| Description |
This dissertation presents experimental and computational investigations of electrolyte negative differential resistance, nanoparticle dynamics in nanopores, and nanobubble formation at nanoelectrodes. Chapter 1 provides an introduction to negative differential resistance and other nonlinear electrical responses in nanopores, an overview of resistive pulse analysis of nanoparticles using nanopores, and current nanobubble research. Chapter 2 describes the first example of electrolyte negative differential resistance (NDR) discovered in nanopores, where the current decreases as the voltage is increased. The NDR turn-on voltage was found to be tunable over a ~1 V window by adjusting the applied external pressure. Finite-element simulations yielded predictions of the NDR behavior that are in qualitative agreement with the experimental observations. Chapter 3 presents the extension of NDR to an aqueous system and demonstrates the potential for chemical sensing based on NDR behavior. Solution pH and Ca2+ in the solution were separately employed as the stimulus to investigate the surface charge density dependence of the NDR behavior. The NDR turn-on voltage was found to be exceedingly sensitive to the nanopore surface charge density, suggesting possible analytical applications in detecting as few as several hundred of molecules. Chapter 4 discusses the technique of controlling the dynamics of single 8 nm diameter gold nanoparticles in nanopores, which is extended from traditional resistive pulse analysis of nanoparticles. A pressure was applied to balance electrokinetic forces acting on the charged Au nanoparticles as they translocate through a ~10 nm diameter orifice at an electric field. This force balance provides a means to vary the velocity of nanoparticles by three orders of magnitude. Finite-element simulations yielded predictions in semiquantitative agreement with the experimental results. Chapter 5 reports the electrochemical generation of individual H2 nanobubbles at Pt nanodisk electrodes immersed in a H2SO4 solution. A sudden drop in current associated with the transport-limited reduction of protons was observed in the i-V response at Pt nanodisk electrodes of radii less than 50 nm. Finite element simulation based on Fick's first law, combined with the Young-Laplace equation and Henry's Law, were employed to investigate the bubble formation and its stabilization mechanism. |
