Journal of Vacuum Science & Technology A, Vol.15, No.6, 2842-2846, 1997
Direct-Current Magnetron-Sputtered W-AIN Cermet Solar-Absorber Films
W-ALN cermet selective surfaces have been investigated using a special direct current (dc) magnetron sputtering technology. During the deposition of the W-AIN cermet layer, both Al and W targets were run simultaneously in a gas mixture of argon and nitrogen. The total sputtering gas pressure was 1 Pa and the reactive nitrogen gas partial pressure was chosen at 2.5 X 10(-2) Pa, which is beyond the transition point from metal phase to dielectric phase in the deposited material. The ceramic ALN component was deposited by de reactive sputtering and the metallic W component by de sputtering due to the excellent nitriding resistance of metallic tungsten. By substrate movement a multi-sublayer system, consisting of alternating W and AlN sublayers, was deposited. This deposited multi-sublayer system can be considered as a macro-homogeneous W-AlN cermet layer with metal volume fraction determined by controlling the thickness of the sublayers. W-AlN cermet selective surfaces with a double cermet layer film structure were deposited. The typical film structure from surface to bottom substrate is an AIN anti-reflection layer on a double W-AlN cermet layer on an Al metal infrared reflection layer. A solar absorptance of 0.92-0.91 with emittance of 0.03-0.05 at room temperature and 0.08-0.10 at 350 degrees C has been achieved for such W-AlN cermet selective surfaces. The W-AlN cermet has excellent thermal stability in vacuum at high operating temperature.