Impacts of structure defects and carboxyl and carbonyl functional groups on the work function of multiwalled carbon nanotubes

The work function is important for achieving the desired performance of many electronic devices. Several investigations have been conducted on the work-function engineering of multiwall carbon nanotubes (MWNTs). Oxidation of carbon nanomaterials is a simple approach to increasing MWNTs' work function without introducing extrinsic metallic elements or altering the nanotubes' morphology; however, few experiments have been conducted to study the mechanism by which different types of oxygen-containing functional groups increase the work function of MWNTs. In this work, we designed and carried out systematic experiments to investigate the influence of the overall oxygen content, structure disorder, and two individual types of functional groups on work-function shifts. Our results demonstrate that the work function is not simply correlated with the overall oxygen concentration, that structure defects are unlikely to change the work function, and that carbonyl groups are the dominant contributor to the increase in the work function of MWNTs. Our results provide distinctive insights into work-function engineering of MWNTs and guide the application of MWNTs in functional devices for photovoltaic and optoelectronic devices. (C) 2016 Elsevier Ltd. All rights reserved.