Raman scattering from boron-substituted carbon films

Raman scattering studies of ${\mathrm{B}}_{\mathit{x}}$ ${\mathrm{C}}_{1\mathrm{-}\mathit{x}}$ films have been carried out for boron concentrations in the range 0≤x≤0.17. The spectra exhibit two broad bands, a graphitic mode (G) centered between 1535 and 1590 ${\mathrm{cm}}^{\mathrm{-}1}$ and a disorder-induced mode (D) centered between 1345 and 1370 ${\mathrm{cm}}^{\mathrm{-}1}$. The G mode is observed to soften as a result of boron substitution, and this behavior has been explained using a simple two-dimensional lattice dynamics model. As the boron concentration is increased, a decrease in the intensity of the D band is also observed. Furthermore, the variation of the intensity of the D band with x is found to be correlated with the interplaner spacing. It is thus concluded that the presence of the D mode is associated with the degree of disorder along the c axis. Finally, a phonon confinement model has been used to correlate the linewidth of the G band with the crystallite size in the materials. The results of fitting the calculated line shapes to the measured spectra provides an estimate for the crystallite dimension ${\mathit{L}}_{\mathit{a}}$ and also indicates that the frequency and linewidth of the G mode are most strongly influenced by the structural order within the a-b hexagonal planes. © 1996 The American Physical Society.