HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY - A NEW PROBE OF SUBGAP ABSORPTION IN AMORPHOUS SOLIDS

The use of high resolution electron energy spectroscopy (HREELS) as a new method for studies of subgap absorption in thin films of amorphous semiconductors is demonstrated. For a-Si films, the alpha(omega) valu es extracted from the measured loss spectra are in quantitative agreem ent with previous optical measurements. The method is also applied to both threefold and diamond-like amorphous carbon films, yielding alpha (omega) down to considerably lower energies (similar to 50 meV) than p reviously reported. The HREELS method is shown to be complementary to existing techniques in that it can access the regime of low energies a nd ultrathin films which is difficult to investigate with the conventi onal methods. (C) 1996 American Institute of Physics.