The influence of prepulse level on the 3p-3s XUV laser output from Ne-like ions of Zn, Cu and Ni

We have studied the effect of prepulses in enhancing the efficiency of generating ASE beams in soft X-ray laser plasma amplifiers based on pumping Ne-like ions, Slab targets were irradiated with a weak prepulse followed by a main plasma heating pulse of nanosecond duration, Time-integrated; time and spectrally resolved and time and angularly resolved lasing emissions on the 3p-3s (J=0-1) XUV lasing lines of Ne-like Ni, Cu and Zn at wavelengths 232 Angstrom 221 Angstrom and 212 Angstrom respectively have been monitored. Measurements were made for pre-pulse/main-pulse intensity ratios from 10(-5)-10(-1) and for pump delay times of 2 ns and 4.5 ns. Zinc is shown to exhibit a peak in output intensity at similar to 2x10(-3) pre-pulse fraction for a 4.5 ns pump delay, with a main pulse pump intensity of similar to 1.3x10(13) W cm(-2) on a 20 mm target. The Zn lasing emission had a duration of similar to 240 ps and this was insensitive to prepulse fraction. The J=0-1 XUV laser output for nickel and copper increased monotonically with prepulse fraction, with copper targets showing least sensitivity to either prepulse level or prepulse to main pulse delay. Under the conditions of the study, the pre-pulse level was observed to haveno significant influence on the output intensity of the 3p-3s (J=2-1) lines of any of the elements investigated.

Polar distribution of ablated atomic material during the pulsed laser deposition of Cu in vacuum: Dependence on focused laser spot size and power density

Experiments have been carried out to investigate the polar distribution of atomic material ablated during the pulsed laser deposition of Cu in vacuum. Data were obtained as functions of focused laser spot size and power density. Thin films were deposited onto flat glass substrates and thickness profiles were transformed into polar atomic flux distributions of the form f(theta)=cos(n) theta. At constant focused laser power density on target, I=4.7+/-0.3X10(8) W/cm(2), polar distributions were found to broaden with a reduction in the focused laser spot size. The polar distribution exponent n varied from 15+/-2 to 7+/-1 for focused laser spot diameter variation from 2.5 to 1.4 mm, respectively, with the laser beam exhibiting a circular aspect on target. With the focused laser spot size held constant at phi=1.8 mm, polar distributions were observed to broaden with a reduction in the focused laser power density on target, with the associated polar distribution exponent n varying from 13+/-1.5 to 8+/-1 for focused laser power density variation from 8.3+/-0.3X10(8) to 2.2+/-0.1X10(8) W/cm(2) respectively. Data were compared with an analytical model available within the literature, which correctly predicts broadening of the polar distribution with a reduction in focused laser spot size and with a reduction in focused laser power density, although the experimentally observed magnitude was greater than that predicted in both cases. (C) 1996 American Institute of Physics.

Microwave-assisted Cu-catalyzed Ullmann ether synthesis in a continuous-flow milli-plant

The combination of milli-scale processing and microwave heating has been investigated for the Cu-catalyzed Ullmann etherification in fine-chemical synthesis, providing improved catalytic activity and selective catalyst heating. Wall-coated and fixed-bed milli-reactors were designed and applied in the Cu-catalyzed Ullmann-type CO coupling of phenol and 4-chloropyridine. In a batch reactor the results show clearly increased yields for the microwave heated process at low microwave powers, whereas high powers and catalyst loadings reduced the benefits of microwave heating. Slightly higher yields were found in the Cu/ZnO wall-coated as compared to the Cu/TiO fixed-bed flow-reactor. The benefit here is that the reaction occurs at the surface of the metal nanoparticles confined within a support film making the nano-copper equally accessible. Catalyst deactivation was mainly caused by Cu oxidation and coke formation; however, at longer process times leaching played a significant role. Catalyst activity could partially be recovered by removal of deposited by-product by means of calcination. After 6h on-stream the reactor productivities were 28.3 and 55.1kgprod/(mR3h) for the fresh Cu/ZnO wall-coated and Cu/TiO fixed-bed reactor, respectively. Comparison of single- and multimode microwaves showed a threefold yield increase for single-mode microwaves. Control of nanoparticles size and loading allows to avoid high temperatures in a single-mode microwave field and provides a novel solution to a major problem for combining metal catalysis and microwave heating. Catalyst stability appeared to be more important and provided twofold yield increase for the CuZn/TiO catalyst as compared to the Cu/TiO catalyst due to stabilized copper by preferential oxidation of the zinc. For this catalyst a threefold yield increase was observed in single-mode microwaves which, to the best of our knowledge, led to a not yet reported productivity of 172kgprod/(mR3h) for the microwave and flow Ullmann CO coupling. © 2012 Elsevier B.V.

Origin of the Increase of Activity and Selectivity of Nickel Doped by Au, Ag, and Cu for Acetylene Hydrogenation

Activity and selectivity are both important issues in heterogeneous catalysis and recent experimental results have shown that Ni catalysts doped by gold exhibit high activity for the hydrogenation of acetylene with good selectivity of ethylene formation. To unravel the underlying mechanism for this observation, the general trend of activity and selectivity of Ni surfaces doped by Au, Ag, and Cu has been investigated using density functional theory calculations. Complete energy profiles from C2H2 to C2H4 on Ni(111), Au/Ni(111), Ag/Ni(111) and Cu/Ni(111) are obtained and their turnover frequencies (TOFs) are computed. The results show that acetylene adsorption on Ni catalyst is strong which leads to the low activity while the doping of Au, Ag, and Cu on the Ni catalyst weakens the acetylene adsorption, giving rise to the increase of activity. The selectivity of ethylene formation is also quantified by using the energy difference between the hydrogenation barriers and the absolute value of the adsorption energies of ethylene. It is found that the selectivity of ethylene formation increases by doping Au and Ag, while those of Cu/Ni and Ni are similar.

In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.

Rapid and nondestructive measurement of labile Mn, Cu, Zn, Pb and As in DGT by using field portable-XRF

The technique of diffusive gradients in thin films (DGT) is often employed to quantify labile metals in situ; however, it is a challenge to perform the measurements in-field. This study evaluated the capability of field-portable X-ray fluorescence (FP-XRF) to swiftly generate elemental speciation information with DGT. Biologically available metal ions in environmental samples passively preconcentrate in the thin films of DGT devices, providing an ideal and uniform matrix for XRF nondestructive detection. Strong correlation coefficients (r > 0.992 for Mn, Cu, Zn, Pb and As) were obtained for all elements during calibration. The limits of quantitation (LOQ) for the investigated elements of FP-XRF on DGT devices are 2.74 for Mn, 4.89 for Cu, 2.89 for Zn, 2.55 for Pb, and 0.48 for As (unit: µg cm(-2)). When Pb and As co-existed in the solution trials, As did not interfere with Pb detection when using Chelex-DGT. However, there was a significant enhancement of the Pb reading attributed to As when ferrihydrite binding gels were tested, consistent with Fe-oxyhydroxide surfaces absorbing large quantities of As. This study demonstrates the value of the FP-XRF technique to rapidly and nondestructively detect the metals accumulated in DGT devices, providing a new and simple diagnostic tool for on-site environmental monitoring of labile metals/metalloids

An efficient Cu(II)-bis(oxazoline)-based polymer immobilised ionic liquid phase catalyst for asymmetric carbon–carbon bond formation

The asymmetric Diels-Alder reaction between N-acryloyloxazolidinone and cyclopentadiene and the Mukaiyama-aldol reaction between methylpyruvate and 1-phenyl-1-trimethylsilyloxyethene have been catalysed by heterogeneous copper(II)-bis(oxazoline)-based polymer immobilised ionic liquid phase (PIILP) systems generated from a range of linear and cross linked ionic polymers. In both reactions selectivity and ee were strongly influenced by the choice of polymer. A comparison of the performance of a range of Cu(II)-bis(oxazoline)-PIILP catalyst systems against analogous supported ionic liquid phase (SILP) heterogeneous catalysts as well as their homogeneous counterparts has been undertaken and their relative merits evaluated.

A low temperature, isothermal gas-phase system for conversion of methane to methanol over Cu-ZSM-5

A low temperature, isothermal, gas-phase, recyclable process is described for the partial oxidation of methane to methanol over Cu–ZSM-5. Activation in NO at 150 °C followed by methane reaction and steam extraction (both at 150 °C) allowed direct observation of methanol at the reactor outlet.

AN ADSORBATE-STABILIZED VACANCY STRUCTURE FOR CU ON W(100) - A SURFACE ALLOY

Deposition of 0.5 ML of Cu on W(100) leads to the formation of a sharp c(2 x 2) structure when the surface is annealed at 800 K. A LEED intensity analysis reveals that the Cu atoms are adsorbed displacively into W sites, forming an ordered 2D surface alloy. Due to the lattice mismatch between copper and tungsten, a substantial buckling of the first layer of the alloy is also observed. The clean, bulk terminated W(100) surface is only just stable relative to the c(2 x 2) vacancy covered W(100) surface. This relative stability of the vacancy structure explains the driving force behind the formation of this alloy.