Bonding regimes of nitrogen in amorphous carbon

Nitrogen can have numerous effects on diamond-like carbon: it can dope, it can form the hypothetical superhard compound C3N4, or it can create fullere ne-like bonding structures. We studied amorphous carbon nitrogen films depo sited by a filtered cathodic vacuum are as a function of nitrogen content, ion energy and deposition temperature. The incorporation of nitrogen from 1 0(-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 abou t 0.4% N, the conductivity changes while the sp(3) content and optical gap remain constant. From 0.4 to similar to 10% N, existing sp(2) sites condens e into clusters and reduce the band gap. Nitrogen contents over 10% change the bonding from mainly sp3 to mainly sp2. Ion energies between 20 and 250 eV do not greatly modify this behaviour. Deposition at higher temperatures causes a sudden loss of sp3 bonding above about 150 degrees C. Raman spectr oscopy and optical gap data show that existing sp2 sites begin to cluster b elow 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%. (C) 2000 Elsevier Science S.A. All rights reserved.