Noncontacting optostriction driven anisotropic and inhomogeneous strain in two-dimensional materials

Strain engineering has been well developed and widely used to manipulate properties of materials. For two-dimensional materials, via nanoindentation technique or depositing the materials onto flexible substrates, one usually triggers tensile strains. It would be intriguing to develop strategies to generate strains via noncontacting schemes, such as an optical field, to eliminate lattice damage and additional interactions. Here we theoretically and computationally illustrate an optomechanical approach (referred to as optostriction), which could induce intrinsic strains in materials. Taking the well-studied transition metal dichalcogenide monolayers as examples, we predict a large in-plane optostriction with strong anisotropy, owing to their unique directional band transition strength. This optically driven strain method can avoid direct and invasive mechanical contacts with materials, which is easily accessible and guarantees the reversibility of materials. Rather than nanoindentation technique and other similar methods, this optomechanical strain can be either tensile or compressive. Owing to its intrinsicality, compressive strains are robust without suffering Euler's instability. In-plane inhomogeneous strains can be easily achieved via illuminating a Gaussian beam onto the material, adding an interesting approach to realize and measure in-plane optoflexoelectricity. Unlike conventional electric field inducing strains in piezoelectrics, no symmetry constraints are required.