High Pressure Enabled Synthesis of Ultrahigh Aspect Ratio Materials for Superconductive and Optoelectronic Applications

Open Access
Author:
Bischof, Jesse Lee
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 14, 2016
Committee Members:
  • John V Badding, Dissertation Advisor
  • John V Badding, Committee Chair
  • Raymond Edward Schaak, Committee Member
  • Christine Dolan Keating, Committee Member
  • Moses HW Chan, Outside Member
Keywords:
  • 1D Superconductivity
  • Superconducting nanowires
  • Ultralong nanowires
  • High pressure materials
  • Pressure assisted melt filling
  • gallium-indium eutectic
  • High pressure chemical vapor deposition
Abstract:
High aspect ratio materials are of interest in both the microscale and nanoscale. These materials are small in the transverse direction and can be synthesized to be hundreds of thousands or even millions of times longer on the axial direction. When a materials is arranged in this manner, it offer opportunities to exploit weak effects in the material due to the large interaction between the material itself and the photons and/or electrons that travel through the material. These structures could be necessary for the next generation of photonic, spintronic, photovoltaic, and electronic devices. The actualization of materials, specifically semiconductors at the micro scale and metals at the nanoscale, in this type of geometry presents a challenge because conventional synthesis techniques do not poses the ability to grow materials in such extreme aspect ratios. The focus of this dissertation will be furthering the development of a high pressure templated growth in the pores of microstructured optical fibers. These meter long, ultra-high aspect ratio materials have been utilized for decades in the telecommunication, medical, and industrial fields; however they are limited in materials that could be incorporated into their structure via traditional drawing techniques. When fabricated with hollow cores, they offer a template that is capable of handling high pressures and moderately high temperatures, as well as a nearly atomically smooth surface to act as the substrate to deposit materials. Two types of synthesis will be described. First is a high pressure chemical vapor deposition technique that was pioneered by former members of the Badding lab. The focus will be on a novel approach to high aspect ratio zinc oxide deposition in which water is created via the reverse water gas shift reaction to act as the oxygen source of the metal oxide. The high pressures involved in the deposition drastically affect the material quality as well as the chemical kinetics and thermodynamics involved in the reaction. The second synthesis described will be metal nanowires that are created via a pressure-assisted melt filling technique. High pressures are necessary to overcome the surface tension and the non-wetting characteristics of many metals on silica and form them into the high aspect ratio shapes. A focus will be on gallium’s interesting surface chemistry and ability to create metastable crystal structures in confined geometries. Investigations into the superconductivity of gallium as well as gallium-indium structures are of interest due an interest in 1-D superconductivity, which long nanowires are required due to proximity effects of contacts to the superconductive wires. One particular structure is utilized to create a non-destructive memory element that is a nano-realization of a Josephson memory device.