XSD Seminars

XSD Seminars are an open forum where speakers from the U.S. and abroad, as well as XSD, present their latest research. All are cordially invited to attend.

Also available in iCalendar formats.

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Past Seminars

2014

May 22
Thursday

The Power and Flexibility of X-Ray Scattering as a Probe of Magnetic Systems: KCuF3 and Fe/Gd Thin Films

Speaker: James C. T. Lee, Advanced Light Source, LBNL
XSD Presentation
431/C010 @ 10:00 AM
View Description
X-ray scattering is an excellent tool for studying both the crystal structure and, via resonant scattering, the electronic structure of the magnetic state. To illustrate the power and flexibility of x-rays as a probe, I will discuss magnetism in orbitally ordered KCuF3 single crystals and Fe/Gd thin films exhibiting perpendicular anisotropy.

Due to its simplicity, KCuF3 is the ideal system of orbital physics, which plays an integral part in many exotic phenomena like colossal magnetoresistance. The basis for nearly all theories of orbital physics Kugel–Khomskii model, being the first to explain the symmetry of orbital and magnetic order in KCuF3. However, no refinement of the Kugel-Khomskii model heretofore could account for other prominent features of KCuF3, such as the disparity of its orbital and spin ordering energy scales. Based on x-ray scattering (done in part at Sector 4ID-D, APS) and Raman scattering experiments, we have found that the missing piece of the puzzle is a direct orbital exchange interaction. This mechanism may play a crucial role in other orbitally active materials. Unlike KCuF3, the magnetic order in Fe/Gd thin films exists over mesoscopic scales. These systems display complex domain structures and phase diagrams. Judiciously made films with large perpendicular anisotropy may show novel domain structures and spin textures. Resonant soft x-ray scattering (RSXS) at the Fe L3 and Gd M5 edges was performed at Beamline 12.0.2.2, ALS, to probe the domain structure with evolving applied magnetic field and sample temperature. Ordered arrays of stripe domains appear well below saturation. As the applied magnetic field increases, a metamagnetic transition occurs and the stripe array smoothly transforms into a hexagonal bubble lattice. The bubble domains may display a skyrmionic spin texture.

Not just limited to single crystals and thin films, RSXS is also an ideal tool for studying lithographically made systems engineered to display exotic magnetism (e.g. nanodot arrays displaying spin ice behavior). The power of RSXS can also be deepened by using x-ray photon correlation spectroscopy to characterize the dynamics of magnetic materials. Such demonstrations of the flexibility and power of x-ray scattering will be made at the new RSXS end station at Sector 29.
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May 21
Wednesday

Electronic Transitions, Coherence, and Hybridization: A Spectroscopic Study of Unusual Electronic Properties in Strongly Correlated Materials

Speaker: Fanny Rodolakis Simoes, University of Illinois-Chicago
XSD Presentation
431/C010 @ 11:00 AM
View Description
Understanding phase transition induced by strong electronic correlations represents one of the major challenges in condensed matter physics. Phenomena presenting great interest both from point of view of basic science and of their potential technological applications, like metal-insulator transitions and high temperature superconductivity, are typical examples of effects determined by collective electronic excitations. On the theoretical side, development of Dynamical Mean Field Theory provided a powerful conceptual approach to interpret these phenomena. On the experimental side, one of the main challenges for the study of strongly correlated materials is the development of techniques giving access to the electronic structure of these systems while tuning external parameters (temperature, pressure, electric field, etc.) across their often complicated thermodynamic phase diagrams.

In this talk I will present an investigation of some of the most remarkable manifestations of strong correlations in materials by using different spectroscopic techniques such as high-resolution X-ray absorption (PFY-XAS) and angular resolved photoemission spectroscopy (ARPES): the metal-insulator transition in the transition metal oxide (V1-xCrx)2O3, the Kondo effect in the heavy fermion compound Ce2RhIn8, and high Tc superconductivity in copper oxide Bi2Sr2CaCu2O8+δ. By shedding the light on their electronic structures, those measurements combined with LDA+DMFT calculation reveal an even more intricate behavior like the inequivalence of temperature, doping and pressure in the vanadium sesquioxide phase diagram, or multiple energy scales in Ce2RhIn8.
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May 20
Tuesday

Correlating Interfacial and Bulk Nanostructure with Performance of Organic Electronic Devices: The Usefulness of Soft X rays

Speaker: Hongping Yan, High-Pressure Collaborative Access Team (HP-CAT), Geophysical Laboratory, Carnegie Institution of Washington
XSD Presentation
431/C010 @ 10:00 AM
View Description
Soft matter systems often consist of multiple components and are naturally or synthetically nanostructured for optimal properties and performance. Near an absorption edge (e.g. carbon 1s), the high energy-dependence of absorption coefficient and index of refraction provides tunable contrast between functional moieties of polymer thin films for improved soft x-ray scattering and reflectivity characterization capability.

In this presentation, the usefulness of resonant soft x-ray reflectivity (R-SoXR) and scattering (R-SoXS) in revealing interfacial width and bulk nanomorphology of organic electronics, including organic solar cells and organic field effect transistors, are demonstrated with corresponding study cases. The morphology characterizations are correlated to device performance for better understanding the impact of processing method on nanomorphology and hence the performance of these organic electronic devices. A practical and accurate method to obtain the complex index of refraction, especially the decrement δ, accross the carbon 1s absorption edge is demonstrated, which is expected to greatly improve the simulation and interpretation of R-SoXR and R-SoXS data.
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Apr 16
Wednesday

Sensors and Systems for Digital Radiography

Speaker: Vivek V. Nagarkar, RMD Inc.
XSD Presentation
401/A1100 @ 1:30 PM
View Description
At RMD we have developed modular digital imaging detectors for applications ranging from hypervelocity projectile tracking and ballistic impact analysis to medical X-ray CT and time-resolved diffraction studies. These systems benefit from recently discovered binary and ternary phase inorganic scintillators and novel ceramic scintillators that demonstrate unprecedented emission efficiencies (70,000 to 100,000 ph/MeV), high densities (5 to 9 g/cc), high effective atomic numbers (Z~50 to 70), and radiate in 450 to 650 nm range with fast decay. These recently discovered scintillators are being fabricated at RMD for use in digital radiography by novel processes like physical vapor deposition (PVD) or laser processing. Our advanced PVD techniques results in the formation of structured scintillators in microcolumnar and/or macrocolumnar format, while our laser processing techniques using solid state laser are capable of forming structured scintillators of arbitrary shapes.

Here we will present novel scintillators fabricated in microcolumnar or pixelated form that minimize the traditional tradeoff between spatial resolution and detector efficiency and are suitable for imaging low (8 keV) to high (450 kVp) energy X-rays and/or thermal neutrons. Performance characteristics of radiographic imaging detectors and systems will also be discussed.
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Mar 27
Thursday

Optimum Performance of the Novel Accelerator for Iterative Phase Retrieval in the Fresnel Region Applied to X-ray Phase Contrast Imaging

Speaker: Nghia Vo, Diamond Light Source
XSD Presentation
431/C010 @ 3:00 PM
View Description
Iterative phase retrieval in the Fresnel region based on Gerchberg-Saxton algorithm suffers from slow convergence and stagnation. Recently, a novel accelerator, named random signed feedback (RSF), was proposed (http://dx.doi.org/10.1063/1.4769046) which shows a superior performance compared with other traditional techniques: hybrid input output (HIO) and conjugate gradient search (CGS). Its feasibility is confirmed by applying on X-ray phase contrast tomographic data, collected at beamline I12 Diamond Light Source, which shows promising results. In this talk, I will present how I investigated the RSF accelerator under various conditions to obtain its optimum performance.
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Mar 27
Thursday

X-ray Diffraction from Perfect Crystals - the 100th Anniversary of the First Calculations by C.G. Darwin

Speaker: Denny Mills, Advanced Photon Source
XSD Presentation
401/A1100 @ 11:00 AM
View Description
In 1914, C. G. Darwin published two papers* that established some of the basic features of x-ray diffraction in perfect crystals. One of those features was near-unity reflectivity over a narrow angular range at the Bragg condition, a phenomenon that is still known as the “Darwin width” of the reflection. The talk will briefly describe his calculational approach to scattering in perfect crystals, impact of those calculations, and other aspects of Darwin’s life and work.

*"The Theory of X-ray Reflexion", by C. G. Darwin, Philosophical Magazine, 27, (1914), p313-333 and “The Theory of X-ray Reflexion Part II”, by C. G. Darwin, Philosophical Magazine, 27, (1914), p675-690.
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Mar 21
Friday

Hybrid Pixel Array Detectors Enabling New Science

Speaker: Clemens Schulze-Briese, Dectris Ltd.
XSD Presentation
401/A1100 @ 2:00 PM
View Description
PILATUS single photon counting Hybrid Pixel Device (HPD) detectors have transformed synchrotron research by enabling new data acquisition modes and even novel experiments. At the same time data quality has improved due to noise-free operation and direct conversion of the X-rays. Millisecond readout times and high-frame rates allow for hitherto unknown speed and efficiency of data acquisition.

At cryogenic temperatures, PILATUS allows to acquire data of optimal quality by collecting high multiplicity data at low dose rate, referred to as dose slicing. Monitoring data quality indicators as a function of frame number reveals the optimal data quality for a given crystal. This overcomes the problem of traditional data collection, where radiation damage may affect data accuracy before a complete data set is collected. In contrast, dose-sliced data collection always enables the exploration of the full diffraction potential of the crystal. The noise-free counting of PILATUS detectors allows the dose per frame to be reduced without loss of data accuracy due to read-out noise. Furthermore, high frame rates enable acquisition of optimally fine f-sliced, high multiplicity data in short time.

In room temperature data collection, the high frame rates featured by PILATUS3 detectors allow for outrunning of radiation damage. Recent experiments demonstrate a systematic increase in the dose tolerance of protein and virus crystals as a function of dose rate. PILATUS3 detectors allow even higher frame rates and further push the boundaries of this successful experimental strategy. Latest results obtained with PILATUS3 reveal a departure from a linear or exponential intensity decay in the diffracting power of protein crystals as a function of absorbed dose. A lag phase observed in these experiments raises the possibility of collecting substantially more data from crystals held at room temperature before a critical intensity decay is reached.

The new EIGER detector series presents a leap in HPD detector technology. Featuring 75 µm pixel size and frame rates up to 3000 Hz in combination with continuous read-out, EIGER detectors will open up new opportunities for advanced dose optimized data acquisition techniques.

HPD detectors with CdTe sensors extend the range of high quantum efficiency to 80 keV. This will allow to fully exploit the potential of new high energy and brightness undulator beamlines at unprecedented signal-to-noise ratios and data acquisition speeds.

An overview of the salient detector properties will be given and illustrated by experimental results in various applications.
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Mar 11
Tuesday

Physics and Chemistry of Vacancy Defects in Graphene Layers: Scanning Tunneling Microscopy and Density Functional Theory Study

Speaker: Maxim Ziatdinov , Tokyo Institute of Technology
XSD Presentation
431/C010 @ 11:00 AM
Mar 6
Thursday

Synthesis of ITO Nanoparticles with Shape Control and their Assembly for Solution-Processed Transparent Electrodes

Speaker: Jonghun Lee, Brown University
XSD Presentation
432/C010 @ 2:30 PM
Feb 10
Monday

Elucidating the Structure-Performance Relationship in Organic Photovoltaics (OPVs) by Grazing Incidence X-Ray Scattering

Speaker: Joseph Strzalka, X-ray Science Division/Time Resolved Research
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Since the introduction of the Bulk Heterojunction (BHJ) architecture in the mid- 90s, organic photovoltaic devices have made steady progress toward improved power conversion efficiency, and are now poised to move from niche products to large scale commercial applications. In the BHJ, the photoactive layer consists of electron donor and acceptor materials in a bicontinuous phase blended on the nanoscale. Grazing incidence x-ray scattering, capable of characterizing thin film nanomorphology of surfaces and interfaces, has emerged as a key technique for investigating OPV materials. The hierarchical variety of lengthscales present in OPV materials requires both grazing incidence small- and wide-angle x-ray scattering, the latter recently enabled by improvements to the GISAXS instrument at 8-ID-E. I will describe grazing-incidence studies at 8-ID-E that have contributed toward unraveling the complex relationship between OPV materials, processing and performance.
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Feb 4
Tuesday

Solving the Phase Diagram of the Model Quantum Magnet SrCu2(BO3)2

Speaker: Sara Haravifard, Argonne National Laboratory & The University of Chicago
XSD Presentation
432/C010 @ 2:00 PM
View Description
Low dimensional quantum magnets provide a framework for exotic phase behavior in new materials, with high temperature superconductivity being the most appreciated example. SrCu2(BO3)2 (SCBO), is a rare example of a quasi two-dimensional quantum magnet for which an exact theoretical solution exists. It serves as an experimental realization of the Shastry-Sutherland model for interacting S=1/2 dimers. The ratio of the intra and inter-dimer exchange interactions in this compound is close to a quantum critical point, where the ground state is predicted to transform from a gapped, non-magnetic singlet state to a gapless long-range ordered antiferromagnetic state as a function of the ratio of the strength of the magnetic interactions. We conducted high resolution neutron scattering measurements on SCBO in its singlet ground state which identified the most prominent features of the spin excitation spectrum, including the presence of one and two triplet excitations and weak dispersion characteristic of sub-leading terms in the spin Hamiltonian. Additionally, we investigated the pressure-driven quantum phase transition in SCBO using synchrotron X-ray diffraction and neutron scattering. In these studies we were able to investigate the evolution of both the magnetic and structural properties of SCBO up to pressures of 6 Gpa, following the development and evolution of long-range magnetic order. Moreover, the resemblance between the spin gap behavior in the Mott insulator SCBO and that associated with high temperature superconductors motivated us to explore the significance of doping on the phase diagram.
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Jan 28
Tuesday

Novel Industrial Ultrafast Lasers and their Applications in Free Electron Lasers and Synchrotrons

Speaker: Yoann A. Zaouter, Amplitude Systemes
XSD Presentation
433/C010 @ 10:00 AM
View Description
he aim of this presentation is to introduce the novel industrial ultrafast laser technologies that are developed at Amplitude Systemes. These lasers benefit from several technological breakthroughs such as direct diode pumping and novel laser architectures, and gain media that allow the laser to operate simultaneously at high energies, average powers and therefore repetition rates. We will also specifically show where they are used in FEL and synchrotron and how they advantageously can replace ageing laser technologies and improve the reliability of photoinjectors, minimize the down times, improve signal to noise ratio of measurements, etc.
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Jan 13
Monday

Probing the Metal-Insulator Transition in Engineered NdNiO3

Speaker: Mary H. Upton, Inelastic X-ray & Nuclear Resonant Scattering (IXN)
XSD Presentation
401/A1100 @ 2:00 PM
View Description
NdNiO3, along with other rare earth nickelates, has been the focus of intense research in the last decade due to its metal-insulator transition (MIT), occurring at ~210 K in NdNiO3. The transition temperature can be tuned (or suppressed) with strain giving rise to the possibility of engineered heterostructures. There are many competing models of the MIT, of which the true nature is not known. It has been suggested that the MIT results from the emergence of a low temperature charge ordered state involving the d electrons. Alternately, it may result from the opening of a charge transfer gap between the Ni d and O p electrons. We report on the effect of epitaxial strain and temperature on d-electrons in NdNiO3 as measured by bulk-sensitive resonant inelastic x-ray scattering.
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Jan 13
Monday

Engineering the Elasticity of Soft Colloidal Materials Through Surface Modification and Shape Anisotropy

Speaker: Lillian C. Hsiao, University of Michigan, Ann Arbor
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Designing complex fluids has always involved the arduous manipulation of system-specific parameters. Recently, we developed a general correlation to predict the flow behavior of a range of soft matter based on their microstructure. By applying the framework of structural rigidity at the macroscale (bridges, buildings, domes) to the microscale, we are able to explain the nonlinear elasticity of colloids flowing at high rates that are typical of industrial processing. In particular, we explore the idea that colloidal gels can be designed with better mechanical properties and stability without resorting to a greater quantity of materials, simply by incorporating particles with different shapes, sizes, and roughness. Biphasic particles with metallic facets have also been proposed to provide extraordinary structural strength due to their interaction anisotropy. We test these ideas by synthesizing monophasic and biphasic colloids of controlled roughness in various ellipsoidal shapes, dispersing the particles in refractive-index matched solvents, and inducing self-assembly and gelation with a measurable and tunable depletion attraction. To quantify their flow properties, rheological measurements are carried out in conjunction with microscopy experiments and direct force measurements using optical tweezers. Our understanding of gel physics and rheology shows that the trial-and-error engineering of viscoelasticity can be mitigated by applying the principle of structural rigidity to material design; for example, engineers can incorporate smaller ellipsoidal particles to increase yield stress without a significant increase in the production cost.
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Jan 10
Friday

Light-X-ray Scattering and Rheology of Soft Matter

Speaker: Yu-Ho Wen, Cornell University
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Soft matter is an important class of molecular materials, typically composed of polymers, colloids, and other mesoscopic constituents. They are indispensible in contemporary technological applications—for example, solid electrolytes in rechargeable lithium batteries and solution-cast thin film in polymer light-emitting diodes (PLEDs). Herein we report on the dynamics and structure of the two advanced materials—nanoparticle salts and conjugated polymers. The nanoparticle salts are created by cofunctionalization of metal oxide nanoparticles with tethered salts and neutral organic ligands, and are shown to exhibit equilibrium, Newtonian flow behaviors. We find that ionic cross-links between the salts can be created/weakened by variations of counterion size and dielectric medium. Scrutiny into the SAXS structure factors and plateau moduli further disclosed that nanoscale interparticle spacing imposed on tethered molecules produces topological constraints analogous to those in entangled polymers, uncovering the molecular origin of a similar plateau modulus shared with polymer-tethered nanoparticles and entangled polymer melts. Time-composition superposition of linear viscoelastic data further indicates stricking dynamical similarities between the two systems. In the second part, we propose a self-consistent formulation for analyzing the dynamic structure factor of aggregate species in conjugated polymer solutions, where a wide size distribution and unknown aggregate morphology, as well as pronounced interferences between translational and interior segmental motions of aggregate clusters have posed stringent challenges for conventional light-scattering analyses. Additionally, in situ rheological and turbidity measurements reveal that an externally imposed flow can result in instant and/or persistent changes in the bulk aggregation state of the precursor solutions.
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Jan 9
Thursday

Hierarchical Semiconductor, Metal and Hybrid Nanostructures and the Study of their Light-Matter Interactions

Speaker: Anna Lee, University of Toronto
XSD Presentation
401/A1100 @ 2:00 PM
View Description
The interdisciplinary work during my Ph.D. and post-doctoral studies (Dept. of Chemistry and Dept. of Electrical Engineering, University of Toronto) explore the optical properties of hierarchical structures composed of nanoscale building blocks ranging from metals to semiconductors and composites, organized through bottom-up design methods.

This talk is comprised of three main research projects for which the common thread is the rational design of nanoscale assembled structures and their interactions with light.

Recent advances in spectrally tunable solution-processed metal nanoparticles have provided unprecedented control over light at the nanoscale. The plasmonic properties of metal nanoparticles have been explored as optical signal enhancers for applications ranging from sensing to nanoelectronics. Specifically, (1) by following the dynamic generation of hot spots in self-assembled chains of gold nanorods (NRs), we have established a direct correlation between ensemble-averaged surface- enhanced Raman scattering (SERS) and extinction properties of these nanoscale chains in a solution state. Experimental results were supported by comprehensive finite-difference time-domain simulations. Building from this, (2) we studied an alternate geometry, namely side-by-side assembled NRs. There is a general misconception that aggregates of metal nanoparticles are more efficient SERS probes than individual nanoparticles, due to the enhancement of the electric field in the interparicle gaps. However, we have shown through theoretical and experimental analyses that this is not the case for side-by-side assembled gold NRs. (3) Progress in colloidal quantum dot photovoltaics offers the potential for low-cost, large-area solar power; however, these devices suffer from poor quantum efficiency in the more weakly-absorbed near infrared portion of the sun’s spectrum. Here, I will talk about a plasmonic-excitonic solar cell that combines two jointly-tuned solution processed infrared materials. We show through experiment and theory that a plasmonic- excitonic design using gold nanoshells with optimized single-particle scattering-to- absorption cross section ratios leads to a strong enhancement in near-field absorption and resultant photocurrent in the performance-limiting near infrared spectral region. The present work offers guidance towards the establishment of “design rules” for the development of colloidal nanoparticle assembled systems for plasmonic sensing applications.
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2013

May 21
Tuesday

Lensless X-ray Imaging of Atomic Surface Structures in the Reflection Geometry using Ptychography

Speaker: Dr. Chenhiu Zhu, Materials Science Division, Argonne National Laboratory
XSD Presentation
401/A5000 @ 11:00 AM
View Description
Coherent x-ray diffraction imaging in the reflection geometry is desirable since it offers many advantages, including (1) lensless technique without need of object lenses, (2) few restrictions on sample size, chambers or environments, (3) suitable for studies of thin films grown on any substrates, (4) no need of pin holes near samples as in holography-based techniques, and (5) easily expandable to resonant coherent x-ray imaging.

We demonstrate by numerical simulation that atomic structures on single crystal surface can be reconstructed using the ptychography coherent x-ray diffraction imaging in the reflection geometry. Our approach is based on the concept of crystal truncation rod. We can obtain the highest surface sensitivity at anti-Bragg condition, and achieve a phase contrast up to from a single atomic step. Ptychograhy scanning scheme allows us to overcome the stringent requirement for isolated samples in typical CDI experiments. We will show experimental results from real platinum (001) surfaces and their ptychography reconstructions. This technique can be readily applied to buried interfaces under catalytic and electrochemical conditions and to nanoscience applications, such as nanowire with stacking faults.
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May 17
Friday

In Situ Crystallographic Studies of Adsorption Processes in Porous Materials

Speaker: Phoebe K. Allan, University of Cambridge
XSD Presentation
433/C010 @ 2:00 PM
May 3
Friday

Transient Absorption of Attosecond Radiation by Laser Dressed Systems

Speaker: Ken Schafer, Louisiana State University
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Attosecond transient absorption (ATA) studies provide a way to push our understanding of the energy transfer between electromagnetic fields and matter to the sub femtosecond time scale. ATA is an all-optical attosecond metrology that complements methods based on the measurement of charged particles, such as attosecond streaking and electron interferometry. In this talk I will review the basics of ATA and summarize recent results in this fast growing field. I will discuss calculations from our attosecond theory group on ATA in laser-dressed atoms that highlight the extent to which attosecond dynamics can be extracted from these measurements.
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May 3
Friday

Development and Applications of X-ray Photon Correlation Spectroscopy in the Ultra-small Angle Scattering Regime

Speaker: Dr. Fan Zhang, NIST
XSD Presentation
401/B4100 @ 10:00 AM
View Description
Partially coherent radiations generated by high-brilliance third generation synchrotron sources have allowed measurements of slow dynamics in various soft and hard material systems. We have recently developed an X-ray photon correlation spectroscopy (XPCS) technique in the ultra-small angle scattering regime, which fills an existing gap between the accessible Q ranges of dynamic light scattering and pinhole-based XPCS and enables studies of low-frequency equilibrium and nonequilibrium dynamics in optically opaque materials. This technique, based on the Bonse-Hart ultra-small angle X-ray scattering instrument at the Advanced Photon Source, requires modifications to the beamline configuration and instrument operations for dynamic measurements. We will review the basic features of this technique, and will discuss in details the optimizations that we made to meet the needs of signal-to-noise limited XPCS studies. We will present the data analysis approaches that we established to quantify the dynamic time scales of measured equilibrium or nonequilibrium processes. Finally, we will use a few examples to illustrate the applications of this technique in understanding of equilibrium dynamics of soft materials and nonequilibrium behavior of both soft and hard materials.
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May 2
Thursday

A Synchrotron X-ray Diffraction from Perovskite Thin Flms: Probing the Effects of Microscopic Structure on Macroscopic Properties

Speaker: Dr. Rebecca Sichel-Tissot, Department of Materials Science and Engineering, Drexel University
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Perovskite oxides are a fascinating class of materials - they exhibit a huge range of properties such as magnetic ordering, ferroelectricity, metal to insulator transitions, piezoelectricity, just to name a few. These properties are extremely sensitive to the position, bonding, and electronic state of the central atom. As a result, small strains or structural changes can have large effects on the functional properties. The perovskites present an exciting opportunity to gain insight into these phenomena by pairing structural characterization with measurements of the macroscopic properties.

In this talk, I will discuss how synchrotron x-ray diffraction can be used to study ferroelectricity, piezoelectricity, and charge disproportionation in perovskite thin films. Ferroelectric domains in (Pb,Zr)TiO3 thin films were written using PFM. X-ray nanodiffraction was used to simultaneously image the domains and probe the structure. By comparing our results with PFM imaging, we find that the strain induced by the writing process is responsible for certain polarizations being less stable than others. In piezoelectric thin films, the film is macroscopically attached (clamped) to its substrate and the average piezoelectric distortion along the film-substrate interface must be zero. We observe very different results at the microscopic level. Using time-resolved x-ray microdiffraction, we find that the piezoelectric response of individual domains in BiFeO3 thin films is not zero and varies on a domain-by-domain basis. Finally, we combine electronic transport measurements with x-ray diffraction from charge disproportionation in La1/3Sr2/3FeO3 thin films. The temperature dependence of the resistivity and intensity and correlation lengths of the charge disproportionation reflections give insight into the nature of this phase transition.
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May 1
Wednesday

Double Photoionization of Aromatic Molecules

Speaker: Dr. Ralf Wehlitz, Synchrotron Radiation Center, University of Wisconsin - Madison
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Electron correlations can be found in various fields of physics whenever we have to go beyond the independent particle model. A convenient method to study electron correlations in atoms and molecules is to measure the probability to remove TWO electrons simultaneously with a single photon (called double photoionization) from the sample. Because a single photon can interact with only one electron, the removal of two electrons is due to electron correlations. I will present our recent results on double photoionization over a broad range of photon energies for several aromatic molecules. Our goal is to find systematic trends as the molecular structure of our different samples changes. Questions that will be addressed in the talk are: How does the structure of a molecule affect the double-photoionization process? Which mechanisms contribute to double photoionization?
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Apr 26
Friday

Atomic Structural Evolution in Cu-Zr and Ni-Nb Liquids and Glasses: A measure of liquid fragility?

Speaker: Dr. Nicholas Mauro, Washington University
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The glass forming ability (GFA) of metallic alloys is widely varied. Bulk metallic glasses (BMGs) have been identified in a number of alloy systems but far more compositions can be formed only when their liquids are rapidly quenched. Understanding the differences between these systems remains one of the most important problems in condensed matter physics. Understanding the structural evolution of metallic liquids as they are supercooled and quenched into glasses is critically important, not only for providing insight into the nature of the glass transition, but also for understanding technical aspects of glass formation and the thermal stability of the glassy solid. In this talk, we discuss the results of high energy X-ray diffraction studies on Cu-Zr and Ni-Nb liquids and glasses. The temperature dependence of the X-ray structure factors has been measured in the glass from room temperature to above the glass transition temperature by means of stationary diffraction in a ! capillary while data in the equilibrium and supercooled liquid state were acquired using the Beamline Electrostatic Levitation technique. As will be shown, both the structure factors as well as the calculated total pair correlation functions display an anomalous evolution indicating a rapid acceleration of short-range order above the glass transition temperature. This behavior contrasts sharply with that observed in high glass forming ability metallic alloys suggesting a structural fragility metric distinguishing good glass formers from poor ones. We discuss the implications for this observation on our fundamental understanding of glass formation.
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Apr 25
Thursday

Towards a Sustainable Future: Hard X-ray Methodologies for Energy and Environmental Applications

Speaker: Olaf Borkiewicz, Miami University
XSD Presentation
401/A5000 @ 10:00 AM
View Description
The anticipated doubling of the worlds energy consumption within the next 50 drives the need for efficient and clean energy. Advanced electrical energy storage systems and nuclear energy are technologies that are crucial to achieving this goal. However, key materials challenges must be overcome before these technologies become viable:
  • For electrical energy storage systems to become practical for transportation and electrical grid application, higher capacity/power and faster recharge times are needed. Gaps in our understanding of the atomic- and molecular-scale processes that control performance and failure of these systems must be addressed by fundamental research.

  • For safe nuclear energy industry, the challenges lay in the effective disposal of the radioactive waste generated by the nuclear fuel cycle. Many solutions involve "multiple-barrier" geological depositories which use a wide range of sequestration agents. Understanding of the structural and chemical properties of these agents, and their interaction with radioactive elements, is key to the fidelity of these facilities.


In both electrical energy storage and nuclear energy, the complexity of the systems and the often metastable and/or disordered nature of the materials pose a significant characterization challenge. This challenge can be addressed through judicious selection and, where necessary, development of incisive characterization tools. We have recently designed an operando electrochemical cell, optimized for a variety of hard X-ray methodologies, and used it to probe next-generation battery materials with an unprecedented level of precision. First-of-the-kind operando pair distribution function measurements have provided a detailed understanding of high-performance electrode materials. In situ time-resolved powder X-ray diffraction data, analyzed through Rietveld refinement, combined with X-ray absorption spectroscopy, scanning electron microscopy and other analyses, have been used to evaluate the use of hydroxylapatite as radionuclide sequestration agent and solid nuclear waste form.
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Apr 24
Wednesday

Resonant Inelastic X-ray Scattering in a Mott Insulator

Speaker: Nandan Pakhira, Department of Physics, Georgetown University
XSD Presentation
401/B4100 @ 3:00 PM
View Description
I will be talking on the recently published calculation of RIXS response in the Falicov-Kimball model. The Falicov-Kimball model is exactly solvable under single site dynamical mean field theory approximation and the RIXS response in this model can also be accurately calculated up to a local background correction. We find that on resonance the RIXS response is greatly enhanced. The response systematically evolves from a single peak structure, arising due to relaxation processes within the lower Hubbard band, to a two peak structure, arising due to relaxation processes within the upper Hubbard band as well as across the Mott gap into the lower Hubbard band, as we vary the incident photon frequency to allow excitations from the lower Hubbard band to the upper Hubbard band. The charge transfer excitations are found to disperse monotonically as we go from the center of the Brillouin zone towards the zone corner. These correlation induced features are found to be robust and survive even for large Auger lifetime broadening effects which can mask the many-body effects by smearing out spectral features. As a comparison, we also calculate the dynamic structure factor for this model, which is proportional to the nonresonant part of the response, and does not show these specific signatures.
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Apr 23
Tuesday

Status of SRX, the NSLS-II Spectromicroscopy Beamline

Speaker: Vincent De Andrade, Brookhaven National Laboratory
XSD Presentation
438/C010 @ 3:00 PM
View Description
The Sub-micron Resolution X-ray spectroscopy beamline (SRX), whose commissioning phase will start in July 2014, is one of the seven project beamlines of NSLS-II at Brookhaven National Laboratory. Operating at energies ranging from 4.65 to 23 keV, SRX will address a wide variety of scientific applications probing heterogeneous complex systems from the meso to the nanoscale. Combined with state of the art optics, the ultralow emittance and stability of the NSLS-II source is particularly suitable for micro- and nanoprobes like SRX. The SRX main optical components consist of a horizontally focusing mirror creating a secondary source whose size is adjustable with slits, an ultra-stable horizontally deflecting monochromator and two sets of Kirkpatrick-Baez mirrors in two inline stations as focusing optics for operations requiring either high flux (microprobe) or high resolution (nanoprobe). The presentation will focus first on the beamline layout that has been optimized with FEA, ray-tracing and wave front propagation simulations using respectively Shadow and SRW. Results demonstrate that the SRX micro- and nanoprobes will provide 1013 and 1012 ph/s respectively in a sub-micron and a 50 nanometer spot, with an excellent energy resolution (close to the Darwin width of the selected crystals). In a second time, the end-station design will be described with highlights on interferometry tests performed on sample stage assemblies as well as considerations to handle high throughput fluorescence signal. One will conclude on possible early science experiments that are expected by the end of the year 2014.
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Apr 23
Tuesday

Microsecond Time-resolved XAS Measurement with the Energy Dispersive EXAFS Setup and Ultrafast (ps) X-ray Scattering on Chemical Reactions

Speaker: Qingyu Kong, Société civile Synchrotron SOLEIL
XSD Presentation
433/C010 @ 1:30 PM
View Description
The energy dispersive EXAFS (EDE) setup at ODE beamline Soleil Synchrotron as well as the recent development of microsecond (µs) time-resolved XAFS data collection and its application to film continuously the electronic and geometric structural kinetics in a thermolysis reaction will be presented. The proposal of a laser pump and XAS probe development using EDE setup will be introduced briefly. In the second part of the talk, the optical pump and X-ray probe setup and ultrafast solution scattering on small molecules studied in ID09B ESRF will be presented, the photofragmentation reaction of triruthenium dodecacarbonyl Ru3(CO)12 in cyclohexane will be used as an example to show the data analysis process and the complementary nature of ultrafast X-ray scattering and ultrafast spectroscopy in the determination of transient molecular structures and chemical reaction mechanisms.
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Apr 23
Tuesday

Fabrication of High-aspect-ratio Nano-structures for X-ray Microscopy Applications

Speaker: Ming Lu, Brookhaven National Laboratory
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Recent efforts of x-ray microscopy research and development are pushing the resolution of state-of-the-art x-ray microscopes toward single digit of nanometer region. Among all the x-ray focusing optics, Fresnel zone plates are superior considering their nature of two-dimensional focusing and a resolution close to diffraction limit. However, high-resolution zone plates operated at x-ray wavelengths, especially in hard x-ray region, require a high-aspect-ratio geometry for their concentric metal zones to efficiently diffract lightwave, a challenge to nanofabrication researchers. In this talk, I will discuss three different approaches for fabricating high-aspect-ratio metallic nanostructures, including methods utilizing stressless electroforming molds, double-patterning, and zone-doubling techniques. Using these techniques we demonstrated hard-x-ray zone plates with 19:1 aspect-ratio and 30 nm outermost zone width, as well as a platinum resolution test pattern featuring 17-nm-wide, 255-nm-tall gratings.
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Apr 22
Monday

Nanoscale Soft X-ray Microscopy at HZB: Current Status of the TXM and Optics Development

Speaker: Stephan Werner, Institute for Soft Matter and Functional Materials, Berlin, Germany
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The Helmholtz-Zentrum Berlin (HZB) operates a full-field transmission X-ray microscope (TXM) in the soft X-ray photon energy range at the undulator beamline U41-FSGM at the BESSY II electron storage ring. Due to the optical setup the HZB-TXM permits cryo X-ray tomographic as well as spectromicroscopic applications in material and life sciences. Some examples of these applications will be shown. The spatial resolution of the full-field microscope is limited by the numerical aperture of the zone plate objective and the wavelength used for imaging. The resolving power can be improved by decreasing the outermost zone width or imaging in higher orders of diffraction. At HZB, we work in our nanotechnology lab on both approaches. Recent results on the nanofabrication of high resolution zone plate objectives will be presented. In addition, the achievable resolution of the HZB-TXM will be discussed.
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Apr 18
Thursday

Pushing the Limits of Powder Diffraction: Determination of the Crystal and Local Structures of Highly Complex Perovskite Materials

Speaker: Graham King, Lujan Neutron Scattering Center, Los Alamos National Laboratory
XSD Presentation
401/B5100 @ 10:00 AM
Apr 17
Wednesday

X-ray Absorption and Phase Retrieval using Energy-resolved Measurements

Speaker: Doga Gursoy, University of Houston
XSD Presentation
431/C010 @ 3:00 PM
View Description
X-ray phase imaging has been of interest in the last couple of decades for potential applications in medical imaging and material characterization. A key aspect in phase imaging is the well known “phase problem” which involves detangling the absorption and phase effects from intensity measurements. In this talk, I will make a topical review of the phase retrieval methods and present a novel single-step method to simultaneously retrieve x-ray absorption and phase images which is valid for a broad range of imaging energies and material properties. The method relies on the availability of spectrally resolved intensity measurements, which is now possible using semiconductor x-ray photon counting detectors. I will discuss the potential and utility of the method and address the engineering challenges in x-ray detection with the currently available spectral detectors.
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Apr 17
Wednesday

Structural and Interfacial H2O/OH Species: Two Case Studies on their Roles in Host Structural Stability

Speaker: Hsiu-Wen Wang, Indiana University
XSD Presentation
401/A1100 @ 10:00 AM
Apr 16
Tuesday

Zone Plates for High Photon Energy Focusing - Lessons from the Past, Reinterpreted

Speaker: Nicolaie Moldovan, Advanced Diamond Technologies
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The presentation reviews the main achievements in zone plates fabrication for X-ray focusing, with accents on how the existent knowledge can be extended to reach the goal of 20 nm resolution at 25 keV photon energy. Several approaches will be discussed, revealing that traditional nanofabrication ways will not work, while new, combined approaches will do the job. Among the discussed methods: sequential height increases by soft x-ray exposure and electroforming, layered depositions and nanolaminates, zone doubling and resolution increase by adding higher order zones, stacking and composing zone plates by MEMS-enabled alignment, diamond Fresnel lenses, and others. Combining the positives of these approaches leads to a heavily-engineered concept of zone plates fabrication, but with good chances of success, and even a perspective for higher photon energies.
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Apr 15
Monday

Characterization of the Fluctuating Charge States in Transition Metal Oxides using Local Structure as a Probe

Speaker: A. M. Milinda Abeykoon, Brookhaven National Laboratory
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Abstract: It is becoming apparent that nanoscale fluctuations in the charge state are important to the physics of transition metal oxides. The temperature evolution of structural modulation associated with charge (co) and spin order (so) in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction [1]. For the first time, we report an anomalous shrinking of the “a” lattice parameter that correlates with Tco, at the temperature where long-range stacking order of charge stripes disappears. We show that this response may be explained as resulting from the energy contributed by the interlayer electrostatic interaction leading to shrinkage of c/a. In addition, we report anomalies in the temperature evolution of the refined atomic displacement parameters (ADP) and local structural parameters in the atomic pair distribution function (PDF), which show quite different temperature dependence consistent with the persistence of localized charges, presumably in the form of short range ordered stripe domains, over a broad temperature range above Tco.
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Apr 10
Wednesday

Surface Octahedral Distortions and Atomic Design of Perovskite Interfaces

Speaker: Bruce A. Davidson, CNR-IOM TASC National Laboratory
XSD Presentation
431/C010 @ 10:00 AM
View Description
Progress in understanding and exploiting the properties of complex oxide heterostructures requires advances in state-of-the-art growth and characterization techniques for these materials, as atomic control of their synthesis is demonstrably inferior to that of their semiconductor counterparts. Here we report significant improvements in the atomic design of perovskite interfaces made possible by advances in in situ control of the surface by reflection high-energy electron diffraction (RHEED) during growth that reveal the surface termination and characteristic octahedral distortions in the surface layer as it is being deposited. This RHEED approach applies generally to growth of polar and nonpolar perovskite unit cells when a desorption-controlled growth regime is not utilized. As an example, we demonstrate its use in the optimization of atomically-designed manganite/titante interfaces that eliminates cation intermixing and anomalous unit cell dilations that have previously been observed. Careful analysis of the crystal structure shows an unusual evolution of the octahedral distortions that include both J-T type and rotations near the interface that are not seen in bulk. These new results should be included in electronic structure calculations modeling the properties of real heterointerfaces.
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Apr 8
Monday

Coherent X-ray Diffraction Imaging of Strain on the Nanoscale

Speaker: Ross Harder, XSD-Microscopy
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Materials often contain fundamental properties that are determined by structures on nanometer length scales. An example of this is the nanometer size pores in synthetic zeolites crystals. The shapes of the pores can define molecular sieves and the composition of the walls can be tailored to catalytic applications. Occlusions in the pores will significantly restrict the function of the material and if occurring below the surface may be difficult to detect. The x-ray diffraction Bragg peaks of crystals contain a wealth of information regarding the structure of the sample. If the x-ray beam used to study a sample is spatially and temporally coherent, the scattered x-rays in the vicinity of the Bragg peak contains local structural information on potentially nanometer length scales. Images are formed by computational inversion from reciprocal space to direct space using phase retrieval algorithms. These images contain both morphological and strain information on tens of nanometer length scales in three dimensions.

This talk will describe the technique of coherent x-ray diffraction (CXD) imaging in the Bragg geometry and show recent results from 34-ID-C, including a study of zeolites being tailored for catalysis of pollutant gases, the response of a nanocrystal to multi gigapascal pressure, and time resolved phonon modes in nanocrystals.
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Apr 4
Thursday

Diamond X-ray Beam Position Monitors

Speaker: Dr. John Smedley, Brookhaven National Laboratory
XSD Presentation
438/C010 @ 2:00 PM
View Description
Ever wonder where your x-rays are? How many photons you have? Where they‘re going? A diamond based x-ray beam position monitor may be for YOU! Advances in CVD diamond growth have made this material an attractive option for x-ray diagnostics. Diamond is radiation hard, solar blind, and has very small leakage current (sub pA). The low Z of diamond makes it attractive for transmission diagnostics, while the high thermal conductivity makes it attractive for high flux applications. This talk will focus on recently demonstrated monitors for both white and monochromatic beams, along with a discussion of goals for future development.
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Apr 3
Wednesday

Wave Propagation in Inhomogeneous Media, and Possible X-ray Applications

Speaker: Professor Nicole Moore, Elmhurst College
XSD Presentation
431/C0101 @ 3:00 PM
Mar 19
Tuesday

Zone Plate Optics for Sub-15 Soft X-ray Microscopy

Speaker: Julia Reinspach, Stanford University
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The development of zone plate lenses is crucial for the progress of high-resolution x-ray microscopy. Since the resolution achievable in imaging is proportional to the outermost zone width of the lens, narrow zones have to be nanofabricated. In addition, high aspect ratios are required to achieve high diffraction efficiencies, thus rendering zone plate nanofabrication challenging. At the Biomedical and X-Physics group at KTH (Stockholm, Sweden) the development and improvement of nanofabrication processes for high-resolution high-diffraction-efficiency soft x-ray optics is a key aspect. Different approaches, such as cold development, cryogenic RIE, or the concept of nickel-germanium zone plates have been investigated and applied, resulting in soft x-ray zone plates with zone widths down to 12 nm and diffraction efficiencies up to 9.6% (at λ=2.48 nm).
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Mar 13
Wednesday

A Route to High Neel Temperatures in 4D and 5D Transition Metal Oxides

Speaker: Priya Mahadevan, S.N. Bose National Centre for Basic Sciences
XSD Presentation
431/C010 @ 11:00 AM
Mar 11
Monday

Roaming Radical Reactions

Speaker: Arthur G. Suits, Department of Chemistry, Wayne State University
XSD Presentation
401/A1100 @ 2:00 PM
View Description
An unusual decomposition mechanism of highly vibrationally excited molecules, dubbed the “roaming mechanism,” has recently been discovered and is now a very active area of investigation. In these reactions, a molecule undergoes partial dissociation to radical fragments by simple bond fission. When the fragments separate to 3-4 Å, “roaming” reorientation becomes feasible as the kinetic energy is low and the angular forces may be comparable to the radial forces. If this leads the system to access a distinct reactive domain, intramolecular abstraction may take place giving unexpected products often with with large vibrational excitation. This pathway may deviate substantially from the nominal minimum energy path, and in some cases appears to avoid the normal transition state geometry entirely. Many of the details have come to light through high-resolution ion imaging studies of formaldehyde, in concert with quasi-classical trajectory calculations from Bowman and coworkers. Many other examples of roaming dynamics have now been reported, both in experiment and theory. I will emphasize recent results documenting “roaming-mediated isomerization” which appears to be a general feature of the decomposition of nitro compounds. In addition, I will introduce new universal probes of reaction dynamics affording isomer and even conformer selectivity.
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Mar 4
Monday

Stimulated Electronic X-ray Raman Scattering with XFEL Sources

Speaker: Dr. Nina Rohringer, Center for Free-Electron Laser Science, Hamburg, Germany
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The invention of x-ray free-electron lasers (XFELs) opens the pathway to transfer powerful spectroscopic techniques from the optical to the x-ray region, to ultimately study the interplay of coherent electronic and vibrational dynamics on the timescale of chemical reactions. Resonant Inelastic X-ray Scattering (RIXS) is a viable spectroscopic tool to study the valence-electronic environment of a target atom, which can be selectively addressed by the resonantly tuned x-ray beam. The cross section for this process is, however, small, so that even with powerful XFEL pulses the recording of single-shot RIXS spectra of dilute samples or molecules in the gas phase are challenging. This hampers the application of RIXS in optical pump x-ray probe experiments, which would, for example, be one method of choice to study light-induced chemical reactions. Here we demonstrate, how this bottleneck can be overcome by stimulating the RIXS process. We present results of a recent experiment o! n stimulated RIXS at the Linac Coherent Light Source XFEL in a gas sample of atomic neon, thereby amplifying the RIXS signal by 6-7 orders of magnitude. Using broadband XFEL pulses, which are characterized by a stochastic, spiky substructure of their spectrum, both “pump” and “dump” photons can be provided in a single pulse, thereby stimulating the scattering process and driving an exponential amplification of the signal. Despite the overall broad bandwidth, high-resolution RIXS spectra can be achieved by statistical analysis of a series of stochastic single-shot spectra. The energy resolution is determined by the spectral coherence of the XFEL source, and in principle allows for vibrational resolution. These findings open up a new class of experiments at XFEL sources, with a colossal increase of the RIXS signal. Results of our recent experiment will be presented, along with a perspective and theoretical feasibility study of stimulated RIXS measurements in small molecules.
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Feb 19
Tuesday

Probing and Reconstructing Transient One-Dimensional Crystalline Strains Using Time-Resolved X-ray Diffraction

Speaker: Yuan Gao, University of Delaware
XSD Presentation
432/C010 @ 12:00 PM
View Description
Since the late 1990s, ultrafast x-ray pulses have been used to probe impulsive strains propagating in the bulk of optically opaque materials. Time-resolved x-ray diffraction has been proven to be a very powerful tool for visualizing transient one-dimensional crystalline strains, ranging from crystal growth to shockwave production.

In this presentation, I will describe a series of time-resolved x-ray diffraction experiments that visualize transient strain formation from nanometer-scaled laser-excited metallic films. Utilizing a table top picosecond x-ray source in conjunction with a high-power optical laser system, the resulting optical pump/x-ray probe spectra reveal that the spatiotemporal structure of the transient acoustic pulse is bipolar with acoustic wave-vectors up to inverse of the film thickness. In addition, I will also discuss the real-world constraints that place limits on the validity of the reconstructed transient acoustic pulse.
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Feb 19
Tuesday

Methods, Machinery, and Money: The LERIX-2 Conceptual Design

Speaker: Jerry Seidler, University of Washington
XSD Presentation
401/A1100 @ 10:00 AM
View Description
I will discuss the scientific motivation for, and technical details of, the recently completed conceptual design for the LERIX-2 spectrometer as part of the APS-U. In the conceptual design, we expand to 144 analyzers while taking the most successful mechanical and operational features of the LERIX-1 and LERIX-1B instruments. Among the issues that need to be resolved for the final design are the selection of detectors and the selection and reliable mass-fabrication of spherically-bent crystal analyzers (SBCA's). If in-house, rather than commercial, fabrication of the needed highly efficient SBCA's is possible, it will result in a factor of two cost savings for this instrument.
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Feb 11
Monday

Fundamental Dynamics in Molecules, Clusters, and Interfacial Systems Studied with Novel XUV and X-ray Light Sources

Speaker: Oliver Gessner, Lawrence Berkeley National Laboratory
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Ultrafast XUV and X-ray light sources offer new opportunities to unravel fundamental electronic and nuclear dynamics in matter. The Chemical Dynamics program at the Ultrafast X-ray Science Laboratory is focused on the application of emerging laboratory- and accelerator-based X-ray techniques to monitor the flow of charge, mass, and energy in molecules, clusters, and interfacial systems. A brief overview of the program will be followed by the discussion of two particular showcase examples of ongoing research: The study of photoinduced charge-transfer dynamics in dye-sensitized nanocrystals by time-resolved X-ray photoelectron spectroscopy and the investigation of quantized fluid dynamics in nano- to micron-scale superfluid helium droplets by single-shot coherent diffractive imaging.

Interfacial charge transfer studies are performed at the Linac Coherent Light Source (LCLS, SLAC National Accelerator Laboratory) and the Advanced Light Source (ALS, Berkeley). Recent LCLS results demonstrate the potential of time-resolved X-ray photoelectron spectroscopy (TRXPS) to monitor charge migration in complex interfacial systems with femtosecond time resolution, chemical sensitivity and element specificity. The visible light induced transient oxidation state of N3 dye molecules adsorbed to nanocrystalline ZnO is characterized in a concerted effort of TRXPS experiments and ab-initio calculations of the interfacial electronic structure.

The superfluid nature of helium droplets presents a rare opportunity to study the onset of macroscopic quantum phenomena in sub-micron scale systems. Pure and doped helium droplets are studied by coherent diffractive imaging (CDI) using femtosecond X-ray pulses from the LCLS. Single-shot CDI data provide the most direct access yet to droplet size- and shape-distributions as well as fundamental dynamics inside the clusters. The results will be discussed in the context of the onset of quantum vorticity in finite three-dimensional quantum systems.
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Feb 5
Tuesday

1913-2013: The Centennial Anniversary of the Birth of X-Ray Crystallography

Speaker: Denny Mills, Advanced Photon Source, Argonne National Laboratory
XSD Presentation
401/A1100 @ 1:00 PM
View Description
The year 2013 marks the 100th anniversary of the publication of Bragg’s Law by W. L. Bragg and the publication of the first crystal structure determination by x-rays, by W.H. Bragg and W.L. Bragg. This presentation will include a brief introductory discussion regarding the knowledge of the generation and scattering of x-rays in this time period, some personal background regarding the Braggs, and how Laue’s famous photograph set the stage for this father and son team to not only win the Nobel Prize for Physics in 1915 "For their services in the analysis of crystal structure by means of X-rays," but to change the world of science for many years to come through their development of x-ray crystallography.
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Jan 25
Friday

Beyond Li-ion Batteries

Speaker: George Crabtree, Director, JCESR
XSD Presentation
401/A1100 @ 1:30 PM
View Description
The Joint Center for Energy Storage Research (JCESR) develops concepts and technologies for portable electricity storage for transportation and stationary electric storage for the electricity grid. Electrified transportation replaces foreign oil with a host of domestic electricity sources such as gas, nuclear, wind and solar, and utility scale electric storage enables the grid to bridge the peaks and valleys of variable wind and solar generation and consumer demand. JCESR looks beyond Li-ion technology to new materials and phenomena to achieve the factor of five increases in performance needed to realize these transformational societal outcomes. JCESR will leave three legacies: a library of fundamental scientific knowledge of materials and phenomena needed for next-generation batteries, demonstration of battery prototypes suitable for scale up to manufacturing for transportation and the grid, and a new end-to-end integrated operational paradigm for battery research and development spanning discovery research, design, and demonstration.
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Jan 24
Thursday

Introduction of JML Optical Industries, LLC

Speaker: Scott Casella, JML Optical Industries, LLC
XSD Presentation
401/B4300 @ 1:30 PM
Jan 22
Tuesday

Tracking Electron Transfer Dynamics in Coordination Chemistry with X-ray Spectroscopy

Speaker: Wenkai Zhang, PULSE Institute, SLAC National Accelerator Laboratory
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The ability of coordination compounds to catalyze chemical reactions and absorb visible radiation makes them appealing targets for the development of photocatalysts. One of the attributes that makes transition metals excellent catalysts – a high density of frontier orbitals – can also lead to ultrafast quenching of electronic excited states. Understanding the properties of coordination complexes that dictate the electronic relaxation dynamics has practical, as well as fundamental importance. Most successful photosensitizers and photocatalysts have utilized 4d and 5d metal centers. The significant cost and low abundance of many 4d and 5d metals has inspired attempts to substitute high cost atoms with isoelectronic 3d metal complexes. But the exchange iron for ruthenium increases the charge transfer relaxation rate by roughly a factor of one million. The huge distinction in lifetimes has generally been attributed to differences in the ligand field excite state energies. But we currently still lack a detailed understanding of how ligand field excited states and charge transfer excited states interact and how this depends upon nuclear and electronic structure. We investigated the role of ligand field excited states in the relaxation dynamics of photogenerated charge transfer states in a series of iron(II) coordination compounds with hard x-ray emission spectroscopy (XES). The tremendous sensitivity of XES to the charge and spin state of the transition metal centers make these techniques ideally suited to investigating the electron dynamics in coordination chemistry. By studying mixed cyanide and bipyridine ligands with advanced x-ray spectroscopy, we discovered that the excited state decay pathway can be controlled and adjusted by systematically tuning the ligand field splitting. We demonstrated that changing the iron ligands lend to a 100-fold increase in the charge transfer excited state lifetime, a critical metric for earth abundant photosensitizers.
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Jan 17
Thursday

Programmable Assembly of Colloidal Crystals with DNA

Speaker: Andrew Senesi, Northwestern University
XSD Presentation
433/C010 @ 3:30 PM
View Description
Nano-structured materials and their assemblies have generated considerable scientific and industrial interest as a result of new chemical and physical interactions as their size is reduced and they are positioned into well-defined spatial arrangements. Indeed, a grand challenge in nanotechnology is to construct materials comprised of positionally encoded elements (i.e. nanoparticles) with fine control over spacing, symmetry, and composition, with single- or sub-nanometer precision and registry. The ability to exercise such control over multiple length scales and in three dimensions for a single system would, in principle, provide researchers with a route to fabrication “materials by design”, in which one could design and build a functional system with programmed chemical and physical properties, useful in material synthesis, optics, biomedicine, energy, and catalysis. In this talk, I will discuss recent progress towards this goal, by using DNA as a programmable ligand to direct the assembly of nanoparticles into crystalline arrays. DNA is ideally suited for this purpose, as synthetically tunable variations in nucleotide sequence allow for precise engineering of the nanoparticle’s hydrodynamic radius and binding properties. These factors, in turn, dictate the crystallographic symmetry and lattice parameters of the assembly. By further employing a DNA-functionalized substrate, thin-film nanoparticle superlattices can be grown in a layer-by-layer fashion with fine control over the number of particle layers in the assembly (i.e. film thickness). Importantly, the judicious choice of DNA substrate-particle interconnects allows one to tune the interfacial energy between various crystal planes and the substrate, and thereby control crystal orientation. A theoretical framework to understand these results is presented. These nanoparticle superlattices can further be patterned in arbitrary locations on a substrate using molecular printing techniques such as dip-pen nanolithography (DPN) and polymer pen lithography (PPL). The principles developed in this work represent a major advance in the bottom-up synthesis of nanomaterials and a major step towards the integration of nanoscale materials into functional device architectures. Lastly, ultrafast pump-probe studies of third-generation materials for future photovoltaics will be presented. One such novel photovoltaic material uses heavy O doping of ZnTe to generate the formation of an intermediate band within the forbidden gap, in order to improve the matching of semiconductor absorption and solar spectra. This approach is believed to become useful for realization of single junction solar cells with very high efficiencies. However, the implementation of such devices requires advanced characterization techniques. Multiphoton optical pulse excitations are demonstrated to induce multiband charge transfer dynamics in ZnTe:O films as revealed when monitoring the time-resolved photoluminescence signals.
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Jan 17
Thursday

Giant Thermoelectric Effect (GTE) in Graded porous micro-nanostructured Thermoelectric Materials

Speaker: D. G. Niarchos, Nuclear Center Demokritos, NCSR Athens, Greece
XSD Presentation
401/A1100 @ 3:00 PM
Jan 17
Thursday

Theoretical Study of the Transparency-like Phenomena in the XUV Induced by Coherent Coupling of the Doubly Excited States in Helium

Speaker: Michal Tarana, Department of Physics, Purdue University
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Presently there is great interest in the application of light in the X-ray regime, produced by high-order harmonics, to investigate novel coherent X-ray optical phenomena. Loh et al. [1] report the observation of EIT-like behavior in the extreme ultraviolet (XUV) by coherent coupling of 2s2p and 2p2 doubly excited states in He, probing with laser-produced high-order harmonics. The EIT-like phenomenon observed in their work is characterized solely by an increase in transmission over the entire unperturbed lineshape. It is the aim of our work [2] to extend the phenomenological theoretical treatment of this effect included in [1]. We present calculations based on the solution of the time-dependent Schrodinger equation in the LS-coupling configuration interaction basis set. The absorbing boundary is represented by the complex absorbing potential and we present here the analysis of the ionization yield obtained. This approach allows for more accurate treatment of the ionization continuum than presented in [1].

[1] Z.H. Loh, C.H. Greene and S.R. Leone, Chem. Phys. 350, 7 (2008).
[2] M. Tarana, C.H. Greene, Phys. Rev. A 85, 013411 (2012).
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Jan 15
Tuesday

Some Software for Beamlines

Speaker: Guy Jennings
XSD Presentation
401/A1100 @ 12:00 PM
View Description
A variety of locally written software is in use on Sectors 11 and 12 at the APS. I will describe the available software and some of the organizing principles behind its design in the hope that it may be more widely useful at other beamlines.

If time/audience interest permits I will also present an overview of a number of relevant features of the Qt framework as related to the software I have written.

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Part of the January 2013 Seminar Series Software for Beamlines. These talks present tools for beamline scientists using spec or python to control data collection or automate alignment or similar beamline tasks.
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Jan 14
Monday

Pushing the Limits of Full Field and Scanning X-ray Microscopy

Speaker: Dr. Hendrik Ohldag, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
XSD Presentation
401/A1100 @ 2:00 PM
View Description
X-ray microscopy has become a commonly available and often used tool for element specific investigations on a nanometer scale. However, with a constantly growing user community, the demand for a more flexible sample environment grows as well. In my talk, I will describe several approaches that were realized at the SSRL and the ALS to push the limits of x-ray microscopy, e.g. how to improve the resolution of PEEM microscopy without any changes to the microscope, how to measure in large magnetic fields with sub 10ps time resolution, or how to follow chemical reactions in situ.
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Jan 14
Monday

Ultrafast Spin, Phonon and Charge Dynamics: From Femtoseconds to Nanoseconds at Nanoscale

Speaker: Vladimir A. Stoica, University of Michigan, Ann Arbor
XSD Presentation
401/A1100 @ 1:00 PM
View Description
The ultrashort-pulse photoexcitation and measurement techniques are of tremendous interest due to their capability to uncover the ultrafast transient response of materials. Among light-based pump-probe techniques, an original approach employing low-power fs-fiber-lasers was developed to acquire, manipulate and modify a wideband spectrum of photoexcitations in thin films and nanostructures.

In epitaxial ferromagnetic films, coherent spin waves are generated with femtosecond laser pulses via thermal excitation mediated by magnon-electron and magneto-elastic coupling. The propagation speeds and attenuation lengths of exchange spin wave modes are determined during the propagation and reflection at the film boundaries, consistent with their dispersion relation. Moreover, photo-thermal excitation could be used to achieve coherent control of the magnetization vector. An optically-induced spin reorientation transition of first-order is revealed and provides a new route to coherent magnetization switching.

Another experimental effort has been focused on phonon dynamics and thermoelectric transport studies. The coherent optical phonon spectroscopy was employed during the fs laser-induced nanostructuring in binary semiconductors such as Sb2Te3 and InSb. Nanostructure fabrication process optimization resulted in highly ordered periodic nanostructures without the adverse effects of residual phase separation. In another case, pump-probe measurements are used to understand the behavior of acoustically mismatched thin films to further assist the design of high-Q acoustic resonators at GHz frequencies.

Lastly, ultrafast pump-probe studies of third-generation materials for future photovoltaics will be presented. One such novel photovoltaic material uses heavy O doping of ZnTe to generate the formation of an intermediate band within the forbidden gap, in order to improve the matching of semiconductor absorption and solar spectra. This approach is believed to become useful for realization of single junction solar cells with very high efficiencies. However, the implementation of such devices requires advanced characterization techniques. Multiphoton optical pulse excitations are demonstrated to induce multiband charge transfer dynamics in ZnTe:O films as revealed when monitoring the time-resolved photoluminescence signals.
[ Hide ]
Jan 11
Friday

Strong-field Physics with Mid-infrared Lasers

Speaker: Anthony DiChiara, The Ohio State University
XSD Presentation
401/B4100 @ 11:00 AM
View Description
Abstract: The strong-field picture of ionization describes the physics of how an isolated atom interacts with an intense ultra-fast laser field. The basic strong-field picture is described as tunnel ionization, which is characterized by the rapid burst of an electron wave packet into the continuum, followed by the classical motion of a quasi-free electron in a strong laser field and recollision with the parent ion. Recollision physics is at the very heart of what makes strong-field science an exciting tool for probing matter on ultrafast time scales. It offers a mechanism to create Attosecond (1 as = 10-18 s) laser pulses through High-Harmonic Generation and it offers a method for controlling electron-ion collisions on sub-femtosecond (1 fs = 10-15 s) time scales.

In my talk I will discuss how wavelength scaling has offered a more robust description of the strong-field picture. In particular, long wavelength lasers provide deep access to tunnel ionization and high energy electrons (several hundred eV) for studying electron recollision. I will discuss two separate aspects of my contributions that have helped to extend the strong-field picture. First, I will discuss inelastic laser driven scattering, or non-sequential ionization, in the long-wavelength limit of a 3.6 μm laser field. Here, large recollision energies (up to 400 eV) driven at modest field strengths result in the impact ionization of charge states up to Xe6+. The multiple ionization pathways are well described by a white electron wave packet and field-free inelastic cross sections, averaged over the intensity-dependent energy distributions for (e,ne) electron impact ionization. Then, I will discuss how wavelength scaling has made possible extending the strong-field picture of ionization to condensed phase systems. Here, we have observed evidence of a dramatic new mechanism for High Harmonic Generation that is unique to crystals yet closely parallels the semi-classical analysis of the strong-field atomic picture.
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Jan 10
Thursday

specpy: Simplifying Python-based beamline scripting

Speaker: Brian Toby
XSD Seminar
401/A1100 @ 12:00 PM
View Description
Part of the January 2013 Seminar Series Software for Beamlines. These talks present tools for beamline scientists using spec or python to control data collection or automate alignment or similar beamline tasks.
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Jan 9
Wednesday

Bent Crystal Optics for Synchrotron Radiation Beamlines

Speaker: Xianbo Shi, European Synchrotron Radiation Facility
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Bent crystals have been widely used as optical elements (e.g., monochromators, focusing optics and spectrometers) of high energy synchrotron radiation beamlines. The effects of bending on the reflectivity of the crystal are discussed within the dynamical theory with a full treatment of the crystal anisotropy and biaxial bending. Such knowledge and its combination with ray tracing and wave propagation are essential in the beamline design process. Two particular examples are presented to illustrate the usage of bent crystals for modern synchrotron radiation beamlines: the design of the X-ray Powder Diffraction (XPD) beamline at NSLS-II and the optimization of high luminosity spectrometers at ESRF and XFEL.

The XPD beamline uses a sagittally bent double-Laue crystal monochromator to provide horizontally focused x-ray beam over a large energy range (30-70 keV). A multi-lamellar model is introduced and implemented in the ray tracing of the monochromator. The instrumental resolution function of the beamline is also described.

Bent crystals are also utilized for high luminosity X-ray emission detection. This presentation will compare various concepts of dispersive/non-dispersive spectrometers with different crystal geometries by means of ray tracing.
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Jan 8
Tuesday

Controlling EPICS from Python: PyEpics

Speaker: Matt Newville
XSD Seminar
401/A1100 @ 12:00 PM
View Description
Part of the January 2013 Seminar Series Software for Beamlines. These talks present tools for beamline scientists using spec or python to control data collection or automate alignment or similar beamline tasks.
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2012

May 22
Tuesday

Using Electronic Coherence to Probe a Deeply Embedded Quantum Well in Bimetallic Pb/Ag Films on Si(111)

Speaker: Dr. Matthew Brinkley
XSD Presentation
438/C010 @ 11:00 AM
View Description
Angle-resolved photoemission studies of Pb films prepared on atomically uniformAg(111) films reveal a striking Fabry-Pérot-like behavior typical of a high-finessePb/Ag/Si(111) electron interferometer. Remarkably, the quantized electronic structure of the underlying Ag films persists despite Pb overlayers much thicker than the photoemission escape depth and an incommensurate Pb/Ag interface. Comprehensive simulations clearly illustrate the manifest coherence of the electronic structures, permitting the characterization of the deeply embedded Ag quantum well. This demonstrated exploitation of electronic coherence will prove useful to applications requiring non-invasive access to buried structures.
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May 18
Friday

Quantum Size Effect in Novel Two-dimensional Electron Systems

Speaker: Dr. Yang Liu
XSD Presentation
438/C010 @ 11:00 AM
View Description
Two-dimensional ultrathin films often exhibit properties dramatically different from their three-dimensional bulk counterparts, due to quantum confinement effect in reduced dimension. In this talk, I will first present our recent study of electronic properties of epitaxial graphene layers, using angle-resolved photoemission spectroscopy (ARPES) with variable light polarizations. Our results demonstrate that the "chiral" electronic states in this two-dimensional system can be unambiguously revealed by this technique. Next I will report our current research progress in quantum confinement effects in ultrathin films of topological insulators (TIs), using ARPES and surface X-ray scattering (SXS). Due to a largely enhanced surface-to-bulk ratio, TI ultrathin films are considered to be a very promising system for practical applications of TIs. It is therefore crucial to understand how the electronic and structural properties in TI thin films converge to their bulk limits. For ultrathin Bi2Te3 films grown on Si(111), we found that the topological surface state converges to its bulk form already at 4 quintuple layer, in remarkable agreement with theoretical prediction for a freestanding film. Our surface X-ray study confirms that the quasi-freestanding Bi2Te3 films are achieved through a buffer layer between the film and substrate, which effectively saturate the dangling bonds of the Si(111) substrate. Finally, if time permits, I would also like to present our recent results on the novel tri-layer growth of ultrathin indium films, using ARPES and SXS.
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May 14
Monday

Nanoscale Motion and Bulk Rheology in Complex Fluids

Speaker: Suresh Narayanan, XSD/TRR
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Complex fluids which encompasses colloidal and nanoparticle suspensions, polymers, nanocomposites, gels, emulsions, etc. exhibit rich viscoelastic behavior over hierarchical structural length scales and a wide range of dynamical time scales. Typically the bulk rheology in such systems are of importance for potential applications. X-ray photon correlation spectroscopy has been successfully used to probe nanoscale dynamics in such systems. In this talk, I will present a few science cases that aim at connecting the motion at nanoscale with bulk rheological properties.
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May 14
Monday

GE Digital Detectors for X-Ray Diffraction

Speaker: Susanne M. Lee, GE Global Research, Photonics Laboratory
XSD Seminar
401/A5000 @ 10:00 AM
View Description
The development of next generation medical and industrial x-ray analysis techniques have been hindered by a paucity of photon flux emitted by laboratory-based x-ray sources. To address this, GE has developed a class of vacuum-compatible multilayer x-ray photonic devices that, in theory, can concentrate up to 2π steradians of high-energy photons (>60keV) from a laboratory source and redirect them into pre-specified spatial and spectral beam shapes. In this presentation, the theoretical design of these photonic devices, which require x-ray reflectivities (XRR) better than 99.9% from the multilayer components, will be discussed. High-energy experimental XRR data on these unusually high-reflectivity multilayers will be shown. During the development of these x-ray photonic devices, x-ray reflectivity and diffraction were performed with GE’s sensitive, high-dynamic range, digital x-ray detectors. These non-medical applications presented different imaging requirements than the medical applications for which the detectors were originally designed and manufactured. This presentation will also contain a discussion on the detector design and how to take advantage of it to obtain optimal detector performance at low (~8keV) and high (~60keV) x-ray energies for x-ray diffraction and other x-ray imaging
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May 5
Saturday

X-rays in the Fourth Dimension

XSD Conference
Park Hyatt Chicago, Chicago
View Description
Relative to space, the dimension of time has been underexploited in x-ray science. Interesting phenomena span a hierarchy of time scales, and the advent of new x-ray facilities bring a broad range of capabilities. The goal of this workshop is to assess the worldwide portfolio of x-ray sources and identify classes of experiments best done at complementary facilities (synchrotrons and FELs) so that researchers can be informed about present and planned capabilities. Attendees will "brainstorm" about potential time-resolved experiments in materials; chemistry; condensed matter physics; atomic, molecular, and optical physics; and more. A summary report will be prepared.
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Apr 26
Thursday

Pixel Detectors: New Developments

Speaker: Christian Bronnimann
XSD Presentation
401/A1100 @ 11:00 AM
Apr 23
Monday

Studies of Molecular Bonding by Inelastic X-ray Scattering

Speaker: Professor Keijo Hamalainen, University of Helsinki, Finland
XSD Forum
401/A1100 @ 11:30 AM
View Description
Pizza will be served
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Apr 19
Thursday

Layered Ruthenates and Iridates: A Novel Playground for Correlated Electrons

Speaker: Shalinee Chikara, University of Kentucky
XSD Presentation
431/C010 @ 11:00 AM
View Description
The 4d and 5d transition metal oxides exhibit many exciting phenomena like ferroelectricity, ferromagnetism, antiferromagnetism, meta-magnetism, metal-insulator transition and superconductivity. The ruthenium and iridium oxides are expected to be more metallic and less magnetic than the 3d and 4f oxides because of the extended nature of the 4d and 5d orbitals. In marked contrast, many ruthenates and iridates are magnetic insulators that exhibit a large array of phenomena not usually seen in other materials. In this talk, I focus on the anomalous physical properties and novel phenomena exhibited by these materials. These include novel borderline magnetism and spinvalve effect in ruthenates, and a novel Jeeff= 1=2 insulating state inthe iridates.
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Apr 17
Tuesday

1K Frame Transfer Fast CCD collaboration with LBNL

Speaker: John Weizeorick
XSD Forum
431/C010 @ 9:30 AM
Apr 9
Monday

Pulse Duration Measurements at LCLS

Speaker: Gilles Doumy, XSD/AMO
XSD Presentation
401/A1100 @ 2:00 PM
View Description
The Linac Coherent Light Source (LCLS) at SLAC has been the first x-ray Free Electron Laser (XFEL) in operation. By providing x-ray pulses with incomparable peak brightness, it opened a new era in x-ray physics. Typical characteristics, available from the soft x-ray to the hard x-ray region (500eV-10000eV), amount to approximately 1012 photons per pulse, in a time believed to be as short as a few tens of femtoseconds (10-15 s). Measuring the exact pulse duration of the x-ray pulses has been a challenge from the start, due to a lack of existing techniques capable of accessing that information. The situation is rendered even more complex by the fact that LCLS lasing is based on SASE (Self Amplified Stimulated Emission), which essentially means that every pulse starts from random noise, producing in the end a purely chaotic source. Ideally, a pulse duration characterization requires a single shot measurement capability. While a lot can be learned from measurements done on the electron beam, as well as from a statistical analysis of the pulse energy and high-resolution spectrum of x-ray pulses, ultimately it is necessary to measure each x-ray pulse itself. I will present attempts to realize that by using the technique known as laser streaking, where photoelectrons released during ionization of a gas target see their final energy modified by a simultaneously present short infrared or terahertz pulse.
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Mar 29
Thursday

Shanghai Synchrotron Radiation Facility (SSRF) User Operation Status and Its Phase-II Project

Speaker: Dr. Tiqiao Xiao
XSD Presentation
401/A1100 @ 10:00 AM
Mar 26
Monday

Development and Characterization of Diffractive X-ray Optics

Speaker: Joan Vila-Comamala, XSD/IMG
XSD Presentation
401/A1100 @ 2:00 PM
View Description
We present the developments on diffractive X-ray optics achieved during the last year at the APS and CNM. Among other results, we demonstrate hard X-ray full-field transmission microscopy with sub-25 nm spatial resolution and tomographic capabilities. We discuss future developments and improvements.
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Mar 23
Friday

X-ray Brightness and Interfacial Studies: Development of a Field

Speaker: Sean Brennan, Fairview Associates
XSD Presentation
402/E1100 @ 11:00 AM
View Description
Abstract:

The field of X-ray surface scattering has blossomed over the past thirty years in large part because of the incredible advances in source brightness provided by facilities such as the Advanced Photon Source. Similarly, x-ray microscopy has been driven by improvements in x-ray sources and optics. In this talk, I will use examples from my own research to highlight improvements in both these areas. Finally, I will discuss the new possibilities for interface studies enabled by the beam line and capabilities that will be built at the upgraded APS. The upgraded APS will enable researchers the opportunity to study surfaces and interfaces in both real and reciprocal spaces, and will bring new insights to this important area of science.
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Mar 15
Thursday

The High Speed Imaging Program at 32-ID

Speaker: Kamel Fezzaa
XSD Presentation
402/E1100 @ 1:30 PM
Mar 15
Thursday

Investigating Energy Storage and Conversion Materials using Hard X-ray Tools

Speaker: Karena Chapman
XSD Presentation
402/E1100 @ 1:00 PM
Mar 15
Thursday

APS Strategy for Optics Development: Alternatives

Speaker: Lahsen Assoufid
XSD Presentation
402/E1100 @ 12:30 PM
Mar 15
Thursday

APS Strategy for Detector Development: Alternatives

Speaker: Chris Jacobsen
XSD Presentation
402/E1100 @ 12:00 PM
Mar 14
Wednesday

The Surface Diffraction Beamline at the ESRF and Recent Advancements in the Comprehension of Heterogeneous Catalysis

Speaker: Roberto Felici, European Synchrotron Radiation Facility
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The aim of this talk is to describe the recently rebuilt surface diffraction beamline of the European Synchrotron Radiation Facility in Grenoble, France, and to provide some examples of the activities carried out. Particular attention will be dedicated to the most recent studies of operando heterogeneous catalysis. A new flow reactor [1], which we have conceived, gives the possibility of performing in-situ studies of the structure and morphology of the catalyzer surface at atmospheric pressure and at high temperatures. Results concerning the CO oxidation on Pd will be shown in details [2,3] together with examples of other reactions.

[1] R. van Rijn, et al., Rev. Sci. Instrum. 81 (2010) 014101
[2] R. van Rijn, et al. Physical Chemistry - Chemical Physics 13 (2011) 13167
[3] B.L.M. Hendriksen, et al., Nature Chemistry 2 (2010) 730
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Mar 9
Friday

Optical Design: From IR to X-Rays

Speaker: Ruben Reininger, Brookhaven National Laboratory
XSD Presentation
401/E1100 @ 11:00 AM
View Description
We will describe the optical design of four beamlines: IRENI, CSX, ISR and FXI. IRENI is an infrared beamline collecting 300 mrad of a bending magnet at SRC and dedicated to FTIR micro-spectroscopy. CSX is the only soft x-ray beamline in the NSLS-II project. It consists of two independent branches covering the energy range 170-2000 eV, one for experiments requiring high coherent flux and the other for fast polarization experiments. The source for CSX are two undulators working either phased or canted. ISR and FXI are two of the second phase beamlines for NSLS-II. The former is based on an undulator and is designed for In-Situ and Resonant Hard X-ray Studies in the energy range 2.1-2.3 keV. The source for FXI is one of the NSLS-II damping wigglers. FXI will be dedicated to Full field X-ray Imaging using an existing x-ray microscope at NSLS.
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Mar 6
Tuesday

Investigating Extreme States of Matter by X-ray Absorption Spectroscopy

Speaker: Sakura Pascarelli, European Synchrotron Radiation Facility, Grenoble, France
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The European Synchrotron Radiation Facility is presently undergoing an important upgrade program. Within this upgrade, eight new beamlines will be constructed and will become operational between 2012 and 2016. One of the first upgrade beamlines (UPBL) is UPBL11, designed to provide state-of-the-art conditions to perform time resolved and extreme conditions x-ray absorption spectroscopy.

UPBL11 hosts two energy dispersive x-ray absorption spectrometers coupled to two experimental stations, and will become fully operational in 2012. This instrument will provide the user community new opportunities for investigating matter at extreme conditions of pressure, temperature and magnetic field. Target experiments for the future include kinetic studies of chemical reactions at high pressure and temperature, and investigation of extreme states of matter that can be maintained only over very short periods of time.

In this presentation, I will make an overview of recent results obtained on the former energy dispersive XAS beamline ID24 in the area of extreme conditions. Examples cover studies of chemical reactions that occur in the interior of planets, the investigation of pressure induced collapse of ferromagnetism in 3d metals, and first attempts to probe the electronic and local structure in melts at high pressures. Future perspectives for the investigation of laser-shocked matter are also discussed.
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Feb 28
Tuesday

Phase Contrast Microtomography using Polychromatic Synchrotron Radiation and Single-distance Phase-retrieval Techniques

Speaker: Alexander Rack, X-ray Imaging Group, European Synchrotron Radiation Facility, Grenoble, France
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Inline X-ray phase contrast is an attractive contrast mode for X-ray imaging techniques due to its increased sensitivity: by leaving an appropriate drift space between the sample and the imaging detector, interfaces within the probed specimen can be visualized. While this information is often useful for visual inspection, any further quantitative is not easily possible: the gray levels within the different materials regions are not necessarily different; they are just varying at the interfaces. But if the transmission radiographs are sent through a phase-retrieval process, the tomograms will exhibit ‘area contrast’ rather than edge-enhancing contrast.

In this presentation, the implementation and application the single-distance phase retrieval approach will be introduced [1, 2]. Advantages of this method are that it can be applied to any inline phase contrast tomographic data set; it allows phase-sensitive imaging without modification of existing experimental installations; it is extremely robust and user friendly; it can handle data from arbitrarily absorbing (multi-constituent) samples as well as tolerates polychromatic illumination. The latter is of crucial importance to progress towards higher data acquisition rates: when operating without monochromators, i.e. so-called pink beam or white beam configurations, the required exposure times can be reduced drastically. Microtomography in combination with pink-beam illumination and Paganin phase-retrieval has become the most demanded configuration at the ESRF beamline ID19: it covers now 30% of the ID19 data processing and about 80% for palaeontological studies.

[1] D. Paganin, et al., "Simultaneous phase and amplitude extraction from a single defocused image of a homogeneous object," J.Microsc. 206 (1), 33 (2002).
[2] T. Weitkamp, A. Rack, et al., "ANKAphase: software for single-distance phase-retrieval from inline X-ray phase contrast radiographs," J. Synchrotron Radiat. 18 (4), 617 (2011).
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Feb 13
Monday

The Scientist' Guide to Optimization

Speaker: Sven Leyffer, Mathematics & Computer Science Division, Argonne National Laboratory
XSD Presentation
401/A1100 @ 1:30 PM
View Description
The Scientist' s Guide to Optimization has a few things to say on the subject of optimization. Optimization, it says, is about the most massively useful tool a scientist can have. Many design, data analysis, and operational problems can be formulated as optimization problems. We present a survey of current research trends in optimization motivated by applications of relevance to the APS. We will touch on applications such as accelerator design, image analysis, and optimal control. In all cases we will highlight the relevant software projects within Argonne' s Mathematics and Computer Science Division.
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Feb 3
Friday

Investigating Heterogeneous Catalysts Synthesis, Reactivity and Deactivation with Combining X-ray and Other Techniques

Speaker: Dr. Haiyan Zhao, X-ray Science Division, Argonne National Laboratory
XSD Presentation
401/A1100 @ 10:00 AM
View Description
Various scales of spatial and temporal dimensions are involved in catalyst synthesis, reactivity and deactivation. Full understanding the catalytic processes and ultimately controlling the catalytic reactions require probes of broad time and length scales. We have combined multiple X-ray techniques and other spectroscopic techniques to study catalyst synthesis, reactivity and deactivation. Two examples will be presented to demonstrate the power of X-ray and combination of scattering and spectroscopy techniques.

First example is using the time resolved pair distribution function (PDF) methods to probe the kinetics, mechanism, and energetics for Ag nanoparticle synthesis in a porous zeolite. Understanding the formation of nanoparticles and how they are influenced by a support, is critically important for optimizing their activity. The PDF method can provide the nanoscale structure detail and fast time resolution which allows a multi-step mechanism delineated, and rate constants and activation energies to be estimated for reduction and surface diffusion steps. Complimentary diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ X-ray absorption near edge spectroscopy (XANES) were used to illustrate the surface functional group and oxidation state changes in the particle formation and growth process.

Second example is about probing the active sites in Ni2P and NiFeP for catalytic hydrodesulfurization (HDS) reaction of a model compound 4,6-dimethyldibenzothiophene (4,6-DMDBT). HDS of 4, 6-DMDBT is dominated by two pathways, hydrogenation (HYD) and direct desulfurization (DDS). EXAFS analysis reveals that HYD is due to the square pyramidal Ni(2) and DDS is due to the tetrahedral sites Ni(1) for Ni2P. Combination of EXAFS and IR suggests the substitution of Fe atom in the active phase and a ligand effect on Ni sites.
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Jan 27
Friday

High Repetition Rate Methods for Efficient Laser/X-ray Pump-Probe Measurements of Molecular Dynamics

Speaker: Anne Marie March, Argonne National Laboratory
XSD Presentation
401/A1100 @ 11:00 AM
View Description
Ultrafast, time-resolved, laser-pump, x-ray-probe experiments are powerful tools for understanding and controlling the behavior of matter at the molecular level. Transient structural changes, both geometric and electronic, of single molecules after excitation by a laser pulse can be probed with high resolution and within complex or disordered environments, such as gases and liquids, taking advantage of the superior spatial resolution, elemental specificity and penetration power of x-rays.

Third generation synchrotron sources, particularly the APS, provide x-rays with a unique combination of properties that are well suited for precision time-resolved measurements which include a high flux (1013 photons/second/0.01% bandwidth) that is distributed in short pulses (~100 ps) with moderate intensity (~106 photons/pulse) at a high repetition rate (MHz). Over the last decade laser-pump, x-ray-probe studies have been carried out at synchrotrons but a major challenge has been the low repetition rate (kHz) of standard amplified lasers resulting in underutilization of the synchrotron’s high flux. In response to this we have implemented a high repetition rate (54 kHz – 6.52 MHz), high power (10 W), laser system at 7ID-D at the APS.

In this talk I will highlight our initial experiments using this laser and the x-ray microprobe at 7ID-D. These include x-ray absorption spectroscopy (XAS) of the metalloporphyrin molecule Ni(II)-tetramesitylporphyrin (NiTMP) in solution at 135 times the rate of previous experiments, combined XAS, x-ray emission spectroscopy (XES), and liquid scattering measurements on the spin-crossover molecule Iron(II)-tris(2,2’)-bipyridine ([Fe(bpy)3]2+) in solution using the full flux available at the APS, and XAS of the photodetachment and recombination of the haloalkane CH2BrI in solution. Our results demonstrate how the use of high repetition rate, short pulse lasers as pump sources can dramatically enhance the duty cycle and efficiency in data acquisition and hence capabilities at synchrotron sources. These techniques will play an important role in the utilization of the SPX, the ~1 ps x-ray pulse source planned in the APS upgrade.
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Jan 20
Friday

Precipitation and Fracture of Notch Tip Hydrides in Zirconium Alloys

Speaker: Matthew Kerr, Office of Nuclear Regulatory Research (RES), US Nuclear Regulatory Commission,
XSD Presentation
401/B4100 @ 10:00 AM
View Description
Abstract Zirconium alloys are of importance to the nuclear industry, with primary application as a structural material for the in-reactor environment. The formation of brittle hydrides within zirconium alloys results in a degradation of the mechanical properties of the component in which they form. Therefore, the characteristics of hydride formation and the subsequent impact of these hydrides are critical factors in the determination of zirconium component service life. This talk summarizes a series of three experimental efforts characterizing the mechanical behavior of hydrides in zirconium alloys with high energy synchrotron X-ray diffraction. Part I focuses on the mechanical response of zirconium hydride within a bulk Zircaloy-2 matrix. Part II studies the near crack tip behavior of unhydrided Zircaloy-2. Part III characterizes the behavior of notch tip hydrides. The aim of this work is to quantify the influence of hydrides on the local notch tip strain field and characterize the internal strains in the hydrides themselves.

* Work conducted while Matthew Kerr was a graduate student at Queen’s University and does not reflect a position of the US NRC.
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Jan 16
Monday

Combined High-Energy Diffraction Microscopy (HEDM) and High-Energy X-Ray Tomography at the APS 1-ID Beamline

Speaker: Peter Kenesei, X-Ray Science Division, Argonne National Laboratory
XSD Presentation
401/A1100 @ 11:00 AM
View Description
The High Energy Diffraction Microscopy (HEDM) program attracts a growing community to the Advanced Photon Source 1-ID beamline. High-energy x-ray diffraction (above 50 keV) has been demonstrated to be a powerful tool for the structural characterization of polycrystalline bulk materials measuring the crystallographic orientation and stress states on the grain and sub-grain scales. High energy tomography provides fast three-dimensional maps using absorption or phase contrast, with spatial resolution at the micrometer scale. Both of these techniques have garnered increased interest towards engineering and industrial applications due to their combination of bulk penetration and high sensitivity.In the presentation I will introduce my HEDM evaluation program DIGIgrain that has been adopted for several user measurements at 1-ID and has proven to provide unique quality, compared to other existing programs, for peak segmentation and data reduction. Case studies of far-field diffraction measurements on metallic and non-metallic materials which have utilized DIGIgrain will also be presented.

The combination of these two complementary contrast mechanisms is highly beneficial for the characterization of inhomogeneities such as cracks or voids. Several case studies will be presented to demonstrate their capability to reveal structural details that cannot be detected by a single technique alone. This is especially true for the near field diffraction technique, which can advance directly by combining tomographic reconstruction and crystallographic orientation mapping from the same data set. This approach enables in situ investigations and avoids the registration problem of independent data sets.
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Jan 12
Thursday

In Situ and Operando Spectroscopies for the Characterization of Catalytic Materials

Speaker: Dr. Camille La Fontaine, Laboratoire de Réactivité de Surface, CNRS-Université Pierre et Marie Curie, Paris
XSD Presentation
401/A1100 @ 10:00 AM
View Description
Although heterogeneous catalysts are widely used among industrial processes, the detailed understanding of catalytic mechanisms still needs deeper investigations. The nature of the active sites, their geometry and local environment are determining parameters for the catalytic performances. A fine characterization is thus required to understand this structure-activity relationship and generally involves spectroscopic techniques, particularly through in situ and operando approaches. To this end, relevant developments regarding the use of time-resolved spectroscopies have been recently achieved. In this context, the formation of active phases and their further evolution under real catalytic conditions will be discussed on the basis of recent studies performed at the French Synchrotron SOLEIL using X-ray absorption spectroscopy and complementary techniques such as Raman spectroscopy. Examples will be detailed to illustrate the characterization of various materials, including supported oxides or metals, which are of wide interest in the area of energy, e.g. for biomass valorization or fuels synthesis.
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Jan 9
Monday

Electronics and Structural Dynamics Studies of Solar Energy Materials using Time-resolved X-ray Spectroscopy

Speaker: Xiaoyi Zhang, XSD/SRS
XSD Presentation
401/A1100 @ 1:30 PM
View Description
Ruthenium and Osmium polypyridyl complexes and their derivatives have attracted increasing interest and have been used as photosensitizers in solar-cells, molecular electronics and light emitting devices. Photoexcitation of those photosensitizers leads to long lived metal-to-ligand charge transfer (MLCT) states. If bonded to proper semiconductor nanocrystals, the photoexcited Ru and Os complexes inject electrons to semiconductors, resulting in interfacial-charge transfer state. We have applied time-resolved X-ray spectroscopy to study the electronic and molecular structures of photosentizers in both MLCT excited state and charge-separated state. A series of Ruthenium and Osmium polypyridyl complexes have been studies. Experimental results were compared with simulations/theoretical calculations, quantitative information on the molecular structure, electronic configuration and molecular orbital energies of ground and excited states have been revealed. The chances in the Ru-ligand distances have been directly characterized and rationalized by the interplay between two important factors governing the metal to ligand bonding, steric hindrance and π-backbonding. These works have demonstrated the great potential of time-resolved X-ray spectroscopy to study fundamental structural-functional correlations in solar electricity and fuel generation for both homogenous systems and heterogeneous interfacial systems.
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Jan 6
Friday

Optics Fabrication Activities at NSLS-II

Speaker: Ray Conley, NSLS-II, Brookhaven National Laboratory
XSD Presentation
401/A1100 @ 2:00 PM
View Description
Diverse optics fabrication activities are currently underway within the Optics Fabrication Group at NSLS-II, including work on crystal optics, multilayer Laue lens (MLL) growth and sectioning, and reflective multilayer optics. Crystal optics production capabilities currently include orientation, slicing, dicing, lapping, etching, and CMP polishing of silicon for high-resolution IXS, channel-cut monochromators, and other applications. The current status of MLL fabrication will be presented, including partial-nitrogen reactive sputtering for stress and interfacial roughness reduction which has recently led to a 70 micron thick single-growth MLL. Significant effort has been focused on the achievement of highly-stable nitrogen gas mixing for multilayer growth and the problems faced along with implemented solutions will be discussed in detail. Recent MLL sectioning results obtained by manual polishing, reactive ion etching, and focused ion-beam milling are promising. Multilayers composed of WSi2/Si, Vxsix/Si, Cr/Sc, V/B4C, and W/B4C benefit when grown with a small percentage of nitrogen. Reflective multilayer optics for a wide variety of applications, from ~200eV high energy-density experiments, to 80KeV synchrotron experiments will be presented. Two ion-beam sources (one RF and one DC) incorporating multiple gas mixing are being installed in the MLL deposition system over the next couple months which will expand our capabilities.
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