Symposium CM04 : In Situ and In Operando Characterization of Materials and Devices by X-Ray and Neutron Diffraction

While energy storage within lithium ion batteries relies on the ability of an electrode phase to reversibly intercalate Li ions, critical performance metrics such as energy density, rate capability, and cycle life often depend on the nanocomposite electrode architecture which mediates electronic and ionic transport to the cathode particles. Delivering higher performance batteries depends not only on the discovery of novel materials but also on the optimization of the nanocomposite architecture. Notably, heterogeneity in the electrode reactivity can develop due to limitations in ionic and electronic conductivity. These can lead to incomplete cycling of parts of the electrode and ultimately limit capacity and device lifetime. Identifying the lengthscale and origin of such heterogeneity in the energy storage reaction is important to designing of improved battery electrodes.
This presentation will describe operando hard X-ray studies identifying reaction heterogeneity in the commercially-important layered transition metal oxide electrode (NCA) that impact performance from the first cycle towards failure.

Anodes that undergo alloying reactions with lithium and sodium are attractive substitutes for graphite in LIBs and SIBs for their high capacities. However, these high-capacity alloy type anodes suffer from short lifetimes associated with severe volume changes upon lithiation and sodiation. It is well-recognized that nanoporous architectures can help accommodate these large volume changes, but this mechanism is not well understood. To improve the lifetime of high-capacity nanoporous anode materials, a fundamental understanding of the structural changes upon cycling is necessary. We utilize nanoporous tin (NP-Sn) and antimony tin (NP-SbSn), synthesized by the selective etching, as a platform to study the deleterious effects of volume change in these alloying-type anodes under transmission X-ray microscopy (TXM).
TXM utilizing hard X-ray’s enables imaging of thick samples during battery operation with a large field of view. Imaging of this type is more representative of the actual electrode environment. The resolution of the final image at the Stanford Synchrotron Research Laboratory beam line 6-2 is ~30 nm, and is well matched to the morphology of our NP-Sn and NP-SbSn. Operando TXM shows that NP-Sn and NP-SbSn expand by 40 and 60% during lithiation, which is significantly less than in bulk Sn (130%). More importantly, the pore system in NP-SbSn stayed completely intact while some degree of fracturing was observed in NP-Sn, suggesting that NP-SbSn is more mechanically stable. This agrees with our observation that NP-SbSn shows better stability than NP-Sn when cycled with sodium. Specifically, we found that NP-Sn and NP-SbSn show comparable performance when cycled with Li⁺ (650 mAhg^-1 initial capacity with 98% capacity retention after 200 cycles for NP-Sn and 560 mAhg^-1 initial capacity with 90% capacity retention over 200 cycles for NP-SbSn). By contrast, NP-SbSn demonstrates much better cycle stability than NP-Sn when cycled with Na⁺ (430 mAhg^-1 initial capacity with 85% capacity retention after 100 cycles for NP-SbSn compared to 550mAhg^-1 initial capacity with only 50% capacity retention after 90 cycles for NP-Sn. It is known that intermetallics reduce the strain of these alloying anodes during ion intercalation by spreading out the intercalation voltages. It appears from our operando TXM studies that in porous materials, intermetallics further help preserve the pore system during cycling, allowing for longer cycle life with high-strain intercalant such as Na⁺. Overall, these nanoporous metals appear to be promising solutions to combat volume expansion due to their well-maintained structures and open pores throughout cycling, allowing for good electrolyte penetration and uniform lithiation and sodiation of these electrode materials.

Effects of superimposed thermal and electric fields on dense 8% yttria doped zirconia (8YSZ) ceramics, which were sintered Flash Sintered at 900 ^oC (FS900) and Sinter Forged at 1400 ^oC (SF1400), were studied with in situ energy dispersive x-ray diffractometry using a polychromatic synchrotron probe with photon energies up to 200 keV. The initial grain size of the FS900 and SF1400 systems were ~200 nm and ~1 μm, respectively, while their initial sintered density was ~97 % and, ~99 %, respectively. No discernible increase in the grain size and sintered density were observed when both systems were heated at 20 ^oC/min to 700 ^oC under an applied dc electric field intensity of 100 V/cm. No local melting at grain boundaries was observed in scanning electron micrographs. Moreover, no theoretical density improvement was measured on both samples. However, a singularity in the unit volume of the FS900 system was observed at 614 ^oC at which point the peak current draw (j_max) was 1.5 A corresponding to 2.14 kW/cm³ instantaneous maximum power absorption density (P_max). The tetragonal unit cell expansion associated with power absorption is 1.64% in addition to the volumetric expansion due to thermal expansion at 614 ^oC. In the SF1400 sample, on the other hand, two singularities were observed at 630 ^oC and 643 ^oC for which j_max is 0.6 and 3.0 A with corresponding P_max of 0.375 kW/cm³ at and 1.36 kW/cm³, respectively. The tetragonal unit cell expansions associated with power absorptions are 0.53 % and 2.61 % in additional to the volumetric expansion due to thermal expansion at 630 ^oC and 643 ^oC, respectively. Neither system exhibit temperature dependent peak broadening under 100 V/cm which suggests no long range vacancy re-arrangement has taken place in the FS900 and SF1400 sintered systems that would otherwise affect both coherently diffracting domain size and d-spacing variation (microstrain). The observed singularities in unit cell expansion are attributed to oxygen vacancy localized rearrangement at the unit scale as no direct electric field strain coupling is possible in an ionic conductor such as 8YSZ. The results reveal that the effects of superimposed temperature and electric fields, which are present in burst mode densification (a.k.a. flash sintering), can indeed be decoupled once grain boundaries are formed upon densification in a given system.

AgCuO₂ is a low band gap, p-type semiconducting material in which both silver and copper present intermediate oxidation state. This compound presents a peculiar electronic structure in which charge is delocalized and, as a result, electronic conductivity is much higher than for other p-type oxides.[1] As a result, AgCuO₂ appears as an attractive semiconductor for use in optoelectronic applications, in particular photosplitting and all/oxide new generation solar cells.
AgCuO₂ can be synthesized by different approaches as bulk powders, including, electrochemical oxidation, oxidation with ozone and oxidative co-precipitation.[2] A hydrothermal approach has also been developed to grow micro-size crystals that allowed the measurement of transport properties in single crystals, using nanocotacts deposited by Focused Ion Beam (FIB).[3] Values of resistivity as low as 10^-2 Ωcm were measured in these single crystals. In the synthesis, solid AgO and Cu(NO₃)₂ are mixed in a basic solution.
We have used a specially designed hydrothermal cell[4] to characterize in situ the reaction mechanism of the hydrothermal formation of AgCuO2 from solid AgO precursor. In this communication we will present the effect of the different experimental parameters on the reaction output. Though this study we have been able to elucidate the formation mechanism of AgCuO₂ and to obtain an activation energy for the reaction. The knowledge obtained from this in situ study sheds light on the formation mechanism of AgCuO₂ by other synthetic approaches.
[1] D. Muñoz-Rojas, et al. J. Phys. Chem. B. 36 (2005) 6193–6203.
[2] D. Muñoz-Rojas, et al.s, Mater. Today. 14 (2011) 119–119.
[3] D. Muñoz-Rojas, et al., Inorg. Chem. 49 (2010) 10977–10983.
[4] A.R.M. Dalod, et al., J. Phys. Chem. C. 121 (2017) 11897–11906.

Interfaces are places where the chemical bond is deeply affected. The result is an unprecedented chemical reactivity and a modification of the electronic properties (charge transfer, appearance of an electric field), which can give rise to various technological applications (electronic devices, photocatalysts, inverse catalysts, photovoltaic devices, etc.). In this context, photoelectron spectroscopies provide essential information at the nanoscale, on atomic environment of atoms and on the energetic positioning of electronic levels, at surfaces, interfaces between dissimilar materials, interfaces between phases (e.g. gas/solid ). A renewal of these spectroscopies is now possible thanks to real time, in situ techniques, epitomized by near ambient pressure XPS (NAP-XPS) using synchrotron radiation. We will take examples from recent experiences performed by our group. We will show how it can be applied to catalytic problems (such as CO oxidation), and we will highlight the wealth of information it provides, but we will also discuss its possible limitations. In the field of aqueous solution surface chemistry we will examine the interesting questions NAP-XPS can tackle, with potential relationship with fields of chemistry such electrochemistry. Finally, we will address the issues related to X-ray beam induced radiolytic effects, which are particularly sensitive for systems in which water is confined. We will examine specifically the case of layered minerals (such as clays), and we will see how a serious concern can transform into a new field of investigation for real-time XPS.

Fuel cells are a viable alternative to mankind’s dependence on fossil fuels. Unfortunately, fuel cells are not yet on the market, mostly because of the lack of efficient and affordable catalysts for the sluggish chemical reactions driving cells’ operation, such as the oxygen reduction reaction (ORR). Indeed, several families of ORR catalysts, for the most part metallic alloy nanoparticles (NPs), have proven excellent in terms of both activity and stability when tested in standard three-electrode cells, i.e. ex situ. When used inside operating fuel cells though, the very promising nanoalloy catalysts produced so far are often found less efficient than expected. The reason is that the nanoalloy particles would undergo specific atomic-level changes that inflict significant losses in their ORR activity, thereby limiting the cells’ performance. Despite extensive research, the driving force, scope and dynamics of atomic-level changes of functioning nanoalloy catalysts remain not well understood and so the resulting losses in their ORR activity remain difficult to limit. We will present results from combined energy dispersive x-ray spectroscopy (EDS) and total high-energy x-ray scattering studies of nanosized metallic NPs from Pd-Sn and Pt-Ni-Cu families as they function at the cathode of an operating proton exchange membrane fuel cell (PEMFC). We will show that the technique allows characterizing ORR catalysts inside PEMFCs with atomic-level precision (~ 0.02 Å) and element specificity (~ 2-3 at. %) in both time (~1 min) and space (~µm) resolved manner. In particular, it provides unique information for the chemical composition, geometric surface area, phase content, 3D structure and strength of interactions between the constituent atoms of studied nanocatalysts. We will also show how the new experimental knowledge obtained provides a firm structural basis for synthesizing improved catalysts for ORR inside PEMFCs.

Catalytic conversion of CO₂ has attracted extensive attention worldwide in recent years, aiming at alleviating the global warming and ocean acidification. Ni-based catalysts are identified as the most promising catalysts for CO₂ hydrogenation due to their considerable catalytic activity and lower cost compared to precious metal catalysts. However, Ni-based catalysts are generally favorable for the Sabatier methanation reaction for CH₄ rather than the reverse water gas shift (RWGS) reaction for CO. In many cases, CO is more desirable than CH₄ as it offers high flexibility to produce long-chain hydrocarbons and synthetic fuels via the methanol synthesis or Fischer–Tropsch reactions. Thus, it is important to promote the selectivity of CO₂ hydrogenation to CO over Ni-based catalysts. In situ characterization methods play an important role in the research of CO₂ hydrogenation over Ni-based catalysts, as they can provide an insight into the material properties and the catalytic mechanisms dynamically. Thus functional catalysts can be designed and applied accordingly.
In this study the LaNiO₃ and LaFe_0.5Ni_0.5O₃ perovskite-type catalysts were synthesized and used for CO₂ hydrogenation. The catalytic results demonstrated that the products selectivity were very different over the two catalysts: LaNiO₃ mostly produced CH₄ while the product over LaFe_0.5Ni_0.5O₃ was almost CO. Ni-related nanoparticles were found over the catalysts after reaction by TEM characterization, demonstrating that partial of the Ni ions were reduced out of the perovskite lattice. Various in situ measurements, including in situ XRD, in situ XAFS, and in situ AP-XPS, were applied to characterize the evolution of the catalysts under reaction conditions. The results of in situ XRD showed that LaNiO₃ was transformed to LaNiO_2.5 during the reaction while the perovskite structure of LaFe_0.5Ni_0.5O₃ could be maintained. Both of the in situ XAFS and in situ AP-XPS demonstrated that metallic Ni was formed over LaNiO₃ while no metallic Ni was founded even in a more reducing atmosphere (40% H₂/Ar) at 673 K over LaFe_0.5Ni_0.5O₃. The more stable perovskite structure of LaFe_0.5Ni_0.5O₃ was able to stabilize the Ni species in a higher oxidation state. Since CO is the key intermediate for CH₄ formation over Ni-based catalysts the reason for different product selectivity might be related to the adsorption and activation of CO over Ni-related species. Density functional theory (DFT) calculations revealed that metallic nickel is responsible for highly selective CH₄ production, while nickel with higher valence state weakens the binding of CO and increases the activation barrier for further CO hydrogenation, leading to a higher selectivity for CO. These findings not only give an understanding of La-Fe-Ni perovskite structure but also establish new correlations between the catalytic performance and structural properties of Ni-based catalysts, providing catalyst synthetic strategies for the application.

Ferroelectric materials are found in many of the electronic devices that are indispensable in the modern world. While macroscopic polarization, displacement, and dielectric measurements provide vital information; the development of in operando capabilities has provided unrivaled insight into the structural response of ferroelectric materials to applied stimuli. The more recent development of time-resolved capabilities has enabled researchers to probe dynamic phenomena. In this paper, time-resolved neutron and X-ray scattering studies of the dynamics of polarization reversal in the (1-x)BaTiO₃-xBiZn_O.5Ti_O.5O₃ system and work identifying the mechanism of polarization reorientation in molecular ferroelectrics are presented. Diffraction results evidence that chemical modification of BaTiO₃ activates an alternative pathway for 180 degrees dipole reversal. Molecular ferroelectrics have been hypothesized to involve proton transfer when the polarization is switched, limiting the use of X-ray tools. In contrast, neutron scattering is sensitive to hydrogen, enabling the investigate of the role of proton transfer in polarization reorientation.

The friction stir welding/processing (FSW/FSP), that uses the unique principles of the severe plastic deformation method, has a great potential as a novel method for the fabrication of bulk ultrafine-grained Mg alloys. Furthermore, there is a great potential to enhance the formability of Mg alloys significantly by using the FSP technique. For example, recent studies show that the FSP can be used for texture manipulation in Mg alloys resulting in significant improvements in mechanical behavior. However, the physics of the microstructure development process during FSP is still not clearly understood. In particular, very limited effort has been made for the fundamental understanding of specific roles that twinning plays in the dynamic recrystallization (DRX) mechanisms, texture changes, and resulting grain refinement. The focus of the current project is to study the transient phenomenon of DRX and critical role that twinning plays in the grain refinement and crystallographic texture development during FSP using in-situ, real-time neutron diffraction measurements.

In this talk, we will present the experimental results from the neutron diffraction measurements performed during FSP of Mg alloy plates using a portable FSP machine at the VULCAN beamline at Spallation Neutron Source. A commercial hot-rolled AZ31B Mg alloy plate was used in this study. The ranges of the FSP parameters used are: 1-5 mm/sec traveling speed and 200-1,500 rpm clockwise FSP tool rotating speed. These conditions allowed us to vary the thermo-mechanical input (in terms of Zener-Hollomon parameter, Z) by more than two orders of magnitude covering both low Z (slip dominant) and high Z (twin prevalent) regimes identified in previous constitutive studies. The main measurement scheme used was quasi-steady state measurement, where the FSP tool is stationary and the Mg plate travels, while neutron-diffraction measurements were performed at a fixed distance from the FSP tool pin (stir zone) over a period of time necessary for adequate statistics. These measurements were performed as a function of distance from the FSP tool pin for a given processing condition. Then, another set of measurements were performed at a different processing condition (Z) and on. We measured five locations each several millimeters apart starting from the tool pin and for four Zener-Hollomon parameters covering low Z, mid Z, and high Z conditions. The variations in the onset and extent of characteristic grain rotations during FSP as a function of location from the tool pin (translated later as a transient evolution along the FSP line) and the Zener-Hollomon parameter (low Z vs. high Z) will be presented. Finally, the in-situ diffraction data will be correlated to our constitutive studies on DRX mechanisms using a Gleeble system.

The small footprint of III-V nanowires allows for their epitaxial defect-free integration on Si substrates. Their large aspect ratio makes them suitable for three-dimensional chip design[1], photovoltaics[2] and sensorics[3]. In order to create any device structures, heterostructures have to be fabricated, e.g. by the deposition of a shell layer[1-3].

We are growing (In,Ga)As core-shell nanowires in a portable MBE chamber based at the Karlsruhe Institute of Technology that is specially designed for time-resolved in-situ X-ray experiments during growth, under true MBE conditions[4]. Using X-ray diffraction (XRD), we are sensitive to the nanowire shape, phase composition, strain and relaxation processes[5]. In order to resolve the temporal evolution of these characteristics during nanowire and shell growth, we utilized the high-brilliance synchrotron radiation at beamline P09 of PETRA III, Hamburg.
During in-situ XRD experiments the crystal structure is monitored by collecting partial reciprocal space maps (RSMs) around the asymmetric (311) and (220) zincblende and (10.3) wurtzite Bragg reflections of In_0.30Ga_0.70As, GaAs and Si with a temporal resolution of about three minutes. Additionally, high resolution three-dimensional in-situ RSMs are done both at growth temperature and at room temperature before and after shell growth. The X-ray beam was tuned to a spot size of several micrometers which allows analyzing an ensemble of nanowires to address the statistical character of the growth process.

During the fabrication of the shell, we observed the gradual appearance of additional (In,Ga)As Bragg peaks. At the same time, the Bragg intensities measuring the GaAs nanowire core were affected. In particular, a decrease of the peak amplitude is attributed to local distortions caused by the introduction of misfit strain. Additionally, the decreasing crystal truncation rod intensity can be interpreted by a reduction of the stacking fault density and the changing ratio of the phase selective Bragg peaks indicate a decreasing wurtzite phase fraction. This demonstrates the sensitivity of the crystal structure of GaAs nanowires when used as core for shell growth. Furthermore, our time-resolved in-situ investigations revealed that this phase change occurs already during the first stage of shell growth. Such insights into the temporal evolution of the microstructure during shell formation are beneficial for future attempts to tailor the crystal structure of core-shell nanowire heterostructures.

[1] Tomioka et al. IEEE J. Sel. Top. Quantum Electron. 17, 1112 (2011)
[2] Dimakis et al. Nano Lett. 14, 2604 (2014)
[3] Cui et al. Science 293, 1289 (2001)
[4] Slobodskyy et al. Rev. Sci. Instrum. 83, 105112 (2012)
[5] Schroth et al. Phys. Rev. Lett. 114, 055504 (2015)

Huge efforts are performed to study energy related materials or devices with new techniques of in situ and in operando methods. In particular large scale facilities are more and more involved in providing unique experiment conditions to support this request e.g. for better understanding of electrochemistry in batteries. Neutrons with their properties of deep penetration in materials and very sensitive to light elements suit well as a probe to monitor full processes in cells as charging/discharging, electrolyte filling or gas formation etc..
The focus in this contribution is to introduce neutron techniques for battery research arising high attention in the last decade. The process of charging and discharging of NMC/graphite cells related to the intercalation of Li in the graphite layers can be observed in situ with neutron diffraction (ND) to monitor LiC_x phases as LiC₆ and LiC₁₂ during the intercalation/de-intercalation process [1]. Under fast charging conditions and low temperatures the phenomenon of Li plating can be detected. By means of voltage relaxation and in situ ND for different C-rates Li plating is investigated [2]. Lithium iron phosphate (LFP), used for stationary energy storage systems, are studied with various types of graphites. Neutrons support the understanding why various losses of the storage capacity occur [3]. Neutron imaging (radiography and tomography) enables a non-destructive view inside the cell to investigate objects on the length scale of >50 micrometer. An important application for industry is the observation of the electrolyte filling process. In the focus is the distribution of the electrolyte in the cell between the layer stacks in a pouch cell during the filling [4]. Neutron induced prompt gamma activation analysis (PGAA) is a powerful tool to explain the capacity loss in NMC/graphite cells caused by tiny metal deposition on the graphite anode after charging/discharging processes [5]. Finally, the method of neutron depth profiling (NDP) will be introduced for near surface studies.
The work was supported by the BMBF project ExZellTUM (grant number 03X4633A) and the Bavarian Ministry of Economic Affairs within the framework of the EEBatt project.
References:
1. V. Zinth, C. v.Lüders, M. Hofmann, J. Hattendorf, I. Buchberger,S.V. Erhard, J. Rebelo-Kornmeier, A. Jossen, R. Gilles, Journal of Power Sources (2014), 271, 152-159.
2. C. v.Lüders, V. Zinth, S.V. Erhard, P.J. Osswald, M. Hofmann, R. Gilles, A. Jossen, Journal of Power Sources (2017), 342, 17-23.
3. N. Paul, J. Wandt, S. Seidlmayer, S. Schebesta, M.J. Mühlbauer, O. Dolotko, H.A. Gasteiger, R. Gilles, Journal of Power Sources (2017), 345, 85-96.
4. T. Knoche, V. Zinth, M. Schulz, J. Schnell, R. Gilles, G. Reinhart, Journal of Power Sources (2017), 331, 267-276.
5. I. Buchberger, S. Seidlmayer, A. Pokharel, M. Piana, J. Hattendorff, P. Kudejova, R. Gilles, H.A. Gasteiger, Journal of the Electrochemical Society (2015), 162(14), A2737-2746.

Three dimensional X-ray diffraction microscopy (3DXRD) is a powerful technique that provides crystallographic and spatial information of a large number, on the order of thousands, of crystalline grains in a sample simultaneously. A key component of every 3DXRD microscopy experiment is the near field detector which provides high resolution spatial information of the grains. We present a novel design for a semi-transparent, 8 megapixel, near field detector which provides double the sample to detector distance then currently possible. This allows larger sample environments, such as high/low temperature chambers, anvils, and tensile strain setups. Previously unattainable in situ and in operando 3DXRD experiments can now be performed.

As opposed to a typical single scintillator phosphor detector, this design, we call the Quad Near Field Detector, uses four quadrants. This enables a total field of view is 5 mm x 5 mm with an effective pixel size of 1.3 µm x 1.3 µm. Each quadrant has a dedicated scintillator phosphor and optical microscope. A number of technical challenges need to be overcome to make a multi-detector solution practical and useful.

Complications arise when going from a single to multiple phosphor configurations, such as relative phosphor alignment and microscope focusing. In all, forty nine parameters need to be defined to obtain high quality reconstructions. Many parameters can be resolved by careful mechanical design. For this reason a novel translation stage for focusing the microscopes was developed, tested, and implemented. The remaining twenty five parameters were addressed by a refinement algorithm.

The near field detector was calibrated and characterized at the Cornell High Energy Synchrotron Source using 40 keV X-rays from the high energy wiggler source. Correction methods were developed for the Quad Near Field Detector to correct for variations in intensity response and spatial distortion. Diffraction data of all four quadrants reproduced crystal orientation of both a ruby and a multi-crystal gold calibration samples.

Knowledge about high-pressure, high-temperature behavior of elemental materials is important for fundamental understanding of bonding evolution, phase transformations, and establishing of PT phase diagrams, which are of high significance for materials’ synthesis and applications. However, theoretical predictions of pressure-induced phase transformations often become long-standing enigmas because of limitations of contemporary available experimental possibilities.
Boron, the fifth element of the Periodic Table, has five currently established allotropes (α-B, β-B, γ-B, δ-B (T-50), and ε-B), and all of them are based on various arrangements of B₁₂ icosahedra, since three valence electrons of boron are insufficient to form a simple covalent structure. However, theoretical calculations suggest a possibility of the existence of a non-icosahedral boron allotrope with the α-Ga type structure.
In the present work in order to verify the theoretical predictions we have investigated the behavior of β-B under extreme conditions using high-purity single crystals synthesized by the high-pressure high-temperature large volume press technique. Laser heating of the diamond anvil cell compressed to 115 GPa led to the synthesis of predicted non-icosahedral boron allotrope (we denoted it as ζ-B). Synchrotron in situ single-crystal X-ray diffraction revealed the α-Ga-type orthorhombic structure (space group Cmce) with the unit cell parameters a = 2.7039(10) Å, b = 4.8703(32) Å, c = 2.9697(6) Å (Z=8). It may be described as a stacking along the (010) direction of distorted and corrugated hexagonal nets with the 3⁶ topology. Measured precisely interatomic distances and linear compressibilities along the major crystallographic directions do not allow interpreting the structure as layered, as earlier proposed. The newly synthesized ζ-B studied in the pressure range from 115 to 132 GPa was found to be less compressible than any other of previously known boron allotropes.

Ferroelectric ceramics are of technological promise because of their wide range of applications in dynamic random access memories (DRAMS), non-volatile memories, pyroelectric detectors and electro-optic devices, etc. Barium strontium titanate (Ba_1-xSr_xTiO₃, hereafter denoted as BST) being ecofriendly material, is considered as one of the most promising candidate for ferroelectric devices due to its excellent properties of high dielectric constant, low leakage current and adjustable Curie temperature (T_C). The doping of magnetic ion ‘Fe’ at ‘Ti’ site not only reduces the dielectric loss but also induces magnetism in it. However, very less is known about the magnetic properties and the electronic structures of the Fe-doped BST solid solutions. X-ray absorption spectroscopy especially X-ray absorption near-edge structure (XANES) when invited with Fe doped BST can provide information about the change in the valency of Fe and Ti ions and chemical bonding information. Present investigation focuses on the structural, magnetic and electronic properties of Fe doped BST ceramics [1]. Bulk samples with composition Ba_0.7Sr_0.3Fe_xTi_1-xO₃ where x =0, 0.1, 0.2, 0.3 were synthesized via conventional solid state reaction route. X-ray diffraction patterns of all the samples clearly show phase formation with the absence of impurity peaks. The Rietveld refinement confirmed the coexistence of the tetragonal and cubic phase for samples with Fe content x= 0, 0.1 and pure cubic phase for x > 0.1. The M–H hysteresis curves for samples with composition x = 0.1 and 0.2 exhibit paramagnetic behaviour even at low temperatures and the composition with x = 0.3 shows the nature of weak ferro- and ferri-magnetic orderings at about 2K. It is inevitable that presence of Fe²⁺ state is responsible for paramagnetism. However, with increasing Fe content mixed valency seem to be setting in. This strange magnetic behavior is due to the presence of mixed valence states and in particular Fe²⁺ state in the samples, as observed from Fe L₃-edge XANES spectra. The Ti L_3,2-edges at the XANES spectra confirmed that the doping of Fe in ABO₃ structure leads to the lattice distortion. This doping induced distortion is also evidenced by the Fe K-edge XAS. The Fe L₃-edge XANES spectra revealed that with increasing the Fe concentration, the mixed valence states and presence of Fe²⁺ are observed. The XANES spectra of the Ba L₃-edge and Sr L₃-edge spectra confirmed that the local structure around Ba²⁺ and Sr²⁺ respectively does not show any influence from the dopants in the BST system.
References
1. “Structural, Magnetic and Electronic Properties of Iron Doped Barium Strontium Titanate” ; Kaur.A et.al RSC Adv., 2016, 6, 112363

Two-dimensional (2D) materials have been extensively studied in recent years due to their unique properties and great potential for energy-related applications. Recently, surface defects or vacancies in catalysts are reported to promote catalytic reaction, such as hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR). Activation and dissociation processes of CO₂ can be controlled by tailoring their electronic structures, charge transport and surface properties. To gain in-depth atomic-level understanding on the correlation between the catalytic surface and reaction mechanism, we have utilized the near-ambient pressure X-ray photoelectron spectroscopy (APXPS) to monitor our reaction in-situ/operando. Here, the MoS₂ thin layers were prepared by vapor transport deposition, followed by hydrogen plasma post-treatment to create S vacancies with controlled concentrations. We observed that the defective surfaces of MoS₂ are more active than its pristine counterpart to split CO₂ under light illumination. Furthermore, the presence of defects helps transforming CO₂ into useful fuels, such as acetaldehyde, acetone, methanol and ethanol, with better selectivity. APXPS data showed that during reaction, CO₂ formed several intermediates, including physisorbed or chemisorbed CO₂ states. In addition, with the introduction of H₂O, formation of oxygenate species, such as hydroxyl, formate or methoxy groups were observed. Valence band offset was also observed due to surface band bending during reaction. Through APXPS study of the electronic structure and active sites during catalytic reaction, we can have improved understanding of the underlying mechanism involved in catalytic reaction, and gain insights in designing and improving carbon dioxide reduction catalysts.

Chalcogenide glasses (ChGs) are amorphous semiconductors with disordered structures and excessive number of defects. Because of this they possess a high concentration of recombination centers and traps in the band gap to capture free carriers produced by ionizing radiation (gamma, beta etc.). Moreover, it is expected that neutron irradiation induced atomic displacement and defects would not increase the total number of defects significantly. This paper addresses the effect of neutron irradiation on the structures of ChGs via Raman spectroscopic (442 nm, 100 K) study. The experiments involved gamma filtered and non-filtered neutron irradiation (with constant flux) for different durations (10 min, 1hr, 8hr) of Ge_xSe_100-x (x= 20, 30, 40) glass thin films. They were thermally deposited on single crystalline silicon wafer. Ag dots were additionally placed on top of them to serve as a source for Ag, creating in this manner structures which could give idea about both - interaction of the ChG with the radiation and radiation induced Ag diffusion in them. The structure of these glasses is usually characterized by corner-sharing (CS), edge-sharing (ES) Se-Se chains and ethane-like structure (ETH). Under irradiation all the structures except for ETH (which is absent at x = 20) for all compositions, show significant changes for low dose radiation but the changes become less responsive to radiation as the dose increases. CS units decrease stability the least and it is seen that with only neutron irradiation Ge₄₀Se₆₀ and Ge₂₀Se₈₀ become more stable (CS/ES ratio higher). Except for ETH units, Ge₃₀Se₇₀ (closest to stoichiometry with less homopolar bonds) does not show much change in structures but as the number of ETH units are very low, this effect is not of high importance. The Ag diffusion in ChGs for two compositions x = 20, 40 studied using optical microscopy reveals that it is a function of the irradiation dose. It occurs because of the high affinity of Ag towards the ChG, formation of charged defects due to irradiation and the relatively opened structure of the ChG. Reason for this structure is the fact that ChGs contain relatively rigid covalent bonds and weaker Van der Waals interconnections. This structure permits the metal ion diffusion though the formed in it voids and channels. Neutron flux induces more defects in the system and thus it is predicted that diffusion would happen at a higher rate in Ge₂₀Se₈₀. The result suggests that as the dose of radiation increases, Ag diffusion saturates and becomes difficult to observe through optical microscope but in general it is found that in Ge₂₀Se₈₀, Ag diffusion rate is higher due to the high affinity between Ag and Se which drives the metal into the chalcogenide film. Discussion is made based on the results about the irradiation effects in the studied glasses related to their specific structure and Ag accommodation.

We study the magnetic structure of multiferroic Ni_3-xCo_xV₂O₈ with x=0.1 and 0.5 using neutron powder diffraction. The temperature dependence of the susceptibility indicates that the magnetic order–disorder transition occurs at T_HTI=8.5 K in both samples. Below T_HTI, the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x=0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x=0.5 exhibits a definite temperature dependence, which differs from the case of the undoped sample (x=0).

The interest in new battery materials, which are able to “follow in the footstep” of the superior lithium ion batteries (LIBs), has increased the recent years. As a suitable candidate for the replacement of LIB employing graphite as the negative electrode, sodium-ion batteries (SIB) have long been investigated due to their intrinsic similarity to LIB, e.g. comparable electrode potentials to that of LIBs. However, due to unfavorable thermodynamics, sodium ions have been found unable to intercalate into graphite unless electrolyte solvents are co-intercalated. Fortunately, hard carbons, or non-graphitic carbons, have been successfully used as anodes. Previous studies proposed the sodiation mechanism to follow a three-stage mechanism characterized by absorption of sodium ions onto pore surfaces, at defect sites and between expanded layers of graphene [1, 2]. However, the continuous, dynamical changes have not yet been addressed and are essential to fully understand the sodiation mechanism.
Using operando X-ray total scattering and Pair Distribution Function (PDF) analysis utilizing a micro-capillary battery cell, the mechanism of hard carbon sodiation has been investigated to obtain information about the local structural changes of the disordered material, which are difficult to address using conventional crystallographic methods due to the amorphous state of the materials. The PDF data reveals that inter-layer and C-C bond distance distortions in the graphene sheets appear upon sodiation. This behavior corresponds to a reversible charge transfer between sodium and the antibonding orbitals in the upper π band of the graphene sheet resulting in in-plane elongation and contraction upon discharge and charge, respectively. However, the data also reveals that the hard carbon structure becomes increasingly disordered upon discharge, in which the initial structure is never fully recovered.


[1] Bommier, C., Surta, T. W., Dolgos, M., & Ji, X., Nano letters, 15(9), 5888-5892 (2015).
[2] Stratford, J. M, Allan, P. K., Pecher, O., Chater, P. A. & Grey, C. P., Chem. Commun., 52, 12430-12433 (2016).

Plastic deformation of otherwise perfect crystals is an unlikely process to be used for production of optical X-ray components due to the detrimental impact of resulting mechanically induced defects would have on the coherence of the diffracted X-ray waves [1]. However, if controlled, such defects in plastically deformed crystals can enable optics solutions that may outperform current options. Understanding the micro-grain structure of plastically deformed crystals is a key for this goal. Particularly interesting optical components for high energy X-rays are the Laue monochromators. At synchrotron beamlines they are preferred over standard Bragg monochromators when using high energy X-rays above 30keV. Advantages of using a bent Laue monochromator include increasing the rocking curve width, and hence, the intensity, as a result of the spread in d-spacing and the change in Bragg plane orientation. Furthermore, Laue monochromators do not demand large crystal beam footprints and allow the focusing of X-rays, which results in increased intensity on a sample or detector. Moreover, plastically deformed Laue crystals versus the more widely used elastically bent design, have the benefits of not needing complicated bender mechanisms and freedom to choose any sagittal and meridional curvature corresponding to the desired shape that meets the exact optical specifications [2].
We have developed high quality curved plastic deformed silicon Laue monochromator crystal. We characterized the crystal at the Cornell High Energy Synchrotron Source and the Canadian Light Source. The crystal monochromator enabled a wide band pass, high throughput monochromatic beam focussed down to 300um seven meters from the monochromator. The micro grain structure is the limiting factor to the fous size and throughput. In order to characterize and understand the limiting nature of the plastic disorder in the crystal, we took advantage of non-traditional multiple beam diffraction technique.
Second-order X-ray diffraction (SOXRD) processes are three-dimensional in nature and capable of probing the relative misorientation between perfect crystal domains [3]. In silicon, forbidden reflections such as the 002 reflection allows observation of SOXRD alone, without intensity contributions from the direct first-order diffraction. In this work, we use a multi-axis diffractometer for mapping the two-dimensional intensity distribution around a few SOXRD from the {111} family of planes in a plastically bent (001) silicon wafer. Each one of these SOXRD takes place at different azimuths, probing the relative grain misorientation along distinct in-plane directions. As we scan the beam footprint across the curvature of the wafer, the evolution of grain misorientation is figured out.

[1] K. Nakajima et al. Nat Mater. 4, 47 (2005).
[2] H. C. Kang et al. Phys. Rev. Lett. 96, 127401 (2006).
[3] S. L. Morelhão, L. P. Cardoso. J. Appl. Cryst. 29, 446 (1996).

High-temperature alloys like Ni-base superalloys are used in gas turbines (both stationary for electric power generation and in aircraft). They fulfill the requirements of high-temperature strength, ductility, corrosion resistance and high creep resistance needed in these applications and have a stable microstructure. Due to the fact, that the service temperature already reached 80% of the Ni melting point, new alloy systems in industry are under consideration to substitute Ni-base superalloys in future. In this contribution CoRe based alloys will be presented as a potential candidate for future applications [1]. Why CoRe alloys? Co-based alloys are already in use as gas turbine material in static components like turbine vanes or in combustor sections because of their intrinsic properties and the ease of manufacturing. The melting point of Co alloys can be considerably enhanced with Re additions (Re has the third highest melting point in the periodic table). The binary Co and Re system is isomorphous with an hcp structure at room temperature. Additions of Ta, C, Cr and B lead to further improvements of the properties in the CoRe alloy. The main contributor to the strength of the CoRe alloy are fine TaC precipitates with sizes below 100 nm which are homogenously distributed in the alloy. In-situ experiments at very high temperatures (up to 1500°C) with neutron scattering techniques have been used in this study because of the high penetration ability of neutrons and the large neutron beam cross section (about 1 cm²). Consequently, these kinds of measurements obtain a large volume representative bulk result from the investigated CoRe alloys. In situ measurements at elevated temperatures comprise observation of phase transformations and the formation of precipitates as well as their stability and growth [2].
Together with the easy handling of sample environments like special developed tensile rigs or high-temperature furnaces, neutrons offer a powerful tool for users in the community to enhance the alloy research with in situ measurements and to support the alloy development including the scale-up to the industrial level.
[1] J. Rösler, D. Mukherji, T. Baranski (2007), Adv. Eng. Mater 9, 876-881.
[2] R. Gilles, D. Mukherji, L. Karge, P. Strunz, P. Beran, B. Barbier, A. Kriele, M. Hofmann, H. Eckerlebe, J. Rösler, J. Appl. Cryst. (2016), 49, 1253-1265.

An understanding of Lithium (Li) spatial distribution within the electrodes of a Li-ion cell, during charge and discharge cycles, is essential to optimize the electrode parameters for increased performance under cycling. Neutron tomography, which enables mapping of the three-dimensional distribution of elements causing significant neutron attenuation, has been applied to investigate the spatial distribution of Li within Vanadium Pentoxide (V₂O₅) electrodes of a small coin cell. The neutron attenuation data has been used to construct the three-dimensional Li spatial images. The attenuation data from bulk sections and three planes parallel to the plane of the electrode have been averaged to quantify the Li distribution at various states of charge/discharge. It is shown that there is sufficient neutron imaging contrast between lithiated and delithiated regions of V₂O₅ electrode making it possible to map Li distributions even in small electrodes with thicknesses < 1 mm. The images reveal that the Li spatial distribution is inhomogeneous and a relatively higher C-rate leads to more non-uniform Li distribution after Li insertion. The non-uniform distribution suggests the limitation of Li diffusion within the electrode during the lithiation process under the relatively high cycling rates.

Thin film solar cells comprised of Cu(In,Ga)Se2 (CIGS) have efficiencies directly competitive with that of silicon devices¹. Much research has focused on how to increase CIGS efficiency further and perhaps the most promising approach thus far comes from the incorporation of alkali elements either during or after the absorber layer deposition. Both techniques can be incorporated in commercial fabrication of CIGS devices at little extra cost, suggesting their industrial relevance.
To date, sodium and potassium are the most heavily researched alkali elements. Many studies have shown that adding sodium and/or potassium to the CIGS layer results in performance increases, although the mechanisms causing this are still greatly in question^2,3,4. Additionally, the method used for incorporating the alkali elements, most commonly through post-deposition treatment (PDT) or substrates containing the elements of interest, influences the effect that the same element may have on the device performance⁵.
Using photoluminescence (PL) to map areas of full devices with a resolution of < 1 µm allows for the acquisition of pixel-by-pixel information of sub-grainsize variations in bandgap and radiative recombination. We simultaneously map the performance by observing the laser beam induced current and voltage (LBIC and LBIV, respectively). Furthermore, we measure Raman spectra at the same resolution to map different phases that may exist in the CIGS layer. From this, we correlate how bandgap, radiative recombination, and phase existence each correlate separately to electrical performance, as well as to each other.
The samples analyzed were deposited on either soda-lime glass (sodium containing) and sapphire substrates (sodium free). Samples were then either exposed or not to a NaF PDT. This work presents a correlative analysis of absorber inhomogeneity within PDT CIGS against the performance to determine the influence that deposition method and sodium content have on device efficiency. Additionally, we explain the effect the different incorporation pathways have on micrometer scale performance. Preliminary results show that increasing sodium content consistently narrows the bandgap distribution in the absorber layer. Additionally, results show that sodium introduction via the substrate results in the elimination of a Raman defect peak at approximately 150 meV. This suggests that sodium incorporation via the substrate better supports defect passivation, although the mechanism for why this is not yet identified.

Spring 2018 MRS Abstract – CM04



¹Green, M. A., et al. Prog. Photovoltaics Res. Appl. 2017. ²Reinhard, P., et al. IEEE J. Photovoltaics, 2015. ³Reinhard, P., et al. A. N. Chem. Mater. 2015. ⁴Aguiar, J. A., et al. M. Adv. Mater. Interfaces 2016. ⁵Hsu, C.-H., et al. Prog. Photovolt Res. Appl. 2015.

Continuing improvement in X-ray sources, softwares and instrumental automation during decades are the major reasons for crystallographic studies been conducted by an increasing number of non-experts in nowadays. However, besides diffracted intensities, the scattering length of X-rays also allows experimental measurements of structure factor phases. Physical phase measurement via dynamical diffraction experiments is the finest tool for probing structural features that are not accessible by other methods. For instance, the most recent example of its potential in crystallography is the detection of electron charges in hydrogen bonds responsible for intermolecular forces between amino acid molecules [1]. Although a lot has been developed lately in terms of how to carry out phase measurements, this method is still at similar situation of the standard X-ray methods decades ago where each successful application demands a lot of effort.
In this work, we carried out phase measurements in amino acid crystals using an in-house X-ray generator, showing that even with a low flux beam hydrogen bonds in biological molecules can be investigated. Synchrotron data is also shown for sake of comparison. One of the greatest challenging to use this method in single crystals of small dimensions (<1mm) is how to perform data collection with the sample spinning around an specific crystallographic direction. We derive an in-situ alignment procedure based on the crystal rotating method commonly used in protein crystallography. It allows a final alignment between the crystallographic direction and the spinning axis better than 0.01 degrees, which is necessary for high quality data aiming absolute refinements of crystal structures [2]. Furthermore, data analysis procedures for retrieving phase values are detailed and compared with theoretical values from model structure for asparagine, glycine, and histidine single crystals.

[1] S. L. Morelhão, C. M. R. Remédios, G. A. Calligaris, G. Nisbet. J. Appl. Cryst. 50, 689 (2017).
[2] S. L. Morelhão, Z. G. Amirkhanyan, C. M. R. Remédios. Acta Cryst. A71, 291 (2015).

The Kondo effect has always been source of intriguing new physics in condensed matter physics. It is intrinsically a many body effect, which is specially manifested in the presence of a Kondo lattice [1]. In CeFe₄P₁₂ crystals, the Ce atoms give rise to a particularly interesting kind of Kondo lattice: it is a Kondo insulator. Below a certain coherence temperature (T), Kondo insulators develop a gap at the Fermi level, displaying an electronic structure which is strongly T-dependent. This change in the electronic structure of the whole can be connected to the local charge and electronic configuration of the Ce atoms which, in accordance, will also be T-dependent. Current understanding [2,3] states that at high-T Ce atoms in CeFe₄P₁₂ will tend to a Ce³⁺ configuration, which will evolve closer to a Ce⁴⁺ configuration at low-T.
In the theoretical part of this work, the possibility of accessing real space charge fluctuation in Kondo lattices by X-ray phase measurements under dynamical diffraction is described. Very recently it has been demonstrated in practice the full potential of phase measurements applied to current trends in crystallography [4], such as capability of probing small charge fluctuations in crystal structures beyond the resolution of other diffraction methods. In the case of CeFe₄P₁₂ crystals, by adopting the 002 plane as a reference reflection, our calculations indicate that it is possible to detect real electron charge at Ce sites with one electron resolution, i.e. to detect the effective ionic charge of Ce in the crystal lattice. To our knowledge, real space resolution of charge fluctuations in Kondo lattices had never been presented. Our calculations suggest phase measurements as a feasible tool to detect this charge fluctuations.
Our experimental data set from both synchrotron and characteristic X-rays multiple diffractions have shown, instead, a surprising phase sensitivity to the photon energy that, by using proper line profile fitting functions, allows an ultra-precise lattice parameter determination (Δa/a = 2.5x10^-5) as a function of temperature. It also shows that detecting electron charge fluctuation in Kondo lattices depends on energy resolution, hence it demands instrumental setup suitable for this kind of experiment, as detailed here.

[1] Piers Coleman, Introduction to Many-Body Physics, Cambridge Press, (2016).
[2] P. A. Venegas, F. A. Garcia, D. J. Garcia, G. G. Cabrera, M. A. Avila, C. Rettori, Phys. Rev. B 94, 235143 (2016).
[3] M. Matsunami, et al, Phys. Rev. B 77, 165126 (2008).
[4] S.L. Morelhao, C. M. R. Remedios, G. A. Calligaris, G. Nisbet. J. Appl. Cryst. 50, 689–700 (2017).

Oxide thin film growth on SrTiO₃ by molecular beam epitaxy (MBE) offers a promising pathway for nanoscale control of electronic and structural properties of interfaces. Previous studies have indicated that deposited oxide layers rearrange dynamically during growth [1], impacting the structure of the resulting interface. However, the impact of a TiO₂-rich termination of the substrate [2], as well as the kinetics and mechanism of the layer-rearrangement process remain unknown. Using X-ray reflectivity (XRR) measurements to determine structure and then first principles calculations to determine surface energetics can offer some insight, but a tighter coupling between theory and experiment can be even more impactful. Integrating constraints from density-functional theory into the refinement of structural models against experimental X-ray data [3] provides a concurrent description of surface structure and energetics during layer-by-layer growth. We use DFT-constrained structure refinement against resonant and non-resonant XRR measurements performed during shuttered deposition to confirm a double layer TiO₂ termination of the bare substrate and demonstrate how this TiO₂-rich surface impacts the dynamic layer rearrangement at each step. We combine measurements of the layer-flipping timescale during growth with DFT calculations of the affinity of the surfaces for deposition of a new monolayer to propose mechanisms for growth. We also leverage DFT alongside diffuse scattering data to explain why some growth protocols lead to formation of islands and more disordered fims while others lead to smoother, higher quality films, impacting best practices in oxide MBE.

[1] J. H. Lee et al, Nature Materials 13, 879–883 (2014)
[2] Erdman et al, Nature 419, 55-58 (2002)
[3] M. Plaza et al, JACS 138 (25), 7816-7819 (2016)

The present work is intended to understand atomic scale mechanism of oxy-ion conduction in co-doped ceria system. The role of aliovalent dopant pairs on oxygen vacancies generation, clustering and dissociation mechanism in ceria system are probed by EXAFS, XANES and Raman spectroscopy. Correlation between atomic positional shift, oxygen vacancy defects, and oxide ion conductivity in doped ceria system are established from X-ray diffraction (XRD) and Raman spectroscopy study at operating temperature (300–600^oC) of Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC).
The Raman spectroscopy study shows additional vibration modes related to ordering of defect spaces and generated due to association of oxygen vacancies and reduced cerium or dopant cations site, which disappear at high temperature; indicating oxygen vacancies dissociation from the defect complex. The experimental evidences of cation-anion positional shifting and oxygen vacancies dissociation from defect complex in the IT-SOFC operating temperature are discussed to correlate with activation energy for ionic conductivity.
To establish a correlation between atomic level structural changes (coordination number, interatomic spacing) formation of dimer and trimer type cation-oxygen vacancies defect complex (intrinsic and extrinsic) and dissociation of oxygen vacancies from defect cluster are closely monitored by EXAFS and XANES. It is a strategic approach to understand key physics of ionic conductivity mechanism in order to reduce operating temperature of electrolytes for intermediate temperature (300–450^oC) electrochemical devices for the first time.

Coherent diffraction continues to develop into a mature technique capable of imaging single nanoparticles and thin film grains in a variety of environments. Its unique sensitivity to structural perturbations, and in particular dislocations, has made it the premier imaging tool for crystalline specimens with sizes of 100 nm to 1 micron. In this talk, I will initially review coherent diffraction in both Bragg and transmission geometries and then spend the majority of the time on applications of the techniques to two materials science systems that share many similarities in their underlying thermodynamics: advanced battery cathodes and hydrogen storage materials. The ultimate goal of this talk is to open new collaborations to address important outstanding questions in physics, chemistry, and materials science.

Low temperature scanning tunneling microscopy (STM) combined with synchrotron based X-rays is a surface sensitive technique to measure elemental, chemical and magnetic contrast at unprecedented resolution. A functionalized tip at a tip-sample junction works as a detector to collect localized information. Recently, we demonstrated that the technique can be utilized to obtain chemical fingerprint of monolayer metal islands [1] and localized magnetic contrast by utilizing polarized beams [2]. Here, we present measurements of chemical distributions on a battery anode material using SX-STM technique. The capability to probe depth sensitive chemical information at high spatial resolution opens door to study localized chemistry on surfaces.

References
[1] N. Shirato et al., Nano Letters 14, 6499 (2014).
[2] A. DiLullo et al., J. Synchrotron Rad. 23, 574 (2016).

Two soft-x-ray spectromicroscopes, scanning photoelectron microscope (SPEM) and scanning transmission x-ray microscope (STXM), are operational at the Pohang Light Source, enabling us to investigate element-, chemical state-, valence state-, crystal structure-, electronic structure-specific local distribution within a sample with a space resolution down to hundreds of nm in SPEM and tens of nm in STXM. As a nano-focused x-ray photoelectron spectroscopy (200 – 1,000 nm x-ray size at the sample), SPEM is operating at 400 – 1,000 eV photon energy and is surface sensitive (less than ~2nm probing depth). SPEM has been practically applied to investigate local chemical states and electronic structure of graphene layers, functionalized graphene layers, single layer of CVD synthesized MoS₂, h-BN encapsulated WSe₂, and laser-illumination-induced phase-changed MoTe₂. As an absorption spectroscopy, STXM normally operates in transmission mode and probes crystal structure, chemical state, and valence state through the sample. The sample thickness is ~hundreds of nm at the photon energy of strong absorption or several micrometers to even thicker at non-absorbing photon energy. Usable photon energy of the STXM ranges from ~200 eV to ~1600 eV. The space resolution is ~30 nm by using a 25 nm outermost zone-wide zone plate in the photon energy range from ~250 eV to ~850 eV, with worse space resolution at higher photon energy. The data acquisition time for one image is typically ~1 min. and thus in-situ or operando investigation is feasible, such as to investigate charging and discharging details of the lithium ion battery materials. Applications to nano-bio materials, energy storage materials, catalyst materials are becoming very active. Recently, we have added a soft x-ray fluorescence measurement setup in order to probe thicker samples’ elemental distribution as well as chemical state information, at a space resolution of ~50 nm. Also, we have implemented Ptychography setup in order to improve the space resolution down to less than 10 nm.

With the advent of high quality x-ray optics, several techniques have been proposed to exploit the imaging under Bragg conditions at synchrotron sources. Within the framework of the ESRF upgrade, a new dedicated instrument has been implemented on beamline ID01 at The European Synchrotron (ESRF). Since April 2017 this instrument is fully operational and has supplied users with Full Field Diffraction X-ray Microscopy (FFDXM) imaging adapted to various sample environments. Compared to more established scanning diffraction techniques, FFDXM offers fast, spatially resolved images on a large sample area without mechanical motions, perfectly suited for in situ and operando experiments.
The concept of FFDXM will be first demonstrated. A set of objective lens is placed downstream the sample to make a dark field image of the diffracted beam. At 6.5 meters away, the illuminated sample area (Field of View : 200×200 μm^{<span style="font-size:10.8333px">2</span>}) is magnified and spatially resolved on a CCD camera with a resolution of 100 nm. Essentially an x-ray strain microscope, the FFDXM is capable of probing lattice tilt, strain and grain orientation at surfaces, buried interfaces or inside functioning devices, which is often unreachable for electron microscopy techniques.
Results of several user and in house experiments will be given next, to illustrate the principle of diffraction topography (strained STO), mosaicity (InGaN nano-pyramids) and strain (buried gas cavities in implanted Si wafers) mapping using FFDXM. Typical image acquisition time is around 1 sec; a complete set of measurement takes just a few minutes.
Thanks to its large FoV, short acquisition time and suitable resolution, the FFDXM is ideal for in situ and operando experiments. This is further demonstrated by two successful examples. In the first experiment, the evolution of strain and lattice tilt of the Si surrounding Cu Through Si Via (TSV) was studied during in situ annealing up to 500°C and during subsequent cooling. In the second experiment, the failure mechanism (defect formation) of planar Si anode was studied during operando cycling of a Li-ion battery.

The growth of metal-surface oxides and its roles in surface reactions have been continuously studied (and debated) as it provide fundamental knowledge on how the surface reaction occurs in the presence of oxides. Among many of those studies, the surface oxides of Pt and Pd have been intensively studied and two different reaction mechanisms, i.e. Langmuir-Hinshelwood mechanism and Mars-van-Krevelen mechanism, have been employed to explain CO oxidation reaction.

Recently, we revisited the study of CO oxidation on Pt(110) and Pd(100) surface using AP-XPS. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure, the presence of surface oxides is observed on both surfaces. Due to exothermic nature of CO oxidation, the temperature of both Pt and Pd surfaces increases as CO oxidation takes places. Interestingly, the gas phase peaks of oxygen behave differently from Pt surface to Pd surface under oxygen rich condition, reflecting opposite reaction properties of surface oxides. The origin of the reaction properties of Pt and Pd will be discussed.

Condensed phase matter in the atmosphere is of paramount importance for hydrology, biogeochemical cycles, climate, ecosystems and human health. Ice in snow and cirrus clouds, aqueous solutions in aerosol particles and clouds, and salt, organics and mineral oxides in other particulate matter suspended in the air are some examples. Increased interest about chemical and physical processes at or near the condensed phase – air interface has led to in situ techniques capable of probing relevant surfaces at the molecular scale (at depths of a few nanometer at most) and the interior of atmospheric particles with submicron resolution. Atmospheric material properties are a strong function of the water vapor partial pressure in the mbar range, while most chemically relevant trace gases are in the 10^-6 mbar range and below. Therefore, in situ techniques must provide chemical selectivity and either sensitivity for the surface or high spatial resolution, while at the same time being able to cope with a high water vapor pressure. For the purpose of addressing interfacial chemistry we have recently developed an in situ cell for ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to study the interaction of trace gases with ice, mineral oxides and aqueous solutions that allows equilibrating these materials at relevant relative humidity and at the same time features fast response times to sticky trace gases. For the purpose of addressing the internal physical and chemical structure of aerosol particles, we have used an environmental cell in conjunction with scanning transmission X-ray microspectroscopy (STXM) to investigate the behavior of authentic and proxy aerosol particles in response to chemical or photochemical stimuli that induce changes in morphology and chemical composition. Recent results obtained with both techniques will be presented.

References

Alpert, P. A., Ciuraru, R., Rossignol, S., Passananti, M., Tinel, L., Perrier, S., Dupart, Y., Steimer, S. S., Ammann, M., Donaldson, D. J., and George, C.: Fatty Acid Surfactant Photochemistry Results in New Particle Formation, Scientific Reports, 7, 12693, 2017.

Artiglia, L., Edebeli, J., Orlando, F., Chen, S., Lee, M.-T., Corral Arroyo, P., Gilgen, A., Bartels-Rausch, T., Kleibert, A., Vazdar, M., Andres Carignano, M., Francisco, J. S., Shepson, P. B., Gladich, I., and Ammann, M.: A surface-stabilized ozonide triggers bromide oxidation at the aqueous solution-vapour interface, Nature Communications, 8, 700, 2017.


Kong, X., Waldner, A., Orlando, F., Artiglia, L., Huthwelker, T., Ammann, M., and Bartels-Rausch, T.: Coexistence of Physisorbed and Solvated HCl at Warm Ice Surfaces, The Journal of Physical Chemistry Letters, 4757-4762, 2017.

For state-of-the-art rechargeable batteries, the working principle is commonly based on the reversible insertion of alkali metal ions into a host structure, usually a layered transition metal oxide for the positive electrode (cathode). The nature of the alkali insertion reaction into the host structure is a key issue for the performance of the electrode material, such as electrode potential and reversible capacity. Both are intimately coupled to the electronic structure of the material and its evolution upon deintercalation. In the past, the electronic structure of intercalation materials has been inferred from the performance of the material such as its electrode potential at different state of charge (SOC), or has been experimentally determined using electrodes which were electrochemically deintercalated using liquid electrolyte and then analyzed after emersion by XPS and XAS (“post mortem analysis”). The results of these studies are subject to uncertainties due to the large surface sensitivity of the measurement techniques. For post mortem studies of cathode materials that were in contact with liquid electrolytes, surface contamination by electrolyte residuals and the solid electrolyte interface (SEI) layer are inevitable and oppose an unambiguous interpretation of the data.

In this contribution we present an in operando XPS study of the cathode material Na_xCoO₂, which to our knowledge is the first study of this kind dealing with a layered oxide cathode material. An all-solid-state-battery with a Na_xCoO₂ cathode was assembled under UHV conditions in such a way that it was possible to measure XPS of the bare cathode surface in operando while cycling the battery. In addition, batteries were precharged in situ and transferred under UHV conditions to the synchrotron facility BESSY II to measure XAS at the cathode surfaces at various charge states.

In the XPS and XAS measurements using the all-solid-state-battery approach we were able to follow the charge process in the core levels (Co2p, O1s, Na1s) as well as in the valence band region without uncertainties caused by electrode-electrolyte interactions. During charging a decrease in alkali content and change in cobalt oxidation state of the cathode material is clearly visible. Already at comparably low deintercalation states -within the reversible region- changes in the O2p orbitals were measured. Correlation of XPS/XAS and electrochemical data indicate a reflection of the electronic structure evolution by the charge curve.

Atomic layer deposition (ALD) and chemical vapour deposition (CVD) are very important methods that enable a highly controlled growth of thin films [1]. The surface chemistry of the underlying processes remains, however, little understood. While idealised reaction mechanisms have been developed, they represent postulates rather than models based on the factual identification of surface species and kinetics [2]. New in situ and operando methods offer the prospect of gaining a much more thorough understanding of the involved molecular and atomic surface processes and (dynamic) structures, which, in turn, means that a much better knowledge basis can be achieved for the future improvement of materials and growth recipes (see, e.g. [3,4]). One such operando method, which can be applied to the investigation of ALD and CVD, is synchrotron-based ambient pressure x-ray photoelectron spectroscopy (APXPS). While conventional x-ray photoelectron spectroscopy (XPS) is limited to vacuum pressures of 10^-5 mbar and below, APXPS can be carried out at realistic pressure. Today, most APXPS machines can operate at pressures up to the 10 mbar regime, which is an ideal match to the pressure regime used in standard ALD reactors.
Here, I will report on our recent efforts to apply synchrotron-based APXPS to the ALD/CVD of oxides (TiO₂, SiO₂, and HfO₂) on semiconductor (InAs and Si) and oxide surfaces (TiO₂, RuO₂) [3-5]. I will show that APXPS allows the identification of the surface species occurring during thin film growth and the real-time monitoring of their evolution, presently with a time resolution of around 1 s. I will also report on our efforts to further improve instrumentation with the goal of achieving a much closer match of the APXPS sample environment with the geometries used in conventional ALD reactors. The development will also open for the use of a wider range of precursors and growth protocols. Further, we work on making the millisecond timescale attainable in the APXPS study of ALD.

[1] V. Miikkulainen et al., J. Appl. Phys. 113 (2013) 021301.
[2] F. Zaera, Coord. Chem. Rev. 257 (2013) 3177.
[3] B. A. Sperling et al. Appl. Spectrosc. 67 (2013) 1003.
[4] K. Devloo-Casier et al., J. Vac. Sci. Technol. 32 (2014) 010801.
[3] S. Chaudhary et al. , J. Phys. Chem. C 119 (2015) 19149.
[4] A. R. Head et al. , J. Phys. Chem. C 120 (2016) 243.
[5] R. Timm et al., submitted (2017).

Water electrolysis is considered as a promising means for converting renewable electricity into hydrogen for storage and on-demand utilization. The sluggish oxygen evolution reaction (OER) at the anode results in considerable energy losses and calls for the development of more efficient electrocatalysts. To guide the catalyst search it is critically important to understand key steps of the OER. In this presentation we will discuss how application of Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and soft X-ray spectroscopy can contribute to advancing the understanding of the oxygen electrocatalysis on metal oxide surfaces. In the first part of the presentation we will consider OER electrocatalysis on Ir- and Ru-based anodes to shed light on the reaction mechanism, on the structure-activity relations and on the nature of degradation processes. We will see that combining NAP-XPS with the complementary soft X-ray spectroscopy (NEXAFS) at the oxygen K-edge allows one to detect reaction intermediates on the electrode surface [1]. We will also discuss the controversial issue related to the formation of Ir(V), and consider metal-support interactions in Ir/SnO₂ supported anode catalysts. We will compare IrO_x anodes with RuO_x and Ir-stabilized RuO_x anodes, where transformation of Ru(IV) into higher oxides may be conveniently followed with NAP-XPS, and discuss the origin of electrochemical instability of Ru-based anodes during the oxygen evolution reaction [2].
The second part of the talk will be devoted to the noble metal-free transition metal (Mn, Co) oxides as promising anode materials for anion-exchange membrane fuel and electrolysis cells. We will touch upon such issues as beam damage in the presence and in the absence of water, structural and compositional transformations under polarization, and relevance of the spectroscopic information obtained in model systems operating at mbar pressures for practical systems.

Acknowledgements
The author is indebted to V. A. Saveleva and S. Zafeiratos (Strasbourg, France), L. Wang, A.S. Gago and K.A. Friedrich (Stuttgart, Germany), D. Techner, M. Haevecker, A. Knop-Gericke and R. Schloegl (Berlin, Germany), J.-J. Gallet and F. Bournel (Paris, France), A. S. Ryabova, D. Antipin, I. Filimonenkov, S. Ya. Istomin, E. V. Antipov, G. A. Tsirlina and K. Stevenson (Moscow, Russia). The research leading to the presented results has received funding within ERA.NET.RUS.PLUS (project #270 NANOMorf), and the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 621237 (INSIDE).

References
[1] V. A. Saveleva, L. Wang, D. Teschner, T. Jones, A. S. Gago, K. A. Friedrich, R. Schloegl, S. Zafeiratos, E. R. Savinova, in preparation.
[2] V. A. Saveleva, L. Wang, W. Luo, S. Zafeiratos, C. Ulhaq-Bouillet, A. S. Gago, K. A. Friedrich, E. R. Savinova, J.Phys.Chem.Lett. 7 (2016) 3240.

In Situ neutron diffraction (ND) is a powerful technique that can be applied to investigate the phase transitions in Li-ion batteries owing to the higher depth of penetration of neutrons and higher neutron scattering cross-section of Li atoms, relative to that in X-ray scattering. The principal difficulty with in situ studies on Li-ion batteries is that neutrons will be incoherently scattered by H and ₃Li⁷ in separator, electrolyte and the non-active components of the cell. We have successfully designed and demonstrated a cell, with single crystal Si sheets as casing material, for in situ electrochemical studies of Li-ion batteries. The objective of this work is to use this cell to understand the phase transitions upon lithiation of Si with columnar architecture. The columnar structure is designed to accommodate the large volume changes upon lithiation of Si. Hence, the real time evolution of structures in Si columns, upon lithiation, can provide insight on the performance of Si electrode. The electrodes were packaged inside the in situ cell and were subjected to full charge-discharge cycle while under neutron diffraction. Neutron diffraction patterns with high signal to noise ratio could be obtained. Interestingly, a peculiar phenomenon, where the diffraction peaks show a large change in peak intensity upon lithiation and with little change in the corresponding interplanar spacing, is observed. The results are analyzed in terms of a possible mechanism of lithiation of Si and the associated formation of Si islands embedded in amorphous lithiated Si, leading to a mosaic structure. The implications of these observations on designing better Si electrodes are discussed.

We present a detailed and instrumentally and conceptually complex study on the structure and transport properties of metal oxides with x-ray and neutron and electroanalytical methods in situ and operando ¹. Pressure and temperature were employed for a parameterization of the processes taking place in ceramic proton conductors<!--[endif]---->². The proton is a structural component in many materials and an electric charge carrier in proton conducting ceramic membranes. We have investigated yttrium doped zirconia and ceria for such electrolyte membrane applications in situ and operando under realistic transport conditions. At low temperatures in humid ambient, water molecules enter the membrane and the oxygen ions of the H2O occupy oxygen vacancies while the proton forms OH bridges in the material with a crystallographic superstructure imposed by the doping, as determined with neutron diffraction and resonant/anomalous XRD ³. As such it is a structural component. Upon rising temperature, lattice vibrations form phonons which couple to the protons and propel it as polaron ⁴ through the lattice, which we have determined with quasi-elastic neutron scattering along with impedance spectroscopy. The transition of the proton from being a structural component to becoming a charge carrier is monitored with ambient pressure resonant XPS on polarized electrolytes. For the particular compounds we could determine the temperature range for this transition to around 700 K. The use of resonant valence band photoemission spectroscopy in situ allowed us to sketch a complete transition of the density of states during the protonation and deprotonation <!--[endif]---->⁵. <!--![endif]----><!--![endif]---->
<!--[endif]----><!--[endif]---->
1. A. Braun: X-ray Studies on Electrochemical Systems - Synchrotron Methods for Energy Materials, (Walter De Gruyter GmbH, Berlin/Boston, 2017).
2. Q.L. Chen, S. Holdsworth, J. Embs, V. Pomjakushin, B. Frick and A. Braun: High-temperature high pressure cell for neutron-scattering studies. High Pressure Research 32, 471 (2012).
3. A. Braun, A. Ovalle, V. Pomjakushin, A. Cervellino, S. Erat, W.C. Stolte and T. Graule: Yttrium and hydrogen superstructure and correlation of lattice expansion and proton conductivity in the BaZr[sub 0.9]Y[sub 0.1]O[sub 2.95] proton conductor. Applied Physics Letters 95, 224103 (2009).
4. A. Braun and Q. Chen: Experimental neutron scattering evidence for proton polaron in hydrated metal oxide proton conductors. Nature Communications 8, 15830 (2017).
5. Q.L. Chen, F. El Gabaly, F.A. Akgul, Z. Liu, B.S. Mun, S. Yamaguchi and A. Braun: Observation of Oxygen Vacancy Filling under Water Vapor in Ceramic Proton Conductors in Situ with Ambient Pressure XPS. Chemistry of Materials 25, 4690 (2013).

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Following phase transformations in battery electrode during the passage of lithium or sodium ions (or other mobile ions) as the redox process takes place during charge or discharge is fascinating. In operando X-ray and neutron diffraction have become standard techniques in studying the insertion reactions in lithium and sodium batteries. Despite this, there are constantly new challenges to tackle as alternate approaches to following dynamic processes in detail are explored. In this presentation, in house in operando X-ray diffraction experiments will be discussed using a study of two different cell chemistries, a lithium ion system including the positive electrode LiFeSO₄F, and an aqueous sulfate Zn/MnO₂ cell. Using these two systems as case studies, the advantage and disadvantage of battery cell-designs coupled with in house and synchrotron-based X-ray diffraction will be considered. Even more challenging is the development of in operando cells for neutron diffraction. While publications have focused on studying commercial cells the true test comes when constructing customs cells for new battery chemistries due to the quantity of material required for adequate neutron scattering. Here we compare two separate approaches to in operando neutron cell designs, a coin-type cell and a larger wound-type cell.

The properties of many thin films are closely linked with material performance. For industrial applications printing functional thin films is of high relevance. We have developed a set-up to print functional materials under various controlled deposition environments to understand and influence the structure formation in printed thin films. [1] Using examples from thin film photovoltaic systems we gain insight into crystallization processes important for device operation. Our controlled deposition process can be carried out in various multi-modal measurement environments including the use of synchrotron radiation.
We use the advanced scattering techniques grazing incidence wide and small angle x-ray scattering (GISAXS/GIWAXS) to investigate in-situ, the structure formation in printed active layers of organic solar cells using an industrial slot-die coater. [2] We can follow the evolution of thin film morphology with appropriate time-resolution to initially track the solvent removal, followed by the crystallization of the polymer and the aggregation of the fullerene. The morphological evolution can be separated into several subsequent phases that take place independently of the drying speed of the film. We can manipulate the processing using different drying times, either by temperature or saturated gas atmosphere and directly observe the changes on the structural development. Furthermore, we can apply this approach to other promising material systems.
Such measurements are highly valuable for understanding the structure formation processes in material systems of interest for industry, where stable, reproducible fabrication conditions are essential.
[1] S. Pröller, D. Moseguí González, C. Zhu, E. Schaible, C. Wang, P. Müller-Buschbaum, A. Hexemer, E. M. Herzig, Review of Scientific Instruments. 88: 066101 (2017)
[2] S. Pröller, F. Liu, C. Zhu, C. Wang, T.P. Russell, A. Hexemer, P. Müller-Buschbaum, E.M. Herzig, Advanced Energy Materials, 6: 1501580 (2016)

The transparent and low-cost nature of dye-sensitised solar cells (DSCs) affords them niche prospects for electricity-generating windows in energy-sustainable buildings. Despite their vast industrial potential, innovation is being held up by a lack of suitable dyes. Better dyes can only be realized if we can better understand how the dye^...TiO₂ interface of a DSC working electrode functions at the molecular level. Previously, no materials characterization technique had managed to probe the interfacial structure of a DSC working electrode while in its full device assembly, where it exists as a buried interface; yet this information is critically important since the structure will undoubtedly change once embedded in its device environment. To this end, this talk presents the world’s first report of an in situ neutron reflectometry study that determines the dye^…TiO₂ interfacial structure of the DSC working electrode while housed in its device environment [1]. The high-performance DSC dye, MK-2 and its molecular building block, MK-44 are the case studies [2]. Probing this buried interface within its device environment sets this study apart from surface chemistry approaches that characterize the exposed interfaces. We show how the electrolyte modulates the structure of these buried interfaces, and thence its photovoltaic properties. The finding that this structural modulation is only observed once the DSC working electrode is atomically probed in its device environment highlights the need to characterize these buried interfaces directly, if DSC functionality is to be properly understood at the molecular scale.

References:
[1] J. McCree-Grey, J. M. Cole, S. A. Holt, P. J. Evans, Y. Gong, “Dye^...TiO₂ Interfacial Structure of Dye-Sensitised Solar Cell Working Electrodes Buried under a Solution of I^-/I₃^- Redox Electrolyte”, Nanoscale, 9 (2017) 11793-11805.

[2] J. M. Cole, M. A. Blood-Forsythe, T. C. Lin, P. Pattison, Y. Gong, A. Vazquez-Mayagoitia, P. G. Waddell, L. Zhang, N. Koumura, S. Mori, “Discovery of S^…CN intramolecular bonding in a thiophenylcyanoacrylate-based dye: realizing charge transfer pathways and dye^…TiO₂ anchoring characteristics for dye-sensitized solar cells”, ACS Appl. Mater. & Interfaces, 9 (2017) 25952-25961.

The Li-ion chemistry is thus far the most advanced chemistry employed in battery technology. To date, Li-ion batteries dominate the market of the electronics and portables devices. However, in the field of electric and hybrid vehicles further improvements are required in terms of performance, safety, and cost. The same set of criteria concerns other systems based on alternative chemistries such as Na-ion and Lithium–Sulfur (Li–S) batteries. Advanced Li-ion batteries and the pre-cited novel systems utilize less understood electroactive materials and thus show new reaction mechanisms during electrochemical cycling, the understanding of which requires new characterization tools and techniques.
Development of a reliable electrochemical cells is thus of a prime importance when studying battery materials in in situ or operando mode during cycling. This is never an easy task, since the design of such cells has to be adequate to the technique of a choice and meet all necessary requirements (i.e. the use of a Be window for operando X-ray diffraction measurement to ensure “transparency” to the X-ray beam). However, once a proper design is found, the surface, the bulk, the interfaces, and finally the combination of those can be studied and lead to the elucidation of the reaction mechanisms, thus further improving the battery technology.
Unfortunately, in most cases the electrochemical cells used for operando measurement are not ideal and suffer from low internal pressure (i.e. poor contact between the electrodes). It shorts the lifespan of the cell and as a consequence most of the studies presented in the literature focus on the first/second cycle. Herein we present different cell designs developed in our laboratory and used for operando/in situ studies. Having overcome earlier mentioned obstacle our operando/in situ cells are able to sustain more than 100 cycles and simultaneously to perform structural studies such as X-ray and neutron diffraction. For the latter one, we also developed a new set-up called stroboscopic mode. It allows operando study of the batteries that are cycling at very high rates (e.g. 10C) with a neutron patterns collected each 1 s along 200 cycles and more.
All these efforts lead us closer to understand the aging phenomena occurring during cycling and to gain the insights into the failure of more academic systems like Na-ion, all solid state batteries and Li-S batteries.
Examples based on different operando/in situ techniques such as X-ray diffraction, neutron diffraction, neutron imaging, and X-ray tomography used to characterize solid-state Li-ion, Na-ion, and Li-S batteries will be presented during the talk.

Supported noble metal nanoparticles are widely used in heterogeneous catalysis. It is well established that the performance of catalytic nanoparticles is closely related to their size, shape and interparticle distance. Synthesis methods that can tailor the structural properties of noble metal nanoparticles are therefore attractive to elucidate performance-structure relationships and tune the catalytic activity, selectivity and thermal stability. In this regard, there is an increasing interest in Atomic Layer Deposition (ALD), a vapor-phase deposition method which proved its efficiency in dispersing noble metal nanoparticles on complex high surface area supports with atomic-scale control over the metal loading (atoms per cm²) and nanoparticle size [1]. However, an improved understanding of how the deposition parameters influence the formation and growth of the noble metal nanoparticles is required to fully exploit the tuning potential of ALD.

We recently designed a synchrotron-compatible high-vacuum setup that enables in situ X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS) monitoring during thermal and plasma-enhanced ALD [2]. Using this setup, we resolved the dynamics of Pt and Pd nanoparticle formation and growth on planar SiO₂ substrates. In situ XRF was used to quantify the metal loading, while analysis of the GISAXS patterns allowed us to correlate the amount of deposited material with the evolution of structural parameters such as cluster shape, average size and areal density. Firstly, we investigated how the choice of reactant (O₂ gas, O₂ plasma, N₂ plasma, NH₃ plasma) affects the island growth and morphology during ALD of Pt with the MeCpPtMe₃ precursor at 300 °C. It was found that O₂ induces atom and cluster surface diffusion and promotes the ripening of the Pt nanoparticles, while diffusion phenomena seem to be suppressed during N₂ and NH₃ plasma-based ALD. This insight provided the ground for the development of a tuning strategy that is based on combining the O₂-based and N₂ plasma-based ALD processes and offers independent control over the Pt nanoparticle size and coverage [3]. Secondly, we carried out a systematic study of plasma-enhanced Pd nanoparticle ALD with the Pd(hfac)₂ precursor at 150°C, comparing a purely reducing chemistry (H₂ plasma as reactant) with a three-step process that includes an oxidizing agent (sequential dosing of H₂ plasma and O₂ plasma [4]). In contrast to the Pt system, it was found that Pd ALD is characterized by a static nanoparticle growth, even when an O₂ plasma step is included in the deposition process. This knowledge is vital to enable efficient synthesis of supported catalysts.

[1] Lu et al., Surf. Sci. Rep. 71 (2016) 410. [2] Dendooven et al., Rev. Sci. Instrum. 87 (2016) 113905. [3] Dendooven et al., Nat. Commun. 8 (2017) 1074. [4] Weber et al., J. Phys. Chem. C 118 (2014) 8702.

Oriented attachment of PbSe nanocubes can result in the formation of two-dimensional (2D) superstructures with long-range nanoscale and atomic order1,2. This questions the applicability of classic models in which the superlattice grows by first forming a nucleus, followed by sequential irreversible attachment of nanocrystals3,4, as one misaligned attachment would disrupt the 2D order beyond repair. Here, we demonstrate the formation mechanism of 2D PbSe superstructures with square geometry by using in situ grazing-incidence X-ray scattering (small angle and wide angle), ex situ electron microscopy, and Monte Carlo simulations. We observed nanocrystal adsorption at the liquid/gas interface, followed by the formation of a hexagonal nanocrystal monolayer. The hexagonal geometry transforms gradually through a pseudo-hexagonal phase into a phase with square order, driven by attractive interactions between the {100} planes perpendicular to the liquid substrate, which maximize facetto- facet overlap. The nanocrystals then attach atomically via a necking process, resulting in 2D square superlattices.

Additive manufacturing (AM) of metals is based on a layer-by-layer additive process, in contrast to traditional manufacturing processes that often require labor-intensive and costly subtraction or forming.¹ AM technologies provide great flexibility in manufacturing parts with complex geometrical shapes and can significantly reduce manufacturing lead times and associated cost. Thus, AM is fast becoming an attractive option for the fabrication of increasingly complex and high-valued metal components in the aerospace, oil & gas, automobile, electronics, and biomedical industries. Unfortunately, elemental segregation can present a ubiquitous problem for AM parts due to solute rejection and redistribution during the rapid solidification process.² We have conducted a series of X-ray synchrotron in situ operando studies, based on simultaneous ultra-small-, small-, & wide-angle X-ray scattering & diffraction, USAXS/SAXS/WAXS (XRD), together with electron microscopy & thermodynamic modeling, to show that in one AM Ni-based superalloy, Inconel 625, deleterious δ-phase precipitates grow on much shorter time scales than in the corresponding wrought alloys (i.e., minutes versus tens of hours).^3,4

The root cause of this δ-phase formation is localized elemental segregation that results in local compositions being outside the bounds of the allowable range set for wrought alloys. The in situ operando USAXS/SAXS experiments reveal that platelet-shaped δ phase precipitates grow continuously, preferentially along their lateral dimensions during stress-relief heat treatments, while their thickness dimension remains constant from very early heat treatment times.⁴ No significant nucleation barrier is observed in the WAXS/XRD measurements. The activation energy for δ-phase growth is ≈ 131 kJ mol^-1. We further find that a subsequent homogenization heat treatment can be effective both in homogenizing the AM alloy and in removing the deleterious δ phase.^3,4 We assert that the methodology established with these measurements could be extended to elucidate the phase evolution during heat treatments in a broad range of AM materials.

[1] I. Gibson, D.W. Rosen & B. Stucker. Additive manufacturing technologies, Springer, 2010.
[2] Y. Idell, L.E. Levine, A.J. Allen, F. Zhang, C.E. Campbell, G. Olson, J. Gong, D. Snyder & H. Deutchman; JOM, 68, 950-959, (2016).
[3] F. Zhang, L.E. Levine, A.J. Allen, C.E. Campbell, E.A. Lass, S. Cheruvathur, M.R. Stoudt, M.E. Williams & Y. Idell; Scripta Mater., 131, 98-102 (2017).
[4] F. Zhang, L.E. Levine, A.J. Allen, M.R. Stoudt, G. Lindwall, E.A. Lass, M.E. Williams, Y. Idell & C.E. Campbell; Acta Mater., submitted (2018).

In quantum electronics the manipulation of strain near isolated point defects and engineered structures is central to harnessing the potential of solid-state qubits for hybrid quantum systems and nanoscale sensing. While lattice strain can be used both statically and dynamically to tune quantum energy levels and engineer hybrid system response, the direct observation of nanoscale strain fields induced near quantum defects is extremely challenging as this strain is localized near a defect potentially microns from surface and varying in time. We report preliminary results of a stroboscopic Scanning X-ray Diffraction Microscopy (s-SXDM) imaging approach using 10keV photons focused to a ~25nm FWHM beam waist at the Center for Nanoscale Materials Hard X-ray Nanoprobe. In this study ~30ps x-ray pulses from the Advanced Photon Source were synchronized to a Surface Acoustic Wave (SAW) launcher in order achieve static time domain and phase sensitive Bragg diffraction imaging at radio frequencies with nanoscale spatial resolution. We use this technique to simultaneously map near-surface microstructure, atomic fluorescence, and acoustically induced lattice curvatures generated by interdigitated transducers fabricated on 4H-SiC which hosts vacancy related spin defects for quantum sensing and information.

Shape memory alloys (SMAs) – a class of functional materials with commercial applications in the biomedical industry – deform primarily by the mechanisms of reversible martensitic phase transformation. The elements of microstructure in SMAs such as nano-scale precipitates, impurity inclusions, and grain boundaries constrain their deformation in various ways. We combined in-situ high-energy X-ray diffraction microscopy (HEDM), a synchrotron-based 3D, non-destructive technique to obtain grain-scale lattice strains and crystal orientations with microstructural modeling to study the influence of these microstructural elements on specific deformation phenomena. First we will present our general methodology for combining data from HEDM to inform and then validate a microstructural model for phase transformation. Then we will present mechanisms for two phenomena in single and polycrystalline NiTi SMAs. In a single crystal, transformation strain produced was lower than theoretically possible due to constraint from inclusions. In a polycrystal, cyclic loading produced spatially heterogeneous residual strains due to constraint from neighboring grains. This combination of HEDM and modeling can also be applied to study the deformation mechanics of SMA devices such as cardiovascular stents.

Determining the in situ nano- and microscale mechanics of hierarchical nanocomposites, whether natural or synthetic, can be technically challenging due to the necessity to experimentally decouple deformation at multiple length scales. Doing so is critically important, as it can illuminate the mechanisms enabling multiple functional optimization in biological composites, as well as test the functionality of bioinspired materials [1]. The cuticle of arthropods (like the mantis shrimp [2]) are materials adapted for high dynamic mechanical resistance [2-3]. Cuticle consists - at the nanometre scale - of mineralized semicrystalline chitin nanofibres embedded in a more amorphous matrix of mineral (calcium carbonate) and protein, which in turn are assembled into parallel layers of fibres arranged in a twisted plywood (Bouligand) motif [2-3]. At the microscale, these plywood layers run parallel to the shell surface, and are interpenetrated by transversely-running pore-canals [2]. Here, we develop and present a novel 3D nanofibrillar orientation-cum-mechanics reconstruction method to determine deformation mechanisms at the nano- and microscale in stomatopod cuticle, which combines synchrotron microbeam X-ray diffraction with in situ deformation and fibre-composite theory [4-5]. The X-ray reconstruction method is solely based on fibre symmetry at the molecular level and hence can have wider applications beyond hierarchical biological composites. We apply the model to measure angularly-resolved deformation and reorientation of chitin nanofibers – embedded in a mineralized protein matrix – in the tergite (exoskeletal segment) of mantis shrimp, using microfocus wide-angle X-ray diffraction combined with scanning and in situ tensile loading. In combination with lamination theory, the method quantifies the internal, anisotropic strain fields inside Bouligand lamellae, is able to decouple internal fibrillar reorientation from whole-body movement, and resolves spatial gradients in fibre strain during physiological bending [4-5]. Our reconstruction technique can be applied more generally to determine the in situ and spatially-resolved dynamics of both natural and synthetic hierarchical nanocomposites.

References:
[1] S. E. Naleway, M. M. Porter, J. McKittrick and M. A. Meyers, Advanced Materials (2015), 27:5455–5476.
[2] J. C. Weaver, G. W. Milliron, A. Miserez, K. Evans-Lutterodt, S. Herrera, I. Gallana, W. J. Mershon, B. Swanson, P. Zavattieri, E. DiMasi and D. Kisailus, Science (2012), 336:1275–1280.
[3] P. Romano, H. Fabritius and D. Raabe, Acta Biomaterialia (2007) 3:301-309.
[4] Y. Zhang, P. De Falco, Y.Wang, E. Barbieri, O. Paris, N. J. Terrill, G. Falkenberg, N. M. Pugno and H. S. Gupta, Nanoscale (2017), 9:11249
[5] Y. Zhang, O. Paris, N. J. Terrill and H. S. Gupta, Scientific Reports (2016), 6:26249.

Many of the states that participate in chemical reactions (e.g. heterogeneous catalysis) or that govern the performance of electronic devices (e.g., interface states of selective contacts of solar cells) have been studied using operando X-ray spectroscopy. Despite the success of X-ray-based techniques, their sensitivity is often not high enough to probe low concentration of such states (<ppm) at, for instance, semiconductor interfaces. Moreover, X-ray spectroscopy is not sensitive to the paramagnetic nature of the states involved in chemical reactions. A complementary spectroscopic technique, that can provide deeper insight into the chemical and electronic nature of above-mentioned states and processes, is electron paramagnetic resonance (EPR). Thanks to the unmatched specificity and its quantitative nature, EPR is amongst the most powerful spectroscopic techniques available today and is gaining significant attention in the research community as an analytical tool in life and materials science. In conventional EPR, the to-be-studied specimen is placed inside a microwave resonator and its paramagnetic states are brought into microwave resonance by sweeping an external magnetic field. Despite its analytical success, up to date only very few operando EPR experiments have been performed. The reason lies in the disadvantage of the resonator approach. It is extremely challenging to design the probe or the chemical reactor for an operando EPR experiment due to (a) the limited probing volume inside the cavity; (b) the reduction in sensitivity when metals or polar liquids are within the probing volume; (c) parasitic signals from the substrates; (d) the bulky nature of the experiment due to the required resonator and electromagnet.
In this lecture, we will present a novel EPR technique referred to as EPR-on-a-chip (EPRoC). EPRoC is no longer restricted by the boundary condition of a resonator and has a three order of magnitude higher spin sensitivity than conventional EPR. The EPRoC sensor is a single coil (or an array of coils) that is scaled-down in size to a few 10-100 µm, depending on application. The sensor and the microwave generating as well as detecting unit are integrated on a small, millimeter-sized silicon chip. Different from conventional EPR, EPRoC is carried out by sweeping the microwave frequency instead of the magnetic field. This enables operation with a constant magnetic field, which at X-band is established by a permanent magnet. Due to its simplicity and compactness, EPRoC can be incorporated in conventional growth reactors, (electro)chemical cells or even the endstation at an X-ray beamline. Here, we will review the recent success of operando EPRoC, discuss the detection principle and demonstrate its superior sensitivity. Finally, we will present first time-domain EPRoC results and a first operando experiment. The potential of EPRoC in combination with X-ray spectroscopy will be highlighted.

Ferroelectric oxide nanocrystals are of interest for a wide variety of functional applications including data storage, energy storage, and within polymer composites for flexible film capacitors. It is known that in the nanoscale size regime, the ferroelectric properties and structural distortion tend to diminish with decreasing size, though ferroelectric properties and structural distortions have been observed for particles as small as 5 nm in recent years. While the effect of size is fairly well characterized, the influence of shape (e.g., sphere vs cube) and surface termination (surrounding matrix or capping ligands) is not as well understood. With regard to surface environment, ligand exchange methods are often employed to change the surface functionalization of the nanoparticles before they are incorporated in polymer composites. However, the effect of different ligands on the structure is largely unknown. In this work, we employed both neutron total scattering and in situ temperature-dependent X-ray total scattering to explore the local and average structures of barium titanate (BaTiO₃) nanocrystals as a function of both size and capping ligand. This study utilizes a series consisting of ~10, ~25, and ~30 nm BaTiO₃ nanocubes with either oleic acid (CH₃(CH₂)₇CH=CH(CH₂)₇COOH) or nitrosonium tetrafluoroborate (NOBF₄) capping ligands. The oleic acid ligands attach during hydrothermal synthesis of the nanocubes while the NOBF₄ ligands can be attached via a simple solution-phase ligand exchange method. In most prior neutron total scattering studies, the capping ligands contained carbon-hydrogen bonding, the presence of which would obscure the Ti-O pair correlations, a key indication of the ferroelectric distortion. However, the NOBF₄-BaTiO₃ system uniquely does not contain hydrogen, and has revealed the existence of a local ferroelectric distortion similar to that found in bulk BaTiO₃ for all nanocrystal sizes studied. Results will also be presented from a study employing in situ X-ray PDFs with elevated temperature (RT – 150°C), showing the effects of size and capping ligand on the tetragonal-to-cubic phase transition, which occurs in bulk BaTiO₃ at 120°C. This work contributes to a better understanding of the interplay between the nanocrystal’s surface environment and structure, and will enable better tuning of ferroelectric properties for composite applications.

Although air is usually used for fuel combustion, it is well known that oxygen enrichment of combustion air enhances the combustion efficiency. Cryogenic oxygen separation is well established for oxygen production at large scale but its costs are relatively high compared to the economic benefit caused by an improved combustion efficiency. Therefore, the development of alternative oxygen separation processes is still an issue. One of the most promising ceramic materials for oxygen separation membranes is the mixed ionic electronic conducting (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ (BSCF5582) with its extremely high oxygen vacancy concentration. In contrast to BSCF5582, La₂NiO_4+δ is an oxygen excess material with oxygen interstitials which possesses an intrinsic stability against CO₂.
We report on ⁵⁷Fe Mössbauer in situ studies of the mixed ionic electronic conducting (MIEC) oxide functional materials (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3-δ (BSCF5582) and on iron-doped La₂NiO_4+δ. Mössbauer measurements have been conducted between room temperature and 1000 °C in atmospheres of variable oxygen content in order to obtain insight into local coordination and valence of iron at working conditions.
The magnetically-split room-temperature Mössbauer spectra of quenched BSCF5582 powder samples equilibrated between 500 and 1000 °C reveal the presence of two inequivalent iron species as well as significant changes in crystal stoichiometry. Evaluation of signal intensities confirms results from theoretical computations on vacancy formation in BSCF which indicate that formation energies of the various types of oxygen vacancies differ by the order of 0.1 eV only. In addition, it is revealed that the distribution of vacancies is far from random. In the paramagnetic high-temperature phase (T ≥ 320 °C), the quadrupole-split signals demonstrate that local symmetry at iron sites is lower than cubic. At 700, 850, and 1000 °C, isomer shifts as well as quadrupole splittings were found to be independent of P_O2, which is discussed in respect to stoichiometry-related changes in valence and local coordination of the iron probes. The analysis of the isothermal decrease of signal intensity with increasing oxygen deficit observed at high temperatures points to peculiarities in the vibrational properties of the highly defective material.
The temperature-dependent Mössbauer measurements (300 ≤ T/°C ≤ 1000) of iron-doped Ruddlesden-Popper phases of type La₂Ni_1-yFe_yO_4+δ (y = 0.02, 0.05, and 0.1) show a clear dependence on oxygen partial pressure at isothermal conditions. It is concluded that quadrupolar interactions increase with decreasing stoichiometric parameter δ. Possible origins of these uncommon observations and their connection with the interstitial oxygen disorder of the material are discussed.

The insertion of lithium ions into solid host structures is the key mechanism for energy storage in lithium ion batteries and has recently been demonstrated as a means to dynamically tune material properties for solid-state switching devices. In situ investigations of lithium insertion processes are complicated by the air-sensitivity of the lithium-containing electrodes and electrolytes. The quantification of the lithium fraction in a certain host particle using electrochemical methods is further complicated by unequal lithiation kinetics in different host particles and side reaction currents originated at current collector-electrolyte interfaces.

Here, we present an experimental platform for the quantitative investigation of lithium insertion into a single-particle host structure, enabling the use of in situ time-resolved x-ray and optical techniques, combined with electrochemical analysis. Using a single flake of MoS₂ as a model host system we demonstrate in situ measurements of the structural evolution, optical properties, thermal properties and the layer-to-layer binding as a function of lithium fraction by means of ultrafast x-ray and optical techniques. Our picosecond time-scale optical pump x-ray diffraction probe experiments define a new method for directly probing cross-plane and interfacial phonon transport as a function of the concentration of an intercalated species.

Organic lead halide perovskites have shown immense potential in high-performance optoelectronic devices. However, significant challenges remain for real-world applications. A fundamental understanding of how the organic cations within inorganic framework affect the structural phase transitions, and optoelectronic properties of the organic-inorganic hybrid perovskite (OIHP) materials is desirable to design new materials and improve device performance. We have used the TOPAZ instrument at the ORNL Spallation Neutron Source to probe the role of hydrogen bonding in structural phase transition of OIHPs by collecting the 3D volume of diffraction pattern from the sample in neutron event mode. In this presentation, I will show our most recent result from real-time in situ variable temperature study that established the path of the organic cation induced anomalous optoelectronic phenomenon [1] in MAPbX₃, where MA is methylammonium, an organic cation that forms a network of hydrogen bonds with the halides X (Br^-, l^-) in the solid states [1-2]. Data from real-time single-crystal neutron diffraction following the initiation of orthorhombic-tetragonal phase transition provided details the change of hydrogen bonding pattern between the organic donor and the inorganic accepter, which not only induces the structural transition that results in anomalous red-shift of PL peak position as temperature increases, but also causes the decrease in dielectric screening, leading to the reduction of non-radiative recombination for stronger PL intensity [1].
References
[1] Yang, B.; Ming, W.; Du, M. H.; Keum, J. K.; Puretzky, A. A.; Rouleau, C. M.; Huang, J.; Geohegan, D. B.; Wang, X. P.; Xiao, K. Manuscript submitted for publication.
[2] Ren, Y.; Oswald, I. W. H.; Wang, X.; McCandless, G. T.; Chan, J. Y. Crystal Growth & Design 2016, 16 (5), 2945-2951.

The oxygen reduction reaction (ORR) is a critical reaction in energy technologies such as fuel cells and metal-air batteries. While Pt-based catalysts are the conventional choice for acidic electrolytes, favorable oxygen reduction kinetics and stability considerations that occur in alkaline electrolytes provide possibility for using non-platinum group metal catalysts, including silver. In particular, bimetallic or alloyed systems of silver and copper have been predicted by theory to be active for the ORR [1]. Recently, we have shown that co-sputtering silver and copper as both thin films and nanoparticles results in ORR catalytic activity that surpasses that of either metal on its own [2]. In order to investigate the mechanism of this improvement, we developed several operando electrochemical cells for use at the Stanford Synchrotron Radiation Lab. In this work we investigate these bimetallic catalysts using in situ x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD) in order to help understand the activity enhancements seen when combining copper and silver for the ORR.

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1. K. Shin, D.H. Kim, and H.M. Lee. ChemSusChem (2013), 6: 1044-1049.
2. Higgins et al., in preparation.

One major challenge hindering the large-scale utilization of high-performing polymer electrolyte membrane fuel cells (PEMFCs) is the durability of catalysts for the cathodic oxygen reduction reaction (ORR). In catalytic systems that show enhanced activity such as faceted platinum-transition metal (Pt-M) bimetallic catalysts (M = Fe, Co, Cu and Ni), continuous leaching of the non-noble, more reactive metals during long-term stability tests contributes to degradation in mass activity. A previous study by the Yang group had demonstrated that carbon-supported truncated octahedral Pt₃Ni electrocatalysts lost 21% of its initial electrochemical surface area (ECSA) and 40% of its mass current density (from 0.55 to 0.33 A/mg_Pt) of commercial catalysts [1]. To control metal leaching and improve catalytic performance and durability, it is essential to understand the underlying mechanism and kinetics of metal leaching in faceted Pt-M bimetallic electrocatalysts. In this study, in situ x-ray absorption spectroscopy (XAS) was used to probe the changes in the electronic structure of Pt-Ni electrocatalysts during accelerated durability tests. Real time data acquisition was enabled by an aqueous electrochemical cell, which was designed and made in house. Current results suggest the catalysts underwent restructuring during the accelerated durability test, as evidenced by an increased to a maximum level of oxidation of Ni after 2500 potential cycles and a strengthening of the Pt-Pt bond over time.

[1] Wu, J.; Yang, H. ChemCatChem 2012, 4 (10), 1572-1577.

Metallic alloy nanoparticles (NPs) constitute promising materials in the field of heterogeneous catalysis. As compared with bulk pure materials, these NPs take the advantage of potential tuning of their catalytic properties by size and synergetic effects. This is for example the case of Au-Cu NPs which display higher reactivity and selectivity than the pure metals for CO oxidation or for the PROX reaction.
Combining several operando techniques opens up the possibility of determining the structure of the bimetallic NPs from their nucleation up to their exposure to reactive gases. In this talk, I will present Grazing Incidence X-Ray Diffraction (GIXD), Photoelectron Spectroscopy (XPS), and Scanning Tunneling Microscopy (STM) results obtained on Au, Cu and Au-Cu NPs grown on TiO₂(110) and exposed to CO and O₂.
I will show that combining these experimental methods allows us to determine nucleation sites and epitaxial relationship, study core-shell or alloy formation, stability under gas exposure, effects of thermal treatments and reaction-induced reorientation or recrystallization of NPs.

The integration of III-V semiconductors on silicon is of great interest regarding a possible combination of direct band-gap material systems with the standard CMOS platform. Despite the large lattice mismatch, an epitaxial connection of both materials can be achieved by growing III-V nanowires on Si substrates using e.g. molecular beam epitaxy (MBE). MBE deposition chambers are typically equipped with Reflecting High-Energy Electron Diffraction (RHEED) systems, whose main purpose is in the field of thin film deposition. For a quantitative interpretation of RHEED during NW growth however, the high scattering cross-section and the grazing incidence angle require the consideration of shadowing effects.
We developed an approach for simulating RHEED intensity patterns from polytypic NWs, taking into account the incidence angle and divergence of the electron beam, the number density and shape of the NWs, and the phase distribution of the NW ensemble. In addition the model allows for simulation of the impact of tapering, facet growth and parasitic interstitial growth. As an important effect we considered the occurance of shadowing in the recorded RHEED intensities, i.e. that NWs are not illuminated because of the electron absorption by another NW.
Our approach has been applied for modeling experimental data obtained during the nucleation phase of self-catalyzed GaAs NWs by simultaneous time-resolved in-situ XRD and RHEED. The in-situ experiment has been performed at beamline P09 at DESY, Germany. We show that the phase composition at the NW base is affected by a variation of the Ga-droplets acting as seed particle in the nucleation process.
Due to the different sensitivity of RHEED and XRD to very small objects, the combination of both in-situ methods can be used to acquire a detailed understanding of the processes happening at the onset of NW growth and allows for investigating the crystal phase evolution with high accuracy. This is a fundamental step of monitoring growth and towards the fabrication of defect free NW based devices.

Cyclic stability of electrochemical energy storage materials is a key challenge in the development of new electrochemical energy storage materials. This work demonstrates ex-situ and operando measurement of x-ray pair-distribution function (PDF) data from microgram quantities of electrochemically active δ-MnO₂. Potassium birnessite was proton-exchanged and chemomechanically exfoliated using tetrabutylammonium hydroxide in an ultrasonic bath. Isolated nanosheets were electrostatically self-assembled and electrophoretically deposited on conductive substrates. PDFs reveals that the Mn-O coordination environment shows contracting bond lengths with increasing charge state, while electrode charging leads to a decrease in surface Frenkel defect concentration. Discharging reverses this process, creating more Mn³⁺ defects. Additionally, we see that interlayer water content varies with charge state: discharging the MnO₂ electrode drives water from the interlayer gallery.

Despite decades of research into nucleation processes, very little is currently known on how nanocluster formation takes places on the atomic scale. We have developed methods which allows using X-ray Total Scattering and Pair Distribution Function analysis to follow nanoparticle nucleation and growth in situ.^1-3 In contrast to conventional crystallographic studies, PDF analysis gives structural information from non-crystalline species, allowing obtaining structural information on the atomic scale, all the way from precursor to the final nanoclusters during synthesis. We have furthermore shown how PDF allows obtaining detailed information on nanocluster structures with no long range order on nanoclusters fundamentally different from bulk materials.⁴
Here, we use in situ PDF to study the formation of anionic bismuth based clusters. Bismuth oxido clusters in solution have recently attracted much attention for a wide range of applications in catalysis, medicine, and as precursors for advanced materials.⁵ Despite the very broad range of applications, the chemical processes involved in the formation of the clusters in solution are not well understood. While the cluster structures have been studied by single crystal diffraction after crystallization to the solid form, it is much more challenging to study the clusters directly in dilute solutions using conventional techniques.
Large bismuth oxido clusters of the type [Bi₃₈O₄₅L₂₄] (where L = ligand, e.g. NO₃^-,) (here abbreviated {Bi₃₈}), form in DMSO through a hexanuclear bismuth oxido cluster, {Bi₆}. We have applied X-ray total scattering studies to follow the formation of ionic bismuth oxido clusters in solution. Using PDF, we can follow the transformation of cluster structures from {Bi₆} units to stable {Bi₃₈} clusters. We see that a disordered cluster containing a {Bi₁₈} motif form as an intermediate structure in the cluster growth, also inducing disorder in the {Bi38} cluster, which orders on ligand exchange. By combining PDF with small angle scattering and ESI-MS, we obtain a unified view of the cluster growth, getting closer to an atomistic understanding of the cluster transformation processes.

1. Jensen, K. M. O.; Christensen, M.; Juhas, P.; Tyrsted, C.; Bojesen, E. D.; Lock, N.; Billinge, S. J. L.; Iversen, B. B. J. Am. Chem. Soc. 2012, 134, (15), 6785-6792.
2. Jensen, K. M. Ø.; Tyrsted, C.; Bremholm, M.; Iversen, B. B. ChemSusChem 2014, 7, (6), 1594-1611.
3. Jensen, K. M. O.; Andersen, H. L.; Tyrsted, C.; Bojesen, E. D.; Dippel, A. C.; Lock, N.; Billinge, S. J. L.; Iversen, B. B.; Christensen, M. ACS Nano 2014, 8, (10), 10704-10714.
4. Jensen, K. M. O.; Juhas, P.; Tofanelli, M. A.; Heinecke, C. L.; Vaughan, G.; Ackerson, C. J.; Billinge, S. J. L. Nat Commun 2016, 7.
5. Schlesinger, M.; Weber, M.; Ruffer, T.; Lang, H.; Mehring, M. Eur. J. Inorg. Chem. 2014, 2014, (2), 302-309.

To gain atomic level understanding of active sites in a multi-functional catalytic process, we have investigated MgAl hydrotalcite (HT) based catalyst that exhibits promising conversion of bioethanol to high value C₄ compounds. The ethanol to higher alcohol conversion goes through multitude of intermediate steps and the reaction pathway depends on chemical and electronic nature of active sites in the material. In particular, addition of copper is expected to promote the catalytic dehydrogenation of alcohols to aldehydes which is the first step in the complex cascade reaction and considered as the rate determining step of the catalytic process. In this study, we studied the concentration dependent dispersion of copper active sites in the MgAl matrix and its relation to catalytic performance. Catalysis experiments were carried out in an indigenously designed plug flow reactor to understand the selectivity and efficiency of copper substituted catalysts during the conversion of ethanol to higher alcohols. Structural, chemical and electronical changes in copper substituted catalysts were studied before and after the catalytic reaction using high resolution transmission electron microscopy (TEM), X-ray diffraction (XRD) and in-situ X-ray absorption – in particular X-ray absorption near edge structure (XANES) analysis. It was observed that different oxidation states of copper and the extent of dispersion of copper in the HT matrix influences catalytic efficiency and selectivity of the process by promoting various side reactions. Synthesis of copper substituted HT derived mixed oxide catalyst plays a major role in controlling the dispersion of the copper in the matrix. Fundamental challenges in achieving higher copper substitution without significant clustering and aggregation effects will be discussed in context of catalytic selectivity and efficiency.

Capturing the structure and properties of water at the interface with a solid surface presents a unique challenge for both Kohn-Sham and classical density-functional theory due to a complex interplay between chemical binding, electrostatic interactions, steric effects, and dispersion. X-ray reflectivity measurements probe the electron density of aqueous interfaces with high precision, but rely on model-dependent fitting to obtain the corresponding structural model. We present a validation protocol which enables calculation of interfacial X-ray structure factors from theory for direct comparison to experimental measurements. We apply this protocol to benchmark joint DFT, classical molecular dynamics, and first principles molecular dynamics simulations of the Al₂O₃/water interface, probing the effect of pressure, temperature, and finite size upon the predicted structural model. We explore the relative strengths and weaknesses of each class of theory, gaining insights into the bonding and structural properties of interfacial water which will aid future development of more accurate electronic and classical density-functionals.

Glasses are important materials for a wide range of applications, due to their high optical transparencies and minimal interactions with other materials. High-strength, fracture-resistant glasses are now routinely available, finished with a toughening (or tempering) process of chemical modification, where traditional Si-rich soda-lime glass is exposed to calcium-doped potassium nitrate (Ca-KNO₃) and heated. Sodium ions at the surface of the glass are swapped for potassium and calcium ions in the solution, which propagate into the bulk through diffusion. The result of this ion exchange is a surface held in a state of static compression, with the core in a state of tension; thus, any microcracks (e.g., scratches) forming at the surface are discouraged from propagating into larger-scale fractures.

While the finishing process is well developed and widely used, a gap exists in understanding the local compositions resulting from the chemical modification. In particular, it is suspected that different tempering procedures may lead to different compositional profiles, but probing this is a challenging task. Glass is a bulk insulator, making it difficult to characterize using electron-based probe sources, while conventional photonic techniques lack the spatial resolution for precise detection of local changes. Recent advancements in X-ray source and optical technologies, however, are now facilitating spatially-resolved chemical analysis with X-ray fluorescence (XRF). These advancements enable spatial resolutions in the single micrometers with detection sensitivities in the parts-per-billion (attogram) regime, providing comparable detection sensitivities to techniques such as ICP-MS but with considerably more streamlined workflows. The detection range and spatial resolution coupling are complimentary to other popular techniques, such as EDS and SIMS, while the non-destructive nature of X-rays preserves the specimen for further analysis using correlative microscopy routines.

Here, we present a comparative study performed on three different commercial tempered glasses using a novel micro-XRF spectrometer for characterization. Each specimen was commercially sourced with Mohs hardness of 9H; however, by studying the elemental profile of Si, K, and Ca across each material’s cross-section, several interesting observations were made. First, it was found that one specimen had local concentrations of Ca, suggesting an incomplete chemical modification in those regions. Furthermore, it was found that two had very similar compositional profiles while the third exhibited a different profile. These results suggest that two of the manufacturers may be using similar overall strategies for fabrication, while the third may be using a different approach. In this presentation, we will briefly introduce the technique of micro-XRF in the context of other local probing techniques, then detail the results of this study as a practical commentary on the present and future of XRF.