A Raman Map of the DWCNT RBM Region

Raman studies on double-wall carbon nanotubes (DWCNTs) obtained from peapods showed that the radial breathing mode (RBM) response of the inner tubes is split into more components than there are geometrically possible inner tubes. This was attributed to the possibility that one inner tube type may form in more than one outer tube type. Recent resonance Raman investigations revealed an even more complex and interesting behavior. The split components appear to be grouped into species belonging to the same inner tube chirality and the width of the splitting increases with decreasing tube diameter. INTRODUCTION Single-wall carbon nanotubes (SWCNTs) [1] have attracted a lot of scientific interest over the last decade due to their unique structural and electronic properties. By annealing fullerenes enclosed in SWCNTs (so-called peapods [2]) it is possible to transform the fullerenes into a secondary inner tube enclosed in the primary outer tube [3]. A Raman study of the radial breathing modes (RBMs) of the inner tubes revealed that these modes have intrinsic linewidths down to about 0.4cm−1 [4]. These small linewidths indicate long phonon lifetimes and therefore highly defect free inner tubes, which is a proof for a nano clean-room reactor on the inside of SWCNTs. A closer inspection of the RBM response of the inner tubes revealed that there are more Raman lines than geometrically allowed inner tubes. This was attributed to the possibility that one inner tube type may form in more than one outer tube type [5]. To study this splitting in more detail, we recorded a Raman map of the DWCNT RBM region between 1.54 and 2.54eV (488 to 803nm) with a spacing of about 15meV (where possible). This experiment revealed that the large number of components of the RBMs are strongly grouped into species belonging to the same inner tube chirality. The grouping is retained during the growth process, i.e., members of the groups appear and grow collectively. Additionally, the groups seem to be unaffected of the carbon source filled into the primary tubes (C60, C70, or fullerenes mixed with toluene). Only the outer tubes diameter distribution can influence the intensity distribution within one series. However, the frequencies of the RBM components remain similar over several samples with different outer tubes diameters. 305 Downloaded 29 Nov 2007 to 131.130.1.18. Redistribution subject to AIP license or copyright; see http://proceedings.aip.org/proceedings/cpcr.jsp 150 200 250 300 350 400 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 (12,5) (13,3) (14,1) (9,7) (10,5) (11,3) (12,1) (9,8) (10,6) (11,4) (12,2) (13,0) (8,7) (14,2) (13,4) (12,6) (11,8) (10,10) (15,0) (12,3) (11,5) (10,7) (9,9) (13,1) (12,0) (11,2) (10,4) (9,6) (8,8) (10,1) (9,3) (8,5) (7,7) (11,0) (10,2) (9,4) (8,6) (9,5) (10,3) (11,1) (7,6) (8,4) (9,2) (10,0) (5,4) (7,3)