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

Abstract

This work investigates the CK-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 CK-edge NEXAFS spectra indicate that the sp2∕sp3 hybridization ratio increases with the amount of tetramethylsilane vapor precursor introduced during deposition. This suggests that Si addition enhances sp2- and reduces sp3-bonding configurations. The increase in sp2 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 significant dopant-induced local ordering in πCC* and σC–H* orbitals. In contrast to the highly oriented pyrolytic graphite, the πCC* orbitals lie parallel to the surface.