Stabilized silicene within bilayer graphene: A proposal based on molecular dynamics and density-functional tight-binding calculations

Freestanding silicene is predicted to display comparable electronic properties as graphene. However, the yet synthesized silicenelike structures have been only realized on different substrates which turned out to exhibit versatile crystallographic structures that are very different from the theoretically predicted buckled phase of freestanding silicene. This calls for a different approach where silicene is stabilized using very weakly interacting surfaces. We propose here a route by using graphene bilayer as a scaffold. The confinement between the flat graphene layers results in a planar clustering of Si atoms with small buckling, which is energetically unfavorable in vacuum. Buckled hexagonal arrangement of Si atoms similar to freestanding silicene is observed for large clusters, which, in contrast to Si atoms on metallic surfaces, is only very weakly van der Waals coupled to the graphene layers. These clusters are found to be stable well above room temperature. Our findings, which are supported by density-functional tight-binding calculations, show that intercalating bilayer graphene with Si is a favorable route to realize silicene.

Figure 1

(a) A single Si atom on top of bilayer graphene. (b)–(j) Ground state configurations [top (side) view on the left (right)] of Si${}_N$ clusters intercalating bilayer graphene. The numbers show the formation energies in eV per Si atom.

Figure 2

(a)–(g) Geometries and formation energies (eV per Si atom) of Si clusters with six-membered rings inside a bilayer graphene (graphene layers are not shown). (h) Silicene sheet (160 Si atom computational unit cell) intercalating bilayer graphene.

Figure 3

Snapshots of Si${}_{18}$ cluster between bilayer graphene at different temperatures during a rapid cooling.

Figure 4

DFTB results: (a) Top and (b) side view of the equilibrium structure of Si${}_{24}$ cluster intercalated inside bilayer graphene with 960 carbon atoms in each layer. (c) Optimized structure of Si${}_{24}$ cluster without graphene. (d) Silicene sheet (160 Si atoms) intercalating bilayer graphene.

Figure 5

Lindemann index of Si${}_N$ clusters intercalating bilayer graphene as a function of temperature for different $N$. Inset shows the melting temperature $T_m$ of quasi-2D Si${}_N$ clusters constructed using the criterion $\delta =0.1$. Panels 1–3 show snapshots of the Si${}_N$ clusters at temperatures indicated in the main panel indicated by filled symbols.