Active oxidation of Cu3Au(1 1 0) using hyperthermal O2 molecular beam

Oxidation of Cu₃Au(1 1 0) using a hyperthermal O₂ molecular beam (HOMB) was investigated by X-ray photoemission spectroscopy in conjunction with a synchrotron light source. From the incident energy dependence of the O-uptake curve, the precursor-mediated dissociative adsorption occurs, where the trapped O₂ molecule can migrate and dissociate at the lower activation-barrier sites, dominantly at thermal O₂ exposures. Dissociative adsorption of O₂ on Cu₃Au(1 1 0) is as effective at the thermal O₂ exposure as on Cu(1 1 0). On the other hand, at the incident energies of HOMB where the direct dissociative adsorption is dominant, it was determined that the dissociative adsorption of O₂ implies a higher activation barrier and therefore less reactivity due to the Au alloying in comparison with the HOMB oxidation of Cu(1 1 0). The dissociative adsorption progresses with the Cu segregation on Cu₃Au(1 1 0) similarly as on Cu₃Au(1 0 0). The growth of Cu₂O for 2 eV HOMB suggests that the diffusion of Cu atoms also contribute to the oxidation process through the open face, which makes the difference from Cu₃Au(1 0 0).     

Influence of elastic scattering on the measurement of core-level binding energy dispersion in X-ray photoemission spectroscopy

We explore the interplay between the elastic scattering of photoelectrons and the surface core level shifts with regard to the determination of core level binding energies in Au(111) and Cu₃Au(100). We find that an artificial shift is created in the binding energies of the Au 4f core levels, that exhibits a dependence on the emission angle, as well as on the spectral intensity of the core level emission itself. Using a simple model, we are able to reproduce the angular dependence of the shift and relate it to the anisotropy in the electron emission from the bulk layers. Our results demonstrate that interpretation of variation of the binding energy of core-levels should be conducted with great care and must take into account the possible influence of artificial shifts induced by elastic scattering.     

Thermodynamical properties and defect energetics of an n-body potential adapted to Cu3Au

By using molecular statics, molecular dynamics, and Monte Carlo techniques we validate a previously developed empirical n-body potential adapted to Cu₃Au. At T=0 K, predicted cohesive energies, lattice parameters, and elastic constants in CuAu and CuAu₃ as well as the formation energy of vacancies in Cu₃Au are in good agreement with experimental data. A satisfactory behavior is also obtained at T 0 K in Cu₃Au, for atomic mean-square displacements and elastic moduli. However, this model underestimates the vacancy migration energy and the order-disorder critical temperature when the latter is evaluated by Monte Carlo including both exchanges between atoms of different species and atomic moves simulating vibrations.     

Andreev states and the Josephson effect in superconducting heterojunctions on thin YBa2Cu3Ox films

Conductance anomalies at low bias voltages and superconducting currents in Au/YBa₂Cu₃O_x and Nb/Au/YBa₂Cu₃O_x heterojunctions in which the c axis of the YBa₂Cu₃O_x (YBCO) epitaxial film is rotated in the (110) YBCO plane through 11° with respect to the normal to the substrate plane were studied experimentally. The films were prepared by laser deposition onto (7 2 10)-oriented NdGaO₃ substrates. The current-voltage characteristics of the heterojunctions exhibit conductance anomalies at low voltages. The behavior of these anomalies is studied at various temperatures and in various magnetic fields. The critical current and Shapiro steps observed in the current-voltage characteristics of Nb/Au/YBa₂Cu₃O_x were evidence of the Josephson effect in these heterojunctions. The experimental results are analyzed in terms of the model of the arising of bound states caused by Andreev reflection in superconductors with d-type symmetry of the superconducting order parameter.     

Cu3Au的电阻率和长程有序

基于作者最近发展的晶态合金电阻理论,本文对Cu₃Au电阻率的温度系数随长程有序度增加而增大的现象给出一个解释,用一个简单的模型赝势计算Cu₃Au的ρT及(dρT/dT),所得结果与实验资料一致。 关键词：     

Atomic configuration of microtwins in alloys having Ll2 superstructure

In the approximation of paired interatomic potentials of the Morse type, modeling is done on the atomic configuration and energy of formation of superstructure stacking faults and superstructure twinning stacking faults in the ordered alloys Cu₃Au and Ni₃Fe, and also in the intermetallide Ni₃Al. Features are observed in the local deformation of the crystal lattice defects near equilibrium (in terms of internal energy), and the principle difference in the state of the atomic surroundings of the examined plane defects is shown. In alloys of Cu₃Au and Ni₃Fe, calculations are done for different values of the long-range order parameter. A difference is detected in the variation of the energy of formation of superstructure twinning stacking faults in alloys of Cu₃Au and Ni₃Fe with the long-range order parameter. This difference correlates with experimental observation of the properties when varying the temperature in the alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 31–36, November, 1987.     

Recovery of copper alloys after neutron irradiation at low temperatures

The effects of fast neutron irradiation near 4.2°K on dilute Cu, Cu₃Au, α-CuZn, β-CuZn and CuNi alloys were studied by electrical resistivity measurements. For Cu₃Au, the recovery stage at ～ 100°K becomes more distinct with increasing long-range order, and is attributed to migration of interstitials. The ratio of the number of replacements to the number of displacements (C _R /C _F ) is estimated to be about 50 for neutron irradiation, in contrast to the previously reported value of ～2 for electron irradiation. For α-CuZn, a large recovery stage at ～150°K is found and attributed to annihilation of interstitids whose migration produces ordering. For β-CuZn, migration of interstitials also produces ordering. It is also suggested that in β-CuZn, the ratio C _R /C _F is larger for neutron irradiation than for electron irradiation as in the case of Cu₃Au. The results on CuNi alloys are presented without explanation.     

Lattice dynamics of some binary alloys

Summary The phonon dispersion frequencies for Cu₃Au, Cu₃Zn and Ni₃Fe alloys have been calculated using the model potential approach. The contribution of a short-range three-body interaction to the dynamical matrix has also been included in the present study. The theoretically computed phonon dispersion curves of these alloys are found to be in good agreement with the experimental data.     

Solid-state synthesis and atomic ordering in thin Cu/Au films (atomic ratio, Cu : Au = 3 : 1)

In situ transmission electron microscopy investigations of the processes of solid-state synthesis and atomic ordering in bilayer Cu/Au nanofilms (atomic ratio, Cu: Au = 3: 1) are conducted. It is found that solid-state synthesis starts at 170°C. A Cu₃Au atomic-disordered structure (Fm3m space group; lattice constant, a = 3.76 ± 0.01 Å) forms at 280°C. Annealing the film for 1 hour at 380°C produced a Cu₃AuI (L1₂ type) atomic-ordered superstructure, a Pm-3m space group, and lattice constant, a = 3.76 ± 0.01 Å in the bulk of the film.     

Hall Mobility of As‐Grown Cu2O Thin Films Obtained Via Electrodeposition on Patterned Au Substrates

Hall measurement of an electrodeposited Cu₂O film is rendered difficult as the bilayer structure of semiconductor on top of a conductive substrate obviates the measurement. Here, we propose the use of a patterned Au on glass substrate in line/space configuration for the Hall measurement of electrodeposited Cu₂O. A continuous, (111) oriented Cu₂O film was electrodeposited on 8 μm/2 μm Au‐line/space on glass substrate and Hall measurement was performed. The room temperature Hall measurement of the Cu₂O film on the patterned substrate indicates p‐type conduction with a hole concentration of 2.2 × 10¹⁷ cm^?3 and mobility of 4.7 × 10^?3 cm² V^?1 s^?1. Additionally, the temperature dependent resistivity exhibits a negative slope that is characteristic of a semiconductor. Therefore, the measured electrical characteristics can be attributed to the electrodeposited Cu₂O semiconductor film rather than the conductive substrate. This method can be applied for the Hall measurement of any other electrodeposited semiconductor by optimizing the line/space geometry of the conductive substrate.     

Observation of the second harmonic in the phase dependence of a superconducting current in Nb/Au/YBCO heterojunctions

The second harmonic in the dependence of a superconducting current on the phase difference of superconducting wave functions of the electrodes was observed experimentally in Nb/Au/(001)YBa₂Cu₃O_x heterojunctions. Possible reasons for its appearance were discussed within the framework of a mixed (d±s) symmetry order parameter of YBa₂Cu₃O_x.     

Long-range order in a polycrystalline Pd-30 at % Au solid solution

Using x-ray analysis, at % the existence of regions with a long-range order of the Cu₃Au type has been established in a polycrystalline Pd-30 at % Au solid solution.     

The electronic structure of ordered Cu3Au(001)

The electronic structure of the (001) face of ordered Cu₃Au was studied using synchrotron radiation at BESSY, in the photon energy range 22–80 eV. The Cu 3d-derived bands in Cu₃Au look like the foldedd-bands of fcc Cu metal. Three Au 5d-derived bands were observed at 5.0, 6.1 and 7.0 eV below the Fermi level, which showed no dispersion with change in photon energy. The Cu 3d- and the Au 5d-derived bands are found to be separated in energy. We have calculated self-consistent energy bands along the (001) direction using the fully relativistic LMTO method. Comparison of these bands with those experimentally determined shows good agreement. From the calculated bands along –X the direction dependent densities of states were determined, which give a consistent account for the non-dispersive Au-bands.     

Slip transfer at coherent twin boundaries in Ni3Al and ordered Cu3Au

Slip transfer at coherent twin boundaries in L1₂-ordered alloys has been investigated by analysis of plastically deformed Cu₃Au and Ni₃Al specimens in a transmission electron microscope. A comparison between the ex situ deformed material and previous in situ experiments is made. In ordered Cu₃Au, antiphase boundaries induced by slip transfer have been found at a coherent twin boundary (CTB), similar to the in situ deformed material. On the other hand, in Ni₃Al superlattice intrinsic stacking faults (SISFs) were detected at CTBs which have not been observed in in situ deformed material. A possible mechanism for SISF formation is discussed. The transfer of slip, and the associated creation of stacking faults at CTBs in both materials is described in terms of absorption of superdislocations in the boundary and the general criteria for slip transfer at grain boundaries.     

Geometric modelling of viscosity of copper-containing liquid alloys

In this work, viscosities of ternary Au–Ag–Cu and Al–Cu–Si liquid alloys have been calculated as a function of gold, aluminium and copper compositions for the sections Au–Ag–Cu (x_Ag/x_Cu = 0.543 at 1373 K), Al_x(Cu₅₀–Si₅₀)_(1–x) and Cu_x(Al₅₀–Si₅₀)_(1–x) at 1375 K using Chou’s general solution model, Muggianu, Kohler, Toop, Hillert, Budai et al., Kozlov et al., Schick et al. and Kaptay et al. models. The present study finds that a comparison of the predicted values of viscosities associated with the geometric and physical models indicate good mutual agreement. The Muggianu model indicates the best agreement with the results obtained for Au–Ag–Cu and Al_x–Cu₅₀–Si₅₀ alloy systems and the Kaptay et al. model, which is a physical model, indicates the best agreement with the results obtained for Al₅₀–Cu_x–Si₅₀.     

Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

Ab Initio Study on Structures and Vibrational Spectra of M+(H2O)Ar2 (M = Cu,Au)

Previous investigations have shown that it is difficult to acquire the infrared (IR) spectra of M⁺(H₂O) (M?=?Cu, Au) using a single IR photon by attaching an Ar atom to M⁺(H₂O). To explore whether the IR spectra can be obtained using the two Ar atoms tagging method, the geometrical structures, IR spectra and interaction energies are investigated in detail by ab initio electronic structure calculations for M⁺(H₂O)Ar₂ (M?=?Cu, Au) complexes. Two conceivable isomeric structures are found, which result from different binding sites for two Ar atoms. CCSD(T) calculations predict that two Ar atoms are most likely to attach to Cu⁺ for the Cu⁺(H₂O)Ar₂ complex, while the Au⁺(H₂O)Ar₂ complex prefers the isomer in which one Ar atom attaches to an H atom of the H₂O molecule and the other one is bound to Au⁺. Moreover, the calculated binding energies of the second Ar atom are smaller than the IR photon energy, and so it is possible to obtain the IR spectra for both Cu and Au species. The changes in the spectra caused by the attachment of Ar atoms to M⁺(H₂O) are discussed.     

Comparisons between statistics of low energy collision cascades generated by full molecular dynamics and by its binary collision approximation

Abstract

Collision cascades in Cu, Au and Cu₃Au are generated by full molecular dynamics (MD) and by its binary collision approximation (BCA) with the Marlowe program. Cu and Au primaries have 1 keV initial energy.

The same Molière repulsive potential is used in both models for close encounters. In the MD model, this potential is carefully splined to the pair component of the N-body potential developed by Ackland and Vitek. In the BCA, this N-body interaction is roughly modeled by a constant isotropic 4 eV binding energy of the target atoms to their rest positions.

Time distributions of the number of atoms moving with a total energy higher than a threshold value E _d are compared and discussed. Recoil range distributions during the cascade development are discussed as well. The agreement between MD and BCA is fairly good in all cases for E _d larger than about 3 eV. In the case of smaller E _d-values, the BCA may result in an overestimate of the number of moving atoms in the late development of the cascades. This discrepancy is suggested to originate in the lack of attractive forces between the moving particles and the surrounding atoms in the BCA.     

Dual structural transition in small nanoparticles of Cu-Au alloy

Cu-Au alloy nanoparticles are known to be widely used in the catalysis of various chemical reactions as it was experimentally defined that in many cases the partial substitution of copper with gold increases catalytic activity. However, providing the reaction capacity of alloy nanoparticles the surface electronic structure strongly depends on their atomic ordering. Therefore, to theoretically determine catalytic properties, one needs to use a most real structural model complying with Cu-Au nanoparticles under various external influences. So, thermal stability limits were studied for the initial L1₂ phase in Cu₃Au nanoalloy clusters up to 8.0 nm and Cu-Au clusters up to 3.0 nm at various degrees of Au atom concentration, with molecular dynamics method using a modified tight-binding TB-SMA potential. Dual structural transition L1₂?→?FCC and further FCC?→?Ih is shown to be possible under the thermal factor in Cu₃Au and Cu-Au clusters with the diameter up to 3.0 nm. The temperature of the structural transition FCC?→?Ih is established to decrease for small particles of Cu-Au alloy under the increase of Au atom concentration. For clusters with this structural transition, the melting point is found to be a linear increasing function of concentration, and for clusters without FCC?→?Ih structural transition, the melting point is a linear decreasing function of Au content. Thus, the article shows that doping Cu nanoclusters with Au atoms allows to control the forming structure as well as the melting point.