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The reductions of and fullerenes in o‐dichlorobenzene (ODCB) electrolytes under controlled potential and convection at rotating disk and ring‐disk electrodes (RDE and RRDE) illuminate several aspects of the electron transfer processes. The stability of the successive one‐electron transfer products (up to and ions) is demonstrated through the RRDE. The diffusion coefficients of both fullerenes in ODCB/0.5M tetra n‐butyl ammonium bromide were measured by two RDE techniques, Levich limiting current behavior and the frequency response of sinusoidal hydrodynamic modulation (SHM). The former gave values of at 25°C for and , respectively, and the latter results were theoretically consistent with the Schmidt number of 17,400 so calculated, confirming the number of electrons transferred without the aid of Faraday's law. Voltammograms of the SHM current at the RDE show kinetic effects at the foot of each successive wave.

We report on growth and characterization of both epitaxial and amorphous films Gd2O3 of (e=14) and Y2O3(e=18) as the gate dielectrics for Si prepared by ultrahigh vacuum vapor deposition. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single-domain films in the Mn2O3 structure. Typical electrical leakage results are 10−3 A/cm2 at 1 V for single domain epitaxial Gd2O3 and Y2O3 films with an equivalent SiO2 thickness, teq of 15 A, and 10−6 A/cm2 at 1 V for smooth amorphous Y2O3 films (e=18) with a teq of only 10 A. For all the Gd2O3 films, the absence of SiO2 segregation at the interface is established from infrared absorption measurements.

Ba1−xKxBiO3 is to date the highest Tc member of a class of superconductors which, it could be argued, belong in the same class of materials as the copper oxides. While there are striking differences between the bismuthates and the cuprates, there are some similarities. In this paper, we will report the results of our tunneling measurements on BKBO. The determination f the energy gap in this material suggests that it is a relativity weakly coupled BCS superconductor - a similar conclusion is reached in the sister compound BaPb1−xBixO3. These results are substantailly different from similar measurements in the cuprates. In addition, we have studied the background tunneling conductance in four of the compounds in this class (BaPbO3, BaPb1−xSbxO3, BaPb1−xBixO3 and Ba1−xKxBiO3) and find a remarkable correlation between the strength of the linear conductance and the superconducting transition temperature. Finally, the Josephson tunneling in these compounds will be discussed.

Resistivity measurements on semiconducting single crystals and thin films of Ba{sub 1{minus}{ital x}}K{sub {ital x}}BiO{sub 3} ({ital x}{lt}0.35) grown by molecular-beam epitaxy follow the Mott variable-range-hopping law {rho}={rho}{sub 0}exp{l brace}({ital T}{sub 0}/{ital T}){sup 1/4}{r brace}. A single crystal with {ital x}=0.13 was measured over 8 orders of magnitude in resistivity at temperatures between 50 K and room temperature. The values of {ital T}{sub 0} are (3--6){times}10{sup 8} K, implying strong localization. Near the insulator-metal transition, the {ital T}{sub 0}'s depend on the stoichiometry and the agreement with the Mott law breaks down. The transport is discussed in the context of the electronic and structural phase diagram of the barium potassium bismuthate system. In particular, we find no evidence of the nonlinear transport which might be expected if incommensurate charge-density waves were the origin of the nonmetallicity of Ba{sub 1{minus}{ital x}}K{sub {ital x}}BiO{sub 3} (0{lt}{ital x}{lt}0.35).

Anodic electrosynthesis of Ba 0.6 K 0.4 BiO 3 leads to millimeter-sized crystals of this cubic superconductor with transition temperatures of 30.5 K. Clusters of these lustrous blue-black crystals are grown on gold anodes in graphite crucibles which conveniently serve as the cathode. Details of the electrochemical procedure utilizing a hydroxide melt are given, along with the characterization of the superconductive transition by microwave absorption and magnetic measurements, and confirmation of the composition and structure with X-ray diffraction. The availability of crystals with cubic facets of up to 10 mm 2 has facilitated characterization and application of this material.

Measurements of the flux of copper species reaching the ring electrode of a rotating Nd2CuO4−xFx disk-gold ring electrode configuration in acidified chloride solutions allow for the real-time analysis of x as the superconductor is etched. The method is based on analyzing the ratio of copper oxidation states arising from the open circuit dissolution reaction of the Nd2CuO4−xFx disk into chloride solutions. Through voltammetry at the gold ring electrode, the Cu2+ and Cu1+ products are measured quantitatively and x determined. For specimens showing a 27 K onset of Tc, the average copper oxidation state is 1.74, corresponding to the stoichiometry Nd2CuO3.74F0.26. Superconductor electrode potentials are determined directly by the Cu2+/Cu1+ ratios.

A nonaqueous plating bath for silver deposition on the Ba2YCu3O7 superconductor has been modified with thiourea to give enhanced coverage of the metal film at low thicknesses. For both porous and high density ceramic substrates, SEM and optical microscopy show nucleation of silver deposits is increased by the additive. The resulting silver-superconductor contact resistances are comparable to those achieved without additives. Adhesion of the deposits and ease of mechanical handling are improved with thiourea. The combination of highly reactive oxidized substrate, nonaqueous solvent, and strongly surface active agent forms a novel extension for electrodeposition science.

THE recent syntheses1,2 of macroscopic quantities of C60 have suggested possible applications in host–guest and organic chemistry, tribology, electrochemistry and semiconductor tech-nology. Here we report the preparation of alkali-metal-doped films of C60 and C70 which have electrical conductivities at room temperature that are comparable to those attained by n-type doped polyacetylene. The highest conductivities observed in the doped films are: 4Scm−1 (Cs/C60), 100 (Rb/C60), 500 (K/C60), 20 (Na/C60), 10 (Li/C60), 2 (K/C70). The doping process is reversed on exposure of the films to the atmosphere. At high doping levels, the films become more resistive. We attribute the conductivity induced in these films to the formation of energy bands from the π orbitals of C60 or C70, which become partially filled with carriers on doping. The smaller alkali metal ions should be able to fit into the interstices in the lattice without disrupting the network of contacts between the carbon spheroids. In the case of C60, this would allow the development of an isotropic band structure, and we therefore propose that these materials may constitute the first three-dimensional 'organic' conductors.

Measurements of the flux of copper species reaching the ring electrode of a rotating Nd2CuO4−xFx disk-gold ring electrode configuration in acidified chloride solutions allow for the real-time analysis of x as the superconductor is etched. The method is based on analyzing the ratio of copper oxidation states arising from the open circuit dissolution reaction of the Nd2CuO4−xFx disk into chloride solutions. Through voltammetry at the gold ring electrode, the Cu2+ and Cu1+ products are measured quantitatively and x determined. For specimens showing a 27 K onset of Tc, the average copper oxidation state is 1.74, corresponding to the stoichiometry Nd2CuO3.74F0.26. Superconductor electrode potentials are determined directly by the Cu2+/Cu1+ ratios.

We have fabricated all‐high Tc superconducting tunnel junctions in the material Ba1−xKxBiO3. The junctions are of very high quality and have a Josephson supercurrent. For the low‐resistance junctions, the IcR product approaches the theoretical limit.

It is known that the RCA Standard Clean 1, which is used repeatedly during device fabrication, can cause etching of Si. In some process flows, such etching can be important when fabricating devices with thin films, for example, in silicon-on-insulator technology. We show that 25-30 A of Si is etched away by a modified version of the SC1 clean (1:8:64 parts by weight of NH4OH, H2O2, and H2O), when it is applied for 10 min to a bare Si layer on top of SiO2. © 1999 The Electrochemical Society. S1099-0062(99)07-069-8. All rights reserved.

Electrodeposition of metallic protection layers on the Ba/sub 2/YCu/sub 3/O/sub 7/ high -T/sub c/ superconductor has been carried out in non-aqueous electrolytes based on the organic solvents acetonitrile, methanol, and propylene carbonate. By lowering the reactivity of the solvent to the strongly oxidized superconductor, the range of potential accessible to cathodic reactions can be extended. In acetonitrile, films of silver, copper, lead, and tin can be deposited, whereas in water it is difficult to achieve more than silver deposits because of the ready reduction of the cuprate compound. Electrochemical techniques with rotating disk and ring-disk electrodes in the nonaqueous electrolytes gave clear voltammetric evidence for the deposition of the metals, their anodic stripping from the substrate, and the ability to cycle the superconductor between plated and uncovered states. Optical microscopy, scanning electron micrographs, and energy dispersive x-ray measurements were used to support the conclusion of high-coverage, microcrystalline metal contacting layers being achieved on the superconductor substrate.

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

Etude de l'oxydation de Ba 2 YCu 3 O 7−x sur une electrode de platine ou de carbone dans des solutions acides de NaCl, NaBr et NaI

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

Amorphous silicon photoanodes in a nonaqueous photoelectrochemical cell show wavelength dependence of their power outputs. This behavior has been studied by maximum power spectroscopy (MPS) and compared to similar experiments with conventional short-circuit spectroscopy. The derivative maximum power output under constant chopped input power (MPS) shows dependence on the wavelength distribution in superimposed fixed beams, whereas the conventional short-circuit measurements do not. Single-crystal substrates of n-Si, n-CdSe, and n-InP do not show any differences between the spectroscopies. Rotating ring-disk electrode studies confirm the regenerative behavior of the n-CdSe and n-InP electrodes with the Fe(HOCH2Cp)2 - Fe(HOCH2Cp)2(+) couple in LiClO4/methanol solution. Fe(HOCH2Cp)2 hydroxymethyl ferrocene. 12 references.

On montre que la generation de courant pour des reactions redox, au-dessous du courant limite de transfert de masse, sur des electrodes en semiconducteurs est controlable par la place et les dimensions du faisceau lumineux. Il est ainsi possible de creer un transfert de trous ou d'electrons en surface sur une jonction electrolyte redox-semiconducteur a l'aide d'un faisceau laser focalise. Les etudes sont faites avec un spot balayant un disque semiconducteur dans une serie d'essai avec une electrode a disque et anneau tournant

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

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

The electrical and magnetic properties of electrodeposits of silver, copper, and lead on Ba2YCu3O7 substrates were evaluated by two‐ and four‐point resistivity measurements and magnetic susceptibility data on the resulting composite structure. With superconductors sufficiently dense to resist significant penetration by the nonaqueous solvents of the plating bath, no degradation of the bulk properties of the superconductor was observed in the magnetic measurements. These conclusions were supported by the resistivity results; furthermore, it was shown that the contact resistance between electrodeposited silver and the superconductor matched that for ultrasonically soldered indium.

Electrodeposition of metallic protection layers on the Ba/sub 2/YCu/sub 3/O/sub 7/ high -T/sub c/ superconductor has been carried out in non-aqueous electrolytes based on the organic solvents acetonitrile, methanol, and propylene carbonate. By lowering the reactivity of the solvent to the strongly oxidized superconductor, the range of potential accessible to cathodic reactions can be extended. In acetonitrile, films of silver, copper, lead, and tin can be deposited, whereas in water it is difficult to achieve more than silver deposits because of the ready reduction of the cuprate compound. Electrochemical techniques with rotating disk and ring-disk electrodes in the nonaqueous electrolytes gave clear voltammetric evidence for the deposition of the metals, their anodic stripping from the substrate, and the ability to cycle the superconductor between plated and uncovered states. Optical microscopy, scanning electron micrographs, and energy dispersive x-ray measurements were used to support the conclusion of high-coverage, microcrystalline metal contacting layers being achieved on the superconductor substrate.

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

Rotating disk electrodes of the high-Tc superconductor are anodized under fixed currents and rotation speeds in several aqueous electrolytes and the electrolyte solutions are subsequently analyzed by ICP-atomic emission spectroscopy.

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