Characteristics of Al & Ti oxide-thin films for thermal solar energy selective absorption applications

Abstract

Controlled oxidation of sputtered layers of Ti and Al results oxide layers with nano-sized thickness comparable to thermal solar selective absorber layers. In this work, RF magnetron sputtering was used to obtain thin layers of Al and Ti on substrates of stainless steels (St. St). Deposited thin films were oxidized at 400 °C and 800 °C for 4 hours and 1 hour, respectively. The as-deposited Ti, and Al layers were air–oxidized and their optical absorbance and emittance were studied. Microstructure, surface topography, structure and new phases formed after oxidation were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). Thin films optical properties were investigated by spectrophotometer & Fourier Transform Infrared (FTIR) Spectroscopy. The new microstructures exhibited a dual metallic and oxide nature. Deposited thin film of Ti had maximum absorbance and lowest emittance about 90% and 1.8% respectively; while after oxidation, the deposited layers changed their selective absorbance pattern. The absorbance values increased, and the emittance values decreased for all wave lengths in the infrared (IR) range. The effect of the oxidation process of both Ti thin film and Al thin film was compared. The Al thin film showed lower absorbance in as-deposited and oxidized states.