Appearance Potential Study of the Band Structure of Transition Metals on Transition Metal Surfaces

Abstract

Soft x-ray appearance potential spectra have been obtained for dilute coverages of transition metals on transition metal surfaces. The appearance potential spectrum of a given core level is the differential excitation probability as a function of sample potential. For transition metals this produces a strong positive threshold peak whose width is related to the unfilled portion of the d band. The titanium-nickel system is of particular interest since, in their pure form, titanium and nickel have nearly empty and nearly filled 3d bands respectively. In preliminary studies of this system, we find the 2p32 peak of nickel in dilute concentration on a titanium surface to be identical to the titanium 2p32 peak obtained from dilute coverages of titanium on a nickel surface. The width of these peaks is intermediate between the clean Ti and Ni values. This result, which suggests a common band model for an alloy of stoichiometry near that of TiNi, is contrasted with recent experimental and theoretical studies of dilute transition metal alloys.