Local Electronic Properties of the Passive Film on Nickel Studied by Scanning Tunneling Spectroscopy

Scanning tunneling spectroscopy has been applied to characterize the electronic properties of the granular and intergranular sites of the passive film grown on Ni(111) single-crystal surfaces in acid solution. The passive film, essentially consisting of NiO, shows p-type grains (valence band edge at 0.54 ± 0.03 eV below Fermi level) with unoccupied Ni 3d surface states at 0.5–1.5 eV above Fermi level in the bandgap. At grain boundaries, the...