Abstract
Al–N films are formed on a glass substrate by rf sputtering using Ar and N2 gas mixture. The concentration of partial N2 gas pressure (cN2) is changed from 0.0%N2 to 16.0%N2. Optical properties are measured in the wavelength range of 0.24 to 2.60 µm. When cN2 is varied at the same film thickness, the specimen with 7.3%N2 shows the highest solar energy absorptance (α) for the air mass one. Then, as the film becomes thicker at this cN2, α increases to 0.95, which is a promising characteristic for application as a solar absorber coating. It is also observed by atomic force microscopy that the surface roughness is enhanced as the film becomes thicker. The essential reason for the high value of α is the antireflection effect due to the gradient-refractive index caused by the enhanced surface roughness during film growth.
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