Rare earth centers properties and electron trapping in SnO2 thin films produced by sol-gel route

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of pH of Colloidal Suspension on the Electrical Conductivity of SnO2 thin Films Deposited Via Sol-Gel-Dip-Coating

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of pH of colloidal suspension on crystallization and activation energy of deep levels in SnO2 thin films obtained via sol-gel

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural Characterization of Nanocrystalline Sb-Doped SnO2 Xerogels by Multiedge X-ray Absorption Spectroscopy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Evaluation of Bulk and Surfaces Absorption Edge Energy of Sol-Gel-Dip-Coating SnO2 Thin Films

The absorption edge and the bandgap transition of sol-gel-dip-coating SnO2 thin films, deposited on quartz substrates, are evaluated from optical absorption data and temperature dependent photoconductivity spectra. Structural properties of these films help the interpretation of bandgap transition nature, since the obtained nanosized dimensions of crystallites are determinant on dominant growth direction and, thus, absorption energy. Electronic properties of the bulk and (110) and (101) surfaces are also presented, calculated by means of density functional theory applied to periodic calculations at B3LYP hybrid functional level. Experimentally obtained absorption edge is compared to the calculated energy band diagrams of bulk and (110) and (101) surfaces. The overall calculated electronic properties in conjunction with structural and electro-optical experimental data suggest that the nature of the bandgap transition is related to a combined effect of bulk and (101) surface, which presents direct bandgap transition.

Theoretical analysis of the energy levels induced by oxygen vacancies and the doping process (Co, Cu and Zn) on SnO2 (110) surface models

Density functional calculation at B3LYP level was employed to study the surface oxygen vacancies and the doping process of Co, Cu and Zn on SnO2 (110) surface models. Large clusters, based on (SnO2)(15) models, were selected to simulate the oxidized (Sn15O30), half-reduced (Sn15O29) and the reduced (Sn15O28) surfaces. The doping process was considered on the reduced surfaces: Sn13Co2O28, Sn13Cu2O28 and Sn13Zn2O28. The results are analyzed and discussed based on a calculation of the energy levels along the bulk band gap region, determined by a projection of the monoelectron level structure on to the atomic basis set and by the density of states. This procedure enables one to distinguish the states coming from the bulk, the oxygen vacancies and the doping process, on passing from an oxidized to a reduced surface, missing bridge oxygen atoms generate electronic levels along the band gap region, associated with 5s/5p of four-/five-fold Sn and 2p of in-plane O centers located on the exposed surface, which is in agreement with previous theoretical and experimental investigations. The formation energy of one and two oxygen vacancies is 3.0 and 3.9 eV, respectively. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Periodic study on the structural and electronic properties of bulk, oxidized and reduced SnO2(110) surfaces and the interaction with O-2

The structural and electronic properties of bulk and both oxidized and reduced SnO2(110) surfaces as well as the adsorption process of O-2 on the reduced surface have been investigated by periodic DFT calculations at B3LYP level. The lattice parameters, charge distribution, density of states and band structure are reported for the bulk and surfaces. Surface relaxation effects have been explicitly taken into account by optimizing slab models of nine and seven atomic layers representing the oxidized and reduced surfaces, respectively. The conductivity behavior of the reduced SnO2(110) surface is explained by a distribution of the electrons in the electronic states in the band gap induced by oxygen vacancies. Three types of adsorption approaches of O-2 on the four-fold tin at the reduced SuO(2)(110) surface have been considered. The most exothermic channel corresponds to the adsorption of O-2 parallel to the surface and to the four-fold tin row, and it is believed to be associated with the formation of a peroxo O-2(2-) species. The chemisorption of O-2 on reduced SnO2(110) surface causes a significant depopulation of states along the band gap and it is shown to trap the electrons in the chemisorbed complex producing an electron-depleted space-charge layer in the inner surface region of the material in agreement with some experimental evidences. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Comparison of non-Ohmic accelerated ageing of the ZnO- and SnO2-based voltage dependent resistors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The influence of area/volume ratio on microstructure and non-Ohmic properties of SnO2-based varistor ceramic blocks

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of degradation on the electrical conduction process in ZnO and SnO2-based varistors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of thermal annealing treatment in oxygen atmosphere on grain boundary chemistry and non-ohmic properties of SnO2 center dot MnO polycrystalline semiconductors

The present work studied the influence of thermal treatment in oxygen rich atmosphere on heterogenous junctions in Mn-doped SnO2 polycrystalline system presenting varistor behavior. The samples were prepared by conventional oxide mixture methodology, and were submitted to heat treatment in oxygen rich atmosphere at 900 degrees C for 2h. The samples were characterized by X-ray diffraction, scanning electron microscopy, dc and ac electrical measurements. The results showed that there is an evident relationship between the microstructure heterogeneity and non-ohmic electrical properties. It was found that for this SnO2 center dot MnO-based varistor system the heat treatment in oxygen rich atmosphere does not necessarily increase the varistors properties, which was related to the decrease in the grain boundary resistance. The results are compared with Co-doped SnO2 varistors and ZnO based varistors. (C) 2008 WILEY-VCH Verlay GmbH & Co. KGaA, Weinheim.

Carbon-coated SnO2 nanobelts and nanoparticles by single catalytic step

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Obtenção e caracterização de filmes SnO2 depositados em vidro borosilicato por silk-screen modificado: SnCl2.2H2O como precursor

O presente trabalho tem como objetivo investigar as características de filmes de SnO2 depositados em substrato de vidro borosilicato por um processo de silk-screen modificado para obtenção de espessura fina compatível com a aplicação em células solares policristalinas de baixo custo. O filme de SnO2 é um dos mais apropriados para obtenção de vidro TCO (transparent conductive oxide) para uso em células solares devido a sua baixa resistividade elétrica e alta transmitância, sendo quimicamente inerte, mecanicamente duro e tem resistência a altas temperaturas, o que facilita então a calcinação das amostras entre 500º C a 550º C. Os filmes foram obtidos a partir de uma solução precursora básica, preparada pela dissolução de SnCl2.2H2O em Etanol (99,5 %). Foi realizado um planejamento fatorial 2(3-1) para analisar a influência dos parâmetros concentração da solução precursora (CETN), temperatura de calcinação (TC) e taxa de aquecimento (tX) na calcinação, sendo a concentração CETN o parâmetro que apresentou maior efeito sobre os parâmetros de respostas investigados: espessura do filme (ω), resistividade de superfície (ρ) e a transmitância relativa (θ). Foi possível obter com a metodologia utilizada, filmes com espessuras da ordem de 1 Nm com resistividade de superfície de 10 / e transmitância relativa entre 70 e 80 %.

Fungal infections of the mucous membrane

A clinical review of three potentially severe fungal diseases, which are characterized in many cases by mucosal involvement, is presented. They are paracoccidioidomycosis, histoplasmosis, and mucormycosis. Mucosal involvement for paracoccidioidomycosis and rhinocerebral mucormycosis is frequent. Thus, oral involvement may provide early clue for diagnosis. In paracoccidioidomycosis, the mucosal lesion classically shows superficial ulcers with granular appearance and hemorrhagic points, usually on lips, palate, and jugal mucosa. In mucormycosis, necrosis of the palate followed for purulent discharge is a hallmark of rhinocerebral disease. Treatment with amphotericin B desoxycholate or the new second-generation triazoles is highly efficacious.