Combination of Confocal Raman Spectroscopy and Electron Microscopy on the Same Individual Bundles of Single-Walled Carbon Nanotubes Chaoyang Jiang, Jixue Li, Jialong Zhao, Ute Kolb, and Alf Mews* Institut fu ¨ r Physikalische Chemie, UniVersita ¨ t Mainz, Mainz D-55099, Germany Received August 7, 2002; Revised Manuscript Received August 30, 2002 ABSTRACT We report a method to investigate the same individual single-walled carbon nanotube (SWNT) bundles with both transmission electron microscopy (TEM) and Raman spectroscopy. Free-standing individual bundles are obtained by depositing a solution of suspend SWNTs on a carbon film with a regular pattern of holes, which can be localized by TEM and also by confocal Raman microscopy. While most of the TEM images predict that the bundles consist of tubes with a similar diameter, we will show that occasionally a certain tube diameter can be associated with a particular radial breathing mode frequency of the Raman spectrum. Single-walled carbon nanotubes (SWNTs) are one-dimen- sional molecular structures with diameters in the range of a few nanometers. The outstanding mechanical and electrical properties of these materials have generated significant activity in both fundamental and applied research. 1,2 For example, scanning probe tips 3 have been made using SWNTs because of their high mechanical strength. Also, the pos- sibility of nanoscale electronic devices was shown by the realization of single-electron transistors made from SWNTs. 4,5 In principle, a SWNT can be either metallic or semicon- ducting, depending on its diameter and chirality. Moreover, SWNTs made by arc-discharge 6 and laser ablation 7 methods usually self-tangle into bundles containing both metallic and semiconducting tubes. Therefore, the structural and electronic analysis of SWNT bundles is of great interest, particularly in the view of bundle applications. The structural properties of individual bundles can be investigated by several microscopic techniques. 6-11 In cases of high resolution transmission electron microscopy (HR- TEM) it was even possible to directly observe cross sections of SWNT bundles when the bundle axis was perpendicular to the image plane. From these experiments it was argued that the triangular lattice of SWNT bundles is formed by nanotubes that are similar in diameter. 6,7 A powerful technique to probe the electronic properties of bundles and also individual SWNTs is the method of Raman microscopy and spectroscopy. 12-14 One of the features in a typical Raman spectrum of SWNTs is the radial breathing mode (RBM) in the region of 100-350 cm -1 . Because the RBM frequency is sensitive to the tube diameter and chirality, 12,15 a structural analysis of the SWNTs can also be performed by the method of Raman spectroscopy. The relationship between the tube diameter d and the RBM frequency ω RBM has been investigated by several groups and can, in principle, be described by the following formula: Bandow and co-authors used a force constant model and calculated a constant value of x ) 224 independent of the chirality of the tubes. 16 Jorio et al. 17 used a combination of theory and Raman experiments where they could assign even the (n,m) chiral vector to individual SWNTs by using a parameter of x ) 248. In addition, there have been many different ab initio calculations on the lattice dynamics of individual SWNTs and bundles. For example, Henrard et al. obtained that the expected RBM frequency is not independent of the tube chirality 11 and also predicted an upshift in frequency by 5-15% for tubes within bundles 18 (see also Figure 4). A possible bundle effect has also been reported by other groups. 19,20 An experimental correlation between the frequency and diameter distributions of SWNT samples can, in principle, be performed by investigating the same set of samples with Raman spectroscopy and TEM or X-ray diffraction. 21,22 In this work we try to avoid averaging over the whole SWNT ensemble by investigating the same SWNTs with TEM and Raman spectroscopy. We present a method to directly correlate the structural and spectroscopic properties of * Corresponding author. E-mail: alf.mews@mail.uni-mainz.de. d[nm] ) x/ω RBM [cm -1 ] (1) NANO LETTERS 2002 Vol. 2, No. 11 1209-1213 10.1021/nl025738o CCC: $22.00 © 2002 American Chemical Society Published on Web 09/28/2002