Electrochemical gate-controlled charge transport in graphene in ionic liquid and aqueous solution

We have studied the electron transport behavior of electrochemically gated graphene transistors in different solutions. In an ionic liquid, we have determined the electron and hole carrier densities and estimated the concentration of charged impurities to be (1-10) × 10¹² cm ^-2. The minimum conductivity displays an exponential decrease with the density of charged impurities, which is attributed to the impurity scattering of the carriers. In aqueous solutions, the position of minimum conductivity shifts negatively as the ionic concentration increases. The dependence of the transport properties on ionic concentration is important for biosensor applications, and the observation is modeled in terms of screening for impurity charges by the ions in solutions.