An EPR study of defects in hydrogenated amorphous carbon thin films

摘要

The defect states, with unpaired spins, in hydrogenated amorphous carbon (a-C:H) films have beenstudied using electron paramagnetic resonance (EPR). These EPR measurements were made atroom temperature at about 9.9 GHz. The a-C:H thin films were deposited using plasma enhancedchemical vapour deposition (PECVD), firstly for various negative self-bias voltages at constantpressure, 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-valueof the single Lorentzian line is unchanged at g = 2.0025±0.0002. Increasing the atomic nitrogencontent from zero to 15% causes the g-value of the single line to shift from 2.0025±0.0002 to2.0033 ±0.0003 while the linewidth and spin populations both decrease. The effect on these defectsof postannealing the films is also reported.