Electrolyte negative differential resistance, nanoparticle dynamics in nanopores, and nanobubble generation at nanoelectrodes

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 H 2 nanobubbles at Pt nanodisk electrodes immersed in a H2SO 4 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.