Fig. 1. (a) Structure model of free silicene; (b) band structure of silicene in free state^[23]; (c), (d) the STM images of different phases of silicene on Ag(111)^[24]; (e) STM image, simulated STM image, theoretical calculation structure of silicene on Ir(111)^[25].

Fig. 2. (a) STM image of germanene on Pt(111); (b) and (c) are the structure and electron localization functions of germanene on Pt(111) surface, respectively; (d) LEED pattern of germanene on Pt(111)^[26]; (e) energy versus hexagonal lattice constant of 2D Ge is calculated for various honeycomb structures; (f) and (g) phonon dispersion curves obtained by force-constant and linear response theory are presented by black and dashed green curves, respectively^[27].

Fig. 3. (a) Top view of both the top and bottom Sn atoms and its STM image; (b) side view of Sn atoms arrangement (layer A is the top layer, layer B is the sub top layer)^[32]; (c) high-resolution STM image of the stanene film; (d) schematic atomic model of the honeycomb stanene; (e) profile along the line in c showing that the adjacent Sn atoms are identical in apparent height; (f) 2D BZs of ultraflat stanene on Cu(111); (g) and (h) ARPES spectra of 0.9 ML stanene on Cu(111) along the M-Γ-K-M₂ (g) and M-Γ-M′-Γ₂ (h) directions^[33].

Fig. 4. (a) and (b) are two-dimensional boron sheets structure figures^[40]; (c) STM topographic image of boron structures on Ag(111), with a substrate temperature of ~570 K during growth; (d) STM image of boron sheets after annealing the surface in Fig.4(c) to 650 K. The two different phases are labelled “S1” and “S2”; (e) high-resolution STM image of S1 phases; (f) high-resolution STM image of S2 phases; (g) top and side views of the S1 model; (h) top and side views of the S2 model^[41].

Fig. 5. (a) STM image and LEED image of hafnium on Ir(111); (b) atomic resolution STM images of hafnium on Ir(111); (c) the 2D charge density in the Hf plane on Ir(111) substrate^[43].

Fig. 6. (a) High-resolution STM image of single layer phosphorus on Au(111); (b) the line profile along the red line in panel (a)^[47]; (c) top and side views of few-layer phosphorene; (d) DFT-calculated band structure of phosphorene monolayer^[46].

Fig. 7. (a) Schematic of monolayer antimonene formed on PdTe₂ substrate; (b) STM image of large antimonene island on PdTe₂; (c) atomic resolution STM image of monolayer antimonene; (d) XPS results before and after sample exposure to air^[53]; (e) the structural model of buck antimonene monolayer and antimonene nanoisland on Cu(111) substrate; (f) side view of panel (e); (g) large-scale STM image and LEED pattern of the antimonene monolayer on Cu(111); (h) atomic resolution STM image of the first buckled layer and island^[54].

Fig. 8. (a) STM image of bismuthene on SiC (0001); (b) high resolution STM image for occupied states; (c) bismuthene on SiC(0001) structural model; (d) theoretical band structure and ARPES measurementsts^[61].

Fig. 9. (a) Structural model of h-BN nanomaterials; (b) STM image of single layer h-BN on Cu (111); (c) contrast-inverted LEED pattern of a single layer h-BN/Cu (111) recorded at room temperature^[70]; (d) thermal conductivity of polymeric composites using BN particles, nanotubes and nanosheets^[71].

Fig. 10. (a) Large-scale STM image of MoS₂ single-layer islands on the Au(111) surface; (b) STM image of a single MoS₂ island with a hexagon shape crossing a single Au(111) step^[75]; (c) bandgap transition of MoS₂^[76] from bulk to monolayer; (d) schematic of monolayer MoS₂ photodetector^[77].

Fig. 11. (a) Structural model of monolayer MoSe₂^[80]; (b) DFT optimized monolayer MoSe₂ atomic model on Au(111) surface; (c) atomic resolution STM image of monolayer MoSe₂; (d) theoretical simulated STM image based on the calculated structure in (b); (e) STM image of singlelayer MoSe₂ islands on Au(111) substrate^[83]; (f) height profile of MoSe₂ islands marked by a dashed blue line in (e).

Fig. 12. (a) Schematic of the fabrication of PtSe₂ thin films by a single step of direct selenization of a Pt(111) substrate; (b) LEED pattern of a PtSe₂ film formed on the Pt(111) substrate; (c) large-scale STM image shows the Moiré pattern of PtSe₂ thin film on Pt(111); (d) atomic resolution STM image of single layer PtSe₂^[88].

Fig. 13. (a) Schematic of the fabrication process of NiSe₂ thin films; (b) NiSe₂ layer has two configurations of T and H^[92]; large-scale STM image (c) and Moiré pattern (d) of the 2D NiSe₂ film^[93].

Fig. 14. (a) Schematic of the crystal structure of monolayer WSe₂^[98]; (b) atomic resolution STM image(75 nm × 75 nm) of WSe₂ film; (c) theoretical band structures of monolayer WSe₂^[100]; (d) photoluminescence of WSe₂/Graphene heterostructure^[101]; (e) atomic structure of single layer 1H and 1T' WSe₂; (f) corresponding 2D Brillouin zones with high symmetry points labeled; (g) ARPES map along ΓY^[102].

Fig. 15. (a) Monolayer VSe₂ formed on HOPG substrate; (b) schematic of the fabrication process; (c) dI/dV spectra measured on the VSe₂ island and the substrate; (d), (e) Gaussian-fitting of the two peaks marked in (c), the peak positions are –0.28 V and 0.23 V, respectively ^[107]; (f) AFM attractive-force image, atomic resolution STM image, simulated STM image, and structural model of 1D-patterned ML VSe₂ match each other^[108].

Fig. 16. (a) Large area and high quality STM image of single layer CuSe; (b) two kinds of triangle holes with opposite orientation and parallelogram holes at boundary; (c) a high resolution STM image of single triangle hole; (d) and (e) STM image of Fe atoms selective adsorption on CuSe surface^[110].

Fig. 17. (a) High resolution STM image of monolayer CuSe with 1 D moiré pattern; (b) atomic structure model of free monolayer CuSe; (c), (d) band structure of monolayer CuSe^[113].

Fig. 18. (a) STM image of large-scale AgTe monolayer on Ag(111) substrate; (b) LEED pattern of monolayer AgTe on Ag(111); (c) large-scale and (d) atomic resolution STM images of the AgTe on Ag(111) with higher Te coverage, showing the patterned hexagonal structure of AgTe^[116].

Fig. 19. (a) STM image of 2D TiTe₂ layer on Au(111) substrate; (b) simulated STM image, showing both and (black parallelogram) superstructures^[120]; (c) STM image of PdSe₂ islands on graphene on SiC(0001)^[122]; (d) STM image (500 nm × 500 nm) of Bi₂Te₃ thin film; (e) structure model of the Bi₂Te₃ topological insulator^[127].

Table 1. Summary of growth substrate, characterization methods, configurations, physical properties, and potential appli-cations of monatomic two-dimensional materials grown by MBE.

Table 2. Summary of growth substrate, characterization methods, configurations, physical properties and potential applications of binary two-dimensional materials grown by MBE.