Bonding regimes of nitrogen in amorphous carbon

Abstract

Abstract Nitrogen can have numerous effects on diamond-like carbon: it can dope, it can form the hypothetical superhard compound C 3 N 4 , or it can create fullerene-like bonding structures. We studied amorphous carbon nitrogen films deposited by a filtered cathodic vacuum arc as a function of nitrogen content, ion energy and deposition temperature. The incorporation of nitrogen from 10 −2 to 10 at% was measured by secondary ion mass spectrometry and elastic recoil detection analysis and was found to vary slightly sublinearly with N 2 partial pressure during deposition. In the doping regime from 0 to about 0.4% N, the conductivity changes while the sp 3 content and optical gap remain constant. From 0.4 to ∼10% N, existing sp 2 sites condense into clusters and reduce the band gap. Nitrogen contents over 10% change the bonding from mainly sp 3 to mainly sp 2 . Ion energies between 20 and 250 eV do not greatly modify this behaviour. Deposition at higher temperatures causes a sudden loss of sp 3 bonding above about 150°C. Raman spectroscopy and optical gap data show that existing sp 2 sites begin to cluster below this temperature, and the clustering continues above this temperature. This transition is found to vary only weakly with nitrogen addition, for N contents below 10%.