Cleaning Transferred Graphene for Optimization of Device Performance

Much has been made of the potential electrical properties of graphene, but still in many cases, unintentional doping leads to these not being fully realized. In the processing of graphene, the step which leads to most of this doping is the transfer from the growth substrate leaving unwanted chemical residue on the graphene surface. A comparison of the techniques most commonly used to remove this residue is presented showing that most effective cleaning can be obtained using ionic solutions rather than the more commonly used organic solvents. The physical and electrical properties of graphene treated using these solutions are assessed by a combination of atomic force microscopy, Raman spectroscopy, Kelvin-Probe force microscopy, and contact resistance/charge neutrality point measurements, and it is shown how to remove residue effectively and reduce contact resistance without adversely affecting the graphene.