Raman Spectroscopy on Double-Walled Carbon Nanotubes

Abstract

Double-walled carbon nanotube (DWNT) is a special MWNT only consisting of two coaxial SWNTs. It is an ideal model to study the effect of interlayer interaction on the phonons and electronic structures of carbon nanotubes (CNTs), and have some unique properties and potential applications as nanodevices, due to its unique double wall structure. For example, it is expected to have some potential applications as molecular conductive wire or molecular capacitor in a memory device, depending on the electronic properties of the two constituent tubes (Saito et al., 1993). Recent studies also indicated that DWNTs are better field effect transistor (FET) channels than SWNTs (Shimada et al., 2004). Therefore, it is very important to realize the controllable synthesis of DWNTs and to identify the diameters and the electronic properties of the two constituent tubes for their promising applications as nano-scale electronic devices. It is well established that every possible nanotube has a distinct electronic and vibrational spectrum, so that there is a one-to-one relation between the nanotube and the singularities in the 1D joint electronic density of states (JDOS) (Dresselhaus et al., 2002). Moreover, the electronic states are highly sensitive to the diameter of nanotubes. In the resonant Raman effect, a large enhancement in the Raman signal occurs only when the incident or scattered photon is in resonance with a singularity in the 1D JDOS of nanotubes (Dresselhaus et al., 2002). Therefore, resonance Raman spectroscopy can be used as a sensitive probe of the geometrical and electronic structure of CNTs through coupling between electrons and phonons in this one-dimensional system. In this review, we will present our recent progress on the controllable synthesis and detailed structural characterization of DWNTs. A floating catalyst chemical vapor deposition (CVD) method was proposed for the synthesis of DWNTs