Figure 1

(a) STM image of large area of silicene (sample bias voltage $V_s=-0.70\mathrm{V}$ and tunneling current $I_t=0.19\mathrm{nA}$. The image size is $35\times 35{\mathrm{nm}}^2$.) (b) High resolution STM image of the $4\times 4$ silicene ($V_S=+0.50\mathrm{V}$ and $I_t=0.30\mathrm{nA}$, $3.65\times 3.65{\mathrm{nm}}^2$). The unit cell is shown by the white rhombus. (c) The STS spectra of silicene for various magnetic fields perpendicular to the sample surface, $B_z$. (d) The STS spectra of HOPG for various $B_Z$. The purple triangles and green circles show the peaks originating from the LLs of massless and massive Dirac fermions, respectively. The $n=0$ LL is marked by the yellow bar and the $n=1$ LL of massive Dirac fermions is not clearly resolved in 3 T due to low magnetic field.Reuse & Permissions

Figure 2

(a), (b), and (c) show the geometric structures of the freestanding lightly-buckled silicene (FLBS), the freestanding distorted silicene (FDS) and the $4\times 4$ silicene, respectively. (d) Brillouin zones (BZ) corresponding to the unit cells drawn by the larger red and smaller blue rhombuses in (a) through (c). The red (blue) hexagon represents the BZ for the red (blue) rhombus drawn in (a) through (c). The black hexagon indicates the BZ of the $1\times 1$ unit cell of Ag(111). (e), (f) and (g) show the band structures of FLBS, FDS and $4\times 4$ silicene, respectively. The ${\overline{K}}_1$ point of the blue BZ is matched with the $\overline{\Gamma }$ point of the red BZ in the extended zone scheme, and thus the Dirac cone of FLBS appears at the $\overline{\Gamma }$ point. The color bar in (g) shows the relative contribution of Si $3p_z$ orbital for each band. The red (blue) shows a higher (lower) contribution. The blue bands are basically derived from the substrate Ag. The cross sections of the total charge distribution along the black dotted line in (a) and (b) are shown for (h) FLBS and (i) FDS. The black (gray) region represents a higher (lower) electron density. The cross section of the differential charge distribution (DCD) is shown for (j) the $4\times 4$ silicene. The black dotted circles represent Si and Ag atoms. The region where the electron density increases (decreases) is colored red (blue). The figures (e)–(j) are rendered by VESTA [33].Reuse & Permissions