An apparatus and process for forming thin films of titanium dioxide in the rutile phase by reactive sputter deposition. In one aspect, a sputtering target and auxiliary plasma generator are positioned in a coating station in a sputtering chamber so that the titanium deposited on a substrate passing through the coating chamber is oxidized by exposure to the auxiliary plasma generated by the plasma generator commingled with the sputter plasma. The plasma may include monatomic oxygen to assist in the formation of rutile titanium dioxide. The target, or a pair of targets may also be operated from pulsed d.c. or a.c. power supplies.