Growth and characterization of thin epitaxial Co3O4(111) films

TL;DR

This paper reports the growth, structural characterization, and surface analysis of epitaxial Co3O4(111) films on a-Al2O3(0001), highlighting the effects of post-growth annealing on film morphology and surface structure.

Contribution

It presents a detailed epitaxial growth process and analysis of Co3O4(111) films, including the impact of annealing on morphology and surface properties, which was not previously documented.

Findings

Films are single crystalline with specific epitaxial relation.

Post-growth annealing improves interface sharpness and surface crystallinity.

Surface remains (1 * 1) despite polarity, explained by surface spinel inversion.

Abstract

The growth and characterization of epitaxial Co3O4(111) films grown by oxygen plasma-assisted molecular beam epitaxy on single crystalline a-Al2O3(0001) is reported. The Co3O4(111) grows single crystalline with the epitaxial relation Co3O4(111)[-12-1]||a-Al2O3(0001)[10-10], as determined from in situ electron diffraction. Film stoichiometry is confirmed by x-ray photoelectron spectroscopy, while ex situ x-ray diffraction measurements show that the Co3O4 films are fully relaxed. Post-growth annealing induces significant modifications in the film morphology, including a sharper Co3O4/a-Al2O3 interface and improved surface crystallinity, as shown by x-ray reflectometry, atomic force microscopy and electron diffraction measurements. Despite being polar, the surface of both as-grown and annealed Co3O4(111) films are (1 * 1), which can be explained in terms of inversion in the surface spinel structure.