Optical investigations and Raman scattering characterisation of carbon bonding in hard amorphous hydrogenated carbon films

Hydrogenated amorphous carbon films were prepared by plasma enhanced chemic al vapour deposition (PECVD) of methane-argon (5%) gas mixtures at low pres sure, in a dual electron cyclotron resonance (ECR)-rf glow discharge. Optic al transmission spectroscopy, Raman spectroscopy, elastic recoil detection analysis (ERDA) and infra-red (IR) absorption spectra were combined to exam ine the relationship between the local microstructure (C-H and C-C bonds) a nd the optical properties at different negative bias voltage. The amount of bonded H, obtained by IR spectra, is higher in series deposited at low bia s voltage, in qualitative agreement with the ERDA results. In ah cases, mos t of the incorporated H is bonded to sp(3)C sites, with a predominance of C H3 methyl groups. These results are also consistent with the Raman spectros copy measurements. The positions, widths, and relative intensities of the t wo characteristic features, the D and G peaks are found to vary systematica lly with deposition conditions and film properties. The series prepared at high bias voltage shows a higher disorder (D) over the graphitic (G) band r atio, which also indicates a structure with a high disorder form of Csp(2) sites. (C) 2001 Elsevier Science B.V. All rights reserved.