Faculty Bibliography

Methods capable of forming highly organized monolayers on top of YBa2Cu3O7 (YBCO), a high T-c superconductor, have been identified and are described for the first time. Here, grazing reflectance infrared fourier transform spectroscopy (GRIFTS) is employed to evaluate the degree of order for these monolayer structures. Through these investigations, it is found that while octadecylamine forms a well-ordered, crystalline like monolayer on the surface of c-axis-oriented YBa2Cu3O7 thin films. the same reagent adsorbed onto polycrystalline YBa2Cu3O7 pellets affords disordered, liquid-like monolayers. Computational studies of alkylamine packing, using a molecular mechanics methodology reveal two plausible structures for the crystalline-like monolayer. A GRIFTS comparison of primary, secondary, and tertiary alkylamine reagents also has been completed, and the substitution pattern dependence of the monolayer order has been assessed experimentally. Moreover, comparisons between amine monolayers on top of YBa2Cu3O7 and alkyl thiol reagents on gold surfaces are made using GRIFTS and thermal desorption experiments. This work documents the initial report of the assembly and characterization of organized monolayers supported on high-T-c superconductor surfaces, the most complex substrate yet reported capable of fostering ordered adsorbate layers.

In order to solve some of the formidable problems related to producing reliable and reproducible cuprate superconductor/normal-metal/superconductor (SNS) junctions, new N-layer compounds from the family of R1-xCaxBa2-yLayCu3-zMzO7-delta (R = Y, Gd and Pr; M = Co, Ni and Zn; 0 less than or equal to x less than or equal to 0.4; 0 less than or equal to y less than or equal to 0.4; 0 less than or equal to z less than or equal to 0.4) have been synthesized and their properties characterized. Thus, a crystal engineering approach has been adopted in an effort to generate reliable materials for use in high T-c superconducting devices. Careful analyses of the various prepared phases reveal optimum substitution levels for selected compositions where the N-layer compounds exhibit structures compatible with common superconductor electrode materials. The new compounds have been used for demonstration purposes as the N-layer material for the construction of ramp-edge-geometry SNS junctions and superconducting quantum interference device sensors. (C) 1998 American Institute of Physics.

We attempted to determine the accuracy of manually splitting hydrochlorothiazide tablets. Ninety-four healthy volunteers each split ten 25-mg hydrochlorothiazide tablets, which were then weighed using an analytical balance. Demographics, grip and pinch strength, digit circumference, and tablet-splitting experience were documented. Subjects were also surveyed regarding their willingness to pay a premium for commercially available, lower-dose tablets. Of 1752 manually split tablet portions, 41.3% deviated from ideal weight by more than 10% and 12.4% deviated by more than 20%. Gender, age, education, and tablet-splitting experience were not predictive of variability. Most subjects (96.8%) stated a preference for commercially produced, lower-dose tablets, and 77.2% were willing to pay more for them. For drugs with steep dose-response curves or narrow therapeutic windows, the differences we recorded could be clinically relevant.

Careful studies of the corrosion, redox, galvanic, and oxygen evolution/uptake reactions associated with YBa2CU3O7-delta and related compounds have been completed. These studies have led to an understanding of the many factors that contribute to the poor material characteristics exhibited by these popular high-T-c phases. With knowledge of the structure-reactivity relationships, a powerful crystal engineering approach has been developed that is capable of producing cation substituted versions of YBa2Cu3O7-delta; the resulting compounds therefrom produced exhibit markedly improved processability, oxygen stability, and durability characteristics. These materials have been combined in thin film structures so as to make prototype SNS junctions and SQUID sensors which exhibit promising device performance characteristics.