Edge or interface effect on bandgap openings in graphene nanostructures: A thermodynamic approach

Abstract As a two-dimensional (2D) material with hexagonal structure, graphene shows high electron mobility, high thermal conductivity, and compatibility to industry-standard lithographic processing for nano and microelectronics applications. Different ways have been adopted to theoretically explore the mechanism of bandgap openings (BOs) in graphene nanostructures with regard to the edge or interface effect, involving the quantum confinement model, the bond-order-length-strength model, the lattice model, and the bandgap thermodynamic approach. By eliminating limitations in other theories, the bandgap thermodynamic approach, free of adjustable parameters, can be applied to systematically elucidate the BO mechanisms in graphene nanostructures. Supported by the energy band theory, this approach correlates the BOs to changes in the atomic cohesive energy of C atoms in graphene nanostructures at the edge or interface, which is associated with coordination imperfections or distinct chemical bonding. Hence, the openings can be modulated by a series of parameters, such as size, dimension, edge geometry, edge saturation, interfacial interaction, and electronic configuration of C atoms. Using the bandgap thermodynamic approach, strikingly, new routes are suggested to engineer and control the bandgaps of graphene and graphene-based nanostructures, helping the design of graphene-based devices for its application in electronics.