Fig. 1. Sn-Se binary phase diagram^[35]

Fig. 2. Schematic diagrams of SnSe crystal structure^{[4, 37]}. (a) Structural diagram of single-layer SnSe; (b) structural diagram of a-b plane; (c) structural diagram of c-d plane; (d) structural diagram of a-c plane; (e) crystal structures of Pnma and Cmcm phases

Fig. 3. Energy band structures of SnSe. (a) Energy band structures of Pnma phase (left) and Cmcm phase (right) of SnSe^[2]; (b) density of states of Pnma phase (left) and Cmcm phase (right) of SnSe^[2]; (c) average Grüneisen parameters along a, b, and c axes^[4]

Fig. 4. Energy band structures of rock salt SnSe (111) film with thickness of 16 nm^[31]. Energy band structures around Γ- point obtained by (a) ARPES and (b) first-principles calculations; energy band structures around

Fig. 5. Theoretical prediction of thermoelectric property of SnSe^[23]. (a) P_F and Z_T of p-type SnSe at 823K obtained by SPB model, and relationship between thermal conductivity and hole concentration; (b) relationship between Z_T and hole concentration p-type SnSe at 823K obtained by SPB model, after optimizing lattice thermal conductivity

Fig. 6. Single crystal preparation methods. (a) Bridgman method^[58]; (b) sample prepared by Bridgman method and its properties^[11]; (c) temperature gradient method^[60]; (d) sample prepared by temperature gradient method and its properties^[12]

Fig. 7. Polycrystalline preparation technologies. (a) SPS^[64]; (b) HP^[65]

Fig. 8. SEM images of SnSe crystals prepared by adding Se and SnCl2[69]. (a) 5 mmol Se+SnCl₂; (b) 3.3 mmol Se+SnCl₂

Fig. 9. SEM images of SnSe prepared by thermal evaporation at various substrate temperatures^[74]. (a) Room temperature; (b) 150 ℃; (c) 250 ℃; (d) 350 ℃; (e) 450 ℃

Fig. 10. Thin film preparation technologies. (a) CVD; (b) MBE

Fig. 11. Thermoelectric properties of SnSe along a, b, and c axes^[4]. (a)--(d) Thermoelectric transport parameters; (e) Z_T varying with temperature

Fig. 12. Z_T values of polycrystalline SnSe manufactured by different technologies^[45]. (a) Change of Z_T with temperature; (b) average Z_T

Fig. 13. STM images of SnSe^[12]. (a) STM image on b-c plane of undoped p-type SnSe; (b) high-resolution STM image extracted from black line area in Fig. 13(a); (c) STM image of n-type doped SnSe at b-c plane

Fig. 14. Photoelectric properties of SnSe thin film^[99]. (a) Relationship between absorption coefficient and photon energy; (b) dark current and photocurrent change with voltage under different illuminance levels. Dark, 1, 2, and 3 indicate illuminance of 0, 600, 1800, and 3000lx, respectively

Fig. 15. Thermoelectric properties of devices. (a) Thermoelectric properties of hydrothermally synthesized SnSe thin films^[106]; (b) thermoelectric properties of highly textured and hole-doped SnSe thin films^[107]

Fig. 16. Flexible sensors^[109]. (a) Sensing mechanisms for temperature and pressure and corresponding signals; (b) translucent fabric gloves equipped with sensors and corresponding experimental diagrams