Self-limited oxide formation in Ni(111) oxidation

TL;DR

This study combines experimental low energy electron microscopy and ab-initio scattering theory to investigate the self-limited oxide formation on Ni(111) surfaces, revealing nanoscale NiO domains and a consistent oxide thickness of about two layers.

Contribution

It provides a detailed experimental and theoretical analysis of Ni(111) oxidation, demonstrating the self-limited nature and nanoscale structure of the oxide layer.

Findings

Formation of nanosized NiO domains at 300 K

Presence of NiO-like nuclei separated by Ni(111) terraces at 750 K

Oxide layer thickness is approximately two NiO layers

Abstract

The oxidation of the Ni(111) surface is studied experimentally with low energy electron microscopy and theoretically by calculating the electron reflectivity for realistic models of the NiO/Ni(111) surface with an ab-initio scattering theory. Oxygen exposure at 300 K under ultrahigh-vacuum conditions leads to the formation of a continuous NiO(111)-like film consisting of nanosized domains. At 750 K, we observe the formation of a nano-heterogeneous film composed primarily of NiO(111)-like surface oxide nuclei, which exhibit virtually the same energy-dependent reflectivity as in the case of 300 K and which are separated by oxygen-free Ni(111) terraces. The scattering theory explains the observed normal incidence reflectivity R(E) of both the clean and the oxidized Ni(111) surface. At low energies R(E) of the oxidized surface is determined by a forbidden gap in the k_parallel=0 projected energy spectrum of the bulk NiO crystal. However, for both low and high temperature oxidation a rapid decrease of the reflectivity in approaching zero kinetic energy is experimentally observed. This feature is shown to characterize the thickness of the oxide layer, suggesting an average oxide thickness of two NiO layers.