Edge Effects on the pH Response of Graphene Nanoribbon Field Effect Transistors

We report the pH response enhancement of the electrolyte-gated graphene field effect transistors by controllably introducing edge defects. An average improvement of pH response from 4.2 to 24.6 mV/pH has been observed after downscaling the pristine graphene into graphene nanoribbon arrays with electron beam lithography (EBL) and oxygen plasma. We attribute the improved pH response in graphene nanoribbons to the increased number of hydroxyl groups attached to edge defects as the edge length to surface area ratio increases with decreasing graphene nanoribbon width. Moreover, the shift of the Dirac point in response to the pH change has been found to be reversible, indicating that the hydroxyl ions are binding to the edge defect sites of the graphene nanoribbons through physical adsorption.