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118 results on '"Rodriguez-Viejo, J."'

1. Growth monitoring with sub-monolayer sensitivity via real time thermal conductance measurements

Author

Ferrando-Villalba, P., Takegami, D., Abad, Ll., Ràfols-Ribé, J., Lopeandía, A., Garcia, G., and Rodríguez-Viejo, J.

Subjects
Physics - Applied Physics
Abstract

Growth monitoring during the early stages of film formation is of prime importance to understand the growth process, the microstructure and thus the overall layer properties. In this work, we demonstrate that phonons can be used as sensitive probes to monitor real time evolution of film microstructure during growth, from incipient clustering to continuous film formation. For that purpose, a silicon nitride membrane-based sensor has been fabricated to measure in-plane thermal conductivity of thin film samples. Operating with the 3{\omega}-V\"olklein method at low frequencies, the sensor shows an exceptional resolution down to {\Delta}({\kappa}*t)=0.065 nm*W/(m*K), enabling accurate measurements. Validation of the sensor performance is done with organic and metallic thin films. In both cases, at early stages of growth, we observe an initial reduction of the effective thermal conductance of the supporting amorphous membrane, K, related with the surface phonon scattering enhanced by the incipient nanoclusters formation. As clusters develop, K reaches a minimum at the percolation threshold. Subsequent island percolation produces a sharp increase of the conductance and once the surface coverage is completed K increases linearly with thickness The thermal conductivity of the deposited films is obtained from the variation of K with thickness.

Published
2018
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2. Probing equilibrium glass flow up to exapoise viscosities

Author

Pogna, E. A. A., Rodríguez-Tinoco, C., Cerullo, G., Ferrante, C., Rodríguez-Viejo, J., and Scopigno, T.

Subjects
Condensed Matter - Disordered Systems and Neural Networks, Physics - Optics
Abstract

Glasses are out-of-equilibrium systems aging under the crystallization threat. During ordinary glass formation, the atomic diffusion slows down rendering its experimental investigation impractically long, to the extent that a timescale divergence is taken for granted by many. We circumvent here these limitations, taking advantage of a wide family of glasses rapidly obtained by physical vapor deposition directly into the solid state, endowed with different "ages" rivaling those reached by standard cooling and waiting for millennia. Isothermally probing the mechanical response of each of these glasses, we infer a correspondence with viscosity along the equilibrium line, up to exapoise values. We find a dependence of the elastic modulus on the glass age, which, traced back to temperature steepness index of the viscosity, tears down one of the cornerstones of several glass transition theories: the dynamical divergence. Critically, our results suggest that the conventional wisdom picture of a glass ceasing to flow at finite temperature could be wrong., Comment: 4 figures and 1 supplementary figure

Published
2015
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3. Acoustic-like dynamics of amorphous drugs in the THz regime

Author

Pogna, E. A. A., Rodriguez-Tinoco, C., Krisch, M., Rodriguez-Viejo, J., and Scopigno, T.

Subjects
Condensed Matter - Disordered Systems and Neural Networks
Abstract

The high frequency dynamics of Indomethacin and Celecoxib glasses has been investigated by inelastic x-ray scattering, accessing a momentum-energy region still unexplored in amorphous pharmaceuticals. We find evidence of phonon-like acoustic dynamics, and determine the THz behavior of sound velocity and acoustic attenuation. Connections with ordinary sound propagation are discussed, along with the relation between fast and slow degrees of freedom as represented by non-ergodicity factor and kinetic fragility, respectively.

Published
2013

26. Evidence of photo- and electrodarkening of (CdSe)ZnS quantum dot composites

Author

Rodriguez-Viejo, J., Mattoussi, H., Heine, J.R., Kuno, M.K., Michel, J., Bawendi, M.G., and Jensen, K.F.

Subjects
Condensed matter -- Research, Photoluminescence -- Research, Quantum electronics -- Research, Semiconductors -- Research, Physics
Abstract

A new study investigates the time decay of photoluminescence and cathodoluminescence of (CdSe)ZnS quantum dot composites.

Published
2000

28. Nucleation and Growth of the Supercooled Liquid Phase Control Glass Transition in Bulk Ultrastable Glasses

Author

Vila-Costa, A., Ràfols-Ribé, Joan, González-Silveira, M., Lopeandia, A. F., Abad-Muñoz, Ll., Rodriguez-Viejo, J., Vila-Costa, A., Ràfols-Ribé, Joan, González-Silveira, M., Lopeandia, A. F., Abad-Muñoz, Ll., and Rodriguez-Viejo, J.

Abstract

We report the anomalous bulk transformation of vapor deposited stable glasses into the liquid state. The transformation proceeds through two competing parallel processes: partial rejuvenation of the stable glass and nucleation and growth of liquid patches within the glass. The kinetics of the transformation extracted from heat capacity curves after isothermal runs is dominated by the heterogeneous nucleation and growth process that initiates at preexisting seeds and propagates radially at a velocity proportional to the alpha relaxation time. Remarkably, the distance between the activation seeds is independent of temperature within experimental uncertainty and amounts to several micrometers, a value in close agreement with the crossover length for TPD glasses. We speculate the initiation sites for the transformation of the glass into the supercooled liquid are localized regions of lower stability (or density).

Published
2020
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32. Multiple glass transitions in vapor-deposited orientational glasses of the most fragile plastic crystal Freon 113

Author

Vila-Costa, A., Ràfols-Ribé, Joan, Gonzalez-Silveira, M., Lopeandia, A., Tamarit, J. Ll, Rodriguez-Viejo, J., Vila-Costa, A., Ràfols-Ribé, Joan, Gonzalez-Silveira, M., Lopeandia, A., Tamarit, J. Ll, and Rodriguez-Viejo, J.

Abstract

We investigate by fast-scanning nanocalorimetry the formation of Freon 113 films from the vapor phase at deposition temperatures ranging from 50 to 120 K, that is, spanning above and below the transition temperature of the glassy crystal to the plastic crystal (T-gc = 72 K). Analysis of the heat capacity curves indicates that vapor deposition at T < T-gc of the highly fragile Freon 113 yields structural and orientational glasses in the as-deposited state depending on the temperature range of deposition. Interestingly, growing above T-gc produces plastic crystals with a conformational ratio C-1/C-s that changes with T-dep above and below 110-120 K, the temperature at which previous works have identified the arrest of the transformations between the C-1 and C-s conformers.

Published
2019
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35. Influence of layer microstructure on the double nucleation process in Cu/Mg multilayers.

Author

Gonzalez-Silveira, M., Rodriguez-Viejo, J., Garcia, G., Pi, F., Ager, F. J., Lábár, J. L., Barna, A., Menyhárd, M., and Kótis, L.

Subjects
*MICROSTRUCTURE, *NUCLEATION, *TRANSMISSION electron microscopy, *BACKSCATTERING, *ELECTRON beams, *DIFFUSION
Abstract

We have investigated by differential scanning calorimetry the thermal evolution of Cu/Mg multilayers with different modulation lengths, ranging from 7/28 to 30/120 nm. The Cu and Mg layers were grown by sequential evaporation in an electron beam deposition system. The phase identification and layer microstructure were determined by cross-section transmission electron microscopy, Rutherford backscattering, and scanning electron microscopy with focused ion beam for sample preparation. Upon heating, the intermetallic CuMg2 forms at the interfaces until coalescence is reached and thickens through a diffusion-limited process. Cross-section transmission electron microscopy observations show a distinct microstructure at the top and bottom of the as-prepared Mg layers, while no significant differences were seen in the Cu layers. We show that this effect is responsible for the observed asymmetry in the nucleation process between the Cu on Mg and the Mg on Cu interfaces. By modeling the calorimetric data we determine the role of both interfaces in the nucleation and lateral growth stages. We also show that vertical growth proceeds by grain development of the product phase, increasing significantly the roughness of the interfaces. [ABSTRACT FROM AUTHOR]

Published
2006
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36. Evidence of photo- and electrodarkening of (CdSe) ZnS quantum dot composites.

Author

Rodriguez-Viejo, J. and Mattoussi, H.

Subjects
*PHOTOLUMINESCENCE, *CATHODOLUMINESCENCE, *QUANTUM dots, *ZINC sulfate
Abstract

Presents information on a study which examined the kinetics of photoluminescence (PL) and cathodoluminescence (CL) degradation of semiconductor quantum dot composites formed by highly luminescent (CdSe) zinc sulphate core-shell nanocrystals. Time decay of PL and CL; Thin film microstructure and optical properties; Cathodoluminescence of thin film quantum dot composites; Conclusions.

Published
2000

37. Residual stress and texture in poly-SiC films grown by low-pressure organometallic chemical-vapor...

Author

Hurtos, E. and Rodriguez-Viejo, J.

Subjects
*POLYCRYSTALS, *RESIDUAL stresses, *SILICON carbide, *THIN films
Abstract

Presents a study which investigated the residual stress and texture in polycrystalline cubic silicon carbide (3C-SiC) thin films grown by low-pressure organomettalic chemical-vapor deposition. Potential application of 3C-SiC; Thin film growth; Morphological characterization of SiC films.

Published
2000

38. Review on measurement techniques of transport properties of nanowires Additions and Corrections. See DOI:10.1039/C3NR03242F Click here for additional data file

Author

Rojo, Miguel Muñoz, Calero, Olga Caballero, Lopeandia, A. F., Rodriguez-Viejo, J., and Martín-Gonzalez, Marisol

Subjects
Chemistry
Abstract

Physical properties at the nanoscale are novel and different from those in bulk materials., Physical properties at the nanoscale are novel and different from those in bulk materials. Over the last few decades, there has been an ever growing interest in the fabrication of nanowire structures for a wide variety of applications including energy generation purposes. Nevertheless, the study of their transport properties, such as thermal conductivity, electrical conductivity or Seebeck coefficient, remains an experimental challenge. For instance, in the particular case of nanostructured thermoelectrics, theoretical calculations have shown that nanowires offer a promising way of enhancing the hitherto low efficiency of these materials in the conversion of temperature differences into electricity. Therefore, within the thermoelectrical community there has been a great experimental effort in the measurement of these quantities in actual nanowires. The measurements of these properties at the nanoscale are also of interest in fields other than energy, such as electrical components for microchips, field effect transistors, sensors, and other low scale devices. For all these applications, knowing the transport properties is mandatory. This review deals with the latest techniques developed to perform the measurement of these transport properties in nanowires. A thorough overview of the most important and modern techniques used for the characterization of different kinds of nanowires will be shown.

Published
2013

40. Temperature dependent thermal conductivity of polycrystalline ZnO films

Author

Alvarez-Quintana, J., Perez-Tijerina, E., Perez-Garcia, S.A., Rodriguez-Viejo, J., and Martinez, E.

Subjects
Zinc oxide -- Thermal properties, Phonons -- Analysis, Heat -- Conduction, Heat -- Analysis, Physics
Abstract

The thermal conductivity of atomic layer deposited polycrystalline zinc oxide (ZnO) films is measured between 30 and 300 K. The phonon-hopping transport model is used for analyzing the effect of the grain size and the transparency of the intergrain boundary on the thermal conductivity.

Published
2010

41. Interfacial effects on the thermal conductivity of a-Ge thin films grown on Si substrates

Author

Alvarez-Quintana, J. and Rodriguez-Viejo, J.

Subjects
Germanium -- Electric properties, Germanium -- Thermal properties, Dielectric films -- Thermal properties, Dielectric films -- Electric properties, Thin films -- Thermal properties, Thin films -- Electric properties, Physics
Abstract

The 3[omega] method is used for measuring the effective thermal conductivity of thin films of amorphous semiconductor materials like amorphous Ge (a-Ge). The reduction in the thermal conductivity is caused by the interfacial thermal resistance that has increased with decreasing temperature.

Published
2008

42. Influence of layer microstructure in the double nucleation process in Cu/Mg multilayers

Author

Gonzalez-Silveira, M., Rodriguez-Viejo, J., Garcia, G., F. Pi, Ager, F.J., Labar, J.L., Barna, A., Menyhard, M., and Kotis, L.

Subjects
Calorimetry -- Analysis, Copper compounds -- Thermal properties, Copper compounds -- Chemical properties, Thin films, Multilayered -- Thermal properties, Thin films, Multilayered -- Mechanical properties, Nucleation -- Analysis, Physics
Abstract

Differential scanning calorimetry is used to investigate the thermal evolution of Cu/Mg multilayers with different modulation lengths. The different microstructures at the top and bottom of the Mg layers are responsible for the double peak in the calorimetric traces and also play a decisive role in the morphology of the Cu[Mg.sub.2] layer after the nucleation and lateral growth stages.

Published
2006

45. Micropower thermoelectric generator from thin Si membranes

Author

Universitat Politècnica de Catalunya. Departament d'Enginyeria Electrònica, Universitat Politècnica de Catalunya. INSIDE - Innovació en Sistemes per al Disseny i la Formació a l'Enginyeria, Pérez Marín, A. P., Lopeandía, A. F., Abad, L., Ferrando-Villaba, P., López Martínez, Antonio Miguel, García, G., Muñoz Pascual, F.X., Rodriguez Viejo, J., Universitat Politècnica de Catalunya. Departament d'Enginyeria Electrònica, Universitat Politècnica de Catalunya. INSIDE - Innovació en Sistemes per al Disseny i la Formació a l'Enginyeria, Pérez Marín, A. P., Lopeandía, A. F., Abad, L., Ferrando-Villaba, P., López Martínez, Antonio Miguel, García, G., Muñoz Pascual, F.X., and Rodriguez Viejo, J.

Abstract

We report the development of a Si-based micro thermogenerator build from silicon-on-insulator by using standard CMOS processing. Ultrathin single-crystalline Si membranes, 100 nm in thickness, with embedded n and p-type doped regions electrically connected in series and thermally in parallel, are active elements of the thermoelectric device that generate thermopower under various thermal gradients. This proof-of-concept device produces an output power density of 4.5 µW/cm2, under a temperature difference of 5 K, opening the way to envisage integration as wearable thermoelectrics for body energy scavenging., Peer Reviewed, Preprint

Published
2014

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