Showing papers on "Copper published in 1996"

Multicopper Oxidases and Oxygenases

Abstract: Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.

The Amyloid Precursor Protein of Alzheimer's Disease in the Reduction of Copper(II) to Copper(I)

Abstract: The transition metal ion copper(II) has a critical role in chronic neurologic diseases. The amyloid precursor protein (APP) of Alzheimer's disease or a synthetic peptide representing its copper-binding site reduced bound copper(II) to copper(I). This copper ion-mediated redox reaction led to disulfide bond formation in APP, which indicated that free sulfhydryl groups of APP were involved. Neither superoxide nor hydrogen peroxide had an effect on the kinetics of copper(II) reduction. The reduction of copper(II) to copper(I) by APP involves an electron-transfer reaction and could enhance the production of hydroxyl radicals, which could then attack nearby sites. Thus, copper-mediated toxicity may contribute to neurodegeneration in Alzheimer's disease.

Selective electroless copper deposited interconnect plugs for ULSI applications

Abstract: A method or utilizing electroless copper deposition to selectively form encapsulated copper plugs to connect conductive regions on a semiconductor. A via opening in an inter-level dielectric (ILD) provides a path for connecting two conductive regions separated by the ILD. Once the underlying metal layer is exposed by the via opening, a SiN or SiON dielectric encapsulation layer is formed along the sidewalls of the via. Then, a contact displacement technique is used to form a thin activation layer of copper on a barrier metal, such as TiN, which is present as a covering layer on the underlying metal layer. After the contact displacement of copper on the barrier layer at the bottom of the via, an electroless copper deposition technique is then used to auto-catalytically deposit copper in the via. The electroless copper deposition continues until the via is almost filled, but leaving sufficient room at the top in order to form an upper encapsulation layer. The SiN or SiON sidewalls, the bottom barrier layer and the cap barrier layer function to fully encapsulate the copper plug in the via. The plug is then annealed.

Use of cobalt tungsten phosphide as a barrier material for copper metallization

Abstract: A technique for electrolessly depositing a CoWP barrier material on to copper and electrolessly depositing copper onto a CoWP barrier material to prevent copper diffusion when forming layers and/or structures on a semiconductor wafer.

The effects of water chemistry on the toxicity of copper to fathead minnows

Abstract: The effects of various water chemistry parameters on the toxicity of copper to larval fathead minnows were investigated. Increased pH, hardness, sodium, dissolved organic matter, and suspended solids each caused toxicity to decrease on the basis of total copper concentrations. In contrast, added potassium resulted in increased toxicity. Alkalinity had no observed effect on total copper LC50s, but its effects might have been masked by those of the cations added with it. In most cases, the effects of water chemistry were found to be similar for different endpoints (growth, survival at different durations), but there were differences in the relative magnitude of some effects across these endpoints. Over all experimental treatments, 96-h total copper LC50s varied 60-fold. Every water chemistry parameter also caused toxicity to vary significantly when expressed on the basis of cupric ion selective electrode measurements, sometimes more so than on the basis of total copper. Therefore, this study does not support attributing to cupric ion a singular importance in regulating toxicity to this test organism. A variety of copper species might be contributing to toxicity and it is evident that toxicity is also affected by water chemistry in ways not related to copper speciation.

Electrochemical Deposition of Copper(I) Oxide Films

Abstract: Films of copper(I) oxide can be electrodeposited by reduction of copper(II) lactate in alkaline solution. Rietveld analysis of electrochemically grown films reveals pure copper(I) oxide with no copper(II) oxide or copper metal present in the films and a lattice parameter of a = 0.4266 nm. The cathodic deposition current is limited by a Schottky-like barrier that forms between the Cu2O and the deposition solution. A barrier height of 0.6 eV was determined from the exponential dependence of the deposition current on the solution temperature. At a solution pH of 9 the orientation of the film is [100], while at a solution pH of 12 the orientation changes to [111]. Atomic force images of the [100] oriented films have crystals shaped as four-sided pyramids, while the [111] films have triangular crystals. The grain size for films grown at 65 °C ranges from 2 to 5 μm. A refractive index of 2.6 was measured from the transmission spectrum for wavelengths between 1350 and 2800 nm. The p-type semiconductor has a dire...

Control of the Shape and the Size of Copper Metallic Particles

Abstract: Colloidal copper particles were prepared in aqueous solution via the reduction of copper dodecyl sulfate, Cu(DS)2, by sodium borohydrate. Below the critical micellar concentration (cmc), it has bee...

Electroless CU deposition on a barrier layer by CU contact displacement for ULSI applications

Abstract: A method of utilizing electroless copper deposition to form interconnects on a semiconductor wafer. Once a via or a trench is formed in a dielectric layer, a titanium nitride (TiN) or tantalum (Ta) barrier layer is blanket deposited. Then, a contact displacement technique is used to form a thin activation seed layer of copper on the barrier layer. An electroless deposition technique is then used to auto-catalytically deposit copper on the activated barrier layer. The electroless copper deposition continues until the via/trench is filled. Subsequently, the surface is polished by an application of chemical-mechanical polishing (CMP) to remove excess copper and barrier material from the surface, so that the only copper and barrier material remaining are in the via/trench openings. Then an overlying silicon nitride (SiN) layer is formed above the exposed copper in order to form a dielectric barrier layer. The copper interconnect is fully encapsulated from the adjacent material by the TiN (or Ta) and the SiN layers.

Protected encapsulation of catalytic layer for electroless copper interconnect

Abstract: A method for utilizing electroless copper deposition to form interconnects on a semiconductor. Once a via or a trench is formed in a dielectric layer, a titanium nitride (TiN) or tantalum (Ta) barrier layer is deposited. Then, a catalytic copper seed layer is conformally blanket deposited in vacuum over the barrier layer. Next, without breaking the vacuum, an aluminum protective layer is deposited onto the catalytic layer to encapsulate and protect the catalytic layer from oxidizing. An electroless deposition technique is then used to auto-catalytically deposit copper on the catalytic layer. The electroless deposition solution dissolves the overlying protective layer to expose the surface of the underlying catalytic layer. The electroless copper deposition occurs on this catalytic surface, and continues until the via/trench is filled. Subsequently, the copper and barrier material are polished by an application of chemical-mechanical polishing (CMP) to remove excess copper and barrier material from the surface, so that the only copper and barrier material remaining are in the via/trench openings. Then an overlying silicon nitride (SiN) layer is formed above the exposed copper in order to form a dielectric barrier layer. The copper interconnect is fully encapsulated from the adjacent material by the TiN (or Ta) barrier layer and the overlying SiN layer.

Development of copper/zinc oxide-based multicomponent catalysts for methanol synthesis from carbon dioxide and hydrogen

Abstract: The role of metal oxides such as Ga 2 O 3 , Al 2 O 3 , ZrO 2 and Cr 2 O 3 contained in Cu/ZnO-based ternary catalysts for methanol synthesis from CO 2 and H 2 was classified into two categories: to improve the Cu dispersion and to increase the specific activity The Cu/ZnO-based multicomponent catalysts developed on the basis of the role of metal oxides were highly active and stable for a long period in a continuous methanol synthesis operation

Precipitation of metal ions by plant polyphenols: optimal conditions and origin of precipitation

Abstract: Precipitation of copper(II) and zinc(II) by low molecular weight phenols, penta-O-galloyl-β-d-glucose, and commercial tannins is studied at pH 5. The extent of copper precipitation, higher than that of zinc, depends on the initial concentration of both copper and phenolic compounds and on the control of acidification which results from complexation. The copper/phenol ratio in the precipitate, determined by elemental analysis, is independent of the initial concentration of catechol. However, it increases with chestnut tannin when the metal concentration is increased to a value corresponding to complexation with all o-dihydroxyphenyl chelating groups in the molecule. Stability of the precipitates obtained with coppper(II) and various polyphenols in water, acetic acid, and ethylenediaminetetraacetic acid solutions is determined. Models for metal/polyphenol precipitation are proposed. Keywords: Polyphenols; tannins; metal ions; copper; zinc; complexation; precipitation

The importance of trace metal speciation to water quality criteria

Abstract: Because the bioavailability of a trace metal, and consequently its toxicity, is dependent on the physical and chemical form of the metal, we have presented a detailed assessment of how speciation of copper would be expected to affect its toxicity. Principles of chemical speciation are applied to demonstrate that inorganic forms will be in constant proportion to each other and to free copper ion during the course of the titration of a sample of natural water with copper or in the various treatments in a toxicity test conducted at constant pH and alkalinity. Binding of copper to dissolved organic matter or to suspended particulate matter may render the copper nonbioavailable. We have considered a simple complexation model to describe the complexation of copper to soluble ligands. Naturally occurring dissolved organic matter is present at concentrations only slightly greater than that of copper. Consequently, titration of water with copper results in a nonlinear relationship between the concentration of copper present as free copper ion plus inorganic copper species. The effects of stability constant of the complex, concentration of ligand, and the total copper concentration are evaluated. We have related bioavailable copper to the concentration of free copper ion plus inorganic copper complexes, which is valid if the pH and alkalinity of the waters used to develop a criteria are not different. On the basis of limited field data for the complexation of copper in Narragansett Bay water, we do not expect that significant differences in water quality criteria (WQC) would result if the criteria were to be based on free copper ion plus inorganic copper complexes rather than total copper concentrations. We examined the effect of speciation of copper in different waters as related to empirical or theoretically calculated water effect ratios (WER). We show that, on the basis of sound chemical principles, it would be expected that the most sensitive organisms would have the greatest WER. This prediction is confirmed by the empirical observations available. For insensitive organisms, knowledge of the concentration of ligand is sufficient to reasonably predict the WER. However, for the more sensitive organisms that give higher WERs, it is necessary to measure or calculate the speciation of copper to predict the WER. Use of predicted WERs may replace use of empirically derived WERs as is now part of regulatory guidance for derivation of site-specific WQC, if correspondence has been demonstrated.

Studies of the Formation of Cerium‐Rich Protective Films Using X‐Ray Absorption Near‐Edge Spectroscopy and Rotating Disk Electrode Methods

Abstract: The deposition of cerium-rich films on copper under cathodic polarization was studied as a model system for understanding the mechanism of corrosion inhibition of copper-containing aluminum alloys. Deposition was also studied on gold and iron for comparison with copper. Inhibition of corrosion of the aluminum alloys is achieved by deposition of a cerium-rich film on the copper-containing intermetallics that blocks the cathodic reduction of oxygen at these sites. X-ray absorption near-edge structure measurements show that cerium-rich films precipitated from aerated solutions are in the tetravalent state. Thermodynamically, the Pourbaix diagram predicts that under these conditions cerium should be in the trivalent state. This indicates that cerium chemistry is determined by processes in the solution rather than the potential of the electrode. Cerium-rich film formation is dependent on reduction of oxygen which influences the oxidation of Ce(III) to Ce(IV) in solution and precipitation of the film by changing the local pH at the electrode. The generation of hydrogen peroxide by oxygen reduction is considered to enhance cerium-rich film formation by oxidizing Ce(III) to Ce(IV) in solution. This was confirmed by addition of hydrogen peroxide to the solution.

A Trinuclear Intermediate in the Copper-Mediated Reduction of O2: Four Electrons from Three Coppers

Abstract: The reaction of metal complexes with dioxygen (O2) generally proceeds in 1:1, 2:1, or 4:1 (metal:O2) stoichiometry. A discrete, structurally characterized 3:1 product is presented. This mixed-valence trinuclear copper cluster, which contains copper in the highly oxidized trivalent oxidation state, exhibits O2 bond scission and intriguing structural, spectroscopic, and redox properties. The relevance of this synthetic complex to the reduction of O2 at the trinuclear active sites of multicopper oxidases is discussed.

Synthesis and Characterization of Copper Sulfide Nanoparticles in Triton-X 100 Water-in-Oil Microemulsions

Abstract: Nanoparticles of copper sulfide have been synthesized by reacting a copper ammonia complex with an equimolar thiourea solution in Triton-X 100/cyclohexane water-in-oil microemulsions. The presence of an exceptionally sharp and blue-shifted peak at 475 ± 2 nm in the UV−vis spectrum reveals the formation of quasi-monodispersed, size-quantized particles. Using absorption spectroscopy, the formation of a chalchocite (Cu2S) phase is inferred. The peak position in the absorption spectra was found to be independent of net micellar water content as well as aging effect. It is attributed to the formation of a Cu(I) thiourea complex on the surface of the particles, which are hydrogen bonded to the polyoxyethylene (POE) chain of Triton-X 100 (TX-100). The role of thiourea in the tailoring of particles to the micellar periphery was confirmed by synthesizing the nanoparticles using other S2- agents like H2S, and Na2S. The role of the POE chain in mediating the adsorption was brought out by carrying out the reaction in...

In-Situ XAFS, Photoluminescence, and IR Investigations of Copper Ions Included within Various Kinds of Zeolites. Structure of Cu(I) Ions and Their Interaction with CO Molecules

Abstract: The characterization of the coordination geometry of copper ions included within zeolites has been carried out with a combination of in-situ XAFS, photoluminescence, and IR measurements in order to obtain a detailed description of the formation of isolated Cu+ monomers with planar 3-coordinate or linear 2-coordinate geometry in the zeolite channels by thermal treatment under vacuum. The Cu+ ions within the zeolites were found to exist as isolated Cu+ monomers and (Cu+−Cu+) dimers, their relative concentrations strongly depending on the type of zeolite used. With ZSM-5 and mordenite zeolites, most of the copper cations were found to exist as isolated Cu+ monomers, in contrast to the case of the Y-zeolite. CO molecules were adsorbed selectively only on isolated Cu+ monomers, distorting the coordination geometry to form stable one-on-one Cu+−CO complexes.

Measurements of stress during vapor deposition of copper and silver thin films and multilayers

Abstract: Copper and silver single layer and multilayered thin films were thermal vapor deposited onto cantilevered substrates [Si(100) with native oxide] near room temperature in ultrahigh vacuum. The total force per unit width (F/w) in the film during and after deposition was determined from the change in substrate curvature measured in situ by a laser scanning technique. The intrinsic component of F/w was obtained by subtraction of the thermal component, which was obtained by measuring the product of the biaxial modulus of the film (Yf) and the difference in coefficients of thermal expansion of the substrate and the film (Δαs−f) while each sample was still in the ultra‐high vacuum deposition chamber. For all samples, the measured value of YfΔαs−f was substantially lower than the calculated value based on the {111} biaxial modulus and the coefficients of thermal expansion of the bulk materials, even though x‐ray diffraction indicated strong {111} film texture. During deposition, a general trend in F/w was found r...

Study of the reducibility of copper in CuOZnO catalysts by temperature-programmed reduction

Abstract: Temperature-programmed reduction (TPR) has been used in this work to study the reduction of copper in CuOZnO catalysts with different Cu Zn atomic ratios using H2 as reducing agent In all catalysts, CuO was completely reduced to metal The influence exerted by ZnO on the reduction of copper was evaluated for a wide range of composition and a scale of reducibility was established ZnO affects the hydrogen reduction of copper, CuOZnO samples showing a different behaviour with respect to the pure copper oxide The reduction is always promoted and, in particular, catalysts with lower copper loading (Cu:Zn

Long-term effects of copper and pH on the nematode community in an agroecosystem.

Abstract: Four copper (0, 250, 500, and 750 kg Cu · haa−1) and pH (4.0, 4.7, 5.4, and 6.1 in 1 M KCl) treatments were applied to an arable agroecosystem. Effects on the nematode community were assessed after 10 years of exposure under field conditions. Both copper and pH had major influences on nematodes. The effect of copper was generally enhanced with decreasing soil pH. The lowest copper application rate which had a significant negative effect on the total number of nematodes was 250 kg. ha−1 at pH 4.0, which is equivalent to a copper concentration of 0.32 mg.L−1 in 0.01 M calcium chloride (Cu-CaCl2). Species composition and the abundance of trophic groups were more sensitive than the total number of nematodes. Combinations of high copper and low pH significantly reduced the number of bacterial-feeding nematodes, whereas the number of hyphal-feeding nematodes increased. Omnivorous and predacious nematodes showed the most sensitive response, becoming extinct when Cu-CaCl2 was 0.8 to 1.4 mg.L−1. Plant-feeding nematodes showed the largest differences in abundance and appeared to reflect the effects of copper and pH on primary production. The results suggest that the nematode community was also affected indirectly by copper and pH via other components of the soil food web. It is concluded that nematodes offer excellent perspectives to assess effects of pollutants at the community level.

Studies on Aerobic Reactions of Ammonia/3,5-Di-tert-butylcatechol Schiff-Base Condensation Products with Copper, Copper(I), and Copper(II). Strong Copper(II)−Radical Ferromagnetic Exchange and Observations on a Unique N−N Coupling Reaction

Abstract: Stoichiometric quantities of 3,5-di-tert-butylcatechol and aqueous ammonia react in pyridine solution to form 2-amino-4,6-di-tert-butylphenol. Under an atmosphere of dioxygen the aminophenol is oxidized to either the corresponding iminosemiquinone or iminobenzoquinone. In the presence of Cu(II) iminosemiquinone condensation with the aminophenol gives the Cat-N-SQ radical ligand obtained as the Cu(py)2(Cat-N-SQ) complex. Metal and ligand magnetic orbitals are orthogonal and couple ferromagnetically to give a S = 1 molecular spin state at temperatures up to 300 K. In nonpolar solvents the complex undergoes ligand oxidation and disproportionation to give Cu(Cat-N-BQ)2. Crystallographic characterization on crystals obtained as the i-propanol solvate [orthorhombic, C2221, a = 19.548(3) A, b = 24.536(5) A, c = 23.655(5) A, V = 11346(4) A3, Z = 8, R = 0.068] show that the expected Jahn−Teller distortion appears in the trans Cu−O lengths of the equatorial plane rather than for the axial Cu−N lengths. Reactions ca...

Copper nitride and tin nitride thin films for write‐once optical recording media

Abstract: The feasibility of using copper nitride and tin nitride thin films as write‐once optical recording media was explored. The Cu3N and SnNx films were obtained by the reactive sputtering method. They were thermally decomposed into Cu and Sn films at 470 and 550 °C, respectively. The Cu film obtained by the thermal decomposition showed a large difference in reflectance which is applicable to the optical recording media. The Sn film obtained by the thermal decomposition included SnO, and consequently it showed a small difference in reflectance from that of SnNx film.

METALLIC GLASS ALLOYS OF Zr, Ti, Cu AND Ni

Abstract: At least quaternary alloys form metallic glass upon cooling below the glass transition temperature at a rate less than 103 K/s. One group of such alloys comprise titanium from 19 to 41 atomic percent, an early transition metal (ETM) from 4 to 21 atomic percent and copper plus a late transition metal (LTM) from 49 to 64 atomic percent. The ETM comprises zirconium and/or hafnium. The LTM comprises cobalt and/or nickel. The composition is further constrained such that the product of the copper plus LTM times the atomic proportion of LTM relative to the copper is from 2 to 14. The atomic percentage of ETM is less than 10 when the atomic percentage of titanium is as high as 41, and may be as large as 21 when the atomic percentage of titanium is as low as 24. Furthermore, when the total of copper and LTM are low, the amount of LTM present must be further limited. Another group of glass forming alloys has the formula: (ETM?1-x?Tix)aCub(Ni1-yCoy)c, wherein x is from 0.1 to 0.3, y?.?c is from 0 to 18, a is from 47 to 67, b is from 8 to 42, and c is from 4 to 37. This definition of the alloys has additional constraints on the range of copper content.

Cadmium and copper uptake and distribution in Mediterranean tree seedlings

Abstract: Copper and cadmium uptake and distribution in 2-week-old seedlings of stone pine (Pinus pinea L.), maritime pine (Pinus pinaster Ait.) and ash (Fraxinus angustifolia Vahl.) were investigated. Seedlings were grown in culture solution at increasing concentrations of CuSO 4 (0.012-5 μM) and CdSO 4 (0.0-5 μM). All species accumulated copper in a larger amount than cadmium. Translocation to the shoot was strongly restricted for both metals, though higher cadmium mobility within the plant could be evidenced. A strong relationship between root content and growth inhibition was detected in the roots in response to copper but not to cadmium treatments. Among species P. pinea seemed to be more tolerant to cadmium, whereas F angustifolia was highly sensitive to both cadmium and copper. X-ray microanalysis of root tip sections showed that copper and cadmium only accumulated in the root tips of F. angustifolia, copper mostly in the cell walls of the cortex layer, cadmium in the inner compartments of the cortex cells. It is suggested that in the two Pinus species the well developed root cap plays a protecting role against metal uptake at the root-tip zone.