Trying to investigate several doping methods for graphene, researchers have found a way to dope graphene with light. This kind of doping is selective and reversibly - meaning that you can change the material attributes using different light colors, angles or polarization. To achieve that doping method, the researchers attached a plasmonic nano antenna to the graphene. The graphene was doped by hot electrons generated from the antenna.
The doping can be controlled by changing the antenna size or the laser's wavelength and power density. n-type graphene provided a larger doping efficiency than p-type graphene.
The researchers used a monolayer graphene sheet on a copper foil which was transferred to a silicon wafer with a 285 nm thick oxide layer. They pattered source and drain electrodes and plasmonic nonamer antennas onto the graphene using electron beam lithography and gold evaporation. They say that this kind of technology can be used to develop graphene switches, photodetectors and even optically-induced electronics: using p-doped (a graphene sheet covered with quantum dots) and n-doped graphene together can create pn junctions - and thus electronic circuitry.
The team is now working on fabricating the antenna without destroying the graphene underneath. They are also finding ways to improve the doping efficiency with an optimized antenna geometry and incident light.