Manipulating graphene mobility and charge neutral point with ligand-bound nanoparticles as charge reservoir

The high carrier mobility of graphene makes it an attractive candidate for future electronic device applications.(1) In SiO2/Si-supported graphene devices, the mobility typically varies from 2000 to ∼2,0000 cm(2) V(-1) s(-1).(2) By removing SiO2,(3,4) much higher mobility (2 × 10(5) cm(2) V(-1) s(-1) in the latter) has been obtained, suggesting the importance of the Coulomb scattering in graphene transport. Although such elaborate device fabrication is clearly effective, the mobility of finished devices is fixed thereafter and can vary from device to device. In this work, we first demonstrate a significant enhancement in carrier mobility in SiO2-supported graphene decorated with a layer of ligand-bound nanoparticles (NPs) such as iron oxide, titanium dioxide, or cadmium selenide acting as a charge reservoir. By transferring charges between graphene and the NP reservoir through the molecules, we show a remarkable reversible tunability in mobility (4000-19000 cm(2) V(-1) s(-1)) in the same device, which unambiguously proves that the charged impurity scattering is the prevailing mechanism for graphene mobility. In addition, the charge neutral point or the Dirac point can also be independently tuned over a wide gate voltage range. The reversible tuning is useful for fabricating large-area graphene devices such as nonvolatile memory with enhanced sensitivity.