Several chemical approaches are known to form a p-n junction of graphene such as gas exposure, polymer-induced doping, and reaction with diazonium salts. These methods require e-beam lithography to define the pattern mask for selective area doping, which suffers from the residue of resist that may heavily affect the electrical properties and the following chemical doping process.
In this study, we report a facile way to modify the specific area of graphene devices by simply ultilizing a polydimethylsiloxane (PDMS) microfluidic channel. The PDMS channel has been widely used in biosensor application, which is capable of modifying the target object with solution-based modification. With the help of PDMS microchannel, the graphene was partially covered by PDMS and left uncovered region for solution passing through the channel. This simple approach have enabled us to achieve spatially selective functionalization or doping in graphene, resist-free p-n junction device. Taking advantage of microfluidic system, we can easily switch the dopant from one to another at will, along with noncovalent modification. We are able to create a high-quality graphene device with high carrier mobility and prominent QHE signature. Although this method seems to be only suitable for micron-scale fabrication, I think this partially-modified graphene devices can be futher patterned or narrowed down into nano-scale by some kind of nanoribbon formation process, such as nanowire-mask approach or e-beam lithography.
