Showing papers in "Journal of The Electrochemical Society in 1983"

Importance of Interatomic Spacing in Catalytic Reduction of Oxygen in Phosphoric Acid

Abstract: A correlation between the nearest-neighbor distance and the oxygen reduction activity of various platinum alloys is reported. It is proposed that the distance between nearest-neighbor Pt atoms on the surface of a supported catalyst is not ideal for dual site absorption of O2 or 'HO2' and that the introduction of foreign atoms which reduce the Pt nearest-neighbor spacing would result in higher oxygen reduction activity. This may allow the critical 0-0 bond interatomic distance and hence the optimum Pt-Pt separation for bond rupture to be determined from quantum chemical calculations. A composite analysis shows that the data on supported Pt alloys are consistent with Appleby's (1970) data on bulk metals with respect to specific activity, activation energy, preexponential factor, and percent d-band character.

XPS Studies of Oxygen Evolution on Ru and RuO2 Anodes

Abstract: Anodic oxidation of Ru and electrodes in has been investigated using x‐ray photoelectron spectroscopy. During evolution on Ru a highly defective hydrated oxide film is formed as a result of corrosion. At a temperature of 310°C in vacuum this film decomposes to metallic ruthenium. The surface of anodes prepared by thermal decomposition of contains some , which is stable during anodic polarization. A reaction path for evolution and corrosion on Ru and anodes is proposed.

Dry Etch Resistance of Organic Materials

Abstract: The dry etch resistance of metal‐free organic materials, mainly resist materials, has been studied. Etch rates have been measured under argon ion‐beam, oxygen ion‐beam, and oxygen plasma etching conditions. It is found that the etch rate under ion bombardment has a linear dependence on the of the etched materials, where , , and denote the total number of atoms in a monomer unit, the number of carbon atoms in a monomer unit, and the number of oxygen atoms in a monomer unit, respectively. The results indicate that the dry etch resistance under ion bombardment is determined by the effective carbon content in a material. The etch rates of the polymers in an oxygen plasma condition have no simple correlation with the effective carbon content in a material. This implies that etching mechanism under ion bombardment differs from the etching mechanism by radical species.

The A‐C Conductivity of Polycrystalline LISICON, Li2 + 2x Zn1 − x GeO4, and a Model for Intergranular Constriction Resistances

Abstract: The a‐c conductivity of a polycrystalline, Li+ ion conducting solid electrolyte, LISICON, , has been measured over the frequency range 10−3–107 Hz and attention focused on the methods of data analysis. The data show intragranular (bulk) and grain boundary effects in which, for a given sample, both effects are characterized by a similar activation energy; a constriction resistance model for the latter is proposed based on air gaps existing in polycrystalline sinters of less than theoretical density. The data only crudely fit a Debye‐like equivalent circuit, composed of frequency independent resistors and capacitors, but fit well an equivalent circuit that contains Jonscher elements, i.e., frequency dependent admittances, in addition to normal and elements. Two such Jonscher elements are needed, one for the grain boundary and one for the intragranular contribution. With this circuit, departures from ideality in, e.g., the cpmplex impedance, admittance, and electric modulus planes are accounted for.

Deposition of GaAs Epitaxial Layers by Organometallic CVD Temperature and Orientation Dependence

Abstract: Epitaxial layers of have been grown in an atmospheric organometallic CVD system, for a wide variety of gas phase reactant partial pressures and over a broad range of temperature (450°–1050°C). The growth rates for (100), , (110), (11l)Ga, and (11l)As substrates are reported as functions of temperature and gas composition. Three distinct temperature dependent regions of growth are identified, corresponding to a mid‐temperature mass transport limited range, a low‐temperature kinetic controlled regime, and a high‐temperature desorption limited region. The growth rate is studied as a function of the growth parameters and substrate orientation, and is related to the decomposition of the two reactants trimethylgallium and arsine. A model for the epitaxial growth of by the organometallic process is proposed, based on these findings.

Polycrystalline Silicon Micromechanical Beams

Abstract: Using the conventional MOS planar process, miniature cantilever and doubly supported mechanical beams are fabricated from polycrystalline silicon. Poly‐Si micromechanical beams having thicknesses of 230 nm to 2.3 μm and separated by 550 nm to 3.5μm from the substrate are made in a wide range of lengths and widths. Two static mechanical properties are investigated: the dependences of maximum free‐standing length and beam deflection on the thickness of the beam. By annealing the poly‐Si prior to beam formation, both of these properties are improved. Nonuniform internal stress in the poly‐Si is apparently responsible for the beam deflection.

Electrochemical and Spectroscopic Studies of Metal Hexacyanometalate Films I . Cupric Hexacyanoferrate

Abstract: A method for the electrodeposition of thin films of cupric hexacyanoferrate on glassy carbon and tin oxide electrodes has been devised. At low scan rates, in , these films exhibit nearly ideal cyclic voltammetric current‐potential waves with a peak potential of +0.69V vs. SCE on glassy carbon. Similar to the Prussian blue films described by Neff (1, 2), Itaya (3), and others (4), potassium ion is transported into the film during reduction. XPS and visible spectroscopy indicate that the redox involves the ferric and ferrous states of the hexacyanoferrate and not . The electrochemical properties as a function of potassium ion concentration and film thickness have been determined primarily from cyclic voltammetric studies, and evidence for electronic conduction through the film has been observed. Optical properties of the films were determined using deposited on tin oxide substrates. Supporting description of the electrochemical properties of the film has been obtained by a‐c impedance measurements. The film behavior is consistent with a model previously reported for Prussian blue films.

Corrosion Study of a Carbon Steel in Neutral Chloride Solutions by Impedance Techniques

Abstract: The electrochemical behavior of a carbon steel in 3% solution has been investigated using a rotating disk electrode. Both steady‐state (diffusional current vs. the disk angular velocity plots) and transient (frequency analysis of the electrohydrodynamical impedance) measurements which specifically sample mass transport phenomena, have been carried out. It is shown that oxygen transport takes place not only in the liquid phase but also through a porous layer of corrosion products. From electrochemical impedance measurements, it was found that at the corrosion potential the oxygen reduction reaction is under either diffusional or mixed (activation + diffusion) control depending on both the electrode rotation speed and on the hold time at the free corrosion potential. In addition, it was shown that the oxygen consumption occurs not only by electrochemical reduction but also by chemical oxidation of ferrous to ferric ions. Finally, because of the possible occurrence of mixed corrosion control, it is emphasized that the use of the polarization resistance in order to evaluate corrosion rates is not always valid.

On the Structural and Luminescent Properties of the M ′ LnTaO4 Rare Earth Tantalates

Abstract: The structure of M YTaO/sub 4/ has been redetermined and was refined to an R value of 0.034. M'YTaO/sub 4/ crystallizes in P2/a symmetry with a = 5.298(1),b = 5.451(1),c = 5.111(1)A,..beta.. = 96.45 deg. At temperatures > 1450/sup 0/C,M'YTaO/sub 4/ will convert by way of a reconstructive transformation into the I4/sub 1//a symmetry of scheelite, and, upon cooling, a second-order ferroelastic transition (4/mF2/m) to M (fergusonite) YTaO/sub 4/ occurs. There are significant structural differences between M and M'YTaO/sub 4/ which are discussed. M'LnTaO/sub 4/ compounds exist from Ln = Sm to Lu. As a host for luminescent ions, M'YTaO/sub 4/ is superior to the M modification, as well as all other compounds in the Y/sub 2/O/sub 2/Ta/sub 2/O/sub 5/ phase diagram.

On the Reaction Mechanism of GaAs MOCVD

Abstract: In this paper, the reaction mechanisms of metalorganic chemical vapor deposition (MOCVD) have been investigated using infrared absorption spectroscopy. The growth of from Ga and under gas atmosphere in a hot wall reactor was studied. The compositions of gases which are sampled through a quartz capillary are observed by infrared spectroscopy. Infrared spectra of , , and systems were measured in the range from room temperature to 930°C. In the system, a new absorption peak at 2080 cm−1 which exists in neither the nor the system is observed. In the system, when is added into the reacting gas, the concentration of decreases drastically. The decomposition of is affected strongly by the addition of .

Lithium Insertion in Wadsley‐Roth Phases Based on Niobium Oxide

Abstract: We have found the Wadsley‐Roth class of crystallographic shear structures in chemical systems based on to undergo lithium insertion reactions at ambient temperature to stoichiometries of 0.4 to 1.4 Li per host metal on reaction with n‐BuLi. For the general case of structures with intersecting shear planes, minimal structural distortion occurs on lithiation even for compounds with the largest block sizes. We report crystal‐chemical data for 14 lithium insertion compounds of this type, and the behavior of selected host compounds mixed with carbon as the positive electrodes in small lithium secondary test cells.

Electrodeposition of Conducting Transition Metal Oxide/Hydroxide Films from Aqueous Solution

Abstract: Donnees sur une methode generale de depot electrolytique de couches minces d'oxyde-hydroxyde de Cu, Ni, Co, Fe et Mn, a partir d'une solution aqueuse, sur une electrode a disque tournant de Pt, soit sous tension constant, soit sous tension variant cycliquement

Oxygen Transfer on Substituted ZrO2, Bi2O3, and CeO2 Electrolytes with Platinum Electrodes. I. Electrode Resistance by D-C Polarization

Abstract: The electrode behavior of Pt-sputtered and PT-gauze electrodes on ZrO2-Y2O3, Bi2O3-Er2O3, and CeO2-Gd2O3 solid electrolyteswas investigated by means of d-c measurements in the temperature region of 770–1050 K and in the oxygen partialpressure region of 10–5 – 1 atm O2 using N2-O2 mixtures. On these different materials the same electrode morphology wasrealized and was preserved during the subsequent experiments. The electrode process is strongly influenced by the natureof the electrolyte. The electrode resistance for Pt electrodes on Bi2O3-Er2O3 was found to be many times lower than onZrO2-Y2O3 and CeO2-Gd2O3. On zirconia- and ceria-based materials diffusion of atomic oxygen on the Pt electrode is therate-determining step in the electrode process, whereas for bismuth sesquioxide-based materials diffusion on the oxidesurfaces is rate determining.

The Electroreduction of Carbon Dioxide and Formic Acid on Tin and Indium Electrodes

Abstract: Etudes a l'aide de mesures d'impedance et de photoemission des processus du titre en solution aqueuse

Characterization of Plasma Silicon Nitride Layers

Abstract: The authors have studied deposition of plasma silicon nitride layers as a function of gas‐phase composition for the system, where is , Ar, or . Most of the depositions were performed at 300°C and at an operating frequency of 50 kHz. The deposited layers were characterized with Anger electron spectroscopy in combination with ion‐bombardment, Rutherford backscattering, and infrared spectroscopy. It is shown that the ratio of the amount of atomic hydrogen atoms bonded to silicon and nitrogen atoms is only a function of the silicon‐nitrogen ratio of the deposited layers. It is further shown that the etch rate of plasma silicon nitride layers in buffered depends primarily on the silicon‐nitrogen ratio and the density of the deposited material.

Solution Growth and Electrodeposited CuInSe2Thin Films

Abstract: Description de la croissance des couches par les deux techniques en vue de l'application aux dispositifs photovoltaiques

Short time annealing

Abstract: Short time annealing has recently become of interest in silicon processing as a technique to activate ion implanted dopants, remove defects, and regrow amorphized silicon, with minimal diffusion of the dopant atoms. Short time annealing is carried out using a variety of energy sources ranging from arc lamps and resistance heaters with heating times of a few tens of seconds, to laser, electron, and ion sources with heating times of a few milliseconds down to nanoseconds. The annealing processes are grouped according to the time durations of the anneal and with reference to the thermal response time of the silicon. These are designated as adiabatic for 10−2 sec. Processes in the adiabatic regime result in surface melting, regrowth of silicon free of extended defects, and complete dopant activation. However, the dopant diffuses throughout the melt zone. In the thermal flux and isothermal annealing regimes the dopant can be activated, and amorphous silicon regrown epitaxially with little dopant diffusion. In the limited results reported to date, the complete removal of extended defects has not been achieved. Further investigation may yield new results in extended defect removal.

Pore Size Distribution in Porous Silicon Studied by Adsorption Isotherms

Abstract: Porous silicon was obtained by anodic attack of single crystal silicon substrates in 25% hydrofluoric acid solutions. Specific surface area, total porous volume, and pore size distribution of porous silicon have been determined. The experimental technique used is based on the measurement of the volume of gas adsorbed at low constant temperature by the porous silicon. The adsorption isotherms show the general behavior found for porous materials, but at the same time, they show clear differences following different preparation conditions of porous layers. Quantitative analysis using models extensively used in the catalysis field lead to large values for the porous silicon specific surface area and sharp pore size distribution. Mean pore radii are found to vary in the range 20–100A when forming current density varies from 10 to 240 mA/cm2.

Stability of Conducting Polythiophene and Derivatives

Abstract: The doped PMeT (poly-3-methylthiophene) reveals that storage in air affects neither the CF3SO3(-) doping level nor the conductivity. These results are supported by the infrared analysis. This conducting polymer is characterized by a large broad band in the near infrared due to free carriers and by absorption patterns associated with the dopant CF3SO3(-). The undoped PMeT is found to behave in the same fashion. PT (polythiophene) and P(Me)2T show the same interesting stability characteristics, in contrast to the experimental precautions that must be taken with other types of organic conducting polymers. These materials have great thermal stability: 200-250 C in air and 700-800 C in an inert atmosphere or vacuum. They are stable in concentrated acidic media but are slowly attacked in basic solutions. Also investigated is the stability under electrochemical treatment.

Experimental Verification of the Space‐Charge Model for Electrokinetics in Charged Microporous Membranes

Abstract: A space‐charge model for electrolyte transport in charged capillary pores was examined experimentally with aqueous solutions of alkali chlorides and in track‐etched mica membranes. The model combines the Gouy‐Chapman view of the double layer with the Nernst‐Planck and Navier‐Stokes transport equations. The pores of experimental membranes were uniform capillaries with a well‐characterized cross section. The pore sizes ranged from an order of magnitude smaller to an order of magnitude larger than the Debye screening lengths of solutions. Three independent quantities were measured: streaming potential, for which an applied pressure across the membrane is the driving force for transport; pore conductivity, for which an applied electrical potential is the driving force; and concentration potential, for which an electrolyte concentration difference is the driving force. Data follow the trends of model predictions but indicate that chloride ions affect the pore wall charge. For monovalent cations, the pore wall charge deduced from pore conductivity measurements yielded theoretical predictions for the streaming potential and for the concentration potential that agree quite well with the data. Such agreement was not obtained with Mg2+, probably because these divalent cations adsorbed onto the negative pore wall. We conclude that, in the absence of strong interaction between the charged pore wall and free ions in solution, the model is quantitatively accurate for pores larger than 30A in radius and for aqueous electrolyte concentrations of 0.1M or lower.

Reduction of Carbon Dioxide to Methanol on n ‐ and p ‐ GaAs and p ‐ InP . Effect of Crystal Face, Electrolyte and Current Density

Abstract: Donnees sur la conversion de CO 2 en CH 3 OH en presence d'electrodes de GaAs-p et -n et d'electrodes InP-p et sur le rendement faradique en methanol, formaldehyde et methane

Polymer Films on Electrodes. 13. Incorporation of Catalysts into Electronically Conductive Polymers: Iron Phthalocyanine in Polypyrrole.

Abstract: Des phtalocyanines de fer tetrasulfonees (Fe PcS) peuvent etre incorporees dans du polypyrrole electroniquement conducteur, par polymerisation electrochimique du pyrrole en presence de FePcS. Les electrodes de carbone vitreux modifiees par FePcS, catalysent la reduction d'O 2 a des potentiels moins negatifs, de 250 a 800 mV, que les electrodes de carbone vitreux non modifiees ou revetues de polypyrrole sans insertion de FePcS. Cependant, aux pH eleves, on observe surtout une reduction d'O 2 en H 2 O a des potentiels moins negatifs, de 250 mV, que les electrodes non catalysees

Modeling and Analysis of Low Pressure CVD Reactors

Abstract: A detailed mathematical model for the hot wall multiple‐disk‐in‐tube LPCVD reactor is developed by using reaction engineering concepts. This model includes the convective and diffusive mass transport in the annular flow region formed by the reactor wall and the edges of the wafers as well as the surface reactions on the reactor wall. In addition, the model describes the coupling of diffusion between and reaction on the wafers. Variations in gas velocities and diffusion fluxes due to net changes in the number of mols in the deposition are also taken into account as are nonisothermal operating conditions. The combined reactor equations are solved by orthogonal collocation. The deposition of polycrystalline Si from is considered as a specific example, and the model is employed in estimation of kinetic rate constants from published reactor measurements. The effects on the growth rates and film thickness uniformity (within each wafer and from wafer to wafer) of variations in flow rates, reactor temperature profiles, and concentration in the feed stream are analyzed. The model predictions show good quantitative agreement with published experimental data from different sources. Finally, recycle of reactor effluent is considered a typical commercial operating conditions, and it is demonstrated that this modification produces higher growth rates and better film uniformity than can be achieved in conventional LPCVD processing.

Corrosion Behavior of SiC / Al Metal Matrix Composites

Abstract: The effect of the phase on the corrosion behavior of metal matrix composites has been studied in , both in the presence and absence of dissolved oxygen. Anodic polarization behavior has been determined, and pitting potentials have been measured for three composite systems: 2024, 6061, and 5456. General corrosion behavior and the effects of anodizing on the corrosion resistance of the composites have been studied by a‐c impedance techniques. The results show that pitting susceptibility is about the same for the composites and their corresponding alloys, except for Al 2024. In this system, the composite is less resistant to pit initiation than the corresponding wrought aluminum alloy. General corrosion is more significantly affected by the presence of oxygen than by the phase. In the absence of oxygen, corrosion resistance is improved for both the alloys and composites. In addition, the corrosion resistance of the composites can be improved by anodizing.

Study of a Decomposing Hydride Phase at Nickel Cathodes by Measurement of Open‐Circuit Potential Decay

Abstract: At Ni or Raney Ni Al‐type electrodes subjected to cathodic polarization with evolution in alkaline solutions, characteristic time dependent currents are observed when measurements are made in the direction of increasing or decreasing potentials. Also, after polarization to high cathodic overvoltage, appreciable quantities of continue to be evolved after interruption of the current or an anodic current is observed at low cathodic overpotentials as the potential is reduced, that is at potentials still negative to the reversible potential. These observations suggest that a three‐dimensional hydride is formed which undergoes decomposition at low overpotentials. The kinetics of decomposition of such a surface or thin layer metal hydride were evaluated by means of open‐circuit potential decay measurements. A mixed "corrosion"‐type mechanism is considered with anodic hydride decompositioncoupled concurrently with cathodic evolution through the stepsand Evidence shows that the anodic process [1] is not Al dissolution. Kinetic treatment of the potential decay on open circuit is given in terms of the above mechanism involving adsorbed H and decomposition of a bulk hydride. Certain conditions are shown to correspond with the observed experimental behavior. Similar behavior with respect to potential decay and evolution is found with electroplated Ni‐Mo‐Cd‐coated cathode preparations.

Dry Etching of Polyimide in O 2 ‐ CF 4 and O 2 ‐ SF 6 Plasmas

Abstract: The plasma etching of the type H Kapton polyimide film has been studied in a parallel plate reactor with two different gas mixtures; and . High etching rate (0.5–3 μm/min) has been obtained in both cases. At a pressure of 0.2 Torr an anomalous loading effect is observed which is attributed to the nitrogen released by the polyimide. The gaseous effluents from etching have been detected by mass spectrometry and indicate that both atomic oxygen and atomic fluorine are the main etchants of the polymer. A comparison with silicon etching in a plasma is made in order to give the main channels of the reaction scheme. XPS measurements of the polyimide surface before and after etching are consistent with the mass spectrometric observations.

Surface Enrichment of Nitrogen during Passivation of a Highly Resistant Stainless Steel

Abstract: Nitrogen, probably in an uncharged form, is enriched on the metal side of the metal film interface after passivation of the number 30 alloy. Molybdenum is probably present in the oxide film, but is depleted compared with the bulk alloy and shows no obvious association with nitrogen. The improvement of passivity by alloying with nitrogen probably results from segregation of nitrogen to the metal surface during preferential dissolution of metal atoms, rather than from its incorporation into an oxide film.

Mathematical Analysis of a Zn / NiOOH Cell

Abstract: A mathematical model has been developed to predict the time dependent behavior of a Zn/NiOOH cell. The model uses experimentally determined polarization expressions to describe the losses between the positive and the negative electrodes. The electronic losses in the plane of the electrode are simulated by a network of resistors. The potential distribution, the current distribution, the cell voltage, the power capability, and the energy of a cell can be predicted. The mathematical model provides an analytical tool to evaluate, for example, the trade-offs between power capability and current collector mass, needed to design an electric vehicle battery.