AN EPR STUDY OF DEFECTS IN HYDROGENATED AMORPHOUS-CARBON THIN-FILMS

The defect states, with unpaired spins, in hydrogenated amorphous carb on (a-C:H) films have been studied using electron paramagnetic resonan ce (EPR). These EPR measurements were made at room temperature at abou t 9.9 GHz. The a-C:H thin films were deposited using plasma enhanced c hemical vapour deposition (PECVD), firstly for various negative self-b ias voltages at constant pressure, and secondly with various nitrogen contents at constant bias. Changing the self bias from -50 to -540 vol ts leads to a reduction in linewidth from approx. 1.4 to 0.3 mTesla al though the g-value of the single Lorentzian line is unchanged at g = 2 .0025 +/- 0.0002. Increasing the atomic nitrogen content from zero to 15% causes the g-value of the single line to shift from 2.0025 +/- 0.0 002 to 2.0033 +/- 0.0003, while the linewidth and spin populations bot h decrease. The effect on these defects of postannealing the films is also reported. (C) 1998 Elsevier Science S.A.