Large‐Area Structure‐Selective Synthesis of Symmetry‐Broken MoSe2 and Their Broadband Nonlinear Optical Response

Abstract Transition metal dichalcogenides (TMDCs) have various electronic and optical properties depending on their structure, so they can be used as a fascinating material in various applications including photonics, electronics, optoelectronics, and valleytronics. In particular, spiral TMDCs grown through the formation of screw dislocations exhibit novel electronic and optical properties different from layer‐by‐layer TMDCs. However, large‐area structure‐selective synthesis of TMDCs remains challenging. Here, this work reports for the first time the large‐area structure‐selective synthesis of monolayer MoSe 2 and spiral MoSe 2 using a flux‐controlled chemical vapor deposition method. Under a low MoSe 2 flux condition, monolayer MoSe 2 is synthesized, whereas thick spiral MoSe 2 is synthesized under a high flux condition. Under a medium flux condition, both monolayer and spiral MoSe 2 are synthesized. In addition, through the nonlinear optical (NLO) signal analysis of monolayer MoSe 2 and spiral MoSe 2 , the giant enhancement of NLO signals induced by the combined effect of breaking inversion symmetry and the excitonic resonance effects in the synthesized MoSe 2 is confirmed. Monolayer MoSe 2 and spiral MoSe 2 synthesized using this method are expected to be used as advanced optical materials for novel electronics, optoelectronics, and NLO applications.