In this work we have prepared Si and SI(1-X)GE(X) nanocrystals by rf magnetron cosputtering method. The eect of annealing parameters and Ge content of x on the structural and optical properties sandwiched SiO2/SiO2: Si: Ge/SiO2 nanostructures have been investigated. For characterization we have used cross-sectional high resolution electron microscope (HREM), X-ray diraction (XRD), Raman spectroscopy (RS), Fourier transform infrared (FTIR), photoluminescence (PL), and temperature dependent PL (TDPL) techniques. It was shown that Ge content of x, annealing temperature, and annealing time are important parameters aecting the structural and optical properties of the nanocrystals. We have observed a uniform SI(1-X)GE(X) nanocrystal formation upon annealing at relatively low temperatures and short annealing time. However, Ge-rich SI(1-X)GE(X) nanocrystals do not hold their compositional uniformity when annealed at high temperatures for enough long time. A segregation process leads to the separation of Ge and Si atoms from each other and formation of Si-rich core covered by a Ge-rich shell. Related to the optical properties of Si and SI(1-X)GE(X) nanocrystals, influence of annealing treatments and Ge content of x on the simultaneous observation and relative contribution of quantum confined and interface related radiative emission to PL spectra are investigated. On the other hand, temperature dependent photoluminescence (TDPL) measurements have been applied to investigate in detail the involving PL mechanisms and the competing thermally activated emission process and the thermally activated escape process of carriers into nonradiative recombination centers and/or tunneling of the excitons into the interface or to larger nanocrystals.

In the present study, the effect of S and Se substitution on structural, electrical and optical properties of AgGa(Se2-xSx) thin films has been investigated. AgGa(Se0.5S0.5 )2 thin films were prepared by using the thermal evaporation method. X-ray diffraction (XRD) analysis has revealed that the transformation from amorphous to polycrystalline structure took place at about 450 oC. The detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure has been obtained by performing both energy dispersive X-ray analysis (EDXA) and X-ray photoelectron spectroscopy (XPS) measurements. AgGaSe2 thin films were deposited by using both electron-beam (e-beam) and sputtering techniques. In e-beam evaporated thin films, the effect of annealing on the structural and morphological properties of the deposited films has been studied by means of XRD, XPS, scanning electron microscopy (SEM) and EDXA measurements. Structural analysis has shown that samples annealed between 300 and 600 oC were in polycrystalline structure with co-existance of Ag, Ga2Se3, GaSe, and AgGaSe2. The variation of surface morphology, chemical composition and bonding nature of constituent elements on post-annealing has been determined by EDXA and XPS analyses. AgGaSe2 thin films were also prepared by using sputtering technique. XRD measurements have shown that the mono-phase AgGaSe2 structure is formed at annealing temperature of 600 oC. The crystal-field and spin-orbit splitting levels were resolved. These levels around 2.03 and 2.30 eV were also detected from the photospectral response measurements. Thin films of Ag-Ga-S (AGS) compound were prepared by using AgGaS2 single crystalline powder and deposition of the excess silver (Ag) intralayer with double source thermal evaporation method. As a consequence of systematic optimization of thickness of Ag layer, Ag(Ga,S) with the stoichiometry of AgGa5S8 and AgGaS2 were obtained and systematic study to obtain structural, electrical and optical properties was carried out.

Orientadores: Lisandro Pavie Cardoso, Marco Sacilotti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T18:38:56Z (GMT). No. of bitstreams: 1 Chiaramonte_Thalita_D.pdf: 12073771 bytes, checksum: d01b6c585fd5556757aea0542ecf63f2 (MD5) Previous issue date: 2007 / Resumo: Os nitretos (Ga, Al, In)N assim como os compostos GaInP, GaCuO2, representam um sistema de materiais muito importante para as aplicações em opto-eletrônica e dispositivos tais como os diodos emissores de luz (LEDs), lasers e nanosensores. Entretanto, o requisito essencial para as aplicações industriais desses materiais é a redução em seus tamanhos. Neste trabalho foram crescidos materiais metálicos formados por nitretos de gálio e também de semicondutores do tipo GaInP, GaCuO2 na forma de estruturas 3D, pela técnica de deposição química de organometálicos em fase vapor (MOCVD). Foi utilizado como precursor organometálico (OM) o trimetil gálio Ga(CH3)3e o nitrogênio N2 como gás portador. A temperatura e a pressão foram controladas durante o crescimento variando entre 500 e 750 o C e 100 a 760 Torr, respectivamente. Duas classes de estruturas 3D foram obtidas a partir da decomposição total ou parcial do gás pre-cursor, devido a interação entre o OM e o substrato que gera diferentes morfologias: i) as ligas metálicas (Ga, Al, In) formando estruturas semelhantes a balões, cetros (hastes com terminações esféricas) e neurônios, todos apresentando uma fina membrana de carbono amorfo que reveste a estrutura. Após o crescimento, estas estruturas foram submetidas ao processo de nitretação sob atmosfera de NH3 para transformá-las em micro/nanocristais de GaN; ii) os fios semicondutores micro/nanométricos com uma esfera metálica em sua terminação (bambus e cetros) . Na formação de ambas as estruturas, os precursores OM são como moléculas catalisadoras do crescimento. Este crescimento é considerado como um método alternativo e original para se obter estruturas 3D. Uma possível associação com o modelo apresentado pelo mecanismo de crescimento Vapor-Líquido-Sólido (VLS), que utiliza uma partícula metálica para promover os nanotubos de carbono e os nanofios semicondutores, ainda está em discussão. Informações estruturais e ópticas dessas novas estruturas crescidas sobre substratos de Cu (grade de difração), Si (001), InP (policristalino) e Al/SiO2/Si (fotolitografia) foram obtidas através da caracterização por difração de raios-X, microscopia eletrônica de varredura e de transmissão em alta resolução, espectroscopia por energia disper-siva, catodoluminescência e a espectroscopia de excitação por dois fótons. Nas amostras nitretadas, micro/nano cristais de GaN obtidos da liga de Ga aparecem impregnados no carbono turbostrático (folhas de carbono sem orientação obtidas do amorfo) que revestem as estruturas, e emitem na região do espectro l £ 365 nm, devido às suas dimensões quânticas. As hastes das estruturas do tipo bambus apresentam nódulos formados por discos monocristalinos de GaInP rotacionados de 60 o um em relação ao outro. Óxidos CuGaO2 e CuGa2O4compondo nanofios, denominados cetros, também foram obtidos / Abstract: Nitride (Ga, Al, In)N as well as GaInP, GaCu O2 compounds represent a very important class of materials to be used in the opto-electronic and devices applications such as light emission diodes (LEDs) lasers and nanosensors. However, the essential requirement to the industrial applications of these materials is the reduction in theirs sizes. In this work 3D structures based on gallium nitride and also GaInP, GaCuO2 semiconductors were grown by metalorganic chemical vapor deposition (MOCVD) technique. Trimethyl-gallium Ga(CH3) was used as the metal-organic (MO) precursor and nitrogen N2as carrier gas. During the growth to the temperature and pressure intervals of 500 - 700 oC and 100 - 760 Torr, respectively. Two 3D material classes were obtained from the total or partial precursor gas decomposition, since the interaction between the MO compound and the substrate gives rise to different morphologies: i) (Ga,In,Al) metallic alloys form ballons, scepters (wires with spherical ends) and neurons like structures, all involved by a thin carbon amorphous membrane. After growth, these structures were turned into GaN micro/nanocrystals by nitridation process under NH3 atmosphere; ii) micro/nanometer semiconductor wires with a metallic sphere at its end (bamboos and scepters). In order to form both structures, the MO precursors are taken as a catalyst molecule of the growth process. This is an alternative and original method to obtain 3D structures and a possible association to the model used in the vapour-liquid-solid (VLS) growth mechanism, in which a metallic particle promotes the carbon nanotubes and semiconductors nanowires is still under discussion. Structural and optical informations on these new structures grown on Cu (diffraction grid), Si(001), InP (polycrystalline) and Si/Al (photolithography) substrates were obtained through the characterization by X-ray diffraction, scanning electron microscope, high resolution transmission electron microscopy, en-ergy dispersive x-rays, cathodoluminescence and two photon excitation. In the nitrided samples, GaN micro/nanocrystals obtained from Ga alloy appear embedded in the turbostratic carbon (C sheets at random obtained from the amorphous) which involves the structures and, they emit in the l £ 365 nm region specter, due to their quantum dimensions. The bamboo rods present nodes consisting of GaInP single crystal discs turned by 60o one with respect to the other. The CuGaO2 and CuGa2O4 oxides compounding nanowires, called scepters, also were obtained. / Doutorado / Física / Doutor em Ciências