In this talk, the structure and electronic properties of two-dimensional (2D) materials including graphene and hexagonal boron nitride (h-BN) will be discussed. Owing to its crystal symmetry, with two carbon atoms in nearly identical environments per unit cell, graphene has a well-known linear dispersion relationship (E. vs. k) near the Fermi energy. This unique feature gives rise to many of the novel electronic properties of graphene. For h-BN, in contrast, the presence of two inequivalent atoms in each unit cell (boron and nitrogen) produces a gap of 6 eV in its band structure. For both materials, there exists an additional set of electronic states located just above the vacuum level, i.e. 5 - 15 eV above the Fermi energy. These so-called interlayer states have wavefunctions that are peaked between the atomic planes (rather than on the planes), and they turn out to be very useful for characterizing the 2D materials. Low-energy electron microscopy has been used to observe the interlayer states in 2D materials, with results that will be presented in the talk. Furthermore, the current-voltage relationship for graphene / h-BN / graphene tunneling tunnel junctions will be described, displaying highly nonlinear behavior that has application for high-speed transistors. Simulation of such devices will be compared with experimental results.
