Thin silicon epitaxial layers on preannealed silicon substrates

Multistep-temperature pretreatment is used to create defect denuded zones at surfaces in conjunction with bulk defects in oxygen rich substrate wafers. Using structural etching, RF–CV measurements, EBIC investigations, and gamma spectroscopy it is shown that bulk defects act as sinks for metallic impurities being fixed at an early stage of bipolar technology, already Etchable defects induced due to subsequent processing steps – e.g., emerging from bulk regions and entering denuded zones – contain less metallic impurities. 2 μm epitaxial layers deposited on such substrates with bulk defects and denuded zones reveal excellent structural and electrical properties.     

Large volume high pressure research using the wiggler port at NSLS

Abstract

A DIA-type cubic-anvil high pressure apparatus (SAM-85) has been interfaced with white x-ray radiation from the superconducting wiggler port of the National Synchrotron Light Source at Brookhaven National Laboratory. Energy-dispersive x-ray diffraction measurements can be obtained for samples with dimensions of the order of 1 mm as a function of pressure and temperature utilizing x-ray energies of up to100 keV.

The sample environment is examined. Pressure is uniform in the sample chamber to within 0.1 GPa, and temperature is constant in the scattering volume to within 5°C.A method is defined for determining deviatoric stress. We find that for a sample containing NaCl and Au, the deviatoric stress increases to about 0.3 GPa as pressure increases to 1.5 GPa and then remains constant, probably reflecting the strength of the sample. Upon heating, the deviatoric stress quickly approaches zero.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991     

Copolyesters of isosorbide,succinic acid,and isophthalic acid: Biodegradable,high Tg engineering plastics

Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl₂ or ZnCl₂ produces satisfactory molar masses. The number average molecular weights (M_n) of most copolyesters fall into the range of 7000–15,000 Da with polydispersities (PD) in the range of 3–9. The MALDI‐TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass‐transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo‐stabilities also followed this trend. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2464–2471     

Spectral broadening of picosecond laser pulses in optical fibres

Picosecond light pulses of a passively mode-locked ruby laser (pulse duration t _L35 ps) are spectrally broadened in optical fibres of core diameters from 4 m to 600 m. Combining the effects of self-phase modulation, stimulated Raman scattering, and parametric four-photon interaction in an 8-m core fibre of 4 m length with the effect of selective spectral attenuation in a ruby rod resulted in rather smooth spectra extending from 685 nm to 830 nm (spectral width 2300 cm^-1).     

Novel tripod ligands for prickly self-assembled monolayers

The new tridentate thioether ligands PhSi(CH2SMe)3 (1) and Ph-p-C6H4Si(CH2SMe)3 (2) have been synthesised and used for the preparation of the chelates fac-[W(kappa3-1)(CO)3] and fac-[W(kappa3-2)(CO)3], which were characterised by single-crystal X-ray diffraction. 1 and 2 were used as tripodal adsorbate molecules for the fabrication of self-assembled monolayers (SAMs) on gold. Film formation from solution was investigated in situ by second harmonic generation (SHG) and ellipsometry, which revealed a two-stepped process (fast adsorption, followed by slow film ordering). SAMs of 2 on gold were further investigated by ex situ methods, viz. high-resolution X-ray photoelectron spectroscopy (HRXPS), Fourier transform infrared reflection absorption spectroscopy (FTIRRAS), and scanning tunneling microscopy (STM). The latter two methods indicated dense packing of the tripodal anchor groups on the surface, with a substantially lower density of the biphenyl pricks. HRXPS showed three different binding states of sulfur, including a standard thiolate-type and a coordination-type state.     

Characterization of alkyl polyglycosides by both reversed-phase and normal-phase modes of high-performance liquid chromatography

Alkyl polyglycosides today represent the most important sugar surfactant. Nonionic sugar surfactants produced via different synthetic routes are mixtures of alkyl homologues, oligomers, anomers and isomers. Alkyl homologues and oligomers of alkyl mono- and diglucosides were separated by reversed-phase high-performance liquid chromatography (HPLC) with methanol-water as the mobile phase using a gradient elution. The gradient was optimized in respect to a simultaneous separation of alkyl glycosides according to their alkyl chain length and alkyl polyoxyethylene glucosides with regard to their length of the polyoxyethylene spacer. The separation of alkyl glycosides into alpha- and beta-anomers was carried out by normal-phase HPLC with isooctane-ethyl acetate (60:40, v/v)-2-propanol in the gradient mode. Light scattering detection was used. Matrix-assisted laser desorption ionization time-of-flight mass spectra of alkyl glucosides and dodecyl glucosides with oxyethylene spacer groups are presented.     

Direct Catalytic Asymmetric Mannich‐Type Reaction of α‐N3 Amide

An α‐N₃ 7‐azaindoline amide serves as a latent enolate to directly engage in an asymmetric Mannich‐type reaction with N‐thiophosphinoyl imines by the action of a cooperative catalyst. The thus‐obtained highly enantioenriched anti‐adduct was transformed into β‐amino‐α‐azido acid in high yield by simple acidic treatment.