Anomalous Current-Voltage Characteristics in Suspended Carbon Nanotubes in Various Gas Environments

Electrically-heated suspended, carbon nanotubes (CNTs) exhibiting negative differential conductance in the high bias regime experience a sudden drop in current (or ``kink'') in various gaseous environments. We study the effect of different gas molecules on these $I-V $characteristics while simultaneously monitoring the changes in the nanotube vibrational structure under high bias voltages using Raman spectroscopy. When the nanotube is electrically biased at the kink, the $G$ band Raman mode is observed to downshift, as is typical of electrically heated devices. However, the $G$ band frequency at the kink ($\omega _G^{kink})$ lies in the narrow range between 1575 and 1579cm$^{-1}$ for all samples measured, regardless of gas environment. The voltage at which the kink occurs depends on the type of the gas environment with the following dependence: $V_{kink}^{Ar}