Simultaneous mapping of cathodoluminescence spectra and backscatter diffraction patterns in a scanning electron microscope.

Electron backscatter diffraction and cathodoluminescence are complementary scanning electron microscopy modes widely used in the characterisation of semiconductor films, respectively revealing the strain state of a crystalline material and the effect of this strain on the light emission from the sample. Conflicting beam, sample and detector geometries have meant it is not generally possible to acquire the two signals together during the same scan. Here, we present a method of achieving this simultaneous acquisition, by collecting the light emission through a transparent sample substrate.

Metrology of crystal defects through intensity variations in secondary electrons from the diffraction of primary electrons in a scanning electron microscope.

Understanding defects and their roles in plastic deformation and device reliability is important for the development of a wide range of novel materials for the next generation of electronic and optoelectronic devices. We introduce the use of gaseous secondary electron detectors in a variable pressure scanning electron microscope for non-destructive imaging of extended defects using electron channelling contrast imaging. We demonstrate that all scattered electrons, including the secondary electrons, can provide diffraction contrast as long as the sample is positioned appropriately with respect to the incident electron beam.

Determining GaN Nanowire Polarity and its Influence on Light Emission in the Scanning Electron Microscope.

The crystal polarity of noncentrosymmetric wurtzite GaN nanowires is determined nondestructively in the scanning electron microscope using electron backscatter diffraction (EBSD). The impact of the nanowire polarity on light emission is then investigated using cathodoluminescence (CL) spectroscopy. EBSD can determine polarity of noncentrosymmetric crystals by interrogating differences in the intensity distribution of bands of the EBSD pattern associated with semipolar planes.

Quantitative imaging of anti-phase domains by polarity sensitive orientation mapping using electron backscatter diffraction.

Advanced structural characterisation techniques which are rapid to use, non-destructive and structurally definitive on the nanoscale are in demand, especially for a detailed understanding of extended-defects and their influence on the properties of materials. We have applied the electron backscatter diffraction (EBSD) technique in a scanning electron microscope to non-destructively characterise and quantify antiphase domains (APDs) in GaP thin films grown on different (001) Si substrates with different offcuts. We were able to image and quantify APDs by relating the asymmetrical intensity distributions observed in the EBSD patterns acquired experimentally and comparing the same with the dynamical electron diffraction simulations.

Spatially-resolved optical and structural properties of semi-polar [Formula: see text] Al Ga N with x up to 0.56.

Pushing the emission wavelength of efficient ultraviolet (UV) emitters further into the deep-UV requires material with high crystal quality, while also reducing the detrimental effects of built-in electric fields. Crack-free semi-polar [Formula: see text] Al Ga N epilayers with AlN contents up to x = 0.56 and high crystal quality were achieved using an overgrowth method employing GaN microrods on m-sapphire.

Diffraction effects and inelastic electron transport in angle-resolved microscopic imaging applications.

We analyse the signal formation process for scanning electron microscopic imaging applications on crystalline specimens. In accordance with previous investigations, we find nontrivial effects of incident beam diffraction on the backscattered electron distribution in energy and momentum. Specifically, incident beam diffraction causes angular changes of the backscattered electron distribution which we identify as the dominant mechanism underlying pseudocolour orientation imaging using multiple, angle-resolving detectors.

Sucrose dependent mineral phosphate solubilization in Enterobacter asburiae PSI3 by heterologous overexpression of periplasmic invertases.

Enterobacter asburiae PSI3 solubilizes mineral phosphates in the presence of glucose by the secretion of gluconic acid generated by the action of a periplasmic pyrroloquinoline quinone dependent glucose dehydrogenase. In order to achieve mineral phosphate solubilization phenotype in the presence of sucrose, plasmids pCNK4 and pCNK5 containing genes encoding the invertase enzyme of Zymomonas mobilis (invB) and of Saccharomyces cerevisiae (suc2) under constitutive promoters were constructed with malE signal sequence (in case of invB alone as the suc2 is secreted natively). When introduced into E.

Derepression of Mineral Phosphate Solubilization Phenotype by Insertional Inactivation of iclR in Klebsiella pneumoniae.

The mode of succinate mediated repression of mineral phosphate solubilization and the role of repressor in suppressing phosphate solubilization phenotype of two free-living nitrogen fixing Klebsiella pneumoniae strains was studied. Organic acid mediated mineral phosphate solubilization phenotype of oxalic acid producing Klebsiella pneumoniae SM6 and SM11 were transcriptionally repressed by IclR in presence of succinate as carbon source. Oxalic acid production and expression of genes of the glyoxylate shunt (aceBAK) was found only in glucose but not in succinate- and glucose+succinate-grown cells.

Artificial citrate operon confers mineral phosphate solubilization ability to diverse fluorescent pseudomonads.

Citric acid is a strong acid with good cation chelating ability and can be very efficient in solubilizing mineral phosphates. Only a few phosphate solubilizing bacteria and fungi are known to secrete citric acids. In this work, we incorporated artificial citrate operon containing NADH insensitive citrate synthase (gltA1) and citrate transporter (citC) genes into the genome of six-plant growth promoting P.

Pyrroloquinoline quinone-secreting probiotic Escherichia coli Nissle 1917 ameliorates ethanol-induced oxidative damage and hyperlipidemia in rats.

Background: Chronic ethanol (EtOH) consumption is associated with oxidative tissue damage, decrease in antioxidant enzyme activities, and increase in hepatic and plasma lipids. This study investigates the effect of modified probiotic Escherichia coli Nissle 1917 (EcN) secreting pyrroloquinoline quinone (PQQ) against EtOH-induced metabolic disorder in rats.

Methods: Male Charles Foster rats were gavaged with EtOH (5 g/kg body weight [acute study] and 3 g/kg body weight per day for 10 weeks [chronic study]).

Pseudomonas fluorescens ATCC 13525 containing an artificial oxalate operon and Vitreoscilla hemoglobin secretes oxalic acid and solubilizes rock phosphate in acidic alfisols.

Oxalate secretion was achieved in Pseudomonas fluorescens ATCC 13525 by incorporation of genes encoding Aspergillus niger oxaloacetate acetyl hydrolase (oah), Fomitopsis plaustris oxalate transporter (FpOAR) and Vitreoscilla hemoglobin (vgb) in various combinations. Pf (pKCN2) transformant containing oah alone accumulated 19 mM oxalic acid intracellularly but secreted 1.2 mM.

Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN.

We combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black-white contrast.

2-ketogluconic acid secretion by incorporation of Pseudomonas putida KT 2440 gluconate dehydrogenase (gad) operon in Enterobacter asburiae PSI3 improves mineral phosphate solubilization.

Enterobacter asburiae PSI3 is known to efficiently solubilize rock phosphate by secretion of approximately 50 mM gluconic acid in Tris-buffered medium in the presence of 75 mM glucose and in a mixture of seven aldosugars each at 15 mM concentration, mimicking alkaline vertisol soils. Efficacy of this bacterium in the rhizosphere requires P release in the presence of low amount of sugars. To achieve this, E.

Repression of oxalic acid-mediated mineral phosphate solubilization in rhizospheric isolates of Klebsiella pneumoniae by succinate.

Two strains of Klebsiella (SM6 and SM11) were isolated from rhizospheric soil that solubilized mineral phosphate by secretion of oxalic acid from glucose. Activities of enzymes for periplasmic glucose oxidation (glucose dehydrogenase) and glyoxylate shunt (isocitrate lyase and glyoxylate oxidase) responsible for oxalic acid production were estimated. In presence of succinate, phosphate solubilization was completely inhibited, and the enzymes glucose dehydrogenase and glyoxylate oxidase were repressed.

Rapid nondestructive analysis of threading dislocations in wurtzite materials using the scanning electron microscope.

We describe the use of electron channeling contrast imaging in the scanning electron microscope to rapidly and reliably image and identify threading dislocations (TDs) in materials with the wurtzite crystal structure. In electron channeling contrast imaging, vertical TDs are revealed as spots with black-white contrast. We have developed a simple geometric procedure which exploits the differences observed in the direction of this black-white contrast for screw, edge, and mixed dislocations for two electron channeling contrast images acquired from two symmetrically equivalent crystal planes whose g vectors are at 120° to each other.

Effect of transgenic rhizobacteria overexpressing Citrobacter braakii appA on phytate-P availability to mung bean plants.

Rhizosphere microorganisms possessing phytase activity are considered important for rendering phytate-P available to plants. In the present study, Citrobacter braakii phytase gene (appA) was over-expressed in rhizobacteria possessing plant growth promoting (PGP) traits for increasing their potential as bioinoculants. AppA was cloned under the lac promoter in the broad host-range expression vector pBBR1MCS2.

Broad-host-range plasmid-mediated metabolic perturbations in Pseudomonas fluorescens 13525.

Genetic engineering of fluorescent pseudomonads for various industrially, agriculturally and environmentally important bioprocesses often involves the use of suitable plasmids. Plasmid-mediated alterations in host physiology and metabolism are poorly understood for this group of organisms. Thus, we investigated the metabolic perturbations in Pseudomonas fluorescens 13525 due to the independent and combined presence of broad-host-range plasmids, pBBR1MCS-2 (copy number 30) and pUCPM18 derived pAB4 and pAB8 (copy number 14-16).

Plasmid load adversely affects growth and gluconic acid secretion ability of mineral phosphate-solubilizing rhizospheric bacterium Enterobacter asburiae PSI3 under P limited conditions.

Effect of the metabolic load caused by the presence of plasmids on mineral phosphate-solubilizing (MPS) Enterobacter asburiae PSI3, was monitored with four plasmid cloning vectors and one native plasmid, varying in size, nature of the replicon, copy number and antibiotic resistance genes. Except for one plasmid, the presence of all other plasmids in E. asburiae PSI3 resulted in the loss of the MPS phenotype as reflected by the failure to bring about a drop in pH and release soluble P when grown in media containing rock phosphate (RP) as the sole P source.

Heterologous expression of phosphoenolpyruvate carboxylase enhances the phosphate solubilizing ability of fluorescent pseudomonads by altering the glucose catabolism to improve biomass yield.

The Synechococcus elongatus PCC 6301 phosphoenolpyruvate carboxylase (ppc) gene was constitutively overexpressed in fluorescent pseudomonads, to increase the supply of oxaloacetate, a crucial anabolic precursor and an intermediate in biosynthesis of organic acids implicated in phosphate (P) solubilization. Pseudomonas fluorescens ATCC 13525, transformed with pAB3 plasmid containing the ppc gene showed a 14-fold increase in PPC activity under P-sufficiency resulting in increased carbon flow through the direct oxidative pathway and reduced metabolic overflow. Under P-limitation, contribution of the direct oxidative pathway significantly increased in P.

Metabolic channeling of glucose towards gluconate in phosphate-solubilizing Pseudomonas aeruginosa P4 under phosphorus deficiency.

Most phosphate-solubilizing bacteria (PSB), including the Pseudomonas species, release P from sparingly soluble mineral phosphates by producing high levels of gluconic acid from extracellular glucose, in a reaction catalyzed by periplasmic glucose dehydrogenase, which is an integral component of glucose catabolism of pseudomonads. To investigate the differences in the glucose metabolism of gluconic acid-producing PSB pseudomonads and low gluconic acid-producing/non-PSB strains, several parameters pertaining to growth and glucose utilization under P-sufficient and P-deficient conditions were monitored for the PSB isolate Pseudomonas aeruginosa P4 (producing approximately 46 mM gluconic acid releasing 437 microM P) and non-PSB P. fluorescens 13525.

In vivo restriction endonuclease activity of the Anabaena PCC 7120 XisA protein in Escherichia coli.

Anabaena PCC 7120 genome contains three elements, which get excised out during late stages of heterocyst differentiation by a site-specific recombination process. The XisA protein, which excises the nifD element, shows sequence homology with the integrase family of tyrosine recombinase. The 11 bp target site of XisA CGGAGTAATCC contains a 3 bp inverted repeat.