Carbon and nitrogen 1s energy levels in amorphous carbon nitride systems: XPS interpretation using first-principles

A series of carbon nitride structures have been generated, by using a classical potential in a Metropolis Monte Carlo liquid quench procedure. The resulting structures are relaxed further using the density functional theory approach. Structures are generated with various mass densities and varying N/C ratios. X-ray photoelectron spectroscopy (XPS) calculations within the first-principles methodology are performed on the generated amorphous carbon nitride systems. Depending on the carbon bonding configuration, the carbon 1s energies are found to vary from 283 to 288 eV while those of nitrogen are found to range from 397 to 405 eV. Additional calculations on model crystalline systems like nitrogen substituted graphite (nitrogen in trigonal structure) and nitrogen substituted diamond support the finding that the C and N 1s energies are not only sensitive to the coordination number of the atom but also to the interatomic distances. Our calculations based on computer generated structures are a viable alternative for the analysis of XPS spectra and support the interpretation of the N 1s energy at 398.4 eV to correspond to two-coordinated N with at least one sp2 C nearest neighbor.