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Noncollinear Magnetic Structures in the Chiral Antiperovskite beta Fe2SeO
No full textWe present the magnetic properties of the chiral, polar, and possibly magnetoelectric antiperovskite amp; 946; Fe2SeO as derived from magnetization and specific heat measurements as well as from powder neutron diffraction and Mössbauer experiments. Our macroscopic data unambiguously reveal two magnetic phase transitions at TN1 amp; 8776; 103 K and TN2 amp; 8776; 78 K, while Rietveld analysis of neutron powder diffraction data reveals a noncollinear antiferromagnetic structure featuring magnetic moments in the a b plane of the trigonal structure and a ferromagnetic moment along c. The latter is allowed by symmetry between TN1 and TN2, weakly visible in the magnetization data yet unresolvable microscopically. While the intermediate phase can be expressed in the trigonal magnetic space group P31, the magnetic ground state is modulated by a propagation vector q 1 2 1 2 0 resulting in triclinic symmetry and an even more complex low temperature spin arrangement which is also reflected in the Mössbauer hyperfine patterns indicating additional splitting of Fe sites below TN2. The complex noncollinear spin arrangements suggest interesting magnetoelectric properties of this polar magne
Linker Conformation Controls Oxidation Potentials and Electrochromism in Highly Stable Zr Based Metal Organic Frameworks
No full textThe development of tailor made electrochromic EC materials requires a large variety of available substances with properties that precisely match the task. Since the inception of electrochromic metal organic frameworks MOFs , the field relies only on a limited set of building blocks, providing the desired electrochromic effect. Herein, we demonstrate for the first time the implementation of a Piccard type system N,N,N amp; 8242;,N amp; 8242; benzidinetetrabenzoate into Zr MOFs to obtain electrochromic materials. With fast switching rates, high contrast ratio, long life stability, and exceptional chemical and physical stability, the novel material is on par with inorganic EC material. The new EC system exhibits an ultrahigh contrast from the bleaching state, with transmittance in the visible region gt;53 , to the colored state with a transmittance of ca. 3 . The 5 amp; 956;m thick film attained up to 90 of the coloring in 12.5 amp; 8201;s and exhibited high electrochemical reversibility. Moreover, the conformational lability of the electrochromic ligand chosen is locked via the topology design of the framework, which is not attainable in the solution. Locked conformations of the redox active linker in distinct polymorphous frameworks DUT 65 and DUT 66 feature different redox characteristics and opens the door to the overarching control of the oxidation pathway in the Piccard type system
The physical and cellular mechanism of structural color change in zebrafish
No full textMany animals exhibit remarkable colors that are produced by the constructive interference of light reflected from arrays of intracellular guanine crystals. These animals can fine tune their crystal based structural colors to communicate with each other, regulate body temperature, and create camouflage. While it is known that these changes in color are caused by changes in the angle of the crystal arrays relative to incident light, the cellular machinery that drives color change is not understood. Here, using a combination of 3D focused ion beam scanning electron microscopy FIB SEM , micro focused X ray diffraction, superresolution fluorescence light microscopy, and pharmacological perturbations, we characterized the dynamics and 3D cellular reorganization of crystal arrays within zebrafish iridophores during norepinephrine NE induced color change. We found that color change results from a coordinated 20 tilting of the intracellular crystals, which alters both crystal packing and the angle at which impinging light hits the crystals. Importantly, addition of the dynein inhibitor dynapyrazole a completely blocked this NE induced red shift by hindering crystal dynamics upon NE addition. FIB SEM and microtubule organizing center MTOC mapping showed that microtubules arise from two MTOCs located near the poles of the iridophore and run parallel to, and in between, individual crystals. This suggests that dynein drives crystal angle change in response to NE by binding to the limiting membrane surrounding individual crystals and walking toward microtubule minus ends. Finally, we found that intracellular cAMP regulates the color change process. Together, our results provide mechanistic insight into the cellular machinery that drives structural color chang
Dipole tunable interfacial engineering strategy for high performance all inorganic red quantum dot light emitting diodes
Get PDFAll inorganic quantum dot QD light emitting diodes AI QLEDs with excellent stability received enormous interest in the past few years. Nevertheless, the vast energy offset and the high trap density at the NiOX QDs interface limit hole injection leading to fluorescence quenching and hampering the performance. Here, we present self assembled monolayers SAMs with phosphonic acid PA anchoring groups modifying NiOX hole transport layer HTL to tune energy level and passivate trap states. This strategy facilitates hole injection owning to the well aligned energy level by interface dipole, downshifting the vacuum level, reducing the hole injection barrier from 0.94 eV to 0.28 eV. Meanwhile, it mitigates the interfacial recombination by passivating surface hydroxyl group OH and oxygen vacancy VO traps in NiOX. The electron leakage from QDs toward NiOX HTL is significantly suppressed. The all inorganic R QLEDs exhibit one of the highest maximum luminance, external quantum efficiency and operational lifetime of 88980 cd m amp; 8722;2, 10.3 and 335045 h T50 100 cd m amp; 8722;2 , respectively. The as proposed interface engineering provides an effective design principle for high performance AI QLEDs for future outdoor and optical projection type display application
Performance enhancement of vanadium redox flow battery with novel streamlined design Simulation and experimental validation
No full textElectrolyte utilization and the consequent concentration polarization significantly limit the potential increase in power density and contribute to electrode degradation in vanadium redox flow batteries during cycling. This study investigates a novel curvature streamlined design, drawing inspiration from natural forms, aiming to enhance the performance of vanadium redox flow battery cells compared to conventional square and rectangular flow through cell designs. The simulated 3D single cell model shows a notably superior uniformity in both current and species concentration distribution within the streamlined design compared to the square and rectangular shapes. Experimental analysis conducted on 3D printed flow frames demonstrated 2 enhanced energy efficiency and 47 improved capacity when compared to rectangular design at 150 mA cm amp; 8722;2, all achieved with minimal increase in pressure dro
Investigation of the solar cell materials Cu In,Ga Se2 and Cu2ZnSnS4 with muon spin spectroscopy and density functional calculations
Get PDFCu In,Ga Se 2 CIGS and Cu2ZnSnS4 CZTS are potential absorber materials for solar cell applications. We report an investigation of these materials using muon spin spectroscopy. In these experiments, positive muons produced at accelerator facilities here the ISIS Facility, Rutherford Appleton Laboratory, U.K. are implanted into the material and come to rest at interstitial sites in the host lattice. The muon is a sensitive local probe to study materials properties on an atomistic level. An advantage of the method is that interface properties can be studied by placing the probe particles at different depths in the sample. Muonium, the positive muon with an electron, can be considered as a light isotope of hydrogen mass ratio 1 9 with almost identical electronic properties to hydrogen. Thus, muon spectroscopy provides also information about hydrogen in the host material. The aim of the present experiment is to obtain information about the muonium hydrogen states formed in CIGS and CZTS solar cell materials. A major goal of the experiment is to obtain information about the physical embedding process of the implanted particle into the host lattice. The present study combines experimental measurements with total energy calculations in the framework of density functional theory. We obtain the final configurations of muonium in CZTS, that we discuss in parallel to those in CIGS. This allows us to deepen our understanding of the influence of the hydrogen impurity on the properties of these materials. We also discuss the final steps in the process of muon implantation in these material
Synthesis and properties of Sr2La2NiW2O12, a new S 1 triangular lattice magnet
No full textMagnetic materials featuring triangular arrangements of spins are frequently investigated as platforms hosting magnetic frustration. Hexagonal perovskites with ordered vacancies serve as excellent candidates for two dimensional triangular magnetism due to the considerable separation of the magnetic planes. In this work, the effects of chemical pressure on the ferromagnetic ground state of Ba2La2NiW2O12 by substitution of Ba2 with Sr2 to produce Sr2La2NiW2O12 are investigated. The two materials are characterized using synchrotron based XRD, XANES and EXAFS in addition to magnetometry in order to correlate their crystal structures and magnetic properties. Both materials form in space group R3, yet as a result of the enhanced bending of key bond angles due to the effects of chemical pressure, the TC value of the magnetic Ni2 sublattice is reduced from amp; 8764;6 amp; 8197;K in Ba2La2NiW2O12 to 4 amp; 8197;K in Sr2La2NiW2O1
Stabilization of intermediate Mo oxidation states by Nb doping enhancing methane aromatization on Mo HZSM 5 catalysts
No full textThe dehydroaromatization of the naturally abundant methane is a promising process to produce aromatics and COx free hydrogen. Low temperature activity, regenerability and time on stream stability are fundamental challenges for the industrial use of the commonly studied benzenoid selective Mo HZSM 5 catalysts. We report a promotional effect of Nb doping on the activity and stability of Mo HZSM 5 catalysts between 600 and 700 C. Nb addition enhances benzene yields measurably at all investigated temperatures. An increased thermal stability of MoNb HZSM 5 compared to Mo HZSM 5 catalysts was found upon exposure to multiple consecutive reaction and oxidative treatment cycles, thus resulting in higher restorability of activity which extends the catalyst lifetime. While high resolution electron microscopy showed homogeneous mixing of Mo and Nb on the catalyst, in situ time resolved Mo K edge X ray absorption spectroscopy, supported by ex situ and time resolved in situ near ambient pressure X ray photoelectron spectroscopy measurements, revealed a distinct interaction between the transition metals, involving a partial reduction of the otherwise stable Nb and concurrent oxidation of Mo which leads to increased stability of Mo5 Mo4 states. These effects were correlated to the enhanced activity and regenerability of the MoNb HZSM 5 catalyst for methane dehydroaromatizatio
Soft X ray spectromicroscopic proof of a reversible oxidation reduction of microbial biofilm structures using a novel microfluidic in situ electrochemical device
No full textIn situ electrochemistry on micron and submicron sized individual particles and thin layers is a valuable, emerging tool for process understanding and optimization in a variety of scientific and technological fields such as material science, process technology, analytical chemistry, and environmental sciences. Electrochemical characterization and manipulation coupled with soft X ray spectromicroscopy helps identify, quantify, and optimize processes in complex systems such as those with high heterogeneity in the spatial and or temporal domain. Here we present a novel platform optimized for in situ electrochemistry with variable liquid electrolyte flow in soft X ray scanning transmission X ray microscopes STXM . With four channels for fluid control and a modular design, it is suited for a wealth of experimental conditions. We demonstrate its capabilities by proving the reversible oxidation and reduction of individual microbial biofilm structures formed by microaerophilic Fe II oxidizing bacteria, also known as twisted stalks. We show spectromicroscopically the heterogeneity of the redox activity on the submicron scale. Examples are also provided of electrochemical modification of liquid electrolyte species Fe II and Fe III cyanides , and in situ studies of electrodeposited copper nanoparticles as CO2 reduction electrocatalysts under reaction condition
Cytosine analogues as DNA methyltransferase substrates
No full textDNA methyltransferases are drug targets for myelodysplastic syndrome MDS , chronic myelomonocytic leukemia CMML , acute myelogenous leukemia AML and possibly amp; 946; hemoglobinopathies. We characterize the interaction of nucleoside analogues in DNA with a prokaryotic CpG specific DNA methyltransferase M.MpeI as a model for mammalian DNMT1 methyltransferases. We tested DNA containing 5 hydroxymethylcytosine 5hmC , 5 hydroxycytosine 5OHC , 5 methyl 2 pyrimidinone in the ribosylated form known as 5 methylzebularine, 5mZ , 5,6 dihydro 5 azacytosine dhaC , 5 fluorocytosine 5FC , 5 chlorocytosine 5ClC , 5 bromocytosine 5BrC and 5 iodocytosine 5IC . Covalent complex formation was by far most efficient for 5FC. Non covalent complexes were most abundant for dhaC and 5mZ. Surprisingly, we observed methylation of 5IC and 5BrC, and to a lesser extent 5ClC and 5FC, in the presence, but not the absence of small molecule thiol nucleophiles. For 5IC and 5BrC, we demonstrated by mass spectrometry that the reactions were due to methyltransferase driven dehalogenation, followed by methylation. Crystal structures of M.MpeI DNA complexes capture the in conformation of the active site loop for analogues with small or rotatable 5mZ 5 substituents and its out form for bulky 5 substituents. Since very similar in and out loop conformations were also observed for DNMT1, it is likely that our conclusions generalize to other DNA methyltransferase