Electronic structure of CuCrO2 thin films grown on Al2O3(001) by oxygen plasma assisted molecular beam epitaxy

Thin films of CuCrO2 have been grown on Al2O3(001) substrates by oxygen plasma assisted molecular beam epitaxy. With a substrate temperature of 700 degrees C or 750 degrees C, the films showed an unanticipated (015) orientation but at a higher substrate temperature of 800 degrees C the expected basal (001) orientation predominates. The optical absorption spectrum of CuCrO2 shows a direct allowed absorption onset at 3.18 eV together with a weak peak at 2.0 eV which is suppressed by Sn doping. This suggests that the low energy peak should be attributed to 3d -> 3d excitations associated with Cu2+ defect states rather than excitations localised on Cr3+. Valence band X-ray photoemission spectra of (001) and (015) oriented CuCrO2 are compared with those obtained from polycrystalline samples. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768726]