Effect of doping with Co and/or Cu on electronic structure and optical properties of ZnO

This paper reports on ab initio numerical simulations of the effect of Co and Cu dopings on the electronic structure and optical properties of ZnO, pursued to develop diluted magnetic semiconductors vitally needed for spintronic applications. The simulations are based upon the Perdew-Burke-Enzerh generalized gradient approximation on the density functional theory. It is revealed that the electrons with energies close to the Fermi level effectively transfer only between Cu and Co ions which substitute Zn atoms, and are located in the neighbor sites connected by an O ion. The simulation results are consistent with the experimental observations that addition of Cu helps achieve stable ferromagnetism of Co-doped ZnO. It is shown that simultaneous insertion of Co and Cu atoms leads to smaller energy band gap, redshift of the optical absorption edge, as well as significant changes in the reflectivity, dielectric function, refractive index, and electron energy loss function of ZnO as compared to the doping with either Co or Cu atoms. These highly unusual optical properties are explained in terms of the computed electronic structure and are promising for the development of the next-generation room-temperature ferromagnetic semiconductors for future spintronic devices on the existing semiconductor micromanufacturing platform.

Cathodic corrosion of Cu substrates as a route to nanostructured Cu/M (M = Ag, Au, Pd) surfaces

The electrochemical formation of nanostructured materials is generally achieved by reduction of a metal salt onto a substrate that does not influence the composition of the deposit. In this work we report that Ag, Au and Pd electrodeposited onto Cu under conditions where galvanic replacement is not viable and hydrogen gas is evolved results in the formation of nanostructured surfaces that unexpectedly incorporate a high concentration of Cu in the final material. Under cathodic polarization conditions the electrodissolution/corrosion of Cu occurs which provides a source of ionic copper that is reduced at the surface-electrolyte interface. The nanostructured Cu/M (M = Ag, Au and Pd) surfaces are investigated for their catalytic activity for the reduction of 4 nitrophenol by NaBH4 where Cu/Ag was found to be extremely active. This work indicates that a substrate electrode can be utilized in an interesting manner t make bimetallic nanostructures with enhanced catalytic activity.

Electrochemical mechanism of eugenol at a Cu doped gold nanoparticles modified glassy carbon electrode and its analytical application in food samples

A simple one-step electrodeposition method was used to construct a glassy carbon electrode (GCE), which has been modified with Cu doped gold nanoparticles (GNPs), i.e. a Cu@AuNPs/GCE. This electrode was characterized with the use of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The eugenol was electrocatalytically oxidized at the Cu@AuNPs/GCE. At this electrode, in comparison with the behavior at the GCE alone, the corresponding oxidation peak current was enhanced and the shift of the oxidation potentials to lower values was observed. Electrochemical behavior of eugenol at the Cu@AuNPs/GCE was investigated with the use of the cyclic voltammetry (CV) technique, and additionally, in order to confirm the electrochemical reaction mechanism for o-methoxy phenols, CVs for catechol, guaiacol and vanillin were investigated consecutively. Based on this work, an electrochemical reaction mechanism for o-methoxy phenols was suggested, and in addition, the above Cu@AuNPs/GCE was successfully employed for the analysis of eugenol in food samples.

Self-assembly of a halogenated molecule on oxide-passivated Cu(110)

The supramolecular self-assembly of brominated molecules was investigated and compared on Cu(110) and Cu(110)[BOND]O(2×1) surfaces under ultrahigh vacuum. By using scanning tunnelling microscopy, we show that brominated molecules form a disordered structure on Cu(110), whereas a well-ordered supramolecular network is observed on the Cu(110)[BOND]O(2×1) surface. The different adsorption behaviors of these two surfaces are described in terms of weakened molecule–substrate interactions on Cu(110)[BOND]O(2×1) as opposed to bare Cu(110). The effect of oxygen-passivation is to suppress debromination and it can be a convenient approach for investigating other self-assembly processes on copper-based substrates.

Glass forming ability and stability: Ternary Cu bearing Ti, Zr, Hf alloys

Four Cu bearing alloys of nominal composition Zr25Ti25Cu50, Zr34Ti16Cu50, Zr25Hf25Cu50 and Ti25Hf25Cu50 have been rapidly solidified in order to produce ribbons. All the alloys become amorphous after meltspinning. In the Zr34Ti16Cu50 alloy localized precipitation of cF24 Cu5Zr phase can be observed in the amorphous matrix. The alloys show a tendency of phase separation at the initial stages of crystallization. The difference in crystallization behavior of these alloys with Ni bearing ternary alloys can be explained by atomic size, binary heat of mixing and Mendeleev number. It has been observed that both Laves and Anti-Laves phase forming compositions are suitable for glass formation. The structures of the phases, precipitated during rapid solidification and crystallization can be viewed in terms of Bernal deltahedra and Frank-Kasper polyhedra.

Oxidation of aqueous sulfur dioxide catalyzed by poly-4-vinylpyridine-Cu(II) complex. Part 1: Homogeneous phase oxidation

The oxidation of aqueous sulfur dioxide in the presence of polymer-supported copper(II) catalyst is also accompanied by homogeneous oxidation of aqueous sulfur dioxide catalyzed by leached copper(II) ions. Aqueous phase oxidation of sulfur dioxide of low concentrations by oxygen in the presence of dissolved copper(II) has therefore been studied. The solubility of SO2 in aqueous solutions is not affected by the concentration of copper(II) in the solution. In the oxidation reaction, only HSO3- is the reactive S(IV) species. Based on this observation a rate model which also incorporates the effect of sulfuric acid on the solubility of SO2 is developed. The rate model includes a power-law type term for the rate of homogeneous phase reaction obtained from a proposed free-radical chain mechanism for the oxidation. Experiments are conducted at various levels of concentrations of SO2 and O-2 in the gas phase and Cu(II) in the liquid phase. The observed orders are one in each of O-2, Cu(II) and HSO3-. This suggests a first-order termination of the free radicals of bisulfite ions.

The effect of ball milling on the melting behavior of Sn-Cu-Ag eutectic alloy

Sn-Ag-Cu (SAC) solder alloys are the best Pb free alternative for electronic industry. Since their introduction, efforts are made to improve their efficacies by tuning the processing and composition to achieve lower melting point and better wettability. Nanostructured alloys with large boundary content are known to depress the melting points of metals and alloys. In this article we explore this possibility by processing prealloyed SAC alloys close to SAC305 composition (Sn-3wt%Ag-0.5wt%Cu) by mechanical milling which results in the formation of nanostructured alloys. Pulverisette ball mill (P7) and Vibratory ball mills are used to carry out the milling of the powders at room temperature and at lower temperatures (-104 A degrees C), respectively. We report a relatively smaller depression of melting point ranging up to 5 A degrees C with respect to original alloys. The minimum grain sizes achieved and the depression of melting point are similar for both room temperature and low-temperature processed samples. An attempt has been made to rationalize the observations in terms of the basic processes occurring during the milling.

Metal chelates in vinyl polymerization: Bulk polymerization of acrylonitrile initiated by Cu(II)-imine complexes

This article deals with the kinetics and mechanism of acrylonitrile (AN) polymerization initiated by Cu(II)-4-anilino 3-pentene 2-one[Cu(II)ANIPO], Cu(II)-4-p-toluedeno 3-pentene 2-one [Cu(II)TPO], and Cu(II)-4-p-nitroanilino 3-pentene 2-one [Cu(II)NAPO] in bulk at 60°C. The polymerization is free radical in nature. The exponent of initiator(I) is 0.5. The initiation step is a complex formation between the chelate and monomer and subsequent decomposition of the intermediate complex giving rise to free radical and Cu(I). This is substantiated by ultraviolet (UV) and electron spin resonance (ESR) studies. The activation energies and kinetic and chain transfer constants have also been evaluated.

Effect of chlorine on the adsorption of oxygen on Cu and Ag surfaces

Based on XPS and UVPS studies, it is shown that oxygen is preferentially adsorbed molecularly in the singlet state on Cu and Ag surfaces containing presorbed chlorine. Adsorption of chlorine on Cu and Ag surfaces containing presorbed atomic oxygen causes a disappearance of the oxygen. Extended Hückel calculations predict the observed behaviour.

Systematic stability analysis of the renormalization group flow for the normal-superconductor-normal junction of Luttinger liquid wires

We study the renormalization group flows of the two terminal conductance of a superconducting junction of two Luttinger liquid wires. We compute the power laws associated with the renormalization group flow around the various fixed points of this system using the generators of the SU(4) group to generate the appropriate parametrization of an matrix representing small deviations from a given fixed point matrix [obtained earlier in S. Das, S. Rao, and A. Saha, Phys. Rev. B 77, 155418 (2008)], and we then perform a comprehensive stability analysis. In particular, for the nontrivial fixed point which has intermediate values of transmission, reflection, Andreev reflection, and crossed Andreev reflection, we show that there are eleven independent directions in which the system can be perturbed, which are relevant or irrelevant, and five directions which are marginal. We obtain power laws associated with these relevant and irrelevant perturbations. Unlike the case of the two-wire charge-conserving junction, here we show that there are power laws which are nonlinear functions of V(0) and V(2kF) [where V(k) represents the Fourier transform of the interelectron interaction potential at momentum k]. We also obtain the power law dependence of linear response conductance on voltage bias or temperature around this fixed point.

Stress-induced martensitic phase transformation in Cu-Zr nanowires

A novel stress-induced martensitic phase transformation in an initial < 100 >/{100} B2-CuZr nanowire is reported for the first time in this letter. Such behavior is observed in a nanowire with cross-sectional dimensions of 19.44 x 19.44 angstrom(2) over a temperature range of 100-400 K and at a strain rate of 1 x 10(9) s(-1) using atomistic simulations. Phase transformation from an initial B2 phase to a BCT (Body-Centered-Tetragonal) phase is observed via nucleation and propagation of {100} twinning plane under high strain rate tensile deformation. (C) 2009 Elsevier B.V. All rights reserved.

Depth profile composition studies of thin film CdS: Cu,S solar cells using XPS and AES

Surface composition and depth profile studies of hemiplated thin film CdS:CuzS solar cells have been carried out using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. These studies indicate that the junction is fairly diffused in the as-prepared cell. However, heat treatment of the cell at 210°C in air relatively sharpens the junction and improves the cell performance. Using the Cu(2p3p)/S(2p) ratio as well as the Cu(LVV)/(LMM) Auger intensity ratio, it can be inferred that the nominal valency of copper in the layers above the junction is Cut and it is essentially in the CUSS form. Copper signals are observed from layers deep down in the cell. These seem to appear mostly from the grain boundary region. From the observed concentration of Cd, Cu and S in these deeper layers and the Cu(LVV)/(LMM) ratio it appears that the signals from copper essentially originate partly from copper in CuS and partly from Cu2t trapped in the lattice. It is significant to note that the nominal valence state of copper changes rather abruptly from Cut to Cuz+ across the junction.

Complexes Of Imidazoline-2-Thione And Its 1-Methyl Analogue With Cu(Ii), Zn(Ii), Cd(Ii) And Hg(Ii) Salts

The reaction of Cu(II), Zn(II), Cd(II) and Hg(II) chlorides and bromides with imidazoline-2-thione (IZT) and its N-methyl derivative (NMIZT) yields complexes of stoichiometry ML3X2 and ML2X (IZT) and its N-methyl derivative (NMIZT) yields complexes of stoichiometry ML3X2 and ML2X (where M=Cu(I)); copper(II) halides yield Cu(I) complexes. On the basis of infrared and 13C n.m.r.

High-Tc superconductivity in the Er---Ba---Cu---O and related systems

ErBa2Cu3O7 and Er0.5Y0.5Ba2Cu3O7 are both high-Tc superconductors attaining zero resistance above 80 K. Preliminary studies indicate that Yb1−xYxBa2Cu3O7 also exhibits zero resistance above 77 K.