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Title:Mechanics of two-dimensional material interfaces under the three-dimensional deformation
Author(s):Yu, Jaehyung
Director of Research:van der Zande, Arend M; Ertekin, Elif
Doctoral Committee Chair(s):van der Zande, Arend M; Ertekin, Elif
Doctoral Committee Member(s):Huang, Pinshane Y; Aluru, Narayan R
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Solid mechanics
2D materials
Abstract:Deformable electronics introduce new functionalities on electronic devices such as wearable, flexible health sensors and foldable, flexible displays. To offer a deformability, electronic materials incorporating functional components are deposited on elastic substrates. Therefore, deposited electronic materials are necessary to be both electronically active and mechanically robust for maintaining their functionalities under deformations such as stretching, compressing, and bending. Two-dimensional (2D) materials are one of the most promising candidates for deformable electronic materials due to their unique mechanical and electronic properties. Mechanically, 2D materials are resilient under deformation based on their ultra-strong in-plane moduli from in-plane covalent bonds between atoms, as well as pliable out-of-plane bending moduli from their atomic scale thicknesses. Electronically, high charge carrier mobilities and tunable electronic bandgap, from insulator (h-BN) to the semi-metal (graphene), make 2D materials promising building blocks for molecular electronics. Furthermore, due to the absence of dangling bonds at the surface, 2D materials form van der Waals interfaces with adjacent surfaces of any material, which enables transfer of 2D materials onto any arbitrary substrates, including silicon, deformable polymers, and other 2D materials. This thesis begins with reviews and the perspectives of the 2D material based electromechanical devices using deformations of 2D materials. Suspended 2D materials has been utilized as impermeable membranes and 2D material based nano-electromechanical devices. Furthermore, engineering in-plane strain and out- of-plane deformations of 2D materials enables tunable optoelectronic devices, highly crumpled electronic membranes, and nanoscale 3D origami. Lastly, engineering stacking and alignment between 2D material layers induces unconventional superconductivity, Moire optoelectronics, and friction-less interfaces. Understanding the mechanics of van der Waals interfaces of 2D materials are crucial to describe mechanical deformations of 2D materials. This thesis addresses the mechanics of three different interfaces formed between 2D material layers and deformable substrates. In the first study, we analyze van der Waals interfaces between commensurate 2D material layers undergoing out-of-plane bending deformation. Through the introduction of nanoscale, controlled bending deformations of Bernal-stacked few-layer graphene, we demonstrate that the bending stiffness of few-layer graphene depends on bending angle, which changes the interlayer interaction between each layer. In the second study, we explore the bending stiffness of multilayers composed of incommensurate van der Waals interfaces, including twisted bilayer MoS2 and graphene-MoS2 heterostructures undergoing out-of-plane bending deformations. Due to the intrinsic superlubricity of the incommensurate interfaces, the bending stiffness of 2D heterostructures can be engineered by tailoring the stacking order and registry between 2D layers. In the last study, we discuss the role of the van der Waals interfaces formed between 2D monolayers and stretchable polymer substrate, which exhibits 3D morphology of buckled structures under compression. In each study, we combine both experiments and theoretical simulations explaining the origins of atomic scale deformations of multilayer 2D materials and substrates. In conclusion, this thesis shows that the mechanics of van der Waals interfaces formed among 2D layers and substrates dominate the behavior of three-dimensional, out-of-plane deformations of 2D materials. Our study shows that commensurate and incommensurate 2D multilayers are ultra-soft when deforming out-of- plane comparable to the theoretical lower limit of mechanical membranes. Furthermore, slip at the van der Waals interfaces between substrates and 2D layers allows control of the nanoscale surface topology of 2D membrane-substrate systems. These understandings shed light on designing 2D material multilayers based highly deformable electronic materials.
Issue Date:2020-05-07
Rights Information:2020 by Jaehyung Yu . All rights reserved.
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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