Electronic properties of bilayer silicene nanoribbons modulated by external electric field and carbon adsorption

With the continuous development of nano-emerging technologies, silicene nanoribbons, a promising nanostructure for a wide range of applications, have attracted much attention due to their potential applications in electronics and optoelectronics. In this paper, we modelled armchair bilayer silicene nanoribbons (ASiNRs) with widths of 4-15 layers by using the self-consistent charge-density functional tight-binding (SCC-DFTB) method and investigated the effects of geometrical structure and electrical properties of the ASiNRs after adsorption of Si atoms and adsorption of C atoms with an electric field of 0.1 V/nm - 5 V/nm applied on top of the C-atom adsorption. It is found that among the two kinds of atom adsorption, the structure after C atom adsorption is more stable, the bandgap of the structure with a narrower width is opened up more, and a weak electric field of 0.1 V/nm is applied to regulate the bandgap of the nanoribbon more effectively. Whether Si atom adsorption or C atom adsorption, the structure with a narrow width is more likely to exhibit semiconductor properties, the wider the width is, the more metallic it is, and the same is true after applying an electric field. Atom adsorption causes ASiNRs to undergo an obvious charge transfer behaviour. The direction of charge transfer is always from the silicene atoms to the adsorbed atoms, with the adsorbed atoms exhibiting negative electronegativity and the corresponding Si atoms all exhibiting positive electronegativity and the amount of charge transfer is significantly higher for C atom adsorption than for Si atom adsorption.