Use of Raman scattering to investigate disorder and crystallite formation in as-deposited and annealed carbon films

Abstract

Carbon films were prepared by ion-beam as well as rf-discharge deposition, and annealed at temperatures up to 950\ifmmode^\circ\else\textdegree\fi{}C. Raman spectra of these films, in the range 1000-1800 ${\mathrm{cm}}^{\ensuremath{-}1}$, were analyzed via a best fit to computer-generated line shapes, used to simulate the $D$ and $G$ lines. Our results are given in terms of the $\frac{I(D)}{I(G)}$ intensity ratio, line position, and linewidth as a function of anneal temperature. The $\frac{I(D)}{I(G)}$ ratio for the rf-discharge-deposited films shows a maximum, and there is a suggestion of similar behavior for the ion-beam-deposited films. This maximum indicates that crystallite growth is promoted by higher anneal temperatures. As suggested by comparison with theory, the down-shifted $G$ line position of 1536 ${\mathrm{cm}}^{\ensuremath{-}1}$ in the as-deposited films indicates the presence of bond-angle disorder. The similarly, down-shifted $D$ line position of \ensuremath{\sim}1283 ${\mathrm{cm}}^{\ensuremath{-}1}$ indicates that the as-deposited films may contain some fourfold-coordinated bonds as well as disorder. The shift of the $D$ and $G$ lines to asymptotes of 1353 and 1598 ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively, as anneal temperature increases, indicates that the crystallites are dominated by threefold over fourfold coordination. The linewidths of both lines decrease in width with increasing anneal temperature. This is also consistent with the removal of bond-angle disorder and the increasing dominance of crystallites as annealing proceeds to higher temperatures.