Understanding surfactant/graphene interactions using a graphene field effect transistor: Relating molecular structure to hysteresis and carrier mobility

Manipulation of transport hysteresis on graphene transistors and understanding electron transfer between graphene and polar/ionic adsorbates are important for the development of graphene-based sensor devices and nonvolatile memory electronics. We have investigated the effects of commonly used surfactants for graphene dispersion in aqueous solution on transport characteristics of graphene transistors. The adsorbates are found to transfer electrons to graphene, scatter carrier transport, and induce additional electron-hole puddles when the graphene is on an SiO ₂ substrate. We relate the change in transport characteristics to specific chemical properties of a series of anionic, cationic, and neutral surfactants using a modification of a self-consistent transport theory developed for graphene. To understand the effects of surfactant adsorbates trapped on either side of the graphene, suspended devices were fabricated. Strong hysteresis is observed only when both sides of the graphene were exposed to the surfactants, attributable to their function as charge traps. This work is the first to demonstrate the control of hysteresis, allowing us to eliminate it for sensor and device applications or to enhance it to potentially enable nonvolatile memory applications.