Faculty Bibliography

By combining patterned high-temperature superconductor thin films with overlayers of molecular materials, a new generation of hybrid optical sensors is obtained. Here, the ability of molecular dye layers to influence the light sensing properties of a high-T-c superconducting bolometer is described. These dye-coated devices are shown to display selective optical responses which are dependent on the properties of the molecular layer. Two different types of molecular absorbing layers prepared from molecular dyes and conductive polymers are examined in this paper. Furthermore, the prospects for producing wavelength tunable detectors from hybrid conducting polymer/superconductor structures are addressed.

Electrochemical procedures are utilized to deposit conductive polymer layers directly onto thin film samples of YBa2Cu3O7-delta and to cycle the polymeric structures between their neutral (non-conductive) and oxidized (conductive) forms. Through changes in the polymer doping level, the superconducting properties of the high-T-c component can be modulated in a controllable fashion. In this regard, large changes in the superconducting critical temperature and critical current values are noted as a result of the doping of the polymer layer. This paper focuses on the role of superconductor weak link structures and how such features influence the magnitude of the modulation of the superconducting properties.

Recently the environmental reactivity behavior of the copper-oxide superconductors has been studied and the following reactivity trends have been established: YBa2Cu3O7 > Ti2Ba2Ca2Cu3O10 > Bi2Sr2CaCu2O8 greater than or equal to La1.85Sr0.15CuO4 > Nd1.85Ce0.15CuO4 > Nd1.85Th0.15CuO4. In this paper, the degradation characteristics of the most reactive cuprate material, YBa2Cu3O7, are compared with those of the fulleride superconductor, K3C60. Conductivity vs. exposure time measurements acquired for thin film samples in eight different environments are utilized to estimate the degradation rates for the two superconductor materials. The cuprate superconductor remains relatively stable in the presence of dry nitrogen, dry oxygen, vacuum, air and acetonitrile environments, but degrades rapidly upon exposure to water solutions. Samples of K3C60 are also unreactive in dry nitrogen and under vacuum, but decompose extremely rapidly upon exposure to dry oxygen, air, acetonitrile or water solutions resulting in the complete loss of the superconducting properties.