Faculty Bibliography

Methods for synthesizing and characterizing high-temperature superconductor/conductive polymer structures are discussed. Both chemical and electrochemical techniques are used to deposit heterocyclic polymers such as polypyrrole and poly(3-hexylthiophene) onto the cuprate materials. These hybrid systems provide the basis for the construction of the first conducting polymer/superconductor electronic device. Moreover, through the analysis of such structures the initial evidence for the induction of superconductivity into the doped conductive polymer layer is obtained.

Methods for preparing and characterizing conductive polymer/high-T-C superconductor bilayers are reported. A number of procedures, such as cyclic voltammetry, chronoamperometry, and spray coating, have been utilized to deposit conductive polymers directly onto thin film samples of YBa2Cu3O7-delta. These structures have been fabricated in order to examine interesting electron and energy transfer phenomena between conductive polymers and superconductors as well as to explore prototype electronic devices and optical sensors. This paper focuses on an analysis of the growth of conductive polymer structures onto high-T-C superconductors. Scanning electron microscopy and electrochemical techniques are utilized to explore the hybrid structures.

The metallic conductivity of both the CuO2 sheets and the CuOx chains of YBa2Cu3O7-delta has been established. We have used double doping in (Y1-xCax)(Ba2-xLax)Cu3O7-delta to destroy the integrity of the CuO1-delta chains while keeping constant the total oxidation state of the Cu-O array. A break-up of the chain segments allows us to establish the temperature dependence of the Seebeck coefficient, alpha(T), due to the CuO2 sheets and, by difference, that of the Cu-1-delta chains in YBa2Cu3O7-delta. We also show that double doping enhances significantly the chemical stability of the superconductive phase. The origin of the chemical stability and of the behavior of alpha(T) is interpreted.

Electrochemical techniques are exploited to fabricate conductive polymer/high-T-c superconductor bilayer structures. Scanning electron microscopy, atomic force microscopy, and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa2Cu3O7-delta films. In such hybrid polymer/superconductor systems, it is found that, when the polymer is oxidized to its conductive state, the transition temperature (T-c) and critical currents (J(c)) of the underlying superconductor film are suppressed. Reversible modulations of the transition temperatures of up to 50 K are noted for these structures. Upon reduction df the conductive polymer layer back to its nonconductive form, both T-c and J(c) are found to return to values close to those acquired for the underivatized YBa2Cu3O7-delta film.