Joseph M. Rosamilia

Voltammetric studies of tellurium film and hydrogen telluride formation in acidic tellurite solution

Abstract The cathodic formation of highly active tellurium deposits and of hydrogen telluride in acidic tellurite solution were studied voltammetrically at gold and tellurium rotating disk electrodes with gold or silver rings. Both generation and detection of H 2 Te are dependent on the activity of the tellurium substrate and the presence of Te(IV) in the solution. Electrodeposited Te in perchloric acid solution produces a very rough surface which affects the hydrodynamics of the electrode and leads to the electrochemical activity. This substrate is highly useful in the electrosynthesis of metal tellurides.

Anodic and dissolution characteristics of Ba/sub 2/YCu/sub 3/O/sub 7/ in aqueous electrolytes

The authors have examined the electrochemical reactions taking place at Ba/sub 2/YCu/sub 3/O/sub 7/ and CuO in several aqueous media under anodic and open-circuit conditions. Understanding of the reactions of these materials in water containing environments may be important in their fabrication into devices. Ba/sub 2/YCu/sub 3/O/sub 7/ is dissolved by aqueous acids at mass transport limited rates up to 0.1M in H/sup +/ concentration in 1M NaCl with no selectivity for metal ions, i.e., they are found in stoichiometric ratios. This conclusion was determined by analysis following controlled exposure of rotating disk electrodes of the high temperature superconductor. When these disks are anodized at constant current in NaCl or NaClO/sub 4/ media, essentially only Ba dissolves. In pH 6.9 phosphate buffer or 1M NaOH, lesser fractions of Ba are found in solution. Anodization in saturated CaCl/sub 2/ produces chlorine and nonselective dissolution of the substrate simultaneously. Chemistry for these various situations is proposed.

Electron transfer reactions to soluble redox couples at Ba2YCu3O7 and CuO electrodes

Abstract As an electrode in aqueous media, Ba 2 YCu 3 O 7 acts as a strongly oxidized, reactive metallic conductor. Understanding this behavior is essential to processing this material and exposing it to atmospheres containing water. Competition between electron transfer reactions to soluble redox couples and substrate degradation limits the potential range over which electrochemistry can be carried out. This aspect has been studied through voltammetry with several kinetically reversible redox systems at Ba 2 YCu 3 O 7 rotating disk electrodes (RDE), supplemented by rotating ring-disk and hydrodynamically modulated RDE techniques to define the reaction paths. Collectively, the data allow prediction of the system behavior from electrode potentials. Parallel experiments with the more stable CuO are performed in each case as a related model substrate.

Electrochemical behavior of several metal ion solutions at Ba/sub 2/YCu/sub 3/O/sub 7/ and CuO electrodes

The electrodeposition of metallic coatings onto Ba/sub 2/YCu/sub 3/O/sub 7/ is desirable for the environmental protection of the underlying superconductor and for providing a parallel current path when the superconductor is in the normal state. Investigations with various voltammetric techniques have been made with simple metal ions in neutral salt media where electrolyte attack of the highly oxidizing substrate can be minimized. Easily reducible metals such as silver and mercury can be plated; the transition to extensive surface reduction of the substrate and failure to plate occurs in the region of potentials required for copper reduction. Ba/sub 2/YCu/sub 3/O/sub 7/ is attacked by most buffer acids - cathodically generated local pH increases in unbuffered salts can lead to precipitation processes. Parallel studies at CuO pellet electrodes and noble metal electrodes have been carried out as models.

Cathodic generation of CdSexTe1−x at Te film electrodes

Abstract CdSe x Te 1− x films have been electrodeposited by the co-reduction of a tellurium substrate (to telluride) and soluble SeSO −2 3 (to selenide) in the presence of cadmium complexes. The tellurium film is itself initially electroplated in acidic media from tellurite. The necessary sequence of electrode reactions to allow CdSe x Te 1− x compositions to be formed is regulated by the potentials maintained in the pH 9.6 ammonia buffer-ethylene diamine tetraacetic acid solution. Photoelectrochemical spectroscopy and X-ray diffraction of annealed films were used to characterize the products. In the absence of cadmium ion, the method allows generation of known fluxes of telluride and selenide downstream of the generating electrode surface for other synthetic purposes.

Etching Behavior and Electrochemistry of a Bi‐Sr‐Ca‐Cu‐O Superconductor in Acidic Media

Bismuth strontium calcium cuprate superconductors with nominal composition, Bi/sub 2/(Sr, Ca)/sub 3/Cu/sub 2/O/sub 8/, have been examined by electrochemical techniques and are found to be both highly oxidizing compounds and reactive towards hydrogen ions. The chemical reactivity of 84K bismuth strontium calcium cuprate is similar to that of Ba/sub 2/YCu/sub 3/O/sub 7/. The dissolution reaction in acid is intrinsically fast; the authors observe H/sup +/ mass transport control in perchlorate solution. Dissolution rates can be altered and made selective by surface filming and post reactions of Bi/sup +3/, as in Cl/sup -/ solution. The stoichiometries of the acid reactions and for the etching of the Bi/sub 2/(Sr, Ca)/sub 3/Cu/sub 2/O/sub 8/ by ethylenediaminetetraacetate have been determined. Several etching solutions readily adaptable to controlled patterning or removal of these substrates are demonstrated.

Electrochemical crystallization of tetraphenylphosphonium and tetraphenylarsonium fullerides

The electrocrystallization of tetraphenylphosphonium and tetraphenylarsonium halide double salts of the C–60 and C–70 fulleride anions has been investigated. The mechanism of precipitation, growth of single crystals and application to separation and generation of various reduced states of the fullerenes are discussed. Electrochemical methods have demonstrated an initial dissolution–precipitation mechanism exhibiting a high level of supersaturation, followed by growth of a solid phase of low solubility in 1,2-dichlorobenzene. Single crystals with at least 400 µm face dimensions have been grown. Methods for generation of fluxes of either the doubly charged anions or of the fullerene precursors from the salts are described.

Applications of Redox Contacts for Metal and Semiconductor Rotating Ring‐Disk Electrodes

A design of a rotating ring-disk electrode with an electrolytic back-contact cell for the disk has been implemented and tested. Both the disk, acting as a bipolar electrode between a conventional cell and back compartment, and the back-electrolyte are made readily interchangeable. The most significant application is to semiconductor disks where ohmic contacts may be intricate to fabricate, as for the p-InP example experimentally investigated. However, control of the back-cell characteristics when there is a front metallic disk allows blocking current flow (anodic or cathodic) in a selected direction over some potential range. Application of this principle to amperometric end-point detection in titrimetry illustrates how selective response to mixed redox couples introduced by this diode-like effect can be put to effective use with conventional metal electrodes.

Maximum Power Spectroscopy for Photovoltaic Devices

Maximum power spectroscopy for the study of photovoltaics is described. The technique is based on analyzing the modulated maximum power output of the photojunction cell for a controlled input spectrum in a dual beam (bias plus modulated monochromatic probe) arrangement. The differential power conversion efficiency is thus measured. The input spectrum is programmed by a computer and servo loop to be either neutral (wavelength independent) or solar in shape, from a stored reference table. The operation of the system, applicable to laboratory spectrum simulation, and the function of the bias beam are demonstrated. Spectra of a p-n Si diode with added series resistance simulate the differences between maximum power efficiency and the conventional short-circuit quantum efficiency. There are advantages to the power measurement in sensitivity to competitive kinetic processes governing cell conversion efficiency and to wavelength dependent effects on junction potential gradients.