Near edge x-ray absorption fine structure of thermally annealed amorphous nitrogenated carbon films

Abstract

The change of structure of tetrahedral amorphous carbon (ta-C) films after nitrogen incorporation, particularly at a high concentration, was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy and it was found to be very close to pyridine. The π* peak at the N K (nitrogen K) edge was decomposed into three components corresponding to different resonances. From a detailed analysis of N K edge by NEXAFS spectroscopy it was revealed that as the nitrogen concentration in the films increases, the σ*/π* intensity ratio decreases, indicating that there is an increase of the amount of C=N relative to the C–N bonds. By thermal annealing at different temperatures, up to 800 °C, the nitrogen concentration in the films is reduced. Intensity as well as the position of the π* peak at the C K edge changed with annealing temperature. At the same time, a decrease of the intensity of the π* peak at the N K edge and a very interesting change of the relative intensities of the three split components of this π* peak have been observed. The possible changes of structure of nitrogenated carbon films by annealing and thermal stability of the films have been thoroughly emphasized.