TMDs二维原子晶体的2H－1T相变及界面特性增强机制研究

Phase transition from trigonal prismatic (2H) structure to octahedral (1T) one accompanied with a sharp change from semiconductor to metal usually takes place in transition metal dichalogenides (TMDs), the representative two-dimensional (2D) materials. Accordingly, seamless joints might be produced between metal electrodes and semiconducting channels, if 2H-1T phase transition is selectively induced in local regions. This might overcome the technical bottleneck of high contact resistance in TMDs devices, and have attracted great concerns from the academic society. The physical mechanism for the 2H-1T phase transition and the condition for the stabilization of 1T phase are the crucial scientific issues for high-performance TMDs 2D devices. In this proposal, taking the typical TMDs 2D materials as examples, molecular dynamics simulations, first-principles calculations and experimental characterization will be combined to study the thermodynamic parameters as well as the occupation and overlapping distribution of electronic orbitals in 2H and 1T phase. Based on this, we will try to disclose the fundamental characteristics, the physical mechanism, size dependence and dominant inducements in the 2H-1T phase transition, to explore the technological approaches of improving the 2H-1T phase transition and stabilizing the 1T phase through adatom adsorption, doping, lattice straining and the combined effects. Finally, photolithography and selective lithium intercalation are combined to induce patterned phase transition and to produce atomically continuous interface between metal and semiconductor in one TMDs sheet. The scattering mechanisms of electrons and phonons across the interface will be investigated systematically to reveal the physical nature of enhanced electronic/thermal conductance. The achievements should be of great guidance value for the design of relevant materials and devices.

伴随TMDs二维材料的2H－1T结构相变，其功能特性发生从半导体到金属的突变。基于区域选择性2H－1T相变，可实现金属电极与半导体导电沟道区域的“无缝对接”，突破TMDs二维器件接触电阻偏高的技术瓶颈，而引起了学术界的高度关注。2H－1T相变机理及1T相趋稳条件是TMDs二维器件高性能化亟待解决的关键科学问题。本项目拟以典型TMDs二维原子晶体为例，结合理论模拟和实验表征，深入考察2H、1T相的基本热动力学参量及电子轨道填充规律，揭示2H-1T相变的基本特征、物理机制、主导诱因及尺寸效应；探索采用原子吸附/掺杂、应力/应变及其复合效应促进2H-1T相变及1T相趋稳的技术途径；制备具有1T/2H“原子连续界面”的横向异质结构，揭示其附近电子/声子的特殊散射机制，建立1T/2H相横向异质结热/电传输特性增强与界面电子态/声子态变化之间的关系，为高性能FETs器件的设计提供重要的材料学参考。

二维过渡金属硫族化合物（TMDs）的2H-1T结构相变伴随半导体-金属功能特性突变，有望通过界面设计，突破二维器件接触电阻偏高的技术瓶颈。本项目以典型TMDs二维原子晶体为例，考察并明确在电荷注入、单轴应变致相变势垒降低以及相变发生的物理本质，研究了光、电、催化、气体传感等功能特性与异质界面的紧密关系，顺利完成了各项研究内容，达到预期目标。部分研究结果已在ACS Nano，Applied Catalysis B, Journal of Materials Chemistry A，Physical Review B，Carbon等国际期刊发表学术论文57篇，其中影响因子大于5.0的论文SCI检索37篇，授权技术发明专利10件。培养硕/博士生19名。应邀参加学术会议并作特邀报告7人次。取得的重要进展有：(1) 阐明了TMDs二维材料发生2H-1T结构相变的电荷注入和应变调控机理，揭示了拉伸应力致二维材料褶皱结构的形貌特征及其影响因素；(2) 阐明了单层MoS2电子态、磁化特性、吸附性能的应变效应和掺杂效应，发现掺杂原子自旋极化的双交换与超交换关系；(3) 阐明了二维MoS2与金属和半导体异质结构电子态的界面效应，揭示了TMDs二维材料与金属的垂直/横向接触特性及界面电子的费米钉扎效应，建立了TMDs/金属叠层结构与场效应晶体管输运特性的关系，提出Mo-MoS2接触电极增强FET器件电流密度的器件结构模型；(4) 采用SiC高温热解方法制备大面积高质量的单层外延石墨烯并揭示其生长机制，阐明外延石墨烯与缓冲层及金属的交互作用机制，揭示了缺陷形成机制及界面莫尔条纹形成的物理本质；(5) 制备出TMDs二维异质叠层分级结构并阐明了其在电池阴极材料领域、电催化剂等领域特性增强机制；(6) 以金属氧化物/石墨烯复合形成的纳米结构为例，发现高指数晶面、离子价态、氧空位、电子态等对气敏性能产生的显著影响。充分展示了结构相变和界面对于新型电催化材料、传感材料及二维FET器件的调控作用，完成预期目标。