An EPR study at X- and W-band of defects in a-C:H films in the temperature range 5-300 K

Electron paramagnetic resonance (EPR) measurements have been made at X-band (approximate to 9.5 GHz) and W-band (approximate to 95 GHz) of a-C:H films on (1 0 0) silicon substrates; the sample temperature was varied in the range 5-300 K. Two types of film were examined. The first type are amorphous hydrogenated carbon (a-C:H) films grown by plasma enhanced chemical vapour deposition (PECVD) with negative self bias voltages in the approximate range 100-500 V. The second type were initially highly polymeric-like a-C:H films grown on Si placed on the earthed electrode of a PECVD system but were subsequently implanted with either 6 X 10(15) cm(-2) B+ or 2 X 10(16) cm(-2) B+ ions. At both X- and W-band and throughout the temperature range 5-300 K the EPR signal of the carbon unpaired electrons consists of a single symmetric line with g = 2.0026 +/- 0.0002. As the temperature is lowered, several samples develop a dependence on sample orientation of the external field required for resonance. This anisotropy is explained in terms of the demagnetising fields more usually encountered in ferromagnetic resonance. (C) 2003 Elsevier Science B.V. All rights reserved.