Raman spectroscopy study of carbon nanotube peapods excited by near-IR laser under high pressure

Abstract

A resonant Raman spectroscopy study has been carried out under high pressure, using a diamond anvil cell, on carbon nanotube peapods ͑C 60 @SWNT͒ synthesized in high yield in our laboratory. The Raman signal was excited by a near IR laser ͑830 nm͒ to avoid photopolymerization of C 60 and thus obtain the intrinsic vibrational information on the C 60 molecules in the nanotubes. It is found that the surrounding tubes create an effective pressure on the encapsulated C 60 due to tube-fullerene interactions, resulting in a shift of the intrinsic A g ͑2͒ vibrational mode to 1474 cm −1 at ambient pressure. High pressure Raman spectroscopy indicates that ͑C 60 ͒ 2 dimers form near 1 GPa, and that a further polymerization of C 60 occurs near 23 GPa, creating linear chains of covalently linked C 60 molecules in the tubes.

Rotational dynamics of confined C 60 from near-infrared Raman studies under high pressure

“…The A g (2) mode of nested C 60 is down-shifted from 1,474 cm Ϫ1 to 1,469 cm Ϫ1 for dimers, and further to 1,465 cm Ϫ1 for the single-chain polymer as discussed in detail in our previous work (15). The dimerization process was induced by applying a gentle pressure of 5 GPa in our study.…”

“…The splitting is caused by the interaction between C 60 and its carbon environment, either the SWNT wall, the two C 60 neighbors, or both. We know that the upward shift of the Ag (2) mode from its intrinsic position can be related to the interaction between C 60 s and tubes, and corresponds to an apparent compression by 1-2 GPa applied pressure, or a cooling by several tens of Kelvin from the NMR results, which implies that the interaction between C 60 and tubes indeed exists (9,15). Regarding the C 60 -C 60 interaction between adjacent molecules, its strength depends on the filling factor of C 60 inside SWNT and it is thus expected that the interaction increases with increasing filling ratio.…”

“…The spectrum of C 60 @SWNT can approximately be considered as a weighted sum of the spectra of C 60 and pure SWNT, with weak lines from the nested fullerenes and strong lines from the host SWNTs. It consists mainly of four characteristic regions: (i) the low frequency modes Ͻ200 cm Ϫ1 , mainly radial breathing modes (RBM) for SWNTs (15); (ii) the high-frequency range between 1,500 and 1,600 cm Ϫ1 , containing tangential modes (the G band) for SWNTs (15,16); (iii) fullerene modes near 1,470 cm Ϫ1 , i.e., the most prominent Ag (2) mode for nested C 60 , which is upshifted from its position at 1,469 cm Ϫ1 in pristine C 60 to 1,474 cm Ϫ1 due to the interaction between C 60 and tubes (15) superposition of the individual modes for fullerene and SWNTs, but instead there are significant splits and shifts. We first assign these modes to either C 60 or SWNTs or both by carefully comparing with original Raman spectra of C 60 and empty SWNTs from the literature (17).…”

“…The filling factor of C60 inside SWNT is Ͼ80% (15, 25). The dimer and single-chain polymer structures were induced by applying high pressures, 5 GPa and 23.5 GPa, respectively, at room temperature using a diamond anvil cell with Ar as the pressure medium as shown in our previous work (15,26). These pristine and polymeric peapod samples were characterized by using Raman spectroscopy (Renishaw inVia) with a NIR (830-nm) excitation laser at room temperature.…”

Properties of K,Rb-intercalated C60 encapsulated inside carbon nanotubes called peapods derived from nuclear magnetic resonance

“…11 However, only very few attempts have been made to modify encapsulated species. At present, these are intercalation of C 60 with alkali metals, 12 high pressure polymerization of C 60 , 13,14 insertion of C 60 inside double-walled carbon nanotubes (DWNTs), 15 and catalyst growth of nanotubes inside SWNTs. 16 Tuning the electronic and magnetic properties of peapods is of paramount scientific and technological interest.…”