Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Mechanical Engineering

Major Professor

Michael Cai Wang, Ph.D.

Committee Member

Wenjun Cai, Ph.D.

Committee Member

Rasim Guldiken, Ph.D.

Committee Member

Stephen Saddow, Ph.D.

Committee Member

Dmitry Voronin, Ph.D.

Keywords

2D polymer, high-pressure compression, metallic nanosheet, nanometallic multilayer, nanoparticle strength, open foam metallic nanosheet

Abstract

Two-dimensional (2D) materials have introduced a transformative era in materials science with extensive research being performed to gain a fundamental understanding of their diverse properties and applications. Amongst the broader 2D material family, 2D metals or 2D metallic nanosheets (2DMNSs) typically denotes the nanometer-scale thin elemental metals, compound, or alloys, which shows superlative chemical and physical properties compared to bulk counterparts due to the reduced dimensionality. 2D materials’ widespread direct physical or chemical isolation techniques have been facilitated due to their intrinsic van der Waals layered morphology, whereas 3D close-packed bulk metals with isotropic bonding hinder their facile isolation in thin 2D form.

Significant research interest has been generated in the 2D metal nanomanufacturing field due to their exciting potential opportunities across diverse areas, from catalysis and optics to electronics and energy applications. Bottom-up (especially wet chemistry-based) 2D metal nanomanufacturing techniques have experienced significant progress and development over the years, uncovering and advancing understanding of many 2D metals' intrinsic properties and practical potentials, however, face many challenges such as control and complexity of the reaction kinetics along with involvement of harmful chemicals and gases. Whereas top-down techniques have shown promising generalizable and versatile mechanical-based routes to achieve large-scale nanomanufacturing of the 2D metals, although remain understudied. In comparison to the widely studied low-dimensional 1D and 0D metallic crystals, the existing broad scope of research in the nanomanufacturing of 2D metals is the primary focus of this dissertation.

This dissertation presents an investigation and understanding of materials’ behavior and response under various stress states (solid-state multiaxial and uniaxial) as they approach nanometer-scale thinness via anisotropic 2D transformation. First, the behavior of bulk metallic foils and edible leaves was investigated via multiaxial stresses generated via rolling-induced thinning down in stacked nanometallic multilayer (NMM) form while investigating their morphological, crystallographic evolution, and the final morphologies of the nanomanufactured 2D metals (monolithic or nanoporous).

Subsequently, the empirical understanding of the effect of precursor size in accessing ultrathin 2D metallic nanostructures led to the investigation of low-dimensional metallic nanocrystals’ behavior under a purely solid-state uniaxial compressive regime (nanoscale goldbeating), gaining deeper insight into the nanoscale metallic deformation. A deterministic control over the shape anisotropy of zero-dimensional (0D) gold nanoparticles was achieved along with the effect of precursor nanocrystal morphology, dimension (diameter, aspect ratio), degree of compression, and on-substrate interparticle separation. The sold-state 2D transformation technique was shown to be generalizable to other low-dimensional nanocrystals (1D – gold nanorods, AuNR), core-shell nanoparticles, bulk metallic materials, and ceramic nanoparticles. Moreover, further investigation on how carbon allotrope nanomaterial - the most stable fullerene, C60 - behaves under a purely uniaxial, solid-state compressive regime was performed, demonstrating their polymerization and 2D transformation into all carbon 2D polyfullerene, where the nature of the intermolecular interaction and bonding of the C60 molecules were explored.

Overall, the behavior and response of materials under various stress states were investigated using a mechanical-based solid-state 2D transformation technique. The generalizable and versatile top-down nanomanufacturing technique provides a deeper understanding of how different bulk and low-dimensional metals’ deformation and anisotropic 2D morphological transformation proceed as they approach extreme nanometer scale thinness, which could facilitate diverse future applications in a wide range of areas.

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