Modeling of interlayer dislocations in heterodeformed bilayer 2D homostructures

Ahmed, MD Tusher

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https://hdl.handle.net/2142/130115 Copy

Description

Title

Modeling of interlayer dislocations in heterodeformed bilayer 2D homostructures

Author(s)

Ahmed, MD Tusher

Issue Date

2025-05-19

Director of Research (if dissertation) or Advisor (if thesis)

Admal, Nikhil Chandra

Doctoral Committee Chair(s)

Admal, Nikhil Chandra

Committee Member(s)

• Johnson, Harley T
• Zande, Arend van der
• Schleife, André

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Bilayer 2D homostructure, Interface Dislocations, Multiscale Modeling, Displacement Shift Complete Lattice, Frictional Anisotropy, Ferroelectricity, Structural Reconstruction, Commensurability

Abstract

Bilayer 2D materials are an exceptional class of engineering materials with interesting structural and electronic properties. One particular feature of these materials is that their properties can be tuned with applied relative twist and/or heterostrain. Such bilayer 2D materials, when subjected to relative twist and/or heterostrain, undergo structural reconstruction mediated by the formation of interface dislocations. Based on the characteristics of the applied heterodeformation, the characteristics of the interface dislocations can be different, thus modifying the subsequent properties of the interface. A large-scale exploration across the vast twist and heterostrain space is practically impossible using experimental and atomic-scale simulations, therefore urging for the development of mesoscale models. This motivates us to develop mesoscale models for characterizing interface dislocations and analyzing interesting structural properties governed by such interface dislocations in heterodeformed bilayer 2D materials. In the first part of the thesis, we present methods of characterizing interface dislocations and associated structural reconstruction in heterodeformed bilayer 2D materials. First, we present Smith normal form (SNF) bicrystallography to quantify the smallest commensurate lattice vectors and translational invariance of arbitrarily heterodeformed bilayer 2D materials. This framework can characterize the interface dislocations that govern the atomic reconstruction in heterodeformed bilayer 2D materials. Second, Using the SNF framework, we show that structural reconstruction is not limited to small heterodeformed bilayer 2D materials. It can also be perceived in large heterodeformed bilayer 2D materials. However, the Burgers vector of such interface dislocation is markedly different from the Burgers vector of interface dislocation in small heterodeformed bilayer 2D materials. We develop a generalized Frenkel–Kontorova (GFK) model to predict atomic reconstruction in small and large heterodeformed bilayer 2D materials. We consider graphene to be the representative 2D material in this study for its numerous applications. The model can predict displacement fields caused by atomic reconstruction in small and large heterodeformed bilayer graphene (BG) as precisely as computed from atomic-scale methods. Next, we present the line directions-Burgers vector pair (LBP) model to predict and quantify the smallest commensurate lattice vectors of arbitrarily heterodeformed bilayer 2D materials from the desired set of line directions and Burgers vector pairs. This model is unique in its approach to the computation of the heterodeformation for generating a moiré superlattice from the desired set of integer coordinates of the line directions and the Burgers vectors. This method shows the degeneracy of moiré superlattices where different heterodeformations can lead to the same moiré periodicity, a feature that can not be achieved in twisted bilayer 2D materials. This method shows an inverse approach where the exact heterodeformation can be calculated from the desired characteristics of interface dislocations required to govern the atomic reconstruction of the interface. This part of the thesis contributes to developing different models that can be useful in predicting structural reconstruction in arbitrarily heterodeformed bilayer 2D materials. In the second part of the thesis, we present multiscale models to predict two structural properties of heterodeformed bilayer 2D materials. First, we present a dynamic Frenkel–Kontorova (DFK) model to predict the interfacial friction drag coefficient of arbitrarily heterodeformed BG interfaces. This model predicts the interfacial friction from the dislocation drag coefficient of the constituent dislocations that govern the atomic reconstruction of such heterodeformed BG. The distinct feature of the DFK model is its robustness, which does not require fitting for individual heterodeformations. Once fitted, it can effectively predict the interface friction drag coefficient of any arbitrarily heterodeformed BG interface. Next, we present the relation of the dislocation drag coefficient of twisted BG with the angle of twist. It has been observed that nodal junctions cause a linear increment in the dislocation drag coefficient with the change in the angle of twist. Motivated by this, we develop a dislocation drag (DDL) law model for predicting the interface friction of heterodeformed BG configurations that belong to a specified family of dislocations. Moreover, we present that pure-sheared and twisted-sheared BG show frictional anisotropy where the direction of sliding velocity does not align with applied shear traction, a property that can not be perceived in twisted BG. Finally, we present a multiscale framework to compute interfacial ferroelectricity in small and large heterodeformed bilayer hexagonal boron nitride (hBN) interfaces. We present that both small and large heterodeformed bilayer hBN can show interfacial ferroelectricity under an applied electric field by deformation of the interface dislocations. This finding is distinct as we first report interfacial ferroelectricity in large heterodeformed bilayer hexagonal boron nitride. We believe this multiscale model will be helpful in the large-scale exploration of interfacial ferroelectricity in different bilayer 2D materials. This segment of the thesis focuses on developing mesoscale models for different structural properties associated with the structural reconstruction where translation/deformation of interface dislocations govern such structural properties.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/130115

Copyright and License Information

Copyright 2025 Md Tusher Ahmed

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