Spark source mass spectrometric assessment of boron and nitrogen concentrations in crystalline gallium arsenide

The residual or doped element concentration [E] in GaAs measured by SSMS is only accurate with respect to the relative sensitivity coefficient RSC_E. For a trace element concentration, the RSC_E = [E]_SSMS/[E]_TRUE is set to unity, if no reference material or method is available to approximate the concentration to the true value. For boron a relative sensitivity coefficient of RSC_B = 0.94 ± 0.08 was obtained using TI-IDMS as a reference method. RSC_N = 1 is used for nitrogen determinations. A boron and nitrogen detection limit of 4.4 × 10¹³ cm^–3 is achieved. SSMS was used as reference method to calibrate the FTIR factor f_E = [E] / I_α due to the integrated local vibrational mode absorption I_α of atomic boron and nitrogen in GaAs. A factor of f_B = (12.0 × 2.7) × 10¹⁶ cm^–1 (517 cm^–1) and f_N = (7.4 ± 0.1) × 10¹⁵ cm^–1 (472 cm^–1) was obtained for a boron and nine nitrogen containing GaAs samples at 77 K and 10 K, respectively. Received: 15 December 1998 / Revised: 8 April 1999 / Accepted: 13 April 1999     

Hydrolysis of Cutin by PET-Hydrolases

Functionalisation of synthetic polymers by using enzymes has been recently demonstrated. The major advantage of enzymes over chemical processes lies in their surface specific and endo-wise mode of action. Surface hydrophilisation of PET with lipases and cutinases leads to a dramatic increase of the surfacial acid and hydroxyl group content while conventional chemical treatment does not cause any change. However, this PET-hydrolysing activity by enzymes from distinct classes has not yet been correlated to activity on natural polyesters. Here, we show that lipases, cutinases and a PHA-depolymerase are all capable of hydrolysing PET, while only lipases and cutinases also hydrolysed cutin to various degrees. Lipases showed a higher specificity for terminal fatty acids while the cutinases preferred hydroxy fatty acids during cutin hydrolysis.     

Mikrochemie

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Enzymatic and chemical hydrolysis of poly(ethylene terephthalate) fabrics

Alkaline and enzymatic hydrolyzes of poly(ethylene terephthalate) fabrics (PET) were mechanistically compared based on released degradation products (HPLC‐UV‐RI) and changes in surface properties [hydrophilicity, cationic dyeing, X‐ray photoelectron spectroscopy (XPS)]. Enzymatic hydrolysis led to an increase in the amount of hydroxyl and carboxyl groups on the surface resulting in an enhanced water absorption and dyeability. Enzymes partially adsorbed to PET fabrics during hydrolysis were completely removed by subsequent extraction according to XPS analysis. In contrast to the enzyme treatment, alkaline hydrolysis did not lead to an increase of hydroxyl and acid groups according to XPS while both treatments caused a substantial increase in hydrophilicity and were more effective on amorphous fibers. Alkaline hydrolysis led to a greater increase in the K/S value after cationic dyeing due to enlarged surface area. Consequently, ESEM‐images demonstrated that alkaline treatment drastically affected the surface morphology of the polymer resulting in crater‐like structures of the fibers, whereas after enzymatic treatment the morphology of the fibers remained unchanged. To reach similar benefits in hydrophilicity, drastically higher amounts of degradation products were released during alkaline hydrolysis as also indicated by >6% weight loss compared to <1% after enzyme treatment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6435–6443, 2008     

CW laser performance of Yb and Er,Yb doped tungstates

 Room temperature cw laser action of Yb³⁺-doped KY(WO₄)₂ and KGd(WO₄)₂ crystals at 1.025 μm and Er, Yb : KY(WO₄)₂ at 1.54 μm has been demonstrated under pumping by both Ti-sapphire laser and InGaAs laser diodes. A slope efficiency of Yb-lasers up to 78% has been obtained. Received: 19 June 1996     

A modular approach toward functionalized three-dimensional macromolecules: from synthetic concepts to practical applications

A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction.