Number Of Cu Atoms Research Articles

Electrochemical formation of quantum-conductance Cu-metal nanobridges

The electrodeposition of copper with formation of narrow nanobridge contacts was investigated. Stable quantum nanobridges (QNB) with ballistic conductance have been obtained by pulsed Cu deposition/electroetching on Cr interdigitated microelectrodes nanolithographed on a quartz wafer. The minimum quantum conductance associated with monatomic-wide constriction in the nanobridge was observed. Stepped differential conductance G = ng 0 (where g 0 is the minimum quantum conductance and n = 1, 2, 3, ...) was generally observed although fractional multiples of go were also found, likely due to the deviations of the nanowire junction geometry from linear configuration and reflection losses. In the layer-by-layer Cu deposition/etching technique employed for junction formation, the current amplification associated with interdigitated electrode pattern was utilized, which allowed us for easy electrochemical control with no need for special instrumentation. Quantum mechanical calculations of the electronic structure of Cu-QNB have been carried out using small-cluster approach with configuration 14-m-14, where m denotes the number of Cu atoms in the monatomic-wide bridge, and the base electrodes are simulated by clusters with 14 Cu atoms each. The calculations performed for m = 1 to 4, indicate that corrugations of electron density along the conductance channel virtually disappear for m = 3, whereas for even number of Cu atoms in the bridge, a distinct, very narrow constriction is formed in the center of the bridge. These results corroborate earlier findings for alkali metals, for which considerable differences between odd and even number of atoms in a monatomic-wide conductance channel have been reported.

Mixed layer formation of copper overlayers on Ni(1 1 0) surface

Copper overlayer formation on the Ni(1 1 0) surface was studied by scanning tunneling microscopy (STM) in an ultrahigh vacuum. Atom-resolved STM images showed that initially deposited Cu is replaced with surface Ni atoms forming atom-size depressions on the Ni(1 1 0) terraces and a Ni-rich quasi-one-dimensional island along the [ 1 1 ¯ 0 ] direction. Further Cu deposition yields a mosaic structure on the islands, indicating Cu/Ni mixed layer formation. From the quantitative measurement of the Cu/Ni ratio on the substrate and the islands, impinging Cu will be replaced with surface Ni whereas expelled Ni and directly impinging Cu to the island form the mixed island. The number of Cu atoms in the islands, however, more than the directly impinging Cu, indicate significant Cu/Ni replacement at the periphery of the island.

Role of copper ion in preventing silver nanoparticles forming in Bi 2O 3–B 2O 3–ZnO glass

In the plasma display panel (PDP) industry, the yellowing phenomenon that occurs in the transparent dielectric decreases both optical and electrical properties greatly. The yellowing phenomenon is one of the main problems that must be solved as soon as possible. In this study, we have investigated the effect of a copper ion on the yellowing phenomenon. We had to carefully add copper oxide in the dielectric composition of the PDPs that had the yellowing phenomenon. The state of Cu atoms in the glass was determined by X-ray photoelectron spectroscopy. Cu atoms that were present were both the Cu + and Cu 2+ ions. We believed that the yellowing phenomenon could be controlled by oxidation or reduction of the number of Cu atoms. The amount of Cu 2+ ions increased due to the fact that we increased the mole fraction of CuO. When we increased the amount of Cu 2+ ions, it caused strong discoloration and decreased the transmittance of the dielectric. Therefore, the content of CuO should properly be controlled to get the best high transmittance possible. This paper presents the preliminary results for the yellowing phenomenon, which influences the transmittance of the dielectric.

First-principle studies of the geometries and electronic properties of CumSin(2 ⩽m+n⩽ 7) clusters

The equilibrium geometries and electronic properties of CumSin (2 ≤ m + n ≤ 7) clusters have been studied by using density functional theory at the B3LYP/6-311+G (d) level. Our results indicate that the structure of CuSin (n < 6) keeps the frame of the corresponding Sin cluster unchanged, while for CunSi clusters, the rectangular pyramid structure of Cu4Si is shown to be a building block in many structures of larger CunSi clusters. The growth patterns of CumSin clusters become more complicated as the number of Cu atoms increases. Both the binding energies and the fragmentation energies indicate that the Si-Si bond is stronger than the Cu-Si bond, and the latter is stronger than the Cu-Cu bond. Combining the fragmentation energies in the process CumSin → Cu+Cum-1Sin and the second-order difference Δ2E(m) against the number of Cu atoms of CumSin, we conclude that CumSin clusters with even number of Cu atoms have higher stabilities than those with odd m. According to frontier orbital analyses, there exists a mixed ionic and covalent bonding picture between Cu and Si atoms, and the Cu d orbitals contribute little to the Cu-Si bonding. For a certain cluster size (m + n = 3, 4, 5, 6, 7), the energy gaps of the most stable CumSin clusters show odd-even oscillation with changing m, the clusters with odd m exhibit stronger chemical reactivity than those with even m.

A new class of “all-metal” aromatic hydrido-bridged binary coinage metal heterocycles. A DFT study

Electronic structure calculations (DFT) suggest that the series of hydrido-bridged binary coinage metal clusters with general formulae cyclo-CunAg3−n(μ2-H)n (n = 1–3), cyclo-CunAg4−n(μ2-H)n (n = 1–4) and cyclo-CunAg5−n(μ2-H)n (n = 1–5) are stable entities. The aromaticity of these bimetallic systems was explored by employing a number of established criteria such as the nucleus-independent chemical shift, the hardness, η, and the electrophilicity index, ω. Aromaticity decreases upon increasing the number of Cu atoms in the metallic ring core structure or increasing its size. The structural, energetic, spectroscopic (IR, NMR, UV-Vis) and electronic properties of these novel classes of inorganic compounds characterized by a common ring-shaped electron density are thoroughly analyzed. The hydrido-bridged binary coinage metal clusters exhibit a composite bonding mode involving both σ-, π- and δ-type components. Noteworthy is the presence of π-type MOs resulting from the bonding interaction of nd AOs of the metal atoms, delocalized over the entire metallic framework analogous to the π-type MOs of the aromatic hydrocarbons.

On the Disorder of the Cl Atom Position in and Its Probable Effect on the Magnetic Properties of (CuCl)LaNb2O7

The magnetic susceptibility of (CuCl)LaNb2O7 shows a spin gap despite the Cu(2+) ions in each CuClO2 layer forming a square lattice. To account for this observation, we explored implications of the disorder of the Cl-atom position in (CuCl)LaNb2O7 by considering possible ordered structures of CuCl4O2 octahedra in each CuClO2 layer, by identifying various spin exchange interactions of a CuClO2 layer and by estimating the relative strengths of these interactions in terms of spin dimer analysis. We then probed what kind of spin lattice is required for each CuClO2 layer to have a spin gap on the basis of the classical spin approximation. Our study suggests that the CuCl4O2 octahedra of each CuClO2 layer should be arranged such that the resulting spin lattice does not have uniform chains but ring clusters containing an even number of Cu atoms. Implications of this conclusion were discussed on the basis of the recently reported neutron scattering and magnetization studies of (CuCl)LaNb2O7.

Kinetic study of copper precipitates under VVER-type reactor conditions

The copper-rich cluster evolution in the neutron-irradiated VVER steels is investigated beginning at the nucleation stage. For this, typical VVER-type reactor conditions are considered. The cluster dynamics approach is used for calculation of the density distribution of copper precipitates related to the number of Cu-atoms or radius, mean radius, volume content, number density of precipitates and the concentration of free Cu-atoms in dependence on the irradiation time. The results for time of one year are compared with the results of small angle neutron scattering experiments which were carried out on specimens irradiated at the surveillance positions of VVER reactors. It has revealed the intermediate type of the evolution kinetics between diffusion and interfacial kinetics limited regimes. The duration of the nucleation and deterministic stages is estimated. The coarsening stage does not occur.

Structures and energies of vacancy-Cu clusters in α-Fe

We study structures and energies of vacancy-Cu clusters in $\ensuremath{\alpha}$-Fe, which provide fundamental information for understanding the mechanism of neutron-irradiation embrittlement of nuclear reactor pressure vessel materials. Extensive molecular-dynamics (MD) and Monte Carlo computer simulations with the use of the embedded atom method (EAM) potential for the Fe-Cu system are performed to obtain energy-minimum structures of vacancy-Cu clusters of various sizes in a $\ensuremath{\alpha}$-Fe matrix. We find that, in general, a vacancy-Cu cluster consists of a vacancy cluster buried at the center of a Cu shell. The formation energies for the vacancy-Cu clusters are calculated from the MD results, and we develop an equation describing the formation energy as a function of the numbers of vacancies and Cu atoms. We find that the number of Cu atoms on the surface of the vacancy cluster plays an important role in determining the formation energy of the vacancy-Cu clusters. The binding energies of a vacancy and a Cu atom to the vacancy-Cu clusters are also calculated. We find that the interaction between vacancies and Cu atoms enhances the binding of the vacancy-Cu clusters.

X-ray photoelectron diffraction study of discommensurate Cu/Ge(111)

We have studied the atomic structure in the interior of discommensurate domains of the Cu/Ge(111) surface by using scanned-angle X-ray photoelectron diffraction (XPED). XPED patterns of Cu 2p 3/2 intensity provided direct information on the local structure in the vicinity of photoelectron emitters. It has been found that a certain number of Cu atoms are embedded within the surface layer, so that the surface has some structural similarity with the discommensurate Cu/Si(111)-‘5×5’.

Molecular dynamics simulation of Cu and Ar ion sputtering of Cu (111) surfaces

In ionized physical vapor deposition, used in Cu interconnect technology, the interaction of energetic ions with the growing Cu film is sensitive to both the impact angle and the energy. Detailed information, such as the angle and energy dependence of the sputter yield and sticking probability, is required for realistic feature scale modeling of film coverage in the metallization of micron-sized features (vias and trenches) in integrated circuits. Here we describe the results of molecular dynamics (MD) simulations of sputtering of Cu (111) surfaces by Cu and Ar ions suitable for incorporation into feature scale simulations. For each impact angle and energy considered (10–100 eV for Cu ions and 50–250 eV for Ar ions), the following averaged properties were calculated: sputter yield (number of Cu atoms sputtered per impact), sticking probability, thermal accommodation coefficient, average reflection angle of the impact ion, and average emission angle of the sputter products. The calculated sputter yields and energy threshold at normal incidence for both Ar and Cu sputtering of Cu are in good agreement with experiment and other MD simulations. Detailed comparisons are also made with previously reported sputter yields calculated with binary collision theory.

Magnetic hyperfine fields at 111 In probes in submonolayer Cu islands on Co(1 0 0) surfaces

Cu islands in the submonolayer coverage regime deposited on Co(1 0 0) have been studied utilizing the PAC spectroscopy. The 111In PAC probes are incorporated into the topmost monolayer, which is corroborated by the presence of a rather unique electric field gradient. In addition, weak magnetic hyperfine fields Bhf between 1.9(2) and 0.37(4) T have been observed depending on the Cu coverage. This is attributed to next neighbours of the PAC probes consisting of mixed Co/Cu configurations. A linear decrease of Bhf as a function of the number of Cu atoms replacing Co is found.

Structure and magnetic properties of SmCo5−xCux alloys

The magnetic properties of polycrystalline SmCo5−xCux (x=1, 1.5, 2, 2.5, 3, 4) samples were studied in the as-cast state as well as after annealing. The Curie temperature decreases whereas the lattice constant increases with increasing Cu content. The hysteresis loop was measured between 10 and 900 K using a pulsed-field system. The coercivity field shows strong time dependence. The temperature dependence of the coercivity and the time dependence are analysed using common models for the magnetic aftereffect. The results strongly support the major effect of the number of Cu atoms acting as local defects on the concentration, time and temperature dependence of the coercivity.

Copper speciation in sulfidic solutions at low sulfur activity: Further evidence for cluster complexes?

The solubility of two a s 0 -buffering assemblages in the Cu-S system have been studied: chalcocite-djurleite (Cc-Dj) and anilite-covellite (An-Cv). Ion activity products, [Cu +]HS −] 1 2 [H +] − 1 2 (25°C, I = 0) at equilibrium, derived from solubility measurements in penicillamine solutions, are 10 −17.01 ± 0.05 (Cc-Dj) and 10 −17.14 ± 0.10 (An-Cv), from which ΔG° f = −82.11 kJ/mol for Cc and −74.77 kJ/mol for An. In the An-Cv assemblage, a Cu 2 S = 0.55 (2 σ = 0.2) vs. 1.00 in the Cc-containing assemblage. The difference in a Cu 2 S between the two assemblages is used in a novel way to estimate stoichiometry of Cu-HS complexes. The solubility of both assemblages (0.7-0.01 M NaHS, pH 7–12.5, 25°C) can be fit with a model incorporating the same two chemical species, one containing an odd number of Cu atoms (Cu(HS) 2− 3, CU 3S 4H 2− 3, or a higher multimer) and the other containing an even number of Cu atoms (Cu 2S(HS) 2 2−, Cu 4S 4H 2 2−, etc.). The trimer-tetramer model fits the combined data for the two assemblages distinctly better than the monomer-dimer model, but this result is very sensitive to uncertainty in a Cu 2 S. Along with EXAFS results, the weight of the evidence favors small cluster complexes (2–5 Cu atoms), but is inconclusive at the present level of resolution. Multimers can be rationalized because condensation of metal-centered monomers to clusters provides a means for soft acid/base elements to maintain favored coordination geometries at low ligand to metal ratios. Based on the fitting methods developed here, previous covellite solubility data from this laboratory are reinterpreted in terms of Cu 2S 2(HS) 3 3−, Cu 2S 3)(S 4) 2−, and Cu(S 9)S 10) 3−; the last of these could also be represented by the trimer, Cu 3(S 7) 3 3−, which is homologous with a known complex. With the measured equilibrium constants, the speciation of Cu in the sulfidic zone of the Black Sea is calculated. Covellite is the stable Cu-S mineral, but the sulfidic water column is vastly supersaturated with respect to it. Most of the sulfidic water column is modestly (2.5–5.5 times) supersaturated with respect to Cc, hinting that this mineral metastably controls ΣCu. The slight supersaturation suggests that Cc occurs as 10–100 nm particles.

A scanning tunneling microscopy study of the interaction of S with the Cu(111) surface

The interaction of sulfur with the Cu(111) surface has been studied with scanning tunneling microscopy in conjunction with low-energy electron diffraction. Two different phases have been observed. At low exposures, ∽ 20 langmuir of H 2S at room temperature, a previously unknown commensurate phase, which is present in six equivalent domain orientations, has been identified as | 4 1 −1 4 | in matrix notation. At higher exposures, a phase transition to a (√7 X √7)R19° structure takes place. During formation, Cu atoms are consumed from step edges. This indicates that the observed phases are not simple S overlayer structures, but involve a reconstruction of the Cu surface to a sulphide overlayer. By measuring the step area consumed as a function of exposure, the number of Cu atoms in the unit cells of the two phases has been determined. The concentration of the S atoms in the ( 7 × 7 )R19° phase has been measured with Rutherford backscattering.

Thin-film growth of Sn On Cu(100)

The deposition of Sn on a Cu(100) surface has been investigated as a function of layer thickness, deposition temperature and subsequent anneal treatment, using a combination of RBS/channeling, LEED and Auger spectroscopy measurements. No evidence of pseudomorphic Sn growth could be detected. At Sn coverages up to about one monolayer, RBS/channeling data indicate that Sn atoms displace a comparable number of Cu atoms from their regular lattice sites, even at the lowest (170 K) deposition temperature studied. LEED studies show evidence of two-dimensional commensurable phase formation whose structure depends strongly on anneal temperature and Sn coverage. Copper-rich phases such as the ϵ-phase (Cu 3Sn) are not observed at submonolayer Sn coverage, even after a 525 K anneal treatment. Thicker Sn layers exhibit two major anneal stages: formation of the η′-phase (Cu 6Sn 5) around 265 K and its subsequent conversion into the ϵ-phase (Cu 3Sn) around 420 K. An isochronal anneal measurement yielded activation energies of 0.65 ± 0.05 and 1.07 ± 0.08 eV for interdiffusion of Sn and Cu in the η′- and ϵ-phases, respectively. RBS/channeling data indicate that the resulting η′-phase is partially (10%–20%) aligned with the Cu(100) substrate. No preferential orientation was observed for the ϵ-phase.

ChemInform Abstract: ELECTRODEPOSITION OF COPPER ON PLATINUM(111) SURFACES PRETREATED WITH IODINE. STUDIES BY LEED, AUGER SPECTROSCOPY, AND ELECTROCHEMISTRY

AbstractDurch Vorbehandlung von Pt(l l U‐Oberflächen mit Iz‐Dampf im Ultrahochvakuum wurde ein Pt(l l l)( /7 x /7)R19.l ° ‐ I‐Übergitter gebildet, daß die Pt‐Oberfläche und die Oberfläche der späteren galvanischen Cu‐Schicht gegen den Angriff des Elektroä lyten und die Verunreinigung durch Restgase schützt.

Electrodeposition of Copper on Platinum (111) Surfaces Pretreated with Iodine: Studies by LEED, Auger Spectroscopy, and Electrochemistry

Studies by low energy electron diffraction (LEED) and Auger spectroscopy of copper electrodeposited on well‐characterized platinum (111) surfaces from aqueous sodium perchlorate solutions are reported. Prior to electrodeposition, the platinum (111) surface was pretreated with vapor in ultrahigh vacuum to form a Pt(111) R19.1°‐I superlattice, which protected the platinum surface and the surface of the electrodeposit from attack by the electrolyte and contamination by residual gases. The results were as follows: electrodeposition took place in two narrow, overlapping underpotential deposition linear scan voltammetric peaks followed by one conventional bulk copper deposition peak. Underpotential deposition produced an ordered layer. The first underpotential deposition peak formed a superlattice in which the unit cell contained four iodine atoms and a comparable number of Cu atoms per nine surface Pt atoms . At completion of the underpotential deposition process a coincidence lattice was present in which and . The iodine Auger signal was not appreciably affected by Cu deposition, indicating that the iodine atoms were present in the topmost layer of the surface at all Cu coverages.

Ascorbate oxidase: Properties of the copper sites and catalytic activity of the native and type 2 Cu depleted enzyme

Ascorbate oxidase (L-ascorbate: O 2 oxidoreductase, E.C. 1.10.3.3) is the subject of numerous biological investigations. Some of the recent developments in the purification of the enzyme, the number of Cu atoms per active molecule, the stoichiometry of the different Cu sites and the mechanism of reduction by L-ascorbate have been previously reviewed [1]. Ascorbate oxidase from squash Cucurbita p.m. contains 8 Cu atoms/140 000 M r of which 50% are detectable by electron paramagnetic resonance (EPR), i.e. three type-1 Cu, one type-2 Cu and four type-3 Cu [2]. The number and stoichiometry of different Cu sites depend very much on environmental conditions maintained during the process of isolation and purification, such as pH, ionic strength or presence of metal chelators. Thus, dialysis of pure enzyme against acetate buffer, pH 4.5–5.5, may lead to drastic changes in the visible region of the electronic spectra (indicated by a decrease of the purity index A 610/A 330 [1]) and of the EPR spectra (indicated by a decrease of the type-1 signal). In the presence of metal chelators, such as EDTA or dimethylglyoxime [3], the type-2 center is removed selectively (= t2d enzyme) as demonstrated by EPR spectroscopy. Depending on dialysis conditions (pH, concentration of metal chelator, aerobic vs. anaerobic) up to four Cu atoms will be dialysed off. As epxected, the activity of these enzyme samples is lowered to less than 4% of the original activity present. The so-called t2d enzyme (5.8 ± 0.3 Cu/140.000 M r) is still reduced by L-ascorbate in the absence of dioxygen, approx. 5.5 electron equivalents are used for total bleaching of the absorbance at 610 nm. Upon exposure to air, enzyme reoxidation begins as indicated by the appearance of the typical blue color (λ max 610 nm) and the type-1 Cu EPR signal. By comparison with native ascorbate oxidase this seems to be a relatively slow process, complete reoxidation is received after a few minutes at 20 °C, pH 7.0. The time course of the reaction of reduced ascorbate oxidase, or reduced t2d enzyme, with dioxygen was followed by stopped-flow spectrophotometry and rapid-freeze EPR spectroscopy. Prior to reaction with molecular oxygen the protein is reduced by an excess of L-ascorbate (6–8 equivalents of reductant per enzyme), hereafter mixing with O 2/buffer solution is achieved under the strict exclusion of air at temperatures between 5 and 10 °C [1]. In the first rapid phase of the reoxidation of the native enzyme (2–4 msec) the characteristic absorption spectrum and EPR signal of the L-ascorbate radical (λ max 365 nm, g = 2.005) can be detected [1], due to the turnover of the enzyme in the presence of reducing substrate and dioxygen. Total reoxidation of ascorbate oxidase occurs very rapidly, within less than 8 msec at 10 °C as shown optically by the appearance of absorbance at 610 nm and by EPR. By comparison with untreated ascorbate oxidase the reduced t2d enzyme is far less reactive towards dioxygen, the reoxidation process takes several minutes under identical conditions of pH, ionic strength, temperature and oxygen concentration. From the kinetic experiments on the anaerobic reduction of ascorbate oxidase and oxidation of the reduced enzyme conclusions are drawn concerning the modes of internal and external electron transfer. Furthermore, mechanistic aspects of the catalytic function of the multicopper oxidase are discussed.

Secondary molecular ion emission from some CuBe and CuAl alloys

Experimental results are presented on cluster ions sputtered by primary ion bombardment from some CuBe and CuAl alloys. Emission intensities of these aggregates present alternations according to the parity of the number of Cu atoms: CunBem cluster ions behave as Cun+ ions with enhancement of n odd numbered ions; CunAlp cluster ions are found to be favoured when n+p is odd. These intensity maxima and minima are related to the external electronic structure and an attempt is made to explain this peculiar behaviour from the Huckel model.