Dennis Tench

Enhanced tensile strength for electrodeposited nickel-copper multilayer composites

The tensile strength of electrodeposited layered composites of the nominal overall composition 90 pct Ni-10 pct Cu is shown to increase sharply to the 1300 MPa range as the thickness of the Cu layers is decreased below ~0.4 ώm. This tensile strength value is almost a factor of three greater than that measured for Ni itself, and more than a factor of two greater than the handbook value for Monel 400.

Protection of Semiconductor Photoanodes with Photoelectrochemically Generated Polypyrrole Films

Results are presented which show that photoelectrochemically generated polypyrrole films protect semiconductor photoanodes (e.g., Cd chalcogenides,, and Si), from degradation while permitting electron exchange between the semiconductor and the electrolyte. The performance characteristics and stability of such film‐covered photoelectrodes are discussed.

Electrochemical Photocapacitance Spectroscopy Method for Characterization of Deep Levels and Interface States in Semiconductor Materials

The recently developed electrochemical photocapacitance spectroscopy (EPS) method for characterization of deep levels in semiconductors is described. Topics discussed include the advantages of the method, experimental considerations, and the determination of state densities and kinetic parameters (associated with state population/ depopulation). Both steady-state and transient capacitance changes are treated mathematically. Data for n-GaAs, p-GaAs, n-CdSe, a-Si and p-Zn/sub 3/P/sub 2/ are presented to illustrate the wide applicability of the method and its sensitivity to both bulk and interface states, including those observed by other characterization methods.

Stabilization of n ‐ CdSe Photoanodes in Nonaqueous Fe ( CN ) 6 3 − / 4 − Electrolytes

The systematic development of a nonaqueous ferro‐ferricyanide electrolyte for stabilization of photoanodes is described. Selection of the solvent is discussed in terms of inherent stability provided, the rate of the redox reaction, the tendency toward specific adsorption of the redox species, and the equilibrium potential of the redox couple with respect to the flatband potential (attainable open‐circuit voltage). Results are presented for cells of the type which have been operated for up to 700 hr at 6 mA/cm2 with no detectable degradation in either the electrode surface or the photoresponse.

Tensile properties of acid copper electrodeposits

For proprietary acid copper sulphate electroplating baths representing two major categories identified previously, deposit tensile properties are presented as functions of the bath additive and chloride concentrations. The effects of species that accumulate in the bath during circuit board plating and of variations in current density and the concentrations of copper sulphate and sulphuric acid are also discussed.

Degradation in nickel-cadmium cells studied by impedance measurements

Abstract The impedance of 12 A h NiCd sealed cells was evaluated as a nondestructive, in situ means of determining cell lifetime, particularly with respect to the probability of premature failure. The NiCd cell impedance was measured (10 000 to 0.0004 Hz) as cells were subjected to charge/ discharge cycle testing under a variety of temperature and depth-of-discharge conditions. The results indicate that cell degradation is reflected in the low frequency impedance characteristics associated with diffusional processes. The slope ( W ) of the low frequency portion of complex plane impedance plots obtained from totally discharged NiCd cells was found to increase with charge/discharge cycling. In addition, based on data for two cells, a high or rapidly increasing W value signals imminent cell failure by one mechanism. Degradation by another mechanism is apparently reflected in a fall-off of the imaginary impedance component at low frequencies. The frequency dependence of the absolute cell impedance at low frequencies (0.5 - 0.005 Hz) was found to vary monotonically with cell state-of-charge.

Electrochemical Photocapacitance Spectroscopy: A New Method for Characterization of Deep Levels in Semiconductors

Electrochemical photocapacitance spectroscopy (EPS) offers advantages over similar solid-state photocapacitance spectroscopic techniques. In the EPS method, the capacitance of a reverse-biased semiconductor electrode is measured as a function of the wavelength of incident sub-bandgap light. In the present work, EPS is shown to be an extremely sensitive means for characterizing deep levels in semiconductor materials. For horizontal Bridgeman-grown n-GaAs, a hole trap, the chromium phototransition, and two electron traps were detected. The energies and densities of states for these levels correspond well with values reported in the literature for solid-state studies of similar materials. 21 refs.

Cadmium Selenide Interface States Studied by Electrochemical Photocapacitance Spectroscopy

In this paper, the electrochemical photocapacitance spectroscopy (EPS) method, which involves measuring the differential capacitance for the reverse-biased semiconductor in an electrolyte as a function of incident subbandgap light, was applied to further elucidate the nature of interface states on n-CdSe. This method has been shown to be an unusually sensitive means for characterization of deep levels in various semiconductor materials (4). In aqueous electrolytes, the interfacial oxide structure might be expected to be similar to that formed in the ambient atmosphere. A key goal in the present work was to establish unequivocally the location of the state associated with oxygen adsorption. An alternate interpretation for previous data was that the observed states actually resided in the bulk and were rendered detectable by the enhanced thickness of the semiconductor space-charge layer resulting from the negative surface charge associated with adsorbed oxygen.

Photoelectrochemical Evaluation of the n ‐ CdSe / Methanol / Ferro ‐ Ferricyanide System

Factors limiting the short‐circuit photocurrent for the system to 17.5 mA/cm2 have been identified. The principal limiting factor is apparently specific adsorption of hexacyanoferrate species on the electrode surface, which occurs at higher redox couple concentrations and slows the overall charge transfer process. Ion pairing also occurs, resulting in a low mass transport rate (smaller diffusion coefficients and increased solution viscosity), and probably enhances the degree of specific adsorption.

Tensile properties and morphology of pyrophosphate copper deposits

New data which precisely define the effects of various operating parameters on the tensile properties of electrodeposits from the dimercaptothiadiazole/copper pyrophosphate system are presented. Two additive concentration ranges yielding high ductility and high tensile strength are delineated. Characteristic deposit microstructures are identified and correlated with the tensile properties. The results are interpreted in terms of the mechanism by which the additive functions, and implications for circuit board plating are discussed.