Reversible and Continuous Tuning Interlayer Coupling in GaSe by Out-of-Plane Uniaxial Tensile Strain

Interlayer interactions play a key role in the electronic, optoelectronic, and magnetic properties of two-dimensional (2D) materials; hence, tuning interlayer interactions is a desirable task for property modulation. Although some strategies, such as chemical intercalation and in-plane strain, have been proposed, approaches that directly apply out-of-plane (OP) uniaxial tensile strain to continuously and reversibly modulate the van der Waals (vdW) gap remain scarce. In this work, OP uniaxial tensile strain was applied to GaSe using micro-electro-mechanical systems technology. The Raman spectra of GaSe exhibited a red shift, while its photoluminescence (PL) displayed a blue shift under tensile strain. Cycling loading and unloading experiments revealed the elastic nature of the OP strain, leading to a reversible linear shift of the PL peak of GaSe. First-principles calculations revealed that the vdW gap is more sensitive to OP tensile strain than the intralayer Ga-Ga bond. Owing to the increased vdW gap, interlayer electron hybridization was reduced, leading to a bandgap increase. A simple tight-binding model based on interlayer hopping explains well the linear bandgap variation under OP tensile strain. This work demonstrates that interlayer interactions in 2D materials can be effectively tuned by applying OP uniaxial tensile strain, providing a strategy for the continuous and reversible manipulation of electronic and optoelectronic properties in 2D materials.