Jan Torben Delitz

Bio: Jan Torben Delitz is an academic researcher from European XFEL. The author has contributed to research in topics: Beamline & Physics. The author has an hindex of 2, co-authored 4 publications receiving 126 citations.

Beamline P02.1 at PETRA III for High-Resolution and High-Energy Powder Diffraction

Abstract: Powder X-ray diffraction techniques largely benefit from the superior beam quality provided by high-brilliance synchrotron light sources in terms of photon flux and angular resolution. The High Resolution Powder Diffraction Beamline P02.1 at the storage ring PETRA III (DESY, Hamburg, Germany) combines these strengths with the power of high-energy X-rays for materials research. The beamline is operated at a fixed photon energy of 60 keV (0.207 A wavelength). A high-resolution monochromator generates the highly collimated X-ray beam of narrow energy bandwidth. Classic crystal structure determination in reciprocal space at standard and non-ambient conditions are an essential part of the scientific scope as well as total scattering analysis using the real space information of the pair distribution function. Both methods are complemented by in situ capabilities with time-resolution in the sub-second regime owing to the high beam intensity and the advanced detector technology for high-energy X-rays. P02.1's efficiency in solving chemical and crystallographic problems is illustrated by presenting key experiments that were carried out within these fields during the early stage of beamline operation.

Synchrotron Powder Diffraction at P02.1 at PETRA III: From Electron Density Distributions to in situ Total Scattering

Abstract: The excellent photon beam quality provided at 3rd generation synchrotron sources opens up new opportunities in materials chemistry using X-ray powder diffraction. Techniques that cover the range from very detailed structure analysis to the observation of rapid structural changes during chemical reactions in real time have become viable. Recent experiments carried out at the High Resolution Powder Diffraction Beamline P02.1 at PETRA III (DESY) demonstrate how to effectively exploit the highly collimated, very intense X-rays of high energies for chemistry and materials science. Two studies are described in detail, which illustrate the outstanding performance of the instrument: the determination of charge density distributions from powder patterns, and atomic rearrangements followed in situ during the formation of metallic and oxide nanoparticles in solution.

Laser heating system at the Extreme Conditions Beamline, P02.2, PETRA III.

Abstract: A laser heating system for samples confined in diamond anvil cells paired with in situ X-ray diffraction measurements at the Extreme Conditions Beamline of PETRA III is presented. The system features two independent laser configurations (on-axis and off-axis of the X-ray path) allowing for a broad range of experiments using different designs of diamond anvil cells. The power of the continuous laser source can be modulated for use in various pulsed laser heating or flash heating applications. An example of such an application is illustrated here on the melting curve of iron at megabar pressures. The optical path of the spectroradiometry measurements is simulated with ray-tracing methods in order to assess the level of present aberrations in the system and the results are compared with other systems, that are using simpler lens optics. Based on the ray-tracing the choice of the first achromatic lens and other aspects for accurate temperature measurements are evaluated.

Real-time spatial characterization of µm-focused X-ray free-electron laser beams

Abstract: A real-time and accurate characterization of the X-ray beam size is essential to enable a large variety of different experiments at free-electron laser facilities. Typically, ablative imprints are employed to determine shape and size of µm-focused X-ray beams. The high accuracy of this state-of-the-art method comes at the expense of the time required to perform an ex-situ image analysis. In contrast, diffraction at a curved grating with suitably varying period and orientation forms a magnified image of the X-ray beam, which can be recorded by a 2D pixelated detector providing beam size and pointing jitter in real time. In this manuscript, we compare results obtained with both techniques, address their advantages and limitations, and demonstrate their excellent agreement. We present an extensive characterization of the FEL beam focused to ≈1 µm by two Kirkpatrick-Baez (KB) mirrors, along with optical metrology slope profiles demonstrating their exceptionally high quality. This work provides a systematic and comprehensive study of the accuracy provided by curved gratings in real-time imaging of X-ray beams at a free-electron laser facility. It is applied here to soft X-rays and can be extended to the hard X-ray range. Furthermore, curved gratings, in combination with a suitable detector, can provide spatial properties of µm-focused X-ray beams at MHz repetition rate.

First commissioning results of the KB mirrors at the SCS instrument of the European XFEL

Abstract: The Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL is a soft X-ray beamline aiming to unravel electronic, spin and structural properties of materials in ultrafast processes at the nanoscale. Various experimental techniques offered at SCS have different requirements in terms of beam size at the sample. Kirkpatrick-Baez (KB) refocusing optics equipped with mechanical benders allows for independent change of the horizontal and vertical beam size. We report here on the first characterization of the SCS KB mirrors by means of a novel diffraction-based technique which images the beam profile on a 2D pixelated detector. This approach provides a quick characterization of micrometer beam sizes. Results are compared with metrology measurements obtained with a non-contact slope profiler.

Tracking Structural Phase Transitions in Lead-Halide Perovskites by Means of Thermal Expansion.

Abstract: The extraordinary properties of lead-halide perovskite materials have spurred intense research, as they have a realistic perspective to play an important role in future photovoltaic devices. It is known that these materials undergo a number of structural phase transitions as a function of temperature that markedly alter their optical and electronic properties. The precise phase transition temperature and exact crystal structure in each phase, however, are controversially discussed in the literature. The linear thermal expansion of single crystals of APbX3 (A = methylammonium (MA), formamidinium (FA); X = I, Br) below room temperature is measured using a high-resolution capacitive dilatometer to determine the phase transition temperatures. For δ-FAPbI3 , two wide regions of negative thermal expansion below 173 and 54 K, and a cascade of sharp transitions for FAPbBr3 that have not previously been reported are uncovered. Their respective crystal phases are identified via powder X-ray diffraction. Moreover, it is demonstrated that transport under steady-state illumination is considerably altered at the structural phase transition in the MA compounds. The results provide advanced insights into the evolution of the crystal structure with decreasing temperature that are essential to interpret the growing interest in investigating the electronic, optical, and photonic properties of lead-halide perovskite materials.

The Extreme Conditions Beamline P02.2 and the Extreme Conditions Science Infrastructure at PETRA III

Abstract: A detailed description is presented of the Extreme Conditions Beamline P02.2 for micro X-ray diffraction studies of matter at simultaneous high pressure and high/low temperatures at PETRA III, in Hamburg, Germany. This includes performance of the X-ray optics and instrumental resolution as well as an overview of the different sample environments available for high-pressure studies in the diamond anvil cell. Particularly emphasized are the high-brilliance and high-energy X-ray diffraction capabilities of the beamline in conjunction with the use of fast area detectors to conduct time-resolved compression studies in the millisecond time regime. Finally, the current capability of the Extreme Conditions Science Infrastructure to support high-pressure research at the Extreme Conditions Beamline and other PETRA III beamlines is described.

Complexion-mediated martensitic phase transformation in Titanium.

Abstract: The most efficient way to tune microstructures and mechanical properties of metallic alloys lies in designing and using athermal phase transformations. Examples are shape memory alloys and high strength steels, which together stand for 1,500 million tons annual production. In these materials, martensite formation and mechanical twinning are tuned via composition adjustment for realizing complex microstructures and beneficial mechanical properties. Here we report a new phase transformation that has the potential to widen the application window of Ti alloys, the most important structural material in aerospace design, by nanostructuring them via complexion-mediated transformation. This is a reversible martensitic transformation mechanism that leads to a final nanolaminate structure of α″ (orthorhombic) martensite bounded with planar complexions of athermal ω (a-ω, hexagonal). Both phases are crystallographically related to the parent β (BCC) matrix. As expected from a planar complexion, the a-ω is stable only at the hetero-interface.

The chemistry of nucleation

Abstract: Nucleation phenomena are of critical importance in numerous areas of science and everyday life. For decades the prevailing models to explain nucleation have been based on thermodynamic arguments without consideration of the chemical nature of the specific system. Even though newer models have included system-dependent variables, the quantitative atomistic differences are largely ignored. As a consequence, nucleation processes are treated on a “particle” or “monomer” level without discussion of the true atomic scale “chemistry of nucleation”. In the past couple of years, in situ studies of solvothermal reactions have considerably changed the experimental insight into nucleation phenomena, and especially the measurement of X-ray total scattering data and the subsequent pair distribution function analysis have proven to be vital tools. Here we discuss in situ results obtained for ten different material systems, and show that nucleation of nanoparticles in solvothermal reactions expose a fascinating chemical richness spanning from mono-metal to complex polymer precursor species, which, through a specific system-dependent multistep reaction mechanism, develop into pristine nanocrystals. It is argued that it is time to introduce a paradigm shift in the general nucleation theory and move away from the “one model fits all” to a chemistry-based approach rooted in atomic scale insight.