The surface segregation of Ti-Nb composite film and its application to a smart getter material

The surface segregation behavior of Ti-Nb composite films and its application to a vacuum getter pump are studied. The Ti-Nb composite film was formed when Nb film deposited on Ti substrate was heated in a vacuum. Its surface composition was very stable in a wide range of heating temperatures and Nb film thickness. The composite film showed getter ability for CO and O-2. From the comparison of surface composition with partial pressures upon specimen heating, it is concluded that the Ti-Nb composite film operates as a getter because Ti on the surface adsorbs residual gases effectively and adsorbed oxygen diffuses rapidly into the Nb film. The co-existence of Ti and Nb is important for the getter property. The recovery rate of surface composition was measured at several temperatures by the dynamic balance between sputter removal of surface Ti and the Ti supply from substrate. The recovery rate was one atomic layer per one min, or several tens min at 700 or 500 K, where a getter may operate. Therefore, the getter material is expected to keep its surface composition by itself and continues to operate as a getter, even if the getter surface receives damage such as ion irradiation. (C) 1998 Elsevier Science Ltd. All rights reserved.