Effect of high-k environment on charge carrier mobility in graphene
  It is widely assumed that the dominant source of scattering in graphene is charged impurities in a substrate. We have tested this conjecture by studying graphene placed on various substrates and in high-k media. Unexpectedly, we have found no significant changes in carrier mobility either for different substrates or by using glycerol, ethanol and water as a top dielectric layer. This suggests that Coulomb impurities are not the scattering mechanism that limits the mean free path currently attainable for graphene on a substrate. 
L. A. Ponomarenko, R. Yang, T. M. Mohiuddin, S. M. Morozov, A. A.   Zhukov, F. Schedin, E. W. Hill, K. S. Novoselov, M. I. K...