Fig. 1. (a) Fabrication process of amorphous silicon nanofilm by using PLD method, (b) TEM images with nanofilm structure of amorphous silicon, (c) preparing process of silicene crystal by using coherent electron beam to irradiate amorphous silicon nanofilm, and (d) TEM image of spot shape occurring with coherent electron beam irradiating surface (left), and TEM image of the silicene crystal (right).

Fig. 2. (a) TEM image of silicene with hexagonal lattices, (b) TEM image of new silicene with rectangular lattices, with inset exhibiting electronic diffraction pattern of rectangular lattice.

Fig. 3. Simulation model of ideal primal 2D silicon with hexagonal lattice passivated by hydrogen atoms (white balls), showing (a) laterally cross-cut structure of ideal primal model in 2D structure with hexagonal lattice, (b) overlook structure of ideal primal model in 2D structure with hexagonal lattice, (c) silicene structure with hexagonal lattice after optimizing process in simulating calculation, in which convex bond angle of silicon atom is about 115°, and (d) TEM image of silicene crystal with hexagonal lattice observed in experiment.

Fig. 4. (a) Energy band structure calculated in simulation model of silicene with hexagonal lattice, where it has a direct bandgap of 1.4 eV and a nearly Dirac-cone-like shape at Γ point, (b) density distribution of states with localized peak near conduction band valley calculated in simulation model of silicene with hexagonal lattice.

Fig. 5. Simulation model of 2D crystal with rectangular lattice, showing (a) laterally cross-cut structure of ideal primal model of 2D structure of silicon crystal with rectangular lattice, and (b) overlook structure of ideal primal model of 2D structure of silicon crystal with rectangular lattice.

Fig. 6. Change process in CASTEP geometry optimization of new silicene crystal with rectangular lattice, showing (a) change process of structure energy in optimization process, (b) new silicene crystal with rectangular lattice after optimizing process in simulating calculation, in which convex bond angle of silicon atom is about 118°, and (c) TEM image of new silicene crystal with rectangular lattice observed in experiment.

Fig. 7. (a) Calculated energy band structure for new silicene crystal with rectangular lattice showing a real direct bandgap of 0.78 eV and a nearly Dirac-cone-like shape in X region, and (b) simulated density distribution of states for new silicene crystal with rectangular lattice, showing localized peaks in bandgap.