Less than 10 defects/cm·μm in molecular beam epitaxy grown GaAs by arsenic cracking

Drastic reduction of irregular defect density in molecular beam epitaxy (MBE) grown GaAs is obtained by using a novel arsenic Knudsen effusion cell with a cracking furnace. A surface defect density of less than 10 cm⁻² is routinely achieved for continuously grown three 3-inch diameter, 1.7 μm thick, metal-semiconductor-field effect transistor (MESFET) structures when the cracking is carried out at about 700°C, which is the critical temperature for the conduction type change, and with the group III Knudsen cell only heated near the orifice of the crucible (top heat cell). These optimized cracking conditions also lead to successful mass production of some microwave devices with not only ultra-low defect density but suitable electrical performances.     

Nanomechanical properties of reversed surfactant bilayers formed in micrometre-sized holes

Nanomechanical properties of free-standing reversed surfactant bilayers, dried foam films (DFFs), were examined via AFM by fitting local force-indentation curves with a Hertzian model. The Young's moduli of four kinds of bilayers were in a range of 10-30 MPa.     

General method for ultrathin free-standing films of nanofibrous composite materials

A simple and general method for the preparation of ultrathin, large-area, free-standing films of nanofibrous composite materials was developed. First, positively charged cadmium hydroxide nanostrands of 1.9 nm in diameter and micrometers in length were prepared by mixing dilute aqueous solutions of cadmium chloride and aminoethanol. Negatively charged dye molecules, proteins, nanoparticles, and water-soluble fullerene or carbon nanotubes were mixed with the nanostrands to give a well-dispersed solution of the corresponding nanofibrous composites. After filtration of the dispersions with a polycarbonate membrane filter, uniform films with a thickness of a few tens to hundreds of nanometers and a diameter of a few centimeters were obtained. The films were readily peeled off from the membrane filter by immersion in ethanol. The resultant free-standing films could be further transferred to other substrates, such as quartz plate, gold electrode, and porous alumina membrane, and were characterized by scanning and transmission electron microscopies. We provide herein various nanofibrous free-standing films with optical, biological, metallic, and magnetic properties.     

A Simple Derivation of Josephson's Formulae in Superconductivity

A simple and general derivation of Josephson's formulae for the tunneling currents is presented on the basis of Sewell's general formulation of superconductivity in relation to off-diagonal long-range order (ODLRO).     

Alternative molecularly imprinted polymeric membranes from a tetrapeptide residue consisting of D- or L-amino acids

Alternative molecularly imprinted polymeric membranes were prepared from a polystyrene resin bearing tetrapeptides consisting of D -amino acids or L-amino acids. The membrane prepared from a DLDE derivative (H-Asp(OcHex)-Leu-Asp(OcHex)-Glu(OBzl) CH₂ ) consisting of D -amino acids and imprinted by Boc-D -Trp recognizes the D-isomer in preference to the corresponding L -isomer and vice versa. The amino acid preferentially adsorbed by the membrane was selectively permeated by applying electrodialysis.     

A new periodic pattern with five‐neighbored domain packing from ABC triblock terpolymer/B homopolymer blend

Self‐assembled structures from poly(isoprene‐b‐styrene‐b‐2‐vinylpyridine)(ISP)/styrene homopolymer blend were investigated. Five terpolymers whose total molecular weight, M, is in the narrow range of 121k < M < 214k, and volume fractions of the center block polystyrenes, ?_S, are similar at around 0.55, were prepared as parent block terpolymers. Their ?_P/?_I ratios, used as an indicator of asymmetry, are varied in the range 0.32 < ?_P/?_I < 2.46. Three low‐molecular weight styrene homopolymers with molecular weights of 3k, 9k, and 12k, respectively, were mixed with those block terpolymers to produce blends with almost constant styrene content within the range 0.65 < ?_S < 0.68. Both ISP/S(3k) and ISP/S(12k) blend series show a morphological transition from tetragonally packed cylinders (TPC) to double hexagonal structure (DHS) with hexagonally arrayed polyisoprene cylinders, each surrounded by six thin cylinders as satellites. If one focuses on ISP‐III(150k)/S blends whose ?_P/?_I is 0.88, TPC for ISP‐III/S(3k) was transformed to DHS for ISP‐III/S(12k), evidently due to the molecular weight effect of the added homopolymer. Finally a new periodic pattern, having P cylinders surrounded by five I cylinders each, has been discovered from ISP‐III/S(9k) at overall composition of ?_I/?_S/?_P = 0.17/0.68/0.15 and polystyrene block/styrene homopolymer ratio of w_S(b)/w_S(h) = 1.4. This structure was confirmed to possess hexagonal symmetry with larger unit cell than regular patterns ever known by X‐ray diffraction experiment. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 907–911     

Vinyl polymerization. 413. Polymerization of vinyl monomer initiated by poly(vinylbenzyltrimethyl)-ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(vinylbenzyltrimethyl)ammonium chloride (Q-PVBACI) was carried out at 85°C. Styrene, p-chlorostyrene, methyl methacrylate, and i-butyl methacrylate were polymerized, whereas acrylonitrile and vinyl acetate were not. The effects of the amounts of vinyl monomer, Q-PVBACI, and water on the conversion of vinyl monomer were studied. The overall activation energy in the polymerization of styrene was estimated as 79.1 kJ mol^?1. The polymerization proceeded through a radical mechanism. The selectivity of vinyl monomer was discussed by “a concept of hard and soft hydrophobic areas and monomers.”     

Adaptive exponential approximation of optical density ratio using third-order regression equations for depth profiling of a blood inclusion in a skin tissue model

We propose the use of the third-order multiple regression equations in approximating an optical density ratio with an adaptive exponential function for measuring depth and thickness of a blood inclusion embedded in a skin tissue model. To ensure accuracy of the exponential approximation, we investigated numerically various relations of optical density ratios versus depth and thickness, on the basis of Monte Carlo simulations for a layered skin tissue model. The third-order multiple regression analysis based on the relations above was used to derive regression equations for the determination of depth and thickness. Experiments with skin tissue phantoms were used to assess this approach.     

Chemical synthesis of homogeneous human glycosyl-interferon-β that exhibits potent antitumor activity in vivo

Chemical synthesis of homogeneous human glycoproteins exhibiting bioactivity in vivo has been a challenging task. In an effort to overcome this long-standing problem, we selected interferon-β and examined its synthesis. The 166 residue polypeptide chain of interferon-β was prepared by covalent condensation of two synthetic peptide segments and a glycosylated synthetic peptide bearing a complex-type glycan of biological origin. The peptides were covalently condensed by native chemical ligation. Selective desulfurization followed by deprotection of the two Cys(Acm) residues gave the target full-length polypeptide chain of interferon-β bearing either a complex-type sialyl biantennary oligosaccharide or its asialo form. Subsequent folding with concomitant formation of the native disulfide bond afforded correctly folded homogeneous glycosyl-interferon-β. The chemically synthesized sialyl interferon-β exhibited potent antitumor activity in vivo.