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Interface-induced enhanced electromagnetic wave absorption property of metal-organic frameworks wrapped by graphene sheets
摘要： Most of metal–organic frameworks (MOFs) themselves have low electrical conductivities, leading to bad electromagnetic wave (EMW) absorption properties. Herein we found that the EMW absorption property of zeolitic imidazolate frameworks-8 (ZIF-8) particles was improved unexpectedly after coupling them with graphene sheets. Experimental results and theoretical calculations indicated that well-defined interfaces between ZIF-8 and the graphene sheets were crucial to the improvement of EMW absorption property. Our strategy presented here may open a new way for designing other MOFs based hybrids for high-performance EMW absorbers.
关键词： Porous structure,Graphene-organics composites,Metal–organic frameworks,Electromagnetic wave absorption,Multiple interfaces
更新于2025-09-04 15:30:14
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Single layer graphene for estimation of axial spatial resolution in confocal Raman microscopy depth profiling
摘要： Single layer graphene (SLG), with its angstrom-scale thickness and strong Raman scattering cross section, was adapted for measurement of the axial (Z-direction) probe beam profile in confocal Raman microscopy depth-profiling experiments. SLG adsorbed to a glass microscope coverslip (SLG/SiO2) served as a platform for estimation of axial spatial resolution. Profiles were measured by stepping the confocal probe volume through the SLG/SiO2 interface while measuring Raman scattering from the sample. Using a high numerical aperture (1.4 NA) oil immersion objective, axial profiles were derived from the graphene 2D vibrational mode and fit to a Lorentzian instrument response function (IRF). Subsequently, the Z-direction spatial resolution in depth-profiling studies of polymer interfaces was estimated through convolution of the Lorentzian IRF with a step function representing the ideal junction separating the phases of interest. In the study of a bipolar polymer membrane, confocal Raman depth profiles of the AEM/CEM (anion exchange membrane / cation exchange membrane) interface show the transition region is broader than the limiting response and are consistent with roughness at the boundary on the order of a few micrometers. Using ClO4- as a Raman active mobile ion probe, application of self-modeling curve resolution (SMCR) to spectral datasets within a profile showed ClO4- ions track the spatial distribution of the AEM phase. Finally, in measurements on a liquid-solid interface formed between 1-octanol and a polydimethylsiloxane (PDMS) membrane, the IRF derived from fitting the experimental profile was slightly narrower than those obtained from profiling SLG, indicating the potential to use polymer-liquid interfaces formed from widely available materials and reagents for estimation of axial spatial resolution in confocal Raman depth-profiling.
关键词： Axial spatial resolution,Polymer interfaces,Confocal Raman microscopy,Single layer graphene,Bipolar membrane,Depth profiling
更新于2025-09-04 15:30:14
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Dynamics of Molecules Physically Adsorbed onto Metal Oxide Nanoparticles: Similarities between Water and a Flexible Polymer
摘要： Water at interfaces is considered present and important within almost all physical processes. Interfacial water shows nonbulk properties, however, its structure/organization and dynamics are on a still open debate. In parallel to that, the interfacial polymer in nanocomposites exhibits modi?ed structure and dynamics, the latter characteristic being widely considered responsible for the improved nanocomposite properties. One of the most suitable tools for studying dynamics of a variety of small molecules and macromolecules is broadband dielectric spectroscopy (BDS), mainly due to its high resolving power. BDS is employed here in combination with isothermal hydration and has proved quite illuminating in recording for the ?rst time striking similarities in the dynamics behavior between water molecules and ?exible polydimethylsiloxane macromolecules, when the latter molecules are individually adsorbed physically on the attractive surfaces of metal oxide nanoparticle. The qualitative similarities between water and polymer interfacial dynamics, for example, in their exhibiting time-scale and the elevation of the respective activation energy upon increasing of interfacial molecules fraction, lay most probably at the origins of the same main surface-adsorbed molecule interaction, i.e.. the hydrogen bonding. Whereas, the quantitative di?erences in molecular dynamics, e.g., slower, more energetically demanding, and cooperative interfacial dynamics for the polymer than for water, arise from the di?erent scale of the two molecular motions (<1 nm for water and ≥1 nm for the polymer) and/or from alternations in interfacial layer density.
关键词： dielectric spectroscopy,water,nanoparticles,polydimethylsiloxane,interfaces,dynamics,hydrogen bonding
更新于2025-09-04 15:30:14
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Nanoparticles at Biomimetic Interfaces: A Combined Experimental and Simulation Study on Charged Gold Nanoparticles/Lipid Bilayers Interfaces
摘要： The poor understanding of the interaction of nanomaterials with biologically relevant interfaces is recognized as one of the major issues currently limiting the development of nanomedicine. The central purpose of this study is to compare experimental (Confocal Microscopy, Fluorescence Correlation Spectroscopy, X-ray Reflectivity) and computational (Molecular Dynamics simulations) results to thoroughly describe the interaction of cationic gold nanoparticles (AuNP) with mixed zwitterionic/anionic lipid membranes. The adhesion of AuNPs to the lipid membrane is investigated on different length scales from a structural and dynamical point of view; with this approach, a series of complex phenomena, spanning from lipid extraction, localized membrane disruption, lateral phase separation and slaved diffusion, are characterized and interpreted from a molecular level to macroscopic observations.
关键词： Nanoparticles,Gold Nanoparticles,Molecular Dynamics,X-ray Reflectivity,Fluorescence Correlation Spectroscopy,Lipid Bilayers,Biomimetic Interfaces,Confocal Microscopy
更新于2025-09-04 15:30:14
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[IEEE 2018 International Semiconductor Conference (CAS) - Sinaia, Romania (2018.10.10-2018.10.12)] 2018 International Semiconductor Conference (CAS) - Second Harmonic Generation: A Non-Destructive Characterization Method for Dielectric-Semiconductor Interfaces
摘要： This paper reviews the application of second harmonic generation (SHG) to characterize dielectric-semiconductor interfaces in microelectronics and photovoltaics. Based on non-linear optics, the method is non-destructive, so particularly advantageous for thin films. The theoretical background shows the possibility to access the electric field at interfaces and consequently to have a non-destructive measurement for interface state densities or fixed charges in oxides. Two more detailed examples of application of SHG characterization will be shown: passivation of silicon using thin film deposited alumina and interface analysis of silicon-on-insulator substrates.
关键词： interface states,dielectric-semiconductor interfaces,fixed oxide charges,interface electric field,second harmonic generation
更新于2025-09-04 15:30:14
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High-density cascade arc plasma sources for application to plasma windows for virtual vacuum interfaces
摘要： We develop two cascade arc plasma sources for application to plasma windows for virtual vacuum interfaces. For windowless vacuum–atmosphere separation, a compact arc discharge source having a channel diameter of 3 mm is fabricated, and an atmospheric Ar thermal plasma is generated. For an alternative differential pumping system, separating low- and high-pressure vacuum chambers, a larger arc device with an 8-mm diameter is also constructed, producing a high-density He plasma. The performances of the two cascade arcs as plasma windows are investigated. The 3-mm arc discharge generates a steep pressure gradient of Ar 100 kPa–100 Pa through the discharge channel, while the 8-mm discharge apparatus isolates the high-pressure side at 7 kPa from the lower pressure of 54 Pa. Emission spectroscopy of visible and vacuum UV radiation reveals the characteristics of the Ar and He plasmas. Spectral analysis yields a plasma temperature of around 1 eV in both discharges. Stark broadenings of the H-b and Ar I lines give an electron density of 6.5 (cid:2) 1016 cm(cid:3)3 for Ar 60 A with a gas ?ow rate of 1.0 l/min and 4.7 (cid:2) 1013 cm(cid:3)3 under a He 100-A and 0.45-l/min condition.
关键词： electron density,plasma temperature,emission spectroscopy,virtual vacuum interfaces,He plasma,cascade arc plasma sources,plasma windows,Ar thermal plasma
更新于2025-09-04 15:30:14
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Simulation and visualization of crystal shapes and interfaces
摘要： Nature often arranges atoms in the shape of perfect crystals, but sometimes she creates defects and multiple domains. The optimal crystal shape at zero kelvin can be found via the Wul? construction, which can be only be carried out analytically for those trivial cases where next nearest neighbour interactions can be neglected. For our system of interest - videlicit the HCP non-Bravais case, numerical simulation is needed. This system is of relevance because we are modeling helium crystals. We have modeled two adjacent crystallites with di?erent orientations in contact creating twist or tilt grain boundaries, and calculated the surface energy of the interface. Experience gained from several aspects of this project have a wider applications, including the condensed matter simulation application to sample construction for multi-domain crystals, and a visualization one for representation in the presence of grain boundaries. The optimization of sample shapes into their groundstates is also related to wavefront optimization in multimirror telescopes.
关键词： surface energy,interfaces,HCP lattice,Wul? construction,crystal shapes,grain boundaries
更新于2025-09-04 15:30:14
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Study of the Interface of the Early Stages of Growth under Quasi-Equilibrium Conditions of ZnO on Graphene/Cu and Graphite
摘要： The study of the early stages of growth of ZnO on graphene supported on Cu and on highly oriented pyrolytic graphite by means of reactive thermal evaporation of metallic Zn at room temperature is presented. This growth method allows to go in depth in the study of the fundamental interaction between ZnO and graphene at the interface in quasi-equilibrium conditions. Quantitative, chemical, and morphological analysis is performed using photoemission spectroscopy, atomic force, and scanning microscopies as experimental characterization techniques and factor analysis and inelastic peak shape analysis as modeling techniques. The growth of ZnO on a highly oriented pyrolytic graphite substrate is also studied using the same growth method for comparison. The results show that, in spite that the first atomic layer of both substrates is identical, the growth kinetics and morphology of the deposits are completely different. A model for the kinetics of the growth of ZnO on both substrates is proposed.
关键词： X-ray photoemission spectroscopy,early stages of growth,ZnO/graphene interfaces,atomic force microscopy,nanostructured ZnO thin films
更新于2025-09-04 15:30:14
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Controlling ZnSe/GaAs interface properties: The role of elemental exposure and photon irradiation during growth initiation
摘要： Incorporating dissimilar semiconductors into a single platform can offer additional degrees of freedom for optoelectronic device design. However, bonding of elements with mixed valence at heterovalent interfaces often leads to defect formation and poor material quality. Using ZnSe/GaAs as a model system, we investigate the use of above-bandgap photon irradiation in combination with elemental surface treatments as a route to modify the interface properties. We find that this approach produces large changes in the behavior of the interfaces. Specifically, treating the GaAs surface with light and a short exposure to Se flux results in strong excitonic emission from both layers and an abrupt interface between them. We propose that these improvements arise from controlled desorption of As atoms from the GaAs surface and the subsequent Se enrichment of the interface. These results suggest that illumination with above-bandgap photons and proper choice of elemental exposure prior to heterovalent epitaxial layer growth may aid the synthesis of heterovalent semiconductor heterostructures.
关键词： interface properties,photon irradiation,heterovalent interfaces,elemental exposure,ZnSe/GaAs
更新于2025-09-04 15:30:14
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Confocal Fluorescence Microscopy and Kinetics of the Cr3+-Chromate Ion Oxidation Equilibria at the Solid Liquid Interface
摘要： Silica-borax pearl samples impregnated with 0.17 and 0.64% Cr3+ were characterized by specific surface area measurements, UV-Vis spectroscopy, energy-dispersive X-ray fluorescence and laser-scanning confocal microscopy. Pearl stability against oxidizing conditions was tested by adding samples to an aqueous hydrogen peroxide solution. The reaction was examined by UV-Vis spectroscopic measurements of the supernatant and laser-scanning confocal microscopy images of the substrate. Overall, hydrogen peroxide-induced Cr3+ to Cr6+ oxidation across the solid-liquid interface promoted solid matrix cleavage pearl degradation and concomitant formation of multiple scattering centers was observed. A dual-detection scheme was employed in the confocal microscopy measurements allowing us to separate scattering and absorptive contributions to the observed signals. The confocal microscopy images indicate that Cr3+ oxidation induced by hydrogen peroxide solutions occurs throughout the entire pearl sample and indicate that oxidation reactions induce leakage of chromate ion into aqueous solutions.
关键词： energy dispersive X-ray fluorescence,confocal fluorescence microscopy,chromium mobility,H2O2 oxidation equilibria,mass transfer phenomena,solid liquid interfaces
更新于2025-09-04 15:30:14