Electronic and Transport Properties of Defected Graphene Nanoribbons

Abstract

Graphene nanoribbons, quasi-one-dimensional structures of carbon, are fascinating materials. These structures can be constructed as strips of graphene sheet, the two dimentional honeycomb lattice of carbon with sp2 hybridization. Geometrically two main types of slice can be cut from a graphene sheet, with zigzag edge and armchair edge (Niimi05; Kobayashi05). The edge geometry is the key parameter which determines the electronic properties of the nanoribbons. Although the two-dimensional graphene is a zero band-gap semi-metal, electronic structure of nanoribbons depend on their edge geomtery (Saito92; Klein94; Fujita96; Son06a). A simple tight-binding model with one orbital per atom predicts that zigzag nanoribbons are metallic. But density functional calculations shows that all graphene nanoribbons are semiconductors at their ground state with band gaps which depend on their width and edge geometry, closing at infinite width, i. e. infinite graphene. Moreover, the electronic structure of graphene nanoribbons can be modified by chemical functionalization, such as functionalization by various atomic sepcies or by functional groups (Maruyama04a; Gunlycke07; Hod07; Gorjizadeh08). A large variety of electronic and magnetic properties, such as semiconducting with a wide range of band gap, metallic, ferromagnetic, antiferromagnetic, half-metallic, half-semiconducting, can be obtained by chamical modifications of the nanoribbons. Modification of the edge or using an adsorbate or substitution of carbons of the nanoribbon with an appropriate host are different options of functionalizations of these materials. These properties, along with the ballistic electronic transport, and the quantum Hall effect (Novoselov05a; Zhang05) and high carrier mobility (Novoselov05a) cause these quasi-1D materials to be promising candidates for nanoelectronics applications (Novoselov04b; Son06b; Obradovic06; Li08; Hod09; Zhu10). Various junctions can be constructed by connecting nanoribbons of different widths and types with perfect atomic interface, and electronic device can be integrated on them by selective chemical funtionalization on a single nanoribbon sheet (Huang07; Yan07; Gorjizadeh08). In order to achieve their potential for these applications it is essential to have a better understanding of the electronic structure of graphene nanoribbons and have ability to control them. From a practical point of view, when nanoribbons are fabricated