A Study of the Chemical Bonding and Microstructure of Ion Beam-deposited CNxFilms Including an XPS C 1s Peak Simulation

The chemical bonding and microstructure of dual ion beam-deposited CNx films with nitrogen contents in the range 20–33 at.% have been examined by Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The FTIR spectra together with other published data have been used to construct a model microstructure of the CNx films. The XPS N 1s peak is composed of two components corresponding to N–sp2 C and N–sp3 C bonds. Using the quantified N 1s data and making certain assumptions, the model microstructure has been used as the basis of a C 1s peak simulation in which nine C components have been combined. At an N content of 20 at.% the simulation agrees well with the experimentally recorded XPS C 1s peak. The FTIR spectra, XPS N 1s peak shape and C 1s peak simulations support a microstructure of N substitution into an amorphous sp2/sp3 hybridized carbon structure. Above an N content of ∽20%, a new (nitrile-like) chemical form also emerges in the material, its abundance increasing with N content. It is proposed that this new structure occurs due to the presence, in the surface region of the condensing film, of C≡N dimers, which are formed when a C atom is surrounded by many N atoms. This molecule becomes trapped in the material and bonds to atoms at neighbouring sites.