We investigate Klein tunneling in graphene heterojunctions under the influence of a perpendicular magnetic field via the non-equilibrium Green’s function method. We find that the angular dependence of electron transmission is deflected sideways, resulting in the suppression of normally incident electrons and overall decrease in conductance. The off-normal symmetry axis of the transmission profile was analytically derived. Overall tunneling conductance decreases to almost zero regardless of the potential barrier height when the magnetic field (B-field) exceeds a critical value, thus achieving effective confinement of Dirac fermions. The critical field occurs when the width of the magnetic field region matches the diameter of the cyclotron orbit. The potential barrier also induces distinct Fabry-Pérot fringe patterns, with a “constriction region” of low transmission when is close to the Fermi energy. Application of B-field deflects the Fabry-Pérot interference pattern to an off-normal angle. Thus, the conductance of the graphene heterojunctions can be sharply modulated by adjusting the B-field strength and the potential barrier height relative to the Fermi energy.

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Based on the first-principle calculations, we present a study of the effect of Ca doping on the electronic properties of LiCoO2. Studies of band structure and densities of states show that hole states, which enhance the conductivity of semiconductor appear in the valence bands of Ca-doped material due to the increase of Co4+concentration. It is further found that the Ca doping concentration should be controlled within 10 mol% of LiCoO2to keep the crystalline structure unchanged. We expect this study might be helpful for synthesizing good conductivity LiCoO2by controlling Ca doping.

With density functional theory, the structural and electronic properties of Au3 and Au2M (M=Ag, Cu, Pd and Pt) clusters have been studied. The structural results indicate that by substituting one Au atom with M atom, the corresponding geometries are changed slightly. To investigate the electronic properties, bonding properties and highest occupied molecular orbital (HOMO) were observed. It is found that most trends in Au2Pd and Au2Pt are similar and it also happens in the other two doped clusters. In addition, the calculated mulliken overlap populations suggest that doping modify the localized electron between Au and Au atom. It is also found that the contributions from various atoms on HOMO and energies of HOMO are changed. These may make difference in the adsorption of clusters.