亚稳相二硫化钼晶体和二维纳米片的拓扑化学反应制备及物性探索

The 2H molybdenum disulfide (MoS2), as a stable hexagonal phase, has been one of the most studied graphene-like layered transition metal dichalcogenides. In the recent years, metastable MoS2 including 1T, 1T’, 1T’’, and 1T’’’ phases, has attracted considerate interests in the research area of both condensed physics and material science. Different from the edge-sharing [MoS6] trigonal prisms in the 2H MoS2 phase, these metastable phases are composed of the edge-sharing [MoS6] octahedra, which endows them with unique crystal structures and band structures. However, the controlled synthesis of pure metastable phases either in the form of bulk crystals or two-dimensional nanosheets remains a big challenge; the accurate crystal structures of various metastable polytypes are unclear, and the exploration of intrinsic physical properties is rare. In this proposal, based on structural similarity, we aim to develop a low-temperature strategy to prepare pure metastable phases of MoS2 via topochemical reaction. In our protocol, ternary alkali metal ions intercalated AxMoS2（A = Li, Na, K, Cs; x = 0-1）cystals are used as the precursors, which are subjected to ion deintercalation to obtain pure metastable crystals and two-dimensional nanosheets. The structural refinement is performed to determine the crystal structure and unit cells, followed by the study of intrinsic physical properties, including electrical conductivity, magnetic property, light absorption and so on. Then the correlations between intrinsic physical properties and crystal structure, band structure, microstructure and dimension are preliminarily discussed.

2H相二硫化钼（MoS2）是研究最为广泛的类石墨层状过渡金属硫族化合物之一。近年来，由于具有独特的晶体结构和能带结构，[MoS6]八面体配位的亚稳相MoS2（1T、1T’、1T’’和1T’’’相等）逐渐成为了凝聚态物理和材料科学研究的热点。但是，当前纯亚稳相块体和二维纳米片的可控制备依然是难题，多个亚稳相的精确晶体结构未知，本征物理性质也研究的较少。本项目从晶体结构相似性出发，拟基于拓扑化学反应原理开发亚稳相MoS2的低温合成方法，即利用三元AxMoS2（A = Li, Na, K, Cs; x = 0-1）晶体的碱金属离子脱嵌制备纯亚稳相MoS2晶体和二维纳米片。本项目还将进行亚稳相MoS2晶体结构解析及能带结构计算，并探索本征物理性质，如电学性质，磁学性质和光学特性等，初步探讨亚稳相MoS2的基本物性与晶体结构、能带结构、微结构和维度的关系。

2H相二硫化钼（2H-MoS2）是研究最为广泛的类石墨层状过渡金属硫族化合物之一。近年来，[MoS6]八面体配位的亚稳相MoS2由于具有独特的晶体结构和能带结构，是当前凝聚态物理和材料科学的前沿研究课题。但是，纯亚稳相块体和二维纳米片的可控制备依然是难题，多个亚稳相的精确晶体结构未知，本征物理性质也研究的较少。针对上述问题，本项目从亚稳相晶体精准合成、结构解析和物性探索等方面开展了系统性研究，取得了如下研究成果：1、提出了低温拓扑化学反应原理的合成新思路，设计了从相似[MX6]八面体结构单元的三元AMX2（A为碱金属；M为Mo、W；X为S、Se）向亚稳相1T'-MX2演化的反应路径，实现了1T'-MX2纯相的低温制备。2、通过调控Ax(H2O)yMoS2的碱金属离子脱嵌过程，实现了不同物相亚稳相MoS2晶体的可控合成，确定了单晶结构，揭示了物相选择性合成的生长规律。3、首次发现了Mo-Mo成键、[MoS6]扭曲八面体配位的新型超导体亚稳相1T'-MoS2；首次发现了Mo-Mo三聚成键、[MoS6]扭曲八面体配位的新型半导体亚稳相1T'''-MoS2及其二阶非线性光学效应；揭示了具有[MoS6]八面体构型的亚稳相MoS2的晶体结构-电子结构-物理性质的关系。