用准分子激光诱导湿刻实现对GaAs的图形转换

本文报告的是利用准分子激光诱导湿刻和光刻技术相结合的方法,实现了对GaAs的图形转换。发现由GaAs表面的金膜、水溶液和GaAs构成的系统中,金膜不仅起了光掩蔽的作用,而且还起了促进刻蚀作用。结果说明这是一个电化学光电池结构。     

Synthesis of isomerically pure carboxylate- and sulfonate-substituted xanthene fluorophores

Xanthene-based fluorophores such as fluorescein and rhodamine are typically prepared by acid-catalyzed condensation of the appropriate resorcinol or 3-aminophenol with phthalic anhydride. Condensation of substituted phthalic anhydride species results in functionalized fluorophores that are formed as mixed isomers. Crystallization approaches to isomer separation have been reported elsewhere for symmetric fluorescein carboxylates. We describe crystallization-based separation of protected fluorescein sulfonates and coupling conditions to form sulfonamides, precursors for carboxylate-substituted rhodamines, and precursors for asymmetrically substituted fluoresceins and rhodafluors.     

Extended‐chain crystals in high‐pressure crystallized poly(ethylene terephthalate)/bisphenol a polycarbonate blends

Morphologies of extended‐chain crystals with different characteristics were observed with scanning electron microscopy (SEM) in the high‐pressure crystallized polyethylene terephthalate/polycarbonate (PET/PC) blends. The crystals memorize their nucleation and growth process, which reveal an involvement of different mechanisms simultaneously. The presence of sliding diffusion during crystal thickening is indicated by a wedge shape of some crystals, while bent crystals suggest the occurrence of transesterification in the formation of the large extended‐chain crystals. The observation of two morphological features on one group of crystals shows that two mechanisms may work simultaneously. The connection between folded‐chain and extended‐chain crystals is demonstrated by the S‐shaped extended‐chain crystals as well as their direct morphological connection observed with SEM. Though transesterification plays the essential role in the formation of the large crystals, which acts in different aspects during the process, the thermodynamic driving force is the enthalpy gain associated with large crystals. This is a high‐pressure self‐assembly with a coupling between crystallization and transesterification, which may be instructive to grow such large crystals in similar polymer systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3148–3156, 2006     

Polylactide compositions. II. Correlation between morphology and main properties of PLA/calcium sulfate composites

Starting from calcium sulfate (gypsum) as fermentation by‐product of lactic acid production process, high performance composites have been produced by melt‐blending polylactide (PLA, L/D isomer ratio of 96:4) and β‐anhydrite II (AII) filler, that is, calcium sulfate hemihydrate previously dehydrated at 500 °C. Characterized by attractive mechanical and thermal properties due to good filler dispersion throughout the polyester matrix, these composites are interesting for potential use as biodegradable rigid packaging. Physical characterization of selected composites filled with 20 and 40 wt % AII has been performed and compared to processed unfilled PLA with similar amorphous structure. State of dispersion of the filler particles and interphase characteristic features have been investigated using light microscopy (LM) and scanning electron microscopy (SEM). Addition of AII did not decrease PLA thermal stability as revealed by thermogravimetry analyses (TGA) and allowed reaching a slight increase of PLA crystallizability during melt crystallization and upon heating from the glassy, amorphous state (DSC). It was found by thermomechanical measurements (DMTA) that the AII filler increased pronouncedly storage modulus (E′) of the composites in comparison with PLA in a broad temperature range. The X‐ray investigations showed stable/unchanged crystallographic structure of AII during processing with molten PLA and in the composite system. The notable thermal and mechanical properties of PLA–AII composites are accounted for by the good filler dispersion throughout the polyester matrix confirmed by morphological studies, system stability, and favorable interactions between components. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2770–2780, 2007     

Cracking in polylactide spherulites

A polylactide of high optical purity was crystallized between 100 and 140 °C, in‐between two glass slides, and its morphology was investigated by polarizing optical microscopy, scanning electron microscopy, and atomic force microscopy, during subsequent heating and cooling cycles between ?15 °C and the crystallization temperature. It was found that dark circular rings show up on cooling on top of the spherulites and represent cracks of about 300 nm in width. This phenomenon is completely reversible, and the heating–cooling curves are centered at about 56 °C, which coincide with the T_g of polylactide. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3308–3315, 2005     

A High-Resolution Laser Setup for Determining Nuclear Moments

A laser spectroscopic setup has been applied in the past to successfully investigate off-line the hyperfine structure splitting of radionuclides. In the present paper, its modification is described which will enable the determination of nuclear magnetic dipole and electric quadrupole moments with higher sensitivity and higher resolution.     

Melt compounding of polylactide/organoclay: Structure and properties of nanocomposites

A Brabender mixer was used to deagglomerate and disperse organomodified montmorillonite Cloisite® 30B (3 wt %) in polylactide (PLA) matrix to obtain nanocomposite systems. The influence of compounding conditions such as blending time (6.5, 10, 20, and 30 min) and compression molding on the nanostructure of nanocomposites was investigated. Molecular weight changes of the PLA matrices induced by melt compounding were determined. Good rheological behavior of the PLA during melt blending with Cloisite® 30B was observed. Prolongation of the blending process improved homogenization of the nanocomposites with the formation of more intercalated and exfoliated structures as revealed by transmission electron microscopy (TEM) and X‐ray analysis. Some orientation of the silicate nanoplatelets induced by compression molding of the nanocomposites was revealed by TEM. It was found that an increase of dispersion degree of the silicate layers modified pronouncedly the physical properties of nanocomposites through an increase of thermal stability as revealed by the thermogravimetric analysis, a decrease of crystallizability of the PLA matrix during melt‐crystallization and upon heating from the glassy, amorphous state. Rheological properties of the nanocomposites determined during dynamic frequency sweep appeared to be very sensitive to the nanostructure evolution. Moreover, the scanning electron microscopy and light microscopy investigations showed the presence of the micron‐size inorganic contaminations in the nanocomposites originating from organoclay Cloisite® 30B. These inclusions were resistive to deagglomeration during melt processing. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3392–3405, 2006     

Composition distributions within poly(vinylidene fluoride) spherulites as grown in blends with poly(methyl methacrylate)

Upon crystalline solidification of one component in a homogeneously molten polymer blend, composition profiles develop outside (i.e., in the rest melt) and behind (i.e., within the spherulites) the crystal growth front. The present article is devoted to the detailed verification and the interpretation of these distributions and their temporal development inside growing spherulites. To this end, the energy dispersive X‐ray emission (EDX) of suitable elements has been recorded locally resolved in a scanning electron microscope and evaluated correspondingly. The investigations were performed at the melt homogeneous blend of poly(vinylidene fluoride) (PVDF) as crystallizing and poly(methyl methacrylate) (PMMA) as steadily amorphous component. If the spherulites are not volume filling, the mean PMMA content 〈?_PMMA〉 inside the PVDF spherulites is for all blends about 0.2 below the starting composition. ?_PMMA increases however slightly from the center of a spherulite to its border. That increase reflects the PMMA concentration in front of the spherulite surface, which increases likewise with time, and is clearly above the initial composition. There is at the spherulite surface, consequently, a remarkable jump in composition from the spherulite internal to its amorphous surroundings. It may amount up to 0.5. With volume filling spherulites, a slight variation of the composition from the center of a spherulite to its border is observed, too. This proves that also at these conditions composition profiles develop in the spherulite's surroundings. They remain however so weak that they do not inhibit crystallization even in its later stages. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 338–346, 2006     

Inelastic scattering on 12Be and disappearance of the N = 8 magic number

Experimental studies on in-beam γ-ray spectroscopy using a ¹²Be radioactive beam are presented. Inelastic scattering of the neutron-rich ¹²Be nucleus on ²⁰⁸Pb, ¹²C, and (CH₂)_n targets has been studied by measuring de-excitation γ-rays in coincidence with scattered particles. The level schemes and transition probabilities are determined for low-lying excited states in ¹²Be. The present paper presents a brief review of the spectroscopic results, which may be associated with the N = 8 shell quenching near the drip line. Received: 1 May 2001 / Accepted: 4 December 2001     

Phase separation and polymer crystallization in a poly(4‐methyl‐1‐pentene)–dioctylsebacate–dimethylphthalate system via thermally induced phase separation

The effects of the polymer concentration and quenching temperature on the phase separation, the membrane morphology and polymer crystallization behavior in a poly(4‐methyl‐1‐pentene) (TPX)‐dioctylsebacate (DOS)‐dimethylphthalate (DMP) system via thermally induced phase separation were studied with a pseudobinary phase diagram, with the weight ratio of DOS:DMP = 1:1. SEM was used to observe the membrane morphology and structure, whereas the TPX crystallization behavior was studied with DSC and WAXD. Liquid‐liquid phase separation occurred, although quenching under the crystallization temperature. As the quenching temperature decreased, the pore size decreased, with better connected pore structure formed. The membranes quenched at 333 and 363 K showed good cellular structures, with an average pore size of about 2.3μm, whereas the pores of the membranes quenched at 393 and 423 K were not well formed, with some lamellar crystals on the inner side. The diluent assisted the mobility of the polymer chain, which improved the polymer crystallization. Dual‐melting‐peak behavior occurred for all the samples studied here. As the quenching temperature increased, the first peak of the melting trace moved to a higher temperature, whereas the second one stayed almost the same. The flexibility of the TPX main chain was restricted by the side groups, which allowed liquid‐liquid phase separation to occur first when quenched below the equilibrium crystallization temperature. This allowed primary and secondary crystallization, which was responsible for the dual‐melting‐peak behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 153–161, 2007