This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Go... more This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam). Noninvasive in situ spectroscopic analysis at several spots on the painting, combined with synchrotron-radiation-based X-ray investigations of two microsamples, revealed the presence of different types of chrome yellow used by Van Gogh, including the lightfast PbCrO4 and the sulfur-rich PbCr1-x Sx O4 (x≈0.5) variety that is known for its high propensity to undergo photoinduced reduction. The products of this degradation process, i.e., Cr(III) compounds, were found at the interface between the paint and the varnish. Selected locations of the painting with the highest risk of color modification by chemical deterioration of chrome yellow are identified, thus calling for careful monitoring in the future.
A hard x-ray scanning microscope based on nanofocusing refractive x-ray lenses is well suited for... more A hard x-ray scanning microscope based on nanofocusing refractive x-ray lenses is well suited for coherent x-ray diffraction imaging, in particular for scanning coherent diffraction microscopy also known as ptychography. Using this technique, the complex transmission function of the object can be obtained with a spatial resolution better than that given by the size of the nanofocus. In addition, the
Materials Research Society Symposium Proceedings, 2012
ABSTRACT Synchrotron-based X-ray techniques are used increasingly to characterize actinide elemen... more ABSTRACT Synchrotron-based X-ray techniques are used increasingly to characterize actinide element speciation in heterogeneous media related to nuclear waste disposal safety. Especially techniques offering added temporal, spatial and energy resolved information are advancing our understanding of f-element physics and chemistry in general and of actinide element waste disposal in particular. Examples of investigations of uranium containing systems using both highly (energy) resolved X-ray emission spectroscopy (HRXES) techniques and spatially resolved techniques with focused X-ray beams are presented in this paper: polarization dependent partial fluorescence yield X-ray absorption near edge structure (PD-PFY-XANES) spectroscopic studies of a single Cs2UO 2Cl4 crystal, which experimentally reveal a splitting of the σ, π and δ components of the 6d valence states [1], and characterization of UO2/Mo thin films prepared on different substrates using a combination of techniques (2D and 3D micro- and nano-X-ray fluorescence, XANES and both holographic and ptychographic tomography).
Stacks of elemental distribution images acquired by XRF can be difficult to interpret, if they co... more Stacks of elemental distribution images acquired by XRF can be difficult to interpret, if they contain high degrees of redundancy and components differing in their quantitative but not qualitative elemental composition. Factor analysis, mainly in the form of Principal Component Analysis (PCA), has been used to reduce the level of redundancy and highlight correlations. PCA, however, does not yield physically meaningful representations as they often contain negative values. This limitation can be overcome, by employing factor analysis that is restricted to non-negativity. In this paper we present the first application of the Python Matrix Factorization Module (pymf) on XRF data. This is done in a case study on the painting Saul and David from the studio of Rembrandt van Rijn. We show how the discrimination between two different Co containing compounds with minimum user intervention and a priori knowledge is supported by Non-Negative Matrix Factorization (NMF).
Micro-X-ray fluorescence ͑-XRF͒ is a rapidly evolving analytical technique which allows visualisi... more Micro-X-ray fluorescence ͑-XRF͒ is a rapidly evolving analytical technique which allows visualising the trace level metal distributions within a specimen in an essentially nondestructive manner. At second generation synchrotron radiation sources, detection limits at the sub-parts per million level can be obtained with micrometer resolution, while at third generation sources the spatial resolution can be better than 100 nm. Consequently, the analysis of metals within biological systems using micro-and nano-X-ray fluorescence imaging is a quickly developing field of research. Since X-ray fluorescence is a scanning technique, the elemental distribution within the sample should not change during analysis. Biological samples pose challenges in this context due to their high water content. A dehydration procedure is commonly used for sample preparation enabling an analysis of the sample under ambient temperature conditions. Unfortunately, a potential change in elemental redistribution during the sample preparation is difficult to verify experimentally and therefore cannot be excluded completely. Creating a cryogenic sample environment allowing an analysis of the sample under cryogenic condition is an attractive alternative but not available on a routine basis. In this article, we make a comparison between the elemental distributions obtained by micro-SR-XRF within a chemically fixed and a cryogenically frozen Daphnia magna, a model organism to study the environmental impact of metals. In what follows, we explore the potential of a dual detector setup for investigating a full ecotoxicological experiment. Next to conventional 2D analysis, dual detector X-ray fluorescence cryotomography is illustrated and the potential of its coupling with laboratory absorption micro-CT for investigating the tissue-specific elemental distributions within this model organism is highlighted.
Advances in Computational Methods for X-Ray Optics II, 2011
Modern hard x-ray scanning microscopes generate x-ray beams with lateral sizes well below 100 nm.... more Modern hard x-ray scanning microscopes generate x-ray beams with lateral sizes well below 100 nm. Characterizing these beams in terms of shape and size by conventional techniques is tedious, requires highly accurate test objects and stages, and yields only incomplete information. Since recently, we use a ptychographic scanning coherent diffraction imaging technique in order to characterize hard x-ray nano beams
ABSTRACT X-ray fluorescence images acquired using the Maia large solid-angle detector array and i... more ABSTRACT X-ray fluorescence images acquired using the Maia large solid-angle detector array and integrated real-time processor on the X-ray Fluorescence Microscopy (XFM) beamline at the Australian Synchrotron capture fine detail in complex natural samples with images beyond 100M pixels. Quantitative methods permit real-time display of deconvoluted element images and for the acquisition of large area XFM images and 3D datasets for fluorescence tomography and chemical state (XANES) imaging. This paper outlines the Maia system and analytical methods and describes the use of the large detector array, with a wide range of X-ray take-off angles, to provide sensitivity to the depth of features, which is used to provide an imaging depth contrast and to determine the depth of rare precious metal particles in complex geological samples.
18 Every infection is a battle for trace elements. Neutrophils migrate first to the infection 19 ... more 18 Every infection is a battle for trace elements. Neutrophils migrate first to the infection 19 site and accumulate quickly to high numbers. They fight pathogens by phagocytosis 20 and intracellular toxication. Additionally, neutrophils form neutrophil extracellular traps 21 (NETs) to inhibit extracellular microbes. Yet, neutrophil trace element characteristics 22 are largely unexplored. We investigated unstimulated and phorbol myristate acetate-23 stimulated neutrophils using synchrotron radiation X-ray fluorescence (SR-XRF) on 24 the sub-micron spatial resolution level. PMA activates pinocytosis, cytoskeletal 25 rearrangements and the release of NETs, all mechanisms deployed by neutrophils to 26 combat infection. 27 By analyzing Zn, Fe, Cu, Mn, P, S, and Ca, not only the nucleus but also vesicular 28 granules were identifiable in the elemental maps. Inductively Coupled Plasma Mass 29 Spectrometry (ICP-MS) revealed a neutrophil-specific composition of Zn, Fe, Cu, and 30 Mn in comparison with J774 and HeLa cells, indicating a neutrophil specific 31 metallome complying with their designated functions. 32 When investigating PMA-activated neutrophils, the SR-XRF analysis depicted typical 33 subcellular morphological changes: the transformation of nucleus and granules and 34 the emergence of void vacuoles. Mature NETs were evenly composed of Fe, P, S, 35 and Ca with occasional hot spots containing Zn, Fe, and Ca. An ICP-MS-based 36 quantification of NETs supernatants revealed a NETosis-induced decrease of soluble 37
X-ray nanobeams are unique non-destructive probes that allow direct measurements of the nanoscale... more X-ray nanobeams are unique non-destructive probes that allow direct measurements of the nanoscale strain distribution and composition inside the micrometer thick layered structures that are found in most electronic device architectures. However, the 2D scanning combined with reciprocal space mapping that has been used to achieve complete strain maps is extremely time consuming and as a result measurements are often constrained to a few or even single objects. Here we demonstrate that by special design of a nanofocused X-ray beam diffraction experiment we can (in a single 2D scan with no sample rotation) measure the individual strain and composition profiles of many structures in an array of upright standing nanowires. We make use of the observation that in the generic nanowire device configuration, which is found in high speed transistors, solar cells and LEDs, each wire exhibits very small degrees of random tilts and twists towards the substrate caused by defects and strain. Althou...
Confocal µ-XRF is a relatively new variant of conventional µ-XRF that allows to visualize majoran... more Confocal µ-XRF is a relatively new variant of conventional µ-XRF that allows to visualize majorand trace element distributions in various materials in three dimensions . Either laboratory sources (i.e., micro-focus X-ray tubes) [1] or synchrotron sources can be employed for this type of investigations that can be readily employed for non-destructive depth profiling of multilayered materials, provided the individual layers feature a sufficiently clear (trace)elemental constrast and have thicknesses in the 5-50 µm range. When employing laboratory sources, a combination of two polycapillary (PC) X-ray lenses is used to resp. focus the primary beam and select the area from which fluorescent radiation can enter the detector [2]. A confocal µ-XRF tabletop set-up was constructed at the University of Antwerp by means of a Mo-anode microfocus X-ray tube. At HASYLAB BL L, an elliptically shaped single bounce capillary (SBC) [5] was used to define the primary beam while different PC half-lenses were used as secondary optic; a multilayer mirror was used to select a 1% energy-band from the bending magnet spectrum. A primary energy of 22.3 keV was employed.
A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray a... more A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray absorption near edge structure (XANES) measurements at the Cr K-edge already allowed us to establish that the photo-reduction of chromates to Cr(III) compounds is the cause of darkening of chrome yellow pigments (PbCr 1Àx S x O 4 , 0 # x # 0.8) in a number of paintings by Vincent van Gogh and in corresponding artificially aged paint models. A silicon drift detector (SDD) was employed to record the Cr-K XRF radiation in these X-ray micro beam-based measurements. However, in view of the limited count rate capabilities and collection solid angle of a single device, m-XRF and m-XANES employing single element SDDs (or similar) are primarily suited for collection of spectral data from individual points.
Annual review of analytical chemistry (Palo Alto, Calif.), 2013
We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were us... more We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were used for nondestructive analysis and characterization of pigments, paint microsamples, and/or entire paintings. We discuss the use of portable laboratory- and synchrotron-based instrumentation and describe several variants of X-ray fluorescence (XRF) analysis used for elemental analysis and imaging and combined with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Macroscopic and microscopic (μ-)XRF variants of this method are suitable for visualizing the elemental distribution of key elements in paint multilayers. Technical innovations such as multielement, large-area XRF detectors have enabled such developments. The use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that take place during natural pigment alteration processes. However, synchrotron-based combinations of μ-XRF, μ-XAS, and μ-XRD are suit...
Elemental distribution images acquired by imaging X-ray fluorescence analysis can contain high de... more Elemental distribution images acquired by imaging X-ray fluorescence analysis can contain high degrees of redundancy and weakly discernible correlations. In this article near real-time non-negative matrix factorization (NMF) is described for the analysis of a number of data sets acquired from samples of a bi-modal α+β Ti-6Al-6V-2Sn alloy. NMF was used for the first time to reveal absorption artefacts in the elemental distribution images of the samples, where two phases of the alloy, namely α and β, were in superposition. The findings and interpretation of the NMF results were confirmed by Monte Carlo simulation of the layered alloy system. Furthermore, it is shown how the simultaneous factorization of several stacks of elemental distribution images provides uniform basis vectors and consequently simplifies the interpretation of the representation.
Gene-targeted, apolipoprotein E and LDL receptor-double knockout (apoE/LDLR À / À ) mice represen... more Gene-targeted, apolipoprotein E and LDL receptor-double knockout (apoE/LDLR À / À ) mice represent a new animal model that displays severe hyperlipidemia and atherosclerosis. The aim of the present study was to show changes in histomorphology and in distribution of selected elements in atherosclerotic plaques of apoE/LDLR À / À mice fed egg-rich proatherosclerotic diet (5% egg-yolk lyophilisate) supplemented or not with perindopril (inhibitor of angiotensin converting enzyme; 2 mg/kg b.w.). Synchrotron radiation micro-X-ray fluorescence spectrometry was combined with histological stainings to determine distribution and concentration of trace and essential elements in atherosclerotic lesions. More advanced atherosclerotic lesions expressed by total area occupied by lipids (oil red-O staining) and by macrophages (CD68 immunohistochemistry) were observed in animals fed egg-rich diet. The perindopril treatment attenuated these effects. No significant differences were observed in the number of intimal smooth muscle cells (smooth muscle actin immunohistochemistry). In animals fed egg-rich diet significantly higher concentrations of Ca and significantly lower contents of S, Cl, , Fe, Cu, Zn and Se in atheromas were seen in comparison to chow diet-fed animals. After pharmacological treatment, concentrations of S, Cl, Fe, Cu, Zn and Se showed the tendency to achieve levels like in animals fed normal diet. K level differed only in group treated with perindopril. Concentration of P did not significantly vary in all experimental groups. Perindopril showed its potency to reduce atherosclerosis, as estimated by the size of the atheroma and content of pro-and antiatherogenic elements.
X-ray scanning microscopy relies on intensive nanobeams generated by imaging a highly brilliant s... more X-ray scanning microscopy relies on intensive nanobeams generated by imaging a highly brilliant synchrotron radiation source onto the sample with a nanofocusing X-ray optic. Here, using a Gaussian model for the central cone of an undulator source, the nanobeam generated by refractive X-ray lenses is modeled in terms of size, flux and coherence. The beam properties are expressed in terms of the emittances of the storage ring and the lateral sizes of the electron beam. Optimal source parameters are calculated to obtain efficient and diffraction-limited nanofocusing. With decreasing emittance, the usable fraction of the beam for diffraction-limited nanofocusing experiments can be increased by more than two orders of magnitude compared with modern storage ring sources. For a diffraction-limited storage ring, nearly the whole beam can be focused, making these sources highly attractive for X-ray scanning microscopy.
Spatially resolved X-ray absorption and fluorescence investigation with a micrometer-scale resolu... more Spatially resolved X-ray absorption and fluorescence investigation with a micrometer-scale resolution on actinide-containing samples provide information necessary for safety assessment of nuclear waste disposal. In this paper one example of such an experiment is presented. This example entails neptunium speciation in a fractured granite bore core from the Swedish Äspö Hard Rock Laboratory following a radiotracer experiment using µ-XAFS and µ-XRF. In order to probe micro-volumes below the surface in the granite samples and thereby avoid potential changes in the Np speciation during cutting of the bore core, a confocal irradiation-detection geometry is employed. µ-XAFS results for a selected granite bore core cross section with~3 nmol Np/g reveal that Np, originally introduced as Np(V) in the tracer cocktail, is present in the granite in its reduced Np(IV) form. The Np(IV) is often present as particles, tens of µm in size. Elemental distribution maps show the tracer Np to be located in fissures and permeable channels not larger than 100 µm. The Np distribution appears often correlated with Zn also present in some fissures. We observe small granite fissures containing Fe (presumably Fe(II)), where we do not detect any Np. It is feasible that inflowing Np(V) has a shorter residence time in large fractures, while in the smaller fissures migration is slower, leading to longer residence times, i.e., reaction times, where it is reduced to less soluble Np(IV) and becomes thereby immobilized.
The determination of trace element mass concentrations in ambient air with a time resolution high... more The determination of trace element mass concentrations in ambient air with a time resolution higher than one day represents an urgent need in atmospheric research. It involves the application of a specific technique both for the aerosol sampling and the subsequent analysis of the collected particles. Beside the intrinsic sensitivity of the analytical method, the sampling interval and thus the quantity of collected material that is available for subsequent analysis is a major factor driving the overall trace element detection power. This is demonstrated for synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) of aerosol samples collected with a rotating drum impactor (RDI) in hourly intervals and three particle size ranges. The total aerosol mass on the 1-h samples is in the range of 10 µg. An experimental detection of the nanogram amounts of trace elements with the help of synchrotron X-rays was only achievable by the design of a fit-forpurpose sample holder system, which considered the boundary conditions both from particle sampling and analysis. A 6-µm polypropylene substrate film has evolved as substrate of choice, due to its practical applicability during sampling and its suitable spectroscopic behavior. In contrast to monochromatic excitation conditions, the application of a 'white' beam led to a better spectral signal-to-background ratio. Despite the low sample mass, a counting time of less than 30 s per 1-h aerosol sample led to sufficient counting statistics. Therefore the RDI-SR-XRF method represents a high-throughput analysis procedure without the need for any sample preparation. The analysis of a multielemental mass standard film by SR-XRF, laboratory-based wavelength-dispersive XRF spectrometry and laboratory-based micro XRF spectrometry showed that the laboratory-based methods were no alternatives to the SR-XRF method with respect to sensitivity and efficiency of analysis.
This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Go... more This paper presents firm evidence for the chemical alteration of chrome yellow pigments in Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam). Noninvasive in situ spectroscopic analysis at several spots on the painting, combined with synchrotron-radiation-based X-ray investigations of two microsamples, revealed the presence of different types of chrome yellow used by Van Gogh, including the lightfast PbCrO4 and the sulfur-rich PbCr1-x Sx O4 (x≈0.5) variety that is known for its high propensity to undergo photoinduced reduction. The products of this degradation process, i.e., Cr(III) compounds, were found at the interface between the paint and the varnish. Selected locations of the painting with the highest risk of color modification by chemical deterioration of chrome yellow are identified, thus calling for careful monitoring in the future.
A hard x-ray scanning microscope based on nanofocusing refractive x-ray lenses is well suited for... more A hard x-ray scanning microscope based on nanofocusing refractive x-ray lenses is well suited for coherent x-ray diffraction imaging, in particular for scanning coherent diffraction microscopy also known as ptychography. Using this technique, the complex transmission function of the object can be obtained with a spatial resolution better than that given by the size of the nanofocus. In addition, the
Materials Research Society Symposium Proceedings, 2012
ABSTRACT Synchrotron-based X-ray techniques are used increasingly to characterize actinide elemen... more ABSTRACT Synchrotron-based X-ray techniques are used increasingly to characterize actinide element speciation in heterogeneous media related to nuclear waste disposal safety. Especially techniques offering added temporal, spatial and energy resolved information are advancing our understanding of f-element physics and chemistry in general and of actinide element waste disposal in particular. Examples of investigations of uranium containing systems using both highly (energy) resolved X-ray emission spectroscopy (HRXES) techniques and spatially resolved techniques with focused X-ray beams are presented in this paper: polarization dependent partial fluorescence yield X-ray absorption near edge structure (PD-PFY-XANES) spectroscopic studies of a single Cs2UO 2Cl4 crystal, which experimentally reveal a splitting of the σ, π and δ components of the 6d valence states [1], and characterization of UO2/Mo thin films prepared on different substrates using a combination of techniques (2D and 3D micro- and nano-X-ray fluorescence, XANES and both holographic and ptychographic tomography).
Stacks of elemental distribution images acquired by XRF can be difficult to interpret, if they co... more Stacks of elemental distribution images acquired by XRF can be difficult to interpret, if they contain high degrees of redundancy and components differing in their quantitative but not qualitative elemental composition. Factor analysis, mainly in the form of Principal Component Analysis (PCA), has been used to reduce the level of redundancy and highlight correlations. PCA, however, does not yield physically meaningful representations as they often contain negative values. This limitation can be overcome, by employing factor analysis that is restricted to non-negativity. In this paper we present the first application of the Python Matrix Factorization Module (pymf) on XRF data. This is done in a case study on the painting Saul and David from the studio of Rembrandt van Rijn. We show how the discrimination between two different Co containing compounds with minimum user intervention and a priori knowledge is supported by Non-Negative Matrix Factorization (NMF).
Micro-X-ray fluorescence ͑-XRF͒ is a rapidly evolving analytical technique which allows visualisi... more Micro-X-ray fluorescence ͑-XRF͒ is a rapidly evolving analytical technique which allows visualising the trace level metal distributions within a specimen in an essentially nondestructive manner. At second generation synchrotron radiation sources, detection limits at the sub-parts per million level can be obtained with micrometer resolution, while at third generation sources the spatial resolution can be better than 100 nm. Consequently, the analysis of metals within biological systems using micro-and nano-X-ray fluorescence imaging is a quickly developing field of research. Since X-ray fluorescence is a scanning technique, the elemental distribution within the sample should not change during analysis. Biological samples pose challenges in this context due to their high water content. A dehydration procedure is commonly used for sample preparation enabling an analysis of the sample under ambient temperature conditions. Unfortunately, a potential change in elemental redistribution during the sample preparation is difficult to verify experimentally and therefore cannot be excluded completely. Creating a cryogenic sample environment allowing an analysis of the sample under cryogenic condition is an attractive alternative but not available on a routine basis. In this article, we make a comparison between the elemental distributions obtained by micro-SR-XRF within a chemically fixed and a cryogenically frozen Daphnia magna, a model organism to study the environmental impact of metals. In what follows, we explore the potential of a dual detector setup for investigating a full ecotoxicological experiment. Next to conventional 2D analysis, dual detector X-ray fluorescence cryotomography is illustrated and the potential of its coupling with laboratory absorption micro-CT for investigating the tissue-specific elemental distributions within this model organism is highlighted.
Advances in Computational Methods for X-Ray Optics II, 2011
Modern hard x-ray scanning microscopes generate x-ray beams with lateral sizes well below 100 nm.... more Modern hard x-ray scanning microscopes generate x-ray beams with lateral sizes well below 100 nm. Characterizing these beams in terms of shape and size by conventional techniques is tedious, requires highly accurate test objects and stages, and yields only incomplete information. Since recently, we use a ptychographic scanning coherent diffraction imaging technique in order to characterize hard x-ray nano beams
ABSTRACT X-ray fluorescence images acquired using the Maia large solid-angle detector array and i... more ABSTRACT X-ray fluorescence images acquired using the Maia large solid-angle detector array and integrated real-time processor on the X-ray Fluorescence Microscopy (XFM) beamline at the Australian Synchrotron capture fine detail in complex natural samples with images beyond 100M pixels. Quantitative methods permit real-time display of deconvoluted element images and for the acquisition of large area XFM images and 3D datasets for fluorescence tomography and chemical state (XANES) imaging. This paper outlines the Maia system and analytical methods and describes the use of the large detector array, with a wide range of X-ray take-off angles, to provide sensitivity to the depth of features, which is used to provide an imaging depth contrast and to determine the depth of rare precious metal particles in complex geological samples.
18 Every infection is a battle for trace elements. Neutrophils migrate first to the infection 19 ... more 18 Every infection is a battle for trace elements. Neutrophils migrate first to the infection 19 site and accumulate quickly to high numbers. They fight pathogens by phagocytosis 20 and intracellular toxication. Additionally, neutrophils form neutrophil extracellular traps 21 (NETs) to inhibit extracellular microbes. Yet, neutrophil trace element characteristics 22 are largely unexplored. We investigated unstimulated and phorbol myristate acetate-23 stimulated neutrophils using synchrotron radiation X-ray fluorescence (SR-XRF) on 24 the sub-micron spatial resolution level. PMA activates pinocytosis, cytoskeletal 25 rearrangements and the release of NETs, all mechanisms deployed by neutrophils to 26 combat infection. 27 By analyzing Zn, Fe, Cu, Mn, P, S, and Ca, not only the nucleus but also vesicular 28 granules were identifiable in the elemental maps. Inductively Coupled Plasma Mass 29 Spectrometry (ICP-MS) revealed a neutrophil-specific composition of Zn, Fe, Cu, and 30 Mn in comparison with J774 and HeLa cells, indicating a neutrophil specific 31 metallome complying with their designated functions. 32 When investigating PMA-activated neutrophils, the SR-XRF analysis depicted typical 33 subcellular morphological changes: the transformation of nucleus and granules and 34 the emergence of void vacuoles. Mature NETs were evenly composed of Fe, P, S, 35 and Ca with occasional hot spots containing Zn, Fe, and Ca. An ICP-MS-based 36 quantification of NETs supernatants revealed a NETosis-induced decrease of soluble 37
X-ray nanobeams are unique non-destructive probes that allow direct measurements of the nanoscale... more X-ray nanobeams are unique non-destructive probes that allow direct measurements of the nanoscale strain distribution and composition inside the micrometer thick layered structures that are found in most electronic device architectures. However, the 2D scanning combined with reciprocal space mapping that has been used to achieve complete strain maps is extremely time consuming and as a result measurements are often constrained to a few or even single objects. Here we demonstrate that by special design of a nanofocused X-ray beam diffraction experiment we can (in a single 2D scan with no sample rotation) measure the individual strain and composition profiles of many structures in an array of upright standing nanowires. We make use of the observation that in the generic nanowire device configuration, which is found in high speed transistors, solar cells and LEDs, each wire exhibits very small degrees of random tilts and twists towards the substrate caused by defects and strain. Althou...
Confocal µ-XRF is a relatively new variant of conventional µ-XRF that allows to visualize majoran... more Confocal µ-XRF is a relatively new variant of conventional µ-XRF that allows to visualize majorand trace element distributions in various materials in three dimensions . Either laboratory sources (i.e., micro-focus X-ray tubes) [1] or synchrotron sources can be employed for this type of investigations that can be readily employed for non-destructive depth profiling of multilayered materials, provided the individual layers feature a sufficiently clear (trace)elemental constrast and have thicknesses in the 5-50 µm range. When employing laboratory sources, a combination of two polycapillary (PC) X-ray lenses is used to resp. focus the primary beam and select the area from which fluorescent radiation can enter the detector [2]. A confocal µ-XRF tabletop set-up was constructed at the University of Antwerp by means of a Mo-anode microfocus X-ray tube. At HASYLAB BL L, an elliptically shaped single bounce capillary (SBC) [5] was used to define the primary beam while different PC half-lenses were used as secondary optic; a multilayer mirror was used to select a 1% energy-band from the bending magnet spectrum. A primary energy of 22.3 keV was employed.
A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray a... more A combination of synchrotron radiation (SR) micro X-ray fluorescence (m-XRF) and XRF mode X-ray absorption near edge structure (XANES) measurements at the Cr K-edge already allowed us to establish that the photo-reduction of chromates to Cr(III) compounds is the cause of darkening of chrome yellow pigments (PbCr 1Àx S x O 4 , 0 # x # 0.8) in a number of paintings by Vincent van Gogh and in corresponding artificially aged paint models. A silicon drift detector (SDD) was employed to record the Cr-K XRF radiation in these X-ray micro beam-based measurements. However, in view of the limited count rate capabilities and collection solid angle of a single device, m-XRF and m-XANES employing single element SDDs (or similar) are primarily suited for collection of spectral data from individual points.
Annual review of analytical chemistry (Palo Alto, Calif.), 2013
We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were us... more We review methods and recent studies in which macroscopic to (sub)microscopic X-ray beams were used for nondestructive analysis and characterization of pigments, paint microsamples, and/or entire paintings. We discuss the use of portable laboratory- and synchrotron-based instrumentation and describe several variants of X-ray fluorescence (XRF) analysis used for elemental analysis and imaging and combined with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Macroscopic and microscopic (μ-)XRF variants of this method are suitable for visualizing the elemental distribution of key elements in paint multilayers. Technical innovations such as multielement, large-area XRF detectors have enabled such developments. The use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that take place during natural pigment alteration processes. However, synchrotron-based combinations of μ-XRF, μ-XAS, and μ-XRD are suit...
Elemental distribution images acquired by imaging X-ray fluorescence analysis can contain high de... more Elemental distribution images acquired by imaging X-ray fluorescence analysis can contain high degrees of redundancy and weakly discernible correlations. In this article near real-time non-negative matrix factorization (NMF) is described for the analysis of a number of data sets acquired from samples of a bi-modal α+β Ti-6Al-6V-2Sn alloy. NMF was used for the first time to reveal absorption artefacts in the elemental distribution images of the samples, where two phases of the alloy, namely α and β, were in superposition. The findings and interpretation of the NMF results were confirmed by Monte Carlo simulation of the layered alloy system. Furthermore, it is shown how the simultaneous factorization of several stacks of elemental distribution images provides uniform basis vectors and consequently simplifies the interpretation of the representation.
Gene-targeted, apolipoprotein E and LDL receptor-double knockout (apoE/LDLR À / À ) mice represen... more Gene-targeted, apolipoprotein E and LDL receptor-double knockout (apoE/LDLR À / À ) mice represent a new animal model that displays severe hyperlipidemia and atherosclerosis. The aim of the present study was to show changes in histomorphology and in distribution of selected elements in atherosclerotic plaques of apoE/LDLR À / À mice fed egg-rich proatherosclerotic diet (5% egg-yolk lyophilisate) supplemented or not with perindopril (inhibitor of angiotensin converting enzyme; 2 mg/kg b.w.). Synchrotron radiation micro-X-ray fluorescence spectrometry was combined with histological stainings to determine distribution and concentration of trace and essential elements in atherosclerotic lesions. More advanced atherosclerotic lesions expressed by total area occupied by lipids (oil red-O staining) and by macrophages (CD68 immunohistochemistry) were observed in animals fed egg-rich diet. The perindopril treatment attenuated these effects. No significant differences were observed in the number of intimal smooth muscle cells (smooth muscle actin immunohistochemistry). In animals fed egg-rich diet significantly higher concentrations of Ca and significantly lower contents of S, Cl, , Fe, Cu, Zn and Se in atheromas were seen in comparison to chow diet-fed animals. After pharmacological treatment, concentrations of S, Cl, Fe, Cu, Zn and Se showed the tendency to achieve levels like in animals fed normal diet. K level differed only in group treated with perindopril. Concentration of P did not significantly vary in all experimental groups. Perindopril showed its potency to reduce atherosclerosis, as estimated by the size of the atheroma and content of pro-and antiatherogenic elements.
X-ray scanning microscopy relies on intensive nanobeams generated by imaging a highly brilliant s... more X-ray scanning microscopy relies on intensive nanobeams generated by imaging a highly brilliant synchrotron radiation source onto the sample with a nanofocusing X-ray optic. Here, using a Gaussian model for the central cone of an undulator source, the nanobeam generated by refractive X-ray lenses is modeled in terms of size, flux and coherence. The beam properties are expressed in terms of the emittances of the storage ring and the lateral sizes of the electron beam. Optimal source parameters are calculated to obtain efficient and diffraction-limited nanofocusing. With decreasing emittance, the usable fraction of the beam for diffraction-limited nanofocusing experiments can be increased by more than two orders of magnitude compared with modern storage ring sources. For a diffraction-limited storage ring, nearly the whole beam can be focused, making these sources highly attractive for X-ray scanning microscopy.
Spatially resolved X-ray absorption and fluorescence investigation with a micrometer-scale resolu... more Spatially resolved X-ray absorption and fluorescence investigation with a micrometer-scale resolution on actinide-containing samples provide information necessary for safety assessment of nuclear waste disposal. In this paper one example of such an experiment is presented. This example entails neptunium speciation in a fractured granite bore core from the Swedish Äspö Hard Rock Laboratory following a radiotracer experiment using µ-XAFS and µ-XRF. In order to probe micro-volumes below the surface in the granite samples and thereby avoid potential changes in the Np speciation during cutting of the bore core, a confocal irradiation-detection geometry is employed. µ-XAFS results for a selected granite bore core cross section with~3 nmol Np/g reveal that Np, originally introduced as Np(V) in the tracer cocktail, is present in the granite in its reduced Np(IV) form. The Np(IV) is often present as particles, tens of µm in size. Elemental distribution maps show the tracer Np to be located in fissures and permeable channels not larger than 100 µm. The Np distribution appears often correlated with Zn also present in some fissures. We observe small granite fissures containing Fe (presumably Fe(II)), where we do not detect any Np. It is feasible that inflowing Np(V) has a shorter residence time in large fractures, while in the smaller fissures migration is slower, leading to longer residence times, i.e., reaction times, where it is reduced to less soluble Np(IV) and becomes thereby immobilized.
The determination of trace element mass concentrations in ambient air with a time resolution high... more The determination of trace element mass concentrations in ambient air with a time resolution higher than one day represents an urgent need in atmospheric research. It involves the application of a specific technique both for the aerosol sampling and the subsequent analysis of the collected particles. Beside the intrinsic sensitivity of the analytical method, the sampling interval and thus the quantity of collected material that is available for subsequent analysis is a major factor driving the overall trace element detection power. This is demonstrated for synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) of aerosol samples collected with a rotating drum impactor (RDI) in hourly intervals and three particle size ranges. The total aerosol mass on the 1-h samples is in the range of 10 µg. An experimental detection of the nanogram amounts of trace elements with the help of synchrotron X-rays was only achievable by the design of a fit-forpurpose sample holder system, which considered the boundary conditions both from particle sampling and analysis. A 6-µm polypropylene substrate film has evolved as substrate of choice, due to its practical applicability during sampling and its suitable spectroscopic behavior. In contrast to monochromatic excitation conditions, the application of a 'white' beam led to a better spectral signal-to-background ratio. Despite the low sample mass, a counting time of less than 30 s per 1-h aerosol sample led to sufficient counting statistics. Therefore the RDI-SR-XRF method represents a high-throughput analysis procedure without the need for any sample preparation. The analysis of a multielemental mass standard film by SR-XRF, laboratory-based wavelength-dispersive XRF spectrometry and laboratory-based micro XRF spectrometry showed that the laboratory-based methods were no alternatives to the SR-XRF method with respect to sensitivity and efficiency of analysis.
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Papers by Gerald Falkenberg