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

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 (A1g) 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.