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 amorphous 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 analysis is also consistent with some N atoms occupying trivalent sigma or pyrrole configurations. The real (epsilon (1)) and imaginary parts (epsilon (2)) of the dielectric function were derived over a wide energy range carrying out a Kramers-Kronig analysis of the loss spectra. The epsilon (2) spectra show 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 its large sp(3) content (similar to 85%). We have determined the ratios of sp(2)/sp(3)-hybridized atoms in the samples by both the C 1s edge and the optical sum rules. (C) 2001 American Institute of Physics.