Influence of O2 and N2 on the conductivity of carbon nanotube networks

TL;DR

This study combines experiments and DFT calculations to reveal how physisorbed O2 and N2 molecules influence the electrical conductivity of carbon nanotube networks, especially at junctions.

Contribution

It demonstrates that physisorbed O2 and N2 affect junction conductance through increased tunneling, a novel insight into nanotube network sensitivity.

Findings

O2 has a larger effect than N2 on conductance.

Semiconducting SWNT junctions are more affected than metallic ones.

Experimental results align with theoretical predictions.

Abstract

We have performed experiments on single-wall carbon nanotube (SWNT) networks and compared with density-functional theory (DFT) calculations to identify the microscopic origin of the observed sensitivity of the network conductivity to physisorbed O2 and N2. Previous DFT calculations of the transmission function for isolated pristine SWNTs have found physisorbed molecules have little influence on their conductivity. However, by calculating the four-terminal transmission function of crossed SWNT junctions, we show that physisorbed O2 and N2 do affect the junction's conductance. This may be understood as an increase in tunneling probability due to hopping via molecular orbitals. We find the effect is substantially larger for O2 than for N2, and for semiconducting rather than metallic SWNTs junctions, in agreement with experiment.