▎ 摘　　要

We consider the problem of electron states related to the strongly localized potential of a single impurity in graphene. Our model simulates the effect of a neutral impurity atom (substituting for the carbon atom) on the energy spectrum of electrons near the Dirac points. The model also can describe the effect of an adatom on the surface of graphene. We take into account the internal spin-orbit interaction, which essentially modifies the structure of electron bands near the Dirac points, leading effectively to an energy gap. This might result in the occurrence of additional impurity states in the vicinity of the energy gap. As a result, the spin-orbit gap in graphene can be experimentally unobservable due to a large number of adsorbed light atoms at the graphene surface, which create the impurity states in the gap. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3598130]