  Graphene is a purely two-dimensional material that has extremely favorable
chemical sensor properties. It is known, however, that conventional
nanolithographic processing typically leaves a resist residue on the graphene
surface, whose impact on the sensor characteristics of the system has not yet
been determined. Here we show that the contamination layer both degrades the
electronic properties of the graphene and masks graphene s intrinsic sensor
responses. The contamination layer chemically dopes the graphene, enhances
carrier scattering, and acts as an absorbent layer that concentrates analyte
molecules at the graphene surface, thereby enhancing the sensor response. We
demonstrate a cleaning process that verifiably removes the contamination on the
device structure and allows the intrinsic chemical responses of graphene to be
measured.
