We have investigated the electron affinity of (111) and (100) single crystalline surfaces of chemical-vapor-deposited diamond with additional treatments. For specimens exposed to hydrogen plasma (H treatment), the
electron affinities are found to be negative from photoyield spectra using ultraviolet synchrotron radiation light,
because the threshold energies of photoyield from these specimens are located at an energy of h ?< 5.5 eV, which
is the indirect band-gap energy of diamond. The threshold energies of photoyield from surfaces annealed in oxygen
atmosphere at 500?C are higher than those from H-treated surfaces. This can be explained in terms of an increase
of work function of the oxygen-adsorbed surfaces.
A remarkable ambient effect on the resistance of CVD diamond during cooling after deposition has been observed. The diamond films that were cooled slowly down to room temperature (RT) in the 10-3 Torr range after deposition showed relatively low resistances in the range of 106∼107 Ω. On the other hand, high resistances over 1013 Ω were observed for diamond films that were cooled down to RT in an oxygen or an air ambient and at atmospheric pressure. Among these surfaces a substantial difference was observed in the electronic structure as studied by electron energy loss spectroscopy.
Diffusion of oxygen atoms into diamond can be introduced by CrO3 treatment followed by an exposure to a hydrogen plasma. From characterization using Rutherford backscattering spectrometry, it is found that the depth distribution of the doped oxygen in the diamond is homogeneous from the surface where its concentration is about 1020 atoms/cm3. The doped oxygen can form cathodoluminescence centers yielding luminescence peaks at 3.75 and 4.64 eV at room temperature. After the diffusion of oxygen atoms, damages in the diamond cannot be detected by Raman scattering spectroscopy.
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