TopoTomo Beamline Research Articles

Characterization of a 2x3 Timepix assembly with a 500μm thick silicon sensor

The Timepix detector can be used for single photon counting or to perform time-over-threshold analyses on single events. By setting an energy threshold, photons can be selected according to their energy. Here, we present the characterization of an assembly of six Timepix chips, bonded to a monolithic 500 μ m thick silicon wafer.Measurements with monochromatic radiation were carried out at the Topo-Tomo beamline at the ANKA synchrotron. With these measurements, an energy calibration was performed and the presampling modulation transfer function (MTFpre) was evaluated for different threshold settings and different photon energies, leading to values from 16.75 to 25.2 mm−1 for a MTFpre of 10 %.The detector was also used for computed tomography in a lab setup with a micro-focus X-ray tube. For these measurements, the detector's thresholds were equalized in order to obtain optimally homogeneous flat field images. With this method, we can increase the dynamic range of the detector without overexposing outlier pixels.

Multi-contrast computed laminography at ANKA light source

X-ray computed laminography has been developed as a non-destructive imaging technique for inspecting laterally extended objects. Benefiting from a parallel-beam geometry, high photon flux of synchrotron sources and modern high-resolution detector systems, synchrotron radiation computed laminography (SRCL) results in a powerful three-dimensional microscopy technique. SRCL can be combined with different contrast modes, such as absorption, phase and dark-field contrasts, in order to provide complementary information for the same specimen. Here we show the development of SRCL at the TopoTomo beamline of the ANKA light source. A novel instrumentation design is reported and compared to the existing one. For this design, experimental results from different contrast modalities are shown.

In-line X-ray lensless imaging with lithium fluoride film detectors

In this work, we present preliminary in-line X-ray lensless projection imaging results at a synchrotron facility by using novel solid-state detectors based on non-destructive readout of photoluminescent colour centres in lithium fluoride thin films. The peculiarities of LiF radiation detectors are high spatial resolution on a large field of view, wide dynamic range, versatility and simplicity of use. These properties offered the opportunity to test a broadband X-ray synchrotron source for lensless projection imaging experiments at the TopoTomo beamline of the ANKA synchrotron facility by using a white beam spectrum (3–40 keV). Edge-enhancement effects were observed for the first time on a test object; they are discussed and compared with simulations, on the basis of the colour centre photoluminescence linear response found in the investigated irradiation conditions.

Optical characterisation of lithium fluoride detectors for broadband X-ray imaging

Novel X-ray imaging detectors based on photoluminescence of colour centres in lithium fluoride (LiF) have been proposed and tested for extreme ultraviolet, soft and hard X-rays up to 10keV. For the first time we present the optical characterisation of LiF crystals and thin films irradiated at the TOPO–TOMO beamline of synchroton light source Anka (Karlsruhe, Germany) in the energy range 6–40keV for different exposure times. Absorption and photoluminescence spectra were analysed to study the optical response of the LiF-based detectors. High resolved X-ray imaging of commercial test patterns has been obtained on LiF crystals and films by optical readout with a confocal laser scanning fluorescence microscope.

Synchrotron measurements of the energy response functions of CdTe Medipix2 MXR detectors with pixel pitches of 110 and 165 μm

The energy resolution of photon counting pixel detectors depends strongly on the pixel pitch. Small pixels increase the effects of characteristic X-rays and the sharing of charges between adjacent pixels. To investigate the effects of different pixel pitches, measurements with Medipix2 MXR detectors attached to CdTe sensors with pixel pitches of 110 and 165 μm were carried out at the Topo-Tomo beamline of the ANKA synchrotron at the Karlsruhe Institute of Technology (KIT). Photo peaks are measured at a number of energies and are used to calculate the fraction of events in the photo peak compared to the total. Finally, we investigate the linearity of the energy calibration curves as a function of the pixel pitch.

X-ray phase-contrast radiography using a filtered white beam with a grating interferometer

Abstract One of the most promising methods of phase-contrast imaging is the Talbot grating interferometry. We report about the optimization of the method for fast imaging, requiring reduced exposure times by keeping sufficient imaging contrast. To do this a new Talbot interferometer working with a broad energy bandwidth beam has been installed at the Topo–Tomo beamline at ANKA. We demonstrate the method with a filtered white beam and without the need of a source grating that is commonly used at moderate-emittance synchrotron sources. Taking advantage of a higher photon flux, the exposure time is significantly reduced. At the same time, images obtained with this setup show a sufficient visibility contrast of 25% on average, which opens the way for new applications in real-time measurements.

Dislocation generation related to micro-cracks in Si wafers: High temperature in situ study with white beam X-ray topography

The generation and propagation of dislocations in Si at high temperature is observed in situ with white beam X-ray topography. For the heating experiments a double ellipsoidal mirror furnace was installed at the Topo–Tomo beamline of the ANKA synchrotron light source, Research Centre Karlsruhe, Germany. Details of the experimental set-up and the first results on the occurrence of dislocations are presented. Artificial damage was generated in commercial (1 0 0) Si wafers using a nanoindenter with various loads. The applied forces for each set of indents were varied from 100 to 500 mN, respectively. After heating to approx. 790 °C large area transmission topographs were taken every 30 min which were then compared to room temperature topographs before and after heating. At the outset straight 60°-dislocations with b = a/2〈1 1 0〉 originate from the 500 mN indents into the direction of the strongest temperature gradient. After 60 min at constant temperature an increase in the length and number of the dislocations in other directions is also observed. As a result of the continual thermal stressing dislocations develop from the 100 mN indents too.

The micro-imaging station of the TopoTomo beamline at the ANKA synchrotron light source

The TopoTomo bending magnet beamline at the ANKA synchrotron facility in Karlsruhe (Germany) operates in the hard X-ray regime (above 6keV). Recently, an X-ray micro-imaging station has been installed at TopoTomo. For typical imaging applications, a filtered white beam or from 2009 on a double-multilayer monochromator is used. In order to optimize the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 14-bit dynamic range CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. Due to the moderate flux of the beamline compared to insertion-device beamlines on third generation light sources, special emphasis has been put on the efficiency of the detectors via a dedicated scintillator concept. The layout of the beamline optics makes optimal use of the coherence properties. Thus, absorption contrast, phase-contrast and analyzer-based imaging can be applied. Additionally, white beam synchrotron topography is performed, using digital indirect X-ray pixel detectors as well as X-ray film.

White beam synchrotron topography using a high resolution digital X-ray imaging detector

X-ray topography is a well known imaging technique to characterise strain and extended defects in single crystals. Topographs are typically collected on X-ray films. On the one hand such photographic films show a limited dynamic range and the production of films will be discontinued step by step in the near future. On the other hand new imaging detectors improved for X-ray tomography become more and more attractive even for topography because of increasing resolution, dynamic range, speed and active area. In this paper we report about the upgrade of the TOPO–TOMO beamline at the synchrotron light source ANKA, Research Centre Karlsruhe, with a high resolution digital camera for the topography use.