Interlayer excitons in advanced, CVD-based van der Waals heterostructures with controlled moiré wavelength

本文提出利用化学气相沉积（CVD）法生长的TMDC单层材料（MLs）制备具有可控摩尔波长的先进过渡金属二硫化物（TMDC）异质结构（HS）。这个过程产生大的（bbb100微米）ML薄片，具有明确的三角形形状，直接锁定在晶体取向上。最近的研究表明，将它们从生长基质中去除并包裹在六方氮化硼（hBN）中，可以产生与剥离的MLs相当的低谱线宽度。因此，这些样品为HS提供了一种新颖而丰富的构建块。此外，我们可以通过简单地测量长而明确的边缘的方向来非常精确地控制扭曲角度，而不是依赖于不那么精确和费力的第二代谐波显微镜。我们将使用各种低温光谱技术，包括微光致发光、法拉第旋转和克尔显微镜，研究这些先进HS中的层间激子（ILEs），以系统地确定互易空间（错）排列和莫尔海姆诱发的超晶格势对ILE能量、光致发光寿命、谷极化动力学和扩散的影响。由于CVD MLs的丰富消除了制造的一个重要瓶颈，我们还计划通过集成铁磁层来构建具有更高复杂性的HS，这将允许我们通过邻近效应打破谷简并。同时，我们将努力进一步优化CVD生长技术，以实现TMDC HS的直接、单工艺生长。在直接CVD生长中，我们可以预期两种TMDCs的外延排列，产生的结构与我们通过确定性堆叠可以制造的任何HS根本不同：直接生长的外延TMDC HS不受莫伊兰相关效应的影响，因此提供了重要的参考。此外，我们将介绍用于CVD生长的新型衬底，例如外延生长的hBN。

We propose to fabricate advanced transition metal dichalcogenide (TMDC) heterostructures (HS) with controlled moiré wavelength using TMDC monolayers (MLs) grown by chemical vapor Deposition CVD). This process yields large (>100 micrometer) ML flakes with well-defined triangular shape, directly locked to crystallographic orientation. It was recently demonstrated that removing them from the growth substrate and encapsulating them in hexagonal boron Nitride (hBN) yields low spectral linewidths comparable to exfoliated MLs. Therefore, these samples present a novel, abundant building block for HS. Additionally, we can control twist angles with great accuracy by simply measuring the orientation of the long, well-defined edges, instead of relying on the less precise and laborious second-harmonic-generation microscopy. We will study interlayer excitons (ILEs) in these advanced HS using various low-temperature spectroscopy techniques, including micro-photoluminescence, Faraday rotation and Kerr microscopy, to systematically determine the influence of the reciprocal space (mis-)alignment and the moiré-induced superlattice potential on ILE energy, photoluminescence lifetimes, valley polarization dynamics and diffusion. Since the abundance of CVD MLs removes an important bottleneck for fabrication, we also plan on building HS with higher complexity by integrating ferromagnetic layers, which will allow us to break valley degeneracy by proximity effects. In parallel, we will endeavor to further optimize the CVD growth techniques for direct, single-process growth of TMDC HS. In direct CVD growth, we can expect an epitaxial alignment of the two TMDCs, generating structures that are fundamentally different from any HS we can fabricate by deterministic stacking: directly grown epitaxial TMDC HS are free of moiré-related effects and thus provide an important reference. Additionally, we will introduce novel substrates for CVD growth, such as epitaxially grown hBN.