Optical properties of d.c. reactively sputtered thin films

Abstract

Deposition parameters, compositions and optical constants n and k have been determined for a range of reactively sputtered composite materials produced in d.c. post cathode magnetron sputtering systems. Optical constants were determined for as-deposited films and films heat treated in vacuum at 400 and 500 °C to assess their suitability for utilization in solar-selective surfaces for evacuated collectors and other optical coatings. The materials were fabricated with aluminium, chromium, stainless steel, silicon and titanium post cathodes, and butane, CO, CF 4, N 2 and O 2 reactive gases. In particular, materials based on AlCO, AlCF and AlN have deposition parameters and optical properties suitable for solar-selective surface. A dielectric material based on AlCF has a refractive index n of about 1.4, a low k value and a relatively high deposition rate, and it may be suitable for transparent protective coatings, antireflection coatings or the low refractive index component in multilayer stacks.