SELECTIVE PROPERTIES OF ROUGH SPUTTERED FILMS

Abstract
Solar selective surfaces based on textured copper have been produced by means of two sputtering techniques. In a novel planar magnetron cosputtering system sputter etching of bulk copper sheet, when seeded by a flux of titanium atoms, led to the formation of microscopically roughened surfaces with unusually complex structural formations. Preliminary sputter etching experiments have also been carried out in a cylindrical magnetron system. Alternatively, a standard planar magnetron system was used to deposit copper films of thickness 0.5 µm to 10.0 µm onto glass at sputtering pressures in the range 0.5 Pa to 100 Pa. This deposition technique also resulted in the formation of microscopically roughened surfaces, in this case characterised by arrays of cones. Optical properties of both types of surface follow well defined trends as deposition conditions vary. High absorptance, low emittance selective surfaces have been produced by coating homogeneous metal carbide films onto suitably textured copper on glass films. This composite selective surface exhibits good stability at temperatures up to 500°C in vacuum.