Length Of Cu Research Articles

Insight into Copper Doping Ratio on Optoelectronics Performance of Two-Dimensional Cu-Doped SnO2 Nanosheets: an Experiment and DFT Study

The optoelectronics performances of two-dimensional Cu-doped SnO2 nanosheets were investigated by first-principles calculations on the basis of density functional theory (DFT) and experiments. First, the crystal structures of Cu-doped SnO2 were built and analyzed by using DFT within the generalized gradient approximation (GGA). The total energy of Cu-doped SnO2 was discussed qualitatively and quantitatively from three aspects: charge density, band structure, and state density. The results show that copper doping has little effect on the charge density distribution because of the similar ionic radius of Cu2+, Sn4+, and the close bond lengths of Cu–O and Sn–O. The calculation results of band structure and state density show that the doping of a copper acceptor leads to the appearance of a new energy level at the top of the valence band and decreases the band gap of SnO2. With the guidance of theoretical calculation, the nanosheets of Cu-doped SnO2 are constructed experimentally, and their optoelectronics performances are investigated. The experimental results exhibit that the Cu atom replaces the Sn atom in the SnO2 lattice, while the Cu-doped SnO2 retains the original rutile phase of the intrinsic SnO2. The sample with a doping ratio of 12.5% has more uniform particle morphology and dispersion characteristics. In addition, the 12.5% Cu-doped SnO2 obtained the largest transient photocurrent of 3 μA/cm2 and the lowest resistance to charge transfer, thereby indicating that the material has a remarkably higher optoelectronics performance under this ratio. The theoretical calculation and experimental results are consistent, which indicates that Cu doping effectively enhances the charge transfer in SnO2 and enables it for high-quality application in optoelectronic catalysis.

Construction of Synergistic Co and Cu Diatomic Sites for Enhanced Higher Alcohol Synthesis

Construction of Synergistic Co and Cu Diatomic Sites for Enhanced Higher Alcohol Synthesis

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Computational studies of the electronic structure of copper-doped ZnO quantum dots

Copper-doped ZnO quantum dots (QDs) have attracted substantial interest. The electronic structure and optical and magnetic properties of Cu3+(d8)-, Cu2+(d9)-, and Cu+(d10)-doped ZnO QDs with sizes up to 1.5 nm are investigated using the GGA+U approximation, with the +U corrections applied to d (Zn), p(O), and d(Cu) orbitals. Taking +Us parameters, as optimized in previous bulk calculations, we obtain the correct band structure of ZnO QDs. Both the description of electronic structure and thermodynamic charge state transitions of Cu in ZnO QDs agree with the results of bulk calculations due to the strong localization of Cu defect energy levels. Atomic displacements around Cu are induced by strong Jahn-Teller distortion and affect Kohn-Sham energies and thermodynamic transition levels. The average bond length of Cu-O and the defect structure are crucial factors influencing the electronic properties of Cu in ZnO QDs. The analysis of the optical properties of Cu in ZnO QDs is reported. The GGA+U results, compared with the available experimental data, support Dingle's model [Phys. Rev. Lett. 23, 579 (1969)], in which the structured green luminescence observed in bulk and nanocrystals originates from the [(Cu+, hole) → Cu2+] transition. We also examine the magnetic interaction between the copper pair for two charge states: 0 and +2, and four positions relative to the center of QDs. Ferromagnetic interaction between ions is obtained for every investigated configuration. The magnitude of ferromagnetism increases for positive charge defects due to the strong hybridization of the d(Cu) and p(O) states.

Determination of spin diffusion length in Bi [formula omitted]-doped Cu films by weak antilocalization measurements

Working with the weak antilocalization measurements, we investigate the spin diffusion length in Bi δ-doped Cu films with the fine-tuned Bi concentration. By exploiting the long spin diffusion length of Cu and the strong spin-orbit coupling of Bi with the δ-doping technique, the spin diffusion length can be tuned artificially. Furthermore, it is found that the spin relaxation is dominated by elastic scatterings from Bi impurities in Bi δ-doped Cu systems, which follows the Elliott-Yafet mechanism.

Reliability analysis of horizontally loaded pile considering spatial variability of soil parameters

In the design and analysis of pile foundations, the horizontal load is an important factor that needs to be considered. The reliability analysis can take the uncertainty of various parameters into consideration and thus reduce the design deviations, especially the uncertainty of soil parameters. This paper proposes a reliability analysis method considering the spatial variability of soil for the horizontally loaded pile. Firstly, a parameter sensitivity analysis was performed by the Sobol sensitivity method, and the critical variables, including the undrained shear strength Cu, the soil strain ε50, which represents the soil strain when principal stress difference reaches half (50%) of the maximum value in triaxial test, and the horizontal load and applied moment, are identified and taken as the random variables. Moreover, the spatial variability of soil parameters (Cu and ε50) are simulated as one-dimensional random field through the orthogonal series expansion method. The failure probabilities of pile foundation under the failure modes of deflection and strength are evaluated by Monte Carlo simulation. Finally, the proposed method is verified through case study in which the influences of the spatial variability of soil parameters, the uncertainty of the horizontal load on the failure probability were investigated. The results show that the uncertainty of horizontal loads and Cu make significant effects on the reliability of pile foundations. The increase of correlation length of Cu and ε50 will lead to the increase of the mean value of pile response, which has different effects on the failure probability under different failure modes.

Effects of minor alloying with Ge and In on the interfacial microstructure between Zn–Sn solder alloy and Cu substrate

The interfacial reactions of Zn30Sn (ZS), Zn30Sn-1Ge (ZS-1Ge), and Zn30Sn–1In (ZS-1In) on the Cu substrate were investigated. After reflowing at 450 °C for 5 min, the ε-CuZn5 (scallop-type), γ-Cu5Zn8 (flat-type), and β’-CuZn (flat-type) intermetallic compounds (IMCs) formed at the interface between the solders and Cu substrate. Phase transformation from ε-CuZn5 and β’-CuZn to γ-Cu5Zn8 was observed with an increasing aging time at 150 °C. The growth of γ-Cu5Zn8 layer was accompanied by the decrease of ε-CuZn5 and β’-CuZn layers. After aging for 360 h. γ-Cu5Zn8 layer became the main IMC layer at the interface. The addition of Ge and In decreased the diffusion rate of Cu and Zn in the intermetallic layer (IML). The first-principles calculations indicated that the diffusion activation energy per unit length of Cu and Zn atoms crossing a specific diffusion channel was similar. Based on first-principles calculations, the atomic concentration ratios of Cu to Zn in the three Cu–Zn IMC phases were calculated via a simple model. When the atomic concentration ratio of Cu to Zn exceeded 0.528, ε-CuZn5 transformed into γ-Cu5Zn8, and when the ratio of Cu to Zn was less than 0.838,β’-CuZn transformed into γ-Cu5Zn8. In addition, the precipitation of Sn–Ge and Sn–In solid phase at the IML suppressed the IMC growth. Accordingly, the diffusivity of Cu on the IMC layer of ZS, ZS-1Ge and ZS-1In solders was calculated to be 5.8 × 10−7, 5.7 × 10−7 and 4.6 × 10−7 m2/s, respectively.

Atomically Defined Undercoordinated Active Sites for Highly Efficient CO2 Electroreduction

AbstractElectrocatalytic reduction of carbon dioxide (CO2ER) in rechargeable Zn–CO2 battery still remains a great challenge. Herein, a highly efficient CO2ER electrocatalyst composed of coordinatively unsaturated single‐atom copper coordinated with nitrogen sites anchored into graphene matrix (Cu–N2/GN) is reported. Benefitting from the unsaturated coordination environment and atomic dispersion, the ultrathin Cu–N2/GN nanosheets exhibit a high CO2ER activity and selectivity for CO production with an onset potential of −0.33 V and the maximum Faradaic efficiency of 81% at a low potential of −0.50 V, superior to the previously reported atomically dispersed Cu–N anchored on carbon materials. Experimental results manifest the highly exposed and atomically dispersed Cu–N2 active sites in graphene framework where the Cu species are coordinated by two N atoms. Theoretical calculations demonstrate that the optimized reaction free energy for Cu–N2 sites to capture CO2 promote the adsorption of CO2 molecules on Cu–N2 sites; meanwhile, the short bond lengths of Cu–N2 sites accelerate the electron transfer from Cu–N2 sites to *CO2, thus efficiently boosting the *COOH generation and CO2ER performance. A designed rechargeable Zn–CO2 battery with Cu–N2/GN nanosheets deliver a peak power density of 0.6 mW cm−2, and the charge process of battery can be driven by natural solar energy.

Generation and Detection of Pure Spin Current in an H-Shaped Structure of a Single Metal.

Distinct from all the existing methods for determining the spin Hall angle with bilayers, we have developed a new approach based on the mesoscopic H-shaped structure, which generates and detects pure spin current in a single metal. Using this approach we have unequivocally addressed the long-standing controversy of the magnitude of the spin Hall angle of gold. By exploiting the long spin diffusion length of Cu and the large spin-orbit coupling of Bi, we have realized a very large spin Hall effect in 10nm Cu films delta doped with 0.15nm of Bi. This new artificial material can generate a large spin-orbit torque to switch an adjacent Fe layer. We have thus demonstrated new artificial materials with a simultaneously large spin Hall angle and long spin diffusion length.

An experimental and theoretical study on soft chemically grown CuS thin film for photosensor application

Herein we report, the photosensitivity of in-situ chemical bath deposition (CBD) grown CuS thin film for the first time, also comparatively very short deposition time of 40min and much lower bath temperature i.e. 45°C are reported. The structural, surface topographical, optical, electronic and electrical properties of as-grown CuS thin film have been investigated. The XRD analysis revealed the formation of Orthorhombic (Covellite) structure with preferential growth along [113] direction having ~14nm average crystallite size. Raman spectrum indicating a sharp peak at 474cm−1 confirms the formation of CuS covellite structure. Polycrystalline nature of the film has been confirmed from the concentric ring pattern obtained from TEM–SAED and AFM revealed the rough surface topography with RMS roughness of ~27nm. The bond lengths of Cu(1)-S(1) and S(1)-S(1) were obtained from the DFT calculations based on GGA approximation, suggest S-S bond is much stronger as compared to Cu-S bond; these results are in good agreement with the Raman result. The film shows higher absorbance in the visible region with a band gap of 2.2eV. The electrical properties show a drastic increase in current after light illumination of 50 W which increases with increasing light intensity and tends to attain a saturation state around 200 W. The highest photosensitivity of ~66% has been calculated for 200 W with fast response time of ~34s and a complete recovery. These results represent CuS thin films promising candidature for photosensor application.

The Structure of the Cu–CuO Sites Determines the Catalytic Activity of Cu Nanoparticles

The effect of nanosized ceria on supported Cu nanoparticles was investigated at an atomic level and correlated to the catalytic activity on the water–gas shift reaction (WGSR) rate. For Cu/Al2O3, increasing the Cu nanoparticle size leads to a decrease in the oxygen coverage and an increase in the bond length of Cu–O. When different loadings of nanosized ceria are introduced to the Cu/Al2O3 catalysts, no significant change occurred in the Cu particle size, the Cu–Cu bond length, or the oxygen coverage. However, ceria is able to interact with the Cu nanoparticles to increase the Cu–O bond length, and a linear correlation between ceria loading, Cu–O bond length, and WGSR rate was found. Hence, while previous reports claim that ceria leads to Cu nanoparticle stabilization or interface active sites, we have shown that the ceria tailors the Cu–O bond length, which has been shown to be a determinant of the WGSR rate.

Light-induced changes in the minority carrier diffusion length of Cu(In,Ga)Se2 absorber material

In this study strong evidence for an illumination-induced change in minority charge carrier diffusion length is given for Cu(In,Ga)Se2 solar cells. After annealing under illumination (light soaking) the cells show the well-known metastable increase in open circuit voltage, but also a metastable reduction in current collection efficiency (which can be reversed by annealing in the dark). Partly, this can be attributed to an increase in doping density causing a reduced space charge region width as verified by capacitance-voltage profiling. Nevertheless, by using time-resolved photoluminescence and electron-beam-induced current measurements we found that the changes in doping density and space charge region width are not sufficient to describe the modification in current collection efficiency. Additionally there seems to be a reduction in minority carrier diffusion length and lifetime after white light soaking. This can be explained by a metastable change of electronic defects as found in temperature-dependent admittance spectroscopy. Device simulations confirm the impact of the found defects on the photocurrent.

Structure, bonding and reactivity of coinage metal complexes TML2 and TML2+ (TM = Cu, Ag, Au) with planar tetracoordinate carbon, a theoretical investigation

The structures and bonding of the complexes TML2 and TML2+ with planar tetracoordinate carbons (TM=Cu, Ag and Au; L=C3H2BCH3 and C3Me2BCMe3) have been investigated using density functional theory M06 method, in which L are the derivatives of 2-borabicyclo[1.1.0]but-1(3)-ene. The lengths of Au–C and Ag–C bonds in AuL2 and AgL2 are longer than those of in TML2+, whereas the lengths of Cu–C bonds in TML2 are shorter than those of in TML2+. The NBO analyses of TML2 and TML2+ reveal that the Cu–C bonds in CuL2 are conjugated π bonds, whereas Ag–C and Au–C in TML2 (TM=Ag and Au) are σ bonds. The first electron transition energies of TML2+ result from the d–π transition, and the wavelengths are close to 260nm. Theoretically, the variations of the Gibbs free energies of the reactions of Ag(C3H2BCH3)2+ and Ag(C3Me2BCMe3)2+ with (tht)AuBr indicate that the two reactions are thermodynamically favorable. We also theoretically obtained the stable Au(III) complexes (C3H2BCH3)2AuBr2+ and (C3Me2BCMe3)2AuBr2+ with planar tetracoordinate carbons from the reactions of Au(C3H2BCH3)2+ and Au(C3Me2BCMe3)2+ with CsBr3.

Spin currents injected electrically and thermally from highly spin polarized Co2MnSi

We demonstrate the injection and detection of electrically and thermally generated spin currents probed in Co2MnSi/Cu lateral spin valves. Devices with different electrode separations are patterned to measure the non-local signal as a function of the electrode spacing and we determine a relatively high effective spin polarization α of Co2MnSi to be 0.63 and the spin diffusion length of Cu to be 500 nm at room temperature. The electrically generated non-local signal is measured as a function of temperature and a maximum signal is observed for a temperature of 80 K. The thermally generated non-local signal is measured as a function of current density and temperature in a second harmonic measurement detection scheme. We find different temperature dependences for the electrically and thermally generated non-local signals, which allows us to conclude that the temperature dependence of the signals is not just dominated by the transport in the Cu wire, but there is a crucial contribution from the different generation mechanisms, which has been largely disregarded till date.

In Situ Visualization of Metallurgical Reactions in Nanoscale Cu/Sn Diffusion Couples

The Cu–Sn metallurgical soldering reaction in two-segmented Cu–Sn nanowires is studied by in situ transmission electron microscopy. By varying the relative lengths of Cu and Sn segments, we show that the metallurgical reaction results in a Cu–Sn solid solution for small Sn/Cu length ratio while Cu–Sn intermetallic compounds (IMCs) for larger Sn/Cu length ratios. Upon heating the nanowires to ∼500 °C, two phase transformation pathways occur, η-Cu6Sn5 → e-Cu3Sn → δ-Cu41Sn11 for nanowires with a long Cu segment and η-Cu6Sn5 → e-Cu3Sn → γ-Cu3Sn with a short Cu segment. The evolution of Kirkendall voids in the nanowires demonstrates that Cu diffuses faster than Sn in IMCs. Void growth results in the nanowire breakage that shuts off the inter-diffusion of Cu and Sn and thus leads to changes in the phase transformation pathway in the IMCs.

Depth Profile of Induced Magnetic Polarization in Cu Layers of Co/Cu(111) Metallic Superlattices by Resonant X-ray Magnetic Scattering at the Cu K Absorption Edge

We investigated induced spin polarization of 4p conduction electrons in Cu layers of antiferromagnetically (AFM) and ferromagnetically (FM) coupled Co/Cu(111) metallic superlattices by resonant X-ray magnetic scattering at the Cu K absorption edge. Magnetic reflectivity profiles of the two superlattices were measured in the magnetic saturation state with circularly polarized synchrotron radiation X-rays at 8985 eV. Depth profiles of the resonant magnetic scattering length of Cu, which corresponds to the induced spin polarization of Cu, were evaluated in the two Co/Cu superlattices by analyzing the observed magnetic reflectivity profiles. We demonstrated that the spin polarization induced in the Cu layer was distributed around the Co/Cu interfaces with an attenuation length of several A in both AFM and FM coupled superlattices. The uniform component, which exists in Au layers of Fe/Au(001) superlattices, was not found in the depth distribution of induced magnetic polarization in the Cu layers of Co/Cu(111)...

In situ visualization of metallurgical reactions in nanoscale Cu/Sn diffusion couples.

The Cu-Sn metallurgical soldering reaction in two-segmented Cu-Sn nanowires is studied by in situ transmission electron microscopy. By varying the relative lengths of Cu and Sn segments, we show that the metallurgical reaction results in a Cu-Sn solid solution for small Sn/Cu length ratio while Cu-Sn intermetallic compounds (IMCs) for larger Sn/Cu length ratios. Upon heating the nanowires to ∼500 °C, two phase transformation pathways occur, η-Cu6Sn5 → ε-Cu3Sn → δ-Cu41Sn11 for nanowires with a long Cu segment and η-Cu6Sn5 → ε-Cu3Sn → γ-Cu3Sn with a short Cu segment. The evolution of Kirkendall voids in the nanowires demonstrates that Cu diffuses faster than Sn in IMCs. Void growth results in the nanowire breakage that shuts off the inter-diffusion of Cu and Sn and thus leads to changes in the phase transformation pathway in the IMCs.

Influence of diamagnetic chelating ligand (L) on spin exchange coupling in heterospin chain complexes, [Cu(L)2NOpy2

The mixtures of dipyridine aminoxyl, NOpy2, and chelated copper complexes, Cu(L)2; L=trifluoroacetylacetonato (tfac), hexafluoroacetylacetonato (hfac), and decafluoroheptanedionato (dfhd), in 1:1 ratios gave polymeric complexes, formulated as [Cu(L)2(NOpy2)]n; L=tfac (1), hfac (2), and dfhd (3). X-ray crystallography for 1, 2, and 3 revealed that the magnetic coupler NOpy2 coordinated with the copper ions in trans configurations to form one-dimensional chain structures. Noticeably, complex 2 showed a unique crystal structure that was analyzed as a static disorder of cis and trans configuration of the pyridine ring. The bond lengths of Cu–Npy for 1, 2, and 3, were 2.40, 2.14, and 2.02Å, respectively and became shorter with increasing the number of fluorine substituents. In the complexes, the aminoxyl centers ferromagnetically interacted with the copper ion. The spin exchange coupling constants, JCu–NO/kB, for 1, 2, and 3, depended on the diamagnetic chelating ligands and were estimated to be 5.7, 32, and 55K, respectively.

Contribution of defects to the spin relaxation in copper nanowires

The contributions to the spin relaxation in copper (Cu) nanowires are quantified by carefully analyzing measurements of both charge and spin transport in lateral spin valves as a function of temperature and thickness. The temperature dependence of the spin-flip scattering solely arises from the scattering with phonons, as in bulk Cu, whereas we identify grain boundaries as the main temperature-independent contribution of the defects in the nanowires. A puzzling maximum in the spin-diffusion length of Cu at low temperatures is found, which can be explained by the presence of magnetic impurities. The results presented here suggest routes for improving spin transport in metallic nanostructures, otherwise limited by confinement effects.

Theory analysis and vestigial information of surface relaxation of natural chalcopyrite mineral crystal

X-ray diffraction was used to measure the unit cell parameters of chalcopyrite crystal. The results showed that the chalcopyrite crystal is perfect, and the arrangement of its atoms is regular. A qualitative analysis of molecular mechanics showed that surface relaxation causes the chalcopyrite surface to be sulfur enriched. Atomic force microscope (AFM) was used to obtain both a microscopic three-dimensional topological map of chalcopyrite surface and a two-dimensional topological map of its electron cloud. The AFM results revealed that the horizontal and longitudinal arrangements of atoms on the chalcopyrite surface change dramatically compared with those in the interior of the crystal. Longitudinal shifts occur among the copper, iron and sulfur atoms relative to their original positions, namely, surface relaxation occurs, causing sulfur atoms to appear on the outermost surface. Horizontally, AFM spectrum showed that the interatomic distance is irregular and that a reconstruction occurs on the surface. One result of this reconstruction is that two or more atoms can be positioned sufficiently close so as to form atomic aggregates. The lattice properties of these models were calculated based on DFT theory and compared with the experimental results and those of previous theoretical works. On analyzing the results, the atomic arrangement on the (001) surface of chalcopyrite is observed to become irregular, S atoms move outward along the Z-axis, and the lengths of Cu—S and Fe—S bonds are enlarged after geometry optimization because of the surface relaxation and reconstruction. The sulfur-rich surface and irregular atomic aggregates caused by the surface relaxation and reconstruction greatly influence the bulk flotation properties of chalcopyrite.