Focused Electron Beam Induced Processing (FEBIP) In Ammonia-Based Liquid Films
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Ahmed, Auwais
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Abstract
In this dissertation, a focused electron-beam-mediated approach to nanoscale synthesis and modification is presented, spanning from fundamental redox studies to the extension of these studies towards unique fabrication strategies in water-ammonia environments. The document comprises three core chapters that collectively investigate how water-ammonia solvents can be harnessed for direct-write nanostructure synthesis via focused electron beam-induced processes. The overarching theme is that the radiolytic chemistry of water-ammonia solutions fundamentally reshapes how reducing and oxidizing pathways compete to form or remove solid material at the nanoscale.
Chapter 2 discusses the influence of introducing ammonia in an aqueous silver nitrate solution on the oxidation-reduction processes under electron beam irradiation. Ammonia preferentially scavenges oxidizing radiolysis products, thereby suppressing the oxidation of metallic silver. At the same time, it changes the role of hydrogen peroxide from an oxidizer of silver in pure water to a dual role as both an oxidizer of silver and a reducer of the silver–ammine complexes. This fundamental shift in chemical pathways makes the environment more reducing, enabling silver deposition at a faster rate but over an extended region around the primary beam spot, rather than being limited to the immediate site of irradiation.
Chapter 3 shows how leveraging the water-ammonia solvent and silver nitrate-based chemistry, a highly reducing environment is created at the point of focused electron beam. At the same time, the environment in the farfield stays oxidizing, avoiding unwanted deposition. This ‘electrochemical lensing’ enhances growth rate in the near-field of the beam without sacrificing lateral resolution, offering high resolution and rapid nanofabrication.
Chapter 4 applies the ammonia-based solvent approach to precursor-free electron-beam patterning of copper, revealing that adjusting ammonia concentration can lead to net oxidation (etching) or reduction (deposition). At lower ammonia concentrations, the oxidizing environment leads to etching of copper at short electron beam exposure times. Over longer beam exposures, the copper ions/ion-complexes released by this initial oxidation are reduced and deposited back into the etched locations, forming peak-in-valley structures. Higher ammonia concentrations result in a high rate of copper–ammine complexation and suppression of oxidizing species, creating a strongly reducing environment that enables copper deposition even at short beam exposures.
Collectively, this dissertation advances the fundamental understanding of electron-beam-induced radiolytic chemistry in water-ammonia solutions and applies these advances to liquid phase Focused Electron Beam Induced Processing of nanomaterials.
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2025-08-07
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Dissertation (PhD)