Electronic Transport and Doping Effects in Reduced Graphene Oxide Measured by Scanning Probe Microscopy
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Electronic Transport and Doping Effects in Reduced Graphene Oxide Measured by Scanning Probe Microscopy Christopher E. Kehayias1, Samuel MacNaughton2, Sameer Sonkusale2 and Cristian Staii1 1 Department of Physics and Astronomy, and Center for Nanoscopic Physics, Tufts University, 4 Colby Street, Medford, MA, 02155, U.S.A. 2 Department of Electrical and Computer Engineering, Tufts University, 161 College Avenue, Medford, MA, 02155, U.S.A ABSTRACT We present a Scanning Probe Microscopy study of doping and sensing properties of reduced graphene oxide (rGO)-based nanosensors. rGO devices are created by dielectrophoretic assembly of rGO platelets onto interdigitated electrode arrays, which are lithographically pre-patterned on top of SiO2/Si wafers. The availability of several types of oxygen functional groups allows rGO to interact with a wide range of organic dopants, including methanol, ethanol, acetone, and ammonia. We perform sensitive Scanning Kelvin Probe Microscopy (SKPM) measurements on patterned rGO electronic circuits and show that the local electrical potential and charge distribution are significantly changed when the device is exposed to organic dopants. We also demonstrate that SKPM experiments allow us to quantify the amount of charge transferred to the sensor during chemical doping, and to spatially resolve the active sites of the sensor where the doping process takes place. INTRODUCTION Graphene and its chemical derivatives are proving to be promising candidates for nanoscale electronics [1-4]. Due to its characteristic two-dimensional honeycomb lattice structure, graphene is very sensitive to perturbations to the surface (mechanical or electronic) [5-7], thus endorsing graphene-related materials for constituents in nanoscopic sensors [2-4]. Moreover, the response of these materials to chemical dopants tends to be much faster than that measured in the corresponding bulk materials. In particular, it has been shown that nanosensors based on reduced graphene oxide (rGO) can be used to detect trace amounts of organic vapors [2,3,8] (including acetone, toluene, methanol, ammonia). The rGO platelets are composed of carboxyl, alcohol, and dangling oxygen groups embedded within the familiar hexagonal lattice of carbon atoms. These groups act as binding sites for chemical doping, which, depending on the analyte, can either add or remove charge carriers from the exposed nanosensor [2,3,8]. Many different types of Scanning Probe Microscopies (SPM) based on the Atomic Force Microscope (AFM) have been developed to study the local electrical properties of these nanoscale objects. In particular Electrostatic Force Microscopy (EFM) and Scanning Kelvin Probe Microscopy (SKPM) have been used to resolve electrostatic interactions within few-layer graphene films [5], and to measure local variations in the surface electrostatic potential of singelayer graphene [7]. Here we present SKPM measurements on electronic sensors fabricated from rGO platelets, which are deposited across lithographically patterned gold electrodes on S
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