二维MoTe2单晶可控相变的铁电调制

Two-dimensional (2D) materials are the ideal blocks for next generation optical/electronic devices, and the properties of which are largely dependent on the phase type. Thus the key for widely utilization of 2D materials in future is to control the phase. However, the energy difference between various phases of 2D materials is generally so large that the phase transition merely takes place under extreme conditions, hindering its further researches and applications. MoTe2 has considerable small energy difference (~ 0.03 eV) between its H (semiconducting) and T’ (semimetallic) phases, thus the phase transition could be triggered under mild conditions. This project is aiming to realize controllable phase transition in chemical vapor deposition grown MoTe2 single crystals via PZT ferroelectric substrate modulated by external electronic field. Ferroelectric substrate can be polarized under electric field and its remanent polarization under zero input fully meets the charge density injection requirement for the phase transition of MoTe2. Meantime, we will focus on the detailed process of phase transition and mainly on the phase transition process in samples with various phase types, layer numbers and stacking modes. This project would shed light on the mechanism of phase transition in 2D materials under electric field, and speed up the utilization process of 2D materials in next generation of optical/electronic devices.

二维材料是构筑下一代光/电子器件的理想载体，其性能主要取决于材料晶相。实现材料晶相的可调控是二维材料未来得到广泛应用的关键。然而，通常二维材料不同相之间能量差异较大，需要通过极端条件才能实现转变，因而难以得到广泛研究和应用。MoTe2由于其H（半导体性）和T’（半金属性）相之间能量差异极小（~ 0.03 eV），因而可以通过并不严苛的外界能量刺激实现相转变。本项目拟通过气相沉积方法制备不同晶相MoTe2单晶，结合PZT铁电衬底，实现电场调控下MoTe2可逆相转变。铁电衬底可以通过电场进行极化，在零能耗条件下，其剩余极化强度能够满足MoTe2相转变的电荷注入浓度要求。同时，关注相转变诱发及其演化的具体过程，主要考察不同晶相，不同层数，不同堆垛模式的二维MoTe2中相转变的演化规律。本项目的研究工作将有助于理解电场调控下二维材料相转变内在机制，加速二维材料在下一代光/电子器件的应用进程。

二维材料的性质很大程度上取决于其晶相结构，如何实现材料晶相结构的可控制备是设计和提升二维材料性能的关键。申请人课题设计最初以具有“最低过渡金属硫族化合物（TMDs）晶相转化能垒”的二维MoTe2为研究对象，期望通过铁电调制的方式实现二维MoTe2在不同晶相结构之间的可控转化，但实验进展有限，后来研究兴趣逐渐拓展延伸至其他二维材料和调控方法，取得的主要成绩如下：1）基于生长热力学和动力学调控，分别通过生长微环境设计和超快激光退火的方式，实现了二维GaTe不同晶相之间的转化；2）通过生长热力学设计，实现了二维VO2内部晶相结构的局域化转变，成功制备了周期性分布的晶相结构，将材料的面内电学各向异性比值提升了两个数量级；3）基于二维ReS2系统研究了电学各向异性的产生机制、调控方式和邻近效应等，实现了电学各向异性比值一个数量级的提升。在Fundamental Research, CCS Chem, Advanced Functional Materials, Small Methods, Nano Reseach等期刊发表通讯论文8篇。本项目旨在通过对二维材料不同晶相结构之间的转化进行研究，有助于深入理解晶相转化的机制和实现途径，为将来二维材料的性能设计和提升提供基础。