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.

To report an event that is not listed, contact webmaster.

Past Seminars

2014

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

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.
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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

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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