X-ray Focusing Optics Research Articles

Ｘ線分光の現在 ＩＩ．走査型Ｘ線顕微鏡を用いた蛍光Ｘ線分析

A recent advance in X-ray microscope is reviewed. X-ray focusing optics such as total-reflection mirror and Fresnel zone plate for high energy X-ray region were developed, and a focused beam size of almost 1μm was achieved in an energy range below 100 keV. This paper also introduces some practical examples, obtained by a scanning X-ray microprobe at SPring-8.

Subcellular Speciation Analysis of Trace Element Oxidation States Using Synchrotron Radiation Micro-X-ray Absorption Near-Edge Structure

Identification of chemical species at a subcellular level is a key to understand the mechanisms involved in the biology of chemical elements. When performed with a microbeam, X-ray absorption near-edge structure (micro-XANES) enables the direct speciation analysis of oxidation states in subcellular compartments avoiding cell fractionation and other preparation steps that might modify the chemical species. Here we report the principal characteristics in terms of spatial resolution, detection limit, reproducibility, and repeatability of a micro-XANES experimental setup based on Kirkpatrick-Baez X-ray focusing optics that maintains high flux of incoming radiation (>10(11) photons/s) at micrometric spatial resolution (1.5 x 4.0 microm2). Applications and limitations of this setup are illustrated by examples of iron and arsenic absorption spectra obtained from the cytosol, nucleus, and mitochondrial network of cultured cells. A better repeatability and sensitivity with no oxidation state modification and minimal beam damage is achieved when cells are analyzed in a frozen hydrated state, as compared to freeze-dried cells. This original experimental setup can now be applied for the direct speciation analysis of most trace elements at the subcellular level.

階段状構造を有するＸ線用多層膜レンズの開発

A multilayer (sputtered-sliced) Fresnel zone plate (FZP) is one of promising focusing optics for high-energy X-rays. In order to attain high diffraction efficiency, two types of multilevel-type multilayer FZPs have been fabricated, and these focusing characteristics have been measured at SPring-8. The FZPs composed of concentric multilayers of alternating high-Z(Cu), low-Z(Al), and several types of composite materials layers by Cu and Al. As a result, (1) no significant difference was observed both the measured beam size and the diffraction efficiency of a FZP during 9 months to the FZP with 4-step structure, (2) the diffraction efficiency of the 1st order focus and the focused beam size measured by the knife-edge scanning were more than 50% and 0.8 μm at 41.3 keV, respectively to the FZP with 6-step structure.

Depth-graded multilayers for application in transmission geometry as linear zone plates

Fresnel zone plates for x-ray focusing optics are typically made using lithographic techniques. To achieve optimum efficiency for hard x rays, a depth of several microns is required, which limits the minimum zone width and hence minimum focal spot size achievable using lithography. We are exploring the fabrication of zone plates by an alternative technique that surmounts these limitations: the growth of a multilayer film to be used in transmission (Laue) diffraction geometry, in which the thickness of consecutive layers gradually increases according to the Fresnel zone formula; the film is sectioned after growth to the required depth. For a planar multilayer, this produces a linear zone plate that can focus x rays in one dimension. Here we report the growth and characterization of a depth-graded multilayer suitable for use as a zone plate for hard x-ray focusing. The multilayer has a total of 470 alternating layers of WSi2 and Si with thicknesses increasing monotonically from 15 to 60 nm, for a total thickness of 11.33μm. One of the major challenges is to understand and select the right material system for this kind of thick multilayer. We have found that WSi2∕Si is a promising system. A comparison between WSi2∕Si and W∕Si multilayers is presented.

Comparison of focusing optics for femtosecond X-ray diffraction

We characterize and compare four different types of focusing optics for hard X-rays, suitable for femtosecond X-ray diffraction experiments, using a tabletop femtosecond laser-based plasma source. We demonstrate a 23 µm focus with a toroidally bent Ge single crystal. A maximum flux of 7 × 10 8 photons/(s mm 2 ) is generated in a 32 µm focus using a multi-layer mirror. An elliptical glass capillary yields the highest number of photons per Bragg angle (2 × 10 5 photons/(s mrad)). The largest number of photons (3 × 10 6 photons/s) per second is obtained in the 105 µm focus of a poly-capillary optical lens system. All numbers are given for characteristic Cu Kα photons.

High spatial resolution stress measurements using synchrotron based scanning X-ray microdiffraction with white or monochromatic beam

Scanning X-ray microdiffraction (μSXRD) combines the use of high brilliance synchrotron sources with state-of-the-art achromatic X-ray focusing optics and large area detector technology. Using either white or monochromatic beams, it allows for orientation and strain/stress mapping of polycrystalline thin films with submicron spatial resolution. The present paper will focus on three applications performed at the Advanced Light Source: the study of local plasticity in aluminum thin films, the study of the spontaneous growth of tin whiskers in lead-free solder finish and the measurement of strain field around thin film bucklings.

Characterization of nano and meso scale deformation structures with intense X-ray synchrotron sources

Advanced polychromatic microdiffraction is sensitive to the organization of dislocations and other defects that rotate the lattice planes. Using ultra-brilliant third-generation synchrotron sources and non-dispersive X-ray focusing optics, it is now possible to analyze individual dislocation cells and walls at a submicron scale that cannot be probed by traditional methods. The method is applied to an Ir weld sample to illustrate how microdiffraction can be used to determine the locally active dislocation system.

Nuclear resonant scattering at high pressure and high temperature

We introduce the combination of nuclear resonant inelastic X-ray scattering and synchrotron Mössbauer spectroscopy with the laser-heated diamond anvil cell technique for studying magnetic, elastic, thermodynamic, and vibrational properties of materials under high pressures and high temperatures. An Nd:YLF laser, operating in continuous donut mode (TEM01), has been used to heat samples inside a diamond anvil cell from both sides. Temperatures of the laser-heated sample are measured by means of spectral radiometry and by the detailed balance principle of the energy spectra. The temperature measured by the detailed balance principle is in very good agreement with values determined from the thermal radiation spectra fitted to the Planck radiation function up to 1700 K. Nuclear resonant scattering on 57Fe-containing materials (i.e., Fe, FeO, Fe2O3) has been studied up to 2500 K and 100 GPa. A detailed description of the laser-heating optics, temperature determination, the X-ray monochromatization, and the X-ray focusing optics is given in this article.

The X-Ray Facility of the Physics Department of the Ferrara University

We will report on the equipment and performance of the X-ray facility of the University of Ferrara. Initially developed to test the PDS (Phoswich Detection System) instrument aboard the BeppoSAX satellite and to perform reflectivity measurements of mosaic crystal samples of HOPG (Highly Oriented Pyrolytic Graphite), with time the facility has been improved and its applications extended. Now these applications include test and calibration of hard X-ray (> 10 keV) detectors, reflectivity measurements of hard X-ray mirrors, reflectivity tests of crystals and X-ray transparency measurements. The facility is being further improved in order to determine the optical axis mosaic crystals in Laue configuration within a project devoted to develop a hard X-ray (> 60 keV) focusing optics (Pisa, A. et al.: in press, Feasibility study of a Laue lens for hard X-rays for space astronomy, SPIE Proc., 5536).

High intensity monocapillary X-ray guide tube with 10 micrometer spatial resolution for analytical X-ray microscope

High-intensity monocapillary X-ray guide tube is studied and compared with a commercially available polycapillary tube. The newly designed monocapillary tube is capable of achieving spatial resolution of 10 μm in beam diameter. In comparison with the polycapillary tube, beam diameter of the present monocapillary tube is not enlarged and allows the sample to be measured at a working distance that is 10 times less. Thus, the monocapillary tube is the more versatile X-ray focusing optics as it provides improvements in spatial analysis of samples.

High Resolution Optics & Detector Systems for Hard X-rays

We describe the development of hard X-ray focusing optics telescopes at the National Space Science and Technology Center.

Hard X-ray focusing optics up to 80 keV for the future missions

X-ray telescopes have been providing high sensitivity X-ray observations in numerous missions. For X-ray telescopes in the future, one of the key technologies is to expand the energy band beyond 10 keV. We designed depth-graded multilayer, so-called supermirrors, for a hard X-ray telescope in the energy band up to 40 keV using lightweight thin-foil optics. They were successfully flown in a balloon flight and obtained a hard X-ray image of Cyg X-1 in the 20–40 keV band. Now supermirrors are promising to realize a hard X-ray telescope. We have estimated the performance of a hard X-ray telescope using a platinum–carbon supermirror for future satellite missions, such as NeXT (Japan) and XEUS (Europe). According to calculations, they will have a significant effective area up to 80 keV, and their effective areas will be more than 280 cm 2 even at 60 keV. Limiting sensitivity will be down to 1.7 × 10 −13 erg cm −2 s −1 in the 10–80 keV band at a 100 ks observation. In this paper, we present the results of the balloon experiment with the first supermirror flown and projected effective areas of hard X-ray telescopes and action items for future missions.

Scanning X-ray microdiffraction with submicrometer white beam for strain/stress and orientation mapping in thin films.

Scanning X-ray microdiffraction (microSXRD) combines the use of high-brilliance synchrotron sources with the latest achromatic X-ray focusing optics and fast large-area two-dimensional-detector technology. Using white beams or a combination of white and monochromatic beams, this technique allows for the orientation and strain/stress mapping of polycrystalline thin films with submicrometer spatial resolution. The technique is described in detail as applied to the study of thin aluminium and copper blanket films and lines following electromigration testing and/or thermal cycling experiments. It is shown that there are significant orientation and strain/stress variations between grains and inside individual grains. A polycrystalline film when investigated at the granular (micrometer) level shows a highly mechanically inhomogeneous medium that allows insight into its mesoscopic properties. If the microSXRD data are averaged over a macroscopic range, results show good agreement with direct macroscopic texture and stress measurements.

Protein Crystal Structure Analysis from High-Resolution X-Ray Powder-Diffraction Data

Although high-resolution powder diffraction of proteins is in its infancy, we can easily see future developments of the method that will allow examination of protein structures that exceed 100 kDa. In particular, current data-collection technology scans the powder-diffraction pattern a few points at a time over a very narrow field of view. The use of high-resolution imaging technology and X-ray focusing optics should improve this 1000-fold or more, making it possible to use powder diffraction on a laboratory X-ray source to screen for the formation of protein/drug complexes and to determine their structures.

X-ray optics fabricated by deep reactive ion etching (invited)

When hard x-ray focusing optics require segmented bending, the focal spot can be minimized by matching segment size to the synchrotron source size and focal ratio. At modern sources this implies features etched or cut into silicon on the 100 μm scale. We describe our experience using photolithography and high aspect ratio reactive ion etching (RIE) to produce sagittal focusing crystals. The work was carried out at the Cornell Nanofabrication Facility. RIE has been of great utility for the manufacture of microelectromechanical systems (MEMS) which contain features typically a few microns in size. We have learned that because of the very large dielectric constant of silicon, a number of important considerations must go into a successful design when features are scaled up for x-ray optics applications. Nevertheless, we have designed, built and tested x-ray optical devices produced using MEMS techniques, and in fact they are in regular use at CHESS. We describe our results from the point of view of mechanical robustness and focus quality, and offer general guidelines for future designers.

X-ray Microdiffraction Images of Antiferromagnetic Domain Evolution in Chromium

Magnetic x-ray diffraction combined with x-ray focusing optics was used to image individual antiferromagnetic spin density wave domains in a chromium single crystal at the micron scale. The cross section for nonresonant magnetic x-ray scattering depends on the antiferromagnetic modulation vector and spin polarization direction and allows these quantities to be extracted independently. The technique was used to show that the broadening of the nominally first-order "spin-flip" transition at 123 kelvin, at which the spins rotate by 90 degrees C, originates at the walls between domains with orthogonal modulation vectors. During cooling, the transition begins at these walls and progresses inward. The modulation vector domains are themselves unchanged.

The fractal properties of a geometric model of the high-resolution X-ray diffractor

Perfect and mosaic crystals are conventionally used in X-ray monochromators operating in the energy range from several hundred to tens of thousands of electronvolts. The focusing X-ray optics for nonparallel beams employs either cylindrical bent crystals (the methods of Johann [1], Johansson [2], and Cauchois [3]) or crystals with spherical or toroidal [4] bending of the crystallographic planes. Special variants of high-resolution stepped-crystal diffractors [5–8] were developed to study the possibility of high-precision focusing of a monochromatic X-ray radiation. The fractal properties of a geometric model of such a high-resolution steppedcrystal diffractor are considered.

Sagittal X-ray beam deviation at asymmetric inclined diffractors

A new approach to focusing X-ray optics based on asymmetric inclined (or rotated inclined) diffraction has been experimentally studied. Using a linear longitudinal W-groove cut into the surface of an asymmetric silicon (111) diffractor perpendicularly to the line of intersection of its surface and crystallographic (111) planes, the out-of-diffraction-plane (or sagittal) deviation of the X-ray diffracted beam has been measured for three angles of asymmetry and constant angle of inclination on BM5 at the ESRF for a wavelength of 0.1 nm. It has been demonstrated that in the grazing-emergence case the sagittal deviation increases with increasing asymmetry angle. A discrepancy with the theoretical value for the largest asymmetry angle and inhomogeneities in the contrast of the diffraction spot have been discussed.

High-efficiency tunable X-ray focusing optics using mirrors and laterally-graded multilayers

A high-efficiency X-ray microfocusing device covering a 7–30 keV energy range has been developed and tested at the ESRF BM5 beamline. It is composed of a mirror mounted on a 2-moments flexural hinge based bender and coated with 2 laterally-graded multilayers and a single-layer of iridium. With a demagnification factor of 128, focal spot sizes down to 1 μm were obtained using an on-line shaping procedure having a sub-μrad precision.

The X-ray response of CdZnTe detectors to be used as future spectroscopic detectors for X-ray astronomy

The next generation of X-ray astrophysics missions may well extend the energy range beyond the current limit of about 10 keV studied by the existing X-ray Astrophysics space missions such as ASCA or future missions such as AXAF and XMM to be launched in the next few years. To address with a high degree of sensitivity the astrophysical problems associated with X-ray emission in the X-ray band from 0.2 to 100 keV a significant extension of the capabilities of focusing X-ray optics and imaging broad band hard X-ray detectors will be required. Future missions such as INTEGRAL, BASIS and EXIST will make use of CdZnTe or CdTe detectors for imaging spectroscopy down to about 5 keV with a spectral resolution between 3% and 7% at 100 keV. This is about a factor of 10 away from what is theoretically possible and mainly caused by the poor crystal quality. In this paper experimental results on the study of the X-ray response of CdZnTe detectors are presented. The detector response to photons with energies between 1 and 5 keV has been investigated using synchrotron radiation and a preliminary model to describe the detector response developed. The limitations on the energy resolution, due to incomplete charge collection and spatial non-uniformities, are presented based on the detailed mapping of the energy response of a detector exposed to highly monochromatised synchrotron radiation. At higher energies results have been obtained using a 241Am radioactive source and an electron cyclotron resonance source so as to establish the detector performance and overall response to medium- and higher-energy X-ray photons up to 60 keV. Based on these results the performance of the detectors are compared with Si(Li) and HPGe solid-state detectors.