Spectroscopic studies of nitrogenated amorphous carbon films prepared by ion beam sputtering

Spectroscopic analysis of the unhydrogenated amorphous carbon nitride (a-CN _x) films, prepared by ion beam sputtering, was done by ellipsometry, Raman scattering and x-ray photoelectron spectroscopic (XPS) studies. The optical gap of the films was estimated from the Tauc's analysis of the (n,k) data obtained from spectroscopic ellipsometry. In addition to the commonly observed D and G bands at ∼1350 cm ^-1 and 1550 cm ^-1, respectively, we detected a separate band at ∼1450 cm ^-1 in the Raman spectrum of a-CN _x films. This intermediate peak was unambiguously identified as the N band arising out of the nitrogen-nitrogen bonding, due to the incorporation of nitrogen in the a-C network. High resolution XPS C 1s and N 1s peaks were used to estimate the nitrogen content in the films and various bonding configurations were identified from their Gaussian deconvolution. An increase in the intensity ratio of CN and CC components, I(CN)/I(CC), in the C 1s spectra signified increasing nitrogenation of the carbon network. Deconvolution of the N 1s spectra revealed that the sp ³-hybridized CN component remained unchanged at ∼40%, however, the sp ¹-hybridized CN component increased in intensity when the nitrogen content in the network increased systematically. Increasing nitrogenation led to the graphitization of the network and resulted in a gradual decrease in the optical gap, along with simultaneous increase in the I _D/I _G and I _N/I _G intensity ratios in the Raman band.