Andrea Somogyi

Internal elemental microanalysis combining X-ray fluorescence, Compton and transmission tomography

Conventional x-ray transmission tomography provides the spatial distribution of the absorption coefficient inside a sample. Other tomographic techniques, based on the detection of photons coming from fluorescent emission, Compton and Rayleigh scattering, are used for obtaining information on the internal elemental composition of the sample. However, the reconstruction problem for these techniques is generally much more difficult than that of transmission tomography, mainly due to self-absorption effects in the sample. In this article an approach to the reconstruction problem is presented, which integrates the information from the three types of signals. This method provides the quantitative spatial distribution of all elements that emit detectable fluorescent lines (Z15 in usual experimental conditions), even when the absorption effects are strong, and the spatial distribution of the global density of the lighter elements. The use of this technique is demonstrated on the reconstruction of a grain of the martian meteorite NWA817, mainly composed of low Z elements not measured in fluorescence and for which this method provides a unique insight. The measurement was done at the ID22 beamline of the European Synchrotron Radiation Facility.

Nanofocusing parabolic refractive X-ray lenses

Parabolic refractive x-ray lenses with short focal distance can generate intensive hard x-ray microbeams with lateral extensions in the 100 nm range even at a short distance from a synchrotron radiation source. We have fabricated planar parabolic lenses made of silicon that have a focal distance in the range of a few millimeters at hard x-ray energies. In a crossed geometry, two lenses were used to generate a microbeam with a lateral size of 380 nm by 210 nm at 25 keV in a distance of 42 m from the synchrotron radiation source. Using diamond as the lens material, microbeams with a lateral size down to 20 nm and below are conceivable in the energy range from 10 to 100 keV.

Nondestructive three-dimensional elemental microanalysis by combined helical x-ray microtomographies

A nondestructive x-ray technique combining simultaneous transmission, fluorescence, and Compton microtomography has been developed. Simultaneous three-dimensional structural information and three-dimensional internal elemental composition maps down to trace concentration levels have been obtained by a helical scan of the sample through an x-ray microbeam. With this method quantitative three-dimensional chemical distributions can be obtained at (sub)micrometric resolution in a nondestructive and noninvasive way, opening unique possibilities for the microanalysis of rare and fragile samples from several research fields.

Mn-rich clusters in GaN: Hexagonal or cubic symmetry?

In this study, we report the application of synchrotron radiation microprobe to the analysis of Mn-rich clusters in GaN. From the Mn and Ga fluorescence line intensity ratio, an average Mn concentration of 11% was deduced. A combination of fluorescence mapping with spectroscopic techniques enabled us to examine not only the cluster elemental nature but also their crystallographic orientation on the submicron scale. The strong polarization-dependent x-ray absorption near-edge structure features showed the preservation of the hexagonal symmetry in both cluster-free and Mn-rich regions. However, from the x-ray absorption data taken inside the clusters, a preferential disorder was observed in the direction parallel to the crystal growth rather than perpendicular to it.

Microimaging and tomography with chemical speciation

Abstract Materials science deals with the study of the morphology of samples, their chemical composition and the relation between both. One general problem is the preservation of the sample throughout the different analyses, like it is often the case for classical chemical analysis. Destruction-free chemical speciation in three dimensions with micrometer resolution can be achieved by combining X-ray spectroscopy and imaging techniques. Highly brilliant radiation is needed for this purpose available at 3rd generation synchrotrons such as the ESRF. X-ray absorption near-edge spectroscopy (XANES) is a non-destructive well-known and established technique in chemistry. 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 to 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. 2D resolved data is acquired using area detectors or by scanning with a focussed 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.

ID22: a multitechnique hard X-ray microprobe beamline at the European Synchrotron Radiation Facility

The ID22 beamline is dedicated to hard X-ray microanalysis allowing the combination of fluorescence, spectroscopy, diffraction and tomography techniques in a wide energy range from 6 to 70 keV. The recent installation of an in-vacuum undulator, a new sample stage and the adaptation of various focusing optics has contributed to a great improvement in the capabilities of the beamline, which is now accessed by a wide user community issued from medical, earth and environmental science, archaeology and material science. Many applications requiring low detection limits for localization/speciation of trace elements together with structural analysis have been developed at the beamline on the (sub)micrometer scale. The possibility of combining simultaneously different analytical probes offers the opportunity of a thorough study of a given sample or scientific problem. This paper presents a review of the recent developments of the beamline and a detailed description of its capabilities through examples from different fields of applications.

Focusing X-rays with simple arrays of prism-like structures.

This report discusses the optimization strategy, the theoretical background and first experimental data of a new refractive lens for focusing X-rays. In order to reduce the absorption of X-rays in this transmission lens, optically passive material was removed from the necessarily concave lens shape in a highly regular pattern. The feature dimensions require lens production and replication by deep X-ray lithography, which allows shaping in only one dimension. Consequently such a lens can focus in one direction only, so a crossed lens pair is needed for two-dimensional focusing. The single lens is composed of two large prisms of millimetre size, which touch each other at one of the tips, like an old sand clock. Each large prism contains a highly regular structure of essentially identical prism-like smaller segments. The first lens prototypes focused an X-ray beam with a vertical size of 500 microm and a photon energy of 8 keV to a line with a width of only 2.8 microm. This is only slightly worse than the line width of 1.73 microm expected for its focal length of f = 2.18 m. The photon density enhancement in the focus was 25, but could have been larger as the lens can intercept a beam height of 2.6 mm.

Quantitative trace element analysis of individual fly ash particles by means of X-ray microfluorescence

A new quantification procedure was developed for the evaluation of X-ray microfluorescence (XRF) data sets obtained from individual particles, based on iterative Monte Carlo (MC) simulation. Combined with the high sensitivity of synchrotron radiation-induced XRF spectroscopy, the method was used to obtain quantitative information down to trace-level concentrations from micrometer-sized particulate matter. The detailed XRF simulation model was validated by comparison of calculated and experimental XRF spectra obtained for glass microsphere standards, resulting in uncertainties in the range of 3-10% for the calculated elemental sensitivities. The simulation model was applied for the quantitative analysis of X-ray tube and synchrotron radiation-induced scanning micro-XRF spectra of individual coal and wood fly ash particles originating from different Hungarian power plants. By measuring the same particles by both methods the major, minor, and trace element compositions of the particles were determined. The uncertainty of the MC based quantitative analysis scheme is estimated to be in the range of 5-30%.

Development of fast, simultaneous and multi-technique scanning hard X-ray microscopy at Synchrotron Soleil

A distributed fast-acquisition system for synchronized multi-technique experiments is presented, in which the collection of metadata and the asynchronous merging of large data volumes from multiple detectors are managed as part of the data collection process. This fast continuous scanning scheme, named FLYSCAN, enables measurement of microscopy data on a timescale of milliseconds per pixel. Proof-of-principle multi-technique experiments, namely scanning X-ray fluorescence spectrometry combined with absorption, differential phase contrast and dark-field imaging, have been performed on biological and geological samples.

Very first tests on SOLEIL regarding the Zn environment in pathological calcifications made of apatite determined by X-ray absorption spectroscopy

This very first report of an X-ray absorption spectroscopy experiment at Synchrotron SOLEIL is part of a long-term study dedicated to pathological calcifications. Such biological entities composed of various inorganic and/or organic compounds also contain trace elements. In the case of urinary calculi, different papers already published have pointed out that these oligo-elements may promote or inhibit crystal nucleation as well as growth of mineral. Use of this analytical tool specific to synchrotron radiation, allowing the determination of the local environment of oligo-elements and thus their occupation site, contributes to the understanding of the role of trace elements in pathological calcifications.