STRUCTURAL, ELECTRICAL AND OPTICAL-PROPERTIES OF RF-SPUTTERED A-C FILMS

Amorphous carbon (a-C) films have been sputtered onto glass substrates and characterized using several techniques: optical absorption, Raman spectroscopy and electrical conductivity. Both the optical gap and el ectrical conductivity have been found to be strongly dependent on the argon pressure, P-Ar, during the deposition. In the range 0.5-2 Pa, th e optical gap increases with P-Ar (0.5-0.9 eV) while the conductivity decreases (from 10(-2) to 2 x 10(-5) Omega-1 cm-l at room temperature) . The annealings in vacuum (10(-4) Pa) at 300 and 500 degrees C for 2 h have two significant effects: a diminution of the optical gap and a considerable increase of the electrical conductivity. A Raman spectros copy study suggests an increase of both the sp(2)/sp(3) ratio and the size of graphitic microcrystallites with annealing temperature.