We demonstrate spin injection into a graphene thin film with high reliability by using non-local magnetoresistance (MR) measurements, in which the electric current path is completely separated from the spin current path. Using these non-local measurements, an obvious MR effect was observed at room temperature; the MR effect was ascribed to magnetization reversal of ferromagnetic electrodes. This result is a direct demonstration of spin injection into a graphene thin film. Furthermore, this is the first report of spin injection into molecules at room temperature.

An anomalous distortion is often observed in the transfer characteristics of graphene fieldeffect transistors. We fabricate graphene transistors with ferromagnetic metal electrodes, which reproducibly display distorted transfer characteristics, and show that the distortion is caused by metal-graphene contacts with no charge-density pinning effect. The pinning effect, where the gate voltage cannot tune the charge density of graphene at the metal electrodes, has been experimentally observed; however, a pinning-free interface is achieved with easilyoxidizable metals. The distortion should be a serious problem for flexible electronic devices with graphene.

Oxygen molecules are found to exhibit non-negligible reactivity with graphene under strong light irradiation in the presence of water. The reaction is triggered by the laser Raman spectroscopy measurement itself, and the D band (ca. 1340 cm-1) becomes larger as the laser irradiation is prolonged. The electronic transport properties of the graphene derivative are also investigated and both the electron and hole mobility are found to be reduced. These results are attributed to oxidation of graphene. This primitive modification method can be exploited to manipulate the structural and electronic properties of graphene.Comment: 22 pages including supporting informatio

Graphene on a dielectric substrate exhibits spatial doping inhomogeneities, forming electron-hole puddles. Understanding and controlling the latter is of crucial importance for unraveling many of graphene's fundamental properties at the Dirac point. Here we show the coexistence and correlation of charge puddles and topographic ripples in graphene decoupled from the metallic substrate it was grown on. The analysis of interferences of Dirac fermion-like electrons yields a linear dispersion relation, indicating that graphene on a metal can recover its intrinsic electronic properties.