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Title: Epitaxy of polar semiconductor Co{sub 3}O{sub 4} (110): Growth, structure, and characterization

The (110) plane of Co{sub 3}O{sub 4} spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co{sup 3+} species at the surface. However, experimental studies of Co{sub 3}O{sub 4} (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10–250 Å) Co{sub 3}O{sub 4} films grown by molecular beam epitaxy in the polar (110) direction on MgAl{sub 2}O{sub 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{sub 3}O{sub 4}/MgAl{sub 2}O{sub 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{sup −1}.
Authors:
; ; ;  [1] ; ;  [2] ; ; ;  [3] ; ;  [4]
  1. Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)
  2. Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)
  3. Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003 (United States)
  4. Materials Science and Engineering Program/Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States)
Publication Date:
OSTI Identifier:
22304489
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 24; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANTIFERROMAGNETISM; ATOMIC FORCE MICROSCOPY; CARBON MONOXIDE; COBALT OXIDES; CRYSTAL STRUCTURE; DENSITY FUNCTIONAL METHOD; ELECTRON DIFFRACTION; ELECTRONIC STRUCTURE; ELLIPSOMETRY; ENERGY-LEVEL TRANSITIONS; FILMS; FOURIER TRANSFORM SPECTROMETERS; INTERFACES; MOLECULAR BEAM EPITAXY; SEMICONDUCTOR MATERIALS; SUBSTRATES; SURFACES; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; X-RAY PHOTOELECTRON SPECTROSCOPY