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 appl ication 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 vacu um. 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 wit h partial pressures upon specimen heating, it is concluded that the Ti -Nb composite film operates as a getter because Ti on the surface adso rbs residual gases effectively and adsorbed oxygen diffuses rapidly in to the Nb film. The co-existence of Ti and Nb is important for the get ter property. The recovery rate of surface composition was measured at several temperatures by the dynamic balance between sputter removal o f surface Ti and the Ti supply from substrate. The recovery rate was o ne atomic layer per one min, or several tens min at 700 or 500 K, wher e a getter may operate. Therefore, the getter material is expected to keep its surface composition by itself and continues to operate as a g etter, even if the getter surface receives damage such as ion irradiat ion. (C) 1998 Elsevier Science Ltd. All rights reserved.