Carbon nitride thin films prepared by nitrogen ion assisted pulsed laser deposition of graphite using KrF excimer laser

Carbon nitride films were prepared by nitrogen ion assisted pulsed KrF excimer laser deposition of graphite onto Si(100) substrates. The energy of nitrogen ions was changed between 25 and 1500 eV. The transport ratio of carbon atoms to nitrogen ions at the substrate was 1.0. The dependence of the stoichiometry and formed chemical bonds on the nitrogen ion energy was investigated. The nitrogen content in prepared films increased with decreasing the nitrogen ion energy, and showed a constant value of 30 at.% below 200 eV. The peak position of C1s spectra as found by X-ray photoelectron spectroscopy (XPS) analysis shifted to higher binding energy with decreasing nitrogen ion energy. The N1s XPS peak was deconvoluted into three peaks with binding energies BE = 398.3, 400.0 and 402.0 eV, which were assigned to sp³ C-N and sp² C-N and N-N bondings, respectively. The ratio of sp³ to sp² bonded nitrogen atoms increased with decreasing ion energy, and showed a maximum value in the energy interval between 50 and 75 eV. The carbon content with the sp³ C-N bond type was estimated at 12.6 at.% from electron energy loss spectroscopy (EELS) analysis. The nitrogen content with the sp³ C-N bond type was estimated at 18.0 at.% by XPS. The ratio of carbon to nitrogen atoms with sp³ bonds was found to be 1.43 in the films grown at nitrogen ion energies of 50 eV, which is close to that of C₃N₄ compound predicted as a superhard material.