The cross-section schematic of the coater is shown in Fig. 1. 32 glass tubes may be accommodated in the vacuum chamber. Borosilicate glass tubes of outside diameter 37 mm and length 1.2 m have been used in our coating experiments. During the coating the glass tubes execute planetary rotation driven by a controlled variable speed dc motor outside the chamber. Typically the tubes are driven around the chamber center at 4 rpm and spun on their axes at around seven times this rate. The SS–AlN cermet material has been investigated as a solar absorbing layer using this coater. The coater contains three cylindrical targets, 1.5 m long and 68 mm in diameter, consisting of aluminium (98purity), stainless steel and copper (99purity) tubes. They are separated by a screen to prevent cross-contamination. Each cylindrical target has a magnetron configuration of six longitudinal plasma columns on the target
surface generated by a permanent magnet unit inside the cathode. The permanent magnet unit, consisting of six longitudinal magnet columns, is assembled from Nd–Fe–B permanent magnet pieces. The maximum field is approximately 0.04 T on the target surface. During sputtering the permanent magnet unit is rotated, driven by a controlled variable speed dc motor outside the chamber, while the target material is static. The six longitudinal plasma columns follow the rotating magnetic field which ensures uniform sputter erosion of target materials both around the circumference and along the length of the target. The typical rotation speed of the magnet unit is 3 rpm.