Previous photoelectron spectroscopy studies of
CrO2
have found either no density of states or a very low density of states at the Fermi level, suggesting
that CrO2
is a semiconductor or a semi-metal. This is in contradiction to calculations that predict that
CrO2 should
be a half-metallic ferromagnet. Recently, techniques have been developed to grow high-quality epitaxial
films of CrO2
on TiO2
substrates by chemical vapour deposition. We present photoelectron spectroscopy measurements of epitaxial
CrO2(110)/TiO2(110) and
CrO2(100)/TiO2(100) grown
using a CrO3
precursor. In addition, measurements of epitaxial
Cr2O3(0001)/Pt(111) films
grown by thermal evaporation of Cr in an oxygen atmosphere are presented as a reference for reduced
CrO2 films. The
measurements of the CrO2
surfaces show no emission at the Fermi level after sputtering and annealing
the surfaces in oxygen, even though our soft core photoemission data and
low-energy electron diffraction measurements provide evidence that stoichiometric
CrO2
is present. The consequence of this is that neither surface of
CrO2
is metallic. This behaviour could result from a metal to semiconductor transition at the
(110) and (100) surfaces.
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