Photoelectric work functions of Ni$z.sbnd;Al alloys: Clean surfaces and adsorption of CO

Abstract

Abstract The work function Φ, the emission constant M , and the increase in work function after CO adsorption ΔΦ have been measured as a function of the overall composition of well annealed Ni-Al alloy films. The work function of the Ni-Al alloys is not constant within the several miscibility gaps of the Ni-Al phase diagram, and is not lower than the work function of the respective pure metals, as was found with Ni-Cu and Pt-Au alloy films within the miscibility gap. Of all compositions studied only the 25% Ni alloy (NiAl 3 ) distinguishes itself by an increased Φ-value. The higher Φ is explained by the higher atomic density of the NiAl 3 compound compared with pure Al and Ni 2 Al 3 . As with other metal alloy systems, an enrichment of the surface by the component with the lower surface energy (Al) is also found with the ordered Ni-Al alloy system. From ΔΦ measurements it appears that up to about 40% Ni the surface of the Ni-Al alloy is composed entirely of Al. The behavior of Φ and ΔΦ in the Ni-rich part is explained by the enrichment of the surface by Al. The tendency to form the surface from Al atoms is strengthened by the existence of suitable crystallographic structures. The emission constant does not distinguish any of the intermetallic compounds and resembles that of the Pt-Au and Pd-Ag alloy films.