二维过渡金属硫族化合物薄膜及其异质结的外延生长和电子掺杂效应调控

Recent experimental advances in two-dimensional transition metal dichalcogenide (2D-TMD) films, such as monolayer MoS2, WTe2 etc., have greatly stimulated considerable research interests due to their unique structure and electronic properties. These materials not only exhibit promising potential applications in optoelectronic transistors and devices, but also provide a new platform for creating a wide range of Van der Waals heterostructures without the constraints of lattice matching and processing compatibility. Since fabricating high quality of 2D-TMD films should be the basic requirement for realizing their rich underlying physics, we in this project propose to grow atomically flat and precise thickness of 2D-TMD films by molecular beam epitaxy (MBE) technique. Combining with low temperature and high magnetic field scanning tunneling microscope/spectroscopy (STM/STS) measurements, we will systematically investigate the variations of crystalline structure and electronic properties induced by different dimensionality (thickness of films), strain and stacking ways at the nano-scale, which would significantly affect the coupling interaction between 2D-TMD interlays. By doping with alkali metal adatoms on the 2D-TMD surface, or in-plane chemical substitution, we will establish the electronic phase diagram under carrier density doping from the parent compound. It’s necessary to develop the close relationship between the possible structure phase transition, charge density wave (CDW) order and superconductivity. Finally, we will use 2D-TMD films as templates to construct complicated 2D-TMD heterostructures by Van der Waals interaction, including possible combinations with topological Weyl semimetals (MoTe2 or WTe2) or Ising superconductors (NbSe2). Our research will provide insights into the curious quantum phenomena under extreme conditions and inspire new clues for exploring new low-dimensional superconductivity, as well as artificial heterostructures and interfaces.

以单层MoS2、WTe2等为代表的二维过渡金属硫族化合物（2D-TMD）因其独特的结构和电学特性，在光电器件领域具有巨大的应用前景，并为构筑新型材料提供了广阔的平台。制备高质量的2D-TMD薄膜是实现许多新奇性质的基础。本项目将利用分子束外延生长技术，获得原子级平整和薄膜层数精确可控的2D-TMD薄膜。结合原位低温强磁场扫描隧道谱学测量，在原子尺度上系统研究维度（层厚）变化、不同应力和堆垛方式下，层间耦合作用强弱对晶体结构和电子态的影响。通过表面碱金属吸附或元素替换掺杂，建立母体受载流子浓度调控的电子相图，并探讨结构相变、电荷密度波、超导等有序电子态等之间的关联。以2D-TMD薄膜为模板，构建二维范德瓦尔斯和拓扑（MoTe2、WTe2）/Ising超导（NbSe2）异质结构，为探索极端条件下的新奇量子现象，以及人工调制低维超导和异质结界面开拓新的思路。

本项目主要制备高质量的二维薄膜和量子材料，并在原子尺度上研究其晶体结构和电子能态性质，探索结构相变、磁性、拓扑、超导等有序电子态等之间的关联。主要成果包括：（1）制备Bi(111)/NbSe2异质结，观察到结构和层厚依赖的一维拓扑边缘态。（2）构建具有准共价键的Bi(110)/NbSe2界面，调控其面内和面外的电子结构。（3）发展了原位调控Na3Bi薄膜化学势的方法，实现了从二维拓扑绝缘体到三维Dirac半金属的拓扑相变。（4）研究了不同层厚Te薄膜形貌结构和电子态的演化过程。（5）实现InSe和In2Se3薄膜之间的可控相变。单层InSe具有二维电子气特征，其局域的应力效应可形成以第一类能带弯曲方式对齐的横向异质结。（6）观察到单原子层极限下In2Se3薄膜具有两类室温稳定的反铁电和铁电有序相，并通过针尖的局域电场效应实现了可控的铁电-反铁电相变。总之，这些研究成果为探索和调控量子材料的新奇物性开拓了新的思路，并在ACS Nano, Adv. Mater., Phys. Rev. B, Phys. Rev. Mater., Nanoscale等知名学术期刊上发表论文13篇。

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