Showing papers on "Copper published in 1994"

Superconductivity in a layered perovskite without copper

Abstract: FOLLOWING the discovery of superconductivity at ∼30 K in La2−xBaxCuO4 (ref. 1), a large number of related compounds have been found that are superconducting at relatively high temperatures. The feature common to all of these materials is a layered crystal structure based on a perovskite template and containing planar networks of copper and oxygen. This raises the question of whether superconductivity can occur in layered perovskites that do not contain copper. To the best of our knowledge, no such material has been found to date, despite nearly a decade of searching. We describe here the discovery of superconductivity in Sr2RuO4, a layered perovskite isostructural with La2−xBaxCuO4 (Fig. 1). Our results demonstrate that the presence of copper is not a prerequisite for the existence of superconductivity in a layered perovskite. But the low value of the superconducting transition temperature (Tc = 0.93 K) points towards a special role for copper in the high-temperature superconductors.

The Chemistry of Metal Cvd

Abstract: CVD of aluminium tungsten copper from Cu(II) percursors copper from Cu(I) precursors gold and silver platinum, pallaium, and nickel assorted metals.

Copper resistance mechanisms in bacteria and fungi

Abstract: Copper is both an essential micronutrient and a toxic heavy metal for most living cells. The presence of high concentrations of cupric ions in the environment promotes the selection of microorganisms possessing genetic determinants for copper resistance. Several examples of chromosomal and plasmid copper-resistance systems in bacteria have been reported, and the mechanisms of resistance have started to be understood at the molecular level. Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced effiux of cupric ions, or copper complexation by cell components. Copper tolerance in fungi has also been ascribed to diverse mechanisms involving trapping of the metal by cell-wall components, altered uptake of copper, extracellular chelation or precipitation by secreted metabolites, and intracellular complexing by metallothioneins and phytochelatins; only the metallothionein chelation mechanism has been approached with molecular detail.

Optical nonlinearities of a high concentration of small metal particles dispersed in glass: copper and silver particles

Abstract: Third-order nonlinearities of glasses doped with a large number of copper or silver particles are studied by degenerate four-wave mixing with an emphasis on particle-size dependence. The nonlinear susceptibility χ(3) exhibits a peak at the wavelength of the absorption peak, with a maximum value of the order of 10−7 esu. The value of χ(3)/α is roughly independent of the absorption coefficient α and increases as the particle radius increases. This result is well explained by the size dependence of the imaginary part of the dielectric constant of metal particles and the local-field factor. The time response of the nonlinearity exhibits two-component behavior: the fast decay time is shorter than the pulse width of the laser (~12 ps), whereas the slow one is 120–200 ps, being weakly dependent on the radius.

Synthesis and superconducting properties of the strontium copper oxy-fluoride Sr2CuO2F2+δ

Abstract: HIGH-PRESSURE synthesis has proved a useful technique for obtaining new, metastable copper oxide superconductors; for example, oxygen insertion into Sr2CuO3 at 6 GPa (ref. 1) yields superconducting Sr2CuO3.i, with transition temperature Tc = 70 K, in which the superconducting CuO2 layers are generated by pressure-induced oxygen migration from apical to equatorial sites. Although the simple structure and high transition temperatures make this family (general formula Srn+1CunO2n + 1+ δ) of interest, the stringent synthesis conditions limit its value for applications. Here we report that fluorine insertion into Sr2CuO3 at ambient pressure causes related structural rearrangements to give superconducting Sr2CuO2F2 + δ with a maximum Tc of 46 K. In this synthesis, the structural changes previously initiated by the thermodynamic effects of high pressure are induced chemically under ambient conditions. The result is a superconducting oxy-fluoride in which fluorine plays a dominant structural role, rather than merely being an electronic dopant as in La2CuO4Fx (ref. 2) and Nd2CuO4−xFy (ref. 3).

Electron paramagnetic resonance studies of copper ion-exchanged zsm-5

Abstract: Electron paramagnetic resonance (EPR) spectroscopy was utilized to probe the oxidation state and coordination environment of copper in ion-exchanged CuZSM-5. EPR spectra of hydrated samples were consistent with octahedral coordination. Square pyramidal and square-planar sites were identified in pretreated CuZSM-5 samples, and the relative concentration of square-pyramidal sites in these samples was linearly correlated with the copper-exchange level. The extent of autoreduction was monitored by EPR and it was determined that a substantial fraction (approximately 40-60%) of the copper was reduced and the reduction process was reversible in the presence of water. A mechanism for the autoreduction of copper is proposed that is consistent with the EPR results. Further, the reactivity of the proposed copper species was probed in reducing and oxidizing environments and in the presence of nitric oxide. The increase in EPR signal intensity that was observed after room-temperature NO exposure of pretreated and oxidized CuZSM-5 is attributed to the formation of copper nitrite and nitrate species. High-temperature in situ EPR experiments revealed that on the time scale of the EPR experiment, the paramagnetic copper environment did not change at elevated temperatures in the presence of nitric oxide. 39 refs., 13 figs., 3 tabs.

Molecular mechanisms of copper resistance and accumulation in bacteria

Abstract: An unusual mechanism of metal resistance is found in certain plant pathogenic strains of Pseudomonas syringae that are exposed to high levels of copper compounds used in disease control on agricultural crops. These bacteria accumulate blue Cu2+ ions in the periplasm and outer membrane. At least part of this copper sequestering activity is determined by copper-binding protein products of the copper resistance operon (cop). Potential copper-binding sites of the periplasmic CopA protein show conservation with type-1, type-2, and type-3 copper sites of several eukaryotic multi-copper oxidases. In addition to compartmentalization of copper in the periplasm, two components of the cop operon, copC and copD, appear to function in copper uptake into the cytoplasm. Copper resistance operons related to cop have been described in the related plant pathogen Xanthomonas campestris and in Escherichia coli, but these resistance systems may differ functionally from the Pseudomonas syringae system.

Semiconductor electrical heater and method for making same

Abstract: A method is disclosed for mechanically and electrically bonding metallic materials and semiconductor materials. The method according to the invention may be used, for example, in forming a semiconductor electrical heater, particularly for use in electrical smoking articles. A metallic element, such as a copper alloy power supply tab, is laser welded to a semiconductor element, such as a doped silicon resistive heater element. A laser beam is directed through a hole in the copper alloy tab to melt some silicon material, which flows into the hole in the copper tab, reacts and intermixes with the copper and solidifies to form a slug containing copper silicide. A protective material such as nickel may be applied to protect the copper silicide from oxidation if desired. An ohmic, low resistance contact and high strength bond is provided between the parts.

Intermetallic compound layer formation between copper and hot-dipped 100In, 50In-50Sn, 100Sn, and 63Sn-37Pb coatings

Abstract: The growth kinetics of intermetallic compound layers formed between four hot-dipped solder coatings and copper by solid state, thermal aging were examined. The solders were l00Sn, 50In-50Sn, 100In, and 63Sn-37Pb (wt.%); the substrate material was oxygen-free, high conductivity Cu. The total intermetallic layer of the 100Sn/Cu system exhibited a combination of parabolic growth at lower aging temperatures and t0.42 growth at the higher temperatures. The combined apparent activation energy was 66 kJ/mol. These results are compared to the total layer growth observed with the 63Sn-37Pb/Cu system which showed parabolic kinetics at similar temperatures and an apparent activation energy of 45 kJ/mol. Both 100Sn and 63Sn-37Pb diffusion couples showed a composite intermetallic layer comprised of Cu3Sn and Cu6Sn5. The intermetallic compound layer formed between In and Cu changed from a CuIn2 stoichiometry at short annealing times to a Cu57In43 composition at longer periods. The growth kinetics were parabolic with an apparent activation energy of 20 kJ/mol. The intermetallic layer growth of the 50In-50Sn/Cu system exhibited extreme variations in the layer thicknesses which prohibited a quantitative assessment of the growth kinetics. The layer was comprised of two compounds: Cu26Sn13In8 which was the dominant phase and a thin layer of Cu17Sn9In24 adjacent to the solder.

X-ray structure and site-directed mutagenesis of a nitrite reductase from Alcaligenes faecalis S-6: roles of two copper atoms in nitrite reduction.

Abstract: Nitrite reductase (NIR) from the denitrifying bacterium Alcaligenes faecalis S-6 is a copper-containing enzyme which requires pseudoazurin, a low molecular weight protein containing a single type I copper atom, as a direct electron donor in vivo. Crystallographic analysis shows that NIR is a trimer composed of three identical subunits, each of which contains one atom of type I copper and one atom of type II copper, and that the ligands to the type I and type II copper atoms are the same as those of the Achromobacter cycloclastes NIR. An efficient NIR expression-secretion system in Escherichia coli was constructed and used for site-directed mutagenesis. An NIR mutant with a replacement of the type II copper ligand, His135, by Lys still retained a type II copper site as well as a type I copper atom, but it completely lost nitrite-reducing activity as measured with methyl viologen as an electron donor. On the other hand, another mutant with a replacement of the type I copper ligand, Met150, by Glu contained only a type II copper atom, but it still retained significant nitrite-reducing activity with methyl viologen. When pseudoazurin was used as an electron donor for the reaction, however, Met150Glu failed to catalyze the reduction of nitrite. Kinetic analysis of the electron transfer between NIR and pseudoazurin revealed that the electron-transfer rate between Met150Glu and pseudoazurin was reduced 1000-fold relative to that of wild-type NIR.(ABSTRACT TRUNCATED AT 250 WORDS)

Borohydride Reduction of Nickel and Copper Ions in Aqueous and Nonaqueous Media. Controllable Chemistry Leading to Nanoscale Metal and Metal Boride Particles

Abstract: The reduction of Ni 2+ (aq), Ni 2+ (diglyme), Cu 2+ (aq), and Cu 2+ (diglyme) by NaBH 4 has been studied with mechanistic and stoichiometric factors as the focus

Pattern Geometry Effects in the Chemical‐Mechanical Polishing of Inlaid Copper Structures

Abstract: We describe an investigation into the pattern dependence of dishing and erosion during the chemical‐mechanical polishing of copper used for delineating inlaid metal patterns Copper dishing is determined to be highly dependent on the width of the copper structure, but only minimally dependent on the density of copper structures Erosion of the dielectric layer is strongly affected by the pattern density, but not affected by changes in the width of the copper lines As a result, both line width and pattern density are important considerations in predicting the final thickness of the copper lines

Copper-based metal polishing solution and method for manufacturing a semiconductor device

Abstract: A copper-based metal polishing solution comprises a water-soluble organic acid capable of reaction with copper to form a copper complex compound which is unlikely to be dissolved in water and has a mechanical strength lower than that of copper. The polishing solution also contains polishing abrasive grains and water. The polishing solution of the particular composition does not dissolve at all copper or a copper alloy when a copper or copper alloy film is immersed in the polishing solution, and permits polishing the copper or copper alloy film at a practical rate in the polishing step.

Effects of the addition of small amounts of Al to copper: Corrosion, resistivity, adhesion, morphology, and diffusion

Abstract: The properties of thin films of Cu with 1 at. % Al are explored. As‐deposited films of Cu(1 at. % Al) oxidize orders of magnitude more slowly than do those of pure Cu. After Cu(1 at. % Al) films are annealed in Ar at 400 °C for 30 min, very thin protective layers of aluminum oxide form on the surface. These thin oxide layers stop further oxidation of the copper. Cu(1 at. % Al) films also adhere better to SiO2 than do films of pure copper. Unlike pure Cu, films of Cu(1 at. % Al) remain microscopically smooth after anneals at temperatures up to 700 °C. In addition, Cu(1 at. % Al) films show no diffusion of Cu (as measured by Rutherford backscattering spectroscopy) into SiO2 at temperatures up to 700 °C. The addition of Al to Cu does increase its resistivity by about 2 μΩ cm per 1 at. % Al, but a possible procedure to avoid this problem is proposed.

Method for capping copper in semiconductor devices

Abstract: A silicon nitride layer (34) has improved adhesion to underlying copper interconnect members (30) through the incorporation of an intervening copper silicide layer (32). Layer (32) is formed in-situ with a plasma enhanced chemical vapor deposition (PECVD) process for depositing silicon nitride layer (34). To form layer (32), a semiconductor substrate (12) is provided having a desired copper pattern formed thereon. The copper pattern may include copper interconnects, copper plugs, or other copper members. The substrate is placed into a PECVD reaction chamber. Silane is introduced into the reaction chamber in the absence of a plasma to form a copper silicide layer on any exposed copper surfaces. After a silicide layer of a sufficient thickness (for example, 10 to 100 angstroms) is formed, PECVD silicon nitride is deposited. The copper silicide layer improves adhesion, such that silicon nitride layer is less prone to peeling away from underlying copper members.

Spectral sensitization of large-band-gap semiconductors (thin films and ceramics) by a carboxylated bis(1,10-phenanthroline)copper(I) complex

Abstract: Photoelectrochemical cells based on colloidal films of titanium dioxide and zinc oxide ceramic electrodes sensitized by a bis(2,9-diphenyl-1,10-phenanthroline)copper(I) complex modified at the para positions with NaO2C groups, were investigated in an aqueous medium using hydroquinone as electron donor. The sensitizing effect is greater with the films due to the enhanced geometric area projection. The photocurrent-action spectrum obtained with this complex covers almost the whole of the solar visible region. The quantum efficiency was found to depend on the degree of surface coverage by the complex. In a solar-cell arrangement the open-circuit photovoltage was 0.6 V with a small short-circuit photocurrent of ca. 0.6 mA cm–2 in iodide-containing propylene carbonate.