In this Letter, we study the structural and electronic properties of single-layer and bilayer phosphorene with graphene. We show that both the properties of graphene and phosphorene are preserved in the composed heterostructure. We also show that via the application of a perpendicular electric field, it is possible to tune the position of the band structure of phosphorene with respect to that of graphene. This leads to control of the Schottky barrier height and doping of phosphorene, which are important features in the design of new devices based on van der Waals heterostructures.

Exploring two-dimensional layered materials, such as molybdenum disulfide (MoS 2 ), for (opto)electronic applications requires detailed knowledge of their electronic band structure. Using first-principles calculations we trace the evolution of the band structure as a function of the number of layers, starting from a monolayer, which has a direct gap, to the bulk material, which has an indirect gap. We find that, with respect to the vacuum level, the valence-band maximum (VBM) increases rapidly with the number of layers, while the conduction-band minimum (CBM) remains almost constant. For two or more layers the VBM always occurs at Γ and the CBM occurs at K.These findings are analyzed in terms of the orbital composition of the valence-and conduction-band edges at the various high-symmetry points in the Brillouin zone.

Very recently two dimensional layers of boron atoms, so called borophene, have been successfully synthesized. It presents a metallic band structure, with a strong anisotropic character. Upon further hydrogen adsorption a new material is obtained, borophane; giving rise to a Dirac cone structure like the one in graphene. We have performed a first-principles study of the electronic and transport properties of borophene and borophane through the Landauer-Büttiker formalism. We find that borophene presents an electronic current two orders of magnitude larger than borophane. In addition we verified the direction dependence of the electronic current in two perpendicular directions, namely, I and I; where for both systems, we found a current ratio, η = I/I, of around 2. Aiming to control such a current anisotropy, η, we performed a study of its dependence with respect to an external strain. Where, by stretching the borophane sheet, η increases by 11% for a bias voltage of 50 mV.

We theoretically investigate the structural, electronic and transport properties of bilayers silicene. Due to the large numbers of degrees of freedom permitted by the buckled structure of the silicene, its bilayer structure can present several possible stacking configurations. We show that in the lowest energy conformation, named AA p , the bilayer silicene looses its buckled structure becoming planar. This structural conformation is established since there is an energy gain if the system loses its π cloud to create extra (σ-like) chemical bonds between the two layers. Simulated STM images show excellent agreement with experimental STM images of bilayers silicene. We also analyze the 2D and 3D features of the band structure of the bilayers silicene. In particular, we show that the analysis of the 3D band structure is fundamental to a complete understanding of the electronic and transport properties in this material. Moreover, we show that different structures present distinct electronic and transport properties (I ds × V ds ), where for some stacks, we verify an anisotropic behavior of the current as a function of the direction of the applied bias.silicene-based devices, since their intrinsic properties, which are highly dependent of the stacking order, can present a directional dependence as well.