This work reports on the properties of GaN films grown by reactive magnetron sputtering onto glass substrate kept at relatively low temperature (400°C), using different RF power applied to the Ga target. Their structural, morphological, vibrational and optical properties were characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and UV-vis spectrophotometry. The films have wurtzite phase with strong preferential orientation in the c-axis direction. Moreover, two clear contributions to the (0002) diffraction peak could be found, indicating the presence of two different morphologies, which were discussed in terms of the formation of an intermediate layer between the substrate and a dominating columnar-like microstructured film.

Abstract This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.

Abstract After two centuries of the discovery, we now know that there are several types of bauxites, in which mineralogy points to the most appropriate application. In the non-metallurgical industry, bauxites with refractory grades have been applied as raw materials in the production of high-alumina refractories for both shaped and unshaped. The increase in the cost of other sources of high-alumina raw materials has encouraged the refractory producers to find a more cost-effective substitute, such as refractory-grade calcined bauxites (RGB). Nowadays, concerns rise regarding the availability of RGB due to the continuous restrictions taking place in China, which has a 95% market share. This work presents a new RGB of high-alumina content (~85%) from a Brazilian source in which process enabled a technology with high refractoriness.

The structural and optical properties of nanocrystalline GaN and GaN:H films grown by RF-magnetron sputtering are focused here. The films were grown using a Ga target and a variety of deposition parameters (N2/H2/Ar flow rates, RF power, and substrate temperatures). Si (100) and fused silica substrates were used at relatively low temperatures (Ts < 420K). The main effects resulting from the deposition parameters variations on the films properties were related to the presence of hydrogen in the plasma. The X-ray diffraction analysis indicates that the grain sizes ( ~ 15nm) and the crystallized volume fraction significantly decrease when hydrogen is present in the plasma. The optical absorption experiments indicate that the hydrogenated films have absorption edges very similar to that of GaN single crystal films reported in the literature, while the non-hydrogenated samples present larger absorption tails encroaching into the gap energies.

During the atmospheric flight of the Brazilian satellite launch vehicle the pressure inside the satellite compartment should be equalised with the atmospheric pressure. This becomes necessary due to the high pressure differences which result when the vehicle reaches high altitudes with decreasing atmospheric pressures, generating high loads acting on the internal surface of the fairing. The equalisation is achieved through venting holes placed around the fairing of the satellite compartment. The design of the venting orifices should be constrained to the restriction of constant evacuation of the compartment, so that, at any time of the trajectory, the pressure difference is minimal. Meeting this constraint becomes complex due to the flight environment of the vehicle which is characterised by very high acceleration levels. So, the flow around the fairing undergoes constant variation of the velocity field going from subsonic to hypersonic velocities. The position, size and number of venting orifices were determined using gas dynamic analysis and calculations and later validated through flight tests. The article describes the mean features of the design process, discusses the venting criterion, and shows the flight results.