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

Abstract

AbstractDue 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.