厚度可调的高质量超薄二维过渡金属碳化物晶体的制备研究

Two dimensional transition metal carbides (2D TMCs) are a kind of new 2D materials, which have unique physical properties and wide application prospects. However, it is very difficult to realize the controllable preparation of the thickness of high quality ultrathin 2D TMCs, especially the preparation of single-unit-cell thick materials. In this project, based on previous chemical vapor deposition (CVD) method which has been suggested by proposer, using double layer metal foils (Cu/TM) as substrate, we propose to finely control the thickness of 2D TMCs by using the supply of transition metal source as a controlling step of the reaction, and the corresponding 2D TMCs of Mo, W, V, Nb and Ta as the study subjects. Through carbonizing the transition metal foils, the supply of transition metal is limited effectively. By controlling the carbonization degree of the TM substrate and further optimizing the growth parameters, the thickness of ultrathin 2D TMCs crystals is finely controlled, and single-unit-cell-thick 2D TMCs crystals are obtained. Based on excellent barrier property of graphene, graphene as protective layer is used to realize the clean damage-free transfer of ultrathin 2D TMCs. The growth mechanism of 2D TMCs is illuminated by the comprehensive analysis of the experimental law of control synthesis and the combination of theoretical computation and simulation. This project implementation can not only provide the basic materials for the study of the physical properties of TMCs under the 2D limit, but also provide the guidance for the controlled synthesis of the other non-layered 2D materials.

二维过渡金属碳化物（2D TMCs）是一种具有独特物理性质和广泛应用前景的新型二维材料。然而，如何实现高质量超薄2D TMCs的厚度可控制备，特别是单胞厚度材料的制备，难度极大。本项目在前期申请人发展的双金属基体(叠层的铜箔/过渡金属箔片)CVD方法基础上，提出以过渡金属源供给作为反应控制步骤，以Mo、W、V、Nb、Ta对应的2D TMCs为研究对象，精细调控其厚度。通过对过渡金属箔片碳化来有效限制2D TMCs生长过程中过渡金属的供给。通过调控碳化程度，优化生长参数，实现超薄2D TMCs晶体的厚度精细调控及单胞厚度晶体的制备；利用石墨烯优异的阻隔性能作为保护层，实现超薄2D TMCs洁净无损转移；通过综合分析控制制备的实验规律和理论计算模拟相结合，阐明2D TMCs的生长机制。本项目的实施，不仅可为研究二维极限下TMC的物理性质提供材料基础，也可为其他非层状二维材料的控制制备提供指导。

本项目系统研究了超薄过渡金属碳化物的厚度调控、无损转移、结构表征及物性研究。取得的主要结果包括：.(1)提出通过碳化预处理双金属基体CVD用过渡金属箔片的新思路，实现了对大量过渡金属源的固定，以Nb为例，揭示了碳化处理后NbCx的存在，以二维NbC和Mo2C的生长证实了碳化处理基底对2D TMCs 晶体的厚度和形核密度调控的有效性。.(2)发现过渡金属碳化预处理可以实现对W的碳化物厚度与物相的双重调控，实现了正交W2C到六方WC相调控，而正交Mo2C与六方Mo2C的相调控表现出不一样的生长机制，并揭示了Mo2C两种物相高压下超导转变迥异的响应。.(3)基于过渡金属基体碳化预处理，结合限域空间CVD生长技术，发展出以二维过渡金属氧化物为模板的超薄NbC和TaC的外延生长，实现了超窄、超薄Mo2C纳米条带的可控制备与无损转移，并揭示了其独特的一维输运特征。.(4)实现了对二维NbC、Mo2C、Cr7C3晶体等的控制制备与结构调控，获得了多种独特结构的材料，包括NbC二维网络和分形、Mo2C环及Cr7C3纳米棒等，发现NbC二维网络的非单调超导转变特征。.(5)提出了三金属基底CVD方法，打破了二维材料难以高浓度均匀掺杂的难题，实现了磁性Cr原子对二维Mo2C超导体的均匀、可控、晶格取代掺杂，揭示了二维超导与磁性掺杂原子之间的交互作用，发现了Cr掺杂诱导的超导-电荷密度波相转变。.(6)提出以石墨烯为外延模板和保护介质，实现了不同晶界角的超薄Mo2C双晶的可控制备与无损转移，揭示了其晶界构型及不同晶界角度对超导转变的调制，发现超薄Mo2C晶体表面独特的缺陷类型及其对Tc的影响。.共发表SCI论文7篇，其中包括1篇Advanced Materials、2篇Nano Letters、1篇NPG Asia Materials。.