Gas sensing mechanism of carbon nanotubes: From single tubes to high-density networks

Gas sensing in carbon nanotubes is still poorly understood. Possible mechanisms are charge transfer between adsorbed gas molecules and the nanotubes or gas-induced changes at the interface between the nanotubes and their metal contacts. For carbon nanotube networks, it is also important to understand how defects and junctions formed by crossing nanotubes affect adsorption. Previous work demonstrates that for devices made with a single carbon nanotube, the response was mainly due to modifications at the nanotube/metal contact interfaces rather than molecular adsorption on the nanotube. Here it is shown that in networks of carbon nanotubes the gas sensitivity is due to both the nanotube/metal contacts and the carbon nanotube network. The network effects are dominated by gas-induced changes in nanotube/nanotube junctions, rather than gas adsorption on regions of the nanotubes away from the junctions.