Session Q33: Focus Session: X-ray and Neutron Instruments and Measurement Science

Science Enabled by the Advanced Photon Source Upgrade

The Advanced Photon Source (APS) at Argonne National Laboratory is embarking on a major Upgrade that will significantly enhance capabilities for research using high brilliance, high energy synchrotron x-ray beams. The APS is a DOE Office of Science user facility that provides access to x-ray scattering, spectroscopy, and imaging instruments through an open, peer-reviewed proposal process. Currently 64 simultaneously operating beamlines are used by more than 4000 researchers each year across the full range of science and technology fields. The APS Upgrade project will provide major improvements to the x-ray sources as well as more than a dozen new or upgraded beamlines. Key areas of emphasis are using penetrating, high energy x-rays for atomic-scale studies of real materials in real time under real conditions, imaging of hierarchical structures on length scales from millimeters to nanometers, and ultrafast studies of chemical and physical processes on time scales down to picoseconds. I will illustrate the science enabled by the APS Upgrade using examples such as developing synthesis of new materials with outstanding properties and probing picosecond dynamics in energy conversion systems.   

Initial Results and Future Plans for the Soft X-ray Instrument for Materials at the Linac Coherent Light Source (LCLS)

For two years ultrafast high intensity x-ray pulses have been available at the Linac Coherent Light Source, the x-ray free electron laser at the SLAC National Accelerator Laboratory. The soft x-ray instrument (SXR) operates at an energy range from 480eV-2000eV and features a plane grating monochromator as well as a bendable refocusing mirror system. The measured performance of the instrument will be presented as well as the future direction for instrumentation development. \\[4pt] Acknowledgement: This research was carried out on the SXR Instrument at the Linac Coherent Light Source (LCLS), a division of SLAC National Accelerator Laboratory and an Office of Science user facility operated by Stanford University for the U.S. Department of Energy. The SXR Instrument is funded by a consortium whose membership includes the LCLS, Stanford University through the Stanford Institute for Materials Energy Sciences (SIMES), Lawrence Berkeley National Laboratory (LBNL), University of Hamburg through the BMBF priority program FSP 301, and the Center for Free Electron Laser Science (CFEL).   

Microfocusing options for sector 3 of the Advanced Photon Source upgrade project

Synchrotron radiation from third generation, high-brilliance rings is an ideal source for x-ray microbeams. The aim of this report is to describe a micofocusing scheme that combines both a toroidal mirror and a Kirkpatrick-Baez (KB) mirrors for upgrading the existing optical system for inelastic x-ray scattering experiments at sector 3 at the Advanced photon Source (APS). Shadow ray tracing simulations show that this combination can provide beam sizes of 4.5 $\mu $m (H) $\times $ 0.6 $\mu $m (V) (FWHM) at the end of the existing D-station (66 m from the source) with a transmission of up to 59 {\%} and a beam size of 3.7 $\mu $m (H) $\times $ 0.46 $\mu $m (V) (FWHM) at the front end of proposed E-station (68 m from the source) with a transmission of up to 57 {\%}. With this new setup, experiments that combine high pressure, low temperature and external magnetic field can be done.   

Advances in X-ray Raman spectroscopy at Stanford Synchrotron Radiation Lightsource

We present a state-of-the-art x-ray Raman spectroscopy end-station recently developed, installed, and operated at the Stanford Synchrotron Radiation Lightsource. The end-station consists of two multicrystal Johann type spectrometers arranged on a Rowland circle of 1m. The first one, positioned at the forward scattering angles (low-q), consists of 40 diced and spherically bended Si(110) crystals of 4" of diameter providing a large solid angle of detection as well as an overall energy resolution of about 270 meV at 6462.20 eV. The second spectrometer, consisting of 14 spherically bent Si(110) crystal analyzers, is positioned at the backward scattering angles (high-q) enabling the study of non-dipole transitions. These features, in particular the improved total resolution with a substantial increase in solid angle, positions the instrumentation as a unique alternative to soft x-ray absorption for difficult sample conditions and bulk sensitive measurements, which allows a systematic implementation of this photon-in/photon-out hard x-ray technique on emerging research of multidisciplinary scientific fields in energy-related science, physics, and material science. Preliminary results and prospects will be presented and discussed, in particular for applications in Energy Science.   

Facility Overview and Double-Focusing Thermal Triple-Axis Spectrometer at the NCNR

We will briefly overview the neutron scattering instrumentation at the NCNR, but will focus the talk on the capabilities of the new thermal triple-axis spectrometer is located at the BT-7 beam port [1]. This spectrometer takes full advantage of the large 165 mm diameter reactor beam to tailor the dual 20$\times $20 cm$^{2}$ double-focusing monochromator system to provide monochromatic fluxes exceeding 10$^{8}$ n/cm$^{2}$/s onto the sample. The two monochromators installed are PG(002) and Cu(220), which provide incident energies for 5 meV to above 500 meV. The computer controlled analyzer system offers six standard modes of operation, including a diffraction detector, a position-sensitive detector (PSD) in diffraction mode, horizontal energy focusing analyzer with detector, a \textbf{Q}-E mode employing a flat analyzer and PSD, a constant-E mode with the analyzer crystal system and PSD, and a conventional mode with a selection of S\"{o}ller collimators and detector. Additional configurations for specific measurement needs are also available. The capabilities and performance will be discussed and examples of published data presented. \\[4pt] [1] J. W. Lynn, Y. Chen, S. Chang, Y. Zhao, S. Chi, W. Ratcliff, II, B. G. Ueland, and R. W. Erwin, J. Research NIST 117 (in press).   

Advanced Thermal Neutron Detectors

With the advent of new high intensity spallation sources, there is a vital need for development of advanced position sensitive detectors. Using neutron conversion in helium 3, which yields a large signal with excellent background rejection capability, our research program focuses on improving the rate capability, resolution, efficiency and long term stability of detectors for neutron scattering studies. We have developed a suite of detectors using proportional chambers, the latest being an array of curved, multi-wire segments with interpolating cathode strip electrodes operating simultaneously and seamlessly in a single gas volume. With rate capability of nearly 1 million per sec, this instrument has significantly advanced the state-of-the-art for protein crystallography. To attain even higher count rates, a new concept based on operation in the ionization mode is being explored, in which direct ionization from a neutron conversion is collected with unity gain on one of many pads that form the anode plane. Each pad is implemented with charge sensitive electronics, using purpose-designed application specific integrated circuits. A prototype device with 48 by 48 pads has been successfully developed. Examples of measurements at major neutron user facilities will be presented.   

The wetting behavior of electrolytes at charged carbon electrode materials probed using neutron scattering

Breakthroughs in the performance of energy storage technologies come from efficient combinations of novel electrolytes and electrode materials. Knowledge of the structure of these materials under applied electric fields is necessary to better tailor them to our energy needs. Neutron scattering, as a structural probe to investigate the ordering of electrolytes at an interface, or the effects of confinement on an electrolyte in a nanoporous matrix, is well suited since the electrolytes commonly used contain hydrogen and the host matrix can often contain active sites that are difficult to discern without the use of contrast matching via isotopic substitution. We present small angle neutron scattering results, conducted at the EQ-SANS (ORNL) instrument and at the Low-Q Diffractometer (LANL), from in situ electrochemical measurements of a deuterated ionic liquid, and of aqueous electrolytes, in a mesoporous carbon membrane at different applied potentials over time. Recent neutron reflectometry measurements (LR, SNS) complement the observed behavior from SANS. We observe a higher electrolyte density near the electrode material surface, compared to without an applied potential. Furthermore, this high density region persists long after the applied potential is removed.   

Combined X-Ray and Neutron Powder Diffraction Studies of Nanoscale Ca$_{5-x}$Fe$_{x}$(PO$_{4})_{3}$OH Systems

Multi-substituted hydroxyapatite (HAp) with crystallite size 4-130 nm is the major mineral phase in physiological apatites. Substitutions at all ionic sites affect their physicochemical properties. Fe is one of the minor substitutions at the Ca sites of HAp. It is important because it reduces the solubility of HAp, functioning as a cavities preventive agent, whereas Fe overload leads to a decreased mechanical strength and osteoporosis. Powder x-ray and neutron diffraction methods as well as energy-filtered transmission electron microscopy were used to study the effect of Fe substitution on the crystal structure properties of the Ca$_{(5-x)}$Fe$_{x}$(PO$_{4})_{3}$OH systems. Single phase HAp is identified in systems with x $\le $ 0.1. Hematite is formed for higher x. Simultaneous Rietveld refinement of the x-ray and neutron diffraction patterns reveals an unexpected increase of the a-lattice constant. It is attributed to the increase of the Ca1-O3 and Ca2-O1 interatomic distances indicating a local lattice relaxation. Fe substitutes in both Ca1 and Ca2 sites with a preference to the Ca2 site and an occupancy up to 0.05 for x=0.3. Magnetic measurements reveal a transition from the diamagnetic state of the HAp to the paramagnetic of the Fe-doped systems.   

Profile retrieval using Spin-Echo Resolved Grazing Incidence Scattering combined with dynamical scattering theory

Spin-echo Resolved Grazing Incidence Scattering (SERGIS) is a novel neutron scattering technique that provides lateral and in-depth characterization of density correlations in thin films and at interfaces. The method can be used to study the self-assembly of materials in a periodic array of nano-channels such as a diffraction grating. Since scattering from such periodic structures is dominated by dynamical effects that are not accounted for in approximate scattering theories, we developed a dynamical theory (DT) model, based on a Parratt formalism, and tested it on SERGIS data collected from a set of nanostructured gratings with different profiles in various scattering geometries. The model shows good agreement with all the data sets obtained so far. We found that the SERGIS technique is very sensitive to slight variations in the scattering geometry and the sample profile and the DT calculations accurately reproduce this sensitivity. This is a very promising step in combining a neutron scattering technique with an exact theory to retrieve profile information of periodic samples with unknown structures and to probe the morphology of self-assemblies in periodic nano-confinements.