Steven M. Savoy

Environmental degradation properties of YBa2Cu3O7−δ and Y0.6Ca0.4Ba1.6La0.4Cu3O7−δ thin film structures

Abstract Utilization of the high temperature superconductor, YBa 2 Cu 3 O 7−δ , 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 YBa 2 Cu 3 O 7−δ and a cation substituted compound, Y 0.6 Ca 0.4 Ba 1.6 La 0.4 Cu 3 O 7−δ , 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.

Single Analyte to Multi-analyte Fluorescence Sensors

The rational design of small molecules for the selective complexation of analytes has reached a level of sophistication such that there exists a high degree of prediction. An effective strategy for transforming these hosts into sensors involves covalently attaching a fluorophore to the receptor which displays some fluorescence modulation when analyte is bound. Competition methods, such as those used with antibodies, are also amenable to these synthetic receptors, yet there are few examples. In our laboratories, the use of common dyes in competition assays with small molecules has proven very effective. For example, an assay for citrate in beverages and an assay for the secondary messenger IP3 in cells have been developed. Another approach we have explored focuses on multi-analyte sensor arrays with attempt to mimic the mammalian sense of taste. Our system utilizes polymer resin beads with the desired sensors covalently attached. These functionalized microspheres are then immobilized into micromachined wells on a silicon chip thereby creating our taste buds. Exposure of the resin to analyte causes a change in the transmittance of the bead. This change can be fluorescent or colorimetric. Optical interrogation of the microspheres, by illuminating from one side of the wafer and collecting the signal on the other, results in an image. These data streams are collected using a CCD camera which creates red, green and blue (RGB) patterns that are distinct and reproducible for their environments. Analysis of this data can identify and quantify the analytes present.

THERMAL DIFFUSIVITY MEASUREMENTS OF SUB-MICRON ORGANIC DYE THIN FILMS USING A HIGH TEMPERATURE SUPERCONDUCTOR BOLOMETER

The thermal diffusivity of a thin organic dye layer deposited atop thin films of the high temperature superconductor YBa2Cu3O7−δ is measured using a pulsed laser flash method. Here, the underlying superconductor acts as a highly sensitive temperature transducer after appropriate conversion of the transient voltage response from 7 ns optical pulses. Film surface temperature decays for several thicknesses of the dye layers were evaluated; these decays exhibited a linear dependence of the time at half temperature maximum versus thickness squared. Three dimensional finite difference modeling was used to study and extract the thermal diffusivity values of the thin organic layers as well as to investigate the transient temperature distributions within the dye and superconductor areas.

Color selective optical sensors based on dye/superconductor assemblies

This paper describes the design, construction and operation of hybrid dye/superconductor optical sensors. A reflective mirror layer positioned between the dye and superconductor components is used as a means to reject light signals that are not absorbed strongly by the dye. On resonance signals are shown to couple effectively with the underlying superconductor where they evoke measurable responses. These structures form the basis for color selective optical sensors.

Optical studies of dye-coated superconductor junctions

The preparation and characterization of a new generation of optical sensors fabricated from high-temperature superconductor (HTSC) thin films is reported herein. These new hybrid devices are fashioned using HTSC thin films which are coated with organic dye overlayers. These systems are shown to respond selectively to those wavelengths which are absorbed strongly by the molecular dye. Methods for fabricating the superconductor element and depositing the dye layer are discussed. Moreover, resistivity versus temperature measurements before and after dye deposition are utilized to characterize these hybrid structures. The unique optical response properties of these hybrid sensors are also detailed.