Angle-resolved Ultra-violet Photoelectron Spectroscopy Study of Epitaxial CrO$_{2}$ films grown on TiO$_{2}$ Substrates

Chromium dioxide is predicted to be a half-metallic oxide. Although there is experimental evidence that CrO$_{2}$ is half-metallic at low temperature, attempts to make devices based on CrO$_{2}$ have yielded very low efficiencies. To study the electronic properties of the surface region of CrO$_{2}$, we have performed ARUPS measurements on epitaxial CrO$_{2}$ films. The CrO$_{2}$ thin films have been deposited on (100) and (110)-oriented TiO2 substrates by chemical vapor deposition, using CrO$_{3}$ as a precursor. The effects of sputtering of the CrO$_{2}$ films to remove the outer layer of Cr$_{2}$O$_{3}$ 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, which is opposite of what would be expected for a half-metallic system. Annealing of the films above 450 $^{o}$C results in spectra similar to Cr$_{2}$O$_{3}$.