Epitaxy of polar semiconductor Co3O4 (110): Growth, structure, and characterization

Abstract

abstract: The (110) plane of Co[subscript 3]O[subscript 4] spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co[superscript 3+] species at the surface. However, experimental studies of Co[subscript 3]O[subscript 4] (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10–250 Å) Co[subscript 3]O[subscript 4] films grown by molecular beam epitaxy in the polar (110) direction on MgAl[subscript 2]O[subscript 4] substrates. Reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and transmission electron microscopy measurements attest to the high quality of the as-grown films. Furthermore, we investigate the electronic structure of this material by core level and valence band x-ray photoelectron spectroscopy, and first-principles density functional theory calculations. Ellipsometry reveals a direct band gap of 0.75 eV and other interband transitions at higher energies. A valence band offset of 3.2 eV is measured for the Co[subscript 3]O[subscript 4]/MgAl[subscript 2]O[subscript 4] heterostructure. Magnetic measurements show the signature of antiferromagnetic ordering at 49 K. FTIR ellipsometry finds three infrared-active phonons between 300 and 700 cm[superscript −1].Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. along with the following message: The following article appeared in 115, 24 (2014) and may be found at http://dx.doi.org/10.1063/1.488504