Oliver Scharf

Discovering Vanished Paints and Naturally Formed Gold Nanoparticles on 2800 Years Old Phoenician Ivories Using SR-FF-MicroXRF with the Color X-ray Camera

Phoenician ivory objects (8(th) century B.C., Syria) from the collections of the Badisches Landesmuseum, Karlsruhe, Germany, have been studied with full field X-ray fluorescence microimaging, using synchrotron radiation (SR-FF-microXRF). The innovative Color X-ray Camera (CXC), a full-field detection device (SLcam), was used at the X-ray fluorescence beamline of the ANKA synchrotron facility (ANKA-FLUO, KIT, Karlsruhe, Germany) to noninvasively study trace metal distributions at the surface of the archeological ivory objects. The outstanding strength of the imaging technique with the CXC is the capability to record the full XRF spectrum with a spatial resolution of 48 μm on a zone of a size of 11.9 × 12.3 mm(2) (264 × 264 pixels). For each analyzed region, 69696 spectra were simultaneously recorded. The principal elements detected are P, Ca, and Sr, coming from the ivory material itself; Cu, characteristic of pigments; Fe and Pb, representing sediments or pigments; Mn, revealing deposited soil minerals; Ti, indicating restoration processes or correlated with Fe sediment traces; and Au, linked to a former gilding. This provides essential information for the assessment of the original appearance of the ivory carvings. The determined elemental maps specific of possible pigments are superimposed on one another to visualize their respective distributions and reconstruct the original polychromy and gilding. Reliable hypotheses for the reconstruction of the original polychromy of the carved ivories are postulated on this basis.

Pushing the limits for fast spatially resolved elemental distribution patterns

A new setup for fast spatially resolved measurements of elemental trace amounts under total reflection conditions using a new colour X-ray camera is described. Samples prepared on conventional total reflection X-ray fluorescence (TXRF) reflectors were measured at BESSY II synchrotron. A spatial resolution of 50 × 50 μm2 was obtained, while the required time for the investigation of a 10 × 10 mm2 sample is 30 seconds. The set-up is up to 350 times faster than conventional X-ray fluorescence systems for elemental traces. The major components of the X-ray camera are polycapillary optics and a pn-CCD chip with an active area of 13 × 13 mm2. This area is divided into 264 × 264 pixels of 48 × 48 μm2. A full X-ray spectrum with a resolution of 152 eV @ 5.9 keV and a chip temperature of 246 K is recorded for each pixel. The chip has a read-out rate of 400 Hz.

Slicing – a new method for non destructive 3D elemental sensitive characterization of materials

Recent advances in synchrotron sources and detector technology have led to substantial improvements in spatial resolution and detection limits for X-ray fluorescence analysis (XRF). However, the non-destructive three-dimensional elemental sensitive characterization of samples remains a challenge. We demonstrate the use of the so-called “Color X-ray Camera” (CXC) for 3D measurements for the first time. The excitation of the sample is realized with a thin sheet-beam. The stepwise movement of the sample allows getting the elemental distribution for each layer with one measurement. These layers can be combined to a full 3D dataset for each element afterwards. Since the information is collected layer by layer, there is no need to apply reconstruction techniques, which quite often are the reason for artifacts in the results achieved by computed tomography (CT). The field of applications is wide, as the 3D elemental distribution of a material contains clues to processes inside the samples from a variety of origins. The technique is of special interest and well suited for biological specimens, because their light matrix minimizes restricting absorption effects. Measurement examples of a hornet and the teeth of a Sorex araneus are shown.

Sub-pixel resolution with a color X-ray camera

The color X-ray camera SLcam® is a full-field, single photon detector providing scanning-free, energy and spatially resolved X-ray imaging. Spatial resolution is achieved with the use of polycapillary optics guiding X-ray photons from small regions on a sample to distinct energy dispersive pixels on a charged-coupled device detector. Applying sub-pixel resolution, signals from individual capillary channels can be distinguished. Therefore, the SLcam® spatial resolution, which is normally limited to the pixel size of the charge-coupled device, can be improved to the size of individual polycapillary channels. In this work a new approach to a sub-pixel resolution algorithm comprising photon events also from the pixel centers is proposed. The details of the employed numerical method and several sub-pixel resolution examples are presented and discussed.

Shading in TXRF: calculations and experimental validation using a color X-ray camera

Absorption effects in total reflection X-ray fluorescence (TXRF) analysis are important to consider, especially if external calibration is to be applied. With a color X-ray camera (CXC), that enables spatially and energy resolved XRF analysis, the absorption of the primary beam was directly visualized for μL-droplets and an array of pL-droplets printed on a Si-wafer with drop-on-demand technology. As expected, deposits that are hit by the primary beam first shade subsequent droplets, leading to a diminished XRF signal. This shading effect was quantified with enhanced precision making use of sub-pixel analysis that improves the spatial resolution of the camera. The measured absorption was compared to simulated results using three different model calculations. It was found they match very well (average deviation < 10%). Thus errors in quantification due to absorption effects can be accounted for in a more accurate manner.

The charge of solid-liquid interfaces measured by x-ray standing waves and streaming current.

Measurements of ion distributions at a charged solid-liquid interface using X-ray standing waves (XSW) are presented. High energy synchrotron radiation (17.48 keV) is used to produce an XSW pattern inside a thin water film on a silicon wafer. The liquid phase is an aqueous solution containing Br and Rb ions. The surface charge is adjusted by titration. Measurements are performed over a pH range from 2.2-9, using the native Si oxide layer and functional (amine) groups as surface charge. The Debye length, indicating the extension of the diffuse layer, could be measured with values varying between 1-4 nm. For functionalized wafers, the pH dependent change from attraction to repulsion of an ion species could be detected, indicating the isoelectric point. In combination with the measurement of the streaming current, the surface charge of the sample could be quantified.

Energy Dispersive X-Ray Diffraction Imaging

Position resolved structural information from polycrystalline materials is usually obtained via micro beam techniques illuminating only a single spot of the specimen. Multiplexing in reciprocal space is achieved either by the use of an area detector or an energy dispersive device. Alternatively spatial information may be obtained simultaneously from a large part of the sample by using an array of parallel collimators between the sample and a position sensitive detector which suppresses crossfire of radiation scattered at different positions in the sample. With the introduction of an X-ray camera based on an energy resolving area detector (pnCCD) we could combine this with multiplexing in reciprocal space.

Synchrotron radiation micro X-ray fluorescence spectroscopy of thin structures in bone samples: comparison of confocal and color X-ray camera setups

To find the ideal synchrotron radiation induced imaging method for the investigation of trace element distributions in bone tissue, experiments with a scanning confocal micro X-ray fluorescence system and a full-field color X-ray camera setup were performed.

Full-Field X-ray Fluorescence Microscopy Using a Color X-ray Camera

Introduction Elemental imaging of several elements simultaneously and with detection limits in the ppb range is achieved by synchrotron-based X-ray fluorescence microscopy, also often referred to as micro-X-ray fluorescence (MXRF). This has been shown, for example, by imaging Cu and U distribution in contaminated sediments [1] and P, Ca, and Zn distribution imaging of single cells and mitochondria [2]. A review on environmental application can be found in reference [3]. XRF micro-probes are available at synchrotrons all around the world and allow for 2D imaging with spatial resolution from several micrometers down to the nanometer range (30–100 nm); the latter mainly at thirdgeneration synchrotrons. X-ray fluorescence (XRF). Interaction of X-rays with matter is in general dominated by the absorption of photons to generate photoelectrons. Because of the relatively high energy of X-ray photons, core shell electrons are often targeted by this process. Relaxation of the core hole occurs by a transition of an outer shell electron and emission of the transition energy as either an Auger electron or a photon, usually in the X-ray energy range. The emitted fluorescent X-ray photon is characteristic of the excited element. This process is the basis for qualitative and quantitative determination of the elements present in the specimen, as well as XRF microscopy. As in other types of microscopy, MXRF can be performed in scanning mode or in full-field mode (Figure 1). Full-field MXRF. In the full-field MXRF mode, the full sample is illuminated by the X rays from the source, and the fluorescence is guided by an optic to the fluorescence array detector. This is illustrated in Figure 1a. Horizontal and vertical slit systems can be used to shape the beam. However, most MXRF setups operate in scanning mode, which means the sample is moved through a focused primary X-ray beam that excites the fluorescent X rays. A single element fluorescence detector can be used. This is illustrated in Figure 1b. The scanning mode comes with disadvantages regarding in situ applications where the sample must remain fairly static or where the sample is brittle or in other ways sensitive to movements. Here full-field MXRF is advantageous. An example is the imaging of elemental distributions in droplets (10–20 μL containing Mn, Ni, Cu, and Sc) while drying. This is shown in Figure 2. The droplets were allowed to dry undisturbed while the elemental information was recorded. Full-field MXRF allows for fast imaging of large areas (for example, 12×12 mm2 at 1,000 frames per second and 264×264 pixels) and therefore simultaneous detection of elemental changes over the entire field of view, which can be important for certain in situ applications. However, the detectability of each element will depend on the fluorescence yield of the element and the total counts acquired. Thus, the recording frequency will be limited by the need to acquire enough counts for detecting specific elements. Full-field MXRF also allows fast 3D elemental imaging by taking images at different depths of the sample using a sheet beam.