Investigation of local ordering and electronic structure in Si- and hydrogen-doped tetrahedral amorphous carbon thin films

This work investigates the C K-edge near-edge x-ray absorption fine structure (NEXAFS) and x-ray reflectivity spectra of Si- and hydrogen-incorporated tetrahedral amorphous carbon (ta-C:Si:H) films. The C K-edge NEXAFS spectra indicate that the sp(2)/sp(3) hybridization ratio increases with the amount of tetramethylsilane vapor precursor introduced during deposition. This suggests that Si addition enhances sp(2)- and reduces sp(3)-bonding configurations. The increase in sp(2) sites correlates well with the decrease in hardness, mass density, and thermal stability. The comparison of angle-dependent NEXAFS spectra of nondoped and Si-doped ta-C films at the K edge reveals significantdopant-induced local ordering in pi(C = C)(*) and sigma(C-H)(*) orbitals. In contrast to the highly oriented pyrolytic graphite, the pi(C = C)(*) orbitals lie parallel to the surface. (c) 2005 American Institute of Physics.