Free-Standing Bilayer Silicene: The Effect of Stacking Order on the Structural, Electronic, and Transport Properties

We theoretically investigate the structural, electronic, and transport properties of bilayer 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 loses its buckled structure, becoming planar. This structural conformation is established since there is an energy gain if the system loses its pi cloud to create extra (sigma-like) chemical bonds between the two layers. Simulated scanning tunneling microscopy (STM) images show excellent agreement with experimental STM images of bilayers silicene. We also analyze the two-dimensional (2D) and three-dimensional (3D) features of the band structure of the bilayer 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 (IdsVds), where for some stacks we verify an anisotropic behavior of the current as a function of the direction of the applied bias.