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鼓舞人心的平台，将原子薄半导体与金属和绝缘体结合起来，以实现迷人的物理和应用。目前的设计理念是使用单独的薄片，并通过在范德华结构中堆叠薄片来组合它们，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族化合物（TMDs）的化学气相沉积（CVD）的新途径，将2D材料的范围扩展到自然存在的晶体之外。该项目将结合3个合作伙伴最近率先取得的3项突破：•耶拿：最近通过引入基于Knudsen渗液细胞的新型生长方法，显著提高了CVD生长TMD单层的可重复性和晶体质量，并将这种生长方法扩展到横向异质结构和双面膜，如SMoSe。•乌尔姆：开发了亚埃低压电子显微镜（SALVE），可以访问清洁单层材料的内在缺陷结构和密度，以及缺陷的电子特性——这是监测耶拿CVD质量进展的关键问题，并揭示了横向界面的原子结构以及缺陷的特性。图卢兹：已经证明CVD生长样品（耶拿），具有确认的低缺陷密度（Ulm），其光学质量可与最高质量的剥离材料相媲美。获得本征光学性质是通过消除介电无序（即外在效应）来实现的，这是迄今为止文献中报道的CVD样品光学研究的主要内容。主要项目目标是：•CVD生长大面积TMD单层在衬底上到处（器件制造的大产量）与控制缺陷密度通过优化生长和反馈从原子分辨率低电压透射电子显微镜技术（TEM）的组合。在适应异质结构和合金的生长之前，建立具有控制缺陷类型和密度的高质量生长是坚实的起点。获取单个缺陷并了解其起源与量子技术相关。•剥落样品中没有等效的MoSe2-WSe2等横向异质结构的生长；避免了堆垛过程中的界面污染问题；TEM中渐合金化与晶界原子锐度的研究激子沿带隙梯度扩散的研究对创造激子“陷阱”的有效，局部发光或未来激子凝聚实验。•具有不同顶部和底部含硫的双面膜（如SMoSe）的生长；在化学（催化）和光电子学方面具有巨大潜力的层；Janus单层膜的透射电镜研究双面膜上的光学：二次谐波的产生，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.