Tilo Baumbach

High-resolution x-ray scattering from thin films and multilayers

Part 1 Experimental realization: basic elements of an equipment resolution elements diffractometers and reflectometers. Part 2 The theory of X-ray diffraction and its realization by the experiment: kinematical X-ray scattering from ideal crystals kinematical X-ray diffraction from deformed thin layers kinematical X-ray diffraction from randomly disturbed layers dynamical X-ray diffraction in perfect layers dynamical X-ray diffraction in slightly deformed layers optical reflection of X-rays from ideal layers optical reflection of X-rays from layers with rough interfaces dynamical X-ray diffraction in strongly asymmetric cases grazing incidence diffraction (GID). Appendices: elements of the formal theory of scattering structure factors, dispersion corrections and extinction length.

High-Resolution X-Ray Scattering

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High-resolution three-dimensional imaging of flat objects by synchrotron-radiation computed laminography

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Hydrophobic Liquid-Infused Porous Polymer Surfaces for Antibacterial Applications

Computed laminography with synchrotron radiation is developed and carried out for three-dimensional imaging of flat, laterally extended objects with high spatial resolution. Particular experimental conditions of a stationary synchrotron source have been taken into account by a scanning geometry different from that employed with movable conventional laboratory x-ray sources. Depending on the mechanical precision of the sample manipulation system, high spatial resolution down to the scale of 1μm can be attained nondestructively, even for objects of large lateral size. Furthermore, high beam intensity and the parallel-beam geometry enables easy use of monochromatic radiation for optimizing contrast and reducing imaging artifacts. Simulations and experiments on a test object demonstrate the feasibility of the method. Application to the inspection of solder joints in a flip-chip bonded device shows the potential for quality assurance of microsystem devices.

LSO-Based Single Crystal Film Scintillator for Synchrotron-Based Hard X-Ray Micro-Imaging

Biofilms represent a fundamental problem in environmental biology, water technology, food hygiene as well as in medical and technical systems. Recently introduced slippery liquid-infused porous surface (SLIPS) showed great promise for preventing biofilm formation owing to the low surface energy of such surface in combination with its self-cleaning properties. In this study we demonstrated a novel hydrophobic liquid-infused porous poly(butyl methacrylate-co-ethylene dimethacrylate) surface (slippery BMA-EDMA) with bacteria-resistance in BM2 mineral medium and long-term stability in aqueous environments. We showed that the slippery BMA-EDMA surface prevents biofilm formation of different strains of opportunistic pathogen Pseudomonas aeruginosa for at least up to 7 days in low nutrient medium. Only ∼1.8% of the slippery surface was covered by the environmental P. aeruginosa PA49 strain under investigation. In uncoated glass controls the coverage of surfaces reached ∼55% under the same conditions. However, in high nutrient medium, more relevant to physiological conditions, the biofilm formation on the slippery surface turned out to be highly dependent on the bacterial strain. Although the slippery surface could prevent biofilm formation of most of the P. aeruginosa strains tested (∼1% surface coverage), the multiresistant P. aeruginosa strain isolated from wastewater was able to cover up to 12% of the surface during 7 days of incubation. RAPD-PCR analysis of the used P. aeruginosa strains demonstrated their high genome variability, which might be responsible for their difference in biofilm formation on the slippery BMA-EDMA surface. The results show that although the slippery BMA-EDMA surface has a great potential against biofilm formation, the generality of its bacteria resistant properties is still to be improved.

On the implementation of computed laminography using synchrotron radiation

X-ray detector systems are powerful tools: in combination with tomographic methods they provide volumetric data of samples in a non-destructive manner which is of high interest for, e.g., biology, medicine or materials research. The detector able to provide images with submicrometer spatial resolution frequently consists of a scintillator screen, light microscopy optics and a digital camera. Here, the scintillator converts the X-rays into a visible light image which is projected onto the camera by the light optics. In order to perform high resolution imaging Single Crystal Film (SCF) scintillators 1 mum to 30 mum thin are required due to the limited depth of focus of the microscopy optics. Thin SCFs can be obtained via liquid phase epitaxy (LPE). A drawback is that a detector working with SCFs suffers from low efficiency (2% at 50 keV) owing to their limited thickness. The detective quantum efficiency (DQE) is here mainly limited by the low absorption of X-rays and the light yield in the thin scintillator layer. Performances, i.e absorption, light yield, afterglow of operational systems at the European Synchrotron Radiation Facility (ESRF) using YAG:Ce (Y3Al5O12:Ce), LAG:Eu (Lu3Al5O12:Eu) and GGG:Eu (Gd3Ga5O12:Eu) scintillators will be presented and compared to new LSO:Tb (Lu2SiO5:Tb) scintillators developed in the framework of an European project , . A new concept to improve the efficiency of detection in the 20 keV - 40 keV energy range with 1 mum spatial resolution will be presented. This concept based on multilayer scintillators is realised by the LPE process as well. First results will be illustrated with X-ray images and will demonstrate the absorption efficiency improvement of the X-ray detector. The expected performance is 7 times better than the LAG-based scintillators.

Phase-contrast and holographic computed laminography

Hard x rays from a synchrotron source are used in this implementation of computed laminography for three-dimensional (3D) imaging of flat, laterally extended objects. Due to outstanding properties of synchrotron light, high spatial resolution down to the micrometer scale can be attained, even for specimens having lateral dimensions of several decimeters. Operating either with a monochromatic or with a white synchrotron beam, the method can be optimized to attain high sensitivity or considerable inspection throughput in synchrotron user and small-batch industrial experiments. The article describes the details of experimental setups, alignment procedures, and the underlying reconstruction principles. Imaging of interconnections in flip-chip and wire-bonded devices illustrates the peculiarities of the method compared to its alternatives and demonstrates the wide application potential for the 3D inspection and quality assessment in microsystem technology.

A hierarchical view on material formation during pulsed-laser synthesis of nanoparticles in liquid.

In-line phase contrast is combined with laminography to image in three dimensions regions of interest in laterally extended flat specimens of weak absorption contrast. The principle of the method and a theoretical description of the imaging process are outlined. The present instrumental implementation enables reconstructing nondestructively the internal structure at different lateral specimen positions with micron resolution. The feasibility and application potential are demonstrated for both phase-contrast and holographic (i.e., using phase retrieval) laminography by the three-dimensional imaging of fuel-cell diffusion layers.

X-ray phase-contrast in vivo microtomography probes new aspects of Xenopus gastrulation

Pulsed-laser assisted nanoparticle synthesis in liquids (PLAL) is a versatile tool for nanoparticle synthesis. However, fundamental aspects of structure formation during PLAL are presently poorly understood. We analyse the spatio-temporal kinetics during PLAL by means of fast X-ray radiography (XR) and scanning small-angle X-ray scattering (SAXS), which permits us to probe the process on length scales from nanometers to millimeters with microsecond temporal resolution. We find that the global structural evolution, such as the dynamics of the vapor bubble can be correlated to the locus and evolution of silver nanoparticles. The bubble plays an important role in particle formation, as it confines the primary particles and redeposits them to the substrate. Agglomeration takes place for the confined particles in the second bubble. Additionally, upon the collapse of the second bubble a jet of confined material is ejected perpendicularly to the surface. We hypothesize that these kinetics influence the final particle size distribution and determine the quality of the resulting colloids, such as polydispersity and modality through the interplay between particle cloud compression and particle release into the liquid.

Charge Summing in Spectroscopic X-Ray Detectors With High-Z Sensors

An ambitious goal in biology is to understand the behaviour of cells during development by imaging—in vivo and with subcellular resolution—changes of the embryonic structure. Important morphogenetic movements occur throughout embryogenesis, but in particular during gastrulation when a series of dramatic, coordinated cell movements drives the reorganization of a simple ball or sheet of cells into a complex multi-layered organism. In Xenopus laevis, the South African clawed frog and also in zebrafish, cell and tissue movements have been studied in explants, in fixed embryos, in vivo using fluorescence microscopy or microscopic magnetic resonance imaging. None of these methods allows cell behaviours to be observed with micrometre-scale resolution throughout the optically opaque, living embryo over developmental time. Here we use non-invasive in vivo, time-lapse X-ray microtomography, based on single-distance phase contrast and combined with motion analysis, to examine the course of embryonic development. We demonstrate that this powerful four-dimensional imaging technique provides high-resolution views of gastrulation processes in wild-type X. laevis embryos, including vegetal endoderm rotation, archenteron formation, changes in the volumes of cavities within the porous interstitial tissue between archenteron and blastocoel, migration/confrontation of mesendoderm and closure of the blastopore. Differential flow analysis separates collective from relative cell motion to assign propulsion mechanisms. Moreover, digitally determined volume balances confirm that early archenteron inflation occurs through the uptake of external water. A transient ectodermal ridge, formed in association with the confrontation of ventral and head mesendoderm on the blastocoel roof, is identified. When combined with perturbation experiments to investigate molecular and biomechanical underpinnings of morphogenesis, our technique should help to advance our understanding of the fundamentals of development.