Table of contents

The gas sensing characteristics of heterocontacts are investigated. heterocontact, with added, showed selective gas sensing properties, while pure heterocontact showed higher sensitivity to than to . It is suggested that the presence of a second phase containing Na⁺ in ceramic is essential for selective gas sensing by a heterocontact.

A new electroless plating process for preparing a copper layer with strong adhesion to glass substrates was developed. This process incorporates a thin film on the glass substrate, instead of etching and sensitizing the substrate surface as in a conventional electroless plating process. The copper layer so obtained had a mirror‐like finish while maintaining strong adhesion, even on a very smooth glass surface . The bond strength measured by pull tests was more than , much greater than that obtained using conventional electroless plating (∼1 kg/2 mm□) and suitable for use in printed circuit boards. We find the thin film to serve as a kind of "adhesive" between the metal layer and glass substrate.

Carbon dioxide reduction at polycrystalline gold cathode in 0.1 M solution has been re‐examined. Like two other group Ib metal cathodes, Ag and Cu, the Au electrode is shown to undergo progressive deactivation during the electrolysis runs. A periodic, electrochemical activation treatment of the gold electrode is described.

grown in a steep temperature gradient acquires a peculiar lamellar morphology, similar to that of layered compound semiconductors. Thin electrodes (of thickness down to 30 to 40 μm) can be prepared by cleavage, reducing series resistance in the bulk of the semiconductor. The liquid junction of with acidic polyiodide medium (2M, 2.5M, 40 mM) was investigated. The best photoanodes attained quantum yields of monochromatic light of about 0.7 and conversion efficiencies above 7% under simulated AMI sunlight. Their performance does not decrease substantially under moderately concentrated sunlight (300 to 400 mW cm⁻²), due to the small ohmic losses. Cell output appears quite stable during the first week of operation, but irregular electrode corrosion is observed, which may be detrimental to long term operation.

Lamellar material grown in a steep temperature gradient shows heterogeneous composition and complex photoeffects. Besides predominant n‐type behavior, the electrode surface has areas with intrinsic or p‐type conductivity, the latter usually corresponding to indium‐rich regions. An inverted (cathodic) photocurrent is observed at n‐type electrodes polarized under accumulation conditions. Both spectral dependence, with a pronounced peak for energies around the bandgap, and quantum yields >1 suggest that these photoeffects originate from photoconductivity phenomena in the crystal bulk. Variability in electronic properties limits the average performance of the material in solar cells.

The electrolytic conductivities of lithium trifluoromethanesulfate and lithium hexafluorophosphate have been investigated as a function of the solvent composition. The organic solvent tested was ethylene carbonate (EC) or propylene carbonate mixed with 1,2‐dimethoxyethane, diethyl carbonate, or dimethyl carbonate (DMC). For each solvent system, the electrolytes containing showed nearly half the values of the conductivity of the corresponding systems with . High discharge capacities (ca.ca. 200 mAh g⁻¹) for charge‐discharge cycling of the carbon fiber electrode with a graphite structure were obtained in electrolytes. Especially, the highest coulombic efficiency (98%) was obtained in the system. The EC‐based electrolyte systems containing were found to be more compatible with the carbon fiber electrode than the systems containing .

A new polymeric material was obtained by the electrochemical oxidation of 1,3‐dimethoxybenzene (MDMB) in dry acetonitrile on platinum electrodes. A shiny, golden polymeric deposit that is insoluble in most common solvents was observed on the platinum surface. The polymerization process obeys a multistep, self‐catalytic type of mechanism, following an instantaneous nucleation and bidimensional growing process during the initial stage of the film formation. The scanning electronic microscopy (SEM) shows the existence of two different layers during electrodeposition: a smooth, compact, thin layer with an average thickness of 50 nm, followed by a porous, thick, stable, and less adherent layer. Electrodes modified with poly‐1,3‐dimethoxybenzene were found to be conductive in solutions, and oxygen evolution signal could be observed in some electrolytic media.

The polarographic behavior of 3‐methyl‐4‐(2'‐substituted benzeneazo)‐2‐isoxazolin‐5‐ones has been studied in 50% v/v dimethylformamide solution in Britton‐Robinson buffer of pH 4.1 at different temperatures (303.15–333.15 K). The reduction is diffusion‐controlled and becomes irreversible at higher temperatures. The shift of values toward more negative potentials and a decrease in the values and suggests that the electrode reaction becomes more irreversible at elevated temperatures. Thermodynamic parameters were evaluated at the different temperatures studied. The results can be explained in the light of a correlation between electrode kinetics and double‐layer structure.

A new experimental technique has been developed and tested to measure the interfacial velocities associated with the coalescence of small, electrolytically generated gas bubbles. The technique involves measuring, by means of a linear photodiode array, the rate of deflection of a laser‐light sheet caused by the movement of a newly formed boundary between coalescing bubbles. Bubble pairs in the 500 to 1000 μm range were generated at precisely controlled rates between two parallel glass‐encased microelectrodes. Correlation of data obtained on the coalescence of two hydrogen bubbles of identical size shows that the position of the interface along the coalescence plane varies with the square‐root of time, in agreement with the hole expansion model advanced by Charles and Mason. Initial interfacial velocities are in the range of 200 to 300 cm/s. Larger numbers of such events occurring simultaneously at gas evolving electrodes will significantly disturb the fluid immediately adjacent to the electrode, thereby improving mass transport rates to and from the surface.

Solid‐solution Al‐Ta alloys possess significantly higher pitting potentials than pure aluminum in Cl⁻ solutions. Dynamic imaging microellipsometry was used to study the passive film formation on solid solution Al‐Ta alloys. Film thickness was measured during growth for alloy compositions of pure Al Al‐8 a/o Ta Al‐25 a/o Ta, and pure Ta at applied potentials of 0.0, 1.0, 2.0, and 5.0 V SCE in a pH 7.2 borate buffer. Increasing the concentration of tantalum resulted in the formation of thinner passive films at all applied potentials. On pure Al and Al‐8 a/o Ta, precipitation of an type film results in a linearly increasing film thickness with time. The relationship of film thickness measurements to the enhanced localized corrosion resistance is discussed.

precipitates act as sites for pit initiation and propagation in Al‐Ta alloys. Dynamic imaging microellipsometry was used to measure the change in oxide film thickness and the refractive indexes of the films that form on the precipitates and matrix to examine the role of the precipitates in breakdown. Film formation was measured on an Al‐1.5 a/o Ta alloy, containing precipitates approximately 50 μm in diameter at applied potentials of 0.0, 1.0, 2.0, and 5.0 V SCE in a pH 7.2 borate buffer solution. At 0.0 V SCE the change in passive film thickness on the precipitate was greater than that on the Al matrix. The changes in film thicknesses at 1.0 V SCE were approximately equal and at higher potentials (2.0 and 5.0 V SCE) the matrix film thickened more than the film on the precipitate. SEM observations demonstrate that the precipitate‐matrix interface is highly susceptible to localized attack when the passive film on the is thicker than on the matrix (at 0.0 V SCE). We propose that pit initiation occurs at both the interface of the precipitation and in the dealloyed region around its periphery.

The pulsed method newly developed by the present authors was applied to electroreduction of on Cu electrodes. It was found that the optimum cathodic bias for generating and was −2.6 V vs. SCE, and the optimum anodic bias for the generation of was slightly more anodic than that of . Total faradaic efficiency for the generation of and became a maximum at 10°C and reached about 65%. Furthermore, increased with increasing reduction time in strong contrast with the conventional potentiostatic electroreduction in which decreased drastically with the reduction time due to the poisoning effect of the products. It was proposed that some surface intermediate formed by the interaction between and the thin oxide layer on a Cu electrode is finally reduced to or , depending on the anodic reactions taking place during the anodic period.

The potential‐pH relations of aluminum wire electrodes were studied in 0.1M potassium chloride and in buffer solutions. Linear pH responses with a slope about −90 mV per pH unit over a pH range of 3 to 14 were obtained. Pretreating the electrodes in alkaline solutions of for several minutes was an essential first step in order to elicit the pH responses.The results are explained with the consideration of the hydration of the aluminum oxide and the formation of aluminum hydrides. The diameter of wires used and the ionic strength of the bathing solutions studied had little effect on the pH responses. The effects of some complexing agents commonly used in buffers were investigated. The reproducibility and the short‐term stability of the electrodes as well as the electrode lifetime were investigated. Practical potential applications and possible ways for improving of the electrode performance are suggested.

The electrochemical interface is treated here as a multi‐input/multi‐output system. This approach allows application of new measurement techniques based on the sinusoidal perturbation or the sinusoidal response of nonelectrical quantities in addition to the usual electrochemical parameters (i.e., potential or current). Used in conjunction with the usual electrochemical impedance, these new transfer functions allow extra information to be obtained on the interface. Some examples are given corresponding to input perturbation related to light, magnetic field, temperature, and angular velocity of the electrode and output responses related to mass, optical reflection, and the currents in a ring‐disk system.

The rotating ring‐disk configuration, consisting of a Pt disk and Si ring, was used to investigate light emission from porous Si in acetonitrile. The electroluminescence (EL) of n‐type porous Si and the chemiluminescence (CL) of n‐ and p‐type porous Si in the presence of an oxidizing agent in solution are reported. The EL and CL characteristics are similar to those observed in aqueous solution. No EL of p‐type porous Si could be observed in the presence of a strong reducing agent, probably due to bandedge unpinning. The photon energy of the EL of n‐type porous Si is in good agreement with that deduced from the relative positions of the redox energy level and the semiconductor bandedges.

The results of a study of the oxidation peak observed with electrodes in the negative potential region are reported. The study was performed with the following three electrodes in 0.1M, , and . electrodes having low carrier concentration exhibited a photovoltage associated with the oxidation peak. These observations signify that plays an active role in this oxidation process and forms a major component of the peak. X‐ray photoemission analyses indicate that the oxidation product of is . Comparison of the voltammograms of with those of metallic indium indicate the possible presence of indium oxide. These observations suggest that the oxidized surface is composed primarily of with minor amounts of .

In situ atomic force microscopy (AFM) was used to observe growth morphology during copper electrodeposition on Pt(100) and Pt(111) surfaces from 0.25M containing 0,10, and 100 μM benzotriazole (BTA). The Pt(100) crystal was misoriented ∼2° to give terraces that were approximately 1 μm in length and 25 to 50 Å high. Deposit morphology was monitored primarily during growth at current densities between 1 and 15 mA/cm² under stagnant conditions. In the absence of BTA, copper selectively deposited on the larger step sites rather than on the smaller steps or terrace regions. From solutions containing 10 μM BTA, copper deposited in clumps along the steps. From solutions containing 100 μm BTA, deposition occurred without regard to substrate features. On Pt(111), three‐dimensional nucleation of copper was monitored at the nanoscale level during cathodic deposition from 0.25M. At overpotentials <70 mV, no nuclei were observed. At 120 and 170 mV overpotential, individual 3‐D clusters were observed, and additional clusters nucleated over time. At higher overpotentials (≥200 mV), uniform nucleation and overlap were observed. The current transients and AFM images recorded during the deposition experiments were compared with theory for 3‐D, solution‐diffusion‐controlled, multiple nucleation with overlap. At high overpotentials, the current transients were consistent with theory, and AFM images indicated that nucleation was three‐dimensional with overlap. At low overpotentials, the current transients were not consistent with theory, and AFM images confirmed that nuclei did not overlap.

Deionized water was oxidized to form ozone at the anode while oxygen was reduced to hydrogen peroxide at the cathode in a proton‐exchange‐membrane electrochemical flow reactor. The conditions for simultaneous generation of these oxidants were determined as a function of the applied voltage, electrode materials (lead dioxide for ozone evolution; gold, carbon, or graphite for peroxide evolution), and electrode configurations. Measured and calculated quantities included cell current, liquid‐ and gas‐phase ozone concentrations, hydrogen peroxide concentrations, current efficiency for ozone and peroxide evolution, and ozone and peroxide production rates. An applied potential of 4.5 V resulted in a current density of 2 A/cm², yielding maximum gas‐ and liquid‐phase ozone concentrations of 60 and 3.1 mg/liter at the anode (4.5% current efficiency) and hydrogen peroxide concentrations between 3 and 5 mg/liter at the cathode (0.8% current efficiency).

Cathode materials that have been synthesized by reduction of lithium‐manganese‐oxide and manganese‐oxide precursors with hydrogen at 300 to 350°C, and with carbon at 600°C have been evaluated in rechargeable lithium cells. The cathodes which initially have a composition close to contain structures related to the lithiated‐spinel phase and/or orthorhombic The orthorhombic component transforms gradually to a spinel structure on cycling. These cathodes are significantly more tolerant to repeated lithium insertion and extraction, when cycled over both the 4 and 3 V regions, than a standard spinel electrode .

The reduction of bromate in alkaline solutions at a dropping mercury electrode has been studied as a function of temperature. Transfer coefficients and apparent enthalpy of activation were calculated. The apparent electrochemical enthalpy of activation was found to change sign in the linear Tafel region. The potential at which the value of is zero is positive with respect to the half‐wave‐potential for the monovalent alkali cations, while it is negative to , at the edge of the linear Tafel region for Ca⁺². In order to correct for diffuse double‐layer effects, different reduction mechanisms were postulated. The best results, in view of the temperature independence of the transfer coefficient, were obtained by postulating a scheme in which the negatively charged bromate ions are adsorbed on a layer of the positive ions of the supporting electrolyte, which dominates the outer Helmholtz plane (OHP) in the range of potentials where the reduction takes place. Other models did not yield strict independence of the transfer coefficient of temperature. However, the involvement of ion pair formation cannot be completely ruled out. The negative apparent electrochemical enthalpy of activation can be explained by a sufficiently negative enthalpy for the preceding adsorption equilibrium, which can lead to a negative apparent electrochemical enthalpy of activation for the overall process, although for the rate‐determining step proper is positive. The observation of a negative apparent electrochemical enthalpy of activation within the linear Tafel region can be used as an important mechanistic tool for elucidating the mechanism of electrode reactions.

The effect of and gas partial pressures on the reduction path at a gold flag electrode has been investigated in , , , , and melts at 615 to 800°C. We carried out precise measurements of the Warburg coefficient of the ac impedance at the rest potential, using a Randles‐Ershler equivalent circuit. Taking into account four possible diffusing species, i.e., , , , and , a graphical reaction order analysis was made using the Warburg coefficients. It was found that only the case of mixed diffusion of and results in a satisfactory linear relationship. Thus, we conclude that the simultaneous diffusion of and is the dominant feature of the oxygen reduction path in the molten carbonate mixtures used in this study. Based on this conclusion, we estimated the diffusion coefficient of and .

The influence of Co content on the corrosion resistance of sputter‐deposited alloy films for magneto‐optical recording media was investigated by means of an immersion corrosion test, electrochemical measurement, x‐ray photoelectron spectroscopy, and transmission electron microscopy. The corrosion resistance of the alloy films in chloride solutions increased with increasing Co content. This is due to the decrease in the growth rate of pits. The stability of passive films on the surface of the alloys increased with increasing Co content. The number of pits, however, increased with increasing Co content. Colonies of microcrystals were locally formed in an amorphous alloy matrix with increasing Co content. Such colonies are presumed to be responsible for the increase in the number of pits.

Branched copper and zinc aggregates were electrodeposited at large overpotentials from unstirred binary electrolyte in a quasi‐two‐dimensional cell. The concentration field was measured during deposition by electro‐optic interferometry. Depending on deposition conditions, either natural convection or electrokinetic convection was induced at the growth tips. In the deposition of zinc dendrites, the onset of electrokinetic convection destabilized the growth tips, resulting in multiple tip splitting. The growth then restabilized into a new pattern where the branch spacing was coupled to the scale of the convection cells.

Electrodeposit of niobium metal from melts at 700°C has been investigated. It was found that the equilibrium oxidation state of niobium was four for initial ratios of up to at least one. On the other hand when a niobium metal sheet was used for the reduction, average oxidation states close to five were obtained. Cyclic voltammetry showed that is reduced in two steps. A mechanism Nb(V) → Nb(IV) → Nb(0) is proposed. When oxide is present, new waves due to reduction of niobium mono‐oxofluoro and dioxofluoro complexes are observed at −0.6 and −0.74 V, respectively. In addition plating experiments were also performed. The substrates in our work were low‐carbon steel, the anodes niobium metal, and the current density was around 90 mA/cm². It was found that the presence of at least 1 mole percent of oxide was necessary to obtain current efficiencies higher than 30%. The highest current efficiencies obtained were around 95%. For oxide/Nb(V) molar ratios equal to or higher than one, partially nonmetallic surface layers were deposited.

Polarization experiments and a potentiostatic pulse technique have been used to show that a monolayer coverage of zinc effectively inhibits the absorption of hydrogen into Monel K500. By depositing a monolayer of zinc on Monel K500, the hydrogen evolution reaction and hydrogen ingress flux rate were reduced by 60%.

A steady‐state method and ac impedance spectroscopy were used to investigate the hydrogen evolution reaction (HER) on porous lanthanum‐phosphate‐bonded nickel (LPBN) electrodes in 9M and solutions at temperatures ranging from 20 to 70°C. The Tafel slopes, exchange current densities, and overpotentials at a current density of 250 mA/cm²were obtained from steady‐state measurements. The ac impedance data were analyzed using the porous‐electrode model, and the kinetic parameters of the HER and double‐layer capacitances were determined. The pore length was deduced to be 64 to 73 μm compared to 1 μm for the diameter. The effect of temperature and the nature of the electrolyte on the intrinsic electrocatalytic activity of the LPBN electrodes are discussed.

A simple, quantitative relationship between the semiconductor surface recombination velocity and the open‐circuit photovoltage of photoelectrochemical systems was derived and verified experimentally. Experimental results obtained for the junction indicate that is controlled by surface recombination. Quantitative analysis of the results using the derived expression yields values of the barrier height and that compare favorably with published data. Application of the equation to other semiconductor/liquid junction cells suggests that the expression may be important in evaluating and understanding the behavior of a wide range of photoelectrochemical systems.

The transported entropy of silver ion, , and the heat of transfer, , for , have been calculated from electromotive force (EMF) measurements in the cell . Results give when. From this we derive in pure silver sulfate and in lithium‐silver sulfate mixtures. For smaller mole fractions of , , increases. The heat of transfer, , is negative and varies with composition. The sign indicates that is enriched on the hot side. The Thomson coefficient for molten pure . From this we derive . Kinetic and thermodynamic models for the transported entropy and heat of transfer are discussed. Some models can be rejected.

Ultrafine particles of binary oxides have been prepared by a sol‐gel process consisting of hydrolysis and condensation of metal alkoxide alcoholic solutions. The binary oxides calcined at 450°C were composed of two rutile‐type oxide phases: and . The Ru metallic phase also was found in the Ru‐rich oxides.

A highly reliable ultrathin tantalum oxide capacitor is fabricated by using oxygen‐plasma annealing after the film deposition. A tantalum oxide film is deposited on a nitrided polycrystalline silicon surface using a mixture of pentaethoxy‐tantalum and oxygen gas. The films are annealed in an oxygen‐plasma at less than 400°C. The oxygen‐plasma annealing greatly reduces the leakage current through tantalum oxide capacitors and produces better time‐dependent dielectric breakdown characteristics than either dry annealing or two‐step annealing (oxygen‐plasma + dry annealings). The reason for the excellent electrical properties is examined using secondary ion mass spectrometry, extended x‐ray absorption fine structure spectroscopy, and transmission electron diffraction patterns. Analytical results show that the oxygen‐plasma annealed tantalum oxide films are densified by the elimination of carbon and hydrogen and by the repair by oxygen of vacant sites in the as‐deposited films, as the films remain amorphous during oxygen‐plasma annealing. In addition, oxygen‐plasma annealing suppresses thickening of the interface layer between the tantalum oxide film and polycrystalline silicon bottom electrode. Therefore, highly reliable ultrathin tantalum oxide capacitors with an equivalent thickness of less than 3 nm can be fabricated by using oxygen‐plasma annealing.

The conventional method of preparing requires repeated firing to form single‐phase cubic material. When a, , , or , or is used as a reaction reagent, however, only a single firing produces single‐phase cubic material. The solid‐liquid phase reaction occurs during firing between the raw oxide materials as well as other by‐products. X‐ray diffraction patterns identify these by‐products as , , , , and . The particle growth is facilitated by a process in which small particles first gather in the contact area between large particles where fluoride melts and forms a liquid film, then dissolve and finally precipitate when saturated to reduce the surface energy.

304 stainless steel samples were oxidized in pure flowing oxygen at 800°C for 20 h, then furnace cooled, either directly to room temperature or to an intermediate temperature, held at that temperature for 24 h and then furnace cooled to room temperature. Cracking and spalling of the oxide scale were monitored by acoustic emission (AE) technique throughout the experiment. Only a few AE events were observed during the isothermal exposure and during furnace cooling to ca. 300°C. A significant number of events was observed starting at ca. 300°C and during further cooling, with a maximum rate at ca.150°C for continuous furnace cooling. If the cooling was interrupted at some temperature < 300°C, the scale fracture process stopped, but then resumed on further cooling. To explain this behavior, it is hypothesized that the stress intensity varies locally within the scale, e.g., due to local variations of stress values or to the variation of the size of flaws across the sample. When the local stress intensity reaches a critical value, , cracks propagate rapidly. An analysis of AE data shows that the conditions for scale cracking follow a log normal distribution with respect to average scale stress.

The kinetics of deposition of on a dense substrate by electrochemical vapor deposition (EVD) were analyzed by taking into account the dependence of ionic and electronic conductivities on oxygen partial pressure, , of both the deposit and the substrate. The analysis shows that the equivalent circuit approach advanced previously satisfactorily explains the numerical and experimental results. The numerically generated rate constants for the film, , and the substrate, , depend on the partial pressure of oxygen, . Specifically, the lower the at the film‐gas phase interface, the higher are and . films were deposited by EVD on dense substrates. Each substrate had a conical depression in the center such that the thickness of the substrate was spatially dependent. Experiments were conducted with and without Ni metal as an oxygen getter placed in the chamber containing precursor. Experiments also were conducted with a mixture of hydrogen and argon introduced on the side. The rate constants of the film, , and the substrate, , were substantially higher when either Ni was placed or hydrogen was circulated on the side. This shows that by judiciously selecting the atmosphere on the precursor side, the kinetics of the EVD process can be increased significantly.

Chemical relaxation experiments were conducted on sintered samples of calcium‐doped lanthanum chromites by abruptly changing the oxygen partial pressure in the atmosphere and following the time change of conductivity. The re‐equilibration kinetics was analyzed by fitting the relaxation data to the solutions of Fick's second law for appropriate boundary conditions. The diffusion equation ignoring the effect of surface reaction failed to describe the transient behavior especially for the initial stage, while that taking the surface effect into account gave a satisfactory interpretation of the overall relaxation process and allowed a precise determination of the two kinetic parameters: oxygen chemical diffusion coefficient and surface reaction rate constant. The chemical diffusion coefficients increased with a decrease of the oxygen partial pressure due to the corresponding change in the concentration of the moving species. The activation energy was similar to that of oxygen vacancy diffusion coefficients in other monocrystalline perovskites, suggesting that the measured diffusion coefficients were attributable to lattice diffusion. The surface reaction rate constant increased with a decrease of the oxygen partial pressure similarly to the reported oxygen nonstoichiometry, which implies that the presence of oxygen vacancies plays an important role in the surface reaction kinetics.

Photoelectrochemical etching of is demonstrated. Although the concentration of thermally generated minority carriers and saturation current are high compared to larger bandgap semiconductors, photocurrent to dark current ratios as high as 4:1 were obtained at low temperature (2°C) and at potentials near the flatband potential. A surface film primarily composed of arsenic oxide was formed during oxidative decomposition of the semiconductor and plays a role in the rate of dissolution and in the current‐voltage response. In 0.2M electrons per were involved in the oxidation dissolution, while only 4 electrons per were found in 0.2M because of the formation of In(I)‐chlo‐ride species.

, , and thin films have been deposited on glass substrates for the first time using atomic layer deposition (ALD) at temperatures between 260 and 400°C. The source materials used are alkaline earth β‐diketonates, zinc acetate dihydrate, and hydrogen fluoride in nitrogen atmosphere. The growth rate of films varies from 20 to 90 pm/cycle depending on materials and temperature. The crystallinity, orientation, stoichiometry, atomic density, optical and electrical properties together with growth properties of the films have been characterized. Also, multilayer structures with alternating materials of high and low (fluoride) index of refraction have been prepared by ALD.

We have studied the incorporation kinetics of oxygen during the chemical vapor deposition (CVD) growth of epitaxial silicon and silicon‐germanium layers at temperatures between 700 and 750°C. In this temperature range, the incorporation of oxygen into the growing film is a kinetically driven process and is not governed by equilibrium conditions. Oxygen concentrations exceeding the solid solubility for interstitial oxygen in silicon can be incorporated into the epitaxial layers. We determine an effective sticking probability for oxygen on the surface of silicon under CVD growth conditions and find it to be 100 times lower than that found in ultrahigh vacuum experiments. This reduction in sticking is due to both hydrogen surface coverage and boundary layer effects. We also have determined the maximum oxygen contamination level allowed in the gas stream for the CVD growth of low oxygen content silicon films.

An in situ scanning tunneling microscopy study of morphological changes during formation and reduction of an oxide monolayer on Au(111) in 0.1M is presented. During oxidation of a freshly prepared surf ace, the arrangement of metal atoms persisted through the hydroxide peak at 1.35 V vs. reversible hydrogen electrode (RHE). At the peak potential for formation (1.55 V vs. RHE), a slightly roughened layer propagated across terraces starting from edges. An ordered oxidized surface structure was not resolved and the surface roughness is approximately . This is ascribed tentatively to the formation of a monolayer of oxide by place exchange. During a slow cathodic sweep, the oxidized surface restructured into wormlike islands of monatomic height at the peak potential for oxide reduction at 1.15 Vvs. RHE. These islands coalesced to form flat terraces with monatomic pits in the surface at potentials within the double‐layer region. Pits eventually fused with terrace ledges to restore the original terrace morphology.

An in situ observation system composed of a latticework, a mirror, and a video camera has been developed to quantitatively determine the transient deformation of wafers when they are pushed into or pulled from a hot horizontal furnace. To observe a silicon wafer in the middle of many silicon wafers on a boat, those wafers that are located in front of the silicon wafer we want to observe are replaced by an equal number of same‐dimension transparent quartz wafers. An approximate relation for obtaining the actual amount of wafer distortion from the experimentally observed image distortion is also derived. Using this observation system, we examined in detail the effects of furnace temperature, boat speed, wafer location, and wafer thickness on transient deformation. This system also provides more complete information on deformation distribution across a wafer, deformation speed, and recovery speed.

We investigate the introduction of metallic contamination from silicon carbide forks into silicon wafers during thermal annealing in a diffusion furnace. By placing one wafer on top of another on the fork, we show that the atmosphere in the furnace is not uniformly contaminated. Instead, metal evaporation from the fork (or local evaporation pressure) may be responsible for the contamination transfer. The dominant contaminants in the fork are iron, copper, and nickel, and the relation between the p‐Si lifetime and the n‐Si lifetime depends on these contaminants. The contamination in the fork may be due to the materials or jigs used in making it. Sodium contamination from the fork is closely related to ambient environment.

The capacitance ^vs. voltage and current density ^vs. voltage characteristics of silicon dioxide films formed by anodization of silicon in dilute ammonium hydroxide solutions have been measured. Postoxidation annealing (POA) at temperatures up to 700°C greatly reduces the leakage currents and results in breakdown voltages in excess of 10 MV/cm. However, leakage currents are still in excess of those obtained by thermal oxidation, possibly indicating some residual structural imperfection such as a transition layer or roughness at the silicon‐silicon dioxide interface. The combination of a POA at 700°C with a postmetallization anneal in forming gas at 400°C have reduced the interface state densities to with fixed charge densities at the interface of .

We present a model to predict the energy and angular distributions of ions which impact the substrate in low (100–450 kHz), high (13.56 MHz), and dual frequency plasmas. The model combines a single and dual frequency plasma sheath model with Monte Carlo simulations of ion transport. The sheath model for single and dual frequency parallel plate plasma systems provides the time dependent sheath thickness and the time and spatially dependent electric field in the sheath, which are necessary for the Monte Carlo simulations. Monte Carlo simulations are used to track the ion motion and to generate the energy and angular distributions. Both charge transfer and hard sphere elastic collisions are included in the Monte Carlo simulations. The model predictions of the ion energy and angular distributions agree well with experimental data for argon plasmas and with the predictions of other analytical models and Monte Carlo simulations in the low (100 kHz) and high (13.56 MHz) frequency limits. Model predictions show that the shapes of the ion angular and energy distributions and the resultant average ion energy and angle become independent of pressure and frequency above 10 Torr. Below 10 Torr, changing the frequency mix from 100% high frequency to 100% low frequency lowers the average ion energy, increases the maximum ion energy, and increases the directionality of the ions.

The dc conductivities and dielectric breakdown strengths of zinc sulfide thin films deposited by various techniques were investigated. The void volume in a film was a function of the deposition method and conditions, and the breakdown strength was inversely proportional to the void volume. The shape of the current‐voltage curve depended on the deposition method. Films deposited by thermal evaporation and low temperature metallorganic chemical vapor deposition had void volumes in the 3 to 5% range, breakdown strengths ca. 2 MeV/cm, and exhibited little bulk conduction before breakdown. The current‐voltage data were consistent with current‐controlled negative differential resistance and filamentary conduction. Breakdown was due to Fowler‐Nordheim tunneling of charge from the contact into the dielectric layer at all temperatures. Layers formed by sputtering a target in argon or argon/oxygen had void fractions ranging from 0.5 to 5%. Layers with low void volumes had breakdown strengths > 3 MeV/cm. The current‐voltage data for sputtered films indicated initial Poole‐Frenkel conduction followed by a continual increase in current with applied bias at room temperature. At 77 K breakdown occurred as a result of tunneling.

A comprehensive study is made of the anodization behavior and electrical and physicochemical properties of anodic oxides for use as thin film transistor (TFT) gate dielectrics. The matrix metals examined are pure Al, Al‐1.1 atom percent (a/o) Ta, Al‐0.5 a/o Ti, and Al‐1.0 weight percent Si, and electrolytes in aqueous solution are ammonium tartrate, triammonium citrate, diammonium hydrogenphosphate, and ammonium tetraborate‐boric acid. Breakdown voltage in anodization, which corresponds to maximum formable thickness, was highest for the oxide of Al‐Ta for all solutions. A dielectric strength of over was achieved for oxides of the combinations Al‐Ta and Al‐Ti/inorganic solution. Leakage current in the anodic oxide annealed at 300°C was lowest for the combination Al/inorganic solution. The oxide of Al‐Si for all solutions was no better than that of Al for any of the properties investigated. The most promising combination for gate dielectrics was Al‐Ta and Al‐Ti/inorganic solution, giving a field effect mobility of 1.0 to 1.5 cm²/Vs and an on‐off current ratio of more than 10⁸ for TFTs fabricated with a double‐layer gate dielectric structure of an anodic oxide layer/a plasma chemically vapor deposited layer.

A process consisting of the deposition of amorphous silicon at low temperatures and subsequent annealing has been proposed for fabricating a boron‐doped polycrystalline silicon film with a low resistivity. This process realized large grain growth up to 3 to 5 μm, leading to a low resistivity of 1.4 mΩ · cm, which one‐half to about one‐third compared with that of direct deposited boron doped polysilicon. In addition to this, extremely low deposition temperature (∼350°C) using a mixture attained uniform boron concentration across the wafers.

A versatile chemical vapor deposition (CVD) technique is proposed which has two noteworthy technical features: (i) alternate or intermittent introduction of source vapors followed by evacuation and (ii) one or more excitations synchronized with the sequence of vapor introduction. Since it can select and identify the place and time for the occurrence of reactions and excitation among source molecules, this technique also promises to be valuable in investigating the use of conventional CVD processes with unfamiliar materials. In this work, the technique is used to investigate the conventional photo and thermal CVD processes of tantalum pentoxide film using tantalum pentachloride and oxygen. The results indicate that significant deposition occurs even without the vapor phase reactions among source vapors and that photoexcitation of the substrate surface greatly enhances film deposition. In the course of the investigation, it was observed that temporary photoexcitation and ozone supply produced a high rate of film deposition even at temperatures lower than 300°C.

The microstructure and kinetics of the polymorphic phase transformation have been studied using samples prepared as in self‐aligned silicide applications. For thin films formed at temperatures of 600 and 625°C on (100) single‐crystal silicon substrates, the effective activation energy was , respectively, for the C49 to C54 phase transformation carried out in the temperature range 600 to 700°C. We concluded that the transformation process occurred by nucleation and growth of the orthorhombic face‐centered (C54) phase from the as‐formed orthorhombic base‐centered (C49) phase. The Avrami exponent of and the optical observations suggest that most of the nucleation occurred during the beginning of the transformation process.

, the silicide most commonly used for a low resistivity self‐aligned salicide process, must become thinner as the junction depth and poly‐Si gate height decrease so as not to affect junction leakage and gate work function. The thermal stability of the thinner during the back‐end thermal process cycles, is an important concern. We report on the thermal stability of 300 to 700 Å thin on As, P, or doped poly‐Si to annealing at 750 to 850°C for 10 to 30 min determined by the increase in the resistance of long 0.3 to 1.5 μm wide poly‐Si meander lines. The increase in line resistance is correlated with changes in the microstructure. Poly‐Si lines ≤0.5 μm wide with ≤500 Å increase their resistance after annealing at 750°C, 30 min. 500 Å is stable on >0.5 μm wide poly‐Si lines after annealing at ≥800°C, 15 min. Silicide instability increases the reverse bias diode leakage measured for ∼1500 Å shallow n⁺ junctions whereas it does not increase diode leakage for ∼2000 Å shallow p⁺ junctions. Increasing thickness improves thermal stability. Dopant type and concentration affect the thermal stability through their effect on the thickness (thinner on As doped Si) sintered with a particular Ti sintering process. We use Rutherford backscattering spectroscopy, transmission electron microscopy, and scanning electron microscopy to correlate the increase in effective sheet resistance of submicron wide poly‐Si lines and the increase in ultra shallow junction leakage with an increase in roughness for 700 Å thick and agglomeration for ≤500 Å thin .

The photovoltages of spray‐deposited indium tin oxide/silicon oxide/n‐Si junction solar cells are found to depend strongly on the spray solvents such as methanol, ethanol, ethyl acetate, water, etc. It is also found that the work function of the indium tin oxide (ITO) films is dependent on the spray solvents, and the higher the work function of the ITO films, the larger the photovoltage. X‐ray photoelectron spectroscopy (XPS) measurements indicate that an In‐OH species, probably formed by reactions of the ITO film with the spray solvents, is present in the deposited film in cases where its work function is high. The resistivity of the ITO films produced using the organic spray solvents is in the range of , leading to high fill factors of the solar cells, while that of the films deposited using water as a spray solvent is as high as , resulting in low fill factors. On the basis of the XPS measurements, the high resistivity of the latter ITO films is attributed to a small amount of tin ions in the films. X‐ray diffraction measurements show that the crystal orientation of the ITO films also depends on the spray solvents, indicating that the film formation mechanism varies with the spray solvents. By use of a mixed solvent of , the photovoltage becomes the highest, and the conversion efficiency of 14% is achieved.

Accurate evaluation methods for interstitial oxygen concentrations by infrared absorptiometry at 1107 cm⁻¹ are investigated for medium resistivity Si crystals with carrier concentrations betwee and , which correspond to resistivities between 5 and 0.5 Ω‐cm for p‐type crystals. Difficulty of accurate measurements for these crystals originates from the strong dependence of the internal multiple reflection effect inside the sample crystal on the free‐carrier absorption intensity. Neglect of this effect introduces an error as large as 1 ppma for a p‐type ∼1 Ω‐cm crystal. Two reliable methods to overcome this difficulty are presented. One is to eliminate the multiple reflection effect physically by applying the p‐polarized light incident on the sample surface at Brewster's angle. The other is to eliminate the effect mathematically by a multiple reflection correction carefully taking account of the free‐carrier absorption. Results obtained by the two reliable infrared absorption methods are consistent with a result by a high precision oxygen evaluation using secondary ion mass spectrometry.

Nucleation of in situ phosphorus‐doped amorphous Si films deposited by pyrolysis of and is studied by scanning laser microscopy and transmission electron microscopy. The incubation time of the nucleation decreases as phosphorus concentration increases. The activation energy of the incubation time for nucleation, which corresponds to the activation energy of the self‐diffusion coefficient of amorphous Si, is ca. 3.2 eV, independent of phosphorus concentration. The nucleation rate abruptly increases when the phosphorus concentration exceeds . The activation energy of the nucleation rate decreases abruptly above the phosphorus concentration of , which resulted from a reduction in the maximum free‐energy change for the nucleation.

The analytical expressions for thickness and of an interface layer from x‐ray reflectivity measurements are obtained for an epitaxial layer/interface layer/Si substrate system. The contaminated interface layer between the defective epitaxial layer and Si substrate is detected by the x‐ray reflectivity. The stacking fault density (SFD) in the epitaxial layer is correlated with the δ of the interface layer. There is a linear relation between the δ and oxygen concentration of the interface layers. The δ of the interface layer is less than that of Si which is mainly due to oxygen in the interface layer. The thicknesses of the interface layers are about 1.4 nm and they do not correlate with the SFDs in the epitaxial layer. The thickness of the interface layer obtained by x‐ray reflectivity agrees with that from TEM observations.

We demonstrate that the use of an absorbing layer on top of an interlevel oxide can be used in lieu of the normal antireflective layer approaches to isolate the lithography of a via or contact window level from the reflections of an underlying metal layer. Specifically, we show the use of a sputtered amorphous silicon layer of 500 Å thickness in a double level metal process using g‐line lithography.

Shallow arsenic junctions were formed in short processing times using gas‐phase rapid thermal diffusion with arsine or tertiarybutylarsine (TBA). A 60 s gas‐phase diffusion at 1100°C using 3.6% arsine in helium at 760 Torr formed 150 nm junctions with a measured sheet resistance of 100 Ω/□. Shallow junctions were also formed with a 12 min diffusion at 900°C using 10% TBA in argon at 10 Torr. These TBA‐formed junctions have arsenic concentration at the silicon surface greater than and a sheet resistance of 244 Ω/□. In addition, TEM cross sections show no process‐induced damage at the junction for gas‐phase doping.

The behavior of boron and fluorine introduced into the system is investigated. Fluorine introduction increases sheet resistances of boron layers in silicon after heat‐treatment in both nitrogen and oxygen atmospheres. Boron depth profiles reveal that fluorine causes boron to migrate into from silicon. This phenomenon can be explained if we assume that fluorine is incorporated into the network together with boron to lower the viscosity of .

To reduce surface damage and achieve vertical profiles during selective etching of polysilicon, uniformity of the polysilicon across the wafer after the bulk etch step must be ensured. The bulk polysilicon gate etch process on a single‐wafer plasma reactor was analyzed using response surface methodology to create models to be used in model‐based process control. In situ etch rate data at the wafer center was collected using a single‐wavelength ellipsometer. Off‐line etch rate measurements at sites across the wafer were also made. The etch rate at each site was modeled as a function of the process factors and the ellipsometer response. By modeling each site as an explicit function of the ellipsometer response, the proposed modeling approach allows the inference of process uniformity using the in situ sensor data only. As a result, the site models can be updated on‐line to reflect the current performance of the process for run‐to‐run model‐based process control. The updated models can be used for process optimization for evaluating the process settings (targets‐to‐settings) prior to running each wafer. In this paper the initial models were optimized to achieve a target etch rate while maintaining a uniform thickness of polysilicon after the bulk etch step (each site within 150 Å of the stopping thickness at the wafer center).

Nucleation and crystallization characteristics of phosphorus‐doped amorphous silicon (a‐Si) "slit nano wire" are studied, which is fabricated by conformal filling of a 100 nm wide trench by HLD (High temperature Low pressure chemical vapor Deposition) oxide, and measures about 10 nm in width and height. Nucleation rate and crystallization rate of the amorphous silicon layer, with a phosphorus doping concentration of are measured for samples annealed between 525 and 560°C between 3 and 120 h. The number of nuclei and the length of grains are observed by transmission electron microscopy with a magnification between 32,000 and 4,000,000. The activation energies of nucleation and crystallization are 1.15 and 1.53 eV, respectively, which are about one quarter and one half those measured for a‐Si layers formed on flat . These characteristics are attributed largely to the effect of interaction of a‐Si "slit nano wire" layers and the slit wall surface.

Czochralski single‐crystal wafers grown with different pulling rates using various hot zone modifications were analyzed with respect to grown‐in defects and gate oxide integrity (GOI). The quality of the wafers characterized by crystal defect density as well as by GOI yield was found to be related strongly with the pulling conditions. Depending on the growth rate two concentric regions, characterized by different GOI and grown‐in defect levels and separated by a ring‐like area with high stacking fault density, were found on the wafers. The single‐bit failure rate in some dynamic random access memory (DRAM) reliability tests turned out to correlate with GOI yield. Thus it is clearly shown that the bulk quality related with crystal pulling conditions correlates with the DRAM reliability.

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Abstract not Available.