Influence of nitrogen and temperature on the deposition of tetrahedrally bonded amorphous carbon

The effect of nitrogen addition on the properties of tetrahedral amorphous carbon (ta-C) has been studied. The ta-C is deposited by a filtered cathodi c vacuum arc. The effect of introducing nitrogen on its plasma was measured by a retarding field analyzer and optical emission spectroscopy. The ta-C: N films were studied as a function of nitrogen content, ion energy, and dep osition temperature. The incorporation of nitrogen was measured over the ra nge of 10(-2)-10 at. % by secondary ion mass spectrometry and elastic recoi l detection analysis. The N content was found to vary slightly sublinearly with the N-2 partial pressure during deposition. A doping regime was found for N contents of up to 0.4 at. %, in which the conductivity changes while the sp(3) content and the optical band gap remain constant. For 0.4%-8% N, the sp(3) fraction remains above 80% but the optical gap closes due to a cl ustering of sp(2) sites. Only above about 10% N, the sp(3) fraction falls. The influence of nitrogen on the a-C was found to be independent of ion ene rgies between 20 and 220 eV. Deposition above 200 degrees C causes a sudden loss of sp(3) bonding. Raman and optical gap data show however that existi ng sp(2) sites begin to cluster below this temperature. (C) 2000 American I nstitute of Physics. [S0021-8979(00)00614-9].