Integration of Indium Gallium Nitride with Nanostructures on Silicon Substrates for Potential Photovoltaic Applications

Ph.DDOCTOR OF PHILOSOPH

Nanoestructurado de materia condensada blanda con aplicaciones en electrónica orgánica

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 21-10-2019Organic, light, flexible materials with functional properties as electrical conductivity and ferroelectricity that can be used in electronic devices are likely to be a safe bet for the future. However, these materials present much lower efficiencies compared with their analog inorganic materials. Therefore, a lot of research is still to be done to put organic materials in the competitive market. Nanostructuring is one of the most important approaches to achieve this objective, due in part to the requirement of miniaturization of electronic devices and because of the possibility of tuning the properties of these materials by modifying their structure at the nanoscale. This Thesis is focused on the fabrication of nanostructures on soft matter, mainly polymeric materials, with semiconducting and/or ferroelectric properties. Three kinds of nanostructures were fabricated: nanolayers or thin films (Chapter 3), surface nanostructures generated by laser irradiation (Chapter 4) and by nanoimprint lithography (Chapter 5), and nanoparticles (Chapter 6)...Los materiales orgánicos que presentan propiedades funcionales como la conductividad eléctrica y la ferroelectricidad, además de sus propiedades de ligereza y flexibilidad, son una apuesta segura para el futuro debido a la posibilidad de emplearlos en dispositivos electrónicos. Sin embargo, comparados con materiales inorgánicos análogos, presentan eficiencias mucho menores. Es por ello que aún debe realizarse un esfuerzo de investigación y desarrollo considerable, con el objetivo de colocar a estos materiales orgánicos en un nivel competitivo en el mercado. La nanoestructuración es uno de los caminos más investigados para conseguir este objetivo, no solo por la demanda actual de miniaturización de dispositivos electrónicos sino también por la posibilidad de modificar las propiedades funcionales de estos materiales mediante la alteración de su nanoestructura. Esta Tesis está enfocada a la fabricación y al estudio de nanoestructuras de materia condensada blanda, principalmente polímeros, con propiedades semiconductoras y/o ferroeléctricas. Se han fabricado tres tipos de nanoestructuras: nanocapas o películas delgadas (Capítulo 3), nanoestructuras superficiales mediante irradiación con láser (Capítulo 4) y nanoestructuras mediante litografía de nanoimpresión (Capítulo 5), así como nanopartículas (Capítulo 6).Fac. de Ciencias FísicasTRUEunpu

Ultra-High-Resolution Patterning And Pattern Transfer Via Nanocrystal Colloidal Lithography

The ability to design, pattern, and process materials at the nanoscale has enabled vast research opportunities ranging from fundamental science to technological applications and device integration. The continued development of nanoscience and nanotechnology relies on pushing the limits of nanoscale fabrication capabilities. After decades of development, this frontier has moved to the sub-10 nm length scale to explore novel physical properties and functionalities for next-generation technology. However, conventional “top-down” strategies that have carried nanofabrication to this point have severe limitations for practically improving the resolution capabilities of deep nanoscale fabrication. In this dissertation, we demonstrate ultra-high-resolution patterning and pattern transfer using nanocrystal (NC) colloidal lithography. This innovative nanofabrication platform integrates bottom-up methods, that combine NC synthesis and self-assembly approaches, with well-established top-down techniques such as dry etching and thin film deposition. We employ monodisperse NC building blocks with self-assembly methods to establish high-density, well-ordered patterns, where the inorganic core of each NC serves as a discrete hard mask used for high-fidelity pattern transfer into a desired substrate material. We demonstrate the use of isotropic NCs to establish various sub-10 nm pattern morphologies and examine the stability of the NC pattern upon dry etching, comparing NC monolayers and bilayers. We extend the NC colloidal lithography scheme using anisotropic NCs to demonstrate high-density, anisotropic pattern transfer into various substrate materials down to the sub-5 nm regime. The presented fabrication strategy offers further opportunities to leverage various combinations of NC morphologies and materials afforded by the extensive NC library for more complex pattern design. Additionally, this approach can be extended to process various substrate material classes at the deep nanoscale. The NC colloidal lithography platform enables broader access to single-digit nanoscale fabrication for the scientific community worldwide, which could impact various research sectors ranging from integrated circuits to memory devices, optoelectronics, metasurfaces, quantum devices and more

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

Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties

The analysis of polymer processing operations is a wide and complex subject; during polymer processing, viscoelastic fluids are forced to deform into desired geometries using non-homogeneous velocity and temperature fields down to solidification. The objective of analysis is the identification of processing conditions, which are finalized in the optimization of product final properties, which, in turn, are determined by the final part morphology. Depending on the operating conditions, the properties of the final part can change more than one order of magnitude. Properties of interest include the mechanical, optical, barrier, permeability, and biodegradability, and any other property of practical relevance including the characteristics of the surfaces as its finishing and wettability, which are connected to one another. The scope of this Special Issue is to select progress in or reviews of the understanding/description of the phenomena involved along the chain of processing–morphology–properties. Along this virtual chain, modeling may be a useful approach, and within the objective of understanding fundamental aspects, it may also be relevant to compare selected characteristics of the process and the material with the characteristics of the resulting morphology and then with the properties of the final part. This approach suggests the title: “Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties”

Effect of nanoimprinted surface relief on Si and Ge nucleation and ordering

Abstract Surface relief formed by nanoimprinting and etching into a thermally grown SiO 2 layer on Si was used to position the initial nuclei formed by chemically vapor deposited Si and Ge. By controlling the deposition conditions, the surface diffusion length was adjusted to be comparable to or larger than the spacing between features, thus favoring nucleation adjacent to steps, rather than random nucleation. Random nucleation was further suppressed by a two-stage deposition process. Ge nucleation on oxide by chemical vapor deposition was enhanced by coating the oxide surface with an organic self-assembled monolayer (SAM) and by the nanoimprinted surface relief. The nanoimprinted surface relief also provides long-range order in the SAM.