Core ionization energies of carbon-nitrogen molecules and solids

摘要

Core ionization energies have been calculated for various carbon-nitrogen molecules and solids. The systems investigated contain many of the bonding possibilities which presumably arise in carbon nitride thin films prepared under varying conditions. The molecular core ionization energies are calculated by the #DELTA#SCF self-consistent field method. Several singly, doubly, and triply bonded C_xN_yH_z species have been considered. Core ionization energies of two C_(11)N_4 C sp~2 and C sp~3 solids have been calculated with the full-potential linearized augmented plane wave method. Molecular C 1s binding energies increase with approximately 1 eV for each singly or doubly bonded nitrogen atom attached. The trend is similar in the solids although variations and saturation effects are obtained due to hybridization and nitrogen content. The 1s binding energies of two-coordinated nitrogen atoms in C sp~2 molecules and of pyramidal three-coordinated nitrogen atoms in C sp~3 molecules are close to each other. The differences depend on the size of the systems and the number of CH_3 groups attached. In the solid state compounds, where no CH_3 groups are present, the energies of two-coordinated nitrogen in a C sp~2 environment are always lower than the energy of pyramidal three-coordinated nitrogen in the C sp~3 solid, by more than 1 eV. Concerning the micro structure in thin CN_x films, comparisons of the computational results with experiment indicate that at low nitrogen concentrations the atomic configuration close to the N atoms are mostly of sp~3 character. At higher N contents more two-coordinated nitrogen atoms are incorporated. The N 1s binding energy shifts observed at high substrate temperatures could be explained by either a gradual formation of three-coordinated N atoms in a graphitic-like C sp~2 environment or by local domains containing high N concentrations.