An in-vacuum x-ray diffraction microscope for use in the 0.7-2.9 keV range

A dedicated in-vacuum coherent x-ray diffraction microscope was installed at the 2-ID-B beamline of the Advanced Photon Source for use with 0.7-2.9 keV x-rays. The instrument can accommodate three common implementations of diffractive imaging; plane wave illumination; defocused-probe (Fresnel diffractive imaging) and scanning (ptychography) using either a pinhole, focused or defocused probe. The microscope design includes active feedback to limit motion of the optics with respect to the sample. Upper bounds on the relative optics-to-sample displacement have been measured to be 5.8 nm(v) and 4.4 nm(h) rms/h using capacitance micrometry and 27 nm/h using x-ray point projection imaging. The stability of the measurement platform and in-vacuum operation allows for long exposure times, high signal-to-noise and large dynamic range two-dimensional intensity measurements to be acquired. Finally, we illustrate the microscope's stability with a recent experimental result.     

Soft X-ray coherent scattering: instrument and methods at ESRF ID08

An experimental setup has been developed to perform soft x-ray coherent scattering at beamline ID08 of the European Synchrotron Radiation Facility. An intense coherent beam was obtained by filtering the primary beam with the monochromator and a circular pinhole. A pinhole holder with motorized translations was installed inside the UHV chamber of the diffractometer. The scattered intensity was recorded in reflection geometry with a back-illuminated charge coupled device camera. As a demonstration we report experimental results of resonant magnetic scattering using coherent beam. The degree of coherence is evaluated, and it is shown that, while the vertical coherence is much higher than the horizontal one at the source, the situation is reversed at the diffractometer. The intensity of the coherent beam is also discussed.     

Plasma ion source for in situ ion bombardment in a soft x-ray magnetic scattering diffractometer

A new plasma ion source for in situ keV He ion bombardment of solid state samples or thin films was designed and built for ion fluences between 1 × 10(12) and 1 × 10(17) ions/cm(2). The system was designed to be mounted to different diffraction chambers for soft x-ray resonant magnetic scattering. Without breaking the vacuum due to He-ion bombardment, structural and magnetic modifications of the samples can be studied in situ and element specifically.     

Absolute x-ray energy calibration over a wide energy range using a diffraction-based iterative method

In this paper, we report a method of precise and fast absolute x-ray energy calibration over a wide energy range using an iterative x-ray diffraction based method. Although accurate x-ray energy calibration is indispensable for x-ray energy-sensitive scattering and diffraction experiments, there is still a lack of effective methods to precisely calibrate energy over a wide range, especially when normal transmission monitoring is not an option and complicated micro-focusing optics are fixed in place. It is found that by using an iterative algorithm the x-ray energy is only tied to the relative offset of sample-to-detector distance, which can be readily varied with high precision of the order of 10(-5) -10(-6) spatial resolution using gauge blocks. Even starting with arbitrary initial values of 0.1 A?, 0.3 A?, and 0.4 A?, the iteration process converges to a value within 3.5 eV for 31.122 keV x-rays after three iterations. Different common diffraction standards CeO(2), Au, and Si show an energy deviation of 14 eV. As an application, the proposed method has been applied to determine the energy-sensitive first sharp diffraction peak of network forming GeO(2) glass at high pressure, exhibiting a distinct behavior in the pressure range of 2-4 GPa. Another application presented is pair distribution function measurement using calibrated high-energy x-rays at 82.273 keV. Unlike the traditional x-ray absorption-based calibration method, the proposed approach does not rely on any edges of specific elements, and is applicable to the hard x-ray region where no appropriate absorption edge is available.     

National Ignition Facility neutron time-of-flight measurements (invited)

The first 3 of 18 neutron time-of-flight (nTOF) channels have been installed at the National Ignition Facility (NIF). The role of these detectors includes yield, temperature, and bang time measurements. This article focuses on nTOF data analysis and quality of results obtained for the first set of experiments to use all 192 NIF beams. Targets produced up to 2×10(10) 2.45 MeV neutrons for initial testing of the nTOF detectors. Differences in neutron scattering at the OMEGA laser facility where the detectors were calibrated and at NIF result in different response functions at the two facilities. Monte Carlo modeling shows this difference. The nTOF performance on these early experiments indicates that the nTOF system with its full complement of detectors should perform well in future measurements of yield, temperature, and bang time.     

A multi-crystal wavelength dispersive x-ray spectrometer

A multi-crystal wavelength dispersive hard x-ray spectrometer with high-energy resolution and large solid angle collection is described. The instrument is specifically designed for time-resolved applications of x-ray emission spectroscopy (XES) and x-ray Raman scattering (XRS) at X-ray Free Electron Lasers (XFEL) and synchrotron radiation facilities. It also simplifies resonant inelastic x-ray scattering (RIXS) studies of the whole 2d RIXS plane. The spectrometer is based on the Von Hamos geometry. This dispersive setup enables an XES or XRS spectrum to be measured in a single-shot mode, overcoming the scanning needs of the Rowland circle spectrometers. In conjunction with the XFEL temporal profile and high-flux, it is a powerful tool for studying the dynamics of time-dependent systems. Photo-induced processes and fast catalytic reaction kinetics, ranging from femtoseconds to milliseconds, will be resolvable in a wide array of systems circumventing radiation damage.     

Adaption of a diamond anvil cell to an automatic four-circle diffractometer for x-ray diffraction

A diamond anvil high-pressure device for x-ray diffraction on single crystals under hydrostatic pressures up to about 100 kilobars has been adapted to the automatic four-circle x-ray diffractometer Philips PW 1100. The mechanical adaption, the centering procedure, and quick pressure calibration on the diffractometer are described. Hints to improve the peak-to-background ratio of the intensity measurements are given.     

X射线多重衍射效应

本文介绍了X射线多重衍射效应的起因,多重衍射图谱的指标化,给出了用普通X射线粉末衍射仪观测多重衍射效应的方法,并简要说明了多重衍射效应的应用。     

Design and performance of a versatile curved-crystal spectrometer for high-resolution spectroscopy in the tender x-ray range

A complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry has been constructed for a 2-6 keV energy range with sub natural line-width energy resolution. The spectrometer is designed to measure x-ray emission induced by photon and charged particle impact on solid and gaseous targets. It works with a relatively large x-ray source placed inside the Rowland circle and employs position sensitive detection of diffracted x-rays. Its compact modular design enables fast and easy installation at a synchrotron or particle accelerator beamline. The paper presents main characteristics of the spectrometer and illustrates its capabilities by showing few selected experimental examples.     

不同本底真空度对SiC/Mg极紫外多层膜性能的影响

摘要：为研究SiC/Mg极紫外多层膜光学性能随制作时不同本底真空度的变化,利用直流磁控溅射方法在不同本底真空条件下制备了峰值反射波长在30.4nm的SiC/Mg周期膜。X射线掠入射反射测试结果表明不同本底真空度条件下制备的SiC/Mg周期多层膜膜层质量有明显差异。用同步辐射测试了SiC/Mg多层膜在工作波长处的反射率,本底真空度为6.0E-5 Pa时的SiC/Mg周期膜反射率为43%,而本底真空度在5.0E-4 Pa时的SiC/Mg多层膜反射率仅为30%。同步辐射反射曲线拟合结果表明：反射率随着本底真空度降低的原因是由于多层膜Mg膜层中Mg的氧化物含量增多造成的。     

A novel approach for x-ray scattering experiments in magnetic fields utilizing trapped flux in type-II superconductors

We introduce a novel approach to x-ray scattering studies in applied magnetic fields by exploiting vortices in superconductors. This method is based on trapping magnetic flux in a small disk-shaped superconductor (known as a trapped field magnet, TFM) with a single-crystal sample mounted on or at close proximity to its surface. This opens an unrestricted optical access to the sample and allows magnetic fields to be applied precisely along the x-ray momentum transfer, facilitating polarization-sensitive experiments that have been impractical or impossible to perform to date. The TFMs used in our study remain stable and provide practically uniform magnetic fields for days, which are sufficient for comprehensive x-ray diffraction experiments, specifically x-ray resonance exchange scattering (XRES) to study field-induced phenomena at a modern synchrotron source. The TFM instrument has been used in a "proof-of-principle" XRES study of a meta-magnetic phase in a rare-earth compound, TbNi(2)Ge(2), in order to demonstrate its potential.     

Characterization of one-dimensional position sensitive detectors with improved efficiency and position resolution for neutron spectrometers

Development and characterization of one-dimentional (1D) position sensitive detectors (PSDs) with improved efficiency and position resolution for neutron scattering applications are reported. The PSDs are characterized for energy resolution, count rate capability, sensitivity, efficiency, position resolution, and uniformity of response over the sensitive length. The studies are carried out to verify the dependence of position resolution on detector geometry, electronic noise, and stopping power of the fill gas. One of the PSDs is mounted on the small angle neutron scattering spectrometer and spectra from CTAB micelle sample are recorded using 5.4 A neutrons. A gain of factors 1.1 and 1.2 is obtained compared to earlier in house made 1D PSD and LND-made 1D PSD, respectively. The diffraction patterns from standard vanadium, nickel, and silicon samples are recorded on a powder diffractometer using newly designed PSDs. Gain in efficiency obtained at shorter wavelength of 0.783 A is by a factor of 1.6. All high pressure PSDs show improvement in the position resolution by 2-3 mm. It is observed that 1D PSD filled with isobutane as stopping gas improves the gamma tolerance and position resolution at lower partial pressures as compared to Kr. It is advantageous to use two or more 36C-type PSDs stacked together. It is economic and gives better efficiency due to scanning more beam height.     

High-pressure-low-temperature x-ray power diffractometer

A high-pressure technique for x-ray diffraction studies at low temperatures is described. The system consists of a Bridgman anvil type high-pressure device with either tungsten carbide or boron carbide anvils, a liquid He cryostat, and x-ray diffractometer operating in Debye-Scherrer geometry. The newly developed boron carbide anvil cell is capable of containing a liquid pressure transmitting medium. The precision of the lattice parameter determination is discussed and the effect of nonisostatic stress components on the diffraction pattern is examined.     

A new large radius imaging plate camera for high-resolution and high-throughput synchrotron x-ray powder diffraction by multiexposure method

A new large radius imaging plate diffraction camera for high-resolution and high-throughput synchrotron x-ray powder diffraction by means of multiple exposures has been developed for an insertion device beamline of SPring-8, Japan. The new imaging plate camera consists of a large radius cylindrical shape imaging plate cassette that is 400 mm in length and 954.9 mm in cylinder radius. The cassette is designed to be mounted on the 2 theta arm of the diffractometer of BL15XU in SPring-8. One imaging plate covers 24 degrees and several times of exposure changing the 2 theta-setting angle is necessary to obtain whole powder diffraction data up to a high angle region. One pixel of the imaging plate corresponds to 0.003 degrees in 2 theta when the readout pixel size is 50 microm squares. Separately collected data are translated to 2 theta-intensity format and are connected by comparing the peak and background intensity included in the overlapped area. The exposure time is less than 120 s for most samples and the readout time is about 3 min; thus, the total measurement time for one powder diffraction pattern is less than 20 min. The measurement time is the same order as the continuous 2 theta-scanning method of the third generation synchrotron powder diffractometer. The angular resolution of the new imaging plate camera was evaluated by comparing the full width at half maximum of the 111 reflection of NBS-Si. The observed angular resolution is not so high as a powder diffractometer with a Si or a Ge analyzer monochromator in the third generation synchrotron facility but higher than a powder diffractometer with a Ge analyzer monochromator at a bending magnet beamline of the second generation synchrotron. The Rietveld analysis of NBS-CeO2 was successfully carried out with the data taken by the new imaging plate camera.     

Simultaneous structure and elastic wave velocity measurement of SiO2 glass at high pressures and high temperatures in a Paris-Edinburgh cell

An integration of multi-angle energy-dispersive x-ray diffraction and ultrasonic elastic wave velocity measurements in a Paris-Edinburgh cell enabled us to simultaneously investigate the structures and elastic wave velocities of amorphous materials at high pressure and high temperature conditions. We report the first simultaneous structure and elastic wave velocity measurement for SiO(2) glass at pressures up to 6.8 GPa at around 500°C. The first sharp diffraction peak (FSDP) in the structure factor S(Q) evidently shifted to higher Q with increasing pressure, reflecting the shrinking of intermediate-range order, while the Si-O bond distance was almost unchanged up to 6.8 GPa. In correlation with the shift of FSDP position, compressional wave velocity (Vp) and Poisson's ratio increased markedly with increasing pressure. In contrast, shear wave velocity (Vs) changed only at pressures below 4 GPa, and then remained unchanged at ~4.0-6.8 GPa. These observations indicate a strong correlation between the intermediate range order variations and Vp or Poisson's ratio, but a complicated behavior for Vs. The result demonstrates a new capability of simultaneous measurement of structures and elastic wave velocities at high pressure and high temperature conditions to provide direct link between microscopic structure and macroscopic elastic properties of amorphous materials.     

Charge-injection-device performance in the high-energy-neutron environment of laser-fusion experiments

Charge-injection devices (CIDs) are being used to image x rays in laser-fusion experiments on the University of Rochester's OMEGA Laser System. The CID cameras are routinely used up to the maximum neutron yields generated (～10(14)?DT). The detectors are deployed in x-ray pinhole cameras and Kirkpatrick-Baez microscopes. The neutron fluences ranged from ～10(7) to ～10(9)?neutrons/cm(2) and useful x-ray images were obtained even at the highest fluences. It is intended to use CID cameras at the National Ignition Facility (NIF) as a supporting means of recording x-ray images. The results of this work predict that x-ray images should be obtainable on the NIF at yields up to ～10(15), depending on distance and shielding.     

Optical detection methods for mass spectrometry of macroions

Detection of macroions has been a challenge in the field of mass spectrometry. Conventional ionization-based detectors, relying on production and multiplication of secondary electrons, are restricted to detection for charged particles of m/z < 1 x 10(6). While both energy-sensitive and charge-sensitive detectors have been developed recently to overcome the limitation, they are not yet in common use. Photon-sensitive detectors are suggested to be an alternative, with which detection of macroions (or charged particles) by either elastic light scattering (ELS) or laser-induced fluorescence (LIF) has been possible. In this article, we provide a critical review on the developments of novel optical detection methods for mass spectrometry of macroions, including both micron-sized and nano-sized synthetic polymers as well as high-mass biomolecules. Design and development of new spectrometers making possible observations of the mass spectra of macroions with sizes in the range of 10-10(3) nm or masses in the range of 1-10(6) MDa are illustrated. The potential and promise of this optical approach toward macroion detection with high efficiency are discussed in practical aspects.     

A new x-ray interface and surface scattering environmental cell design for in situ studies of radioactive and atmosphere-sensitive samples

We present a novel design of a purpose-built, portable sample cell for in situ x-ray scattering experiments of radioactive or atmosphere sensitive samples. The cell has a modular design that includes two independent layers of containment that are used simultaneously to isolate the sensitive samples. Both layers of containment can be flushed with an inert gas, thus serving a double purpose as containment of radiological material (either as a solid sample or as a liquid phase) and in separating reactive samples from the ambient atmosphere. A remote controlled solution flow system is integrated into the containment system that allows sorption experiments to be performed on the diffractometer. The cell's design is discussed in detail and we demonstrate the cell's performance by presenting first results of crystal truncation rod measurements. The results were obtained from muscovite mica single crystals reacted with 1 mM solutions of Th(IV) with 0.1 M NaCl background electrolyte. Data were obtained in specular as well as off-specular geometry.     

Monte Carlo simulations of microchannel plate detectors. I. Steady-state voltage bias results

X-ray detectors based on straight-channel microchannel plates (MCPs) are a powerful diagnostic tool for two-dimensional, time-resolved imaging and time-resolved x-ray spectroscopy in the fields of laser-driven inertial confinement fusion and fast Z-pinch experiments. Understanding the behavior of microchannel plates as used in such detectors is critical to understanding the data obtained. The subject of this paper is a Monte Carlo computer code we have developed to simulate the electron cascade in a MCP under a static applied voltage. Also included in the simulation is elastic reflection of low-energy electrons from the channel wall, which is important at lower voltages. When model results were compared to measured MCP sensitivities, good agreement was found. Spatial resolution simulations of MCP-based detectors were also presented and found to agree with experimental measurements.