Interface and electronic characterization of thin epitaxial Co3O4 films

TL;DR

This study investigates the interface and electronic structure of epitaxial Co3O4(110) films grown on MgAl2O4(110), revealing how post-growth annealing improves surface order and structure, with detailed surface characterization and a proposed surface model.

Contribution

It provides detailed analysis of the surface and interface structure of Co3O4(110) films and demonstrates the effects of annealing on surface order and termination.

Findings

Annealing improves surface order and sharpens LEED patterns.

Surface termination switches from O-rich to Co2O2 after annealing.

Atomic force microscopy shows terraces and atomic steps in annealed films.

Abstract

The interface and electronic structure of thin (~20-74 nm) Co3O4(110) epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl2O4(110) single crystal substrates have been investigated by means of real and reciprocal space techniques. As-grown film surfaces are found to be relatively disordered and exhibit an oblique low energy electron diffraction (LEED) pattern associated with the O-rich CoO2 bulk termination of the (110) surface. Interface and bulk film structure are found to improve significantly with post-growth annealing at 820 K in air and display sharp rectangular LEED patterns, suggesting a surface stoichiometry of the alternative Co2O2 bulk termination of the (110) surface. Non-contact atomic force microscopy demonstrates the presence of wide terraces separated by atomic steps in the annealed films that are not present in the as-grown structures; the step height of ~ 2.7 A corresponds to two atomic layers and confirms a single termination for the annealed films, consistent with the LEED results. A model of the (1 * 1) surfaces that allows for compensation of the polar surfaces is presented.