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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Synchrotron-based Spectroscopy In On-Surface Polymerization of Covalent Networks
摘要： Synchrotron radiation is a powerful tool to probe physical properties of materials on the nanoscopic scale. It can provide a chemical fingerprint of a nanomaterial with unrivalled resolution, it can measure the geometric structure down to thousands of a nanometer with not only elemental sensitivity but also chemical sensitivity, and it can study charge transfer dynamics in the sub-nanosecond regime. Within this article the application of synchrotron radiation to studying on-surface catalysis, to the view of forming two-dimensional covalent networks, will be explored.
关键词： covalent networks,on-surface polymerization,Normal Incidence X-ray Standing Waves,Synchrotron radiation,X-ray Photoemission Spectroscopy,Near Edge X-ray Absorption Fine Structure
更新于2025-09-10 09:29:36
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AgI-BiOI-graphene composite photocatalysts with enhanced interfacial charge transfer and photocatalytic H2 production activity
摘要： BiOI-based photocatalysts were proved to exhibit photocatalytic H2 production activity. AgI-BiOI-graphene showed better H2 production activity than BiOI and BiOI-graphene. The surface chemistry, electronic property, phase structure, morphology, optical property and photocatalytic performance of these photocatalysts were studied. The interfacial electronic states of the photocatalysts were investigated through their C K-edge near-edge X-ray-absorption fine-structure (NEXAFS) spectra. Based on the in situ NEXAFS spectra measured with and without illumination, a mechanism about the transport of photoelectron from AgI to graphene through BiOI is proposed for the photocatalytic H2 production process. The incorporation of graphene restricted the three-dimensional self-assembly of BiOI nanocrystals and led to the formation of less extensively crystallized BiOI domains through a confined-space effect. Addition of AgNO3 precursor altered the crystal structure of BiOI from flower-like to horizontally stacked flat plates. The results of NEXAFS spectra, photoluminescence spectra and photocurrent tests reveal that the improved photocatalytic activity of the AgI-BiOI-graphene photocatalyst is attributable to the interfacial interaction among AgI, BiOI and graphene, which enhanced the separation of photogenerated electrons to generate H2. AgI-BiOI-graphene photocatalyst was a stable photocatalyst for the production of H2. After three cycles, 86 % activity of recycled photocatalysts was retained.
关键词： X-ray absorption spectra,Near edge X-ray absorption fine structure,Interfacial electronic states,Photocatalytic H2 production,BiOI
更新于2025-09-10 09:29:36
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Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the <i>F</i> <sub/>1</sub> and <i>F</i> <sub/>2</sub> spin-rotation levels of the CN products
摘要： One of the most spectacular yet unsolved problems for the ICN ~A-band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N ? 1/2 populations for each rotation level N of the CN fragment. The F1/F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2P3/2) and I (2P1/2) are energetically available or not as the dissociation partner. First, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen–Zener–Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N. We have derived semiclassical formulae for f(N) and the orientation parameters including the 3A0 and 4A0 electronic states, and with a two-state model including the 3A0 through 6A0 electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare’s group and Hall’s group, respectively.
关键词： nonadiabatic transitions,dipole-quadrupole interactions,Rosen-Zener-Demkov nonadiabatic transitions,quantum interference effect,ICN photodissociation,F1 and F2 spin-rotation levels,fine structure splitting
更新于2025-09-09 09:28:46
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New bounds on dark matter coupling from a global network of optical atomic clocks
摘要： We report on the first Earth-scale quantum sensor network based on optical atomic clocks aimed at dark matter (DM) detection. Exploiting differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e., the cold atoms and the optical reference cavity, we can perform sensitive searches for DM signatures without the need for real-time comparisons of the clocks. We report a two orders of magnitude improvement in constraints on transient variations of the fine-structure constant, which considerably improves the detection limit for the standard model (SM)–DM coupling. We use Yb and Sr optical atomic clocks at four laboratories on three continents to search for both topological defect and massive scalar field candidates. No signal consistent with a DM coupling is identified, leading to considerably improved constraints on the DM-SM couplings.
关键词： massive scalar fields,quantum sensor network,dark matter,topological defects,optical atomic clocks,fine-structure constant
更新于2025-09-09 09:28:46
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Ferromagnetic Behavior and Electronic Characterization of ZnO Nanoparticles
摘要： In this work, Al-doped ZnO nanoparticles encapsulated with amorphous SiO2 were prepared by the wet chemical method. The obtained precursor was annealed and the nanoparticle sizes were controlled by adjusting the annealing temperature. These nanomaterials showed ferromagnetic behavior, even though the ZnO bulk crystal was diamagnetic. The results of electrical conductivity and XANES suggested that ferromagnetism of the Al-doped nanoparticles was results of carrier transport and oxygen vacancies. The Al-doped ZnO nanoparticles are extremely interesting from the perspective of solid state physics. [DOI: 10.1380/ejssnt.2018.406]
关键词： Nano-particles, quantum dots, and supra-molecules,Magnetic, structural, and other properties of nanostructures,Zinc oxide,Luminescence,Near edge extended X-ray absorption fine structure (NEXAFS)
更新于2025-09-04 15:30:14