The disclosure provides an improved solar selective multilayer coating
having higher thermal stability and a process therefor. According to the
disclosure, a tandem stack of three layers of TiAlN, TiAlON and
Si.sub.3N.sub.4 is deposited on metal and non-metal substrates using a
planar reactive magnetron sputtering process. The first two layers
function as the absorber and the third antireflection layer further
enhances the coating's absorptance. The solar selective coatings were
annealed in air and vacuum to test the thermal stability at different
temperatures and durations. The coatings deposited on copper substrates
are stable in air up to a temperature of 625.degree. C. and exhibit
higher solar selectivity and these coatings also show no change in the
absorptance and the emittance values even after vacuum annealing at
600.degree. C. for 3 hours. The solar selective coatings exhibit high
hardness, high oxidation resistance, chemical inertness and stable
microstructure.