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Development of epitaxial silicon lattice-matched insulators: silicon heterostructures for quantum confinement

Epitaxial films of the wide-bandgap II–VI beryllium chalcogenide semiconductors, BeTe, BeSe, and BeSeTe were grown on arsenic-terminated silicon substrates by MBE. Silicon was also epitaxially regrown on Be-chalcogenide films. Initial structural characterization revealed the desired smooth two-dimensional nature of the layer growth. The composition of BeSeTe ternary films was governed by the Be/Se flux ratio during deposition rather than by the Se/Te flux ratio. The variation in Be/Se flux ratio or in the sticking coefficients due to temperature gradients led to radial compositional inhomogeneity. Current versus temperature measurements of the Be-chalcogenide films at elevated temperatures analyzed assuming thermionic emission over the heterojunction barrier, showed conduction band offsets of 1.2 eV for the BeSe_0.41Te_0.59/As/Si and 1.3 eV for the BeSe/As/Si heterostructures. At room temperature, current density through BeSe/Si and BeSe_0.41Te_0.59/Si films was mid-10 ^{− 9}A cm ^{− 2}at 0.1 MV cm ^{− 1}, similar to previously reported values for ZnS/Si, while BeTe/Si films had orders of magnitude higher current density, possibly due to interfacial recombination.     

Peapod‐Type Nanocomposites through the In Situ Growth of Gold Nanoparticles within Preformed Hexaniobate Nanoscrolls

A facile in situ method to grow Au nanoparticles (NPs) in hexaniobate nanoscrolls is applied to the formation of plasmonic Au@hexaniobate and bifunctional plasmonic‐magnetic Au‐Fe₃O₄@hexaniobate nanopeapods (NPPs). Utilizing a solvothermal treatment, rigid multiwalled hexaniobate nanoscrolls and partially filled Fe₃O₄@hexaniobate NPPs were first fabricated. These nanostructures were then used as templates for the controlled in situ growth of Au NPs. The resulting peapod structures exhibited high filling fractions and long‐range uniformity. Optical measurements showed a progressive red shift in plasmonic behavior between Au NPs, Au NPPs, and Au‐Fe₃O₄ NPPs; magnetic studies found that the addition of gold in the Fe₃O₄@hexaniobate NPPs reduced interparticle coupling effects. The development of this approach allows for the routine bulk preparation of noble‐metal‐containing bifunctional nanopeapod materials.     

Dilatometric Study of the Kinetics of the Polymerization of Pure meta-and Pure para-Divinylbenzenes

Abstract

A comparison of the dilatometrically determined rates of polymerization of pure meta-and pure para-divinylbenzenes confirms the previous observation that the meta isomer polymerizes more rapidly than the para isomer. This difference shows up also in the initiator square root rate dependencies, the gel times, and the conversions at gel point. The effect of added regulator (carbon tetrabromide) on the polymerization of the meta isomer is to decrease the gel time and conversion at gel time.     

“Reviews in Macromolecular Chemistry”

Abstract

In the homopolymerization and copolymerization of vinyl acetate with dibutyl maleate in the presence of the sodium salt of sulfosuccinic acid semiester with nonylphenol ethoxylated with 25 mol ethylene oxide, the initiator, potassium persulfate (KPS), has a higher decomposition rate than in water even after consumption of monomer. The value of the initiator productivity, P, defined as the ratio of the formed polymer over the decomposed KPS, decreases as the batch stage of the semicontinuous process proceeds. The initiator reacts either with free surfactant molecules or with those grafted on poly(vinyl acetate) chains. During the stage of continuous addition of monomers and KPS, a smaller initiator concentration no longer provides proportionality between the added and decomposed amounts of initiator. The increased monomer concentration at the beginning of continuous addition causes the rate of KPS splitting to decrease as most of the surfactant is bound to the surface monomer/polymer particles.     

Whey protein concentrate production by continuous ultrafiltration: Operability under constant operating conditions

There is limited information available on quantifying the operability of continuous ultrafiltration plants used for the production of whey protein concentrates. Based on modelling of the process, the operability studies demonstrate that a standard 12 loop commercial ultrafiltration plant is able to produce the desired specifications of the concentrates. The studies also indicate that mid-run washing of the plant is necessary to reduce the effects of long-term membrane fouling. Although it becomes more difficult to achieve the desired product flowrate as protein concentration in the feed increases, proper knowledge of process variations makes it possible to compensate for the effects from fluctuations in whey composition in order to maintain the desired specifications of the concentrates.     

The Cu-catalyzed exo-selective asymmetric multicomponent [C+NC+CC] coupling reaction

A novel Cu^I-catalyzed exo-selective asymmetric [C+NC+CC] coupling reaction is reported that provides unprecedented access to a variety of highly functionalized 4,5-trans disubstituted pyrrolidines in a single operation. The reaction complements and extends our Ag^I-catalyzed endo-selective [C+NC+CC] asymmetric coupling reaction.     

In situ analysis of agrochemical residues on fruit using ambient ionization on a handheld mass spectrometer

We describe a rapid in situ method for detecting agrochemicals on the surface or in the tissue of fruit using a portable mass spectrometer equipped with an ambient ionization source. Two such ionization methods, low temperature plasma (LTP) and paper spray (PS), were employed in experiments performed at a local grocery store. LTP was used to detect diphenylamine (DPA) directly from the skin of apples in the store and those treated after harvest with DPA were recognized by MS and MS/MS. These data therefore allowed ready distinction between organic and non-organic apples. DPA was also found within the internal tissue of purchased apples and its distribution was mapped using LTP. Similarly, thiabendazole residues were detected on the skin of treated oranges in a grocery store experiment in which paper spray was performed by wiping the orange surface with a moist commercial lens wipe and then applying a high voltage to ionize the chemicals directly from the wipe. The handheld mass spectrometer used in these measurements is capable of performing several stages of tandem mass spectrometry (up to MS(5)); the compounds on the fruit were identified by their MS/MS fragmentation patterns. Protonated DPA (m/z 170) produced a characteristic MS(2) fragment ion at m/z 92, while thiabendazole was identified by MS(3) using precursor to fragment ion transitions m/z 202 →m/z 175 →m/z 131. These particular examples exemplify the power of in situ analysis of complex samples using ambient ionization and handheld mass spectrometers.