STRUCTURAL-CHANGES IN DIAMOND AND AMORPHOUS-CARBON INDUCED BY LOW-ENERGY ION IRRADIATION

In the present work we describe an investigation of the influence of l ow-energy ion irradiation (1-keV Ar+) on the surface structure of poly crystalline diamond and amorphous carbon films with various degrees of graphitization. Photoelectron spectroscopy (PES) with excitation ener gies in the ultraviolet and x-ray regime is employed to monitor the ra diation-induced modification of the electronic structure of the surfac e which is closely linked to the local bonding environment of the carb on atoms.;A comparison of the mean photoelectron escape depth and the thickness of the irradiation affected layer also illustrates the suita bility of PES for this investigation. For the chemical vapor depositio n (CVD)-diamond film a gradual change from typical diamond features to amorphous carbon is observed for ion doses surpassing 6x10(14) cm(-2) . The structural changes in the diamond lattice are expressed in a bro adening of the C Is core-level peak, and increasing contributions from p-pi states around 3-4 eV in the valence-band spectra. Likewise the p eak located at 13 eV (He II, h nu=40.82 eV), characteristic of diamond , is no longer apparent for ion doses exceeding 3x10(15) cm(-2). The d iamond surface clearly shows a tendency to amorphize rather than graph itize under ion irradiation. To complement the results for the diamond film, we irradiated two amorphous carbon films with different microst ructures: (A) a predominantly amorphous film, and (B) a film with grap hitic inclusions. The destruction of graphitic structures in film (B) is apparent even for the lowest ion dose (1.5x10(14) cm(-2)), and expr essed in an increase in the width of the C Is core-level peak and a sm earing out of the valence-band spectral features. The resultant valenc e-band and core-level spectra (total ion dose: 3x10(15) cm(-2)) are ve ry similar to the one obtained for the amorphous film (A), which, on t he other hand, does not show any significant changes in its structure upon irradiation. The irradiation of both diamond and graphitic struct ures with low-energy Arf ions leads to the formation of a predominantl y amorphous surface layer.