Proceedings Volume 2516

X-Ray Microbeam Technology and Applications

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Proceedings Volume 2516

X-Ray Microbeam Technology and Applications

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Volume Details

Date Published: 25 September 1995
Contents: 4 Sessions, 24 Papers, 0 Presentations
Conference: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation 1995
Volume Number: 2516

Table of Contents

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Table of Contents

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  • X-Ray Microbeam Focusing Optics
  • Techniques and Imaging Systems
  • Applications
  • Poster Session
  • Applications
X-Ray Microbeam Focusing Optics
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Fabrication of high-resolution x-ray diffractive optics at King's College London
Pambos S. Charalambous, Peter A. F. Anastasi, Ronald E. Burge, et al.
The fabrication of high resolution x-ray diffractive optics, and Fresnel zone plates (ZPs) in particular, is a very demanding multifaceted technological task. The commissioning of more (and brighter) synchrotron radiation sources, has increased the number of x-ray imaging beam lines world wide. The availability of cheaper and more effective laboratory x-ray sources, has further increased the number of laboratories involved in x-ray imaging. The result is an ever increasing demand for x-ray optics with a very wide range of specifications, reflecting the particular type of x-ray imaging performed at different laboratories. We have been involved in all aspects of high resolution nanofabrication for a number of years, and we have explored many different methods of lithography, which, although unorthodox, open up possibilities, and increase our flexibility for the fabrication of different diffractive optical elements, as well as other types of nanostructures. The availability of brighter x-ray sources, means that the diffraction efficiency of the ZPs is becoming of secondary importance, a trend which will continue in the future. Resolution, however, is important and will always remain so. Resolution is directly related to the accuracy af pattern generation, as well as the ability to draw fine lines. This is the area towards which we have directed most of our efforts so far.
Microfocusing optics for hard xrays fabricated by x-ray lithography
Azalia A. Krasnoperova, Zheng Chen, Franco Cerrina, et al.
Lithographic techniques for fabrication of hard x-ray Fresnel zone plates are discussed. Practical results achieved at the Center for X-ray Lithography of the University of Wisconsin- Madison are presented. Fabrication technology includes replication of an e-beam written master mask into a thick photoresist by synchrotron radiation x-ray lithography, and subsequent electroplating of a metal zone plate structure using photoresist pattern as a mold.
Bragg-Fresnel optics at the ESRF: microdiffraction and microimaging applications
Bragg-Fresnel optics shows excellent compatibility with ESRF sources and are capable of obtaining monochromatic submicron focal spots with 108 - 109 photons/sec in an energy bandwidth of 10-4 - 10-6 and in a photon energy range between 2 - 100 keV. Microprobe and microimaging techniques based on Bragg-Fresnel optics were realized at the ESRF beamlines.
New generation of multilayer Bragg-Fresnel lenses
Alexei I. Erko, Alexander A. Firsov, Andrey E. Yakshin, et al.
A new type of Bragg-Fresnel multilayer lens (BFML) has been fabricated at IMT RAS and tested at LURE. The idea to combine different diffraction orders of a zone plate in one focal spot introduced by Simpson and Michette has been realized in a BFML with extended aperture. Matching of the two diffraction orders, the first and third, into one focal plane increases the output flux by a factor of two and the spatial resolution in the same order of magnitude.
Microfocusing 4-keV to 65-keV xrays with bent Kirkpatrick-Baez mirrors
Peter J. Eng, Mark L. Rivers, Bingxin X. Yang, et al.
We present the test results of micro-focusing a continuous spectrum (4 KeV - 65 keV) of x rays using two, 100 mm long, actively bent mirrors in a Kirkpatrick-Baez geometry. The mirrors are figured by applying in situ two different moments on the ends resulting in a surface figure that approximates an ellipse. We have demonstrated the ability to doubly focus NSLS bending magnet x rays from 4 KeV to 13 KeV to a spot size less than 4 microns in diameter with a net gain of 2000 over a similar size beam produced with slits. In the bending magnet test the beam was focused in the vertical direction with a high quality rhodium coated Si mirror with a rms surface roughness and slope error less than 2 angstrom and 2 (mu) rad, respectively. The horizontal mirror consisted of uncoated float glass with significantly greater roughness and slope error. This combination of mirrors worked extremely well, pointing the direction for inexpensive micro-focusing optics. Vertical focusing tests were also performed using only the high quality Si mirror. On the bending magnet, x rays were focused to 30 KeV using an incidence angle of 2 mrad achieving a best focus of 2.5 microns FWHM, resulting in a net gain of 91. Additional high energy focusing tests were carried out at the NSLS superconducting wiggler beamline X17. In this case a continuous x-ray spectrum was vertically focused using the Si mirror with an energy cutoff of 65 KeV (at an incident angle of 1 mrad) achieving a focal spot size of 3.3 microns FWHM and a net gain of 20.
Parameter optimization for producing an elliptical surface from a spherical surface by differential deposition
Zhonghou Cai, Wenbing Yun, P. Plag
At present, manufacturing an elliptical surface is much more difficult than producing a spherical surface. Differential deposition seems to be a promising technique for producing elliptical focusing mirrors for synchrotron x-ray beams. Here we describe a way to generate deposition profiles that turn spherical surfaces into elliptical surfaces. All parameters of the elliptical surface, the spherical surface, and thus, the deposition profile are optimized with the parameters of the optical system, i.e., the source-image distance, the magnification factor, the critical angle for x-ray total reflection, and the acceptance angle of the mirror. It was found that most deposition profiles generated for synchrotron radiation can be implemented with currently existing deposition techniques.
Development of a novel x-ray focusing technique using crystals with a two-dimensionally modulated surfaces
William Z. Chang, Ernst-Bernhard Kley, Hans-Joerg Fuchs, et al.
Theoretical investigations for obtaining x-ray point focusing by using crystals with two- dimensionally modulated surfaces are carried out. Based on the Bragg and Fresnel diffraction principles, formulae of modulated surfaces (structures) are derived for both flat and bent crystals for focusing x rays to micron or submicron size. It is found that elliptically shaped and linearly modulated structures are suitable for flat and cylindrically bent crystals, respectively. For the given Ti K(alpha) radiation and geometric parameters, Si (111) and InSb (111) reflections are used for the calculations of flat and bent crystals in terms of their focus characteristics, namely the focusing efficiency and the focus width. The influence of the distribution of the Bragg amplitude on flat and bent crystals is also discussed.
Techniques and Imaging Systems
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Scanning transmission x-ray microscope at the NSLS: from XANES to cryo
The Stony Brook scanning transmission x-ray microscope (STXM) has been operating at the X1A beamline at the NSLS since 1989. A large number of users have used it to study biological and material science samples. We report on changes that have been performed in the past year, and present recent results. To stabilize the position of the micro probe when doing spectral scans at high spatial resolution, we have constructed a piezo-driven flexure stage which carries out the focusing motion of the zone plate needed when changing the wavelength. To overcome our detector limitation set by saturation of our gas-flow counter at count rates around 1 MHz, we are installing an avalanche photo diode with an active quenching circuit which we expect to respond linearly to count rates in excess of 10 MHz. We have improved the enclosure for STXM to improve the stability of the Helium atmosphere while taking data. This reduces fluctuations of beam absorption and, therefore, noise in the image. A fast shutter has been installed in the beam line. We are also developing a cryo- STXM which is designed for imaging frozen hydrated samples at temperatures below 120 K. At low temperatures, radiation sensitive samples can tolerate a considerably higher radiation dose than at room temperature. This should improve the resolution obtainable from biological samples and should make recording of multiple images of the same sample area possible while minimizing the effects of radiation damage. This should enable us to perform elemental and chemical mapping at high resolution, and to record the large number of views needed for 3D reconstruction of the object.
X-ray microscopy with high-resolution zone plates: recent developments
Gerd Schneider, Thomas Wilhein, Bastian Niemann, et al.
In order to expand the applications of x-ray microscopy, developments in the fields of zone plate technology, specimen preparation and imaging techniques have been made. A new cross- linked polymer chain electron beam resist allows us to record zone plate pattern down to 19 nm outermost zone width. High resolution zone plates in germanium with outermost zone widths down to 19 nm have been developed. In addition, phase zone plates in nickel down to 30 nm zone width have been made by electroplating. In order to enhance the image contrast for weak absorbing objects, the phase contrast method for x-ray microscopy was developed and implemented on the Gottingen x-ray microscope at BESSY. The effects of x ray absorption on the structure of biological specimen limits the maximum applicable radiation dose and therefore the achievable signal to noise ratio for an artifact-free x-ray image. To improve the stability especially of biological specimen, a cryogenic object chamber has been developed and tested. It turns out that at the operating temperature T less than or equal to 130 K unfixed biological specimen can be exposed to a radiation dose of 109 - 1010 Gy without any observable structural changes. A multiple-angle viewing stage allows us to take stereoscopic images with the x-ray microscope, giving a 3D-impression of the object. As an example for the applications of x-ray microscopy in biology, erythrocytes infected by malaria parasite have been examined. Studies of the aggregation of hematite by sodium sulfate gives an example for the application of x-ray microscopy in the field of colloid research.
Ultrahigh-resolution soft x-ray tomography
Waleed S. Haddad, James E. Trebes, Dennis M. Goodman, et al.
Ultra high resolution three-dimensional images of a microscopic test object were made with soft x rays using a scanning transmission x-ray microscope. The test object consisted of two different patterns of gold bars on silicon nitride windows that were separated by approximately 5 micrometer. A series of nine 2-D images of the object were recorded at angles between -5 to +55 degrees with respect to the beam axis. The projections were then combined tomographically to form a 3-D image by means of an algebraic reconstruction technique (ART) algorithm. A transverse resolution of approximately 1000 angstrom was observed. Artifacts in the reconstruction limited the overall depth resolution to approximately 6000 angstrom, however some features were clearly reconstructed with a depth resolution of approximately 1000 angstrom. A specially modified ART algorithm and a constrained conjugate gradient (CCG) code were also developed as improvements over the standard ART algorithm. Both of these methods made significant improvements in the overall depth resolution, bringing it down to approximately 1200 angstrom overall. Preliminary projection data sets were also recorded with both dry and re-hydrated human sperm cells over a similar angular range.
Soft x-ray imaging and vector diffraction theory
Ronald E. Burge, XiaoCong Yuan
A comprehensive computational analysis of soft x-ray imaging has been undertaken for both thin transmitting objects and lossy dielectric, potentially binary, objects and some representative results are given here. Both near-field and far-field computations are considered. The theoretical treatment derives from Maxwell's vector electromagnetic equations rather than scalar diffraction theory. A range of computational approaches is used in the computations ranging from the integral method, to the coupled wave method, and the finite element methods. The relationships between these methods are considered. The results bear upon a range of imaging protocols from contact x-ray images and images taken with high resolution zone plate optics with feature dimensions of a few wavelengths to x-ray masks with sub-micron feature sizes interpreted as lossy waveguides several hundreds of x-ray wavelengths thick. Consideration is also given to the use of vector theory in the investigation of the focal plan intensity profile of a circular Fresnel zone plate when the widths of the outermost zones approach wavelength dimensions.
Simulations and experiments on capillary optics for x-ray microbeams
G. Slade Cargill III, K. Hwang, J. W. Lam, et al.
We describe simulations and experiments with straight and tapered glass capillaries for 5 keV - 25 keV x rays. Effects of tilting capillaries on the exiting pattern of x rays have been investigated in experiments and simulations. The simulations have employed two dimensional ray tracing. We have also used simulations to investigate effects of source-to-capillary distance and of source size on transmitted x ray flux for straight and tapered capillaries. A system using x-ray microbeams for spatially resolved mapping of microstructure, strain, and composition is also briefly described.
Toward a micrometer resolution x-ray tomographic microscope
Near-micrometer resolution, three-dimensional computed tomographic images were made of a test object using the hard x-ray microscope developed by the National Institute of Standards and Technology (NIST). The microscope uses a cooled CCD camera with direct conversion of the incident x rays by a 512 multiplied by 512 chip with 19 micrometer by 19 micrometer cells. Magnification by a factor of 20 is achieved using asymmetric Bragg diffraction from a pair of silicon crystals. The imaging system is designed for samples of the order of 0.50 mm diameter by 0.50 mm height. From beamline X23A3 at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL) 8.17 keV x rays were used. Two hundred, 512 multiplied by 512 two-dimensional projections were collected every 0.9 degrees about the test object using the NIST microscope. The projections were digitized and sent to a computer for volume tomographic reconstruction by a parallel-beam, convolution-backprojection algorithm into a 5123 image with (1 micrometer)3 voxels. The test object consisted of glass and nickel microspheres with distributions from about 4 t 40 micrometer (glass) or to 24 micrometer (nickel) diameters suspended in epoxy in order to demonstrate near one micrometer resolution in all three dimensions and probe contrast sensitivity. The effect and interplay of photon statistics and energy, and sample composition, density and size on tomographic performance are discussed as are resolution limitations and image artifacts from Fresnel diffraction.
Applications
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Chemical state mapping on material surfaces with the X1A second-generation scanning photoemission microscope (X1A SPEM-II)
Cheng-Hao Ko, Janos Kirz, Klaus Maier, et al.
The second generation scanning photoelectron microscope at beamline X1A of the National Synchrotron Light Source (X1A SPEM-II) is designed for spatially resolved elemental and chemical analysis by x ray photoelectron spectroscopy (XPS) on material surfaces. This microscope can focus photon energies between 300 to 800 eV with submicron spatial resolution. Multiple photoelectron images can be acquired simultaneously with the use of a hemispherical sector analyzer (HSA) with multi-channel detection (MCD), which enables a technique called 'parallel imaging for chemical state mapping' (PICSM). The PICSM technique was demonstrated using a Si/SiO2 pattern.
Direct observation of microscopic inhomogeneities in high-Tc superconductors using energy-dispersive diffraction of synchrotron-produced xrays
Earl F. Skelton, Syen B. Qadri, Michael S. Osofsky, et al.
Evidence of micron-sized structural inhomogeneities in several high transition temperature (Tc) superconductors is presented. By illuminating samples with high energy, highly collimated x rays produced on a synchrotron wiggler, small changes in the lattice were detected over a spatial scale as small as 10 micrometer. In the YBa2Cu3O7-(delta ) crystals, these changes are interpreted as evidence of variations in the oxygen content and in the Nd2-xCexCuO4-y crystal, as a variation in the cerium content. Each type of inhomogeneity can affect the superconducting properties.
Microdiffraction measurements of the effects of grain alignment on critical current in high-temperature superconductors
Eliot D. Specht, A. Goyal
While single crystals and epitaxial thin films of high temperature superconductors can carry large current densities, devices useful for applications such as power transmission and magnets cannot be produced because polycrystalline material cannot carry sufficient current densities. Efforts are underway to produce polycrystalline material in which grains are aligned to carry high current densities. We report x-ray and electron microdiffraction measurements of local grain alignment and models of how this grain alignment affects the critical current densities. TlCa2Sr2Cu3Ox samples can be grown on polycrystalline substrates with good c axis alignment but no overall a axis alignment. In TlCa2Sr2Cu3Ox, high critical current occurs in regions in which there is local a axis alignment. X-ray microdiffraction measurements of grain orientation were made with a monochromatic, 100 micrometer diameter beam produced by inserting a pinhole at the focus of an NSLS bending magnet beamline. Local grain orientation was measured by observing Bragg reflection as the sample was rotated. While x-ray data was taken at this low resolution over large areas, the orientation of individual grains was measured over small regions by measuring the Kikuchi pattern produced by inelastic scattering from a 100 nm electron beam. In both cases, the sample position was scanned to map grain orientation. With advanced x-ray optics currently under development, high-resolution maps of grain orientation will be available without the elaborate surface preparation required for electron diffraction. This will facilitate study of samples prepared in a wider variety of forms.
Hard x-ray microanalytical beam line at the CAMD synchrotron
Mark C. Petri, Leonard Leibowitz, Paul Schilling
Argonne National Laboratory (ANL) is collaborating with Louisiana State University (LSU) in constructing a synchrotron x-ray micro-analytical beamline at the Center for Advanced Microstructures and Devices (CAMD) in Baton Rouge, Louisiana. This project grew from earlier work at the National Synchrotron Light Source (NSLS), where a team of ANL researchers developed techniques to examine small-scale structures in diffusion zones of a variety of materials. The ANL/CAMD beamline will use x-ray fluorescence, diffraction, and absorption spectroscopy techniques to reveal both compositional and structural information on a microscopic scale.
Soft x-ray microscopy and microanalysis: applications in organic geochemistry
George D. Cody, Robert E. Botto, Harald Ade, et al.
Soft x-ray imaging and C-NEXAFS microanalysis have been used to analyze the organic geochemistry of bio/geo-macromolecules (sporopollenin) in-situ and in a rank variable suite of organic rich sediments extending from recent up to the equivalent of medium volatile bituminous rank. The acquisition of images with the monochromator tuned to 285.5 eV, corresponding to the 1s - (pi) * transition of unsaturated carbon, reveals a homogeneous chemical structure in the spore outer wall (exine). Across the rank range absorption at 288.1 eV, corresponding to the 1s - 3p/(sigma) * transition of aliphatic carbon, matches that of the surrounding, matrix, vitrinite suggesting that the aliphatic carbon within the two macerals undergoes a parallel chemical structural evolution over the rank interval analyzed. Carbon near edge absorption fine structure spectroscopic microanalysis reveals clear trends in the chemistry of sporopollenin/sporinite. The most pronounced being an increase in the concentration of sp2 hybridized carbon. The rate of increase exceeds that of similar aromatization trends in the surrounding vitrinite. Increases in the concentration of unsaturated carbon are compensated by losses of aliphatic and alkyl carbon bonded to oxygen. The concentration of COOH,R groups is low and does not change across the rank range analyzed.
Poster Session
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X-ray supermirrors for BESSY-II
Alexei I. Erko, Franz Shaefers, Bernard Vidal, et al.
X-ray multilayer supermirrors for the energy range up to 22 KeV have been theoretically studied and experimentally measured with synchrotron radiation. A multilayer mirror with 50 W/Si bi-layers of different thicknesses on an Si substrate has a smooth reflectivity of up to 32% in the whole energy range from 5 KeV to 22 KeV at a grazing incidence angle of 0.32 degrees.
BESSY Bragg-Fresnel multilayer beam monitors
Karsten Holldack, Alexei I. Erko, William B. Peatman
X-ray optical systems based on Bragg-Fresnel multilayer components imaging an electron beam in a storage ring with micrometer resolution are presented. Design concepts are compared to alternative methods, and the aberrations and limits of Bragg-Fresnel multilayer optics are discussed. Experimental results of imaging the BESSY I source with sub 10 micrometer resolution are presented and the development of a compact Bragg-Fresnel multilayer telescope as a BESSY II standard beam monitor is described.
Tomographic scanning microscope for 1 to 4-KeV xrays
Ian McNulty, Yipeng Feng, Waleed S. Haddad, et al.
X-ray microtomography enables three-dimensional imaging at sub-micron resolution with elemental and chemical state contrast. The 1 - 4 KeV energy region is promising for microtomography of biological, microelectronics, and materials sciences specimens. To capitalize on this potential, we are constructing a tomographic scanning x-ray microscope for 1 - 4 KeV x rays on a spherical grating monochromator beamline at the advanced photon source. The microscope, which uses zone plate optics, has an anticipated spatial resolution of 100 nm and an energy resolution of better than 1 eV.
Elliptical wiggler beam line with minimum focal spot size at the ALS
A beamline for circularly polarized radiation produced by an elliptical wiggler has been designed at the ALS. It covers a broad energy range from 50 eV to 2000 eV. The rigorous theory of grating diffraction efficiency has been used to maximize throughput. This is a challenging optical problem due to the nature of the elliptical wiggler insertion device. The wiggler has a large source size in the vertical and horizontal directions, and the monochromator requires high resolution (small slits), a wide tuning range, and cooling for high heat loads. These problems have been solved by using a variable included angle monochromator with high demagnification onto the entrance slit, aberration correction of the grating for the large vertical aperture, and cooled optics.
White-light spacial frequency multiplication using soft xrays
Max Wei, Eric M. Gullikson, James H. Underwood, et al.
We have patterned a 0.25-micron period grating in SAL-601 photoresist using soft x-ray white-light spatial frequency multiplication. The configuration is that of a grating interferometer using two transmission gratings having the same period ((Lambda) equals 0.5 micron) and fabricated by electron beam lithography and lift-off. The first transmission grating splits an incoming x-ray beam into two paths and the second grating, operating in higher order, combines the two beams. A standing wave pattern is obtained at the intersection of the two beams and recorded by a photoresist coated substrate. This patterning technique has the advantage of multiplying the spatial frequency of the interferometer gratings by an even integer factor. Furthermore, the recording geometry is insensitive to both the longitudinal and transverse coherence of the illumination. Synchrotron bending magnet radiation from the advanced light source located at the Lawrence Berkeley National Laboratory was used as the source. The grating interferometer geometry has been used in the past to record white-light interference fringes using visible and ultraviolet light sources. We have used a two-grating interferometer to provide an initial demonstration of white-light spatial frequency doubling at soft x-ray wavelengths. By using this technique with shorter period parent gratings, it should be possible to patten gratings with higher resolution than electron beam lithography.
Applications
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Capillary xray compressor: principle versus practice
Dale L. Brewe, Steve M. Heald, Bill Barg, et al.
Guiding x rays down the inside of tapered capillaries is a means to increase the flux density of x rays from synchrotron light sources without some of the disadvantages inherent in other techniques. We have demonstrated that a process based on techniques for fabrication of glass fibers may be used to produce tapered capillaries with inlet diameters on the order of 150 micrometers or more, and outlets on the order of 1 micrometer or less. We present a description of the capillary fabrication and results of tests of the performance of several capillaries, along with a comparison with calculations of performance. We also summarize refinements to the fabrication process that will provide additional improvements. The transmission of x rays from linear capillaries with inlet diameters of approximately 150 micrometers and outlet diameters of 1.3 - 1.4 micrometer is on the order of 2%, with corresponding intensity gains of up to 274. Initial results indicate that the capability exists for producing convex profiles necessary for optimal transmission. Calculated and measured transmission efficiencies are in fairly good agreement, leading to the expectation that efficiencies predicted by calculations to be attainable from optimal profiles are a realistic goal, given the ability to manufacture these profiles.