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Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.


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TL;DR: In this paper, polycrystalline ZnO thin films were deposited on a glass substrate by a spray pyrolysis technique using solution of zinc acetate and air as the carrier gas at 400 °C temperature.
Abstract: Polycrystalline ZnO thin films were deposited on a glass substrate by a spray pyrolysis technique using solution of zinc acetate and air as the carrier gas at 400 °C temperature. Optical constants such as refractive index n and extinction coefficient k, were determined from transmittance spectrum in the ultraviolet-visible-near infrared (UV-VIS-NIR) regions using envelope methods. The films were found to exhibit high transmittance (>90 %), low absorbance and low reflectance in the visible regions. Absorption coefficient a, and the thickness of the film t were calculated from interference of transmittance spectra. The energy band gap, and the thickness of the films were evaluated as 3.27 eV and 0.31-0.52 pm respectively. The crystallographic structure of these films was analyzed with x-ray diffractometer. The films were polycrystalline in nature with preferred (002) orientation perpendicular to substrate surface and the grain size estimated to be 40 nm. The extended x-ray absorption fine structure (EXAFS) calculations above the K-edge of Zn in the ZnO thin film have been performed by using real-space multiple scattering of photoelectrons. For ZnO thin films, the values of the correlated mean square relative displacements of nearest-neighbor atoms derived from EXAFS spectra show good agreement with those measured from the x-ray diffraction experiments.

136 citations

Journal ArticleDOI
TL;DR: It is shown that the Sn does not randomly insert into the beta-zeolite structure but rather occupies identical, specific, crystallographic sites in the six-membered rings, which suggests that there is likely a symbiotic relationship between the structure-directing agent in the zeolite synthesis and the Sn heteroatoms during the framework formation.
Abstract: The Sn silicate zeolite, Sn-β, has been shown to be an efficient, selective heterogeneous catalyst for Baeyer−Villiger oxidations. Using primarily a multishell fit to extended X-ray absorption fine structure (EXAFS) data, we show that the Sn does not randomly insert into the β-zeolite structure but rather occupies identical, specific, crystallographic sites. These sites are the T5/T6 sites in the six-membered rings. Moreover, the Sn is substituted in pairs on opposite sides of these six-membered rings. We believe that it is the specific, uniform crystallographic location of the Sn in the β crystal structure that leads to sites with uniform catalytic activity, and consequently to the high chemical selectivity demonstrated for this catalyst. This manifests itself in the almost enzyme-like selectivity of this catalyst in Baeyer−Villiger oxidations. This uniform site distribution of the Sn suggests that there is likely a symbiotic relationship between the structure-directing agent in the zeolite synthesis and...

136 citations

Journal ArticleDOI
TL;DR: In this paper, the molecular orientation in self-assembled fims of methyl-, hydroxyl-, and carboxylic acid-terminated alkanethiols of different chain lengths (n-docosanethiol [DCT], 22-mercaptodocosanol [MDO], 22mercaptodecosanoic acid [MDC], n-hexadecanethiol (HDT), 16mercaptohexadecanecanol [MHO], 16-mercatenadecanoic acid (MHC)) on Au substr

135 citations

Journal ArticleDOI
TL;DR: In this paper, the promoting impact of alkali metals (i.e., Li, Na, K, Rb, Cs) on the carburization rate of Fe in Fe/Si catalysts was investigated by X-ray absorption spectroscopy.
Abstract: The promoting impact of alkali metals (i.e., Li, Na, K, Rb, Cs) on the carburization rate of Fe in Fe/Si catalysts was investigated by X-ray absorption spectroscopy. A multisample holder was used, allowing nearly simultaneous examination of the catalysts during activation in a CO/He mixture. With the white line intensity and shape as a fingerprint for oxidation state, TPR/XANES analysis enabled us to measure the relative composition of the different compounds as a function of the carburization time, temperature, and atomic number of the group 1 promoter. At the same time, TPR/EXAFS provided information on the changes in local atomic structure that accompanied the oxidation state changes. The rate of carburization increased in the following order: unpromoted < Li < Na < K = Rb = Cs. After 10 h of treatment the samples containing K, Rb, and Cs were completely carburized, and residual quantities of iron oxides were detected in both unpromoted and Li-promoted samples. The EXAFS spectra after carburization cou...

135 citations

Journal ArticleDOI
TL;DR: In this article, the structural evolution and the diffusion processes which occur during the phase transformation of nanoparticles (NPs), e-Co to Co2P to CoP, from a reaction with tri-n-octylphosphine (TOP).
Abstract: We report the structural evolution and the diffusion processes which occur during the phase transformation of nanoparticles (NPs), e-Co to Co2P to CoP, from a reaction with tri-n-octylphosphine (TOP). Extended X-ray absorption fine structure (EXAFS) investigations were used to elucidate the changes in the local structure of cobalt atoms which occur as the chemical transformation progresses. The lack of long-range order, spread in interatomic distances, and overall increase in mean-square disorder compared with bulk structure reveal the decrease in the NP’s structural order compared with bulk structure, which contributes to their deviation from bulk-like behavior. Results from EXAFS show both the Co2P and CoP phases contain excess Co. Results from EXAFS, transmission electron microscopy, X-ray diffraction, and density functional theory calculations reveal that the inward diffusion of phosphorus is more favorable at the beginning of the transformation from e-Co to Co2P by forming an amorphous Co-P shell, while retaining a crystalline cobalt core. When the major phase of the sample turns to Co2P, the diffusion processes reverse and cobalt atom out-diffusion is favored, leaving a hollow void, characteristic of the nanoscale Kirkendall effect. For the transformation from Co2P to CoP theory predicts an outward diffusion of cobalt while the anion lattice remains intact. In real samples, however, the Co-rich nanoparticles continue Kirkendall hollowing. Knowledge about the transformation method and structural properties provides a means to tailor the synthesis and composition of the NPs to facilitate their use in applications.

134 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023110
2022264
2021156
2020164
2019164
2018151