A CYLINDRICAL MAGNETRON SPUTTERING SYSTEM FOR DEPOSITING METAL ALUMINUM NITRIDE CERMET SOLAR COATINGS ONTO BATCHES OF TUBES

A cylindrical direct current (dc) magnetron sputtering system of comme rcial scale for coating glass tubes with metal-aluminium nitride (M-Al N) cermet solar selective surfaces is described. The stainless steel-a luminium nitride (SS-AlN) cermet material has been investigated as a s olar absorbing layer. During the deposition of a SS-AlN cermet layer, both an Al metal target and stainless steel target are sputtered simul taneously in a gas mixture of argon and nitrogen. The nitrogen partial pressure is set sufficiently high at the aluminum target side to ensu re that a nearly pure AlN ceramic sublayer is deposited onto the surro unding tubes by dc reactive sputtering. The excellent nitriding resist ance of stainless steel leads to a nearly pure SS sublayer being depos ited onto the tubes. Tube planetary rotation results in a deposited mu lti-layered system consisting of alternating SS and AlN sublayers. Thi s multi-sublayer system can be considered as a macro-homogeneous cerme t layer with the metal volume fraction determined by controlling the t hicknesses of SS and AlN sublayers. Varying the SS target current achi eves different SS volume fractions in the cermet layers. Following thi s procedure the SS-AlN cermet solar selective coatings with a double c ermet layer structure were deposited onto 32 borosilicate glass tubes of 37 mm outside diameter and 1.2 m long. A solar absorptance of 0.93- 0.95 and emittance of 0.04-0.05 at room temperature has been achieved. (C) 1998 American Vacuum Society.