The understanding of real complex geological, environmental and geo-biological processes depends increasingly on in-depth non-invasive study of chemical composition and morphology. In this paper we used scanning hard X-ray nanoprobe techniques in order to study the elemental composition, morphology and As speciation in complex highly heterogeneous geological samples. Multivariate statistical analytical techniques, such as principal component analysis and clustering were used for data interpretation. These measurements revealed the quantitative and valance state inhomogeneity of As and its relation to the total compositional and morphological variation of the sample at sub-μm scales.
The Nanoscopium 155 m-long scanning nanoprobe beamline of Synchrotron Soleil (St Aubin, France) is dedicated to
quantitative multi-modal imaging. Dedicated experimental stations, working in consecutive operation mode, will provide
coherent scatter imaging and spectro-microscopy techniques in the 5-20 keV energy range for various user communities.
Next to fast scanning, cryogenic cooling will reduce the radiation damage of sensitive samples during the measurements.
Nanoscopium is in the construction phase, the first user experiments are expected in 2014. The main characteristics of
the beamline and an overview of its status are given in this contribution.
Scanning hard X-ray nanoprobe imaging provides a unique tool for probing specimens with high sensitivity and
large penetration depth. Moreover, the combination of complementary techniques such as X-ray fluorescence,
absorption, phase contrast and dark field imaging gives complete quantitative information on the sample
structure, composition and chemistry.
The multi-technique “FLYSCAN” data acquisition scheme developed at Synchrotron SOLEIL permits to
perform fast continuous scanning imaging and as such makes scanning tomography techniques feasible in a
time-frame well-adapted to typical user experiments. Here we present the recent results of simultaneous fast
scanning multi-technique tomography performed at Soleil. This fast scanning scheme will be implemented at the
Nanoscopium beamline for large field of view 2D and 3D multimodal imaging.
The design and implementation of a pair of 100 mm-long grazing-incidence total-reflection mirrors for the hard
X-ray beamline Nanoscopium at Synchrotron Soleil is presented. A vertically and horizontally nanofocusing
mirror pair, oriented in Kirkpatrick-Baez geometry, has been designed and fabricated with the aim of creating a
diffraction-limited high-intensity 5 − 20 keV beam with a focal spot size as small as 50 nm. We describe the design
considerations, including wave-optical calculations of figures-of-merit that are relevant for spectromicroscopy,
such as the focal spot size, depth of field and integrated intensity. The mechanical positioning tolerance in the
pitch angle that is required to avoid introducing high-intensity features in the neighborhood of the focal spot
is demonstrated with simulations to be of the order of microradians, becoming tighter for shorter focal lengths
and therefore directly affecting all nanoprobe mirror systems. Metrology results for the completed mirrors are
presented, showing that better than 1.5 °A-rms figure error has been achieved over the full mirror lengths with
respect to the designed elliptical surfaces, with less than 60 nrad-rms slope errors.
The focusing efficiency of binary Fresnel zone plate lenses is fundamentally limited and higher efficiency requires a
multi step lens profile. To overcome the manufacturing problems of high resolution and high efficiency multistep zone
plates, we investigate the concept of stacking two different binary zone plates in each other’s optical near-field. We use a
coarse zone plate with π phase shift and a double density fine zone plate with π/2 phase shift to produce an effective 4-
step profile. Using a compact experimental setup with piezo actuators for alignment, we demonstrated 47.1% focusing
efficiency at 6.5 keV using a pair of 500 μm diameter and 200 nm smallest zone width. Furthermore, we present a
spatially resolved characterization method using multiple diffraction orders to identify manufacturing errors, alignment
errors and pattern distortions and their effect on diffraction efficiency.
This report describes the optimization, first experimental data and the performance outlook for a special refractive lens for the focusing of x-rays. The lens was obtained by applying the strategy of Fresnel to lighten a lens by removing efficiently optically passive material. This strategy was applied to objects, which were produced by deep x-ray lithography and which can thus be shaped in only one dimension. Consequently this class of lenses can focus in only one dimension. While in the normal Fresnel lenses as much material as possible is removed, in the present lens the remaining segments were kept as large as possible, in order to finally obtain a rigid and deep structure. The resultant structure is composed of small prisms of almost identical shape, which are combined such that the final lens looks like an hour glass, i.e. two large prisms touch each other at one of their tips. Such a lens has better transmission than a normal refractive lens of equal focal length. And even though it has worse transmission than the normal Fresnel lenses, it could be produced with an unprecedented geometrical aperture of 2.6 mm for 8 keV photon energy. The uniformly etched structure depth was found to be at least 0.4 mm, over which the lens can focus free of aberrations. A lens with focal length 2.183 m was found to provide after very rapid alignment a focus size of 2.8 μm, while slightly better 1.73 μm were ideally expected.
Sets of planar SU-8 cross lenses focusing in two directions have been fabricated by tilted deep X-ray lithography using an X-ray mask with tilted absorber structures. The profile of the absorber structures on the mask take into account the lithographic peculiarities of SU-8 resist to reproduce the designed profile of the lens elements exactly. The cross lenses are placed on one substrate and have identical focal distances, which allow to scan the spectral range from 5 keV to 30 keV by stepping the lens substrate from one lens to the next. Another set of cross lenses was developed with different quasi-parabolic profiles to obtain a large focus depth (up to several centimeters) with uniform intensity distribution in the micron focal spot. This together with the stepping possibilities between lenses satisfies the requirement of static spectroscopy experiments. For the truncated parabolic profile, these cross lenses consist of separate segments arranged in a new mosaic form. In comparison with the known “fern”-like kinoform profile, the lenses have been developed with smaller gain loss. The testing of the new sets have been performed at the undulator ID-18F and ID-22 beamlines (ESRF, Grenoble, France) and the experimental results are compared to simulations.
Fluorescence microtomography is a hard x-ray scanning microscopy technique that has been developed at synchrotron radiation sources in recent years. It allows one to reconstruct non-destructively the element distribution on a virtual section inside a sample. The spatial resolution of this microbeam technique is limited by the lateral size of the microbeam. Since recently, nanofocusing refractive x-ray lenses (NFLs) are under development that were shown to produce hard x-ray microbeams with lateral resolution in the range of 100nm. Future improvements of these optics might reduce the microbeam size down to below 20nm. Using nanofocusing lenses, fluorescence microtomography with sub-micrometer resolution was performed. As an example, the element distribution inside a small cosmic dust particle is given. Tomographic reconstruction was done using a refined model including absorption effects inside the sample.
In various scientific fields -- such as materials sciences, biology or even astrophysics -- the relation between morphology and the chemical composition is a key for the understanding of structures and their function. Hard x-ray tomography is a suitable tool for structural analyzes on the micrometer scale and can give additional chemical information by combining this imaging technique with spectroscopic methods. In chemistry, X-ray absorption near-edge spectroscopy (XANES) is a well-known and established technique. By scanning the X-ray energy in the vicinity (50-100 eV) of the absorption edge of an element, information can be obtained about the oxidation state of the probed atoms. We used a fast read-out and low noise detector for XANES imaging and were able to distinguish different oxidation states in three dimension performing tomographic scans at different characteristic energies of the probed atom.
Since 1998 we have developed X-Ray fluorescence tomography for microanalysis. All aspects were tackled starting with the reconstruction performed by FBP or ART methods. Self-absorption corrections were added and combined with Compton, transmission and fluorescence tomographies to obtain fully quantitative results. Automatic "smart scans" minimized overhead time scanning/aligning non-cylindrical objects. The scans were performed step-by-step or continuously with no overhead time. Focusing went from 5 to 1 micron range, using FZP or CRL lenses, and finally KB bent mirrors which yield sub-micron high intensity beams. Recently, we have performed the first quantitative 3D fluo-tomography by helical scanning. We are now studying energy dependent fluo-tomography for chemically-sensitive imaging of the internal structure of samples. This chronology yielded the present level of sophistication for both experiments and data treatment and finally a method ready for wide dissemination among scientists.
In recent years, hard x-ray full field microscopy and tomography has been developed for synchrotron radiation sources based on parabolic refractive x-ray lenses. These optics are used as objective lens in a hard x-ray microscope that can image objects in transmission free of distortion. Using beryllium as lens material, an optical resolution of about 100nm has been reached in a field of view that is larger than 500 micrometers. In the future, the spatial resolution may be improved to below 50nm. Recording a large number of micrographs from different perspectives allows one to reconstruct non-destructively the 3-dimensional inner structure of an object with resolutions well below one micrometer. Different contrast mechanisms can be exploited, such as absorption and near field phase contrast. The method is demonstrated using a microchip as a test sample.
In chemistry, x-ray absorption near-edge spectroscopy (XANES) is a well-known and established technique. By scanning the x-ray energy in the vicinity (50-100 eV) of the absorption edge of an element, information can be obtained about the oxidation state of the probed atoms. The (conventional) technique mainly employed until now applies for homogeneous, specifically prepared flat samples where the measured signal can be considered as the average over the whole irradiated volume. This restriction for samples is partially released when the XANES method is combined with imaging techniques. Two-D resolved data is acquired using area detectors or by scanning with a focused beam. X-ray absorption tomography is a method of choice for investigating the 3D structure of objects and its dual energy version is used for getting information about the 3D distribution of a given element within the sample. Although the combination of XANES and tomography seems to be a natural extension of dual-energy tomography, in practice several experimental problems have to be overcome in order to obtain useable data. In the following we describe the results of XANES imaging and tomography obtained measuring a phantom sample of pure molybdenum compounds using a FreLoN 2000 camera system at the ESRF undulator beamline ID22. This system allowed making volume resolved distinctions between different oxidation states with spatial resolution in the micrometer range.