层数可控的二维晶体1T-TaS2生长与掺杂研究

Construction and property investigation of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is an emerging highlighted research interest in recent years. Typical TMDCs material, such as 1T-TaS2, exhibits some dimensionality related properties, such as superconducting and charge-density-wave (CDW). The correlation between dimensionality and physical properties of 1T-TaS2 could provide unique material systems to study the physical mechanism and laws of CDW property. TMDCs growth of 1T-TaS2 crystal by chemical vapor deposition has been receiving attention recently. However, the explosion of the precursor during the heating process is unable to control accurate amounts of reacted reagents and the synthesis process, resulting in uncontrollable layer number of the produced TMDCs crystal. To solve this problem, we propose a modified reagent delivery system during the chemical vapor deposition process to precisely control the layer number of the 1T-TaS2 crystal. In our procedure, the volatile halide precursor TaCl5 and sulfide vapor are applied outside the reaction chamber, respectively. By precisely controlled flows of the two precursors, the intermittent chemical vapor deposition will synthesize the layer-by-layer stacked 2D 1T-TaS2 crystal with controllable layer number. Furthermore, during the synthesis process, the in situ doping atoms (with Na, Cu, et. al.) can be used to modulate the CDW phase transition temperature of 1T-TaS2 and also induce its superconductivity. Overall, the construction layer number and doping effects on the CDW property of 1T-TaS2 2-D crystal will be systematically investigated.

二维过渡金属硫族化合物(TMDCs)的控制生长与性能研究是二维材料的研究热点，尤其以二维晶体1T-TaS2为代表的金属性TMDCs呈现出与材料维度密切相关的超导、电荷密度波(CDW)等特性，为研究CDW的物理机制与规律提供了独特的材料体系。而目前通过化学气相沉积法生长1T-TaS2二维晶体时，由于在升温过程中前驱体的爆发性反应，不能确定参与反应量和控制反应进程，决定了生成的二维晶体无法精确地控制层数，针对此问题，本项目通过改进化学气相沉积法进料方式，提出层数可控1T-TaS2生长的新思路：在反应器外部，分别气化TaCl5和单质硫两种前驱体，通过控制载气流量操控前驱体定量、间歇式供应，精确实现1T-TaS2二维晶体的层数可控生长。并在生长过程中原位掺杂Na、Cu等原子调控1T-TaS2的CDW相转变温度，诱导其超导电性，研究层数和掺杂对1T-TaS2二维晶体CDW性质的影响。

金属性过渡金属硫族化合物（MTMDCs）因其优异性能而获得广泛关注。作为金属性过渡金属硫族化合物（MTMDCs）的一员，二硫化钽（TaS2）是一种典型的电荷密度波（CDW）材料，在低温诱导下，发生晶格畸变，可经历从金属态到绝缘态的转变。这种具有新奇物理效应的TaS2二维原子晶体为研究凝聚态物理新现象与规律提供了独特的材料。本项目利用改进的CVD方法成功制备1T-TaS2二维原子晶体，并对热力学和动力学过程进行了详细的探究，在此基础上制备不同厚度的1T-TaS2纳米片进行CDW相变研究。主要研究成果和创新点如下：.本项目通过改进化学气相沉积法进料方式，提出二维TMDCs层数可控生长的新思路，在反应器外部，分别气化两种前驱体，实现前驱体定量、间歇式供应。通过优化反应条件，在云母基底上逐层生长1T-TaS2二维晶体，成功制备了从单层到数百层厚度的晶体。证实了本实验方法合成的二维晶体材料可以实现层数可控。.在此基础上，利用Raman, AFM, HRTEM,XPS, XRD等测试手段分析了1T-TaS2二维晶体的基本物性，表征了形貌信息和内部结构，证实了材料的高质量和高结晶性。采用低温共聚焦拉曼系统，测量温度从78 K到260 K的升温过程中不同温度下的拉曼特征峰，确定了CDW相变点在140-160 K之间。通过光刻，电子束蒸发电极等微加工工艺制备电极，与样品连接测量材料随温度变化的电阻。结果表明，升温过程中测得的相变温度在150-160 K之间，与拉曼测试结果吻合。此外还测试了降温过程中的CDW相变温度高于230 K，呈现与厚度相关的相变温度特征。.发表相关SCI论文3篇，专利8项。.