High-repetition rate pulsed laser deposition of ZrC thin films

ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that the films were crystalline. Films deposited under residual vacuum or 2 × 10^− 3 Pa of CH₄ atmosphere exhibited a (200)-axis texture, while those deposited under 2 × 10^− 2 Pa of CH₄ atmosphere were found to be equiaxed. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES), showed the usual high oxygen contamination of carbides. Once the topmost − 3-5 nm region was removed, the oxygen concentration rapidly decreased, being around 3-4% only in bulk. Scanning electron microscopy (SEM) investigations showed a smooth, featureless surface morphology, corroborating the roughness values below 1 nm (rms) obtained from simulations of the X-ray reflectivity (XRR) curves. From the same simulations we also estimated films mass density values of around 6.32-6.57 g/cm³ and thicknesses that correspond to a deposition rate of around 8.25 nm/min. Nanoindentation results showed a hardness of 27.6 GPa and a reduced modulus of 228 GPa for the best quality ZrC films deposited under an atmosphere of 2 × 10^− 3 Pa CH₄.     

Heat Treatment and Chemical Composition of Fatty Acids and Rosin Acids Mixtures: Effects on Their Thermal Properties and Morphology

Mixtures of fatty acids and rosin acids are industrially important products utilized as a raw material for several purposes. Their thermal properties, especially cold stability and crystallization behavior is also important. Several fatty acid and rosin acid mixtures both from industrial products and from commercially available fatty and rosin acids were prepared and treated for 30 min at 80 °C under an inert atmosphere. Thereafter, the mixture was cooled to the desired temperature. Determination of the cloud point, chemical analysis of liquid and solid phase, thermal analysis by differential scanning calorimetry as well as morphology analysis by scanning electron microscopy were performed. The results revealed that crystallization was more rapid when it occurred at 10 °C compared to 25 °C. The crystal sizes increased with decreasing the crystallization temperature. Furthermore, crystals were of irregular shape and agglomerated when rapid cooling of the mixture occurred. Chemical analysis revealed that liquid phase was enriched with stearic acid, whereas crystals contained large amounts of abietic, dehydroabietic and linoleic acids. The cloud point of the mixtures increased with increasing amount of stearic and rosin acids. Dehydroabietic acid addition improved the cold stability of the synthetic fatty acid–rosin acids mixture.     

Simultaneous translational temperature measurements of different atomic species in plasma flows using scanning Fabry-Perot interferometry

A revised scientific instrument to measure simultaneously kinetic temperatures of different atoms from their optical emission profile is reported. Emission lines are simultaneously detected using one single scanning Fabry-Perot-interferometer (FPI) for a combined spectroscopic setup to acquire different emission lines simultaneously. The setup consists in a commercial Czerny-Turner spectrometer configuration which is combined with a scanning Fabry-Perot interferometer. The fast image acquisition mode of an intensified charge coupled device camera allows the detection of a wavelength interval of interest continuously while acquiring the highly resolved line during the scan of the FPI ramp. Results using this new setup are presented for the simultaneous detection of atomic nitrogen and oxygen in a high enthalpy air plasma flow as used for atmospheric re-entry research and their respective kinetic temperatures derived from the measured line profiles. The paper presents the experimental setup, the calibration procedure, and an exemplary result. The determined temperatures are different, a finding that has been published so far as due to a drawback of the experimental setup of sequential measurements, and which has now to be investigated in more detail.     

Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region

A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of ~8 to ~120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.     

MRT letter: Nanoscopy of protein colocalization in living cells by STED and GSDIM

We report the use of superresolution fluorescence microscopy for studying the nanoscale distribution of protein colocalization in living mammalian cells. Nanoscale imaging is attained both by a targeted and a stochastic fluorescence on-off switching superresolution method, namely by stimulated emission depletion (STED) and ground state depletion microscopy followed by individual molecular return (GSDIM), respectively. Analysis of protein colocalization is performed by bimolecular fluorescence complementation (BiFC). Specifically, a nonfluorescent fragment of the yellow fluorescent protein Citrine is fused to tubulin while a counterpart nonfluorescent fragment is fused to the microtubulin-associated protein MAP2 such that fluorescence is reconstituted on contact of the fragment-carrying proteins. Images with resolution down to 65 nm prove a powerful new way for studying protein colocalization in living cells at the nanoscale.     

Activation of Ni/A12O3 catalysts through modification of the Al2O3 support

The effect of alumina pretreatment on the performance of alumina supported nickel catalysts was demonstrated in gas phase hydrogenation of toluene to methylcyclohexane. The state of the alumina was changed from pure to pure phase through various heat treatments in air. The catalysts were prepared from vapor phase by saturating the accessible binding sites on the pretreated alumina with the nickel precursor. The highest number of active sites for hydrogenation was observed for catalysts prepared on alumina having an incomplete phase transition and a / alumina phase ratio between 0.5 and 10. Results from temperature programmed desorption (TPD) studies revealed that a maximum in weakly chemisorbed hydrogen as well as in total amount of desorbed hydrogen was found for the same catalysts. By hydrogen chemisorption studies the total hydrogen uptake was found to correlate with the observed hydrogenation maximum. It is suggested that both the chemical and physical properties of the alumina influence the activity. An optimal metal-support interaction and structural defects on the alumina due to the phase transition can explain the observed maximum in the number of active sites and in hydrogen uptake.     

Zeolite HNU-87: synthesis, characterization and catalytic properties in the shape-selective conversion of methylnaphthalenes

The synthesis of the high-silica zeolite NU-87 and its physicochemical characterization are reported. The catalytic properties of zeolite HNU-87 were investigated in the conversion of 1- and 2-methylnaphthalene. Both isomerization to the corresponding methylnaphthalene and transalkylation to naphthalene and dimethylnaphthalenes are observed. The influence of reaction temperature and the modified residence time on the product distributions is reported and discussed in terms of shape selectivity effects in the peculiar pore system of NU-87. For comparison, typical results obained with zeolite HMCM-22, which possesses a similar pore architecture, are also included. The results of methylnaphthalene conversion over HNU-87 are compared to those obtained in the alkylation of naphthalene with methanol on the same zeolite catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Slope deposits and water paths in a spring catchment, Frankenwald, Bavaria, Germany

The spring catchment under study is underlain by shale, on which several layers of slope sediments (cover-beds) are deposited. The upper of these layers contain eolian fines mixed into shale-derived debris, which latter material entirely comprises the basal cover-bed. Due to its dislocation by solifluction, the shale debris has a tegular structure. This leads to hydraulic anisotropy, particularly where no fine earth occurs. Thus, water that seeps into such material is forced to flow laterally while vertical movement is impeded. The basal cover-bed therefore hosts a deep aquifer. Only during major discharge events, excess hydrostatic pressure makes water flow into upper parts of the soils, being mixed with surficially interflowing water. Most of the time, however, there are two levels of water flow at different depths with different dwelling times, which finding is supported by probably geogenic sulphur isotopes in the deeply flowing water that are different from precipitation water.KurzfassungDas bearbeitete Quelleinzugsgebiet liegt in Tonschiefer, welcher mit Deckschichten bedeckt ist. In die oberen Deckschichten wurde Löß eingearbeitet, während die untere ausschließlich aus umgelagertem Anstehenden besteht. Dieses Material wurde solifluidal verlagert und dabei mit einer dachziegelartigen Struktur abgelagert. Diese führt zu hydraulischer Anisotropie besonders in feinerdearmen Schichten. Wasser, das darin einsickert, fließt bevorzugt lateral, während vertikale Bewegungen stark behindert werden. Deshalb ist in der Basislage ein tieferes Aquifer entstanden. Während ausgeprägter Abflußereignisse wird der Überdruck darin jedoch so groß, daß es zu einem Aufpressen des Wasser in hangende Schichten und dort zur Vermischung mit höherem Zwischenabfluß kommt. Zumeist aber gibt es zwei unterschiedliche Interflow-Stockwerke in verschiedenen Tiefen. Dies wird bestätigt durch eine wahrscheinlich geogene Sulfatbeimischung im tieferen Stockwerk, die sich vom Niederschlagswasser in den Isotopen unterscheidet.