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.

The 1T polymorph of layered transition metal dichalcogenide compound TaS2 undergo phase transition towards low temperature with a periodic structural distortion where the electrons organize themselves in regular pattern which is widely known as charge density wave (CDW) [1]. The commensurate CDW phase of 1T-TaS2 has widely been treated as a quasi two-dimensional phenomenon that coexist with a Mott insulating state. However, recent theoretical calculations predicted the coexistence of CDW phase with a nearly one-dimensional metallic dispersion perpendicular to the crystal planes. In this presentation, I will show the angle-resolved photo emission spectroscopy results which confirms the existence of this metallic band [2]. The experimental band width of this metallic band is in excellent agreement with the predicted stacking order of CDW between the adjacent layers and its periodicity along c axis.

Reliable and controlled interfacing with conventional dielectrics or barrier films remains a critical issue for 2D materials. Early attempts to grow atomic-layer deposited (ALD) layers directly on graphene resulted in inhomogeneous film growth. However, frequently used seed layers can negatively affect the as-grown interface. Here we present a detailed study of ALD Al2O3 nucleation on chemical vapour deposited (CVD) graphene films. By optimizing precursor exposure to promote Al2O3 nucleation, we show high-quality, dense ALD films directly on graphene without the need for seed layers [1]. These techniques have been shown to be suitable to grow sub-nanometre Al2O3 tunnel junctions directly on graphene for spintronic devices [2]. Film thicknesses of 90nm can virtually eliminate gate hysteresis for CVD graphene-based field-effect devices [3]. In addition, unintentional doping is significantly reduced and the room temperature field-effect mobility of encapsulated devices greatly increases. These results are relevant for 2D materials integration with conventional thin film and ultra-large-scale integration technologies.

Jack Alexander-Webber holds Research Fellowship from the Royal Commission for the Exhibition of 1851 and is a Junior Research Fellow of Churchill College Cambridge. He graduated from Royal Holloway, University of London in 2009 with an MSci in Physics. After a summer studentship working for the National Physical Laboratory he began his DPhil in the group of Prof Robin Nicholas at the University of Oxford. His doctoral research was on the properties of low-dimensional nanostructures such as graphene, carbon nanotubes and III-V semiconductors with a particular focus on high magnetic field effects studied both in Oxford and at the European Magnetic Field Laboratory facilities in Grenoble and Toulouse. After completing his DPhil in 2013, Jack undertook an EPSRC Doctoral Prize fellowship at Oxford. He is currently working in the group of Prof Stephan Hofmann in the Department of Engineering at the University of Cambridge. His current research interests lie in developing scalable techniques to integrate low-dimensional nanomaterials in electronic and optoelectronic device applications.