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Este trabajo de fin de grado (TFG) recoge el proceso llevado a cabo en la revisión y mejora de un sistema de medida LBIC ("Light Beam Induced Current") para estudio y mapeado de corriente inducida y luz reflejada en células solares. Esta revisión y mejora se realizará tanto de su parte hardware como del software. El aspecto en el que se centra especialmente esta mejora es en el estudio de los parámetros del electrómetro del sistema y cómo afectan estos a los mapas resultantes, la configuración y la realización del barrido de las medidas de intensidad, previendo la necesidad de incluir un algoritmo de enfoque en función de las características propias de cada muestra. Para ello se emplea el entorno de programación LabVIEW en el que está desarrollado el software actual., This diploma thesis work reports the process undertaken to review and improve a Light Beam Induced Current (“LBIC”) measurement system for studying and mapping induced current and reflected light in solar cells. This review and improvement will be applied to both the hardware and software components of the system. The primary focus of this improvement is the study of the system’s electrometer parameters and how they affect the resulting maps. This includes setting up and performing intensity measurement sweeps and anticipating the need to incorporate a focusing algorithm based on the unique characteristics of each sample. The current software, developed in the LabVIEW programming environment will be used as a starting point for this purpose., Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía, Grado en Ingeniería Eléctrica

The integration of both optical and electronic components on a single chip, despite several challenges, holds the promise of compatibility with complementary metal-oxide semiconductor (CMOS) technology and high scalability. Among all candidate materials, III-V semiconductors exhibit great potential for optoelectronics and quantum-optics based devices, such as light emitters and harvesters. The control over geometry, and dimensionality of the III-V nanostructures, enables one to modify the band structures, and hence provide a powerful tool for tailoring the optoelectronic properties of III-V compounds. One of the most creditable approaches towards such growth control is the combination of using a patterned wafer and the self-assembled epitaxy. This work presents monolithically integrated catalyst-free InP nanowires grown selectively on Si nanotip-patterned, CMOS compatible (001) Si substrates using gas-source molecular-beam epitaxy. We use nanoheteroepitaxy approach to selectively grow InP nanowires on Si nanotips, which holds benefits due to its peculiar substrate design. In addition, our methodology allows the switching of dimensionality of the InP structures between one-dimensional nanowires and three-dimensional bulklike InP nanoislands by thermally modifying the shape of silicon nanotips surrounded by the silicon dioxide layer during the thermal cleaning of the substrate. The structural and optical characterization of nanowires indicates the coexistence of both zincblende and wurtzite InP crystal phases in nanowires. The two different crystal structures were aligned with a type-II band alignment. The luminescence from InP nanowires was measured up to 300 K, which reveals their promising optical quality for integrated photonics and optoelectronic applications., German Research Foundation, DAAD

GaP as one of the III−V semiconductors has an indirect band gap in its natural zinc-blend (ZB) crystal phase, limiting its applications in optoelectronics. The atomic arrangements of the ZB GaP, however, can be changed by adding energy to the system, for example, using strain and defects. In such a way, GaP can be crystallized in the wurtzite (WZ) phase with a direct band gap in the yellow−green range and promising new optical properties. GaP nanostructures offer the great possibility to induce strain, and hence, one can expect to obtain the WZ phase by modifying the geometry and dimensionality of GaP. In this work, we present GaP nanowires (NWs) grown on SiO2 substrates by gas-source molecular beam epitaxy. Raman measurements on individual GaP NWs indicate that NWs are poly-type crystal structures with the starting growth of the WZ phase, transforming into the ZB phase, and ending as the WZ phase. Photoluminescence at 9 K from an ensemble of NWs shows emissions at 2.09−2.14 eV, which are related to the direct band gap of the WZ phase and peaks between 2.26 and 2.3 eV due to the ZB phase. The emission of the WZ GaP phase is observable up to 160 K. Cathodoluminescence at 83 K shows directly the emission between 2.09 and 2.14 eV along the single NWs, indicating the presence of the WZ phase. Our results demonstrate the realization of poly-type, ZB, and WZ GaP NWs on SiO2 by gas-source molecular beam epitaxy., German Research Foundation, Agencia Española de Investigación

En el presente trabajo se desarrolla y construye un prototipo funcional de un huerto hidropónico vertical automatizado capaz de trabajar en exteriores e interiores. Además del prototipo, se ha generado un panel de control que permite al usuario monitorear y controlar el huerto de forma remota, así como notificarle mediante alarmas la necesidad de hacer una intervención física. El prototipo es totalmente autosuficiente mediante el uso de placas solares y baterías. Igualmente, está construido con materiales reutilizables en la medida de lo posible y con optimización de los materiales adquiridos., In this study, a functional prototype of an automated hydroponic garden capable of working outdoors is developed and built. In addition, a control dashboard has been designed and coded that allows the user to monitor and control the garden remotely, and to be notified by alarms about the need of a physical intervention. The prototype is equipped with energy autonomy through solar panels and batteries. Likewise, it is built with reusable materials to the maximum extent possible and optimization of the materials acquired., Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía, Grado en Ingeniería en Electrónica Industrial y Automática

Este TFG trata sobre el diseño y programación de una aplicación en Python que permita controlar un láser de alta potencia, capturar imágenes de una cámara, y sincronizar medidas de foto- y electroluminiscencia con una fuente de alimentación para poder tomar medidas en on y off. El objetivo de este trabajo es automatizar en la medida de lo posible el proceso antes descrito, reduciendo la manipulación de los equipos por acción humana. De esta manera se mejoran las condiciones de trabajo personal y se facilita el proceso de obtención de datos y resultados con mayor rapidez. Para desarrollar el programa se ha elegido desarrollarlo en Python ya que es un lenguaje de programación de alto nivel que se utiliza para desarrollar aplicaciones de todo tipo. A diferencia de otros lenguajes como Java o .NET, se trata de un lenguaje interpretado, es decir, que no es necesario compilarlo para ejecutar las aplicaciones escritas en Python, sino que se ejecutan directamente en el ordenador utilizando un programa denominado interpretador, por lo que no es necesario “traducirlo” a lenguaje máquina. Los instrumentos que se han utilizado para este proyecto han sido una fuente de alimentación modelo CPX400D de AIM-TTi, un sistema diodo láser DS3-11312-101- K635F09FN-0.40W de BWT Beijing y una cámara digital DCAM-API., Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía, Grado en Ingeniería en Electrónica Industrial y Automática

Semiconductor nanowires are promising materials for the next generation of tandem solar cells. Its dimension allows one to combine a large variety of materials not allowed in planar solar cells because of the large lattice mismatch. Nanowires have also shown great potential in electrical, biomedical, photonics, and other applications. Different configurations, doping, and concentrations have been used. Therefore, understanding the nanowire properties is crucial to grow nanowires for different applications. In that context, optical techniques are very powerful non-invasive tools for charac- terizing semiconductor nanowires. In this work, we have characterized axially hetero-structured InP/InGaP nanowires with micro-Raman spectroscopy, micro-photoluminescence, tip-enhanced Raman spectroscopy, tip-enhanced photoluminescence, and energy-dispersive X-ray analysis. We found peculiar optical phenomena along the nanowire, which consists of two p n junctions made of InP and InGaP, respectively, axially bridged by a n+-InP/p+-InGaP tunnel diode. In particular, a local resonance at the tunnel junction is accompanied by the breakdown of the Raman selection rules. Furthermore, plasmon damped mode was observed in the heavily p-type doped side of the tunnel junction. Photoluminescence measurements allowed to detect the presence of a parasitic InGaP layer grown laterally at the bottom of the nanowire., Los nanohilos semiconductores son materiales prometedores para la próxima generación de células solares tándem. Su dimensión permite combinar una gran variedad de materiales no permiti- dos en las células solares planas debido a la gran diferencia en los parámetros de red. Los nanohilos también han mostrado un gran potencial en aplicaciones eléctricas, biomédicas, fotónicas y otras. Se han utilizado diferentes configuraciones, dopaje y concentraciones. Por lo tanto, comprender las propiedades de los nanohilos es crucial para desarrollar nanohilos para diferentes aplicaciones. En ese contexto, las técnicas ópticas son herramientas no invasivas muy poderosas para caracterizar nanohilos semiconductores. En este trabajo, hemos caracterizado nanohilos InP/InGaP axialmente heteroestructurados con espectroscopia micro-Raman, micro-fotoluminiscencia, espectroscopia Raman mejorada con la punta (TERS), fotoluminiscencia mejorada con la punta (TEPL) y análisis de rayos X de dispersión de energía. Encontramos asombrosos fenómenos ópticos en los nanohilos de InP/InGaP investigados, que consisten en dos uniones p-n hechas de InP y InGaP y conectadas axialmente mediante un diodo túnel formado por n+-InP/p+-InGaP. En particular, hallamos una resonancia local en el espectro RAman correspondiente a la union túnel acompañada por la ruptura de las reglas de selección Raman. Además, se observó un modo amortiguado de plasmón en el lado fuertemente dopado de tipo p de la unión túnel. Las mediciones de fotoluminiscencia permitieron detectar la presencia de una capa de InGaP parásita que creció lateralmente en la parte inferior del nanohilo., Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía, Máster en Física

En el presente trabajo se explica detalladamente el proceso llevado a cabo en la mejora y actualización de un sistema de medida LBIC (“light beam induced current”). Dicha actualización la realizaremos tanto en la parte software que controla el sistema utilizando para ello el entorno de programación LabVIEW, optimizando el programa utilizado hasta ahora, como en lo relacionado al hardware, realizando los cambios oportunos sobre los dispositivos que conforman el sistema, además se acoplará a este un espectrómetro dotado de un detector para realizar medidas de emisión de fotoluminiscencia de manera síncrona o alternada con las medidas LBIC. This document explains in detail the process carried out to improve and update a LBIC (light beam induced current) measurement system. This update will be carried out in the software part that controls the system using LabVIEW programing environment, optimizing the program used so far. As wellaas in relation to the hardware, making the appropiate changes to the devices that make up the system a spectrometer will also be added to it to perform photoluminescence emisión measurements synchronously or alternately with the LBIC measurements., Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía, Grado en Ingeniería en Electrónica Industrial y Automática

Es sabido que las energías renovables, y en España en especial la solar, están en auge y tendrán un crecimiento exponencial en los próximos años. Este crecimiento también significa que toneladas de residuos de paneles solares serán desechados próximamente. Para lograr un medio ambiente más sostenible se puede alargar la vida útil de los paneles fotovoltaicos dándoles un segundo uso. Con el desarrollo de esta nueva industria se incrementará el autoconsumo entre particulares, quienes estarán interesados en paneles menos exigentes como los de segunda mano y el que hayan sido evaluados les aportará la confianza y seguridad sobre el buen estado del panel. El objetivo de este Trabajo de Fin de Grado es realizar un estudio de viabilidad de la creación de un sello de calidad para paneles solares de segunda mano, para lograr disminuir el impacto ambiental y apoyar la economía circular. Para lograrlo, se ha empleado un estudio DELPHI para prever la evolución del sector de energía solar y la posible cabida de un sello de calidad dentro del sector de segunda mano. Con esta información, posteriormente se desarrolla un proceso de evaluación del sello, en el que se explica el protocolo que se deberá llevar a cabo para la valoración del estado del panel y su rendimiento, It is known that renewable energies, and especially solar energy in Spain, are on the rise and will grow exponentially in the coming years. This growth also means that tons of solar panel waste will soon be disposed of. To achieve a more sustainable environment, the useful life of photovoltaic panels can be extended by giving them a second use. With the development of this sector, selfconsumption by individual family units will increase. Some of them are likely to be interested in less demanding and more affordable panels such as second-hand ones and a certified inspection will provide them with the confidence and security of the good condition of the panel. The objective of this Final Degree Project is to carry out a feasibility study for the creation of a quality seal for second-hand solar panels, in order to reduce the environmental impact and support the circular economy. To achieve this, a DELPHI study has been used to foresee the evolution of the solar energy sector and the potencial of a quality seal within the second-hand sector. With this information, a panel evaluation process is subsequently designed and developed, which contains the protocol to be carried out to assess the panel state and perfomance., Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía, Departamento de Organización de Empresas, Grado en Ingeniería en Organización Industrial

En este proyecto se estudia la viabilidad de crear una spin-off basada en un modelo de negocio en el mercado de paneles solares fotovoltaicos de segunda mano. Para la consecución de este objetivo, se ha planteado un estudio colaborativo cotutelado (profesores del Departamento de Organización de Empresas y Comercialización e Investigación de Mercados y del Departamento de Física de la Materia Condensada, Cristalografía y Mineralogía) por parte de cuatro estudiantes de la Universidad de Valladolid. Por ello, se ha dividido el estudio en 4 proyectos diferentes: dos trabajos fin de grado (TFG) y dos trabajos de fin de máster (TFM). Los TFGs investigan, en uno de ellos, el sector de calidad para paneles solares junto con su marco legal y las normativas europeas aplicando las cinco fuerzas de Porter y, en el otro TFG, un análisis en profundidad la viabilidad técnico-económica para posibles inversiones en paneles solares de segunda mano. Uno de los TFMs está orientado a la creación de un plan de empresa para la creación de la spin-off. El otro TFM, que se presenta en el presente documento, profundiza en el conocimiento de los stakeholders involucrados en el sector de paneles solares de segunda mano, y en el futuro del mercado de paneles solares de segunda mano, mediante un análisis prospectivo a través del método Delphi. Se analizan los resultados del estudio y se aplica el conocimiento obtenido de cada uno de los TFG y TFM, todos complementarios entre sí, en un diagnóstico final que sirve para mostrar el diseño de un modelo de negocio en el que sustentar la creación de la spin-off., This project studies the feasibility of creating a spin-off based on a business model in the second-hand photovoltaic solar panel market. To achieve this objective, a co-supervised collaborative study has been proposed (professors from the Department of Business Organization and Marketing and Market Research and the Department of Physics of Condensed Matter, Crystallography and Mineralogy) by four students from the University of Valladolid. For this reason, the study has been divided into 4 different projects: two final degree projects (TFG) and two final Master degree projects (TFM). The TFGs report on, in one of them, the quality of the sector for solar panels together with its legal framework and European regulations applying the five forces of Porter and, in the other TFG, the technical-economic viability for possible investments in second-hand solar panels is analyzed in depth. One of the TFMs aims at creating a business plan for the creation of the spin-off. The other TFM, presented in this document, delves into the knowledge of the stakeholders involved in the second-hand solar panel sector, and in the future of the second-hand solar panel market, through a prospective analysis through the Delphi method. The results of the study are analyzed and the knowledge obtained from each of the TFG and TFM, all complementary to each other, is applied in a final diagnosis that serves to show the design of a business model in which to support the creation of the spin-off., Departamento de Organización de Empresas y Comercialización e Investigación de Mercados, Máster en Administración de Empresas

Ecuadorian pottery is renowned for its beauty and the particularly rich colour of its pigments. However, a major challenge for art historians is the proper assessment of the provenance of individual pieces due to their lack of archaeological context. Of particular interest is the Jama-Coaque culture, which produced fascinating anthropomorphic and zoomorphic pottery from ca. 240 B.C. until the Spanish Conquest of 1532 A.D. in the coastal region of Ecuador. Using a combination of microscopic and spectroscopic techniques, i.e., transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), energy-dispersive x-ray spectroscopy (EDX), and scanning electron microscopy (SEM); we are able to characterize these pieces. We have found several kinds of iron-oxide based nanostructures in all the colour pigments we investigated for the Jama-Coaque culture, suggesting the same unique volcanic source material was used for their clay. Such nanostructures were absent from the pigment samples studied from other contemporary coastal-Ecuadorian cultures, i.e., the Tumaco-La Tolita and Bahía cultures. In the yellow pigments of goethite we find carbon nanofibres, indicating these pigments were subjected to a thermal treatment. Finally, in the blue, green, and black pigments we detect modern pigments (phthalocyanine blue, lithopone, and titanium white), suggesting modern restoration. Our results demonstrate the power of TEM, Raman, FTIR, EDX, and SEM archaeometric techniques for characterizing pieces without a clear archaeological context. Furthermore, the characterization of nanostructures present in such pieces could be used as a possible fingerprint for a provenance study.

This paper presents an intelligent system aimed at detecting a person’s posture when sitting in a wheelchair. The main use of the proposed system is to warn an improper posture to prevent major health issues. A network of sensors is used to collect data that are analyzed through a scheme involving the following stages: selection of prototypes using condensed nearest neighborhood rule (CNN), data balancing with the Kennard–Stone algorithm, and reduction of dimensionality through principal component analysis. In doing so, acquired data can be both stored and processed into a micro controller. Finally, to carry out the posture classification over balanced, pre-processed data, and the K-nearest neighbors algorithm is used. It turns to be an intelligent system reaching a good tradeoff between the necessary amount of data and performance is accomplished. As a remarkable result, the amount of required data for training is significantly reduced while an admissible classification performance is achieved being a suitable trade given the device conditions.

The high pressure lattice dynamics of rhombohedral antimony have been studied by a combination of diffuse scattering and inelastic x-ray scattering. The evolution of the phonon behavior as a function of pressure was analyzed by means of two theoretical approaches: density functional perturbation theory and symmetry-based phenomenological phase transition analysis. This paper focuses on the first structural phase transition, SbI-SbIV, and the role of vibrations in leading the transition. The phonon dispersion exhibits complex behavior as one approaches the structural transition, with the branches, corresponding to the two transitions happening at high pressure in the Va elements (A7-to-BCC and A7-to-PC) both showing softening., NSF, DOE, Texas Advances Computer Center

We investigate the hydrostatic pressure dependence of the zone center optical phonons of c-plane and a-plane wurtzite InN epilayers grown on GaN substrates. The longitudinal to transverse mode splitting for the A1 and E1 modes was found to increase with increasing pressure, whereas the associated transverse effective charge decreases for both modes as e∗T(A1)=2.93–9.9×10−3P and e∗T(E1)=2.80–10.6×10−3P (in units of elementary charge and P in GPa). These observations are well in line with results for other II–VI, III–V, and group-IV semiconductor compounds as far as the relation between the magnitude and sign of the pressure derivative of e∗T and the bond ionicity is concerned. As the latter increases so does |∂e∗T/∂P| with a sign change from positive to negative for bond ionicities around fi=0.46 for compounds with anions belonging to the first row of the Periodic Table. A comparison of the results for InN and other nine tetrahedrally bonded compounds indicate that the pressure behavior of the transverse effective charge is mainly determined by the strength of the Pauli repulsion between cation valence electrons and those of the anion core. We also perform ab initio calculations in order to address the origin of the observed increase in linewidth of the Ehigh2 mode which is found to arise from a pressure-induced increase in the rate of two-phonon decay processes. This broadening is associated with tuning into resonance of a steep edge in the two-phonon density of states around 460 cm−1 with the frequency of the Ehigh2 mode.

This work presents a comparative study of prototype selection (PS) algorithms. Such a study is done over data-from-sensor acquired by an embedded system. Particularly, five flexometers are used as sensors, which are located inside a glove aimed to read sign language. Measures were taken to quantify the balance between classification performance and reduction training set data (QCR) with k neighbors equal to 3 and 1 to force the classifier (kNN) to the maximum. Two tests were used: (a)the QCR performance and (b) the embedded system decision in real proves. As result the Random Mutation Hill Climbing (RMHC) algorithm is considered the best option to choose in this data type with removed instances at 87% and classification performance at 82% in software tests, also the classifier kNN must be with k=3 to improve the classification performance. In a real situation, with the algorithm implemented. The system makes correct decisions at 81% with 5 persons doing sign language in real time.

We report evidence of a nonadiabatic Kohn anomaly in boron-doped diamond, using a joint theoretical and experimental analysis of the phonon dispersion relations. We demonstrate that standard calculations of phonons using density-functional perturbation theory are unable to reproduce the dispersion relations of the high-energy phonons measured by high-resolution inelastic x-ray scattering. On the contrary, by taking into account nonadiabatic effects within a many-body field-theoretic framework, we obtain excellent agreement with our experimental data. This result indicates a breakdown of the Born-Oppenheimer approximation in the phonon dispersion relations of boron-doped diamond., European Union Horizon 2020, Leverhulme Trust, United Kingdom Engineering and Physical Sciences Research Council, University of Oxford Advanced Research Computing facility, ARCHER United Kingdom National Supercomputing Service, European Synchrotron Radiation Facility - ESRF

Ultrathin passive films effectively prevent the chemical attack of stainless steel grades in corrosive environments; their stability depends on the interplay between structure and chemistry of the constituents iron, chromium, and molybdenum (Fe-Cr-Mo). Carbon (C), and eventually boron (B), are also important constituents of steels, although in small quantities. In particular, nanoscale inhomogeneities along the surface can have an impact on material failure but are still poorly understood. Addressing a stainless-type glass-forming Fe50Cr15Mo14C15B6 alloy and using a combination of complementary high-resolution analytical techniques, we relate near-atomistic insights into increasingly inhomogeneous nanostructures with time- and element-resolved dissolution behavior. The progressive elemental partitioning on the nanoscale determines the degree of passivation. A detrimental transition from Cr-controlled passivity to Mo-controlled breakdown is dissected atom by atom, demonstrating the importance of nanoscale knowledge for understanding corrosion., MICINN, Generalitat de Catalunya, DAAD, Conacyt, European Union - Marie Curie IEF

Metallic glasses are often referred as glassy or amorphous alloys. They lack long-range order and microstructural defects that are characteristics in crystals, such as grain and phase boundaries and dislocations. These new materials have demonstrated very interesting structural and mechanical properties derived from their homogeneity in composition and the absence of grain boundaries. Structural, mechanical or chemical properties, among others, may be even superior to those observed in conventional metallic alloys, and therefore attracted great scientific and technological interest. In this thesis project three different families of metallic glasses were selected to achieve a better understanding of amorphous alloys. First, a Ce-based alloy has been used to analyze a polyamorphic transition upon application of pressure to a more densely packed structure. X-ray diffraction and inelastic x-ray scattering data show a polyamorphic transition in the 2-10 GPa range, and this transition presents a hysteresis cycle between both compression and decompression data. The effect of this transition on mechanical properties is then evaluated. Second, a family of Fe-based metallic glasses, or amorphous steels, was selected to study their mechanical and electrochemical properties as a function of the structure and composition. The composition of the base alloy was first modified by addition of Yttrium in different concentrations as microalloying element and the structure was changed by thermal annealing, forming intermediate crystal/amorphous composites, up to a complete crystallization state. Finally, an entirely new alloy for biocompatible purposes has been designed, synthesized, and characterized. The basic structural characterization of this new Zr-Ti based amorphous alloy shows that is possible to produce the amorphous state in an alloy that does not contain toxic or unhealthy elements., Los vidrios metálicos, comúnmente conocidos como aleaciones amorfas o vitrificadas, carecen de orden a largo alcance así como de defectos microestructurales comunes en los cristales, tales como dislocaciones o fronteras de grano y/o de fase. Esta nueva clase de materiales ha demostrado poseer propiedades muy interesantes derivadas de la ausencia de microestructura y la homogeneidad en su composición. Estas propiedades, estructurales, mecánicas y químicas, entre otras, pueden llegar a ser incluso superiores a las observadas en materiales convencionales, y por lo tanto los vidrios metálicos han atraído gran interés por parte de la comunidad científica así como de carácter tecnológico. En este proyecto de tesis se pretende obtener un mayor conocimiento sobre aleaciones metálicas amorfas, para lo cual se propusieron tres familias diferentes de vidrios metálicos. Primero, se utilizó una aleación de base Ce para analizar transiciones poliamórficas, entre un estado de baja densidad hacia una estructura densamente empaquetada, por efecto de la presión. Los resultados obtenidos por difracción de rayos X y dispersión inelástica de rayos X muestran una transición en un rango de presiones de 2 a 10 GPa presentando además histéresis con respecto a los datos obtenidos en compresión y descompresión. El efecto de dicha transición en las propiedades mecánicas de la aleación es también evaluado. En segundo lugar se eligió una familia de aleaciones de base Fe, conocidos también como aceros amorfos. Las propiedades mecánicas y electroquímicas en función de la estructura y la composición fueron evaluadas mediante la introducción de itrio como elemento microaleante y la modificación de la estructura por medio de tratamientos térmicos con la obtención de estructuras compuestas nanocristal-amorfo hasta una completa cristalización. Finalmente, se diseñó y sintetizó una aleación completamente nueva con el propósito de evaluar biocompatibilidad. La caracterización estructural básica de esta n, Postprint (published version)

The behavior of acoustic modes in solids can yield information on the glass dynamics at different length and frequency scales. Inelastic X-ray scattering (IXS) using Synchrotron radiation allows us to obtain detailed information on the sound speed behavior at different length scales as well as approaching the macroscopic limit. This gives an insight to the microscopic mechanisms responsible for the mechanical properties in the THz frequency domain. IXS also provides a method to investigate the fragility of glass-forming liquids via the non-ergodicity factor of the corresponding glasses. Moreover, some questions arise about how phenomena such as the polyamorphism, observed, e.g. in Ce55Al44 upon application of pressure, affect the mechanical properties of a metallic glass at a microscopic level. In this article we reveal a change in the high frequency response at the mesoscopic length scale with respect to the ultrasounds limit in metallic glasses. We will also review further applications of IXS on Pd and Ce-based metallic glasses to determine elastic constants, changes in sound speed due to polyamorphism and to investigate their fragility., Generalitat de Catalunya, CICYT, European Synchrotron Radiation Facility - ESRF

Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy optic phonon dispersion relations of thin wurtzite indium nitride films. Indium nitride is an especially relevant example, due to the technological interest for optoelectronic and solar cell applications in combination with other group III nitrides., CICYT, Generalitat de Catalunya, European Synchrotron Radiation Facility - ESRF, CONACYT, Universitat Polytechnica de Valencia

The mechanical response of bulk metallic glasses is ultimately controlled by interatomic forces between the randomly distributed atoms. The study of collective dynamics in amorphous systems, either liquid or glassy, opens a window to better understand this interaction. We present here results of recent IXS experiments performed at the ID16 beamline of the European Synchrotron Radiation Facility (ESRF) on a metallic glass. In particular, the high-frequency response of Pd77Si16.5Cu6.5 alloys, produced as a ribbon with an ultra-fast quenching rate (∼106 K/s) and as a bulk with a slow one (∼102 K/s), was determined. Previous experiments showed a discrepancy between the sound speed of metallic glasses measured by ultrasounds and by IXS. This was explained as a consequence of density fluctuations in the glass, although other explanations are possible. Here, the dispersion relation of the acoustic modes at room temperature and pressure are measured for both samples, allowing us to compute the sound speed and discuss the differences in the acoustic properties of both samples., European Synchrotron Radiation Facility - ESRF, CICYT, Generalitat de Catalunya

Amorphous steels are promising materials with potential structural applications. The glass-forming ability (GFA) and mechanical properties of metallic glasses are intimately related to the local structure. In Fe-based alloys, Cr and Mo content seem to play a key role in stabilizing the amorphous atomic-level structure. Here we present a study on the effects of changing Mo content in Fe72−xC7Si3.3B5.5P8.7Cr2.3Al2Mox amorphous steels. We study the local structure of these alloys by Synchrotron X-ray diffraction and Mössbauer spectroscopy. The results show how the amorphous phase evolves from a ferromagnetic Fe-rich structure to a structure with predominance of paramagnetic environments with the increase of Mo content. The changes in the distribution of magnetic environments cannot be attributed only to the Fe–Mo substitution but to a change of local configuration in the amorphous phase., CICYT, European Synchrotron Radiation Facility - ESRF, Generalitat de Catalunya

Using high resolution inelastic x-ray scattering we studied the collective dynamics of the Pd77Si16.5Cu6.5 metallic glass, focusing on the energy-momentum region where the boson peak appears. The dispersion relation and the width of the acoustic excitations are determined showing how the longitudinal acoustic modes maintain their dispersive character for frequencies well above the boson peak frequencies. Moreover, we prove that close to these frequencies there is a softening of the apparent sound speed indicating a failure of the Debye continuum approximation at the boson peak frequencies and challenging previous results on other metallic glasses.

The anisotropy of the valence energy-loss function of hexagonal boron nitride (hBN) is shown to be largely enhanced by the highly inhomogeneous character of the excitonic states. The energy loss with momentum transfer parallel to the BN layers is dominated by strongly bound, quasi-two-dimensional excitons. In contrast, excitations with momentum transfer perpendicular to the layers are influenced by weakly bound three-dimensional excitons. This striking phenomenon is revealed by a combined study using high-precision nonresonant inelastic x-ray scattering measurements supported by ab initio calculations. The results are relevant in general to layered insulating systems., Academy of Finland, Spanish MEC, European Union, ANR, DoE, European Synchrotron Radiation Facility - ESRF, Red Española de Supercomputación, IDRIS

We report here on a polyamorphic-phase transition upon application of pressure on a Ce-based metallic glass, Ce70Al10Ni10Cu10, investigated by x-ray diffraction and inelastic x-ray scattering. This alloy is found to display a strong hysteresis in volume per atom upon application and subsequent release of pressure. The observed structural changes are correlated with changes observed by inelastic x-ray scattering in the elastic constants, acoustic mode frequencies, and sound speed. The results reported here point toward three different amorphous phases for this alloy existing in the 0–25 GPa pressure region: low- and high-density states and an intermediate mixed state that displays a hysteresis behavior. Finally, we discuss the impact of Ce concentration on the polyamorphic transition for a series of Ce-based metallic glass alloys and link it to the phase transformation between ¿ -Ce and a-Ce under pressure., Peer Reviewed, Postprint (published version)

Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy optic phonon dispersion relations of thin wurtzite indium nitride films. Indium nitride is an especially relevant example, due to the technological interest for optoelectronic and solar cell applications in combination with other group III nitrides, Postprint (published version)

Amorphous steels are promising materials with potential structural applications. The glass-forming ability (GFA) and mechanical properties of metallic glasses are intimately related to the local structure. In Fe-based alloys, Cr andMocontentseemto play a key role in stabilizing the amorphous atomic-level structure. Here we present a study on the effects of changing Mo content in Fe72−xC7Si3.3B5.5P8.7Cr2.3Al2Mox amorphous steels.Westudy the local structure of these alloys by Synchrotron X-ray diffraction and Mössbauer spectroscopy. The results show how the amorphous phase evolves from a ferromagnetic Fe-rich structure to a structure with predominance of paramagnetic environments with the increase of Mo content. The changes in the distribution of magnetic environments cannot be attributed only to the Fe–Mo substitution but to a change of local configuration in the amorphous phase., Postprint (published version)

Mechanical properties are becoming the focus in research on bulk metallic glasses (BMG), as they are the limiting factor for structural applications. A wide range of experimental techniques gives complementary macroscopic data that are often difficult to correlate with the microscopic structural knowledge of the same materials. Recently, high resolution inelastic X-ray scattering (IXS) was applied to determine the high frequency dynamics of BMG [T. Scopigno, J.-B. Suck, R. Angelini, F. Albergamo, G. Ruocco, Phys. Rev. Lett. 96 (2006) 135501]. This technique offers a new approach to the mechanic properties helping to bridge the gap between the microscopic and the macroscopic picture. Here we will present results of IXS experiments on bulk metallic glasses with different fragility values, obtained at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France)., European Synchrotron Radiation Facility - ESRF, CICYT, Generalitat de Catalunya

Zinc oxide is a key material for optoelectronic applications, whose transport properties are typically dominated by the lattice vibrations. We report here the phonon-dispersion relations of wurtzite ZnO at 10 K, as determined by using inelastic neutron scattering. The experimental data are analyzed with the aid of ab initio calculations based on density-functional perturbation theory. A complete picture of the lattice dynamics is drawn from the present results, thus contributing to the understanding of mechanical, thermodynamical, and transport properties of wurtzite optoelectronic materials., CICYT, Generalitat de Catalunya, CONACYT, Universitat Polytechnica de Valencia, CNS IPICYT

The purpose of this project is to synthetize and to characterize green and yellow pigments used by the painters of Catalan Gothic period. The concerned pigments are the green, yellow typical 1 (which the chemical formula is Pb2SnO4) and yellow typify 2 (which the chemical formula is Pb (Sn, If) O3). To synthetize them, it is necessary to know their chemical compositions. It is so possible to reproduce pigments. Once pigments were reproduced, the objective was to characterize them. For that purpose, the spectroscopy in infrared was used at first. We put the sample in the form of capsule by applying it a strong pressure after the credit note to mix in some oxide of bromide. Secondly, the diffraction by X-rays used too. Pigments were sent in Grenoble, to the European Synchrotron Radiation Facility. It was thus possible to characterize them and to know their exact compositions. Other part of this study was to observe the reaction of these pigments mixed on one hand in some oil of it in and on the other hand to egg yolk according to time.

Este trabajo tiene como objetivo el estudio de una propiedad de un tipo de materiales poco utilizado hasta ahora: los vidrios metálicos. Debido al descubrimiento reciente de los vidrios metálicos, sus características no son bien conocidas y por ello proponemos el estudio de una de estas características, la Dureza. La Dureza es un parámetro mecánico cuantificando la resistencia a la penetración de un material. Se mide con un durómetro, un microdurómetro o un nanodurometro, dependiendo de la dimensión de las muestras. La medida consiste someter la superficie del material a una deformación plástica en la superficie del material, con un indentador de forma conocida. La dureza se obtiene calculando el cociente de la fuerza aplicada por la superficie de la huella. Los vidrios metálicos son vidrios a base de elementes metálicos. Como los vidrios, son sólidos que tienen una estructura atómica desordenada, o amorfa, similar a un líquido congelado, mientras que un sólido cristalino se compone de varios cristales hechos de átomos organizados y alineados en una disposición regular, propia a la composición del material. Se obtienen enfriando una aleación metálica en fase líquida, bastante rápidamente para que no se formen cristales de metal y que la estructura se mantenga amorfa. Son difíciles de producir porque los metales muestran una gran tendencia a cristalizar cuando pierden calor, y por ello se necesitan velocidades de enfriamiento muy elevadas. Este proyecto tenía dos etapas: la primera parte fue la medida de la dureza de cintas de una aleación amorfa de base de hierro con diferentes concentraciones de itrio, utilizando un microdurómetro controlado por un ordenador; la segunda parte fue una comparación de los resultados obtenidos anteriormente, para ver como varía la Dureza con la composición de la aleación Acero - Itrio, o con el espesor de las cintas.

The goal of this training course was the production and the characterization of two amorphous alloys, named metallic glasses too. The amorphous state correspond to a specific atomic structure which is very similar than the liquid structure but applied to a solid. It means that in standard condition there is no relative motion between atoms. The first one is an Fe-based alloy with the following atomic composition: Fe65-xCrxMo14C15B6.It was produced at the liquid state, by injection inside a cooled copper mould. The second one is an Zi-based alloy but its composition is kept secret. It was obtained by rapid quenching, using a melt-spinner system. Both of those processes have been analyzed on computer, during a thermal study, in order to obtain max and min-values of the cooling rate. The cooling rate is an important parameter which act directly on final structure, after solidification of the melted alloy. The knowledge of those values permit to qualify the amorphous state, before analyzing it with other test.

The measurement of fragility of glass-forming liquids involves either the determination of viscosity at different temperatures above the glass transition or the measurement of the dynamic glass–liquid transition by calorimetry or dilatometry at different heating rates. Significant data dispersion is observed when comparing fragility parameters obtained by different techniques. Dynamic mechanical analysis (DMA) is widely used for characterizing glass transition in polymer science while it is still seldom used in metallic glasses. In this work we determine the relaxation time ( ) vs temperature of a Pd77.5Si16.5Cu6 glass by means ofDMAmeasurements. The measured range of relaxation times cover the whole region from glass transition ( > 100 s) to times of the order of 10−2 s. The fragility parameter obtained for this alloy is found significantly higher than the values obtained from previous viscosity and calorimetric techniques. The application range, limitations and correctness of the technique are discussed., Postprint (published version)

The two-dimensional mapping of the phonon dispersions around the K point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at K. We observe an almost degeneracy of the three TO-, LA-, and LO-derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal warping effect opposite to that of the electronic band structure. We determined the electron-phonon coupling constant to be 166 (eV/Å)2 in excellent agreement to GW calculations. These results are fundamental for understanding angle-resolved photoemission, double-resonance Raman and transport measurements of graphene-based systems., Austrian Academy of Sciences, MICINN, Spanish MEC, Generalitat de Catalunya, European Union, IDRIS, Red Española de Supercomputación

En aquest vídeo s'explica el fenomen de la superconductivitat a altes temperatures i es presenta una pràctica demostrativa d'un tren levitant degut al refredament d'una pastilla superconductora per sota de la temperatura crítica, posant en evidència l'absència de fregament amb les vies. També es mostra com les línies de camp magnètic queden atrapades en el superconductor al ser refredat.

The metallic glasses represent a new class of materials. They were discovered in 1960 and they have interesting structural and mechanical properties, which made them attractive for applications in several fields. They have been used since a few decades ago because of its magnetic properties and now the mechanical ones have captured the interest of the scientific community. The objective of this project is to produce and characterize a Pd-based metallic glass, more specifically Pd77Si16.5Cu6.5, using different techniques. An Arc- Melting device, a setup that produces an electric arc employed to melt the constituent elements into balls, and a Melt-Spinner, a rapidly quenching machine to produce micrometer thick ribbons, were utilized for production of ribbons. In order to test the sample quality, they were analyzed with the Scanning Electron Microscopy (SEM) technique, capable of extract the actual composition with a small error. As characterization techniques, we employed Inelastic Neutron Scattering (INS) to unveil some of their vibrational properties. Also, a second prefabricated alloy, Ce70Al10Ni10Cu10, was characterized using a Dynamic Mechanical Analysis (DMA) which gave us information about its mechanical properties. Two fundamental parameters were found: the glass transition temperature and the fragility of the material. This project contains two basic parts: production and characterization, where the above mentioned methods and their results are explained. Furthermore, each part contains its own conclusions. Finally, the project conclusions are presented as a summary of the whole project with the most important data and some suggestions for further research on these exciting materials.

El descubrimiento de los vidrios metálicos ha supuesto un avance muy significativo en la ciencia de los materiales. Debido a su estructura amorfa, estas aleaciones presentan propiedades estructurales y mecánicas muy interesantes para su aplicación en ingeniería, además de en otros ámbitos como la medicina, el deporte, la electrónica e incluso en el ámbito de la joyería. En el ámbito aeronáutico resulta interesante su gran resistencia a rotura bajo esfuerzos de deformación plástica, efecto debido a la práctica inexistencia de dislocaciones en su estructura interna. Este hecho permitirá realizar un seguimiento de las curvas de tensión-deformación que dan a conocer el estado interno del material, optimizando los tiempos de vida de las piezas utilizadas, lo cual se traduce en una mayor seguridad a bordo de las aeronaves. En este proyecto se caracteriza dinámica y mecánicamente una aleación amorfa de Pd77,5Si16,5Cu6 obtenida mediante enfriamiento rápido con Melt-Spinner, en las instalaciones de la Escuela Politécnica Superior de Castelldefels (EPSC). Para ello se ha contado con un equipo conocido como DMA (Dynamic Mechanical Analyzer) que ha permitido realizar ensayos de tensión-deformación a las diversas muestras utilizadas. En cada uno de los ensayos realizados se han modificado los rangos de temperatura estudiados, así como los intervalos de aplicación de los esfuerzos de tensión, las velocidades de calentamiento que se han aplicado a cada una de las muestras y otros muchos parámetros que se analizarán en profundidad a lo largo de este trabajo, todo ello con la intención de determinar, lo más detalladamente posible, las propiedades físicas de esta aleación. Al final del trabajo se muestran las conclusiones obtenidas a partir de los resultados de los ensayos, animando a futuros estudiantes a continuar analizando esta nueva generación de materiales.

Raman spectra of aluminum nitride (AlN) under pressure have been measured up to 25GPa, i.e., beyond the onset of the wurtzite-to-rocksalt phase transition around 20GPa. The experimental pressure coefficients for all the Raman-active modes of the wurtzite phase are reported and compared to those obtained from ab initio lattice dynamical calculations, as well as to previous experimental and theoretical results. The pressure coefficients of all the Raman-active modes in wurtzite-type semiconductors (AlN, GaN, InN, ZnO, and BeO), as well as the relatively low bulk modulus and phase transition pressure in wurtzite AlN, are discussed in the light of the pressure dependence of the structural crystal anisotropy in wurtzite semiconductors. On pressure release, AlN partially returns to the wurtzite phase below 1.3GPa but the presence of a rocksalt phase in AlN was observed at pressures as low as 1.3GPa, as evidenced by comparing the experimental Raman spectra to calculated one- and two-phonon densities of states of the rocksalt phase., MCYT, Generalitat de Catalunya, Generalitat Valenciana, Spanish MEC, CONACYT, CNS IPICYT

During the past five years the low-temperature heat capacity of simple semiconductors and insulators has received renewed attention. Of particular interest is its dependence on isotopic masses and the effect of spin-orbit coupling in ab initio calculations. Here we concentrate on the lead chalcogenides PbS, PbSe, and PbTe. These materials, with rock salt structure, have different natural isotopes for both cations and anions; a fact that allows a systematic experimental and theoretical study of isotopic effects, e.g., on the specific heat. Also, the large spin-orbit splitting of the 6p electrons of Pb and the 5p of Te, using a computer code which includes spin-orbit interaction, allows an investigation of the effect of this interaction on the phonon-dispersion relations and the temperature dependence of the specific heat, and on the lattice parameter. It is shown that agreement between measurements and calculations significantly improves when spin-orbit interaction is included., CICYT, CONACYT, Generalitat de Catalunya, CNS IPICYT

We report ab initio calculations of the lattice dynamics of antimony as a function of pressure. Analysis of reported Raman data using calculated two-phonon densities of states allows us to weigh the contribution of anharmonicity to the observed broadening upon increase of pressure. We discuss other plausible mechanisms required to account for the pressure dependence of the Raman linewidths., CICYT, CONACYT, CNS IPICYT

A DuMond analysis of X-ray diffraction patterns has been carried out in the case of a combined [sigma]-[pi] polarization configuration, obtained using a setup with a double-crystal monochromator in reflection (Bragg) geometry and an analyser in transmission (Laue) geometry. The derived analytical expressions allow the characterization of the bending of the analyser and the quantitative estimation of the curvature radius and its sign from the width of the crystal rocking curves. The theoretical analysis is applied to the case of a thin, accidentally bent, Si crystal., CICYT, Generalitat de Catalunya

Lead sulfide is an important semiconductor that has found technological applications for over a century. Raman spectroscopy, a standard tool for the investigation and characterization of semiconductors, has limited application to this material because of the forbidden nature of its first order scattering and its opacity to visible lasers. Nevertheless, useful vibrational spectra from two-phonon processes are obtained with red lasers, probably because of a resonance in the concomitant electronic transitions. Herewith, we report temperature dependent Raman spectra covering the 10–300 K range, for two samples with different sulfur isotopic compositions. The results are analyzed by comparison with ab initio cal- culations of the lattice dynamics of PbS and the corresponding densities of one and two-phonon states. Emphasis is placed on the analysis of the two phonon band centered at ∼430 cm–1. The combined use of ab initio calculations and an extended temperature range (compared to previous reports) allows an unequivocal identification of some of the main features in the second-order Raman spectra. Our study also provides a much firmer background for the understanding of anomalous temperature dependences in the anharmonic shifts of second-order Raman spectra in PbS., CONACYT, Royal Society of New Zealand, UC MEXUS

Bismuth selenide, a benchmark topological insulator, grows in a trigonal structure at ambient conditions and exhibits a number of enticing properties related to the formation of Dirac surface states. Besides this polytype, a metastable orthorhombic modification with Pnma space group has been produced by electrodeposition and high-pressure high-temperature synthesis displaying upon Sb doping significant thermoelectric properties in the midtemperature range. However, very little experimental information is available on the fundamental properties of this polytype, such as, e.g., the electronic band gap and the lattice dynamics. We report here the temperature dependence of the Raman spectra of orthorhombic Bi2Se3 between 10 K and 300 K, which displays an anharmonic behavior of the optical phonons that can be modelled with a two-phonon decay channel. In order to analyze the data we performed ab initio calculations of the electronic bandstructure, the phonon frequencies at the center of the Brillouin zone, and the phonon dispersion relations along the main symmetry directions, examining the effect of spin-orbit coupling in both phonon and electronic energies. Lastly, we report here cathodoluminescence experiments at 83 K that set a lower limit to the electronic bandgap at 0.835 eV, pointing to an indirect nature, in agreement with our calculations. These results shed light to essential properties of orthorhombic Bi2Se3 for further understanding of the potential of this semiconductor for thermoelectrics and new applications., MEC, AEI, FEDER, TED - MTED

The measurement of fragility of glass-forming liquids involves either the determination of viscosity at different temperatures above the glass transition or the measurement of the dynamic glass–liquid transition by calorimetry or dilatometry at different heating rates. Significant data dispersion is observed when comparing fragility parameters obtained by different techniques. Dynamic mechanical analysis (DMA) is widely used for characterizing glass transition in polymer science while it is still seldom used in metallic glasses. In this work we determine the relaxation time ( ) vs temperature of a Pd77.5Si16.5Cu6 glass by means ofDMAmeasurements. The measured range of relaxation times cover the whole region from glass transition ( > 100 s) to times of the order of 10−2 s. The fragility parameter obtained for this alloy is found significantly higher than the values obtained from previous viscosity and calorimetric techniques. The application range, limitations and correctness of the technique are discussed., Postprint (published version)