Structures and Electronic Properties of Graphene with Vacancy Defects
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Structures and Electronic Properties of Graphene with Vacancy Defects J. Sugimoto and K. Shintani Department of Mechanical Engineering and Intelligent Systems, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
ABSTRACT The structures and electronic properties of graphene with defects consisting of one to six atomic vacancies are investigated using first-principles calculation. All of the geometrically possible initial structures of a movacancy or a multivacancy in graphene are equilibrated. The formation energies and electronic band structures for the equilibrated defective structures are calculated. It is suggested non-zero bandgaps may be induced in graphene by introducing some types of monovacancy or multivacancy although further checks regarding supercell size are necessary to ensure the present results. INTRODUCTION The impact of creation of graphene by exfoliation [1,2] opened a new era of materials science. Especially in recent years, there occurred an explosion of the number of research papers which cover the growth [3], characterization of the fundamental properties [4], and applications [5] of graphene. Pristine graphene is itself a zero-bandgap semiconductor. Hence, various ideas to create nonzero bandgaps in graphene are suggested; engineering the electronic structure of epitaxial graphene by transfer doping and atomic intercalation [6], strain engineering of graphene [7], fabrication of graphene nanoribbons with various edge modifications [8], functionalization by dopants, impurities, and defects [9] etc. The electronic properties of graphene with multivacancies are focused on in this paper. As for vacancies in graphene, Saito et al. [10] studied the stabilities and atomic geometries of multivacancies using first-principles calculation. They examined the formation energies of a monovacancy V1 and multivacancies V2～V8, and concluded that pentagon formation in their relaxed systems stabilizes the defects and the magic number of the multivacancies are 2, 4, and 6. Lehtinen et al. [11] studied the effects of ion irradiation on graphene using analytical potential and density-functional theory models. They showed all defects beyond single and double vacancies are formed via in-plane recoils. Ugeda et al. [12] identified a common twofold symmetry point defect in irradiated graphene on different substrates by low-temperature scanning tunneling microscopy. Their first-principles calculation revealed that in this type of defects, two adjacent missing atoms accommodate themselves in a rearranged atomic network consisting of two pentagons and one octagon. Kotakoski et al. [13,14] transformed graphene into a two-dimensional amorphous carbon membrane using electron irradiation. Controlling carefully the electron energy, they selectively enhanced and suppressed the two defect production mechanisms, which were shown to be atom ejection and bond rotation through the comparison of the experimental images with density-functional theory (DFT) calculations. From the DFT calculations, they
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