Room-temerature oxidation of Ni(110) at low and atmospheric oxygen pressures

Abstract

Oxidation of atomically clean (110) nickel single crystals has been studied at room temperature and in pure oxygen or air at pressures from 1×10−9 torr to atmospheric. X-ray photoelectron (XPS) and Auger electron spectroscopic (AES) data indicate that the standard regimes of dissociative chemisorption, oxide nucleation, and oxide lateral growth to coalescence were observed at low pressures. After the NiO layer coalesced at low pressures, exposure of the sample to atmospheric oxygen or air did not cause further growth of the oxide thickness at room temperature. Instead the growth of a high-energy shoulder on the O 1s XPS peak indicated the formation of Ni(OH)2 on the surface. The presence of the hydroxide is consistent with high-resolution, electronenergy-loss spectroscopy (HREELS) data and chemical shifts in the Ni 2p spectra. While the oxide thickness is constant, the hydroxide thickness increased with exposure and time at high pressure. Surface analysis and lowpressure techniques are appropriate for the study of room-temperature, ambient-oxide formation and allow a determination of the kinetics and reaction products critical to the passivation of Ni.