Tutorial EQ07: Mechanics and Moirés in 2D Materials

The tutorial will focus on the fundamental science of the mechanical behavior and the moiré superlattice of 2D materials. Currently, strain has been adopted to modulate a wide range of physical properties of 2D materials, where the strain engineering of 2D materials requires a thorough understanding of their mechanical behaviors. Recently, the moiré superlattice and the atomic reconstruction were observed under periodic strain potential, which can lead to some emergent and intriguing properties, such as unconventional superconductivity and unique optoelectronic behaviors. The tutorial will cover the fundamental understanding of the elastic and plastic behaviors of 2D materials and interfaces in various deformation modes, including stretching, bending, wrinkling, crumpling, fracture, and delamination, from multiscale (atomistic to continuum) perspectives. The tutorial will also provide an overview of the theory of emerging properties associated with 2D material moiré superlattice and their applications into twistronics.

Mechanics of 2D Materials and Interfaces 
Rui Huang, The University of Texas at Austin

Atomically thin materials such as graphene and other 2D materials are promising for a wide range of applications. Among many unique and attractive properties of 2D materials, mechanical properties play important roles in manufacturing, integration and performance for their potential applications. Mechanics is indispensable in the study of mechanical properties, both theoretically and experimentally. This tutorial aims to summarize the current understanding on the mechanics of 2D materials including linear and nonlinear elasticity, strength and toughness, as well as mechanical interactions such as adhesion and friction at the interfaces of 2D materials. Theoretical and computational models will be presented along with experimental methods for predicting and measuring the mechanical and interfacial properties of 2D materials.

Outline:

• Linear and nonlinear elasticity
• Strength and toughness
• Adhesion and friction

Electronic Properties of Moiré Superlattices 
Allan H. MacDonald, The University of Texas at Austin

When two or more van der Waals material layers are overlaid with small differences in lattice constant are overlaid with small relative twist angles they form two-dimensional moiré superlattices with unit cell areas that can be thousands of times larger than the unit cell areas of the underlying two-dimensional crystals. When the moiré superlattice materials are semiconductors or semimetals, low-energy electronic properties are accurately described by low-energy models that have the periodicity of the superlattice. These moiré materials act like crystals with artificial giant atoms. One of the most attractive properties of moiré materials is that the number of electrons per unit cell can be changed by more than one using electrical gates. MacDonald will survey the electronic properties of moiré materials, focusing on systems that have been achieved experimentally, including graphene bilayers and multilayers and systems based on tradition metal dichalcogenide layer building blocks.