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Resolving orbital pathways for intermolecular electron transfer
摘要： Over 60 years have passed since Taube deduced an orbital-mediated electron transfer mechanism between distinct metal complexes. This concept of an orbital pathway has been thoroughly explored for donor–acceptor pairs bridged by covalently bonded chemical residues, but an analogous pathway has not yet been conclusively demonstrated for formally outer-sphere systems that lack an intervening bridge. In our present study, we experimentally resolve at an atomic level the orbital interactions necessary for electron transfer through an explicit intermolecular bond. This finding was achieved using a homologous series of surface-immobilized ruthenium catalysts that bear different terminal substituents poised for reaction with redox active species in solution. This arrangement enabled the discovery that intermolecular chalcogen?iodide interactions can mediate electron transfer only when these interactions bring the donor and acceptor orbitals into direct contact. This result offers the most direct observation to date of an intermolecular orbital pathway for electron transfer.
关键词： electron transfer kinetics,Marcus equation,ruthenium catalysts,intermolecular interactions,orbital-mediated electron transfer
更新于2025-09-23 15:21:21
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European Microscopy Congress 2016: Proceedings || The microstructure of ZnSnO and its correlation to electrical and optical properties
摘要： Over the last years, the interest in the field of transparent conductive oxides (TCOs) has grown dramatically due to their wide applicability and improved properties that may be reached when incorporating these materials into devices. TCOs are mainly used in the industry of low-emissivity windows, flat panel displays, light emitting diodes and photovoltaics [1]. For photovoltaic applications, the main purpose of TCOs is to let light enter into the solar cell and to extract the electric charges allowing them to be drifted towards the electric contacts. Therefore, it is necessary for these materials to be as transparent and as conductive as possible [2]. Ideally, TCOs should be indium-free, as indium is scarce and hence expensive [3]. The goal is therefore to optimize a material that is earth-abundant, low-cost and with good electrical and optical properties. As many steps in photovoltaic device fabrication require a high temperature, a crucial requisite for TCOs is also thermal stability. Based on these criteria, an amorphous compound of Zn-Sn-O (ZTO) deposited by sputtering was selected for the present study [4]. The microstructure of ZTO is known to strongly influence its electrical and optical properties, as well as its thermal stability. In that regard, transmission electron microscopy (TEM), in situ X-ray diffraction (XRD) experiments and conventional electrical and optical characterization were performed to assess the links between annealing treatments, ZTO microstructure and optical and electrical properties. First, samples were annealed in air, in an oven up to 150 and 500 °C and then investigated by transmission electron microscopy. While electrical and optical properties were measured to change significantly upon annealing, no major microstructural change was observed in TEM images. In situ theta-2theta XRD experiments were then performed by increasing the temperature up to 1000-1200°C in air and vacuum. Substrates resistant to these temperatures were employed, namely fused silica and sapphire. Different heating rates were used, ranging from 3°C/min up to 10°C/min. The XRD results (Fig.1) demonstrate that the amorphous phase is stable up to >500 °C when annealed in air and > 900 °C when annealed in 10-4 mbar, hence highlighting a strong influence of the annealing atmosphere on the crystallisation temperature. Rutile SnO2 is the first phase to crystallize and remains the main crystal structure observed throughout the whole process, with Al2ZnO4 forming at higher temperatures as a result of an interaction between the TCO layer and the sapphire substrate. Electrical properties were measured to decrease after annealing, with TEM measurements demonstrating that Zn migration at high temperature leads to the formation of a defective crystalline structure (Fig.2). This effect is more severe when annealing in air when compared to vacuum conditions. Indeed, the presence of oxygen in the surrounding atmosphere facilitates the formation of crystalline SnO2, a process that repeals Zn atoms to grain boundaries and surfaces of the TCO layer (Fig.3). On the other hand, the formation of crystalline SnO2 and the release of zinc are both delayed when annealing in vacuum. In general, crystallisation and Zn evaporation are observed to be detrimental to the electrical properties as it leads to the formation of voids in the structure. On a technological level, the high thermal stability of the defect-free amorphous ZTO microstructure in oxygen-poor atmospheres may enable its application in high efficiency photovoltaic architectures.
关键词： TEM,XRD,crystallization kinetics,transparent conductive oxides
更新于2025-09-23 15:21:21
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Degradation kinetics of anthocyanin and physicochemical changes in fermented turnip juice exposed to pulsed UV light
摘要： In this study, the effects of pulsed UV (PUV) light on the degradation kinetics of anthocyanins and physicochemical properties of turnip juice were investigated. PUV light was applied to turnip juice at 3 different distances (5, 8, 13 cm) from the quartz window of the xenon lamp for 5 different times (5, 15, 30, 45, 60 s). The pH, total acidity (% lactic acid), monomeric anthocyanin content, color density, hue, brightness, and percent color components (yellow, red, and blue) of turnip juice changed significantly after PUV-light treatments at each level. The maximum degradation of anthocyanin after PUV-light treatments was found to be about 63%. The anthocyanin degradation, brightness, yellow and blue color (%) increased, while red color (%) decreased with longer treatment time and shorter distance. The degradation of monomeric anthocyanins in turnip juice exposed to PUV light was described by the Weibull model (R2 0.982–0.998, RMSE 0.087–0.133) more accurately than the first-order kinetics (R2 0.906–0.992, RMSE 0.071–0.192).
关键词： Degradation kinetics of anthocyanin,Pulsed UV light,Physicochemical properties,Turnip juice,Weibull model
更新于2025-09-23 15:21:21
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<i>In Vitro</i> Ligand Binding Kinetics Explains the Pharmacokinetics of [ <sup>18</sup> F]FE-PE2I in Dopamine Transporter PET Imaging
摘要： Two of the most popular positron emission tomography (PET) tracers, [11C]PE2I and [18F]FE-PE2I, used to quantify dopamine transporters (DAT), display dissimilar kinetic behavior in in vivo assays. This difference can be explained by comparing values of kinetic rate constants, which characterize interaction of these tracers with DAT sites in vitro. At the same time, this kinetic analysis showed that the overall binding mechanism is similar for these two tracers and includes a fast step of complex formation followed by a slow isomerization step of this complex. Comparison with previous PE2I data revealed that isomerization of the DAT complex with PE2I occurs three times faster than in the case of FE-PE2I, which leads to the slower onset of peak specific binding of the former tracer in the DAT-rich regions. Therefore, ligands with slower isomerization on-rate, including [18F]FE-PE2I, seem to be better tracers in vivo, and their properties can be predicted in vitro.
关键词： isomerization,ligand binding kinetics,FE-PE2I,Dopamine transporter,DAT,PET,PE2I
更新于2025-09-23 15:21:21
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Stages of the Excitation Relaxation in a Superconductor after the Impact of a Femtosecond Laser Pulse Taking into Account the Momentum Distribution of Quasiparticles
摘要： A theoretical model is formulated for the description of the nonequilibrium state of a superconductor on the basis of the nonequilibrium distribution function of phonons and quasiparticles on a finite momentum lattice convenient for numerical simulation. The simulation is performed under conditions of pulsed optical impact demonstrating the role of excess quasiparticles in suppressing the order parameter and the main stages of the relaxation process in the absence of electric current.
关键词： superconductivity,kinetics simulation,nonequilibrium processes,ultrashort laser pulse
更新于2025-09-23 15:21:01
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In Situ Study of Sputtering Nanometer-Thick Gold Films onto 100 Nanometer-Thick Spiro-OMeTAD Films: Implications for Perovskite Solar Cells
摘要： The performance of many perovskite solar cells is closely related to the spiro-OMeTAD/gold interface since gold is used as top contacts, which renders the detailed understanding of the interface formation very important. In this work, sputter deposition as an industry-relevant, high-rate, large-scale and well-controllable deposition technique is used to prepare gold electrodes on top of a 100 nm thick spiro-OMeTAD film. In situ grazing incidence small angle X-ray scattering (GISAXS) is used to study the nanostructure-growth kinetics of the gold contact on top of the spiro-OMeTAD film during the sputter process. The results show that the gold grows in nanoscale clusters, which then coalesce into a complete yet still nanogranular layer forming the top contact with a thickness of 90 nm. Based on simulations of the 2D GISAXS patterns additional information about the shape of the nanosized gold cluster is gained at the different cluster growth stages. Furthermore, the diffusion of gold into the spiro-OMeTAD film occurs during the sputter process as verified with X-ray reflectivity. In a depth of 3.5 nm below the gold contact the gold doping level of the spiro-OMeTAD film is 6.3 % irrespective of the final gold contact thickness. Thus, the interface between the spiro-OMeTAD film and the Au contact is not sharp as commonly sketched as well as the contact is grainy, which will be both of importance for the performance of device such as perovskite solar cells.
关键词： gold contacts,spiro-OMeTAD film,sputter deposition,in situ GISAXS,growth kinetics
更新于2025-09-23 15:21:01
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Luminescence relaxation dynamics for planar and rolled-up CdSe nanocrystals in a photonic-crystal matrix
摘要： Samples of inverted photonic-crystal films, containing planar and rolled-up (in the form of scrolls) CdSe nanocrystals, are studied. The transmission spectra of these structures are recorded. These spectra (along with the change in colour) confirm the incorporation of nanocrystals into the films. The photoluminescence decay dynamics is investigated. It is shown that the photonic-crystal matrix affects significantly the luminescence kinetics of nanostructures. The differences in the decay curves measured for nanocrystals in a photonic-crystal matrix and for their ensemble on a glass substrate are explained by the influence of the photonic-crystal stop band and the orientational effect of crystalline matrix, which orients anisotropic nanocrystals and prevents them from aggregation. The results obtained may be important for potential applications in optoelectronic devices.
关键词： nanoscrolls,luminescence kinetics,photonic crystal,nanoplates,CdSe
更新于2025-09-23 15:21:01
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Photoluminescencea??Based Characterization of Halide Perovskites for Photovoltaics
摘要： Photoluminescence spectroscopy is a widely applied characterization technique for semiconductor materials in general and halide perovskite solar cell materials in particular. It can give direct information on the recombination kinetics and processes as well as the internal electrochemical potential of free charge carriers in single semiconductor layers, layer stacks with transport layers, and complete solar cells. The correct evaluation and interpretation of photoluminescence requires the consideration of proper excitation conditions, calibration and application of the appropriate approximations to the rather complex theory, which includes radiative recombination, non-radiative recombination, interface recombination, charge transfer, and photon recycling. In this article, an overview is given of the theory and application to specific halide perovskite compositions, illustrating the variables that should be considered when applying photoluminescence analysis in these materials.
关键词： halide perovskites,photoluminescence,photovoltaics,charge carriers,recombination kinetics
更新于2025-09-23 15:21:01
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Leaching Kinetics of Yttrium and Europium Oxides from Waste Phosphor Powder
摘要： Phosphor powder sample was characterized, and the leaching kinetics of yttrium, and europium in hydrochloric acid were investigated. Under optimized leaching conditions, 98% Y and 97% Eu were extracted, and a reaction curve was generated using the percentage of extraction as a function of time and temperature. Based on R2 values, shrinking spherical particle and shrinking core model were not applicable. SEM analysis also con?rmed shrinking core behavior was not applicable due to the lack of core–shells in the leach residue. The kinetic data were best ?tted by a logarithmic rate expression of the empirical model. Activation energy was calculated to be 77.49 kJ/mol for Y and 72.75 kJ/mol for Eu in the temperature range of 298–343 K.
关键词： Leaching,Phosphor powder,Rare earth elements,Waste ?uorescent lamp,Kinetics
更新于2025-09-23 15:21:01
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[Methods in Enzymology] || Fluorescence Depolarization Kinetics to Study the Conformational Preference, Structural Plasticity, Binding, and Assembly of Intrinsically Disordered Proteins
摘要： Fluorescence depolarization kinetics measured by the time-resolved fluorescence anisotropy decay serves as a sensitive and powerful methodology to study the conformational dynamics of macromolecules. This methodology allows us to delineate the different modes of biomolecular motional dynamics including the local, segmental, and global rotational dynamics on the timescale ranging from picoseconds to nanoseconds. In this chapter, we describe the principles and applications of this methodology to obtain unique molecular insights into the intrinsically disordered proteins (IDPs). Fluorescence depolarization kinetics, when performed in a site-specific manner, can offer a reliable tool to monitor the intrinsic backbone torsional dynamics of expanded IDPs and is capable of discerning the conformational preference of IDPs. Additionally, the time-resolved fluorescence anisotropy measurements allow us to investigate the mechanism of binding and assembly of a wide range of IDPs that are involved in crucial function and disease.
关键词： Fluorescence depolarization kinetics,conformational dynamics,time-resolved fluorescence anisotropy decay,biomolecular interactions,intrinsically disordered proteins
更新于2025-09-23 15:21:01