Bundling effects on the intensities of second-order Raman modes in semiconducting single-walled carbon nanotubes

Abstract

The second-order Raman modes in the range of 380-650 cm −1 were investigated for individually dispersed and aggregated HiPco single-walled carbon nanotubes ͑SWNTs͒ using a 700-985 nm tunable laser source. For individually dispersed SWNTs, this Raman region displays relatively weak response from both intermediate frequency modes ͑IFMs͒ and the overtones of the radial breathing mode ͑RBM͒, with the latter dominating. In contrast, for aggregated SWNTs, the IFMs dominate and gain significant intensity relative to the RBM fundamental. Utilizing the correlation between RBM overtone and RBM fundamental intensity ratio as a function of laser energy, we derived Huang-Rhys factors for several ͑n , m͒ nanotube species in both individually dispersed and aggregated states. These values were further used to obtain the corresponding absolute values of the exciton-phonon interaction matrix element for these nanotube species. It is demonstrated that the chiral-angle dependence of exciton-phonon coupling parameters is similar for dispersed and bundled samples. However, we find that bundling results in a decrease in the exciton-phonon coupling for the RBM, while the IFMs display the opposite behavior. These findings are particularly relevant for further clarifying the factors that govern Raman intensities and provide a tool for the selective characterization of various mod͑n − m ,3͒ =2 ͑n , m͒-SWNTs as a function of their aggregation state.

Cross-polarized excitons in carbon nanotubes

“…Such perturbations affect properties of cross-polarized excitations because of their complete delocalization in the radial dimension. Indeed, recent experiments report that the optical signatures of cross-polarized excitations are more pronounced in bundles as compared with individual tubes (45).…”

Tunable filter Raman spectroscopy of purified semiconducting and metallic carbon nanotubes

“…However, a Kataura plot can be built with other Raman bands (most notably the G -band [26]). Experimental REMs have also been shown for intermediate frequency modes (IFMs) [27,28] and RBM overtones [29]. The D band REP has been investigated for polyfluorenesorted SWCNTs [30].…”

Ultrafast Generation of Fundamental and Multiple-Order Phonon Excitations in Highly Enriched (6,5) Single-Wall Carbon Nanotubes

“…Peak #4 at 574 cm −1 can be assigned to a combination of three different symmetry modes, that is, the RBM (A 1 , 294 cm Previous Raman measurements on chirality-mixed SWCNT samples detected some IFMs in the 600-1100 cm −1 frequency range excited in the E 33 /E 44 region 26 as well as in the 370-480 cm −1 frequency range excited in the E 11 /E 22 region. 29,30 Fantini et al observed only two peaks associated with the oTO mode combined with acoustic phonon modes. 26 The so-called 'step-wise' dispersive behaviors were observed in these studies because the IFMs have a strong chirality-and diameter-dependence, which jumps when the excitation photon energy goes from one 2n + m family to another.…”

“…In addition, the weaker IFM peaks at 623 cm −1 (Peak #5) and 1145 cm −1 (Peak #10) can also be the sum and difference, respectively, of the oTO mode and the sum of i) and ii) (three phonon combinations) although it is also likely that Peak #5 is the RBM overtone as previously observed in Raman. 30 Furthermore, there are two other IFM peaks, that is, Peaks #3 and #4. Peak #3 at 487 cm −1 can be assigned to a combinational mode between the RBM (294 cm −1 ) and the 2 nd E 1 mode (LAlike, 213 cm −1 ).…”