Radiation defects and electron disordering in proton-irradiated diamond films

The absorption spectra are studied in the region of the fundamental absorption band and its longwave boundary for the 0.6 μm thick diamond films deposited onto Al2O3 single crystal underlayers and irradiated by 100 keV and 50 keV protons at fluences of 1013-1016 cm-2. The E0β(6.10-5.9eV) and E0α(5.51-5.43eV) maxima and the exponential tails towards lower energies are resolved in the spectra of initial films. The halfwidths of the maxima and a weak temperature dependence of their parameters and of the Urbach tail slope are indicative of disordering of the film structure. The intrinsic maxima near and above the indirect absorption boundary in diamond Γ25'-Δ are identified with transitions in the disordered cubic and hexagonal phases of the diamond films. The proton irradiation stimulates the intensity redistribution of the intrinsic maxima, the absorption enhancement, and the change of the Urbach tail slope. The character of radiolysis has been found to depend on the composition of the nonirradiated carbon films and on proton fluence. (author). 8 refs.; 3 figs