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

Metabolic profiling detects early effects of environmental and lifestyle exposure to cadmium in a human population

Background: The ‘exposome’ represents the accumulation of all environmental exposures across a lifetime. Topdown strategies are required to assess something this comprehensive, and could transform our understanding of how environmental factors affect human health. Metabolic profiling (metabonomics/metabolomics) defines an individual’s metabolic phenotype, which is influenced by genotype, diet, lifestyle, health and xenobiotic exposure, and could also reveal intermediate biomarkers for disease risk that reflect adaptive response to exposure. We investigated changes in metabolism in volunteers living near a point source of environmental pollution: a closed zinc smelter with associated elevated levels of environmental cadmium. Methods: High-resolution 1H NMR spectroscopy (metabonomics) was used to acquire urinary metabolic profiles from 178 human volunteers. The spectral data were subjected to multivariate and univariate analysis to identify metabolites that were correlated with lifestyle or biological factors. Urinary levels of 8-oxo-deoxyguanosine were also measured, using mass spectrometry, as a marker of systemic oxidative stress. Results: Six urinary metabolites, either associated with mitochondrial metabolism (citrate, 3-hydroxyisovalerate, 4- deoxy-erythronic acid) or one-carbon metabolism (dimethylglycine, creatinine, creatine), were associated with cadmium exposure. In particular, citrate levels retained a significant correlation to urinary cadmium and smoking status after controlling for age and sex. Oxidative stress (as determined by urinary 8-oxo-deoxyguanosine levels) was elevated in individuals with high cadmium exposure, supporting the hypothesis that heavy metal accumulation was causing mitochondrial dysfunction. Conclusions: This study shows evidence that an NMR-based metabolic profiling study in an uncontrolled human population is capable of identifying intermediate biomarkers of response to toxicants at true environmental concentrations, paving the way for exposome research. Keywords: metabonomics, cadmium, environmental health, exposome, metabolomics, molecular epidemiolog

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

Atomistic mechanisms for the ordered growth of Co nano-dots on Au(788): comparison of VT-STM experiments and multi-scaled calculations

Hetero-epitaxial growth on a strain-relief vicinal patterned substrate has revealed unprecedented 2D long range ordered growth of uniform cobalt nanostructures. The morphology of a Co sub-monolayer deposit on a Au(111) reconstructed vicinal surface is analyzed by Variable Temperature Scanning Tunneling Microscopy (VT-STM) experiments. A rectangular array of nano-dots (3.8 nm x 7.2 nm) is found for a particularly large deposit temperature range lying from 60 K to 300 K. Although the nanodot lattice is stable at room temperature, this paper focus on the early stage of ordered nucleation and growth at temperatures between 35 K and 480 K. The atomistic mechanisms leading to the nanodots array are elucidated by comparing statistical analysis of VT-STM images with multi-scaled numerical calculations combining both Molecular Dynamics for the quantitative determination of the activation energies for the atomic motion and the Kinetic Monte Carlo method for the simulations of the mesoscopic time and scale evolution of the Co submonolayer

Self-assembly of quantum dots: effect of neighbor islands on the wetting in coherent Stranski-Krastanov growth

The wetting of the homogeneously strained wetting layer by dislocation-free three-dimensional islands belonging to an array has been studied. The array has been simulated as a chain of islands in 1+1 dimensions. It is found that the wetting depends on the density of the array, the size distribution and the shape of the neighbor islands. Implications for the self-assembly of quantum dots grown in the coherent Stranski-Krastanov mode are discussed.Comment: 4 pages, 6 figures, accepted version, minor change

Electrical properties of ZnO nanorods studied by conductive atomic force microscopy

ZnO nanostructures are promising candidates for the development of novel electronic devices due to their unique electrical and optical properties. Here, we present a complementary electrical characterization of individual upright standing and lying ZnO nanorods using conductive atomic force microscopy (C-AFM). Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps. The current maps were recorded simultaneously with the topography acquired by contact mode AFM. Further, C-AFM was utilized to determine the local current-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. Current-voltage characterization revealed a characteristic similar to that of a Schottky diode. Detailed discussion of the electrical properties is based on local I-V curves, as well as on the 2D current maps recorded from specific areas. © 2011 American Institute of Physics.published_or_final_versio