Crystallography and mechanics at the graphene-metal interface

Surana, Mitisha

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https://hdl.handle.net/2142/122224 Copy

Description

Title

Crystallography and mechanics at the graphene-metal interface

Author(s)

Surana, Mitisha

Issue Date

2023-11-29

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

Tawfick, Sameh

Doctoral Committee Chair(s)

• Tawfick, Sameh
• Huang, Pinshane

Committee Member(s)

• Johnson, Harley T
• Shoemaker, Daniel
• Bellon, Pascal

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Graphene
• 2D materials
• Chemical vapor deposition
• Faceting
• Flexible electronics

Abstract

Graphene is a single layer of carbon atoms with truly astounding properties. Synthesis and integration of graphene are crucial steps to realize its recognized potential in commercial applications. Chemical vapor deposition (CVD) has emerged as a promising method to synthesize graphene for device applications, owing to its cost-effectiveness, reliability, and ability to achieve high quality. CVD of graphene is typically performed on metal catalysts. Based on the final application, graphene can be either directly used post-growth, such as in composites and functional coatings, or requires a further step of wet or dry transfer to other substrates, for instance in electronic devices. In both cases of use, the quality of the graphene devices is strongly affected by its interaction with its catalyst substrate during CVD. The interaction between graphene and the metal catalyst plays a critical role in the properties and quality of graphene, resulting strain, wrinkles, moiré patterns, thereby strongly affecting its electronic properties such as bandgap and mobility. A visually striking consequence of this interaction is the surface faceting of the metal substrate. A flat metal catalyst layer develops a topography reminiscent of mountains and valleys after growth. The periodic facets are ubiquitous, occurring in all metals, though their crystallographic orientations vary with underlying metal grains, emphasizing the role of surface energy anisotropy. This phenomenon affects both the transport properties post-transfer, as well as the ability to transfer the graphene by dry-picking with a stamp. Overall, understanding the mechanism of this faceting phenomenon could shed light on suitable crystal orientation for graphene growth, transfer, and integration. This thesis develops an approach to quantitatively study the orientation-dependent facet topographies observed on the catalyst under graphene using electron backscatter diffraction and atomic force microscopy. We find that the original flat catalyst surface transforms into two facets: a low-energy low-index surface, e.g (111), and a vicinal (high-index) surface, contrary to expectation from a surface energy perspective. The critical role of graphene strain, besides anisotropic interfacial energy, in forming the observed topographies is revealed by molecular simulations. We identify the sources of strain in the graphene-metal interface, and use this to reveal the formed topographies. The thesis presents a simple analytical model to study faceting and its sizes. The model considers the interfacial binding, surface and the bending energies of graphene, in addition to macro-strain resulting from the synthesis and topographical changes. Insights on the role of graphene bending and interfacial energy on faceting can be obtained using the model, while enabling study of large systems that are not easily accessible by molecular simulations. The thesis also presents a large data set of graphene-driven faceting of catalyst surfaces. Statistical analysis is performed by defining the geometric parameters - facets widths, angles, orientation proximity to low-index surfaces, and periodicity, as dependent variables. The independent parameters include the growth conditions and catalyst composition and metal crystal orientation. Several valuable correlations are found from the data including the role of the number of layers and carbon-metal interaction on the periodicity of the facets. The increasing demand for high-performance wearable devices is accompanied by a need for developing damage-resistance and durable flexible conductors. We tackle this issue using a CVD-grown graphene-metal composite thin film to manufacture flexible devices. This application is an example of the direct benefit of the enhanced interaction eliminating graphene-transfer process. The metal-graphene nanocomposite is patterned into a serpentine geometry which imparts flexibility and stretchability. This 2D material-enhanced system results in an improvement of both performance and reliability, sustaining electrical connection even under high mechanical strains of 40\% and under fatigue loading. The work demonstrates the potential of graphene nanocomposites in the manufacturing of reliable flexible electronics as well as the prospective applications of interfacial interaction in a 2D/3D material system.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Mitisha Surana

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