Activation Energy Of Cu Research Articles

Low voltage resistance switching characteristics of Cu/MoS2/Cu/ITO devices

The resistive switching behavior is observed in the Cu/MoS2/Cu/ITO structures, which has been deposited by magnetron sputtering. With the increase in MoS2 thickness, the resistive switching behavior is gradually weakened. The optimal device with a MoS2 thickness of 120[Formula: see text]nm has a lower Set voltage and Reset voltage, where Set voltage is 0.14–0.3[Formula: see text]V and Reset voltage is −0.24[Formula: see text]V to −0.08[Formula: see text]V. The device also has a resistive switching ratio of up to 105 high resistance state/low resistance state, a data retention time over 104[Formula: see text]s, and can endure more than 103 cycles. As the limiting current increases, the resistance switching (RS) characteristics of devices with MoS2 thickness of 200[Formula: see text]nm at both positive and negative biases are improved. There is no RS behavior in ITO/MoS2/ITO devices fabricated by the same method, which indicates that sulfur vacancies have little effect on the RS characteristics of Cu/MoS2/Cu/ITO devices. Moreover, since the migration barrier and diffusion activation energy of Cu in MoS2 are lower than those of sulfur vacancy, combined with the data fitting structure, it is shown that the RS behavior is formed because Cu ions control the connectivity and fracture of conductive filaments through the diffusion and migration of MoS2 layer.

Investigation of deformation comprised microstructure and precipitation of Cu–Sn–Ti alloy during hot deformation

The hot deformation behavior of Cu–Sn–Ti–(Cr) alloys was studied using Gleeble-1500D thermo-mechanical simulator ranging from 550 to 950 °C, and the strain rate was 0.001–10 s−1. The microstructure evolution of the alloy was analyzed using characterization methods such as electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Cu–Sn–Ti–(Cr) alloys were calculated by establishing the constitutive equation of the alloy. The activation energies of Cu–Sn–Ti and Cu–Sn–Ti–Cr alloys are 275.884 and 283.550 kJ/mol, respectively. The results indicate that the addition of Cr element has an inhibitory effect on the nucleation and improve refinement of dynamic recrystallization (DRX) in Cu–Sn–Ti alloy. The texture of Cu–Sn–Ti alloy is Cu texture at 750 °C and the texture contained in Cu–Sn–Ti alloy is Goss texture, Cubic texture and Cu texture when the temperature is raised to 950 °C. The texture of Cu–Sn–Ti–Cr alloy at 750 °C is Goss texture. The Goss texture transforms into Cubic texture and Cu texture when the temperature is raised to 950 °C. The precipitates present in Cu–Sn–Ti alloy include CuSn3Ti5 phase and Cu4Ti phase. The addition of Cr element adds a new phase of Cr to the alloy and also makes the distribution of precipitates more uniform and increases in quantity.

A comprehensive study on the extraction of transition metals from waste random access memory using acetic acid as a chelating solvent

The reduced lifespan of electrical and electronic equipment results in the generation of electronic waste (e-waste), one of the fastest-growing solid waste streams. A systematic and practical approach is needed for the sound management of e-waste and metal recovery. We report an effective and comprehensive study for metal extraction from waste random access memory using acetic acid as a chelating solvent. Under the optimized conditions, Cu, Pb, Zn, and Ni extraction was 97.5%, 88.2%, 79.3%, and 83.7%, respectively. Subsequently, the kinetic study revealed that the diffusion-controlled mechanism governs the metal extraction. The calculated activation energy for Cu, Pb, Zn, and Ni are 11.3, 12.6, 17.6, and 13.3 kJ/mol, respectively, which indicates Cu-extraction could be more favourable than the rest of the metals. Furthermore, the metal leached salt was recovered from the leached solution and was thoroughly characterized to understand the nature of the compound formed and the corresponding leaching mechanism. It was observed that the leached salt could be comparable with standard copper acetate, revealing the acetic acid's ligation property. Finally, the Cu-content in the cathode was recovered as 92.7 wt% from the leached solution using the electrowinning process. We believe, our contribution can be a paradigm for promoting the effective extraction of transition metals from waste random access memory.

Temperature-dependant active sites for methane continuous conversion to methanol over Cu-zeolite catalysts using water as the oxidant

Methane-selective continuous conversion to methanol is highly challenged by the high CH dissociation energy and the facile over-oxidation of methane. In this work, we reported continuous methane conversion to methanol over Cu-zeolites using water as the oxidant at different reaction temperatures (200–450 °C) and found that the space–time yield (STY) of methanol depended on the reaction temperature, with a high methanol STY of 189.9 μmol/gcat./h (578.7 mmol/molCu/h) at the selectivity of 91 % on Cu-SSZ-13 being achieved at the optimal temperature of 350 °C. Increasing the reaction temperature from 200 to 350 °C resulted in the increase of the kinetic orders of methane and water for catalytic oxidation of methane. An important reason was indicated that higher reaction temperatures not only enhanced a high methane conversion rate but also triggered the reactivity of more Cu species on Cu-zeolites based on the quantification analysis of the available active sites and in-situ spectroscopic study. It was revealed that the CuxOy clusters (e.g., [Cu2(μ-O)]2+) as the active sites exhibited the reactivity at 200 °C, while the Cu(II)–OH species on 8-membered rings and the isolated Cu2+ ions on 6-membered rings presented the reactivity at higher temperatures (≥300 °C). This could be attributed to higher activation energies of Cu(II)–OH species and isolated Cu(II) sites. Besides, isotope labeling experiments indicated that the combination of methyl and hydrogen dissociated from water and methanol reforming resulted in a low methanol yield at high temperatures (≥350 °C).

Investigation of interdiffusion behavior in the Ti–Zr–Cu ternary system

Abstract The interdiffusion behavior of diffusion couples Ti-25Zr/Cu, Ti-50Zr/Cu and Ti-75Zr/Cu (at.%) at 973–1073 K was investigated by using electron probe microanalysis. The results show that the diffusion paths in all diffusion couples deviate away from the faster-diffusing Cu–Ti side. The diffusion paths pass the tie-line, across or parallel to, corresponding to the different diffusion layer structures and phase morphologies. The average effective interdiffusion coefficients and activation energies of Cu in both solid solutions and intermetallic compounds were determined. The diffusion coefficients of Cu in β(Ti, Zr) solid solution increase slightly and then decrease with the increase in Zr content, while the diffusion coefficients of Cu in Cu(Ti,Zr)2 intermetallic compound decrease with the increase in Zr content. The diffusion coefficients of Cu in Cu51Zr14 are the largest among all the intermetallic compounds in diffusion couples.

Kinetic study on extraction of metal-cyanide complex ions by the N263-TBP system

In this study, the extraction of metal-cyanide complex ions in gold-leaching, cyanide-containing wastewater by a trioctylmethylammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene system was investigated. The effects of N263 and TBP concentrations, the aqueous phase pH, and phase ratio (O/A) on the extraction were investigated by adopting the response surface methodology, and the operating parameters were optimized. The optimal solution was obtained by solving the model optimally. A Cu ion concentration of 3,000 mg/L, an N263 concentration of 0.459 mol/L, a TBP concentration of 0.214 mol/L, an initial pH of the aqueous phase of 10.064, and O/A of 0.900 were determined to be optimal for realizing an extraction yield of 99%. The effects of column height, oil droplet volume, metal ion concentration, N263 and TBP concentrations, and temperature on the mass transfer rate were investigated using the single droplet method. Kinetic studies showed that the kinetic equation for the extraction system was Rf (Mass transfer rate) = 1.57 × 10-4·CCu·CTBP·CN263. The apparent activation energy of Cu(I) was 15.186 kJ/mol. The extraction process was controlled by the diffusion process. Furthermore, the chemical reaction occurred at the two-phase interface, where the copper cyanide complex ions preferentially bound to TBP at the interface between the two phases, and the bound anion cluster then reacted with the N263 cation to form the extractive complex, which then entered the organic phase from the interface.

Green dehydrogenation of dimethylamine borane catalyzed by cheaply copper(0) nanocatalysts without any stabilizer at nearly room temperature.

In this work, the findings of the work on the green dehydrogenation behavior of molten dimethylamine borane (DMAB) catalyzed by the precatalyst copper(II) acetylacetonate (Cu(acac)2) in solvent-free medium (green) at near room temperature (nRT, 30.0+0.1°C) were reported. Herein, a complete study has been presented, which includes the following steps: (i) synthesis and catalytic activity of Cu(0) NCats in solvent-free medium, (ii) determination of activation energy for Cu(0) NCats catalyzed green dehydrogenation of DMAB, (iii) demonstration of catalytic lifetime of Cu(0) NCats, (iv) test of isolability and reusability of Cu(0) NCats, (v) poisoning experiments using carbon disulfide on a per-active-copper-atom basis, (vii) characterization of Cu(0) NCats by UV-vis, XRD, XPS and TEM/HRTEM/TEM-EDX spectroscopies. In addition, ATR-FTIR and 11B NMR techniques were use to characterize the cyclic aminoborane product obtained as a result of dehydrogenation of dimethylamine-borane.

Effect of vanadium on the microstructure and kinetics of discontinuous precipitation in Cu–3.2Ti–0.2Fe alloy

The microstructure and kinetics of discontinuous precipitation in Cu–3.2Ti–0.2Fe– x V ( x = 0, 0.1, 0.2 and 0.3 wt.%) alloys aged at 723, 773, 823 and 873 K were studied by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS), with the help of CALculation of PHAse Diagram (CALPHAD) method and Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. The volume fraction of Laves_C14 was increased with raising V content, leading to the effective grain refinement during casting and the inhibiting grain growth in solution treatment process. The activation energies of Cu–3.2Ti–0.2Fe– x V ( x = 0, 0.1, 0.2 and 0.3 wt.%) alloys were 196.4, 172.9, 147.4, 154.1 kJ mol −1 , respectively. The discontinuous precipitation was promoted and controlled by grain boundary diffusion in the early stages at low temperature, while it was inhibited by bulk diffusion at high temperature or in the later stages at low temperature. In addition, the peak-aged hardness was improved with proper amount of V addition due to the strengthening of Laves_C14 and grain refinement, as well as the inhibition of discontinuous precipitation.

Efficient recovery of Cu and Ni from WPCB via alkali leaching approach

The large generation of electronic waste (e-waste) is posing a serious threat to society. It is important to develop sustainable technology for the effective management of e-waste and the recovery of valuable metals from it. The present study employed hydrometallurgical approach for Cu and Ni extraction from waste printed circuit boards (WPCB) of mobile phones. This study demonstrates the application of ammonia-ammonium sulfate leaching for the maximum recovery of Cu and Ni. Investigations revealed that the most favourable reaction parameters for efficient metal extraction are – ammonia concentration – 90 g/L, ammonium sulfate concentration – 180 g/L, H2O2 concentration – 0.4 M, time – 4 h, liquid to solid ratio – 20 mL/g, temperature – 80 °C and agitation speed – 700 rpm. Under these conditions, 100% Cu and 90% Ni were extracted. Furthermore, the kinetic study was performed using the shrinking core model which revealed that the internal diffusion is the rate-controlling step for Cu and Ni extraction. The activation energies for Cu and Ni extraction were found out to be 4.5 and 5.7 kJ/mol, respectively. Finally, Cu was recovered with 98.38% purity using electrowinning at a constant DC voltage of 2.0 V at Al cathode. The present study provides a solution for concurrent extraction of Cu and Ni from the raw WPCB of mobile phones and selective recovery of Cu from metal leached solution. The process has the potential to recover the resources from WPCB while minimising the pollution caused by mismanagement of WPCB.

Diffusion coefficients and atomic mobilities in fcc Ni–Cu–Mo alloys: Experiment and modeling

Kinetic characteristics for Ni–Cu–Mo alloys are critically important for the establishment of the atomic mobility database in Ni-based superalloys. In the present work, the interdiffusion coefficients in fcc Ni–Cu–Mo alloys at 1273, 1373 and 1473 K have been determined from the concentration profiles across the solid–solid diffusion couples by means of EPMA (Electron Probe MicroAnalysis). The kinetic parameters for fcc Ni–Mo alloys are reassessed due to the discordance of self-diffusivity for Ni in fcc Ni–Mo and Ni–Cu phases. On the basis of the obtained interdiffusion coefficients in this work together with the thermodynamic description available in the literature, atomic mobilities of fcc Ni–Cu–Mo alloys were optimized as a function of the temperature and composition by means of CALTPP (CALculation of Thermo-Physical Properties) program. The three-dimensional surfaces for interdiffusivities, pre-exponential factor and activation energy for Cu and Mo were depicted for the purpose of understanding the variation of kinetic phenomenon. Good agreements between the calculated diffusivities, concentration profiles and diffusion paths and the experimental ones indicate that the presently obtained atomic mobilities of fcc Ni–Cu–Mo system are reliable.

An investigation of the effect of temperature on the oxidation processes of metallic diesel engine fuel system materials and B100 biodiesel from used cooking oil in exposure testing

Biodiesel is increasingly being used in automotive and other engine applications because of its potential to contribute to the reduction of CO2 and other harmful emissions. However, biodiesel is known to be more corrosive in contact with metallic components than petroleum diesel. This work explores the corrosion of aluminium, steel, brass and copper metallic coupons exposed to B100 biodiesel at 25, 80, 90, 100, 110 and 120 °C. The metals that were chosen are commonly found in automotive engines. The B100 in each experiment was sampled at 48, 100, 150, 200 and 270 h and examined by GCMS to determine compositional changes. It was found that corrosion rates for copper were 10x faster than brass and approximately 100x faster than for mild steel, Al7075 and Al1050. Activation energies for corrosion were calculated from mass loss and ICP, with good correlation between the two methods for Cu containing samples. By mass loss, the activation energies for Cu, Brass, Al7075 and Al1050 were calculated to be −47.9 kJ mol−1, −85.4 kJ mol−1, −86.7 kJ mol−1 and −54.4 kJ mol−1, respectively. By ICP analysis, the activation energies for Cu, Brass, and Al7075 were calculated to be −57.9 kJ mol−1, −90 kJ mol−1 and −140 kJ mol−1, respectively. Corrosion rates in brass and copper samples were faster owing to the direct reaction of copper with the fatty acid. The copper was found to cause chain scission and greater degradation of the biodiesel.

Removal of Cu(II) ions from aqueous solutions using petroleum coke-derived microporous carbon: investigation of adsorption equilibrium and kinetics

Petroleum coke (PC)-derived porous carbons were developed through chemical activation using KOH and applied to adsorb Cu(II) ions from aqueous solutions. The effects of KOH/PC mass ratio and activation temperature on the preparation and physical properties of porous carbon were studied. Also, the effects of the initial solution pH, contact time, operating temperature, dosage of adsorbent, and initial Cu(II) concentration on adsorption were investigated in detail. A maximum Cu(II) ion adsorption capacity of 89.85 mg g−1 was attained at 30 °C using PCK3-450, the porous carbon sample prepared using a KOH/PC mass ratio of 3:1 at 450 °C. Adsorption isotherms were analyzed using the Langmuir, Freundlich, and Temkin models, and the experimental data fit well with the Freundlich model. Pseudo first-order, pseudo second-order, Elovich, and intra-particle diffusion models were used to describe the adsorption kinetics, and the rate of adsorption conformed to the pseudo second-order kinetic model. The activation energy of Cu(II) ion adsorption on PCK3-450 was estimated at 29.61 kJ mol−1, and thermodynamic parameters were discussed. The porous carbon adsorbents developed in this study are inexpensive and effective for Cu(II) ion removal from aqueous solutions.

Electrochemical deposition of praseodymium (III) and copper (II) and extraction of praseodymium on copper electrode in LiCl-KCl melts

Cyclic voltammogram and square wave voltammograms indicated that Cu (II) ion being reduced to Cu(0) was a two-electron process: Cu(II) + e− → Cu(I) and Cu(I) + e− → Cu(0). The diffusion activation energy for Cu (I) ions was calculated as 42.85 kJ mol−1. The equilibrium potential and apparent standard potential for Cu (I)/Cu(0) redox couple was measured by open circuit chronopotentiometry at a temperature of 773–923 K. Three reduction peaks, corresponding to the formation of PrxCuy intermetallic compounds, were detected from cyclic voltammogram and square wave voltammogram obtained by co-reduction of Pr (III) and Cu (II) or electrodeposition of Pr (III) on Cu electrode. Furthermore, potentiostatic electrolysis was performed to extract the element Pr on Cu electrode, and the electrolytic products were analyzed by scanning electron microscopy equipped with energy dispersive spectrometry. Meanwhile, the highest extraction efficiency of Pr (III) ions could reach about 99.81% at − 2.20 V for 22 h at 823 K.

Diffusion behavior of Cu/Ta heterogeneous interface under high temperature and high strain: An atomistic investigation

Three-dimensional (3D) integration technology using Cu interconnections has emerged as a promising solution to improve the performance of silicon microelectronic devices. However, Cu diffuses into SiO2 and requires a barrier layer such as Ta to ensure acceptable reliability. In this paper, the effects of temperature and strain normal to the interface on the inter-diffusion of Cu and Ta at annealing conditions are investigated using a molecular dynamics (MD) technique with embedded atomic method (EAM) potentials. Under thermal annealing conditions without strain, it is found that a Cu-rich diffusion region approximately 2 nm thick is formed at 1000 K after 10 ns of annealing. Ta is capable of diffusing into the interior of Cu but Cu hardly diffuses into the inner lattice of Ta. At the Cu side near the interface an amorphous structure is formed due to the process of diffusion. The diffusion activation energy of Cu and Ta are found to be 0.9769 and 0.586 eV, respectively. However, when a strain is applied, a large number of crystal defects are generated in the sample. As the strain is increased, extrinsic stacking faults (ESFs) and lots of Shockley partial dislocations appear. The density of the dislocations and the diffusion channels increase, promoting the diffusion of Cu atoms into the inner lattice of Ta. The thickness of the diffusion layer increases to 4 times the value when only a temperature load of 700 K is applied. The MD simulations demonstrated that Ta is very effective as a barrier layer under thermal loading only, and its effectiveness is impaired by tensile strain at the Cu/Ta interface. The simulations also clarified the mechanism that caused the impairment. The methodology and approach described in this paper can be followed further to study the effectiveness of barrier layers under various annealing and strain conditions, and to determine the minimum thickness of barrier layers required for a particular application.

Atomistic mechanisms of copper filament formation and composition in Al2O3-based conductive bridge random access memory

Conductive filament formation and composition in Oxide-based Conductive Bridge Random Access Memory (CBRAM) are investigated. To this end, Al2O3/Cu-based CBRAM is electrically characterized and studied. Current-voltage characteristics exhibit different forming behaviors depending on device polarization exposing the charged species involved during the forming process. In order to get more insights at the microscopic level, ion diffusion is investigated in depth by first-principles calculations. We study different point defects in Al2O3 which can come either from the post-process of the material itself or after top electrode deposition or during device operation. Since the role of Oxygen Vacancies (VO) and Copper (Cu) ions is core to the switching mechanism, ab initio calculations focus on their displacements. For different charge states in Al2O3, we extract the thermodynamic and activation energies of Cu, Te, Al, and O related point defects. The results reveal that Cu is not the only ion diffusing in the Al2O3-based CBRAM switching mechanism while Te ions appear unfavorable. A Cu/VO based hybrid filament model is proposed, and the impact of Aluminum Vacancies (VAl) on the forming process is demonstrated.

Effects of temperature and operation parameters on the galvanic corrosion of Cu coupled to Au in organic solderability preservatives process

In this work, we quantitatively examined the effects of temperature and operation parameters such as anode (Cu) to cathode (Au) area ratio, stirring speed, and Cu ion concentration on the galvanic corrosion kinetics of Cu coupled to Au (icouple (Cu-Au)) on print circuit board in organic solderability preservative (OSP) soft etching solution. With the increase of temperature, galvanic corrosion rate (icouple (Cu-Au) was increased; however, the degree of galvanic corrosion rate (icouple (Cu-Au) - icorr (Cu)) was decreased owing to the lower activation energy of Cu coupled to Au, than that of Cu alone. With the increase of area ratio (cathode/anode), stirring speed of the system, icouple (Cu-Au) was increased by the increase of cathodic reaction kinetics. And icouple (Cu-Au) was decreased by the increase of the Cu-ion concentration in the OSP soft etching solution.

(Invited) Resistive RAM Memories from a Material Perspective: Exploration of the Switching for Several Oxides Using Ab Initio Simulations

The Resistive RAM memories are among the most promising technologies opening new perspectives beyond the current FLASH memory characteristics [1]. Several options compatible with a CMOS integration exist imposing constraints in term of electrode materials and dielectric layers. Indeed, many options are tested since a few years and the actual literature shows a wide dispersion of very encouraging results. In the same time the theoretical effort to simulate and to model the RRAM essential features has rapidly grown. By sustaining the technological efforts, we need to provide sound basis in order to pursue the RRAM development by decreasing the trial error period. Nevertheless, the origin of the mechanisms at the heart of a RRAM is sufficiently complex to resist to both semi-classical and empirical approaches inherited from the microelectronics. One of the main reason is that these devices mix two types of motions: the electronic current and the ionic rearrangement mainly for the dielectric, which can also interfere in turn with the electrode. Therefore, the atomistic simulation appears as the main alternative to analyze the situation without doing too strong assumptions. Our contribution is based onto our previous works for a Ti/HfO2 OxRRAM [2-4] and a Cu/Al2O3 CBRAM [5-6] plus a new and original mechanism for the HfO2 dielectric breakdown. Depending onto the electrode work function and its oxygen solubility, we show that the Forming step is mainly governed by the available charge states for the oxygen vacancy and the oxygen interstitial. For the Ti electrode and HfO2 dielectric, this leads to only one scenario where several oxygen rails leave the dielectric toward the reactive electrode. Thereafter we propose a Forming scenario for a Ti/HfO2 OxRRAM up to obtaining a conductive filament through the dielectric, see Fig. 1. This filamentary mode is obtained by basing our thinking onto equilibrium thermodynamics in between Ti oxides and Hf oxides. This model is then used to evaluate the activation energies implied in the SET and RESET steps: in order to move an oxygen inward and outward the conductive filament. In parallel, the density of states is then analyzed to evaluate relative change of filament conductivity. Then in a second part, we show that a Cu/Al2O3 CBRAM shares the same principles for the oxygen movements but in a more complex way. By analyzing the activation energies for Cu, O and Al, we show that oxygen movements need to be combined with the copper interstitial. A copper based electrode reacts with the dielectric by a combined motion: copper ions eventually end their run in substitutional oxygen sites. This movement can also be accompanied by a slight reorganization of some aluminum atoms which is usually not possible with HfO2 where Hf atoms stay at rest due to their low diffusivity. In conclusion we draw a possible track to follow in order to combine both types of mechanisms in between OxRRAM and CBRAM. Bibliography [1] M. Ueki, K. Takeuchi, T. Yamamoto, A. Tanabe, N. Ikarashi, M. Saitoh, T. Nagumo, H. Sunamura, M. Narihiro, K. Uejima, K. Masuzaki, N. Furutake, S. Saito, Y. Yabe, A. Mitsuiki, K. Takeda, T. Hase, and Y. Hayashi, in VLSI Technology (VLSI Technology), 2015 Symposium on (2015) pp. T108-T109[2] K.-H. Xue, B. Traore, P. Blaise, L. R. C. Fonseca, E. Vianello, G. Molas, B. D. Salvo, G. Ghibaudo, B. Magyari-Köpe, and Y. Nishi, IEEE Transactions on Electron Devices 61, 1394 (2014). [3] B. Traore, P. Blaise, E. Vianello, E. Jalaguier, G. Molas, J. Nodin, L. Perniola, B. De Salvo, and Y. Nishi, in IEEE IRPS (2014) pp. 5E.2.1-5E.2.5.[4] B. Traore, P. Blaise, E. Vianello, L. Perniola, B. De Salvo, and Y. Nishi, Electron Devices, IEEE Transactions on Electron Devices 63, 360 (2016). [5] J. Guy, G. Molas, P. Blaise, A. Roule. G. LeCarval, V. Delaye, A. Toffoli, G. Ghibaudo, F. Clermidy, B. de Salvo, L. Perniola, in IEEE Transactions on Electron Devices 62, pp. 3482-3489, (2015). [6] C. Nail, P. Blaise, G. Molas, SISC proceedings (2015) Figure 1

Effect of Cr-doping on CuCl2-KCl-CeO2/γ-Al2O3 catalysts for ethane oxychlorination

Chromium-doped CuCl2–KCl–CeO2–Crx/γ-Al2O3 with different content (Cr 0, 1, 3, 5, 7 and 9wt.%) were synthesized by co-impregnation method and characterized by XRD, BET, SEM, H2-TPR and XPS techniques. It is found that the addition of chromium species increases a large amount of capping oxygen species on the catalysts surface, reduces the reduction activation energy of Cu(II)→Cu(I) process efficiently, and accelerates the transition of redox group Cu(II)/Cu(I). Meanwhile, the addition of chromium species also affects the crystal size of CeO2 on the surface. The best catalyst is CuKCeCr3 with Cr (3wt.%), which exhibited highest conversion of C2H6 (97.8%) and best selectivity to C2H3Cl (68.2%).

The competition between metastable and equilibrium S (Al2CuMg) phase during the decomposition of Al[sbnd]Cu[sbnd]Mg alloys

The decomposition sequence of the supersaturated solid solution leading to the formation of the equilibrium S (Al2CuMg) phase in AlCuMg alloys has long been the subject of ambiguity and debate. Recent high-resolution synchrotron powder diffraction experiments have shown that the decomposition sequence does involve a metastable variant of the S phase (denoted S1), which has lattice parameters that are distinctly different to those of the equilibrium S phase (denoted S2). In this paper, the difference between these two phases is resolved using high-resolution synchrotron and neutron powder diffraction and atom probe tomography, and the transformation from S1 to S2 is characterised in detail by in situ synchrotron powder diffraction. The results of these experiments confirm that there are no significant differences between the crystal structures of S1 and S2, however, the powder diffraction and atom probe measurements both indicate that the S1 phase forms with a slight deficiency in Cu. The in situ isothermal aging experiments show that S1 forms rapidly, reaching its maximum concentration in only a few minutes at high temperatures, while complete conversion to the S2 phase can take thousands of hours at low temperature. The kinetics of S phase precipitation have been quantitatively analysed for the first time and it is shown that S1 phase forms with an average activation energy of 75kJ/mol, which is much lower than the activation energy for Cu and Mg diffusion in an Al matrix (136kJ/mol and 131kJ/mol, respectively). The mechanism of the replacement of S1 with the equilibrium S2 phase is discussed.

Barrier performance of ultrathin amorphous Nb–Ni film between copper and silicon

We have fabricated the Cu (50nm)/Nb–Ni (5nm)/Si heterostructures, annealed at various temperatures up to 800°C in a high vacuum system, to investigate the barrier performance of the ultrathin amorphous Nb–Ni film between Cu and Si. No impurity peaks are observed from the X-ray diffraction patterns of the Cu/Nb–Ni/Si heterostructures annealed up to 800°C. The island-like surface is observed for the 800°C annealed sample, indicating the failure of the Nb–Ni barrier layer, which is attributed to agglomeration of Cu film resulting from the dewetting of Cu with the underlying Nb–Ni layer during high temperature annealing. The activation energy for Cu dewetting with Nb–Ni layer is estimated to be 0.86eV. Our result demonstrates that ultra-thin amorphous Nb–Ni film can be an ideal diffusion barrier layer for Cu interconnection.