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

• Published in: Journal of applied physics 2014-06, Vol.115 (24)
• Main Authors: Kormondy, Kristy J., Posadas, Agham B., Slepko, Alexander, Dhamdhere, Ajit, Smith, David J., Mitchell, Khadijih N., Willett-Gies, Travis I., Zollner, Stefan, Marshall, Luke G., Zhou, Jianshi, Demkov, Alexander A.
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Applied physics; Atomic force microscopy; Carbon monoxide; charge transport; Cobalt oxides; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; defects; Density functional theory; Electron diffraction; Electronic structure; Electrons; Ellipsometry; energy storage (including batteries and capacitors); Energy transmission; Epitaxial growth; First principles; Heterostructures; Infrared signatures; Magnetic measurement; materials and chemistry by design; MATERIALS SCIENCE; Microscopy; Molecular beam epitaxy; Phonons; solar (photovoltaic); Structural analysis; Substrates; synthesis (novel materials); synthesis (self-assembly); Thin films; Transmission electron microscopy; Valence band; X ray spectra; X-ray diffraction
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4885048

The (110) plane of Co3O4 spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co3+ species at the surface. However, experimental studies of Co3O4 (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10–250 Å) Co3O4 films grown by molecular beam epitaxy in the polar (110) direction on MgAl2O4 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 Co3O4/MgAl2O4 heterostructure. Magnetic measurements show the signature of antiferromagnetic ordering at 49 K. FTIR ellipsometry finds three infrared-active phonons between 300 and 700 cm−1.