Photophoresis in single walled carbon nanotubes

Abstract

We report optically induced, macro-scale motion of pristine, pure single walled carbon nanotubes (SWNT). Rapid motion is observed in aggregates of SWNTs under UV, visible and NIR illumination. Experiments show optically directed, well-controlled motion of SWNT aggregates. SWNT aggregates show both positive and negative photophoresis in solution i.e. motion away and towards light respectively. Part of the aggregates of pristine SWNT, moving to the top of the vial under UV and visible lamp were separated from the ones at the bottom and characterized using absorption and Raman spectroscopy. Aggregates separated from the top under UV illumination show enrichment in metallic SWNTs whereas ones collected from the top under visible illumination were found enriched in semiconducting SWNTs. This phenomenon of induced motion in selective SWNTs under illumination of specific frequency is also verified using pre-separated (95% pure), metallic and semiconducting SWNTs dispersed in solution. Metallic SWNTs show enhanced photophoresis under an UV lamp, whereas pre-separated semiconductor SWNTs exhibit rapid motion under broadband visible lamp. However, under NIR lamp, no specificity was observed and all particles were seen rapidly moving.