Abstract:
This work investigated the effect of thermal treatment of as-deposited chromium (Cr) thin films in a vacuum and argon/oxygen ambient for effective deposition of spectral selective solar absorber multilayer films. The DC sputtered Cr thin films were thermally exposed at different temperatures in a controlled argon/oxygen environment. Both as-deposited films and those thermally treated in vacuum and in oxygen–argon ambient revealed a weak XRD diffraction peak at 2θ≈44.3° corresponding to (110) plane of BCC structure of Cr metal. Raman analysis revealed one peak at 846 cm−1 corresponding to Cr–O vibration bonds for films thermally treated at 300 °C in a vacuum and 150 °C and 300 °C in argon–oxygen ambient. As determined by AFM and FE-SEM, surface roughness decreased with temperature increase for films thermally treated in a vacuum. Besides, a mixed trend in the evolution of surface roughness was observed for films thermally treated in argon/oxygen ambient. The average spectral transmittance for samples thermally treated in a vacuum decreased with an increase in temperature; however, the samples thermally treated in an argon–oxygen environment exhibited an increasing trend in average spectral transmittance with the increase in temperature. The results clearly show that post-deposition processing at elevated temperatures, particularly in argon–oxygen ambient, influences the structural and optical properties of prior-deposited Cr thin films. This should be considered when designing and depositing multi-layered dielectric/Cr spectral selective solar absorber films.
