GAUSSIAN INTERPRETATION OF THE OPTICAL-ABSORPTION EDGE TAIL IN AMORPHOUS HYDROGENATED CARBON A-C-H

Amorphous hydrogenated carbon films of thickness from 260 to 320 nm we re obtained by glow discharge decomposition of benzene vapours under p ressure 0.05, 0.2 and 0.5 Torr. Changes introduced by annealing to tem peratures 200, 300, 350, 400, 450, 500, 550 degrees C were studied by optical absorption edge measurements. A Gaussian plot (instead of Urba ch law) was found to be useful for interpretation of the lower part of the edge (for alpha < 10(4) cm(-1)). Such a character of the optical absorption edge tail was theoretically derived from normal distributio n of sp(2)-cluster sizes. The Gaussian plot parameters E(tau), epsilon and alpha give information about the sizes, variability and number of sp(2) clusters in a-C:H.