Carbon Nanotubes Analysis

- Affordable Raman instrument solutions for rapid characterization of Carbon Nanotubes

Since their discovery, carbon nanotubes (CNTs) have been the focus of intense research in their unique physical properties and in a variety of applications. As the increase of carbon nanotubes in commercial productions, a quick analytical tool for quality verification of the nanotubes becomes more and more important.

Raman spectroscopy has been established as a powerful technique to characterize the structure and electronic properties of carbon nanotubes materials with minimal sample preparation. The main features in the Raman spectra of carbon nanotubes are: the radial breathing mode (RBM); the disorder-induced D-band, and its corresponding second-order G'-band; and the tangential G-band. The information revealed in Raman spectra provide the important information about the diameter, chirality and phonon structure of carbon nanotubes, which are related to the mechanical and electrical properties. For example, they can be either metallic or semiconducting, depending on their chirality.

Radial Breathing Mode (RBM) is specific to SWNT and usually observed in the region from 100 cm-1 to 300 cm-1. Raman peak position, which is inversely proportional to the tube diameter, of this mode are used to classify the diameter distribution in carbon nanotubes.

The G band, a tangential shear mode, corresponds to the stretching mode of the carbon-carbon bond in the graphite plane. The fine structure seen in the G-band depends on tube diameter and chirality. The lineshape of the band can be used to help identify metallic and semiconducting nanotubes. The D band is often referred as the disorder or defect band. The D band/ G band ratio is usually used for evaluating the quality of carbon nanotubes.

Visible to NIR laser excited Raman spectroscopy of CNTs are resonance process, which is excitation wavelength dependence of the spectra resulting from the electronic band structure. During the measurement it is important to keep the low laser power to decrease heating effect since Raman shift/shape is dependent on temperature.

Below show the Raman spectra of single-walled carbon nanotubes (SWCNT) using Enwave’s ProRaman-L-785/532, and multi-walled carbon nanotubes (MWCNT) using the ProRaman-L-532.