Caracterización estructural y funcional de películas delgadas nanoporosas mediante microscopías electrónicas de transmisiónbarrido y espectroscopías ópticas

Nano-structuration of materials at the mesoscale to give rise to porosity-controlled coatings represents an important breakthrough in the area of Materials Science and Engineering, offering new and enhanced functionalities of interest in fields such as optics, optronics and optoelectronics. In order to optimize their performances, in-depth analyses are required: local information about the morphology, composition and atomic structure, the compactness distribution, but also layer homogeneity, interface and interpenetration between stacked layers or oxidation are extremely important factors that can ruin their way of operation. In this particular context, the objective of the present PhD Thesis is to make significant contributions to the study and development of multifunctional porous nanostructured systems, from their design and elaboration, to the maximum knowledge of their structure and properties, through advanced (S)TEM methods, including 3D reconstructions, elemental analyses at the nanoscale and atomic-scale imaging, combined with optical spectroscopy techniques. In the first instance, given the great potential of the slanted nanostructures generated by means of oblique angle depositions, in which the refractive index gradient can be tuned by the columns tilt and density imposed via the growth angles and parameters, OAD broadband antireflective coatings based on Si, Ge or SiO2 OAD films have been designed, manufactured, and extensively characterized with the aim of maximizing the performance of the optical elements in the vis-IR wavelength range. This same approach has also been implemented to enhance the antireflective capabilities of transparent conductive ITO thin films in the near-IR window without compromising too much their electrical response. On the other hand, the advanced structural and functional characterization of porosity-controlled GaN NW arrays grown by plasma-assisted MBE through (S)TEM methods and vis-IR SE elliposmetry, has helped not only to improve growth processes but also to optimize their resulting optical and electrical properties. Finally, the knowledge and methodologies acquired during the study and optimization of the previous porous systems have been transferred to the development of a two-step procedure, based on the deposition and the subsequent fast oxidation of vanadium-based OAD films in open air atmosphere, for the synthesis of thermochromic VO2 coatings of tunable metal-to-insulator response and controlled grain sizes and crystallinities

Reactivity of Vanadium Nanoparticles with Oxygen and Tungsten

A mechanistic study was carried out on the optimal methods of fabrication of products containing higher loads of thermochromic VO2(M1) fabricated by thermal treatments of V nanoparticles in air, that, once achieved, are more stable than other commercial products upon natural aging or reiterated reheating. At the best temperatures for single runs, 55% of VO2 can be attained by the reactions of a limited number of the species initially formed in a process, that, if not stopped, can degrade the product by solid state reactions of oxidations and reductions without O-2 consumption. This fact supports the use of two-step treatments at lower temperatures and faster cooling rates that reach 65% of VO2; such reactions should, ideally, take place in the 550-625 degrees C temperature range. The impregnation of V with a tungstate salt is an ideal and simple doping platform that can decrease the energy of activation of the 2-cycle process, allowing higher yields and enthalpies of transformation (71% of VO2, 26 J/g) than undoped counterparts or trademarks. A good balance is reached for 1% at. of W, with a reduction in T-c of 20 degrees C not significantly resenting the enthalpy of the reversible metal-to-insulator transition. For higher W amounts, the appearance of tetragonal VO2, and W alloyed V3O7 and V2O5, decrease the fractions of increasingly and effectively doped M1-VO2 achieved till 2% of W, a concentration for which T-c attains the stimulating values of 35 degrees C on heating and 25 degrees C on cooling

A Novel Route for the Easy Production of Thermochromic VO₂ Nanoparticles

In this work, a simple, fast and dry method for the fabrication of a thermochromic product with a high load of VO2 (M1) consisting of the controlled heat treatment of pure vanadium nanoparticles in air is presented. After a complete design of experiments, it is concluded that the most direct way to attain the maximum transformation of V into VO2 (M1) consists of one cycle with a fast heating ramp of 42°Cs-1 , followed by keeping 700°C for 530-600 seconds, and a subsequent cooling at 0.05°Cs-1 . Careful examination of these results lead to a second optimum, even more suitable for industrial production (quicker and less energy-intensive because of its lower temperatures and shorter times), consisting of subjecting V to two consecutive cycles of temperatures and times (625°C for 5 minutes) with similar preheating (42°Cs-1 ) but a much faster postcooling ( 8°Cs-1 ). These green reactions only use the power for heating a tube open to atmosphere and a vanadium precursor; without assistance of reactive gases or catalysts, and no special vacuum or pressure requirements. The best products present similar thermochromic properties but higher thermal stability than commercial VO2 particles. These methods can be combined with VO2 doping.A. J. Santos would like to thank the IMEYMAT Institute and the Spanish Ministerio de Educación y Cultura for the concessions of grants (ICARO-173873 and FPU16-04386). University of Cádiz and IMEYMAT are also agreed by financing the mutual facilities available at the UCA R&D Central Services (SC-ICYT), the UCA project references “PUENTE PR2020-003” and “OTRI AT2019/ 032”, and the IMEYMAT projects “PLP2019120-3” and “PLP2021120-1”. Additional support was given by the Spanish State Agency of Research through the “Retos” call (Project No. 1572, Ref. PID2020-114418RB-I00/ AEI / 10.13039/ 501100011033). The regional government of Andalusia with FEDER cofunding also participates through the projects AT-5983 Trewa 1157178 and FEDER-UCA18-10788, and the contract hiring M. Escanciano

Controlled grain-size thermochromic VO2 coatings by the fast oxidation of sputtered vanadium or vanadium oxide films deposited at glancing angles

An original, simple and cost-effective oxidation strategy to attain thermochromic vanadium dioxide thin films is reported. This two-step procedure comprises the initial deposition of DC magnetron-sputtered vanadium or vanadium oxide films by the combination of glancing angle deposition and, if needed, reactive gas pulsing process, followed by fast oxidation of such layers in air atmosphere at high temperatures. Thanks to the careful control of the thermal treatment parameters, and taking advantage of the superior reactivity of the high surface-to-volume porous deposited structures, the formation of pure VO2 (M1) layers was achieved. The comprehensive characterization of such oxidized systems by means of scanning electron microscopy, Raman spectroscopy and scanning-transmission electron microscopy techniques such as electron energy-loss spectroscopy, not only confirmed the presence of the VO2 (M1) phase, but also allowed to shed light on the key role that reaction time plays in the selective formation of vanadium dioxide films of adjustable grain size and crystallinity. The optimal conditions to stabilize thermochromic VO2 consists in using large deposition angles (85 degrees) and short oxygen pulses (<= 2 s) during the growth, followed by fast and short thermal treatments (<= 45 s with a heating rate of 42 degrees C s(-1)) in air atmosphere at 550 degrees C. The metal-to-insulator response of the accomplished VO2 layers was finally evaluated by means of temperature dependent Kelvin probe force microscopy measurements, evidencing surface potential drops at heating, greater than those reported in the literature to date for VO2 thin films.A. J. Santos would like to thank the IMEYMAT Institute and the Spanish Ministerio de Educacion y Cultura for the concessions of grants (ICARO-173873 and FPU16-04386) . The "Talent Attraction Program" of the University of Cadiz is acknowledged by supporting B. Lacroix contract code E-11-2017-0117214. University of Cadiz and IMEYMAT are also agreed by financing the mutual facilities available at the UCA R&D Central Services (SC-ICYT) , the UCA projects reference "PUENTE PR2018-040 '' and "PUENTE PR2020-003 '', and the IMEYMAT project references "LINEAS PRIORITARIAS PLP2019120-3 and PLP2021120-1 ''. This work was supported by the Spanish State R&D project (Retos y Generacion de Conocimiento) ref. PID2020-114418RB-I00/AEI/10.13039/501100011033. The regional government of Andalusia with FEDER cofunding also participates through the projects AT-5983 Trewa 1157178 and FEDER-UCA18-10788. M. Dominguez acknowledges financial support from the Spanish Ministerio de Ciencia e Innovacion under project reference EQC 2018-004704-P FEDER 2014-2020, "Modernizacion del Servicio de Microscopia de Fuerza Atomica (AFM) del IMEYMAT"

Texture in ITO films deposited at oblique incidence by ion beam sputtering

Texture of crystalline In2O3:Sn (ITO) thin films prepared by combining ion beam sputtering (IBS) at room temperature and oblique angle deposition (OAD) has been studied depending on the vapor incidence on Si substrates (alpha, ranging from 50 degrees to 85 degrees) and the ions used to sputter the target (argon or xenon accelerated at 1.2 keV). Films obtained using Xe ions show an unusual evolution depending on the deposition angle alpha, with the development of a dual biaxial (1 1 1) off-axis texture for alpha 70 degrees that leads to a biaxial (0 0 1) texture at highest deposition angles. These behaviors are well described by mechanisms involving a maximization of the direct capture of the adatoms on {1 1 1} planes, which can however be hindered when mobilities are exalted such as in the case of Ar deposition. The tuning of adatoms mobilities through the IBS process mixed with the control of the deposition angle offered by the OAD geometry appears as an efficient route to achieve an upgraded texture engineering in nanostructured ITO thin films

(S)TEM structural and compositional nanoanalyses of chemically synthesized glutathione-shelled nanoparticles

This work is focused on the characterization by transmission and scanning–transmission electron microscopy-related techniques of core–shell nanoparticles synthesized via chemical methods. Diferent semiconducting, pure metallic or oxide materials have been utilized as the core (cadmium telluride, gold, magnetite, or magnetite covered with gold) of the nanoparticle, while they have been, in all cases, functionalized by a thin amorphous glutathione layer, with the goal of using the nanoparticles in biomedical applications such as biomarkers, and computerized tomography and image magnetic resonance contrast agents. The results show that it is possible to visualize the glutathione layer using spectroscopic and imaging techniques, associated with electron microscopy (such as energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy images), that this layer is present at the surfaces of all observed nanoparticles, and that it is no thicker than a few nanometers. Electron microscopy also revealed that the nanoparticles core is crystalline and, in average, around 5-nm size.Spanish Ministry of Economy and Competitiveness MAT2015-67354-R (Program “Plan I+D+i”, subprogram “Retos”)Spanish Ministry of Education and Culture Grants ICARO-173873Spanish Ministry of Education and Culture Grants FPU16-0438

Puesta a punto de un reactor de tratamiento termoquímico y diseño de una estación de enfriamiento súbito para materiales de interés industrial.

Resumen del proyecto de líneas prioritarias titulado "Puesta a punto de un reactor de tratamiento termoquímico y diseño de una estación de enfriamiento súbito para materiales de interés industrial" del IMEYMAT

Superficial Characteristics and Functionalization Effectiveness of Non-Toxic Glutathione-Capped Magnetic, Fluorescent, Metallic and Hybrid Nanoparticles for Biomedical Applications

An optimal design of nanoparticles suitable for biomedical applications requires proper functionalization, a key step in the synthesis of such nanoparticles, not only for subsequent crosslinking to biological targets and to avoid cytotoxicity, but also to endow these materials with colloidal stability. In this sense, a reliable characterization of the effectiveness of the functionalization process would, therefore, be crucial for subsequent bioconjugations. In this work, we have analyzed glutathione as a means to functionalize four of the most widely used nanoparticles in biomedicine, one of which is a hybrid gold-magnetic-iron-oxide nanoparticle synthetized by a simple and novel method that we propose in this article. We have analyzed the colloidal characteristics that the glutathione capping provides to the different nanoparticles and, using information on the Z-potential, we have deduced the chemical group used by glutathione to link to the nanoparticle core. We have used electron microscopy for further structural and chemical characterization of the nanoparticles. Finally, we have evaluated nanoparticle cytotoxicity, studying cell viability after incubation with different concentrations of nanoparticles, showing their suitability for biomedical applications

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics

This work presents results in the feld of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fred Ceramics has been used, as a noncrystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these felds of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using diferent bufer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes

Diseño de una planta para la producción y purificación de biodiesel a partir de borra seca de café

El objetivo del presente proyecto es el diseño de una planta industrial para la producción y purificación de biodiésel y glicerina para su posterior comercialización, empleando como materia prima la borra seca de café. En este proyecto se lleva a cabo el diseño y dimensionado de las principales unidades del proceso de la planta industrial y se realiza una descripción general de las etapas secundarias. Se pretende obtener biodiésel de un residuo innovador y abundante, como es la borra de café, empleando una reacción de transesterificación in situ, como alternativa para disminuir los costes de producción, puesto que su aplicación elimina la etapa de extracción mecánica o con solventes, evita los procesos de refino del aceite e incrementa el rendimiento de ésteres a partir de una masa dada de semillas, en comparación con el proceso convencional que parte del aceite previamente extraído. En definitiva, lo que se propone es un proceso que emplee residuos de otras industrias y evite la demanda de materia prima fósil, un proceso libre de generación de residuos, donde se aprovechen todos los subproductos, además, que dé lugar a un combustible alternativo de alta calidad, biodegradable y que en su utilización disminuya las emisiones de agentes contaminantes a la atmósfera cumpliendo la normativa medioambiental