AVS 53rd International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI-TuA

Paper MI-TuA7
Angle-Resolved Photoelectron Spectroscopy Study of Epitaxial CrO@sub 2@ Films Grown on TiO@sub 2@ Substrates

Tuesday, November 14, 2006, 4:00 pm, Room 2006

Session: Magnetic Thin Films and Multilayers
Presenter: C.A. Ventrice, University of New Orleans
Authors: D.R. Borst, University of New Orleans
C.A. Ventrice, University of New Orleans
G.X. Miao, University of Alabama
A. Gupta, University of Alabama
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Chromium dioxide is predicted to be a half-metallic oxide. Although there is experimental evidence that CrO@sub 2@ is half-metallic at low temperature, attempts to make devices based on CrO@sub 2@ have yielded very low efficiencies. One possible reason for these poor device performances is a non-stoichiometric surface region, in particular the formation of Cr@sub 2@O@sub 3@. To study the electronic properties of the surface region of CrO@sub 2@, ARUPS measurements have been performed at the 3m-TGM beamline of the CAMD synchrotron on epitaxial CrO@sub 2@ films. The CrO@sub 2@ thin films have been deposited on (100) and (110)-oriented TiO@sub 2@ substrates by chemical vapor deposition. The effects of sputtering of the CrO@sub 2@ films to remove the outer non-stoichiometric layer and of annealing the films in oxygen to heal surface defects has been studied. Sputtering results in shifts in the onset of valence emission away from the Fermi edge by as much as 0.5 eV. Annealing of the films in 10@super -6@ Torr of oxygen heals the surface and shifts the onset of emission towards the Fermi level. However, none of our spectra show evidence of a true Fermi edge. From analysis of the Cr 3p to O-2s core emission ratios for epitaxial CrO@sub 2@/TiO@sub 2@ films and Cr@sub 2@O@sub 3@(0001)/Pt(111) films grown in-situ by vapor deposition of Cr in an O@sub 2@ atmosphere and the observation of the correct symmetry in our CrO@sub 2@ LEED images, we conclude that the surface region of our epitaxial CrO@sub 2@ films is primarily CrO@sub 2@, not Cr@sub 2@O@sub 3@, even after annealing to 450 °C. These results indicate that CrO@sub 2@ is actually a narrow gap semiconductor at room temperature, not a metallic oxide as previously assumed.