Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.

Formamidinium lead triiodide (FAPbI3) is the leading candidate for single-junction metal-halide perovskite photovoltaics, despite the metastability of this phase. To enhance its ambient-phase stability and produce world-record photovoltaic efficiencies, methylenediammonium dichloride (MDACl2) has been used as an additive in FAPbI3. MDA2+ has been reported as incorporated into the perovskite lattice alongside Cl-. However, the precise function and role of MDA2+ remain uncertain. Here, we grow FAPbI3 single crystals from a solution containing MDACl2 (FAPbI3-M). We demonstrate that FAPbI3-M crystals are stable against transformation to the photoinactive δ-phase for more than one year under ambient conditions. Critically, we reveal that MDA2+ is not the direct cause of the enhanced material stability. Instead, MDA2+ degrades rapidly to produce ammonium and methaniminium, which subsequently oligomerizes to yield hexamethylenetetramine (HMTA). FAPbI3 crystals grown from a solution containing HMTA (FAPbI3-H) replicate the enhanced α-phase stability of FAPbI3-M. However, we further determine that HMTA is unstable in the perovskite precursor solution, where reaction with FA+ is possible, leading instead to the formation of tetrahydrotriazinium (THTZ-H+). By a combination of liquid- and solid-state NMR techniques, we show that THTZ-H+ is selectively incorporated into the bulk of both FAPbI3-M and FAPbI3-H at ∼0.5 mol % and infer that this addition is responsible for the improved α-phase stability.

Filamentary High-Resolution Electrical Probes for Nanoengineering.

Confining electric fields to a nanoscale region is challenging yet crucial for applications such as high-resolution probing of electrical properties of materials and electric-field manipulation of nanoparticles. State-of-the-art techniques involving atomic force microscopy typically have a lateral resolution limit of tens of nanometers due to limitations in the probe geometry and stray electric fields that extend over space. Engineering the probes is the most direct approach to improving this resolution limit. However, current methods to fabricate high-resolution probes, which can effectively confine the electric fields laterally, involve expensive and sophisticated probe manipulation, which has limited the use of this approach. Here, we demonstrate that nanoscale phase switching of configurable thin films on probes can result in high-resolution electrical probes. These configurable coatings can be both germanium-antimony-tellurium (GST) as well as amorphous-carbon, materials known to undergo electric field-induced nonvolatile, yet reversible switching. By forming a localized conductive filament through phase transition, we demonstrate a spatial resolution of electrical field beyond the geometrical limitations of commercial platinum probes (i.e., an improvement of ∼48%). We then utilize these confined electric fields to manipulate nanoparticles with single nanoparticle precision via dielectrophoresis. Our results advance the field of nanomanufacturing and metrology with direct applications for pick and place assembly at the nanoscale.

Giant Fine Structure Splitting of the Bright Exciton in a Bulk MAPbBr3 Single Crystal.

Exciton fine structure splitting in semiconductors reflects the underlying symmetry of the crystal and quantum confinement. Because the latter factor strongly enhances the exchange interaction, most work has focused on nanostructures. Here, we report on the first observation of the bright exciton fine structure splitting in a bulk semiconductor crystal, where the impact of quantum confinement can be specifically excluded, giving access to the intrinsic properties of the material. Detailed investigation of the exciton photoluminescence and reflection spectra of a bulk methylammonium lead tribromide single crystal reveals a zero magnetic field splitting as large as ∼200 µeV. This result provides an important starting point for the discussion of the origin of the large bright exciton fine structure splitting observed in perovskite nanocrystals.

Iso-propyl stilbene: a life cycle signal?

Members of the Gram-negative bacterial genus Photorhabdus are all highly insect pathogenic and exist in an obligate symbiosis with the entomopathogenic nematode worm Heterorhabditis. All members of the genus produce the small-molecule 3,5-dihydroxy-4-isopropyl-trans-stilbene (IPS) as part of their secondary metabolism. IPS is a multi-potent compound that has antimicrobial, antifungal, immunomodulatory and anti-cancer activities and also plays an important role in symbiosis with the nematode. In this study we have examined the response of Photorhabdus itself to exogenous ectopic addition of IPS at physiologically relevant concentrations. We observed that the bacteria had a measureable phenotypic response, which included a decrease in bioluminescence and pigment production. This was reflected in changes in its transcriptomic response, in which we reveal a reduction in transcript levels of genes relating to many fundamental cellular processes, such as translation and oxidative phosphorylation. Our observations suggest that IPS plays an important role in the biology of Photorhabdus bacteria, fulfilling roles in quorum sensing, antibiotic-competition advantage and maintenance of the symbiotic developmental cycle.

Mycoplasma tullyi sp. nov., isolated from penguins of the genus Spheniscus.

A mycoplasma isolated from the liver of a dead Humboldt penguin (Spheniscus humboldti) and designated strain 56A97T, was investigated to determine its taxonomic status. Complete 16S rRNA gene sequence analysis indicated that the organism was most closely related to Mycoplasma gallisepticum and Mycoplasma imitans(99.7 and 99.9 % similarity, respectively). The average DNA-DNA hybridization values between strain 56A97T and M. gallisepticum and M. imitans were 39.5 and 30 %, respectively and the Genome to Genome Distance Calculator gave results of 29.10 and 23.50 %, respectively. The 16S-23S rRNA intergenic spacer was 72-73 % similar to M. gallisepticum strains and 52.2 % to M. imitans. A partial sequence of rpoB was 91.1-92 % similar to M. gallisepticum strains and 84.7 % to M. imitans. Colonies possessed a typical fried-egg appearance and electron micrographs revealed the lack of a cell wall and a nearly spherical morphology, with an electron-dense tip-like structure on some flask-shaped cells. The isolate required sterol for growth, fermented glucose, adsorbed and haemolysed erythrocytes, but did not hydrolyse arginine or urea. The strain was compared serologically against 110 previously described Mycoplasma reference strains, showing that, except for M. gallisepticum, strain 56A97T is not related to any of the previously described species, although weak cross-reactions were evident. Genomic information, serological reactions and phenotypic properties demonstrate that this organism represents a novel species of the genus Mycoplasma, for which the name Mycoplasma tullyi sp. nov. is proposed; the type strain is 56A97T (ATCC BAA-1432T, DSM 21909T, NCTC 11747T).

Laboratory investigations into the origin of Mycoplasma synoviae isolated from a lesser flamingo (Phoeniconaias minor).

BACKGROUND: The role of wild birds in the transmission and spread of mycoplasmas is not clear. Up to now different Mycoplasma species have been isolated from wild birds many of which are not considered pathogens sensu stricto for domestic flocks. This report describes the first isolation of Mycoplasma synoviae in a captive lesser flamingo (Phoeniconaias minor) held in a zoo in Italy and the laboratory investigations performed to elucidate its origin. Results showed that the strain was similar to the MS-H vaccine strain using the vlhA methods although no vaccination with this product was used in the zoo. CASE PRESENTATION: This paper describes investigations into a case in which 10 of 12 adult lesser flamingos (Phoeniconaias minor) died after having recently been moved from the Netherlands to a new zoo in Northern Italy. While most of the birds appeared to have died from the stress of movement and poor adaptation to their new environment, Mycoplasma synoviae, an important poultry pathogen in the layer and meat industry, was isolated for the first time from the trachea of one animal presenting catarrhal tracheitis and fibrinous airsacculitis. Genetic analysis of the conserved region of the vlhA was not able to differentiate the flamingo strain from the MS-H vaccine strain. However differences in the sequences of the obg gene of the flamingo and vaccine strain were detected. A test for temperature-sensitivity (ts) gave a ts (-) phenotype for the flamingo strain, in contrast to the ts (+) status of the MS-H strain. Based on this information and knowing that the flamingos were not vaccinated against M. synoviae, it is highly likely that the flamingo was infected with a genetically similar wild strain by contact with infected birds. CONCLUSIONS: This case provides evidence for the potential role of international trade of ornamental birds as a possible route of introduction of new mycoplasma strains between countries, and moreover highlight that vlhA gene sequencing was not sufficient to discriminate the wild strain isolated from the flamingo from the MS-H vaccine strain.

Surface-Effect-Induced Optical Bandgap Shrinkage in GaN Nanotubes.

We investigate nontrivial surface effects on the optical properties of self-assembled crystalline GaN nanotubes grown on Si substrates. The excitonic emission is observed to redshift by ∼100 meV with respect to that of bulk GaN. We find that the conduction band edge is mainly dominated by surface atoms, and that a larger number of surface atoms for the tube is likely to increase the bandwidth, thus reducing the optical bandgap. The experimental findings can have important impacts in the understanding of the role of surfaces in nanostructured semiconductors with an enhanced surface/volume ratio.

Thiophene-based dyes for probing membranes.

We report the synthesis of four new cationic dipolar push­pull dyes, together with an evaluation of their photophysical and photobiological characteristics pertinent to imaging membranes by fluorescence and second harmonic generation (SHG). All four dyes consist of an N,N-diethylaniline electron-donor conjugated to a pyridinium electron-acceptor via a thiophene bridge, with either vinylene (­CH=CH­) or ethynylene (­C≡C­) linking groups, and with either singly-charged or doubly-charged pyridinium terminals. The absorption and fluorescence behavior of these dyes were compared to a commercially available fluorescent membrane stain, the styryl dye FM4-64. The hyperpolarizabilities of all dyes were compared using hyper-Rayleigh scattering at 800 nm. Cellular uptake, localization, toxicity and phototoxicity were evaluated using tissue cell cultures (HeLa, SK-OV-3 and MDA-231). Replacing the central alkene bridge of FM4-64 with a thiophene does not substantially change the absorption, fluorescence or hyperpolarizability, whereas changing the vinylene-links to ethynylenes shifts the absorption and fluorescence to shorter wavelengths, and reduces the hyperpolarizability by about a factor of two. SHG and fluorescence imaging experiments in live cells showed that the doubly-charged thiophene dyes localize in plasma membranes, and exhibit lower internalization rates compared to FM4-64, resulting in less signal from the cell cytosol. At a typical imaging concentration of 1 µM, the doubly-charged dyes showed no significant light or dark toxicity, whereas the singly-charged dyes are phototoxic even at 0.5 µM. The doubly-charged dyes showed phototoxicity at concentrations greater than 10 µM, although they do not generate singlet oxygen, indicating that the phototoxicity is type I rather than type II. The doubly-charged thiophene dyes are more effective than FM4-64 as SHG dyes for live cells.

Carbon nanotube/polymer composites as a highly stable hole collection layer in perovskite solar cells.

Organic-inorganic perovskite solar cells have recently emerged at the forefront of photovoltaics research. Power conversion efficiencies have experienced an unprecedented increase to reported values exceeding 19% within just four years. With the focus mainly on efficiency, the aspect of stability has so far not been thoroughly addressed. In this paper, we identify thermal stability as a fundamental weak point of perovskite solar cells, and demonstrate an elegant approach to mitigating thermal degradation by replacing the organic hole transport material with polymer-functionalized single-walled carbon nanotubes (SWNTs) embedded in an insulating polymer matrix. With this composite structure, we achieve JV scanned power-conversion efficiencies of up to 15.3% with an average efficiency of 10 ± 2%. Moreover, we observe strong retardation in thermal degradation as compared to cells employing state-of-the-art organic hole-transporting materials. In addition, the resistance to water ingress is remarkably enhanced. These are critical developments for achieving long-term stability of high-efficiency perovskite solar cells.

Hyperspectral imaging of exciton photoluminescence in individual carbon nanotubes controlled by high magnetic fields.

Semiconducting carbon nanotubes (CNTs) provide an exceptional platform for studying one-dimensional excitons (bound electron-hole pairs), but the role of defects and quenching centers in controlling emission remains controversial. Here we show that, by wrapping the CNT in a polymer sheath and cooling to 4.2 K, ultranarrow photoluminescence (PL) emission line widths below 80 µeV can be seen from individual solution processed CNTs. Hyperspectral imaging of the tubes identifies local emission sites and shows that some previously dark quenching segments can be brightened by the application of high magnetic fields, and their effect on exciton transport and dynamics can be studied. Using focused high intensity laser irradiation, we introduce a single defect into an individual nanotube which reduces its quantum efficiency by the creation of a shallow bound exciton state with enhanced electron-hole exchange interaction. The emission intensity of the nanotube is then reactivated by the application of the high magnetic field.

Low-temperature processed electron collection layers of graphene/TiO2 nanocomposites in thin film perovskite solar cells.

The highest efficiencies in solution-processable perovskite-based solar cells have been achieved using an electron collection layer that requires sintering at 500 °C. This is unfavorable for low-cost production, applications on plastic substrates, and multijunction device architectures. Here we report a low-cost, solution-based deposition procedure utilizing nanocomposites of graphene and TiO2 nanoparticles as the electron collection layers in meso-superstructured perovskite solar cells. The graphene nanoflakes provide superior charge-collection in the nanocomposites, enabling the entire device to be fabricated at temperatures no higher than 150 °C. These solar cells show remarkable photovoltaic performance with a power conversion efficiency up to 15.6%. This work demonstrates that graphene/metal oxide nanocomposites have the potential to contribute significantly toward the development of low-cost solar cells.

Pathogens Associated with Bovine Mastitis: The Experience of Bosnia and Herzegovina.

To obtain improved insights into the complex microbial aetiology of bovine mastitis, this study investigated the pathogens involved in cattle mastitis in Bosnia and Herzegovina. A total of 179 milk samples from cows with clinical mastitis (CM) and subclinical mastitis (SCM), as well as eight bulk tank milk (BTM) samples from 48 dairy farms, were analysed by standard bacteriological and mycological methods. Mycoplasma detection and identification were performed using culture techniques and real-time polymerase chain reaction (PCR). A total of 88 (49.2%) mastitis samples were positive for known mastitis pathogens at 32 of 47 farms (68.1%). Mycoplasma bovis was a predominant pathogen (25/187; 13.4%) in the majority of herds (14/48; 29.2%) and accounted for 48.9% of positive CM samples. Escherichia coli was the second most dominant CM pathogen (34%), followed by Streptococcus agalactiae (10.6%), whereas Staphylococcus aureus and coagulase-negative staphylococci were the most common in SCM samples (17.1%). Other mastitis pathogens included Candida spp. and Prototheca zopfii. Two BTM samples were positive for M. bovis only, and one was positive for a mixed culture of S. aureus and Streptococcus uberis. The finding of various causative agents of bovine mastitis, with M. bovis emerging as the main pathogen, emphasizes the significance of comprehensive testing that includes not only common mastitis pathogens but also mycoplasmas, fungi, and algae.

Differential Gene Expression in Porcine Lung Compartments after Experimental Infection with Mycoplasma hyopneumoniae.

Mycoplasma hyopneumoniae (Mhyo) is the causative agent of porcine enzootic pneumonia (EP), as well as one of the main pathogens involved in the porcine respiratory disease complex. The host-pathogen interaction between Mhyo and infected pigs is complex and not completely understood; however, improving the understanding of these intricacies is essential for the development of effective control strategies of EP. In order to improve our knowledge about this interaction, laser-capture microdissection was used to collect bronchi, bronchi-associated lymphoid tissue, and lung parenchyma from animals infected with different strains of Mhyo, and mRNA expression levels of different molecules involved in Mhyo infection (ICAM1, IL-8, IL-10, IL-23, IFN-α, IFN-γ, TGF-ß, and TNF-α) were analyzed by qPCR. In addition, the quantification of Mhyo load in the different lung compartments and the scoring of macroscopic and microscopic lung lesions were also performed. Strain-associated differences in virulence were observed, as well as the presence of significant differences in expression levels of cytokines among lung compartments. IL-8 and IL-10 presented the highest upregulation, with limited differences between strains and lung compartments. IFN-α was strongly downregulated in BALT, implying a relevant role for this cytokine in the immunomodulation associated with Mhyo infections. IL-23 was also upregulated in all lung compartments, suggesting the potential involvement of a Th17-mediated immune response in Mhyo infections. Our findings highlight the relevance of Th1 and Th2 immune response in cases of EP, shedding light on the gene expression levels of key cytokines in the lung of pigs at a microscopic level.

Emissive brightening in molecular graphene nanoribbons by twilight states.

Carbon nanomaterials are expected to be bright and efficient emitters, but structural disorder, intermolecular interactions and the intrinsic presence of dark states suppress their photoluminescence. Here, we study synthetically-made graphene nanoribbons with atomically precise edges and which are designed to suppress intermolecular interactions to demonstrate strong photoluminescence in both solutions and thin films. The resulting high spectral resolution reveals strong vibron-electron coupling from the radial-breathing-like mode of the ribbons. In addition, their cove-edge structure produces inter-valley mixing, which brightens conventionally-dark states to generate hitherto-unrecognised twilight states as predicted by theory. The coupling of these states to the nanoribbon phonon modes affects absorption and emission differently, suggesting a complex interaction with both Herzberg-Teller and Franck- Condon coupling present. Detailed understanding of the fundamental electronic processes governing the optical response will help the tailored chemical design of nanocarbon optical devices, via gap tuning and side-chain functionalisation.

Polaronic Mass Enhancement and Polaronic Excitons in Metal Halide Perovskites.

In metal halide perovskites, the complex dielectric screening together with low energy of phonon modes leads to non-negligible Fröhlich coupling. While this feature of perovskites has already been used to explain some of the puzzling aspects of carrier transport in these materials, the possible impact of polaronic effects on the optical response, especially excitonic properties, is much less explored. Here, with the use of magneto-optical spectroscopy, we revealed the non-hydrogenic character of the excitons in metal halide perovskites, resulting from the pronounced Fröhlich coupling. Our results can be well described by the polaronic-exciton picture where electron and hole interactions are no longer described by a Coulomb potential. Furthermore, we show experimental evidence that the carrier-phonon interaction leads to the enhancement of the carrier's effective mass. Notably, our measurements reveal a pronounced temperature dependence of the carrier's effective mass, which we attribute to a band structure renormalization induced by the population of low-energy phonon modes. This interpretation finds support in our first-principles calculations.

Production of high-purity single-chirality carbon nanotube hybrids by selective polymer exchange.

A scalable method to coat monochiral (7,5) semiconducting single-walled carbon nanotubes with a monolayer coating of a range of technologically useful polymers such as poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) is presented. Optical spectroscopy and atomic force microscopy measurements show that the semiconducting tube purity (>99%) obtained from the selective wrapping of nanotubes by polymers such as poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) can be transferred to these other nanotube-polymer combinations by polymer exchange.

Contagious Bovine Pleuropneumonia: A Passage to India.

The World Organization for Animal Health (WOAH)-listed contagious bovine pleuropneumonia (CBPP) emerged first in Europe and then spread to Eastern Asia, including Japan and China, from the Northern Territories of Australia at the end of the 19th century. Its route to India, however, is less well known as there is little evidence for large importations of cattle from Australia. The lack of accurate diagnostic tests at this time meant veterinary authorities relied solely on clinical and pathological signs, many of which were non-specific. Consequently, any diagnoses of CBPP reported in the early 20th century must be viewed with caution. More convincing reports of CBPP confirmed by laboratory tests were made in the 1930s and 1940s in the Indian state of Assam. Eradication campaigns began in the 1940s with immunizations of live attenuated vaccines and then more comprehensively in the 1950s and 1960s, supplemented with serological screening and the establishment of quarantine centres at international borders. The last case of CBPP, reported to WOAH, was seen in 1990, but the launch of a new awareness campaign in Assam in 2002 and recent reports of the disease in Pakistan suggests the disease has persisted in the Indian subcontinent well into the 21st century.

Genome sequence of Mycoplasma hyorhinis strain GDL-1.

Mycoplasma hyorhinis impacts swine health and production in many countries, either as a primary pathogen or as a component of a polymicrobial infection. Isolates of this species are also common contaminants of tissue culture lines. The genome sequence of the cell culture isolate M. hyorhinis GDL-1 is presented herein.

Ultrafast charge separation at a polymer-single-walled carbon nanotube molecular junction.

We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are individually embedded in the P3HT matrix.

Seroepidemiological survey of sheep flocks from Northern Japan for Mycoplasma ovipneumoniae and Mycoplasma agalactiae.

Sheep flocks from Hokkaido, Iwate and Aomori, three northern prefectures of Japan, were screened for antibodies to Mycoplasma ovipneumoniae and Mycoplasma agalactiae by ELISA. Sixty four animals out of 246 (26%) were seropositive to M. ovipneumoniae, with positive results obtained from all three prefectures. None of the sera tested were serologically positive to M. agalactiae.