Growth of 2D MoP single crystals on liquid metals by chemical vapor deposition

Two-dimensional (2D) transition metal phosphides (TMPs) are predicted with many novel properties and various applications. As a member of TMPs family, molybdenum phosphide (MoP) exhibits many exotic physicochemical properties. However, the synthesis of high-quality 2D MoP single crystals is not reported due to the lack of reliable fabrication method, which limits the exploration of 2D MoP. Here, we report the growth of high-quality ultrathin MoP single crystals with thickness down to 10 nm on liquid metals via chemical vapor deposition (CVD). The smooth surface of liquid Ga is regarded as a suitable growth substrate for producing 2D MoP single crystals. The Mo source diffuses toward the Ga surface due to the high surface energy to react with phosphorus source, thus to fabricate ultrathin MoP single crystals. Then, we study the second harmonic generation (SHG) of 2D MoP for the first time due to its intrinsic non-centrosymmetric structure. Our study provides an new approach to synthesize and explore other 2D TMPs for future applications.