Silicene on metallic quantum wells: An efficient way of tuning silicene-substrate interaction

We propose a powerful method for controlling interaction between silicene and a substrate utilizing quantum size effect, which allows growing silicene with tailored electronic properties. As an example we consider silicene on ultrathin Pb(111) layers and demonstrate how the properties of silicene, including the binding energy and the Dirac bands, can easily be tuned by quantum well states of the substrate. We also discover a novel mechanism of protecting the Dirac electrons from the influence of the substrate. This is associated with a special arrangement of a part of the Si atoms in silicene. These findings emphasize the essential role of interfacial coupling and open new routes to create silicenelike two-dimensional structures with controlled electronic properties.

Figure 1

(a) The binding energy of silicene to Pb films (blue line) and of the top Pb layer to the rest of the slab (red line) as a function of different numbers of Pb layers. Evolution of the energy gap at the Dirac point (b), position of the Dirac point (c), and charge transfer between silicene and Pb substrate (d) with Pb QW thickness.

Figure 2

(a) Constant-current STM topography of silicene on a 3-ML-thick Pb film, calculated at the bias voltage of $-1\mathrm{V}$. (b) and (c) corresponding images for 4 and 5 MLs. Arrows point to the bright protrusions most strongly affected by the QSE.

Figure 3

Evolution of the band structure of silicene on Pb layers as a function of Pb thickness. Black solid lines show the unsupported silicene band structure, which has been calculated by fixing positions of Si atoms as obtained in the full slab calculations and removing the substrate.

Figure 4

Projected band structure of silicene on a 4-ML-thick Pb film. (a) Contribution of Pb $6p_z$, (b) top Si $3p_z$, and (c) bottom Si $3p_z$ states to the electronic bands.

Figure 5

The same as in Fig. 4 for silicene on a 5-ML-thick Pb film.