In situ X-ray analysis of solid/electrolyte interfaces: electrodeposition of Cu and Co on Si(1 1 1):H and GaAs(0 0 1) and corrosion of Cu3Au(1 1 1)

Electrochemical deposition of Cu and Co in monolayer amounts on hydrogen terminated Si(1 1 1) was studied ex situ and in situ by X-ray techniques. The X-ray beam was found to have a strong effect on the deposit causing desorption under the beam. Cu deposition on GaAs(0 0 1) from UHV is compared with electrodeposited Cu on the same surface, elucidating similarities and differences of electrochemical and UHV deposition. Roughening due to corrosion of Cu₃Au(1 1 1) is observed by crystal truncation scattering. The observed behaviour of passivation of this surface is explained by the formation of Au clusters, increasingly covering the surface at higher oxidation potential.     

Structure of Ag(111)-p(4 x 4)-O: no silver oxide

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.     

Marine natural products-XVI : Polyhalogenated acyclic monoterpenes from the red alga plocamium of antarctica

Examination of the red alga Plocamium sp. collected near the Antarctic penninsula yielded three new acyclic halogenated monoterpenes (1–3). A structure revision is proposed for a compound previously reported to have structure 1. X-ray diffraction provided the structure of 1 including absolute stereochemistry. The structures of 2 and 3 followed from proton and ¹³C NMR spectral interpretation.     

Structural properties of high-quality sputtered Fe films on Al2O3(1120) and MgO(001) substrates

High-quality thin Fe films were deposited on MgO(001) and Al₂O₃(1120) substrates in the thickness range from 7 to 50 nm. The structural properties have been studied by out-of-plane and in-plane X-ray scattering experiments. From the out-of-plane measurements the electron density profile was determined together with interface and surface roughness parameters. Fe on Al₂O₃ grows along the [110]-direction with a structural coherence length comprising about the total film thick ness and a very small mosaicity. From in-plane scattering experiments a three-domain structure was observed. On MgO(001) substrates Fe grows in the [001]-direction, with the Fe [100]-axis parallel to the MgO [110]-axis. On both substrates, the Fe films exhibit a very small surface and interface roughness, indicative for a high quality of the sputtered samples.     

Initial oxidation of MgO-supported Rh nanoparticles studied by TEM

The formation of ultrathin oxide layers on the facets of MgO(0 0 1) supported Rh nanoparticles is revealed by high-resolution transmission electron microscopy (HRTEM) and spatially-resolved electron energy-loss spectroscopy (EELS). An O–Rh–O trilayer surface oxide has been observed on both {1 1 1} and (0 0 1) facets, which is confirmed by image simulation using the atomic model of a two-dimensional surface oxide obtained by density functional theory (DFT). The spacing between the oxide layer and the Rh {1 1 1} facet is however markedly smaller, indicating a variation of interface bonding in the case of nanoparticles. When the oxide layer is slightly thicker with two Rh planes, the structure of the surface oxide is different from corundum Rh₂O₃ bulk oxide, and the trilayer surface oxide persists as terminating layer. The spacing between the oxide layer and the Rh(1 1 1) facet is found to vary, being smaller in the middle of the oxide layer. It is also found that oxidation is more pronounced at the intersections of the nanoparticles’ facets.     

Non‐uniform nanosecond gate‐delay of hybrid pixel detectors

A simple experiment to characterize the gating properties of X‐ray area detectors using pulsed X‐ray sources is presented. For a number of time‐resolved experiments the gating uniformity of area detectors is important. Relative gating delays between individual modules and readout chips of PILATUS2 series area X‐ray detectors have been observed. For three modules of a PILATUS 300K‐W unit the maximum gating offset between the modules is found to be as large as 30 ns. On average, the first photosensor module is found to be triggered 15 ns and 30 ns later than the second and the third modules, respectively.     

Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures

The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.     

Syntheses and reactions of some fluorinated dienes,cyclobutenes and furans

There are many reports¹ of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically

useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed.We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described.

For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.

     

ChemInform Abstract: The Ground-State Potential Energy Surface of Diazene

has been studied by using a complete active space MCSCF wave function generated by distributing eight electrons among eight orbitals.