Optical and photoemission studies of DLC films prepared with a systematic variation of the sp3: sp2 composition

The optical and photoemission properties of hydrogen-free DLC films prepared under conditions which result in different types of carbon bonding (previously determined from electron energy loss spectroscopy) are reported. The films were prepared using a mass selected ion beam deposition system covering the C+ energy range 10 eV - 2 keV, mostly on Si held at room temperature. Previous measurements have shown that the sp3 content of these films varied from 0 to > 80 per cent. The optical constants (n, k absorption coefficient (a)) of theses films were measured by ellipsometry. The energy gaps were derived from Tauc plots (Eg) and from alpha = 10(exp4) cm(exp-1) values (E(0.4)). The enrgy gaps were found to vary with the sp3 content from E < 1 eV (10 per cent sp3) up to E = 2,4 eV (85 per cent sp3). The photoemission absolute quantum efficiencies of these films were independently measured in the UV region using a monochromator system and were compared to those of CVD diamond films and grap hite.