▎ 摘　　要

We report on the topographical and electrical characterisations of 1 nm thick Al2O3 dielectric films on graphene. The Al2O3 is grown by sputtering a 0.6 nm Al layer on graphene and subsequentially oxidizing it in an O-2 atmosphere. The Al2O3 layer presents no pinholes and is homogeneous enough to act as a tunnel barrier. A resistance-area product in the mega-ohm micrometer-square range is found. Comparatively, the growth of Al2O3 by evaporation does not lead to well-wetted films on graphene. Application of this high quality sputtered tunnel barrier to efficient spin injection in graphene is discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765348]