Types of nanotube structures

Figure 1 illustrates the structures of three SWNTs that differ in chiral angle and diameter. Armchair SWNTs are always metallic in electronic character. The zigzag and intermediate forms, however, will be either semimetallic or semiconducting, depending on their structure. One factor delaying practical applications of SWNTs has been the inability of researchers to easily measure and interpret the molecules’ detailed optical absorption and emission spectra. As a result, it has been difficult to tell which structural types are present in a given sample, and in what quantities. Common identification techniques include Raman spectroscopy and microscopic methods. The metallic conductivity of SWNTs is predicted using a first-principles local density-functional band structure approach and tight-binding model. The electronic properties of SWNTs were found to depend on their atomic structures, which are described by their chiral angle and diameter. SWNTs come in many structural forms, and their electronic properties vary with differences in their structures. Each batch that is produced by Smalley’s HiPco process contains about 50 different species of nanotubes, each with a characteristic diameter and chiral angle, the angle at which it is rolled.