Schottky barrier height and negative electron affinity of titanium on (111) diamond

Titanium was deposited on a natural type IIb diamond surface with a (111) orientation. The titanium-diamond interface was studied with ultraviolet photoemission spectroscopy, using 21.2 eV light. Prior to deposition, the diamond was chemically cleaned, and a sharp (0.5 eV full width at half-maximum) peak was observed at the position of the conduction band, indicating a negative electron affinity surface. After a subsequent argon plasma clean this peak disappeared, while the spectrum shifted 0.5 eV towards higher energies. Upon submonolayer titanium deposition the spectrum shifted 0.5 eV down, while the negative electron affinity peak reappeared. Further titanium depositions caused this titanium induced negative electron affinity peak to be attenuated, indicating that the emission originated from the interface. By determining the relative positions of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond (111) was measured and found to be 1.0±0.2 eV. A model for the observed titanium induced negative electron affinity is proposed, based on the Schottky barrier height of titanium on diamond, and the work function of titanium.