Browsing by Author "Jones, Matthew R"
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Item Advancing Control Over Two-dimensional Noble Metal Nanoparticle Self-assembly(2024-04-19) Kress, Rachael Nicole; Jones, Matthew RSelf-assembly is utilized by many natural processes to make large-scale complex structures and materials from much smaller, simpler components. These structures are stable without the continuous influx of energy. It is a “bottom-up” approach that is not restricted by scale and is therefore a very promising approach for the fabrication and manufacturing of both new synthetic materials or mimics of biological materials. This is especially true in the field of nanomaterials. Objects that exist on the nanoscale often have unique and interesting properties that are dependent on their size, which makes them very appealing for a variety of applications. Most of these applications depend on arranging nanoparticles into very specific patterns on a large scale. Currently, many of the fabrication techniques that excel in terms of order and control, such as lithography-based techniques, lack scalability. Self-assembly is one conceivable pathway for achieving a high degree of control in a scalable manufacturing process. In this thesis, I present investigations into two different nanoparticle two-dimensional (2D) self-assembly systems, which advance our understanding of the principles that govern them and provide the groundwork for further exploration into these systems. In Chapter 1, I discuss the basic principles of self-assembly at the nano-length scale. This discussion includes highlighting the most common forces used to drive self-assembly, and how different components of a nanoparticle system can be used to alter those forces. I also provide additional analysis on the specific challenges and merits of 2D self-assembly as compared to 3D self-assembly. Chapter 2 is a commentary that provides a structure and language for discussing interparticle interactions and how self-assembly systems can carry the information that directs them. The terms valency, directionality, and specificity are used to describe the type and degree of information that is encoded into a system. In Chapter 3, I present an investigation into the role of DNA flexibility during the DNA-mediated 2D self-assembly of gold nanospheres. Introducing an “ambidextrous” design of the sticky end of the DNA strands directing the self-assembly, I was able to deconvolute the particle-particle interactions and the particle-surface interactions in a 2D system. This revealed that the system favored softer, more flexible particle-particle interactions but harder, more energetically stable particle-substrate interactions. I performed additional experimentation and analysis that suggests the preference for hard particle-substrate interactions is most likely a result of having faster kinetics under those circumstances, while the softer particle-particle interaction is more strongly dictated by the ability of softer ligand shells to overcome lattice defects. The final chapter presents a second 2D self-assembly system in which cubes and orthocentric bitetrahedra are co-assembled into two distinct superstructures based on the size and sharpness of both shapes. While this project is still in its infancy, the initial work for determining a standard and the boundary conditions for each of the different elements of the system is present. In this chapter, I also discuss the promising initial results and the future experiments needed to resolve standing questions and to quantify my observations. Self-assembly is a simple and universal principle that governs many of the most complex materials in our lives. Understanding and applying it, however, is anything but simple. The discussions, observations, and results presented in this thesis add to the growing body of knowledge about this ubiquitous process so that it may one day be utilized with accuracy and efficiency in the fabrication of complex materials and structures.Item Chemistry Mediated Mechanical Behavior of Inorganic Nanostructures(2021-08-31) Rehn, Sarah M; Jones, Matthew RUnique and fascinating chemistry transpires at surfaces that cannot take place in bulk materials due to the presence of dangling bonds as well as strained or otherwise unusual coordination environments. As the size of an object becomes smaller, the fraction of surface atoms to bulk atoms increases. Ultimately, for nanometer-sized particles, surface effects become so large that the behavior of the system can change completely, leading to many of the unique properties associated with nanoscale materials. At this length scale, forces that would ordinarily have little to no influence on atoms in the bulk can have an enormous impact on surface atoms and thus dictate the behavior of the system. Since all inorganic nanoparticles are capped with organic ligands that provide them stability in solution, the chemistry at the surface atom-ligand interface can be leveraged to drive new chemical processes or physical phenomena that would be impossible at any other length scale. Colloidal silver nanoplates can be readily synthesized that are several nanometers thin, maximizing the fraction of surface atoms and making them an ideal candidate for studying the effects of surface chemistry on nanoparticle properties. Their high aspect ratio renders them unusually flexible such that when draped over much small spherical nanoparticles, the plates deform, a process that can be observed via distinctive bend contours in electron microscopy images. Topographically, this locally deformed region presents as an axially symmetric bump on the surface of the nanoplate, as confirmed by atomic force microscopy measurements. To understand the structural nature of this deformation, an analytical model based on Kirchhoff-Love plate theory was developed. This reveals that the local deformation of the nanoplate around the spherical particle is driven by the Van der Waals (VdW) interaction between the nanoplate and the experimental substrate. The ability for the VdW interaction to deform the nanoplate is shown to be heavily dependent on the thickness of the nanoplate; and it is estimated that structures thicker than ~10 nm would not be deformable. For the experimentally observed deformation to be possible, the analytical model must include plastic deformation, the occurrence of which was further confirmed by finite element simulations (COMSOL) as well as electron microscopy studies. The size of the described bend contour is related to the extent of the topographical deformation in the nanoplate. This was confirmed by varying the size of the sphere over which the nanoplate was deformed, displaying that the size of the bend contour was directly related to the size of the spherical nanoparticle. With this in mind, we hypothesized that the bend contours could be used to study the potential influence of surface chemistry on mechanical properties. As synthesized, the nanoplates are capped with a weakly bound citrate ligand which can be replaced with a library of other commonly used molecules: pyrrolidone (PVP), a phosphine, a thiol, and an N-heterocyclic carbene. It was found that the spatial extent of the bend contour changed proportionally to the binding strength of the surface ligand, suggesting that the mechanical strength of the nanoplate is also proportionally related to binding strength. We postulate that this mechano-chemical coupling arises from the atomic reorganization of surface atoms upon interactions with increasingly strongly binding ligands, changing the surface stress and the yield strength. In the case of more strongly binding ligands, the atomic reorganization of the surface layers of atoms is so severe that the nanoplate becomes stronger and the extent of the spatial deformation is larger than for weaker bound ligands. This work investigates a fundamentally new size-dependent interaction driven by the surface chemistry of inorganic nanoparticles. We envision using these results as a basis for being able to create a new class of nanoscale materials capable of physical bending and structurally reconfiguring themselves via chemical cues to adapt to the needs of a given application.Item The Controlled Deformation and Assembly of Anisotropic Nanostructures(2023-09-05) Gerrard-Anderson, Theodor Maxwell; Jones, Matthew RThe desirable properties of inorganic nanostructures are, in large part, determined by their morphologies, whether it be their plasmon resonance, surface chemistry, or assembly behavior. Therefore, great effort has been expended over the last two decades into growing the library of available inorganic nanostructures, primarily through the development of more sophisticated synthetic techniques utilizing directing ligands and differing facet reactivity. Particularly sought after are methods to fabricate low symmetry nanostructures, as these frequently exhibit more exotic properties, such as optical chirality, or the ability to organize into highly anisotropic superlattices with unique crystal habits and lattice structures. The difficulty in fabricating low symmetry inorganic nanostructures originates in the inherent isotropy of the chemical conditions used to grow them, forcing these methods to rely on the inherent asymmetry of a given material’s crystal structure or that imposed by carefully chosen directing ligands. As such, these protocols are designed ad hoc for each material, leading to a gradual expansion of available morphologies over time. The mechanical deformation of inorganic nanostructures is a promising route toward accessing novel low symmetry morphologies and a rapid expansion of the existing library. Mechanical deformation involves the imposition of an anisotropic force onto a nanostructure, leading to bending strain and a lower symmetry product. We have recently developed a method of inorganic nanostructure deformation wherein a template particle is used to direct the shape change. In this method, noble metal nanoplates are deposited onto spherical template particles and deform to their shapes due to cumulatively strong Van der Waals interactions across the large surface area of the nanoplate. In this work we demonstrate templated deformation of micron sized silver nanoplates over 15 nm template particles, characterizing their morphology through transmission electron microscopy and producing a Kirchhoff-Love theory derived analytical model to elucidate the relationship between nanoplate thickness and final deformation morphology and demonstrate that Van der Waals forces are sufficient to induce plastic deformation in the nanoplate. We extend this model to show the effect binding ligands have on the overall mechanical properties of thin silver nanoplates and demonstrate this method could be applied to other materials. We also develop a synthesis for high aspect ratio gold nanoplates and show that their deformation around template particles on the same order of size yields high morphological diversity in the products, as well as curvature control which can be exerted by altering the size of the template particle. Using a combination of cross-section TEM imaging, chemical nanoplate overgrowth experiments, and tomographic reconstruction, we show the nanoplates are deformed elastically and accurately measure their curvature landscapes. Finally, we develop a method for the functionalization of 2 nm wide and ~1 micron long ultra-thin gold nanowires, desirable for their simultaneous flexibility and electrical conductivity, with a stimulus responsive thiol ligand based on carboxyl group chemistry. The ultra-thin gold nanowires assemble and disassemble in response to specific chemical stimuli and can be assembled into macroscopic fibers, demonstrating preliminary work that could be continued to develop fibers of these functionalized ultra-thin gold nanowires as functional materials. Overall, this work breaks new ground on the use of deformable and flexible nanostructures in generating low symmetry morphological diversity and functional anisotropic superstructures.