Unraveling the mechanisms responsible for the interfacial region formation in 4H-SiC dry thermal oxidation

Aiming to understand the processes involved in the formation of the transition region between SiO2 and SiC, known as the interfacial region, early steps of SiC oxidation were investigated using mainly nuclear reaction analyses. Oxidation kinetics reveals that an abrupt change in the oxidation mechanism is observed in C-face oxide films when their thickness is around 10 nm, while a continuous change in the oxidation mechanism is observed in Si-face oxide films with thicknesses up to about 4 nm. This last thickness corresponds to the maximum width of the interfacial region. Changes observed in the oxidation mechanism were related to oxidation reaction and interfacial atom emission that may take place during oxide film growth. Besides, the activation energies of such processes were obtained

Determinação da quantidade de oxigênio em filmes finos utilizando técnicas de RBS e canalização

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Comissionamento de reatores utilizados na determinação do mecanismo de crescimento térmico de filmes dielétricos crescidos sobre SiC

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Initial stages of SiC oxidation investigated by ion scattering and angle-resolved x-ray photoelectron spectroscopies

Initial stages of oxidation of single-crystal, Si-faced silicon carbide were investigated using ion scattering and angle-resolved x-ray photoelectron spectroscopies. The very first oxidation products are shown to be silicon oxycarbides (SiCxOy), while, for longer oxidation times, a mixture of SiCxOy and SiO2 is formed in the near-surface region of the growing oxide film. The composition of the near-surface region of such thin films is very similar to that reported in previous investigations for the near-interface region when thicker oxides films are grown on SiC

Determinação do teor de metal em catalisadores metalocênicos para polimerização por XRF, RBS e ICP-OES

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Effectiveness of polymeric gloves in radioprotection against contamination in nuclear medicine

When handling unsealed radioactive sources, radiological protection attention must be taken to avoid unnecessary exposure and radioactive contaminations, and an important and necessary practice to prevent such contaminations is the use of gloves when handling these sources. The present work aimed to determine the effectiveness of contamination protection provided by different types of disposable polymeric gloves used in Nuclear Medicine Service in Clinic Hospital of Porto Alegre, testing the main radiopharmaceuticals used at this site: [99mTc]sodium pertechnetate, [18F]FDG and [131I]sodium iodide. The analysis was performed using the wipe test inside gloves intentionally contaminated on the outside with these radiopharmaceuticals. The radiation detector used to measure the contamination was a NaI(Tl) scintillator well-type counter. The results indicate that three types of gloves analyzed protect the user from [99mTc]sodium pertechnetate and [18F]FDG contamination, for permanence times with the glove after contamination for up to 15 min (interval tested). For [131I]sodium iodide, gloves are completely effective in protection as long as they are used for a time interval after contamination of the external surface of up to: Latex – 5 min; Vinyl – 5 min; Nitrile – 10 min. Among them, the nitrile glove are the most effective, since contamination was not observed on the inner face for times equal to or less than 10 min; and, for an interval of 15 min, the percentage of permeation obtained was lower than the other two types: 3.3 times lower than vinyl glove permeation and 1.3 times lower of the latex glove permeation. It was also possible to estimate the skin dose rate due to contamination caused by iodine permeation for each glove case and time tested

Interaction of SiC thermal oxidation by-products with SiO2

We investigated oxygen incorporation and exchange during thermal growth of silicon oxide films on silicon carbide. This investigation was carried out in parallel with the thermal growth of silicon oxide films on silicon for comparison.We provide experimental evidence that oxidation by-products of silicon carbide out-diffuse and interact with the silicon oxide overlayer, incorporating C and O. This and other results are in sharp contrast to those obtained for silicon samples, constituting a key issue in the stability of any dielectric material used on silicon carbide

Enhanced initial growth of atomic-layer-deposited metal oxides on hydrogen-terminated silicon

A route is presented for activation of hydrogen-terminated Si(100) prior to atomic layer deposition. It is based on our discovery from in situ infrared spectroscopy that organometallic precursors can effectively initiate oxide growth. Narrow nuclear resonance profiling and Rutherford backscattering spectrometry show that surface functionalization by pre-exposure to 108 Langmuir trimethylaluminum at 300 °C leads to enhanced nucleation and to nearly linear growth kinetics of the high-permittivity gate dielectrics aluminum oxide and hafnium oxide

Elemental concentration and sulfur chemical speciation in the amazonian plant andira surinamensis using synchrotron radiation techniques (SR-XRF, XANES), RBS and WD-XRF

The inorganic composition of the bark and leaf of a plant from the Amazon rainforest, Andira surinamensis, was determined using two non-destructive, multi-element techniques: X-ray fluorescence (XRF) and Rutherford backscattering spectrometry (RBS). XRF measurements were made using both a conventional X-ray source and synchrotron radiation. It was observed that although magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, and potassium are present in higher concentrations in the leaf, calcium is about three times more concentrated in the bark. Manganese, iron, copper, zinc, strontium and barium were also detected, with barium showing a concentration above the minimum toxicity level for plants. Chemical speciation of sulfur, performed using the X-ray absorption near edge structure (XANES) technique, showed that sulfur is present in several oxidation states, with a much larger contribution from the inorganic sulfate in the leaves. The article evidences that the combined use of synchrotron radiation and non-destructive multielement techniques allows for an efficient and accurate determination of the inorganic composition and chemical speciation in plants. © 2019 Sociedade Brasileira de Química