Graphene exhibits astonishing mesoscopic effects hosting massless Dirac quasiparticles that can travel with little scattering and behave like light rays. Mean free paths of up to 28 mm have been reached at low temperature [1], while ballistic transport in the micrometre scale has become accessible even at room temperature. Electrons in such devices undergo negative refraction when passing p-n junctions and can be manipulated by external electromagnetic fields, paving the way to a new concept of electronics based on the principles of optics [2]. One interesting perspective is a “2D Dirac fermion microscope” (DFM), where electron guns, tunable lenses, deflectors, and detectors are combined in a graphene “vacuum chamber” to image different types of targets [3]. We aim at performing multi-scale simulations of ballistic graphene devices starting from atoms, combining density functional theory (DFT) and large-scale tight-binding (TB) models in a non-equilibrium Green’s functions (NEGF) framework. As an application, we use a NEGF+TB model to reproduce key features of electron transport in a DFM, such as electron beam collimation, deflection and scattering off circular p-n junctions. For targets with size larger than the Fermi wavelength (mesoscopic limit), our results resemble those of semiclassical simulations, but quantum coherence leads to a richer emission and reflection structure which may be utilized to extract more detailed information.

Gaetano Calogero is currently a PhD student at the Danish Technical University (DTU), in the Theoretical Nanoelectronics group led by Prof. M. Brandbyge. He is primarily interested in theory and multi-scale atomistic simulations of ballistic graphene nanoelectronics. He received his B.S. degree in Physics from University of Catania (IT) in 2013, with a thesis on the role of basis sets on the unfolding of supercell bandstructures. He got his M.S. degree in Physics from the same university (2015), after spending a research period of 5 months as Erasmus+ student at the Debye Institute of Utrecht University (NL), where he worked on density functional theory simulations of atomic force microscopy of nitrogen-doped graphene.