A scanning probe microscopy based assay for single-walled carbon nanotube metallicity.

Low-frequency dielectric polarization of single-walled carbon nanotubes (SWNTs) not only affects charge carrier transport in SWNT-based nanoelectronic devices but also determines their interaction with molecules, other nanomaterials, and external fields. Differential dielectric responses of metallic and semiconducting SWNTs are critical in electronic-type sorting of SWNTs. Here, we describe the measurement of low-frequency dielectric polarization of individual SWNTs without making electrical contacts to the nanotubes. Qualitative contrast is observed between metallic and semiconducting SWNTs due to drastically different longitudinal polarizabilities. This is developed into a facile assay for metallic and semiconducting contents in SWNT samples.