Investigation of Etching Behavior of Single-Walled Carbon Nanotubes Using Different Etchants

As gas-phase etching has become an important method to obtain single-walled carbon nanotubes (SWCNTs) with specific electronic structures, numerous etchants were studied in the past decades. However, the understanding of the dynamic process as well as the etching state is still limited. Herein, we investigated the etching process of SWCNTs at the level of the individual tube in real time using an improved polarized optical microscope equipped with a miniature chemical vapor deposition (CVD) system. Experiments showed a universal etching behavior in a SWCNT oxidation process under different etchants (O-2, H2O, and CO2), that is, the random appearance of etching sites and the self-terminating phenomenon. We built a new etching model at the level of the individual tubes to describe the etching rate. Based on this model, a new constant R, the ratio of etching rates between metallic and semiconducting SWCNTs, was defined to describe the etching selectivity. Optical spectroscopy was used to identify the chirality of SWCNTs, and it was found that the etching selectivities followed the order: H2O (R = 17.1, 850 degrees C) > CO2 (R = 3.6, 850 degrees C) > O-2 (R = 1.2, 610 degrees C). Field effect transistor (FET) performance of the SWCNT arrays also verified the statistical results.