THERMALLY-INDUCED STRUCTURAL-CHANGES IN AMORPHOUS-CARBON FILMS OBSERVED WITH ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY

We used the characteristic changes in the electronic structure of the valence band of amorphous carbon films upon the formation of graphitic clusters to monitor the temperature induced graphitization of a varie ty of hydrogen-containing (a-C:H) as well as hydrogen-free (a-C) films . The valence band spectra of the films. which were prepared in situ b y ion-beam deposition and electron beam evaporation, were determined u sing photoelectron spectroscopy with excitation energies in the ultrav iolet regime (ultraviolet photoemission spectroscopy, HeI, hv = 21.22 eV and HeII, hv = 40.82 eV). By choosing a variety of deposition param eters we are able to illustrate that the extent of temperature induced structural changes is on one hand determined by the bulk and surface diffusion coefficients of carbon atoms, and on the other hand by the i on irradiation which inhibits the graphitization process. (C) 1997 Ame rican Institute of Physics.