Properties of Diamondlike Carbon and Nitrogen Containing Diamondlike Carbon Films.

Diamondlike carbon and nitrogen containing diamondlike carbon films were made from a dual ion beam system and an RF plasma discharge deposition system. Non-hydrogenated carbon films (a-C and a-C:N) were made using nitrogen and argon ion beam sputtering of a graphite target in an ion beam system. Hydrogenated diamondlike carbon (a-C:H) and nitrogen containing diamondlike films were made from methane with and without the addition of Ar and nitrogen at various ion energies. As-deposited films were characterized using optical absorption, Raman spectroscopy, Rutherford backscattering and elastic recoil detection spectroscopies. The films made from mixtures of argon and methane have a decreasing optical band gap, an increasing tail absorption and no obvious band edge shift. a-C:N and a -C:N:H films have a downward shift in band edge absorption and a decreasing optical gap tail absorption. The decreasing gap and tail absorption and the shift of the band edge absorption suggest a possible formation of C-N, C=N, C equivN, and N-H bonds. The absorption at 500 nm has a nonlinear relationship with hydrogen content, regardless of the deposition conditions. A slight modification of a model proposed by Bloomer and Forouhi is used to fit the optical absorption k spectra. The deconvoluted k spectra and the fitted parameters of a-C:N and a-C:N:H films show a downward shift of the band edge absorption. Plasma diagnosis was performed to better understand the formation mechanisms. Nitrogen in methane and argon in methane plasmas were observed to be different from a plasma of pure methane. The nitrogen -methane plasma contains nitrogen-related radicals and ions to form films. A decreasing optical gap with an increasing nitrogen to methane ratio is observed in the films made in an RF deposition system. The films were also characterized by Raman spectroscopy. The deconvoluted Raman parameters were correlated with the composition and feedstock parameters. The a-C:H films have a D band position at about 1330 cm^ {-1}, a G band at about 1530 cm ^{-1} and a low I(D)/I(G) ratio. The a-C:N:H films have upward shifts of the D band and G band positions to 1380 and 1560 cm^{-1}, respectively. The I(D)/I(G) ratios of a-C:N and a-C:N:H films are larger than the ratios found for a-C:H and a-C films. Structures of the a-C:H and a-C:N:H films are suggested based on the changes of the Raman parameters. Carbon and hydrogen contents of the films are found to have a linear relationship in nitrogen containing DLC films.