Showing papers on "Oxide published in 1993"

Fast Ion Transport in Solids

Abstract: Preface. 1. New routes in the development of chemical sensors: surface devices S. Pizzini. 2. Materials and concepts for solid state electrochemical devices W. Weppner. 3. Optical properties of transition-metal and rare earth ions in beta aluminas G. Mariotto. 4. Intercalation compounds M.S. Whittingham. 5. Polymer electrolytes and intercalation electrodes: fundamentals and applications P.G. Bruce. 6. Is there a future for lithium-batteries as high energy density source in electrical engine vehicles? Some recent trends C. Delmas, I. Saadoune, H. Auradou, M. Menetrier, P. Hagenmuller. 7. Ion mobility in chalcogenide semiconductors Room temperature creation of bipolar junction transistor D. Cahen, L. Chernyak, G. Dagan, A. Jakubowicz. 8. Mixed conductors for negative electrodes R.A. Huggins. 9. Surface oxygen exchange kinetics of solid oxide ion condutors B.A. Boukamp, I.C. Vinke, K.J. De Vries, A.J. Burggraaf. 10. Ionic conduction in sulphates A. Lunden. 11. Copper solid electrolyte-copper(I) halide and alkali halide systems O. Yamamoto. 12. Ionic conduction in glasses A. Magistris. 13. Chemical vapor deposition techniques for thin films of solid electrolytes and electrodes V.E.J. van Dieten, J.P. Dekker, A.A. van Zomeren, J. Schoonman. 14. Silver solid state energy storage devices B.B. Owens. 15. Bismuth-based oxide conductors novel structural and electrical features G. Mairesse. 16. Anisotropy in the ionic conductivity of K3NdSi3O8(OH)2 S.M. Hale, J. Maier, B.J. Wuensch, R.A. Laudise. 17. Peculiarities in the low temperature ion and electron conductivity of solid oxide eletrolytes H. Nafe. 18. Chemical analysis and structural investigations of sodium and lanthanide ion-exchanged beta-aluminas F. Tietz, W. Urland. 19. Electrical releaxation in polymer electrolytes I. Albinsson, B.-E. Mellander. 20. Quadrupole-broadened NMR-MAS spectra of disordered materials: acquisition and analysis P. Mustarelli. 21. Experimental working group report: What is the experimental status of solid state ionics (SSI)? R.J. Nowak, E. Zanghellini, H. Nafe, V. van Dieten. 22. Experimental working group report: What are the major contributions of solid state ionics to technology in the past and future? J.S. Lunsgaard, C. Arbizzani, M. Gina, T. Kawada, J. Lane. Final remarks W. van Gool.

Opening carbon nanotubes with oxygen and implications for filling

Abstract: CAPPED hollow carbon nanotubes1,2 can be modified into nanocomposite fibres by simultaneous opening of the caps (by heating in the presence of air and lead metal) and filling of the interior with an inorganic phase3. To generalize this approach, greater understanding is needed of the reaction mechanism between the tube caps and oxygen. Here we report that the oxidation of carbon nanotubes in air for short durations above about 700 °C results in the etching away of the tube caps and the thinning of tubes through layer-by-layer peeling of the outer layers, starting from the cap region. The oxidation reaction follows an Arrhenius-type relation with an activation energy barrier of about 225 kJ mol−1 in air. Heating of closed nanotubes with an oxide (Pb3O4) in an inert atmosphere lowers the activation barrier for the reaction and opening of the tubes occurs at lower temperatures. Contrary to intuition, however, open tubes are much more difficult to fill with inorganic materials than in the one-step filling of tubes reported previously3. But various other experiments might be possible in the inner nano-cavities of the open tubes such as studies of catalysis and of low-dimensional chemistry and physics.

Superconductivity at 94 K in HgBa 2 Cu0 4+δ

Abstract: FOLLOWING the discovery1 of high-transition-temperature (high-Tc) superconductivity in doped La2CuO4, several families of related compounds have been discovered which have layers of CuO2 as the essential requirement for superconductivity: the highest transition temperatures so far have been found for thallium-bearing compounds2. Recently the mercury-bearing compound HgBa2Rcu2O6+δ (Hg-1212) was synthesized3 (where R is a rare-earth element), with a structure similar to the thallium-bearing superconductor TlBa2CaCu2O7 (Tl-1212), which has one T1O layer and two CuO2 layers per unit cell, and a Tc of 85 K (ref. 2). But in spite of its resemblance to Tl-1212, Hg-1212 was found not to be superconducting. Here we report the synthesis of the related compound HgBa2CuO4+δ (Hg-1201), with only one CuO2 layer per unit cell, and show that it is superconducting below 94 K. Its structure is similar to that of Tl-1201 (which has a Tc of < 10 K)4, but its transition temperature is considerably higher. The availability of a material with high Tc but only a single metal oxide (HgO) layer may be important for technological applications, as it seems that a smaller spacing between CuO2 planes leads to better superconducting properties in a magnetic field5.

Impact ionization, trap creation, degradation, and breakdown in silicon dioxide films on silicon

Abstract: Degradation of silicon dioxide films is shown to occur primarily near interfaces with contacting metals or semiconductors. This deterioration is shown to be accountable through two mechanisms triggered by electron heating in the oxide conduction band. These mechanisms are trap creation and band‐gap ionization by carriers with energies exceeding 2 and 9 eV with respect to the bottom of the oxide conduction band, respectively. The relationship of band‐gap ionization to defect production and subsequent degradation is emphasized. The dependence of the generated sites on electric field, oxide thickness, temperature, voltage polarity, and processing for each mechanism is discussed. A procedure for separating and studying these two generation modes is also discussed. A unified model from simple kinetic relationships is developed and compared to the experimental results. Destructive breakdown of the oxide is shown to be correlated with ‘‘effective’’ interface softening due to the total defect generation caused by both mechanisms.

Structural study on the micelle formation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer in aqueous solution

Abstract: The phase behavior of the triblock copolymers dissolved in water has been studied using SANS. The structural properties have been studied as a function of polymer concentration and temperature. At low temperature (T ≤ 15°C) and low polymer concentrations the unimers are fully dissolved Gaussian chains with radius R g =17 A. Close to ambient temperature, the hydrophobic nature of PPO causes aggregation of the polymers into spherical micelles with core sizes of the order of 40-50 A, somewhat temperature dependent. The concentration of micelles increased roughly linearly with temperature, until either a saturation is reached,where all the polymers are part of a micelle, or the volume density of micelles is so high that they lock into a crystalline structure of hard spheres

Fabrication and properties of epitaxial ferroelectric heterostructures with (SrRuO3) isotropic metallic oxide electrodes

Abstract: Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off‐axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X‐ray diffraction, Rutherford backscattering spectroscopy, and cross‐sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.

Crystal Structure of the Polymer Electrolyte Poly(ethylene oxide)3:LiCF3SO3.

Abstract: Ionically conducting polymers (polymer electrolytes) are under intensive investigation because they form the basis of all solid-state lithium batteries, fuel cells, and electrochromic display devices, as well as being highly novel electrolytes. Little is known about the structures of the many crystalline complexes that form between poly(ethylene oxide) and a wide range of salts. The crystal structure is reported of the archetypal polymer electrolyte poly(ethylene oxide)(3):LiCF(3)SO(3), which has been determined from powder x-ray diffraction data. The poly(ethylene oxide) (PEO) chain adopts a helical conformation parallel to the crystallographic b axis. The Li(+) cation is coordinated by five oxygen atoms-three ether oxygens and one from each of two adjacent CF(3)SO(3)(-) groups. Each CF(3)SO(3)(-) in turn bridges two Li(+) ions to form chains running parallel to and intertwined with the PEO chain. There are no interchain links between PEO chains, and the electrolyte can be regarded as an infinite columnar coordination complex.

Bright blue electroluminescence from poly(N‐vinylcarbazole)

Abstract: Electroluminescent devices were fabricated using poly(N‐vinylcarbazole) (PVK) as a hole‐transporting emitter layer and a double layer of 1,2,4‐triazole derivative (TAZ) and tris(8‐quinolinolato)aluminum(III) complex (Alq) as an electron transport layer. A cell structure of glass substrate/indium‐tin‐oxide/PVK/TAZ/Alq/Mg:Ag was employed. In this cell structure, carrier injection from the electrodes to the PVK layer and concomitant electroluminescence from PVK were observed. Blue emission peaking at 410 nm and a luminance of 700 cd/m2 were achieved at a drive voltage of 14 V.

Anion-exchange reactions of hydroxy double salts

Abstract: Hydroxy double salts (HDS's) comprise a class of layered materials which are similar to layered double hydroxides (LDH's) and show a comparable intracrystalline reactivity. All samples described in this paper were prepared by reacting a solid oxide MeO with various solutions.

Interaction of oxygen with Al(111) studied by scanning tunneling microscopy

Abstract: The interaction of oxygen with Al(111) was studied by scanning tunneling microscopy (STM). Chemisorbed oxygen and surface oxides can be distinguished in STM images, where for moderate tunnel currents and independent of the bias voltage the former are imaged as depressions, while the latter appear as protrusions. An absolute coverage scale was established by counting O adatoms. The initial sticking coefficient is determined to so=0.005. Upon chemisorption at 300 K the O adlayer is characterized by randomly distributed, immobile, individual O adatoms and, for higher coverages, by small (1×1) O islands which consist of few adatoms only. From the random distribution of the thermalized O adatoms at low coverages a mobile atomic precursor species is concluded to exist, which results from an internal energy transfer during dissociative adsorption. These ‘‘hot adatoms’’ ‘‘fly apart’’ by at least 80 A, before their excess energy is dissipated. A model is derived which explains the unusual island nucleation scheme by trapping of the hot adatoms at already thermalized oxygen atoms. Oxidation starts long before saturation of the (1×1) O adlayer, at coverages around ΘO≂0.2. For a wide coverage range bare and Oad covered surfaces coexist with the surface oxide phase. Upon further oxygen uptake both chemisorbed and oxide phase grow in coverage. Oxide nucleation takes place at the interface of Oad islands and bare surface, with a slight preference for nucleation at upper terrace step edges.Further oxide formation progresses by nucleation of additional oxide grains rather than by growth of existing ones, until the surface is filled up with a layer of small oxide particles of about 20 A in diameter. At very large exposures up to 5×105 L they cover the entire surface as a relatively smooth, amorphous layer of aluminum oxide. The difference in Al atom density between Al metal and surface oxide is accommodated by short range processes, with no indication for any long range Al mass transport. Based on our data we discuss a simpler two step model for the interaction of oxygen with Al(111), without making use of an additional subsurface oxygen species. The complex spectroscopic data for the O/Al(111) system are rationalized by the wide coexistence range of bare and Oad covered surface with surface oxide and by differences in the electronic and vibronic properties of the surface atoms depending on the number of neighboring O adatoms in the small Oad islands.

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers in aqueous solution. The influence of relative block size

Abstract: The phase behavior of a series of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), E m P n E m , triblock copolymers dissolved in water has been studied using SANS and dynamic light scattering. All copolymers show the characteristics of fully dissolved polymers at low temperatures, whereas aggregates are formed at elevated temperatures due to the hydrophilic-to-hydrophobic transition in PPO.

Electrochromic Reactions in Manganese Oxides I . Raman Analysis

Abstract: Like nickel oxide, manganese oxide is a widely studied material in the primary batteries field. The reactions taking place during voltametric cycling of manganese oxides can be determined using in situ Raman spectroscopy. The main difficulty for the oxide identification is to obtain relevant Raman reference spectra because of the many possible compounds and, for some of these compounds, of their instability in the laser beam. As a consequence, several modifications of different tetra-, tri- and divalent manganese oxides and oxyhydroxides were carefully studied. The electrochromic behavior of three types of manganese oxides, two prepared by thermal oxidations and the other by electrochemical deposition, were then compared. The presence of nonstoichiometry in the pristine material was necessary to obtain a reversible electrochromic effect. The reaction during electrochromic cycling is more complicated than a simple passage from MnO[sub 2] to MnOOH.

Micellization of poly(ethylene oxide)-poly(propylene oxide) block copolymers in aqueous solution

Abstract: The micellization in an aqueous solution of polymers containing ethylene oxide (EO) and propylene oxide (PO) was modeled on the basis of a mean-field lattice theory for multicomponent mixturesof copolymers with internal states occurring in heterogeneous systems. The critical micelle concentration, the aggregation number, and the hydrodynamic radius, as well as their temperature dependence of these, were examined for a number of Pluronic triblock copolymers and for two related block copolymers. A semiquantitative description of the strong temperature dependence of these quantities is observed experimentally for Pluronic F127 [(EO) 99 (PO) 68 (EO) 99 ] was obtained

Light emission in thermally oxidized porous silicon: Evidence for oxide‐related luminescence

Abstract: The luminescence behavior of thermally oxidized porous silicon has been examined at various temperatures and times. No blue shifting of the photoluminescence has been noted with extended oxidation time (3–120 min), in a range where a 30% oxide thickness increase has been reported. This result does not easily fit the quantum confinement model, since the luminescence does not appear to depend on particle sizes. An oxide related luminescence, which is broad, in the red, and stable at high temperatures will be discussed as a possible source of this light emission.

Activity of substrates in the catalyzed nucleation of glass-forming melts. II. Experimental evidence

Abstract: Methods for determining the nucleating activity of substrates are considered. Experimental data on the activity of nucleating catalysts in various organic and inorganic glass-forming melts are summarized and discussed in terms of the theoretical approach developed in Part I of the present investigation. The nucleation of the same melt induced by different substrates is analysed. In this respect, the data for sodium metaphosphate, lithium metaphosphate, poly(ethylene terephthalate), poly(vinyl chloride), sodium tetraborate nucleated with noble metal cores, for poly(decamethylene terephthalate), lithium disilicate, poly(ethylene) and water initiated by oxide and halide catalysts give a direct proof for the validity of the concepts, developed in Part I.

Performance of Solid Oxide Fuel Cell Using Proton and Oxide Ion Mixed Conductors Based on BaCe1 − x Sm x O 3 − α

Abstract: ceramics were synthesized and their ionic conduction was investigated. These ceramics showed protonic and oxide ionic mixed conduction under fuel cell condition. While protonic conduction was predominant below 1027 K, oxide ionic conduction became significant as the temperature increased. Using these oxides as solid electrolyte, hydrogen‐air fuel cell could be constructed. exhibited the best cell performance among the electrolytes examined. The maximum short‐circuit current density was about 900 mA/cm2 at 1273 K. The polarization at each electrode was low. Porous nickel could be used as anode material instead of expensive platinum and as cathode material.

Copper transport in thermal SiO2

Abstract: The transport of copper in silicon dioxide thermally grown on single crystalline silicon was studied by capacitance techniques, secondary ion mass spectroscopy (SIMS) analysis, and Rutherford backscattering spectrometry (RBS). Metal/oxide/silicon (MOS) capacitors were used to study the penetration of copper into the oxide as a function of temperature and applied electric field. The role of a titanium layer between the copper and the oxide was also studied. Bias‐thermal stress (BTS) studies of MOS structures were conducted at 150°C to 300°C with an electric field of 1 MV/cm for times ranging between 10 min and 168 h. It is shown that without bias a relatively small amount of copper reaches the silicon/silicon dioxide interface, with a maximum surface concentration of about 1017 cm−3 that drops exponentially with depth in the oxide. The high‐frequency (100 kHz) capacitance vs. voltage (CV) characteristics of the MOS devices changed drastically when a positive bias was applied to the gate and copper reached the silicon/silicon‐dioxide interface. The penetration time for copper through the oxide was characterized as a function of the temperature. The copper drift velocity, mobility and diffusivity in the oxide were determined and the copper profiles in the capacitors were characterized by SIMS. The activation energy for the diffusivity and mobility models was found to be . Devices without a barrier layer, which were stressed under a positive electric field, showed high copper concentration in the oxide, up to 1021 cm−3. At high temperatures and long stress times a significant amount of copper was also found in the silicon substrate. A titanium layer thicker than 5 nm acted as effective barrier even after 30 h of BTS at 300°C.

A Study of the Oxidation of Phenol at Platinum and Preoxidized Platinum Surfaces

Abstract: The oxidation of phenol at the platinum electrode was studied in aqueous acidic solutions. The effects of electrode surface oxide on the oxidation reactions of phenol and on electrode passivation by reaction products were investigated using cyclic voltammetry and chronoamperometry. X‐ray photoelectron spectrometry was used to detect changes in the nature of the passive film. Phenol reacted at both the inner and outer Helmholtz layers at platinum metal electrodes. Phenol in the inner Helmholtz layer is adsorbed irreversibly and is conductive. Its oxidation involves ring cleavage with a greater than 18 eq/mol. The outer Helmholtz layer reactions are characterized by rapid simple oxidations involving minimal rearrangement of the reactant molecule. This implies that once stable oxidized products such as benzoquinone and polymers with quinone or ether structures are formed they must move from the outer to the inner Helmholtz layer to be oxidized further by ring‐cleavage reactions. We postulate that the bulk of the initial current flow during phenol oxidation is due to the simple fast outer Helmholtz reactions. This initial current continues until the buildup of unreactive products blocks further outer Helmholtz reactions and the slower inner layer reactions predominate. This electrode behavior changed if the electrode was preoxidized producing a platinum oxide coating. The inner layer reactions were greatly reduced at a platinum oxide coated electrode resulting in lower passivated electrode current flow. The onset of passivation however was delayed at the oxide coated electrode. This is attributed to a weaker adsorption of reaction products at the electrode surface requiring additional reaction to produce a stable passive film. The final resulting passive films at platinum and platinum oxide electrodes were chemically similar based on x‐ray photoelectron spectrometric analysis but differed in thickness indicating that the electrode passivation is not due simply to the thickness of the passive film.

Correlation of stress-induced leakage current in thin oxides with trap generation inside the oxides

Abstract: Increases in pre-tunneling leakage currents in thin oxides after the oxides are subjected to high voltage stresses are correlated with the number of traps generated inside of the oxides by the high-voltage stresses. The densities of the traps are calculated using the tunneling front model and analyzing the transient currents that flowed through the oxide after removal of the stress voltage pulses. It is found that the trap distributions are relatively uniform throughout the small portion of the oxide sampled by the transient currents. The trap densities increase as the cube root of the fluence of electrons that passes through the oxide during the stress, independent of the stress polarity. The voltage dependence of the low-level pretunneling current is dependent on the sequence in which the stress voltage polarities and the low-level current measurement polarities are applied. The portion of the low-level pre-tunneling current that is not dependent on the polarity sequence is best fitted by a voltage dependence consistent with Schottky emission. >

Spontaneous formation of silver particles in basic 2-propanol

Abstract: Silver ions are spontaneously reduced in basic, air-saturated solutions of 2-propanol to yield stable Ag colloids in the presence of powdered Nafion. The metal particles (7.4 nm mean diameter) react with oxygen to form Ag 2 O upon exposure to UV light. Changes in the absorption band of the Ag colloid are observed when the metal particles are in contact with Ag 2 O particles. The optical changes are explained in terms of surface effects of the metal particles that arise from metal-metal oxide interactions. Kinetic results indicate that the reduction of Ag + ions is an autocatalytic process. Small metal particles deposited on the surface of larger oxide particles act as catalyst for reduction process

Towards miniaturized electrophoresis and chemical analysis systems on silicon: an alternative to chemical sensors☆

Abstract: The concept of a multi-manifold flow system integrated on a silicon substrate, with valveless switching of solvent flow between channels and electro-osmotic pumping of an aqueous solvent, is presented. A device consisting of two intersecting channels has been micromachined in silicon to test the concept of applying 50–1500 V to the channels to effect electro-osmotic pumping of fluid and electrophoretic separation of sample components. The dielectric breakdown voltages of oxide/nitride films in aqueous solution, in combination with the reverse-bias breakdown potential of silicon itself, are determined. The results show devices that withstand potentials of over 1000 V can be fabricated. Sample volumes on the order of 6–300 pl are defined at the intersection of sample and sensing channels using silicon micromachining. With a pH 8.5 boric acid/tris(hydroxymethyl)aminomethane buffer in 50 μm channels of a device a solvent flow rate of about 0.01 cm/s at 31 V/cm is estimated. A migration rate for the fluorescent indicator fluorescein of 0.003 cm/s is observed, in agreement with theoretical predictions. Coupling to a fluorescence detection system gives detection limits of 10 −8 M.

Stabilisation of aluminas by rare earth and alkaline earth ions

Abstract: The effect of added rare earth and alkaline earth oxides on the resistance of two aluminas to loss of surface area at high temperature has been investigated. In tests of short duration ( <4 h) at llOO”C, Las+ and Ce’+ are equally effective in reducing loss of area for a commercial y-alumina. However, in extended tests (24 h) La3+ is much more effective than Ce ‘+. X-ray diffraction shows that the latter has segregated as CeOz and the alumina is largely a-phase. No separate rare earth oxide phase can be observed with La103 and &alumina is dominant. The same effects are discernable at higher temperature and with a washcoat alumina. Tests with other ram earth oxides and alkaline earth oxides show that an ion size effect is operative. Under severe conditions Ca’+, Yb3+ and Sm3+ are ineffective, Pr3+ and SF are moderately effective while La’+ and Ba’+ are the most effective. Samples containing the latter both exhibit the presence of a hexaaluminate-type phase after tests at 1200°C. Diffuse reflectance infrared spectroscopy has been used to investigate surface hydroxyl groups formed after reequilibration of samples with ambient air. The groups present on sintered alumina differ only slightly from those on unsintered material. There is a good correlation between hydroxyl group band area, in Kubelka-Munk units, and surface area. Samples with added Laz03 and CeOx show only AlOH groups which also closely resemble those present on alumina alone. However the band area for oxide stabilised samples appears to be slightly below that for pure alumina of equivalent area. At most 30% of the surface is made up of a capping layer of the added oxide. X-ray photoelectron spectroscopy (XPS) binding energies, and La/ Al and Cc/Al atom ratios determined by XPS, are consistent with the above picture.

High-temperature oxidation of ion-plated TiN and TiAlN films

Abstract: The high-temperature oxidation of TiN, Ti0.9Al0.1N, and Ti0.6Al0.4N films which were deposited onto stainless steel substrates using an arc ion-plating apparatus was studied at temperatures ranging from 923 to 1173 K for 0.6 to 60 ks in air. The oxidation rate obtained from mass gain as a function of time was found to fit well to a parabolic time dependence. From their temperature dependence, the apparent activation energies of oxidation were determined. With increasing Al contents, the oxidation rate decreased, and the activation energies of oxidation reaction increased. Formed oxide layers were analyzed by XRD, SEM, and EPMA. With increased Al content in TiAlN films, the rate-determining step changes from oxygen ion diffusion in formed rutile to oxygen or aluminum ion diffusion in the formed Al2O3 layer.