Effects of nitrogen incorporation on structure of a-C:H films deposited on polycarbonate by plasma CVD

Nitrogen-incorporated-hydrogenated amorphous carbon (a-C:H:N) films were deposited on polycarbonate (PC) substrates by r.f. plasma-enhanced chemical vapor deposition (PECVD). Effects of nitrogen incorporation on microstructure, bonding states, chemical composition, internal stresses, and friction coefficients of deposited films were investigated. The films were characterized by X-ray photoelectron microscopy, infrared microscopy (IR), Raman spectroscopy and friction tests. Results from the measurement indicate that incorporated nitrogen content has considerable effects on film properties. Raman spectra of the a-C:H:N films are broad, asymmetric and centered at around wavenumber of 1500 cm−1. Shifting of the G-peak toward the higher wavenumber, narrower bandwidth of the G-peak and an increase of the ID/IG ratio demonstrate the graphitic character of the a-C:H:N films with the further increase of the atomic fraction of nitrogen (N/C). IR spectra demonstrate nitrogen bonded to carbon and hydrogen as CN, CN, N-H and C-H bonding configurations in the a-C:H:N films. The internal stress considerably decreased as well as the friction coefficient is low when the N/C fraction increased. The surface roughness of the a-C:H:N films estimated by atomic force microscopy (AFM) seems to be less smooth with the increase in the N/C fraction.