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  • Local atomic structure of gold nanoparticles in silica glasses by using to EXAFS and DFT modeling

    Plasmonic nanoparticles make it possible to localize the electromagnetic field at scales smaller than the optical wavelength. This property is useful for the application of same objects for the creation of nanodetectors, in the processes of energy conversion and storage, in the tasks of data processing and transmission. In particular, the creation of computer chips with plasmonic elements instead of traditional semiconductors will increase their performance and energy efficiency. Our main purpose is obtaining implanted in the matrix of glass the arrays of plasmonic nanoparticles with controlled optical properties. Their properties can be varied by changing the conditions of their synthesis and post-processing. Nanoparticles are created by UV-laser influence on the gold film, precipitated on the glass surface. One of the proposed methods is long-term heating at 300 ̊C of already synthesized samples. This research presents the results of the study of the effect of temperature treatment on the atomic structure of Au nanoparticles. The study of the nanoparticles atomic structure was performed by using EXAFS-spectroscopy at the Au L3-edge. EXAFS-functions were fitted by using Stepwise EXAFS fitting-code, obtained models of the NPs atomic structure were confirmed by using DFT-optimization. The fact, that the atomic structure of NPs before and afted thermal treatment is strongly dependent of the thickness of initial gold layer (6, 10 and 70nm), is established. These differencies can be explainde by different interaction between gold film & NPs and glass matryx.

    Keywords: nanoparticles, Au, nanoplasmonics, EXAFS, DFT, atomic structure

  • The Analysis of EXAFS Spectra with Strongly Correlated Structural Parameters

    The technique of determination of local atomic structure in the vicinity of absorbing atom in the case of the presence of strong correlation between fitting parameters is proposed. This technique is applied to three test signals simulating the Pt L3-edge EXAFS spectra of Pt/Ag bimetallic nanoparticles. The test results demonstrates the improvements in precision of determined parameters comparing with common technique.

    Keywords: Extented X-ray Absorbtion Fine Structure, EXAFS, multiparameter curve fitting, correlation between fitting parameters, bimetallic nanoparticles, local atomic structures, CUDA

  • Determination of the atomic structure of bimetallic Pt-Ag nanoparticles in metal-carbon catalysts by X-ray absorption spectroscopy data

    The atomic structure of bimetallic nanoparticles of Pt-Ag composition, which are the part of metal-carbon electro-catalysts PtAg/C, is studied by means of EXAFS spectroscopy using the suggested technique. These materials have been prepared by methods of consistent and simultaneous deposition of Ag and Pt atoms from aqueous ethylene glycol solutions of their salts with subsequent acid treatment. The values ​​of the structural parameters of the near environment of platinum atoms are determined. The nature of the distribution of components in nanoparticles is established. Cluster models of nanoparticles are constructed. The fraction of Pt atoms in the working shell and its dependance on preparation methods in each case are determined.

    Keywords: Metal-carbon electrocatalysts, bimetallic nanoparticles, Catalysis, Platinum, X-ray absorption spectroscopy, atomic structure