Correlation of the optical gaps and Raman spectra of hydrogenated amorphous carbon films

Abstract

The Raman and infrared absorption spectra, optical gaps, and electron spin densities of amorphous carbon films deposited from hydrocarbon plasmas have been systematically studied as a function of deposition conditions and Raman probe wavelength. Although all other probes are consistent with a monotonic increase in intermediate‐range order with substrate bias voltage V_b, the optical gap decreases with increasing V_b (consistent with increasing graphitic domain size) only up to the onset of sputtering, where the gap sharply increases. We propose a simple structural model for a‐C:H which is consistent with these results and requires no sp³ bonding.