XPS study of pulsed laser deposited CNx films -: art. no. 235416

The C 1s and N 1s core levels of carbon nitrides are composed of several contributions whose assignment is controversial due to the lack of appropriate reference materials and the great variety of configurations of carbon and nitrogen. From the comparison of nitrogen-containing polymeric compounds and solid carbon references an assignment of the individual lines of the C 1s and N 1s core levels is given. Nitrogen-containing polymeric compounds are used as reference materials as they provide a more adequate account of the screening of the ionized states in the photoemission process than molecular references. This screening effect is even more pronounced in case of aromatic or cyanogen-type bonds where delocalized pi electrons strongly affect the screening of the core hole. In the second part of the paper these assignments are used to interpret the changes of the chemical environment in pulsed laser deposited carbon nitride films as a result of systematic changes in laser fluence, nitrogen pressure, and target-to-substrate distance. The effect of subsequent annealing and sputtering by argon ions is also discussed. The chemical structure of the films is dominated by nitrile, N(pyramidal)-C(trigonal) and nitrogen in sp(2) hybridization (with the electron doublet out of plane) inserted into carbon graphitic network at high laser fluence, and nitrile and pyridinic sp(2)-hybridized configurations at low laser fluence, in good line with the fact that sp(3) and sp(2) hybridization states around carbon and nitrile configuration with nitrogen, are preferred.