Some Aspects Regarding I. R. Absorbing Materials Based On Thin Alumina Films for Solar-Thermal Energy Conversion, Using X-Ray Diffraction Technique
Solar energy is the most “available”, ecological and clean energy. This energy can be used in active or passive mode. The active mode implies the transformation of solar energy into a useful energy. The solar energy can be transformed into thermal energy, using solar collectors. In these collectors, the active and the most important element is the absorber, material which performs the absorption of solar radiation and, in at the same time, limits its reflection. The paper presents some aspects regarding the IR absorbing material – a type of cermets, used as absorber in the solar collectors, by X Ray Diffraction Technique (XRD) characterization. Keywords—Alumina films, solar energy, X-ray diffraction.
Characterization of α-Phase Aluminium Oxide Films Deposited by Filtered Vacuum Arc
Abstract Aluminum oxide (Al2O3) films were deposited by the filtered vacuum arc method, using a highly pure aluminum cathode and oxygen gas. Substrate temperature as high as 780°C was necessary for the formation of corundum structured α-Al2O3. Applying RF power and thus negative bias voltage to the substrate enables to increase and control the energy of substrate bombarding ions. With a negative bias voltage of 200 V, it was possible to deposit films containing α-Al2O3 with pre-heating the substrate to a temperature lower than 500°C. Increasing the voltage, thus increasing the ion energy, resulted in lowering of the critical pre-heating substrate temperature for formation of α-phase. Additionally, there was a clear difference in crystal orientation of α-Al2O3 between the films grown with and without substrate bias voltage, which was confirmed by infrared spectroscopy. Structure and phase evolution of the film were also studied by cross-sectional transmission electron microscopy.
GROWTH AND CHARACTERIZATION OF CUBIC BORON NITRIDE THIN FILMS
Boron nitride (BN) thin films have been grown on [100] oriented single crystal Si, diamond, Cu and Ni substrates by ion beam assisted deposition using electron beam evaporation of boron together with simultaneous bombardment by nitrogen and argon ions. Characterization by Fourier‐transform infrared spectroscopy and high‐resolution transmission electron microscopy showed that the films on Si and diamond consisted of initial noncubic (amorphous and hexagonal BN) layers, followed by the growth of cubic BN (c‐BN). This growth sequence was attributed primarily to increasing compressive intrinsic stress with increased film thickness. Increasing the substrate temperature above 400 °C led to the onset of c‐BN at a greater film thickness while increased ion flux resulted in earlier growth of this phase. These results may be explained by the relaxation of the intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ...