Investigation of the intrinsic defects role on optical and optoelectronic properties of tran-sition metal dichalcogenides monolayers and lateral heterostructures prepared by their tailored synthesis

石墨和二硫化钼等层状材料提供了一个令人鼓舞的平台，将原子级薄的半导体与金属和绝缘体联合收割机结合起来，实现迷人的物理和应用。目前的设计概念是使用单独的薄片，并通过将薄片堆叠成货车德瓦尔斯结构来将它们联合收割机组合，以获得新的功能。在这里，我们提出了一种非常不同的方法，通过探索过渡金属二硫属化物（TMD）的化学气相沉积（CVD）的新途径，将2D材料的所有功能扩展到天然晶体之外。该项目将结合联合收割机的3个最新的突破，由3个合作伙伴率先：·耶拿：最近通过引入一种基于Knudsen泻流细胞的新型生长程序，显着提高了CVD生长TMD单层的再现性和晶体质量，并将这种生长方法扩展到横向异质结构和Janus单层，如SMoSe。·乌尔姆：该公司开发了亚埃低压电子显微镜（SALVE），能够获得清洁单层材料中的固有缺陷结构和密度以及缺陷的电子特性-这是监控耶拿CVD质量进展和揭示横向界面原子结构以及缺陷特性的关键问题。·图卢兹：已经表明，具有确认的低缺陷密度（乌尔姆）的CVD生长样品（耶拿）显示出与最高质量的剥离材料相当的光学质量。通过消除介电无序（即，外部效应），这在文献中报道的CVD样品的光学研究中占主导地位。主要项目目标是：·通过优化生长和原子分辨率低电压透射电子显微镜技术（TEM）的反馈，在衬底上到处CVD生长大面积TMD单层（器件制造的高产率），并控制缺陷密度。建立具有受控缺陷类型和密度的高质量生长是适应异质结构和合金生长之前的坚实起点。识别个体缺陷并理解它们的起源与量子技术有关。·在剥离样品中生长横向异质结构如MoSe 2-WSe 2而没有等效物;我们避免了堆叠过程中的界面污染问题;在TEM中研究边界的原子锐度与逐渐合金化;研究激子沿着带隙梯度扩散;朝向产生激子“陷阱”，用于有效的局部光发射或未来的激子凝聚实验。具有不同顶部和底部硫族元素的Janus单层的生长，例如SMoSe;在化学（催化）和光电子学方面具有巨大潜力的层; Janus单层的TEM研究; Janus单层的光学：二次谐波产生，主要光学跃迁的电场调谐。

Layered materials such as graphite and MoS2 provide an inspiring platform to combine atomically thin semiconductors with metals and insulators for fascinating physics and applications. The current design concept is to use individual flakes and combine them by stacking thin sheets in van der Waals structures, to access new functionalities. Here we propose a very different approach to extend the repertoire of 2D materials beyond the naturally occurring crystals by exploring new avenues in Chemical Vapour Deposition (CVD) of transition metal dichalcogenides (TMDs). The project will combine 3 very recent breakthroughs pioneered by the 3 partners: •Jena: has recently significantly improved the reproducibility and crystal quality of CVD grown TMD monolayers by introducing a novel growth procedure based on Knudsen effusion cells and will extend this growth approach to lateral heterostructures and Janus monolayers such as SMoSe. •Ulm: developed sub-Angstrom low-voltage electron microscopy (SALVE), enabling access to the intrinsic defect structure and density in clean monolayer materials as well as to the electronic properties of the defects – this is a key issue for monitoring the CVD quality progress from Jena and uncover the atomic structure of the lateral interfaces as well as the defect’s properties. •Toulouse: has shown that the CVD grown samples (Jena), with confirmed low defect densities (Ulm) show optical quality comparable to the highest quality exfoliated material. Accessing the intrinsic optical properties is achieved by eliminating dielectric disorder (i.e., extrinsic effects), which dominates so far the optical studies reported of CVD samples in the literature. The main project objectives are: • CVD growth of large area TMD monolayers everywhere on the substrate (large yield for device fabrication) with controlled defect density through optimised growth and feedback from a combination of atomic-resolution low-voltage transmission electron microscopy techniques (TEM). Establishing high quality growth with controlled defect types and densities is solid starting point before adapting growth for heterostructures and alloys. Accessing individual defects and understanding their origin is relevant for quantum technologies. • Growth of lateral heterostructures such as MoSe2-WSe2 without equivalent in exfoliated samples; we avoid problem of interface contamination during stacking; investigation of atomic sharpness of boundaries versus gradual alloying in TEM; investigation of exciton diffusion along bandgap gradient; towards creation of exciton “traps” for efficient, localized light emission or future exciton condensation experiments.• Growth of Janus monolayers with different top and bottom chalcogen such as SMoSe; layers with great potential in chemistry (catalysis) and optoelectronics; TEM investigation of Janus monolayers; optics on Janus monolayers: second harmonic generation, electric field tuning of main optical transitions.