Development and study of high-Tc superconductor conductive polymer assemblies
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This dissertation presents the development and study of organic polymeric conductor/High-Tc superconductor bilayers, for exploration of the superconductor proximity effect. A major obstacle to this research is the instability of the High-Tc superconductor towards H2O and CO2 as it is necessary to create hybrid structures where the two conductors have intimate contact. For this reason, a study of the corrosion characteristics of the RBa2Cu3O7 (R=Y, Eu, Nd) series was undertaken. In this study, R=Nd was shown to have enhanced corrosion resistance. In an effort to develop chemical processing methods that allow for the production of intimate contact between the cuprate superconductor and the conductive polymer systems, a study of alkyl amine adsorbed onto the surface of the superconductor is presented. In the electrochemical part of the study, alkyl amine ferrocene adsorbed onto the surface revealed that the amines are strongly adhered to the superconductor while still allowing electrons to pass from the superconductor to the ferrocene moiety. The self-assembled monolayer (SAM) structure of CF3(CF2)3(CH2)11NH2 atop the superconductor was elucidated by employing several techniques, including atomic scale atomic force microscopy (AFM). A novel multistep bilayer sample preparation protocol is presented involving thin film fabrication by pulsed laser deposition (PLD), patterning by shadow mask ablation, sample thinning by scanning probe and electropolymerization of the polymer. Scanning probe thinning yields a smooth superconductor surface, a known superconductor thickness, and if a blocking layer is employed prior to thinning, the localization of polymer growth. Studies of the response of a bilayer structure of Y0.6Ca0.4Ba1.6La0.4 Cu3O7/poly pyrrole to polymer redox cycling showed a semi-reversible suppression of transition temperature qualitatively consistent with a combination of corrosion and superconductor proximity effect. Quantitative analysis in the framework of the proximity effect shows evidence suggestive of an unexpected long superconductor coherence length. A qualitative model based on grain boundaries is postulated to explain this effect.