▎ 摘　　要

We built graphene nanoflakes doped or not with C atoms in the sp(3) hybridization or with Si atoms. These nanoflakes are isolated, i.e. are not connected to any object (substrate or junction). We used a modified tight binding method to compute the pi and sigma density of states. The nanoflakes are semiconducting (due to the armchair geometry of their boundaries) when they are pure but they become conducting when doped because doping removes the degeneracy of the density of states levels. Moreover, we showed that the it Fermi level and the pi Fermi level of both pi and sigma electrons are not superimposed for small isolated nanoflakes. (c) 2010 Elsevier B.V. All rights reserved.