ILW is a heterogeneous wasteform that contains substantial amounts of cellulosic material encased in concrete. Upon resaturation of the facility with groundwater, alkali conditions will dominate and will lead to the chemical degradation of cellulose, producing a substantial amount of organic co-contaminants, particularly isosaccharinic acid (ISA). ISA can form soluble complexes with radionuclides, thereby mobilising them and posing a potential threat to the surrounding environment or ‘far field'. Alkaliphilic microorganisms sampled from a legacy lime working site, which is an analogue for an ILW-GDF, were able to degrade ISA and couple this degradation to the reduction of electron acceptors that will dominate as the GDF progresses from an aerobic ‘open phase' through nitrate- and Fe(III)-reducing conditions post closure. Furthermore, pyrosequencing analyses showed that bacterial diversity declined as the reduction potential of the electron acceptor decreased and that more specialised organisms dominated under anaerobic conditions. These results imply that the microbial attenuation of ISA and comparable organic complexants, initially present or formed  High pH environments are present on Earth. They can be natural, for example, some geothermal springs and soda lakes, or man-made, for example, effluent ponds from paper pulping industries, lime working sites and closed structures made of cement. One such engineered structure is the deep geological disposal facility (GDF) that is being proposed for the safe disposal of radioactive waste. The largest volume of waste deposited into a GDF will be intermediate-level waste (ILW), which will be immobilised in steel containers backfilled with cementitious material to form a physical barrier in the form of a cement matrix . The cheThe GDF has previously been considered to be an extreme environment where stresses including hyperalkalinity, radiation and radionuclide toxicity may play a role in limiting microbial colonisation. However, it is becoming clear that microbes may tolerate such extreme conditions 2 and left to react for 3 days under anaerobic conditions and at room temperature. The mixture was then boiled for 6 h, keeping the volume constant by adding dd H2O. The solution was then filtered while hot, and the volume of the filtrate reduced to ∼100 ml by boiling. The remaining solution was stored overnight at 4 °C. The white precipitate that formed was filtered and then washed sequentially with water, ethanol and acetone and dried overnight at 50 °C. The dry precipitate was redissolved at a ratio of 1.2 g in 100 ml of dd H2O by boiling. While still hot, the solution was filtered and the volume of the filtrate was reduced to ∼10 ml by boiling. The white precipitate that formed was washed sequentially with water, ethanol and acetone and then dried overnight at 50 °C.Preparation of the Ca salt of α-ISA was performed following the procedure reported by M NaHCO3, 4.7 mM NH4Cl, 4.4 mM NaH2PO4.H2O, 1.4 mM KCl and 2 ml of mineral and vitamin solutions (M Ca(ISA)2. The bottles were closed with a foam bung before autoclaving to allow the passage of air in and out of the bottles while preventing contamination from the surrounding environment. A ‘sterile' control along with a ‘no electron donor' control that did not contain any added carbon source were also prepared. All samples were prepared in triplicate and the pH was adjusted to 10 using 10 M NaOH before autoclaving. The cultures were left in a 20 °C incubator for the period of the experiment (until the stationary phase (assessed by turbidity) of the enrichment culture was reached). Samples (1 ml) were removed inside a laminar flow cabinet and the pH and absorbance at 600 nm were measured. The samples were frozen at −20 °C until the end of the experiment, when they were analysed by ion-exchange chromatography for ISA and a range of geochemical indicators. The test cultures were subcultured 4 times by taking 200 μl of the culture and adding it to freshly prepared medium under the same conditions. The data from the last subculture are shown.Aerobic cultures were prepared in 100 ml serum bottles where 19.5 ml of minimal medium, containing 30 mM NaNO3, as the terminal electron acceptor (TEA), was added to the culture medium and the bottles were stoppered with rubber butyl stoppers and then degassed with N2 for 30 min before being autoclaved and the inoculum added. The same controls were used as in the aerobic culture experiments, in addition to a ‘no electron acceptor' control that contained 2 mM Ca(ISA)2 without NaNO3 added as the electron acceptor. Samples were taken with a 1 ml syringe and the pH and absorbance at 600 nm measured, and then they were frozen at −20 °C until they were analysed using ion-exchange chromatography. The test cultures were subcultured 3 times and the data from the last subculture are shown.Nitrate-reducing cultures were prepared following the same procedure as used with the aerobic cultures. However, 24 m2 for 30 min, autoclaved and poured into petri dishes inside a laminar flow cabinet. After solidification of the agar, the plates were transferred into an anaerobic chamber and left upside down for 4 days. A subsample from the last subculture of the nitrate-reducing culture (the same one that was used for pyrosequencing studies) was spread onto the plates with a sterile disposable plastic spreader. The inoculated plate and a control plate were put in a sealed GasPak jar , closed and incubated at 20 °C under anaerobic conditions. After 3 days, small transparent colonies were observed and five representative colonies were isolated using a sterile 5 μl microbiology loop and transferred to 20 ml of sterile minimal medium supplemented with 2 mM Ca(ISA)2 and 24 mM NaNO3. These bottles were incubated at 20 °C for 10 days, during which they were monitored for bacterial growth, pH change, ISA degradation and nitrate reduction. After the stationary growth phase was reached, 10 ml of the liquid culture was centrifuged at 4000 g for 10 min and the pellet was used for DNA extraction and microbial identification using Sanger sequencing of PCR amplified 16S rRNA gene.The same minimal medium that was used for growth of the planktonic nitrate-reducing cultures was supplemented with 1% agar, pH adjusted to 10, flushed with N−1 of insoluble Fe(III) oxyhydroxide (ferrihydrite) (3 as the TEA. The concentration of Fe(II) was determined spectrophotometrically after reaction with ferrozine (Fe(III)-reducing cultures were prepared and sampled in the same way as the nitrate-reducing cultures, except that 30 mmol lhydrite)  was addeerrozine . The tes3 was replaced with 6 mM Na2SO4. These samples were not subcultured because, after 60 days of incubation of the primary enrichment culture, no reduction of sulphate or degradation of ISA was observed under the conditions imposed.Sulphate-reducing cultures were prepared and sampled following the same procedure as the nitrate-reducing culture, but the NaNOg for 5 min at room temperature to remove bacteria and any solid material. These samples were diluted 50 times and then analysed by ion-exchange high-performance liquid chromatography using a Dionex ICS5000 Dual Channel Ion Chromatograph with a conductivity detector . The samples were put in 2 ml glass vials with pre-split septa and cooled to 15 °C, and then 0.4 μl was injected into the chromatograph through a Dionex AS-AP autosampler. Molecule separation was achieved by passing the samples through a 250 × 0.4 mm Dionex AS11-HC capillary column with a 4 μm pore size, operating at 30 °C, with a typical operating pressure of 3400 psi and a flow rate of 0.015 ml min−1. The mobile phase used was a KOH solution, prepared in high-purity water, electronically injected to produce a gradient from 1 to 60 mM over a 38 min run time, followed by a 10 min re-equilibrium before the next injection. The chromatograph was calibrated at 4 points ranging from 0.5 to 30 mg l−1 for nitrate, nitrite and sulphate, 0.5–10 mg l−1 for acetate, formate, lactate, propionate and butyrate and 0.01–0.1 mM for ISA.The frozen samples were thawed at room temperature, vortexed for homogenisation and then centrifuged at 13 000 CCATCTCATCCCTGCGTGTCTCCGACTCAG-3′, followed by the 10 bp barcode sequence specific to each sample, where the background sediment had the sequence 5′-CTCGCGTGTC-3′, the aerobic sample 5′-CGTGTCTCTA-3′, the nitrate-reducing sample 5′-ATATCGCGAG-3′ and finally the Fe(III)-reducing sample had the sequence 5′-TCTCTATGCG-3′. The bold and underlines differentiate between the 454 Life Sciences adapter sequence and the barcode sequence in the forward primers we used for each sample. The barcode sequence was followed by the universal 27F primer sequence 5′-AGAGTTTGATCMTGGCTCAG-3′. The PCR mastermix contained, per sample, 40 μl sterile purified H2O, 5 μl of 10 × PCR reaction buffer, 1 μl dNTP mix, 0.8 μl of 25 μM 338R primer and 0.4 μl High Fidelity Enzyme Blend. To perform the PCR, 47.2 μl of this mastermix was transferred into a sterile 50 μl PCR reaction tube, where 0.8 μl of one of each barcoded 27F primer and 2 μl of DNA, taken from the sample corresponding to each specific barcode, were added to separate tubes. A negative and a positive control for the PCR reaction, which contained 2 μl sterile H2O or DNA extracted from Geobacter sulfurreducens, respectively, were also prepared. The PCR conditions were: initial denaturation at 95 °C for 2 min, followed by 35 cycles of denaturation at 95 °C for 30 s, primer annealing at 55 °C for 30 s and extension at 72 °C for 45 s, followed by a final extension step at 72 °C for 5 min. At the end of the PCR run, the whole PCR product was mixed with 12.5 μl of 5 × gel-loading dye, and 35 μl of the mixture was loaded on a 2% Tris-Acetate-EDTA/agarose gel. A 2000–100 bp ladder was also loaded on the gel that was run at 80 mV for ∼2 h. At the end of the run, the DNA bands were observed on a Gel Doc XR system  and the band corresponding to 400 bp size for each sample was excised from the gel. DNA extraction and cleanup from the excised gel were performed using a QIAquick Gel Extraction Kit , according to the manufacturer's protocol. DNA was quantified on a Nanodrop ND-1000 (Thermo Scientific) and all samples were diluted to 10 ng μl−1. The DNA product was then stored at 4 °C until it was sequenced using a 454 GS Junior pyrosequencing system (Roche), using the facility in the Faculty of Life Sciences, University of Manchester.DNA was extracted from samples of aerobic, nitrate-reducing and Fe(III)-reducing cultures and the background sediment using the PowerSoil DNA isolation kit  according to the manufacturer's protocol. Pyrosequencing PCR was performed using the FastStart High Fidelity PCR System  and the 27F and 338R universal primers to cover the V1–V2 hypervariable regions of the 16S rRNA gene . The 338Analysis of the raw 454 pyrosequencing data was done using the Quantitative Insights Into Microbial Ecology pipeline  through 2O, 5 μl of 10 × Ex buffer, 4 μl dNTP mix, 1 μl of 25 μM 8F and 1492R primers and 0.3 μl Ex TaKaRa Taq polymerase. To perform the PCR, 48 μl of this mastermix was transferred into a sterile 50 μl PCR reaction tube and 2 μl of the extracted DNA was added. A negative and a positive control for the PCR reaction, which contained 2 μl sterile H2O or DNA extracted from Geobacter sulfurreducens, respectively, were also prepared. The PCR conditions were: initial denaturation at 94 °C for 4 min, followed by 30 cycles of denaturation at 94 °C for 30 s, primer annealing at 55 °C for 30 s and extension at 72 °C for 1.5 min, followed by a final extension step at 72 °C for 5 min. The purity of the amplified product was determined by running 8 μl of the PCR product with 2 μl of 5 × gel loading dye on a 1% Tris-Acetate-EDTA/agarose gel against a 2000 bp DNA ladder. The PCR product (∼1500 bp) was cleaned from the PCR salts using the ExoSap  protocol, where 0.08 μl Exonuclease I , 1.5 μl rAPid Alkaline Phosphatase  and 1.42 μl dd H2O were mixed with 3 μl of the PCR product, incubated at 37 °C for 30 min and then at 80 °C for 15 min. Nucleotide sequences were determined by the dideoxynucleotide method by cycle sequencing using an ABI Prism 377 DNA sequencer . A presequencing PCR step was performed using the ABI Prism BigDye Terminator Cycle Sequencing Kit v 3.1 (Applied Biosystems) and the 16S gene universal 8F primer. The PCR mastermix contained 0.75 μl Terminator BigDye, 3.65 μl 5 × buffer, 0.15 μl 8F primer and 14.95 μl dd H2O. The DNA template from the cleanup step was quantified on a Nanodrop ND-1000 (Thermo Scientific) and diluted to get 40 ng of DNA per PCR reaction. The PCR conditions were: initial denaturation at 96 °C for 2 min, followed by 30 cycles of denaturation at 96 °C for 40 s, primer annealing at 55 °C for 15 s and 60 °C for 3 min, followed by a final extension step at 72 °C for 5 min. The PCR product was then precipitated following the ethanol/EDTA precipitation protocol supplied with the kit. The data produced were analysed against the NCBI database, using the Basic Local Alignment Search Tool (megaBLAST) programme package and matched to known 16S rRNA gene sequences.DNA was extracted from the pellets of the five isolates of the nitrate-reducing culture using the PowerSoil DNA isolation kit (MO BIO Laboratories) according to the manufacturer's protocol. The 16S rRNA gene was amplified by PCR using the TaKaRa Ex Taq Polymerase  and universal primers 8F (with the sequence 5′-AGAGTTTGATCCTGGCTCAG-3′) and 1492R (with the sequence 5′-TACGGYTACCTTGTTACGACTT-3′) for the whole 16S rRNA gene (2 as a product of ISA degradation (the latter linked to acidification of the medium via the formation of bicarbonate). Under nitrate-reducing conditions (M) were produced between the initial time point and day 6 of incubation. The produced acetate was then degraded between days 6 and 15 of incubation, and part of the remaining nitrate was reduced to nitrite. Similar to the aerobic samples, the turbidity increased under nitrate-reducing conditions whereas the pH dropped, confirming bacterial growth and metabolism. Furthermore, bacteria in the nitrate-reducing cultures were also able to grow and cause a drop in the pH of the medium at a range of temperatures  in cultures incubated at starting pH values of 10 and 11  historic lime workings were inoculated into defined minimal medium containing ISA as the sole electron donor and either oxygen (as air), nitrate, Fe(III) or sulphate as an electron acceptor. Under aerobic conditions , all thenditions , a broad0 and 11 , whereas0 and 11 , only ∼30 and 11  did not Aquimonas. The bacterial genera that dominated the nitrate-reducing cultures were the facultative anaerobic denitrifiers Azoarcus (65%), and the obligate anaerobes Paludibacter (12%) and Anaerobacillus (21%), with the latter almost completely dominating the Fe(III)-reducing enrichment cultures (99.5%). Further analysis was carried out using the megaBLAST programme package that matched the pyrosequencing data to known 16S rRNA gene sequences to find the closest known relatives to the OTUs identified in the nitrate- and Fe(III)-reducing enrichment cultures. This analysis showed that the OTU that dominated the nitrate-reducing cultures (65%) was a close relative (at 97% identity) of the facultative denitrifying bacterium Aromatoleum aromaticum (which belongs to the Azoarcus cluster) (Azoarcus buckelii (Anaerobacillus macyae(previously known as Bacillus macyae)  . Furthermore, analysis of the partial 16S rRNA gene sequence (1050 bp) of the isolates showed that all the isolates showed 98% similarity to the bacterium This study shows for the first time that bacteria are able to degrade ISA  at high pH (∼10) under a wide range of biogeochemical conditions, and can couple ISA metabolism to the bioreduction of a number of TEAs relevant to an evolving ILW-GDF. Furthermore, the rates of ISA biodegradation, TEA reduction and the bacterial diversity of the cultures were proportional to the reduction potential of the TEA, in the order aerobic≈nitrate>Fe(III), with no reduction of sulphate detected at pH 10. Collectively, these results are consistent with the observation that a range of anaerobic processes can support ISA oxidation, and that decreasing the reduction potential of the respiratory process redox couple results in progressively more streamlined microbial communities dominated by more specialist microorganisms, as noted previously in high pH environments  and potentially using cellulose-bearing ILW under prolonged incubation. Collectively, these studies can play an important role in removing unnecessary pessimism in performance assessment evaluations for GDFs.It is probable that microbial metabolism of ISA will become more pronounced as the pH drops with time and distance from the GDF, and as the extant geosphere microbial communities adapt to the high pH conditions in and around the GDF over prolonged periods of time. Furthermore, in these scenarios potential ISA degraders could be sourced from the deep geosphere, or could survive in the initial hyperalkaline pH as recalcitrant spores, and then germinate when the conditions are more suitable for growth. It should be noted that Gram-positive Bacilli, well known to sporulate as a survival mechanism (


High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system.Epitaxial transparent oxide Ni The wide-band gap semiconductor NiO 3.7 eV) is one of the few p-type transparent conductive oxides demonstrating good electrical properties for application in optoelectronic devices2.7 eV is 46xMg1−xO thin films over the entire composition range can be grown with high crystalline quality on MgO single crystalsxMg1−xO system is unique in demonstrating a great flexibility for band gap tuning from 3.7 eV to 7.8 eVxMg1−xO is increasingly receiving interest for application in deep UV photodetectors8111213xMg1−xO band gap evolution as a function of composition and to be able to accurately describe it using an analytical equation.The epitaxial growth of NiO on MgO single crystal substrates offers a promising platform for the preparation of complete UV-transparent oxide devices. Both NiO and MgO crystallize in the cubic rock-salt structure and NixB1−xC as a function of composition x follows the parabolic function15Experimentally it has been shown that the band gap dependence in most semiconductor alloys or solid solutions Ab is the bowing parameter. Since the band gap of the semiconductor alloy is generally smaller than indicated by the linear interpolation between the band gaps of its pure end members, the bowing parameter b is a positive constant. It has been proposed that the band gap bowing results from the aperiodic variation of the crystal potential in substitutional alloys, arising from random variations in occupation of the metal sites in the alloy by elements A and B, and its magnitude is a symmetric function of composition proportional to x(1 − x)where xMg1−xO band gap dependence has been determined by optical absorption spectra of epitaxial thin films on MgO substrates prepared by molecular beam epitaxy14xMg1−xO band gap increases only marginally to 4.8 eV, even at a small NiO fraction of only 8 at.%. A density functional theory (DFT) calculation of the NixMg1−xO band gap dependence on composition has investigated superstructures with NiO contents of 25, 50 and 75 at.%x < 0.25, no band gap discontinuity has been identified and the underlying NixMg1−xO electronic band structure has not been investigated.The NixMg1−xO band gap bowing. Regardless of the strongly non-parabolic band gap dependence on composition, the standard bowing theory has been rigidly applied in previous studies to describe the band gap evolution in the NixMg1−xO system1112141820xMg1−xO microstructure and the underlying NixMg1−xO electronic structure with a particular focus on the dilute NiO concentration regime , the present work demonstrates that I) the origin of the irregular NixMg1−xO band gap dependence shall not be attributed to apparent structural or compositional inhomogeneities in NixMg1−xO films and II) the standard bowing theory is inapplicable to describe the non-parabolic composition dependence of the NixMg1−xO band gap because deep Ni 3d gap states evoke a highly anomalous bowing trend and significantly reduce the NixMg1−xO band gap even at small NiO fractions of only 3.7 at.%.The present work combines experiment and theory to resolve the controversy over the Niω − 2θ high resolution X-ray diffraction (HRXRD) patterns of the NixMg1−xO thin films  only the 200 and 400 diffraction peaks are observed, indicating that films are single-phase and grown in 100-orientation on the MgO(100) substrates . The relatively narrow NixMg1−xO 200 diffraction peak in the in-plane Qy direction in reciprocal space as compared to the MgO substrate indicates the high crystalline quality and low degree of mosaicity of the thin films. In particular, the out-of-plane width of the NixMg1−xO 200 diffraction peaks along Qz  to MgO (4.212 Å). Reciprocal space map analysis of the asymmetric NiO 204 reflection shows that the in-plane lattice parameter ax is larger than the unstrained reference  elemental map employing the Ni Lα,β (green) and Mg Kα (red) emission lines was recorded  HRTEM image  image of the Nirecorded . The croubstrate . The verEM image  of the rxMg1−xO thin films  indicate about 80% transparency in the visible and UV region until the onset of their fundamental absorption 2, where α denotes the absorption coefficient, which is valid for direct transitions in semiconductors at the absorption edge . Both LDA + U and HSE calculation methods demonstrate that the variation in the band gap between NiO and Ni0.125Mg0.875O is only about 0.7 eV. However, the difference between the calculated band gaps of Ni0.037Mg0.963O and pure MgO of 1.8 eV is surprisingly large. More than 65% of the total band gap variation in the NixMg1−xO is observed after alloying just a few percent of NiO to MgO.The calculated electronic band gaps obtained from DFT calculations of both ordered and special quasi-random structures (SQS) of Nigap plot . To acco0.074Mg0.926O and that of pure MgO obtained within the LDA + U method is shown in 0.074Mg0.926O band structure shows deep localized levels almost entirely derived from Ni 3d eg states at about 3 eV inside the MgO band gap. The Ni 3d eg impurity-like level remains localized as there is only a negligible contribution from hybridization with O 2p states of the surrounding atoms. Both the Ni0.074Mg0.926O valence and conduction band show a nearly unperturbed electronic structure derived from pure MgO. Since the extended states of the MgO conduction band are not affected by the localized Ni 3d eg states, the approximation of employing a composition-independent +2 eV energy shift for the calculated band gaps obtained within the LDA + U method is justified to compare these results with experiment.A superposition of the calculated band structure of NixMg1−xO  is shown in eg and t2g states just above the MgO valence band, which is occupied, and II) the energy level almost entirely derived from Ni 3d eg states at about 3.5 eV. Both of these features show localized levels similar to those introduced by impurities, even though a concentration of 3.7 at.% NiO is considered in the alloying regime. With increasing NiO concentration, the lower energy Ni 3d eg and t2g levels merge with the O 2p states at the top of the valence band while the density of the higher energy Ni 3d eg impurity level increases and broadens to form the Ni0.5Mg0.5O conduction band.The calculated density of states (DOS) of Ni0.037Mg0.963O. For MgO doped with impurity concentrations below 3.7 at.% NiO a band gap discontinuity is expected. It is obvious that the standard bowing equation cannot be applied to describe the anomalous NixMg1−xO band gap trend, because the bowing term bx(1 − x) only accounts for a parabolic deviation of the interpolated band gaps as a function of composition x, as a result of the aperiodic variation of the crystal potential in the random alloy.By alloying with MgO, the NiO band gap increases about linearly from 3.7 eV to 4.9 eV in NixMg1−xO 200 diffraction spots obtained by HRXRD shown in Qz component in reciprocal space indicating that compositional fluctuations on a macroscopic level are insignificant. Compositional inhomogeneities are further very unlikely to be observed as it has been shown experimentally that NiO and MgO are fully miscible, typically forming a homogeneous NixMg1−xO solid solution2426xMg1−xO is evident from the HRTEM images showing a defect-free NixMg1−xO/MgO interface and suggesting single-domain epitaxial growth without evidence of either ordering or clustering .Electronic structure calculations of 3d transition metal  impurities in MgO reveal that deep energy levels in the band gap are formed by combination of the metal 3d orbitals with O 2p orbitals to form xMg1−xO band gap bowing is fundamentally different from that of most substitutional semiconductor alloys, for which the standard bowing equation holds. Instead, the non-parabolic NixMg1−xO bowing behaviour induced by the Ni 3d-derived localized states can be related to the band gap narrowing observed for highly mismatched III-V semiconductor alloys such as GaNxAs1−xxTe1−x36xMg1−xO solid solution system is different in that the localized Ni 3d eg states remain as localized impurity states well inside the MgO band gap while no perturbation of the host conduction band structure is observed . DFT calculations of the NixMg1−xO band structure and density of states demonstrate that localized Ni 3d impurity levels are introduced at an energy well below the MgO conduction band and account for the pronounced band gap narrowing as confirmed by optical absorption spectra. The standard bowing theory is inapplicable to describe the NixMg1−xO band gap dependence and may in general not be applied to semiconductor systems, for which one of the alloy end members creates such deep levels in the band gap.Despite forming a completely miscible and compositionally homogeneous solid solution, alloys of NiO and MgO exhibit a strikingly anomalous band gap bowing behaviour. The non-parabolic NixMg1−xO ceramic targets were prepared by sintering high purity NiO (99.999%) and MgO (99.995%) powders at temperatures of 1200–1550 °C for 5 h, applying higher temperatures for the targets of high MgO content. NixMg1−xO thin films were grown on single-crystal MgO (100) substrates by pulsed laser ablation of the NixMg1−xO ceramic targets using a 248 nm KrF excimer laser. The growth temperature was 600 °C and the deposition pressure was 0.7 Pa O2. The NixMg1−xO ceramic targets were ablated with a laser beam fluency of 0.8 J/cm2 per pulse at a frequency of 10 Hz, resulting in a film thickness of about 300 nm.Single-phase polycrystalline NixMg1−xO thin films was accurately determined by EDX in a JEOL JSM-6010LA scanning electron microscope (SEM). Using a primary beam voltage of 5 kV, EDX spectra of the Ni Lα (852 eV), Ni Lβ (869 eV) and Mg Kα (1254 eV) X-ray emission lines were recorded. The background-corrected, integrated peaks of the Ni Lα, Ni Lβ and the Mg Kα emission for all NixMg1−xO thin films were evaluated based on a calibration curve obtained using data from the polycrystalline NixMg1−xO targets of known composition. It was confirmed that the 5 kV primary electron beam is entirely probing the NixMg1−xO thin films and does not reach the MgO substrate by investigating NixMg1−xO thin films of equal layer thickness grown onto Si substrates for which the Si Kα emission (1740 eV) was not observed.The composition of the NixMg1−xO thin films on MgO substrates was studied by HRXRD employing a Philips PANalytical MRD diffractometer equipped with a Cu-Kα1 X-ray source (1.5406 Å) utilizing parallel beam geometry. The structure and crystalline quality of the NixMg1−xO thin films on MgO were further investigated by HRXRD carried out on beamline B16 at the Diamond Light Source, UK, using a 6 keV (2.067 Å) monochromated X-ray source. The area detector was fixed at the expected 2θ value of the NixMg1−xO 200 diffraction peak while scanning the incidence angle ω to record 2-dimensional δ-χ diffraction patterns, where δ is the angle between the detector arm and the horizontal plane and χ is the angle between the detector arm and the vertical plane. 3-dimensional (3D) reciprocal space maps were calculated from the obtained data set which show the NixMg1−xO 200 diffraction peak intensity as a function of the components of the scattering vector Qx, Qy and Qz in reciprocal space. In this notation, Qx and Qy represent two orthogonal in-plane components and Qz represents the out-of-plane component of the scattering vector in the specimen frame of reference.The crystal structure of the NixMg1−xO/MgO interface. EDX spectral images were acquired recording Ni Lα, Ni Lβ and Mg Kα X-ray emission lines and were analysed using the INCA software (ETAS group). The optical transmission of the NixMg1−xO thin films were measured with a Cary 5000 UV-Vis-NIR spectrophotometer using a bare MgO substrate as 100% transmission reference.The electron transparent cross-sectional TEM specimen was prepared by grinding, polishing and dimpling until the specimen thickness was below 10 μm, followed by Ar ion milling using a PIPS Ion miller (Gatan USA). Conventional HRTEM and STEM using the HAADF detector and STEM-EDX was performed using a JEOL 2100 microscope equipped with a field emission gun operating at 200 keV. The high magnification HRTEM image was filtered using an ABSF. STEM-HAADF and STEM-EDX studies were used to identify the NixMg1−xO band gap trend, DFT calculations were performed using the LDA + U approach of Dudarev et al.4043−1. For all NixMg1−xO calculations, the Coulomb and exchange energy parameters, U = 4.3 eV and J = 1.0 eV, were applied to the Ni 3d states according to previous studiesUeff = U − J of 3.3 eV. The HSE approximation was chosen since it provides more accurate band gap values for semiconductors and insulators compared to traditional density functional approximations. In the HSE approximation the usual Hartree-Fock exchange mixing coefficient of 0.25 was used and the range separation parameter was set to 0.2 Å−1.To describe the NixMg1−xO may order antiferromagnetically and therefore calculations on NixMg1−xO were performed based on the rock-salt derived structure of NiO with AF ordered layers of Ni atoms along the [111] direction  were used47x = 0.75, 0.5 and 0.25. For all concentrations, the pair correlation functions for the first four atomic shells matched exactly with the pair correlation functions of the ideal unordered NixMg1−xO solid solution. Using this method the obtained structures contained a total of 64, 32 and 64 atoms for x = 0.75, 0.5 and 0.25, respectively. In addition to the SQS model structures, calculations were performed using ordered supercells based on 2 × 2 × 2 and 3 × 3 × 3 repetitions of the rock-salt derived AF NiO structure. Both approaches were applied to investigate the influence of atomic ordering on the calculation results. The lattice constants of the NixMg1−xO solid solution were determined from the experimentally measured lattice constants of NiO (4.177 Å) and MgO (4.212 Å) according to Vegard’s lawNiO is an antiferromagnet (AF), in which different Ni layers along the [111] direction have magnetic moments pointing in opposite directions. Thus magnetic moments on the Ni atoms in Nicf. refs  and 46. It shall be noted that other approaches such as the Green’s function based methods employing the coherent potential approximation (CPA) can provide an accurate description of random compound alloys5148How to cite this article: Niedermeier, C. A. et al. Band gap bowing in NixMg1−xO. Sci. Rep.6, 31230; doi: 10.1038/srep31230 (2016).


Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms.Carbenes of platinum and palladium, PtC Analysis of the rotational spectra reveals that each molecule has a linear geometry and an MCCC connectivity . The results are a successful test of a model proposed by Pyykkö et al.The importance of industrial catalysis by platinum and palladium has prompted extensive studies of their gas‐phase chemistry.3 and PdC3. For PdC3, the range of effective precursors includes C3H4 , C2H2, C2H4, CH4, and C4H4O (furan). For PtC3 the range is narrower, including C3H4 , C2H4, and CH4, all of which were found to be effective. Broadband microwave spectra of the target molecules were recorded between 6.5 and 18.5 GHz  a geometry that is slightly bent at equilibrium but quasilinear in the v=0 state, and 2) an equilibrium (re) geometry that is linear. The ab initio calculations suggest that both molecules are linear at equilibrium. The intensities of PdC3 transitions were found to be highly dependent on the choice of precursor, in the order C3H4>C2H4>CH4. Transition intensities were lower when the population of PdC3 was divided across many isotopic permutations and isotopically enriched allene is prohibitively expensive. These factors prevented measurement of the spectrum of any PdC3 isotopologue that contains both 12C and 13C isotopes. The intensities of PtC3 transitions were insensitive to the choice of precursor and it was possible to generate and record spectra for many isotopic permutations of PtC3  using samples prepared by mixing 12CH4 and commercially supplied 13CH4. It was also found that PtC3 can be generated from a mixture of 12C2H2 and 13CH4 precursors with the result that the spectra of 194Pt12C12C13C, 194Pt12C13C12C, and 194Pt13C12C12C were detected with equal intensities. The observation that the 13C isotope does not preferentially occupy an end position of the C3 subunit strongly implies that the C≡C bond of C2H2 cleaves during the sequence of reactions that generates PtC3 from this set of precursors.Spectra were measured for isotopologues of PtC3 units by rotational spectroscopy. Transition‐metal dicarbides, such as ScC2 and YC2, have been studied previously.3 and PtC3 are calculated at the MP2 level to be 6.1 and 5.6 D, respectively. The lengths of bonds within PtC3 were fitted to experimentally determined rotational constants using Kisiel's STRFIT.3 where the set includes every permutation of C3 that it is possible to generate from 12C and 13C isotopes. The bond lengths thus determined are compared with those in isolated PtC, C3 and OC3 molecules in Table r0 geometry of PtC3 is in good agreement with the re geometry calculated at the CCSD(T) level. The Pt−C bond in PtC3 is longer than found in diatomic PtCr(MC) in PtC3 and in PtCO,3/CO subunits. The r(MC) parameter in PtC3 is shorter than the same quantity in PtCO by 0.031 Å. The first C=C bond (that which is contiguous with the Pt−C bond) of PtC3 is longer than the C=C bond in isolated C3 by 0.022 Å. The set of isotopologues studied is less extensive for PdC3 than for PtC3 and does not permit determination of all bond lengths from the experimental data. If the lengths of C=C bonds within the molecule are fixed as shown in Table r(PdC) is determined to be 1.79898(4) Å. Values of vibrational wavenumbers calculated ab initio are provided in the Supporting Information.The present study is believed to be the first to characterize MC2C3.3 units identified herein and the linear carbon chains that are interceded by Pt/Pd atoms which are a feature of many synthetic coordination polymers.3 and PtC3. It is possible that a fraction of the population of each forms through gas‐phase association of individual metal atoms with intact C3 or other units generated independently of any metal atom.3→MC3 association reactions to yield linear MC3 units are calculated to be −295 kJ mol−1 and −417 kJ mol−1 when M=Pd and M=Pt, respectively . However, it is also possible that the metals themselves initiate the sequence of chemical reactions that leads to dehydrogenation of the precursor. There is extensive evidence from previous studies that both Pt and Pd atoms undergo bond‐insertion and cleavage reactions with hydrocarbons.2 and MCCH2 have both been generated2 are expected to be above the upper frequency limit of the spectrometer and both MCH2 and MCCH2 will have comparatively low dipole moments which significantly decrease the intensity of their rotational transitions relative to those of MC3.The described results confirm that the heavier elements of Group 10 can form linear arrangements similar to that previously identified for Ni3 relative to MC2 or MC4. Calculations of the geometries of CAu2+, CAu3+, Pt2C, Pt2C3, and Au2C2 revealed analogies between the behavior of each of Au+ and Pt and a chalcogen atom such as O.106s0 configuration is analogous to the 2pσ0 hole on oxygen, and the 5dπ orbitals of platinum participate in π‐bonding interactions analogous to those involving the 2pπ orbital of oxygen. The existence of a family of stable molecules was thus predicted. An orbital energy level diagram for PtC3 is presented in Figure S1 in the Supporting Information. There are striking similarities between the geometries of MC3 measured during the present work and that reported earlier for OC3 by Brown et al.2C3 are analogues of the well‐known, stable oxocarbons carbon dioxide, monoxide, and suboxide, respectively, each of which have been known since the 19th century. Similarly, PtSi2C2 would be ethylene dione,3, but not yet PtC2, have been detected. The results of the present work thus support the suggestion that platinum can be regarded an isoelectronic, isolobal counterpart of oxygen. The proposal can be further assessed with reference to previous works.An empirical model proposed by Pyykkö et al.4 and CO on Ptn clustersnOm clusters3C+ cluster ion12O9) is known to be stable, suggesting that Pt9C12 might be generated in an equivalent structural form. An experimental studyn+ and CuCn+ revealed ion intensities in the mass spectra that are significantly stronger where n=3 than for clusters of other sizes.3+ relative to other cluster sizes from these results. As in the present work, the experiment performed by Ticknor et al.3 was generated with a significantly higher abundance2 within the expanding gas sample and this may cause the generation of AuC3+ to be favored over the generation of clusters of other sizes, regardless of the thermodynamic stability of AuC3+. Indeed, during a previous study, signals for NiC3+ and NiC6+ were detected in mass spectra with higher intensity than units containing 1, 2, 4, or 5 carbon atoms,+ ion is not isoelectronic and isolobal with O. However, the reported fragmentation behavior of AuCn+ is also notable. Clusters where n is odd lose only the metal atom on photodissociation whereas those with an even value of n display an additional loss channel corresponding to the loss of an odd number of carbon atoms. The overall result is that chains  containing an odd number of carbon atoms tend to be formed during photofragmentation, consistent with the proposal of Pyykkö et al. The perspective thus emerging from the collected results of spectroscopic experiments is that the proposal+ centers with the O atom is powerful and useful with respect to structural trends in gas‐phase clusters that contain Pt, Pd, Au+, and C centers.Reports of clusters containing multiple carbon and platinum or palladium atoms are scarce. The adsorption of, and reactions of, CHAs a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


It was found that the PEG layer in G = 5 generations dendrimer is “frozen” at high temperatures (above 260 K), but it unexpectedly becomes “unfrozen” at temperatures below 250 K . The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors.We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by  Copolymer structures are an important research direction in terms of both fundamental investigations and practical applications. The modification of terminal segments is a natural way to obtain copolymer dendrimers. Typically modified terminal segments differ from inner segments in their physical and/or chemical properties, such as hydrophobicity/hydrophilicity, polarity, rigidity, flexibility, and others123456In our recent paperThakur et al.).The purpose of this paper is to demonstrate the additional properties of dendrimer systems in which a “hollow” core can form89Hu et al. and, for instance, recent refs The present study concerns carbosilane dendrimers with terminal mesogenic groups attached by PEG spacers  with terminal mesogenic groups. The terminal segments are phenylbenzoate mesogenic groups connected by oligo(ethylene glycol) spacers (PEG-BUT or TG1). Additionally we present experimental NMR data for the G5 dendrimer with terminal chiral ethyl-L-lactate-containing mesogenic groups (Und-BPL or TG2). The structural formulas of the studied dendrimers are shown in The investigated systems are dilute chloroform solutions of carbosilane dendrimers of the 1H NMR spectra were obtained with the number of accumulations between 8 and 64 depending on dendrimer concentrations. The residual proton signal of deuterated chloroform with a chemical shift (δ) 7.26 ppm was used as the internal reference for the calibration of chemical shifts δ of spectral lines. No temperature correction was made for the reference δ (CНCl3). The proton spin-lattice relaxation times, T1H, were measured using the conventional inversion-recovery π-td-π/2 pulse sequence with 6 μs duration of π/2 pulse, 14 scans for each T1H measurement, and 9s recycle delay time between scans. The latter was longer than any measured 5T1H. The temperature dependences were obtained in a temperature range limited by the room temperature and the freezing point of the solvent (298 K–218 K). It is more convenient in the discussion to use the inverse value of T1H, i.e., the spin-lattice relaxation rate R1H = 1/ T1H.The measurements were carried out at 400 MHz using a BRUKER AVANCE 400 spectrometer. The 1H NMR spectra of the dendrimers in the range of 0 to 5 ppm at room temperature (298 K). The full spectra of studied systems with the identification of spectral peaks in accordance with refs α, β, γ in ascending order of chemical shifts  of individual groups in the investigated objects. This allows us to estimate the mobility of separate molecular groups in more details.Thus, we have to conclude that the G5TG1 dendrimer becomes “unfrozen” with decreasing temperatures. This is an unexpected effect. Therefore, we have carried out the spin-lattice α, β, and γ) are presented in R1 values for CH2-O groups of the PEG spacer (γ-group) of the G5TG1 dendrimer have a sharp increase under temperature growing in the same range where the peculiarities in NMR spectra were detected. The similar but weaker effect takes place for CH3-groups (α- and β-groups).The experimental results for the spin-lattice relaxation rates of protons for a few molecular groups (1H nuclei (protons) gives:In order to obtain an additional information on the observed effect we tried to analyze our relaxation data in details. Temperature dependences of spin-lattice relaxation rates in objects with high molecular mobility are usually interpreted with BPP–Solomon theory23242526J is the spectral density of the fluctuating interaction, which determines the relaxation process; τc is the correlation time, which characterizes the orientational mobility of an observed group; ωH is the cyclic resonance frequency (2πf0) for 1H nuclei; A0 is a constant that does not depend on temperature and frequency. For the 1H nucleus this constant is given by the expression: ħ is the reduced Planck constant (h/2π); rHH is the distance between hydrogen atoms in a group; γH is the gyromagnetic ratio for 1H nucleus; N = 1 and 2 for CH2- and CH3-groups, respectively. Recent theoretical and experimental studies have shown the applicability of the spin-lattice NMR-relaxation method for the investigation and characterization of the orientational mobility in dendrimer12151H nuclei of dendrimers the spectral density J can be described using so-called “free model” approach with two correlation times:28where τin and τrot are the correlation times which correspond to intrinsic mobility and the rotation of a dendrimer as a whole, respectively; S is the generalized order parametern = 1, 2.where τinis the characteristic time of the orientational mobility of an individual dendrimer branch and τrot is determined by the volume of macromolecules (i.e. strongly depends on G)R1 in accordance with Eq. 2, that will be discussed below.In the case of dendrimers 3 groups in dendrimer solutions the conditions S2 ≪ 1 and τin ≪ τrotis realized, and for the explanation of the results  and external (β) CH3 groups of dendrimers. It is evident that the R1H values for the G1TG1 and G3TG1 are practically identical. Moreover, such behavior is typical for carbosilane dendrimers with terminal mesogenic groups where the PEG fragment is absent. For example, these dependences coincide with the R1H temperature dependence for G5TG2  of the R1H values for G1TG1 are greater than for G3TG1. For the explanation of this fact we suggest to take into account that the first generation of i.e. the dendrimer does not have a complete dendrimer structure. It seems the contribution of the rotation of a dendrimer molecule as a whole plays the more important role for PEG groups in G1TG1because in this case τrot is the shortest rotational time for the studied dendrimers. Thus, the relation τrot ~ τin can be expected for G1TG1 that leads to the superposition of two maxima in the R1 temperature dependence which, in turn, results in increasing the overall maximum  the “freezing” of the rotational mobility of the PEG groups  at high temperatures and (ii) the “unfreezing” of the mobility at low temperatures. It is important that the dendrimer is soluble at all temperatures investigated due to the fact that chloroform is a “good” solvent for the rest part of the dendrimer (dendrimer core and mesogenic groups)It has previously been shown that carbosilane dendrimers with terminal mesogenic groups possess a “hollow” core and more dense outside layer at room temperature8930In the case of water solutions LCST was observed and studied in detail for PEG polymers3334353 solvent allowed us to estimate the interaction between water molecules and PEG spacer atoms by investigating the chemical shifts of the water peak in NMR spectra (other parts of the macromolecules are hydrophobic). In chloroform without dendrimers the water chemical shift δ increases by only on ≈ 0.2 ppm when the temperature changes from 298 K to 223 K . A similar effect does not occur for the structures of smaller generations of dendrimers. After decreasing the temperature to 250 K, the mobility of the PEG groups in G5TG1 becomes similar to one in dendrimers with a smaller number of generations, i.e., the PEG groups begin to “unfreeze”. We suppose that the observed effect is the result of the specific conformation of the dendrimer structure: hollow core - dense peripherals. This structure is caused by the high concentration of terminal segments on the periphery of the macromolecule that, in turn, must lead to the increase in the concentration of PEG groups in the proper layer when the number of generations increases. The growth of PEG concentration in G5TG1 decreases the LCST to a temperature up to 250 K–260 K.Thus, we present for first time the evidence that in the dilute chloroform solution at room temperature the PEG groups “gum up” together in G5TG1 which consists of  - [PEG spacer] - [solvophilic group]. The transition temperature  can be regulated by selecting certain dendrimer structural parameters such as the number of generations, the functionality of the core or the branching points, and the length of PEG spacers. Therefore, we believe that the observed effect is of considerable practical interest for both the improvement of existing encapsulation methods and the design of new types of dendrimer nanocontainers or nanoreactors.How to cite this article: Markelov, D. A. et al. Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform. Sci. Rep.6, 24270; doi: 10.1038/srep24270 (2016).


We use Hyper Rayleigh Scattering and polarization resolved multiphoton microscopy to investigate simultaneously the second and third-order nonlinear response of Potassium Niobate and Bismuth Ferrite harmonic nanoparticles. We first derive the second-to-third harmonic intensity ratio for colloidal ensembles and estimate the average third-order efficiency of these two materials. Successively, we explore the orientation dependent tensorial response of individual nanoparticles fixed on a substrate. The multi-order polarization resolved emission curves are globally fitted with an analytical model to retrieve individual elements of susceptibility tensors. Increasing nonlinear order corresponds to a further increase in the number of different signals that can be accessed and prospectively exploited for sensing or imagingχn)〉 up to 160 pm/V8χ(3)| ∝ |χ(2)|2An interesting model system for exploring these phenomena is represented by Harmonic Nanoparticles (HNPs), which have been introduced as bio-labelling agents for multiphoton microscopy approximately ten years ago34I, because of the different nonlinear dependence of the two signals:Very recently, a few authors have observed the simultaneous emission of second and third harmonic  by individual HNPs in microscopy11893, KN in the following) and Bismuth Ferrite . The former, has the advantage to be a widespread nonlinear medium for laser applications well characterized in its bulk form in terms of χ(2)χ(3) tensor elements available in the literature3In the following, we focus on two noncentrosymmetric metal oxide HNPs which have already been investigated in their nanometric form: Potassium Niobate (KNbOKN particles produced by sol-gel method were kindly supplied by FEE GmbH (Germany). BFO were synthesized by an auto-combustion process by FEE GmbH and provided in stable colloidal suspensions by TiBio SA (Switzerland). Typical concentrations of 0.1 mg/ml were obtained for both samples after sonication and sedimentationWedge HB, Bright solutions, pulse width 1 ns) is focused by a 20 cm focal length lens into a UV fused quartz cuvette containing the sample. SH and TH scattering is collected perpendicularly to the fundamental beam thought a short pass colored glass filter and an interferometric filter  placed in front of a photomultiplier. A half-wave plate associated with a polarizer cube is used to adjust the incident power. Maximum mean power was set to 220 mW during the experiments leading to 11 GW/cm2 intensity at the focus of a f = 20 cm lens. Note that in our set-up no polarization analyser is present in front of the detector as the application of HRS was limited to the derivation of orientation-averaged quantities.A Hyper Rayleigh Scattering (HRS) set-upλ0 = 790 nm  is modulated in amplitude at 4.88 MHz by a high frequency module  driven by the RF output signal generated by a lockin amplifier , a quarter wave plate, and a polarization analyser. The pulses are then anti-chirped by a prism compressor  to pre-compensate for dispersion through the optical elements. The linear laser polarization is freely modified by a λ/2 plate mounted on a motorized rotation stage. The beam is finally injected into a high N.A. objective and focused onto a single HNP, with a peak intensity of the order of 10 GW/cm2. In this case the sample was prepared by casting a drop of HNPs solution and letting it dry prior to measurements, as previously reported9λ0/2 and detected by a photomultiplier. The signal is finally processed by the high frequency lockin at the HFM driving frequency. The TH emission is forward collected by Schwarzschild objective , spectrally filtered and detected by a dedicated photomultiplier. Note that the use of a reflective objective allows to circumvent the issue of transmission cut-off of collection optics at the TH of Ti:Sapphire laser, a problem which can alternatively be solved using a For the polarization response of individual HNPs, the 80 MHz output of a Ti:Sapphire oscillator centred at e HFM in  comprisiIgorPro v.637 by Wavemetrics.Multiple fitting procedures were run on a standard personal computer using the Global Analysis Package of I from HRS along with their fits by a power law. As expected, the curves are proportional to In with In the right column of ckground . The SH 2 excitation intensity. Based on this ratio, we can calculate the orientationally averaged third order efficiency 〈χ(3)〉 (at 1064 nm) for both nanomaterials (Equation S4). The value extracted for KN is 〈χ(3)〉 = 1 × 10−19 m2/V2. For a reference, Bosshard et al. reported 2/V2 from bulk measurements at 1318 nm and they extrapolated a value of 1.2 × 10−20 m2/V at 1064 nm using a model which does not account for absorption effectsχ(3)〉 is 5.5 × 10−18 m2/V 2. We remark that for typical oxide materials, the measured values are fairly high but are probably related to electronic resonance at TH frequency which falls within the absorption band in particular for BFO. Moreover, TH signal can originate both from a pure third order process as well as from cascaded second order processes. The two mechanisms cannot be easily distinguished but the relative contribution of each should scale as (χ(3)/(χ(2))2)2χ values are knownet al. in a very recent paper−14 to 10−19 m2/V2.Considering exclusively the linear part of the intensity versus concentration curves and taking into account the different collection efficiencies for the SH and TH wavelengths, the SH/TH ratio could be estimated at 30 for BFO and 322 for KN for 11 GW/cmγ of the linearly polarized excitation laser and for horizontal (red) and vertical (blue) position of the polarization analysers (see 20Ex = Ecos(γ) and Ey = Esin(γ), ignoring the longitudinal field component similarly to previous works by ours and other groups17202122In the following, we focus on the tensorial character of the nonlinear signals generated by HNPs assuming only pure TH contribution. sers see . In geneϕ, θ, ψ} defining the orientation of the crystal axis with respect to the laboratory frame {x, y, z} as in In the equation, three successive rotation operations χ(2) tensor was simplified to a 6 × 3 matrix using Voigt notationmm2 point group symmetry associated with KN, For modelling the SH response, the During the fitting procedure, all The approach was successively extended to account also for third order polarization. Briefly, keeping the same formalism introduced above, the polarization vector is now written aset al. on bulk samplesmm2 symmetry of the material. Note that to over-determine the system to be solved and increase the statistical significance of the analysis, the TH responses of two particles were simultaneously fitted keeping the Euler angles retrieved at the SH harmonic as local fixed parameters, and the unknown To our best knowledge, there exists no complete quantitative description of all the caveat applies here: the bold values - although absolute - were determined by Bosshard at a different wavelength than the one used in this work. Therefore, although the relative relationships among the tensor elements are informative for 800 nm excitation, their absolute values including the elements in bold font might be different.An import m which corresponds to 8 nonzero elements (4 independent) for relativeχ(2)〉 determined at 160 pm/V by Schwung et al.χ(2) BFO tensor were then estimated. Note that without Kleinmann symmetry in the case of 3m crystals and for a vertically polarized laser with no analyser in the detection path, 〈χ(2)〉2 can be expressed as by developing HRS full polarization formalism originally introduced for nonlinear molecules3334We then repeated the procedure just outlined for analysing the multi-order polarization plots of BFO HNPs. The data are reported in from which we obtained :Using this matrix we could determined the angles of various HNPs like the two reported in For the BFO TH response the situation is more complicated, as only the Again, the derivation of an expression equivalent to 2 intensity at 1064 nm which allowed us to estimate the orientationally averaged third order nonlinear efficiencies for these two nanomaterials (−18 m2/V2vs2/V2). For KN the retrieved value is in line with previous worksvs 16.6 pm/V) is indeed very favourable for setting-up multi-harmonic detection protocols13χ matrices provided in full (second order) or only partially (third order) in the literature. This agreement sets a convenient ground for applying the same approach to BFO which enabled us to derive the relative values of its χ(3) matrix. A part from the fundamental interest of the method just demonstrated for investigating the relationship between single elements of susceptibility tensors at different nonlinear orders, this approach can bring benefits to protocols of orientation retrieval of HNPs .


Lithium–oxygen cells have attracted extensive interests due to their high theoretical energy densities. The main challenges are the low round-trip efficiency and cycling instability over long time. However, even in the state-of-the-art lithium–oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials. Here we report a reaction mechanism at an oxygen cathode, ruthenium and manganese dioxide nanoparticles supported on carbon black Super P by applying a trace amount of water in electrolytes to catalyse the cathode reactions of lithium–oxygen cells during discharge and charge. This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles. The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium–oxygen cells. The main challenges in lithium-oxygen batteries are the low round-trip efficiency and decaying cycle life. Here, the authors present that a trace amount of water in electrolytes facilitates oxygen cathode reactions, enabling the batteries to be operated with small overpotential and good cycling stability. Exploring new reaction mechanisms at the oxygen cathodes to significantly improve the round-trip efficiency and cycling stability is essential and urgently necessary for the development of Li–O2 cells.The success of deploying Li–O0 V refs , 12, 13.4 V refs , 22, 23.2 atmosphere resulted in rapid charge potential increase and hence cell death after several cycles26272O2, a byproduct LiOH was also detected2 cells, a trace amount of water in electrolytes and electrolytic mangnese oxide  nanoparticles are both utilized to favour the transformation of the discharge product from Li2O2 to LiOH and its following decomposition on charging. The MnO2 incorporated in Ru/SP (Ru/MnO2/SP) also allows for the water regeneration at the cathode during the discharge/charge cycles. This enables the Li–O2 cell to operate with a small discharge/charge potential gap and superior cycling stability. A reaction mechanism by converting Li2O2 to LiOH in the presence of both water and Ru/MnO2/SP is proposed.Although water in electrolytes has been found to affect the morphologies of discharge products and increase the discharge capacity24252 cells were constructed with Ru/MnO2/SP pressed onto a carbon paper as cathodes, 0.5 M LiClO4 in DMSO containing 120 p.p.m. of H2O as electrolytes and LiFePO4 in replacement of Li anodes. The LiFePO4 is not a practical anode, but is able to avoid the reaction of Li metal and the trace amount of H2O and any contamination from formation of the solid electrolyte interface layer on the Li anode+/Li regardless of the state of charge and favours the investigation on the discharge/charge behaviour in the presence of H2O and the underlying reaction mechanism specifically at the oxygen cathode. The discharge/charge potentials at the oxygen cathode of the Li–O2 cells are converted to against Li for discussion.The Li–O2 cell with Ru/MnO2/SP as cathode and the DMSO-based electrolyte containing p.p.m.-leveled H2O is discharged and charged at 500 mA g−1  surface area of Ru/MnO2/SP) as shown in Q/dV curve in 2/SP cathode that has a large contact angle of 62°, compared with the discharge and charge profiles of the Li–O2 cell with a dimethoxyethane-(DME-)-based electrolyte and the good wettability of DME on the cathode in 2O in electrolytes is demonstrated to play a crucial role on reducing charge overpotentials of Li–O2 cells in all the widely used electrolytes, which was empirically considered as a negative factor in a Li-ion cellThe carbon paper has been demonstrated to have negligible contribution to cell performance . The Li–2/SP cathodes in the DMSO-based electrolyte containing water have been characterized by X-ray diffraction (XRD). As shown in 2O2, referring to the standard powder diffraction files of 01-085-0777 and 00-009-0355, respectively. The diffraction peaks of LiOH become sharper and stronger at the cathode with a discharge capacity of 4,000 mAh g−1 and addition of more electrolyte +2H2O(l)→H2O2(l)+2LiOH(aq)302O2 further oxidizes iodide to iodine, the titrated target. The LiOH and Li2O2 in the discharged cathode were titrated via two steps  did not show any plateaus at ∼3.2 V but instead at >3.6 V , the best disproportionation catalyst of H2O2 (ref. 2O via 2H2O2(l)→2H2O(l)+O2(g) and make H2O circulate during cycles and improve cycling stability of the Li–O2 cell.In the Ru/MnO122 ref.  and SP35t >3.6 V . Only th2O2 ref. , was inc2 cell with Ru/MnO2/SP and the DMSO-based electrolyte containing p.p.m.-leveled H2O was examined at varied current densities, as shown in −1. The overpotential in the discharging and charging process at 250 mA g−1 is 0.11 V and 0.21 V, respectively, leading to a small discharge/charge potential gap of 0.32 V. The Li–O2 cell was continuously discharged and charged at 500 mA g−1 for 200 cycles and ∼800 h, and the selected runs of discharge and charge are shown in 372 cell, which is in sharp contrast to that without MnO2 in 2O2 to LiOH. The reversible formation and decomposition of LiOH and Li2O2 during the 200 cycles are further confirmed by ex situ XRD patterns in 2 cell are rewarded by the ‘water catalysis' at the Ru/MnO2/SP cathode.The Li–O+/Li based on Nernst equation342O and LiClO4 are both the solutes and DMSO is the solvent. The equilibrium potential of LiOH is dependent on the concentration of H2O, and it can be roughly estimated to be ∼3.20 V, considering a concentration of 100 p.p.m. of H2O in the electrolyte . Although Step (i) is an equilibrium2O2 to H2O over MnO2 via Step (ii)2O2 to LiOH as long as H2O remains in the electrolyte. This has been confirmed by the presence of substantial LiOH in discharged cathodes as revealed by both of the XRD patterns and the IR spectra in et al.et al.2O in electrolytes is possibly consumed by the employed Li anode or saturated by the product LiOH, and the lack of a promoter like MnO2 for Step (ii) made the equilibrium reaction in Step (i) to move backward and result in the major discharge product Li2O2 as detected.Based on the above results, a mechanism for the discharging and charging process of the cell with Ru/MnO2O2 refs , 41, 42.2O at low charge potentials, by which the residual Li2O2 is then converted to LiOH via Steps (i and ii) and oxidized. To demonstrate the feasibility of Step (iii), commercial LiOH was ball-milled and then thoroughly mixed with Ru/SP with a ratio of 30:70 (wt/wt). The electrodes of Ru/SP with and without LiOH under Ar atmosphere were subjected to linear scanning voltammetry (LSV) at a low scan rate of 0.01 mV s−1 as depicted in 2 by a gas chromatography (GC) mounted with a thermal conductivity detector, as evidenced by the sharp GC signal of O2 in 2O is not consumed and can be circulated to behave like a catalyst. The total electrochemical reaction occurring at the oxygen cathode is 2Li++O2+2e−↔Li2O2, consistent with the Li–O2 cell chemistry.In the following charging process, the resultant LiOH can be directly oxidized via Step (iii) to regenerate H2O in electrolytes is shown in 2O2 and in good agreement with the literatrues10111213142O2 via the sequential Steps (i and ii) in 2/SP in both the discharging and charging processes. However, when the concentration of water in the electrolyte is increased to 281 p.p.m., the charge potential plateau is shortened and increased. It may be induced by the LiOH on the surface of the discharge product, which is surrounded/adsorbed by H2O molecules in the electrolyte, and hence has high oxidation potentials following the Nernst equation1732The dependence of the charge potentials on the concentration of H2 cells, the discharge product can be ranged from LiOH only to a majority of Li2O2 plus LiOH with the same amount of electrolytes used in cells. The cathode with a relatively small discharge capacity of 250 mAh g−1 was covered with LiOH, on which no Li2O2 was detected by iodometric titration. It is in the shape of thin disks as shown in 2O in electrolytes in −1, as shown in 2O molecules in the electrolyte can be consumed by Li2O2, producing surface-clean LiOH/Li2O2 in the cathode. This suggests that the relative amounts of H2O, LiOH and Li2O2 coexisting at a cathode side affect the charging overpotentials. The detailed formation/decomposition mechanism of LiOH and Li2O2 in the presence of water in electrolytes and the dependence of their decomposition potentials on their morphologies deserve further investigation.In addition, by controlling the discharge depth of the Li–O+/Li and provides a possible solution to the current challenges of Li–O2 cells. With the Ru/MnO2/SP cathode and the DMSO-based electrolyte containing p.p.m.-leveled H2O, the Li–O2 cell presents a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles ∼800 h. These have not been achieved before, and are rewarded by the proposed reaction mechanism. Although the LiFePO4 applied in cells is not a practical anode of Li–O2 cells, the reaction mechanism at the oxygen cathode may be extended to a practical Li–O2 cell by using a Li+ ion-conducting ceramic membrane to separate the electrolyte with water and the Li anode22O2 to LiOH, and it will make the cheap and lightweight carbon possible as cathodes in Li–O2 cells, which has been suggested to avoid. This investigation will enable the cell to operate in ambient air by eliminating CO2 and advance the Li–O2/air cell technology.The ‘water catalysis' at the oxygen cathode side has been demonstrated to reduce the charge overpotentials to ∼0.24 V, corresponding to ∼3.20 V vs Li2  was received from TOSOH, Japan and ball-milled to nanometre scale. Ru/SP was synthesized as follows: 85 mg of SP was stirred into a solution of ethylene glycol  containing 7.5 mg of Ru in RuCl3·xH2O , and its pH was adjusted to 13 with 0.1 M of NaOH in EG. The suspension was then heated to 160 °C for 3 h with flowing N2. After cooling to 80 °C, its pH was adjusted to 3 using 0.1 M HCl and the resulting mixture was further stirred for 12 h. The final product Ru/SP was centrifuged, washed with de-ionized water until the solution pH reached ∼7 and dried at 80 °C in a vacuum oven for 12 h. For the preparation of MnO2/Ru/SP, the as-synthesized Ru/SP and MnO2 nanoparticles with a weight ratio Ru/MnO2/SP=7.5:7.5:85 were sonicated into an ethanol aqueous solution for 3 h and stirred overnight. Then, the product MnO2/Ru/SP was collected and dried at 80 °C under vacuum for 12 h.Electrolytic MnO4 and lithium bis(fluorosulfonyl)imide were used as received from Wako Chemicals. The water in the prepared electrolytes was from the Li salts and measured on a desk-top Karl–Fisher Titration instrument.DMSO, DME, G3 and G4 were firstly dried over 4 Å molecular sieves and then using Li metal. The Li salts of LiClO2/SP or Ru/SP and PTFE  with a ratio of 85:15 wt% was rolled with a glass rod. The mass loading of Ru/MnO2/SP or Ru/SP is ∼0.5 mg cm−2. The electrode film was pressed onto a hydrophobic carbon paper  to work as a cathode. The anode was consisted of LiFePO4 (Sumitomo Osaka Cement), SP and PTFE (70/20/10) pressed on an Al mesh. The amount of DMSO- and DME-based electrolytes in a coin cell was 100 μl and G3- and G4-based electrolyte was 50 μl, considering their different vapour pressures. The employed separator was a glass microfibre filter paper . The Li–O2 cell assembly in 2032 coin cells was conducted in an Ar-filled glove box that has a dew point of around −90 °C (∼0.1 p.p.m. of H2O) and O2 content below 5 p.p.m.. The cells stored in a glass chamber with a volume capacity of 650 ml were purged with O2 (99.999%) before electrochemical tests.The electrode film composed of Ru/MnO2/SP was measured to be 70.6 m2 g−1 on Belsorp 18 via nitrogen adsorption–desorption. XRD was performed on a Bruker D8 Advanced diffractometer with Cu Kα (λ=1.5406 Å) radiation with a scan rate of 0.016° per s. Galvanostatic discharge/charge was conducted on a Hokuto discharging/charging system. All the electrochemical measurements were conducted at 25 °C. The specific capacities and currents are based on the mass of Ru/MnO2/SP or Ru/SP in cathodes. The discharged and charged cathodes were extracted in the glove box and washed with dried dimethoxyethane. SEM was obtained on Hitachi S4800. The Ru/MnO2/SP was mixed with KBr and then pressed to a pellet for Fourier transform infrared spectroscope (FTIR) characterization on a JASCO instrument of FT/IR-6,200 from 2,000 to 400 cm−1 with a resolution of 2 cm−1. The electrolytes during cycles were collected by washing the glass fibre filter separators with acetone-d6, and subjected to 1H NMR .The contact angles of electrolytes on the cathode were examined on AST Products with a model of Optima. The BET surface area of Ru/MnOHow to cite this article: Li, F. et al. The water catalysis at oxygen cathodes of lithium–oxygen cells. Nat. Commun. 6:7843 doi: 10.1038/ncomms8843 (2015).Supplementary Figures 1-14, Supplementary Table 1, Supplementary Notes 1-3 and Supplementary Methods


A receptor‐mediated inhibition: phasic or classical inhibitory postsynaptic currents (IPSCs) generated by the activation of synaptic GABAA receptors (sGABAAR) and tonic inhibition generated by extra‐ or peri‐synaptic GABAA receptors (eGABAAR) A inhibition in TC neurons has not been examined. Here, we investigated whether 5‐HT and its 5‐HT1A, 5‐HT2A and 5‐HT2C receptors exert a control over tonic and phasic GABAA currents in dLGN TC neurons. We used whole cell patch clamp recordings in coronal slices (300 mm) containing the dLGN from postnatal day 20–25 Wistar rats. Data analysis and experimental procedures were similar to those previously described A current are shown in Table A inhibition , but has no action on tonic inhibition. These effects are identical to those observed following 5‐HT1A/7R activation with 8‐OH‐DPAT. On the other hand, α‐M‐5‐HT and mCPP enhances and reduces, respectively, both phasic and tonic GABAA inhibition. These effects are dependent on 5‐HT2AR and 5‐HT2CR activation, respectively, as they are blocked by co‐perfusion with selective antagonists, ketanserin, and SB242084. Thus, the lack of 5‐HT modulation of tonic inhibition might be explained by the counterbalance of co‐activation of 5‐HT2ARs and 5‐HT2CRs by the endogenous ligand  neurons, including those of the dorsal lateral geniculate nucleus (dLGN), one of the visual sensory thalamic nuclei, exhibit two forms of GABA2ARs  1AR‐dependent suppression of protein kinase A (PKA) activity) 1A/7R activation in the dLGN.Our findings are in agreement with recent evidence in visual cortex showing that 5‐HT enhances phasic inhibition by activating 5‐HTin vivo studies in which stimulation of the dorsal raphe nucleus decreased TC neuron firing in the dLGN in vitro intracellular recordings of ferret TC cells found that 5‐HT is predominantly hyperpolarizing in all thalamic nuclei tested except for the dLGN, medial geniculate and in a subset of pulvinar neurons, in which depolarizing responses were observed 2CR activation with α‐M‐5‐HT and the highly selective ligand CP‐809,101 produced depolarization of TC neurons shifting their firing from bursts to tonic 1A/7 are present in the thalamus 2CR immunoreactivity has been detected, although not somatically, in dLGN TC neurons 2AR immunostaining did not reach detectable levels 2AR and 5‐HT2CR mRNA are expressed in the dLGN GABAergic interneurons of young rats 2Rs on dendritic F2 terminals of dLGN interneurons, as previously shown Moreover, our study is in agreement with previous 1A/7R and 5‐HT2A/2CRs might also be located postsynaptically on TC neurons, and their activation may lead to phosphorylation of different subunits of sGABAARs and eGABAARs acting to differentially modulate their function. The binding of 5‐HT to 5‐HT1A/7R and 5‐HT2A/2CRs might activate multiple signal transduction cascades, which ultimately activate different protein kinases, such as PKA or protein kinase C (PKC) and differently regulate sGABAARs and eGABAARs, as indicated by our results. On the other hand, the potential contribution of 5‐HTRs on retinal and cortical terminals can be ruled out as glutamatergic function was blocked in our preparations through the addition of kynurenic acid to the recording solution.Nevertheless, 5‐HTA current by 5‐HTRs in the thalamus and also to highlight that phasic and tonic inhibition in the dLGN are modulated by 5‐HT through different receptor subtypes, leading to a finely tuned balance of sensory information processing in the dLGN. By showing a differential modulation of phasic versus tonic GABAA inhibition, our results demonstrate a novel mechanism by which the ascending serotonergic afferents can control the thalamic gate to the visual cortex in a behavioral state‐dependent manner. Moreover, because of the putative role for thalamic tonic GABAA inhibition in sleep regulation and pathological oscillations, such as those present in absence epilepsy, the opposing effects of 5‐HT2ARs and 5‐HT2CRs activation may provide suitable targets for pharmacological intervention in sleep and other CNS disorders.Overall, this study is the first to show a modulation of tonic GABA


The drift time has been measured to obtain the mobility for each charge carrier. The Hecht equation has been employed to evaluate the lifetime. The measured values for μτe/h (mobility-lifetime product) are in agreement with earlier published data.We report on the measurement of drift properties of electrons and holes in a CdTe diode grown by the travelling heating method (THM). Mobility and lifetime of both charge carriers has been measured independently at room temperature and fixed bias voltage using charge integration readout electronics. Both electrode sides of the detector have been exposed to a  The large difference between the hole and the electron mobilities  for CdTe and CdZnTe increases the time walk and hence the timing resolution. This timing limitation is one of the main drawbacks of using CdZnTe in fast triggering schemes such as Time Of Flight (TOF).CdTe and CdZnTe detectors are nowadays a good choice for gamma ray detection due to their excellent energy resolution, easy segmentation into voxels and relatively good detection efficiency. When the ionizing radiation interacts with the bulk, a cloud of free charged particles is created, either with negative charge, the electrons, or with positive charge, the holes. Due to the bias voltage applied on the semiconductor electrodes, the charge carriers drift in opposite directions. Their velocity depends on the magnitude of the bias voltage and the structure of the crystal lattice of the material. The mobility (τ) is the average time for a charge carrier to get trapped in the material. The higher the level of impurities in the material, the shorter τ becomes and more trapping effect is observed. The product of μ and τ is called the trapping length, l = μτ, and is an estimation of how long the charge carrier can move among the material without being trapped.The charge carriers can be trapped in the lattice due to impurities or recombinations, resulting in a total charge loss. The lifetime  A250 from AMPTEK has been coupled to the detector output. The preamplifier output has been recorded with an oscilloscope TDS3024B from Tektronix. A Labview executable has been used to acquire the full charge vs time curve for each event. The diode has been biased with a Keithley 2410 power supply. In order to avoid the polarization effect of the bias voltage in the diode, it has been ramped down every 100 s and kept at 0 V for 30 s and then ramped up again to −500 V.μ.The mobility of a charge carrier can be evaluated when the detector thickness (D), the bias voltage applied (V) and its drift time along the diode (Δ t) are fixed using τ. The function used for the fit is a combination of the Hecht t), the depth of interaction point (x0) and μ and τ for each charge carrier, f. For events with full contribution of electrons or holes x0 is 0 or D respectively and the dependency of the function becomes f. The value of μe\h has been previously determined with the aforementioned method so it becomes a function with one variable, t, and one parameter, τe\h. The example of an event with the result fit function is shown in The charge induction curve for each event has been fit to obtain an average value of μe=(1090±40) cm2/(V·s) and μh=(110±10) cm2/(V·s).The distribution of the drift time for electrons and holes are shown in τ for electron and holes are shown in μτe ~ 2.7·10−3m2/(V·s) and μτh ~ 1.8·10−4m2/(V·s).The distributions of μ and μτ are summarized next to some previously published results.In 241Am source to detect alpha particles and the outcoming signals have been recorded with an oscilloscope. The measured drift time and mobility values of μe =(1090±40) cm2/(V·s) and μh=(110±10) cm2/(V·s) have been obtained.A setup to measure the mobility and lifetime of electrons and holes has been built. It consists of a CdTe diode coupled to a preamplifier. Both electrodes have been exposed to a τ values. For holes, τh ~ 1.6 whereas for electrons τe~2.7. The μτ products are approximately eμτ~2.9·10−3m2/(V·s) and μτh~1.8·10−4m2/(V·s) which are similar to those measured for CdTe diodes in [The same curves have been fit to obtain the The values obtained in this work are those expected for CdTe as one can compare with other publication with the values shown in


Using a combined approach of pulse chase labeling and single-particle tracking of Crb3A or 3B loaded vesicles we collected trajectories of different vesicle population in living podocyte cells and evaluated statistically their different mobility patterns. Differences in their intracellular mobility and in their directed transport correspond well to the role of Crb3A and 3B in renal plasma membrane sorting   Specifications TableValue of the data•Renal plasma membrane proteins Crb3A and Crb3B can be assigned to different vesicle subpopulations.•The different membrane proteins can be used as distinct vesicle marker to identify and track different vesicle populations.•Differences in mobility pattern and trafficking dynamics might be related to intracellular redistribution of Crb3A and Crb3B and their respective plasma membrane portion.1momentum scaling spectrum was computed and its slope calculated SMSS  as it is shown in Djuric et al. Single vesicles loaded with different membrane proteins fused to a SNAP-tag were tracked in living cells after fluorescence labeling . From si22.1The SNAP-tag fusion protein expressing AB8 cells were seeded on cover slides and incubated in standard RPMI 1640 medium containing 10% FCS and supplements and 1% antibiotics (Pen/Strep). Directly before the measurements the cells were incubated with the fluorescent SNAP-tag substrate (BG594) according to the manufacturer׳s protocol. After incubation free dye was removed by washing several times.2.2Cells were imaged using an inverted custom-built single-molecule microscope based on an Axiovert 200TV  equipped with a 63×NA 1.2 water immersion objective lens 2.3x/y coordinates of the trajectories were exported to Origin8  and further analyzed used a custom-built OriginC script, which allowed automated calculation of the so called momentum scaling spectrum (MSS) and its slope, SMSS. For each trajectory i the moments of displacement  were calculated for ѵ=1, …, 6 as a function of time according to:We followed an approach from Ewers et al. xi(n) designates the position vector of trajectory i at time nΔt, where Δt is the inverse frame rate and n a specific frame number: n=0, 1, …, Mi−1 (Mi is the trajectory length). For ѵ=2 this matches with the “classical” mean square displacement analysis. Using all momenta allowed construction of the MSS for each single trajectory µѵ,i(nΔt) was plotted versus nΔt in a double logarithmic plot ~nΔtγѵγѵ versus ѵ will finally give the respective MSS (Here, mic plot C and D. tive MSS E and F.


This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi Although they tend to exhibit exciting optoelectronic behaviours, the difficulty in fabricating chemically bonded two-dimensional layered heterojunctions has hindered progress in the area. Here, the authors synthesize sandwich-substructured Bi2WO6 monolayers and investigate their photocatalytic activity. This means that such a monolayer material maybe regarded as the stacks of different monolayer oxides by chemical bonds, and may possess oxygen-depleted surfaces that expose a huge number of active sites.Semiconductor-based heterojunctions are able to facilitate fast charge separation, and thus have emerged as one of important strategies for creation of efficient solar energy conversion systems123568910111213141618It is well known that monolayer materials maybe achieved on a small scale by mechanical exfoliation or chemical vapour deposition26272930322WO6 has a sandwich substructure of [BiO]+–[WO4]2−–[BiO]+, mimicking heterojunction interface with space charge. The Br− ions from CTAB strongly adsorb on the monolayers surfaces and thus make the monolayers negatively charged. In the self-assembly process, stacking of the monolayers is blocked by Coulomb repulsion forces and the hydrophobic chains of CTA+ ions. The Br− ions on surface induce a decrease in the bandgap energy of the monolayers. The surface Bi atoms are coordinatively unsaturated and thus the monolayers surfaces expose a huge number of active sites. On irradiation, holes are directly generated on the active surfaces and electrons in the middle layer, leading to ultrafast charge separation. Both the highly active surface and the ultrafast charge separation contribute to the superior photocatalytic performances of the monolayer material. In the presence of positive dyes, the visible light activity of the monolayers can be greatly enhanced due to photosensitization of the strongly adsorbed dye.We develop a cetyltrimethylammonium bromide (CTAB)-assisted bottom-up route to fabricate such freestanding monolayer materials. The successfully synthesized monolayer Aurivillius oxide Bi2WO6 is a layered material built up of [Bi2O2] layers and corner-shared WO6 octahedral layers. Monolayer Bi2WO6 has two possible configurations: [BiO]+–[WO4]2−–[BiO]+ (sandwich substructure) and [Bi2O2]2+–[WO4]2− (non-sandwich substructure). Density functional theory (DFT) calculations show that the surface energy of the sandwich configuration is 0.86 J m−2, notably smaller than that of the non-sandwich substructure (2.27 J m−2). It can be deduced accordingly that the monolayer Bi2WO6 has the sandwich structure, as presented in As shown in 2WO6 exposes coordinatively unsaturated Bi atoms on surface 3·5H2O and Na2WO4·2H2O (Br/Bi atomic ratio is 1:20). The X-ray diffraction patterns of the resulted sample are shown in 2WO6 phase with lattice parameters a=5.457 Å, b=5.436 Å and c=16.427 Å (JCPDS No. 73-2020). The transmission electron microscopy (TEM) image in 2WO6 with a sheet-shaped structure. Inset in 2WO6 nanosheets expose {001} facets. The atomic force microscopic (AFM) image and the corresponding height histograms of the nanosheets are presented in 2WO6 sheet along [001] direction (corresponding to 1/2 of the unit cell size in c-axis direction). This shows that the Bi2WO6 monolayers can be achieved by a Br ions-assisted hydrothermal method. Unfortunately, some bilayer nanosheets are observed in the products.As expected, the monolayer Bi− ions. When CTAB instead of KBr was used in the synthesis, the CTA+ ions would adsorb on the surface with bonding of Br− ions to the monolayers surfaces. Thus, the extra surface repulsion from the hydrophobic chains of CTA+ further prevents stacking of the monolayers, as showed in 2WO6 was successfully prepared. The X-ray diffraction result reveals that the obtained sample is pure phase Bi2WO6  occur at higher binding energies, indicating higher electropositive Bi appearing in the monolayers. This can be indicative of some Bi atoms bonded with the surface Br atomss spectra, two peaks at 529.9 eV and 531.7 eV are observed for both samples, which are assigned respectively to lattice oxygen and bridging hydroxylsf spectra are almost comparable for two samples, which can be explained by [WO4]2− locating at the middle layers of the monolayers and hardly affected by the surface Br atoms.X-ray photoelectron spectroscopic (XPS) characterizations were conducted to reveal the chemical compositions of the monolayer BiWO6 ref. . The Br rf peaks , indicat2WO6 sample, of which the Bi/W ratio is almost identical to that of the nanocrystals. This result implies that the Br− ions are non-stoichiometrically coordinated to [BiO]+ layers together with the CTA+. An additional experiment shows that the CTA+ ions on the monolayers surfaces can be removed by washing , an important class of functional materials including photocatalysts, superconductors, and ferroelectric materials40412O2] layers in crystal structure. Thus, a huge number of monolayer Aurivillius materials can be formed by the similar mechanism of self-assembly.To verify the universal applicability of this self-assembly route, preparation of monolayer Bi2WO6 samples. The bandgap energies of the samples were estimated from the plots of (αhv)1/2 versus the energy of absorbed light  than the nanocrystals (0.19 mg g−1), though the specific surface area of the monolayers (43 m2 g−1) is less than twice that of the nanocrystals (28 m2 g−1). All above results confirm that the surface of monolayer Bi2WO6 is open and can strongly interact with surrounding species such as water, anions Cl− or Br− and positively charged organics  spin-trapping electron paramagnetic resonance (EPR) technique . As shown in 2 production from water solution under visible light. 2 evolution over the nanocrystals, monolayers and RhB sensitized monolayers (λ≥420 nm) with 0.3 wt% Pt loading as a function of time. The H2 evolution activity of Bi2WO6 has been reported to be very low (1.6 μmol h−1 g−1) even under a 450 W high pressure mercury lamp2WO6 has been considered to have no activity for visible-light-driven H2 production2 evolution activity, but surprisingly the monolayers exhibit a good H2 evolution activity under visible light. As adding RhB into the reaction system, ca. fourfold higher activity is observed due to the sensitization effect of RhB. Both the ultrafast charge separation and the highly active surface make the monolayers possess superior performances in solar energy conversion than other nanostructures composed of two or more layers 3·5H2O and 0.05 g CTAB were added in 80 ml deionized water. After 30 min stirring, the mixed solution was poured into a 100 ml Teflon-lined autoclave. Then the autoclave was sealed into a stainless steel tank and treated at 120 °C for 24 h. Finally, the product was collected and washed several times with deionized water and dried at 60 °C in air for 10 h. In the preparation of monolayer Bi2WO6 companied with few layers, 0.1 mmol KBr instead of CTAB was added in the mixture, while keeping other parameters unchanged. The Bi2WO6 nanocrystals were prepared without CTAB and KBr assistances.In the preparation of Bi2O2CO3 monolayers were prepared by the same route. A total of 2 mmol Bi(NO3)3 and 0.05 g CTAB were added in 80 ml of 1 M HNO3 solution. After the mixture became a clear solution, 10 mmol Na2CO3 was added and a white precipitate appeared immediately. This suspension was magnetically stirred for 30 min to complete the precipitation reaction. Then the suspension was poured into a 100 ml Teflon-lined autoclave and the autoclave was sealed into a stainless steel tank. The sample was treated at 60 °C for 24 h. Then the reactor was naturally cooled to room temperature. The obtained sample was collected and washed several times with deionized water and dried at 60 °C in air for 10 h.Bi4 was used as a reflectance standard. TEM images were obtained using a JEOL model JEM 2010 EX instrument at an accelerating voltage of 200 kV. AFM images were recorded using Agilent 5,500 AFM . All the images were acquired using tapping mode under ambient conditions . The used Si cantilevers/tips (Bruker) have a spring constant of 40 N m−1 and a resonance frequency of 300 kHz. During an AFM experiment, sample was dispersed in ethanol using an ultrasonic bath for 20 min and then the dispersion was diluted in ethanol. A drop of the above diluted dispersion was deposited on a new cleaved mica surface and dried in air. The instrument parameters  were adjusted for the best resolution of images. Electron spin resonance spectra were obtained over Bruker ESP 300 E electron paramagnetic resonance spectrometer.The X-ray diffraction patterns were recorded on a Bruker D8 Advance X-ray diffractometer with Ni filtered Cu Kα radiation at 40 kV and 40 mA. Ultraviolet–visible diffuse reflectance (ultraviolet–visible diffuse reflectance spectrum) spectra were obtained with a self-supporting sample disk on a ultraviolet–visible spectrophotometer (Cary 500), where BaSO−1) solution. The dispersion was stirred in the dark for 30 min to reach the adsorption equilibrium. Then the visible light was turn on for the photodegradation tests. Three millilitres of the sample solution were taken at given time intervals and separated by centrifugation. The residual concentration of the organics in solution was analysed using a Varian Cary 50 Scan ultraviolet–visible spectrophotometer. The selective adsorption experiments were performed by the same method. The methyl orange (20 p.p.m.), methylene blue (10 p.p.m.) and salicylic acid (500 μmol l−1) solutions were used. 50 mg of the catalyst was used to test the adsorption performances.The photodegradation of dyes were performed in a glass vessel under visible-light irradiation by a 300 W Xe lamp with a 420 nm cutoff filter. Twenty milligram of the photocatalyst was added into 80 ml RhB  as a sacrificial reagent. This system was evacuated for 30 min to remove air prior to irradiation. A 300-W Xe lamp with an optical cutoff filter (λ≥420 nm) was used as a light source. The produced hydrogen was quantified by gas chromatography . For the RhB sensitization system, RhB (10 μmol l−1) was contained in solution.The photocatalytic Hab initio simulation package482WO6 systems. Vanderbilt ultrasoft pseudo-potentials were used to describe the interactions between the ion cores and valence electrons for all atoms, and the kinetic cutoff energy was set to 400 eV. In the calculations, the convergence energy threshold for self-consistent iteration was set to 10−4 eV per atom, along with the residual atomic forces were <0.03 eV Å−1. For the bulk Bi2WO6, the optimized lattice constants are a=5.480 Å, b=5.468 Å and c=16.760 Å, which agrees well with the experimental values of a=5.457 Å, b=5.436 Å and c=16.427 Å. A (2 × 2) periodic slab model was adopted to simulate different Bi2WO6 nanosheets, which were constructed from the Bi2WO6 (001) surface. During the structural optimization, the positions of all atoms and the lengths of two translation vectors of the nanosheet were allowed to relax. The spacing between the adjacent slabs was set about 10 Å, and a (3 × 3 × 1) Monkhorst–Pack k-point mesh was used for integration in the reciprocal space. To investigate the thermodynamic stability of different Bi2WO6 nanosheets, the surface free energy (γ) was calculated, which is defined as following,First-principles DFT calculations were carried out utilizing the Vienna Eslab is the total energy of the slab, 2WO6 unit in the bulk, N is the number of Bi2WO6 unit found in the slab, NBr is the number of Br atom, EBr is the ground state energy of Br atom, and A is the area of the slab surface.where How to cite this article: Zhou, Y. et al. Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis. Nat. Commun. 6:8340 doi: 10.1038/ncomms9340 (2015).Supplementary Figures 1-21, Supplementary Table 1 and Supplementary Reference