Photophoresis in Single Walled Carbon Nanotubes

TL;DR

This study demonstrates optically induced motion in pristine single-walled carbon nanotubes (SWNTs), enabling their separation based on metallic or semiconducting properties through photophoresis influenced by light frequency and intensity.

Contribution

It provides the first direct evidence of positive and negative photophoresis in SWNTs and shows how light frequency can selectively separate metallic and semiconducting nanotubes.

Findings

Photophoresis depends on light frequency and intensity.

Metallic and semiconducting SWNTs respond differently to specific light wavelengths.

Separation of SWNTs based on their electronic properties was achieved using photophoresis.

Abstract

We report specifically two things, one the phenomenon of optically induced motion in pristine single walled carbon nanotubes (SWNT) on the macro-scale and other the consequent separation of metallic and semiconducting enriched SWNT aggregates. Experiments provide direct evidence of both positive and negative photophoresis of SWNTs in solution i.e. motion away and towards light respectively. This optically induced motion was found to be dependent on frequency and intensity of light. Aggregates of pristine SWNT, moving under UV and Visible lamp were separated and characterized using absorption and Raman spectroscopy. Aggregates separated from pristine SWNT show enrichment in metallic or semiconducting SWNTs, depending on the spectral frequency of the lamp. Photophoresis in selective SWNTs show direct relation between frequency of illumination and absorption of specific nanotubes. The observed phenomenon is also verified using pre-separated, metallic and semiconducting SWNTs in solution. Metallic SWNTs show enhanced photophoresis with an UV lamp, whereas pre-separated semiconductor SWNT exhibit motion with a mercury lamp with broadband visible frequency. However, under IR lamp, both metallic and semiconducting enriched SWNT show continuous motion, as seen for un-separated pristine SWNTs, where no specificity was observed and all particles were seen moving.