Making contacts to n-type organic transistors using carbon nanotube arrays.

We investigated the performance of carbon nanotube (CNT) array electrodes applied to n-type and ambipolar phenyl-C61-butyric acid methyl ester (PCBM) thin film transistors on a SiO(2) dielectric substrate. Compared to conventional Au electrodes, CNT arrays provide better injection efficiency, improved switching behavior, higher electron mobility, and lower contact resistance. Experiments on ambipolar PCBM transistors indicate that the injection performance is enhanced by the electrostatics of the CNT contacts, which promotes electron and hole tunneling across Schottky barriers at the PCBM/nanotube interface. The use of CNT arrays is a valid replacement to low workfunction metals, which are often reactive in air and difficult to process. Our work paves the way for a widespread use of carbon nanotube array electrodes in high-performance n-type and p-type organic thin film transistors.

Probing charge transfer at surfaces using graphene transistors.

Graphene field effect transistors (FETs) are extremely sensitive to gas exposure. Charge transfer doping of graphene FETs by atmospheric gas is ubiquitous but not yet understood. We have used graphene FETs to probe minute changes in electrochemical potential during high-purity gas exposure experiments. Our study shows quantitatively that electrochemistry involving adsorbed water, graphene, and the substrate is responsible for doping. We not only identify the water/oxygen redox couple as the underlying mechanism but also capture the kinetics of this reaction. The graphene FET is highlighted here as an extremely sensitive potentiometer for probing electrochemical reactions at interfaces, arising from the unique density of states of graphene. This work establishes a fundamental basis on which new electrochemical nanoprobes and gas sensors can be developed with graphene.