Deposition, surface chemistry, and electrochemistry of YBa₂Cu₃O₇₋(subscript delta) materials
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While high-temperature superconductors have been around for over 15 years, implementation of these materials into devices has been hindered by their poor materials properties. Work described in this dissertation targets the development of a fundamental understanding of the interfacial properties exhibited by common cuprate superconductors. This dissertation is organized such that the core introductory topics are covered in this chapter with more details provided in subsequent chapters as relevant. Chapter 2 covers the subject matter associated with the optimization of YBCO thin films created by pulsed laser deposition. Using an experimental design methodology, the laser energy, temperature and oxygen partial pressure are varied to create high quality c-axis oriented thin film. In addition, the temperature of a seed layer is varied with the deposition of a YBCO layer to create high quality aaxis films. These films are evaluated and characterized by their x-ray diffraction and resistivity versus temperature. The surface quality is evaluated by scanning electron microscopic imaging. Once these films are created, the electrochemistry on their surface is characterized. Chapter 3 of this dissertation uses electrochemical methods to determine the relationship between electrode response and surface corrosion. Here, XPS is also used to determine the surface quality of the films and the effectiveness of integration of a pulse laser ablation facility with a glove box to control surface corrosion. By comparing the XPS data with that obtained by the electrochemical responses, a more complete understanding of the surface chemistry and relative reactivity characteristics of YBCO films of different orientations is obtained. In addition, a-axis oriented grains are evaluated as are their c-axis counterparts to explore the capacity for both to support electrodeposition of silver upon the surface. These results are compared to those obtained on unoptimized corroded films treated by chemisorbed layers to improve their electrochemical response. As a prelude to future studies of organized molecular/polymeric conductor assemblies atop cuprate samples, new methodologies are required to create such organized motifs. To enable such futuristic studies, initial attempts have been made to organize amphiphilic polythiophene structures atop water surface using the Langmuir-Blodgett methodology. In Appendix A, detailed studies of the electrochemistry of amphiphilic regioregular monolayers of polythiophenes are examined. Two regioregular structures with ethylene oxide side chains are examined: one containing a 12-carbon side-chain and the other lacking this hydrophobic group. These polymers are ordered and deposited on gold substrates by the Langmuir-Blodgett technique before being examined with regard to their orientation in relation to the electrode surface. Comparison between these two polymers provides insight into the relative importance on the hydrocarbon side chains. In addition, multilayer structures of these two polymers are examined to gain a more thorough understanding of highly ordered regioregular polythiophene nanothreads that have been reported recently to have high conductivity. These structures will be examined for future study in combination with high-Tc thin films.