Thermal stability of electrodeposited nickel on vanadium: evidence for oxygen diffusion and intermetallic phase formation

The thermal stability of Ni overlayers electrochemically prepared on a polycrystalline vanadium (V) surface, was studied by means of X-ray and UV photoelectron spectroscopies (XPS, UPS). The results showed that upon cathodic polarization, a mixed Ni–Ni(OH)2 adlayer is formed, while V surface becomes partially oxidized into vanadium oxide (V2Ox). The applied potential during nickel electrodeposition is crucial for both Ni–Ni(OH)2 composition and V2Ox film thickness. Annealing the Ni–Ni(OH)2/V2Ox interface under UHV conditions leads to the gradual reduction of the films and the formation of a new Ni–V intermetallic phase. A solid state reaction accompanies the decomposition of nickel and vanadium oxides resulting in oxygen migration from the Ni adlayer to the V support. The electronic structure of Ni–V intermetallic phase formed after oxide decomposition is compared to previously reported results for Ni alloys and intermetallic compounds.