▎ 摘　　要

By applying nonequilibrium Green's functions in combination with density-functional theory, we have investigated the effects of two side groups, NH2 and NO2, on the electronic transport properties of the trigonal graphene flake. It has been found that the rectifying ratios (RR) and direction can be significantly tuned by the type and the attached positions of side groups. The NH2 group shows an obvious electron-donating characteristic, whereas NO2 group demonstrates a poorly electron-accepting behavior in these systems. The analysis on the spatial distribution and the energy level of frontier orbitals, transmission spectra, and electrostatic potential distribution give an inside view of the observed results. (C) 2012 Elsevier B.V. All rights reserved.