Studying the materials chemistry in solution utilizing X-ray spectroscopic and scattering studies

Resume : Colloidal inorganic nanocrystals (NCs) are complex structures for a which a single technique is insufficient to completely elucidate the total structure. Here,[1,2] we analyze zirconia NCs that are synthesized in tri-n-octylphosphine oxide (TOPO). Through a combination of transmission electron microcopy, x-ray pair distribution function analysis, dynamic light scattering and nuclear magnetic resonances (both liquid and solid state) we interrogate the NC structure at different length and time scales. First, we establish that the NCs have a distorted tetragonal crystal structure. Disregarding a small structural misfit in the low-r region of the PDF (from ligand-NC correlations that are not included in the refinement), the agreement factor Rw is exceptionally low, approaching the value for the Ni calibrant, thus indicating a very high phase purity of the nanocrystal. Second we show that the NC surface is capped by di-n-octylphosphinate and P,P′-(di-n-octyl) pyrophosphonate. In addition, hydrogen chloride associates with the metal oxide NC surface and protonates TOPO. The resulting hydroxyl-tri-noctylphosphonium is tightly associated with the NC surface due to electrostatic interactions and hydrogen bonding. As such, we have elucidated both the core and the surface structure of these ZrO2 NCs, arriving at a complete structural model. [1] Rijckaert, H. et al, Materials, 2018, 11, 1066 [2] De Roo, J. et a. Chemistry of Materials 2017, 29, 10233

Resume : For more than 20 years, the development of nanomaterials has been at the heart of many technological innovations, ranging from catalysis to optics and electronics. In any case, it is always necessary to use materials whose characteristics of size, crystallinity, purity, composition, etc. are perfectly controlled. It is in this context that the technology implementing supercritical fluids is an interesting alternative. Indeed, where the so-called conventional methods can reach their limits for the production of particles of a few nanometers, this technology enables the continuous synthesis of high-quality nanocrystals in a single step. Nevertheless, the synthesis being fast (a few seconds), it is necessary to develop in situ tools in order to track in real time the formation of these nanocrystals from the molecular organization in solution to the nanocrystals growth. This allows us to better understand the reaction mechanisms and therefore improve our control over the nanocrystals produced in terms of size, size distribution, crystallinity, etc. To do this, the use of large instruments is essential because it allows to perform absorption or X-ray diffraction analysis in situ with a good compromise between acquisition time and signal resolution. In this paper, we first propose to introduce this innovative synthesis process using fluids under supercritical conditions. Then, we will present the reactors developed to meet the specificities of large instruments in order to perform in situ measurements. Finally, we will illustrate our presentation by presenting the study of ZrO2 nanocrystals the formation, notably by the total X-ray scattering method and in particular the analysis of the pair distribution function (PDF).

Resume : Using a combination of steady-state and ultrafast X-ray and deep-ultraviolet (UV) spectroscopies, we have investigated: a) the electron dynamics and charge trapping in anatase TiO2 nanoparticles (NPs) in solution.(1) While free carriers relax at extremely fast time scales (<50 fs) to the bottom of the conduction band,(2) charge trapping also takes place immediately after their creation.(3,4) The electron traps are due to pentacoordinated defects in the defect rich shell region of the NPs.(3) b) we also report on electron cooling in ZnO, which turns out to be much slower than in TiO2. Furthermore, time-resolved X-ray absorption and emission spectroscopy reveals signatures of hole trapping in ZnO NPs,(5) which is found to proceed slowly (>1 ps). These results are discussed from a fundamental point of view, but also in relation to applications in photovoltaics and photocatalysis. References: 1. Strongly bound excitons in anatase TiO2 single crystals and nanoparticles E. Baldini, L. Chiodo, S. Moser, J. Levallois, E. Pomarico, G. Auböck, A. Magrez, L. Forro, M. Grioni, A. Rubio and M. Chergui. Nature Communications 8 (2017) 13 2. Clocking the Ultrafast Electron Cooling in Anatase Titanium Dioxide Edoardo Baldini, Tania Palmieri, Enrico Pomarico, Gerald Auböck, and Majed Chergui ACS Photonics 5 (2018) 1241−1249 3. Mapping the trapping of electrons in photoexcited TiO2 by picosecond X-ray absorption spectroscopy M. Hannelore Rittmann-Frank, C.J. Milne, J. Rittmann, M. Reinhard, T. J. Penfold and M. Chergui Angewandte Chemie International Edition 53 (2014) 5858 –5862 4. Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2 F. G. Santomauro, A. Lübcke, J. Rittmann, E. Baldini, A. Ferrer, M. Silatani, P. Zimmermann, S. Grübel, J. A. Johnson, S. O. Mariager, P. Beaud, D. Grolimund, C. Borca, G. Ingold, S.L. Johnson, M. Chergui Scientific Reports 5 (2015) 14834-1-6 5. Revealing hole trapping in ZnO nanoparticles by time-resolved X-ray spectroscopy Thomas J. Penfold, Jakub Szlachetko, Fabio G. Santomauro, Alexander Britz, Wojciech Gawelda, Gilles Doumy, Anne Marie March, Stephen H. Southworth, Jochen Rittmann, Rafael Abela, Majed Chergui and Christopher J. Milne. Nature Communications 9 (2018) 478

Resume : Magnetic properties of superparamagnetic iron oxide nanoparticles (SPION) in solution are routinely determined using volume magnetometry probes, namely VSM or SQUID. However, quantitative analysis of these results is often challenged by uncertainty in concentration, size distribution and chemical composition of particles, especially when probed directly after synthesis and/or separation. In this talk we will assess the application of hard X-ray photon-in photon-out magnetic spectroscopy, namely 1s2p RIXS-MCD, for in-situ quantitative probing of SPION magnetic properties. Details of the experimental procedure and results of preliminary measurements performed on dispersions of maghemite, zinc doped iron oxide and cobalt ferrite nanoparticles will be discussed. We will present the feasibility of probing site selectively magnetic properties of iron ions simultaneously with their site distribution in spinel ferrite lattice. Moreover, we will demonstrate that carrier-free magnetization profiles of SPION can be directly derived from the field dependence of RIXS-MCD intensity. Thus, the distribution of magnetic diameters of SPION in solution can be derived without the uncertainty related to diamagnetic contribution of carrier fluid.

Resume : The main goal of synthetic chemistry is to achieve the rational design of materials to be used in applications. However, for inorganic metal oxide nanoparticles there is a lack in mechanistic understanding of formation, making it difficult to synthesize the exact particle of interest. In fact, in the case of nanoparticles, only broad mechanistic models, like classical nucleation and growth theory, are used to describe their formation and therefore, the specific chemistry of the material being formed is overlooked. By studying the properties of spinel iron oxide nanoparticles we have shown that the specific chemistry of the system makes an impact because different synthetic techniques produce particles with different magnetic properties though they have the same core diameter. A new synthetic technique, a continuous growth method, allows for sub nanometer control of particle diameter. Particles made by continuous growth were analyzed by Total X-Ray Scattering with Pair Distribution Function analysis in order to obtain structural information on particles from 3-8 nm in diameter. With an increased understanding of how structure evolves over size, we are able to explain observed growth behavior in the continuous growth method. From this we gain mechanistic insight on how particles form and how the changing size of the nanoparticle core impacts growth. This work is an example of how Total X-ray Scattering studies can be used to enable rational design of metal oxide nanoparticles.

Resume : Ce3+-doped Y3Al5O12 nanocrystals (YAG:Ce NCs) are under development for light converters based on their potential high photoluminescence efficiency, with foreseen applications in nanostructured white LED devices. Two parameters are key to produce highly efficient YAG:Ce Ncs: the control of the NC crystal quality and the minimization of the quantity of Ce4+ ions, which are detrimental for photoluminescence properties. In this context, size-controlled highly crystalline NCs were synthesized by a modified solvothermal route, which offers fine control over nucleation and growth steps during YAG:Ce formation. Cerium oxidation state was determined during the NC synthesis by in situ XANES. Using high energy resolution fluorescence-detected X-ray absorption spectroscopy, Ce3+ and Ce4+ XANES signals could be distinguished, allowing the quantification of each ion within the nanocrystals. Thus, we showed that partial oxidation of luminescent Ce3+ into optically-silent Ce4+ was favoured at high synthesis temperatures (≥ 400°C). The Ce3+/Ce4+ ratio was also determined for other types of garnet-type NCs, showing that the host nature influences significantly the oxidation rate of cerium dopant. These results underpin a better understanding of the origin of cerium partial oxidation, thus opening the route to YAG:Ce NCs syntheses with reduced Ce4+ ions presence.

Resume : Self-assembly occurring in colloidal suspensions generates a broad range of structures with fascinating properties. The formation and utilization of such colloidal assemblies has been an extensive subject of research and a promising route for the fabrication of advanced materials. Among the various techniques employed to characterize the properties of colloidal suspensions, Static (SLS) and Dynamic (DLS) Light Scattering stand out as extremely versatile and powerful tools. Accurate characterization using SLS and DLS methods mandates the measurement and analysis of singly scattered light. Structures however typically only appear in concentrated samples. The suppression of multiple scattering is therefore required to obtain meaningful results. To achieve this, the so-called Modulated 3D cross-correlation technique [1,2] uses two temporally separated light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. In this presentation, we will give an overview of the Modulated 3D technology and its performances in Static Light Scattering studies. Using a charge-stabilized suspension of Poly-n-Butylacrylamide-Polystyrene copolymer, we demonstrate the measurement of a structure factor. We will show how the Modulated 3D cross-correlation technology enables us to fully characterize the sample properties by detecting features not accessible by traditional light scattering techniques. [1] Patent EP2365313 A1 [2] Ian D. Block and Frank Scheffold, “Modulated 3D cross-correlation light scattering: Improving turbid sample characterization”, Rev. Sci. Instrum. 81, 123107 (2010).

Resume : We are developing an aqueous synthesis platform for thin films and nanostructured piezoelectric oxide materials based on an in situ characterization toolbox to gain knowledge about the nucleation and growth mechanisms. This knowledge gives us valuable information to design materials with desired properties. Aqueous chemical synthesis is environmental friendly and highly flexible route to tailored thin films and nanostructured piezoelectric materials. For studies of hydrothermal synthesis an in situ cell using synchrotron X-ray radiation has been developed. We have investigated the formation mechanisms of lead-free MNbO3 (M = K, Na), BaTiO3 and SrxBa1-xNb2O6 piezoelectrics from salt and oxide precursors. Fast detectors and high brilliance synchrotron X-ray source facilitates the investigation of the nucleation and formation on a sub-second scale even for dilute chemical reactions that is required to obtain a high control and reproducibility. Chemical solution deposition of piezoelectric thin films demands a strong control of processing parameters to obtain phase pure oriented films and we have developed an in situ cell with atmospheric control for synchrotron X-ray studies of the pyrolysis step during aqueous chemical solution deposition processing. Understanding the evolution of the nucleation and crystallization of K0.5Na0.5NbO3, BaTiO3 and SrxBa1-xNb2O6 thin films guide designing the optimal procedure for fabrication and tuning the desired piezoelectric properties.

Resume : X-ray absorption (XAS) and emission (XES) spectroscopy of liquid water are one of the cutting-edge techniques to determine the local hydrogen bond structure of liquid water through observation of the valence electronic structure.[1-3] An XES study of liquid water at an interface gives us a good opportunity to explore isolated or highly ordered water molecules unexpected in bulk liquid water. In this paper, XES studies on such “unique” water molecules are presented. Water encapsulated in an electrolyte polymer brush, Poly(2-(methacryloyloxy)ethyl trimethylammonium chloride), is well suited for the investigation of interaction between water and polymers as well as confinement of water by these polymer brushes.[4,5] The apparent relationship between each XAS/XES spectral profile and a specific hydrogen bond configuration characterized by its strength and local symmetry is demonstrated. The results indicated that the confined water has tetrahedrally coordinated hydrogen bonds with a uniform distortion like high pressure ice, which should be naturally connected to control the antifouling and lubricating functions of polyelectrolyte brushes. [1] T. Fransson, Y. Harada, N. Kosugi et al., Chem. Rev. 116, 7551 (2016). [2] S. Myneni, Y. Luo, L.-Å. Näslund et al. J. Phys.: Condens. Matter 14, L213 (2002). [3] T. Tokushima, Y. Harada, O. Takahashi et al., Chem. Phys. Lett. 460, 387 (2008). [4] K. Yamazoe, Y. Higaki, Y. Inutsuka et al., Langmuir 33, 3954 (2017). [5] M. Kobayashi, Y. Terayama, H. Yamaguchi et al., Langmuir 28, 7212 (2012).

Resume : The Co4Cat (colloids for catalysts) synthesis is a recently reported method to produce colloidal dispersions of surfactant-free precious metal nanoparticles (NPs) in alkaline mono-alcohols [1]. The Co4Cat technology leads to NPs with superior catalytic performances versus industrial benchmarks. To optimise the synthesis and the catalytic properties, a detailed understanding of the NP growth mechanism is gained using X-ray absorption spectroscopy but also in-situ small angle X-ray scattering and transmission electron microscopy. The growth mechanism strongly differs in the two simplest mono-alcohols suitable for the synthesis: in methanol a fast nucleation and moderate growth is achieved whereas in ethanol nucleation is followed by a continuous growth [2]. Together with infra-red spectroscopy studies these results are explained by the in-situ formation of CO adsorbed on the NP surface by oxidation of the solvent (or absence of these species due to poor oxidation properties) while the original Pt(IV) precursor is reduced to Pt(II) and Pt(0) during the synthesis. This knowledge leads to optimised syntheses, e.g. to achieve a fast nucleation at room temperature [3] and propose different strategies to achieve NP size control. Pair distribution function analyses are currently performed to gain further knowledge and control on the formation of the surfactant-free NPs. [1] Quinson et al. Angew. Chem. 2018, 57, 12338. [2] Quinson et al. In preparation. [3] Quinson et al. In preparation.

Resume : The future of materials research depends on understanding their crystallization process for precisely optimizing their structure-related properties and designing rational synthesis protocols. On the one hand, in-situ X-ray diffraction (XRD) analysis is a powerful tool for monitoring phenomena like nucleation, crystal growth and phase transitions. On the other hand, it is not able to characterize amorphous (intermediate) phases, ions in solutions or very small nanoparticles and depends on synchrotron radiation for penetrating the reactor walls, limiting the availability of this method. In order to overcome these limitations, in-situ XRD can be combined with the so-called in-situ luminescence analysis of coordination sensors (ILACS) approach. This technique introduces emissive ions like the lanthanides or transition metals to the structure of the studied compound as local sensors. The spectroscopic properties of these ions are influenced by changes in the coordination environment, allowing to track structural transformations under real reaction conditions using fast charge-coupled device (CCD)-based detectors, in combination with in-situ XRD in the synchrotron facilities and also in common university laboratories. This work shows the remarkable symbiosis of these techniques for monitoring the events happening not only inside the solid materials but also in the liquid media surrounding elucidating the wet chemical synthesis of emissive complexes, bioceramics and quantum dots.

Resume : Nano-sized particles of MoO2 are studied for applications both as anode material for Li/Na batteries and in catalysis. The structure of pristine MoO2 is a distorted rutile, however upon nanosizing, the structure is changed due to defects in the connectivity of the [MoO6]-octahedra that make up the structure. This change in structure has a profound influence on the properties of MoO2, and thus control of the defect formation during synthesis must be achieved, in order to obtain the desired properties in any application. With this goal in mind, we have studied the hydrothermal synthesis of MoO2 using in-situ total scattering and pair distribution function (PDF) analysis. In solution, molybdenum ions form a range of polyoxometalate ions, POMs, where [MoO6] units are arranged in large, closed-shell clusters. Upon synthesis, these break down to form the MoO2 structures, and the POM may be considered pre-nucleation clusters. The nature of the POM present in solution is highly dependent on solvent properties, temperature and pH. By utilizing this, we alter the prenucleation cluster structure, and in this way control the synthesis product to obtain both the pristine and highly defected MoO2 structure. Similarities are evident in the local structure of the prenucleation clusters and the local structure of the obtained products. The differences in the structure of the products are explained by the distinct reaction pathways from the clusters to the final product.

Resume : Nanosized one dimensional (1D) ferroelectrics are investigated for applications in sensors, actuators and energy harvesting devices. Hydrothermal synthesis, being a cheap, clean and low temperature synthesis route, with a large parameter space for optimization, stands out as one of the best routes for controlled synthesis of 1D nanostructured ferroelectrics. Today, optimization relies mainly on trial-and-error processes, which is time consuming and costly, and there is a general agreement in the field that a better understanding of the nucleation and growth mechanisms are needed for better control, further development and to improve reproducibility. Here we present in situ synchrotron diffraction studies for hydrothermal synthesis of SrxBa1-xNb2O6 (SBN), giving insight into the nucleation and growth. SBN is a tetragonal tungsten bronze with interesting ferroelectric and optical properties. A combination of conventional powder X-ray diffraction with Rietveld refinement and X-ray total scattering with PDF analysis is used to follow the reactions from the non-crystalline precursors, all the way to final crystalline product. Batch reciprocal and real space Rietveld refinement was used to extract time dependent development of relative amount, size, strain, lattice parameters and thermal parameters of the crystalline and amorphous phases. X-ray total scattering and PDF analysis allowed studies of the systems before crystallization, aiding in understanding the early formation stages.

Resume : Nanomaterials made from earth-abundant elements are of particular interest in current energy-related research. Specially, cobalt oxides have shown high catalytic efficiency for example in artificial photosynthetic systems. Size, shape and crystal structure of nanoparticles are decisive for their performance. Knowledge on the formation mechanism, ligand interaction and surface intermediates is essential for a well-controllable synthesis of cobalt-based nanomaterials from solution. Here, we investigated the formation mechanism of cobalt oxide nanoparticles from cobalt(III) acetylacetonate in benzyl alcohol. Multicomponent curve resolution−alternating least squares (MCR-ALS) analysis of in situ high energy resolution fluorescence-detected (HERFD) XANES data measured at the 1s2p transition (Kα1) revealed the reduction of the Co3 precursor to cobalt(II) acetylacetonate, followed by the formation of a CoO phase. Pair distribution functions (PDF) obtained from total X-ray scattering measurements indicate the presence of more than one crystalline phases throughout the reaction, where the final product matches with CoO. Finally, HERFD-XANES spectra measured at multiple energies around the 1s3p (Kβ1,3) emission line provide intrinsic species-selectivity due to a shift of the emission energy depending on the chemical environment of cobalt, thus complementing the MCR-ALS analysis of HERFD-XANES data measured at Kα1.

Resume : Platinum has been widely studied for catalysis due to e.g. its high activity for the oxygen reduction reaction, ORR, in fuel cells [1]. However, large-scale implementation is challenged by high Pt cost and low stability towards reaction intermediates [2]. Instead, intermetallic nanoparticles composed of noble metals (i.e. palladium, Pd) and inexpensive metals (i.e. copper, Cu) have attracted significant interest by demonstrating excellent catalytic activity [3]. The ordering transformation of the intermetallic structure (Pm-3m) from a disordered face-centered cubic (fcc) alloy (Fm-3m) is known to be crucial for the catalytic properties and is dependent on the size of the particles [4,5]. However, synthesizing small intermetallic nanoparticles in a controllable manner remains a challenge due to highly varying redox properties of the metals involved, and often, intermetallics are therefore prepared at rather high temperatures hindering structural engineering on the nanoscale. Recent work has led to the development of new synthesis pathways applying organic solvents for controlled reactions, but the reaction mechanisms are still unknown [6]. In order to tailormake designed intermetallic catalysts, we must obtain insight into their formation, as well as their metal order/disorder and dealloying. Through in situ total scattering and pair distribution function analysis (PDF), the disorder-order transformation was revealed to involve an intermediate stage characterized as an ordered fcc structure followed by further ordering into the intermetallic bcc structure. References [1] Zhang, J. (Ed.), Springer Science & Business Media, 2008. [2] Wu, G., More, K. L., Johnston, C. M., & Zelenay, P., Science, 2011, 332, 443-447. [3] Jiang, K., Wang, P., Guo, S., Zhang, X., Shen, X., Lu, G., ... and Huang, X., Angewandte Chemie International Edition, 2016, 55, 9030-9035. [4] Wang, C., Chen, D. P., Sang, X., Unocic, R. R., and Skrabalak, S. E., ACS nano, 2016, 10, 6345-6353. [5] Luo, M., Sun, Y., Wang, L., & Guo, S., Advanced Energy Materials, 2017, 7, 1602073. [6] Bai, S., Shao, Q., Wang, P., Dai, Q., Wang, X., & Huang, X, 2017, Journal of the American Chemical Society, 139, 6827-6830.

Resume : In-situ and nano X-ray diffraction beamline at the PETRA III storage ring at DESY went into user operation in September 2018. The scientific case of the beamline concentrates on physics and chemistry of systems dominated by low dimensional and confinement effects, with an emphasis on in situ and operando techniques. The beamline offers a variety of diffraction methods, ranging from conventional single crystal, powder and surface diffraction to nano-scale, coherent beam and time-resolved techniques. The currently available absorption and secondary emission methods include anomalous scattering, x-ray fluorescence analysis, XANES and conventional and X-ray excited optical luminescence. The beamline undulator source and optics are optimized to provide up to 10^13 photons/sec in the energy range 5-35 keV into variable spot sizes from 1 mm and down to sub-micrometer values. The beamline currently operates one experimental hutch equipped with a custom designed HUBER diffractometer, which can carry user sample cells with up to 150 kg in the 4 circle mode and up to 15 kg on an Eulerian cradle in the 5+2 circle mode. The beamline instrumentation pool is aimed for multiscale analysis of nanostructured materials and devices. In the presentation, we shall show the possibilities provided by the new beamline, present the results of some experimental applications, including in situ electrochemistry, chemical gas and liquid reactors, and discuss the plans for future developments.

Resume : The single step of « Spray Pyrolysis » technique was developed for preparing Cu2NiSnS4 (CNTS) thin films followed by an annealing treatment process. Originally, the spray technique was successfully used to deposit the samples onto glass substrates at 250 °C for 60 min spray duration. Again, the prepared samples were annealed in sulfur atmosphere at a temperature of 500 °C during 30 min. Herein, The annealed sample exhibits (111), (220) and (311) orientations corresponds well to cubic CNTS structure. The SEM data exhibit a uniform, rough and compact topography. The absorption coefficient is found to be higher than 104 cm-1 in the visible region while the direct band energy of 1.3 eV, which is eminently suitable for use in solar cell. The complex impedance diagrams indicate the decrease of resistance by increasing temperature, which attribute to a semiconductor behavior. The close values of activation energies 1.22 and 1.09 eV determined from both angular frequency and DC conductivity indicate that the carrier transport mechanism is thermally activated.

Resume : The correlation between structure and properties in molecular chemistry is indisputable.1 While the solid state structure can be easily obtained with single-crystal X-ray diffraction2, determining the dynamic solution structure is—particularly for f-elements–less straight forward.3 Advances in solution phase total scattering are being made constantly.4 There is, however, a pressing need for a way of directly connecting solution structure and observed solution properties. Our approach incorporates a study of molecular structures from single-crystal X-ray diffraction, as well as doped structures with isolated distinctive properties, to individual molecules in solution. Extensive research has been done on the kinetically inert Ln[DOTA]- complexes, primarily as a direct consequence of the use of Gd(III) complexes in magnetic resonance imaging.5 Despite the rigid nature, Ln[DOTA]- complexes in solution exists as four structural ligand conformers6, which gives rise to different physicochemical properties.7 By employing solid state structures to map dis-tinct structure-property relations, we aim to understand dynamic structures and averaged properties in solution. Solid state and solution state are bridged by dilute solid state structures of Ln[DOTA]- complexes. This makes it possible to isolate physicochemical properties coming from a specific form in the solid state and relate that to what is observed in solution. 1. L. G. Nielsen, A. K. R. Junker and T. J. Sørensen, Dalton transactions, 2018, 47, 10360-10376. 2. M. E. Boulon, G. Cucinotta, J. Luzon, C. Degl'Innocenti, M. Perfetti, K. Bernot, G. Calvez, A. Caneschi and R. Sessoli, Angewandte Chemie, 2013, 52, 350-354. 3. a) P. Caravan, J. J. Ellison, T. J. McMurry and R. B. Lauffer, Chemical Reviews, 1999, 99, 2293-2352. b) T. J. Sørensen and S. Faulkner, Acc Chem Res, 2018, 51, 2493-2501. 4. Kirsten M. Ø. Jensen, Mogens Christensen, Pavol Juhas, Christoffer Tyrsted, Espen D. Bøjesen, Nina Lock, Simon J. L. Billinge, and Bo B. Iversen, Journal of the American Chemical Society, 2012, 134 (15), 6785-6792 5. a) E. M. Gale, P. Caravan, A. G. Rao, R. J. McDonald, M. Winfeld, R. J. Fleck and M. S. Gee, Pediatric Radiology, 2017, 47, 507-521. b) P. Caravan, J. J. Ellison, T. J. McMurry and R. B. Lauffer, Chemical Reviews, 1999, 99, 2293-2352. 6. a) L. G. Nielsen, A. K. R. Junker, T. J. Sørensen, Dalton Trans., 2018,47, 10360-10376. b) P. Caravan, J. J. Ellison, T. J. McMurry and R. B. Lauffer, Chemical Reviews, 1999, 99, 2293-2352. 7. a) Silvio Aime, Mauro Botta, and Giuseppe Ermondi, Inorganic Chemistry, 1992, 31 (21), 4291-4299. b) D. Parker, R. S. Dickins, H. Puschmann, C. Crossland and J. A. K. Howard, Chemical Reviews, 2002, 102, 1977-2010.

Resume : Metal oxides of bismuth and its oxido clusters in solution have attracted much attention with potential applications ranging from antibacterial agents to photocatalysis. In order to improve the photocatalytic activity of β-Bi2O3, it has been shown that easily accessible {Bi38O45}-based clusters represent well suited molecular precursors [1]. However, the chemical processes involved in the cluster formation are not well understood: While the molecular structures of various clusters have been solved by single crystal diffraction, it is much more challenging to study structures of such clusters directly in solution. Bismuth oxido clusters exist in a range of sizes, most of them built up by simple or edge-sharing octahedral {Bi6OX} units, but studies on their conversion processes are restricted to electrospray mass spectrometry. Here, we use in situ X-ray total scattering with PDF analysis to study the formation of a {Bi38O45} cluster starting from [Bi6O5(OH)3(NO3)5]·(H2O)3 crystals dissolved in DMSO. The PDF analysis gives unique insight into the structural rearrangements on the atomic scale. By combining with Small Angle X-ray Scattering, SAXS, we furthermore investigate the size, morphology and size dispersion of the clusters taking place in the process. These two techniques complement each other, allowing us to follow the cluster chemistry as it takes place. [1] M. Schlesinger, et. al, Dalton T 42 (2013), 1047-1056 [2] M. Mehring in Metal Oxido Clusters of Group 13–15 Elements, in Clusters – Contemporary Insight in Structure and Bonding, Editor S. Dehnen, Springer International Publishing: Cham. (2017), p. 201-268. [3] C. Falaise et. Al, J Am Chem Soc, 135(42): (2013) ,15678-81. [4] K. J. Mitchell, K.A. Abboud, and G. Christou, Nat Commun., 8(1) (2017), 1445. [5] L. Söderholm et. al., Angew. Chem. Int. Ed. Engl., 47(2) (2008), 298-302.

Resume : X-ray absorption near edge structure (XANES) imaging technique has been developed to visualize the oxidation state of elements. One of the most issued materials in XANES imaging is the lithium-ion battery such as LFP or NMC, which has delithiation process that switches the oxidation state depending on charging level. The oxidation state of an interesting sample in a partially charged state is measured with reference samples in the pristine state and the fully charged. The samples are prepared with micro-sized pieces or practical cell-types. Synchrotron based X-ray absorption images are acquired in a range of K-edge energies at 7C X-ray nano imaging beamline at Pohang Light Source II. X-ray absorption coefficients are obtained by the imaging process; reference correction, objective alignment and spectral normalization. The final process maps the linear-combination (LC) fitting result. The sample is also captured by the tomographic technique. We confirms the charging distribution using the 2D LC mapping data as well as the 3D tomogram. This method has the potential as a tool to analyze the charging distribution of Li-ion batteries.

Resume : A deep understanding of the X-ray mirror coating materials is a key point to produce optimized and durable mirrors, which are the main parts of the optical elements in any astronomical instrumentation. Therefore, it is necessary to evaluate the true composition of coating materials and contaminants to reveal the cause and their effects on the mirror performance. We analyzed the fine-scale structures of the multilayer mirrors using transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS). The X-ray reflectivity performance of iridium-based X-ray mirrors is investigated at desired grazing angle and energy range. This research helps to gain insights into the mirror coatings from the surface to the depth and at interfaces. In addition, the optimized methodology research is applicable to future studies on a wide range of X-ray mirrors.

Resume : The phenomenon of radiation fluxes waveguide-resonance propagation is featured by the uniform interference field of X-ray standing wave appearing and device worked in frame of the phenomenon is called the planar X-ray waveguide-resonator (PXWR) [1]. In works devoted to decreasing of angular divergence at integral intensity retention of PXWR emergent beam we revealed that the effect is achieved at use the composite planar X-ray waveguide-resonator (CPXWR) consisted of two simplest PXWR deposited one after another on some distance with mutual aligning. The observed effect was the result of mutual influence of X-ray standing waves interference fields excited inn both PXWRs [2]. Inasmuch as the interference picture appearing is a feature of any radiation fluxes reflection one can expect that the waveguide-resonance propagation mechanism will be characteristic of its. By virtue of the wave-corpuscle dualism the flux particles propagation mechanism possessing by non zero rest mass will be characterized by the radiation standing wave interference field appearing. So, we can expected that interference field interaction will be able to prepare new materials by its the mutual influence use. These radiation standing waves interference fields must be excited by atomic fluxes of initial substances, portraying the low energy nuclear synthesis cold fusion of materials. [1] V. Egorov, E. Egorov. X-ray Spectrometry. v33 (2004) 360. [2] V. Egorov, E. Egorov. Optics and Spectroscopy. v124 (2018) 838.

Resume : An understanding of the surface reducibility of a catalytically active oxide support is a pre-requisite to understanding its catalytic behaviour. In this work, we report that through a stringent control over the phase and morphology of catalytically active MnO2 supports, a control over the surface reducibility can be achieved. Through temperature-programmed reduction (TPR), we prove a higher availability of lattice oxygen for the α-MnO2 phase, compared to that of β-MnO2. X-ray photoelectron spectroscopy is used to comment of the surface reducibility in both the materials. Furthermore, by modifying the synthesis method, we could engineer the morphology of the α-phase into nanoflowers which in turn leads to a higher surface area, further enhancing the activity. On the engineered support, decoration of Pt nanoparticles can lower the full conversion temperature for CO oxidation as low as ~90 oC.

Resume : Developing highly active electrocatalysts for oxygen evolution reaction (OER) is critical for the commercial effectiveness of water splitting to produce hydrogen fuels. Low-cost spinel oxides have attracted increasing interest as alternatives to noble-metal-based OER catalysts. A rational design of spinel catalysts can be guided by studying the structural/elemental properties which determine the reaction mechanism and activity. The exploring on these properties relies on characterization methods. Here, from density functional theory (DFT) calculations, we find that the relative position of O p-band and MOh (Co and Ni in octahedron) d-band centre in ZnCo2-xNixO4 (x=0-2) correlates with its stability as well as the possibility for lattice oxygen to participate in OER. We therefore testified it by synthesizing ZnCo2-xNixO4 spinel oxides, investigating on their OER performance and surface evolution by X-ray absorption spectroscopy (XAS) and Transmission electron microscope (TEM). Stable ZnCo2-xNixO4 (x=0-0.4) follows adsorbates evolving mechanism (AEM) under OER conditions. Lattice oxygen participate in the OER of metastable ZnCo2-xNixO4 (x=0.6, 0.8) which gives rise to continuously formed oxyhydroxide as surface-active species and consequently enhanced OER activity. This surface change has been evidenced by XAS. ZnCo1.2Ni0.8O4 exhibits performance superior to the benchmarked IrO2. X-ray spectroscopies works as a crucial tool for our understanding of the surface reconstruction of highly active metastable spinel electrocatalysts. Our work illuminates the design of electrocatalysts through the prediction of the reaction mechanism and OER activity by determining the relative positions of the O p-band and MOh d-band centre.