SEPARATION OF THE SP(3) AND SP(2) COMPONENTS IN THE C1S PHOTOEMISSIONSPECTRA OF AMORPHOUS-CARBON FILMS

Two different types of amorphous carbon films were deposited on Si sub strates, with film hardness of 22 GPa and 40 GPa, by pulsed laser evap oration of graphite targets. The x-ray photoemission spectra (XPS) of the Cls core level in these films shown two components at 284.3 +/- 0. 1 eV and 285.2 +/- 0.1 eV, which were identified with the sp(2) and sp (3) hybrids forms of carbon. The sp(3)/sp(2) concentration ratio deduc ed from the area of the components had a value of 2/5 for the harder a morphous carbon film and 1/4 for the softer. Upon annealing the harder film at different temperatures, the sp(3)/sp(2) ratio remained nearly constant up to about 900 K and then decreased until reaching a value of zero above 1100 K. The C Is core level shifted 0.3 +/- 0.1 eV towar d lower binding energy in the films for annealing temperatures above 9 00 K. This shift was correlated with an increase in the asymmetry of t he C Is XPS spectra and of the density of states at the Fermi level, a s observed by ultraviolet photoemission spectroscopy. There was no det ectable a plasmon in the harder films below 900 K, despite the presenc e of sp(2) atoms and pi bonds at those temperatures.