Raman-scattering diagnostics of the structure of hydrogenated amorphous diamond-like carbon films

Abstract

Hydrogenated amorphous diamond-like carbon (DLC) films produced by RF-glow discharge deposition from hydrocarbon mixtures in a parallel diode-type plasma reactor were investigated. The DLC films were obtained at various gas mixture compositions and bias voltages (Vb). Raman spectra of DLC films in the range 1000 - 1800 cm -1 were analyzed. Our results are given in terms of I(D)/I(G) intensity ratio, bands position, and width (FWHM) as a function of bias voltage and gas mixture. The analysis of Raman spectra shows that bias voltage value is critical for the DLC films structure. The increase of Vb from -200 V to -700 V results in the essential high-frequency shift of G- and D-bands and change of their intensities ratio I(D)/I(G) from 0.64 (Vb equals 200 V) to 3.2 (Vb equals 700 V). Similar high-frequency shift, change of FWHM and I(D)/I(G) intensities ratio were observed at the variation of methane concentration in gas mixture composition from 100 to 20%.