Discrimination of individual semiconducting and metallic single-walled carbon nanotubes by multi-wavelength photothermal microscopy

Abstract The coexistence of semiconducting and metallic single-walled carbon nanotubes (SWCNTs) after synthesis is one of the factors preventing their practical applications. A method for quantifying the purity of a nanotube sample with high accuracy is essential because each type has different applications. In this study, we investigated the accuracy in distinguishing between semiconducting and metallic SWCNTs using multi-wavelength photothermal microscopy. Linear discrimination analysis of the multi-wavelength signals of individual nanotubes was performed to show that the two types of SWCNTs could be distinguished with more than ∼95% accuracy when the SWCNTs were embedded in a dry polymer film. In contrast, the discrimination rate decreased to about 80% when the SWCNTs were dispersed in aqueous media. The optimal wavelength combinations, number of lasers required for discrimination, and relationship between the signal-to-noise ratio and discrimination rate are also discussed.