Nanometer and sub-nanometer thin oxide films at surfaces of late transition metals

TL;DR

This paper reviews recent advances in understanding the formation and properties of nanometer and sub-nanometer oxide films on late transition metals, highlighting their unique structures and potential catalytic functionalities.

Contribution

It provides a comprehensive review of recent experimental and theoretical studies on the atomic-scale properties and formation mechanisms of ultrathin oxide films on late transition metals.

Findings

Initial oxide overlayers differ from bulk oxides in structure and electronic properties.

Nanometer-scale oxide films can exhibit unique functionalities not present in bulk materials.

Surface oxides may form naturally during oxidation and influence catalytic behavior.

Abstract

If metal surfaces are exposed to sufficiently oxygen-rich environments, oxides start to form. Important steps in this process are the dissociative adsorption of oxygen at the surface, the incorporation of O atoms into the surface, the formation of a thin oxidic overlayer and the growth of the once formed oxide film. For the oxidation process of late transition metals (TM), recent experimental and theoretical studies provided a quite intriguing atomic-scale insight: The formed initial oxidic overlayers are not merely few atomic-layer thin versions of the known bulk oxides, but can exhibit structural and electronic properties that are quite distinct to the surfaces of both the corresponding bulk metals and bulk oxides. If such nanometer or even sub-nanometer surface oxide films are stabilized in applications, new functionalities not scalable from the known bulk materials could correspondingly arise. This can be particularly important for oxidation catalysis, where technologically relevant gas phase conditions are typically quite oxygen-rich. In such environments surface oxides may even form naturally in the induction period, and actuate then the reactive steady-state behavior that has traditionally been ascribed to the metal substrates. Corresponding aspects are reviewed by focusing on recent progress in the modeling and understanding of the oxidation behavior of late TMs, using particularly the late 4d series from Ru to Ag to discuss trends.