The structural evolutions of a-C:H thin films prepared by r.f. plasma-enhanced chemical vapor deposition from a CH yAr or 4 CH yHe gas mixture have been investigated. Elastic recoil detection analysis, infrared and Raman spectroscopies have been used 4 to quantify, respectively, hydrogen content, the bonding and sp proportion carbon of thin films. The variations of electron spin 2 resonance parameters, the peak-to-peak linewidth DH , g-factor and the spin density, as a function of the film preparation are pp discussed on the basis of the complete physico-chemical characterization. The type of defects do not change drastically when the conditions of the film preparation vary contrary to the spin–spin interaction: a stronger exchange resulting from the greater delocalization of the p-electron occurs when the bias voltage increases. Moreover, the hyperfine interaction of the spins with the hydrogen atoms decreases. We have found that the optical band gap E of these films decreases with the loss of hydrogen g (bonded and unbonded) and the increasing of sp content while E gap increases. These results have been related to the spin densities.
