Optical properties of nitrogenated tetrahedral amorphous carbon films

The chemical composition, structural, and optical properties of nitrogenated tetrahedral amorphous carbon (ta-C:N) films deposited by a pulsed filtered vacuum arc deposition system were characterized by non-Rutherford backscattering spectroscopy, Raman spectroscopy, and ultraviolet-visible spectroscopy. It was observed that the amount of nitrogen atoms incorporated into the ta-C:N films, as well as the sp(2) fraction of the films, increased with increasing nitrogen pressure P-N during deposition. As a result, the optical band gap of the ta-C:N films also decreased with increasing P-N. At a fixed nitrogen partial pressure of 4x10(-3) Pa, the nitrogen content was found to first increase with increasing substrate negative bias voltage (-U-s), up to a maximum of about 14.5 at. % at -U-s of 100 and 150 V, then decreases with further increase of -U-s. The sp(2) fraction however increased monotonically with increasing -U-s. The optical band gap of the ta-C:N films initially increased with increasing -U-s, up to a maximum at a certain -U-s, and then decreased with further increase in -U-s. The variation of the optical band gap with the negative substrate bias voltage was discussed in terms of the different sp(2)-bonded carbon configurations existing in the films and the graphitization of the ta-C:N films, as indicated by the Raman and density measurement results. (C) 2002 American Institute of Physics.