| This work was carried out in order to develop the selective solar absorbing surface by thin film AlN/Al metal-dielectric composite coating process. In order to reduce problems related to film adhesion anc undesirable interference effect in IR, film thickness was restricted to 0.5㎛. As the thickness of film changed gradually from 3000Å, 4000Å and 5000Å, the measured absorptance resulted 0.87, 0.91 and 0.90, and measured emirtances were 0.18, 0.19 and 0.22, respectively. The reason was believed that the interference minima had shifted further toward longer wavelength(i.e. 1㎛, 1.7㎛ and 1.9㎛). If N₂ partial pressure was increased during sputtering, the structure of AlN protective dielectric layer changed from multi-orientation film to C-axis oriented film. As the structure of AlN protective layer changed from multi-oriented structure to C-axis oriented one, optical properties of selective solar surface were improved by increasing the solar absortance from 0.87 to 0.9 and reducing the emittance from 0.29 to 0.1. |
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