Crystalline Orientation‐Tunable Growth of Hexagonal and Tetragonal 2H─PtSe₂ Single‐Crystal Flakes

Abstract Due to the narrow bandgap, environment stability, and Pt vacancy‐induced magnetism, PtSe₂ has been considered a promising candidate for future broadband photodetection and electronics. However, the growth of single‐crystal PtSe₂ is still a challenge. Herein, the synthesis of hexagonal and tetragonal 2H─PtSe₂ single‐crystal flakes by precisely tailoring the growth temperature is reported. Through atomic structure analysis, hexagonal and tetragonal flakes are proven c‐axis and a‐axis orientations of 2H─PtSe₂, indicating the preferred nucleation orientations are along the basal plane and vertically basal plane, respectively. The crystalline orientation‐dependent properties are studied including high‐pressure and polarized in situ‐Raman, electrical transport. The out‐of‐basal plane vibration (A_1g) is sensitive to pressure showing 2.744 and 3.282 cm⁻¹ GPa⁻¹ corresponding to c‐2H─PtSe₂ and a‐2H─PtSe₂, respectively. The conductivity of c‐2H─PtSe₂ is 57 times higher than that of a‐2H─PtSe₂. Furthermore, by studying magnetic transport at low temperatures, both c‐2H─PtSe₂ and a‐2H─PtSe₂ exhibit butterfly‐shaped magnetoresistance hysteresis suggesting their ferromagnetic property. The c‐2H─PtSe₂ has a higher |MR| ratio and higher coercive field compared with a‐2H─PtSe₂, indicating that across multilayer carrier regulation for c‐2H─PtSe₂ is more difficult than intra‐layer carrier regulation for a‐2H─PtSe₂. This study opens the way to grow different crystalline orientations of 2D materials and will bring more abundant properties.