Abstract
The evolution of $s{p}^{2}$ hybrids in amorphous carbon (a-C) films deposited at different substrate temperatures was studied experimentally and theoretically. The bonding structure of a-C films prepared by filtered cathodic vacuum arc was assessed by the combination of visible Raman spectroscopy, x-ray absorption, and spectroscopic ellipsometry, while a-C structures were generated by molecular-dynamics deposition simulations with the Brenner interatomic potential to determine theoretical $s{p}^{2}$ site distributions. The experimental results show a transition from tetrahedral a-C (ta-C) to $s{p}^{2}$-rich structures at $\ensuremath{\sim}500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The $s{p}^{2}$ hybrids are mainly arranged in chains or pairs whereas graphitic structures are only promoted for $s{p}^{2}$ fractions above 80%. The theoretical analysis confirms the preferred pairing of isolated $s{p}^{2}$ sites in ta-C, the coalescence of $s{p}^{2}$ clusters for medium $s{p}^{2}$ fractions, and the pronounced formation of rings for $s{p}^{2}$ fractions $>80%$. However, the dominance of sixfold rings is not reproduced theoretically, probably related to the functional form of the interatomic potential used.
Published Version
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