Raman characterization of boron-doped multiwalled carbon nanotubes

We present first- and second-order Raman spectra of boron-doped multiwalled carbon nanotubes. The Raman intensities are analyzed as a function of the nominal boron concentration. The intensities of both the D mode and the high-energy mode in the first-order spectra increase with increasing boron concentration, if normalized with respect to a second-order mode. We interpret this result as an indication that the high-energy mode in carbon nanotubes is defect-induced in a similar way as the D mode. Based on this result, we provide a preliminary quantitative relation between the boron concentration and the Raman intensity ratios.