Outside dislocations generated from phosphorus implanted silicon layers

The growth, movement and nature of outside dislocation, which propagate from heavily phosphorus (>10¹⁵ ions/cm²) implanted (111), (100), and (110) silicon layers into unimplanted outside regions by a compressive strain induced during 1100° C wet O₂ annealing, are investigated using transmission electron microscopy and x-ray diffraction topography. Outside dislocations are formed, mainly on (111) planes., by the glide motion of dislocation networks formed in implanted layers during early annealing. This results in dislocations extending into the unimplanted areas to different degrees, in the order of, from the largest to smallest, (111), (110), and (100) wafers. In (110) wafers, the [001] oriented dislocations in the implanted regions rise to the surface at the implant and unimplant boundary. On the other hand, the [110] dislocations penetrate into the unimplanted region. Two sets of orthogonal 〈110〉 oriented dislocations generated in (100) implanted wafers behave in the same manner as the [001] dislocations in (110) wafers. Some sources of the compressive strain related to the generation of these dislocations are discussed.     

Experimental evidence for the p-d hybridization in the Cd-Ca quasicrystal: origin of the pseudogap

Ca 2p-3d resonant photoemission spectroscopy of a Cd6Ca crystalline approximant unambiguously demonstrates that the low-lying unoccupied 3d levels of calcium are lowered below the Fermi energy by the formation of the approximant, as suggested from electronic structure calculations [Phys. Rev. Lett. 87, 206408 (2001)]]. Moreover, the Ca 3d partial density of states (DOS) obtained near the Fermi energy is in reasonable agreement with theoretical Ca 3d DOS. These results verify the unconventional picture that the origin of the pseudogap in the Cd-based quasicrystals is due to hybridization of the Ca 3d band with the Cd 5p band.     

A novel procedure for the preparation of zinc reagents: a practical synthesis of (+)-biotin

The use of bromine for activation of zinc dust allowed smooth and reproducible reduction of iodide 1 to the corresponding zinc reagent 2. The zinc reagent 2 obtained by the present protocol was allowed to the Fukuyama coupling reaction with thiolactone 3 to provide a key intermediate 4 for (+)-biotin in high yield using a reasonably fair amount of 1 (1.4 equiv).     

Local plasticity of Al thin films as revealed by x-ray microdiffraction

Grain-to-grain interactions dominate the plasticity of Al thin films and establish effective length scales smaller than the grain size. We have measured large strain distributions and their changes under plastic strain in 1.5-microm-thick Al 0.5% Cu films using a 0.8-microm-diameter white x-ray probe at the Advanced Light Source. Strain distributions arise not only from the distribution of grain sizes and orientation, but also from the differences in grain shape and from stress environment. Multiple active glide plane domains have been found within single grains. Large grains behave like multiple smaller grains even before a dislocation substructure can evolve.     

Amino acids and peptides. XXXVIII. Facile synthesis of laminin-related peptide-poly(ethylene glycol) hybrids by the solid phase method

Poly(ethylene glycol) (PEG) has been studied as a drug-carrier for proteins, but not for small peptides. Laminin, a cell adhesive protein, has Tyr-Ile-Gly-Ser-Arg (YIGSR) sequence and peptides containing this sequence inhibit experimental metastasis. We have studied PEG hybrids of YIGSR and other small laminin-related peptides. In a previous paper, we reported preparation of YIGSR-PEG hybrids by combination of the solid phase method and the solution method, but the synthetic procedure was problematic. Here we report a facile synthesis of PEG hybrids of YIGSR (PEG-YIGSR, YIGSR-PEG, PEG-YIGSR-PEG) by the solid phase method.     

Enantioselective total synthesis of the potent anti-HIV nucleoside EFdA

A concise enantioselective total synthesis of 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), an extremely potent anti-HIV agent, has been accomplished from (R)-glyceraldehyde acetonide in 18% overall yield by a 12-step sequence involving a highly diastereoselective ethynylation of an α-alkoxy ketone intermediate.     

Synthesis of 2-substituted 4,5-dihydro-4-oxo-3-furancarboxylates using acylative intramolecular cyclization of sulfonium salts

A simple and efficient synthesis of 4,5-dihydro-4-oxo-3-furancarboxylates using an acylative intramolecular cyclization of sulfonium salts is described. The reaction involved the efficient formation of a mixed anhydride between a linear carboxylic acid and trifluoroacetic anhydride in the presence of N-methylimidazole, followed by the sequential conversion into a highly reactive acylammonium species in situ. This procedure is easily handled, uses readily available inexpensive reagents, and provides a variety of 2-substituted 4,5-dihydro-4-oxo-3-furancarboxylates.     

Photoluminescence measurements in Be-δ-doped back-gated quantum well

We measured the photoluminescence (PL) spectra of a two-dimensional electron system induced in a Be-δ-doped GaAs/AlGaAs quantum well (QW) with a back gate. The electron density is controlled by means of the back-gate voltage. We estimated the electron density using the magneto-optical method and the PL linewidth, and also by undertaking transport measurements. We show that a uniform 2DES as large as 1 mm² is induced by the back-gate operation from 2.5 × 10¹⁰ cm⁻². This experiment indicates that optical measurement with a back-gated QW is advantageous for studying the low-density 2DES.