Charge-trapping effects caused by ammonia in carbon nanotubes

Hysteretic behaviors caused by low-concentration ammonia gas are found in single-walled carbon nanotube based field-effect transistors. The transfer curves are found to shift towards negative gate voltage when the gate voltage is swept forwardly upon introducing ammonia. In contrast, no significant change in the transfer curves is observed for the backward sweeping of the gate voltage. This phenomenon is repeatable even after the devices are annealed in dry air at 200 degrees C for 2 hrs. Our findings can be interpreted in terms of additional charge traps induced by the adsorbed ammonia molecules. The observed hysteretic behavior enables the devices to work as memory cells, in which the carbon nanotube field-effect transistors act as readout and ammonia molecules play roles of charge storage.