▎ 摘　　要

We report first-principles calculations of atomic and electronic structures of epitaxial single-layer graphene on Si-terminated 4H-SiC(0 00 1) surface under homogeneous transverse electric fields. We find that atomic positions are insensitive to applied electric fields, but the electronic band structures of the graphene layer are shifted in energy, depending strongly on the applied electric fields, while those of the buffer layer are almost unchanged. This effect finally results in field-induced closing of the energy gap at the Dirac energy point and recovery of the conic feature of the low-energy band structures of freestanding graphene, which are verified and analyzed further with a tight-binding model consisting of the single-layer and the buffer-layer graphene only. The recovery of conical dispersion of the single-layer graphene and ambipolar field-effect behavior, despite the band-gap closure under electric field, makes epitaxial single-layer graphene one of the promising alternatives to current state-of-the-art transistors for radiofrequency applications. (C) 2011 Elsevier Ltd. All rights reserved.