An EPR study of defects in hydrogenated amorphous carbon thin films

The defect states, with unpaired spins, in hydrogenated amorphous carbon (a-C:H) films have been studied using electron paramagnetic resonance (EPR). These EPR measurements were made at room temperature at about 9.9 GHz. The a-C:H thin films were deposited using plasma enhanced chemical vapour deposition (PECVD), firstly for various negative self-bias voltages at constant pressure, and secondly with various nitrogen contents at constant bias. Changing the self bias from -50 to -540 volts leads to a reduction in linewidth from approx. 1.4 to 0.3 mTesla although 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 +/- 0.0002 to 2.0033 +/- 0.0003, while the linewidth and spin populations both decrease. The effect on these defects of postannealing the films is also reported. (C) 1998 Elsevier Science S.A.