Study of nitrogen pressure effect on the laser-deposited amorphous carbon films

The series of amorphous carbon films (a-C) deposited at a vacuum of 2x10(-3) Pa and nitrogenated amorphous carbon films (a-CN) deposited at different nitrogen pressures were grown by the pulsed laser deposition method. The influence of the molecular nitrogen pressure in the deposition chamber on the film properties was investigated. Electrical resistivity, intrinsic stress and UV-Vis transmission of the films were measured for this purpose. The optical bandgap was calculated from the absorption edge of the UV-Vis spectra. Changes of the structure, of the chemical bonding and of the stoichiometry were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy respectively. Carbon nitride formation was indicated. The promotion of the sp(2) bonding is indirectly indicated by Raman spectroscopy. A rapid enhancement of electrical resistivity of samples deposited at nitrogen pressure p(N) above 5 Pa was observed. We concluded that two contradictory effects result in non-monotonous dependence of the electrical resistivity and optical bandgap on the nitrogen pressure p(N): graphitization and carbon nitride formation. The high compressive stress decreased with increasing nitrogen pressure p(N) and it even changed to tensile stress above 5 Pa. Formation of the voids in the structure is discussed.