Moire engineering in 2D heterostructures with process-induced strain

We report deterministic control over a moire 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 x film thickness) and patterned stressor geometry, respectively. We examine strain and moire interference with Raman spectroscopy through in-plane and moire-activated phonon mode shifts. Results support systematic C-3 rotational symmetry breaking and tunable periodicity in moire 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 moire interference without additional twisting but also to allow for a systematic pathway to explore different van der Waals based moire superlattice symmetries by deterministic design.

Automated summary

We demonstrate controllable manipulation of a moire superlattice interference pattern in twisted bilayer graphene through the use of designable device-level heterostrain. By depositing stressed thin films onto the graphene samples, we can control the magnitude and directionality of heterostrain. Raman spectroscopy and simulations confirm the breaking of C-3 rotational symmetry and tunable periodicity in the moire superlattices under uniaxial or biaxial strain.