Effects of substrate temperature and antireflection coating on the structural and optical properties of DC-sputtered chromium thin films for selective solar absorber applications

The Cr and Cr/Al x O y thin films were deposited by DC sputtering onto soda lime glass and polished Al substrates at various deposition temperatures. The structural analysis of the multilayered coatings revealed a weak XRD diffraction peak at 2 θ ≈ 43.3° ascribed to (110) plane of BCC structure of Cr metal. No phase of Al x O y was detected most likely due to the amorphous nature of the films. SEM and AFM analysis demonstrated the skewed distribution of small particles with an average surface roughness ranging between 4.0 and 13 nm. The optical analysis of the films revealed an increase in the steepness of the reflectance curve along the transition/plasma wavelength and blue shifting of this wavelength with the increase in substrate temperature. Also, a decrease in reflectance was observed upon employment of Al x O y antireflection coating as a result of shifting the transition wavelength toward longer wavelengths. These results suggest that substrate temperature and Al x O y antireflection coating are potential for improving the optical properties of Cr films for selective solar absorbers applications.