Strain-tunable van der Waals interactions in few-layer black phosphorus

Interlayer interactions in 2D materials, also known as van der Waals (vdWs) interactions, play a critical role in the physical properties of layered materials. It is fascinating to manipulate the vdWs interaction, and hence to “redefine” the material properties. Here, we demonstrate that in-plane biaxial strain can effectively tune the vdWs interaction of few-layer black phosphorus with thickness of 2-10 layers, using infrared spectroscopy. Surprisingly, our results reveal that in-plane tensile strain efficiently weakens the interlayer coupling, even though the sample shrinks in the vertical direction due to the Poisson effect, in sharp contrast to one’s intuition. Moreover, density functional theory (DFT) calculations further confirm our observations and indicate a dominant role of the puckered lattice structure. Our study highlights the important role played by vdWs interactions in 2D materials during external physical perturbations. Layered materials governed by van der Waals (vdW) interactions offer opportunities for interlayer tuning of the materials' properties. Here, the authors demonstrate that in-plane tensile strain can effectively tune the vdW interactions of few-layered black phosphorus and weaken its interlayer coupling even though the sample shrinks in the vertical direction.