Wolfgang Malzer

A new 3D micro X-ray fluorescence analysis set-up: First archaeometric applications

A new 3D micro X-ray fluorescence (micro-XRF) analysis method based on a confocal X-ray set-up is presented. The capabilities of this new method are evaluated and illustrated with depth sensitive investigations of paint layers in ancient Indian Mughal miniatures. Successive paint layers could be distinguished non-destructively with a depth resolution of about 10 μm. Major and minor elements are detectable and can be discriminated in different layers. New light could be shed on ancient painting techniques and materials with this new 3D micro-XRF set-up.

Reconstruction of thickness and composition of stratified materials by means of 3D micro X-ray fluorescence spectroscopy.

The recently developed 3D micro X-ray fluorescence spectroscopy (3D Micro-XRF) enables three-dimensional resolved, nondestructive investigation of elemental distribution in samples in the micrometer regime. Establishing a reliable quantification procedure is the precondition to render this spectroscopic method into a true analytical tool. One prominent field of application is the investigation of stratified material. A procedure for the quantitative reconstruction of the composition of stratified material by means of 3D Micro-XRF is proposed and validated. With the procedure, it is now possible to determine nondestructively the chemical composition and the thickness of layers. As no adequate stratified reference samples were available for validation, stratified reference material has been developed that is appropriate for 3D Micro-XRF or other depth-sensitive X-ray techniques.

Performance of a polycapillary halflens as focussing and collecting optic—a comparison

Polycapillary halflenses are widely used to focus X-ray radiation onto a small spot. Additionally they can reduce the field of view of a semiconductor detector when placed in front of one. In 3D micro X-ray fluorescence spectroscopy (3D Micro-XRF) with synchrotron radiation, two polycapillary halflenses are used in a confocal geometry. Up until now, characterization measurements in the focal plane have only been performed in the case of the lens focusing parallel radiation. Assumptions have been made, that in the other case, when isotropic radiation from a spot source is transported to a detector, the acceptance distribution in the focal plane is also Gaussian. We performed measurements with an electron beam as well as a proton beam which confirm this assumption. In addition, a comparison between measurements in collecting and focusing mode show differences in spot size and transmission. These differences exemplify the fact that there is not one global spot size or transmission function of a polycapillary halflens. Illumination and divergence effects can alter both characteristic lens parameters.

3D Micro PIXE—a new technique for depth-resolved elemental analysis

A novel experimental technique, 3D micro-particle-induced X-ray emission (PIXE) is described in the present paper. 3D Micro-PIXE is realized by using an X-ray optic in front of the detector, thus creating a confocal arrangement together with the focused proton micro-beam. This confocal setup defines a probing volume from which information on elemental distribution is obtained. If a sample is moved through the probing volume, depth-resolved measurements become possible. The confocal setup was characterized with respect to its spatial and depth resolution. As an example of application for this new non-destructive analytical technique, an archaeological ceramic fragment was examined. A first approach to simulate the complex experimental results is performed. The potential of 3D micro-PIXE to provide advanced qualitative information on the elemental distribution in the sample is discussed.

Chemical U-Th-Pb dating of monazite by 3D-Micro X-ray fluorescence analysis with synchrotron radiation

A confocal set-up for three-dimensional (3D) micro X-ray fluorescence (micro-XRF) was used at the mySpot beamline at BESSY II, which allows compositional depth profiling for various applications. We present results obtained with a confocal 3D micro-XRF set-up for chemical age dating using the U, Th and Pb concentrations of monazite within rock thin sections. The probing volume was determined to be approximately 21 × 21 × 24 μm 3 for W- L α using an excitation energy of 19 keV. The relative detection limits particularly for Pb are below 10 ppm (for counting times of 1000 s). Therefore, this 3D micro-XRF set-up is suitable for dating of minerals with low Pb concentrations as long as all Pb is radiogenic, allowing spatial resolution comparable to ion microprobe or laser ablation techniques. The set-up was tested on monazites that are well characterized by isotopic techniques and have a wide range of ages, varying from 20 Ma to 1.82 Ga. Reference materials (GM3, F6, 3345) can be reproduced within error. The spread in the ages of all points determined by 3D micro-XRF is within 8 % of the isotopic reference value. The average 3D micro-XRF dates reproduce the reference ages with discrepancies between 10 and 13 Ma which translate to deviations of 1–4 %. Younger monazite samples from the European Alps (Baceno2, Bi9801) show slightly older 3D micro-XRF dates than those determined by isotopic techniques and table-top micro-XRF on whole grains. We interpret this to be related to age heterogeneities smaller than the spatial resolution and/or contributions by common Pb, which is a limitation for this technique. The method was then applied to monazites of unknown age from sapphirine-bearing granulites originating from the Gruf Complex (Alps, N-Italy). The 3D micro-XRF mean date was determined as 33 ± 4.4 Ma (2 σ) and was verified by ID-TIMS techniques. This age can be reliably interpreted as the age of the high-temperature (H T ) event because the monazites are included in and intergrown with H T minerals (sapphirine, high-Al orthopyroxene).

Reconstruction Procedure for 3D Micro X-ray Absorption Fine Structure

A new approach for chemical speciation in stratified systems using 3D Micro-XAFS spectroscopy is developed by combining 3D Micro X-ray Fluorescence Spectroscopy (3D Micro-XRF) and conventional X-ray Absorption Fine Structure Spectroscopy (XAFS). A prominent field of application is stratified materials within which depth-resolved chemical speciation is required. Measurements are collected in fluorescence mode which in general lead to distorted spectra due to absorption effects. Developing a reliable reconstruction algorithm for obtaining undistorted spectra for superficial and in-depth layers is proposed and validated. The developed algorithm calculates the attenuation coefficients of the analyte for the successive layers facilitating a new spectroscopic tool for three-dimensionally resolved nondestructive chemical speciation.

X-ray Fluorescence Analysis of Iron Gall Inks, Pencils and Coloured Crayons

Abstract The qualitative and quantitative investigation of historical writing materials using micro X-ray fluorescence analysis (micro-XRF) is a suitable method for obtaining ‘composition fingerprints’ of different inks and coloured crayons. The quantitative analysis is based on a model that takes into account the heterogeneity and the layer structure of historical samples. Starting from these composition fingerprints, it is possible to distinguish between different iron gall inks used by an individual artist in order to establish a chronology of their use and, furthermore, to date unknown fragments that have not been integrated into the oeuvre of an artist until now. Qualitative and quantitative analyses of several manuscripts of Johann Wolfgang von Goethe clarify the chronology within the genesis of these works. Investigation of Achim von Arnims manuscript ‘Studien zu Naturwissenschaften’ indicated that various degradation mechanisms of iron gall inks could also be related to different inorganic compositions. Further measurements on coloured crayons in Friedrich Nietzsches notebooks reveal that it is possible to distinguish between different notes written by Nietzsche and his successors. Finally the analyses of two different pencils from Goethes work shows that it might be possible to distinguish between sketches completed before and after 1800.

Analysis of low Z elements on Si wafer surfaces with synchrotron radiation induced total reflection X-ray fluorescence at SSRL, Beamline 3-3: comparison of droplets with spin coated wafers☆

Abstract The unique properties of synchrotron radiation, such as high incident flux combined with low divergence, its linear polarization and energy tunability, make it an ideal excitation source for total reflection X-ray fluorescence (TXRF) spectroscopy in order to non-destructively detect trace impurities of transition metals on Si wafer surfaces. When used with a detector suitable for the determination of low energy radiation this technique can be extended to the detection of low-Z elements, such as Al, Na and Mg. Experiments have been performed at SSRL Beamline 3-3, a bending magnet beamline using monochromatic radiation from a double multilayer monochromator. The wafer was mounted vertically in front of the detector, which was aligned along the linear polarization vector of the incoming synchrotron radiation. This configuration allows the detector to accept a large solid angle as well as to take advantage of the reduced scattered X-ray intensity emitted in the direction of the linear polarization vector. A comparison between droplet samples and spin coated samples was done, in order to compare the capabilities of vapor phase decomposition (VPD-TXRF) with conventional SR-straight-TXRF. Detection limits in the range of 50 fg corresponding to 2E10 atoms/cm2 have been obtained for Na. The spin coated samples, prepared from solutions containing an equal amount of Na, Mg and Al showed an unexpected result when performing a scan of the angle of incidence of the incoming X-rays suggesting a different adsorption behavior of the elements in a multielement solution on the wafer surface. The observation of this behavior is important because the spin coating technique is the standard method for the preparation of surface standards in semiconductor quality control. This effect could be characteristic of the Na, Mg, Al solution used, but the angle dependence of the fluorescence signal of a standard should always be investigated before using the standard for calibration of the apparatus and quantification.

Development of a nondestructive method for underglaze painted tiles—demonstrated by the analysis of Persian objects from the nineteenth century

AbstractThe paper presents an analytical method developed for the nondestructive study of nineteenth-century Persian polychrome underglaze painted tiles. As an example, 9 tiles from French and German museum collections were investigated. Before this work was undertaken little was known about the materials used in pottery at that time, although the broad range of colors and shades, together with their brilliant glazes, made these objects stand out when compared with Iranian ceramics of the preceding periods and suggested the use of new pigments, colorants, and glaze compositions. These materials are thought to be related to provenance and as such appropriate criteria for art-historical attribution. The analytical method is based on the combination of different nondestructive spectroscopic techniques using microfocused beams such as proton-induced X-ray emission/proton-induced γ-ray emission, X-ray fluorescence, 3D X-ray absorption near edge structure, and confocal Raman spectroscopy and also visible spectroscopy. It was established to address the specific difficulties these objects and the technique of underglaze painting raise. The exact definition of the colors observed on the tiles using the Natural Color System®© helped to attribute them to different colorants. It was possible to establish the presence of Cr- and U-based colorants as new materials in nineteenth-century Persian tilemaking. The difference in glaze composition (Pb, Sn, Na, and K contents) as well as the use of B and Sn were identified as a potential marker for different workshops. FigureUV fluorescence and visible spectroscopy are two of the non-destructive analytical methods used to investigate the coloring agents of underglaze painted tiles. Imaging of the uranium-containing areas was carried out by UV photography and identification of the chemical species by visible spectroscopy.

3D Micro-XRF for Cultural Heritage Objects: New Analysis Strategies for the Investigation of the Dead Sea Scrolls

A combination of 3D micro X-ray fluorescence spectroscopy (3D micro-XRF) and micro-XRF was utilized for the investigation of a small collection of highly heterogeneous, partly degraded Dead Sea Scroll parchment samples from known excavation sites. The quantitative combination of the two techniques proves to be suitable for the identification of reliable marker elements which may be used for classification and provenance studies. With 3D micro-XRF, the three-dimensional nature, i.e. the depth-resolved elemental composition as well as density variations, of the samples was investigated and bromine could be identified as a suitable marker element. It is shown through a comparison of quantitative and semiquantitative values for the bromine content derived using both techniques that, for elements which are homogeneously distributed in the sample matrix, quantification with micro-XRF using a one-layer model is feasible. Thus, the possibility for routine provenance studies using portable micro-XRF instrumentation on a vast amount of samples, even on site, is obtained through this work.