Intrinsic Temperature\nDependence of Raman-Active Modes\nin Individual Isolated Single- and Double-Walled Carbon Nanotubes

The intrinsic temperature dependence of Raman-active\nmodes in carbon\nnanotubes (CNTs), particularly the radial breathing mode (RBM), has\nbeen a topic of a long-standing controversy. In this study, we prepared\nsuspended individual CNTs to investigate how their Raman spectra depend\non temperature and to understand the effects of environmental conditions\non this dependency. We analyzed the intrinsic temperature dependence\nof the main Raman-active modes, including the RBM, the moiré-activated\nR feature, and the G-band in double-walled carbon nanotubes (DWCNT)\nand single-walled carbon nanotubes (SWCNTs) after complete desorption\nof air. The inner tube of the DWCNT, like the desorbed SWCNTs, was\nfree from environmental influences, resulting in minimal temperature-induced\nRBM frequency shifts. We show that the larger RBM shift of SWCNTs\nupon initial heating is not intrinsic but is due to air desorption.\nThe R feature, attributed to moiré-activated phonon scattering\nand nondispersive in nature, demonstrated a quasi-linear temperature\ndependence, akin to the G-band but with a lower temperature coefficient.\nThe G-band, which was largely unaffected by environmental conditions,\nexhibited a consistent temperature coefficient across SWCNTs, DWCNTs,\nand small SWCNT bundles.