Gabriel Vieira Soares

Oxygen reaction-diffusion in metalorganic chemical vapor deposition HfO2 films annealed in O2

Composition, atomic transport, and chemical reaction were investigated following annealing in O2 of ultrathin HfO2 films deposited on Si substrates thermally nitrided in NO. The as-prepared thin film composition was established by Rutherford backscattering spectrometry, nuclear reaction analysis, and x-ray photoelectron spectroscopy as a HfO2 film on an intermediate layer containing silicon oxynitride, hafnium silicate, and possibly hafnium–silicon oxynitride. O penetration, incorporation in the bulk of the HfO2/SiOxNy structure, and oxidation of the substrate forming SiO2 were observed.

Nitrogen bonding, stability, and transport in AlON films on Si

The chemical environment of N in nitrided aluminum oxide films on Si(001) was investigated by angle-resolved x-ray photoelectron spectroscopy. Two different bonding configurations were identified, namely N–Al and N–O–Al, suggesting the formation of the AlN and AlO2N compounds. The near-surface region is N-rich and AlN compounds therein are more abundant than AlO2N, whereas in bulk regions the proportions of these two compounds are comparable. Rapid thermal annealing at 1000 °C for 10 s in vacuum or in low-pressure oxygen atmosphere led to the breakage of N–Al bonds in AlN, releasing N and Al. The mobile N is partly lost by desorption from the surface and partly fixed by reacting with the network to form AlO2N. The released Al atoms, which remain immobile, react with oxygen from the film or from the gas phase. Characterization of the films outermost surfaces by low-energy ion scattering revealed that the migration of Si atoms from the substrate across the films, reaching the surface and being oxidized ther...

Integrity of hafnium silicate/silicon dioxide ultrathin films on Si

Rapid thermal annealing at 1000 °C of (HfO2)1−x(SiO2)x pseudobinary alloy films deposited on Si were performed in N2 or O2 atmospheres. The effects on the atomic transport, structure, and composition were investigated using isotopic substitution of oxygen, high-resolution transmission electron microscopy, nuclear reaction analyses, narrow nuclear reaction resonance profiling, and grazing angle x-ray reflection.

Morphological and compositional changes in the SiO2∕SiC interface region induced by oxide thermal growth

Changes in morphology and composition of interfacial regions of thermally grown SiO2 films on SiC in dry O2 induced by reoxidations were investigated using atomic force microscopy and oxygen profiling. The gradual oxygen profile near the interface in oxides grown at 1100°C evidences a transition region between SiO2 and SiC. Reoxidation at 950°C leads to a decrease of the transition region thickness, while reoxidation at 1100°C increases the transition region thickness. These results are discussed in terms of the role played by the reoxidation temperature on the formation and consumption of carbon compounds in the SiO2∕SiC interface region.

Effects of nitrogen incorporation on the interfacial layer between thermally grown dielectric films and SiC

C-containing interlayers formed between the SiC substrate and dielectric films thermally grown in O2, NO, and in O2 followed by annealing in NO were investigated. X-ray reflectometry and x-ray photoelectron spectroscopy were used to determine N and C incorporation in dielectric films and interlayers, as well to determine their mass densities and thicknesses. The thickest C-containing interlayer was observed for films thermally grown in O2, whereas the thinnest one was observed for films directly grown in NO, evidencing that the presence of N decreases the amount of carbonaceous compounds in the dielectric/SiC interface region.

Natural Green Coating Inhibits Adhesion of Clinically Important Bacteria

Despite many advances, biomaterial-associated infections continue to be a major clinical problem. In order to minimize bacterial adhesion, material surface modifications are currently being investigated and natural products possess large potential for the design of innovative surface coatings. We report the bioguided phytochemical investigation of Pityrocarpa moniliformis and the characterization of tannins by mass spectrometry. It was demonstrated that B-type linked proanthocyanidins-coated surfaces, here termed Green coatings, reduced Gram-positive bacterial adhesion and supported mammalian cell spreading. The proposed mechanism of bacterial attachment inhibition is based on electrostatic repulsion, high hydrophilicity and the steric hindrance provided by the coating that blocks bacterium-substratum interactions. This work shows the applicability of a prototype Green-coated surface that aims to promote necessary mammalian tissue compatibility, while reducing bacterial colonization.

Presence and Resistance to Wet Etching of Silicon Oxycarbides at the SiO2 / SiC Interface

The formation and solubility of silicon oxycarbides at the SiO 2 /SiC interface was investigated using nuclear reaction analyses. The amount of silicon oxycarbides formed by thermal oxidation of SiC in dry O 2 was seen to be independent of substrate polytype, surface termination, and oxidation temperature. Oxide growth was retarded on surfaces containing residual silicon oxycarbides, and none of several acid and oxidizing wet etch chemistries was able to remove them.

Hydrogen and deuterium incorporation and transport in hafnium-based dielectric films on silicon

Hydrogen and deuterium incorporation into nitrided and non-nitrided hafnium silicate films on Si during thermal annealing in H1- and H2-containing atmospheres was investigated. H1 profiling was accessed by means of nuclear resonant reaction profiling, whereas H2 incorporation was quantified by nuclear reaction analysis. The effects of preannealing in different atmospheres and temperatures were determined, as well as the losses of H1 and H2 from these structures during postannealing in vacuum. The results reveal a rather uniform depth distribution of incorporated H1, in striking contrast with previous studies on hydrogen in silicon oxide and oxynitrides and hafnium oxide films on Si. These results are discussed in terms of the defects present in each one of the structures studied here.

Oxygen transport and GeO2 stability during thermal oxidation of Ge

Oxygen transport during thermal oxidation of Ge and desorption of the formed Ge oxide are investigated. Higher oxidation temperatures and lower oxygen pressures promote GeO desorption. An appreciable fraction of oxidized Ge desorbs during the growth of a GeO2 layer. The interplay between oxygen desorption and incorporation results in the exchange of O originally present in GeO2 by O from the gas phase throughout the oxide layer. This process is mediated by O vacancies generated at the GeO2/Ge interface. The formation of a substoichiometric oxide is shown to have direct relation with the GeO desorption.

Sequential thermal treatments of SiC in NO and O2: Atomic transport and electrical characteristics

Sequential thermal oxidations and oxynitridations of SiC were performed using O218 and NO. The resulting films were characterized by x-ray photoelectron spectroscopy, ion beam analyses, and capacitance-voltage measurements. The best electrical characteristics were obtained from films directly grown in NO. A subsequent oxidation in O2 degraded the interface due to negative flatband-voltage shift, removal of N, and formation of C compounds, while a further annealing in NO brought the flatband shift in the C-V curves to rather moderate figures. This shift is related to competitive processes taking place during dielectric film formation which are discussed.