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

## TL;DR

This study demonstrates that in-plane biaxial strain can effectively tune van der Waals interactions in few-layer black phosphorus, revealing counterintuitive weakening of interlayer coupling under tensile strain, confirmed by experiments and DFT calculations.

## Contribution

It introduces a method to control vdWs interactions in 2D materials via strain, with experimental and theoretical validation, advancing understanding of tunable interlayer forces.

## Key findings

- Tensile strain weakens interlayer coupling in black phosphorus.
- Infrared spectroscopy confirms strain-induced vdWs tuning.
- DFT calculations highlight the role of lattice structure.

## Abstract

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.

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Source: https://tomesphere.com/paper/1906.01825