Edges Of Cu Research Articles

Equipment-friendly encapsulation structure of SiO2/Cu for efficient infrared shield

SiO2/Cu equipment-friendly infrared interfering agent was built from tetraethoxysilane and flake copper powder through in-situ synthesis reaction. SEM images indicated the encapsulation structure of the samples. FT-IR, XPS and XRD spectra revealed the presence of SiO2 that was coated into the surface and edge of Cu. The shielding performance and the electrical property could be controlled by adjusting the content of SiO2. The infrared transmittance of SiO2/Cu was 23.29% at 1 ∼ 3 μm, 22.92% at 3 ∼ 5 μm and 21.70% at 8 ∼ 14 μm. The mass extinction coefficient was 1.47 m2·g−1 at 1 ∼ 3 μm, 1.48 m2·g−1 at 3 ∼ 5 μm and 1.54 m2·g−1 at 8 ∼ 14 μm, and the resistivity was 1.20 × 1010 Ω·cm at 10 MPa. There was no significant difference found between the shielding performance of Cu and SiO2/Cu. Deposition of SiO2 in this structure supplies high resistivity and excellent shielding performance, and provides highly efficient infrared interfering agent without damaging the basic structure of Cu. This work demonstrates that in-situ synthesis method is a facile and efficient strategy to obtaining optimal shielding performance of SiO2/Cu equipment-friendly infrared interfering agent and met the expectations and synthesis methods from our original material design.

Dramatic Change in the Step Edges of the Cu(100) Electrocatalyst upon Exposure to CO: Operando Observations by Electrochemical STM and Explanation Using Quantum Mechanical Calculations

Systematic structure–activity correlations in the electrochemical surface science of CO2 reduction (CO2R) are typically anchored on low Miller-index (hkl) surfaces with characterization directed at the dominant well-defined basal planes. The present investigation focused on the visualization of the step edges of unreconstructed Cu(100), with and without CO dissolved in 0.1 M KOH, at the early onset-potential region of CO2R. Operando electrochemical scanning tunneling microscopy revealed that the step-edge direction changed dramatically upon the adsorption–desorption of CO at potentials of −1.0 to −0.8 V. Quantum mechanical calculations corroborated the favorable transformation of the step-edge direction from ⟨110⟩ to ⟨001⟩ as the pristine surface was decorated by CO.

Formation of a Ti-Cu(111) single atom alloy: Structure and CO binding.

A single atom Ti-Cu(111) surface alloy can be generated by depositing small amounts of Ti onto Cu(111) at slightly elevated surface temperatures (∼500 to 600K). Scanning tunneling microscopy shows that small Ti-rich islands covered by a Cu single layer form preferentially on ascending step edges of Cu(111) during Ti deposition below about 400K but that a Ti-Cu(111) alloy replaces these small islands during deposition between 500 and 600K, producing an alloy in the brims of the steps. Larger partially Cu-covered Ti-containing islands also form on the Cu(111) terraces at temperatures between 300 and 700K. After surface exposure to CO at low temperatures, reflection absorption infrared spectroscopy (RAIRS) reveals distinct C-O stretch bands at 2102 and 2050cm-1 attributed to CO adsorbed on Cu-covered Ti-containing domains vs sites in the Ti-Cu(111) surface alloy. Calculations using density functional theory (DFT) suggest that the lower frequency C-O stretch band originates specifically from CO adsorbed on isolated Ti atoms in the Ti-Cu(111) surface alloy and predicts a higher C-O stretch frequency for CO adsorbed on Cu above subsurface Ti ensembles. DFT further predicts that CO preferentially adsorbs in flat-lying configurations on contiguous Ti surface structures with more than one Ti atom and thus that CO adsorbed on such structures should not be observed with RAIRS. The ability to generate a single atom Ti-Cu(111) alloy will provide future opportunities to investigate the surface chemistry promoted by a representative early transition metal dopant on a Cu(111) host surface.

Characterization of matrix effects for Pb L-shell energy dispersive X-ray fluorescence (EDXRF) in binary compounds of cadmium, copper, molybdenum, and zinc

Matrix effects on the intensity of characteristic L X-rays were investigated for X-ray fluorescence (XRF). Lead was selected to be the analyte and samples were prepared with powders of several elements. In XRF analysis, if the sample analyzed is a composite, the emitted characteristic X-rays of an element can be enhanced or weakened by emission from other elements. The weight fraction of Pb and accompanying element in the matrices prepared as tablets of PbCCu1-C, PbCZn1-C, PbCMo1-C and PbCCd1-C by powder metallurgy using pure powders were varied from 10% to 90% with 10% intervals. The K shell absorption edge of Cu and Zn is just below the characteristic L X-ray energies of Pb. However, Mo and Cd emits K X-rays with energies just above the L shell absorption edge of Pb when stimulated by primary photons. All samples were analyzed by XRF using a Si(Li) detector with good resolution and an Am-241 radioactive source to provide characteristic X-ray spectra. The intensities for and X-rays were plotted as a function of the Pb concentration and the results were evaluated to characterize matrix enhancement and absorption upon L-shell X-rays.

Resonant X-ray diffraction studies on modulation structures of high temperature superconducting sample Sr<sub>2</sub>CuO<sub>3.4</sub>

<sec>Sr<sub>2</sub>CuO<sub>3+<i>δ</i></sub> is cuprate, a high temperature superconducting (HTS) material that has a single copper oxide layer and a relatively high critical temperature. Its structure is simple and contains fewer atoms, but there are many modulation structures in it. A lot of studies have pointed out that the modulation structure is related to its superconductivity. In order to further study the relationship between modulated structure and superconductivity in Sr<sub>2</sub>CuO<sub>3.4</sub> HTS sample, a new explanation for the formation mechanism of modulation structure is proposed in this paper. </sec><sec>The synchrotron radiation resonant X-ray diffraction (RXD) technique is used to detect the variation of modulation structure near the absorption edge of Cu atom. Cu<sup>2+</sup>, Cu<sup>3+</sup> valence order is detected and used to explain the formation mechanism of modulation structure in Sr<sub>2</sub>CuO<sub>3.4</sub> high temperature superconducting sample. The energy values of incident light are selected to be 8.52, 8.95, 8.98, 9.05, 9.5, and 10.0 keV near the edge of Cu <i>K</i>. The energy resolution is about 1.5 eV. The detector used in the experiment is Mar165 CCD surface detector. The distance from the detector to the sample is about 315 mm. The two-dimensional diffraction pattern recorded by the CCD plane detector is processed by Fit2D software to obtain the diffraction integral intensity. In addition, the energy calibration for each of the copper foil samples is carried out prior to the start of the experiment and in the process of varying energy value.</sec><sec>The experimental results show that the Bragg diffraction peaks corresponding to <i>T</i><sub>c</sub> = 48 K and the modulation structures of <i>Fmmm</i> and <i>Pmmm</i> are visible and calibrated. The intensity of the corresponding (2/5, 4/5, 0) diffraction peak of <i>Fmmm</i> is energy-dependent near the Cu <i>K</i> edge and first increases and then decreases abruptly near the absorption edge. This indicates that a stable ordered arrangement structure of Cu<sup>2+</sup> and Cu<sup>3+</sup> is formed at this time. The weak diffraction signal of this ordered arrangement structure confirms the fact that the copper-O bonding is stronger.</sec><sec>The experiments indicate that oxygen vacancies occupy both the apical position and the CuO<sub>2</sub> plane. The ordering arrangement of oxygen vacancies results in the ordering of copper ions with variable valence. The Cu<sup>2+</sup>, Cu<sup>3+</sup> valence order is related to the superconductivity of Sr<sub>2</sub>CuO<sub>3.4</sub>.</sec>

Electronic structure and x-ray spectroscopy of Cu2MnAl1–xGax

We explore the electronic and related properties of Cu2MnAl1–xGax with a first-principles, relativistic multiscattering Green function approach. We discuss our results in relation to existing experimental data and show that the electron-core hole interaction is essential for the description of the optical spectra especially in describing the X-ray absorption and magnetic circular dichroism spectra at the L2,3 edges of Cu and Mn.

Relaxation and diffusion barriers at step edges of Cu, Ag and Au homo- and heterogeneous systems: Case of (100) facet

Abstract Using molecular dynamics simulations based on the embedded atom method, we present the calculations of adsorption and activation energies for the diffusion of adatoms (Cu, Ag or Au) on Cu (100), Ag (100) or Au (100) surfaces with steps. We have also examined the relaxation trends and bond lengths of the adatoms for both fourfold and bridge sites. We note that the vertical distance of the adatom relaxation to the first nearest neighbors is the largest (1.56 %) for Ag on Cu (100) and the shortest (–14.58 %) for Cu on Au (100) as compared to other systems. On the other hand, for Cu on the Au (100) system, we find the adatom barrier for hopping along the step edges to be 0.44 eV, which is the highest for this process among the systems studied here, but the lowest barrier is found for Ag on Cu (100) compared to other systems and costs only 0.20 eV. Attention has also been focused on the evaluations of the adsorption and activation energies for the nine systems in the presence of step edges. The diffusion barriers over and along step edges are interpreted in terms of the cohesive energies of the adatoms and substrates. Moreover, these results can offer some basic rules for forecasting precise atomic surface morphologies in homo- and hetero-epitaxial growth.

First-principles study on the electronic structures and optical properties of Cu, Fe doped LiNbO_3 crystals

The binding energies, electronic structures and optical properties of LiNbO3 and Cu/Fe doped LiNbO3 crystals are investigated by first principles based on the density functional theory in this paper. The supersell structures of crystals are established each with 60 atoms, including five models: pure LiNbO3, LN1 (Cu2+ occupy Li+ site), LN2 (Fe3+ occupy Li+ site), LN3 (Cu2+ occupy Li+site and Fe3+ occupy Li+ site) and LN4 (Cu2+ occupy Li+ site and Fe3+ occupy Nb5+ site). The optimized results show that the total energies of all models can achieve certain stable values, which means that the models accord with the actual crystal structures. The impurity energy levels of Cu and Fe doped LiNbO3 crystals appear within the band gaps, which are contributed by Cu 3d orbital, Fe 3d orbital and O 2p orbital; in co-doped LiNbO3, Cu offers deep energy level and Fe offers shallow energy level within the band gaps. There are two wide absorption peaks appearing respectively at 445 nm and 630 nm in co-doped LiNbO3 crystal, which correspond to the electron transitions from Eg orbital of Cu to Nb 4d orbital and T2g orbital of Fe to Nb 4d orbital respectively; the absorption edge of Cu, Fe mono and co-doped LiNbO3 crystals are red-shift successively, which coincides with the variation of band gape. The light absorption intensity of co-doped LiNbO3 crystal is stronger than that of mono-doped LiNbO3 crystal. The co-doped sample light absorption property is related to Fe site occupation. In this paper, it is suggested that the co-doped sample with Fe at Nb site is more competitive than that with Fe at Li site in optical volume holographic storage applications, and that reducing properly [Fe2+]/[Fe3+] value may be conducible to the formation of this advantage.

Swinging Symmetry, Multiple Structural Phase Transitions, and Versatile Physical Properties in RECuGa3 (RE = La-Nd, Sm-Gd).

The compounds RECuGa3 (RE = La-Nd, Sm-Gd) were synthesized by various techniques. Preliminary X-ray diffraction (XRD) analyses at room temperature suggested that the compounds crystallize in the tetragonal system with either the centrosymmetric space group I4/mmm (BaAl4 type) or the non-centrosymmetric space group I4mm (BaNiSn3 type). Detailed single-crystal XRD, neutron diffraction, and synchrotron XRD studies of selected compounds confirmed the non-centrosymmetric BaNiSn3 structure type at room temperature with space group I4mm. Temperature-dependent single-crystal XRD, powder XRD, and synchrotron beamline measurements showed a structural transition between centro- and non-centrosymmetry followed by a phase transition to the Rb5Hg19 type (space group I4/m) above 400 K and another transition to the Cu3Au structure type (space group Pm3̅m) above 700 K. Combined single-crystal and synchrotron powder XRD studies of PrCuGa3 at high temperatures revealed structural transitions at higher temperatures, highlighting the closeness of the BaNiSn3 structure to other structure types not known to the RECuGa3 family. The crystal structure of RECuGa3 is composed of eight capped hexagonal prism cages [RE4Cu4Ga12] occupying one rare-earth atom in each ring, which are shared through the edge of Cu and Ga atoms along the ab plane, resulting in a three-dimensional network. Resistivity and magnetization measurements demonstrated that all of these compounds undergo magnetic ordering at temperatures between 1.8 and 80 K, apart from the Pr and La compounds: the former remains paramagnetic down to 0.3 K, while superconductivity was observed in the La compound at T = 1 K. It is not clear whether this is intrinsic or due to filamentary Ga present in the sample. The divalent nature of Eu in EuCuGa3 was confirmed by magnetization measurements and X-ray absorption near edge spectroscopy and is further supported by the crystal structure analysis.

Copper Induces a Core Plasmon in Intermetallic Au(144,145)-xCux(SR)60 Nanoclusters.

The electronic structure and optical absorption spectra of intermetallic thiol-stabilized gold-copper clusters, having 144-145 metal atoms and 60 thiols, were studied by ab initio computations. The widely known icosahedral-based cluster model from the work of Lopez-Acevedo et al. (2009) was used, and clusters doped with one to 30 copper atoms were considered. When doped inside the metal core, copper induces dramatic changes in the optical spectrum as compared to the previously studied all-gold Au144(SR)60. An intense broad absorption peak develops in the range 535-587 nm depending on the amount of doping and doping sites. This result agrees very well with recent experiments by the Dass group for Au144-xCux(SR)60 (x ≤ 23). The analysis of the peaks shows a collective plasmon-like dipole oscillation of the electron density in the metal core. Internal charge transfer from copper to gold and an almost perfect alignment of the upper edges of Cu(3d) and Au(5d) bands are observed in the metal core, contributing to the plasmon-like absorption. The calculations also predict energetically preferable doping of the ligand layer by copper, but such clusters are nonplasmonic.

Cation disorder in CZTS materials from anomalous diffraction at KMC-2 (BESSY)

The compound semiconductor Cu2ZnSnS4 (CZTS) is a promising alternative for absorber layers in thin film solar cells, as it has a nearly ideal band gap of about 1.5 eV, a high absorption coefficient for visible light, and contains only earth abundant and non-toxic elements. Besides chemical composition and phase purity, the efficiency of CZTS thin film solar cells depends strongly on the concentration of Cu- and Zn-antisites and copper vacancies in the kesterite-type structure. However, Cu(I) and Zn(II) are isoelectric and thus cannot be distinguished by conventional X-ray diffraction. In prior work we determined Cu-Zn-distribution successfully from neutron scattering [1]. Here we present experiments utilizing anomalous X-ray diffraction on the K-edges of Cu and Zn. Anomalous scattering coefficients are heavily wavelength-dependent close to the absorption edges of the respective element. This is utilized for contrast enhancement. Usage of multiple wavelengths above, below and between the absorption edges of Cu and Zn ensures significant overdetermination, so that the Cu-, Zn-, and vacancy concentrations can be refined reliably for the independent crystallographic sites. Experiments were conducted at the diffraction end station of the KMC-2 beamline [2] at BESSY (Berlin, Germany). KMC-2 provides X-ray radiation with both very stable energies and intensities. The accessible energy range of 4 – 14 keV is ideally suited for the K-edges of Cu (8979 eV) and Zn (9659 eV). A 6-circle goniometer in psi-geometry allows both powder and grazing incidence diffraction, so that bulk samples and thin films can be measured. The instrument can be equipped with either a scintillation point detector (Cyberstar) or an area detector (Bruker Vantec), allowing to optimize resolution and intensity to the needs of the experiment.

平行束缪子透射成像蒙特卡罗模拟

The Monte Carlo method-based Geant4 program is used to simulate the parallel muons (which are perpendicular to the ideal detectors) injecting into the French Test Object (FTO) model. Six ideal detectors, three over the model and three under it, are used to output the positions of muons, with which the incident and scattered muons tracks can be determined. Different transmission images of the FTO model can be obtained through calculating the transmission ratio before and after the model with three methods. The resolution of the first method and the second method is 2 mm2 mm, while the resolution of the third method is 1 mm1 mm and the edge of Cu and W can be distinguished obviously. Even the air sphere in the center of the FTO model can be observed visibly. Through all the three methods, the boundaries of the FTO model and the air outside it are very clear. The simulation results of transmission imaging indicate that the methods of parallel incident muons is feasible and practicable.

First-principles study of electronic structures and optical properties of Cu, Ag, and Au-doped anatase TiO2

We perform first-principles calculations to investigate the band structure, density of states, optical absorption, and the imaginary part of dielectric function of Cu, Ag, and Au-doped anatase TiO2 in 72 atoms systems. The electronic structure results show that the Cu incorporation can lead to the enhancement of d states near the uppermost of valence band, while the Ag and Au doping cause some new electronic states in band gap of TiO2. Meanwhile, it is found that the visible optical absorptions of Cu, Ag, and Au-doped TiO2, are observed by analyzing the results of optical properties, which locate in the region of 400–1000nm. The absorption band edges of Cu, Ag, and Au-doped TiO2 shift to the long wavelength region compared with the pure TiO2. Furthermore, according to the calculated results, we propose the optical transition mechanisms of Cu, Ag, and Au-doped TiO2. Our results show that the visible light response of TiO2 can be modulated by substitutional doping of Cu, Ag, and Au.

New technique for EXAFS data processing and its application

A new technique for analysis of the extended X-ray absorption fine structure is developed. It is proposed to separate out the oscillating part of the spectra on the basis of the variational principle. By analyzing the dependence of spectrum processing results on the Fourier transform window, the boundaries of the Fourier window are found within which the Fourier analysis of spectra yields the most correct results. Using the developed technique, the spectra of human ceruloplasmin near the K edge of Cu and Li4Ti5O12 compound near the K edge of Ti were analyzed. The environment of Cu atoms in a ceruloplasmin molecule is hypothesized. The composition of the Li4Ti5O12 sample is estimated.

CO Oxidation on Inverse CeOx/Cu(111) Catalysts: High Catalytic Activity and Ceria-Promoted Dissociation of O2

A Cu(111) surface displays a low activity for the oxidation of carbon monoxide (2CO + O(2) → 2CO(2)). Depending on the temperature, background pressure of O(2), and the exposure time, one can get chemisorbed O on Cu(111) or a layer of Cu(2)O that may be deficient in oxygen. The addition of ceria nanoparticles (NPs) to Cu(111) substantially enhances interactions with the O(2) molecule and facilitates the oxidation of the copper substrate. In images of scanning tunneling microscopy, ceria NPs exhibit two overlapping honeycomb-type moiré structures, with the larger ones (H(1)) having a periodicity of 4.2 nm and the smaller ones (H(2)) having a periodicity of 1.20 nm. After annealing CeO(2)/Cu(111) in O(2) at elevated temperatures (600-700 K), a new phase of a Cu(2)O(1+x) surface oxide appears and propagates from the ceria NPs. The ceria is not only active for O(2) dissociation, but provides a much faster channel for oxidation than the step edges of Cu(111). Exposure to CO at 550-750 K led to a partial reduction of the ceria NPs and the removal of the copper oxide layer. The CeO(x)/Cu(111) systems have activities for the 2CO + O(2) → 2CO(2) reaction that are comparable or larger than those reported for surfaces of expensive noble metals such as Rh(111), Pd(110), and Pt(100). Density-functional calculations show that the supported ceria NPs are able to catalyze the oxidation of CO due to their special electronic and chemical properties. The configuration of the inverse oxide/metal catalyst opens new interesting routes for applications in catalysis.

Single crystal growth and characterization of copper aluminum indium disulfide chalcopyrites

Single crystals of Cu(Al x In 1− x )S 2 (0≤ x≤1) with x=0, 0.2, 0.4, 0.5, 0.6, 0.7, and 1.0 were grown by chemical vapor transport method using ICl 3 as a transport agent. The results of X-ray measurement indicated that the as-grown crystals are single phase and isostructural. The formation of {1 1 2} face is preferable for the crystallization of whole series Cu(Al x In 1− x )S 2 (0≤ x≤1) chalcopyrite crystals. Electronic structure of Cu(Al x In 1− x )S 2 (0≤ x≤1) was probed experimentally by X-ray photoelectron spectroscopy (XPS) and thermoreflectance (TR) measurements. The experimental results enabled to identify the electron configuration, and determine energies of valence and conduction band edges of the chalcopyrites. The energies of near-band-edge transitions in the Cu(Al x In 1− x )S 2 (0≤ x≤1) were determined accurately by TR measurements. Composition dependences of transition energies near band edge were evaluated. The obtained energies were assigned to the particular interband transitions of Cu(Al x In 1− x )S 2 (0≤ x≤1). Based on the experimental analyses of TR and XPS, the electronic band structure near the fundamental band edge of Cu(Al x In 1− x )S 2 (0≤ x≤1) was thus constructed. The good correspondence of the TR and XPS results as well as the proposed band diagram verifies the crystalline quality of the chalcopyrites.

Crystal field and low energy excitations measured by high resolution RIXS at the L3 edge of Cu, Ni and Mn

Resonant inelastic x-ray scattering in the soft x-ray regime has been profiting much from technical advances that have lowered considerably the instrumental linewidth. At the ADRESS beam line of the Swiss Light Source the SAXES spectrometer can be used to measure RIXS spectra at the L edges of the 3d transition metals with unprecedented energy resolution, of the order of 100meV for Mn, Ni and Cu. We present here some preliminary spectra on CuO, malachite, NiO, NiCl2, MnO and LaMnO3. The dd excitations are very well resolved allowing accurate experimental evaluation of 3d state energy splitting. The low energy scale becomes accessible opening the way to the study of collective excitations in strongly correlated electron systems, like magnons and orbitons.

SAXES, a high resolution spectrometer for resonant x-ray emission in the 400–1600eV energy range

We present a 5m long spectrometer for soft x rays to be used at a synchrotron radiation beamline for resonant x-ray emission spectroscopy and resonant inelastic x-ray scattering in the 400–1600eV energy range. It is based on a variable line spacing spherical grating (average groove density of 3200mm−1, R=58.55m) and a charge coupled device two dimensional detector. With an x-ray spot on the sample of 10μm, the targeted resolving power is higher than 10 000 at all energies below 1100eV and better than 7000 at 1500eV. The off-line tests made with Al and MgKα1,2 fluorescence emissions indicate that the spectrometer can actually work at 12 000 and 17 000 resolving power at the L3 edges of Cu (930eV) and of Ti (470eV), respectively. SAXES (superadvanced x-ray emission spectrometer) is mounted on a rotating platform allowing to vary the scattering angle from 25° to 130°. The spectrometer will be operational at the ADRESS (advanced resonant spectroscopies) beamline of the Swiss Light Source from 2007.

Formate-induced destabilization of the Cu(1 1 0) surface

Scanning tunneling microscopy (STM) images show that adsorbed formate has a profound affect on the step edges of Cu(1 1 0) surfaces at room temperature. For low exposures, the presence of formate enhances step fluctuations as confirmed by a correlation function analysis. For formate coverages approaching 0.5 monolayers, drastic restructuring of step edges is observed. Quantum chemical calculations help to explain this behavior.

End electronic states in Cu chains on Cu(111):Ab initiocalculations

The state-of-the-art ab initio calculations are performed to study the effect of surface-state electrons of Cu(111) on electronic states in Cu chains. We reveal the existence of localized electronic edge states at energies close to the surface-state band edge of Cu(111). These states are shown to be similar to the bound states at single adatoms on Cu(111) recently detected by the low-temperature scanning tunneling microscopy [Limot et al., Phys. Rev. Lett. 94, 036805 (2005) and Olsson et al., Phys. Rev. Lett. 93, 206803 (2004)].