Spectra Identify Nanotube Species

Daniel S. Burgess

Chemists at Rice University in Houston have reported that spectrofluorometry is an effective tool in identifying various species of single-walled carbon nanotubes. They suggest that the technique may be used to guide the selective production of desired types of the structures or to help sort bulk samples into families.

Using spectrofluorometry, chemists at Rice University have identified species of single-walled carbon nanotubes. Each species displays a unique optical signature. Courtesy of R. Bruce Weisman.

Using a spectrofluorometer from Jobin Yvon equipped with a nitrogen-cooled InGaAs near-IR detector, the researchers, led by R. Bruce Weisman, measured fluorescence intensity at 52,000 combinations of excitation and emission wavelengths for nanotube samples suspended in deuterated water. They observed distinct peaks from 33 species of semiconducting nanotubes. Additional information was obtained from resonance Raman spectra of breathing mode frequencies taken with multiple laser wavelengths. Through careful analysis of the optical and Raman data, they mapped each optical transition to a specific nanotube structure with known diameter and chiral angle.

Promise for manufacturing

The properties of single-walled carbon nanotubes depend on their physical structure. For example, approximately two-thirds of the three families of nanotubes are semiconductors, and the other third are metals. The ability to select which type is produced in a growth process or to separate the species of interest from the bulk could enable their entry into commercial and industrial manufacturing.