Vacancies In Cu Research Articles

Transition metal modified Mn-based catalysts for CO-SCR in the presence of excess oxygen

The CO-SCR technology based on transition metal is of great significance for NOx removal in large-scale industrial production. However, excess oxygen usually hinders the deNOx reaction in the actual industrial process. In this paper, a series of Mn-based catalysts modified by transition metals (Fe, Ni, Cu) were prepared using the co-precipitation method, which aimed to obtain good CO-SCR performance under O2-rich condition. The results showed that the Cu-Mn2 sample exhibited excellent deNOx performance. Regardless of the presence or absence of oxygen, the NO conversion of Cu-Mn2 catalyst was remain about 60% and 95% at 350 and 400 ℃, respectively. Differently, the NO conversion of Fe-Mn2 catalyst significantly increased from approximately 10% to 61% at 400 ℃ after introducing oxygen, which proved that excess oxygen could promote the CO-SCR process over Fe-Mn2 sample. The varied physical and chemical properties of the prepared materials were thoroughly evaluated through BET, SEM, XRD, XPS and in situ DRIFTS technologies. The results demonstrated that perovskite α-Mn2O3, decahedral Mn5O8, Fe2O3 and Fe3O4 crystals were the dominant structures promoting deNOx reaction on the Fe-Mn2 catalyst. The oxidation of low valence nitrogen oxides by decahedral Mn5O8 on Fe-Mn2 catalyst was an important factor for oxygen resistance. And the various spinel structures over Ni-Mn2, and Cu-Mn2 indicated strong synergistic effects. For the Cu-Mn2 catalyst, the strong synergistic effect of Cu-□-Mn species could promote the dissociation of intermediate -NONO. O2 tended to occupy the surface synergetic oxygen vacancies in Cu-□-Mn species at high temperatures, which could inhibit the dissociation of -NONO and enhance the CO oxidation reaction. The possible reaction mechanisms for CO-SCR over Mn-based catalysts were discussed specifically.

Light Emission from Single Oxygen Vacancies in Cu2O Films Probed with Scanning Tunneling Microscopy.

Global photoluminescence (PL) and spatially resolved scanning tunneling microscopy (STM) luminescence are compared for thick Cu2O films grown on Au(111). While the PL data reveal two peaks at 750 and 850 nm, assigned to radiative electron decays via localized gap states induced by O vacancies, a wide-band emission between 700 and 950 nm is observed in STM luminescence. The latter is compatible with cavity plasmons stimulated by inelastic electron tunneling and contains no spectral signature of the Cu2O defects. The STM luminescence is nonetheless controlled by O vacancies that provide inelastic excitation channels for the cavity plasmons. In fact, the emission yield sharply peaks at 2.2 V sample bias, when tip electrons are resonantly injected into O defect states and recombine with holes at the valence-band top via plasmon stimulation. The spatially confined emission centers detected in photon maps of the Cu2O films are therefore assigned to excitation channels mediated by single or few O vacancies in the oxide matrix.

Gradient Graphdiyne Induced Copper and Oxygen Vacancies in Cu0.95 V2 O5 Anodes for Fast-Charging Lithium-Ion Batteries.

Vacancies can significantly affect the performance of metal oxide materials. Here, a gradient graphdiyne (GDY) induced Cu/O-dual-vacancies abundant Cu0.95 V2 O5 @GDY heterostructure material has been prepared as a competitive fast-charging anode material. Cu0.95 V2 O5 self-catalyzes the growth of gradient GDY with rich alkyne-alkene complex in the inner layer and rich alkyne bonds in the outer layer, leading to the formation of Cu and O vacancies in Cu0.95 V2 O5 . The synergistic effect of vacancies and gradient GDY results in the electron redistribution at the hetero-interface to drive the generation of a built-in electric field. Thus, the Li-ion transport kinetics, electrochemical reaction reversibility and Li storage sites of Cu0.95 V2 O5 are greatly enhanced. The Cu0.95 V2 O5 @GDY anodes show excellent fast-charging performance with high capacities and negligible capacity decay for 10 000 cycles and 20 000 cycles at extremely high current densities of 5 A g-1 and 10 A g-1 , respectively. Over 30 % of capacity can be delivered in 35 seconds.

Gradient Graphdiyne Induced Copper and Oxygen Vacancies in Cu0.95V2O5 Anodes for Fast‐Charging Lithium‐Ion Batteries

AbstractVacancies can significantly affect the performance of metal oxide materials. Here, a gradient graphdiyne (GDY) induced Cu/O‐dual‐vacancies abundant Cu0.95V2O5@GDY heterostructure material has been prepared as a competitive fast‐charging anode material. Cu0.95V2O5 self‐catalyzes the growth of gradient GDY with rich alkyne‐alkene complex in the inner layer and rich alkyne bonds in the outer layer, leading to the formation of Cu and O vacancies in Cu0.95V2O5. The synergistic effect of vacancies and gradient GDY results in the electron redistribution at the hetero‐interface to drive the generation of a built‐in electric field. Thus, the Li‐ion transport kinetics, electrochemical reaction reversibility and Li storage sites of Cu0.95V2O5 are greatly enhanced. The Cu0.95V2O5@GDY anodes show excellent fast‐charging performance with high capacities and negligible capacity decay for 10 000 cycles and 20 000 cycles at extremely high current densities of 5 A g−1 and 10 A g−1, respectively. Over 30 % of capacity can be delivered in 35 seconds.

Electronic and magnetic properties of pure and Cu doped non-polar ZnO (101¯0) surfaces

In the present work, the electronic and magnetic properties of pure and Cu doped ZnO thin films in the non-polar [101¯0] direction have been investigated in the framework of density functional theory. The bandgap of pure surface was slightly lower than that of the bulk. By doping Cu impurity in the surface, the bandgap decreased relative to that of the pure surface, which is in the visible light region. Furthermore, the spin up and down behaved differently, presenting half-metallic behavior with a net magnetization as large as 1 μB/cell. These results imply that Cu doped ZnO surface can be applicable in spintronic and optical applications. By including O vacancy in Cu doped surface configurations, the bandgap was decreased leading to the metallic behavior. Furthermore, different magnetization was obtained for each configuration. It states that the presence of O vacancy in Cu doped ZnO surface may affect the induced magnetization in ZnO thin films.

Formation of Interfacial Cu-[OX ]-Ce Structures with Oxygen Vacancies for Enhanced Electrocatalytic Nitrogen Reduction.

Electrochemical nitrogen reduction powered by renewable electricity is a promising strategy to produce ammonia. However, the lack of efficient yet cheap electrocatalysts remains the biggest challenge. Herein, hybrid Cu2 O-CeO2 -C nanorods are prepared on copper mesh through a metal-organic framework template route. The Cu-loaded Ce-MOF is thermally converted to Cu2 O-CeO2 heterojunctions with interfacial Cu-[OX ]-Ce structures embedded in carbon. Theoretical calculations reveal the lower formation energy of oxygen vacancies in Cu-[OX ]-Ce structures than in the Cu2 O or CeO2 phase. The Cu-[OX ]-Ce structures with oxygen vacancies enable the formation of interfacial electron-rich Cu(I) species which show significantly enhanced performance toward electrocatalytic nitrogen reduction with an NH3 yield of 6.37 × 10-3 µg s-1 cm-2 and a Faradaic efficiency of 18.21% in 0.10 m KOH at -0.3V versus reversible hydrogen electrode. This work highlights the importance of modulation of charge distribution of Cu-based electrocatalysts to boost the activity toward nitrogen reduction.

Hydrogen-Enhanced Vacancy Diffusion in Metals.

Vacancy diffusion is fundamental to materials science. Hydrogen atoms bind strongly to vacancies and are often believed to retard vacancy diffusion. Here, we use a potential-of-mean-force method to study the diffusion of vacancies in Cu and Pd. We find H atoms, instead of dragging, enhance the diffusivity of vacancies due to a positive hydrogen Gibbs excess at the saddle-point: that is, the migration saddle attracts more H than the vacancy ground state, characterized by an activation excess ΓHm ≈ 1 H, together with also-positive migration activation volume Ωm and activation entropy Sm. Thus, according to the Gibbs adsorption isotherm generalized to the activation path, a higher μH significantly lowers the migration free-energy barrier. This is verified by ab initio grand canonical Monte Carlo simulations and direct molecular dynamics simulations. This trend is believed to be generic for migrating dislocations, grain boundaries, and so on that also have a higher capacity for attracting H atoms due to a positive activation volume at the migration saddles.

Generating oxygen vacancies in Cu 2+ ‐doped TiO 2 hollow spheres for enhanced photocatalytic activity and antimicrobial activity

Developing cheap photocatalysts with highly visible-light activity is greatly desired for environmental pollution treatment. In this work, the authors designed and synthesised Cu2+-doped TiO2 (Cu-TiO2) hollow spheres with enhanced photocatalytic activity and antimicrobial activity using a simple hydrothermal process. The X-ray powder diffraction (XRD) results revealed that Cu-TiO2 hollow spheres were anatase crystal phase. The Cu2+-doped into TiO2 can be confirmed by XRD, Raman spectra, and UV–Vis spectrum. The photocatalytic activity of Cu-TiO2 samples was evaluated by the degradation of methyl orange. Comparing to the undoped TiO2, 6% Cu-TiO2 sample exhibited remarkably high photocatalytic towards methyl orange under simulated sunlight irradiation, which was attributed to the fact that copper ion doping produced numerous oxygen vacancies (VO) in the material. In addition, it also showed improved antibacterial properties against both Gram-positive Staphylococcus aureus (S.aureus) and Gram-negative Escherichia coli (E.coli) bacteria. These results establish that Cu2+ doping can obviously improve the photocatalytic performance of TiO2 under simulated sunlight.

Solution-processed Cu(In,Ga)(Se,S)2 solar cells prepared via a surface sulfurization process

The photovoltaic (PV) characteristics of solution-coated Cu(In,Ga)Se2 films were effectively improved via a surface sulfurization in this study to overcome the complexity to control the appropriated amounts of sulfur ionsduring the sulfurization process.After sulfurization treatment, the Cu(In,Ga)(Se,S)2 films with double-graded band gap were obtained because the incorporation of sulfur-ion intoCu(In,Ga)Se2 films increasedthe band gap near the surface region.The formation of selenium vacancies in Cu(In,Ga)(Se,S)2 films were effectively diminished by adjusting H2S concentration. Band gap gradients and defect passivation reduced the interface recombination and improved the carrier collection in the devices. As the H2S concentration was raised from 0 to 1.0 vol%, the open-circuit voltage was increased from 541 to 596 mV, thereby boosting the conversion efficiency from 10.71to 12.40%. The reduction of vacancy defects and surface roughness suppressed the formation of shunt paths, resulting ina decrease indiode factor and leakage current. Compared with the Cu(In,Ga)(Se,S)2 films deriving from vacuum processes, solution-coated Cu(In,Ga)(Se,S)2 films with relatively small grains facilitated the sulfur diffusion along the grain boundaries into the films.Therefore, the appropriate H2S concentration used in the solution-coated Cu(In,Ga)(Se,S)2 films was less than vacuum processes. This investigation demonstrates that adjusting the concentrationof H2S is vital for enhancing the PV properties of thesolution-processed Cu(In,Ga)(Se,S)2 PV cells.

Visualization of Kirkendall Voids at Cu-Au Interfaces by In Situ TEM Heating Studies

Gold-plated copper alloys are used extensively in electrical contacts where diffusional processes are known to cause contact degradation. An in situ transmission electron microscopy (TEM) heating study was carried out to provide fundamental understanding of the aging phenomena in reasonable timescales. Samples to visualize the interface in TEM were prepared by focused ion beam (FIB) microscopy and heated in situ up to 350°C while holding at intermediate temperatures to enable imaging. The grain boundaries in Au coatings, specifically the columnar boundaries, provided rapid pathways for diffusion of Cu all the way to the Au surface. This unequal diffusion created vacancies in Cu which coalesced into Kirkendall voids. This in situ technique has been applied to visualize the diffusion pathways in electroplated and sputtered Au films deposited directly on Cu, as well the role of Ni and NiP as barrier layers for mitigating Cu diffusion.

Decomposition of Nickel(Ⅱ)−Ethylenediaminetetraacetic acid by Fenton−Like reaction over oxygen vacancies-based Cu−Doped Fe3O4@γ−Al2O3 catalyst: A synergy of oxidation and adsorption

Nickel (Ⅱ)−ethylenediaminetetraacetic acid (Ni−EDTA) complexes are widely present in electroplating effluents. Owing to its chemical stability, Ni−EDTA is hardly removed in traditional Fenton/Fenton-like processes with conventional iron (Fe)−based catalyst. In this study, oxygen vacancies were introduced into our highly efficient and novel Fe3O4@γ−Al2O3 catalysts using Cu doping for Ni−EDTA decomposition in Fenton−like system. Without noble−metal cocatalyst, the introduction of oxygen vacancies in Cu−doped Fe3O4@γ−Al2O3 catalysts exhibit excellent Fenton−like activity even in neutral or alkaline conditions. Experimental results revealed that, without the aid of extra energy, Ni−EDTA complexes could be effectively decomposed over oxygen vacancies−based catalyst. Electron paramagnetic resonance (EPR), X−ray photoelectron spectroscopy (XPS), oxygen temperature−programmed desorption (O2−TPD), and hydrogen temperature−programmed reduction (H2−TPR) were used to get a deep insight into the decomposition mechanism. Additionally, by employing the Al−containing support, stable layered double−hydroxide phases of NiAl could be formed, indicating that a synergy of oxidation and adsorption could simultaneously take place, which led to the recovery of released Ni2+ ions and also reduction in secondary pollution. To investigate the decomposition process of Ni−EDTA over oxygen vacancies−based catalyst, liquid chromatography−quadrupole/electrostatic field orbitrap high resolution mass spectrometry (LC−MS/MS) was employed to identify the generated intermediates, and thus, a plausible decomposition pathway was successfully conceived.

Interfacial void segregation of Cl in Cu-Sn micro-connects

A scanning transmission electron microscopy and an energy dispersive X-ray analysis of one non-annealed and one annealed sample (423 K for 4 hours) was performed. The results showed small and large voids appearing within the non-annealed and annealed samples respectively. In addition, chlorine segregated from the bulk into the voids. Ab initio calculations determined the formation energies for dilute solutions of chlorine and vacancies in Cu, Cu3Sn and Cu6Sn5. Results suggest that dilute solutions energetically favor vacancies, indicating a low chlorine solubility and a driving force for segregation.

Full-Potential KKR calculations for Lattice Distortion around Impurities in Al-based dilute alloys, based on the Generalized-Gradient Approximation

The presence of a point defect in a crystal, such as a vacancy or an impurity atom, generally cause a displacement of the neighboring host atoms from their ideal lattice positions. For examples, the experimental results are shown in Refs.1–3. From the theoretical point of view the treatment of structural relaxation due to defects in crystals is a difficult task. The problem of the lattice distortion has been mostly dealt with on a phenomenological basis, e.g., by applying models of lattice statics or continuum theory. A reliable microscopic description of lattice relaxation effects based on first-principles electronic structure calculations requires very accurate total energies or forces and has mostly been attempted so far for simple metals and semiconductors on the basis of pseudopotential treatments. The difficulty arises mainly from the fact that energy differences due to local atomic displacements are quite small, of the order of 0.1 ev, compared with, e.g., the cohesive energy (~5eV) of the solid. At present we can calculate accurately the atomic volumes of impurities in transition metals, by using ab-initio all-electron calculations of the electronic structure of solids, based on the FPKKR Green’s function method and the density functional theory. Papanikolaou et al succeeded in calculating the atomic volumes of 3d, 4sp, 4d, and 5sp impurities in Cu [4]. We also succeeded in calculating the lattice relaxation energies of vacancies in Cu and Al [5].

First-principles study of solute–vacancy binding in Cu

Solute–vacancy binding is a key quantity in understanding diffusion kinetics, and may also have a considerable impact on the hardening response in Cu alloys. However, the binding energies between solute atoms and vacancies in Cu are largely unknown and difficult to measure accurately. A large database of solute–vacancy binding energies in Cu from first-principles calculations based on density functional theory was presented in the paper. The trends in the binding energies in terms of super cell size, solutes size and magnetic moments are analyzed. The calculated binding energies agree well with experimental measurements available.

Ab initio local energy and local stress: application to tilt and twist grain boundaries in Cu and Al

The energy-density and stress-density schemes (Shiihara et al 2010 Phys. Rev. B 81 075441) within the projector augmented wave (PAW) method based on the generalized gradient approximation (GGA) have been applied to tilt and twist grain boundaries (GBs) and single vacancies in Cu and Al. Local energy and local stress at GBs and defects are obtained by integrating the energy and stress densities in each local region by the Bader integration using a recent algorithm (Yu et al 2011 J. Chem. Phys. 134 064111) as well as by the layer-by-layer integration so as to settle the gauge-dependent problem in the kinetic terms. Results are compared with those by the fuzzy-Voronoi integration and by the embedded atom method (EAM). The features of local energy and local stress at GBs and vacancies depend on the bonding nature of each material. Valence electrons in Al mainly located in the interatomic regions show remarkable response to structural disorder as significant valence charge redistribution or bond reconstruction, often leading to long-range variations of charges, energies and stresses, quite differently from d electrons in Cu mainly located near nuclei. All these features can be well represented by our local energy and local stress. The EAM potential for Al does not reproduce correct local energy or local stress, while the EAM potential for Cu provides satisfactory results.

The influence of Cu–Nb interfaces on local vacancy concentrations in Cu

The sink strength of Cu–Nb interfaces was investigated by measuring the steady-state vacancy concentration profile adjacent to Cu–Nb interfaces during 1.8 MeV Kr + irradiation. Broadening of dilute nanoscale Au tracer layers in Cu quantified position-dependent values for radiation-enhanced diffusivity and, accordingly, vacancy concentration. The measured vacancy profile corresponds to results calculated from a steady-state kinetic rate equation that assumes perfect sink efficiency at the Cu–Nb interface, indicating that it behaves like an ideal sink for vacancies in Cu.

Effect of sputtering power on structural, morphological, chemical, optical and electrical properties of Ti:Cu3N nano-crystalline thin films

A sintered Ti1 3 Cu 87 bi-component target was sputtered by reactive DC magnetron sputtering in nitrogen ambient under various sputtering powers. Ti included Cu 3 N (Ti:Cu 3 N) thin films were deposited on Si (1 1 1), KBr (potassium bromide), quartz and glass slide substrates. Crystalline phases of the films were identified by X-ray diffraction (XRD) technique. Crystalline quality and phase stability are strongly dependent on sputtering power. Formation of copper vacancies in Cu 3 N cell substituted by Ti atoms and subsequent excess of interstitial nitrogen (N-rich) result in lattice constant expansion. Bonding environment in these films was obtained from fourier transform infrared (FTIR) spectroscopy. Surface morphology of the films that were studied by a scanning electron microscope (SEM) indicates a granular structure. Atomic Ti:Cu ratio of Ti:Cu 3 N films, determined by energy dispersive X-ray (EDX) spectroscopy, is less than that of original target. Optical study was performed by Vis-near IR transmittance spectroscopy. Film thickness, refractive index and extinction coefficient were extracted from the measured transmittance using pointwise unconstrained minimization approach. The TiCu 3 N films are direct semiconductor with bandgap energy with the range of 2.79–3.34 eV. Ti incorporation and subsequent N-rich have a significant role in bandgap widening and lattice constant expansion. The films electrically show quasi-metallic behavior.

ENHANCEMENT OF FERROMAGNETISM IN NANOCRYSTALLINE Zn1-xCuxO(0.03 ≤ x ≤ 0.07)

We report room temperature ferromagnetism (RTFM) in nanocrystalline Zn 1-x Cu x O (0.03 ≤ x ≤ 0.07) materials synthesized by autocombustion technique. The average particle sizes are in the range of 60 nm. The saturation magnetization and coercivity of 7% Cu -doped ZnO is enhanced significantly in comparison to 3% and 5% Cu -doped ZnO . There is not much variation in the optical band gap due to Cu doping, thus suggesting the uniform distribution of Cu in the ZnO matrix. Micro-Raman and photoluminescence analysis predict the presence of clusters of oxygen vacancies in Cu -doped system which improves with the increase in Cu concentration. This study provides further evidence that oxygen vacancies play an important role in the enhancement of room temperature ferromagnetic property in Cu -doped ZnO .

Atomistic Simulations of Copper Precipitation and Radiation Induced Segregation in α-Iron

We present Monte Carlo simulations of the first stages of the coherent precipitation of Cu in α-Fe during thermal ageing and under irradiation. The simulations are based on a diffusion model by vacancy and self-interstitial jumps, the parameters of which are fitted on ab initio calculations. The simulations of precipitation kinetics during thermal ageing are compared with experimental ones. They reveal that precipitates containing up to several tens of atoms can be much more mobile than individual copper atoms, due to the trapping of vacancies in Cu. Monte Carlo simulations are also used to analyze the coupling between fluxes of point defects and Cu which occurs under irradiation and the possible resulting radiation induced segregation phenomena.

Atomistic study of self-diffusion in Cu–Ag immiscible alloy system

Combining molecular dynamic (MD) simulation with modified analytic embedded-atom method (MAEAM) potential, the formation, migration and activation energies have been calculated for four-kind migrations of Cu vacancy and three-kind migrations of Ag vacancy in Cu–Ag immiscible alloy system. The equilibrium concentration of Cu vacancies is greater than that of Ag vacancies owing to the formation energy of Cu vacancy (1.012 eV) is lower than that of Ag vacancy (1.169 eV). Comparing the migration or activation energy needed for four-kind migrations of Cu vacancy and three-kind migrations of Ag vacancy show that the favorable migration mechanism is the nearest-neighbor (NN) jump for Cu vacancy, while the straight [0 1 0] six-jump cycle (6JC) for Ag vacancy. Furthermore, the activation energy of the NN jump of Cu vacancy (2.164 eV) is lower than that of straight [0 1 0] 6JC of Ag vacancy (2.404 eV) also show that the former is more favorable. We conclude accordingly that the primary migration mechanism is the NN jump of an abundance of Cu vacancies.