SURFACE CHARACTERIZATION OF DIAMOND-LIKE AMORPHOUS-CARBON FOILS BY (E,2E) SPECTROSCOPY AND TRANSMISSION ELECTRON-ENERGY-LOSS SPECTROSCOPY

We have measured the spectral momentum densities of thin foils of diamond-like carbon using (e,2e) spectroscopy. Transmission electron energy loss spectra and (e,2e) spectra were measured before and after annealing a thin foil at around 900 degrees C and before and after thinning the foil using reactive ion etching in an argon-oxygen plasma. The valence band spectral momentum densities are compared with spherically averaged graphite and diamond band theory calculations. After annealing the surface sensitive (e,2e) data are closer to the graphite theory for the foil. Before annealing and also after plasma etching the (e,2e) data compare more favourably with the diamond theory. Bulk-sensitive transmission energy loss spectra for the annealed sample show a weak graphitic plasmon at around 6 eV energy loss which disappears after subsequent plasma etching. These measurements show that the diamond-like carbon films become graphitic only at the surface after annealing and that the graphitic surface layer can be easily removed by reactive ion etching.