Plasma polishing of multi-walled carbon nanotubes towards single-walled limit

This article reports that plasma exposure decreases the wall thickness of multi-walled carbon nanotubes (MWCNTs), which can be one of the promising techniques for mass production of single-walled carbon nanotubes (SWCNTs) in the future. This technique is attractive because MWCNTs have a significant advantage in the production rate. In this article, we first observed the reduction of the wall thickness with a transmission electron microscope (TEM) to investigate CNT morphology after plasma exposure. Then, we randomly selected more than 500 nanotubes from the TEM pictures to measure the wall thickness. Our histogram of the wall thickness showed that plasma exposure reduced a few layers of MWCNTs. We then confirmed the plasma-exposed CNTs with Raman spectroscopy, which again shows the reduction of the wall thickness of MWCNTs by observing the ratio of the two characteristic intensities, as known as G/D ratio. In conclusion, our observations were consistent so that plasma exposure can apply to future mass production from MWCNTs to SWCNTs after decent optimization.