Purity and Defect Characterization of Single-Wall Carbon Nanotubes Using Raman Spectroscopy

We investigated the purity and defects of single-wall carbon nanotubes (SWCNTs) produced by various synthetic methods including chemical vapor deposition, arc discharge, and laser ablation. The SWCNT samples were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Raman spectroscopy. Quantitative analysis of SEM images suggested that the G-band Raman intensity serves as an index for the purity. By contrast, the intensity ratio of G-band to D-band (G/D ratio) reflects both the purity and the defect density of SWCNTs. The combination of G-band intensity and G/D ratio is useful for a quick, nondestructive evaluation of the purity and defect density of a SWCNT sample.

Far Infrared Characterization of Single and Double Walled Carbon Nanotubes

ABSTRACTHigh resolution far infrared absorption measurements were carried out for single walled and double walled carbon nanotubes samples (SWCNT and DWCNT) encased in a polyethylene matrix to investigate the temperature and bundling effects on the low frequency phonons associated with the low frequency circumferential vibrations. At a temperature where kBT is significantly lower than the phonon energy, the broad absorption features as observed at room temperature become well resolved phonon transitions. For a DWCNT sample whose inner tubes have a similar diameter distribution as the SWCNT sample studied, a series of sharp features were observed at room temperature at similar positions as for the SWCNT samples studied. The narrow linewidth is attributed to the fact that the inner tubes are isolated from the polyethylene matrix and the weak inter-tubule interactions. More systematic studies will be required to better understand the effects of inhomogeneous broadening and thermal-excitation on the detailed position and lineshape of the low frequency phonon features in carbon nanotubes.

Effects of Nitric Acid and Heat Treatment on Hydrogen Adsorption of Single-Walled Carbon Nanotubes

The effects of nitric acid treatment and subsequent heat treatment on the hydrogen adsorption properties of single-walled carbon nanotube (SWCNT) samples were investigated. The hydrogen adsorption and desorption isotherms of SWCNTs treated with nitric acid alone and SWCNTs treated with nitric acid and then heated were measured at 77 and 303 K over the hydrogen pressure range 0–3.5 MPa. Nitric acid treatment increased hydrogen adsorption by opening the nanotubes and changing the bundle structure. Subsequent heat treatment of the acid-treated SWCNT sample further increased hydrogen adsorption by removing functional groups introduced by the acid treatment.