UC Irvine

Lattice deformation via substrate-driven mechanical straining of 2D materials can profoundly modulate their bandgap by altering the electronic band structure. However, such bandgap modulation is typically short-lived and weak due to substrate slippage, which restores lattice symmetry and limits strain transfer. Here, it is shown that a non-volatile thermomechanical strain induced during hot-press synthesis results in giant modulation of the inherent bandgap in quasi-2D tellurium nanoflakes (TeNFs). By leveraging the thermal expansion coefficient (TEC) mismatch and maintaining a pressure-enforced non-slip condition between TeNFs and the substrate, a non-volatile and anisotropic compressive strain is attained with ε = −4.01% along zigzag lattice orientation and average biaxial strain of −3.46%. This results in a massive permanent bandgap modulation of 2.3 eV at a rate S (ΔEg) of up to 815 meV/% (TeNF/ITO), exceeding the highest reported values by 200%. Furthermore, TeNFs display long-term strain retention and exhibit robust band-to-band blue photoemission featuring an intrinsic quantum efficiency of 80%. The results show that non-volatile thermomechanical straining is an efficient substrate-based bandgap modulation technique scalable to other 2D semiconductors and van der Waals materials for on-demand nano-optoelectronic properties.