Raman scattering from boron-substituted carbon films

Raman scattering studies of BxC1-x films have been carried out for baron concentrations in the range 0 less than or equal to x less than or equal to 0.17. The spectra exhibit two broad bands, a graphitic mode (G) centered between 1535 and 1590 cm(-1) and a disorder-induced mode (D) centered between 1345 and 1370 cm(-1). The G mode is observed to soften as a result of baron 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 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 L(a) and also indicates that the frequency and linewidth of the G mode are mast strongly influenced by the structural order within the a-b hexagonal planes.