Showing papers in "Journal of The Electrochemical Society in 1974"

Oxides and Oxide Films

Abstract: One day, you will discover a new adventure and knowledge by spending more money. But when? Do you think that you need to obtain those all requirements when having much money? Why don't you try to get something simple at first? That's something that will lead you to know more about the world, adventure, some places, history, entertainment, and more? It is your own time to continue reading habit. One of the books you can enjoy now is oxides and oxide films volume 3 here.

The Current Understanding of Charges in the Thermally Oxidized Silicon Structure

Abstract: Generally accepted facts along with unanswered questions, concerning the four charges, , , , and , associated with the thermally oxidized silicon system are presented and briefly discussed. The discussions and information presented are based on comprehensive investigations carried out in the semiconductor industry over the past ten years. Although reasonably good empirical information concerning charge dependence on device processing is available, much remains to be learned regarding the physical origin of these charges. A simplified model is presented which indicates that most of the charges can be related to silicon bond defects in the thermally oxidized silicon structure.

Initiation of Pitting at Sulfide Inclusions in Stainless Steel

Abstract: Equilibrium calculations on some sulflde systems actual in commercial stainless steel have shown that the sulfides cannot thermodynamically exist at the potential of the passive steel. The ions released by the dissolution of the sulfides give rise to an acid solution in microareas. A pitting corrosion mechanism based on the sulfides themselves is suggested. The sulfides are polarized to the potential of the passive steel surface and tend to dissolve. During the dissolution a virgin metal surface is exposed to the environment. When the solution in the microarea thus developed has reached a certain composition, the contacting metal can no longer passivate and the metal starts to dissolve.

Thermodynamics and Kinetics of Pack Aluminide Coating Formation on IN‐100

Abstract: An investigation of the effects of pack variables on the formation of aluminide coatings on nickel-base superalloy IN-100 was conducted. Also, the thermodynamics and kinetics of coating formation were analyzed. Observed coating weights were in good agreement with predictions made from the analysis. Pack temperature rather than pack aluminum activity controls the principal coating phase formed. In 1 weight percent aluminum packs, aluminum weight gains were related to the halide pack activator. Solid-state nickel diffusion controlled coating formation from sodium fluoride and chloride and ammonium fluoride activated packs. In other ammonium and sodium halide activated 1 weight percent aluminum packs, gaseous diffusion controlled coating formation.

On the Origin of the Photocatalytic Deposition of Noble Metals on TiO2

Abstract: In connection with studies on the photographic properties of the photocatalytic deposition of palladium and the electrochemical properties of were investigated. In order to study both phenomena simultaneously the experiments were performed with thin, layers deposited on a conducting substrate. It could be shown that the primary step is an anodic photocurrent (O2 evolution) which catalyzes the cathodic deposition of palladium under open‐circuit conditions. Various parameters such as space charge effects, film thickness, and doping were studied and are discussed in detail.

Optical and Electrochemical Studies of Underpotential Deposition of Lead on Gold Evaporated and Single‐Crystal Electrodes

Abstract: Linear sweep voltammetry and reflectance spectroscopy have been used to examine the underpotential deposition of lead on gold in Pb2+; containing solutions. The voltammetry curves and reflectance‐change data provide evidence that the lead is first deposited as ions although their effective ionic charge is probably reduced substantially from +2 through their strong interaction with the band structure of the gold substrate. At more cathodic potentials, still well below the reversible potential of bulk lead, a sharp transition is observed over a 5–10 mV range. On the basis of the reflectance and voltammetry data, this transition appears to involve a two‐dimensional phase transition leading to a metalliclike lead layer. Adsorption isotherms have been evaluated from the reflectance changes. Alternating potential electromodulation techniques and complex plane analysis have been used to examine the kinetics of the lead adsorption‐desorption and to evaluate the apparent exchange current density for the process.

The Formation of Monolayer Metal Films on Electrodes

Abstract: The two‐ and three‐dimensional nucleation and the metal ion adsorption process are discussed as initial steps for electrocrystallization on the same or on a foreign substrate. The metal ion adsorption takes place in the underpotential range, which is more positive than the equilibrium potential of the nucleated metal/metal ion electrode. Thermodynamic considerations show that an overlapping of disturbing processes in the underpotential range can be characterized by a factor , which is called charge‐coverage coefficient or electrosorption valency. It is a function of different independent variables. The metal monolayer model is satisfied only in the simplest case for (valency of metal ions in solution).The different experimental methods for determining the thermodynamics, kinetics, and structure of metal ion adsorbates are critically discussed. The most reliable thermodynamic results are obtained by the twin‐electrode thin‐layer technique. Kinetic data can be obtained by pulse measurements under potentiostatic‐galvanostatic conditions. The structure of metal films can be determined by combining different methods including optical investigations.Results are given for different systems. In the systems Au/Ag+ , Au/Tl+, and Au/Pb++ the metal monolayer model is practically valid. In the case of Cu++ ion adsorption on Au the redox reaction forming Cu+ ions acts as a disturbing process. A cosorption of anions takes place in the system Ag/Pb++. The formation of alloys in the underpotential range was observed in the systems Pt/Pb++ and Bi/Pb++.The structure of metal ion adsorbates must be in correlation with the nucleation phenomena at more negative potentials. In many systems no three‐dimensional nucleation overvoltage is observed by using a quasi‐steady‐state experimental technique. The density of the crystal imperfections and the crystallographic orientation of the surface planes influence the metal ion adsorption process and the structure of films. The results obtained in the systems Ag (poly‐ and monocrystalline)/Tl+ can be explained by assuming the formation of superlattices on the electrode surface.Kinetic investigations in the systems Au/Ag+, Au/Tl+, and Au/Pb++ show relatively high exchange current densities for the metal ion adsorption process. In these cases the experimental results can be explained by assuming surface diffusion of adions as the rate determining step in the adsorption process. In the system Au/Cu++, a charge transfer step is rate determining, which probably forms precedingly Cu+ ions.

The Kinetics of Silicon Deposition on Silicon by Pyrolysis of Silane A Mass Spectrometric Investigation by Molecular Beam Sampling

Abstract: The kinetics of silane pyrolysis on a silicon (111) surface has been investigated mass spectrometrically by molecular beam sampling over the silane pressure range Torr and specimen temperature range 20°–1200°C. Silane decomposition was found to occur by the mechanism where both the amount of adsorbed silane and decomposition rate depend linearly on silane pressure. The activation energy for decomposition was and the surface reaction efficiency (α) was found to obey the equation At silane pressures , small quantities of disilane formed by the bimolecular surface reaction were detected with an activation energy for production of .Measurements of silicon growth rate as a function of silane pressure supported the first‐order mechanism for decomposition. The condensation coefficient (σ) of silicon adatoms, determined from measurements of the silicon growth rate as a function of temperature and the surface reaction efficiency, was found to be less than 0.3 over the entire temperature range 700°–1200°C, indicating that the majority of silicon adatoms were desorbed. This behavior was accounted for on the basis of a step flow model for silicon growth and an activation energy for surface diffusion of derived. Addition of arsine to the silane was found to inhibit silane pyrolysis. The measurements suggest an activation energy of for desorption of arsenic adsorbed on the silicon (111) surface. Additions of more than 1% diborane to the silane, on the other hand, resulted in a significant increase in silane reaction efficiency.

Electrochemically Generated Colored Films of Insoluble Viologen Radical Compounds

Abstract: Electrochemical reactions that produce a change of light absorption in the visible region can be used in display devices. The reduction of the 4,4'‐di‐pyridinium compounds or viologens to stable blue radicals is very promising in this respect. It was found that in aqueous solution the solubility of the radical is remarkably lower than that of the oxidized form. It turned out that the solubility depends on the kind of anion and the magnitude of the viologen radical ion.

Fine Structure in the Optical Spectra of Divalent Europium in the Alkaline Earth Sulfates

Abstract: Fine structure has been observed in the fluorescence and excitation spectra of Eu+2 in and in the fluorescence spectrum of Eu+2 in . The fine structure in the fluorescence of Eu+2 in is identified as a zero phonon line with many sharp phonon replicas. The fine structure in its excitation spectrum is due to the closely spaced energy levels in the excited state produced by a strong exchange interaction splitting of the 4f65d states. The fine structure in the fluorescence of Eu+2 in is due to the normal splitting of the 4f7 excited state and the dominance of 4f7 → 4f7 transitions.

A New Generation of “Deluxe” Fluorescent Lamps, Combining an Efficacy of 80 Lumens/W or More with a Color Rendering Index of Approximately 85

Abstract: It has been shown previously that color‐rendering capability and luminous efficacy of fluorescent lamps depend on the spectral composition of the emitted light. Three spectral regions appear to be of special interest, the blue at 450 run, the green at 540 nm, and the orange‐red at 610 nm. Among the hexagonal aluminates blue‐emitting and green‐emitting , together with orange‐red‐emitting are particularly suited in a new generation "deluxe" fluorescent lamps. Lamps with a color temperature >2350°K can be made. The efficacy of the lamps ranks from approximately 82 lm/W at 3000°K to 80 lm/W at 6000°K. The color‐ rendering index is 81–85. A small increase of is achieved when Mn2+ is incorporated in , giving rise to an additional green emission at 515 nm. The new blend is compared to other blends and further prospects in fluorescent lamp developments are outlined.

The Growth of Hydrous Oxide Films on Aluminum

Abstract: The weight gains of Al specimens immersed for short times in water at 50°–70°C were measured. An analysis of these data and published results at other temperatures indicated that the kinetics of pseudoboehmite film growth in the temperature range 50°–100°C is determined initially by the nucleation and growth of hydrolysis sites on the amorphous oxide surface, and subsequently by solid‐state diffusion through the pseudoboehmite layer. At 40° C, pseudoboehmite and bayerite were observed to grow simultaneously at first, with bayerite crystallization eventually becoming the dominant process. The two oxide phases occupied completely separate layers.

A Survey of a Group of Phosphors, Based on Hexagonal Aluminate and Gallate Host Lattices

Abstract: A group of photoluminescent materials, which may have great influence on future fluorescent lamp development, is surveyed. The materials are based on hexagonal aluminates and gallates which are structurally related to the magnetoplumbites and (β‐alumina. When activated with Mn2+, Eu2+, Tl2+, Ce3+ , and Tb3+ , or combinations of these ions, they are phosphors, some of them having a high efficiency and good temperature dependence.

The Cathodic Behavior of CuS , MoO3, and MnO2 in Lithium Cells

Abstract: The cathodic behavior of and was studied in lithium cells discharged at current densities in the neighborhood of 2 mA/cm2 Two electrolytes, and tetrahydrofuran 1,2 dimethoxyethane (DME) were investigated for both of the cathodes, and it was found that the THF‐DME electrolyte greatly increased the coulombic efficiency The cells that were discharged after one year of storage showed a 19% loss of capacity which has been attributed to trace impurities A study of the rechargeability of the cell was also undertaken, and for the fifth cycle an ampere‐hour charging efficiency of 452% was obtained

Phase Equilibria and Vapor Pressures of Pure Phosphorus and of the Indium/Phosphorus System and Their Implications Regarding Crystal Growth of InP

Abstract: The vapor pressure as a function of temperature of several commercial grades of red phosphorus and a specially prepared crystalline sample has been measured. For crystalline red P we obtain a heat of sublimation, . The commercial grades yield vapor pressures, which above 450°C are described by the equation In . The sublimation equilibrium of red P can be utilized for controlling phosphorus pressures, , with a reproducibility of 10% if commercial P of at least 5N purity is used. Measurements of the pVT relation of phosphorus vapor in the regimes and reveal deviations up to 10% from ideal gas behavior. Excellent accuracy in describing the behavior of phosphorus vapor is obtained when van der Waals equation is used in conjunction with the critical data of Marckwald and Helmholz and a critical coefficient of 0.375 for calculation of both the co‐volume and the interaction parameter. Consideration of the pressure dependence of the equilibrium constant Kp for the reaction yielded approximate values for the fugacity constant at 1000° and 1100°C. The pTx relation at the liquidus in the vicinity of stoichiometric InP for indium‐rich and phosphorus‐rich compositions were established by simultaneous vapor pressure and DTA measurements. The melting point of stoichiometric InP is and the corresponding equilibrium phosphorus pressure is . T−x liquidus data calculated with the assumption of ideal behavior of the liquid are in good agreement with our experimental data. Interpretation of the liquidus pressure data yields values of the standard enthalpies and entropies at 298° K for the reaction and for the reaction These results are in excellent accord with the standard enthalpies reported by Panish and Arthur and agree within 3% with literature data on the standard entropies of the reactants. The growth of n‐ and p‐type InP crystals via the gradient freeze technique is discussed and the degree of control of the liquidus concentration is evaluated for various conditions of crystal growth.

Asymmetric Cracking in III – V Compounds

Abstract: Experimental evidence for unidirectional cracking in III – V compounds is presented The crack direction is shown to be a function of the sign of the applied stress and follows the asymmetry of the zinc blende structures The critical stress for cracking in in tension was found to be Cracks in and grown on substrates are related to the zinc blende asymmetry with the aid of Sirtl's etch A fracture mechanism which introduces asymmetric dislocations into the Cottrell fracture mechanism is advanced Asymmetries in elastic bending and "cross‐hatch" patterns are discussed The question of "glide" vs "shuffle" dislocations is also considered

High Temperature Reactions in the Silicon‐Hydrogen‐Chlorine System

Abstract: The partial pressures of the gaseous species in equilibrium with solid silicon in the Si‐H‐Cl system are presented as a function of temperature for different Cl/H ratios and total pressures. Computations were performed using our recently determined value of . Experimental data concerning the deposition and dissolution of silicon over a temperature range of 1200°–1700°K are compared to the equilibrium data and general conclusions drawn about the probable reaction mechanisms involved, especially for decomposition of the compounds and . Particular emphasis is put on attempting to integrate the diverse body of experimental data that exists for silicon deposition from and mixtures at high temperatures.

The Synthesis and Photoluminescence of M II M 2 III ( S , Se ) 4

Abstract: The compositions , In were prepared by reaction of the elements in evacuated silica tubes with iodine as a mineralizer. All members except , which is cubic, exhibit the pseudo‐orthorhombic type structure. They are high resistivity p‐type semiconductors; they exhibit Eu+2‐activated fluorescence which varies from red to blue as the electropositive character of the cations increase. Fluorescence activated by Yb+2 is seen at low temperature. Studies were made of the fluorescence decay lifetimes, temperature dependence, excitation spectra, and optical adsorption of : Eu in order to relate the Eu+2‐activated fluorescence to the host bandgap. It is concluded that the most efficient phosphors are those in which the Eu+2 excited states lie farthest from the fundamental edge.

Measurement of Cathode Mass Transfer Coefficients in Electrowinning Cells

Abstract: A recently developed, simple technique for determining cathode mass transfer coefficients in full scale electrowinning cells is discussed. The approach involves the determination of the limiting current for mass transfer controlled codeposition of silver in the cathode deposit. A rotating disk electrode was used to establish the validity of the method. Examples demonstrate the usefulness of the method for mapping local values of the mass transfer coefficient on the cathode under typical natural and forced convection flow regimes in electrowinning cells.

Oxidative vaporization kinetics of Cr2O3 in oxygen from 1000 to 1300 C

Abstract: Rates of oxidative vaporization of Cr2O3 on preoxidized resistively heated chromium were determined in flowing oxygen at a pressure of 0.115 Torr for temperatures from 1000 to 1300 C. Reaction controlled rates were obtained from experimental rates by a gold calibration technique, and these rates were shown to agree with those predicted by thermochemical analysis. The activation energy obtained for the oxidative vaporization reaction corresponded numerically with the thermochemical enthalpy of the reaction. A theoretical equation is given for calculating the rate from thermodynamic data using boundary-layer theory.

Determination of the Solidus and Gallium and Phosphorus Vacancy Concentrations in GaP

Abstract: The Ga concentration in crystals prepared by a variety of techniques (pulled by the liquid encapsulation Czochralski technique from stoichiometric or nonstoichiometric melts, solution grown, and annealed) has been determined by precision coulometric titration, yielding the experimental solidus boundary which exhibits an excess of Ga along the Ga‐rich liquidus. Based on a thermodynamic model, assuming that neutral Ga and P vacancies are the predominant native defects, the analysis of the solidus data permitted the evaluation of the vacancy concentrations over a wide temperature range. At the melting point of (1465°C) there are 8 × 1018 and 1.3 × 1019 cm−3 Ga and P vacancies, respectively, in the crystal. The calculated solidus curve well represents the totality of experimental data and shows retrograde temperatures at 1375° and 1400°C on the Ga‐ and P‐rich sides, respectively. The enthalpies and entropies associated with vacancy formation are given and discussed. It is shown that the data provide strong additional support to the previous identification of Ga vacancies with killer centers in .

Liquid Phase Epitaxy of InP

Abstract: Liquid phase epitaxy by conventional tipping technique has been employed for the growth of high purity epitaxial layers. The layers were grown at 720°‐560°C on (100) and (111) oriented InP substrates. Characteristic surface structures for the substrate orientations as a function of the growth temperature were observed. The layers were characterized by Hall data and photoluminescence measurements at low temperatures. The simultaneous observation of the band‐acceptor and donor‐acceptor pair transition due to the main acceptor in our LPE‐layers is reported. The binding energy of this acceptor is determined to .

Dielectric Breakdown Properties of SiO2 Films Grown in Halogen and Hydrogen‐Containing Environments

Abstract: Thermal oxidation of silicon, in the presence of chlorine or bromine compounds, effectively improved the dielectric breakdown characteristics (as measured with a voltage ramp) of the resulting films. At high halogen concentrations the oxidation rate was erratic; the optimal initial breakdown properties were attained by oxidizing with about one‐half of the halogen‐containing additive that would cause etching of the Si. Oxidation in the presence of halides increased the resistance of films to dielectric breakdown under accelerated bias‐temperature stressing. The maximum time to failure varied semilogarithmically with concentration and increased by 0.3 to 0.65 decade per per cent of (0–3% range) for applied fields from 2 to 7 MV/cm, respectively. Higher oxidation temperatures further improved the resistance of oxides to dielectric wear‐out. The longer wear‐out times were attributed to hydrogen rather than the halogen and could be achieved by oxidation in small concentrations of , annealing in H2, or.implantation of H2 or .