Development of crystal optics for Multi-Projection X-ray Imaging for synchrotron and XFEL sources

X-ray Multi-Projection Imaging (XMPI) is an emerging technology that allows for the acquisition of millions of 3D images per second in samples opaque to visible light. This breakthrough capability enables volumetric observation of fast stochastic phenomena, which were inaccessible due to the lack of a volumetric X-ray imaging probe with kHz to MHz repetition rate. These include phenomena of industrial and societal relevance such as fractures in solids, propagation of shock waves, laser-based 3D printing, or even fast processes in the biological domain. Indeed, the speed of traditional tomography is limited by the shear forces caused by rotation, to a maximum of 1000 Hz in state-of-the-art tomography. Moreover, the shear forces can disturb the phenomena in observation, in particular with soft samples or sensitive phenomena such as fluid dynamics. XMPI is based on splitting an X-ray beam to generate multiple simultaneous views of the sample, therefore eliminating the need for rotation. The achievable performances depend on the characteristics of the X-ray source, the detection system, and the X-ray optics used to generate the multiple views. The increase in power density of the X-ray sources around the world now enables 3D imaging with sampling speeds in the kilohertz range at synchrotrons and megahertz range at X-ray Free-Electron Lasers (XFELs). Fast detection systems are already available, and 2D MHz imaging was already demonstrated at synchrotron and XFEL. In this work, we explore the properties of X-ray splitter optics and XMPI schemes that are compatible with synchrotron insertion devices and XFEL X-ray beams. We describe two possible schemes designed to permit large samples and complex sample environments. Then, we present experimental proof of the feasibility of MHz-rate XMPI at the European XFEL.Comment: 47 pages, 17 figure

Röntgenstrukturanalyse von Halbleiter-Isolator-Schichtsystemen

Reaching the nanometerscale, new approaches for the fabrication of thin and smooth heteroepitaxial films have to be found. Here, the material system CaF2/Si is a promising candidate due to small lattice mismatch (0.6%) and similar lattice structure. In this work the growth of CaF2 on Si(111) and the following deposition of Si and Ge on the CaF2 films was investigated by means of surface x-ray diffraction (SXRD), x-ray reflectivity (XRR) and atomic force microscopy (AFM). Films were grown at temperatures of 500 degrees C and 600 degrees C with thicknesses of 1-10nm. With decreasing thickness and temperature the adlayer partially relaxes as can clearly be seen in the lateral seperation of the CaF2 reflexes. However, the intensity distribution of the crystal truncation rods (CTR) leads to a model of a very smooth and crystalline film. The following deposition of semiconductors in a two step method (RT deposition and annealing under surfactant flux) results in crystalline layers with small roughness

X-ray Structure Analysis of Semiconductor Insulator Film Systems

Reaching the nanometerscale, new approaches for the fabrication of thin and smooth heteroepitaxial films have to be found. Here, the material system CaF2/Si is a promising candidate due to small lattice mismatch (0.6%) and similar lattice structure. In this work the growth of CaF2 on Si(111) and the following deposition of Si and Ge on the CaF2 films was investigated by means of surface x-ray diffraction (SXRD), x-ray reflectivity (XRR) and atomic force microscopy (AFM). Films were grown at temperatures of 500 degrees C and 600 degrees C with thicknesses of 1-10nm. With decreasing thickness and temperature the adlayer partially relaxes as can clearly be seen in the lateral seperation of the CaF2 reflexes. However, the intensity distribution of the crystal truncation rods (CTR) leads to a model of a very smooth and crystalline film. The following deposition of semiconductors in a two step method (RT deposition and annealing under surfactant flux) results in crystalline layers with small roughness

High-throughput microwave-assisted discovery of new metal phosphonates

A systematic study was carried out to investigate the influence of linker geometry, metal ionic radius as well as the nature of the counter ions on the structure formation of metal tetraphosphonates. Two tetraphosphonic acids p- and m-(H2O3PCH2)2N-CH2-C6H4-CH2-N(CH2PO3H2)2, six metal ions (Ca2+, Mn2+, Co2+, Ni2+, Zn2+, and Cd2+) and two different counter ions (Cl− and NO3−) were employed using high throughput methods. Microwave (MW)-assisted heating led to the discovery of ten new metal-phosphonates which crystallize in three different crystal structures. The combination of direct methods and force field calculations allowed us to establish the crystal structures. The counter ion and the ionic radii of the metal ions have a profound influence on the crystallinity and the formed crystal structure. All compounds were characterized in detail by thermogravimetric analyses, IR spectroscopy and magnetic susceptibility measurements. The proton conductivity of two selected compounds is also reported

Structural transitions and relaxation processes during the epitaxial growth of ultrathin CaF2CaF_2 films on Si(111)

The structure and morphology of ultrathin lattice matched CaF2 films of very few monolayers thickness, which were deposited on Si(111) substrates by molecular-beam epitaxy, have been studied in situ by synchrotron based grazing incidence x-ray diffraction. Even for the thinnest investigated film of three monolayers thickness, the in-plane structure of the CaF2 film is determined by a lateral separation in two domains: a pseudomorphic phase assuming the lateral lattice constant of the Si(111) substrate and a completely relaxed phase. Analysis of the crystal truncation rods verifies that both phases adopt the entire homogeneous CaF2 film thickness. Therefore, we propose that atomic steps of the substrate bypass the nucleation barrier for the formation of (Shockley partial) dislocations so that the film starts to relax below the classical critical film thickness. While the relaxed phase assumes also the CaF2 bulk lattice constant for the vertical direction, the vertical lattice constant of the pseudomorphic phase increases due to the compressive lateral strain at the interface. This vertical expansion of the pseudomorphic phase, however, is larger than expected from the elastic constants of the CaF2 bulk. The fraction of the pseudomorphic CaF2 phase decreases with increasing film thickness. The interface between the pseudomorphic CaF2 phase and the Si(111) substrate is characterized by Ca on T4 sites, a smaller distance between the Si(111) substrate and the CaF interface layer and an expanded layer distance between CaF interface layer and the completely stoichiometric CaF2 film

Laser-induced, single droplet fragmentation dynamics revealed through megahertz x-ray microscopy

The fragmentation dynamics of single water droplets from laser irradiation is studied with megahertz frame rate x-ray microscopy. Owed to the nearly refraction-free and penetrating imaging technique, we could look into the interior of the droplet and reveal that two mechanisms are responsible for the initial explosive fragmentation of the droplet. First, reflection and diffraction of the laser beam at the droplet interface result in the formation of laser ray caustics that lead to non-homogeneous heating of the droplet, locally above the critical temperature. Second, homogeneous cavitation in the droplet that is likely caused from shockwaves reflected as tension waves at the acoustic soft boundaries of the droplet. Further atomization occurs in three stages, first a fine sub-micrometer sized mist forms on the side of the droplet posterior to laser incidence, then micrometer sized droplets are expelled from the rim of an expanding liquid sheet, and finally into droplets of larger size through hole and ligament formation in the thinning liquid sheet where ligaments pinch off

Development towards high-resolution kHz-speed rotation-free volumetric imaging

X-ray multi -projection imaging (XMPI) has the potential to provide rotation -free 3D movies of optically opaque samples. The absence of rotation enables superior imaging speed and preserves fragile sample dynamics by avoiding the centrifugal forces introduced by conventional rotary tomography. Here, we present our XMPI observations at the ID19 beamline (ESRF, France) of 3D dynamics in melted aluminum with 1000 frames per second and 8 mu m resolution per projection using the full dynamical range of our detectors. Since XMPI is a method under development, we also provide different tests for the instrumentation of up to 3000 frames per second. As the high -brilliance of 4th generation light -sources becomes more available, XMPI is a promising technique for current and future X-ray imaging instruments. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen

The interplay of local electron correlations and ultrafast spin dynamics in fcc Ni

The complex electronic structure of metallic ferromagnets is determined by a balance between exchange interaction, electron hopping leading to band formation, and local Coulomb repulsion. By combining high energy and temporal resolution in femtosecond time-resolved X-ray absorption spectroscopy with ab initio time-dependent density functional theory we analyze the electronic structure in fcc Ni on the time scale of these interactions in a pump-probe experiment. We distinguish transient broadening and energy shifts in the absorption spectra, which we demonstrate to be captured by electron repopulation respectively correlation-induced modifications of the electronic structure, requiring to take the local Coulomb interaction into account.ISSN:2166-383