Using ion implantation to adjust the transition temperature of superconducting films

We summarize a continuing investigation into using ion implantation to alter the transition temperature of superconducting thin films. The primary motivation for the work presented here was to study the feasibility of using magnetic ion doping to replace the bi-layer T_c control process currently used for certain cryogenic detector applications at National Institute for Standards and Technology. The results from work with various ion species implanted into aluminum, molybdenum, titanium and tungsten host films are presented.     

Synthesis of LiFePO4 with fine particle by co-precipitation method

LiFePO₄ is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO₄ because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe²⁺ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO₄ is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO₄ fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property.     

Physical modeling of gas/liquid mass transfer in a gas stirred ladle

The absorption of gas through the plume eye and of an injected gas in a steelmaking ladle process was investigated, using a physical model of CO₂ absorption into a NaOH solution. The results show that the inert gas escaping through the plume eye is ineffective in protecting the bath from the atmosphere, and placing an oil layer (simulated slag) decreases the absorption rate significantly. Increasing the flow rate of the inert gas not only exposes more of the liquid surface to the CO₂ atmosphere, but also increases the mass transfer coefficient at the surface. The overall mass transfer between an injected CO₂ gas and NaOH solution includes the mass transfer through the surface of the bath as well as the mass transfer in the bubble dispersion zone. The difference between the mass transfer in the bubble dispersion zone and the overall mass transfer was found to be significant for relatively low gas flow rates. The mass transfer coefficient of CO₂ in the bubble dispersion zone was estimated using available information regarding the bubble size and velocity. Mass transfer coefficient estimated for the constant bubble frequency regime shows a dependence on gas flow rate. However, if a constant characteristic size of bubbles is assumed as an alternative approach, the mass transfer coefficient is independent of the gas flow rate.     

High dielectric constant thin film EBG power/ground network for broad-band suppression of SSN and radiated emissions

We experimentally demonstrated the great advantages of a high dielectric constant thin film electromagnetic bandgap (EBG) power distribution network (PDN) for the suppression of power/ground noises and radiated emissions in high-performance multilayer digital printed circuit boards (PCBs). Five-layer test PCBs were fabricated and their scattering parameters measured. The power plane noise and radiated emissions were measured, investigated and related to the PDN impedance. This successfully demonstrated that the bandgap of the EBG was extended more than three times, covering a range of hundreds of MHz using a 1-cm /spl times/ 1-cm EBG cell, the SSN was reduced from 170 mV to 10 mV and the radiated emission was suppressed by 22 dB because of the high dielectric constant thin film EBG power/ground network.     

A simplified expression for the hard-sphere dimer fluid radial distribution function

Recently, in our laboratory a closed form expression for the correlation function of the hard-sphere dimer fluid obtained from Wertheims multidensity Ornstein-Zernike integral equation theory with Percus-Yevick approximation was presented by Kim et al. [2001]. However, it is difficult to apply its expression to perturbation theory and vapor-liquid equilibria calculations, since it is of very complex form. In this work, we present a simplified expression for the first shell of the radial distribution function (RDF) of the hard-sphere dimer fluid using a series expansion of the analytical expression. The expansion is carried out in terms of both the packing fraction and the radial distance. Expressions are also obtained for the coordination number and its first and second derivatives as functions of radial distance and packing fraction. These expressions, which are useful in perturbation theory, are simpler to use than those obtained from the starting equation, while giving good agreement with the original expression results. Then we present an simplified equation of state for the square-well dimer fluid of variable well width (λ) based on Barker-Henderson perturbation theory using its expression for the radial distribution function of the hard-sphere dimer fluid, and test its expression with NVT and Gibbs ensemble Monte Carlo simulation data [Kim et al., 2001].     

Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopic studies on the ferroelectric behavior of poly(vinylidene fluoride–trifluoroethylene) ultrathin films

Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopy was used to characterize the ferroelectric behavior of a thin poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) copolymer. The lab-built GIRA-FTIR apparatus allowed the heating and corona poling process to be carried out whilst collecting the GIRA spectra of the thin polymer film. The Curie transition from the ferroelectric to paraelectric phase was confirmed from the abrupt change in intensity of the 849 cm⁻¹ band in the RA-FTIR spectrum. It was found that the Curie temperature dropped dramatically when the film thickness was lowered to below a certain critical value of approximately 100 nm. The switching of the CF₂ dipoles in the ferroelectric crystals after applying the external electric field could be determined by monitoring the change in the 849 cm⁻¹ band intensity. For the 600 nm thick P(VDF–TrFE) film, the switching of the dipoles appears to occur almost instantaneously, while the kinetics of dipole switching of the 75 nm thick film were significantly retarded. The repeated switchability of the CF₂ dipoles upon the application of a bipolar cyclic electric field was also confirmed. The bistability of the film due to remnant polarization was also confirmed from the absorbance of the 849 cm⁻¹ band after removing the applied voltage during corona poling.     

Protein binding study of isoflavone, perillyl alcohol and S-ibuprofen by high-performance frontal analysis

High-performance frontal analysis (HPFA) was used for a protein binding study of isoflavones (daidzein, genistin, and genistein), enantiomers of perillyl alcohol and S-ibuprofen to human serum albumin (HSA). The analyses were performed on a Develosil and Inertsil 100-Diol-5 column (10 cm×4.6mm). Sodium phosphate solution (pH 7.4, ionic strength 0.17) was used as the mobile phase at a flow rate of 1 ml/min. To ensure the drug to be eluted as a trapezoidal peak with a plateau, injection volumes were each fixed up the zonal profile with an evident plateau appears. The unbound drug concentration was determined from a plateau height of the plateau region after that experimental data were fitted by Scatchard equation. The binding constants (K) and total binding affinities (nK) of drugs to HSA were calculated, respectively.     

A simple mathematical analysis on the effect of sand in Cr(VI) reduction using zero valent iron

A simple mathematical model was proposed to analyze the enhancement of Cr(VI) reduction when sand materials are added to the zero valent iron (ZVI). Natural decay of Cr(VI) in a control experiment was analyzed by using a zero-order decay reaction. Adsorption kinetics of Cr(VI) to sand was modeled as a first-order reversible process, and the reduction rate by ZVI was treated as a first-order reaction. Natural decay of Cr(VI) was also included in other experiments, i.e., the adsorption to sand, the reduction by ZVI, and both adsorption and reduction when sand and ZVI are present together. The model parameters were estimated by fitting the solution of each model to the corresponding experimental data. To observe the effect of sand addition to ZVI, both adsorption and reduction rate models were considered simultaneously including the natural decay. The solution of the combined model was fitted to the experimental data to determine the first-order adsorption and reduction rate constants when sand as well as ZVI is present. The first-order reduction rate constant in the presence of sand was about 35 times higher than that with ZVI only.