The exceptional penetration power of the high-flux, high-energy x-ray beams in liquid solutions and reaction vessels (e.g., glass flasks) enables the direct probing of nanophase evolution in large-volume reactors that are usually used in conventional wet chemistry laboratories. The weak absorption of the high-energy x-ray beams in reactants and solvent molecules eliminates the possible side reactions during nanoparticle growth and transformation. As a result, time-resolved, high-energy synchrotron x-ray techniques represent one class of ideal methods for non-invasive probing of growth/transformation mechanism of colloidal nanocrystals in conventional reactors. In this presentation, the time-resolved high-energy synchrotron x-ray diffraction is demonstrated to monitor the nanophase evolution involved in the synthesis of colloidal Ag nanocubes and the physical/chemical transformation of colloidal Ag nanowires to nanoparticles/nanotubes.
This work has been performed at the Center for Nanoscale Materials, a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357.

The properties of magnetic iron oxide nanoparticles are highly dependent on particle characteristics such as crystallite size, morphology, crystallinity, and structural defects. To obtain particles with tailor-made properties for specific applications in e.g. biomedicine or data storage, it is therefore crucial to understand the mechanisms that govern these characteristics during material synthesis. For this purpose, in situ studies of particle synthesis have proven very powerful.[1] Here, in situ Total Scattering (TS) studies of the hydrothermal synthesis of γ-Fe2O3 will be presented. In situ total scattering with Pair Distribution Function (PDF) analysis has recently shown to be an efficient tool for understanding the fundamental chemical processes that happens during particle crystallization.[2][3] TS data provides information on both short and long range atomic order in the sample, thereby capable of describing the structure of both amorphous and crystalline species. From in situ total scattering data, the full γ-Fe2O3 crystallization process from ionic complexes over nanoclusters to crystalline particles can thus be followed and material formation mechanisms may be deduced. The study shows that when γ-Fe2O3 crystallize from aqueous solutions of ammonium iron citrate, disordered maghemite-like nanoclusters with both tetrahedrally and octahedrally coordinated iron form quickly after the initiation of hydrothermal synthesis. The bond distances in the clusters are elongated compared to the final crystalline phase, and the majority of the iron is found with octahedral coordination. However, the condensation of the nanoclusters into nanocrystalline maghemite occurs along the tetrahedrally coordinated iron atoms, which thus play a large role in the formation and growth of the crystalline particles. As the particles crystallize, vacancies appear on the tetrahedral site. The vacancy concentration is highly dependent on the crystallite size, indicating that their presence is linked to the particle surface.
The study thus reveals changes in material characteristics (atomic structure, particle size/shape/distributions, crystallinity) throughout the synthesis to give a comprehensive description which may be used to design particle synthesis on a larger scale.
[1] Sun, Y. and Ren, Y. (2013), Part. Part. Syst. Charact., doi: 10.1002/ppsc.201300033
[2] Jensen, K.M.Oslash;; Christensen, M; Juhas, P; Tyrsted, C; Bojesen, E.D.; Lock, N; Billinge, S.J.L; Iversen, B. B.; J. Am. Chem. Soc. 2012, 134, 6785-6792
[3] Tyrsted, C; Jensen, K.M.Oslash;; Boslash;jesen, E.D.; Lock, N.; Christensen, M.; Billinge, S.J.L; Iversen, B.B., Angew. Chem. Int. Ed. 2012, 51, 36, 9030-9033

ZnO is a multifunctional material that is optically transparent with a direct band-gap of 3.37 eV and a large exciton binding energy (60 meV). Its wurtzite crystal structure allows for piezo- and pyroelectric behavior and it is photocatalytically active. There is currently great interest in the growth of ZnO nanowires (NWs), which are promising building blocks for a wide variety of optical and electrical devices. While NW synthesis can be accomplished by several different methods, we focus on chemical bath deposition (CBD), a low-cost, low-temperature deposition technique readily suitable for scale-up and NW growth on on flexible materials. In order to gain improved control over the aspect ratio, orientation, and density of the NW arrays, obtaining detailed information on array morphology during the growth process is necessary. We utilize in situ synchrotron X-ray techniques (namely grazing incidence small angle x-ray scattering - GISAXS - and surface x-ray diffraction - SXRD) to monitor the nucleation and evolution of ZnO NWs grown on either O- or Zn-polar ZnO (0001) substrates. A two stage growth process was observed at the standard chemical precursor concentration (0.03M), with the first part of growth dominated by an increase in the vertical size of the NWs; the duration of the stage was observed to depend slightly on the temperature of the bath. During the second stage of growth, the NWs grew primarily in the lateral directions. At lower concentration (0.005M), growth proceeded along both the vertical and horizontal directions at the same rate, even if the vertical growth is predominant during the last minutes of the NW synthesis. At a higher precursor concentration, we found that the precursors reacted immediately on the substrate surface, even at room temperature. Details concerning the reaction of the ZnO substrate surface (of either polarity) with the hydroxyl group present in the solution will be discussed.

There are many outstanding questions regarding the nucleation and growth of oxyhydroxide minerals from aqueous solution. In recent years, a number of non-traditional nucleation models have been proposed, in order to explain their complex precipitation behavior. However, these proposals have been difficult to test, due to uncertainty about the fundamental parameters that control nucleation rates (ie, interfacial energy and stoichiometry of the critical nuclei).
We apply time-resolved small angle x-ray scattering (SAXS) to directly track the early precipitation of β-FeOOH (akaganeite) nanoparticles from aqueous solution by thermal hydrolysis of acidic ferric chloride solutions. This synthesis method generates highly monodisperse nanoparticles, with fine control over precipitation rate, particle size, and particle shape. SAXS allows for a direct determination of crystal growth rates and nucleation rates in this system, as functions of time and solution chemistry. We show that these datasets can be used to determine the physical parameters that control nucleation, using the framework of classical nucleation and growth theory.
The interfacial energy (interfacial tension) of FeOOH nucleation clusters is shown to be strongly pH dependent, indicative of a protonated surface, and the absolute values of the interfacial energy are significantly lower than traditional estimates that are obtained at near-neutral pH. We also show that the critical nucleus size at the onset of precipitation is extremely small (containing between 4 and 30 iron atoms in our range of experimental conditions). These results confirm the validity of classical nucleation theory, but can also be used to predict regimes where the classical nucleation mechanisms may break-down.

Perovskite metal oxide nanoparticles have been dragging a tremendous attention since the discovery of their ferroelectric behavior in 1940s and find many applications in modern technology. The two main processes to industrially produce such materials are the solid state synthesis and the Sol-Gel one however each of them present some limitations. Although the solid state synthesis enables a large scale production, the purity and homogeneity of the final material can be an issue. In addition it can be time and energy consuming (the synthesis take several hours at temperature above 1000°C). On another side the Sol-Gel process enables a good control of the produced material (size, purity) but require several steps such as a sintering one making it time and energy consuming.
The supercritical fluids technology can be seen as a promising alternative to those two techniques.
This scalable and sustainable process operating at moderate temperature (<400°C) and mainly based on the use of green solvents such as water or ethanol enables the fast synthesis (tens of seconds) in a single step of high quality metal oxide nanoparticles. Adjusting experimental parameters such as the reactor&’s pressure and temperature, the type of solvent, the nature of the precursors, their concentration or the residence time it is possible to control the nanoparticles size, morphology, structure, composition and crystallinity. Using this reliable and versatile technology we are able to synthesize various kind of metal oxide nanomaterials, among them the Ba1-xSrxTiO3 (with 0 < x < 1) and BaTi1-yZryO3 (with 0 < y < 1) nanoparticles, over their entire solid solution.
This presentation will focus first on the supercritical fluids material&’s processing technology followed by a study on the understanding of the nanoparticles nucleation and growth through the coupling of in situ synchrotron wide angle X-rays scattering measurements with ex situ spectroscopic (FITIR, Raman, XPS) ones.

The mechanisms by which nanocrystals grow and are transformed during chemical reactions are an active topic of interest. We are particularly interested in developing real-time in-situ methods for observing such phenomenon. We have been able to examine such chemical transformations using x-ray techniques at synchrotrons, using new liquid cells for the transmission electron microscope. This presentation will contain examples of such transformations. For instance cation exchange, and will compare the relative strengths of the three approaches.

Environmental friendly solution processing of macroelectronic devices such as photovoltaics and thin film transistor (TFT) devices utilizing earth abundant and benign elements has been long-term goal for developers. The focus has been on finding good active layer materials and promising candidate materials are tin chalcogenide based compounds. In the development of advanced tailor-made functional nanomaterials, understanding the mechanisms controlling formation and growth during synthesis is of key importance.
We have used in situ X-ray total scattering with a time resolution of few seconds to study the formation of SnS2 nanoparticles from an aqueous ammonium tin(IV) sulfide solution. Recently, we have shown that high quality SnS2 thin films acting as active layer in TFTs can be deposited by thermal decomposition of an ammonium tin(IV) sulfide solution. The dimeric complex [Sn2S6]4- present in ammonium and hydrazine tin(IV) sulfide solutions has been utilized as molecular metal chalcogenide surface ligands and as a building block in nanocrystalline macroelectronic devices owing to the significant enhancement of the electronic properties. Hence, it is vital for future improvements that the thermal decomposition of ammonium tin(IV) sulfide and subsequent condensation of tin sulfide complexes is fully understood. In the present study, we have studied the time and temperature dependent transformation of tin-sulfur coordination. We will shown, how the tetrahedrally coordinated SnS4 units in the form of edge-sharing dimers [Sn2S6]4- in aqueous ammonium tin(IV) sulfide evolves to the octahedral sulfur coordinated SnS6 in 2D layered SnS2.

Semiconducting nanoparticles (quantum dots) provide due to their size-dependent optical and electrical properties1,2 a large variety of applications, e.g. light emitting devices3. Although many synthesis routes are already well developed and widely applied4, the fundamental mechanisms of nucleation and particle growth during the very early stages of crystal formation is poorly understood. In this contribution we present microsecond-resolved simultaneous in-situ SAXS and WAXS investigations along a free liquid jet starting at 100 µs after mixing and addressing the first stages of crystallization of CdS quantum dots. Starting at this early reaction time we follow both the particle morphology (SAXS) and the crystalline structure (WAXS) in-situ by focusing the X-ray beam of a synchrotron source (APS, 12 ID-B) to different positions along a free continuous liquid jet containing the reactants, which are mixed in a Y-shaped micro mixer before the ejection of the jet . With this setup the time scale is converted into a length scale and the reaction time is determined by the jet velocity and the distance from the mixing point. It allows us to access very early reaction times down to 100 µs with a resolution of 10 µs while the exposure time can be kept in the second regime as needed for sufficient statistics even at powerful synchrotron sources like the beamline 12 ID-B at the APS.
This novel setup enabled us to get a microsecond resolved insight into the particle sizes, growth rates and the crystalline structures of the particles within the first 2.5 ms of CdS quantum dot formation, by mixing Na2S and CdCl2 in aqueous solutions. Based on these experiments and findings we propose the following formation mechanism: in the first 100 µs after mixing primary 1 nm CdS clusters are already formed by diffusion and instantaneous reaction of Cd2+ and S2- ions. Further growth is driven by oriented attachment of these precursors to each other, while ongoing precursor formation is simultaneous observed as a result of the ongoing mixing process (both observed in the SAXS and the WAXS signal). After 2.5 ms, our last data point, the growing particles have reached a median diameter of about 5 nm while 1 nm clusters are still present.
1. Brus, L. Electronic wave functions in semiconductor clusters: experiment and theory. J. Phys. Chem. 90, 2555-2560 (1986).
2. Nirmal, M. et al. Fluorescence intermittency in single cadmium selenide nanocrystals. Nature 383, 802-804 (1996).
3. Mashford, B. S. et al. High-efficiency quantum-dot light-emitting devices with enhanced charge injection. Nat Phot. 7, 407-412 (2013).
4. Trindade, T., O&’Brien, P. & Pickett, N. L. Nanocrystalline Semiconductors: Synthesis, Properties, and Perspectives. Chem. Mater. 13, 3843-3858 (2001).

Oxygen-deficient, fluorite-related praseodymium oxide Pr6O11 nanocrystals with size of ~35 nm were compressed in a symmetric diamond anvil cell (DAC) at ambient temperature and studied in situ using synchrotron X-ray diffraction. The cubic, fluorite-type structure was found to transform to an orthorhombic alpha-PbCl2-type structure at approximately 24 GPa. This high pressure phase was stable up to at least 65 GPa, and could not be quenched to ambient conditions. The refined cell parameters for the orthorhombic phase at 65 GPa are as follows: a = 5.60(2) Å, b = 3.33(1) Å, and c = 6.41(2) Å, and the calculated density is 9.462 g/cm3. The cubic to orthorhombic phase transformation accompanied with about 7.9 % volume decrease. The volume compression for both phases was fit to second-order Birch-Murnaghan equations of state (EOS). The zero pressure, isothermal bulk moduli, B0, for the cubic and orthorhombic phases were about 140(2) GPa and 331(6) GPa, respectively, with a fixed first pressure derivative B0' = 4. It is expected that vacancy defects and nanoscale size may favor deformation of the crystal structure under high pressure. More theoretical and experimental research is in progress to understand this pressure-induced phenomenon in oxygen-deficient Pr6O11 nanocrystals. Q. Guo is supported by the Natural Science Foundation of Fujian Province (2010J05034), the Fundamental Research Funds for the Central Universities (2012121034), the SRF for ROCS, SEM (44), and the Program for New Century Excellent Talents in University of the Ministry of Education of China (NCET-09-0670). CHESS is supported by the NSF (DMR-0936384).

The recent discoveries of natural gas (as shale gas and others) have renewed the interest in the reforming of methane reactions as source for syngas (CO+H2) and hydrogen production. As an endothermic reaction, high temperatures are required, being the coke formation and the deactivation of catalysts the main issues for industrial practices. Nickel or cobalt as active phases are the best candidates to the more expensive noble metals, due to their availability and lower cost. These metals present also some disadvantages: the Ni produces coke deposits, while the Co is less resistant to oxidation under reaction conditions [1]. In this context, we have focused the study to bimetallic Ni-Co systems supported on La2O3 prepared by reduction of a LaNi1-xCoxO3 perovskite.
The LaNi1-xCoxO3 perovskites were prepared by the spray pyrolysis method [2]. The physicochemical state of the powders was characterized by means of SEM, XRD, TPR, XPS, etc. The measurements of the catalytic performance in the DRM/SRM reactions were accomplished using an atmospheric flow reactor. XAS spectra were collected in transmission mode at the BM25 station of the ESRF synchrotron facility, while the Ambient Pressure Photoemission Spectroscopy (APPES) experiments were performed at beam line U49/2-PGM1 at BESSY II (Berlin, Germany).
Results/Discussion
The nickel phase in the reduced LaNiO3 and LaNi0.5Co0.5O3 samples, analyzed by operando XAS, evolves from a mixture of Ni3+ and Ni2+ in the original samples, to metallic Ni0 under both, hydrogen reduction treatment and DRM reaction. This behavior contrasts with the partial oxidation of nickel observed under SRM reaction [3]. The results obtained by in situ XAS for Co phase for DRM and SRM in the LaCoO3 and LaNi0.5Co0.5O3, reveal that in both cases the cobalt phase is partially oxidized, remaining visibly less oxidized in the LaNi0.5Co0.5O3 that in the monometallic catalysts. These results could be explained considering the formation of a NiCo bimetallic alloy after hydrogen reduction of the original Ni-Co perovskite.
The APPES spectra obtained for the LaNi0.5Co0.5O3 sample submitted to a hydrogen reduction treatment agree with the XAS results. The differences observed in the XPS spectra obtained for the LaNi0.5Co0.5O3 sample during a treatment with H2 at 600C with two different photon energies (200 and 600 eV, related respectively with the surface and bulk composition of the metallic particles), allow us to propose the depicted structure for the bimetallic particles, where the metals are arranged as a “pseudo core-shell” Ni-Co.
References.
1. K. Takanabe, K. Nagaoka, K. Nariai, K. Aika; J. Catal., 232 (2005) 268.
2. E. Loacute;pez-Navarrete, M. Ocaña; J. Europ. Cer. Soc., 22 (2002) 353-359.
3. R. Pereñíguez, V.M. González-DelaCruz, J.P. Holgado, A. Caballero; Appl. Catal. B: Env., 93 (2010) 346-353.

This is the first successful report on the application of undulator synchrotron X-ray irradiation (Beam Line: Photon Factory Advanced Ring NW2A) for reduction of metal ions in an aqueous solution while recording energy disperse X-ray absorption structure (DXAFS) spectra. To clarify the process of radiation-induced reduction of metal ions in an aqueous solutions with or without carbon particles as support materials, in situ time-resolved DXAFS measurements of Au ions were performed under synchrotron X-ray irradiation.
Tetrachloroauric acid tetrahydrate (HAuCl4_4H2O) was used as the Au ion source. Untreated carbon black powder (Vulcan XC-72R) was used as the hydrophobic carbon particles. Hydrophilic carbon particles were prepared by immersing the hydrophobic carbon particles in concentrated nitric acid (69 wt.% HNO3) for 45 min at 90 ± 5 °C while stirring. Aqueous solutions (1.6 mL) containing Au ions were prepared in 5 mL acrylic cells with 6 mm thickness, wherein a portion of the walls in the acrylic cells was cut away for the synchrotron X-ray path. Polyimide (PI) films were used for windows of the cells. The solution was irradiated with undulator synchrotron X-rays. Changes in the chemical states of Au were investigated by comparing the time-resolved DXAFS spectra around the Au-LIII edge of the solution with those of the reference materials HAuCl4 and a Au foil.
For Sample 1, which has no carbon particles, metallic Au is observed on parts of the PI film. This result indicates that metallic Au is deposited only on the spot irradiated by the synchrotron X-ray in the absence of support particles. In contrast, for Sample 2, which contains hydrophobic carbon particles in the solution, metallic Au deposit is observed on the carbon nanoparticles instead of on the PI film. On the other hand, for Sample 3, which also has hydrophilic carbon particles in the solution, metallic Au is deposited on not only the PI film but also the inner walls of the acrylic cell. These results for Samples 2 and 3 indicate that the wettability of carbon particles as the support material affects the deposited spot. The results indicate that (1) Au ions reduce at the irradiated interface between solid and liquid. (2) The synchrotron X-ray-induced reduction of the Au ions in an aqueous solution is not dependent on the wettability of support materials. (3) Metallic Au is easily deposited on hydrophobic surfaces.
Changes in the shape of the X-ray absorption near-edge spectra (XANES) indicated a rapid reduction from ionic to metallic Au in the solution owing to synchrotron X-ray irradiation. As the irradiation time is increased, the shape of the XANES spectra of Sample 2 approaches that of a Au foil. After irradiation for 22 min, the reduction of Au ions is almost complete. These results demonstrate that in situ time-resolved DXAFS measurements are useful for tracking the radiation-induced reduction of metal ions in an aqueous solution.

Recently, sensitivity of rare-earth-oxycarbonates based sensors to CO2 was reported[1]. However, the physical origin of the charge transfer between a relatively inert CO2 and rare-earth-oxycarbonates, which leads to increase of the sensor&’s resistance is not understood. Here, the challenge is to collect the complementary information about the reversible changes of the La state at the surface of nanoparticles and the orbitals that are involved in bonding during the CO2 interaction. We overcome this task by increasing the surface area of La2O2CO3 nanoparticles and increasing the porosity of the sensing layers. This morphology is chosen to increase the number of sites available for the interaction with CO2 at the surface of nanoparticles that enables the application of in-situ HERFD X-ray absorption and emission spectroscopy to study the origin of this interaction. We fabricate, the sensitive layer in two steps: First, we synthesize La(OH)3 nanoparticles in organic solvent using a CEM microwave oven, with average size of 8 nm. Second, we dip-coat those nanoparticles on a substrate and anneal them under air to obtain a porous film of La2O2CO3 particles with average particle sizes of 11 nm and a thickness of 2 mu;m. Such a sensor shows sensitivity to CO2 with a sensor signal of more than 15 in synthetic air with 50% relative humidity at 250°C and 10000 ppm of CO2. Measuring the lanthanum L3 edge of this sensor under those conditions reveals a rise in the intensity during CO2 exposure and a sharpening of the white line, which represents oxidation of the La-atoms. With FEFF calculations we can reproduce the features of the XANES spectra before CO2 exposure. By adding CO2 to the calculated cluster different bonding opportunities occur. We show with FEFF calculations that an oxygen atom from the gas adsorbs at a lanthanum atom. While XAS gives information about the unoccupied states, valence-to-core XES contains information about the occupied valence states just below the Fermi-energy. The two main features are at 38.5 eV and 10.1 eV below the elastic peak. Interestingly, even the deeper states change during the interaction with CO2.
1. Haensch, A., et al., Rare earth oxycarbonates as a material class for chemoresistive CO2 gas sensors. Procedia Engineering, 2010. 5(0): p. 139-142.

Hexagonal boron nitride (hBN) has a lattice structure similar to that of graphite with a slightly larger lattice parameter in the basal plane. This, among other properties, makes it an excellent substrate in place of graphite, eliciting some important differences. This work is part of a larger effort to examine the interaction of alkanes with magnesium oxide, graphite, and boron nitride surfaces. In our current presentation, we will discuss the interaction of decane with these surfaces. Decane exhibits a fully commensurate structure on graphite and hBN at monolayer coverages. In this particular experiment, we have examined the monolayer structure of decane adsorbed on the basal plane of hBN using synchrotron x-ray radiation at Diamond Light Source. Additionally, we have examined the system experimentally with volumetric isotherms as well as computationally using molecular dynamics simulations. The volumetric isotherms allow us to calculate properties which provide important information about the adsorbate&’s interaction with not only neighboring molecules, but also the interaction with the adsorbent boron nitride.

Dynamic in-situ experiments are finding increasing use as direct methods to explore the relationships among materials&’ processing methods, microstructure and functional properties. X-ray microscopy can provide information about changes in chemical structure of materials with high spatial resolution during dynamic in-situ experiments. Observing solid-liquid interfaces with high resolution is important for comprehension of physical, chemical and biological interactions between material and fluid. A more detailed knowledge of these interactions can substantially improve our understanding of the processes that occur during nanostructure synthesis, degradation of materials inside battery, as well as the operation of biological systems.
We will present results from an in-situ study of X-ray induced gold nanoparticle synthesis and growth using a newly developed continuous flow environmental cell for X-ray microscopes. Gold nanoparticles were imaged using both X-ray Full Field imaging and X-ray Fluorescence Microscopy at the Advanced Photon Source Had X-ray Nanoprobe beamline. The combination of full filed imaging and fluoresce microscopy allows for both rapid imaging and precise elemental discrimination and localization. Hard X-rays are well suited for both transmission an fluorescence microscopy of liquid environments as demonstrate by the low attenuation of the gold X-ray fluorescence and strong absorption contrast for nanoscale gold particles. This fluid cell system not only allows for in situ X-ray studies in liquid environments, but also transfers directly to the transmission electron microscope for correlative imaging.

HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) is a relatively insensitive high explosive at room temperature. Nanometer to Micron sized voids are thought to influence sensitivity and detonation properties in polymer bound explosive compositions, where HMX crystals are mixed with, for example, ~5% Viton. HMX molecular crystals undergo a solid-solid phase transition from the so-called beta- to delta- phases at elevated temperatures around 170 Celsius, an prior to this study, little was known about how this phase transition affected mesoscale voids. We have measured the ultra-small angle x-ray scattering (USAXS) concurrently with the molecular diffraction as the molecular crystallites were heated through this phase transition. The USAXS is sensitive to structure from about 10 nm to about 5 microns, and shows how the porosity in these size regimes evolves during the phase change. X-ray computed microtomography was also performed before and after temperature cycling to observe changes on length scales larger than a micron. These results enable studies to determine how the mesocale porosity affects detonation properties in heated HMX-based explosives, and demonstrate the use of USAXS to statistically measure phenomena during heating on length scales simultaneously from nanometers to microns.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Nanodomains present on the shell of mixed monolayer protected gold nanoparticles (NPs) play a crucial role in determining the interfacial properties of these nanomaterials dissolved in solution. Given the importance of interfacial nanostructured morphology, there is an unmet need for bulk characterization methods able to give a detailed characterization of the interfacial nanodomains present on nanoparticles in solution. Measurements for determining the presence of nanodomains were performed on limited number of particles using microscopy techniques and assumptions were made on the persistence of nanodomains between different states and media. Here we present a new method based on Small Angle Neutron Scattering (SANS) on gold nanoparticles dissolved in an organic solvent. Neutrons were chosen as they have the unique property to differentiate hydrogenous and deuterated moieties due to a different scattering length density. Two hybrid dodecanethiol: hexanethiol (C12: C6) nanoparticle samples dissolved in chloroform were investigated. The hybrid nanoparticles have the same composition and size distribution, but they contain one of the two ligands (either C6 or C12) deuterated. Two SANS profiles were collected and fitted to a unique model. This low resolution model reconstructed ab initio by simultaneous fitting reveal striped patterns of C6 and C12 on the gold surface. We also prove that the SANS data are highly sensitive to the distribution of C6 and C12 in the shell by testing alternative models of ligand shell morphologies, specifically the Janus morphology and the morphology with randomly mixed C6 and C12 molecules in the shell. In both cases poor agreement with the experimental data for these morphological conformations is found. In particular, the Janus morphology showing a clear segregation between the C6 and C12 moieties, is not compatible with the SANS data. The SANS results are also in agreement with the Scanning Tunneling Microscopy images in liquid of the same nanoparticles. In conclusion, we present a full characterization of stripe-like domains for NPs in solution obtained by using both a bulk characterization technique and microscopy.

Nanoparticles form the cornerstone in many applications of nanotechnology, and their properties are highly dependent on specific particle characteristics. We have focused on synthesis in supercritical fluids since this approach offers an energy efficient green route for the production of nanomaterials with a very high degree of control of the particle characteristics [1]. However, in order to tailor nanoparticle characteristics insight into their formation and growth is vital and this can be achieved through in situ studies. During recent years, we have developed unique in situ reactors capable for studies of reactions in sub- and supercritical fluids [2]. By means of Small Angle X-ray Scattering (SAXS), Wide Angle X-ray Scattering (WAXS), Total scattering and EXAFS we have obtained knowledge on the formation and growth of a range of important nanoparticles and in the talk recent results will be discussed.
[1] (a) Hald et al, J. Solid State Chem. 2006, 179, 2671-2677; (b) Becker et al., ACSNANO 2008, 2, 1058-1068; (c) Mi et al, ACSNANO 2010, 4, 2523-2530; (d) Mi et al., Chem. Mater. 2011, 23, 1158-1165; (e) Laumann et al., J. Electrochem. Soc. 2012, 159, A166
[2] (a) Jensen et al., Angew. Chem. 2007, 46, 1113-1116; (b) Bremholm et al., Angew Chem. 2009, 48, 4788-4791; (c) Bremholm et al., Adv. Mater. 2009, 21, 3572-3575; (d) Lock et al, Angew Chem. 2011, 50, 7045-7047; (e) Jensen et al., J. Am. Chem. Soc. 2012, 134, 6785-6792; (f) Tyrsted et al, Angew. Chem. 2012, 51, 9030-9033; (g) Noslash;rby et al., RSC Adv. 2013, 3, 15368; (h) Eltzholtz et al., Nanoscale 2013, 5, 2372

In-situ X-ray Absorption Spectroscopy (XAS) measurements during nanoparticle synthesis in an organic solvent provide information of all species existing in the reaction mixture. Thus, each recorded spectrum usually contains the signal from many components that are present or evolving during nanoparticle formation. Here, on an example of CoO/Co synthesis in benzyl alcohol, we show that Multivariate Curve Resolution - Alternating Least Squares (MCR-ALS) method can be successfully applied to recover the interdependence between processes that occur during the synthesis in solution.¹ The most common approach in in-situ XAS spectra analysis is to quantify the individual components in the mixture by fitting standard spectra. However, the electronic structure of nanoparticles may strongly differ from their bulk counterparts because of their size, crystallinity and ligands attached to their surface. Hence, XAS spectra of bulk powders measured ex-situ do not represent well the electronic structure of nanoparticles growing in the solution. Therefore, instead of common approach, such as Linear Combination Analysis (LCA), we apply the MCR-ALS method without any standards&’ spectra and any previous knowledge about the correlations in the system. To illustrate the application of the MCR-ALS to the in-situ recorded XAS spectra we study the synthesis of cobalt nanoparticles in benzyl alcohol, where besides Co nanoparticles also CoO particles are formed. The in-situ X-ray absorption measurements of the synthesis at 140 °C visualize that partial oxidation of Co²⁺ to Co³⁺ and reduction of Co²⁺ to Co⁰ are taking place simultaneously. It is followed by a rapid formation of Co₃O₄ nanoparticles and its consecutive solid-state reduction to CoO, accompanied by growing of Co nanoparticles. Based on this synthesis, we show that by means of MCR-ALS method, applied to the in-situ XAS spectra, it is possible to demonstrate interdependence between the oxidation and reduction reactions that are taking place during the Co/CoO synthesis. Moreover, by combining the results from MCR-ALS analysis with in-situ X-ray diffraction data it is feasible not only to find the correlation between processes that occur during the synthesis, but also precisely assign them a physical and chemical meaning.
1. Staniuk, M. et al., Puzzling Mechanism Behind Simple Synthesis of Cobalt and Cobalt Nanoparticles: in-situ Synchrotoron X-ray Absorption and Diffraction Studies; submitted October 2013.

For the large-scale application of lithium-ion batteries, such as in electric vehicles and grid-scale storage, it is desirable to develop cost-effective methods for synthesizing electrode materials. The low temperature, soft chemistry method, such as hydrothermal, is inexpensive and flexible for synthesis of wide variety of electrode materials for Li-ion batteries. However there are a variety of synthesis parameters (precursor concentration, temperature, pressure, pH value, cation type and reaction time) that can have a strong influence on the material properties (crystal structure, morphology, particle size) and electrochemical performance. Most solution-based reactions are carried out in a sealed autoclave and therefore the reactor is a black box - the inputs and outputs are known, but little is known about intermediate phases and the overall reaction pathway. In-situ, real-time probes of synthesis reactions can provide the details of nucleation and growth of intermediate and final phases, elucidating how temperature, pressure, time and the precursor concentrations affect the reaction pathways. The results of such studies enable strategies to optimize synthesis reactions, particularly the formation of materials of desired phases and properties. In this presentation, we will show the development and application of in situ reactors and time-resolved synchrotron X-ray diffraction (XRD) techniques specialized for hydrothermal synthesis of nanostructured Cu-V-O cathodes. In situ synchrotron XRD and X-ray absorption (XAS) have been also applied for identifying the lithium reaction process and possible mechanisms responsible for poor cycling stability of this material.
Acknowledgements This work was supported by DOE-EERE under the Batteries for Advanced Transportation Technologies (BATT) Program, under Contract No. DE- AC02-98CH10886.

In this presentation the concept of millifluidic devices will be introduced. In comparison with traditional microfluidic reactors, we show with examples that millifluidic devices offer simplified solutions for carrying out kinetic studies and have the potential to revolutionize a broad range of fields from chemistry, catalysis, and nanotechnology. Particularly, in combination with spectroscopy tools such as synchrotron radiation-based XAS, SAXS and other spectroscopy probes like UV-Vis spectroscopy, Raman spectroscopy, FT-IR, this tool can be utilized to obtain time resolved information on chemistry of nanoparticle formation and also to investigate the mechanistic aspects of a vast number of catalytic reactions. While our most recent investigations reported here are focused on the chemistry of gold and platinum nanostructures, the technique can be applied to analyze the time-resolved growth of other types of nanostructured metals and metal-oxides.

Achieving morphology control of nanoparticles through solution based techniques has proven challenging due to limited knowledge of morphology development in nanosyntheses. To overcome these complications, we investigated nanoparticle nucleation rate and subsequent growth via either adatom diffusion or nanoparticle aggregation and found that these processes were affected by the local ligand environment. Specifically, it was determined that strongly coordinated ligands delay burst-like nucleation to generate spherical Pd nanoparticles and ligands with intermediate binding affinity regulate the gradual reduction of the Pd(II) precursor to promote aggregated assembly of Pd nanodendrites. Here, this study couples ex-situ studies with a new in-situ perspective providing detailed understanding of Pd(II) metal precursor transformation and induction time, its direct relation to nanoparticle morphology development, and the ligand influence towards the formation of structurally complex metal nanostructures, using in-situ synchrotron X-ray Diffraction (XRD) and Ultra Small-Angle X-ray Scattering (USAXS). By applying these findings, particle morphologies are manipulated to form either poly-crystalline nanodendrites or single-crystalline spherical particles. These outcomes provide a direct connection between fundamental principles of coordination chemistry and nanoparticle formation and a stronger foundation for the predictive synthesis of future nanostructures with defined features. These principles were also found to be generally applicable to more complex PdPt architectures.

A grand challenge of nanomaterial synthesis is to understand fundamental nanoscale mechanisms by in-situ analysis of their reactions, structures, phase transformations, and growth processes. Chemical transformations of nanoparticles are reactions that are performed on first-generation (as-synthesized) nanoparticles to modify their size, morphology, atomic structure, or chemical composition. Recent advances in chemical transformations of nanoparticles have resulted in new nanoparticle forms that are inaccessible from conventional “hot-injection” syntheses. In this talk I will discuss our work where we have applied synchrotron radiation techniques to study these transformation reactions. Specifically, we are using x-ray absorption spectroscopy (XAS) coupled with more common techniques to gain a more comprehensive understanding of the mechanisms of the chemical transformation process and the resulting structure of the novel nanomaterials. XAS is a powerful method to characterize short-range atomic arrangements of atoms and is thus well-suited for these studies because it enables local phase and composition changes to be examined even for amorphous structures.
We study a galvanic chemical transformation process that leads to hollow nanoparticles through the nanoscale Kirkendall effect, which arises from asymmetric diffusion rates between two atomic components in a diffusion couple and results in hollow nanoparticles. Using experimental characterization (XAS, XRD, TEM) and theoretical modeling (DFT) we examine the atomic structural changes and diffusion process during this transformation and find that the mechanism of the nanoscale Kirkendall effect is more complex than previously believed: the Kirkendall hollowing is not simply due to two different diffusion rates but involves phase-related diffusion constants and processes. A two-stage pathway occurs during the nanoscale Kirkendall effect as cobalt nanoparticles transform into cobalt oxide or cobalt phosphide hollow particles. The Oxygen/Phosphorus in-diffusion is initially faster than Cobalt out-diffusion. Once the amorphous shell crystallizes into CoO/Co₂P then this trend inverts and the characteristic Kirkendall hollowing is seen. Further, we identified a new metastable amorphous-crystalline core-shell form that precedes the Kirkendall hollowing. This metastable material could be useful for further tailoring of properties. For insight into the kinetics of oxygen diffusion we determine oxygen concentration from EXAFS models and plot this in time, finding a logarithmic increase. Results from EXAFS also show that all transformed phases are rich in Co, indicating that the “final” phase during a chemical transformation may never be pure. By understanding the mechanisms we can use these chemical transformations to design functional nanoparticles for energy applications. Synchrotron radiation techniques are powerful means toward achieving this goal.

An electroless, wet-chemical copper deposition process provides access to simple metallization of flexible substrate foils and spherical template particles.^[1] Transformation of metal-coated polyimide substrates into conducting line patterns is highly attractive for flexible electronics applications. Controlled three-dimensional coating of template spheres allows for the creation of porous metal shells as building blocks for macroscopic spongy structures with complex geometries and different relative densities.^[2] The common underlying chemical mechanism based on simply reacting copper(II) acetylacetonate Cu(acac)₂ with benzyl alcohol turns out to follow a chronological step-wise change in the metal&’s oxidation state. For time resolved identification of consecutively forming crystalline species in-situ synchrotron diffraction measurements were performed. The results prove the dissolution of the precursor, followed by the formation of crystalline Cu₂O and its final reduction to metallic copper Cu⁰. There is no indication for the initial crystallization of CuO. Simultaneously conducted X-ray absorption spectroscopy measurements contribute to a better understanding of this intriguing process and provide information on non-crystalline species in the reaction solution. The process is not a simple electroless deposition, where metal ions are reduced by assistance of catalysts, and therefore the understanding of the crystallization mechanism is a milestone in further developments and extensions of the process.
[1] N. Kränzlin, S. Ellenbroek, D. Duran-Martin, M. Niederberger, Angewandte Chemie-International Edition 2012, 51, 4743.
[2] N. Kränzlin, M. Niederberger, Advanced Materials 2013, 25, 5599.

The making of bonds during the formation of inorganic solid phases from solution usually follows a series of complex steps. The fact that the emergent species are often structurally nano-particulate and in many cases unstable, dictates that ideally they must be characterised not just at length-scales < 100 nm but also as in situ as possible. To this effect, solution-based X-ray scattering methods constitute one of the most versatile tools in studying nano-structured materials as they form. However, due to very physics of the scattering phenomena it is unavoidable to encounter apparent difficulties in real-space information retrieval from the evolving inorganic systems. This results from the concurrent occurrence of different shapes of particles, considerable polydispersity, and strong interparticle interactions. We demonstrate on a recent case study of CaSO4 precipitation that the scattering data interpretation is indeed non-trivial, but far from hopeless as one can benefit from the fact that scattering patterns are time-resolved and hence correlated with each other in terms of the structural information.
The CaSO4 precipitation from the respective salt solutions was followed by SAXS using a flow-through cell. We found that at the particles appearing in the first stages of the reaction, were anisotropic in shape and could be very well described using the cylindrical form factor of the cross-section diameter of 1 nm and length of 3 nm. Furthermore, it was possible observe the evolution of the emergent structure factor demonstrating itself by the sudden drop in the scattering intensity at lower angles, and originating from the hard-type interactions between the cylindrical particles. As the system further developed, the scattering pattern became gradually dominated by the evolution of very large particles appearing as surface fractals. The evolution of that massive contribution was included in the scattering model in which the scattering from the surface fractals was separated from that of the smaller cylindrical species. It turned out that the smaller cylindrical particles, as well as their interparticle structure factor were still developing despite the increasing scattering from the large structures. We derived analytical models describing the interaction of smaller anisotropic particles and based primarily on Polymer Reference Interaction Site Model (PRISM) [1] and Random Phase Approximation (RPA) [2] theories.
The as-obtained real-space information from SAXS is in accord with the earlier work [3] on the formation of CaSO4 phases, where the aggregates of small anisotropic particles can be attributed to the formation of bassanite, whereas the large fractal surfaces originate most likely from the >100 nm crystals of gypsum.
[1] Schweizer, K.S., Curro, J.G. (1994) Adv. Polym. Sci., 116, 319-377.
[2] Shimada, T. et al. (1988). J. Chem. Phys., 88, 2815-2821.
[3] Van Driessche, A.E.S. et al. (2012) Science, 336, 69-72.

Natural materials, such as wood, skeletal elements, shells or tissues are generally based on proteins or polysaccharides and a variety of minerals. A hierarchical organization confers these materials an exceptional toughness and damage tolerance. Scanning x-ray scattering is an ideal tool to study such materials at multiple scales from the nanometer range (accessible through the analysis of scattering patterns) to micrometer sizes (accessible by scanning the x-ray beam). Moreover, x-ray scattering allows the study of biological materials in the native hydrated state which opens the possibility of in-situ experiments studying their deformation behavior. The talk will discuss recent examples for the use of scanning x-ray scattering in studying biological materials.

Development in nanoscale engineering has enabled bioelectronics that can mimic and/or interact with the biological systems. Lipid bilayer-functionalized Si nanowires are considered as a promising candidate for the construction of bioelectrochemical devices. These biomimetic lipid bilayers serve as a general host matrix for bio-functional components such as membrane proteins. Though meaningful technological advancement of these materials has been made, critical questions about their structural and chemical composition remain. Small-angle and wide-angle x-ray scattering (SAXS/WAXS) and Scanning Transmission X-ray Spectroscopy (STXM) techniques are used to investigate both lateral-averaged structural characteristics and local self-organizations of the lipid bilayers upon coating on Si nanowires. Preliminary analyses on the SAXS-derived Electron Density Profile (EDP) of the lipid bilayers suggest that the nanowire acts like a template for the lipid attachment, and induces an asymmetric packing order of the lipid head groups in the lipid bilayers. Furthermore, polarization effects of near-edge x-ray absorption fine structure (NEXAFS) at C K-edge have been observed, providing insight to the degree of order in the lipid bilayers coated on Si nanowires. The results shed light on a number of unresolved questions that are crucial for the comprehensive understanding this class of materials.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The formation of crystals from solution is a subject that despite many years of research is still not clearly understood. Crystallization from amorphous precursors has been found to be a major pathway in many biotic and abiotic mineral systems. One of these is the mineral hydroxylapatite, Ca₅(PO₄)₃(OH), found in bone. In the present contribution we use in situ synchrotron X-ray diffraction to follow the formation of apatite nanocrystals from amorphous calcium phosphate in water. We find that the introduction of carbonate ions into the amorphous phase significantly influenced the crystallization kinetics and even a simple exchange of counter ion, K⁺ for Na⁺, had a profound impact on the crystallization behavior.
Diffraction experiments were performed in situ with better than 10 s time resolution using a custom X-ray diffraction cell with high thermal stability [1]. Rietveld refinement allowed us to follow the amount of crystalline material, the average nanocrystal size and the lattice constants over time. The apatite nanoparticles were assumed to be needle shaped. In the early time points we clearly observed amorphous scattering from the precursor phase, which gradually disappeared as nanocrystalline apatite formed [1,2].
The crystallites were found to be almost spherical just after nucleation. They proceeded to grow rapidly along the crystallographic c-direction to form needle-like crystals. The nanocrystals then matured further through Ostwald ripening. At lower starting pH, the initial crystal shape was not spherical but anisotropic at the earliest time particles were detected. The crystal aspect ratio gradually decreased to a stable value as the particles grew. A significant compressive and expansive strain of the c- and a-lattice parameters respectively, was present at early times and relaxed to stable values throughout the growth period. Using K⁺ rather than Na⁺ as the counter-ion lead to slower crystallization and different particle sizes and size anisotropy. This can be attributed to the lack of sodium co-substitution of dissolved carbonate ions.
Adding potassium carbonate as an additive retarded the crystallization by stabilizing the amorphous phase. The magnitude of the stabilization was found to increase with carbonate concentration. We observed a dose-dependent reduction of the crystal sizes. The size reduction was accompanied by an asymmetric change of the lattice parameters likely due to direct incorporation of carbonate ions into the unit cell by a mechanism other than co-substitution.
Taken together these results provide insight into growth dynamics of anisotropic crystals showing how a range of factors may influence crystallization behavior including supposedly innocent counter ions.
1. C. S. Ibsen and H. Birkedal, J. Appl. Cryst.45, 976-981 (2012)
2. C. S. Ibsen and H. Birkedal, Nanoscale2, 2478-2486 (2010)

Biological materials are complex hierarchical 3D multicomponent materials. Their multifaceted structure makes their characterization very challenging. Many biological materials present several biomineral phases. Using tomographic reconstructions of X-ray diffraction data rather than absorption signals allows mapping distributions of crystalline phases. Diffraction tomography investigations of the complex mineralized attachment organ of a mussel will be discussed as a model for advanced underwater adhesive systems [1]. The diffraction information allows determining chemical substitution effects in the biomineral lattices and even microstructural information. Diffraction tomography thus bridges the atomic and tomographic length scales and recent progress shows that the technique is amenable to in situ studies e.g. as a function of external load.
[1] Leemreize et al., J. Roy. Soc. Interface (2013), 10, 20130319

With the increased use of engineered nanomaterials such as ZnO and CeO2 nanoparticles (NPs), these materials will inevitably be released into the environment, with unknown consequences. In addition, the potential storage of these NPs or their biotransformed products in edible/ reproductive organs of crop plants can cause them to enter into the food chain, and the next plant generation. Few reports thus far have addressed the entire life cycle of plants grown in NP-contaminated soil. Soybean (Glycine max) seeds were germinated and grown to full maturity in organic farm soil amended with either ZnO NPs at 500 mg/kg or CeO2 NPs at 1000 mg/kg. At harvest, synchrotron mu;-XRF and mu;-XANES analyses were performed on soybean tissues, including pods, to determine the forms of Ce and Zn in NP-treated plants. The X-ray absorption spectroscopy studies showed no presence of ZnO NPs within tissues. However, µ-XANES data showed O-bound Zn, in a form resembling Zn-citrate, which could be an important Zn complex in the soybean grains. On the other hand, the synchrotron mu;-XANES results showed that Ce remained mostly as CeO2 NPs within the plant. The data also showed that a small percentage of Ce(IV), the oxidation state of Ce in CeO2 NPs, was biotransformed to Ce(III).
To the authors&’ knowledge, this is the first report on the presence of CeO2 and Zn compounds in the reproductive/edible portion of the soybean plant grown in farm soil with CeO2 and ZnO NPs.

The application potential of graphene depends entirely on the development of large-area growth and integration techniques that are scalable and allow an adequate level of structural control and material quality. Catalytic growth, e.g. chemical vapor deposition (CVD), is widely seen as the most promising approach to achieve this. The mechanisms by which mono-/few layer graphene forms during catalytic growth are however ambiguous and thus growth control remains rudimentary. This motivates our in-situ approach which aims to develop a detailed understanding of graphene formation and thus enable rational optimisation of the growth process.
We perform time- and depth- resolved high-pressure X-ray photoelectron spectroscopy (XPS) and in-situ time resolved X-ray diffractometry (XRD) and X-ray reflectometry (XRR) on polycrystalline Ni catalyst films during hydrocarbon exposures at elevated temperatures (~300-700°C),^1,2 and on Ni/tetrahedral amorphous carbon (ta-C) stacks during solid-state growth by vacuum annealing (~300-700°C).³ The use of synchrotron radiation [BESSY (Berlin), ESRF (Grenoble)] is critical in obtaining high-intensity X-rays with tunable energy to give the necessary time- and depth-resolution. Time-resolved XPS allows a detailed comparison of transient states prior to and during graphene formation and corresponding C/metal core level signatures. We thus reveal that graphene growth occurs isothermally on Ni during hydrocarbon exposures, rather than just by precipitation on cooling and that dissolved C in the catalyst subsurface plays an important role.^1,2 Similarly for solid-state growth from Ni/ta-C stacks, we are able to observe the dissolution of the ta-C layer using XRR, and the subsequent graphene formation using time-resolved XPS and XRD. We thus find that the solid-state graphene growth occurs predominantly during ramping up and annealing by carbon dissolution and diffusion through the catalyst, and again the contribution of carbon precipitation on subsequent cooling is minor.³
We combine these in-situ, synchrotron-based measurements with in-situ, atomic-scale, scanning tunnelling microscopy measurements of graphene growth,⁴ and the understanding of the growth kinetics we have previously developed⁵ to present a coherent model for graphene formation on metal catalysts with finite C solubility. We demonstrate that this model is an effective tool in optimising large-area graphene growth and can be used to rationally engineer improvements in the growth, such as catalyst alloying and controlled feeding of a solid carbon supply.^1,3
(1) Weatherup et al. Nano Lett. 2011, 11, 4154-4160
(2) Weatherup et al. ChemPhysChem 2012, 13, 2544-2549
(3) Weatherup et al. Nano Lett. 2013, 13, 4624-4631
(4) Patera et al. ACS Nano 2013, 7, 7901-7912
(5) Weatherup et al. ACS Nano 2012, 6, 9996-10003

The growth of 2D materials such as graphene and hexagonal boron nitride h-BN by chemical vapour deposition (CVD) has attracted a lot of research interest. However, the growth mechanisms of graphene and h-BN have so far been described by rather simplistic models of elemental solubility of the constituent elements (eg: C, B etc.) in metallic catalysts eg: Ni (high solubility - precipitation from bulk) and Cu (low solubility - surface reaction). These models are speculatively based on ex-situ experiments and critical in-situ experimental evidence remains elusive. [1,2]
Here, using a combination of high-pressure depth and time resolved in-situ X-ray photoelectron spectroscopy (XPS) at the BESSY II synchrotron in Berlin [1,2] and in-situ X-ray diffraction (XRD) at the ESRF synchrotron in Grenoble, [1,2] at industrially relevant CVD conditions, i.e. pressure (~0.001 - 0.5 mbar) and extreme temperatures (800-1000oC) we study the behaviour of polycrystalline transition metal catalyst films and foils during CVD.
These experiments allow us to observe elemental incorporation into the 2D structure on the catalyst surface as it happens by identifying the state of the catalyst and the elemental species at any point of time during CVD. The growth of the 2D nanostructures is found to be predominantly isothermal along with some precipitation on cooling for both Ni[3] and Cu[3], i.e. we observe catalyst behaviour during growth as a complex interplay of isothermal and precipitation based growth mechanisms with kinetic effects playing an important role.
We highlight the use of this approach as a generic framework to study the growth other 2D and 1D nanostructures during CVD.[4]
1. Kidambi et al. (manuscript in preparation)
2. Kidambi et al. Nano Letters 13 (10), 4769-4778 (2013).
3. Kidambi et al. J. Phys.Chem. C. 116, 42, 22492-22501 (2012).
4. Kidambi et al. PSS RRL. 5, 9, 341-343 (2011).

Semiconductor quality single-crystalline silicon grown by the Czochralski method contains some 10¹⁷ cm^-3 atoms of interstitial oxygen. Being in a supersaturated solid solution in the as-grown state, the oxygen forms clusters upon thermal treatment at temperatures exceeding 800 °C. Such precipitates have been investigated extensively with various methods because of their relevance for a proper functioning of integrated circuits by internal gettering. Due to their volume misfit with the host lattice the precipitates distort the otherwise highly perfect silicon matrix, and the resulting diffuse scattering signal in X-ray diffraction is the fingerprint of the size, the morphology and the density of the precipitates.
We have measured a set of six samples being annealed for different times to study the temporal evolution towards the final defect configuration. We recorded the diffuse X-ray scattering in the vicinity of the 400 Bragg peak as well as the static Debye-Waller factor being an extremely sensitive measure for the crystal perfection. The recently published dynamical theory of diffraction for imperfect crystals [1] allowed us to combine the two above mentioned methods. Fitting the rocking curves with this theory gives detailed insights into the precipitate radii, their concentrations, and the polydispersity of the precipitate radii including their temporal evolutions.
We identify two populations of defects differing in size and density by orders of magnitude. One population could be confirmed by complementary TEM measurements, while the other population is not accessible with any other method because of its low concentration. In addition, the rocking curves show clear evidence of a spread of radii within the populations. Such information is extracted for the first time from X-ray measurements.
As a particularly valuable aspect we mention that this highly quantitative approach is applicable in in-situ experiments as carried out by us at temperatures of up to 1165 °C with high-energetic synchrotron radiation. We measured the precipitation behavior of two silicon samples which showed a distinct response to a boron doping with concentrations of 10¹⁵ cm^-3 - 10¹⁹ cm^-3.
[1] Molodkin et al., Phys. Rev. B, Vol. 78, 22, 224109 (2008)

A novel method for producing powder metallurgy components through the process termed Hydrogen Sintering and Phase Transformations (HSPT) has demonstrated exceptional mechanical properties and shows promise for producing titanium components at dramatically reduced cost, compared to wrought processing. Hydrogen plays a crucial role in commercial production of titanium powders via the hydride-dehydride process, in thermo-hydrogen processing, and during vacuum sintering and hydrogen sintering of titanium alloys using Ti hydride powders. HSPT samples present a refined grain structure, compared to vacuum sintered PM or wrought materials, due to solid state phase transformations during cooling, but additionally appear to form nanoscale Ti3Al, generally referred to as α2, and/or nano-scale α grains, an aluminum rich phase in Ti-6Al-4V. While the literature reveals disparate views on the advantages and disadvantages of the α2 phase in titanium alloys, a dispersed nano-structured α2 has been sought and hypothesized to have the potential to increase strength. Due to the high diffusion rates of hydrogen in titanium, standard quench experiments coupled with conventional XRD experiments have significant limitations in terms of accuracy. The current work has, therefore, undertaken in situ studies of the (Ti-6Al-4V)-H system to determine phase equilibria as a function of temperature and atmospheric composition, as well as to study the kinetics of the phase transformations. The study utilized a modified tube furnace with mass flow control of the partial pressure of hydrogen, located within the beam path of the 11-ID-C beamline at the Advanced Photo Source, Argonne National Lab, using a high energy x-ray source (115 keV, wavelength = 0.1080 Å). Results of these experiments are evaluated in conjunction with TGA, high resolution SEM, TEM and EDS, and present evidence that may significantly change the phase diagram for this system, incorporating the α2 phase, as well as presenting an explanation for the improved tensile properties observed in HSPT samples.

Hydrogen is recognized as a potential and extremely interesting energy carrier system, but a remaining major challenge in a future ‘hydrogen economy&’ is the development of a safe and efficient means of hydrogen storage [1]. Here we report our recent research results within nano-confinement of different types of metal hydrides [2-6]. Furthermore, new series of rare earth metal borohydrides may have multi-functionality and both store significant amounts of hydrogen and simultaneously have magnetic, electronic and optical properties or may be new ion-conductors [1, 7-9]. The new metal borohydrides opens new ways for tailoring properties and possibly rational design of new materials.
New sample environments and techniques are developed for in situ synchrotron radiation powder X-ray diffraction of solid-gas reactions, which allow investigation of e.g. hydrogen release and uptake reactions [10]. In some cases new intermediates are discovered which may be solid-solutions or new compounds. Diffraction data measured at variable temperature provide a powerful approach and allows grouping diffraction peaks according to their behavior, that is, by peak intensity change or peak shift owing to decomposition, melting, or a chemical reaction in the sample. A group of reflections may be associated with a new compound and used for indexing and structure solution using Rietveld refinement. This approach may be denoted “decomposition aided indexing and structure solution" [11]. Our sample environment allow fast changes of pressure, e.g. 200 to 10-2 bar within ~10 s, and gas and can be operated in the temperature range RT to 700 C [10]. A new modification is pressure rated to 700 bar.
References:
[1] L. Rude, et al, Physica Status Solidi 2011, 208(8) 1754. [2] T. K. Nielsen, et al, Nanoscale, 2011, 3, 2086. [3] T. K. Nielsen, et al, ACS Nano, 2009, 3, 3521. [4] T. K. Nielsen, et al, ACS Nano, 2010, 4, 3903. [5] Nielsen, et al, ACS Nano, 2011, 5, 4056. [6] T. K. Nielsen, et al, Nanoscale, 2013, DOI: 10.1039/c3nr03538g. [7] M. B. Ley, et al. Chem. Mater. 2012, 24, 1654minus;1663. [8] J. E. Olsen, et al., RSC Advances, 2013, submitted. [9] S. Marks, et al. J. Am. Chem. Soc. 2012, 134, 16983-16986. [10] T. R. Jensen, et al, J. Appl. Cryst. 2010, 43(6), 1456-1463. [11] Dorthe B. Ravnsbaelig;k, et al, Angew. Chem. Int. Ed. 2012, 51, 3582 -3586.

The electronic behavior of any materials has a profound influence on its final functionalities. To study the same in real operating condition is very demanding in order to understand its properties in a careful way. The soft XAS provides a room to study it with the help of a specially built UHV compatible flow cell which is separated from the main ultra-high vacuum chamber by a thin silicon nitride window. The main focus of this project is the development of an in - situ flow electrochemical cell for studying the operando electronic structure of energy generating materials such as hematite. The cell developed allows better control of chamber pressure with a good signal to noise ratio for the detector. The stability of the sample window is far better in the current cell and it does not allow the window to break apart during experiment which lacked in the cell developed earlier. With the modified cell, electrochemical experiment such as cyclic volatmmetry has been performed for 10 cycles with a good stability of sample window. Besides these, we also carried out the X ray absorption spectroscopy on an Atomic layer deposited hematite by triggering the photoelectrochemical reaction in the electrochemical flow cell at O K edge and F e L edge. For it, we have run the electrochemical flow cell at a base pressure of 1x10e-8Torr in ISAAC end- station in beamline 6.3.2.1 at Advanced Light Source, LBNL. The experiment performed on n-type hematite reproduces two peaks obtained in an earlier experiment with atmospheric pressure chemical vapor deposited (APCVD) Si doped hematite sample during light on condition. During earlier study, the evolution of two holes was believed to be associated with both charge transfer and upper Hubbard band [1]. Here, we have also carried out the Fe L edge XAS investigation on n type hematite. The quantitative analysis of spectra by spectral intensity ratio of L3 and L2 peak reveals that the amount of d-orbital occupancy getting increase on increasing the applied voltage for light on condition. This means the higher ligand to metal charge transfer through bulk at higher overpotential.
Ref: [1] A. Braun et. al.,The Journal of Physical Chemistry C 116 (32), 16870-16875, 2012.

Lithium ion batteries using germanium as the anode material are drawing more attention recently due to their higher conductivity and lithium ion diffusivity relative to silicon. Despite recent studies on Ge electrode reactions, there is still limited understanding of the reaction mechanisms governing crystalline Ge and the transformations into intermediate amorphous phases that formed during the electrochemical charge and discharge process. In this work, we carry out in operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies on Ge anodes in carbonate-based electrolyte. These two probes track both crystalline (from XRD) and amorphous (from XAS) phase transitions with time, which allows detailed information on the Ge anode to be obtained. We find that crystalline Ge lithiates inhomogeneously, first forming amorphous Li9Ge4 clusters during the beginning stage of lithiation, followed by the conversion of the remaining crystalline Ge to amorphous Ge. The lithiation of amorphous Ge then forms amorphous clusters resembling LiGe. As lithiation proceeds, amorphous LiGe and Li9Ge4 clusters convert to amorphous Li7Ge2 clusters, which are then further lithiated to form crystalline Li15Ge4. During delithiation, crystalline Li15Ge4 transforms directly into amorphous Li7Ge2 clusters, which eventually form amorphous Ge, and interestingly, no amorphous Li9Ge4 clusters are detected. Both our in operando XRD and XAS results present new insights into the reaction mechanism of Ge as anodes in LIBs, and demonstrate the importance of correlating electrochemical results with in operando studies.

Carbon aerogels (CAs) are a class of nanostructured, porous materials that have demonstrated applications in electrical energy storage (EES) due to their very high surface area, chemical and electrochemical stability, and relatively low cost. Tailoring these materials towards improved ESS performance can be significantly enhanced by a better understanding of nanostructured materials in aqueous environments under various potential gradients; therefore, we have pursued advanced in situ characterization techniques capable of probing the electronic structure and bonding of these electrode materials during charge-discharge cycling. We report the successful development of a cell for in situ soft x-ray absorption spectroscopy (XAS) studies of EES materials and the application of this cell to the investigation of CA supercapacitors. Our XAS measurements, combined with complementary ab initio modeling, reveal profound changes in the structure and bonding of the CAs in operando, which will be discussed in terms of their macroscopic physical properties. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Grid-level energy storage demands low-cost, safe, reliable battery chemistry. One technology which satisfies these requirements is the Zn-MnO2 alkaline battery chemistry. This battery type has high energy density (comparable to that of a Li-ion battery), low cost per kilowatt-hour, and is relatively safe. However, their rechargeability is limited by phase transformations which occur in the MnO2 cathode during discharge by more than one electron, which transform it into an spinel phase which is generally considered to be electrochemically inert. As a result, depth of discharge is limited to no more than 10-20% of the cells capacity. We have studied this phase transformation and the failure modes of alkaline batteries using synchrotron-based energy dispersive X-ray diffraction (EDXRD) techniques. Using EDXRD, we directly observed the phase transformation occurring in the cathode in a commercial cell as function of rate and time in real time for a range of different discharge rates. We see that previous predictions of anodic passivation are supported. Our observations also suggest that the transformed material is not in fact electrochemically inert, and that the phase transformation which occurs in the cathode may be reversible. This suggests that Zn-MnO2 rechargeable batteries can possess sufficient energy density to enable economical grid-scale energy storage and potentially even power electric vehicles.

Due to the size- and shape-dependent properties, nanoparticles have been successfully used as functional building blocks to fabricate multi-dimensional (D) ordered assemblies for the development of ‘artificial solids&’ (e.g., metamaterials) with potential applications in nanoelectronic and optical devices. At ambient pressure, entropy driven self-assembly of monosized or binary nanoparticles generally results in polycrystalline 2- or 3D close-packed arrangements, and extensive efforts have been made to develop structural perfection of nanoparticle arrays or ‘single crystal-like&’ domain structures with precise long range order for their definite advantages for electron or energy transfer. To date, fabrications of ordered nanoparticle assemblies have been relied on specific interparticle chemical or physical interactions such as van der Waals interactions, dipole-dipole interaction, chemical reactions, and DNA-templating, etc. The consequent self-assembly scenario is the formation of higher dimensional nanoparticle architectures from single nanoparticles. Recently we have discovered a pressure-directed assembly (PDA) in which an external pressure has been utilized to engineer nanoparticle assembly and to fabricate new nanoparticle architectures without relying on specific nanoparticle interactions. The PDA process essentially allows precise and systematic tuning of interparticle separation distance, which with control of applied pressure can be manipulated reversibly at the angstrom level until the particles make contact and sintering occurs. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink, allowing fine-tuning of interparticle separation distance. Under a uniaxial pressure field, nanoparticles are forced to contact and coalesce, forming hierarchical nanostructures. Depending on the orientation of the initial nanoparticle arrays, 1-3D ordered nanostructures including nanorod, nanowire, and cubic network can be fabricated through this pressure induced assembly method. Moreover, we discovered for the first time a transition from an ordered polycrystalline nanoparticle mesophase to quasi-single crystalline nanoparticle lattices induced by PDA process. Exerting pressure-dependent control over the structure of nanoparticle arrays provides a unique and robust system to understand collective chemical and physical characteristics and to develop novel electronic and photonic behavior for energy transduction related applications.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

The term mesocrystal has been used to describe large, 3D particles which diffract as single crystals and yet exhibit internal structures comprising oriented nanoparticles. Evidence for mesocrystal structures is therefore based on structural analysis of crystalline particles by techniques including scanning electron microscopy (SEM), surface area analysis (BET), and transmission electron microscopy (TEM) of thin sections. Here, we use calcium carbonate as a model system to evaluate the effectiveness of these techniques for identifying a nanoparticulate sub-structure. Indeed, although it is now common-place to assign mesocrystal structures based on broadening of XRD peaks and apparent nanoparticulate surface structures, we demonstrate that both of these approaches have to be treated with care. Therefore, high resolution synchrotron XRD analysis demonstrates that line broadening often arises from lattice strain rather than a subunit structure. Finally, electron backscattered X-ray diffraction (EBSD) is used to provide a direct structural comparison of biogenic calcite mesocrystals with their synthetic counterparts.

Self-assembly of nanoparticles into ordered structures is a promising strategy for production and design of nanostructured materials with novel properties. While the assembly of spheres into dense-packed structures is well-established, the assembly of non-spherical, polyhedral nanoparticles is now attracting an increased interest due to the possibility to tune the electronic, optical and magnetic properties by controlling not only the size and shape of the nanosized building blocks, but also utilize the rich structural diversity of the self-assembled arrays that are formed.
We have previously demonstrated how it is possible to assemble iron oxide nanocrystals into ordered arrays or superlattices with both translational and orientational order (mesocrystals) through evaporation-induced self-assembly [1-3]. Here, we will present recent work on the structural diversity and the formation kinetics of highly ordered mesocrystals of superparamagnetic, monodisperse iron oxide nanocubes of different sizes using a combination of time-resolved grazing incidence small angle X-ray scattering (GISAXS), Quartz crystal microbalance with dissipation (QCM-D), video microscopy together with scanning and transmission electron microscopy. The influence of the evaporation rate and the application of external magnetic fields on the crystallographic texture will be discussed and related to recent modeling studies which showed that the degree of truncation and the particle interactions have a pivotal influence on the structures of the self-assembled arrays [4]. The time-resolved investigation show that ordered arrays can form both under convection-controlled and diffusion-controlled conditions and will discuss how growth rates can be extracted from the time-resolved data.
References:
[1] S. Disch, E. Wetterskog, R. P. Hermann, G. Salazar-Alvarez, P. Busch, T. Brückel, L. Bergström, S. Kamali, Nano Letters, (2011), 11, 1651
[2] A. Ahniyaz, Y. Sakamoto, Y. L. Bergström, L. Proc. Natl. Acad. Sci., (2007) 104, 17570
[3] S. Disch et al, Nanoscale, (2013), 5, 3969
[4] N. Volkov, A. Lyubartsev, L. Bergström, Nanoscale, (2012), 4, 4765

A mussel-inspired synthesis method for making iron(III) oxide nanoparticles was developed and the kinetics of nanocrystal formation was studied using in situ X-ray diffraction (XRD).
The magnetic properties of nanoparticles, such as magnetite or maghemite, depend strongly on their size, a feature used in the design of superparamagnetic nanoparticles for magnetic resonance imaging contrast agents. In order to gain control of the nanoparticle size it is important to understand how the particles nucleate and grow, in other words to understand the crystallization kinetics. This can be achieved using e.g. in situ XRD. Magnetite was recently found to form via particle aggregation in solution without the initial formation of an intermediate amorphous phase (1).
Nanoparticle growth can be controlled by additives (2,3). The blue mussel utilizes the catechol containing amino acid DOPA to adhere to inorganic surfaces. The adhesion is facilitated by coordination bonds between metal ions and the catechol. The very strong Fe(III) catechol bond makes the catechol a good candidate for controlling the formation of iron oxide nanoparticles. In this study dopamine and hydrocaffeic acid were used as additives. Thereby nanoparticles decorated with dopamine or hydrocaffeic acid should result.
An Fe(II)/Fe(III) solution containing the organic additive was added dropwise to a warm basic solution, inspired by Larsen et al. (4). In situ XRD studies were performed at MAXLAB using a CCD detector and a custom flow cell with very high temperature stability (3). The flow prevents sedimentation during the reaction.
Rietveld refinement of ex situ XRD data showed that the syntheses result in a sub-stoichiometric maghemite phase, Fe_2-xO_3-1.5x indicating that the added Fe(II) is oxidized during the reaction. The lack of Fe(II) was confirmed by Mössbauer spectroscopy. In situ XRD showed that nucleation happens almost instantaneously upon addition of the iron-containing solution. The crystalline phase co-exists with an amorphous phase that most likely is a highly disordered ferrihydrite. The ratio between the amorphous and crystalline phase is dependent on the additive. For hydrocaffeic acid, the amorphous phase transforms into the crystalline phase, but for dopamine there is a rearrangement of the ferrihydrite phase seen as changes in d-spacing of the broad amorphous peak.
The in situ results shed light on the mechanism of particle formation which is useful for the future development of improved synthesis procedures.
References:
1 J. Baumgartner et al; Nature Materials, 12, 2013, 310-314
2 C. J. S. Ibsen and H. Birkedal; Nanoscale, 2, 2010, 2478-2486
3 C. J. S. Ibsen and H. Birkedal; J. Appl. Cryst, 45, 2012, 976-981
4 E. K. U. Larsen et al; ACS Nano, 3, 2009, 1947-1951

The accurate elucidation of the often complex structure-property relationships in functional nanoporous materials, such as metal-organic frameworks (MOFs), presents a crucial step in their advancement toward industrially important energy applications. This requires the development of in situ structural techniques, such as synchrotron-based X-ray scattering, to precisely monitor the structural response of materials under the conditions (e.g., industrially relevant temperatures, pressures, and chemical environments) in which they perform their targeted functions. Here, we will present in situ structural studies carried out at the at the Advanced Photon Source (Argonne National Laboratory) on a novel nanoporous MOF system exhibiting a crystalline-amorphous phase transition upon activation.

The broad coverage of the synchrotron radiation source, reaching into the infrared and THz spectral regions, has become increasingly important for the study of novel materials, including materials with sub-micron length scales such as graphene. Like most optical techniques, infrared spectroscopic methods are typically non-contacting and allow the sample material to be situated in a variety of complex and extreme field, pressure and temperature environments. Microspectroscopy techniques allow small areas to be probed while in situ electrical connections enable photoresponse studies, potentially on a 10s of picoseconds time scale. This presentation will describe the various existing infrared synchrotron methods and the capabilities under development for the new NSLS-II facility at Brookhaven.
This work supported by the U.S. Department of Energy under contract DE-AC02-98CH10886 at Brookhaven National Laboratory

The large penetration depth of a hard X-ray probe is interesting in a broad range of applications in materials science research because of its bulk sensitivity and the compatibility with in-situ conditions. Most hard X-ray techniques, however, address the atomic structure while analysis of the electronic configuration is hampered by the large spectral broadening and only few tools for theoretical analysis are available. The presentation will discuss the information that can be obtained on the electronic structure using resonant hard X-ray emission spectroscopy. The various techniques including magnetic circular dichroism will be briefly introduced and recent results on Pt, CeO2 and Fe3O4 nanoparticles will be presented.
The full information content in inner-shell spectra can only be accessed by theoretical modeling of the data. We used density functional theory (FEFF, ORCA, Wien2k) codes and ligand field multiplet theory to simulate the experimental data. We find that many spectra can be modeled using a surprisingly simple approach. This allows for a detailed analysis of the electronic structure. The limitations of this approach are discussed.

This paper focused on size/composition/shape/structure and function relationship in C-H bond activation using noble, transition metal and doped oxides. Our experimental studies are based on 1) fabrication of technologically relevant supports, 2) physical size- and composition selected cluster deposition with atomic precision control, 3) ex situ and in situ microscopies and 4) in situ synchrotron X-ray characterization of cluster size/shape and oxidation state under realistic working conditions, combined with mass spectroscopy analysis of the reaction products. The experimental studies are complemented with DFT calculations. Using model size-selected clusters and cluster synthesized by wet chemical routes, this contribution will outline the applicability of the outlined approach on example of selective C-H bond activation in the oxidative and non-oxidative dehydrogenation of cyclohexane and cyclohexene on subnanometer cobalt oxide clusters, cluster-based assemblies, and nanometer size Co3O4 and (Au)Co3O4 particles under both oxidative and non-oxidative conditions.
References
1. “Oxidative Dehydrogenation of Cyclohexane on Cobalt Oxide (Co3O4) Nanoparticles: The Effect of Particle Size on Activity and Selectivity”, by E. C. Tyo, C. Yin, M. Di Vece, Q. Qian, S. Lee, B. Lee, S. Seifert, R. E. Winans, R. Si, B. Ricks, S. Goergen, M. Rutter, B. Zugic, M. Flytzani-Stephanopoulos, Z. Wang, R. E. Palmer, M. Neurock, and S. Vajda, ACS Catal. 2, p. 2409minus;2423 (2012)
2. “Support-Dependent Performance of Size-Selected Subnanometer Cobalt Cluster-Based Catalysts in the Dehydrogenation of Cyclohexene", S. Lee, M. Di Vece, B. Lee, S. Seifert, R. E. Winans and S. Vajda, Chem. Cat. Chem. 4, p. 1632-1637 (2012)
3. “Oxidative Dehydrogenation of Cyclohexene on Size Selected Subnanometer Cobalt Clusters: Improved Catalytic Performance via Evolution of Cluster-Assembled Nanostructures", S. Lee, M. Di Vece, B. Lee, S. Seifert, R. E. Winans and S. Vajda, Phys. Chem. Chem. Phys., 14, p. 9336 - 9342 (2012)
4. “Subnanometre Platinum Clusters as Highly Active and Selective Catalysts for the Oxidative Dehydrogenation of Propane”, S. Vajda, M. J. Pellin, J. P. Greeley, C. L. Marshall, L. A. Curtiss, G. A. Ballentine, J. W. Elam, S. Catillon-Mucherie, P. C. Redfern, F. Mehmood and P. Zapol, Nat. Mater. 8, 213-216 (2009)
5. “Improved Oxidative Dehydrogenation of Cyclohexane via Decoration of Cobalt Oxide (Co3O4) Nanoparticles with Gold Clusters”, E Tyo, M. DiVece, S. Lee, Z. Wang, R. Palmer, Q. Qian, M. Neurock, S, Vajda et al., in preparation

Information from traditional ex situ characterization techniques falls short in accurately describing complex materials systems, such as solid oxide fuel cells, which require specific conditions for optimal operation. Operando x-ray absorption spectroscopy (XAS) fills the gap by providing element-specific information on the chemical phenomena responsible for performance deficiencies. A La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) thin film quasi-symmetrical cathode cell was tested in air contaminated with H2O and CO2 at 400 and 700°C and simultaneously examined with glancing angle operando XAS using a custom built testing platform, which is also described. Whereas impedance spectroscopy indicates increased polarization resistance in the cathode in both atmospheres at 750°C, XAS near-edge and extended fine structure data indicated that the oxidative behavior of H2O and CO2 on Fe and Co cations have diverging behaviors with increasing temperatures. In particular, the degree of oxidation according to absorption edge shift varies with temperature and cation and comparison with the impedance data showed some correlation between the degree of oxidation and amount of increase in the polarization resistance as a function of temperature. The local atomistic structure of the Co was also observed to be more severely affected by H2O and CO2 than that of the Fe, which showed stability in its local structure under all of the testing conditions.
Synchrotron-based in situ x-ray photoelectron spectroscopy was performed to complement the study with surface-specific information. Spectroscopy at high temperature and post-gas exposure discovered the removal and formation of a carbonate species, the irreversible formation of a new Co phase, and the related evolution of different oxygen moieties, such as surface, lattice, and hydroxide oxygen, all as a function of temperature and atmosphere. The combined information suggests that the segregation of the Co cation from the perovskite phase into an oxide phase via the formation and subsequent decomposition of a carbonate phase at operating temperature is strongly suspected as a mechanism by which H2O and CO2 cause degradation in the LSCF cathode.
Additionally, a comparison of the results from operando and in situ testing revealed that cathodic bias has some interaction with the CO2 gas. While cathodic bias caused a slight reduction of Fe and Co and CO2 gas caused an oxidation of Fe and Co, the combination of those parameters in the operando experiment caused more severe oxidation of both Fe and Co. In conclusion, the operando results cannot be predicted by their in situ components, strengthening the rationale for conducting operando experiments, despite their challenges.

Most of the electrochemistry processes occur within the thin layer of electrolyte at the electrolyte / electrode interfaces, commonly denoted as the electrical double layer (EDL). In spite of some classic EDL theories, very limited experimental information is available about these solvent or solute species within such EDLs. We have developed in-situ liquid cells to study such electrolyte / electrode interfaces by means of soft x-ray absorption spectroscopy. Because the fluorescence x-ray photon has much larger mean free path in condensed matters than the secondary electrons, by comparing the total fluorescence yield (TFY) and total electron yield (TEY) spectra, we can extract useful information about the compositional, structural or chemical difference between the bulk and the interfacial electrolyte. Under different bias, by using a mechanical chopper system to modulate the incident x-ray, the TEY current becomes alternating. This allows us to separate the tiny AC TEY current from the dominant faradaic current so that we can obtain surface-sensitive TEY signal under electrochemical conditions.
With this in-situ and operando XAS technique, we characterized the interfacial water at the gold electrode surfaces. It was found that the interfacial water layer has significantly different hydrogen-bonding network structure compared to the bulk water. Under different bias, the polar water molecules will respond to the external electrical field and reorient at the gold electrode surface, which significantly changes the amount of distorted or broken hydrogen bonds. Copper under-potential deposition (UPD) on gold electrode was also studied to demonstrate the surface-sensitivity of such XAS technique.

[1]. J. J. Velasco-Velez, C. H. Wu, M. B. Salmeron, in preparation.

The extraordinary mechanical, thermal, electronic and optical properties of carbon nanotubes (CNTs) have garnered considerable interest in a wide range of academic fields. CNTs are attractive candidates as fillers in composite materials, considerably improving the properties of the host. Recently, vast research has been undertaken to investigate the active properties of some polymer-CNT composites, with potential applications ranging from Micro-opto-electro-mechanical systems (MOEMS) to neuroscience. The development of this field is hindered, however, as the mechanics of actuation at the molecular level in these composites is still not well understood and a unified model explaining this behaviour is missing. Consequently, there is no method to predict whether specific materials exhibit this “smart behaviour”.
Near edge X-ray absorption fine structure (NEXAFS) spectroscopy is a valuable synchrotron technique for the study of nanocomposites, offering a wealth of information about local chemistry of the system, all with excellent energy resolution. Additionally, the use of a highly polarized beam allows for assessment of conformational arrangement of soft matter, which is of critical importance when the system is governed by non-covalent interactions.
In this study, films of thermally active EVA|MWCNT composites are studied through in-situ NEXAFS spectroscopy in an attempt to correlate spectral progression of the system with macroscopic observations of mechanical actuation. The effects of straining to promote CNT alignment and the role of dispersants are also addressed. Systematic variations in NEXAFS spectra with increasing temperature identify emissions from specific chemical groups as possible actors in the actuation mechanism, and suggest a high degree of conformational effects. An actuation model based on molecular orientation is later proposed which supports our findings. These are the initial steps towards forming a systematic database aiming at active behaviour prediction of polymer nanocomposites, and the production of materials by design.

X-ray Absorption Spectroscopy (XAS) is one of the core competencies of synchrotron science. With sensitivity both to chemical state and to the local configurational environment, the unique view of matter offered by XAS has become an indispensable tool for a broad range of scientific disciplines. With the advent of high-flux, third-generation synchrotron sources, new experiments probing the structure of inner shell electrons are now possible. In this talk, I will discuss recent developments in crystal-based spectrometry. Among the new capabilities are XAS with energy below the level of the core-hole lifetime, X-ray emission spectroscopy providing a complementary view of electromic and chemical state, X-ray Raman spectroscopy which allows access to low energy absorption edges and dipole forbidden transitions, and XAS measured at ultra-low absorber concentration. Special emphasis will be placed on instrumentation under development for beamlines at NSLS-II.

We will present our development of an experimental system that allows us to explicitly correlate the results of x-ray absorption spectroscopy (XANES and EXAFS) and atmospheric-pressure transmission electron microscopy (AP-TEM), through the use of operando methods. We have demonstrated that it is possible to utilize the microfabricated 'closed cell' systems that are increasingly used in liquid-cell TEM experimentation to conduct atmospheric pressure catalysis experiments in both XAS beamlines and within the TEM. By delivering equivalent gas streams and measuring reaction products directly, we can confirm that the measurements made with each approach are being made from the exact same catalytic system in the exact same working condition. Critically, we demonstrate that the small sample requirements necessitated by TEM do not preclude high quality measurements using XANES and EXAFS approaches. The resulting experimental approach not only overcomes the ‘materials gap&’ and ‘pressure gap&’ that exists between studies of planar, model catalysts in ultrahigh vacuum and how they perform in real working environments, but also the ‘complexity gap&’ that results from the inability of global-average techniques to properly describe the existence and effects of sample heterogeneity. We will present our data on the exploitation of this approach towards understanding how heterogeneity in particle size distributions affect our understanding of the catalytic mechanisms through the use of size-selected Pt nanoclusters on SiO2 supports, with a focus on ethylene dehydrogenation. Finally, we will show how this initial demonstration of correlative photon/electron experiments can be expanded to other areas, including x-ray diffraction, Raman spectroscopy and Fourier Transform Infrared Spectroscopy, giving a holistic experimental approach to understanding the function of both catalyst and support during reaction.

Nanocatalyst plays important roles in various gas phase reaction. One example is the reduction of CO2 by H2, one of the promising approaches to recycle the green house gas and generate hydrocarbon fuels. However, the selectivity of the reduction reaction remains a great challenge. To better understand the reaction mechanism and guide the nanocatalyst design, it is of great importance to characterize such nanocatalyst in-situ under realistic working conditions. For this purpose, we have developed a high pressure gas cell for in-situ soft x-ray absorption spectroscopy (XAS) study of nanocatalyst. The gas cell is consisted of a small reaction chamber, a gas delivery system and a laser heating system. A 100nm Si3N4 membrane at the front end of the reaction chamber separates reaction chamber at ~1bar with the UHV soft x-ray chamber. The heating of the sample (up to 400C) is realized by using an infrared laser, which avoids the electrical noise commonly induced by traditional resistive heating. With this gas cell, a variety of nanocatalyst with different size, shape and composition can be deposited on gold foils, loaded in the reaction chamber, and characterized by in-situ XAS.
To demonstrate the capability of this high-pressure gas cell, NiCo core/shell nanoparticles was studied in-situ under different gas mixtures and at different temperatures. In order to remove the surfactant on the nanoparticles surfaces, multiple oxidation/reduction cycles were performed before exposing to CO2/H2 mixture. By monitoring the L-edge TEY spectra of Co or Ni, we were able to follow the oxidation states evolution. It was found that after cleaning cycles, Ni moves outwards to the surface, evidenced by increasing spectra intensity at the Ni L-edge. Such compositional change on the nanoparticle surface is expected to affect the catalyst activity and/or selectivity. Further characterization under CO2/H2 mixture is currently underway. With soft x-ray absorption spectroscopy, we were not only able to track the oxidation states evolution of the metals under reaction conditions, but also monitor the absorption/desorption of CO2 on the nanoparticle surfaces, by collecting K-edge TEY spectra of C or O.

We prepared size-controlled Co nanoparticles in the 2-11 nm size range by using colloidal chemistry and supported them in porous metal oxides with the general formula MO2 (M=Ti, Zr, Ce and Mn). We screened the Co/MO2 catalyst for the catalytic CO2/H2 reaction, and demonstrated that the turnover rates increased up to 15 fold and the hydrogen insertion to CO/CO2 improved dramatically compared to the Co/SiO2 reference catalysts. The Co/TiO2 catalysts produced formaldehyde at significant yields; the Co/CeO2 catalysts exclusively led to the formation of methane (i.e. complete hydrogenation); and the Co/MnO2 catalysts showed enhanced selectivity for the methanol production. Furthermore, we evaluated the chemical and bonding structures of the Co/MO2 catalysts by using several in situ techniques: Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS), Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS). We found that all the MO2 are partially reduced in H2 atmospheres in the presence of Co nanoparticles. We also found a strong correlation between the oxidation states of the metals (Co and M) and the catalytic enhancement obtained during the hydrogenation of CO2.

Supported platinum particles in zeolite X are used as bifunctional catalysts for disproportionation, dehydrogenation, cracking, and aromatization reactions. Some of these reactions are structure sensitive and require small Pt particle sizes. In this study we used in situ high energy synchrotron X-ray diffraction to study the Pt particle growth under reduction conditions using time resolved pair distribution function (PDF). Because these particles grow inside the pores of zeolite X, PDF is able to give insight to unique information at the short and medium interatomic distance range that cannot be readily obtained with other techniques. Among the information obtained are the evolvement of the Pt particle sizes, which were corroborated with TEM, average Pt-Pt distances and the identification of growth steps.

Coupling of the nano-structural properties of materials with their targeted arrangement at mesoscale is at the heart of next-generation technologies in sustainable energy, environmental remediation and health. Understanding how the nanostructured materials evolve and interact inside real operating devices is essential to optimize performance. Of the various techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering and idealized samples of isolated components, not as they function in operating devices. Here we describe a method that combines X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and their structure spatially mapped with micron-scale resolution. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous Pd catalyst system, which clearly revealed a non-uniform distribution of Pd particles, with larger particles on the surface and smaller ones on the inside of the device. The method will have impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health.

Recent advances in the engineering of in situ cells and their combination with conventional and new spectroscopic, microscopic and scattering techniques at synchrotron radiation sources have enabled new insight into the preparation of nanomaterials and the understanding of their function. Here, focus is laid on materials applied in catalysis and chemical sensing.
In the first part of the talk the use of in situ X-ray absorption spectroscopy and X-ray diffraction for the preparation of nanomaterials, e.g. by hydrothermal and solvothermal synthesis is discussed. Recently, the use of time-resolved EXAFS turned out to be very powerful to improve the data quality and to trace the kinetics in a better way.
Next the design of in situ cells for obtaining structure-activity relationships for nanomaterials applied in catalysis and chemical sensing are presented. The spectroscopic setup should resemble as closely as possible the catalytic and sensor experiment. For each study both the spectroscopic side and the engineering solution should be optimized to finally find the best compromise. The potential is demonstrated with recent results that give a better understanding into structural transformations of catalysts used in energy-related processes and sensors.
Finally, newer trends will be tackled, such as time-resolved studies, new photon-in/photon-out techniques (e.g. XES, RIXS, HERFD-XAS) and spatially resolved studies including new opportunities using hard X-ray microscopy. For the latter techniques especially the availablility of new high brilliant and high intensity synchrotron radiation sources are required, but combination of structure and function still need the availability of well performing “working horse” beamlines. They also allow to combining several characterization techniques at the same time.
[1] J.-D. Grunwaldt, M. Rohr, M. Ramin, A. Michailovski, G.R. Patzke, A. Baiker, Rev. Sci. Instr. 76, 054104 (2005).
[2] I. Olliges-Stadler, J. Stötzel, D. Koziej, M.D. Rossell, J.-D. Grunwaldt, M. Nachtegaal, R. Frahm, M. Niederberger, Chem. Eur. J. 18, 2305 (2012)
[3] J.-D. Grunwaldt, M. Caravati, S. Hannemann, A.Baiker, Phys. Chem. Chem. Phys. 6, 3037 (2004).
[4] F. Studt, F. Abild-Pedersen, Q. Wu, A.D. Jensen, B. Temel, J.-D. Grunwaldt, J.K. Norskov, J. Catal. 293, 51 (2012).
[5] M. Huebner, D. Koziej, M. Bauer, N. Barsan, K. Kvashninad, M.D. Rossell, U. Weimar, J.-D. Grunwaldt, Angew. Chem. 50, 2841 (2011).
[6] J.-D. Grunwaldt, J.B. Wagner, R.E. Dunin-Borkowski, ChemCatChem 5, 62 (2013).

Reforming of methane is one of the most important industrial reactions, partially due to the huge reserves of natural gas. Ni-based catalysts are the best catalytic systems for this hydrocarbon reforming reactions, and in particular for the steam reforming of methane (SRM) [1]. Beside this reaction, the dry reforming of methane (DRM), using carbon dioxide as oxidant, has been lately extensively studied as an alternative [2]. There is also a great potential in the application of DRM in environmental areas, such as the elimination of CO2 emissions.
However, these Ni-based materials are very sensible to the coke deposition, hindering their use as a long term catalyst. Several papers have stated that the dispersion, morphology and interaction of the nickel metallic phase with the support or other metals as cobalt, strongly determine the catalytic performances of these catalysts [3].
We have prepared several Ni-Co/ZrO2 samples. They were characterized by XRD, TPR, SEM, in situ XAS, and catalytic activity. The X-ray absorption spectra (XAS) were recorded in situ at the BM25 beam line (SPLINE) of the ESRF synchrotron in transmission mode. Spectra were collected at different temperatures during treatments of the samples. Once extracted from the XAS spectra, the EXAFS oscillations were Fourier transformed in the range 2-11.0 Åminus;1. Spectra were analyzed using the software package IFEFFIT. The theoretical paths for Ni-Ni and Ni-O species used for fitting the first coordination shell of the experimental data were generated using the ARTEMIS program and the FEFF 7.0 program. The coordination number, interatomic distance, Debye-Waller factor and inner potential correction were used as variable parameters for the fitting procedures.
Results/Discussion
The XANES region were obtained from the in situ XAS spectra accomplished for the monometallic Ni/ZrO2 and bimetallic Ni-Co/ZrO2 catalysts at the Ni K-edge. In both systems nickel is reduced after hydrogen treatment at 750C and contacting with the DRM mixture at RT. While nickel in the bimetallic system remains reduced by treatment with the CO2/CH4 reaction mixture at any temperature up to 750C, the metal in monometallic catalysts is partially oxidized in DRM reaction conditions at 600C, being completely reduced at 750C. This oxidation process is evident at RT after the DRM reaction. So, the bimetallic systems are resistant to oxidation by CO2, showing a synergic effect between nickel and cobalt. Considering the results obtained by XRD and TPR, the formation of Ni-Co bimetallic particles seems to protect each other from the surface oxidation of particles, which appears as a main factor affecting the catalytic performance, activity and selectivity, better in the case of the bimetallic catalyst.
References.
1. J.N. Armor, Appl. Catal. A 176 (1999) 159.
2. D. Lee, P. Hacarlioglu, S.T. Oyama, Top. Catal. 29 (2004) 45.
3.- V.M. Gonzalez-DelaCruz, J.P. Holgado, R. Pereñiguez, A. Caballero, J. Catal. 257 (2008) 307

We will present results from in situ synchrotron X-ray diffraction experiments coupled to atomic pair distribution function analysis aimed at determining the effect of reactive gas atmosphere on the atomic-scale structure of metallic particles less than 10 nm in size [1,2]. We will show evidence that metallic nanoparticles, single and multicomponent, expand and contract radially when thermally treated in oxidizing (O2) and reducing (H2) atmospheres, respectively. The contraction/expansion is reproducible and reversible following changes in the reactive gas atmosphere. It affects mostly the top 3-4 surface layers of the nanoparticles and may lead to changes in the interatomic distances of the order of several tenths of Angstroems. The implications of this effect to the physico-chemical properties of metallic nanoparticles, in particular catalytic ones, will be discussed as well.
[1] V. Petkov et al., Phys. Rev. Lett. 109 (2012) 125504.
[2] V. Petkov et al., Nanoscale 5 (2013) 7379.

The overall focus of this work is to understand the nature of the nano-catalysts and the mechanisms for catalytic transformation of biomass derived molecules. New catalysts are being designed and synthesized which are stable and selective under some of the unusual conditions found in biomass conversion. Small angle X-ray scattering (SAXS) techniques are being used to characterize the new catalysts, follow in situ reactions being used in the synthesis and in situ studies of fate of catalysis under reaction conditions. SAXS provides size, shape and distribution of nanoparticles and in addition, porosity and surface properties of the supports. New catalysis such as those which can form in nano-cavities, be stabilized by over-coating or use natural protein assemblies to prepare nanoparticles are being studied.

The manufacture of Portland cement is energy intensive and releases carbon dioxide, ~800-900 kg CO2 per tonne of clinker. Process efficiencies cannot be much improved without entailing excessive expenditure on plant. An alternative solution is to use different type of cements; calcium sulfoaluminate (CSA) cements are being developed using a novel thermal cycle having as its objective lowering specific emissions by ~50% relative to the Portland benchmark.
However, proving the performance of novel cements is a potential problem. “Performance” is difficult to define because concrete, the product whose performance depends on the resistance of the cement to environmental conditions, experiences a wide range of in-service conditions. Important attributes of performance include the intrinsic resistance of the solid matrix to penetration of aggressive agents and the consequences of penetration. The least permeable materials may not be the most desirable because other qualities are strongly influenced by pores and pore size distributions and pore interconnectivity, e.g., thermal conductivity.
Porosity and permeability measurements help define the engineering properties but their measurements are influenced by the choice of experimental protocols. In the present study we use Portland cement at different water/ cement ratios as benchmarks but define conditions to enable comparison to be made with CSA cement matrices at equal degrees of maturation: typically, CSA cements require more water for complete hydration than does Portland cement.
Our paper reports on the use of synchrotron-sourced radiation for in-situ micro-CT (Computerized Tomography) and 3D image re-construction of the internal microstructure of OPC and CSA cement pastes. Analytical models of ionic moisture transport, thermal conductivity and mechanical strength that are being developed to simulate the performance of these complex materials, based on the insights of microstructure that have been gained, are briefly outlined. The results of simulation are compared against porosity and permeability measurements, traditionally obtained using Mercury Intrusion Porosimetry (MIP), guarded hot plate thermal conductivity measurements and laboratory crushing strength measurements.
It is anticipated that CSA cements will have good resistance to sulfate attack whereas Portland cements, even sulfate resistant types, have variable and often poor resistance. Failure typically occurs with swelling and cracking. Our long-term objective is to develop a robust theoretical model of sulfate attack in cement and to calibrate and validate the model using empirical data from trials. However reactions with aggressive solutions are typically slow and it will be 12 to 18 months before first results of exposure trials, now in progress and based on exposure to sodium sulfate solutions, can be reported. However the principles underlying optimization of sulfate resistance are discussed.

Standard methodology in the research of solder compounds consists of thermally annealing multiple samples for varied lengths of time, then cross-sectioning them prior to analysis. This allows for the analysis of intermetallic compound growth and fault formation on the macro to micro scale from different samples at discreet time intervals. Due to the destructive nature of cross-sectioning the samples it is impossible to study the evolution of intermetallic compounds and faults at the nanoscale/single grain or void level. Presented here is work demonstrating in-situ x-ray full field imaging and nano-fluoresence microscopy of lead free solder junctions during annealing. The combination of full field imaging and fluorescence microscopy allows for real time imaging of evolving nanoscale three-dimensional structures and unambiguous elemental localization.
The dynamics of the formation of individual intermetallic compound and fault domains is a difficult problem to study as it takes place embedded in a three dimensional solid. We have shown it is possible, using x-ray full field imaging, to directly image the formation of singular intermetallic compound domains in near real time. Using x-ray fluorescence microscopy we can further differentiate intermetallic compounds, look for surface wetting, and examine the role and localization of the trace silver in the SAC305 lead free solder formulation.
Studying the dynamics of intermetallic and fault growth is key to developing strategies to minimize or eliminate fault formation in lead free solders. X-rays are an excellent in-situ probe and advances in light sources and optics have made it increasingly easier access the required length and time scales for imaging these dynamics. However, the problem is still difficult due to the three dimensional nature, relevant length scales, and thermal instability in instrumentation due to sample heating, beam stability, and flux required. The interplay of these difficulties with the imaging of solder dynamics is discussed as future instrumentation development for in-situ nanoscale synchrotron research will have to be designed with these problems in mind.
Work at the Advanced Photon Source and the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract DE-AC02-06CH11357.

In recent years, low-dimensional materials attracted enormous attention due to size effects originating from their spatial confinement. These size effects influence the chemical and physical properties (such as the electronic transport and the mechanical behavior) of the nanostructures. For instance, nanoscale objects may show ultra-high strengths reaching the theoretical limit of the material. However, the elastic and plastic behaviors of low-dimensional materials are not fully understood yet. In-situ mechanical testing studies on individual nanostructures may shed additional light improving the understanding of the mechanics in low-dimensional materials. For this purpose, we developed an atomic force microscope (AFM) which can be installed at synchrotron beamlines to combine AFM imaging and mechanical testing with X-ray diffraction techniques.
This new tool is an improved version of the device developed at the ESRF in Grenoble [1, 2]. It allows for in-situ AFM imaging combined with scanning X-ray diffraction mapping and fluorescence mapping. Therefore, the sample topography, the crystallinity, and the elemental distribution can be accessed simultaneously with a spatial resolution defined by the beam size (presently few hundred nanometers at the ID01 beamline). Moreover, a well-defined force can be applied on a selected nano-object and the deformation of the atomic lattice is examined by nanofocused X-ray diffraction (coherent XRD and µLaue diffraction) giving access to the mechanical behavior of low-dimensional materials. The capabilities of this new instrument for imaging the sample topography and acquiring diffraction and fluorescence information with high spatial resolution simultaneously as well as its performance for in-situ mechanical tests on low-dimensional materials will be demonstrated on few recent examples (Cu nanowires and Au islands).
This work has been funded by ANR within the framework of the MECANIX project (ANR-11-BS10-01401).
[1] T. Scheler, M. Rodrigues, T.W. Cornelius, C. Mocuta, A. Malachias, R. Magalhatilde;es-Paniago, F. Comin, J. Chevrier, T.H. Metzger, Appl. Phys. Lett. 94 (2009) 023109
[2] M.S. Rodrigues, T.W. Cornelius, T. Scheler, C. Mocuta, A. Malachias, R. Magalhatilde;es-Paniago, O. Dhez, F. Comin, T.H. Metzger, J. Chevrier, J. Appl. Phys. 106 (2009) 103525

Many metallic nanostructured multilayered films (NMFs) exhibited improved strengthening, ductility and supermodulus effect due to their large portion of interfaces compared to their corresponding bulk ones. In the past decade, the micromechanical behaviors of free-standing multilayers and multilayers with substrates have been investigated both experimentally and theoretically. The results presented a strong relation between the exhibited micromechanical behaviors and the complicated interface structures, where interface stress may arise from either the contribution of chemical mixing, or the strongly sheared sublayers with different moduli. Understanding how the interface stress evolves during the tensile deformation and how it connects to the materials failure are necessary for the successful development of advanced NMFs. To date, most work on the interface stress study has been done through molecular dynamics simulation and experimental work was very limited. Synchrotron X-ray diffraction is a powerful tool for stress analysis due to its high beam flux and low emittance compared to the lab XRD. Elastic strain with high strain sensitivity through the changes of hkl interplanar spacings can be analyzed from the diffraction peaks, which bring a breakthrough in stress analysis, particularly for the NMFs. In this paper, Cu/Ag NMFs with two interface ratios (Cu/Ag/Cu/Ag/Cu (s-Cu) and Ag/Cu/Ag/Cu/Ag (s-Ag) ) were investigated by synchrotron X-ray diffraction during the tensile deformations to study the interface stress. The lattice strains of the samples were carefully traced and analyzed for interpreting the deformation behaviors. The preliminary results showed that the stress partition, which was usually observed in the dual or multiple phase bulk materials, was first observed here in the two-constituent phase NMFs. The micromechanical behavior of these two Cu/Ag nanostructured multilayers presented a similar three stage deformation like in the bulk materials: elastic regime, elasto-plastic regime, and stable plastic regime. However, the NMFs also exhibited a significant layer-to-layer interaction. This interface stresses were calculated accordingly for the current NMFs and the results showed that the interface stress was closely related to the micromechanical deformation of the NMFs, leading the failure of the materials.

The elemental semiconductors silicon and germanium in their diamond-cubic structure form the basis of the current day semiconductor technology. Interestingly however, different crystalline structures of Si and Ge can be created through pressure induced phase transformations yielding new structures upon pressure release. These pressure-induced crystalline structures exhibit highly valuable properties such as significantly altered band gap characteristics, better overlap with the solar spectrum or different resistance to etching. Traditionally such phases are created in diamond anvil cells, but if point loading is used as the mode of pressure application nanovolumes as small as ~100 nm across and ~20 nm in depth can be created. To control the metastable structure formed on pressure release however, a full understanding of the transition pathways is necessary. In this regard particularly the dependence on the presence of shear stresses, unloading rates and temperature are not understood yet and this study addresses this issue.
The transition pathways on unloading are studied in situ in a diamond-anvil cell using synchrotron X-ray radiation. Nanoindentation (point loading) allows for explicit control of the unloading rate. This is replicated in a diamond-anvil cell for the first time through the use of a purpose built gas assisted pressure release system. Variations in the presence of shear stresses as present in nanoindentation experiments are implemented through the use of different pressure media in the diamond anvil cell case.
In silicon the phase formation upon pressure release is found to be critically rate dependent, with fast unloading yielding an amorphous and slow unloading a body-centered cubic (bc8) structure. No significant dependence on the shear component is found. In contrast for germanium however, no strong dependence on the unloading rate is observed. But in this case hydrostatic conditions yield the bc8 structure, while non-hydrostatic conditions yield a different structure with simple tetragonal (st12) symmetry. This improved understanding of the phase transition pathways can now be mapped onto point loading experiments and thus allows for the controlled formation of a nanovolume of the desired end phase.

The mechanical behavior of films made from copolymers of ethylene and α-olefins, is dependent on the morphology of the films. This morphology can be modified in part, by the choice of the molecular weight, branch content and distribution. By carefully controlling these three parameters, the crystalline and the amorphous content of the semi crystalline polymer and thereby its response to mechanical loading can be manipulated. However, the direct correlation between the molecular architecture and the macroscopic mechanical behavior is not well understood. Clearly to address this issue requires characterizing the true macro-scale mechanical response of these films directly to their morphology and their molecular architecture. To achieve this we exploit tensile testing of polymer films with in situ synchrotron small- and wide-angle X-ray scattering (SAXS and WAXS, respectively).
In this study, we have investigated melt-blown films made from branched polyethylenes that exhibit different film specific mechanical properties. By using high flux synchrotron X-ray sources we have been able to determine the molecular and mesoscale structure of the polyethylenes as a function of strain rate under continuous uniaxial deformation. Due to the initial anisotropy of the blown films, we have studied the deformation behavior when applying the load both parallel and perpendicular to the initial orientation (MD). At low strains, large differences in the morphological development of the polymers are observed when deformed in the MD direction or perpendicular to it, i.e. the transverse direction (TD). At high strains well beyond the yield point, deformation behavior in both MD and TD are qualitatively similar, indicating that the molecular deformation mechanisms in the plastic deformation and strain hardening zones are comparable. Although the basic scattering behavior between the different polymers is superficially similar, as may be anticipated due to the architectural likenesses between them, subtle but distinct differences between the different polyethylenes are observed. Additional scattering studies from off-axis measurements, where the X-ray beam is not perpendicular to the polymer surface also shows unique insight into the through thickness molecular orientation and structure that cannot be determined with conventional measurement approaches. Through these in situ scattering measurements, we are beginning to provide insight into the molecular origin and mechanisms of the mechanical behavior.