Engineering strain and interlayer excitons of 2D materials via lithographically engraved hexagonal boron nitride substrates

Strain engineering has recently emerged as a viable option to modify the electronic, optical, and magnetic properties of two-dimensional (2D) materials, e.g., by introducing a giant pseudo-magnetic field and unconventional Hall effects [1,2]. However, it remains challenging to arbitrarily control the strain distribution and magnitude, limiting the extent to which straintronics can operate and advance. Here, by using atomic-scale etching to create any desired surface topography or nanostructures in hexagonal boron nitride (hBN) substrates, we can arbitrarily manipulate the strain of molybdenum disulfide (MoS₂) flakes placed onto the hBN. The phonon and exciton emissions are shown to vary in accordance with our strain (structure) designs, enabling us to create arbitrary phonon vibration and photoluminescence color images. Moreover, the strain engineering is found to substantially enhance the interlayer excitons. Such an enhancement is significant because the conventional uniaxial strain does not affect the oscillator strength of interlayer excitons. The proof-of-concept demonstration of our strain engineering may well open new opportunities for 2D straintronics and optoelectronics.

1. Guinea, F., Katsnelson, M. & Geim, A. Energy gaps and a zero-field quantum Hall effect in graphene by strain engineering. Nature Physics 6, 30 (2010).

2. Ho, S.-C. et al. Hall effects in artificially corrugated bilayer graphene without breaking time-reversal symmetry. Nature Electronics 4, 116 (2021).