Inversion Symmetry Broken 2D 3R‐MoTe2

Inversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the strong spin-orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo-Te bond and the small energy imparity among phases make it a big challenge to obtain pure-phase single crystalline MoTe2, especially; it is still a virgin land to obtain two-dimensional (2D) 3R-MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R-MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as-synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer-independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as-synthesized 3R-MoTe2 is demonstrated as well.