air pores like ellipsoidal voids of different sizes, while the second one arises from the analysis of the scanning-electron-microscope images of the paste cross-sections through the finite element method. The predictions of both approaches are consistent with each other and show that the reduction of the thermal conductivity of porous pastes can be minimized with spherical pores and maximized with pancake-shaped ones, which are the most efficient to block the thermal conducting pathways. A thermal conductivity of 151.6 W/m K is numerically determined for a sintered silver sample with 22% of porosity. This thermal conductivity agrees quite well with the one measured by the Lateral Thermal Interface Material Analysis for a suspended sample and matches, within an experimental uncertainty smaller than 16%, with the values obtained by means of Raman thermometry and the 3u technique, for two samples buried in a silicon chip. The consistence between our theoretical and experimental results demonstrates the good predictive performance of our theoretical models to describe the thermal behavior of porous thermal interface materials and to guide their engineering with a desired thermal conductivity. © 2016 Elsevier Masson SAS.


  • Nanophononics: State of the art and perspectives

    Volz S., Ordonez-Miranda J., Shchepetov A., Prunnila M., Ahopelto J., Pezeril T., Vaudel G., Gusev V., Ruello P., Weig E.M., Schubert M., Hettich M., Grossman M., Dekorsy T., Alzina F., Graczykowski B., Chavez-Angel E., Sebastian Reparaz J., Wagner M.R., Sotomayor-Torres C.M., Xiong S., Neogi S., Donadio D. European Physical Journal B; 89 (1, 15) 2016. 10.1140/epjb/e2015-60727-7. IF: 1.223

    Understanding and controlling vibrations in condensed matter is emerging as an essential necessity both at fundamental level and for the development of a broad variety of technological applications. Intelligent design of the band structure and transport properties of phonons at the nanoscale and of their interactions with electrons and photons impact the efficiency of nanoelectronic systems and thermoelectric materials, permit the exploration of quantum phenomena with micro- and nanoscale resonators, and provide new tools for spectroscopy and imaging. In this colloquium we assess the state of the art of nanophononics, describing the recent achievements and the open challenges in nanoscale heat transport, coherent phonon generation and exploitation, and in nano- and optomechanics. We also underline the links among the diverse communities involved in the study of nanoscale phonons, pointing out the common goals and opportunities. © The Author(s) 2016.


  • Nanoscale pillar hypersonic surface phononic crystals

    Yudistira D., Boes A., Graczykowski B., Alzina F., Yeo L.Y., Sotomayor Torres C.M., Mitchell A. Physical Review B; 94 (9, 094304) 2016. 10.1103/PhysRevB.94.094304.

    We report on nanoscale pillar-based hypersonic phononic crystals in single crystal Z-cut lithium niobate. The phononic crystal is formed by a two-dimensional periodic array of nearly cylindrical nanopillars 240 nm in diameter and 225 nm in height, arranged in a triangular lattice with a 300-nm lattice constant. The nanopillars are fabricated by the recently introduced nanodomain engineering via laser irradiation of patterned chrome followed by wet etching. Numerical simulations and direct measurements using Brillouin light scattering confirm the simultaneous existence of nonradiative complete surface phononic band gaps. The band gaps are found below the sound line at hypersonic frequencies in the range 2-7 GHz, formed from local resonances and Bragg scattering. These hypersonic structures are realized directly in the piezoelectric material lithium niobate enabling phonon manipulation at significantly higher frequencies than previously possible with this platform, opening new opportunities for many applications in plasmonic, optomechanic, microfluidic, and thermal engineering. © 2016 American Physical Society.


  • Orthotropic Piezoelectricity in 2D Nanocellulose

    García Y., Ruiz-Blanco Y.B., Marrero-Ponce Y., Sotomayor-Torres C.M. Scientific Reports; 6 ( 34616) 2016. 10.1038/srep34616. IF: 5.228

    The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ∼pm V-1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies. © 2016 The Author(s).


  • Self-sustained coherent phonon generation in optomechanical cavities

    Navarro-Urrios D., Gomis-Bresco J., Alzina F., Capuj N.E., García P.D., Colombano M.F., Chavez-Angel E., Sotomayor-Torres C.M. Journal of Optics (United Kingdom); 18 (9, 094006) 2016. 10.1088/2040-8978/18/9/094006. IF: 1.847

    Optical forces can set tiny objects in states of mechanical self-sustained oscillation, spontaneously generating periodic signals by extracting power from steady sources. Miniaturized self-sustained coherent phonon sources are interesting for applications such as mass-force sensing, intra-chip metrology and intra-chip time-keeping among others. In this paper, we review several mechanisms and techniques that can drive a mechanical mode into the lasing regime by exploiting the radiation pressure force in optomechanical cavities, namely stimulated emission, dynamical back-action, forward stimulated Brillouin scattering and self-pulsing. © 2016 IOP Publishing Ltd.


  • Spatially controlled growth of highly crystalline ZnO nanowires by an inkjet-Printing catalyst-Free method

    Güell F., Martínez-Alanis P.R., Khachadorian S., Zamani R.R., Franke A., Hoffmann A., Wagner M.R., Santana G. Materials Research Express; 3 (2, 025010) 2016. 10.1088/2053-1591/3/2/025010. IF: 0.968

    High-density arrays of uniform ZnO nanowires with a high-crystal quality have been synthesized by a catalyst-free vapor-transport method. First, a thin ZnO film was deposited on a Si substrate as nucleation layer for the ZnO nanowires. Second, spatially selective and mask-less growth of ZnO nanowires was achieved using inkjet-printed patterned islands as the nucleation sites on a SiO2/Si substrate. Raman scattering and low temperature photoluminescence measurements were applied to characterize the structural and optical properties of the ZnO nanowires. The results reveal negligible amounts of strain and defects in the mask-less ZnO nanowires as compared to the ones grown on the ZnO thin film, which underlines the potential of the inkjet-printing approach for the growth of highcrystal quality ZnO nanowires. © 2016 IOP Publishing Ltd.


  • Thermal conductivity of MoS2 polycrystalline nanomembranes

    Sledzinska M., Graczykowski B., Placidi M., Reig D.S., El Sachat A., Reparaz J.S., Alzina F., Mortazavi B., Quey R., Colombo L., Roche S., Torres C.M.S. 2D Materials; 3 (3, 035016) 2016. 10.1088/2053-1583/3/3/035016. IF: 9.611

    Heat conduction in 2D materials can be effectively engineered by means of controlling nanoscale grain structure. Afavorable thermal performance makes these structures excellent candidates for integrated heat management units. Here we show combined experimental and theoretical studies for MoS2 nanosheets in a nanoscale grain-size limit.Wereport thermal conductivity measurements on 5 nm thick polycrystalline MoS2 by means of 2-laser Raman thermometry. The free-standing, drum-like MoS2 nanomembranes were fabricated using a novel polymer- and residue-free, wet transfer, in which we took advantage of the difference in the surface energies between MoS2 and the growth substrate to transfer the CVD-grown nanosheets. The measurements revealed a strong reduction in the in-plane thermal conductivity down to about 0.73 ± 0.25 W m-1 K-1. The results are discussed theoretically using finite elements method simulations for a polycrystalline film, and a scaling trend of the thermally conductivity with grain size is proposed. © 2016 IOP Publishing Ltd.


  • Thermal transport in suspended silicon membranes measured by laser-induced transient gratings

    Vega-Flick A., Duncan R.A., Eliason J.K., Cuffe J., Johnson J.A., Peraud J.-P.M., Zeng L., Lu Z., Maznev A.A., Wang E.N., Alvarado-Gil J.J., Sledzinska M., Sotomayor Torres C.M., Chen G., Nelson K.A. AIP Advances; 6 (12, 121903) 2016. 10.1063/1.4968610. IF: 1.444

    Studying thermal transport at the nanoscale poses formidable experimental challenges due both to the physics of the measurement process and to the issues of accuracy and reproducibility. The laser-induced transient thermal grating (TTG) technique permits non-contact measurements on nanostructured samples without a need for metal heaters or any other extraneous structures, offering the advantage of inherently high absolute accuracy. We present a review of recent studies of thermal transport in nanoscale silicon membranes using the TTG technique. An overview of the methodology, including an analysis of measurements errors, is followed by a discussion of new findings obtained from measurements on both "solid" and nanopatterned membranes. The most important results have been a direct observation of non-diffusive phonon-mediated transport at room temperature and measurements of thickness-dependent thermal conductivity of suspended membranes across a wide thickness range, showing good agreement with first-principles-based theory assuming diffuse scattering at the boundaries. Measurements on a membrane with a periodic pattern of nanosized holes (135nm) indicated fully diffusive transport and yielded thermal diffusivity values in agreement with Monte Carlo simulations. Based on the results obtained to-date, we conclude that room-temperature thermal transport in membrane-based silicon nanostructures is now reasonably well understood. © 2016 Author(s).


  • Titanium particle incorporation in block copolymer templates

    Kreuzer M., Simão C., Diaz A., Sotomayor Torres C.M. Polymer (United Kingdom); 105: 195 - 202. 2016. 10.1016/j.polymer.2016.10.009. IF: 3.586

    Template-directed formation of titanium structures on block copolymer templates has been recently reported [1]. Here, the incorporation of titanium in a thin film template is studied. We show that the surface free energy contrast in microphase-separated polystyrene-block-polyethylene oxide templates is not limited to the template film surface, but directs the assembly of titanium atoms in the template thin film. The details of the self-assembly of titanium particles on the block copolymer nanostructured surface and inside the 3D film structure are studied with selected amounts of titanium. Evaporated titanium preferentially wets the polystyrene block of the block copolymer film and diffuses inside the film, conserving the block copolymer nanostructure. Increasing deposition leads to the formation of a mesoporous titanium layer on the block copolymer film, which reproduces that of the underlying template, in this particular case with a thickness of 12 nm and a periodic pore-to-pore distance of 35 nm. The formation of a mesoporous titanium layer prevents from further titanium diffusion inside the block copolymer film. The combination of the X-ray scattering techniques presented here provides sufficient sensitivity to follow the titanium formation in the three dimensional network of the block copolymer films. © 2016 Elsevier Ltd


  • Two-Dimensional Phononic Crystals: Disorder Matters

    Wagner M.R., Graczykowski B., Reparaz J.S., El Sachat A., Sledzinska M., Alzina F., Sotomayor Torres C.M. Nano Letters; 16 (9): 5661 - 5668. 2016. 10.1021/acs.nanolett.6b02305. IF: 13.779

    The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder. © 2016 American Chemical Society.


2015

  • A diffractometer for quality control in nano fabrication processing based on subwavelength diffraction

    Kreuzer M., Gomis Bresco J., Sledzinska M., Sotomayor Torres C.M. Proceedings of SPIE - The International Society for Optical Engineering; 9424 (942426) 2015. 10.1117/12.2085924. IF: 0.000

    Mass production of nanostructured surfaces relies on the periodic repetition of micrometre scale patterns. A unit cell with nanometre features in the micrometre size range is repeated thousands of times. The ensemble can used as a diffraction grating for visible light. The relative intensity distribution of the diffraction orders is characteristic for the grating and sensitive to nanometre scale changes. A newly designed subwavelength diffraction setup allows the measurement in real time of the diffraction pattern of an illuminated polymer grating with only one detector image. The setup records diffraction patterns of, for example, polymer gratings with intentionally low scattering contrast and line features ranging from 610 to 80 nm. Thus, sub-100 nm features can be traced. The comparison of the measured diffraction patterns with simulated patterns allows to sense nanometre scale deviations from fabrication goals. © 2015 SPIE.


  • A Hooke's law-based approach to protein folding rate

    Ruiz-Blanco Y.B., Marrero-Ponce Y., Prieto P.J., Salgado J., García Y., Sotomayor-Torres C.M. Journal of Theoretical Biology; 364: 407 - 417. 2015. 10.1016/j.jtbi.2014.09.002. IF: 2.116

    Kinetics is a key aspect of the renowned protein folding problem. Here, we propose a comprehensive approach to folding kinetics where a polypeptide chain is assumed to behave as an elastic material described by the Hooke[U+05F3]s law. A novel parameter called elastic-folding constant results from our model and is suggested to distinguish between protein with two-state and multi-state folding pathways. A contact-free descriptor, named folding degree, is introduced as a suitable structural feature to study protein-folding kinetics. This approach generalizes the observed correlations between varieties of structural descriptors with the folding rate constant. Additionally several comparisons among structural classes and folding mechanisms were carried out showing the good performance of our model with proteins of different types. The present model constitutes a simple rationale for the structural and energetic factors involved in protein folding kinetics. © 2014 Elsevier Ltd.


  • A self-stabilized coherent phonon source driven by optical forces

    Navarro-Urrios D., Capuj N.E., Gomis-Bresco J., Alzina F., Pitanti A., Griol A., Martínez A., Sotomayor Torres C.M. Scientific Reports; 5 ( 15733) 2015. 10.1038/srep15733. IF: 5.578

    We report a novel injection scheme that allows for phonon lasing in a one-dimensional opto-mechanical photonic crystal, in a sideband unresolved regime and with cooperativity values as low as 10'2. It extracts energy from a cw infrared laser source and is based on the triggering of a thermo-optical/free-carrier-dispersion self-pulsing limit-cycle, which anharmonically modulates the radiation pressure force. The large amplitude of the coherent mechanical motion acts as a feedback that stabilizes and entrains the self-pulsing oscillations to simple fractions of the mechanical frequency. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.


  • A single-source precursor route to anisotropic halogen-doped zinc oxide particles as a promising candidate for new transparent conducting oxide materials

    Lehr D., Wagner M.R., Flock J., Reparaz J.S., Torres C.M.S., Klaiber A., Dekorsy T., Polarz S. Beilstein Journal of Nanotechnology; 6 (1): 2161 - 2172. 2015. 10.3762/bjnano.6.222. IF: 2.670

    Numerous applications in optoelectronics require electrically conducting materials with high optical transparency over the entire visible light range. A solid solution of indium oxide and substantial amounts of tin oxide for electronic doping (ITO) is currently the most prominent example for the class of so-called TCOs (transparent conducting oxides). Due to the limited, natural occurrence of indium and its steadily increasing price, it is highly desired to identify materials alternatives containing highly abundant chemical elements. The doping of other metal oxides (e.g., zinc oxide, ZnO) is a promising approach, but two problems can be identified. Phase separation might occur at the required high concentration of the doping element, and for successful electronic modification it is mandatory that the introduced heteroelement occupies a defined position in the lattice of the host material. In the case of ZnO, most attention has been attributed so far to n-doping via substitution of Zn2+ by other metals (e.g., Al3+). Here, we present first steps towards n-doped ZnO-based TCO materials via substitution in the anion lattice (O2- versus halogenides). A special approach is presented, using novel single-source precursors containing a potential excerpt of the target lattice 'HalZn·Zn3O3' preorganized on the molecular scale (Hal = I, Br, Cl). We report about the synthesis of the precursors, their transformation into halogene-containing ZnO materials, and finally structural, optical and electronic properties are investigated using a combination of techniques including FT-Raman, low-T photoluminescence, impedance and THz spectroscopies. © 2015 Lehr et al.


  • ArF excimer laser microprocessing of polymer optical fibers for photonic sensor applications

    Athanasekos L., Vasileiadis M., El Sachat A., Vainos N.A., Riziotis C. Journal of Optics (United Kingdom); 17 (1, 015402) 2015. 10.1088/2040-8978/17/1/015402. IF: 2.059

    A study of polymer optical fiber microstructuring by use of deep ultraviolet excimer laser radiation at 193 nm wavelength is performed. The ablation characteristics of the fiber cladding and core materials are analyzed comparatively. The laser irradiation effects are dynamically studied by on-line monitoring of the laser ablation induced waveguiding losses, the latter being correlated with the spatial structuring parameters. The fiber surface is modified to incorporate cavities, which are subsequently employed as sensitive material receptors for the development of customized photonic sensors. The sensing capability of the microstructured plastic optical fibers is demonstrated by ammonia and humidity detection. © 2015 IOP Publishing Ltd.


  • Assessment of block and random copolymer overlayers on polymer optical fibers toward protein detection through electrostatic interaction

    El Sachat A., Meristoudi A., Pispas S., Riziotis C. Journal of Polymer Science, Part B: Polymer Physics; 53 (5): 327 - 334. 2015. 10.1002/polb.23632. IF: 3.830

    A simple fiber optic based scheme for the selective detection of proteins, based on surface electrostatic interactions, is presented. The implementation of this method is conducted using a modified polymer optical fiber's surface and thin overlayers of properly designed sensitive copolymer materials with predesigned molecular characteristics. Block poly(styrene-b-2vinylpyridine) (PS-b-P2VP) and random PS-r-P2VP copolymers of the same monomers and similar molecular weights, were modified and used as sensing materials. This configuration proved to be efficient concerning the fast detection of charged proteins, and also the efficient discrimination of differently charged proteins such as lysozyme and bovine serum albumin. Results on the sensing performance of block and random copolymers are also discussed drawing conclusion on their efficiency given their considerable different fabrication cost. © 2014 Wiley Periodicals, Inc.


  • Electrical properties and strain distribution of Ge suspended structures

    Shah V.A., Rhead S.D., Finch J., Myronov M., Reparaz J.S., Morris R.J., Wilson N.R., Kachkanov V., Dolbnya I.P., Halpin J.E., Patchett D., Allred P., Colston G., Sawhney K.J.S., Sotomayor Torres C.M., Leadley D.R. Solid-State Electronics; 108: 13 - 18. 2015. 10.1016/j.sse.2014.12.004. IF: 1.504

    Germanium membranes and microstructures of 50-1000 nm thickness have been fabricated by a combination of epitaxial growth on a Si substrate and simple etching processes. The strain in these structures has been measured by high-resolution micro-X-ray diffraction and micro-Raman spectroscopy. The strain in these membranes is extremely isotropic and the surface is observed to be very smooth, with an RMS roughness below 2 nm. The process of membrane fabrication also serves to remove the misfit dislocation network that originally forms at the Si/Ge interface, with benefits for the mechanical, optical and electrical properties of the crystalline membranes. © 2015 Elsevier Ltd. All rights reserved.


  • Elucidation of the wettability of graphene through a multi-length-scale investigation approach

    Amadei C.A., Lai C.-Y., Esplandiu M.J., Alzina F., Vecitis C.D., Verdaguer A., Chiesa M. RSC Advances; 5 (49): 39532 - 39538. 2015. 10.1039/c5ra04397b. IF: 3.840

    Univocal conclusions around the wettability of graphene exposed to environmental conditions remain elusive despite the recent efforts of several research groups. The main discrepancy rests on the question of whether a graphene monolayer (GML) is transparent or not to water and more generally what the role is that the substrate plays in determining the degree of wetting of the GML. In this work, we investigate the water transparency of GML by means of a multi-length-scale approach. We complement traditional static contact angle measurements and environmental scanning electron microscopy experiments with atomic force microscopy based force spectroscopy to assess the role that intermolecular interactions play in determining the wetting of GML. To gain deeper insight into the wetting transparency issue, we perform experiments on inert metals, such as gold and platinum, covered or not covered by GML. The comparison of the results obtained for different systems (i.e. GML covered and uncovered inert metals), provides unambiguous evidence that supports the non-wetting transparency theory of GML. This work aims to assist the development of technologies based on graphene-water interaction, such as graphitic membranes for water separation processes. © The Royal Society of Chemistry 2015.


  • In-line metrology setup for periodic nanostructures based on sub-wavelength diffraction

    Kreuzer M., Gomis Bresco J., Sledzinska M., Sotomayor Torres C.M. Proceedings of SPIE - The International Society for Optical Engineering; 9628 ( 96281Q) 2015. 10.1117/12.2191346. IF: 0.000

    The analysis of diffracted light from periodic structures is shown to be a versatile metrology technique applicable to inline metrology for periodic nanostructures. We show that 10 nm changes in periodic structures can be traced optically by means of sub-wavelength diffraction. Polymer gratings were fabricated by electron beam lithography. The gratings have a common periodicity of 6 μm, but different line width, ranging from 370 to 550 nm in 10 nm steps. A comparison between the resulting diffraction patterns shows marked differences in intensity which are used to sense nanometre scale deviations in periodic structures. © 2015 SPIE.


  • Mapping self-assembled dots and line arrays by image analysis for quantification of defect density and alignment

    Simao C., Tuchapsky D., Khunsin W., Amann A., Morris M.A., Sotomayor Torres C.M. Proceedings of SPIE - The International Society for Optical Engineering; 9423 (942322) 2015. 10.1117/12.2085748. IF: 0.000

    Bottom-up alternative lithographic masks from directed self-assembly systems have been extending the limits of critical dimensions in a cost-effective manner although great challenges in controlling defectivity remain open. Particularly, defectivity and dimensional metrology are two main challenges in lithography due to the increasing miniaturisation of circuits. To gain insights about the percentage of alignment, defectivity and order quantification, directed self-assembly block copolymer fingerprints were investigated via an image analysis methodology. Here we present the analysis of hexagonal phase of polystyrene-b-polydimethylsiloxane (PS-b-PDMS) forming linear patterns in topological substrates. From our methodology, we have performed dimensional metrology estimating pitch size and error, and the linewidth of the lines was estimated. In parallel, the methodology allowed us identification and quantification of typical defects observable in self-assembly, such as turning points, disclination or branching points, break or lone points and end points. The methodology presented here yields high volume statistical data useful for advancing dimensional metrology and defect analysis of self- and directed assembly systems. © 2015 SPIE.


  • Nanoparticle shape anisotropy and photoluminescence properties: Europium containing ZnO as a Model Case

    Gerigk M., Ehrenreich P., Wagner M.R., Wimmer I., Reparaz J.S., Sotomayor Torres C.M., Schmidt-Mende L., Polarz S. Nanoscale; 7 (40): 16969 - 16982. 2015. 10.1039/c5nr02550h. IF: 7.394

    The precise control over electronic and optical properties of semiconductor (SC) materials is pivotal for a number of important applications like in optoelectronics, photocatalysis or in medicine. It is well known that the incorporation of heteroelements (doping as a classical case) is a powerful method for adjusting and enhancing the functionality of semiconductors. Independent from that, there already has been a tremendous progress regarding the synthesis of differently sized and shaped SC nanoparticles, and quantum-size effects are well documented experimentally and theoretically. Whereas size and shape control of nanoparticles work fairly well for the pure compounds, the presence of a heteroelement is problematic because the impurities interfere strongly with bottom up approaches applied for the synthesis of such particles, and effects are even stronger, when the heteroelement is aimed to be incorporated into the target lattice for chemical doping. Therefore, realizing coincident shape control of nanoparticle colloids and their doping still pose major difficulties. Due to a special mechanism of the emulsion based synthesis method presented here, involving a gelation of emulsion droplets prior to crystallization of shape-anisotropic ZnO nanoparticles, heteroelements can be effectively entrapped inside the lattice. Different nanocrystal shapes such as nanorods, -prisms, -plates, and -spheres can be obtained, determined by the use of certain emulsification agents. The degree of morphologic alterations depends on the type of incorporated heteroelement Mn+, concentration, and it seems that some shapes are more tolerant against doping than others. Focus was then set on the incorporation of Eu3+ inside the ZnO particles, and it was shown that nanocrystal shape and aspect ratios could be adjusted while maintaining a fixed dopant level. Special PL properties could be observed implying energy transfer from ZnO excited near its band-gap (3.3 eV) to the Eu3+ states mediated by defect luminescence of the nanoparticles. Indications for an influence of shape on photoluminescence (PL) properties were found. Finally, rod-like Eu@ZnO colloids were used as tracers to investigate their uptake into biological samples like HeLa cells. The PL was sufficient for identifying green and red emission under visible light excitation. © 2015 The Royal Society of Chemistry.


  • Optical and mechanical properties of nanofibrillated cellulose: Toward a robust platform for next-generation green technologies

    Simão C.D., Reparaz J.S., Wagner M.R., Graczykowski B., Kreuzer M., Ruiz-Blanco Y.B., García Y., Malho J.-M., Goñi A.R., Ahopelto J., Sotomayor Torres C.M. Carbohydrate Polymers; 126: 40 - 46. 2015. 10.1016/j.carbpol.2015.03.032. IF: 4.074

    Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. To elucidate the optical and mechanical stability of nanofibrillated cellulose as a standalone platform, herein we report on three main findings: (i) for the first time an experimental determination of the optical bandgap of nanofibrillated cellulose, important for future modeling purposes, based on the onset of the optical bandgap of the nanofibrillated cellulose film at Eg ≈ 275 nm (4.5 eV), obtained using absorption and cathodoluminescence measurements. In addition, comparing this result with ab-initio calculations of the electronic structure the exciton binding energy is estimated to be Eex ≈ 800 meV; (ii) hydrostatic pressure experiments revealed that nanofibrillated cellulose is structurally stable at least up to 1.2 GPa; and (iii) surface elastic properties with repeatability better than 5% were observed under moisture cycles with changes of the Young modulus as large as 65%. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applications. ©2015 Elsevier Ltd. All rights reserved.


  • Phonon dispersion in hypersonic two-dimensional phononic crystal membranes

    Graczykowski B., Sledzinska M., Alzina F., Gomis-Bresco J., Reparaz J.S., Wagner M.R., Sotomayor Torres C.M. Physical Review B - Condensed Matter and Materials Physics; 91 (7, 075414) 2015. 10.1103/PhysRevB.91.075414. IF: 3.736

    We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significantly modify the propagation of thermally activated GHz phonons. We use numerical modeling based on the finite element method to analyze the experimental results and determine polarization, symmetry, or three-dimensional localization of observed modes. © 2015 American Physical Society.


  • Polymer-induced swelling of solid-supported lipid membranes

    Kreuzer M., Trapp M., Dahint R., Steitz R. Membranes; 6 (1, 2) 2015. 10.3390/membranes6010002. IF: 0.000

    In this paper, we study the interaction of charged polymers with solid-supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes by in-situ neutron reflectivity. We observe an enormous swelling of the oligolamellar lipid bilayer stacks after incubation in solutions of poly(allylamine hydrochloride) (PAH) in D2O. The positively charged polyelectrolyte molecules interact with the lipid bilayers and induce a drastic increase in their d-spacing by a factor of ~4. Temperature, time, and pH influence the swollen interfacial lipid linings. From our study, we conclude that electrostatic interactions introduced by the adsorbed PAH are the main cause for the drastic swelling of the lipid coatings. The DMPC membrane stacks do not detach from their solid support at T > Tm. Steric interactions, also introduced by the PAH molecules, are held responsible for the stabilizing effect. We believe that this novel system offers great potential for fundamental studies of biomembrane properties, keeping the membrane’s natural fluidity and freedom, decoupled from a solid support at physiological conditions. © 2015 by the authors; licensee MDPI, Basel, Switzerland.


  • Reconstructing phonon mean-free-path contributions to thermal conductivity using nanoscale membranes

    Cuffe J., Eliason J.K., Maznev A.A., Collins K.C., Johnson J.A., Shchepetov A., Prunnila M., Ahopelto J., Sotomayor Torres C.M., Chen G., Nelson K.A. Physical Review B - Condensed Matter and Materials Physics; 91 (24, 245423) 2015. 10.1103/PhysRevB.91.245423. IF: 3.736

    Knowledge of the mean-free-path distribution of heat-carrying phonons is key to understanding phonon-mediated thermal transport. We demonstrate that thermal conductivity measurements of thin membranes spanning a wide thickness range can be used to characterize how bulk thermal conductivity is distributed over phonon mean free paths. A noncontact transient thermal grating technique was used to measure the thermal conductivity of suspended Si membranes ranging from 15-1500 nm in thickness. A decrease in the thermal conductivity from 74-13% of the bulk value is observed over this thickness range, which is attributed to diffuse phonon boundary scattering. Due to the well-defined relation between the membrane thickness and phonon mean-free-path suppression, combined with the range and accuracy of the measurements, we can reconstruct the bulk thermal conductivity accumulation vs. phonon mean free path, and compare with theoretical models. © 2015 American Physical Society.


  • Residual layer-free Reverse Nanoimprint Lithography on silicon and metal-coated substrates

    Fernández A., Medina J., Benkel C., Guttmann M., Bilenberg B., Thamdrup L.H., Nielsen T., Sotomayor Torres C.M., Kehagias N. Microelectronic Engineering; 141: 56 - 61. 2015. 10.1016/j.mee.2014.11.025. IF: 1.197

    In this work we demonstrate that Reverse Nanoimprint Lithography is a feasible and flexible lithography technique applicable to the transfer of micro and nano polymer structures with no residual layer over areas of cm2 areas on silicon, metal and non-planar substrates. We used a flexible polydimethylsiloxane stamp with hydrophobic features. We present residual layer-free patterns imprinted using a commercial poly(methylmethacrylate) thermoplastic polymer over silicon, nickel and pre-patterned substrates. Our versatile patterning technology is adaptable to free form nano structuring and has coupling to adhesion technologies. © 2014 Elsevier B.V. All rights reserved.


  • Structural characterisation of slightly Fe-doped SrTiO3 grown via a sol–gel hydrothermal synthesis

    Fuentes S., Muñoz P., Barraza N., Chávez-Ángel E., Sotomayor Torres C.M. Journal of Sol-Gel Science and Technology; 75 (3): 593 - 601. 2015. 10.1007/s10971-015-3730-4. IF: 1.532

    Abstract: A detailed structural study of the incorporation of Fe into SrTiO3 nanoparticles is reported. Slightly iron-doped strontium titanate nanoparticles with 0, 1, 3 and 5 mol% concentration of iron were grown using a sol–gel hydrothermal process and characterised using Raman scattering, X-ray photoelectron and X-ray diffraction spectroscopy. The amorphisation of the nanostructures was observed as the iron content increased, which was confirmed by the TEM images. The XPS results indicated that the oxidation states of the Sr atoms were maintained in 2+. However, a mixture of Fe3+ and Fe4+ atoms was observed as the Fe content increased, resulting in a significant number of oxygen vacancies in the perovskite structure. The analysis of Raman spectra indicated that the intensity, linewidth and frequency shift of the TO4 phonon can be used as an indicator of the Fe content as well as a local temperature probe for future thermal analysis. Graphical abstract: Temperature evolution of the Raman spectra of STO:Fe 1 mol%. The peaks with star correspond to the second-order processes. (b) Temperature dependence of the TO4 phonon mode. Blue dots denote measured Raman spectra, and the red solid lines are the Lorentzian fits to respective spectra.[Figure not available: see fulltext.] © 2015, Springer Science+Business Media New York.


  • Tuning of heat transport across thin films of polycrystalline AlN via multiscale structural defects

    Jaramillo-Fernandez J., Ordonez-Miranda J., Ollier E., Sanatinia R., Kataria H., Chavez-Angel E., Volz S., Sotomayor-Torres M. ECS Transactions; 69 (9): 53 - 64. 2015. 10.1149/06909.0053ecst. IF: 0.000

    The effective thermal conductivity of nanocrystalline films of AlN with inhomogeneous microstructure is investigated experimentally and theoretically. This is done by measuring the thermal conductivity of the samples with the 3-omega method and characterizing their microstructure by means of electron microscopy. The relative effect of the microstructure and the interface thermal resistance on the thermal conductivity is quantified through an analytical model. Thermal measurements showed that when the thickness of an AlN film is reduced from 1460 to 270 nm, its effective thermal conductivity decreases from 8.21 to 3.12 WYm-1?K-1, which is two orders of magnitude smaller than its bulk counterpart value. It is shown that both the size effects of the phonon mean free paths and the intrinsic thermal resistance resulting from the inhomogeneous microstructure predominate for thicker films, while the contribution of the interface thermal resistance strengthens as the film thickness is scaled down. The obtained results demonstrate that the structural inhomogeneity in polycrystalline AlN films can be efficiently used to tune their cross- plane thermal conductivity. In addition, thermal conductivity measurements of epitaxially grown InP layers on silicon using Raman spectroscopy are reported. ©The Electrochemical Society.


  • Tuning Thermal Transport in Ultrathin Silicon Membranes by Surface Nanoscale Engineering

    Neogi S., Reparaz J.S., Pereira L.F.C., Graczykowski B., Wagner M.R., Sledzinska M., Shchepetov A., Prunnila M., Ahopelto J., Sotomayor-Torres C.M., Donadio D. ACS Nano; 9 (4): 3820 - 3828. 2015. 10.1021/nn506792d. IF: 12.881

    A detailed understanding of the connections of fabrication and processing to structural and thermal properties of low-dimensional nanostructures is essential to design materials and devices for phononics, nanoscale thermal management, and thermoelectric applications. Silicon provides an ideal platform to study the relations between structure and heat transport since its thermal conductivity can be tuned over 2 orders of magnitude by nanostructuring. Combining realistic atomistic modeling and experiments, we unravel the origin of the thermal conductivity reduction in ultrathin suspended silicon membranes, down to a thickness of 4 nm. Heat transport is mostly controlled by surface scattering: rough layers of native oxide at surfaces limit the mean free path of thermal phonons below 100 nm. Removing the oxide layers by chemical processing allows us to tune the thermal conductivity over 1 order of magnitude. Our results guide materials design for future phononic applications, setting the length scale at which nanostructuring affects thermal phonons most effectively. © 2015 American Chemical Society.


2014

  • A novel contactless technique for thermal field mapping and thermal conductivity determination: Two-Laser Raman Thermometry

    Reparaz, J.S.; Chavez-Angel, E.; Wagner, M.R.; Graczykowski, B.; Gomis-Bresco, J.; Alzina, F.; Sotomayor Torres, C.M. Review of Scientific Instruments; 2014. 10.1063/1.4867166. IF: 1.584


  • A one-dimensional optomechanical crystal with a complete phononic band gap

    Gomis-Bresco, J.; Navarro-Urrios, D.; Oudich, M.; El-Jallal, S.; Griol, A.; Puerto, D.; Chavez, E.; Pennec, Y.; Djafari-Rouhani, B.; Alzina, F.; Martinez, A.; Sotomayor Torres, C.M. Nature Communications; 2014. 10.1038/ncomms5452. IF: 10.742


  • A physics-based scoring function for protein structural decoys: Dynamic testing on targets of CASP-ROLL

    Ruiz-Blanco, Y.B.; Marrero-Ponce, Y.; García, Y.; Puris, A.; Bello, R.; Green, J.; Sotomayor Torres, C.M. Chemical Physics Letters; 610-611: 135 - 140. 2014. 10.1016/j.cplett.2014.07.014. IF: 1.991


  • A Study of the Kinetics and Mechanism of Rapid Self- assembly in Block Copolymer Thin Films during ¿Solvo-microwave¿ Annealing

    Mokarian-Tabari, P. ; Cummins, C. ; Rasappa, S. ; Simão, C. C. D.; Sotomayor Torres, C. M.; Holmes, J. D.; Morris, M. A. Langmuir : the ACS journal of surfaces and colloids; 30 (35): 10728 - 10739. 2014. 10.1021/la503137q. IF: 4.384


  • Acoustic phonon propagation in ultra-thin Si membranes under biaxial stress field

    Graczykowski, B. ; Gomis-Bresco, J.; Alzina, F.; Reparaz, J.S.; Shchepetov, A.; Prunnila, M.; Ahopelto, J.; Sotomayor Torres, C.M. New Journal of Physics; 2014. 10.1088/1367-2630/16/7/073024. IF: 3.671


  • Defect analysis and alignment quantification of line arrays prepared by directed self-assembly of a block copolymer

    Simao, C.; Tuchapsky, D.; Khunsin, W.; Amann, A.; Morris, M.A.; Sotomayor Torres, C.M. Proceedings of SPIE - The International Society for Optical Engineering; 2014. . IF: 0.000


  • Dynamical back-action at 5.5 GHz in a corrugated optomechanical beam

    Navarro-Urrios, D.; Gomis-Bresco, J.; El-Jallal, S.; Oudich, M.; Pitanti, A.; Capuj, N.; Tredicucci, A.; Alzina, F.; Griol, A.; Pennec, Y.; Djafari-Rouhani, B.; Martínez, A.; Sotomayor Torres, C.M. AIP Advances; 2014. 10.1063/1.4902171. IF: 1.590


  • Electrocatalytic tuning of biosensing response through electrostatic or hydrophobic enzyme-graphene oxide interactions

    Baptista-Pires, L.; Pérez-López, B.; Mayorga-Martinez, C.C.; Morales-Narváez, E.; Domingo, N.; Esplandiu, M.J.; Alzina, F.; Torres, C.M.S.; Merkoçi, A. Biosensors and Bioelectronics; 61: 655 - 662. 2014. 10.1016/j.bios.2014.05.028. IF: 6.451


  • Embedded inkjet printed silver grids for ITO-free organic solar cells with high fill factor

    Burgués-Ceballos, I.; Kehagias, N.; Sotomayor-Torres, C.M.; Campoy-Quiles, M.; Lacharmoise, P.D. Solar Energy Materials and Solar Cells; 127: 50 - 57. 2014. 10.1016/j.solmat.2014.03.024. IF: 5.030


  • Formation of Titanium Nanostructures on Block Copolymer Templates with Varying Molecular Weights

    Kreuzer, M.; Simão, C.; Diaz, A.; Sotomayor Torres, C.M. Macromolecules; 47 (24): 8691 - 8699. 2014. 10.1021/ma501605s. IF: 5.927


  • High quality single crystal Ge nano-membranes for opto-electronic integrated circuitry

    Shah, V.A.; Rhead, S.D.; Halpin, J.E.; Trushkevych, O.; Chavez-Angel, E.; Shchepetov, A.; Kachkanov, V.; Wilson, N.R.; Myronov, M.; Reparaz, J.S.; Edwards, R.S.; Wagner, M.R.; Alzina, F.; Dolbnya, I.P.; Patchett, D.H.; Allred, P.S.; Prest, M.J.; Gammon, P.M.; Prunnila, M.; Whall, T.E.; Parker, E.H.C.; Sotomayor Torres, C.M.; Leadley, D.R. Journal of Applied Physics; 2014. 10.1063/1.4870807. IF: 2.185


  • Hypersonic phonon propagation in one-dimensional surface phononic crystal

    Graczykowski, B.; Sledzinska, M.; Kehagias, N.; Alzina, F.; Reparaz, J.S.; Sotomayor Torres, C.M. Applied Physics Letters; 2014. 10.1063/1.4870045. IF: 3.515


  • Influence of the relative molecular orientation on interfacial charge-transfer Excitons at donor/acceptor Nanoscale heterojunctions

    Aghamohammadi, M.; Fernández, A.; Schmidt, M.; Pérez-Rodríguez, A.; Goñi, A.R.; Fraxedas, J.; Sauthier, G.; Paradinas, M.; Ocal, C.; Barrena, E. Journal of Physical Chemistry C; 118 (27): 14833 - 14839. 2014. 10.1021/jp5041579. IF: 4.835


  • Li-doped ZnO nanorods with single-crystal quality-non-classical crystallization and self-assembly into mesoporous materials

    Lizandara-Pueyo, C.; Dilger, S.; Wagner, M.R.; Gerigk, M.; Hoffmann, A.; Polarz, S. CrystEngComm; 16 (8): 1525 - 1531. 2014. 10.1039/c3ce41670d. IF: 3.858


  • Modification of Akhieser mechanism in Si nanomembranes and thermal conductivity dependence of the Q-factor of high frequency nanoresonators

    Chávez-Ángel, E.; Zarate, R.A.; Gomis-Bresco, J.; Alzina, F.; Sotomayor Torres, C.M. Semiconductor Science and Technology; 2014. 10.1088/0268-1242/29/12/124010. IF: 2.206


  • Nanoarchitecture effects on persistent room temperature photoconductivity and thermal conductivity in ceramic semiconductors: Mesoporous, yolk-shell, and hollow ZnO spheres

    Dilger, S.; Wessig, M.; Wagner, M.R.; Reparaz, J.S.; Sotomayor Torres, C.M.; Qijun, L.; Dekorsy, T.; Polarz, S. Crystal Growth and Design; 14 (9): 4593 - 4601. 2014. 10.1021/cg500680g. IF: 4.558


  • Nanostructured p-type Cr/V2O5 thin films with boosted thermoelectric properties

    Loureiro, J.; Santos, J.R.; Nogueira, A.; Wyczisk, F.; Divay, L.; Reparaz, S.; Alzina, F.; Sotomayor Torres, C.M.; Cuffe, J.; Montemor, F.; Martins, R.; Ferreira, I. Journal of Materials Chemistry A; 2 (18): 6456 - 6462. 2014. 10.1039/c3ta15168a. IF: 0.000


  • Optical and mechanical mode tuning in an optomechanical crystal with light-induced thermal effects

    Navarro-Urrios, D. ; Gomis-Bresco, J. ; Capuj, N. E.; Alzina, F. ; Griol, A. ; Puerto, D. ; Martínez, A. ; Sotomayor-Torres, C. M. Journal of Applied Physics; 2014. 10.1063/1.4894623. IF: 2.185


  • Optomechanic interaction in a corrugated phoxonic nanobeam cavity

    Oudich, M.; El-Jallal, S.; Pennec, Y. ;Djafari-Rouhani, B. ; Gomis-Bresco, J. ; Navarro-Urrios, D. ; Sotomayor Torres, C. M.; Martínez, A.; Makhoute, A. Physical Review B - Condensed Matter and Materials Physics; 2014. 10.1103/PhysRevB.89.245122. IF: 3.664


  • Order and defectivity nanometrology by image processing and analysis of sub-20 nm BCPs features for lithographic applications

    Simao, C.; Tuchapsky, D.; Khunsin, W.; Amann, A.; Morris, M.A.; Sotomayor Torres, C. Proceedings of SPIE - The International Society for Optical Engineering; 2014. . IF: 0.000


  • Order quantification of hexagonal periodic arrays fabricated by in situ solvent-assisted nanoimprint lithography of block copolymers

    Simão, C.; Khunsin, W.; Kehagias, N.; Salaun, M.; Zelsmann, M.; Morris, M.A.; Sotomayor Torres, C.M. Nanotechnology; 2014. 10.1088/0957-4484/25/17/175703. IF: 3.672


  • Ordered 2D colloidal photonic crystals on gold substrates by surfactant-assisted fast-rate dip coating

    Armstrong, E.; Khunsin, W.; Osiak, M.; Blömker, M.; Torres, C.M.S.; O'Dwyer, C. Small; 10 (10): 1895 - 1901. 2014. 10.1002/smll.201303616. IF: 7.514


  • Reduction of the thermal conductivity in free-standing silicon nano-membranes investigated by non-invasive Raman thermometry

    Chávez-Ángel, E.; Reparaz, J.S.; Gomis-Bresco, J.; Wagner, M.R.; Cuffe, J.; Graczykowski, B.; Shchepetov, A.; Jiang, H.; Prunnila, M.; Ahopelto, J.; Alzina, F.; Sotomayor Torres, C.M. APL Materials; 2014. 10.1063/1.4861796. IF: 0.000


  • Synthetic Routes for the Preparation of Ordered Vanadium Oxide Inverted Opal Electrodes for Li-Ion Batteries

    Armstrong, E.; Khunsin, W.; Sotomayor Torres, C.M.; Osiaka, M.; O'Dwyera, C. ECS Transactions; 58 (25): 7 - 14. 2014. 10.1149/05825.0007ecst. IF: 0.000


  • Tensile strain mapping in flat germanium membranes

    Rhead, S.D.; Halpin, J.E.; Shah, V.A.; Myronov, M.; Patchett, D.H.; Allred, P.S.; Kachkanov, V.; Dolbnya, I.P.; Reparaz, J.S.; Wilson, N.R.; Sotomayor Torres, C.M.; Leadley, D.R. Applied Physics Letters; 2014. 10.1063/1.4874836. IF: 3.515


  • Transparent aluminium zinc oxide thin films with enhanced thermoelectric properties

    Loureiro, J.; Neves, N.; Barros, R.; Mateus, T.; Santos, R.; Filonovich, S.; Reparaz, S.; Sotomayor-Torres, C.M.; Wyczisk, F.; Divay, L.; Martins, R.; Ferreira, I. Journal of Materials Chemistry A; 2 (18): 6649 - 6655. 2014. 10.1039/c3ta15052f. IF: 0.000


2013

  • Anisotropic 18O tracer diffusion in epitaxial films of GdBaCo2O5+δ cathode material with different orientations

    Zapata, J.; Burriel, M.; García, P.; Kilner, J.A.; Santiso, J. Journal of Materials Chemistry A; 1: 7408 - 7414. 2013. 10.1039/c3ta10749c. IF: 6.108


  • Chemical strain kinetics induced by oxygen surface exchange in epitaxial films explored by time-resolved X-ray diffraction

    Moreno, R.; García, P.; Zapata, J.; Roqueta, J.; Chaigneau, J.; Santiso, J. Chemistry of Materials; 25: 3640 - 3647. 2013. 10.1021/cm401714d. IF: 8.238


  • Comparison of two types of vertically aligned ZnO NRs for highly efficient polymer solar cells

    Gonzalez-Valls, I.; Angmo, D.; Gevorgyan, S.A.; Sebastián Reparaz, J.; Krebs, F.C.; Lira-Cantu, M. Journal of Polymer Science, Part B: Polymer Physics; 51: 272 - 280. 2013. 10.1002/polb.23214. IF: 2.221


  • Core-shell tin oxide, indium oxide, and indium tin oxide nanoparticles on silicon with tunable dispersion: Electrochemical and structural characteristics as a hybrid Li-ion battery anode

    Osiak, M.J.; Armstrong, E.; Kennedy, T.; Sotomayor Torres, C.M.; Ryan, K.M.; ODwyer, C. ACS applied materials & interfaces; 5 (16): 8195 - 8202. 2013. 10.1021/am4023169. IF: 5.008


  • Direct measurement of room-temperature nondiffusive thermal transport over micron distances in a silicon membrane

    Johnson, J.A.; Maznev, A.A.; Cuffe, J.; Eliason, J.K.; Minnich, A.J.; Kehoe, T.; Torres, C.M.S.; Chen, G.; Nelson, K.A. Physical Review Letters; 2013. 10.1103/PhysRevLett.110.025901. IF: 7.943


  • Electrical detection of spin precession in freely suspended graphene spin valves on cross-linked poly(methyl methacrylate)

    Neumann, I.; Van De Vondel, J.; Bridoux, G.; Costache, M.V.; Alzina, F.; Torres, C.M.S.; Valenzuela, S.O. Small; 9 (1): 156 - 160. 2013. 10.1002/smll.201201194. IF: 7.823


  • Epitaxial growth of an antireflective, conductive, graded index ITO nanowire layer

    O'Dwyer, C.; Sotomayor Torres, C. Frontiers of Physics; 0 0 2013. 10.3389/fphy.2013.00018. IF: 0.000


  • Epitaxial growth of visible to infra-red transparent conducting In 2O3 nanodot dispersions and reversible charge storage as a Li-ion battery anode

    Osiak, M.; Khunsin, W.; Armstrong, E.; Kennedy, T.; Torres, C.M.S.; Ryan, K.M.; ODwyer, C. Nanotechnology; 2013. 10.1088/0957-4484/24/6/065401. IF: 3.842


  • Er-doped light emitting slot waveguides monolithically integrated in a silicon photonic chip

    Ramírez, J.M.; Ferrarese Lupi, F.; Berencén, Y.; Anopchenko, A.; Colonna, J.P.; Jambois, O.; Fedeli, J.M.; Pavesi, L.; Prtljaga, N.; Rivallin, P.; Tengattini, A.; Navarro-Urrios, D.; Garrido, B. Nanotechnology; 24 2013. 10.1088/0957-4484/24/11/115202. IF: 3.842


  • Fabrication of highly ordered sub-20 nm silicon nanopillars by block copolymer lithography combined with resist design

    Salaun, M.; Zelsmann, M.; Archambault, S.; Borah, D.; Kehagias, N.; Simao, C.; Lorret, O.; Shaw, M.T.; Sotomayor Torres, C.M.; Morris, M.A. Journal of Materials Chemistry C; 1 (22): 3544 - 3550. 2013. 10.1039/c3tc30300d. IF: 6.108


  • Global stability of protein folding from an empirical free energy function

    Ruiz-Blanco, Y.B.; Marrero-Ponce, Y.; Paz, W.; García, Y.; Salgado, J. Journal of Theoretical Biology; 321: 44 - 53. 2013. 10.1016/j.jtbi.2012.12.023. IF: 2.351


  • Influence of reactant type on the Sr incorporation grade and structural characteristics of Ba1-xSrxTiO3 (x=0-1) grown by sol-gel-hydrothermal synthesis

    Fuentes, S.; Chávez, E.; Padilla-Campos, L.; Diaz-Droguett, D.E. Ceramics International; 39 (8): 8823 - 8831. 2013. 10.1016/j.ceramint.2013.04.070. IF: 1.789


  • Laser emission in Nd3+ doped barium-titanium-silicate microspheres under continuous and chopped wave pumping in a non-coupled pumping scheme

    Martin, L.L.; Navarro-Urrios, D.; Ferrarese-Lupi, F.; Perez-Rodriguez, C.; Martin, I.R.; Montserrat, J.; Dominguez, C.; Garrido, B.; Capuj, N. Laser Physics; 23 2013. 10.1088/1054-660X/23/7/075801. IF: 2.545


  • Lasing in nanoimprinted two-dimensional photonic crystal band-edge lasers

    Reboud, V.; Romero-Vivas, J.; Lovera, P.; Kehagias, N.; Kehoe, T.; Redmond, G.; Sotomayor Torres, C.M. Applied Physics Letters; 2013. 10.1063/1.4790646. IF: 3.794


  • Lifetimes of confined acoustic phonons in ultrathin silicon membranes

    Cuffe, J.; Ristow, O.; Chávez, E.; Shchepetov, A.; Chapuis, P.-O.; Alzina, F.; Hettich, M.; Prunnila, M.; Ahopelto, J.; Dekorsy, T.; Sotomayor Torres, C.M. Physical Review Letters; 110 (9) 2013. 10.1103/PhysRevLett.110.095503. IF: 7.943


  • Martensitic phase transition in Cu-14%Al-4%Ni shape memory alloys studied by Brillouin light scattering

    Graczykowski, B.; Mielcarek, S.; Breczewski, T.; No, M.L.; San-Juan, J.; Mroz, B. Smart Materials and Structures; 22 (8) 2013. 10.1088/0964-1726/22/8/085027. IF: 2.024


  • MBE Growth and Structural and Electrochemical Characterization of Tin Oxide and Indium Tin Oxide Nanoparticles Grown on Silicon for Li-ion Battery Anodes

    Osiak, M.; Armstrong, E.; Kennedy, T.; Sotomayor Torres, C. M.; Ryan, K.; O'Dwyer, C. ECS Transactions; 53 (10): 1 - 10. 2013. 10.1149/05310.0001ecst. IF: 0.000


  • Metallic nanoparticles enhanced the spontaneous emission of semiconductor nanocrystals embedded in nanoimprinted photonic crystals

    Reboud, V.; Lévêque, G.; Striccoli, M.; Placido, T.; Panniello, A.; Curri, M.L.; Alducin, J.A.; Kehoe, T.; Kehagias, N.; Mecerreyes, D.; Newcomb, S.B.; Iacopino, D.; Redmond, G.; Torres, C.M.S. Nanoscale; 5 (1): 239 - 245-245. 2013. 10.1039/c2nr32134c. IF: 6.233


  • Nanoscale imaging of InN segregation and polymorphism in single vertically aligned InGaN/GaN multi quantum well nanorods by tip-enhanced Raman scattering

    Poliani, E.; Wagner, M.R.; Reparaz, J.S.; Mandl, M.; Strassburg, M.; Kong, X.; Trampert, A.; Sotomayor Torres, C.M.; Hoffmann, A.; Maultzsch, J. Nano Letters; 13 (7): 3205 - 3212-3212. 2013. 10.1021/nl401277y. IF: 13.025


  • Non Local Corrections to the Electronic Structure of Non Ideal Electron Gases: The Case of Graphene and Tyrosine

    García, Y.; Cuffe, J.; Alzina, F.; Sotomayor Torres, C. M. Journal of Modern Physics; 4 (4): 522 - 527. 2013. 10.4236/jmp.2013.44074. IF: 0.000


  • Rechargeable Li-Ion Battery Anode of Indium Oxide with Visible to Infra-Red Transparency

    Osiak, M.; Khunsin, W.; Armstrong, E.; Kennedy, T.; Sotomayor Torres, C.M.; Ryan, K.M.; O¿Dwyer, C. ECS Transactions; 53 (6): 53 - 61. 2013. 10.1149/05306.0053ecst. IF: 0.000


  • Soft-graphoepitaxy using nanoimprinted polyhedral oligomeric silsesquioxane substrates for the directed self-Assembly of PS-b-PDMS

    Borah, D.; Simao, C.D.; Senthamaraikannan, R.; Rasappa, S.; Francone, A.; Lorret, O.; Salaun, M.; Kosmala, B.; Kehagias, N.; Zelsmann, M.; Sotomayor-Torres, C.M.; Morris, M.A. European Polymer Journal; 49 (11): 3512 - 3521-3521. 2013. 10.1016/j.eurpolymj.2013.08.011. IF: 2.562


  • Spatial mapping of exciton lifetimes in single ZnO nanowires

    Reparaz, J. S.; Callsen, G. ; Wagner, M. R.; Güell, F. ; Morante, J. R.; Sotomayor Torres, C. M. ; Hoffmann, A. Applied Physics Letters; 1: 12103. 2013. 10.1063/1.4808441. IF: 3.794

    Open Access


  • Synthesis and structural characterization of nanocrystalline batio3 at various calcination temperatures

    Fuentes, S.; Céspedes, F.; Muñoz, P.; Chávez, E.; Padilla-Campos, L. Journal of the Chilean Chemical Society; 58 (4): 2077 - 2081. 2013. . IF: 0.000


  • Toward a 1.54 $mu$m Electrically Driven Erbium-Doped Silicon Slot Waveguide and Optical Amplifier

    Tengattini, A.; Gandolfi, D.; Prtljaga, N.; Anopchenko, A.; Ramirez, J.M.; Lupi, F.F.; Berencen, Y.; Navarro-Urrios, D.; Rivallin, P.; Surana, K.; Garrido, B.; Fedeli, J.-M.; Pavesi, L. Journal of Lightwave Technology; 31: 391 - 397. 2013. 10.1109/JLT.2012.2231050. IF: 2.555


  • Ultra-thin free-standing single crystalline silicon membranes with strain control

    Shchepetov, A.; Prunnila, M.; Alzina, F.; Schneider, L.; Cuffe, J.; Jiang, H.; Kauppinen, E.I.; Sotomayor Torres, C.M.; Ahopelto, J. Applied Physics Letters; 2013. 10.1063/1.4807130. IF: 3.794


2012

  • Calculation of the specific heat in ultra-thin free-standing silicon membranes

    Chávez, E. ; Cuffe, J.; Alzina, F. ; Sotomayor Torres, C. M. Journal of Physics: Conference Series; 395: 12105. 2012. .


  • Enhanced light extraction in ITO-free OLEDs using double-sided printed electrodes

    Reboud, V.; Khokhar, A.Z.; Sepúlveda, B.; Dudek, D.; Kehoe, T.; Cuffe, J.; Kehagias, N.; Lira-Cantu, M.; Gadegaard, N.; Grasso, V.; Lambertini, V.; Sotomayor Torres, C.M. Nanoscale; 4 (11): 3495 - 3500. 2012. .


  • Enhancement of extraction efficiency in nanoimprinted optical device structures

    Reboud, V. ; Sotomayor Torres, C. M. Proceedings of SPIE - The International Society for Optical Engineering; 84280B: 1. 2012. 10.1117/12.925189 .


  • Erbium emission in MOS light emitting devices: From energy transfer to direct impact excitation

    Ramírez, J.M.; Ferrarese Lupi, F.; Jambois, O.; Berencén, Y.; Navarro-Urrios, D.; Anopchenko, A.; Marconi, A.; Prtljaga, N.; Tengattini, A.; Pavesi, L.; Colonna, J.P.; Fedeli, J.M.; Garrido, B. Nanotechnology; 23 2012. 10.1088/0957-4484/23/12/125203.


  • Limit to the erbium ions emission in silicon-rich oxide films by erbium ion clustering

    Prtljaga, N.; Navarro-Urrios, D.; Tengattini, A.; Anopchenko, A.; Ramírez, J.M.; Rebled, J.M.; Estradé, S.; Colonna, J.-P.; Fedeli, J.-M.; Garrido, B.; Pavesi, L. Optical Materials Express; 2: 1278 - 1285. 2012. 10.1364/OME.2.001278.


  • Local characterization of rare-earth-doped single microspheres by combined microtransmission and microphotoluminescence techniques

    Navarro-Urrios, D.; Baselga, M.; Ferrarese Lupi, F.; Martín, L.L.; Pérez-Rodríguez, C.; Lavin, V.; Martín, I.R.; Garrido, B.; Capuj, N.E. Journal of the Optical Society of America B: Optical Physics; 29(12): 3293 - 3298. 2012. .


  • Noise-Assisted Crystallization of Opal Films

    Khunsin, W. ; Amann, A. ; Kocher-Oberlehner, G. ; Romanov, S. G.; Pullteap, S. ; Cheng Seat, H. ; O'Reilly, E. P.; Zentel, R.; Sotomayor Torres, C. M. Advanced Functional Materials; 22: 1812 - 1821. 2012. DOI: 10.1002/adfm.201102605.


  • Phonons in Slow Motion: Dispersion Relations in Ultra-Thin Si Membranes

    Cuffe, J. ; Chavez, E.; Shchepetov, A. ; Chapuis, P.O.; El Boudouti, E. H.; Alsina, F.; Dudek, D. ; Gomis-Bresco, J. ; Pennec, Y.; Djafari-Rouhani, B.; Prunnila, M.; Ahopelto, J.; Sotomayor Torres, C. M. Nano Letters; 12: 3569 - 3573. 2012. DOI: 10.1021/nl301204u.


  • Polymer photonic band-gaps fabricated by nanoimprint lithography.

    Reboud, V. ; Kehoe, T.; Romero Vivas, J.; Kehagias, N.; Zelsmannd, M.; Alsina, F.; Sotomayor Torres, C.M. Photonics and Nanostructures - Fundamentals and Applications; 10: 632 - 635. 2012. .


  • Silicon nanocluster sensitization of erbium ions under low-energy optical excitation

    Prtljaga, N.; Navarro-Urrios, D.; Pitanti, A.; Ferrarese-Lupi, F.; Garrido, B.; Pavesi, L. Journal of Applied Physics; 111 2012. 10.1063/1.4712626.


  • Soft graphoepitaxy of hexagonal PS-b-PDMS on nanopatterned POSS surfaces fabricated by nanoimprint lithography

    Simao, C.; Francone, A.; Borah, D.; Lorret, O.; Salaun, M.; Kosmala, B. ; Shaw, M.T.; Dittert, B.; Kehagias, N.; Zelsmann, M.; Morris, M.A.; Sotomayor Torres, C.M. Journal of Photopolymer Science and Technology; 25(2): 239 - 244. 2012. .


  • Synthesis, structure and luminescence of Er 3+-doped Y 3Ga 5O 12 nano-garnets

    Venkatramu, V.; León-Luis, S.F.; Rodríguez-Mendoza, U.R.; Monteseguro, V.; Manjón, F.J.; Lozano-Gorrín, A.D.; Valiente, R.; Navarro-Urrios, D.; Jayasankar, C.K.; Muñoz, A.; Lavín, V. Journal of Materials Chemistry; 22: 13788 - 13799. 2012. 10.1039/c2jm31386c.


  • Ultrafast Relaxation Dynamics via Acoustic Phonons in Carbon Nanotubes

    Dyatlova, O.A.; Köhler, C.; Malic, E.; Gomis-Bresco, J.; Maultzsch, J.; Tsagan-Mandzhiev, A.; Watermann, T.; Knorr, A.; Woggon, U. Nano Letters; 12 (5): 2249 - 2253. 2012. .


  • Zinc oxide nanostructures by solvothermal synthesis

    Segovia, M.; Sotomayor Torres, C.M.; González, G.; Benavente, E. Molecular Crystals and Liquid Crystals; 555: 40 - 50. 2012. 10.1080/15421406.2012.634363.


2011

  • An inter-laboratory stability study of roll-to-roll coated flexible polymer solar modules

    Gevorgyan, S.A.; Medford, A.J.; Bundgaard, E.; Sapkota, S.B.; Schleiermacher, H.-F.; Zimmermann, B.; Würfel, U.; Chafiq, A.; Lira-Cantu, M.; Swonke, T.; Wagner, M.; Brabec, C.J.; Haillant, O.; Voroshazi, E.; Aernouts, T.; Steim, R.; Hauch, J.A.; Elschner, A.; Pannone, M.; Xiao, M.; Langzettel, A.; Laird, D.; Lloyd, M.T.; Rath, T.; Maier, E.; Trimmel, G.; Hermenau, M.; Menke, T.; Leo, K.; Rösch, R.; Seeland, M.; Hoppe, H.; Nagle, T.J.; Burke, K.B.; Fell, C.J.; Vak, D.; Singh, T.B.; Watkins, S.E.; Galagan, Y.; Manor, A.; Katz, E.A.; Kim, T.; Kim, K.; Sommeling, P.M.; Verhees, W.J.H.; Veenstra, S.C.; Riede, M.; Greyson Christoforo, M.; Currier, T.; Shrotriya, V.; Schwartz, G.; Krebs, F.C. Solar Energy Materials and Solar Cells; 95: 1398 - 1416. 2011. 10.1016/j.solmat.2011.01.010.


  • Direct top-down ordering of diblock copolymers through nanoimprint lithography

    Salaün, M.; Kehagias, N.; Salhi, B.; Baron, T.; Boussey, J.; Sotomayor Torres, C.M.; Zelsmann, M. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures; 29 2011. 10.1116/1.3662399.


  • Fine control of critical dimension for the fabrication of large bandgap high frequency photonic and phononic crystals

    Cuffe, J. ; Dudek, D.; Kehagias, N.; Chapuis, P.O.; Reboud, V.; Alsina, F. ; McInerney, J.G.; Sotomayor Torres, C.M. Microelectronic Engineering; 2011. .


  • Low temperature direct imprint of polyhedral oligomeric silsesquioxane (POSS) resist

    Kehagias, N.; Zelsmann, M.; Chouiki, M.; Francone, A.; Reboud, V.; Schoeftner, R.; Sotomayor Torres, C. Microelectronic Engineering; 2011. .


  • Semiconducting properties of layered cadmium sulphide-based hybrid nanocomposites

    López-Cabaña, Z.; Sotomayor Torres, C.M.; González, G. Nanoscale Research Letters; 2011. . IF: 0.000


  • Surface-Directed Dewetting of a Block Copolymer for Fabricating Highly Uniform Nanostructured Microdroplets and Concentric Nanorings

    Farrell, R.A.; Kehagias, N.; Shaw, M.T.; Reboud, V.; Zelsmann, M.; Holmes, J.D.; Sotomayor Torres, C.M.; Morris, M.A. ACS Nano; 2011. .


  • The morphology of graphene sheets treated in an ozone generator

    Tao, H.; Moser, J.; Alzina, F.; Wang, Q.; Sotomayor-Torres, C.M. Journal of Physical Chemistry C; 115: 18257 - 18260. 2011. 10.1021/jp2050756.


  • Zinc oxide/carboxylic acid lamellar structures

    Segovia, M.; Lemus, K.; Moreno, M.; Ana, M.A.S.; González, G.; Ballesteros, B.; Sotomayor, C.; Benavente, E. Materials Research Bulletin; 46: 2191 - 2195. 2011. 10.1016/j.materresbull.2011.06.040.


2010

  • Damaging graphene with ozone treatment: A chemically tunable metal - Insulator transition

    Leconte N., Moser J., Ordejón P., Tao H., Lherbier A., Bachtold A., Alsina F., Sotomayor Torres C.M., Charlier J.-C., Roche S. ACS Nano; 4 (7): 4033 - 4038. 2010. 10.1021/nn100537z.

    We present a multiscale ab initio study of electronic and transport properties of two-dimensional graphene after epoxide functionalization via ozone treatment. The orbital rehybridization induced by the epoxide groups triggers a strong intervalley scattering and changes dramatically the conduction properties of graphene. By varying the coverage density of epoxide defects from 0.1 to 4%, charge conduction can be tuned from a diffusive to a strongly localized regime, with localization lengths down to a few nanometers long. Experimental results supporting the interpretation as a metal - insulator transition are also provided. © 2010 American Chemical Society.


  • Layer-by-layer all-inorganic quantum-dot-based LEDs: A simple procedure with robust performance

    Bendall, J.S.; Paderi, M.; Ghigliotti, F.; Pira, N.L.; Lambertini, V.; Lesnyak, V.; Gaponik, N.; Visimberga, G.; Eychmüller, A.; Torres, C.M.S.; Welland, M.E.; Gieck, C.; Marchese, L. Advanced Functional Materials; 20: 3298 - 3302. 2010. 10.1002/adfm.201001191.


  • Magnetotransport in disordered graphene exposed to ozone: From weak to strong localization

    Moser, J.; Tao, H.; Roche, S.; Alzina, F.; Sotomayor Torres, C.M.; Bachtold, A. Physical Review B - Condensed Matter and Materials Physics; 81 2010. 10.1103/PhysRevB.81.205445.


  • Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

    Kail, F. ; Farjas, J.; Roura, P.; Secouard, C.; Nos, O.; Bertomeu, J.; Alzina, F.; Roca i Cabarrocas, P. Applied Physics Letters; 2010. .


  • Tuning the Intensity of Metal-Enhanced Fluorescence by Engineering Silver Nanoparticle Arrays

    Yang, B.; Lu, N.; Qi, D.; Ma, R.; Wu, A.; Hao, J.; Liu, X.; Mu, Y.; Reboud, V.; Kehagias, N.;Sotomayor Torres, C.M.; Yin Chiang Boey, F.; Chen, X.; Chi, L. Small; 2010. .


2009

  • Bottom-up growth of fully transparent low refractive index top-contact layers of indium tin oxide nanowires for LEDs

    C. O'Dwyer; M. Szachowic; G. Visimberga; V. Lavayen; S.B. Newcomb; C.M. Sotomayor Nature Nanotechnology; 4: 239 - 244. 2009. .


  • Inline metrology configuration for sub-wavelength diffraction using microscope optics

    T. Kehoe; V. Reboud; N.Kehagias; C.M. Sotomayor Microelectronic Engineering; 86 (04-juny): 1036 - 1039. 2009. .


  • Lanthanides-clay nanocomposites: synthesis, characterization and optical properties

    C. Seledon; C. Quiroz; G. González; C.M. Sotomayor; E. Benavente Materials Research Society Symposium - Proceedings; 44 (5): 1191 - 1194. 2009. 10.1016/j.materresbull.2008.09.043.


  • Nanoimprinted plasmonic crystals for light extraction applications

    V. Reboud; N. Kehagias; T. Kehoe; G. Leveque; C. Mavidis; M. Kafesaki.; C.M. Sotomayor Microelectronic Engineering; 87: 1367 - 1369. 2009. 10.1016/j.mee.2009.12.030.


  • Physical properties of thin nanoimprint polymer films measured by photo-acoustic metrology

    T. Kehoe; J. Bryner; V. Reboud; J. Vollmann; C. M. Sotomayor Torres Proceeding of the 10th IEEE International Conference on Solid Dielectrics; SPIE 7271: 72711V. 2009. 10.1117/12.814162.


  • Reduced surfactant uptake in three dimensional assemblies of Vox nanotubes improves reversible Li+Intercalation and charge capacity

    C. O'Dwyer; V. Lavayen; D.A. Tanner; S.B. Newcomb; E. Benavente; G. González; C.M. Sotomayor Advanced Functional Materials; 19: 1736 - 1745. 2009. .


  • Resonance amplification and saturation of defect emission in ZnO inverted opal

    W. Khunsin; M. Scharrer; L. Aagesen; S.G. Romanov; R.P.H. Chang; C.M. Sotomayor Optics Letters; 34: 1519 - 1521. 2009. .


  • Site-selective self-assembly of colloidal photonic crystals

    S. Arpiainen; F. Jonsson; J.R. Dekker; G. Kocher; W. Khunsin; C. M. Sotomayor; J. Ahopelto Advanced Functional Materials; 19: 1247 - 1253. 2009. 10.1002/adfm.200801612.


  • Stamp replication for thermal and UV nanoimprint lithography using a UV sensitive silsesquioxane resist

    N. Kehagias; V. Reboud; J.de Girolamo; M. Chouiki; M. Zelsmann; J. Boussey; C.M. Sotomayor Microelectronic Engineering; 86: 1036 - 1039. 2009. 10.1016/j.mee.2009.01.052.


  • Tuning the intensity of metal enhanced fluorescence by engineering silver nanoparticle arrays

    B. Yang; N. Lu; D. Qi; Q. Wu; J. Hao; R. Ma; X. Liu; Y. Mu; V. Reboud; N. Kehagias; C. M. Sotomayor; F.Y. Chiang; X. Chen and L. Chi Small; 6 (9): 1038 - 1043. 2009. 10.1002/smll.200902350.


2008

  • An investigation into the growth conditions and defect states of laminar ZnO nanostructures

    J S Bendall; G Visimberga; M Szachowicz; N O V Plank; S Romanov; C M Sotomayor-Torres; M E Welland Journal of Materials Chemistry; 18: 5259 - 5266. 2008. 10.1039/B812867G .


  • Bleaching-induced evolution of emission directionality of dye-loaded opals

    W. Khunsin; S. G. Romanov; M. Bardosova; D. Whitehead; M. Pemble; C. M. Sotomayor Torres Journal of Optics A: Pure and Applied Optics; 10 (11): 115201. 2008. 10.1088/1464-4258/10/11/115201.


  • Chemosorption-related shift of photonic band gap in photoconductive inverted ZnO opal

    W. Khunsin; S.G. Romanov; M.Scharer; L.Aagesen; R.P.H. Chang; C.M. Sotomayor Torres Optics Letters; 33 (5): 461 - 465. 2008. 10.1364/OL.33.000461.


  • Electron beam induced electronic transport in alkyl amine-intercalated VOx nanotubes

    C. O¿Dwyer; V. Lavayen; C. Clavijo-Cedeño; C. M. Sotomayor Torres Physica Status Solidi (B): Basic Research; 245: 2102. 2008. 10.1002/pssb.200879566.


  • Fabrication of defect-free nanoimprinted photonic crystal for laser applications

    V Reboud; N Kehagias; M Striccoli; T Placido; A Panniello; M L Curri; M Zelsmann; F Reuther; G Gruetzner; C M Sotomayor Torres Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes; 47: 5139 - 5141. 2008. 10.1143/JJAP.47.5139.


  • Inelastic Light scattering by longitudinal acoustic phonons in thin silicon layers: from membranes to silicon-on-insulator structures,

    J Groenen; F Poinsotte; A Zwick; C M Sotomayor Torres; M Prunnila; J Ahopelto Physical Review B - Condensed Matter and Materials Physics; 77: 45420. 2008. 10.1103/PhysRevB.77.045420.


  • Light Emitting Diodes with Semiconductor Nanocrystals

    A. Rogach; N. Gaponik; J M Lupton; C. Bertoni; D. E. Gallardo; S. Dunn; N. Li Pira; M. Paderi; P. M. Repetto; S. G. Romanov; C. O¿Dwyer; C. M. Sotomayor Torres; A. Eychmüller Angewandte Chemie - International Edition; 47: 6538 - 6548. 2008. 10.1002/anie.200705109.


  • Low-dimensional hinged barcode metal oxide and free-standing ordered organic nanostructures from turbostratic vanadium oxide

    C. O'Dwyer; V. Lavayen; D. Fuenzalida; H. Lozano; E. Benavente; M. A. Santa Ana; G. González; C. M. Sotomayor Torres Small; 4: 990 - 1000. 2008. 10.1002/smll.200701014.


  • Modification of emission of CdTe nanocrystals by the local field of Langmuir-Blodgett colloidal photonic crystals

    S.G. Romanov; M. Bardosova; D. Whitehead; M. Pemble; C.M. Sotomayor Torres; N. Gaponik; A. Eychmüller Indian Journal of Pure and Applied Physics; 104: 103118. 2008. 10.1063/1.2981087.


  • Modification of spontaneous emission of (CdSe)ZnS nanocrystals embedded in nanoimprinted photonic crystals

    V. Reboud; N. Kehagias; M. Zelsmann; M. Striccoli; M. Tamborra; M. L. Curri; A. Agostiano; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Journal of Nanoscience and Nanotechnology; 8: 535 - 539. 2008. 10.1166/jnn.2008.A143.


  • Nanoimprint lithography and surface modification as prospective technologies for heterogeneous integration

    N Kehagias; W Hu; N Lu; L Chi; H Fuchs; A Genua; J A Alduncin; J A Pomposo; D Mecerreyes; C M Sotomayor Torres Physica Status Solidi (C) Current Topics in Solid State Physics; 5: 3671 - 3575. 2008. 10.1002/pssc.200780226 .


  • Optical transmission of triple-film hetero-opals

    W. Khunsin; S. G. Romanov; C. M. Sotomayor Torres; J. Ye and R. Zentel Journal of Applied Physics; 92: 13527. 2008. 10.1063/1.2951958.


  • Quantitative Analysis of Lattice orderingin thin-film opal-based photonic crystals

    W. Khunsin; G. Kocher; S. G. Romanov; C. M. Sotomayor Torres Advanced Functional Materials; 18: 2471 - 2479. 2008. 0.1002/adfm.200701431.


  • Residual layer thickness in nanoimprint: experiments and coarse-grain simulation

    N Kehagias; V Reboud; C M Sotomayor Torres; V Sorotin; A Svintsov; S Zaitsev Microelectronic Engineering; 85: 846 - 849. 2008. 10.1016/j.mee.2007.12.041.


  • Rotational symmetry of transmission patterns and ordering of opal photonic crystals

    W. Khunsin; S. G. Romanov; C. M. Sotomayor Torres; J. Nonlinear Optical Journal of Nonlinear Optical Physics and Materials; 17: 97 - 104. 2008. 10.1142/S0218863508004020 .


  • Understanding of transmission in the range of high-order photonic bands in thin opal film: Towards the mystery of high-order photonic bands in thin film opal crystals

    S.G. Romanov; M. Bardosova; I. M. Povey; M. E. Pemble; C.M. Sotomayor Torres Applied Physics Letters; 92: 19106. 2008. 10.1063/1.2920443.


2007

  • Anisotropic vanadium oxide nanostructured host matrices for lithium ion intercalation

    C. O¿Dwyer; V. Lavayen; M. A. Santa Ana; E. Benavente; G. Gonzalez; C. M. Sotomayor Torres Research Letters in Physical Chemistry; 2007: 32528. 2007. 10.1155/2007/32528.


  • Benchmarking of 50¿nm features in thermal nanoimprint

    C. Gourgon; N. Chaix; H. Schift; M. Tormen; S. Landis; C. M. Sotomayor Torres; A. Kristensen; R. H. Pedersen; M. B. Christiansen; I. Fernandez-Cuesta; D. Mendels; L. Montelius; T. Haatainen Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures; 2007. .


  • Effect of template defects in radiative energy relaxation of CdTe nanocrystals in nanotubes of chrysotile asbestos

    M Bardosova; SG Romanov; CM Sotomayor Torres; N. Gaponik; A. Eychmueller; YA Kumzerov; J Bendell Microporous and Mesoporous Materials; 107: 212 - 218. 2007. 10.1016/j.micromeso.2007.05.035.


  • Embedded nano channels fabricated by non-selective reverse contact UV nanoimprint lithography technique

    N. Kehagias; G. Chansin; V. Reboud; M. Zelsmann; C. Schuster; M. Kubenz; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Microelectronic Engineering; 10: 1016. 2007. .


  • Emission pattern of planar CdTe nanocrystal light source coated by two dimensional Langmuir-Blodgett photonic crystal

    S.G Romanov; M Bardosova; M Pemble; CM Sotomayor Torres; N Gaponik; A Ecychmuller Materials Science and Engineering; C27: 968 - 971. 2007. .


  • Erasing diffraction orders ¿ opal versus Langmuir-Blodgett colloidal crystals

    S.G. Romanov; M. Bardosova; M. Pemble; C.M. Sotomayor Torres Applied Physics Letters; 2007. 10.1063/1.2714198.


  • Functional patterns obtained by nanoimprinting lithography and subsequent growth of polymer brushes

    A Genua; J. A. Alduncín; J. A. Pomposo; N Kehagias; V. Reboud; C. M. Sotomayor Torres; D. Mecerreyes Nanotechnology; 2007. 10.1088/0957-4484/18/21/215301.


  • Inorganic Fullerenes: From Lamellar precursors to functionalized nanotubes

    Vladimir Lavayen; Eglantina Benavente; Clivia M. Sotomayor Torres; G. Gonzáles Solid State Phenomena; 2007. 10.4028/www.scientific.net/SSP.121-123.1.


  • Integration of SOI-Based 2D- and Si-Based 3D Photonic Crystals

    G Kocher; W. Khunsin; J Romero Vivas; K. Vynck; S. Arpiainen; S.G Romanov; B Lange; M Mulot; F Jonsson; T Charvolin; E Hajdi; D Cassagne; R Zentel; J. Ahopelto; C.M Sotomayor Torres ECS Transactions; 2007. .


  • Lanthanides¿clay nanocomposites: Synthesis, characterization and optical properties

    E Benevente; Y Echeverria; V Lavayan; CM Sotomayor Torres; G Gonzalez Materials Research Bulletin; 2007. .


  • Light emission from three-dimensional ensembles of CdTe nanocrystal wires templated in nanotubes of chrysotile asbestos

    M. Bardosova; S.G Romanov; C.M Sotomayor Torres; N. Gaponik; A. Eychmueller; Y.A Kumzerov Physica E: Low-Dimensional Systems and Nanostructures; 37: 218 - 221. 2007. 10.1016/j.physe.2006.10.020.


  • Multicolor Emission on Prepatterned Substrates Using a Single Dye Species

    W. Hu; N. Lu; H. Zhang; Y. Wang; N. Kehagias; V. Reboud; C. M. Sotomayor Torres; J. Hao; W. Li; H. Fuchs; L. Chi Advanced Materials; 19: 2119 - 2123. 2007. 10.1002/adma.200602491.


  • Nanoimprinted photonic crystals for the modification of the CdSe(ZnS) nanocrystals light emission

    M Bardosova; SG Romanov; CM Sotomayor Torres; N. Gaponik; A. Eychmueller; YA Kumzerov; J Bendell Microelectronic Engineering; 2007. .


  • Photoluminescence enhancement in metallic nanocomposite printable polymer

    V. Reboud; N. Kehagias; M. Striccoli; T. Placido; A. Panniello; M. L. Curri; M. Zelsmann; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures; 2007. .


  • Photoluminescence enhancement in nanoimprinted photonic crystals and coupled surface plasmons

    V. Reboud; N. Kehagias; M. Zelsmann; C. Schuster; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Optics Express; 2007. .


  • Reverse-contact UV nanoimprint lithography for multilayered structure fabrication

    N Kehagias; V Reboud; G Chansin; M Zelsmann; C Jeppesen; C Schuster; M Kubenz; F Reuther; G Gruetzner; C M Sotomayor Torres Nanotechnology; 2007. .


  • Site-controlled growth of Ge nanostructures on Si (100) via pulsed laser deposition nanostenciling

    Cojocaru CV; Bernardi A.; Reparaz JS; Alonso MI; MacLeod JM; Harnagea C.; Rosei F. Applied Physics Letters; 91: 113112. 2007. .


  • Six-Fold Rotationally Symmetric Vanadium Oxide Nanostructures by a Morphotropic Phase Transition

    C. O'Dwyer; V. Lavayen; D. Fuenzalida; S. B. Newcomb; M. A. Santa Ana; E. Benavente; G. Gonzalez; C. M. Sotomayor Torres Physica Status Solidi (B): Basic Research; 11: 4157 - 4160. 2007. .


  • Spontaneous emission control of colloidal nanocrystals using nanoimprinted photonic crystals,

    V. Reboud; N. Kehagias; M. Zelsmann; M. Striccoli; M. Tamborra; M. L. Curri; A. Agostiano; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Applied Physics Letters; 90: 11114. 2007. .


  • Spontaneous emission of nanocrystals in nanoimprinted photonic structures

    V. Reboud; N. Kehagias; M. Zelsmann; M. Striccoli; M. Tamborra; M. L. Curri; A. Agostiano; M. Fink; F. Reuther; G. Gruetzner; C. M. Sotomayor Torres Microelectronic Engineering; 10: 1016. 2007. .


  • Stochastic Resonances in photonic crystal growth

    A Amann; W Khunsin; G Kocher; C M Sotomayor Torres; E P O¿Reilly Proceedings of SPIE - The International Society for Optical Engineering; 6603: 660321. 2007. doi:10.1117/12.724561.


  • Surfactant-Mediated Variation of Band-Edge Emission in CdS Nanocomposites

    C. O'Dwyer; V. Lavayen; N. Mirabal; M. A. Santa Ana; E. Benavente; S. Ormazabal; G. Gonzalez; Z. Lopez; O. Schops; C. M. Sotomayor Torres; U. Woggon Photonics and Nanostructures - Fundamentals and Applications; 5: 45 - 52. 2007. .


  • The formation of Nanotubes and Nanocoils of Molybdenum Disulphide

    V Lavayen; N Mirabel; C. O Dywer; E. Benavente; CM Sotomayor Torres; G. Gonzalez Applied Surface Science; 253(12): 5185 - 5189. 2007. .


  • Towards Si-based photonic circuits: integrating photonic crystals in Silicon-on-Insulator platforms

    G. Kocher; W. Khunsin; S. Arpiainen; J. Romero-Vivas; S. G. Romanov; J. Ye; B. Lange; F. Jonsson; R. Zentel; J. Ahopelto; C. M. Sotomayor Torres Solid-State Electronics; 51: 333 - 336. 2007. .


  • Towards thiol functionalization of vanadium pentoxide nanotubes using gold nanoparticles

    V. Lavayen; C. O'Dwyer; G. Gonzalez; G. Cardenas; C. M. Sotomayor Torres Materials Research Bulletin; 42: 674 - 685. 2007. .


  • Two-dimensional polymer photonic crystal band-edge lasers fabricated by nanoimprint lithography

    V. Reboud; P. Lovera; N. Kehagias; M. Zelsmann; C. Schuster; F. Reuther; G. Gruetzner; G. Redmond; C. M. Sotomayor Torres Applied Physics Letters; 91: 15110. 2007. .


  • Vanadate Conformation Variations in Novel Vanadium Pentoxide Nanostructures

    C. O'Dwyer; V. Lavayen; M. A. Santa Ana; E. Benavente; G. Gonzalez; C. M. Sotomayor Torres Journal of the Electrochemical Society; 154: K29 - K35. 2007. .


2006

  • Photoluminescence of CdSe quantum dots with Zn0. 38Cd0. 23Mg0. 39Se barriers under hydrostatic pressure

    Reparaz, JS; Goni, AR; Alonso, MI; Perez-Paz, MN; Tamargo, MC Physica Status Solidi (B): Basic Research; 244 (1): 397. 2006. 10.1002/pssb.200672523.