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.
Effect of oxidized Al prelayer for the growth of polycrystalline Al2O3 films on Si using ionized beam deposition
Abstract Polycrystalline Al2O3 thin films have been grown on Si substrates by ionized beam deposition using an aluminum solid source in O2 environments. To prevent the aluminum interdiffusion to Si at high substrate temperature (Ts>500°C), the oxidized Al prelayer with a thickness of 3 nm was deposited on the Si substrate at room temperature before Al2O3 deposition, and subsequently polycrystalline Al2O3 films were grown at 700°C. Although Al interdiffusion increased at the interface with increasing Ts, the oxidized Al prelayer was effective as a buffer layer on which to grow stoichiometric and crystalline Al2O3 films up to Ts=800°C.