PHOTOELECTRON-SPECTROSCOPY OF ION-IRRADIATED B-DOPED CVD DIAMOND SURFACES

Chemical vapour deposition (CVD) diamond films were irradiated by 1 ke V argon ions at room temperature with doses ranging from 3.6 x 10(12) to 1.1 x 10(16) Ar+ cm(2). The influence of sputtering on the valence band density of states of a boron-doped CVD diamond film was investiga ted by ultraviolet photoelectron spectroscopy and the changes in the p lasmon features were observed by X-ray photoelectron spectroscopy of t he carbon Is core level and its loss region. A gradual change from typ ical diamond features to amorphous carbon was observed after prolonged bombardment times. Above a critical dose D-crit of 5.8 x 10(14) Ar+ c m(2) the damaged surface layer is characterized by a splitting of the C 1s bulk peak into two components: a bulk-like diamond peak at 285.3 eV binding energy and a defect peak with 1 eV lower binding energy, wh ich is attributed to the production of an amorphous sp(2)-rich carbon matrix. Moreover additional occupied states in the range of 0-4 eV bin ding energy, completely different to those observed on reconstructed d iamond surfaces, were observed in the valence band spectra of the ion- irradiated diamond surface. These filled states can also be attributed to the amorphous carbon matrix which is formed at high doses. At very low doses (<3 X 10(14) ions cm(2)) only a band bending of the C Is di amond core level peak, along with the formation of some occupied state s in the band structure at around 3.8 eV binding energy was observed. A comparison with annealed hydrogen-free CVD diamond surfaces shows so me similarities concerning these filled states. The obtained spectra a re compared with other crystalline and amorphous forms of carbon and t he results are discussed in terms of an irradiation-induced change in the atomic structure of the surface. A comparison of ion bombarded and annealed diamond samples clearly shows that no graphitization takes p lace in the latter case.