APS Today: Archives beta

Advanced heavy ion/rare isotope accelerators present very different challenges compared to traditional electron and proton machines. The range of particle velocities that must be accepted for a wide variety of accelerated ions implies a robust system of various accelerating cavity types. The Facility for Rare Isotope Beams (FRIB) project requires such a system and research and development of new techniques and technologies to address these issues in a timely and practical manner have been undertaken at Michigan State University (MSU). While the low-energy section of the FRIB linear accelerator uses more established superconducting Quarter-Wave Resonators (QWRs), the decision was made to pursue two different types of superconducting Half-Wave Resonators (HWRs) for high-energy accelerating section of FRIB. In this talk, a brief overview of the FRIB project and its use of HWRs will be given, along with the relevant theory of superconducting accelerator cavities. The interaction between simulation, mechanical design, and fabrication will be highlighted as essential to achieving a cavity design with reliable, repeatable performance. Results of a cavity test performed at MSU will be presented as an example of this process.
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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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The complement of insertion devices installed on the Canadian Light Source (CLS) includes two superconducting wigglers. These wigglers were built by the Budker Institute and installed on the CLS in 2005 and 2007. Dr. Sigrist has graciously agreed to present the operating experience with these wigglers. He will also outline the remaining complement of IDs at the CLS.
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Modeling and simulation of physical behavior of materials and/or optimization of MEMS device is vitally important to design and develop innovative products and also important to reduce time to deploy technology and expenditure of the process. This presentation discusses steady state and transient simulations of pH-sensitive hydrogel, a MEMS hybrid actuator, and micro fluidics devices utilizing multi-physics approach and coupling various partial differential equations. The transient swelling behavior of a pH -sensitive hydrogel is simulated using an approach that fully couples the chemo-electro-mechanical effects for a 3-dimensional finite element model. The results of the finite element method simulation are based on three nonlinear, partial differential equations that represent three distinct physical phenomena responsible for the swelling behavior. The results of the simulated swelling behavior are compared with published experimental results. Development of hybrid device is discussed. Actuation is achieved by combined effect of thermal expansion, electromagnetic force, and magnetostatic force. The proof of concept was tested initially followed by optimization of design parameters on basis of minimum power consumption and large actuation. This MEMS device consists of two arms of the actuator, a perm-alloy core, an electromagnetic coil and a permanent magnet. The third part of the presentation covers development of microfludics devices to be used for in situ analyzing polymer nanocomposite particles for USAXS study at sector 15. All simulations were performed for coupled system of equations/
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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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Metallic nano-particle (NP) catalysts have been used for reactions such as WGS and biomass reforming. Bimetallic catalysts offer superior performance for activity, selectivity and stability; however, a fundamental understanding of how the electronic and surface structure and resulting chemistry is altered in bimetallic NP’s is not fully understood. Changes induced by metal-metal bonding and reactant and product chemisorption is very useful to understand the behavior of the catalysts.

Methods of synthesis, with control of substrate, particle size, and composition, of supported single metal (e.g. Pt, Pd) and bimetallic catalysts (e.g. PdPt) were developed. TEM and EDX were performed to characterize the size and composition profile of the as-prepared catalysts. EXAFS, at both metal edges (Pt L3 and Pd K), reveal alloy formation of the bimetallic catalyst and an average Pt-rich nano-particle structure. For Pt and Pd, their valance levels locate at 5d and 4d, therefore the L3 edges are a perfect indicator to help understand the electronic structure changes on Pt and Pd atoms due to new bonding or adsorbates. The bimetallic Pd-Pt catalysts show significant changes in the XANES spectra compared to those of Pt or Pd only, indicating a significant modification of the Pd and Pt electronic structures. L3 edge XANES are also strongly modified upon chemisorption, for example with CO. Changes in the XANES can be due to the electron transfer between the metal and ! CO. By comparing the XANES with CO adsorption on single metal and bimetallic catalysts, the fraction of surface Pt and Pd on the bimetallic catalysts can be quantified. To further understand the impact of alloy formation on binding sites of adsorbates, Diffuse Reflectance FTIR was conducted on single metal and bimetallic catalysts with CO exposure. Comparing with the adsorption in single metal Pd catalyst, the compression of CO at bridging site of Pd in the bimetallic PdPt catalyst indicate that Pt may block the bridging sites of Pd when alloy forms. This method of both qualified and quantified characterization will be very useful to understand and compare the properties of bimetallic catalysts, leading to a guideline on how to make catalysts with better performance.
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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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There are growing demands on electron RF linacs for industrial applications, such as radiation processing, industrial X-ray imaging, and radiosurgery. Radiation processing requires a higher electron beam power to increase the processing speed. PAL and POSTECH developed a high-power electron linac for irradiation applications adopting L-band RF technology. It is capable of producing a 10-MeV electron beam with limited undesirable neutron generation and a beam power of 30 kW. The accelerating structure is a disk-loaded waveguide operated with 2π/3-mode traveling-waves. The bunching cells are included in the main accelerating section for a compact structure suitable for industrial applications. Commissioning results of the L-band linac are presented. A brief introduction on a C-band SW accelerating structure for industrial X-ray imaging and SRF cavities for the heavy ion linac of the Korean rare isotope accelerator will be presented in this talk.

* Work partly supported by POSTECH Physics BK21 Program and KAPRA.
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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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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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he focus of this workshop is to shape the final design of a new sector for X-ray Interface Science at APS. As a part of strategic initiative of Argonne National Lab and Advanced Photon Source, this new sector will have nine experimental stations allowing four stations (one tunable, three with fixed energies) to run simultaneously.

It is expected that teams will form after this workshop to build specialized instrumentation for materials synthesis such as oxide-MBE, ALD, MOCVD, and other new capabilities. This sector will serve a diverse community with interests in catalysis, oxide film growth, geochemistry, surface physics, nanoscience, tribology, electrochemistry, and more.

Workshop location: Advanced Photon Source, Argonne National Laboratory On-line registration:
http://www.regonline.com/builder/site/Default.aspx?EventID=1043944
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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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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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Agenda:

- Budget update - Mancini
- Green Sheet reporting - Pile
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