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We demonstrate a technique to strain two-dimensional hexagonal boron nitride (hBN) and graphene by depositing stressed thin films to encapsulate exfoliated flakes. We choose optically transparent stressors to be able to analyze strain in 2D flakes through Raman spectroscopy. Combining thickness-dependent analyses of Raman peak shifts with atomistic simulations of hBN and graphene, we can explore layer-by-layer strain transfer in these materials. hBN and graphene show strain transfer into the top four and two layers of multilayer flakes, respectively. hBN has been widely used as a protective capping layer for other 2D materials, while graphene has been used as a top gate layer in various applications. Findings of this work suggest that straining 2D heterostructures with evaporated stressed thin films through the hBN capping layer or graphene top contact is possible since strain is not limited to a single layer. 

We report deterministic control over a moiré superlattice interference pattern in twisted bilayer graphene by implementing designable device-level heterostrain with process-induced strain engineering, a widely used technique in industrial silicon nanofabrication processes. By depositing stressed thin films onto our twisted bilayer graphene samples, heterostrain magnitude and strain directionality can be controlled by stressor film force (film stress × film thickness) and patterned stressor geometry, respectively. We examine strain and moiré interference with Raman spectroscopy through in-plane and moiré-activated phonon mode shifts. Results support systematic C 3 rotational symmetry breaking and tunable periodicity in moiré superlattices under the application of uniaxial or biaxial heterostrain. Experimental results are validated by molecular statics simulations and density functional theory based first principles calculations. This provides a method not only to tune moiré interference without additional twisting but also to allow for a systematic pathway to explore different van der Waals based moiré superlattice symmetries by deterministic design.