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X-WR-CALNAME:IXAS: The International X-ray Absorption Society
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X-WR-CALDESC:Events for IXAS: The International X-ray Absorption Society
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DTSTART:20190101T000000
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BEGIN:VEVENT
DTSTART;VALUE=DATE:20200601
DTEND;VALUE=DATE:20200602
DTSTAMP:20260718T110822
CREATED:20200512T153844Z
LAST-MODIFIED:20200604T042831Z
UID:365-1590969600-1591055999@xrayabsorption.org
SUMMARY:Anne Marie March:  Capturing photochemical reaction intermediates with time-resolved synchrotron x-ray spectroscopy
DESCRIPTION:The pump-probe technique allows for measurement of timescales that are shorter than a detector’s response time. Using a MHz-repetition-rate laser to pump a sample\, the full x-ray flux of synchrotrons such as the Advanced Photon Source (APS) can be used to probe the ensuing photoinduced reaction(s). The obtained time-resolved XAS and XES spectra can be used to capture the electronic and geometric structure of short lived intermediate species. In this presentation\, I will give a brief introduction to the pump-probe measurement technique as implemented at Sector 7 of the APS and present recent studies of the photoinduced aquation reaction of [FeII(CN)6]4-\, where we were able to detect an intermediate species with a lifetime 4x shorter than the x-ray probe pulse duration.  \nReferences: \n\nhttps://doi.org/10.1063/1.5117318\nhttps://doi.org/10.1107/S1600577519012268\n\n 
URL:https://xrayabsorption.org/events/journlclub-anne-marie-march/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200604
DTEND;VALUE=DATE:20200605
DTSTAMP:20260718T110822
CREATED:20200512T160713Z
LAST-MODIFIED:20200606T233732Z
UID:367-1591228800-1591315199@xrayabsorption.org
SUMMARY:Maryjo Brounce: The oxidation state of sulfur in Apollo-era lunar rocks and curation best practices for future sample return missions
DESCRIPTION:Lunar apatites contain hundreds to thousands of parts per million of sulfur. This is puzzling because lunar basalts are thought to form in low oxygen fugacity (fO2) conditions where sulfur can only exist in its reduced form (S2–)\, a substitution not previously observed in natural apatite. We present measurements of the oxidation state of S in lunar apatites and associated mesostasis glass that show that lunar apatites and glass contain dominantly S2–\, whereas natural apatites from Earth are only known to contain S6+. It is likely that many terrestrial and martian igneous rocks contain apatites with mixed sulfur oxidation states. The S6+/S2– ratios of such apatites could be used to quantify the fO2 values at which they crystallized\, given information on the portioning of S6+ and S2– between apatite and melt and on the S6+/S2– ratios of melts as functions of fO2 and melt composition. Such a well-calibrated oxybarometer based on this the oxidation state of S in apatite would have wide application. \nReferences: \n\nBrounce\, M.\, Boyce\, J.\, McCubbin\, F.M.\, Humphreys\, J*.\, Reppart\, J.\, Stolper\, E.\, and Eiler\, J. (2019) The oxidation state of sulfur in lunar apatite. American Mineralogist\, 104\, 307-312. doi: https://doi.org/10.2138/am-2019-680\n\n 
URL:https://xrayabsorption.org/events/journalclub-maryjo-brounce/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200608
DTEND;VALUE=DATE:20200609
DTSTAMP:20260718T110822
CREATED:20200514T015707Z
LAST-MODIFIED:20200609T025341Z
UID:382-1591574400-1591660799@xrayabsorption.org
SUMMARY:Jerry Seidler:  Overview of lab XAFS/XES
DESCRIPTION:After decades of relative silence\, lab-based spectroscopy has made a comeback in recent years. Modern spectrometers have energy resolution comparable to synchrotron XAS beamlines and have performances demonstrated in dozens of recent publications. Here\, I will briefly summarize the various technical approaches before focusing on examples for XAFS and XES in the hard and tender regime. A unifying theme of much of this work can be termed “analytical XAS”\, where many applications require very high access for iterative measurement of material properties — a use model that fits poorly with synchrotron scheduling. I will conclude with a discussion of several schemes for the interplay between synchrotron and lab-based XAS\, with an emphasis on the already clear fact that these two approaches are generally complemnetary rather than competitive. \n  \nReferences: \n\nhttp://dx.doi.org/10.1063/1.5049383 \nhttp://dx.doi.org/10.1021/acs.analchem.8b00302 \nhttp://dx.doi.org/10.1063/1.4901599 \nhttp://dx.doi.org/10.1063/1.4994739\n\n 
URL:https://xrayabsorption.org/events/journalclub-jerry-seidler_june2020/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200611
DTEND;VALUE=DATE:20200612
DTSTAMP:20260718T110822
CREATED:20200514T015818Z
LAST-MODIFIED:20200617T021645Z
UID:384-1591833600-1591919999@xrayabsorption.org
SUMMARY:Alessandra Leri: XANES Spectroscopy to Illuminate Biogeochemical Cycling of Halogens in Environmental Systems
DESCRIPTION:The halogens chlorine and bromine have high electron affinities and exist in seawater mainly as chloride and bromide anions\, which have generally been considered unreactive in the environment. Using Cl and Br K-edge XANES spectroscopy\, we have measured high concentrations of organo-chlorine and -bromine in naturally degraded particulate organic matter (POM) from oceanic sediment traps. While organobromine speciation in marine POM is exclusively aromatic\, organochlorine is fractionated into aliphatic and aromatic particles that appear in a heterogeneous distribution. The major precursor of sediment trap material is phytoplankton biomass\, the detritus of which under-goes oxidative breakdown as part of the marine carbon cycle. We hypothesized that unsaturated lipid and protein moieties in phytoplankton detritus would be susceptible to halogenation through oxidative degradation mechanisms. Using model experiments\, we showed that algal particulates are readily chlorinated and brominated through various abiotic pathways\, including photochemical and Fenton-like reactions. These processes produce organohalogens in particulate algal detritus at levels exceeding 0.1% by mass. In contrast with the exclusively aromatic organobromine observed in natural marine POM\, the lab-based experiments generate aliphatic organobromine in algal particulates; however\, the aliphatic organobromine produced appears to be labile and susceptible to debromination on relatively short (3-week) timescales under highly oxidizing conditions. These findings have implications for the transformation and stabilization of marine organic carbon prior to sedimentary burial.\nWe have also measured high concentrations of non-volatile organochlorine and -bromine in several varieties of edible kelps. Such compounds are likely to contribute to organohalogen body burden in humans and other organisms.\n \nReferences: \n\nA. Leri\, M. Dunigan\, R. Wenrich\, and B. Ravel (2019). Particulate organohalogens in edible brown seaweeds. Food Chemistry 272\, 126. https://doi.org/10.1016/j.foodchem.2018.08.050\nA. Leri\, L. Mayer\, K. Thornton\, P. Northrup\, M. Dunigan\, K. Ness\, and A. Gellis (2015). A marine sink for chlorine in natural organic matter. Nature Geoscience 8\, 620. https://www.nature.com/articles/ngeo2481\nA. Leri\, L. Mayer\, K. Thornton\, and B. Ravel (2014). Bromination of marine particulate organic matter through oxidative mechanisms. Geochimica et Cosmochimica Acta 142\, 53. https://doi.org/10.1016/j.gca.2014.08.012\nA. Leri and B. Ravel (2014). Sample thickness and quantitative concentration measurements in Br K-edge XANES spectroscopy of organic materials. Journal of Synchrotron Radiation 21\, 623. https://doi.org/10.1107/S1600577514001283\n\n\n 
URL:https://xrayabsorption.org/events/journalclub-alessandra-leri/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200615
DTEND;VALUE=DATE:20200616
DTSTAMP:20260718T110822
CREATED:20200522T142834Z
LAST-MODIFIED:20200617T021815Z
UID:413-1592179200-1592265599@xrayabsorption.org
SUMMARY:Anna Zymakova: Introduction to ELI-Beamlines
DESCRIPTION:Introduction to ELI-Beamlines – a new user facility in the heart of Europe. Status and prospective of ELI X-ray spectroscopy end-station \nImproved access to state-of-the-art facilities is a key element to groundbreaking advances in science. One such facility is the Extreme Light Infrastructure (ELI); a pan-European project of which one pillar (ELI-Beamlines) is located near Prague in Czech Republic. The new facility utilizes ultra-high power lasers in research projects aimed at studying intense light/matter interactions as well as making use of short pulsed lasers to drive secondary X-ray and XUV sources (such as Plasma X-ray sources\, Betatron\, High-order Harmonic generation etc.) and particle accelerators (electrons and ions) for applications in material science\, biomedicine\, laboratory astrophysics etc. The E1 experimental hall at ELI Beamlines houses a few secondary sources that generate beams in wide\, complementary\, energy ranges\, as well as end-stations that will be used for correlative ultrafast experiments. Particularly\, the station for time-resolved experiments with X-rays (TREX) includes diffractometry and spectroscopy setup for pump-probe X-ray experiments. These will use plasma X-ray sources driven by the in-house developed L1-ALLEGRA laser (1kHz\, 100mJ\, <20fs laser pulses @830nm)\, as well as conventional support lasers. The presentation will give a short overview of the ELI project and ELI-Beamlines structure. I will focus on the status and outlook of the x-ray spectroscopy station currently under development for an improved user availability for high demand ultrafast x-ray techniques. \nReferences: \n\nF. Batysta et al.\, Opt. Express 24\, 17843 (2016) https://doi.org/10.1364/OE.24.017843\n\n 
URL:https://xrayabsorption.org/events/journalclub-anna-zymakova/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200618
DTEND;VALUE=DATE:20200619
DTSTAMP:20260718T110822
CREATED:20200522T142943Z
LAST-MODIFIED:20200714T011612Z
UID:415-1592438400-1592524799@xrayabsorption.org
SUMMARY:Anatoly Frenkel:	Machine learning - assisted analysis of material’s structure using XANES and EXAFS spectra
DESCRIPTION:Tracking the structure of functional nanomaterials (e.g.\, metal catalysts) remains a challenge due to the paucity of experimental techniques that can provide atomic-level information for metal species in harsh conditions\, often required for studying chemical transformations. Here we report on the use of X-ray absorption spectroscopy (XANES and EXAFS) and supervised machine learning (SML) for determining the three-dimensional geometry of monometallic and alloy nanoparticles [1]. Artificial neural network (NN) is used to unravel the hidden relationship between the XANES features and material’s geometry [2]. In the case of EXAFS\, NN is used to obtained the partial radial distribution function (PRDF) directly from the spectra [3]. In other words\, we trained computer to learn how to ‘invert” the unknown spectrum and obtain the underlying structural descriptors. Training of the NN was performed by using theoretical spectroscopy codes. These applications are demonstrated by reconstructing the compositional distributions of nanocatalysts from the coordination numbers obtained by NN-XANES\, or from the PRDF obtained by NN-EXAFS. The first applications of these method to the determination of structure of nanocatalysts in reaction conditions will be demonstrated [4-6]. \nReferences: \n\nJ. Timoshenko\, A. I. Frenkel. “Inverting” X-ray Absorption Spectra of Catalysts by Machine Learning in Search of Activity Descriptors. ACS Catalysis (Perspective) 9\, 10192-10211 (2019).  https://pubs.acs.org/doi/10.1021/acscatal.9b03599\nJ. Timoshenko\, D. Lu\, Y. Lin\, A. I. Frenkel. Supervised machine learning-based determination of three-dimensional structure of metallic nanoparticles. J. Phys. Chem. Lett.\, 8\, 5091-5098 (2017). https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.7b02364\nJ. Timoshenko\, et al. Artificial neural network approach for characterizing structural transformations by X-ray Absorption Fine Structure spectroscopy. Phys. Rev. Lett. 120\, 225502 (2018). https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.225502\nN. Marcella\, Y. Liu\,et al Neural network assisted analysis of bimetallic nanocatalysts using X-ray absorption near edge structure spectroscopy. Phys. Chem. Chem. Phys. (2020) Early view. https://pubs.rsc.org/en/content/articlehtml/2020/cp/d0cp02098b\nJ. Timoshenko\, et al . Probing atomic distributions in mono- and bimetallic nanoparticles by supervised machine learning. Nano Letters 19\, 520-529 (2019). https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04461\nY. Liu\,et al . Mapping XANES spectra on structural descriptors of copper oxide clusters using supervised machine learning. J. Chem. Phys. 151\, 164201 (2019).  https://aip.scitation.org/doi/full/10.1063/1.5126597\n\n\n 
URL:https://xrayabsorption.org/events/journalclub-anatoly-frenkel/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200622
DTEND;VALUE=DATE:20200623
DTSTAMP:20260718T110822
CREATED:20200522T143357Z
LAST-MODIFIED:20200714T011226Z
UID:417-1592784000-1592870399@xrayabsorption.org
SUMMARY:Lijia Liu:	XEOL studies of Light-Emitting Materials
DESCRIPTION:X-ray excited optical luminescence (XEOL) is a photon-in-photon-out process which monitors the visible luminescence emitted from materials upon X-ray excitation. Unlike using low energy excitation source such as UV\, during X-ray excitation\, core electrons are excited and the production of luminescence is a much more complicated process. Because of this\, X-ray excited luminescence can be correlated with the decay process of a specific core electron. In this talk\, I will introduce the fundamental process of XEOL and the unique information it provides\, when combining with X-ray absorption near-edge structure (XANES)\, in revealing the origin of the luminescence. Two materials systems\, nanostructured TiO2 and metal-doped lead halide perovskite\, will be used as examples to demonstrate the XEOL-XANES analysis technique.  \nReferences: \n\nLi et al\, https://doi.org/10.1021/acs.chemmater.5b00363\nMa et al\, https://doi.org/10.1039/c9nr00143c\n\n 
URL:https://xrayabsorption.org/events/journalclub-lijia-liu/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200625
DTEND;VALUE=DATE:20200626
DTSTAMP:20260718T110822
CREATED:20200522T143526Z
LAST-MODIFIED:20200630T151432Z
UID:419-1593043200-1593129599@xrayabsorption.org
SUMMARY:Sara Lafuerza:	 The chemical sensitivity of core-to-core XES in 3d transition metals
DESCRIPTION:K-fluorescence X-ray emission spectroscopy (XES) is receiving a growing interest in all branches of natural sciences to investigate the local spin in 3d transition metal complexes. Unlike the valence-to-core emission lines\, the core-to-core transitions in Kβ (3p to 1s) and Kα (2p to 1s) do not probe the valence shell directly and the chemical sensitivity is thus indirect. In Kβ and Kα emission\, the local spin sensitivity stems from the exchange interaction between the 3p (Kβ) or 2p (Kα) core-hole and the 3d valence shell spin of the transition metal ion\, which is larger for Kβ than Kα [1]. The magnitude of the exchange interaction depends for a given element on the valence shell spin\, which is defined by the metal atom oxidation and spin state within an ionic picture. This is a very crude description of the electronic structure and the influence of covalence in Kβ has been pointed out by several authors [1\,2].\nIn this talk\, the results of a systematic investigation of Kβ and Kα XES spectra measured on a wide range of iron compounds will be presented. More than 30 samples with different oxidation state (+2\, +3\, +4 and mixed-valence)\, spin (high-spin\, low-spin and mixed-spin)\, ligands (fluorides\, oxides\, sulfides\, etc.) or local coordination (octahedral\, tetrahedral) were measured at beamline ID26 of the ESRF synchrotron. We analysed the experimental spectra in terms of commonly used quantitative parameters (Kβ1\,3-first moment\, Kα1-full width half maximum\, and integrated absolute difference –IAD– [3]) and we carefully examined the difference spectra. We also performed multiplet calculations to elucidate the underlying mechanisms that lead to the chemical sensitivity.\nOur results confirm a strong influence of covalency on both Kβ and Kα lines. We establish a reliable spin sensitivity of Kβ XES as it is dominated by the exchange interaction whose variations can be quantified by either Kβ1\,3-first moment or Kβ-IAD and result in a systematic difference signal lineshape. We find an exception in the Kβ XES of Fe3+ and Fe2+ in aqueous solution\, where a new difference spectrum is identified that cannot be explained by scaling the exchange integrals. We explain this with strong differences in orbital mixing between the valence orbitals. This result calls for caution in the interpretation of Kβ XES spectral changes as due to spin variations without careful analysis of the lineshape. For Kα XES\, the smaller exchange interaction together with the influence of other electron-electron interactions make it difficult to extract a quantity that directly relates to the spin. \nReferences: \n\n P. Glatzel and U. Bergmann\, Coord. Chem. Rev. 249\, 65 (2005); https://doi.org/10.1016/j.ccr.2004.04.011 \nC. J. Pollock\, M. U. Delgado-Jaime\, M. Atanasov\, F. Neese and S. De Beer\, J. Am. Chem. Soc. 136\, 9453 (2014); https://doi.org/10.1021/ja504182n\n G. Vankó\, T. Neisius\, G. Molnár\, F. Renz\, S. Kárpáti\, A. Shukla\, and F. M. F. de Groot\, J. Phys. Chem. B 110\, 11647 (2006); https://doi.org/10.1021/jp0615961 \n\n 
URL:https://xrayabsorption.org/events/journalclub-sara-lafuerza-2/
CATEGORIES:XAFS Journal Club
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200629
DTEND;VALUE=DATE:20200630
DTSTAMP:20260718T110822
CREATED:20200522T143648Z
LAST-MODIFIED:20200630T151555Z
UID:421-1593388800-1593475199@xrayabsorption.org
SUMMARY:Feng Lin: Ion Reactions to Modulate Solid-State Electrochemistry for Batteries and Electrocatalysis
DESCRIPTION:Ion reactions offer a huge playground for tuning the electronic and crystal properties of inorganic solids for energy applications. Our research focuses on resolving a longstanding question in materials electrochemistry regarding redox active solids: how does the mesoscale chemical distribution influence ion reactions at different length scales? Through manipulating the thermodynamics and kinetics of the ion intercalation chemistry\, our goal is to develop experimental methodologies and establish novel design principles to enhance the electrochemical properties of ion-intercalating solids for batteries and electrocatalysis. Our studies are largely facilitated by synchrotron X-ray spectroscopic and imaging techniques that provide fundamental insights into intercalation chemistries. In this presentation\, we will first highlight our recent progress in understanding and improving electrode materials for lithium and sodium batteries. We design novel synthetic approaches to overcome the surface challenges of oxide cathode materials for high energy density\, high power density and long cycle life. Then\, we will discuss how we make use of interfacial ion reactions to modulate the electronic properties of water splitting electrocatalysts. We will highlight that tailoring the phase segregation at the catalyst-electrolyte interface constitutes a large space for stabilizing catalytic activity. \n 
URL:https://xrayabsorption.org/events/journalclub-feng-lin/
CATEGORIES:XAFS Journal Club
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