▎ 摘　　要

Using the nonequilibrium Green's function theory, transport properties of nanoscale graphene structures deposited on a SiO2/Si substrate have been investigated taking into account the influence of both lattice defects and charged impurities. The calculation argues the metallic lead-graphene coupling responsible for the asymmetric transport of electrons and holes, and shows that the conductivity is generally suppressed by these scattering processes. However, at the charge neutrality point, the screening seems to weaken such a suppression, leading to the minimum conductivity value of 4e(2)/pi h even for the impurity density higher than 10(12) cm(-2), while it is strongly diminished to zero for the vacancy density of 10(11) cm(-2). Obtained results for the conductivity and the charge mobility are also discussed to highlight available experimental data. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3176956]