James A. Bruce

Electrostatic binding of electroactive and nonelectroactive anions in a surface-confined, electroactive polymer: selectivity of binding measured by Auger spectroscopy and cyclic voltammetry

Abstract : Electrodes derivatized with electroactive polymers or with charged, nonelectroactive polymers can be significantly influenced by the nature of the electrolyte and other ions present in a solution contacted by the derivatized electrode. It has been shown that charged, nonelectroactive polymers can persistently bind significant quantities of charged, electroactive species such as Fe(CN)(6)(4-) by surface polyvinylpyridinium or Ru(bipyridine)(3)(2+) by Nafion. Theses examples illustrate how electrostatic binding may be exploited for anlaysis, preparation of a variety of modified electrodes, and study of electrocatalysis. Electroactive polymers are charged in at least one of their accessible redox states and both selectivity of counterion binding and the movement of ions in and out of the surface polymer associated with change of redox state may affect electrochemical behavior. Electrodes coated with electroactive polymers may have a number of uses, including desalting of H20, that depend on the behavior of solution ions.

Characterization of the Interface Energetics for N‐Type Cadmium Selenide/Nonaqueous Electrolyte Junctions

Abstract : Single-crystal, n-type CdSe photoanodes have been studied in 0.1 M (n-Bu4N)aCl04/CH3CN solutions containing low concentrations of fast, outer-sphere, one electron redox reagents. A number of redox couples were studied spanning a wide range of redox potentials. We find that reversible electrochemical response is seen at both dark and illuminated (632.8 nm light) n-CdSe for couples with redox potentials more negative than -1.2 V vs. SCE, e.g. Ru(bpy)3(2+/+/0/-. For couples with redox potentials positive of -1.2 V vs SCE we find that CdSe is blocking to the oxidation of the reduced form of the redox couple in the dark, but illumination results in its oxidation. The photoanodic current peak in a cyclic voltammogram occurs more negative than at a Pt electrode, the difference between theses values is the photovoltage, EV, taken to approximate the barrier height, EB. The effect of a number of different etches on the interface energetics of CdSe was investigated, since it was previously determined that an oxidizing or reducing etch would yield quite different results for n-CdTe. For CdSe, however, the different etches do not give significantly different results with respect to EB vs redox potentials, despite large variation in surface composition deduced from Auger and XPS spectra.

Study of textured n-type silicon photoanodes: Electron microscopy, auger and electroanalytical characterization of chemically derivatized surfaces

Abstract Polished (111), (100) and textured (100) single-crystal, n-Si surfaces have been studied in relation to their use as photoanode materials in a photoelectrochemical device. Textured (100) Si is prepared by chemically etching the polished (100) surface. The textured surface consists of pyramids having (111) sides, necessitating the study of polished (111) Si as a comparison. Electron microscopy and Auger spectroscopy have been employed to characterize textured and polished surfaces functionalized with the electroactive reagents (1,1′-ferrocenediyl)dimethylsilane and (1,1′-ferrocenediyl)dichloosilane. Electrochemical techniques have been used to determine coverage of electroactive material, and the textured surface is found to bind about twice as much material as the polished surfaces. The chargetransfer properties of the surface-confined material on the polished (100) and (111) Si are virtually identical: the position of the photoanodic wave corresponding to uphill ferrocene oxidation is within 30 mV and the ferricenium reduction peak is also at the same potential. The textured (100) Si surface shows a slightly more positive (100 mV) photoanodic and dark cathodic peak. Photoelectrochemical cells based on textured (100) Si vs. polished (100) Si are about 20% better in overall efficiency due to lower reflection losses associated with the textured surface.

Effect of Humidity on Photoresist Performance

This paper discusses the effect of varied humidity on lithographic performance during photoresist exposure. In the presence of water, exposure causes the sensitizer to be converted into acid; without water, a less soluble ester forms. The effect of humidity on the resist chemistry was measured using infrared spectroscopy. To completely convert the sensitizer to acid, humidities exceeding 40% were needed. At lower humidities, significant amounts of ester, rather than acid, were formed. The effect of humidity during exposure was also measured using lithographic techniques. As humidity decreased from 40 to 20%, the dissolution rate decreased by up to 65%, dose-to-clear (E 0 ) increased by up to 25%, the dose-to-print increased by up to 15%, and contrast decreased by up to 10%. The magnitude of these effects was resist-dependent. The time of equilibration of water into and out of the resist film was less than 30 s.