Publications
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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
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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
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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).
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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.
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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
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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.
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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.
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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).
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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.
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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.
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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).
