Electrical characteristics of carbon nanofibers in air and vacuum

We present a study on the effect of ambient gases on the electrical properties of carbon nanofibers (CNFs). The resistances of a CNF placed horizontally on a substrate in air and in vacuum are compared. CNFs in air show much lower current capacities compared to those in vacuum. Joule heat produced by constant current stressing results in desorption of gas molecules responsible for carrier trapping, leading to a lower resistance. In air, the resistance returns to its room-temperature value after cooling down. However, in vacuum, where most desorbed gaseous species are evacuated before any significant re-adsorption can occur, the room-temperature resistance continues to decrease with increasing stress current. A model is proposed to describe these observations, and is used to estimate the number of adsorbed molecules on the CNF.