The effect of ozone oxidation on single-walled carbon nanotubes

TL;DR

This study investigates how UV-generated ozone oxidizes single-walled carbon nanotubes at room temperature, increasing their electrical resistance through defect formation, with potential applications in chemical functionalization.

Contribution

It demonstrates that ozone oxidation occurs on the sidewalls of nanotubes, not at end caps, and shows UV-generated ozone as a controllable, low-thermal process for nanotube functionalization.

Findings

Ozone oxidation increases nanotube resistance irreversibly.

Defect density rises due to oxidation, as shown by spectroscopy.

Resistance increase correlates with removal of pi-electron states.

Abstract

Exposing single-walled carbon nanotubes to room temperature UV-generated ozone leads to an irreversible increase in their electrical resistance. We demonstrate that the increased resistance is due to ozone oxidation on the sidewalls of the nanotubes rather than at the end caps. Raman and x-ray photoelectron spectroscopy show an increase in the defect density due to the oxidation of the nanotubes. Using ultraviolet photoelectron spectroscopy we show that these defects represent the removal of pi-conjugated electron states near the Fermi level, leading to the observed increase in electrical resistance. Oxidation of carbon nanotubes is an important first step in many chemical functionalization processes. Since the oxidation rate is controllable with short exposures, UV-generated ozone offers the potential for use as a low-thermal budget processing tool.