Electronic structure studies of undoped and nitrogen-doped tetrahedral amorphous carbon using high-resolution electron energy-loss spectroscopy

The electronic structure of undoped and nitrogen-doped tetrahedral amorphou s carbon (ta-C) has been studied using high-resolution electron energy-loss spectroscopy in transmission to determine the local bonding of the carbon and nitrogen atoms. We found that the carbon and nitrogen atoms are mainly sp(3)-bonded for nitrogen contents up to 10 at. %. However, the data analys is is also consistent with some N atoms occupying trivalent sigma or pyrrol e configurations. The real (epsilon (1)) and imaginary parts (epsilon (2)) of the dielectric function were derived over a wide energy range carrying o ut a Kramers-Kronig analysis of the loss spectra. The epsilon (2) spectra s how two features due to the excitation of the pi and sigma valence states. The pi feature is very small in ta-C deposited at 100 eV, consistent with i ts large sp(3) content (similar to 85%). We have determined the ratios of s p(2)/sp(3)-hybridized atoms in the samples by both the C 1s edge and the op tical sum rules. (C) 2001 American Institute of Physics.