Date of Award

2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Mechanical Engineering & Applied Mechanics

First Advisor

Haim H. Bau

Abstract

The advent of the electron microscope has fostered major advances in a broad spectrum of disciplines. The required vacuum environment of standard electron microscopy, however, precludes imaging of systems containing high vapor pressure liquids. The recent development of liquid cells like the Penn nanoaquarium overcomes this limitation, enabling imaging of temporally evolving processes in liquids with nanoscale resolution at video frame rates. We used Liquid Cell Electron Microscopy to investigate the morphological evolution of the electrode-electrolyte interface during electroplating, the onset of diffusive instabilities in electrodeposits, beam-mediated nucleation, growth, and dissolution of metallic nanoparticles, the nucleation and growth of nanobubbles, and the fundamentals of the electron-water interactions (Radiation Chemistry). The control of interfacial morphology in electrochemical processes is essential for applications ranging from nanomanufacturing to battery technologies. Critical questions still remain in understanding the transition between various growth regimes, particularly the onset of diffusion-limited growth. We present quantitative observations at previously unexplored length and time scales that clarify the evolution of the metal-electrolyte interface during deposition. The interface evolution during initial stages of galvanostatic Cu deposition on Pt from an acidic electrolyte is consistent with kinetic roughening theory, while at later times the behavior is consistent with diffusion limited growth physics. To control morphology, we demonstrate rapid pulse plating without entering the diffusion-limited regime, and study the effects of the inorganic additive Pb on the growth habit. The irradiating electrons used for imaging, however, affect the chemistry of the suspending medium. The electron beam's interaction with the water solvent produces molecular and radical products such as hydrogen, oxygen, and hydrated (solvated) electrons. A detailed understanding of the interactions between the electrons and the irradiated medium is necessary to correctly interpret experiments, minimize artifacts, and take advantage of the irradiation as a tool. We predict the composition of water subjected to electron irradiation under conditions relevant to liquid cell electron microscopy. We interpret experimental data, such as beam-induced colloid aggregation and observations of crystallization and etching of metallic particles as functions of dose rate. Our predictive model is useful for designing experiments that minimize unwanted solution chemistry effects, extend liquid cell microscopy to new applications, take advantage of beam effects for nanomanufacturing such as the patterning of nanostructures, and properly interpreting experimental observations.

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