Anti-Stokes Raman Scattering of the Smallest Carbon Nanowires Made of Long Linear Carbon Chains Inserted inside Single-Walled Carbon Nanotubes

Abstract

The smallest carbon nanowires, i.e., single-walled carbon nanowires (SWCNWs, LLCCs@SWCNTs) made of long linear carbon chains (LLCCs, sp) inserted inside single-walled carbon nanotubes (SWCNTs, sp2), were successfully mass produced recently, making the refined strong Stokes Raman characterization of LLCCs@SWCNTs possible. This work reports the observation of anti-Stokes Raman scattering of LLCCs@SWCNTs with normal Raman spectroscopy, and their Stokes and anti-Stokes Raman scattering at a wide temperature range of 80–850 K has been systematically studied. It was found that the normalized intensity of L-band at 1835 cm–1 of LLCCs@SWCNTs decreased as the temperature increased, which obeys a quadratic polynomial fitting for Stokes and cubic fitting for anti-Stokes peaks. The absolute intensity of Stokes peaks decreased and that of anti-Stokes increased with the increasing temperature. Meanwhile, a softening of Stokes and anti-Stokes peaks was observed as the temperature increased. Furthermore, both the high-energy longitudinal phonon (G+) of SWCNTs hosting LLCCs and the L-band originating from LLCCs inside SWCNTs exhibit a quasi-linear variation with temperature, having temperature coefficients of −0.0192 and −0.0296 cm–1·K–1 for Stokes and 0.0200 and 0.0334 cm–1·K–1 for anti-Stokes, respectively. The linear temperature dependence of peak positions of L-band implies that the crystal, vibrational, and electronic structures of LLCCs inside SWCNTs can be easily tuned via the temperature. This work paves the way for studying the mechanism of Raman process and fundamental properties of both LLCCs/carbyne and SWCNWs (LLCCs@SWCNTs), as well as their potential applications in nanoscale temperature monitoring.