Showing papers on "Copper published in 1997"

Computer simulation of point defect properties in dilute Fe—Cu alloy using a many-body interatomic potential

Abstract: The behaviour of copper atoms in dilute solution in α-iron is important for the microstructural changes that occur in ferritic pressure vessel steels under fastneutron irradiation. To investigate the properties of atomic defects that control this behaviour, a set of many-body interatomic potentials has been developed for the Fe—Cu system. The procedures employed, including modifications to ensure suitability for simulating atomic collisions at high energy, are described. The effect of copper on the lattice parameter of iron in the new model is in good agreement with experiment. The phonon properties of the pure crystals and, in particular, the influence of the instability of the metastable, bcc phase of copper that precipitates during irradiation are discussed. The properties of point defects have been investigated. It is found that the vacancy has lower formation and migration energy in bcc copper than in α-iron, and the self-interstitial atom has very low formation energy in this phase of coppe...

Copper mobility in a copper-contaminated sandy soil as affected by pH and solid and dissolved organic matter

Abstract: The effects of solid, dissolved organic matter and of pH on copper mobility in a copper-contaminated sandy soil has been studied in the laboratory as well as in the field. The soil, with pH ranging from 3.8 to 5.7, had been polluted with copper in the range from 0.13 to 1.9 mmol/kg more than 1 decade ago. Copper bound by dissolved organic matter (purified humic acid) was determined by a Cu ion selective electrode (Cu-ISE) in a pH range from 4 to 8 and a free copper range from 10-4 to 10-12 mol/L. Column experiments were carried out to investigate the mobility of DOC itself and the effect of DOC on Cu mobility. Copper binding by dissolved organic matter (DOC) as well as copper binding by (soil) solid organic matter (SOC) could be described well with the non-ideal competitive adsorption (NICA) model and with the Two Species Freundlich (TSF) model. Both models could be used to predict the copper concentration at different depths in a field using the total Cu content, pH, and solid and dissolved organic matte...

Copper solubility and speciation of in situ contaminated soils : Effects of copper level, pH and organic matter

Abstract: This study attempts to identify the soil properties controlling the fractionation of copper into various soil pools and determine the influence of pH and metal loading on soil-solution free copper activity (pCu2+). The pCu2+ was determined in 0.01 M CaCl2 soil extracts using a copper ion selective electrode. We analyzed a wide variety of soils: urban, agricultural and forest soils from the Province of Quebec, New York State and Denmark. The pCu2+ ranged from 12.21 to 6.18. The relationships among pCu2+, total soil copper, total dissolved copper and soil pH are studied for their variability within and between sites as well as for the whole data set. Regression equations are presented for predicting soluble copper as a function of total soil copper and also for predicting pCu2+ as a function of total soil copper and soil pH.

Synthesis, Characterization, and Nonlinear Optical Properties of Copper Nanoparticles

Abstract: In this paper, copper nanoparticles were prepared by the reduction of copper(II) acetate in water and 2-ethoxyethanol using hydrazine under reflux. The synthesized nanoparticles exhibit a distinct absorption peak in the region 572−582 nm. The average size variation from 6.6 to 22.7 nm in ethoxyethanol and from 15.5 to 30.2 nm in water was achieved by the addition of various amounts of a protective polymer (poly(N-vinylpyrrolidone)). The nonlinear optical properties of the copper colloids were first measured using the Z-scan technique. The χ(3)/α0 values obtained were found to be of the magnitude of 10-11−10-12 esu cm, which are in good agreement with the reported values obtained for copper nanoparticles embedded in glass.

Photoluminescence and electroluminescence of ZnS:Cu nanocrystals in polymeric networks

Abstract: ZnS:Cu nanocrystals were synthesized in polymeric networks. X-ray photoemission spectroscopy and atomic absorption data show that the Zn and Cu ion mass contents were about 8.2% and 0.12%, respectively. The particle size of ZnS:Cu nanocrystals was about 3.0 nm, measured by UV-vis spectrum. Due to the quantum size effects, the band gap energy of ZnS nanocrystals was about 4.2 eV. Compared with the photoluminescence of ZnS which peaks at 390 nm, the photoemission of ZnS:Cu/polymer thin films was peaking at 415 nm because of Cu acting as luminescent centers. The ZnS:Cu/polymer was also used to fabricate light-emitting diode (LED), as the emitting layer of LED, the blue light of electroluminescence was observed at room temperature, and its turn-on voltage was less than 4 V.

Nanofabrication of Small Copper Clusters on Gold(111) Electrodes by a Scanning Tunneling Microscope

Abstract: The use of scanning tunneling microscopy in an electrochemical environment as a tool for the nanoscale modification of gold electrodes was demonstrated. Small copper clusters, typically two to four atomic layers in height, were precisely positioned on a gold(111) electrode by a process in which copper was first deposited onto the tip of the scanning tunneling microscope, which then acted as a reservoir from which copper could be transferred to the surface during an appropriate approach of the tip to the surface. Tip approach and position were controlled externally by a microprocessor unit, allowing the fabrication of various patterns, cluster arrays, and “conducting wires” in a very flexible and convenient manner.

Method for fabricating copper-aluminum metallization

Abstract: A method for fabricating copper-aluminum metallization utilizing the technique of electroless copper deposition is described. The method provides a self-encapsulated copper-aluminum metallization structure.

Optical and Photochemical Properties of Nonstoichiometric Cadmium Sulfide Nanoparticles: Surface Modification with Copper(II) Ions

Abstract: Nonstoichiometric cadmium sulfide nanoparticles ([Cd2+]/[S2-] = 3) in 2-propanol were surface-modified with Cu2+ ions. Addition of copper(II) perchlorate to CdS nanoparticles leads to binding of copper ions onto the surface of the semiconductor, accompanied by rapid reduction of Cu2+ to Cu+, as confirmed by EPR and absorption spectra. Copper(II) perchlorate also quenches the recombination luminescence of CdS nanoparticles effectively. The quenching data obey a static interaction model, which confirms the binding of copper ions onto CdS. The latter was confirmed also by ultrafiltration and ICP spectroscopy. Copper ions bound onto the surface of CdS lead to formation of a new, red-shifted, luminescence band. The maximum of the new band is at 14 700 cm-1 compared to that of the original band at 17 900 cm-1. It is suggested that, at low copper ion concentrations, copper ions bound onto the surface of CdS nanoparticles exist as isolated Cu+ ions. They create a new energy level in the bandgap at about 1.2 eV be...

Revised Pourbaix Diagrams for Copper at 25 to 300°C

Abstract: The Pourbaix diagrams (potential-pH diagrams) for copper at 25 to 300°C have been revised. Extrapolation of thermochemical data to elevated temperatures has been performed with the revised model of Helgeson-Kirkham-Flowers, which also allows uncharged aqueous complexes, such as CuOH(aq) and Cu(OH) 2 (aq), to be handled. Calculated high temperature thermodynamic data have been fitted against experimental data at elevated temperature. The hydrolysis of copper(I) and (II) is included with two and four hydroxide complexes, respectively. The Pourbaix diagrams show that the oxides (Cu 2 O(cr) and CuO(cr)) are stable at 25 to 200°C at 10 -6 mol kg -1 of dissoived species, and at 300°C only CuO is stable. The oxides are stable at 25°C at 10 -6 mol kg -1 , but at 100 to 300°C no solid compound is stable.

Method for filling high aspect ratio openings of an integrated circuit to minimize electromigration failure

Abstract: A method for filling, with a conductive material, a high aspect ratio opening such as a via hole or a trench opening within an integrated circuit minimizes the formation of voids and seams. This conductive material such as copper which fills the high aspect ratio opening is amenable for fine line metallization. The method of the present invention includes steps for enhancing copper plating processes such as copper electroplating or copper electroless plating. This method includes a first step of copper plating for depositing a thin layer of copper within the integrated circuit opening. This thin layer preferably has a thickness on the field regions surrounding the opening that is less than 1/2 of the width of the opening. Then, copper reflow heats this thin deposited copper layer within the opening to minimize the occurrence of any seams within this copper layer. Finally, a second step of copper plating completely fills the integrated circuit opening. This two-step copper plating process with intermittent copper reflow minimizes formation of seams and subsequently minimizes eletromigration failure within filled integrated circuit openings having high aspect ratio.

Evidence for polaronic supercarriers in the copper oxide superconductors La 2–x Sr x CuO 4

Abstract: High-temperature superconductivity is known to involve the pairing of charge carriers, but the precise nature of these carriers and the mechanism of their pairing remain unclear. The copper oxides are known to exhibit a strong Jahn–Teller effect — in which spontaneous lattice distortions remove the degeneracy of the electronic ground state — and it has been suggested that the charge carriers are Jahn–Teller polarons (bare charge carriers accompanied by local lattice distortions). In fact, the demonstration1 that a strong Jahn–Teller effect can lead to the formation of such polarons led to the original discovery of high-temperature superconductivity2. Still, direct evidence that Jahn–Teller polarons exist in the superconducting state of the copper oxides has been lacking, although some indirect evidence comes from their recent discovery3 in the structurally similar but non-superconducting manganite La1–xCaxMnO3. Here we report the results of magnetization and thermal expansion measurements on samples of the copper oxide superconductor La2–xSrxCuO4 which characterize the oxygen-isotope effects on the carrier density and on the in-plane penetration depth. We find a negligible isotope effect on the former, but a large effect on the latter. Specific quantitative features of the results show that polaronic charge carriers exist and condense into Cooper pairs in the copper oxide superconductors.

Partial oxidation of methanol to produce hydrogen over CuZn-based catalysts

Abstract: In this work CuZnO and Cu/ZnO/Al2O3 catalysts have been studied for the partial oxidation of methanol with oxygen to produce hydrogen. These CuZn based catalysts showed high activity for the partial oxidation of methanol and it was found that the catalytic activity is directly related to the copper metal surface area. In the series CuZn with copper relative content of 20–70 wt%, the catalyst Cu40Zn60 (Cu 40 wt% and Zn 60 wt%) which showed the highest copper area gave the best results for the partial oxidation of methanol. The activation energies and TOF (turnover frequencies) varied with the CuZn catalyst composition. For catalysts with low copper loading very high Ea and TOF were obtained (for Cu30Zn70 Ea=482 kJ/mol and TOF ca. 200 min−1 at 497–499 K) whereas for higher copper contents the Ea and TOF decreased tending to constant values (for Cu70Zn30 Ea=71 kJ/mol and TOF=160 min−1 at 497–499 K). These results are discussed in terms of a possible effect of the CuZnO interaction which depends on the catalyst composition. Catalytic experiments with Cu40Zn55Al5 (Cu 40 wt%, Zn 55 wt% and Al 5 wt%) showed that the presence of aluminium has an inhibiting effect producing slightly lower methanol conversion. On the other hand, higher selectivities for H2 and CO2 were obtained with only traces of the undesirable carbon monoxide. Moreover, the Al is very important for catalyst stability and life-time experiments showed that Cu40Zn55Al5 is stable during the partial oxidation of methanol with no significant change in activity and selectivity even after 110 h operation at 503 K. The catalyst Cu40Zn60 with no Al, deactivates rapidly after 20 h reaction at 503 K. Experiments using N2O as oxidant showed higher activity to convert methanol but producing large amounts of H2O and CO. The impregnation of catalyst with Na produced similar effect increasing the selectivity for H2O and CO. The results presented seem to indicate that the copper metal is active for partial oxidation of methanol to H2 and CO2 whereas Cu+1 favour the formation of H2O and CO. Cu+2 as CuO shows very low activity for methanol conversion producing only CO2 and H2O.

Pulse electroplating copper or copper alloys

Abstract: High aspect ratio openings in excess of 3, such as trenches, via holes or contact holes, in a dielectric layer are voidlessly filled employing a pulse or forward-reverse pulse electroplating technique to deposit copper or a copper-base alloy. A leveling agent is incorporated in the electroplating composition to ensure that the opening is filled substantially sequentially from the bottom upwardly.

Electrochemically and Photochemically Driven Ring Motions in a Disymmetrical Copper [2]-Catenate.

Abstract: By applying the three-dimensional template effect of copper(I), previously used for making various interlocking ring systems, a new disymmetrical [2]-catenate has been made which consists of two different interlocking rings. One ring contains a 2,9-diphenyl-1,10-phenanthroline (dpp) unit whereas the other cycle incorporates both a dpp motif and a 2,2',6',2''-terpyridine (terpy) fragment, the coordination site of these two chelates pointing toward the inside of the ring. Depending on the oxidation state of the central metal (Cu(I) or Cu(II)), and thus on its preferred coordination number, two distinct situations have been observed. With monovalent copper, the two dpp units interact with the metal and the terpy fragment remains free, at the outside of the molecule. By contrast, when the catenate is complexed to divalent copper, the terpy motif is bonded to the metal and it is now a dpp ligand which lies at the periphery of the complex. This dual coordination mode leads to dramatically different molecular shapes and properties for both forms. The molecular motion which interconverts the four- and the five-coordinate complexes can be triggered chemically, electrochemically, or photochemically by changing the oxidation state of the copper center (II/I). The process has been studied by electrochemistry and by UV-vis spectroscopy. Interestingly, once the stable 4-coordinate copper(I) complex has been oxidized to a thermodynamically unstable pseudo-tetrahedral copper(II) species, the rate of the gliding motion of the rings which will afford the stable 5-coordinate species (copper(II) coordinated to dpp and terpy) can be controlled at will. Under certain experimental conditions, the changeover process is extremely slow (weeks), and the 4-coordinate complex is more or less frozen. By contrast, addition of a coordinating counterion to the medium (Cl-) enormously speeds up the rearrangement and leads to the thermodynamically stable 5-coordinate complex within minutes.

Nickel filament polymer-matrix composites with low surface impedance and high electromagnetic interference shielding effectiveness

Abstract: The processing of nickel filaments of 0.4 Μm diameter gives polyethersulfone-matrix composites with high electromagnetic interference shielding effectiveness, high reflection coefficient and low surface impedance at 1-2 GHz. With 7 vol.% nickel filaments, the composite exhibited shielding effectiveness 87 dB (compared to 90 dB for solid copper), surface impedance 1.2 Ω (same as for solid copper), tensile strength 52 MPa, modulus 5 GPa, ductility 1.0%, and density 1.87 g/cm3.

Corrosion Mechanisms and Products of Copper in Aqueous Solutions at Various pH Values

Abstract: The corrosion behavior of copper in aqueous solutions of different pH values was investigated using electrochemical and surface analysis methods. It was shown that the corrosion mechanism changed with pH and was associated with morphology of the surf ace films formed. In solution of pH 3, the copper surface was covered with porous corrosion products of cuprous oxide (Cu2O). Corrosion was controlled predominately by diffusion in solution. In solutions of pH 4 to pH 5, formation of cubic Cu2O on the copper surface provided a diffusion barrier to copper dissolution. The anodic process was controlled by a mixed diffusion of copper ions in oxide films and in solution. In solutions of pH 6 to pH 9, the oxide films (Cu2O) became more protective. Diffusion in the oxide films became a rate-determining step of anodic dissolution. In pH 10 solution, a thin, compact Cu2O film formed, and spontaneous passivation was observed. At pH 12 and pH 13, analysis by x-ray photoelectron spectroscopy (XPS) and scanning ...

Chemical mechanical polishing (CMP) slurry for polishing copper interconnects which use tantalum-based barrier layers

Abstract: A method for forming a copper interconnect on an integrated circuit (IC) begins by forming a dielectric layer (20) having an opening. A tantalum-based barrier layer (21), such as TaN or TaSiN, is formed within the opening in the layer (20). A copper layer (22) is formed over the barrier layer (21). A first CMP process is used to polish the copper (22) to expose portions of the barrier (21). A second CMP process which is different from the first CMP process is then used to polish exposed portions of the layer (21) faster than the dielectric layer (20) or the copper layer (22). After this two-step CMP process, a copper interconnect having a tantalum-based barrier is formed across the integrated circuit substrate (12).

Equilibrium Parameters for the Sorption of Copper, Cadmium and Zinc Ions onto Peat

Abstract: This paper details a study into the sorption of three divalent metal ions—namely cadmium, copper and zinc—onto peat, in single component, binary and ternary systems. The Langmuir Freundlich and Redlich–Peterson equilibrium isotherms for each metal ion in each system have been determined and correlated. The Langmuir isotherms have been found to have the highest regression correlation coefficients. © 1997 SCI.

Application of Transition Metal Catalysts in Organic Synthesis

Abstract: Catalysts, Ligands and Reagents Procedures for the Preparation of Halogen Compounds Cross Coupling between 1-Alkynes and 1-Bromoalkynes Copper Catalyzed Aminoalkylation of Acetylenes Copper(I)halide Catalyzed Oxidative Coupling of Acetylenes Copper(I)halide Catalyzed Substitution of sp2-Halogen by Alkoxide Copper Catalyzed Carbon-Carbon Bond Formation by 1,1- and 1,3-Substitution Reactions Nickel Catalyzed Iodo-Dechlorination and Iodo-Debromination of sp2-Halides Nickel and Palladium Catalyzed Cyanation of sp2-Halides and sp2-Triflates Couplings of Acetylenes with sp2-Halides Nickel and Palladium Catalyzed Cross Coupling Reactions with Organometallic Intermediates.

Thermophysical properties of some key solids: An update

Abstract: In 1985, the CODATA Bulletin published a Report of its Task Group on Thermophysical Properties of Solids which analyzed available data on, and gave recommended values for, the heat capacity of Cu, Fe, W, and Al2O3, the thermal expansion of Cu, Si, W, and Al2O3, the electrical resistivity of Cu, Fe, Pt, and W, the thermal conductivity of Al, Cu, Fe, and W, and the absolute thermopower of Pb, Cu, Pt, and W. The analysts for the different properties were R. B. Castanet, S. J. Collocott, P. D. Desai, C. Y. Ho, J. G. Hust, R. B. Roberts, C. A. Swenson, and G. K. White. The present paper is an updated version of the earlier report and includes more recent data which change some of the recommended values. notably the heat capacity of Cu and W and the thermal expansion of Si and W.