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

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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.