ABSTRACT
This chapter discusses the ion sensing mechanism of the graphene-based device. It demonstrates the controlled assembly of graphene sheets on a substrate with high precision and high yield. The dielectrophoretically assembled graphene sheets are inspected with scanning electron microscopy. The deposited graphene is electrically characterized using a liquid-gated field-effect transistor configuration. Thermal annealing was used to improve the contact between the graphene and the electrodes as well as to enhance the adhesion between the graphene and the substrate. Graphene can be viewed as a two-dimensional honeycomb lattice that is constructed with a single layer of carbon atoms. Alternatively, graphene can be directly grown on substrates with chemical vapor deposition and epitaxy methods. The assembled graphene sheets demonstrate high sensitivity toward pH values in an aqueous environment with excellent reversibility and repeatability. The electrodes used for graphene assembly are fabricated on a 4-inch silicon wafer with a 200-nm-thick surface thermal oxide layer.
