Faculty Bibliography

A new method for enhancing the wavelength selectivity and responsivity of hybrid dye/superconductor optical sensors is described. Here, reflective ''mirror layers'' deposited atop the high-temperature superconductor, YBa2Cu3O7-delta, are used to enhance the optical performance characteristics of such hybrid sensors. Quantification of the wavelength selectivity for such detector structures is detailed for both dye/high-T-c superconductor and dye/mirror-layer/high-T-c superconductor systems. Optical studies suggest that the inclusion of the mirror layer serves to enhance the wavelength selectivity by reducing the amount of off-resonance signal generated by the detector. On the other hand, the on-resonance signals captured by the dye layer are effectively sensed by the superconductor element. Measurement of the wavelength-dependent optical responsivity of the mirror-layer-modified. hybrid detectors shows that energy transfer between the dye and superconducting elements is not diminished by the presence of this reflective layer.

Electrochemical techniques are exploited to fabricate conductive polymer/high-T-c superconductor bilayer structures. Scanning electron microscopy, x-ray fluorescence and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto oriented YBa2Cu3O7 thin 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 current (J(c)) of the underlying superconductor film are suppressed. Here described are new methods for the fabrication of superconductor thin film layers which possess multiple points of weak electrical contact. Such weak links are very susceptible to the influence of external forces making them well suited for the creation of hybrid polymer/superconductor structures. Moreover, measurements recorded as a function of temperature of the polymer/superconductor interface resistance show dramatic decreases in resistivity at T-c. Collectively, these results are consistent with observations of conductive polymer proximity effects.

Utilization of the high temperature superconductor, YBa2Cu3O7-delta, in commercial applications is becoming increasingly feasible. Before full advantage of this material can be taken, however, the lifetime, oxygen stability and processability of this ambient reactive superconductor must be improved. Corrosion resistance of YBa2Cu3O7-delta and a cation substituted compound, Y0.6Ca0.4Ba1.6La0.4Cu3O7-delta, were studied and their lifetimes in aqueous environments were determined. Results indicate a dramatic enhancement in the stability against environmental degradation for the cation substituted phase. Important mechanistic factors responsible for the enhanced corrosion resistance of the substituted phase over the parent compound are discussed.

Organic monolayers on high-T-c superconductors have allowed for the precise structural control of composite organic conductor/high-T-c superconductor assemblies. These hybrid systems display a number of novel electronic and structural properties. This paper discusses the utility of the monolayer self-assembly procedure for the preparation of both conductive polymer and crystalline charge transfer salt layers which are supported directly on top of cuprate superconductor thin film samples.

In this report, a monolayer of N-(3-aminopropyl) pyrrole is used as a template layer for the controlled growth of polypyrrole on polycrystalline and oriented films of the high temperature superconductor, YBa2Cu3O7. Large increases in the growth rate and smoothness of the polymer layer are obtained with the use of the monolayer template as compared with the bare superconductor electrodes. Observation of the electrochemical growth characteristics as well as polymer morphological properties allows for an evaluation of the local surface conductive properties of superconductor-based ceramic and thin film samples. The use of the amine substituted pyrrole self-assembled monolayer serves to drastically alter the polymer growth characteristics and the surface adhesion properties.