Staff directory
Jordi Fraxedas Calduch
CSIC Scientific Researcher
jordi.fraxedas(ELIMINAR)@icn2.cat
Thermal Properties of Nanoscale Materials
- ORCID: 0000-0002-2821-4831
Publications
2017
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A statistical analysis of nanocavities replication applied to injection moulding
Pina-Estany J., Colominas C., Fraxedas J., Llobet J., Perez-Murano F., Puigoriol-Forcada J.M., Ruso D., Garcia-Granada A.A. International Communications in Heat and Mass Transfer; 81: 131 - 140. 2017. 10.1016/j.icheatmasstransfer.2016.11.003. IF: 3.718
The purpose of this paper is to investigate both theoretically and experimentally how nanocavities are replicated in the injection moulding manufacturing process. The objective is to obtain a methodology for efficiently replicate nanocavities. From the theoretical point of view, simulations are carried out using a submodeling approach combining Solidworks Plastics for a first macrosimulation and Fluent solver for a subsequent nanosimulation. The effect of the four main factors (melt temperature, mould temperature, filling time and cavity geometry) are quantified using an statistical 24 factorial experiment. It is found that the main effects are the cavity length, the mould temperature and the polymer temperature, with standardized effects of 5, 3 and 2.6, respectively. Filling time has a negative 1.3 standardized effect. From the experimental point of view, Focused Ion Beam technique is used for mechanizing nanocavities in a steel mould. The replication achieved in polycarbonate injection is quantified using an Atomic Force Microscope. It is observed how both the geometry and the position of the cavities in the mould affect its replication. © 2016 Elsevier Ltd
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Functional dependence of resonant harmonics on nanomechanical parameters in dynamic mode atomic force microscopy
Gramazio F., Lorenzoni M., Pérez-Murano F., Trinidad E.R., Staufer U., Fraxedas J. Beilstein Journal of Nanotechnology; 8 (1, 90) 2017. 10.3762/bjnano.8.90. IF: 3.127
We present a combined theoretical and experimental study of the dependence of resonant higher harmonics of rectangular cantilevers of an atomic force microscope (AFM) as a function of relevant parameters such as the cantilever force constant, tip radius and free oscillation amplitude as well as the stiffness of the sample's surface. The simulations reveal a universal functional dependence of the amplitude of the 6th harmonic (in resonance with the 2nd flexural mode) on these parameters, which can be expressed in terms of a gun-shaped function. This analytical expression can be regarded as a practical tool for extracting qualitative information from AFM measurements and it can be extended to any resonant harmonics. The experiments confirm the predicted dependence in the explored 3-45 N/m force constant range and 2-345 GPa sample's stiffness range. For force constants around 25 N/m, the amplitude of the 6th harmonic exhibits the largest sensitivity for ultrasharp tips (tip radius below 10 nm) and polymers (Young's modulus below 20 GPa). © 2017 Gramazio et al.
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Identifying the nature of surface chemical modification for directed self-assembly of block copolymers
Evangelio L., Gramazio F., Lorenzoni M., Gorgoi M., Espinosa F.M., García R., Pérez-Murano F., Fraxedas J. Beilstein Journal of Nanotechnology; 8 (1, 198) 2017. 10.3762/bjnano.8.198. IF: 3.127
In recent years, block copolymer lithography has emerged as a viable alternative technology for advanced lithography. In chemicalepitaxy- directed self-assembly, the interfacial energy between the substrate and each block copolymer domain plays a key role on the final ordering. Here, we focus on the experimental characterization of the chemical interactions that occur at the interface built between different chemical guiding patterns and the domains of the block copolymers. We have chosen hard X-ray high kinetic energy photoelectron spectroscopy as an exploration technique because it provides information on the electronic structure of buried interfaces. The outcome of the characterization sheds light onto key aspects of directed self-assembly: grafted brush layer, chemical pattern creation and brush/block co-polymer interface. © 2017 Evangelio et al.
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In Situ Determination of the Water Condensation Mechanisms on Superhydrophobic and Superhydrophilic Titanium Dioxide Nanotubes
Macias-Montero M., Lopez-Santos C., Filippin A.N., Rico V.J., Espinos J.P., Fraxedas J., Perez-Dieste V., Escudero C., Gonzalez-Elipe A.R., Borras A. Langmuir; 33 (26): 6449 - 6456. 2017. 10.1021/acs.langmuir.7b00156. IF: 3.833
One-dimensional (1D) nanostructured surfaces based on high-density arrays of nanowires and nanotubes of photoactive titanium dioxide (TiO2) present a tunable wetting behavior from superhydrophobic to superhydrophilic states. These situations are depicted in a reversible way by simply irradiating with ultraviolet light (superhydrophobic to superhydrophilic) and storage in dark. In this article, we combine in situ environmental scanning electron microscopy (ESEM) and near ambient pressure photoemission analysis (NAPP) to understand this transition. These experiments reveal complementary information at microscopic and atomic level reflecting the surface wettability and chemical state modifications experienced by these 1D surfaces upon irradiation. We pay special attention to the role of the water condensation mechanisms and try to elucidate the relationship between apparent water contact angles of sessile drops under ambient conditions at the macroscale with the formation of droplets by water condensation at low temperature and increasing humidity on the nanotubes' surfaces. Thus, for the as-grown nanotubes, we reveal a metastable and superhydrophobic Cassie state for sessile drops that tunes toward water dropwise condensation at the microscale compatible with a partial hydrophobic Wenzel state. For the UV-irradiated surfaces, a filmwise wetting behavior is observed for both condensed water and sessile droplets. NAPP analyses show a hydroxyl accumulation on the as-grown nanotubes surfaces during the exposure to water condensation conditions, whereas the water filmwise condensation on a previously hydroxyl enriched surface is proved for the superhydrophilic counterpart. © 2017 American Chemical Society.
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Petrographic and geochemical evidence for multiphase formation of carbonates in the Martian orthopyroxenite Allan Hills 84001
Moyano-Cambero C.E., Trigo-Rodríguez J.M., Benito M.I., Alonso-Azcárate J., Lee M.R., Mestres N., Martínez-Jiménez M., Martín-Torres F.J., Fraxedas J. Meteoritics and Planetary Science; 52 (6): 1030 - 1047. 2017. 10.1111/maps.12851. IF: 2.391
Martian meteorites can provide valuable information about past environmental conditions on Mars. Allan Hills 84001 formed more than 4 Gyr ago, and owing to its age and long exposure to the Martian environment, and this meteorite has features that may record early processes. These features include a highly fractured texture, gases trapped during one or more impact events or during formation of the rock, and spherical Fe-Mg-Ca carbonates. In this study, we have concentrated on providing new insights into the context of these carbonates using a range of techniques to explore whether they record multiple precipitation and shock events. The petrographic features and compositional properties of these carbonates indicate that at least two pulses of Mg- and Fe-rich solutions saturated the rock. Those two generations of carbonates can be distinguished by a very sharp change in compositions, from being rich in Mg and poor in Fe and Mn, to being poor in Mg and rich in Fe and Mn. Between these two generations of carbonate is evidence for fracturing and local corrosion. © 2017 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society.
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Photochemically Activated Motors: From Electrokinetic to Diffusion Motion Control
Zhang K., Fraxedas J., Sepulveda B., Esplandiu M.J. ACS Applied Materials and Interfaces; 9 (51): 44948 - 44953. 2017. 10.1021/acsami.7b15855. IF: 7.504
Self-propelled micro/nanomotors that can transform chemical energy from the surrounding environment into mechanical motion are cutting edge nanotechnologies with potential applications in biomedicine and environmental remediation. These applications require full understanding of the propulsion mechanisms to improve the performance and controllability of the motors. In this work, we demonstrate that there are two competing chemomechanical mechanisms at semiconductor/metal (Si/Pt) micromotors in a pump configuration under visible light exposure. The first propulsion mechanism is driven by an electro-osmotic process stemmed from a photoactivation reaction mediated by H2O2, which takes place in two separated redox reactions at the Si and Pt interfaces. One reaction involves the oxidation of H2O2 at the silicon side, and the other the H2O2 reduction at the metal side. The second mechanism is not light responsive and is triggered by the redox decomposition of H2O2 exclusively at the Pt surface. We show that it is possible to enhance/suppress one mechanism over the other by tuning the surface roughness of the micromotor metal. More specifically, the actuation mechanism can be switched from light-controlled electrokinetics to light-insensitive diffusio-osmosis by only increasing the metal surface roughness. The different actuation mechanisms yield strikingly different fluid flow velocities, electric fields, and light sensitivities. Consequently, these findings are very relevant and can have a remarkable impact on the design and optimization of photoactivated catalytic devices and, in general, on bimetallic or insulating-metallic motors. © 2017 American Chemical Society.
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Preface
Fraxedas J. Applied Surface Science; 391: 1 - 2. 2017. 10.1016/j.apsusc.2016.09.164.
[No abstract available]
2016
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Evaluating the compressive stress generated during fabrication of Si doubly clamped nanobeams with AFM
Lorenzoni M., Llobet J., Gramazio F., Sansa M., Fraxedas J., Perez-Murano F. Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics; 34 (6, 06KK02) 2016. 10.1116/1.4967930. IF: 1.398
In this work, the authors employed Peak Force tapping and force spectroscopy to evaluate the stress generated during the fabrication of doubly clamped, suspended silicon nanobeams with rectangular section. The silicon beams, released at the last step of fabrication, present a curved shape that suggests a bistable buckling behavior, typical for structures that retain a residual compressive stress. Both residual stress and Young's modulus were extracted from experimental data using two different methodologies: analysis of beam deflection profiles and tip-induced mechanical bending. The results from the two methods are compared, providing an insight into the possible limitations of both methods. © 2016 Author(s).
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Multiscale study of mononuclear CoII SMMs based on curcuminoid ligands
Díaz-Torres R., Menelaou M., Roubeau O., Sorrenti A., Brandariz-De-Pedro G., Sañudo E.C., Teat S.J., Fraxedas J., Ruiz E., Aliaga-Alcalde N. Chemical Science; 7 (4): 2793 - 2803. 2016. 10.1039/c5sc03298a. IF: 9.144
This work introduces a novel family of CoII species having a curcuminoid (CCMoid) ligand, 9Accm, attached, namely [Co(9Accm)2(py)2] (1) and [Co(9Accm)2(2,2′-bpy)] (2), achieved in high yields by the use of a microwave reactor, and exhibiting two different arrangements for the 9Accm ligands, described as "cis"(2) and "trans"(1). The study of the similarities/differences of the magnetic, luminescent and surface behaviors of the two new species, 1 and 2, is the main objective of the present work. The determined single-crystal structures of both compounds are the only CoII-CCMoid structures described in the literature so far. Both compounds exhibit large positive D values, that of 1 (D = +74 cm-1) being three times larger than that of 2 (D = +24 cm-1), and behave as mononuclear Single-Molecule Magnets (SMMs) in the presence of an external magnetic field. Their similar structures but different anisotropy and SMM characteristics provide, for the first time, deep insight on the spin-orbital effects thanks to the use of CASSCF/NEVPT2 calculations implementing such contributions. Further magnetic studies were performed in solution by means of paramagnetic 1H NMR, where both compounds (1 and 2) are stable in CDCl3 and display high symmetry. Paramagnetic NMR appears to be a useful diagnostic tool for the identification of such molecules in solution, where the resonance values found for the methine group (-CH-) of 9Accm vary significantly depending on the cis or trans disposition of the ligands. Fluorescence studies show that both systems display chelation enhancement of quenching (CHEQ) with regard to the free ligand, while 1 and 2 display similar quantum yields. Deposition of 1-2 on HOPG and Si(100) surfaces using spin-coating was studied using AFM; UV photoemission experiments under the same conditions display 2 as the most robust system. The measured occupied density of states of 2 with UV photoemission is in excellent agreement with theoretical DFT calculations. © The Royal Society of Chemistry 2016.
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Synthesis, characterization, and thermoelectric properties of superconducting (BEDT-TTF)2I3 nanoparticles
Chtioui-Gay I., Faulmann C., De Caro D., Jacob K., Valade L., De Caro P., Fraxedas J., Ballesteros B., Steven E., Choi E.S., Lee M., Benjamin S.M., Yvenou E., Simonato J.-P., Carella A. Journal of Materials Chemistry C; 4 (31): 7449 - 7454. 2016. 10.1039/c6tc01378c. IF: 5.066
The synthesis of (BEDT-TTF)2I3 in the presence of two neutral amphiphilic molecules [N-octylfurfurylimine and 1-octanamine, N-(2-thienylmethylene)] leads to single and aggregated nanoparticles of 2 to 6 nm size. The samples contain highly crystalline nanoparticles of the βCO-(BEDT-TTF)2I3 phase, confirmed by XRD. Temperature dependent resistance and magnetic susceptibility studies evidence the superconducting transition characteristics of the βCO-(BEDT-TTF)2I3 phase. The I-V curve of a single nanoparticle aggregate, measured using AFM, exhibits an expected semiconductor-like behaviour. Thermoelectric studies led to a ZT of 1.47 × 10-3 at 300 K. © The Royal Society of Chemistry 2016.
2015
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Continuous monitoring of tip radius during atomic force microscopy imaging
Fraxedas J., Pérez-Murano F., Gramazio F., Lorenzoni M., Rull Trinidad E., Staufer U. Proceedings of SPIE - The International Society for Optical Engineering; 9636 ( 96360O) 2015. 10.1117/12.2196951. IF: 0.000
We present a continuous tip monitoring method during atomic force microscopy imaging based on the use of higher harmonics, which are generated in the repulsive regime as a result of the nonlinear interactions between the cantilever tip and the surface under study. We have applied this method to commercial rectangular microfabricated silicon cantilevers with force constants in the 45 N/m range and fundamental frequencies in the 300-400 kHz range and with tip radii below 10 nm. We have focused in the resonance of the 2nd flexural mode and the 6th harmonic using polystyrene surfaces. The simultaneous acquisition of topographic and higher harmonic images allows a continuous control of the state of the tip. The experimental results have been rationalized with computer simulations taking into account both the cantilever dynamics and the tip-surface interactions. © 2015 SPIE.
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Creation of guiding patterns for directed self-assembly of block copolymers by resistless direct e-beam exposure
Evangelio L., Fernandez-Regulez M., Borrise X., Lorenzoni M., Fraxedas J., Perez-Murano F. Proceedings of SPIE - The International Society for Optical Engineering; 9423 (942326) 2015. 10.1117/12.2085830. IF: 0.000
We present a novel approach for the creation of guiding patterns to direct the self-assembly of block copolymers. A neutral layer of a brush polymer is directly exposed by electrons, causing the cross-linking of the brush molecules, and thus changing its local affinity. The advantage relies on the achievable resolution and the reduction of the process steps in comparison with deep UV and conventional electron beam lithography, since it avoids the use of a resist. We envision that this method will be highly valuable for the investigation of novel high-chi DSA materials and complex guiding pattern designs, where pattern placement and resolution is becoming critical. © 2015 SPIE.
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Creation of guiding patterns for directed self-assembly of block copolymers by resistless direct e-beam exposure
Evangelio L., Fernández-Regúlez M., Borrisé X., Lorenzoni M., Fraxedas J., Pérez-Murano F. Journal of Micro/ Nanolithography, MEMS, and MOEMS; 14 (3, 033511) 2015. 10.1117/1.JMM.14.3.033511. IF: 1.428
We present an approach for the creation of guiding patterns to direct the self-assembly of block copolymers. A neutral layer of a brush polymer is directly exposed by electrons, causing the cross-linking of the brush molecules, and thus changing its local affinity. The advantage relies on the achievable resolution and the reduction of the process steps in comparison with deep UV and conventional electron beam lithography, since it avoids the use of a resist. We envision that this method will be highly valuable for the investigation of high-chi directed self-assembly materials and complex guiding pattern designs, where pattern placement and resolution are becoming critical. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).
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Spin density wave and superconducting properties of nanoparticle organic conductor assemblies
Winter L.E., Steven E., Brooks J.S., Benjamin S., Park J.-H., De Caro D., Faulmann C., Valade L., Jacob K., Chtioui I., Ballesteros B., Fraxedas J. Physical Review B - Condensed Matter and Materials Physics; 91 (3, 035437) 2015. 10.1103/PhysRevB.91.035437. IF: 3.736
The magnetic susceptibilities of nanoparticle assemblies of two Bechgaard salts (TMTSF)2PF6 and (TMTSF)2ClO4, have been studied vs temperature and magnetic field. In the bulk these materials exhibit a spin density wave formation (TSDW=12K) and superconductivity (Tc=1.2K), respectively. We show from inductive (susceptibility) measurements that the nanoparticle assemblies exhibit ground-state phase transitions similar to those of randomly oriented polycrystalline samples of the parent materials. Resistivity and diamagnetic shielding measurements yield additional information on the functional nanoparticle structure in terms of stoichiometric and nonstoichiometric composition. © 2015 American Physical Society.
2011
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Modulation of surface charge transfer through competing long-range repulsive versus short-range attractive interactions
Fraxedas J., García-Gil S., Monturet S., Lorente N., Fernández-Torrente I., Franke K.J., Pascual J.I., Vollmer A., Blum R.-P., Koch N., Ordejón P. Journal of Physical Chemistry C; 115 (38): 18640 - 18648. 2011. 10.1021/jp2050838.
We report a combined experimental and theoretical study of the modulation of surface charge transfer on the tetrathiafulvalene (TTF)/Au(111) interface as a function of coverage in the submonolayer regime by combining low-temperature scanning tunneling microscopy, high-resolution photoemission spectroscopy using synchrotron radiation, and density functional theory (DFT) calculations. The modulation is induced by the competition between long-range repulsive Coulombic interactions and short-range attractive hydrogen-bonding interactions. The system shows the characteristic pattern evolution, from monomeric stripes at low coverages to two-dimensional islands, with the formation of labyrinths in the crossover. © 2011 American Chemical Society.
2010
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Orbital specific chirality and homochiral self-assembly of achiral molecules induced by charge transfer and spontaneous symmetry breaking
Mugarza A., Lorente N., Ordejón P., Krull C., Stepanow S., Bocquet M.-L., Fraxedas J., Ceballos G., Gambardella P. Physical Review Letters; 105 (11, 115702) 2010. 10.1103/PhysRevLett.105.115702.
We study the electronic mechanisms underlying the induction and propagation of chirality in achiral molecules deposited on surfaces. Combined scanning tunneling microscopy and ab initio electronic structure calculations of Cu-phthalocyanines adsorbed on Ag(100) reveal the formation of chiral molecular orbitals in structurally undistorted molecules. This effect shows that chirality can be manifest exclusively at the electronic level due to asymmetric charge transfer between molecules and substrate. Single molecule chirality correlates with attractive van der Waals interactions, leading to the propagation of chirality at the supramolecular level. Ostwald ripening provides an efficient pathway for complete symmetry breaking and self-assembly of homochiral supramolecular layers. © 2010 The American Physical Society.