Implications of phase coexistence in VO(2) thin-films across the metal-insulator transition

[eng] A Metal-insulator transition (MIT) is the ability of some materials to change between metal and insulator electric behaviours as a function of some external stimuli such as temperature, stress, voltage, magnetic field or light. The Fermi level position with respect to the band structure determines one character or the other, and in some materials this band structure is very sensitive to electron-electron correlations. This is the case of some transition metal oxides, which despite having partially filled bands allowing, in theory, metallic conduction, electron- electron interactions split the half-filled band in a lower energy band that is full first and a higher energy sub-band still empty, resembling an insulator. An archetypical example is vanadium dioxide (VO2), a system with a 3d electronic configuration which leads to a first-order MIT happening near room temperature (~68 ºC) with a change in conductivity of several orders of magnitude, accompanied by a structural phase transition (SPT) that occurs simultaneously. This results in a high-temperature state given by a metallic rutile (tetragonal) phase that turns into a semiconductor with monoclinic M1 structure at the low-temperature state. Thus, the electronic and structural elements of the transition in VO2 are tightly entangled, whereby mechanical stress induces lattice deformations in the crystal that distort the surroundings of V atoms affecting the orbital properties within the unit cell, the lattice’s electrostatic potential field and vibrational modes. This thesis explores in detail the consequences of in-plane tensile strain in epitaxial VO2 thin films grown on rutile (001)-oriented TiO2 substrates by the pulsed laser deposition (PLD) technique, how the strain relaxes as film thickness increases, and how the strain relaxation itself gives raise to new phases and phase coexistence phenomena of interest. What makes this work novel with respect to other strain studies is the focus on the relation between local properties and global behaviour. As the thesis will show, space-averaged measurements of transport properties or X-ray diffraction (XRD) can miss out on a lot of interesting and important physics that happens on a nanoscopic level, including nano-tweeds or phase coexistence in the form of metal-insulator (M-I) phase boundaries. This work has used various microscopy techniques effective at different scales, from optical microscopy (micron scale) to scanning-probe microscopy (nanoscale) to transmission electron microscopy (atomic scale), yielding a very complete picture of the MIT in strained VO2 films across the different scales. After a brief introductory chapter contextualizing the thesis, chapter one describes the growth and average structural characteristics of the films, including their evolution due to aging. It was grown a thickness set from ~2 nm up to ~150 nm and surprisingly, the films do not relax with thickness neither conventionally nor progressively, resulting in crack formation, M-I phase separation toward the cracks and strong-strain gradients within the film. The microstructure far from crack-edges is presented in chapter two. It shows that the strained VO2 regions are not stabilized in the standard high-temperature rutile phase but in a metrically tetragonal structure that triples the rutile periodicity with monoclinic (2/m) symmetry. Moreover, the orientational variants of this new phase (x3M) coexist forming tweed patterns of few nanometers in size. Chapter three explores the functional consequences of the coexistence between strain- relaxed insulating phase near the films’ cracks and metallic phase away from them. The peculiar pattern induced by crack formation leads to the concept of “self-pixelation”, whereby each island of VO2 bounded by insulating cracks behaves de facto as a “pixel” whose MIT can be individually triggered independently of the rest of the film. Finally, the last chapter contains the general conclusions and outlook for future work.[cat] Una transició metall-aïllant (MIT) es la habilitat d’alguns materials per canviar el seu comportament elèctric de metall a aïllant en funció d’estímuls externs com la temperatura, estrès, voltatge, camp magnètic o la llum. Aquest és el cas d’alguns òxids de metalls de transició, els quals malgrat tenir bandes d’energia parcialment ocupades permetent, en teoria, conducció metàl·lica, les interaccions electró-electró divideixen aquesta banda parcialment ocupada en una d’energia més baixa que s’omple primer i una altra d’energia major que queda buida, semblant a un aïllant. Un arquetip d’això és el diòxid de vanadi (VO2), un sistema amb configuració electrònica 3d1 i una MIT de primer ordre, que succeeix ~68ºC amb un canvi de conductivitat de varis ordres de magnitud, produint-se també una transició de fase estructural (SPT) simultàniament. Aquesta dualitat resulta en un estat d’alta temperatura metàl·lic amb estructura rutil (tetragonal) que es transforma en un semiconductor amb estructura monoclínica M1 en el seu estat de baixa temperatura. Per tant, els elements electrònics i estructurals de la transició al VO2 estan estretament entrelligats. L’estrès mecànic indueix deformacions a la xarxa del cristall que distorsiona els voltants dels àtoms de V afectant les propietats orbitals dins de la cella unitat, camp de potencial electrostàtic i modes vibracionals. Aquesta tesi explora en detall les conseqüències de la tensió en el pla, en capes primes epitaxials de VO2 crescudes sobre substrats rutil de TiO2 orientats en (001), per la tècnica de dipòsit de làser polsat (PLD). El que fa que sigui diferent respecte la resta d’estudis amb estrès mecànic és la focalització en la relació que hi ha entre propietats locals i comportament global del material. Com es mostrarà a la tesi, les mesures espacials mitjana poden perdre’s processos físics importants a nivell nanoscòpic, com nano-tweeds o coexistència de fases amb fronteres metall-aïllant (M-I), i per això les mostres s’han caracteritzat amb varies microscòpies a diferents escales (micro, nano i escala atòmica) aconseguint una visió completa de la MIT en capes tensionades de VO2

Analysis of the economic feasibility and reduction of a building’s energy consumption and emissions when integrating hybrid solar thermal/PV/micro-CHP systems

The aim of this paper is to assess the performance of several designs of hybrid systems composed of solar thermal collectors, photovoltaic panels and natural gas internal combustion engines. The software TRNSYS 17 has been used to perform all the calculations and data processing, as well as an optimisation of the tank volumes through an add-in coupled with the GENOPT® software. The study is carried out by analysing the behaviour of the designed systems and the conventional case in five different locations of Spain with diverse climatic characteristics, evaluating the same building in all cases. Regulators, manufacturers and energy service engineers are the most interested in these results. Two major contributions in this paper are the calculations of primary energy consumption and emissions and the inclusion of a Life Cycle Cost analysis. A table which shows the order of preference regarding those criteria for each considered case study is also included. This was fulfilled in the interest of comparing between the different configurations and climatic zones so as to obtain conclusions on each of them. The study also illustrates a sensibility analysis regarding energy prices. Finally, the exhaustive literature review, the novel electricity consumption profile of the building and the illustration of the influence of the cogeneration engine working hours are also valuable outputs of this paper, developed in order to address the knowledge gap and the ongoing challenges in the field of distributed generation

Simplifying the process to perform air temperature and UHI measurements at large scales: Design of a new APP and low-cost Arduino device

The main purpose of Urban Heat Island (UHI) studies and the monitoring of ambient temperatures at large scales is to gather temperature information in a certain area, so as to understand temperature heterogeneity and its drivers or detect locations that lack thermal comfort. However, these studies originate mostly from some research projects, with sufficient budget and manpower to carry out the measurements and the necessary calculations. Thus, there is a scarcity of air temperature information, making it difficult to implement appropriate mitigation actions worldwide. The present work aims to greatly simplify the process to monitor air temperatures and carry out UHI estimations through mobile transects. This is done by introducing the design of a low-cost device and a new APP, which performs automatically most necessary UHI calculations. A web tool based on the Inverse Distance Weighting interpolation method is also included to obtain heat maps. The methodology is illustrated using case studies in Seville (Spain) and New York city (USA). By introducing a straightforward and reproducible methodology, we aim to open the path for a more widespread availability of ambient temperature data anywhere in the world, without the need for costly equipment and many hours of dedication by the researcher

Mitigating energy poverty: Potential contributions of combining PV and building thermal mass storage in low-income households

The issue of energy poverty has devastating implications for the society, and it has been aggravated in the past years due to the economic crisis and the increase of energy prices. Among the most affected are those with low incomes and living in inefficient buildings. Unfortunately, the bitter reality is that sometimes this part of the population are facing the next question: Heating, or eating? The declining prices of distributed energy technologies such as photovoltaics provides an opportunity for positive social change. Although their use does not address energy poverty directly, substantial contributions may be made. Measurements of indoor temperatures in a social housing district of southern Spain in 2017 have revealed the unbearable temperatures that the occupants have to endure, both in summer and winter. Using this district as a case study, the present work aims to evaluate the benefits of exploiting its rooftop PV potential to cover part of the electricity consumption of the district (reducing the energy bills), and use the surplus electricity to supply power for the heat pumps in the district. Optimal alternatives regarding maximum PV production, maximum self-sufficiency ratio and minimum investment costs have been found, considering as well different options when sharing the available electricity surplus to improve the thermal comfort of the occupants. As far as the authors know, no previous study has followed an approach aimed at energy poverty alleviation such as the one presented in this work. The results show that using the surplus electricity to heat or cool the whole dwellings would improve the thermal comfort of the occupants in average up to 11% in winter and 26% in summer. If all the PV generation was used or more buildings in the area were employed to install PV modules, improvements up to 33% in winter and 67% in summer could be obtained, reducing at the same time the thermal comfort differences among the dwellings of the district

Contributions of heat pumps to demand response: A case study of a plus-energy dwelling

- Premio ETSI al mejor artículo científico del Trimestre. Junio 2018. - Artículo subido a idUS con permiso de su primera autora (Laura Romero Rodríguez), que proporciona las versiones preprint y postprint.Demand Response programs are increasingly used in the electricity sector, since they allow consumers to play a significant role for balancing supply and demand by reducing or shifting their electricity consumption. For that purpose, incentives such as time-based rates have been proposed. The present study analyzes the potential benefits of operating the heat pump of a plus-energy dwelling which participates in a dynamic pricing market, benefitting from the thermal storage capacity of the building. The software TRNSYS 17 has been used to model the building and the supply system. A validation of the model was carried out by using available measurements of the dwelling. Three setpoint temperature scenarios have been considered for sixteen different strategies which depend on temperature and electricity price thresholds, with the aim of determining which alternatives could lead to significant savings while maintaining an acceptable thermal comfort. Several factors such as cost savings, heat pump consumption, ratio of self-consumption of the dwelling and use of the heat pump during peak hours were also evaluated in every case. The results show that dynamic price thresholds should be used instead of fixed price thresholds, which may cause low activations of the heat pump or overheat the building above the comfort limits. Cost savings up to 25% may be achieved by using optimal strategies, increasing the self-consumption ratio, having almost no influence on the thermal comfort and achieving significant peak reductions on the grid. The outcomes of this study show the importance of looking at the implications of such strategies on several criteria within a demand response framework.Ministerio de Economía y CompetitividadUniversidad de Sevilla. V Plan Propio de Investigación (VPPI-US)Unión Europea. Horizon2020. Grant agreement No. 69596

Diseño, intervención y propuesta de mejora para trabajar la coeducación en Educación Primaria

El Trabajo Fin de Grado que se muestra a continuación es una propuesta de intervención sobre “Coeducación”. Se trata de un tema que está a la orden del día, debido a la desigualdad entre hombres y mujeres existente en la sociedad. Se pretende fomentar la igualdad de género en las aulas para que en el futuro tengan un concepto diferente respecto al tema. En este proyecto el alumnado aprenderá el significado del concepto coeducación y todo lo que implica. La propuesta ha sido llevada a cabo con niños y niñas de 5º de Primaria de tres centros educativos de distintas zonas de Sevilla. En la presenta investigación se indican las actividades realizadas y las ideas de los discentes, así como un análisis de las mismas acompañado de sus respectivas conclusiones y propuestas de mejora.Universidad de Sevilla. Grado en Educación Primari

Nume

Realización dun prototipo de publicación dixital interactiva centrada na vida cultural e artística de Galicia, que trata diversos temas que poden ser de interese ou que poden afectar á comunidade galega, sempre e cando conteñan algún tipo de valor estético, creativo, artístico ou sensorial.Traballo fin de grao (UDC.COM). Comunicación audiovisual. Curso 2019/202

Two-Sided Antibacterial Cellulose Combining Probiotics and Silver Nanoparticles

This work was funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades (MICIU) (projects FEDER PID2019-111461GB-I00 and Ramon y Cajal RYC-2016-21042). L.S. acknowledges the Spanish MICIU for the predoctoral contract within the FPU program (FPU16/01360).The constant increase of antibiotic-resistant bacteria demands the design of novel antibiotic-free materials. The combination of antibacterials in a biocompatible biomaterial is a very promising strategy to treat infections caused by a broader spectrum of resistant pathogens. Here, we combined two antibacterials, silver nanoparticles (AgNPs) and living probiotics (Lactobacillus fermentum, Lf), using bacterial cellulose (BC) as scaffold. By controlling the loading of each antibacterial at opposite BC sides, we obtained a two-sided biomaterial (AgNP-BC-Lf) with a high density of alive and metabolically active probiotics on one surface and AgNPs on the opposite one, being probiotics well preserved from the killer effect of AgNPs. The resulting two-sided biomaterial was characterized by Field-Emission Scanning Electron Microscopy (FESEM) and Confocal Laser Scanning Microscopy (CLSM). The antibacterial capacity against Pseudomonas aeruginosa (PA), an opportunistic pathogen responsible for a broad range of skin infections, was also assessed by agar diffusion tests in pathogen-favorable media. Results showed an enhanced activity against PA when both antibacterials were combined into BC (AgNP-BC-Lf) with respect to BC containing only one of the antibacterials, BC-Lf or AgNP-BC. Therefore, AgNP-BC-Lf is an antibiotic-free biomaterial that can be useful for the therapy of topical bacterial infections.Spanish Ministerio de Ciencia, Innovacion y Universidades (MICIU) (project FEDER) PID2019-111461GB-I00Spanish Ministerio de Ciencia, Innovacion y Universidades (MICIU) (Project Ramon y Cajal) RYC-2016-21042Spanish MICIU FPU16/0136

Estratègies de modulació de l'oxidació d'àcids grassos com a tractament per combatre l'obesitat

L'estil de vida actual, amb dietes d'alt contingut calòric i falta d'exercici físic, fa que la incidència d'obesitat s'incrementi notablement. Augmentar la degradació de greixos o bé reduir la ingesta calòrica poden ser potencials estratègies terapèutiques. L'enzim carnitina palmitoïltransferasa I (CPT1) és el pas limitant de l'oxidació dels àcids grassos. En aquest article, es mostra com la modulació de la seva activitat en diferents teixits, com el fetge, el teixit adipós o l'hipotàlem, pot ser clau a l'hora d'augmentar la despesa energètica i controlar la ingesta d'aliments.Current lifestyles, with high-energy diets and little exercise, are triggering an alarming growth in obesity. Strategies that enhance fat degradation or reduce caloric food intake could be considered therapeutic interventions to reduce not only obesity, but also its associated disorders. The enzyme carnitine palmitoyltransferase I (CPT1) is the critical rate-determining regulator of fatty acid oxidation. In this paper, we show that this enzyme might play a key role in different tissues, such as liver, adipose tissue and hypothalamus, increasing energy expenditure and controlling food intake

Optimization of the process of aromatic and medicinal plant maceration in grape marc distillates to obtain herbal liqueurs and spirits

BACKGROUND Herbal liqueurs are alcoholic beverages produced by the maceration or distillation of aromatic and medicinal plants in alcohol, and are also highly valued for their medicinal properties. The process conditions, as well as the number and quantity of the plants employed, will have a great influence on the quality of the liqueur obtained. The aim of this research was to optimize these important variables. RESULTS A BoxBenhken experimental design was used to evaluate the independent variables: alcohol content, amount of plant and time during the experimental maceration of plants in grape marc distillate. Four plants were assessed, with the main compound of each plant representing the dependent variable evaluated with respect to following the evolution of the maceration process. Bisabolol oxide A in Matricaria recutita L., linalool in Coriander sativum L. and eucalyptol in Eucalyptus globulus Labill. were quantified using a gas chromatography-flame ionization detector. Glycyrrhizic acid in Glycyrrhiza glabra L was determined using a high-performance liquid chromatography-diode array detector. Other dependent variables were also evaluated: total phenolic content, color parameters and consumer preference (i.e. appearance). CONCLUSION The experimental designs allowed the selection of the optimal maceration conditions for each parameter, including the preference score of consumers: 70% (v/v) of ethanol, 40 g L1 plant concentration and a maceration process of 3 weeks.Spanish Ministry of Economy and Competitiveness - (project CTQ2015-71436-C2-1-R)FEDER funds of the European UnionFundação para a Ciência e Tecnologia a (FCT) - grant SFRH/BD/87953/201