Surface Nucleation of Magnetic Twist in Artificial Fe/Gd Multilayers

D. Haskel1, G. Srajer1, Y. Choi1, D. R. Lee1, J.C. Lang1, J. Meersschaut2, J.S. Jiang3, and S. D. Bader3

1Experimental Facilities Division, Argonne National Laboratory
2Instituut voor Kern- & Stralingsfysica
3Materials Science Division, Argonne National Laboratory

Artificial magnetic multilayers can exhibit complex inhomogeneous magnetic structures wherein the magnetization varies throughout the thickness of the multilayer. Surfaces and interfaces can act as nucleation centers for such inhomogeneous states. We present direct evidence for nucleation of such state at the surfaces of Fe-terminated Fe/Gd multilayers. This surface nucleation was predicted more than a decade ago but its experimental confirmation has not been realized until now.

Magnetic Domain Imaging in Nanoscale Structures Using X-ray Photoemission Electron Microscopy

D. Keavney1, J. Freeland1, W. C. Uhlig2, D. Wu2, and J. Shi2

1Experimental Facilities Division, Argonne National Laboratory
2University of Utah

The ability to fabricate patterned magnetic structures at submicron length scales has generated significant interest in using these structures in new applications, such as magnetic random access memories and advanced recording media. In addition, patterned structures enable the study of fundamental magnetic behavior at new length scales. We used photoemission electron microscopy at the Advanced Photon Source 4-ID-C beamline to examine magnetostatic interactions between individual structures in high-density arrays.

Two series of Co dot arrays were studied in which the dot size and longitudinal and transverse separation distance were varied. The arrays were grown on Si wafers via electron-beam lithography. In the first series with 500 x 1000-nm dot size, we find significant interplay between the longitudinal magnetostatic coupling and the ground state of the dots. When the dots are separated by more than 250 nm, they are uncorrelated and in the multidomain state... Strong coupling occurs for gaps of 250 nm or less. Below this gap, a single domain state is more common and clear correlations in the direction of magnetization are seen between neighboring dots. The 200 x 600 nm dots are all single domain even in arrays with large dot separations. We find strong longitudinal coupling at a gap of 100 nm, with clearly correlated lines of dots. A statistical analysis of the near-neighbor correlations shows that the interactions extend to the fourth-nearest neighbor dot. For arrays in which the transverse gap is small, there is no evidence for transverse coupling for gaps down to 300 nm.

Nanoscale Modulations in YBCO High-Tc Superconductors

Z. Islam1, J.C. Lang1, D. Haskel1, D.R... Lee1, G. Srajer1, D.R. Haeffner1, X. Liu2, S...K. Sinha2, S. Moss3, P. Wochner4, and U. Welp5

1 Experimental Facilities Division, Argonne National Laboratory
2 University of California, San Diego
3 University of Houston
4 Max-Planck-Institut für Metallforschung
5 Materials Science Division, Argonne National Laboratory

We provide unambiguous evidence that a four-unit-cell superstructure q0 (1/4, 0, 0) forms along the shorter Cu-O-Cu bond in the optimally doped Yba2Cu3O6.92 superconductor. We find that a complex set of correlated atomic displacements on CuO2, BaO and CuO planes, respectively, give rise to diffuse superlattice peaks at ± q0 away from Bragg points. Correlation lengths of these displacements are only a few unit cells long in the CuO2 planes and a fraction of a unit cell in the perpendicular direction. These observations are similar to those in Yba2Cu3O6.63 where the ordering is (2/5, 0, 0). In both cases, however, diffuse scattering is enhanced at cryogenic temperatures in contrast to the temperature-independent behavior of two unit-cell periodic O-ordered superstructure in Yba2Cu3O6.41.

Dedicated High-Resolution Powder Diffraction Beamline at the Advanced Photon Source

P.L. Lee1, M.A. Beno1, D. Shu1, M. Ramanathan1, J.F. Mitchell2, J.D. Jorgensen2, and R.B. Von Dreele1,3

1Experimental Facilities Division, Argonne National Laboratory
2 Materials Science Division, Argonne National Laboratory
3 Intense Pulsed Neutron Source, Argonne National Laboratory

A high-resolution x-ray powder diffraction beamline that exploits the high flux, high-energy resolution and precise energy tuning of the third-generation synchrotron source will be built at the Advanced Photon Source (APS). The goal is to establish a high-resolution, high-throughput dedicated powder instrument at the APS to serve the powder community. We describe design of the instrument that is able to measure a complete high-resolution powder pattern in one hour or less, uses automation to optimize throughput, has the ability to readily tune over a wide range of x-ray energies quickly and easily covering important absorption edges for resonant data measurements, and has the ability to accommodate various environmental devices for high-temperature, low-temperature, or time-resolved data collection.

Actinide Chemistry at the Advanced Photon Source

L. Soderholm1,2,4, S. Skanthakumar1,2, M.R. Antonio1, J. Neuefeind1, A. Locock4,5, P.C. Burns4,5, and J. Linton3

1Chemistry Division
2Actinide Facility
3Experimental Facilities Division, Argonne National Laboratory
4Environmental Molecular Sciences Institute
5University of Notre Dame

The juxtaposition, at ANL, of facilities for handling radioactive samples and a third-generation synchrotron allows the execution of experiments that involve in situ chemical manipulation, such as titrations or electrochemistry, which are unique in the world. The actinide series of elements, composing the 5f (bottom) row of the periodic table, are all radioactive and most are heavy-metal poisons. These elements have physical properties that are intermediate between the d-transition elements and the 4f, lanthanide series. They have rich redox behavior and quasi-localized valence electrons that provide the opportunity for studying such diverse areas as correlated electrons, atomic correlations, optical properties, and catalysis. From an environmental perspective, the actinides have enormously complex solution chemistry that needs to be elucidated before adequate modeling can be undertaken of the transport of these pollutants under relevant geologic conditions.

We take full advantage of the unique ANL capabilities to examine questions of 5f-electron hybridization/bonding and their effects on chemical and physical properties of actinide-containing materials. Results will be presented on actinide in situ spectroelectrochemistry, XAFS studies, analyzer-crystal XANES studies, and high-energy scattering experiments. The implications of these efforts will be addressed from both the basic and environmental sciences perspectives.

Selected aspects of this work are done under the auspices of the Environmental and Molecular Sciences Institute at the University of Notre Dame. Support is acknowledged from the U.S. DOE – BES, Chemical Sciences, under Contract W-31-109-ENG-38.

In Situ X-ray Studies of Ferroelectric Thin Films

G.B. Stephenson11, D.D. Fong1, S.K. Streiffer1, J.A. Eastman1, O. Auciello1, P.H. Fuoss1, G.-R. Bai1, M. E. M. Aanerud2, and C. Thompson2,1

1Materials Science Division, Argonne National Laboratory
2Northern Illinois University

Synchrotron x-ray scattering techniques have been used to study the ferroelectric phase transition in coherently strained, epitaxial PbTiO3 thin films grown on SrTiO3, as a function of film thickness [1]. We observe that 180° stripe domains occur below the ferroelectric transition in these films, in order to reduce depolarization field energy. Such domains are known from studies of bulk crystals, arising from a fascinating competition between polarization, strain, and electric field. The 180° stripe domains have been predicted to significantly affect the properties of ferroelectric films [2,3], but have not previously been directly observed in thin films. The dependence of the stripe period on film thickness is in agreement with theory. However, the suppression of the transition temperature as a function of film thickness is significantly larger than that expected solely due to 180° stripe domains, indicating that intrinsic surface effects may also be important. These experiments also confirm that the ferroelectric phase transition occurs above room temperature in coherently-strained epitaxial PbTiO3 films with thicknesses as small as three unit cells.

[1] S.K. Streiffer, J.A. Eastman, D.D. Fong, Carol Thompson, A. Munkholm, M.V.R. Murty, O. Auciello, G.R. Bai, and G.B. Stephenson, Phys. Rev. Lett. 89, 067601 (2002).
[2] A. Kopal, P. Mokry, J. Fousek, and T. Bahnik, Ferroelectrics 223, 127 (1999).
[3] A. M. Bratkovsky and A. P. Levanyuk, Phys. Rev. Lett. 84, 3177 (2000).

This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under contract W-32-109-ENG-38, and by the State of Illinois under HECA.

Direct Observation of Orthoclase Mineral Dissolution: Mechanism and Kinetics

P. Fenter1, H. Teng2, L. Chang1, Z... Zhang3, C. Park1, and N. C. Sturchio4

1Environmental Research Division, Argonne National Laboratory
2The George Washington University
3Northwestern University
4University of Illinois at Chicago

Feldspars having the end-member compositions of K[AlSi3O8], Na[AlSi3O8] and Ca[AlSi3O8] are the most common crustal minerals and consist of six of the eight most abundant elements in the Earth's crust. Orthoclase is a feldspar having the composition K[AlSi3O8]. Feldspar weathering results in the release of nutrients (e.g., K, Na, Ca...) and the formation of clay minerals, which are the building blocks of soils. The nominal weathering reaction is:

2K[AlSi3O8] + 2H+ +9H2O => Al2Si2O5(OH)4 + 4H4SiO4 (aq) + 2K+

On the molecular scale the weathering process is poorly understood. We use x-ray scattering techniques to directly reveal the structures, processes and kinetics associated with dissolution at the orthoclase-water interface.

This work was supported by the Geoscience Research Program, Office of Basic Energy Sciences, Department of Energy, under Contract W-31-109-ENG-38.

Time-Resolved and Anomolous SAXS at the BESSRC ID-12-B&C Undulator Beamline

S. Seifert2, J. V. Beitz1, K. A. Carrado1, J. P. Hessler1, S. Skanthakumar1, D. M. Tiede1, P. Thiyagarajan3 , and R. E. Winans1

1Chemistry Division
2Experimental Facilities Division
3Intense Pulsed Neutron Source, Argonne National Laboratory

A small-angle x-ray scattering (SAXS) facility at BESSRC (Advanced Photon Source sector 12) has been implemented to study problems in biology, materials, and chemistry, with emphasis on in situ, time-resolved and anomalous experiments. SAXS has been used to map the distribution of particles in a flame with the ability of observing small molecules. A new detector is being designed to increase the sensitivity and permit time resolved experiments as short as the time constant of the storage ring. The anomalous small-angle x-ray scattering effect has been observed for actinide oxide nanophases embedded in vitreous silica, which is important in the study of a new nuclear waste treatment process. The mechanisms of formation in clay synthesis have been elucidated with SAXS. Wide-angle scattering is being used to resolve te structure and dynamics of functional molecular assemblies with 0.1-Å precision.

This work was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract W-31-109-ENG-38.

High-Energy SAXS/WAXS: A Versatile Tool for Materials Analysis

J. Almer, U. Lienert, and D. Haeffner

Experimental Facilities Division, Argonne National Laboratory

One of the primary tools for studying nanoscale inhomogeneities, such as pores and precipitates, is small-angle x-ray scattering (SAXS). Wide-angle scattering (WAXS), on the other hand, can be used to investigate amorphous and/or crystalline phases and their internal strain and texture states. Here we present a combined SAXS/WAXS probe which uses high-energy x-rays (HEX) from the sector 1-ID Advanced Photon Source beamline. Key camera features include intense HEX brilliance, which enables spatial and temporal resolution, and the high penetrating power of HEX (several mm in most materials at 80 keV), which enables in situ experiments and samples bulk behavior. We illustrate the use of spatial and temporal modes with recent results on thermal barrier coatings and in situ annealing of bulk-metallic glasses, respectively.

This work and use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract number W-31-109-Eng-38.

Phase Enhanced Live Imaging of Small Insects

W.-K. Lee1 and M. Westneat2

1Experimental Facilities Division, Argonne National Laboratory
2Field Museum of Natural History

Synchrotron radiation is proving to be a powerful new tool for the study of small insects. The partial beam coherence at the Advanced Photon Source, coupled to its high beam brilliance, has allowed for a real-time look into the internal workings of these small animals. Using phase enhanced live imaging, we have discovered a lung-like tracheal compression in the pro-thorax of several species of insects (Science, 24 January 2003). This work has generated considerable interest in the insect physiology community. Some of the current and future experiments will study mouthpart kinetics and coordination, digestive system of ants, air-sac development and function of grasshoppers, the reproductive stages of female grasshoppers, and the escape mechanisms of the click beetle.

High-Pressure Studies with Nuclear Resonant Inelastic Scattering Studies

W. Sturhahn1, E. E. Alp1, T. Toellner1, J... Zhao1, H. K. Mao2, V. V. Struzhkin2, G. Shen3, V. Prakapenka3, H. Kobayash4, and T. Kannimura4

1 Experimental Facilities Division, Argonne National Laboratory
2 Carnegie Institute of Washington
3 GeoSoilEnviroCARS, University of Chicago
4 Tohoku University, Japan

Nuclear resonant inelastic x-ray scattering is applied to study the dynamical behavior of materials under high pressure and at high temperatures. Thermodynamic and elastic parameters extracted from the data are used to understand electrical, chemical, and magnetic property changes under pressure and temperature. Several examples will be given, including Fe, FeO, and FeS. Instrumentation developments that drive these experiments, including the high-resolution monochromator, microfocusing optics, and infra-red laser system, will be explained.

High-Resolution Inelastic X-ray Scattering in Liquids and Solids

H. Sinn, A. Alatas, A. Said, T. Toellner, J. Zhao, W. Sturhahn, and E. E. Alp

Experimental Facilities Division, Argonne National Laboratory

Recent measurements to study the collective excitations in liquid-crystalline DNA and high-temperature liquids, such as sapphire and boron, above 2000K are described. Phonon dispersion measurements in uranium are given to show the possibility of inelastic x-ray scattering of heavy elements such as actinides. Also explained will be instrumentation developments such as the dynamical spherical bender and the multi-element analyzer for the newly developed beamline of the Inelastic X-ray Scattering Collaborative Development Team at sector 30.

High-Throughput X-ray Microtomography

F. DeCarlo and B. Tieman

Experimental Facilities Division, Argonne National Laboratory

X-ray microtomography is rapidly becoming the tool of choice for three-dimensional (3D) imaging of thick structures at the 1-10 µm scale. The fast microtomography system at Advanced Photon Source beamline 2-BM is a new class of instrument offering near video-rate acquisition of tomographic data combined with pipelined processing, reconstruction, and visualization. This system can acquire and reconstruct 720 projections (1024 x 1024 pixels) at 0.25° angular increments in under 5 min using a dedicated 32-node computer cluster. At this throughput, up to 100 specimens can be imaged in a 24 h experiment. Alternatively, time-dependent 3D sample evolution can be studied on practical time scales.

The 2-BM fast x-ray microtomography system has been applied to a variety of materials science and biological problems with unprecedented results. These include studies of new ceramic thermal barrier coatings for turbine components, micro-anatomy of millimeter-scale organisms, and biomineralization processes. For example, conventional anatomical study of millimeter-scale organisms by histological sectioning is notoriously time consuming and artifact-prone. Using 7.5-keV x-rays, we employed the 2-BM system to map the anatomy of the ostracod Scutigera coleoptrat in a few hours. Many anatomical details (e.g., micron-scale myostriation) were revealed that would otherwise be inaccessible by visible-light microscopy. We are also using fast x-ray microtomography to study strategies that sea urchins use to optimize biomechanical strength and toughness through biomineralization, which might one day be used to achieve controlled synthesis of complex structures. Sea urchin ossicles are an important model because many aspects of echinoderm calcification resemble those in mammalian dental systems. The speed of the 2-BM system has proven instrumental in obtaining a good statistical base for such studies by aiding analysis of a large sample number. This work was partly supported by Argonne National Laboratory's Laboratory Directed Research and Development funds (2001-2002).

Reconstructed slice of a tooth fragment from the sea urchin Lytechinius variegatus. The two rows of dark channels extending through the mineral appear not to have been noted previously and may play a role in nutrient transport.

Fig. 1. Reconstructed slice of a tooth fragment from the sea urchin Lytechinius variegatus. The two rows of dark channels extending through the mineral appear not to have been noted previously and may play a role in nutrient transport.

X-ray Diffraction Microscopy for Structural Characterization Down to Nanometer Length Scales

Y. Xiao, A. Tkachuk, Y. Chu, Z. Cai, and B. Lai

Experimental Facilities Division, Argonne National Laboratory

X-ray diffraction microscopy, with its capability to spatially resolve crystallographic phases, lattice strains, and microstructures, has revolutionized material characterizations from microns to nanometers length scales. We have developed new techniques at sector 2 of the Advanced Photon Source that allow x-ray diffraction characterization on a single nano-object and structural characterization of combinatorial materials.

Structures of individual nanobelts of tin oxide synthesized through thermal evaporation of condensed materials were directly studied with a 150-nm x-ray beam. Larger grain disorientation distributions around the long axes of the nanobelts than that around their perpendicular axes were observed among nanobelts with cross sections from 35 nm x 200 nm down to 10 nm x 30 nm. The grain disorientation distributions in both directions become larger when the cross section was reduced, strongly suggesting an intrinsic relation between the structures and dimensions of these nanomaterials.

We investigated the structure of CoMnGe magnetic thin-films at a spatial resolution of 1~50 µm. The films were synthesized using combinatorial molecular beam epitaxy techniques in which the doping profiles across each substrate were controlled, making it possible to study the structure-property relation of these complex systems. By probing the phase diagram and measuring the evolution of interfacial structure as a function of composition, we obtained evidence for a strain compensation effect in this system. This effect is expected to find significant application in the new field of spintronics.

Tunneling electron microscopy image (left) of nanobelts of tin oxide as synthesized illustrates a rectangular cross section. Scanning electron microscopy image (middle) displays a single nanobelt. X-ray diffraction image (right) from the nanobelt, captured with a CCD detector.

Fig. 1. Tunneling electron microscopy image (left) of nanobelts of tin oxide as synthesized illustrates a rectangular cross section. Scanning electron microscopy image (middle) displays a single nanobelt. X-ray diffraction image (right) from the nanobelt, captured with a CCD detector.

Biological X-ray Fluorescence Microscopy

S. Vogt, J. Maser, B. Lai, D. Legnini, and Z. Cai

Experimental Facilities Division, Argonne National Laboratory

The importance of trace metals in the biological and medical sciences has received increased recognition. Synchrotron-based hard x-ray fluorescence microscopy is a powerful technique to study the extra- and intracellular distributions of the elements from Si to Zn and above, with sub-optical spatial resolution. Due to its inherent low background, x-ray fluorescence is particularly well suited to detect elements in trace quantities, down to the level of attograms. The possibility of selecting the incident x-ray energy with a bandwidth of ?E/E= 10-4 enables microspectroscopy and chemical state mapping in order to determine the speciation of elements of interest. These unique capabilities of x-ray fluorescence microscopy complement other modern microscopy techniques and have been employed in diverse biomedical applications.

We will discuss the instrumentation and methods that we have implemented and demonstrate their application in several ongoing collaborations, ranging from the investigation of TiO2-DNA nanocomposites in mammalian cells, to mycobacteria in macrophages, to the toxicity and effectivity of Pt-based anticancer drugs.

X-ray fluorescence maps (P, Ti, and Zn) of a cell transfected with titanium dioxide nanocomposites (green), showing introduction of the nanocomposites in the cell.

Fig. 1. X-ray fluorescence maps (P, Ti, and Zn) of a cell transfected with titanium dioxide nanocomposites (green), showing introduction of the nanocomposites in the cell.

From Flat Substrate to Elliptical Kirkpatrick-Baez Mirror by Profile Coating

C. Liu, R. Conley, L. Assoufid, Z. Cai, J. Qian, and A. T. Macrander

Experimental Facilities Division, Argonne National Laboratory

For microfocusing x-ray mirrors, an elliptical shape is essential for aberration-free optics. However, it is difficult to polish elliptical mirrors to x-ray-quality smoothness. Profile coatings have been applied on both cylindrical and flat Si substrates to make the desired elliptical shape..... In a profile-coating process, the sputter source power is kept constant, while the substrate is passed over a contoured mask at a constant speed to obtain a desired profile along the direction perpendicular to the substrate-moving direction. The shape of the contour was derived from a desired profile and the thickness distribution of the coating material at the substrate level. The thickness distribution was measured on films coated on Si wafers using a spectroscopic ellipsometer with computer-controlled X-Y translation stages. The mirror coating profile is determined from the difference between the ideal surface figure of a focusing ellipse and the surface figure obtained from a long-trace profiler measurement on the substrate. The number of passes and the moving speed of the substrate are determined according to the required thickness and the growth-rate calibration of a test run. A Kirkpatrick-Baez (K-B) mirror pair was made using Au as a coating material and cylindrically polished mirrors as substrates. Synchrotron x-ray results using this K-B mirror pair showed a focused spot size of 0.4 x 0.4 ?m2. This technique has also been applied for making elliptical K-B mirrors from flat, commercially available Si substrates. Test mirrors of 60 and 120 mm focus lengths have been successfully fabricated. It has been demonstrated that it is possible to use a single mask to make multiple elliptical K-B mirrors (with the same design parameters) for synchrotron undulator beamlines.

This work supported by the U.S. DOE, BES, Office of Science, under contract No. W-31-109-ENG-38.

Development of a Linear Stitching Interferometric System for Evaluation of Very Large X-ray Synchrotron Radiation Substrates and Mirrors

L. Assoufid1, M. Bray2, and D. Shu1

1Experimental Facilities Division, Argonne National Laboratory
2MB-Optique SARL, 26-ter, rue Nicolai, 75012 Paris, France

Stitching interferometry, using small-aperture, high-resolution, phase-measuring interferometric systems has been investigated for quite some time as a metrology technique to obtain surface profiles of oversized optical components and substrates. The technique offers the potential for providing three-dimensional (3D) measurements of mirror surfaces with nanometer accuracy and resolution. The aim of this work is to apply this technique to the specific case of large, flat, grazing-incidence x-ray mirrors, such as those used in beamlines at synchrotron radiation facilities around the world. In the case of x-ray mirrors, obtaining a 3D surface profile can be particularly useful in many instances, for example, in selecting the best reflecting stripe on a mirror surface to be used for undulator beams. The measurement data can be used for simulating and predicting mirror performance under realistic conditions, etc. A fully automated system based on this technique is currently being developed at the metrology laboratory of the Advanced Photon Source. Tests performed on a 460-mm-long flat float glass substrate and on a 300-mm-long superpolished silicon substrate are presented. The stitched profiles showed no obvious overlap errors, and the results agree well with those obtained using other techniques.

This work supported by the U.S. DOE, BES, Office of Science, under contract No. W-31-109-ENG-38.

Dual Canted Undulators at the Advanced Photon Source

P. K. Den Hartog1, C. Benson1, B. Brajuskovic1, J. Collins1, G. Decker2, L... Emery2, M. Erdmann1, Y. Jaski3, E. Trakhtenberg1, and G. Wiemerslage1

1Experimental Facilities Division, Argonne National Laboratory
2APS Operations Division, Argonne National Laboratory
3Accelerator Systems Division, Argonne National Laboratory

At the Advanced Photon Source, 34 straight sections are reserved for the installation of insertion devices for users. Each straight section allows space for up to two 2.4-m-long devices. By sacrificing 0.4 m of undulator from each device and introducing a 1 mrad chicane with three small electromagnets, two separate experimental programs can be conducted using the same straight section, thereby potentially doubling the scientific output with the same real estate. The design of the straight section and front end, and plans for implementation and commissioning of this scheme, are presented. This work was supported by the U.S. Department of Energy, Office of Science, under Contract No. W-31-109-Eng-38.

Design and Development of a Robot-Based Automation System for Cryogenic Crystal Sample Mounting at the Advanced Photon Source

D. Shu1, C. Preissner1, D. Nocher1, Y. Han1, J. Barraza1, P. Lee1, W-K. Lee1, Z. Cai1, S. Ginell2, R. Alkire2, K. Lazarski2, R. Schuessler2, and A. Joachimiak2

1Experimental Facilities Division
2Biosciences Division/Structural Biology Center, Argonne National Laboratory

X-ray crystallography is the primary method to determine the three-dimensional (3D) structures of complex macromolecules at high resolution. In the years to come, the Advanced Photon Source (APS) and similar third-generation synchrotron sources elsewhere will become the most powerful tools for studying atomic structures of biological molecules. One of the major bottlenecks in the x-ray data collection process is the constant need to change and realign the crystal sample. This is a very time- and manpower-consuming task. An automated sample-mounting system will help to solve this bottleneck problem. We have developed a novel robot-based automation system for cryogenic crystal sample mounting at the APS. Design of the robot-based automation system, as well as its on-line test results at the Argonne Structural Biology Center 19-BM experimental station, are presented in this paper.

This work was supported by the U.S. Department of Energy, Office of Science, under Contract No. W-31-109-Eng-38.

New High-Heat-Load Front End for Multiple In-Line Undulators at the Advanced Photon Source

Y. Jaski

Experimental Facilities Division, Argonne National Laboratory

A new high-heat-load front end is being designed to handle a maximum total power of 21 kW with a peak power density of 590 kW/mrad2. This is about 3.8 times the heat load compared with current operation of a single 3.3-cm-period, 2.4-m-long undulator (Undulator A) at 100-mA stored beam current. Installation of this front end is planned for the Inelastic X-ray Scattering Collaborative Development Team sector during October 2004 and for Nano-CAT during January 2005. This front end will allow operation of three in-line Undulator A's at K=2.0 with 150 mA of stored beam, or two in-line Undulator A's at K=2.76 with 180 mA. In this poster, the overall front-end high-heat-load management plan is discussed and front-end layout and aperture design are presented. A new design concept is used in key high-heat-load components such as photon shutters, fixed masks, and exit mask to handle the high power density. The design, thermal analysis, and fabrication plan for these components are presented.

This work was supported by the U.S. Department of Energy, Office of Science, under Contract No. W-31-109-Eng-38.

In Situ High-Energy X-ray Powder Diffraction Studies in Heterogenous Catalysis: Coupling the Study of Long Range and Local Structural Changes

P. J. Chupas1, C. P. Grey1, J. C. Hanson2, J. Rodriguez2, X. Qiu3, S. J. L. Billinge3, and P. L. Lee4

1State University of New York at Stony Brook
2Brookhaven National Laboratory
3Michigan State University
4Experimental Facilities Division, Argonne National Laboratory

The application of in situ time resolved powder diffraction to study structural changes that occur during chemical reactions has become a standard method at synchrotron sources. With respect to heterogeneous catalysis, the understanding of the structural changes, both on the local and long-range length scales, that are the consequence of reaction conditions is paramount to fully understanding the functioning of many catalysts. Time resolved diffraction experiments, which combine high-energy x-rays (>80 keV) with area detectors open the possibility of coupling both reciprocal and real-space methods to probe both long-range and local structural changes simultaneously. This is particularly advantageous in the study of chemically induced structural changes, commonly encountered in heterogeneous catalysis. Here we illustrate the application of the approach to monitor the phase transition of α-AlF3 and the migration of oxygen in and out of the CeO2 crystal structure.

Phase-Contrast Microscopy

D. Paterson, Y.S. Chu, S. Vogt, B. Lai, and I. McNulty

Experimental Facilities Division, Argonne National Laboratory

The advent of highly coherent x-ray beams at modern synchrotrons has revolutionized phase-contrast microscopy. At high x-ray energies, the real part of the complex index of refraction is several orders of magnitude larger than the imaginary part. Consequently, x-ray imaging of low-density samples such as thin sections of mammalian cells or bacteria can benefit significantly from phase contrast methods. We are developing powerful new phase contrast techniques at sector 2 of the Advanced Photon Source (APS) that uniquely capitalize on the high brilliance of APS x-ray sources. They include phase contrast enhancement of defects in weakly diffracting matter such as protein crystals, differential phase contrast of weakly absorbing biological samples using configured detectors in scanning x-ray microscopes, and absolute determination of the phase of materials science specimens such as atomic force microscopy tips using coherent full-field imaging. These sensitive x-ray phase contrast methods, in addition to being advantageous for imaging weakly absorbing or scattering features with minimum attendant radiation dose, are also useful for fundamental measurements of wavefields. As a result, we are also utilizing them to characterize coherent x-ray beamlines.

Quantitative three-dimensional  reconstructions of the real part of the refractive index (phase) of an atomic force microscope tip.

Fig. 1. Quantitative three-dimensional reconstructions of the real part of the refractive index (phase) of an atomic force microscope tip.