Philosophiae Doctor - PhD / This project is aimed at fabricating a smart material. Zinc oxide and vanadium dioxide have received a great deal of attention in recent years because they are used in various applications. ZnO semiconductor in particular has a potential application in optoelectronic devices such as light emitting diodes (LED), sensors and in photovoltaic cell industry as a transparent electrode. VO2 also has found application in smart windows, solar technology and infrared smart devices. Hence the need to synthesis or fabricate a new smart material using VO2 and an active ZnO based nano-composites family in which ZnO matrix will be hosting thermally active VO2 nano-crystals is the basis of this study. Since VO2 behave as an MIT Mott’s type oxides and exhibits a thermally driven semiconductor-metal phase transition at about 68 oC and as a direct result ZnO:VO2 nano-composites would exhibit a reversible and modulated optical transmission in the infra-red (IR) while maintaining a constant optical transmission in the UV-Vis range. The synthesis is possible by pulsed laser deposition and ion implantation. Synthesis by pulsed laser deposition will involve thin films multilayer fabrication. ZnO buffer layer thin film will be deposited on the glass and ZnO single crystals and subsequent layer of VO2 and ZnO will be deposited on the substrate. X-ray diffraction (XRD) reveals that the series of ZnO thin films deposited by Pulsed Laser Deposition (PLD) on glass substrates has the hexagonal wurtzite structure with a c-axis preferential orientation. In addition the XRD results registered for VO2 samples indicate that all thin films exhibits a monoclinic VO2 (M) phase. UV-Vis NIR measurements of multilayered structures showed the optical tunability at the near-IR region and an enhanced transparency (>30 %) at the visible range.

Alternative plasmonic materials of Transparent Nitrides and Conductive Oxides (TNCOs) including Indium Tin Oxide (ITO), Al-doped ZnO (AZO) and Titanium Nitride (TiN), have been proposed as novel material platforms for Si-compatible plasmonics and metamaterials, showing enhanced light-matter interaction over a broad spectral range. It has been recently shown that these materials feature reduced optical losses compared with conventional noble metals such as Au and Ag in the visible and near-infrared spectral range. However, it is still an open challenge to tailor the structural and optical properties of these materials, and to further reduce their optical losses, in order to effectively utilize them in photonic devices. In this thesis work, I demonstrate wide tunability of the optical and structural properties of ITO, AZO and TiN thin films, by using post-deposition annealing treatments, enabling significant reduction of their optical losses. By measuring the optical bandgaps of the investigated materials, I show that the tunability of the optical properties originates from the modulation of the free carrier concentration induced by the annealing treatment. Moreover, I perform XRD characterization of the fabricated films, indicating that the annealing also effectively tunes the grain size, which is consistent with the change of the optical properties. Eventually, I investigate the role of the annealing gases for ITO and AZO, demonstrating that free-carrier modulation in ITO and AZO is due to the change in the density of oxygen vacancies after post-deposition annealing. In particular, TNCOs possess epsilon-near-zero (ENZ) condition in near-infrared range with optical loss ε^"<1, thus providing enhanced internal fields in the medium at the ENZ condition. In collaboration with Prof. Nader Engheta and the previous post-doc in our group Dr. Antonio Capretti, we demonstrate enhanced second-harmonic generation (SHG) and third-harmonic generation (THG) from ITO thin films driven by ENZ condition. It results that the SHG generation efficiency is comparable with that of a crystalline quartz plate of thickness 0.5 mm, and that the THG generation efficiency is ∼600 times larger than crystalline silicon. As an application for the fabricated TiN material, I investigate PL intensity and lifetime in Hyperbolic Metamaterials (HMMs) coupled with emitting Si Quantum Dots (QDs). In collaboration with Hiroshi Sugimoto in Prof. Minoru Fujii’s group and the previous post-doc in our group Dr. Sandeep Inampudi, we demonstrate up to 1.6-times enhanced decay rate of QDs emission. Photonic devices based on TNCO plasmonic materials offer an effective approach for the engineering of novel Si-based photonic devices with enhanced light-matter coupling over a broad spectral range. As an application for the fabricated ITO, in collaboration with Hongwei Zhao in Prof. Jonathan Klamkin’s group, electro-absorption modulators are numerically investigated to show high extinction ration of greater than 6dB, while insertion loss is less than 1.3dB for wavelength range from 1.25 µm to 1.42 µm. Additionally, we demonstrate tunable optical properties of ITO thin films in mid-infrared spectrum by thermal annealing of ITO in oxygen environment. In collaboration with Sajan Shrestha and Adam Overvig in Prof. NanFang Yu’s group, we fabricate 2D periodic arrays of ITO and show wide tuning of plasmonic resonances of ITO nanostructure from 4 µm to 10 µm. Combining with the tunability of ITO thin films in near-infrared, the ITO material platform provides a promising method for the control and engineering of Si-based tunable plasmonic and metamaterial devices in the infrared spectrum. Finally, in collaboration with my colleague Ren Wang, we experimentally demonstrate silicon nanodisk arrays with tunable anapole mode excitation in the visible spectrum. The proposed high index nanostructures can be used to enhance absorption rate for applications in semiconductor photodetector.

Indium tin oxide (ITO) thin films have been used as transparent electrodes in many technological applications such as display panels, solar cells, touch screens and electrochromic devices. Commercial grade ITO thin films are usually deposited by sputtering. Solution-based coating methods, such as sol-gel however, can be simple and economic alternative method for obtaining oxide films and also ITO. In this thesis, &ldquo / ITO sols&rdquo / and &ldquo / ITO nanoparticle-incorporated hybrid ITO coating sols&rdquo / were prepared using indium chloride (InCl3

abstract: The object of this study is to investigate and improve the performance/stability of the flexible thin film transistors (TFTs) and to study the properties of metal oxide transparent conductive oxides for wide range of flexible electronic applications. Initially, a study has been done to improve the conductivity of ITO (indium tin oxide) films on PEN (polyethylene naphthalate) by inserting a thin layer of silver layer between two ITO layers. The multilayer with an optimum Ag mid-layer thickness, of 8 nm, exhibited excellent photopic average transmittance (~ 88 %), resistivity (~ 2.7 × 10-5 µ-cm.) and has the best Hackee figure of merit (41.0 × 10-3 &#937;-1). The electrical conduction is dominated by two different scattering mechanisms depending on the thickness of the Ag mid-layer. Optical transmission is explained by scattering losses and absorption of light due to inter-band electronic transitions. A systematic study was carried out to improve the performance/stability of the TFTs on PEN. The performance and stability of a-Si:H and a-IZO (amorphous indium zinc oxide) TFTs were improved by performing a systematic low temperature (150 °C) anneals for extended times. For 96 hours annealed a-Si:H TFTs, the sub-threshold slope and off-current were reduced by a factor ~ 3 and by 2 orders of magnitude, respectively when compared to unannealed a-Si:H TFTs. For a-IZO TFTs, 48 hours of annealing is found to be the optimum time for the best performance and elevated temperature stability. These devices exhibit saturation mobility varying between 4.5-5.5 cm2/V-s, ION/IOFF ratio was 106 and a sub-threshold swing variation of 1-1.25 V/decade. An in-depth study on the mechanical and electromechanical stress response on the electrical properties of the a-IZO TFTs has also been investigated. Finally, the a-Si:H TFTs were exposed to gamma radiation to examine their radiation resistance. The interface trap density (Nit) values range from 5 to 6 × 1011 cm-2 for only electrical stress bias case. For "irradiation only" case, the Nit value increases from 5×1011 cm-2 to 2×1012 cm-2 after 3 hours of gamma radiation exposure, whereas it increases from 5×1011 cm-2 to 4×1012 cm-2 for "combined gamma and electrical stress". / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2011

Thesis (Master of Engineering in Mechanical Engineering)--Cape Peninsula University of Technology, 2017. / Transparent conductive oxides (TCOs), which are widely used in transparent electronics, possess a spectral selectivity that is suitable for a solar material absorber. TCO materials have a plasma wavelength in the infrared region. Consequently electromagnetic waves shorter than a plasma wavelength are transmitted through the material, while longer electromagnetic waves are reflected on the surface. In contrast to the opaque solar selective absorbers, the plasma wavelength in TCO materials can be easily tuned by controlling the heavy doping process to match the peak shift of thermal radiation at higher temperatures. Furthermore, the use of TCO in conjunction with a solar absorber relaxes the spectral selectivity of the latter and thus widens the selection of the solar absorber; subsequently the only requirement is a thermally stable black body. Aluminum doped Zinc Oxide (AZO) is a class of TCO materials which is cost effective to manufacture due to abundance ZnO, and Aluminum raw materials. This thesis is based on the synthesis of Al doped ZnO thin films nanostructure using radio frequency RF magnetron sputtering process. The influence of the deposition parameters, including argon working pressure and substrate temperature, on the structural and optical properties of the AZO thin films is investigated by means of X-ray diffraction (XRD) and optical spectroscopy (UV-VIS-NIR). The optical constants of AZO films are extracted from transmittance and reflectance spectra using a combination of Drude and Lorentz dielectric function model. A computer simulation is developed to calculate the radiative properties of Al doped ZnO thin films nanostructure. The thermal emittance and solar absorptance is predicted indirectly from optical reflectance and transmittance of AZO films by invoking Kirchhoff’s law. A Special attention has been paid to the parameters that influence the spectral properties of the AZO films including carrier’s mobility, Al doping concentration and film thickness. Carrier’s mobility turned out to have the most significant influence on the spectrally selective performance of AZO films.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / The growing interest in the use of new materials and their applications for photovoltaic systems has been a constant concern of the scientific community in recent years. This work is primarily engaged in the collection, characterization and photoactivity testing photovoltaic solar cells made of thin SnO2 doped fluoride films, the films were deposited by the technique of "spray-pyrolysis" and the Sol-Gel method in substrate glass. In glasses microscopy work with dimensions of 2.5 x 7.5 x 1 mm are used as matrices for the conductive substrates or transparent conductive oxides (TCO). These glasses have electrical resistance and transmittance adequate for the manufacture of photoelectrochemical solar cells activated by dyes. Besides making the glasses must be made conductive depositing a layer of titanium oxide, preparation of electrolyte, dye, assembly and characterization of the cells. The conductive substrate has a film of tin dioxide doped with fluorine (SnO2: F), the deposition is made with the aid of a compressor and a spray gun on the glass at a temperature of 600 C from a solution made by the method Sol- gel (MSG). As characterization techniques were used: x-ray diffraction (EDX), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV-Vis and Van der Pauw method. The conductive glass has transmittance of 80% (400 nm - 800 nm). The cell with mesoporphyrin dye has Vac = 0.34V and Icc ~ 150&#956;A. The experimental results obtained from these cells may contribute to the development of prototypes that can be used commercially in the capture of solar energy and its consequent transformation into electricity. / O crescente interesse no uso de novos materiais e suas aplicaÃÃes, para sistemas fotovoltaicos tem sido uma constante preocupaÃÃo da comunidade cientifica nos Ãltimos anos. O presente trabalho tem por objetivo principal a obtenÃÃo, caracterizaÃÃo e testes de fotoatividade de cÃlulas solares fotovoltaicas constituÃdas de filmes finos de SnO2 dopados com flÃor, os filmes foram depositados pela tÃcnica de âspray-pirÃliseâ e pelo mÃtodo Sol-Gel em substrato de vidro. Neste trabalho vidros de microscopia com dimensÃo de 2,5 x 7,5 cm x 1 mm, sÃo usados como matrizes para os substratos condutores ou Ãxidos condutores transparentes (OCTâs). Estes vidros possuem resistÃncia elÃtrica e transmitÃncia adequadas para confecÃÃo de cÃlulas solares fotoeletroquÃmicas ativadas por corantes. AlÃm de tornar os vidros condutores deve ser feita a deposiÃÃo de uma camada de Ãxido de titÃnio, preparaÃÃo de eletrÃlito, corante, montagem e caracterizaÃÃo das cÃlulas. O substrato condutor possui um filme de diÃxido de estanho dopado com flÃor (SnO2:F), a deposiÃÃo à feita com o auxilio de um compressor e uma pistola aerogrÃfica sobre o vidro à temperatura de 600ÂC a partir de uma soluÃÃo feita pelo mÃtodo Sol-Gel (MSG). Como tÃcnicas de caracterizaÃÃo foram usadas: difraÃÃo de raios-x (EDX), microscopia eletrÃnica de varredura (MEV), espectroscopia de energia dispersiva (EDS), Uv-Vis e mÃtodo de Van der Pauw. O vidro condutor apresenta transmitÃncia 80% (400 nm â 800 nm ). A cÃlula com corante mesoporfirina apresenta Vca = 0,34 V e Icc ~ 150&#956;A. Os resultados experimentais obtidos dessas cÃlulas poderÃo contribuir para o desenvolvimento de protÃtipos que possam ser utilizados comercialmente na captaÃÃo de energia solar e sua conseqÃente transformaÃÃo em energia elÃtrica.

Orientador: Luiz Fernando Zagonel / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T03:52:44Z (GMT). No. of bitstreams: 1 Ramos_Raul_M.pdf: 5673835 bytes, checksum: 005e134cbd8cbb241cbdf367a75f35a3 (MD5) Previous issue date: 2015 / Resumo: Eletrodos condutores transparentes (TCE) possuem grande importância para tecnologias de informação e geração de energia. O TCE mais eficiente na atualidade é o ITO (In2O3 dopado com Sn), que pode alcançar resistividades em torno de 2.10-4 ?cm e uma transmitância ótica de 80% a 90% na região do visível. Entretanto, a escassez dos recursos naturais de Índio e sua grande demanda sugerem a necessidade de materiais alternativos. O presente estudo tem por objetivo investigar as propriedades óticas, eletrônicas e estruturais de filmes finos de TiO2 (fase anatase) dopados com Nitrogênio. A deposição dos filmes foi feita por Deposição por Feixe de Íons (IBD) por bombardeamento de um alvo de titânio puro com íons de Ar+ em atmosfera de O2. Os filmes, com uma espessura de ?90 nm, foram depositados em substrato de quartzo amorfo (Herasil-1) a temperaturas de 400 ou 500°C. Depois, os filmes são dopados com implantação iônica, variando o tempo de 10 a 60 minutos, com feixe de íons misto a baixa energia de N2+ e H2+ com 150 eV e sob a mesma temperatura de crescimento. Após a implantação, medidas Hall indicam que a densidade de portadores majoritários nos filmes de anatase dopados com nitrogênio chegam até ?1019 cm?3 (enquanto filmes não dopados tem densidade de cargas de ?1012 cm?3). A resistividade dos filmes dopados chegam até 10?1 ?cm enquanto mantem boa transmissão ótica (>80%). De fato, dependendo do tempo de dopagem e da temperatura do substrato durante o processo, a transmissão de até 85% podem ser obtida em 550 nm com tal resistividade (?10?1 ?cm). Espectroscopia de fotoelétrons emitidos por raio-x (XPS) realizadas in situ mostram que a composição na superfície é compatível com TiO2?xNx com concentração de nitrogênio de até ? 20%. Difração de raio-x com ângulo de incidência rasante (GIXRD) confirmaram a estrutura cristalina anatase dos filmes antes e após a implantação iônica à baixa energia (150 eV). Este estudo indica que é possível dopar a amostra anatase com nitrogênio através do uso de um feixe de íons de baixa energia. Tal abordagem é interessante por permitir um controle da concentração de dopantes (Nitrogênio através de um precursor gasoso) de forma mais controlada do que usualmente obtido por sputtering reativo / Abstract: Transparent conductive electrodes (TCE) have great importance for information and energy technologies. The most efficient TCE is currently the ITO (Sn-doped In2O3), which may have a resistivity lower than 2·10?4 ?cm and an optical transmittance of 80% to 90% in the visible region. However, the scarcity of natural resources of Indium and its great demand suggests the need of alternative materials. The present study aims to investigate the optical, electronic and structural properties of thin films of TiO2 (anatase phase) doped with nitrogen. The films deposition is made by Ion Beam Deposition (IBD) by bombarding a pure titanium target with Ar+ ions in O2 atmosphere to a thickness of about 90 nm. The films are deposited on an amorphous quartz substrate (Herasil-1) at 400 or 500 °C. Afterwards, the films are doped by ion implantation with low-energy ion beam mixed of N2+ and H2+ at 150 eV and under the same temperature of the growth for times ranging from 10 to 60 minutes. After implantation, Hall measurements indicated that the majority carrier density in the nitrogen doped anatase films reaches up to ? 1019 cm?3 (while the undoped films have a carrier density of ? 1012 cm?3). The resistivity of the doped films is as low as 10?1 ? cm while maintaining good optical transmission. Indeed, depending on the doping time and substrate temperature, transmission of up to 90% could be obtained at 550 nm with this resistivity. X-ray photoelectron spectroscopy (XPS) performed in situ shows that the surface composition is compatible with N:TiO2?x with nitrogen concentrations of up to ? 20%. Small angle x-ray diffraction measurements (SAXRD) confirmed the anatase crystal structure of the films before and after the low energy ion implantation. This study indicates that it is indeed possible to dope anatase thin films with nitrogen by low energy ion beam. This approach is interesting for allowing a greater control of doping concentration with respect to what is usually obtained by reactive sputtering / Mestrado / Física / Mestre em Física / 2013/118682-8 / CAPES

No description available.

O óxido de índio dopado com estanho é um semicondutor degenerado de alta transparência no espectro visível e alta condutância elétrica. Por suas propriedades, ele é utilizado como eletrodo transparente em diversas aplicações. Algumas destas aplicações exigem que os filmes sejam depositados sobre substratos poliméricos, que degradam em temperaturas acima de 100 °C. Por este motivo, métodos de deposição que utilizam baixas temperaturas são necessários. O objetivo deste trabalho é o desenvolvimento de técnicas de deposição de filmes de óxido de índio dopado com estanho, em baixas temperaturas (< 100 °C), pelo método de magnetron sputtering de rádio fequência. Filmes foram obtidos sobre substratos de silício, vidro e policarbonato, e suas propriedades físicas, elétricas, ópticas, químicas e estruturais foram analisadas por perfilometria, elipsometria, curvas corrente-tensão, prova de quatro pontas, medidas de efeito Hall, difratometria de raios-X e espectrofotometria. Filmes depositados sobre silício e vidro tiveram resistividade elétrica mínima da ordem de 10^-4 Ohm.cm, enquanto a resistividade do filme obtido sobre policarbonato foi da ordem de 10^-3 Ohm.cm. A transmitância óptica média no espectro visível das amostras variou de 66 a 87 %. Do ponto de vista estrutural, as amostras tenderam a apresentar fase amorfa e cristalina, com orientação preferencial ao longo da direção [100]. De modo geral, as amostras obtidas de 75 a 125 W tiveram as melhores propriedades para serem utilizadas em aplicações que exijam eletrodos transparentes, considerando aspectos elétricos e ópticos. / Indium-tin oxide is a degenerate semiconductor that shows high transmittance in the visible region of the spectrum and high electrical conductance. Because of its properties, this material is used as transparent electrode in a wide variety of applications. Some of these applications demand the indium-tin oxide layer to be deposited over polymer substrates, which degrade at temperatures above 100 °C. Because of this degradation problem, deposition methods at low temperatures are needed. The purpose of this work is the development of low temperature (< 100 °C) indium-tin oxide deposition processes by radio frequency magnetron sputtering method. Thin films were deposited over silicon, glass and polycarbonate substrates, and their physical, electrical, optical, chemical and structural properties were analyzed by surface high step meter, ellipsometry, current-voltage curves, four-point probe analysis, Hall effect measurements, X-ray diffractometry and spectrophotometry. Films deposited over silicon and glass substrates showed minimal electrical resistivity in the order of 10^-4 Ohm.cm, while the resistivity of the film obtained over polycarbonate was in the order of 10^-3 Ohm.cm. The average transmittance in the visible spectrum varied over the range 66 to 87 %. According to the structural study, the films present both amorphous and crystalline phases, with crystallites showing preferential orientation along the [100] direction. In general, films deposited with power varying over the range 75 to 125 W showed the best results to be applied as transparent electrodes, considering electrical and optical aspects.

O óxido de índio dopado com estanho é um semicondutor degenerado de alta transparência no espectro visível e alta condutância elétrica. Por suas propriedades, ele é utilizado como eletrodo transparente em diversas aplicações. Algumas destas aplicações exigem que os filmes sejam depositados sobre substratos poliméricos, que degradam em temperaturas acima de 100 °C. Por este motivo, métodos de deposição que utilizam baixas temperaturas são necessários. O objetivo deste trabalho é o desenvolvimento de técnicas de deposição de filmes de óxido de índio dopado com estanho, em baixas temperaturas (< 100 °C), pelo método de magnetron sputtering de rádio fequência. Filmes foram obtidos sobre substratos de silício, vidro e policarbonato, e suas propriedades físicas, elétricas, ópticas, químicas e estruturais foram analisadas por perfilometria, elipsometria, curvas corrente-tensão, prova de quatro pontas, medidas de efeito Hall, difratometria de raios-X e espectrofotometria. Filmes depositados sobre silício e vidro tiveram resistividade elétrica mínima da ordem de 10^-4 Ohm.cm, enquanto a resistividade do filme obtido sobre policarbonato foi da ordem de 10^-3 Ohm.cm. A transmitância óptica média no espectro visível das amostras variou de 66 a 87 %. Do ponto de vista estrutural, as amostras tenderam a apresentar fase amorfa e cristalina, com orientação preferencial ao longo da direção [100]. De modo geral, as amostras obtidas de 75 a 125 W tiveram as melhores propriedades para serem utilizadas em aplicações que exijam eletrodos transparentes, considerando aspectos elétricos e ópticos. / Indium-tin oxide is a degenerate semiconductor that shows high transmittance in the visible region of the spectrum and high electrical conductance. Because of its properties, this material is used as transparent electrode in a wide variety of applications. Some of these applications demand the indium-tin oxide layer to be deposited over polymer substrates, which degrade at temperatures above 100 °C. Because of this degradation problem, deposition methods at low temperatures are needed. The purpose of this work is the development of low temperature (< 100 °C) indium-tin oxide deposition processes by radio frequency magnetron sputtering method. Thin films were deposited over silicon, glass and polycarbonate substrates, and their physical, electrical, optical, chemical and structural properties were analyzed by surface high step meter, ellipsometry, current-voltage curves, four-point probe analysis, Hall effect measurements, X-ray diffractometry and spectrophotometry. Films deposited over silicon and glass substrates showed minimal electrical resistivity in the order of 10^-4 Ohm.cm, while the resistivity of the film obtained over polycarbonate was in the order of 10^-3 Ohm.cm. The average transmittance in the visible spectrum varied over the range 66 to 87 %. According to the structural study, the films present both amorphous and crystalline phases, with crystallites showing preferential orientation along the [100] direction. In general, films deposited with power varying over the range 75 to 125 W showed the best results to be applied as transparent electrodes, considering electrical and optical aspects.