Mechanical cleaning of graphene
  Contamination of graphene due to residues from nanofabrication often introduces background doping and reduces charge carrier mobility. For samples of high electronic quality, post-lithography cleaning treatments are therefore needed. We report that mechanical cleaning based on contact mode AFM removes residues and significantly improves the electronic properties. A mechanically cleaned dual-gated bilayer graphene transistor with hBN dielectrics exhibited a mobility of ~36,000 cm2/Vs at low temperature. 
A. M. Goossens, V. E. Calado, A. Barreiro, K. Watanabe, T. Taniguchi,   L. M. K. Vandersypen
cond-mat.mtrl-sci cond-mat.other