Self-built tensile strain in large single-walled carbon nanotubes

Abnormal Raman scattering from a large-diameter ultralong single-walled carbon nanotube (SWCNT) is studied in detail. Along the SWCNT, the Raman spectra show the frequencies of 1553, 1563, and 2597 cm^-1 for G⁺, G^-, and Ǵ peaks, respectively, much lower than the corresponding frequencies well-reported both experimentally and theoretically. The significant downshifts in the peaks frequencies can be attributed to self-built tensile strain, which is likely caused by carbon nanodots decorated on the tube. After infrared laser heating is performed to one point of it, all of the Raman modes are found to shift to higher frequencies and approach their conventional values. We suggest that the SWCNTs with larger diameters easily possess such self-built strain compared to small-diameter SWCNTs because of the weaker curvature effect for the larger ones.