Deep Elastic Strain Engineering of 2D Materials and Their Twisted Bilayers

Abstract

Conventionally, tuning materials’ properties can be done through strategies such as alloying, doping, defect engineering, and phase engineering, while in fact mechanical straining can be another effective approach. In particular, elastic strain engineering (ESE), unlike conventional strain engineering mainly based on epitaxial growth, allows for continuous and reversible modulation of material properties by mechanical loading/unloading. The exceptional intrinsic mechanical properties (including elasticity and strength) of two-dimensional (2D) materials make them naturally attractive candidates for potential ESE applications. Here, we demonstrated that using the strain effect to modulate the physical and chemical properties toward novel functional device applications, which could be a general strategy for various 2D materials and their heterostructures. We then show how ultralarge, uniform elastic strain in free-standing 2D monolayers can permit deep elastic strain engineering (DESE), which can result in fundamentally changed electronic and optoelectronic properties for unconventional device applications. In addition to monolayers and van der Waals (vdW) heterostructures, we propose that DESE can be also applied to twisted bilayer graphene and other emerging twisted vdW structures, allowing for unprecedented functional 2D material applications.

Anisotropic Mechanics of 2D Materials

“…Experimentally, interlayer twist [ 175 ] and strain engineering [ 33 ] have been adopted to modulate the physical properties of 2D materials, the combination of these two strategies will allow great potential to the systematic control of not only their electronic and optoelectronic behavior, [ 176 ] but also their mechanical properties. For example, it has been reported that the elastic Young's modulus and breaking strength of 2D materials are closely related to the interlayer sliding, [ 177 ] and the introduction of interlayer twist may provide an efficient knob to modulate these mechanical properties.…”

Two-dimensional Janus MGeSiP4 (M = Ti, Zr, and Hf) with an indirect band gap and high carrier mobilities: first-principles calculations

“…Strain engineering has been reported as a favorable approach to modulating the electronic properties of Janus monolayers. 49,50 It is noted that the electronic characteristics of 2D layered-structures are particularly sensitive to structural fluctuations. The crystal structure, including the chemical bond lengths between atoms, is changed when strain is applied, leading to a significant change in the hopping energy.…”

Tunable electrical properties and multiple-phases of ferromagnetic GdS2, GdSe2 and Janus GdSSe monolayers

“…It may reach the strain state with high magnitude even beyond the theoretical strength and allow continuous and reversible modulation of electronic and mechanical properties. 27,28 For example, a reversible strain of 15% was achieved in nanowires of silicon. 29 An unprecedented reversible ferroelastic strain of 73.2% was reported in 2D honeycomb monolayers, including the Janus VSSe monolayer, 30 BN and stanene.…”