Corrosion protection of Cu by atomic layer deposition

Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0-14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5-7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade. Published by the AVS

Reconstrução por série focal do Telureto de Bismuto utilizando microscopia eletrônica de transmissão de alta resolução

Exportado OPUSMade available in DSpace on 2019-08-12T15:56:50Z (GMT). No. of bitstreams: 1 dissertacao_thais_milagres_de_oliveira.pdf: 23323106 bytes, checksum: 499052c6088c833b02c0a6bb2fd97b8f (MD5) Previous issue date: 14A microscopia eletrônica de transmissão de alta resolução permite a determinação da estrutura cristalina de materiais. Hoje em dia existem pelo menos duas abordagens: a difração de elétrons similar à difração de raios-X e a determinação da estrutura através reconstrução por série focal de imagens de microscopia eletrônica de transmissão de alta resolução. Adicionalmente, a microscopia eletrônica de transmissão e varredura de alta resolução (STEM), aliada a espectroscopia de perda de energia de elétrons (EELS) em microscópios de ultra alta resolução com corretores de aberração esférica e monocromador tem mostrado bons resultados em diversos casos. Contudo, a interpretação e quantificação de imagens de alta resolução é complexa, devido à forte interação do feixe de elétrons com a matéria. Além disto, a função de onda emitida pela amostra é modificada pelos componentes do microscópio. As imagens de microscopia de alta resolução são uma convolução da função de onda do feixe incidente difratada pela amostra com a função de onda do microscópio, de forma que cada contraste observado na imagem representa um efeito de interferência. Para realizar esse estudo foram utilizados dois materiais, o Silício, que é bem conhecido na literatura e o Telureto de Bismuto, um material termoelétrico e com propriedades de isolante topológico. O objetivo principal é estudar e aplicar a técnica de reconstrução por série focal no telureto de bismuto para num futuro próximo determinar estrutura atômica em ligas de telureto de bismuto intercaladas com estanho, selênio e outros elementos.High-resolution transmission electron microscopy is turning into a very powerful technique in crystal structure determination. Nowadays there are at least two different approaches: electron diffraction, similar to X-ray diffraction and structure determination by through focal series reconstruction of high-resolution transmission electron microscopy images. Additionally, scanning transmission electron microscopy (STEM), with electron energy loss spectroscopy (EELS) in high-resolution transmission electron microscopes with aberration correctors and monochromator have shown good results in many cases. However, high-resolution images interpretation and quantification is complex, due to strong radiation-matter interaction. Besides, the samples exit wave is modified by the microscope, so the contrast observed in the image represents an interference effect and cannot be interpreted directly. To perform this research two materials were used, Silicon, which is well known in the literature and Bismuth Telluride, a thermoelectric material and topological insulator. The main aim of this research is establish the focal series reconstruction procedure for bismuth telluride and in the near future try to determine the atomic positions of intercalated bismuth telluride with tin, selenium and other elements

Oxidation barrier for Cu and Fe powder by atomic layer deposition

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Oxidation barrier of Cu and Fe powder by atomic layer deposition

Atomic Layer Deposition (ALD) is a vapor based technique which allows to deposit uniform, conformal films with a thickness control at the atomic scale. In this research, Al2O3 coatings were deposited on micrometer-sized Fe and Cu powder (particles) using the thermal trimethylaluminum (TMA)/water (H2O) process in a rotary pump-type ALD reactor. Rotation of the powder during deposition was required to obtain a pinhole-free AID coating. The protective nature of the coating was evaluated by quantifying its effectiveness in protecting the metal particles during oxidative annealing treatments. The Al2O3 coated powders were annealed in ambient air while in-situ thermogravimetric analysis (TGA) and in-situ x-ray diffraction (XRD) data were acquired. The thermal stability of a series of Cu and Fe powder with different Al2O3 thicknesses were determined with TGA. In both samples a dear shift in oxidation temperature is visible. For Cu and Fe powder coated with 25 nor Al2O3, we observed an increase of the oxidation temperature with 300-400 degrees C. For the Cu powder a thin film of only 8 nm is required to obtain an initial increase in oxidation temperature of 200 degrees C. In contrast, for Fe powder a thicker coating of 25 nm is required. In both cases, the oxidation temperature increases with increasing thickness of the Al2O3 coating. These results illustrate that the Al2O3 thin film, deposited by the thermal ALD process (TMA/H2O) can be an efficient and pinhole-free barrier layer for micrometer-sized powder particles, provided that the powder is properly agitated during the process to ensure sufficient vapor-solid interaction

Corrosion protection of Cu by atomic layer deposition

Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0-14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5-7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade. Published by the AVS

Disentangling the effect of seed size and crystal habit on gold nanoparticle seeded growth

Oxidative etching was used to produce gold seeds of different sizes and crystal habits.</p