Surface and Coatings Technology, 65 ( 1994) 37-39 Hydrogen effect on atomic structure of ion-irradiated carbon L. Calcagno, G. Compagnini and G. Foti Dipartimento di Fisica del/‘Uniuersitci, Corso Italia 57. 195129 Catania (Italy) Abstract The structure of ion-irradiated hydrogenated amorphous carbon has been investigated by electron and optical spectroscopies. Trigonal and tetragonal carbon bond fractions are the crucial physical parameters for the final atomic configuration. The trigonal clusters are found to control the electronic properties as is well predicted by molecular simulation for amorphous carbon. 37 1. Introduction Hydrogenated amorphous carbon (a-C:H) exhibits very diverse properties such as resistent coating, optical transparency in the IR range, high hardness and inert- ness against chemical agents. Various experimental pro- cedures have been adopted to synthesize a-C:H films such as plasma chemical vapour deposition of hydro- carbons, sputtering of graphite in a hydrogen atmo- sphere or high energy irradiation of polymeric films [l-4]. Two chemical states are possible for carbon atoms: electron bonds associated with pairs of sp2 (trigonal) carbon sites or 0 electron bonds formed between atoms of either sp2 or sp3 tetrahedral hybridization. The wide variety in the physical and chemical behaviours of a-C:H films appears to arise from the complex structure of the sp3 and sp2 carbon site configuration. The- amount of hydrogen (X,=5%-35%) in a-C:H modifies the optical gap (0.5-1.5 eV), and the film hard- ness (20-100 GPa), both correlated to the sp3 to sp2 ratio [S]. In this paper we give an overview of the effect of hydrogen on the atomic configuration in high energy ion-irradiated carbon. The structural properties of amor- phous carbon (a-C) and a-C:H films are investigated by photon and electron spectroscopies. to measure the relative densities of 7~ and c electrons. From the electron densities it is possible to obtain the fraction of sp2 or sp3 carbon sites, through the relation- ship IA7 3 CSP21 (la/ls)graphite = 4 - CsP21 The trigonal component increases very quickly with the ion lluence and reaches the value of 80% for an ion fluence of 2.2 x 1Ol5 ions cme2. A quite different trend is observed for ion-irradiated graphite (pure trigonal bonds) where the sp2 site component shows only a small decrease (see Fig. l(b)) for an argon beam at 3 x 10ls cmm2 fluence. The full set of experimental data 1 2. Ion-irradiated amorphous carbon Major changes in the structure of diamond (pure tetrahedral bonds) films are observed after 0.5 keV argon beam irradiation as shown in Fig. l(a), where the electron energy loss spectra are reported as a function of ion fluence. Electron energy loss spectroscopy analysis in the high energy loss region (i.e. C 1s edge), allows one w Energy Loss(eV) Fig. 1. Electron energy loss spectra of (a) diamond and (b) crystalline graphite before and after irradiation with a 0.5 keV Ar beam (au., arbitrary units). 0257~8972/94/!§7.00 SSDI 0257-8972(94107064-X 0 1994 - Elsevier Science S.A. All rights reserved