Direct Observation of the Oxidation of Aluminum Single-Crystal Surfaces

Abstract

A new technique has been developed by which naturally and anodically formed aluminum oxide produced on single‐crystal specimens has been studied in the electron microscope. The low‐temperature amorphous oxide grown by the transport of cations was smooth at the metal‐oxide interface. However, the oxide‐oxygen interface exhibited topography on certain crystal orientations. A high‐temperature crystalline oxide was found to grow by the transport of anions. Epitaxial growth was observed on several orientations. The anisotropy of oxide thickness which occurred at elevated temperatures is discussed. The above results are considered in terms of the structure of the metal‐oxide interface.