Two Dimensional Electron and Hole Gases at the Surface of Graphite
  We report high-quality two-dimensional (2D) electron and hole gases induced at the surface of graphite by the electric field effect. The 2D carriers reside within a few near-surface atomic layers and exhibit mobilities up to 15,000 and 60,000 cm2/Vs at room and liquid-helium temperatures, respectively. The mobilities imply ballistic transport at micron scale. Pronounced Shubnikov-de Haas oscillations reveal the existence of two types of carries in both 2D electron and hole gases. 
S.V. Morozov, K.S. Novoselov, D. Jiang, A. A. Firsov, S.V. Dubonos &   A.K. Geim