Nitrogênio em semicondutores amorfos

Orientador: Ivan Emilio ChambouleyronTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Neste trabalho estão contidas informações experimentais relativas aos efeitos causados, nas propriedades opto-eletrônicas, pela introdução de nitrogênio em semicondutores amorfos à base de silício e de germânio. Segundo este estudo, tanto a presença de átomos nitrogênio, quanto a sua respectiva concentração (conforme determinada por meio de reações nucleares), são responsáveis por importantes modificações em várias das propriedades opto-eletrônicas, bem como características estruturais, dos mencionados semicondutores. Em linhas gerais, a presença de nitrogênio a baixas concentrações atua como uma impureza doadora nas versões hidrogenadas do a- Si e do a-Ge; a altas concentrações, no entanto, grandes mudanças nas propriedades opto- eletrônicas e estruturais são observadas. Todas as amostras foram depositadas, sob a forma de filmes finos, através da técnica de ri reactive sputtering em atmosferas controladas de Ar+(H2)+N2. Diferentes técnicas de espectroscopia (absorção óptica nas regiões de visível e infra-vermelho, espalhamento Raman e estudos de fotoemissão) foram empregadas para a análise das principais propriedades ópticas e eletrônicas destes semicondutores; segundo suas respectivas concentrações de nitrogênio. Uma atenção especial foi dedicada às caracterizações eletrônicas incluindo medidas de transporte (condutividade no escuro em função da temperatura) e estudos de fotoemissão através de espectroscopia de elétrons excitados por fótons com energias típicas de raios-x moles e ultra-violeta (XPS e UPS, respectivamente)Abstract: This work presents experimental data referring to the effects resulting from the introduction of nitrogen into amorphous silicon and germanium. AlI the samples studied in this work were deposited as thin films using the rf reactive sputtering technique in highly controlled Ar+(H2)+N2 gaseous atmospheres. It is shown that either the nitrogen presence and its content (as determined from nuclear reaction analysis measurements) are responsible for profound changes in several opto-electronic properties as well in the structure of the mentioned semiconductors. Roughly, nitrogen at low concentration levels acts as a donor-like impurity in both hydrogenated a-Si and a-Ge. High nitrogen contents, on the other hand, induce significant modifications in their optical band-gap and network structure. Different spectroscopic methods (optical absorpion, infra-red, Raman scattering and photoemission) were employed to analyze the main optical and electronic properties of these nitrogen containing semiconductors. Special emphasis was devoted to the electronic characterization, including transport measurements (dc dark conductivity as a function of temperature) and photoemission studies by means of x-ray and ultraviolet photoelectron spectroscopies (XPS and UPS, respectively)DoutoradoFísicaDoutor em Ciência

Effect of thermal annealing treatments on the optical properties of rare-earth-doped AIN films

Aluminium–nitrogen (AlN) films doped with samarium, europium or ytterbium have been\ud prepared by conventional radio frequency sputtering. Because of the deposition method and conditions the as-deposited films are amorphous with Sm, Eu or Yb concentrations at low 0.5 at%. After deposition the films were submitted to cumulative isochronal thermal annealing (TA) treatments and investigated by optical transmission spectroscopy, photo- (PL) and cathodoluminescence (CL) measurements. For comparison purposes one undoped AlN film was also prepared and investigated in detail. The experimental results indicate that (a) all samples exhibit PL and CL at room temperature, (b) the main spectral features present in the AlN samples are due to defect-related transitions (undoped film) or the rare-earth (RE) ions, (c) in both cases (undoped and Sm-, Eu- or Yb-doped films) the luminescence intensity scales\ud with the temperature of TA and (d) for the present AlN samples, there is a clear relationship between their luminescence intensity and respective energy of optical bandgaps. Finally, the effect of TA on the excitation–recombination mechanisms involving the RE ions is presented and discussed.FAPESPCNP

A construção do conceito de caboclo como demarcador social de inferioridade no sul do Brasil

A construção social do conceito de “caboclo” está relacionada aos processos de erradicação do trabalho escravo e de promoção da imigração europeia para o Brasil. Trata-se de uma nomenclatura criada para dar conta da disseminação da “mistura de raças” cujas consequências levam ao fortalecimento dos estereótipos acerca da população mestiça brasileira. Caboclo surge como um termo de demarcação social que prioriza certas características físicas (mestiço de branco e índio, de pele acobreada e cabelo liso) e raciais (raça híbrida, inferior e degenerada). Posteriormente, as pesquisas empíricas desenvolvidas por Antropólogos e Sociólogos permitiram superar esta construção inicial, agregando fatores de classe, posição social, localização geográfica e sobretudo étnicos. Com isso, começaram a se evidenciar variações de sentido do termo caboclo. No entanto, antes de denotar uma condição étnico-racial, o termo caboclo é uma formação discursiva elaborada para inferiorizar um grupo de indivíduos no processo relacional e contrastante da construção das identidades – algo que fica evidente na região Sul do Brasil, influenciada pelos ideais progressistas característicos da política de colonização

STUDY OF AMORPHOUS GERMANIUM-NITROGEN ALLOYS THROUGH X-RAY PHOTOELECTRON AND AUGER ELECTRON SPECTROSCOPIES

In this work, experimentally determined values of electron spectroscopic shifts induced by nitrogen in Ge core levels of substoichiometric amorphous germanium-nitrogen (a-GeN) alloys are discussed and presented. X-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES) are employed to study the behavior of the Ge 3d and LMM spectra, respectively, and combined the corresponding XPS and Auger core levels shifts to determine Δα′, the modified Auger parameter shift, which is exempt from problems inherent in the interpretation of XPS and XAES shifts. It is demonstrated how one can use Δα′ to reliably estimate ΔnGe, the change in Ge valence charge in the alloys, and how one can calibrate XPS shifts of Si and Ge based alloys in terms of approximate values of ΔnGe

Development of the 'MN''SI IND. 1.7' phase in 'MN'-containing 'SI' films

Thin films of Si with Mn concentrations up to 20 at.% were prepared by conventional radio frequency sputtering. After deposition, the films were submitted to thermal annealing treatments and their properties were investigated by composition analysis, Raman scattering, microscopic techniques, optical transmission, and electrical transport. The experimental results show that all as-deposited films are amorphous, with the Mn atoms being effective and controllably incorporated into the Si matrix. Moreover, thermal annealing at increasing temperatures induces the crystallization of the films as well as the growth of the MnSi1.7 silicide phase in the Mn-containing samples. Along with sample crystallization, some films become covered by small structures that are randomly distributed all over their surfaces. These structures are essentially Mn-containing Si crystals with typical sizes in the (sub-) micrometer range and, as the thermal annealing advances, the density of structures increases at the expense of their individual average dimension. The development and characteristics of the observed superficial structures are discussed in view of the main structural and morphological properties of the samples.FAPESPCNP

Effect of ''O IND. 2' POT. +', ''H IND. 2' POT. +' + ''O IND. 2' POT. +', and ''N IND. 2' POT.+' + ''O IND. 2'POT. +' ion-beam irradiation on the field emission properties of carbon nanotubes

The effect of O2 +, H2 ++ O2 +, and N2 ++ O2 +ion-beamirradiation of carbon nanotubes(CNTs) films on the chemical and electronic properties of the material is reported. The CNTs were grown by the chemical vapor deposition technique (CVD) on silicon TiN coated substrates previously decorated with Ni particles. The Ni decoration and TiN coating were successively deposited by ion-beam assisted deposition (IBAD) and afterwards the nanotubes were grown. The whole deposition procedure was performed in situ as well as the study of the effect of ion-beamirradiation on the CNTs by x-ray photoelectron spectroscopy(XPS). Raman scattering, field-effect emission gun scanning electron microscopy (FEG-SEM), and field emission (FE) measurements were performed ex situ. The experimental data show that: (a) the presence of either H2 + or N2 + ions in the irradiationbeam determines the oxygen concentration remaining in the samples as well as the studied structural characteristics; (b) due to the experimental conditions used in the study, no morphological changes have been observed after irradiation of the CNTs; (c) the FE experiments indicate that the electron emission from the CNTs follows the Fowler-Nordheim model, and it is dependent on the oxygen concentration remaining in the samples; and (d) in association with FE results, the XPS data suggest that the formation of terminal quinone groups decreases the CNTs work function of the material.FAPESP (05/53926-1)CNPqUBA (IP X191)CONICET (PIP 5215; 5959)ANPCyT (PICT 10-25834; 06-10621)CAPES - Ministério de Educación, Ciência y Tecnologia da Argentina, Secretaria de Políticas Universitárias (SPU

Raman spectroscopy analysis of structural photoinduced changers in GeS2+Ga2O3 thin films

Photoexpansion and photobleaching effects have been observed in amorphous GeS2 + Ga2O3 (GGSO) thin films, when their surfaces were exposed to UV light. The photoinduced changes on the surface of the samples are indications that the structure has been changed as a result of photoexcitation. In this paper, micro-Raman, energy dispersive X-ray analysis (EDX) and backscattering electrons (BSE) microscopy were the techniques used to identify the origin of these effects. Raman spectra revealed that these phenomena are a consequence of the Ge-S bonds’ breakdown and the formation of new Ge-O bonds, with an increase of the modes associated with Ge-O-Ge bonds and mixed oxysulphide tetrahedral units (S-Ge-O). The chemical composition measured by EDX and BSE microscopy images indicated that the irradiated area is oxygen rich. So, the present paper provides fundamental insights into the influence of the oxygen within the glass matrix on the considered photoinduced effects

Influence of film thickness on the optical transmission through subwavelength single slits in metallic thin films

Silver and gold films with thicknesses in the range of 120-450 nm were evaporated onto glass substrates. A sequence of slits with widths varying between 70 and 270 nm was milled in the films using a focused gallium ion beam. We have undertaken high-resolution measurements of the optical transmission through the single slits with 488.0 nm (for Ag) and 632.8 nm (for Au) laser sources aligned to the optical axis of a microscope. Based on the present experimental results, it was possible to observe that (1) the slit transmission is notably affected by the film thickness, which presents a damped oscillatory behavior as the thickness is augmented, and (2) the transmission increases linearly with increasing slit width for a fixed film thickness.FAPESPCNPqCePOF / INCT - INO

Revisão crítica sobre o grau de conversão de monômeros resinosos detectados por métodos de análise direta

Objectives: The aim of this study was to carry out\ud a review on the methods of direct detection of the\ud conversion degree of composite resins. Materials &\ud methods: The authors searched the Cochrane Library,\ud Embase, PubMed, and the Web of Science (ISI) for\ud papers dated from January 1991 to November 2011.\ud The search was complemented by manual searches of\ud the reference lists from each identified relevant paper.\ud The main search terms were: “degree of conversion”,\ud “monomers”, “polymers”, “composite”, “pre-gel”,\ud “post-gel”, “residual monomers” and “double bond”.\ud The inclusion criteria were studies that evaluated\ud consolidated methods in the literature to directly\ud evaluate the degree of conversion. Excluded studies\ud were those considered to be unrelated to the\ud question addressed, such as mechanical and physical\ud properties and also monomers from adhesive systems\ud and compomers. The selected papers were assigned\ud to a score (A, B or C), according to the predetermined\ud criteria. Results: A total of 45 papers were selected\ud and 15 papers were included in the critical appraisal.\ud Two articles were labeled as grade A, nine articles\ud were labeled as grade B, and four articles were\ud labeled as grade C. Conclusions: According to the\ud definitions of evidence levels, the current article\ud study showed a strong evidence of review. Clinical\ud significance: The degree of conversion predicts the\ud quality of polymers because the higher degree of\ud conversion, the higher strength of the resin matrix.Objetivos: O objetivo deste estudo foi revisar os métodos\ud de detecção direta do grau de conversão de resinas\ud compostas. Material e Métodos: Os autores pesquisaram\ud artigos publicados no período de Janeiro de 1991 a\ud novembro de 2011, nas bases de dados Cochrane Library,\ud Embase, PubMed e Web of Science (ISI). A pesquisa\ud foi complementada por pesquisa manual das listas de\ud referências de cada artigo identificado como relevante\ud sobre o tema. Os principais termos pesquisados foram:\ud “grau de conversão”, “monômeros”, “polímeros”, “compósito”,\ud “pré-gel”, “pós-gel”, “monômeros residuais” e\ud “dupla ligação”. Os critérios de inclusão foram estudos\ud que avaliaram diretamente o grau de conversão utilizando\ud métodos consolidados na literatura. Os estudos\ud excluídos foram aqueles considerados não relacionados\ud à questão abordada, como estudos sobre propriedades\ud físicas e mecânicas e também sobre monômeros de sistemas\ud de união e compômeros. Os artigos selecionados\ud foram divididos na classificação A, B ou C, de acordo\ud com critérios pré-determinados. Resultados: Quarenta\ud e cinco artigos foram selecionados e quinze artigos\ud foram incluídos na avaliação. Dois artigos foram classificados\ud como grade A, nove artigos como grade B e\ud quatro artigos como grade C. Conclusões: De acordo\ud com as definições dos níveis de evidência, o presente\ud estudo apresentou forte evidência de revisão. Significância\ud Clínica: O grau de conversão prediz a qualidade\ud dos polímeros formados, uma vez que quanto maior o\ud grau de conversão, mais resistente é a matriz resinosa

Nitrogênio como um dopante em filmes de a-Ge: H

Orientador: Ivan Emilio ChambouleyronDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Neste trabalho são apresentados dados experimentais referentes a propriedades ópticas e elétricas de filmes, de qualidade melhorada, de germânio amorfo hidrogenado e não hidrogenado, dopados com nitrogênio. Mostra-se que a inclusão de pequenas quantidades de átomos de nitrogênio na rede do a-Ge dá origem a importantes mudanças nas propriedades opto-eletrônicas do material. Eles podem produzir grandes alterações na condutividade de amostras com baixa densidade de defeitos no pseudo-gap. As amostras são depositadas por RF sputtering de um alvo de Ge em uma atmosfera de argônio e nitrogênio (e hidrogênio, nas amostras hidrogenadas). Medidas de transmissão óptica e condutividade de escuro vs temperatura são apresentadas e discutidas. O nível doador introduzido por nitrogênio coordenado tetraedricamente é encontrado a aproximadamente 50 meV abaixo da borda da banda de condução. No que diz respeito às propriedades ópticas, apenas bandas de absorção (vibracionais), na região de IR, devido aos dipolos Ge-N puderam ser observados na série não hidrogenada, que por sua vez, foram utilizadas na determinação do conteúdo de nitrogênio ligado. Um acréscimo na densidade de defeitos pode ser observado e associado à incorporação de nitrogênio. Toda a interpretação é consistente com o processo de dopagem de elementos do Grupo V em semicondutores amorfos coordenados tetraedricamente. Em principio, qualquer elemento do Grupo V (nitrogênio, fósforo, arsênio, antimônio e bismuto) pode atuar como um doador em a-Ge. Devido à toxicidade de compostos como arsina (AsH3) e fosfina (PH3), comumente utilizados para dopagens, o nitrogênio a aparece como um material doador bastante interessanteAbstract:This work presents experimental data referring to the electrical and optical properties of nitrogen-doped hydrogenated and un-hydrogenated amorphous germanium (a-Ge) films of improved quality. It is shown that the inclusion of minute amounts of nitrogen atoms in the a-Ge network produces important changes in the opto-electronic properties in the material. They can produce large changes in the conductivity of samples having a low density of electronic states in the pseudo-gap. The samples were deposited by RF sputtering a Ge target in an argon plus nitrogen (and hydrogen in the hydrogenated samples) atmosphere. Optical transmission and dark conductivity vs temperature measurements are presented and discussed. The donor level introduced by fourfold coordinated nitrogen is found to be around 60 meV below the conduction band edge. In the a-Ge:N series. absorption bands due to Ge-N vibrations are measured in the IR region of the spectrum. and used to determine the N content. An increase in the density of detects can be observed and associated to nitrogen incorporation. The overall picture is consistent with the doping process of Group V elements in tetrahedrally coordinated amorphous semiconductors. In principle any of the Group V elements (nitrogen. phosphorus. arsenic. antimony and bismuth) could act as donors in a-Ge. Because of the toxicity of such compounds as arsine (AsH3) and phosphate (PH3) which are commonly used for doping. nitrogen appears attractive as a donor materialMestradoFísicaMestre em Físic