Influence of surface modifications on the electronic properties of CVD diamond films

The effects of different surface treatments, including ex-situ H-2 and H-2 + O-2 plasma exposure, chromic acid treatment and in-situ vacuum annealing al elevated temperatures, on the electronic properties, particularly the electron affinity of microwave plasma-grown polycrystalline diamond films, were investigated using UV photo-electron spectroscopy (UPS) and X-ray photo-electron spectroscopy (XPS), H-2 and H-2 + O-2 plasma exposure results in a negative electron affinity (NEA) for all diamond films, independent of morphology, thickness or phase purity. An additional peak in the region of low kinetic energies of the UPS spectra correlates with plasma-generated defects that art removed by in-situ vacuum annealing for several minutes at 700 degrees C. NEA is not affected by this annealing procedure. Oxidation of the diamond surface by hot chromic acid results in a positive electron affinity (PEA) that correlates with a pronounced increase in film surface resistivity and complete suppression of electron emission. NEA alone is not sufficient to ensure good electron emission properties.