22 research outputs found
Core-Shell Structure of Palladium Hydride Nanoparticles Revealed by Combined X-ray Absorption Spectroscopy and X-ray Diffraction
No full textWe report an in situ, temperature and H2 pressure-dependent, characterization of (2.6 +/- 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core-shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner “core” and surface “shell” regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended X-ray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In whole temperature range (085 °C), XRPD the analysis confirms the existence of two well-separated α- and β- hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell interatomic distances obtained from EXAFS exhibit a smoother behavior in the phase transition region, typical for nanostructured palladium. Such difference is explained by distinct properties of bulk “core” which has crystalline structure and sharp phase transition, and surface “shell” which is amorphous and absorbs hydrogen gradually without forming distinguishable α- and β- phases. Combining EXAFS and XRPD we extract, for the first time, the Pd-Pd first-shell distance in the amorphous shell of the nanoparticle, that is significantly shorter than in the bulk core and relevant in catalysis. The core/shell model is supported by the EXAFS analysis of the higher shells, in the frame of the multiple scattering theory, showing that the evolution of the third shell distance (DeltaR3/R3) is comparable to the evolution of (Deltaa/a) obtained from XRPD since amorphous PdHx shell gives a negligible contribution in this range of distances This operando structural information is relevant for the understanding of structure-sensitive reactions. Additionally, we demonstrate the differences in the evolution of the thermal parameters obtained from EXAFS and XRPD along the hydride phase formation
Formation of silver nanoparticles in silicate glass using excimer laser radiation: Structural characterization by HRTEM, XRD, EXAFS and optical absorption spectra
No full textPlasmonic silver nanostructures in surfaces of soda-lime silicate glasses were generated using Ag+ Na+ ion exchange and UV laser irradiation (ArF laser, 193 nm) with different number of ns laser pulses (from 2 to 5000). To identify the correlations between the optical properties (surface plasmon resonance (SPR) parameters) and atomic structure of silver nanoparticles and their agglomerations, characterization of the samples was performed by HRTEM, XRD, optical absorption in visible range and Ag K-edge EXAFS spectra. Analysis of the optical spectra was performed using a Mie theory approach, accounting for the most plausible defect centers in silicate glass like hole trap centers and non-bridging oxygen hole centers. Processing of Ag K-edge EXAFS yielded values of Ag-Ag and Ag-O interactions averaged over ionic and neutral states of silver. The consistent treatment of HRTEM and XRD data, the behavior of features in optical spectra and the obtained dependence of Ag-Ag and Ag-O structural parameters upon the number of laser pulses enabled to suggest a mechanism of plasmonic Ag nanoparticles formation in silicate glass under UV laser irradiation. (C) 2016 Elsevier B.V. All rights reserved
Local Atomic Structure in InAs at Low Pressures. Fourier-Transform Analysis of As X-ray Absorption Spectra
No full textAbstract. Local structural distortions in Indium Arsenide at 11 GPa are studied applying the Fourier-transform analysis to As K-edge XAFS restricted to a short exploitable energy range of ~ 250 eV above the edge, due to the Bragg reflections from the diamond anvils. The best model for the radial distribution of In-atoms around As is obtained by combining available XRD data with a fitting procedure of the XAFS data, where alternative models for As coordination have been tested. InAs at 0.4 GPa was used as reference compound to minimize the number of variable parameters
Potential effects and electron dissipation effects during the structure formation of the x-ray absorption atomic spectra in the material and auge- and photoelectron angular distribution, radiating by surface atoms
No full textThe hydrogasodynamics and technology a of melt treatment out of furnace by high-implused jets of neutral gas were studied. The conception of a jet synthesis, blowing regimes and devices to solve problems of melt treatment in ladle was developed. The appropriatenesses of melt degassing and homogenizig in ladle at the blowing by trans- and ultrasonic jets of neutral gas were obtained experimentaly. The approptiatenesses of gas-powder jets outflow were studied and a new class of blowing regimes and devices for powder material injection was developed. The principles of construction and optimization of regime parameters of blowing devices, regimes and devices for melt degassing by trans- and ultrasonic jets of neutral gas to inject the powder materials in a melt, technological decisions, concerning the correction of the chemical composition and temperature of a melt in ladle were developed. The principles of a temperature melting regime optimization were developed. The results obtained were applied in the West-Siberian Metallurgical works. The increase of the metal quality allowed to decrease the reject by 20-30%. The yield of steel was increased by 0,1-0,3%, the steel temperature on tap was decreased by 10-25% the specific expense of cast iron was decreased by 2-4 kg/t, the ferroalloy expense was reduced by 3-8%. The results may be use in steelmakingAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio
Ilona Svetlikova, _The Moscow Pythagoreans: Mathematics, Mysticism, and Anti-Semitism in Russian Symbolism_, Palgrave Macmillan, 2013, 184 pp.
No full textThis is a review of an interdisciplinary work of intellectual history on the Moscow philosophical-mathematical school. The author, Ilona Svetlikova, is primarily interested in the thought of the late nineteenth and early twentieth-century mathematician and philosopher Nikolai Bugaev, of his son Boris Bugaev — better known under his nom de plume Andrei Belyi —, of Nikolai Bugaev’s student Pavel Nekrasov, and of other disciples of Bugaev, especially Vissarion Alekseev, the Baron Mikhail Taube, and Pavel Florensky. The book explores the views of these thinkers, all of whom were more or less closely associated with the Moscow Mathematical Society, on issues at the crossroads of mathematics, philosophy, literature, religion, and political ideology. Since he was the originator and pillar of the Moscow philosophico-mathematical circle, my critical comments focus on Nikolai Bugaev
Optoelectronics and defect levels in hydroxyapatite by first-principles
No full textHydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.</p
Formation and implantation of gold nanoparticles by ArF-excimer laser irradiation of gold-coated float glass
No full textUltra-Broadband Plasmon Resonance in Gold Nanoparticles Precipitated in ZnO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Glass
No full textOptical materials with a tunable localized surface plasmon resonance (LSPR) are of great interest for applications in photonics and optoelectronics. In the present study, we explored the potential of generating an LSPR band with an ultra-broad range of over 1000 nm in gold nanoparticles (NPs), precipitated through a thermal treatment in ZnO-Al2O3-SiO2 glass. Using optical absorption spectroscopy, we demonstrated that the LSPR band’s position and shape can be finely controlled by varying the thermal treatment route. Comprehensive methods including Raman spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy were used to study the glass structure, while computational approaches were used for the theoretical description of the absorption spectra. The obtained results allowed us to suggest a scenario responsible for an abnormal LSPR band broadening that includes a possible interparticle plasmonic coupling effect taking place during the liquid–liquid phase separation of the heat-treated glass. The formation of gold NPs with an ultra-broad LSPR band in glasses holds promise for sensitizing rare earth ion luminescence for new photonics devices
Effect of Gold Nanoparticles on the Crystallization and Optical Properties of Glass in ZnO-MgO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> System
No full textGold nanoparticles precipitated in transparent glass-ceramics could pave the way for the development of multifunctional materials that are in demand in modern photonics and optics. In this work, we explored the effect of gold nanoparticles on the crystallization, microstructure, and optical properties of ZnO-MgO-Al2O3-SiO2 glass containing TiO2 and ZrO2 as nucleating agents. X-ray diffraction, transmission electron microscopy, Raman, and optical spectroscopy were used for the study. We showed that gold nanoparticles have no effect on the formation of gahnite nanocrystals during the glass heat treatments, while optical properties of the glass-ceramics are strongly dependent on the gold addition. A computational model was developed to predict optical properties of glass during the crystallization, and the possibility for adjusting the localized surface plasmon resonance band position with the heat treatment temperature was shown
Electronic Structure of Pt and Au Compounds Measured by X‑ray Emission and X‑ray Absorption Spectroscopies
No full textThe electronic structure of the filled and unfilled states
and
the formation of the chemical bonding in PtO2, PtCl4, PtS2, and Au2S are studied by measured
Pt and Au Lβ5 X-ray emission spectra (XES) and L3-edge X-ray absorption spectra (XAS). The study is based on
the comparative analysis of the calculated local partial densities
of electronic states (LPDOS) on the noble atom and on the neighboring
ligands. It is revealed that theoretical description of experimental
spectra requires going beyond MT-approximation and therefore the full-potential
linearized augmented-plane-wave method realized in the code WIEN2k
is applied. The effect of a static screened 2p core-hole potential
of Pt and Au on the calculated Pt L3-edge XAS is examined
with a supercell approach. The obtained agreement of theoretical spectra
with the experimental ones validates the results of the LPDOS analysis
and the made conclusions on electronic structure of the studied compounds
