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

摘要

Electron paramagnetic resonance (EPR) measurements have been made at X-band (≈9.5 GHz) and W-band (≈ 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 6×10{sup}15 cm{sup}(-2) B{sup}+ or 2×10{sup}16 cm{sup}(-2) B{sup}+ 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.