Catalytic hydrogenation of α,β-unsaturated carboxylic acid derivatives using copper(i)/N-heterocyclic carbene complexes

A simple and air-stable copper(I)/N-heterocyclic carbene complex enables the catalytic hydrogenation of enoates and enamides, hitherto unreactive substrates employing homogeneous copper catalysis and H2 as a terminal reducing agent. This atom economic transformation replaces commonly employed hydrosilanes and can also be carried out in an asymmetric fashion.TU Berlin, Open-Access-Mittel - 201

Evaporative gold nanorod assembly on chemically stripe-patterned gradient surfaces

Experimentally we explore the potential of using pre-defined motion of a receding contact line to control the deposition of nanoparticles from suspension. Stripe-patterned wettability gradients are employed, which consist of alternating hydrophilic and hydrophobic stripes with increasing macroscopic surface energy. Nanoparticle suspensions containing nanorods and nanospheres are deposited onto these substrates and left to dry. After moving over the pattern and evaporation of the solvent, characteristic nanoparticle deposits are found. The liquid dynamics has a pronounced effect on the spatial distribution. Nanoparticles do not deposit on the hydrophobic regions; there is high preference to deposit on the wetting stripes. Moreover, the fact that distributed nanoparticle islands are formed suggests that the receding of the contact line occurs in a stick-slip like fashion. Furthermore, the formation of liquid bridges covering multiple stripes during motion of the droplet over the patterns is modeled. We discuss their origin and show that the residue after drying, containing both nanoparticles and the stabilizing surfactant, also resembles such dynamics. Finally, zooming into individual islands reveals that highly selective phase separation occurs based on size and shape of the nanoparticle

The effect of extraction techniques on calcium concentrations and isotope ratios of marine pore water

Comparing two different techniques applied for the extraction of marine pore water samples from sediments, the well-established whole round (WR) method and the more recent Rhizon method, in terms of their effects on stable calcium isotope ratios in extracted pore waters, we recognize a systematic offset between the two sampling methods. Higher δ44/40Ca values are associated with lower Ca concentrations for the Rhizon sampling technique and lower δ44/40Ca values are associated with higher Ca concentrations for the corresponding WR-derived pore water samples. Models involving Rayleigh fractionation and mixing calculation suggest that the observed offset is most likely caused by a combined process of CaCO3 precipitation and ion exchange taking place during Rhizon sampling-induced CO2 degassing. Changing pressure, extraction time or extraction yield during WR pressing does not lead to a variation in δ44/40Ca, indicating that no Ca isotope fractionation takes place during the sampling of pore water. On the basis of analytical and modelling results, WR samples appear to provide δ44/40Ca values that are more representative of the ‘true’ pore water isotopic composition. While the difference between the sampling techniques is close to the present-day analytical precision of Ca isotope analysis, it may become more relevant with increasing analytical precision in the future

Is keV ion induced pattern formation on Si(001) caused by metal impurities?

We present ion beam erosion experiments performed in ultra high vacuum using a differentially pumped ion source and taking care that the ion beam hits the Si(001) sample only. Under these conditions no ion beam patterns form on Si for angles below 45 degrees with respect to the global surface normal using 2 keV Kr ions and fluences of 2 x 10^22 ions/m^2. In fact, the ion beam induces a smoothening of preformed patterns. Simultaneous sputter deposition of stainless steel in this angular range creates a variety of patterns, similar to those previously ascribed to clean ion beam induced destabilization of the surface profile. Only for grazing incidence with incident angles between 60 degrees and 83 degrees pronounced ion beam patterns form. It appears that the angular dependent stability of Si(001) against pattern formation under clean ion beam erosion conditions is related to the angular dependence of the sputtering yield, and not primarily to a curvature dependent yield as invoked frequently in continuum theory models.Comment: 15 pages, 7 figures. This is an author-created, un-copyedited version of an article published in Nanotechnology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Nanoscale electrical characterization of arrowhead defects in GalnP thin films grown on Ge

In this work the authors present an electrical characterization of the so called arrowhead defects (ADs) in GaInP thin films grown on Ge(100) substrates misoriented by 6° toward (111). The samples have been evaluated by means of conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). It is shown that the ADs have terminating planes which are composed from two alternating subplanes inclined 12° (close to {105} plane) and 6° (close to {109}) with respect to the (100) plane. The terminating planes of the arrowhead defects possess higher conductivity compared to their surrounding. The terminating planes differ also in their electrical behavior from each other, demonstrating different values of conductivity (C-AFM) and bucking voltages (KPFM). The difference in current densities between two terminating planes was found to be ∼ 170±35 μA/m2 at −3 V, and the difference in the bucking voltages was ∼ 70 mV at 5 V of the electrical excitation signal in the lift mode. It is suggested that the distinctive electrical behavior of the ADs is caused by an ordering effect which leads in this case to the degraded electrical properties of the ADs

Effects of polymethylmethacrylate-transfer residues on the growth of organic semiconductor molecules on chemical vapor deposited graphene

Scalably grown and transferred graphene is a highly promising material for organic electronic applications, but controlled interfacing of graphene thereby remains a key challenge. Here, we study the growth characteristics of the important organic semiconductor molecule para-hexaphenyl (6P) on chemical vapor deposited graphene that has been transferred with polymethylmethacrylate (PMMA) onto oxidized Si wafer supports. A particular focus is on the influence of PMMA residual contamination, which we systematically reduce by H2 annealing prior to 6P deposition. We find that 6P grows in a flat-lying needle-type morphology, surprisingly independent of the level of PMMA residue and of graphene defects. Wrinkles in the graphene typically act as preferential nucleation centers. Residual PMMA does however limit the length of the resulting 6P needles by restricting molecular diffusion/attachment. We discuss the implications for organic device fabrication, with particular regard to contamination and defect tolerance.B.C.B acknowledges a College Research Fellowship from Hughes Hall, Cambridge. P.R.K. acknowledges the Lindemann Trust Fellowship. A.M. and G.R. acknowledge support by the Serbian MPNTR through Projects OI 171005 and III 45018. R.S.W. acknowledges a research fellowship from St. John’s College, Cambridge. S.H. acknowledges funding from EPSRC (GRAPHTED, Grant No. EP/K016636/1). We want to thank Dr. Sarah M. Skoff (Vienna University of Technology, Austria) for fruitful discussions.This is the author accepted manuscript. The final published version is available via AIP at http://scitation.aip.org/content/aip/journal/apl/106/10/10.1063/1.4913948