Jun 12, 2013
Kelvin probe microscopy measures chemical doping of reduced graphene oxide
Reduced graphene oxide (RGO) is an electronically hybrid material with remarkable chemical sensing properties. RGO–based chemical sensors are typically obtained by exposing water-dispersed graphene oxide to different types of reducing agents. The resulting RGO platelets are composed of carboxyl, alcohol and dangling oxygen functional groups embedded within the familiar hexagonal lattice of carbon atoms. The availability of these functional groups allows RGO to interact with a wide range of chemical analytes, which act as either electron donors or electron acceptors on the sample surface. These interactions lead to a significant change in the resistance of the RGO-based gas-sensing electronic devices. The RGO sensors are therefore amenable to chemical modifications that, in principle, permit a very high degree of control over their chemical sensitivity and selectivity.
The team, which includes scientists from the Department of Physics and Astronomy and the Department of Electrical and Computer Engineering at Tufts University, used dielectrophoretic assembly to pattern RGO platelets in a field effect transistor geometry on SiO2/Si substrates. Transport measurements show that these chemical sensors display highly selective and reversible responses to the measured analytes, as well as fast response and recovery times on the order of tens of seconds.
Optimizing device design
Kelvin probe microscopy (KPM) measurements on RGO-based sensing devices allowed the researchers to obtain high-resolution maps of the surface potential and the local charge distribution both before and during the exposure of these sensors to different chemical species. KPM images were used 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 chemical gating process takes place. The data was also used to measure directly the contact resistance between the RGO platelets and the metallic electrodes.
The methods of measurement and analysis are general, and can be applied to the quantitative study of charge-transfer mechanisms in any two-dimensional chemical sensor.
Full details can be found in the journal Nanotechnology.
About the author
The study was conducted by a team of researchers from Tufts University. Christopher Kehayias is an undergraduate student majoring in physics. He performed the Kelvin probe microscopy and electrical transport measurements. Samuel MacNaughton is a graduate student in electrical engineering. He was involved in RGO sample preparation and in the chemical sensing experiments. Sameer Sonkusale is an associate professor in the Department of Electrical and Computer Engineering. His research interests span many areas in the fields of nanosensor science and technology, active metamaterials and flexible macro- and microelectronics. Cristian Staii is an assistant professor in the Department of Physics and Astronomy at Tufts University. Prof. Staii’s research interests include biological physics, scanning probe microscopy and experimental condensed matter physics. Prof. Sonkusale and Prof. Staii guided the project.