The Fate of a Cluster Colliding onto a Substrate Dissipation of Translational Kinetic Energy

The fate of clusters emitted onto a substrate falls into several categories including repulsion, soft landing, migration, and explosion, depending on the interaction between the cluster and the substrate. This dynamic behavior of the clusters controls thin-film formation processes from clusters such as cluster ion beam deposition and chemical vapor deposition. Here we describe the collision processes of both Al and Au clusters with a kinetic energy of 0.56 eV/atom onto an amorphous SiO₂ substrate studied by molecular dynamics simulation, focusing on the dissipation of translational kinetic energy during the collision process. The simulation elucidated that the activation of thermal vibrational energy of the substrate promoted the sticking of the colliding clusters on the substrate. This result suggests that the dissipation of the translational kinetic energy of the colliding cluster is one of the factors that determine the structure formed on a substrate from vapor phase.     

End‐functionalized copolymers prepared by the addition–fragmentation chain‐transfer method: Vinyl acetate/methacrylonitrile system

Copolymers of vinyl acetate and methacrylonitrile were prepared by free‐radical polymerization in the presence of the chain‐transfer agent (CTA) ethyl‐α‐ (t‐butanethiomethyl)acrylate. Molecular weight measurements showed that the chain‐transfer constants increased with the vinyl acetate content of the comonomer mixture, ranging from 0.42 for methacrylonitrile to 6.3 for the copolymerization of a vinyl acetate‐rich monomer mix (89/11). The bulk copolymer composition was not appreciably affected by the amount of CTA used in the copolymerization. The efficiency of the addition–fragmentation mechanism in producing specifically end‐functionalized copolymers was investigated with ¹H NMR spectroscopy. Spectral peaks consistent with all the expected end groups were observed for all comonomer feeds. Peaks consistent with other end groups were also observed, and these were particularly prominent for copolymers made with lower CTA concentrations. At the highest concentrations used, quantitative measurements of end‐group concentrations indicated that 70–80% of the end groups were those expected on the basis of the addition–fragmentation chain‐transfer mechanism. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2911–2919, 2001     

Superior Nanoporous Polyimides via Supercritical CO2 Drying of Jungle‐Gym‐Type Polyimide Gels

We report novel nanoporous polyimides formed from jungle‐gym‐type rigid polyimide gels by supercritical CO₂ drying. By virtue of supercritical CO₂ drying to avoid the collapse of nanostructure, porosity above 90 vol.‐% was achieved. We found a rich variety of nanoporous structures in the range of 50–800 nm such as crisp fragments, minute network, and highly‐connected beads. These characteristic structures were formed by the competitive progress of liquid‐liquid phase separation and crystallization induced due to the two chemical reactions of end‐crosslinking and thermal imidization during gelation.

     

An organopalladium(II) compound including enolate oxy­gen‐ and sp3‐carbon‐bound 1,3‐di­methyl­barbiturate ligands: (1,2‐di­amino­ethane)­bis(1,3‐di­methyl­barbiturato)­palladium(II) 5.5‐hydrate

In the title compound, [Pd(C₆H₇N₂O₃)₂(C₂H₈N₂)]·5.5H₂O, the Pd atom is coordinated by two 1,3‐di­methyl­barbiturate anions through a deprotonated tetrahedral carbon and the enolate oxy­gen. The Pd—N bond length of 2.078 (2) Åtrans to the C atom is shorter than the Pt—N distance of 2.098 (3) Å in the Pt analog.     

Facets formation of pyramidal Si nanocrystals selectively grown on Si(0 0 1) windows in ultrathin SiO2 films

We have used in situ scanning tunneling microscopy (STM) to study the facet formation in the selective growth of pyramidal Si nanocrystals on Si(0 0 1) windows in ultrathin 0.3-nm-thick SiO₂ films. Broad (0 0 1) surfaces developed as the top of the crystals, and {1, 1, (2n+1)} (n=1–6) facets formed the sidewalls. As growth continued, the slope angle of sidewall facets increased, and {1, 1, 9} and {1, 1, (2m+1)} (0 <m < 4) facets often came to coexist on the sidewalls. On well-oriented Si(0 0 1) surfaces, layer-by-layer growth in the [0 0 1] direction was dominant. On vicinal Si(0 0 1) surfaces, lateral step growth took place in the initial stage, and the layer-by-layer growth was suppressed until after a large (0 0 1) surface had formed as the top of the crystal.     

Effect of substrate dielectric anisotropy on the frequency behaviorof microstrip circuits

In this paper, we carry out a full-wave analysis of shielded two-port microstrip circuits, in which the metallizations are embedded in a multilayered substrate that may contain isotropic dielectrics and/or anisotropic dielectrics. The Galerkin's method in the spectral domain is applied for determining the current density on the metallizations of the circuits when their feeding lines are excited by means of delta-gap generators, and the matrix pencil technique is subsequently used for deembedding the scattering parameters from the computed current densities. Results are presented for the scattering parameters of some microstrip discontinuities and filters printed on both isotropic dielectric substrates and anisotropic dielectric substrates. These results show that when substrate dielectric anisotropy is ignored, errors arise when computing the scattering parameters of microstrip discontinuities and when predicting the operating frequency band of microstrip filters     

Quantitative determination of paclitaxel and its metabolites, 6α‐hydroxypaclitaxel and p‐3′‐hydroxypaclitaxel,in human plasma using column‐switching liquid chromatography/tandem mass spectrometry

A column‐switching liquid chromatography/electrospray ionization tandem mass spectrometry to determine paclitaxel and its metabolites, 6α‐hydroxypaclitaxel and p‐3′‐hydroxypaclitaxel, in human plasma was developed. The analytical system had a Shim‐Pack MAYI‐ODS (10 × 4.6 mm i.d.) trapping column with deproteinization ability that concentrates analytes and removes water‐soluble components. This method covered a linearity range of 5–5000 ng/mL of concentrations in plasma for paclitaxel, a range of 0.87–870 ng/mL for 6α‐hydroxypaclitaxel and a range of 0.87–435 ng/mL for p‐3′‐hydroxypaclitaxel. The intra‐day precision and inter‐day precision of analysis were less than 11.1%, and the accuracy was within ±14.4% at concentrations of 5, 50, 500 and 5000 ng/mL for paclitaxel, 0.87, 8.7, 87 and 870 ng/mL for 6α‐hydroxypaclitaxel, and 0.87, 8.7, 87 and 435 ng/mL for p‐3′‐hydroxypaclitaxel. The total run time was 30 min. Our method was successfully applied to clinical pharmacokinetic investigation. Copyright © 2012 John Wiley & Sons, Ltd.     

A One-Dimensional Propagation of Shock Wave Supported by Atmospheric Millimeter-Wave Plasma

A shock wave supported by an atmospheric breakdown plasma caused by a high-power millimeter-wave beam was studied. The shadow graph image in a shock tube visualized the one-dimensional shock-wave generated by the millimeter-wave breakdown in atmosphere for the first time. It was revealed that a normal shock wave propagated through the tube at the constant velocity while it was detached from the ionization front of the plasma whenever the propagation velocity of the ionization front was supersonic or subsonic. And it was visually clarified that the atmospheric millimeter-wave breakdown had the combined structure of the normal shock wave and the heating region of the millimeter-wave plasma. The measured pressure of the shock front was as equal as the normal shock which propagated at measured Mach number.