DIAMOND-LIKE HYDROGENATED AMORPHOUS-CARBON FILMS STUDIED BY X-RAY-EMISSION SPECTROSCOPY

The occupied electronic states of diamond-like hydrogenated carbon (a- C:H) were studied by X-ray emission spectroscopy. We measured (i) the C K emission bands and (ii) the optical band gaps obtained from transm ission measurements via the Tauc correlation. For comparison we also m easured the C K emission bands of diamond, graphite, some samples of a morphous carbon (a-C) and fullerene C-60. In addition ab initio calcul ations of the C K-emission bands of diamond (sp(3) tetrahedral C-C-4 b onds) and graphite (sp(2) planar C-C-3 + p(z) bonds) were performed. E xcellent agreement was found between the measured and calculated spect ra, thus enabling us to identify all observed features and to understa nd their origin. Additionally we observed that the relative intensitie s of shoulders in the C K-emission bands at 281.3 eV formed by p(z)-li ke electrons (pi states in graphite) correlate with the widths of the optical band gaps. (C) 1997 Elsevier Science S.A.