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Distributed Bragg reflectors (DBRs) based on alternating layers of porous and non-porous GaN have previously been fabricated at the wafer-scale in heteroepitaxial GaN layers grown on sapphire substrates. Porosification is achieved via the electrochemical etching of highly Si-doped layers, and the etchant accesses the n+-GaN layers through nanoscale channels arising at threading dislocations that are ubiquitous in the heteroepitaxial growth process. Here, we show that the same process applies to GaN multilayer structures grown on silicon substrates. The reflectance of the resulting DBRs depends on the voltage at which the porosification process is carried out. Etching at higher voltages yields higher porosities. However, while an increase in porosity is theoretically expected to lead to peak reflectance, in practice, the highest reflectance is achieved at a moderate etching voltage because etching at higher voltages leads to pore formation in the nominally non-porous layers, pore coarsening in the porous layers, and in the worst cases layer collapse. We also find that at the high threading dislocation densities present in these samples, not all dislocations participate in the etching process at low and moderate etching voltages. However, the number of dislocations involved in the process increases with etching voltage. [ABSTRACT FROM AUTHOR]

The effects of thermal annealing on the optical properties of Mg-doped cubic zincblende GaN epilayers grown by metalorganic chemical vapor deposition on 3C-SiC/Si (001) substrates are investigated. The photoluminescence spectra show near band edge features and a blue luminescence band that depend on Mg concentration, temperature, and excitation power density. Annealing the sample in a N2 atmosphere causes the intensity of the blue band to increase by a factor of 5. Power dependent photoluminescence measurements show a reduction in the laser excitation density required for saturation of the blue band after annealing, indicating an increase in the recombination lifetime. Time decay measurements confirm this increase, which is attributed to a reduction in the concentration of non-radiative defects after annealing. The results presented here are compared to those reported previously for Mg-doped hexagonal wurtzite GaN. [ABSTRACT FROM AUTHOR]

Growing green and amber emitting InGaN/GaN quantum wells in the zincblende, rather than the wurtzite, crystal phase has the potential to improve efficiency. However, optimization of the emission efficiency of these heterostructures is still required to compete with more conventional alternatives. Photoluminescence time decays were used to assess how the quantum well width and number of quantum wells affect the recombination rates, and temperature dependent photoluminescence was used to determine the factors affecting recombination efficiency. The radiative recombination lifetime was found to be approximately 600 ps and to increase weakly with well width, consistent with a change in the exciton binding energy. The relative efficiency at room temperature was found to increase by a factor of five when the number of wells was increased from one to five. Furthermore, the efficiency increased by factor 2.2 when the width was increased from 2.5 to 7.5 nm. These results indicate that thermionic emission is the most important process reducing efficiency at temperatures in excess of 100 K. Moreover, the weak dependence of the rate of radiative recombination on well width means that increasing well thickness is an effective way of suppressing thermionic emission and thereby increasing efficiency in zincblende InGaN/GaN quantum wells, in contrast to those grown in the wurtzite phase. [ABSTRACT FROM AUTHOR]

Current cubic zincblende III-Nitride epilayers grown on 3C-SiC/Si(001) substrates by metal-organic vapor-phase epitaxy contain a high density of stacking faults lying on the {111} planes. A combination of high-resolution scanning transmission electron microscopy and energy dispersive x-ray spectrometry is used to investigate the effects of alloy segregation around stacking faults in a zincblende III-nitride light-emitting structure, incorporating InGaN quantum wells and an AlGaN electron blocking layer. It is found that in the vicinity of the stacking faults, the indium and aluminum contents were a factor of 2.3 ± 1.3 and 1.9 ± 0.5 higher, respectively, than that in the surrounding material. Indium and aluminum are also observed to segregate differently in relation to stacking faults with indium segregating adjacent to the stacking fault while aluminum segregates directly on the stacking fault. [ABSTRACT FROM AUTHOR]

Two thin film deposition routes were studied for the growth of high quality single crystalline Ru (0001) epitaxial films on c-Al2O3 substrates using radio frequency-magnetron sputtering. Such films are very important as buffer layers for the deposition of epitaxial non-collinear antiferromagnetic Mn3X films. The first route involved depositing Ru at 700 °C, leading to a smooth 30 nm thick film. Although, high resolution x-ray diffraction revealed twinned Ru film orientations, in situ post-annealing eliminated one orientation, leaving the film orientation aligned with the substrate, with no in-plane lattice rotation and a large lattice mismatch (13.6%). The second route involved the deposition of Ru at room temperature followed by in situ post-annealing at 700 °C. Transmission electron microscopy confirmed a very high quality of these films, free of crystal twinning, and a 30° in-plane lattice rotation relative to the substrate, resulting in a small in-plane lattice mismatch of –1.6%. X-ray reflectivity demonstrated smooth surfaces for films down to 7 nm thickness. 30 nm thick high quality single-crystalline Mn3Ga and Mn3Sn films were grown on top of the Ru buffer deposited using the second route as a first step to realize Mn3X films for antiferromagnetic spintronics applications. [ABSTRACT FROM AUTHOR]

Porous GaN distributed Bragg reflectors (DBRs) provide strain-free, high-reflectivity structures with a wide range of applications across nitride optoelectronics. Structural characterization of porous DBRs is currently predominantly achieved by cross-sectional scanning electron microscopy (SEM), which is a destructive process that produces local data and has accuracy limited to around 3% by instrument calibration uncertainty. Here, we show that high-resolution x-ray diffraction (XRD) offers an alternative, nondestructive method for characterizing porous nitride structures. XRD scans of porous GaN DBRs show that despite the constant lattice parameter across the DBR layers, characteristic satellite peaks still arise, which are due to the interference between x-rays reflected from the porous and nonporous layers. By comparing the intensities and positions of the satellite peaks through diffraction patterns simulated from a kinematic model, the structural properties of the porous GaN DBRs can be analyzed. Using our method, we have measured a series of DBRs with stop bands from the blue wavelength region to the IR and compared their structural values with those from SEM data. Our results show that the XRD method offers improvements in the accuracy of determining layer thickness, although uncertainty for the value of porosity remains high. To verify the results gained from the XRD and SEM analysis, we modeled the optical reflectivity using the structural values of both methods. We found that the XRD method offered a better fit to the optical data. XRD, therefore, offers accurate, nondestructive characterization of porous DBR structures based on macroscale measurements and is suitable for full wafer analysis. [ABSTRACT FROM AUTHOR]

The photoluminescence spectra of a zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time. [ABSTRACT FROM AUTHOR]

Abstract: We report on the growth of semipolar AlN by metal-organic vapor phase epitaxy on sapphire. High temperature nitridation and nucleation at a V/III ratio of 1050 provide single phase AlN with mirror like crack free surfaces, even for layer thicknesses larger than . Increasing reactor pressure results in lower growth rates because of gas phase particle formation. The in-plane relationship is and and therewith similar to MBE grown AlN and MOVPE and HVPE grown GaN on m-plane sapphire. The AlN reflex is anisotropically broadened in XRD. The surface shows an undulation along as typical for oriented nitride epilayers. Transmission spectroscopy measurements exhibit a sharp absorption edge at 5.95eV, which is 130meV shifted towards lower energies compared to c-plane AlN. [Copyright &y& Elsevier]

We report on metal-organic vapor phase epitaxial growth of ([formula]) InN on ([formula]) GaN templates on m-plane ([formula]) sapphire substrates. The in-plane relationship of the ([formula]) InN samples is [[formula]]InN||[0001]sapphire and [[formula]]InN||[[formula]]sapphire, replicating the in-plane relationship of the ([formula]) GaN templates. The surface of the ([formula]) InN samples and the ([formula]) GaN templates shows an undulation along [[formula]]InN,GaN, which is attributed to anisotropic diffusion of indium/gallium atoms on the ([formula]) surfaces. The growth rate of the ([formula]) InN layers was 3-4 times lower compared to c-plane (0001) InN. High resolution transmission electron microscopy showed a relaxed interface between the ([formula]) InN layers and the ([formula]) GaN templates, consistent with x-ray diffraction results. Basal plane stacking faults were found in the ([formula]) GaN templates but they were terminated at the InN/([formula]) GaN interface due to the presence of misfit dislocations along the entire InN/GaN interface. The misfit dislocations were contributed to the fully relaxation and the tilts of the ([formula]) InN layers. X-ray photoelectron spectroscopy was used to determine the polarity of the grown ([formula]) InN sample, indicating an In-polar ([formula]) InN. The valence band maximum was determined to be at (1.7 ± 0.1) eV for the ([formula]) InN sample, comparable to In-polar c-plane InN. [ABSTRACT FROM AUTHOR]

Abstract: We report on the growth of semipolar AlGaN in the entire composition range on sapphire by metal–organic vapor phase epitaxy. Growth rates increase linearly with the metal–organic supply and have been realized up to . The Al content determined by photoluminescence and transmission measurements depends linearly on the Al/Al+Ga ratio in the gas phase. The growth rate and the Al incorporation are higher for AlGaN than for (0001) AlGaN. This is attributed to different adatom mobility and desorption. The in-plane relationship of AlGaN is and [0001], as typical for semipolar nitrides on m-plane sapphire. For Al contents up to 60% triangle-like structures dominate the surface. For Al contents above 70% it transforms into an undulation along and additional dot-like structures. The smoothest surface morphologies with a rms roughnesses of 2nm were achieved for Al mole fractions of . [Copyright &y& Elsevier]

Zincblende GaN has the potential to improve the efficiency of green- and amber-emitting nitride light emitting diodes due to the absence of internal polarisation fields. However, high densities of stacking faults are found in current zincblende GaN structures. This study presents a cathodoluminescence spectroscopy investigation into the low-temperature optical behaviour of a zincblende GaN/InGaN single quantum well structure. In panchromatic cathodoluminescence maps, stacking faults are observed as dark stripes, and are associated with non-radiative recombination centres. Furthermore, power dependent studies were performed to address whether the zincblende single quantum well exhibited a reduction in emission efficiency at higher carrier densities-the phenomenon known as efficiency droop. The single quantum well structure was observed to exhibit droop, and regions with high densities of stacking faults were seen to exacerbate this phenomenon. Overall, this study suggests that achieving efficient emission from zinc-blende GaN/InGaN quantum wells will require reduction in the stacking fault density., (Creative Commons Attribution license.)

The regular use of antimicrobials in livestock production selects for antimicrobial resistance. The potential impact of this practice on human health needs to be studied in more detail, including the role of the environment for the persistence and transmission of antimicrobial-resistant bacteria. During an investigation of a pig farm and its surroundings in Brandenburg, Germany, we detected abundant cephalosporin- and fluoroquinolone-resistant Escherichia coli in pig faeces, sedimented dust, and house flies (Musca domestica). Genome sequencing of E. coli isolates revealed large phylogenetic diversity and plasmid-borne extended-spectrum beta lactamase (ESBL) genes CTX-M-1 in multiple strains. [Correction added on 28 February 2023, after first online publication: In the preceding sentence, 'and TEM-1' was previously included but has been deleted in this version.] Close genomic relationships indicated frequent transmission of antimicrobial-resistant E. coli between pigs from different herds and across buildings of the farm and suggested dust and flies as vectors for dissemination of faecal pathogens. Strikingly, we repeatedly recovered E. coli from flies collected up to 2 km away from the source, whose genome sequences were identical or closely related to those from pig faeces isolates, indicating the fly-associated transport of diverse ESBL-producing E. coli from the pig farm into urban habitation areas. The observed proximity of contaminated flies to human households poses a risk of transmission of antimicrobial-resistant enteric pathogens from livestock to man., (© 2023 The Authors. Environmental Microbiology published by Applied Microbiology International and John Wiley & Sons Ltd.)

Understanding the growth mechanisms of III-nitride nanowires is of great importance to realise their full potential. We present a systematic study of silane-assisted GaN nanowire growth on c -sapphire substrates by investigating the surface evolution of the sapphire substrates during the high temperature annealing, nitridation and nucleation steps, and the growth of GaN nanowires. The nucleation step - which transforms the AlN layer formed during the nitridation step to AlGaN - is critical for subsequent silane-assisted GaN nanowire growth. Both Ga-polar and N-polar GaN nanowires were grown with N-polar nanowires growing much faster than the Ga-polar nanowires. On the top surface of the N-polar GaN nanowires protuberance structures were found, which relates to the presence of Ga-polar domains within the nanowires. Detailed morphology studies revealed ring-like features concentric with the protuberance structures, indicating energetically favourable nucleation sites at inversion domain boundaries. Cathodoluminescence studies showed quenching of emission intensity at the protuberance structures, but the impact is limited to the protuberance structure area only and does not extend to the surrounding areas. Hence it should minimally affect the performance of devices whose functions are based on radial heterostructures, suggesting that radial heterostructures remain a promising device structure., Competing Interests: There is no conflict of interests., (This journal is © The Royal Society of Chemistry.)

During a field experiment applying broiler manure for fertilization of agricultural land, we detected viable Clostridioides (also known as Clostridium) difficile in broiler faeces, manure, dust and fertilized soil. A large diversity of toxigenic C. difficile isolates was recovered, including PCR ribotypes common from human disease. Genomic relatedness of C. difficile isolates from dust and from soil, recovered more than 2 years after fertilization, traced their origins to the specific chicken farm that had delivered the manure. We present evidence of long-term contamination of agricultural soil with manure-derived C. difficile and demonstrate the potential for airborne dispersal of C. difficile through dust emissions during manure application. Clostridioides genome sequences virtually identical to those from manure had been recovered from chicken meat and from human infections in previous studies, suggesting broiler-associated C. difficile are capable of zoonotic transmission., (© 2021 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.)

The suitability of Ti as a band gap modifier for α-Ga 2 O 3 was investigated, taking advantage of the isostructural α phases and high band gap difference between Ti 2 O 3 and Ga 2 O 3 . Films of (Ti,Ga) 2 O 3 were synthesized by atomic layer deposition on sapphire substrates, and characterized to determine how crystallinity and band gap vary with composition for this alloy. We report the deposition of high quality α-(Ti x Ga 1-x ) 2 O 3 films with x = 3.7%. For greater compositions the crystalline quality of the films degrades rapidly, where the corundum phase is maintained in films up to x = 5.3%, and films containing greater Ti fractions being amorphous. Over the range of achieved corundum phase films, that is 0% ≤ x ≤ 5.3%, the band gap energy varies by ∼270 meV. The ability to maintain a crystalline phase at low fractions of Ti, accompanied by a modification in band gap, shows promising prospects for band gap engineering and the development of wavelength specific solar-blind photodetectors based on α-Ga 2 O 3 .

Clostridioides difficile is the primary infectious cause of antibiotic-associated diarrhea. Local transmissions and international outbreaks of this pathogen have been previously elucidated by bacterial whole-genome sequencing, but comparative genomic analyses at the global scale were hampered by the lack of specific bioinformatic tools. Here we introduce a publicly accessible database within EnteroBase (http://enterobase.warwick.ac.uk) that automatically retrieves and assembles C. difficile short-reads from the public domain, and calls alleles for core-genome multilocus sequence typing (cgMLST). We demonstrate that comparable levels of resolution and precision are attained by EnteroBase cgMLST and single-nucleotide polymorphism analysis. EnteroBase currently contains 18 254 quality-controlled C. difficile genomes, which have been assigned to hierarchical sets of single-linkage clusters by cgMLST distances. This hierarchical clustering is used to identify and name populations of C. difficile at all epidemiological levels, from recent transmission chains through to epidemic and endemic strains. Moreover, it puts newly collected isolates into phylogenetic and epidemiological context by identifying related strains among all previously published genome data. For example, HC2 clusters (i.e. chains of genomes with pairwise distances of up to two cgMLST alleles) were statistically associated with specific hospitals ( P <10 -4 ) or single wards ( P =0.01) within hospitals, indicating they represented local transmission clusters. We also detected several HC2 clusters spanning more than one hospital that by retrospective epidemiological analysis were confirmed to be associated with inter-hospital patient transfers. In contrast, clustering at level HC150 correlated with k -mer-based classification and was largely compatible with PCR ribotyping, thus enabling comparisons to earlier surveillance data. EnteroBase enables contextual interpretation of a growing collection of assembled, quality-controlled C. difficile genome sequences and their associated metadata. Hierarchical clustering rapidly identifies database entries that are related at multiple levels of genetic distance, facilitating communication among researchers, clinicians and public-health officials who are combatting disease caused by C. difficile .

To trace the routes and frequencies of transmission of Clostridioides difficile in a tertiary-care hospital in Madrid (Spain), we sequenced the genomes from all C. difficile isolates collected over 36 months (2014-2016) that were indistinguishable from any other isolate by PCR ribotyping. From a total of 589 C. difficile infection cases, we cultivated and PCR-ribotyped 367 C. difficile isolates (62%), of which 265 were genome-sequenced. Based on close relatedness of successively collected isolates (≤2 SNPs difference in their genomes), whole-genome sequencing revealed a total of 17 independent, putative transmission clusters, caused by various C. difficile strains and each containing 2 to 18 cases, none of which had been detected previously by standard epidemiological surveillance. Proportions of linked isolates varied widely among PCR ribotypes, from 3% (1/36) for ribotype 014/020 to 60% (12/20) for ribotype 027, suggesting differential aptitudes for nosocomial spread. Remarkably, only a minority (17%) of transmission recipients had direct ward contact to their presumed donors and specific C. difficile genome types frequently went undetectable for several months before re-emerging later, suggesting reservoirs for the pathogen outside of symptomatic patients. Taken together, our analysis based on genome sequencing suggested considerable within-hospital epidemic spread of C. difficile, even though epidemiological data initially had been inconspicuous.

Clostridium (Clostridioides) difficile is the main cause of nosocomial diarrhoea. Ribotype 018 (RT018) has been recognized as the predominant strain responsible for C. difficile infection (CDI) in Italy, whereas in most other European countries only sporadic RT018 cases occur. Between August and October 2015, a suspected C. difficile outbreak at two associated hospitals in Southern Germany was investigated by comprehensive molecular typing. Surprisingly, RT018 was detected in 9/82 CDI patients, which has never been described before in a German outbreak. Phenotypic analysis revealed fluoroquinolone and macrolide resistance. Genetic subtyping using multiple-locus variable-number tandem-repeat analysis (MLVA) and whole genome sequencing (WGS) was performed and outbreak isolates were directly compared to sporadic German RT018 isolates and to epidemic ones from Milan, Northern Italy. Molecular typing confirmed a hospital outbreak with closely related RT018 isolates. Both, MLVA and WGS revealed high similarity of outbreak strains with epidemic isolates from Italy, but low similarity to other German isolates. Comparison between both typing strategies showed that ribotyping in combination with MLVA was appropriate to identify related isolates and clonal complexes, whereas WGS provided a better discrimination with more detailed information about the phylogenetic relationship of isolates. This is the first hospital outbreak in Germany presumably caused by cross-national transmission of an Italian epidemic RT018 strain., (Copyright © 2019 Elsevier GmbH. All rights reserved.)

We investigated inflow of a wastewater treatment plant and sediment of an urban lake for the presence of Clostridioides difficile by cultivation and PCR. Among seven colonies we sequenced the complete genomes of three: two non-toxigenic isolates from wastewater and one toxigenic isolate from the urban lake. For all obtained isolates, a close genomic relationship with human-derived isolates was observed., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The kelp forest of the Pacific temperate rocky marine coastline of Monterey Bay in California is a dominant habitat for large brown macro-algae in the order of Laminariales . It is probably one of the most species-rich, structurally complex and productive ecosystems in temperate waters and well-studied in terms of trophic ecology. However, still little is known about the microorganisms thriving in this habitat. A growing body of evidence suggests that bacteria associated with macro-algae represent a huge and largely untapped resource of natural products with chemical structures that have been optimized by evolution for biological and ecological purposes. Those microorganisms are most likely attracted by algae through secretion of specific carbohydrates and proteins that trigger them to attach to the algal surface and to form biofilms. The algae might then employ those bacteria as biofouling control, using their antimicrobial secondary metabolites to defeat other bacteria or eukaryotes. We here analyzed biofilm samples from the brown macro-algae Macrocystis pyrifera sampled in November 2014 in the kelp forest of Monterey Bay by a metagenomic shotgun and amplicon sequencing approach, focusing on Planctomycetes and Verrucomicrobia from the PVC superphylum. Although not very abundant, we were able to find novel Planctomycetal and Verrucomicrobial species by an innovative binning approach. All identified species harbor secondary metabolite related gene clusters, contributing to our hypothesis that through inter-species interaction, microorganisms might have a substantial effect on kelp forest wellbeing and/or disease-development.

Cell sorting coupled with single-cell genomics is a powerful tool to circumvent cultivation of microorganisms and reveal microbial 'dark matter'. Single-cell Raman spectra (SCRSs) are label-free biochemical 'fingerprints' of individual cells, which can link the sorted cells to their phenotypic information and ecological functions. We employed a novel Raman-activated cell ejection (RACE) approach to sort single bacterial cells from a water sample in the Red Sea based on SCRS. Carotenoids are highly diverse pigments and play an important role in phototrophic bacteria, giving strong and distinctive Raman spectra. Here, we showed that individual carotenoid-containing cells from a Red Sea sample were isolated based on the characteristic SCRS. RACE-based single-cell genomics revealed putative novel functional genes related to carotenoid and isoprenoid biosynthesis, as well as previously unknown phototrophic microorganisms including an unculturable Cyanobacteria spp. The potential of Raman sorting coupled to single-cell genomics has been demonstrated., (© 2016 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

We report on the growth of semi-polar GaN (11[Formula: see text]2) templates on patterned Si (113) substrates. Trenches were etched in Si (113) using KOH to expose Si {111} sidewalls. Subsequently an AlN layer to prevent meltback etching, an AlGaN layer for stress management, and finally two GaN layers were deposited. Total thicknesses up to 5 [Formula: see text]m were realised without cracks in the layer. Transmission electron microscopy showed that most dislocations propagate along [0001] direction and hence can be covered by overgrowth from the next trench. The defect densities were below [Formula: see text] and stacking fault densities less than 100 cm [Formula: see text]. These numbers are similar to reports on patterned r-plane sapphire. Typical X-ray full width at half maximum (FHWM) were 500" for the asymmetric (00.6) and 450" for the (11.2) reflection. These FHWMs were 50 % broader than reported for patterned r-plane sapphire which is attributed to different defect structures and total thicknesses. The surface roughness shows strong variation on templates. For the final surface roughness the roughness of the sidewalls of the GaN ridges at the time of coalescence are critical.