Resumo Diferentes espessuras de camadas de fotorresiste foram depositadas sobre a lâmina de Ti, de forma a diminuir a corrente inicial durante o processo de síntese e, assim, evitar ou reduzir a formação da camada inicial compacta de TiO2 sobre os nanotubos. Foi realizado um estudo dos estágios iniciais de crescimento dos nanotubos (NTs) para a síntese convencional e com a presença das camadas de fotorresiste. Os NTs de TiO2 foram caracterizados pela técnica de microscopia eletrônica de varredura. Eletrodos de pH foram fabricados com os NTs obtidos e foram caracterizados. Notou-se a total ausência da camada porosa de TiO2 com o uso da camada de fotorresiste e os eletrodos de pH apresentaram melhora em sua sensibilidade e a ausência do efeito de histerese quando comparados aos fabricados com os nanotubos crescidos sem a camada de fotorresiste.

Abstract Different thicknesses of photoresist layers were deposited on the Ti foil in order to decrease the initial current during the anodization process, avoiding or diminishing in this way the formation of the initial compact TiO2 layer. The studies of the initial synthesis stages were performed in both cases, for the conventional synthesis and for that with photoresist layer on top of the Ti foil. TiO2 nanotube pH electrodes were fabricated to study the effect of this change in the anodization process. The nanostructure morphology was analyzed through scanning electron microscopy technique. Total removal of the undesirable layer and a complete release of the nanotube mouth were obtained. The pH electrodes were characterized utilizing a buffer solution and improved pH sensitivity and absence of hysteresis effects were observed for the devices fabricated with TiO2 nanotubes obtained with the optimized process.

Amorphous silicon thin film transistors (TFT's), utilizing silicon dioxide (SiO2), silicon oxynitride (SiOxNy) and silicon nitride (Si3N4) obtained by PECVD as gate insulating material, are fabricated through just one masking process and characterized by drain current vs drain voltage and by drain current vs gate voltage (Ids vs. Vds and Ids vs. Vgs) measurements.

Son fabricados con apenas una etapa de fotolitografía transistores de capa fina de silicio amorfo utilizando, como material dieléctrico de compuerta, dióxido de silicio (SIO2), oxinitruro de silicio (SiOxNy) y nitruro de silicio (Si3N4) crecidos por PECVD. Los dispositivos son caracterizados por medio de mediciones de corriente de dreno vs voltaje de dreno y corriente de dreno vs voltaje de compuerta (Ids vs. Vds y Ids vs. Vgs)

In this work we study the structural properties of amorphous oxynitride films (a-SiOxNy), grown by plasma enhanced chemical vapour deposition (PECVD)at 320° C. The films were deposited at different ow ratio of N2O and SiH4. The atomic composition of the samples was determined by means of Rutherford backscattering spectrometry (RBS). The local order structure was studied by X-ray absorption spectroscopy (XAS) and the chemical bondings were investigated by Fourier transform infrared (FTIR) spectroscopy. The results evidence a tetrahedric arrangement of the oxynitride network. The tetrahedrons are similiar to SiO3N for x values between 1.43 and 1.64. For x values higher than 1.64 the tetrahedrons are similar to SiO4.

This work describes a systematic study of the preparation of nano-crystalline thin h-BN films by Plasma-Enhanced Chemical Vapor Deposition (PECVD) technique. The samples were prepared at low temperatures using B2H6 and N2 as gas precursors. It is shown that the flow ratio among these gases has an important influence on the size of the crystallites (deduced by Raman spectroscopy). The 2H6/N2 flow ratio was varied from 1,6 x 10-2 to 6.7 x 10-4 leading to films presenting a crystallite size, which varied from 90 nm to amorphous, respectively. The XRD spectra show two peaks at 2 values around 42° and 44°, which are associated to <img src="http:/img/fbpe/bjp/v32n2a/menor.gif"> 110 <img src="http:/img/fbpe/bjp/v32n2a/maior.gif"> and <img src="http:/img/fbpe/bjp/v32n2a/menor.gif"> 100 <img src="http:/img/fbpe/bjp/v32n2a/maior.gif"> h-BN crystalline directions, indicating, a <img src="http:/img/fbpe/bjp/v32n2a/menor.gif"> 002 <img src="http:/img/fbpe/bjp/v32n2a/maior.gif"> preferential orientation for the h-BN crystallites. The thermo-mechanical properties, as stress, hardness, and Young modulus were also studied and correlated with the structural properties. The composition of the films was obtained by RBS and EDS indicating Boron to Nitrogen ratio, close to stoichiometry for all the studied deposition conditions.

We have shown that close to stoichiometry RF PECVD amorphous silicon carbon alloys deposited under silane starving plasma conditions exhibit a tendency towards c-SiC chemical order. Motivated by this trend, we further explore the effect of increasing RF power and H2 dilution of the gaseous mixtures, aiming to obtain the amorphous counterpart of c-SiC by the RF-PECVD technique. Doping experiments were also performed on ordered material using phosphorus and nitrogen as donor impurities and boron and aluminum as acceptor ones. For nitrogen a doping efficiency close to device quality a-Si:H was obtained, the lower activation energy being 0,12 eV with room temperature dark conductivity of 2.10-3 (omega.cm). Nitrogen doping efficiency was higher than phosphorous for all studied samples. For p-type doping, results indicate that, even though the attained conductivity values are not device levels, aluminum doping conducted to a promising shift in the Fermi level. Also, aluminum resulted a more efficient acceptor than boron, in accordance to observations in crystalline SiC material.