A "Blue" Shift of Optical Absorption Bands of Single-Wall Nanotubes Grown from C:BN Mixtures by Arc-Discharge Technique

The electron and phonon properties of single-wall nanotubes synthesized from C:BN mixtures by arc-discharge technique have been analyzed. The BN content was varied from 0 to 50 weight%. The direct measurements of the absorption spectra of hetero-tubes obtained were performed for the suspensions of individual single-wall nanotubes in 1%-SDBS/D2O solution. The main optical absorption bands E^sem₁₁, E^sem₂₂, E^met₁₁… were shifted toward the "blue" part of the spectrum while the BN content was increased in the initial mixture used for synthesis. Under all BN contents (0–50%) the typical features of carbon single-wall nanotubes were observed in the Raman spectra of heterotubes grown. No significant changes in G-mode (at 1592 cm⁻¹) have been detected. In a low-frequency range a position of the dominating Raman breathing mode showed a "blue shift" while the BN content in the initial mixture increased. This was interpreted as an evidence of the bandgap increase in C:BN heterotubes. The "blue" shift of the optical absorption bands (about 140 nm) has been ascribed to the effect of incorporation of B and N atoms or BN clusters into the graphitic lattice of the nanotube wall. This led to the bandgap enlarge.