Two-dimensional (2D) materials are unique platform with rich physics and chemistry, promising for diverse technological applications. While extensive progress has been made in conventional 2D materials such as graphene, h-BN, and transition metal dichalcogenides, there are plenty of exciting new opportunities to explore. In this talk, I will present our recent effort on the discovery, design, and understanding of 2D materials from first-principles theoretical calculations and molecular dynamics based on machine learning force field. First, I will highlight elastic strain engineering as a powerful approach to engineer novel functionalities in 2D materials. While homogeneous strain can be applied to change the electronic and optical bandgap and induce piezoelectric response, inhomogeneous strain can lead to exciton funneling effect due to strain gradient. Elastic strain can also induce topological phase transition in 2D materials, enabling strain controlled topological switching.  In the second part of my talk, I will report our discovery of strongly-coupled ferroelectric-ferroelastic multiferroics in monolayer group IV monochalcogenides as well as their phase transition behavior. These 2D multiferroics possess a few distinct characteristics including strongly-coupled giant ferroelectricity and ferroelasticity, large anisotropic optical properties, sizable exciton binding energies, and low domain wall energy and migration barrier, suggesting their great potentials for tunable multifunctional devices. I will then present the intriguing nature of phase transition as well as the stress induced domain switching in this 2D multiferroics using our recently developed machine learning force fields. Finally, I will discuss about the opportunities and challenges in the understanding and predicting complex physical behaviors of 2D materials upon mechanical deformation and van der Waals heterostructuring.


Strain Engineering and Phase Transition in 2D Materials

The Virtual Technical Meeting of the Society of Engineering Science 2020 is the first fully virtual meeting of the SES community to envision and connect during the hiatus created by Covid-19, providing a platform for the exchange of ideas, and to showcase the latest research in the field of engineering science.

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