Phenomenological analysis of the optoelectrochemical behavior of electrochromic intercalation devices

A set of phenomenological analysis tools have been developed for the characterization of the optoelectrochemical behavior of electrochromic intercalation devices. Both step current and step potential excitations are considered. Great simplification is afforded by working with the passed charge as the primary independent variable; consideration is also given, however, to the transmission or built-in device potential as independent variables. It is shown that quasi-static intercalation efficiency curves, generated from step current measurements, can elucidate the intercalation site-energy distribution; these curves are also compared to dynamic intercalation efficiency curves obtained from step potential measurements. Quasi-static and dynamic optical efficiencies are also considered and compared. The scaling properties of some of the phenomenological parameters may be used to generate master curves which unify sets of data obtained under a variety of conditions (applied voltages, imposed currents, film thicknesses, etc.). Quantitative predictions can be made of device behavior under conditions not probed experimentally. Received: 17 April 1997 / Accepted: 2 September 1997     

Global uniqueness for an inverse boundary problem arising in elasticity

Summary We prove that we can determine the Lamé parameters of an elastic, isotropic, inhomogeneous medium in dimensionsn3, by making measurements of the displacements and corresponding stresses at the boundary of the medium.Oblatum 14-VI-1993 & 22-XII-1993Partially supported by NSF Grant DMS-9100178 and ONR grant N 0014-93-1-0295     

Segregation of inorganic ions at surfaces of polar nonaqueous liquids.

We present a short review of recent computational and experimental studies on surfaces of solutions of inorganic salts in polar nonaqueous solvents. These investigations complement our knowledge of aqueous interfaces and show that liquids such as formamide, liquid ammonia, and ethylene glycol can also surface-segregate large polarizable anions like iodide, albeit less efficiently than water. For liquids whose surfaces are covered with hydrophobic groups (e.g. methanol), the surface-ion effect all but disappears. Based on the present data a general picture of inorganic-ion solvation at the solution-vapor interface of polar liquids is outlined.     

EPMA Investigation of Roman Coin Silvering Techniques

Ancient Roman silver coins, especially forgeries, contain various amounts of silver on the surfaces. The state of preservation of the outer layer can vary strongly among different areas of the same coin, thus an investigation of the entire surface is indispensable. The measurement of the silver distribution is a first step towards uncovering the manufacturing techniques. Element mapping by electron probe micro-analysis (EPMA) with increasing step size allows a survey of the complete coin surface. The suitability of this approach is shown and applied to coins having a dark optical appearance and unknown minting technique.     

Optical and electrical properties of lead silicate glasses

The optical and electrical properties of PbO-SiO₂ glasses containing 24.6 to 65 mole % PbO have been determined. While the short-wavelength cutoff increases continuously in wavelength with increasing PbO concentration, an abrupt lightening in color is observed in the vicinity of 38–40% PbO. The darker color of glasses containing 30–38% PbO has been associated with a scattering process. The origin of this scattering is discussed and is tentatively identified with the formation of microcrystals of SiO₂ in the glasses. The alternative process of liquid-liquid phase separation seems less likely, but cannot be ruled out with certainty.The electrical conductivity of all glasses investigated exhibits an Arrhenian temperature dependence. The activation energy decreases from about 1.23 eV for the 30% PbO composition to about 1.11 eV for the 50% PbO composition, and remains about constant for glasses containing higher concentrations of PbO. Addition of NH₄Cl or Sb₂O₃ to the batch or use of Pb(NO₃)₂ or Pb₃O₄ instead of PbO as a raw material does not affect the electrical properties. The dielectric constant at 1kHz increases continuously with increasing PbO concentration, from a value in excess of 20 for the 55% PbO composition. The implications of these results for the conduction mechanism in PbO-SiO₂ glasses are discussed.     

Tuning of surface properties of thin polymer films by electron beam treatment

The aim of our work was to understand the impact of electron treatment on polymer thin films, particularly on their surface properties as well as the possibilities and limitations to tune these properties. Two different polymers, polystyrene (PS) and poly-2-vinlypyridine (P2VP), were chosen to form thin polymer films by grafting of end-terminated linear polymer chains to a surface with sufficient grafting density, forming so called “polymer brushes”. We were able to identify the surface properties and specify ongoing physico-chemical changes after electron beam treatment by using zeta potential and contact angle measurements. By varying the absorbed dose it was possible to tune the surface properties over a wide range. The detailed knowledge about the latitude of functionalization of the tested polymers was a prerequisite for the creation of wettability gradients by electron beam treatment by adapting a special mask of known thickness and density. Hence, electron beam treatment opens an easy reproducible way to generate surface gradients in functionality.     

Characteristic space-time estimates for the wave equation

Received August 16, 1999; in final form November 25, 1999 / Published online December 8, 2000