X-ray microscopy provides higher resolution than optical microscopy and higher penetration power than electron microscopy. Therefore, x-ray microscopy allows high resolution imaging of thick hydrated samples. The two dominating processes determining the contrast in x-ray microscopy are photoelectric absorption and phase shift. Phase contrast is especially suited to visualize features in hydrated cells with low natural amplitude contrast. Living cells are damaged by ionizing radiation, e.g. soft x-rays. For this reason an object stage for cryogenic specimen was developed and implemented on the Goettingen transmission x-ray microscope at the electron storage ring BESSY. It allows objects to be imaged at temperatures below 120 K in cryogenic nitrogen gas at atmospheric pressure. This system was used to perform experiments with initially living biological objects, e.g. cells, algae and chromosomes. The preparation of the sample only comprised shock freezing in liquid ethane to cryogenic temperatures. The structural stability of these frozen-hydrated samples is increased by about four orders of magnitude compared to unfixed wet specimens at room temperatures. For this reason micro-tomography is possible with high spatial resolution, which reveals the 3D morphology, e.g. the 3D distribution of organic compounds, close to the natural, functional state. In addition, cryo x-ray microscopy will also allow investigations of kinetic processes. The cooling time to produce a vitrified sample is on the order of a millisecond, thus an active process in a cell can be stopped by freezing at a well defined state.
A bend magnet at the advanced light source is sufficiently bright to illuminate a scanning transmission x-ray microscope, with a zone plate lens to focus the soft x-ray beam at the diffraction limit. The beam line must be carefully optimized for this one purpose of high count-rates, of the order of 1MHz, are to be achieved in the microscope. Such a design is described. The nominal resolving power is 2000 from 150eV to 600eV using a single spherical diffraction grating. Twice the resolving power is available at reduced flux, and the intensity can be traded independently against the spatial and spectral resolution.
Scanning transmission x-ray microscopes (STXM) are well matched to the optics of high resolution monochromators, offer a variety of imaging modes and can minimize radiation damage to the specimen. We describe the Stony Brook STXM at the NSLS. This microscope is used for a variety of studies by many users; we briefly outline its use for studies of hydrated colloidal system and for dark field microscopy on immunogold labeled specimens as examples. In order to keep pace with developments in zone plate optics, spectroscopy and a variety of imaging modalities, the microscope is being redesigned and its characteristics are discussed. Its preliminary x-ray detector will be a new multiware proportional counter with high count rate capability.
Progress with an x-ray microprobe for radiobiological studies is described. The instrument uses laboratory soft x-ray sources to give either continuum radiation or pulsed line radiation. A zone plate forms a fine probe from the x-ray beam which may be used to target individual cells or sub-cellular components with defined radiation doses. A preliminary experiment has shown a definite biological effect.
We performed an x-ray nanotomography experiment at the Advanced Photon Source for the purpose of making a 3D image of a sample contain an integrated circuit interconnect. Nine projections of the sample were made over an angular range of 140 degrees using 1573 eV photons and scanning transmission x-ray microscope having a focal spot size of about 150 nm. Reconstructions of experimental and simulated data, using a simultaneous iterative reconstruction technique, show that a sample that is highly opaque along certain lines of sight must be strategically oriented with respect to the rotation axis to minimize the attenuation of photons through the sample and maximize the contrast in each image.
Understanding the fate of environmental contaminants is of fundamental importance in the development and evaluation of effective remediation strategies. Among the factors influencing the transport of these contaminants are the chemical speciation of the sample and the chemical and physical attributes of the surrounding medium. Characterization of the spatial distribution and chemical speciation at micron and submicron resolution is essential for studying the microscopic physical, geological, chemical, and biological interfaces that play a crucial role in determining contaminant fate and mobility. Hard x-ray spectroscopy and imaging are powerful techniques for the element-specific investigation of complex environmental samples at the needed micron and submicron resolution. An important advantage of these techniques result from the large penetration depth of hard x-rays in water. This minimizes the requirements for sample preparation and allows the detailed study of hydrated samples. This paper discuses some current problems in environmental science that can be addressed by using synchrotron- based x-ray imaging and spectroscopy. These concepts are illustrated by the results of recent x-ray microscopy studies at the Advanced Photon Source.
Two laboratory scale x-ray microscopes using laser generated plasma sources are being developed at King's College. One system uses dark field imaging while the other is a scanning x-ray microscope and progress with both is described. In particular, preliminary results from an extensive characterization of the laser plasma source at the Lasers for Science Facility, CLRC Rutherford Appleton Laboratory, are discussed. This characterization has shown that the source is eminently suitable for x-ray microscopy.
We have constructed a high resolution scanning x-ray microscopy at the 2-ID-B beamline at the Advanced Photon Source for 1-4 keV x-ray imaging and microspectroscopy experiments. The microscope uses a Fresnel zone plate to focus coherent x-ray undulator radiation to a 150 nm focal spot on a sample. The spectral flux in the focus is 108 ph/s/0.1 percent BW. X- ray photons transmitted by the sample are detected by an avalanche photodiode as the sample is scanned to form an absorption image. The sample stage has both coarse and fine translation axes for raster scanning and a rotation axis for microtomography experiments. The incident x- ray beam energy can also be scanned and a rotation axis for microtomography experiments. The incident x-ray beam energy can also be scanned via the 2-ID-B monochromator while the sample is kept in focus to record spatially resolved absorption spectra. We have measured the performance of the instrument with various test objects. THe microscope hardware, software, and performance are discussed in this paper.
X-ray microprobe techniques require both a good spectral resolution and a high intensity. Actually, these two competitive conditions can be obtained only by x-ray spectrometers with focusing optics made by cylindrical curved crystals or by doubly curved on spherical or toroidal surface crystal monochromators. However, these devices do not allow collection of a large solid angle and therefore the experiments are limited by the source brilliance. Here we present a special device for the analysis of the x-ray secondary emission based on a new diffractor design. The device has a special shape of the reflecting surface, i.e., a pseudo- spherical stepped surface characterized by a constant angle width per step, that allows to collect the large solid angel necessary to guarantee an intense flux for the experiments of microanalysis. We will demonstrate that the efficiency of this diffractor is superior to a commercial device of similar size having a spectral resolution of 410-4 with a potential gain of about one order of magnitude.
The ID21 x-ray microscopy beamline at the ESRF has two branchlines: one is dedicated to scanning microscopy techniques and the second to full-field imaging microscopy. The scanning x-ray microscope end station is designed for use over a relatively wide spectral range ranging from 0.2 to 8keV giving access to absorption edges from a wide range of elements of interest in both the biological and materials sciences. The microscope is operating initially with Fresnel zone plate optics and, apart from conventional absorption contrast imaging, is designed to accept a variety of complementary imaging modes. In particular considerable effort has been made to optimize the design for spectromicroscopy using both fluorescence imaging and scanning of the primary x-ray probe energy for XANES imaging. A brief overview of the beamline design is given. This is followed by a discussion of the implications of both the source characteristics and the required wide spectral range upon the optical design of the microscope and, leading from this, the technological choices which have been made. Preliminary results obtained with the microscope are presented.
Phase zone plates are commonly used in x-ray microscopy techniques when high spatial resolution and high photon flux in the focal spot are desired. Extending the fabrication techniques of phase zone plates for use in the soft x-ray region to higher photon energies becomes difficult due to the high aspect ratios of the zone structures which have to be created. As an alternative, the sputtered sliced zone plate method has been applied. In this technology, a thin microwire is deposited alternately with two different materials. Zone plates are generated from the rod by slicing it perpendicular to its axis and thinning the slices down the required zone plate thickness. Theoretical investigations on the demands on generating these zone plates as well as the generation process are discussed. Recent measurements will be presented.
High-resolution x-ray microscopy has applications in the fields of biology, colloid physics, and solid state physics. For each of these applications it is essential that the micro zone plates used as objectives in the x-ray microscope combine high resolution with optimal diffraction efficiency, so as to minimize exposure time and the x-ray dose absorbed by the specimen. The outermost zone width constitutes an important property of the zone plate, since the first-order spatial resolution scales linearly with this parameter. The other fundamental property of a micro zone plate is its diffraction efficiency, which should be both high and uniform. The combination of small outermost zones and the zone height required for optimal diffraction efficiency leads to high aspect ratios of the nanostructures. We report here the technique to manufacture these micro zone plates using microscopic glavanoforms and electrodeposition. Copolymer galvanoforms for nickel micro zone plates were irradiated with high doses of x-ray radiation to increase the degree of cross-linking of the copolymer network in this way, exact pattern replication in the galvanoform was obtained for zone aspect ratios of up to 8:1. Using these galvanoforms, nickel micro zone plates were produced for the soft x-ray wavelength 2.4 nm, with smallest zone widths of 30 nm and 40 nm, achieving first-order diffraction efficiencies of up to 15 percent and 20 percent, respectively.
A 1D Bragg-Fresnel lens for monochromatizing and focusing hard x-rays has been developed using a multilayer zone plate and a crystal. Ti and Al have ben chosen as material for phase modulation type zone plate. About 400 payers of Ti and Al were alternately deposited on a plane substrate according to the Fresnel's formula using a helicon plasma sputtering technique, in which Ar gas pressure was less than 1 mTorr. The total thickness of the layers is about 128 micrometers . The multilayered plane was sliced vertically and glued onto Ge(211) crystal, and thinned to about 10 micrometers . The synchrotron light source was focused one dimensionally, and the focal line width was measured by a knife edge scan techniques.
Fresnel zone plates (ZP) have gained popularity as the optics of choice for advanced microfocusing applications. The main virtues of ZP are high resolution, high efficieny, low background, coherence preservation, and ample working distance. Zone plates are also unique because they are a normal incidence x-ray optics, which are much easier to align and use compared to other grazing incidence optics. We will report here recent progress that has drastically enhanced the performance of ZPs in 1) higher spatial resolution, 2) higher focusing efficiency, and 3) extension to higher energies. With the new developments, zone plates have proven to be one of the best microfocusing optics for monochromatic x-ray beams.
We have developed an x-ray microprobe facility utilizing mirror bending techniques that allow white light x-rays from the Advanced Light Source Synchrotron to be focused down to spot sizes of micron spatial dimensions. We have installed a 4 crystal monochromator prior to the micro-focusing mirrors. The monochromator is designed such that it can move out of the way of the input beam, and allows the same micron sized samples to be illuminated with either white or monochromator radiation. Illumination of the sample with white light allows for elemental mapping and Laue x-ray diffraction, while illumination of the sample with monochromatic light allows for elemental mapping, micro-x-ray absorption spectroscopy and microdiffraction. The performance of the system will be described as will some of the initial experiments that cover the various disciplines of Earth, Material and Life Sciences.
We present the optical designs, modeling, bender design and test results of x-ray micro- focusing optics used to micro-focus monochromatic undulator x-rays at the Advanced Photon Source (APS). The system uses two 100mm long, actively bent mirrors in a Kirkpatrick Baez arrangement. A detailed analytical model of the system's performance is described along with ray tracing result. A description of the integration of the benders into a compete micro- focusing system is provided. The system is easy to setup and use and is presently used in earth science research coupled to techniques such as micro-spectroscopy, fluorescence microprobe, and energy dispersive diffraction. The optics' performance is measured on the GeoSoilEnviroCARS microprobe experimental station at APS sector 13. Focusing tests using 10keV undulator x-rays result in a double focused beam with a horizontal and vertical full width at half maximum of 0.80micrometers X 0.85micrometers , and flux density gain greater than 105.
The use of synchrotron x-ray sources for diffraction and fluorescence analysis has permitted the study of a sample with improved structure resolution respectively. However, even the highly-intense x-ray spectra available using synchrotron sources may be insufficient to perform some analysis on weakly-diffracting or low-concentration samples. The available x- ray intensity per unit irradiated volume and detector noise level impose a lower limit on detection sensitivity. Even where sufficient intensity is available to make a single measurement, time constraints may still preclude diffraction data collection over sufficient reciprocal space volume or high-resolution fluorescence data collection over a large sample area.
Square-channel capillary, or 'Lobster-eye' arrays have been shown to be the optimum geometry for array optics. This configuration leads to a novel class of conditioning devices for x-ray and neutron beams. We present the first result of the focusing of neutrons with a lead glass square-channel array. This array, designed for soft x-rays, performs comparably with neutrons. Finally, we describe a novel method for the fabrication of glass square channel arrays.
We describe the theory, fabrication and experimental results of novel, compact optical elements for collimating and/or focusing beams of x-rays or thermal neutrons. These optical elements are solid composites consisting of regular stacks of alternating micro-foils, analogous in action to Soller slits. They are made out of pairs of metals with suitable refractive indices for reflection and/or absorption of the radiation. The performance of these proof-in-principle collimating elements is limited only by the choice of micro-foil materials and the uniformity of their interfaces.
Recent development of anew refractive x-ray lens at SPring-8 is reported. This is the first refractive x-ray lens with a string of spherical lens in-spite of the string of cylindrical holes. Two types of the lends were developed which consists of a string of bubbles formed in a viscous liquid and a string of hollow plastic balls on pure water. They are sealed inside a container made from an acrylic resin. The x-ray focusing properties were investigated with the monochromated beam at an undulator beam line BL47 in SPring-8. Demagnified images of the source for these tow types of lens were observed at the energy of 19.0-24.5 keV with the focal length of approximately 5m. For the bubble lens, a gain of about 12 was observed. The observed vertical image size, 48 micrometers , was 6 times larger than the expected size. The method to improve the focusing capability is discussed.
This paper reports on recent developments on lamellar multilayer gratings fabricated by ions implantation. Comparative investigations between conventional etched multilayer grating and implanted ones are made and outline the potentialities of the original process of fabrication. In addition, simulations were carried for different types of Cu K(alpha) 1 x-ray measurements by using a rigorous theory of diffraction recently revised. The quality of the fits obtained with this method easily applicable to the implanted multilayer grating appears as an essential tool in the improvement of x-ray diffractive optics fabrication processes.
An electron-tubes-LTD 129EM electron multiplier tube has been modified to act as a detector of soft x-rays. the first dynode was coated with 100 nm of CsI and the assembly was mounted in a small vacuum chamber with 100 nm thick silicon nitride entrance window. Initial tests show the detector is linear up to an input flux of approximately 1MHz on a synchrotron source and has proved effective in providing pulse height discrimination when used on a pulsed laser plasma source.
Third-generation storage rings have small particle beam emittances. The size of the particle beam can be determined from the measured image size of the focused radiation source. Undulators are preferred as radiation sources at third-generation storage rings, the radiation emitted by an undulator has both small size and divergence. The effect of the small beam divergence on determination of the source size is discussed here. The analysis is performed in an approximation of a Gaussian distribution of the radiation intensity. The paraxial approximation and matrix methods were also used for this derivation. It was fond that the effect of the small beam divergence depends on the ratio of the angular acceptance of the source to the divergence of the emitted radiation.
The distortion of transmission spectra by the combination of monochromator band pass and sample attenuation has been modeled and characterized for soft x-ray energies. The model was used to predict the distortion to the transmission spectrum of CO2 as obtained with a monochromator of moderate band pass. Experimental measurements of the CO2 spectrum at a range of concentrations were used to confirm the validity of the model. The application of the model to overcome band pass and thickness distortions to the quantitative measurement of mass absorption coefficients and mass thickness are discussed.