Hamburger Synchrotronstrahlungslabor Research Articles

Note: Grazing incidence small and wide angle x-ray scattering combined with imaging ellipsometry

The combination of grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence wide angle x-ray scattering (GIWAXS) with optical imaging ellipsometry is presented as an upgrade of the available measurement techniques at the wiggler beamline BW4 of the Hamburger Synchrotronstrahlungslabor. The instrument is introduced with the description of the alignment procedure to assure the measurement of imaging ellipsometry and GISAXS∕GIWAXS on the same sample spot. To demonstrate the possibilities of the new instrument examples of morphological investigation on films made of poly(3-hexylthiophene) and [6,6]-phenyl-C(61) butyric acid methyl ester as well as textured poly(9,9-dioctylfluorene-alt-benzo-thia-diazole) are shown.

Grazing incidence wide angle x-ray scattering at the wiggler beamline BW4 of HASYLAB

We present an upgrade of the available measurement techniques at the wiggler beamline BW4 of the Hamburger Synchrotronstrahlungslabor (HASYLAB) to grazing incidence wide angle x-ray scattering (GIWAXS). GIWAXS refers to an x-ray diffraction method, which, based on the measurement geometry, is perfectly suited for the investigation of the material crystallinity of surfaces and thin films. It is shown that the overall experimental GIWAXS setup employing a movable CCD-detector provides the capability of reliable and reproducible diffraction measurements in grazing incidence geometry. Furthermore, the potential usage of an additional detector enables the simultaneous or successive measurement of GIWAXS and grazing incidence small angle x-ray scattering (GISAXS). The new capability is illustrated by the microbeam GIWAXS measurement of a thin film of the conjugated polymer poly(3-octylthiophene) (P3OT). The investigation reveals the semicrystalline nature of the P3OT film by a clear identification of the wide angle scattering reflexes up to the third order in the [100]-direction as well as the first order in the [010]-direction. The corresponding microbeam GISAXS measurement on the present morphology complements the characterization yielding the complete sample information from subnanometer up to micrometer length scales.

Valence and environment of rare earth ions in CaAl 2O 4:Eu 2+,R 3+ persistent luminescence materials

The existence of the different R 2+/R 3+/R IV (R: rare earth) ions as well as the modifications in the structural environment around the dopant and co-dopants in CaAl 2O 4:Eu 2+,R 3+ persistent luminescence materials was studied by L III edge X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) measurements at Hamburger Synchrotronstrahlungslabor (HASYLAB) at Deutsches Elektronen-Synchrotron (DESY) (Hamburg, Germany). The measurements were carried out at 10 and 296 K for selected rare earth (co-)dopants (Eu 2+; Ce 3+, Nd 3+, Sm 3+, and Yb 3+). The XANES results indicated the co-existence of both divalent and trivalent europium in all co-doped CaAl 2O 4:Eu 2+,R 3+ materials, but only divalent europium in CaAl 2O 4:Eu 2+. The measurement temperature did not affect the XANES results. The interatomic distances extracted from the EXAFS data of the CaAl 2O 4:Eu 2+,R 3+ materials indicated that co-doping creates distortions around the Eu 2+ ions suggesting dopant aggregation.

Possibilities and limitations of synchrotron X-ray powder diffraction with double crystal and double multilayer monochromators for microscopic speciation studies

The performance of a combined microbeam X-ray fluorescence/X-ray powder diffraction (XRF/XRPD) measurement station at Hamburger Synchrotronstrahlungslabor (HASYLAB) Beamline L is discussed in comparison to that at European Synchrotron Radiation Facility (ESRF) ID18F/ID22. The angular resolution in the X-ray diffractograms is documented when different combinations of X-ray source, optics and X-ray diffraction detectors are employed. Typical angular resolution values in the range 0.3–0.5° are obtained at the bending magnet source when a ‘pink’ beam form of excitation is employed. A similar setup at European Synchrotron Radiation Facility beamlines ID18F and ID22 allows to reach angular resolution values of 0.1–0.15°. In order to document the possibilities and limitations for speciation of metals in environmental materials by means of Hamburger Synchrotronstrahlungslabor Beamline L X-ray fluorescence/X-ray powder diffraction setup, two case studies are discussed, one involved in the identification of the crystal phases in which heavy metals such as chromium, iron, barium and lead are present in polluted soils of an industrial site (Val Basento, Italy) and another involved in the speciation of uranium in depleted uranium particles (Ceja Mountains, Kosovo). In the former case, the angular resolution is sufficient to allow identification of most crystalline phases present while in the latter case, it is necessary to dispose of an angular resolution of ca. 0.2° to distinguish between different forms of oxidized uranium.

RE 3+ VUV d → f luminescence investigated by synchrotron radiation excitation at HASYLAB

Although known since many years, the vacuum ultraviolet (VUV) 4f n ↔ 4f n−15d transitions of heavier trivalent rare-earth ions have been investigated in detail only during the past decade. An essential pre-requisite was synchrotron radiation as a tunable source of photon excitation in the VUV range. Luminescence spectroscopy under state-selective VUV excitation turned out to be particularly useful in characterizing the 4f n ↔ 4f n−15d transitions. Most of the progress has been achieved at the Hamburger Synchrotronstrahlungslabor HASYLAB with its unique VUV luminescence facilities. The experiments stimulated calculations for a deep understanding of the transitions. Results of the main groups involved at HASYLAB will be compared. Besides the achievements, limitations and restrictions of the experiments and of the theoretical models get obvious. This may help to stimulate future work.

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB, beamline L

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm 2 active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm 2 silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni. Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al 2O 3. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits of 170 ng/l of As in xylem sap were achieved.

Preparation of tissue samples for X-ray fluorescence microscopy

As is well-known, trace elements, especially metals, play an important role in the pathogenesis of many disorders. The topographic and quantitative elemental analysis of pathologically changed tissues may shed some new light on processes leading to the degeneration of cells in the case of selected diseases. An ideal and powerful tool for such purpose is the Synchrotron Microbeam X-ray Fluorescence technique. It enables the carrying out of investigations of the elemental composition of tissues even at the single cell level. The tissue samples for histopathological investigations are routinely fixed and embedded in paraffin. The authors try to verify the usefulness of such prepared tissue sections for elemental analysis with the use of X-ray fluorescence microscopy. Studies were performed on rat brain samples. Changes in elemental composition caused by fixation in formalin or paraformaldehyde and embedding in paraffin were examined. Measurements were carried out at the bending magnet beamline L of the Hamburger Synchrotronstrahlungslabor HASYLAB in Hamburg. The decrease in mass per unit area of K, Br and the increase in P, S, Fe, Cu and Zn in the tissue were observed as a result of the fixation. For the samples embedded in paraffin, a lower level of most elements was observed. Additionally, for these samples, changes in the composition of some elements were not uniform for different analyzed areas of rat brain.

A new X-ray spectrometer with large focusing crystal analyzer

A new focusing spectrometer employing Johann geometry has been built and permanently installed at the wiggler beamline W1 at the Hamburger Synchrotron Strahlungslabor (HASYLAB) am Deutschen Elektronen Synchrotron (DESY). It is now available for user operation. The design of the spectrometer is optimized for the use of a large source spot size at the DORIS storage ring as well as for simple operation and robustness under user-mode conditions. Nevertheless, the ideal source for enlarging the number of possible applications in the future would be an undulator at one of the PETRA III beamlines. In the following the spectrometer design is described and boundary conditions such as the available energy range for future experiments are discussed. Two benchmark experiments, resonant inelastic X-ray scattering (RIXS) and X-ray absorption fluorescence spectroscopy (XAFS), on samples with complicated matrices demonstrate the performance of the new instrument.

Comparison of synchrotron radiation total reflection X-ray fluorescence excitation–detection geometries for samples with differing matrices

The linear polarization of synchrotron radiation (SR) in the orbital plane leads to a background reduction in total reflection X-ray fluorescence (TXRF) analysis if a side-looking detector is used. The optimum orientation of the sample carrier in a SR-TXRF experiment, however, is determined by a trade-off between the exploitation of the linear polarization, the efficiency of excitation and the solid angle of detection and depends on the nature and size of the sample. SR-TXRF measurements on different sample types and using different reflector orientations have been carried out at the Hamburger Synchrotronstrahlungslabor bending magnet beamline L. A NIST standard water sample, a steel sample and an oil standard were analyzed with both a horizontal and a vertical sample carrier orientation. Strongly scattering samples led to lower detection limits with a horizontal reflector whereas weakly scattering samples showed lower detection limits with a vertical reflector configuration. On an intentionally contaminated wafer absolute detection limits of 6.6 fg for Ni could be extrapolated.

Demands on a detector for intravenous coronary angiography—experience after 379 patients

At the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY, the NIKOS system was developed for intravenous coronary angiography. To date 379 patients were examined with this system. This made it possible to exactly determine the optimal parameters of the system. The system consists of six main components. One of them, the two-line detector, is described in detail. This ionization chamber with a horizontal pixel size of 0.4 mm has a large dynamic range and low noise as well as high quantum efficiency. The fourth version of the NIKOS-detector fulfils the requirements of intravenous coronary angiography with its dynamic range of up to 300 000:1 each at four different setup modes, an equivalent photon noise of maximal 7.6, and a spatial resolution of 1.25 lp/ mm in the minimum. The detective quantum efficiency reaches 85% at a readout time of 0.2 ms/ line , which is faster than the necessary 0.8 ms/ line . These parameters ensure that the image quality is not decreased by the detector.

An in situ cell for small-angle scattering experiments on nano-structured catalysts

The design, construction and operation of an in situ cell covering the temperature range from room temperature to 870 K with the sample in a controlled gas flow is demonstrated. The setup is designed specifically for acquiring small angle X-ray scattering data at the JUSIFA beam line at the Hamburger Synchrotronstrahlungslabor although it can be employed at other beam lines with only slight modifications. The cell is used for studying dynamic changes in size and morphology of nano structured catalyst particles.

The X-ray response of TlBr

We present the results of a series of X-ray measurements on several prototype TlBr detectors. The devices were fabricated from mono-crystalline material and were typically of size 2.7×2.7×0.8 mm3. The material is extremely pure, having impurity concentrations <100 ppm. The measured electron and hole mobility–lifetime products were found to be 3×10−4 and 1×10−5 cm2 V−1, respectively, which are about an order of magnitude higher than previously reported values. Three detectors were fabricated and extensively tested over the energy range 2.3–100 keV at three synchrotron radiation facilities: the Physikalisch-Technische Bundesanstalt (PTB) laboratory at the Berliner Elektronenspeicherring fur Synchrotronstrahlung (BESSY II), the European Synchrotron Radiation Research Facility (ESRF) and the Hamburger Synchrotron-strahlungslabor (HASYLAB) radiation facility. Room temperature energy resolutions under full-area illumination of 1.8 and 3.3 keV FWHM have been achieved at 5.9 and 59.95 keV, respectively. At reduced detector temperatures of −30°C, these fall to 800 eV and 2.6 keV FWHM, respectively. Under monochromatic pencil beam illumination, the measured energy resolutions at 6 and 60 keV were 664 eV and 3 keV FWHM at the same temperature. For energies <20 keV, the measured spectra display symmetric photopeaks. However, the peaks become increasingly tailed at higher energies. At the highest energies, the energy-losses due to the electrons and holes are clearly separated. Whilst the detectors gave reproducible results over 12 months of operation, it was observed that for synchrotron beam measurements above 45 keV, they were unstable, showing rate dependent gain shifts and polarization effects. These were not observed at lower energies. The spatial uniformity of the detectors was measured using a 50×50 μm2, 12 keV mono-energetic X-ray beam, raster scanned over the forward active area. Whilst two detectors were spatially uniform to a level commensurate with statistics, the third was not. In all cases, evidence was found for charge collection problems caused by field fringing.

Hard X-ray spectroscopy using a small-format TlBr array

We report X-ray measurements on a prototype 3 � 3 TlBr pixel array, produced to assess the technological feasibility of making a Fano limited imager, which can operate near room temperature. The device was fabricated on monocrystalline material of size 2.7 � 2.7 � 1.0 mm 3 . It has a pixel size of 350 � 350mm 2 and pitch of 450mm. Measurements were carried out on all pixels over the energy range 5.9–662 keV using radioactive sources. The leakage currents were found to be low enough to allow room-temperature operation, with typical energy resolutions of B20 keV FWHM at 59.95 keV under full-area illumination. At a reduced detector temperature of –301C, these fell to B4 keV FWHM. Although the spectral performance of the present array is currently impaired by material limitations, its spectral acuity was found to be greatly enhanced by the small pixel effect. Additional photon metrology was carried out at the Hamburger Synchrotron-strahlungslabor radiation facility. Under monochromatic pencil beam illumination, the measured energy resolutions at 20 keV were B3 keV FWHM at � 301C. The spatial uniformity of the array was measured using a 50 � 50mm 2 , 20 keV monoenergetic X-ray beam, raster scanned over the entire active area. The response, in terms of count rate, gain and energy resolution was found to be uniform at the few percent level, consistent with statistics. It was observed during these measurements, that the X-ray response of the pixels was unstable, showing time-dependent gain shifts indicative of polarization effects. The magnitude of the effect was proportional to the total energy deposition per unit time. Lastly, the use of TlBr arrays in nuclear medicine applications is discussed with particular emphasis on radio-guided surgical probes. Recommendations for an optimized design are given. r 2002 Elsevier Science B.V. All rights reserved.

High resolution x-ray spectroscopy using GaAs arrays

We have produced a number of small format gallium arsenide (GaAs) arrays to address the material, electronic, and technological problems that need to be solved in order to develop mega pixel, Fano-limited spectroscopic x-ray imagers. Results will be presented of a series of x-ray measurements carried out on a prototype 5×5 array, fabricated from 40 μm thick epitaxial GaAs. The device has pixel sizes of 200×200 μm2 and pitch 250 μm. As a preliminary investigation of performance, two pixels have been instrumented. Measurements from 5.9 to 98 keV were carried out both in our laboratory and at the Hamburger Synchrotronstrahlungslabor research facility in Hamburg, Germany. Both pixels were found to be remarkably uniform, both in their spectral and spatial response to x-rays. The average nonlinearity in the spectral response is &amp;lt;1% across the energy range 5.9–98 keV. Using a 12 keV, 20×20 μm2 pencil beam, the spatial uniformity was found to be better than 98% over the entire pixel surfaces, consistent with the statistical precision of the measurement. The energy resolution at −40 °C is 400 eV full width at half maximum (FWHM) at 5.9 keV rising to 700 eV FWHM at 98 keV. No difference in energy resolution was found between full area and pencil beam illumination. An analysis of the resolution function has shown that the detector is dominated by electronic noise at low energies and Fano noise at energies above 30 keV. By best-fitting the expected resolution function to the entire data set, we derive a Fano factor of 0.140±0.05, together with a charge transport factor as low as 1.4×10−3. Further improvement in the resolution function has been achieved by replacing the conventional resistive feedback preamplifiers with a new resistorless design, which provides a lower component of electronic noise. In this case, a resolution of 266 eV FWHM at 5.9 keV has been achieved at room temperature (23 °C) and 219 eV FWHM with only modest cooling (−31 °C). The expected Fano noise at this energy is ∼140 eV.

A high performance angle-resolving electron spectrometer

We report on our new versatile photoelectron spectrometer Angular Spectrometer for Photoelectrons with High Energy REsolution (ASPHERE) which is part of beamline W3.2 (photon energies from 5 to 40 eV) but also compatible with beamline BW3 (40–1500 eV) at the Hamburger Synchrotronstrahlungslabor (HASYLAB). ASPHERE is a 180° spherical analyzer ( r 0=100 mm) with a four-element input lens and is mounted on a two-axes goniometer with computer-controlled stepper motors which enables sequential angle-scanned measurements. The input lens is equipped with an iris aperture so that the angular resolution can be continuously adjusted from 0.2° to 5°. The fringe field of the condenser has been corrected for by tilting the angle of the input lens against the base plane of the hemispheres resulting in an overall energy resolution of 10 meV. To improve the speed of data acquisition three standard channeltron detectors are installed in the image plane of the analyzer which will be replaced by a multidetection system in the near future.

The residual gas analyzer system for the HASYLAB beamline vacuum system

At the Hamburger Synchrotronstrahlungslabor (HASYLAB) residual gas analyzer systems are used to permanently control the partial pressure of the beamline vacuum system. The system is used to detect leaks in beryllium windows terminating the beamline as well as searching for hydrocarbons to avoid mirror contamination. The system runs fully automatic and is easily accessible via the local ethernet. A server program allows the permanent registration of selected partial pressures. This tool allows to observe the temporal partial pressure development over an extended time period.

A high sensitive two-line detector with large dynamic range for intravenous coronary angiography

The medical community is highly interested in methods for non-invasive imaging of coronary arteries. One method under development is dichromography. This method allows imaging of small fast moving objects like the coronary arteries including distal parts and sidebranches after intravenous injection of contrast material. Two images with monochromatic X-rays at energies just below and above the K-edge of iodine at 33.17keV are simultaneously taken. After logarithmic subtraction coronary arteries down to 0.7mm diameter with extremely low iodine concentrations of 10mg/ml become visible.At the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY in Hamburg, Germany the system NIKOS was developed for dichromography. In this system the detector is one of the main components.This two-line detector is an ionization chamber for the two energies. The two gaps are separated by the drift cathode. A Frisch-grid for shielding the ions in a distance of 3mm defines the conversion room. The 336 anode strips per line with a length of 56mm in the direction of the beam are connected to the frontend electronics. The parameters of the current version of the detector in one setting are: noise equivalent of 7.6 photons, dynamic range of 300000:1, readout time for the two lines (672 pixels) 0.18ms.

Intravenous coronary angiography with synchrotron radiation

Coronary angiography is the established routine imaging modality for patients with coronary artery disease. In recent years, the number of these procedures has increased remarkably. Complications associated with this invasive approach are in the range of 1.5% and the mortality is 0.1%. A further reduction of risk appears difficult to achieve because of the invasive nature of the procedure. Therefore, efforts have been made to image coronary arteries by non-invasive or minimally invasive techniques. One method under development is dichromography. This technique is based on subtraction of two images at different energies. Dichromography allows imaging of small fast-moving objects like the coronary arteries including distal parts and sidebranches after intravenous injection of a contrast material. Two images with monochromatic x-rays just below and above the absorption K-edge of the contrast agent iodine at 33.17 keV are obtained simultaneously and logarithmically subtracted. Monochromatic x-rays of sufficient intensity to visualize coronary arteries of 1 mm diameter with a low iodine mass density of are only provided by synchrotron radiation. At the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY in Hamburg, Germany the system NIKOS was developed for dichromography. This system consists of six main parts: a wiggler beamline, a two beam monochromator, a safety system, a scanning device with a seat for the patient, a two-line detector, and a computer system. After initial experimental studies with dogs, human patients have been investigated since 1990. Results of investigated patients demonstrate the feasibility and safety of the method together with high diagnostic accuracy. All cases were follow-up investigations after bypass surgery or interventions like angioplasty with a balloon catheter or rotablation with a very fast milling tool. A large-scale study has been underway since June 1997 to validate the diagnostic sensitivity and specificity compared with selective coronary angiography.

Adaptive indirectly cooled monochromator crystals at HASYLAB.

The high-heat-load monochromator, based on the HASYLAB (Hamburger Synchrotronstrahlungslabor) 'Torii' design, has been used successfully for 2 years at the BW2 wiggler beamline. The bowing of the reflecting surface induced by the heat load and water pressure is compensated mechanically. This is achieved by mounting the specially shaped crystal in a bending mechanism and by heat transfer from the directly water-cooled crystal. We present the latest step in the development of this design. The piezoceramic-driven actuators are replaced by actuators based on the thermal expansion of copper rods. The direct water cooling of the crystal is replaced by a safer indirect water-cooling scheme. Characterization results of the crystal are presented. The Si(111) rocking-curve width at 9.5 keV was measured to be 8.3 arcsec under 500 W heat load.

Kinetic and microstructural studies of the crystallisation of coesite from quartz at high pressure

Abstract The kinetics of the α-quartz to coesite transition have been studied in the pressure range of 3.2 GPa to 5.2 GPa and in the temperature range 950 K–1175 K by in situ X-ray diffraction using a MAX80 cubic anvil high-pressure apparatus at the Hamburger Synchrotronstrah-lungslabor (HASYLAB). During the phase transition, X-ray diffraction patterns were collected at intervals of 60 s. The transformed volume fraction has been calculated from the diffracted intensities of the respective phases as a function of time. By fitting a fundamental rate equation for grain boundary nucleation and interface-controlled growth to the transformation-time data, rates of nucleation and growth have been calculated. A discrepancy between the experimental determined and theoretical calculated phase boundary is discussed. After quenching the samples, the reaction products could be investigated by TEM images. A specific feature of the synthesised coesite crystals was a concentrated microtwinning. Its influence on the crystal structure and thus on the thermodynamic behaviour of the α-quartz-coesite phase transition is illustrated.