Microscopic distribution of extended defects and blockage of threading dislocations by stacking faults in semipolar (1101)(1101)()(1101)() GaN revealed from spatially resolved luminescence

Spatial distribution of extended defects in semipolar -oriented GaN layers grown on patterned(001) Si substrates with striped grooves of varying width was investigated by optical means only using near-field scanning optical microscopy (NSOM) and cathodoluminescence (CL). A high density of basal and prismatic stacking faults was observed in the c− wings, and the threadingdislocations in c+ wings, which appear as dark patterns in the NSOM and CL images, were found to bend toward the surface during the initial stages of growth. In the case when growingc+ front of GaN made contact with the SiO2 masking layer during growth, stacking faults were found to form also in the c+ wings. These additional stacking faults effectively blocked propagation of dislocations along the c+ direction, resulting in high quality stripes virtually free of defects. As revealed by optical means only without the need for any structural investigation, such control over the threading dislocation density using select growth geometries is potentially advantageous for improving semipolar GaN

Optical studies of strain and defect distribution in semipolar (1(1)over-bar01) GaN on patterned Si substrates

Formation of defects in semipolar ( 11¯01 )-oriented GaN layers grown by metal-organic chemical vapor deposition on patterned Si (001) substrates and their effects on optical properties were investigated by steady-state and time-resolved photoluminescence (PL) and spectrally and spatially resolved cathodoluminescence (CL). Near-band edge emission is found to be dominant in the c +-wings of semipolar ( 11¯01 )GaN, which are mainly free from defect-related emission lines, while the c – wings contain a large number of basal stacking faults. When the advancing c+ and c — fronts meet to coalesce into a continuous film, the existing stacking faults contained in c — wings continue to propagate in the direction perpendicular to the c-axis and, as a result, the region dominated by stacking fault emission is extended to the film surface.Additional stacking faults are observed within the c+ wings, where the growing c+ wings of GaN are in contact with the SiO2 masking layer. Out-diffusion of oxygen/silicon species and concentration of strain near the contact region are considered as possible causes of the stacking fault formation. CL linescans performed along the surface and across the thickness of the non-coalesced and coalesced layers revealed that, while most of the material in the near-surface region of the non-coalesced layers is relaxed, coalescence results in nonuniform strain distribution over the layer surface. Red-shifted near-band-edge emission from the near-surface region indicates tensile stress near the surface of a coalesced layer, reaching a value of 0.3 GPa. The regions near the GaN/AlN/Si(111) interface show slightly blue shifted, broadened near-band-edge emission, which is indicative of a high concentration of free carriers possibly due to incorporation of shallow-donor impurities (Si and/or O) from the substrate or SiO2 mask. Steady-state and time-resolved PL results indicate that semipolar ( 11¯01 )GaN on patterned Si exhibits optical properties (PL intensity and carrier lifetimes) approaching to those of the state-of-the-art c-plane GaN grown using in situ SiNx nanonetwork mask on c-plane sapphire. Long PL lifetimes (∼2 ns) for the ( 11¯01 )GaN layers show that the semipolar material holds promise for light emitting and detecting devices

Aspekte des Einsatzes pflanzlicher Traegermaterialien in der biotechnologischen Fermentation Prozessuntersuchungen an Hefezell-Traeger-Konjugaten

In der vorliegenden Arbeit wurden lebende Hefezellen (Saccharomyces cerevisiae Kolin, Saccharomyces uvarum,. Kluyveromyces fragilis H22) an abgetoetete Zellwandhuellen der Zwergwasserlinse Wolffia arrhiza (L.) immobilisiert, die delipidisiert und entproteinisiert als Cellulose-Pektinat-Geruest vorlagen. Mittles lich- und rasterelektronenmikorskopischer Methoden wurde die Immobilisierung als eine Kombination von physikalischer Adsorption und aktivem Einschluss charakterisiert. Die mit Biomasse (S. cerevisiae Kolin) bis 152,5 g HTS/1 beladenen Traeger wurden in Fluidbettfermentoren (Fluidisierung duch in-situ-CO_2-Produktion) zur kontinuierlichen Ethanolfermentation genutzt. Im Wirbelschichtfermentor (Rueckkesselverhalten) wurde mit Volumina von 0,1 l; u l; 6.5 l und 10 l unter den Aspekten der Massstabuebertragung, der Langzeitstabilitaet und der Raum-Zeit-Ausbeute gearbeitet (H:D=2:1 bzw. 8,5:1; YEP(S)-Medium; T=25 C; element of =0,4). Im Fliessbettfermentor (Stroemungsrohrverhalten) konnte bei einem Arbeitsvolumen von 9 l (H:D=80 l) und einem element of =0,2 eine kontinuierliche Langzeit-Melassefermentation realisiert werden. (orig./EF)Living cells of yeast (Saccharomyces cerevisiae Kolin, Saccharomyces uvarum, Kluyveromyces fragilis H22) were immobilized on devitatlized cell walls of Wolffia arrhiza (L.) which were available in dielipidized and deprotermized form as a cellulose-pectrivate skeleton. Using light microscopy and scanning electrode microscopy, immobilisation was characterized as a combination of physical adsorption and active confinement. The substrates burdened with biomass (s. cerevisiae kolin) up to 152.5 g HTS/l were used for continuous fermentation of ethanol in fluidized-bed ferments (fluidisation by n-situ Co_2 production). In the agilator-type fluidized-bed fermenters, volumes of 0.1l; 1 l; 6.5 l and 10 l were analyzed with a view to scaling-up, long-term stability, and space-time yield (H:D=2.1 rsp. 8.5 l; YEP(S) medium; T=25 , element of =0.4). In the flow-tube fluidized-bed fermenters, continuous long-time fermentation of melasse was possible with a working volume of 9 l (H:D=80:1) and element of =0.2. (orig./EF)SIGLEAvailable from TIB Hannover: DW 9914 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Determination of carrier diffusion length in p- and n-type GaN

International audienceDiffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p-GaN or 1300 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photogeneration near the surface region by above bandgap excitation. Taking into consideration the absorption in the active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be about 92 +/- 7 nm and 68 +/- 7 nm for Mg-doped p-type GaN and 432 +/- 30 nm and 316 +/- 30 nm for unintentionally doped n-type GaN, respectively. Cross-sectional cathodoluminescence line-scan measurement was performed on a separate sample and the diffusion length in n-type GaN was measured to be 280 nm

Validation of a nonaqueous capillary electrophoretic method for the enantiomeric purity determination of R-flurbiprofen using a single-isomer amino cyclodextrin derivative

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of R-flurbiprofen using 6-monodeoxy-6-mono(2-hydroxy)propylamino-beta-cyclodextrin (IPA-beta-CD) as chiral selector. The nonaqueous BGE was made up of 20 mM IPA-beta-CD, 20 mM ammonium camphorsulfortate and 40 mM ammonium acetate in methanol. Flufenamic acid was selected as internal standard. The CE method was carefully optimized in order to prevent the adsorption of the cationic CD onto the capillary wall, and therefore, to avoid loss of peak efficiency and enantioresolution. To achieve this goal, the addition of ammonium camphorsulfonate was found to be necessary. In the selected conditions, the determination of 0.1% of S-flurbiprofen in R-flurbiprofen could be performed using the method of standard additions. The NACE method was then fully validated by applying a novel strategy using accuracy profiles. (c) 2008 Elsevier B.V. All rights reserved

Metabolic and evolutionary origin of actin-binding polyketides from diverse organisms

International audienceActin-targeting macrolides comprise a large, structurally diverse group of cytotoxins isolated from remarkably dissimilar micro- and macroorganisms. In spite of their disparate origins and structures, many of these compounds bind actin at the same site and exhibit structural relationships reminiscent of modular, combinatorial drug libraries. Here we investigate biosynthesis and evolution of three compound groups: misakinolides, scytophycin-type compounds and luminaolides. For misakinolides from the sponge Theonella swinhoei WA, our data suggest production by an uncultivated 'Entotheonella' symbiont, further supporting the relevance of these bacteria as sources of bioactive polyketides and peptides in sponges. Insights into misakinolide biosynthesis permitted targeted genome mining for other members, providing a cyanobacterial luminaolide producer as the first cultivated source for this dimeric compound family. The data indicate that this polyketide family is bacteria-derived and that the unusual macrolide diversity is the result of combinatorial pathway modularity for some compounds and of convergent evolution for others