Mechanism for puddle formation in graphene
  When graphene is close to charge neutrality, its energy landscape is highly inhomogeneous, forming a sea of electron-like and hole-like puddles, which determine the properties of graphene at low carrier density. However, the details of the puddle formation have remained elusive. We demonstrate numerically that in sharp contrast to monolayer graphene, the normalized autocorrelation function for the puddle landscape in bilayer graphene depends only on the distance between the graphene and the source of the long-ranged impurity potential. By comparing with available experimental data, we find quantitative evidence for the implied differences in scanning tunneling microscopy measurements of electron and hole puddles for monolayer and bilayer graphene in nominally the same disorder potential. 
Shaffique Adam, Suyong Jung, Nikolai N. Klimov, Nikolai B. Zhitenev,   Joseph A. Stroscio, M. D. Stiles
cond-mat.mes-hall cond-mat.mtrl-sci