Storage Ring BESSY Research Articles

Multi-Scale Analysis of Lithium-Sulfur Pouch Cells Using Imaging Methods

Lithium-sulfur batteries (Li-S) are promising energy storage technologies. Its high gravimetric energy density, the abundance of sulfur and low costs at high production volume, this battery type is especially applicable for automotive and aerospace applications. In recent years, the number of reported prototype cells has increased, as well as their accessible energy density. This underlines the progress of technology readiness of the Li-S system. However, despite this important breakthrough density and cycling stability have to be overcome in the Li-S research. Additionally, the influence of the cathode porosity as well as the surface of the carbon material and the electrolyte composition play an important role on the conversion of sulfur and the performance of prototype cells.Hard X-ray beamlines, as BAMline at the electron storage ring BESSY II in Berlin, Germany, have now been in service for over two decades. Several improvements have been implemented, allowing for operando tomography and fast radiographic measurements on the micrometer scale by using well-shaped synchrotron X-ray beam. In this study, operando X-ray imaging measurements on Li-S pouch cells are complemented by scanning and transmission electron microscopy and focused-ion-beam measurements on the nanometer scale delivering unique and multi-scale results about the morphology of sulfur inside the porous cathode material. Therefore, tiny pouch cells designs have been developed, allowing for operando tomography of stacked cells. Figure 1

Metrology with synchrotron radiation at PTB

The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of the Federal Republic of Germany and has been using synchrotron radiation (SR) for more than 40 years. Starting at the former facility BESSY I, the storage ring BESSY II (see corresponding article in this volume) has been used for this purpose since 1998, especially in the X-ray range, as well as PTB's own metrology light source (MLS) for lower photon energies since 2008. Both facilities are located in Berlin-Adlershof and are operated by the Helmholtz-Zentrum Berlin within the framework of contractual agreements with PTB. The basic motivation of the work is radiometry. The two storage rings MLS and BESSY II are used as primary source standards and cryogenic radiometers as primary detector standards. The article gives a brief overview of the present status, scientific highlights, the technological development and upgrade plans for the decade 2023–2033 as well as a perspective of next scientific challenges.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP at BESSY II.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the `low-α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields arepresented.

Cross-Correlation of THz Pulses from the Electron Storage Ring BESSY II

Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. These micro-instabilities are investigated at the electron storage ring BESSY II by means of cross-correlation of the THz fields from successive bunches. The investigations allow deriving the longitudinal length scale of the micro bunch fluctuations and show that it grows faster than the current-dependent bunch length. Our findings will help to set the limits for the possible time resolution for pump-probe experiments achieved with coherent THz synchrotron radiation from a storage ring.

Vacuum-compatible photon-counting hybrid pixel detector for wide-angle x-ray scattering, x-ray diffraction, and x-ray reflectometry in the tender x-ray range.

A vacuum-compatible photon-counting hybrid pixel detector has been installed in the ultra-high vacuum reflectometer of the four-crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin, Germany. The setup is based on the PILATUS3 100K module. The detector can be used in the entire photon energy range accessible at the beamline from 1.75 keV to 10 keV. Complementing the already installed vacuum-compatible PILATUS 1M detector used for small-angle x-ray scattering (SAXS) and grazing incidence SAXS, it is possible to access larger scattering angles. The water-cooled module is located on the goniometer arm and can be positioned from -90° to 90° with respect to the incoming beam at a distance of about 200 mm from the sample. To perform absolute scattering experiments, the linearity, homogeneity, and angular dependence of the quantum efficiency, including their relative uncertainties, have been investigated. In addition, the first results of the performance in wide-angle x-ray scattering, x-ray diffraction, and x-ray reflectometry are presented.

Validation of the probability density function for the calculated radiant power of synchrotron radiation according to the Schwinger formalism

Electron storage rings with appropriate design are primary source standards, the spectral radiant intensity of which can be calculated from measured parameters using the Schwinger equation. PTB uses the electron storage rings BESSY II and MLS for source-based radiometry in the spectral range from the near-infrared to the x-ray region. The uncertainty of the calculated radiant intensity depends on the uncertainty of the measured parameters used for the calculation. Up to now the procedure described in the guide to the expression of uncertainty in measurement (GUM), i.e. the law of propagation of uncertainty, assuming a linear measurement model, was used to determine the combined uncertainty of the calculated spectral intensity, and for the determination of the coverage interval as well. Now it has been tested with a Monte Carlo simulation, according to Supplement 1 to the GUM, whether this procedure is valid for the rather complicated calculation by means of the Schwinger formalism and for different probability distributions of the input parameters. It was found that for typical uncertainties of the input parameters both methods yield similar results.

Characterization of HAPG mosaic crystals using synchrotron radiation

Highly annealed pyrolytic graphite (HAPG) is an advanced type of pyrolytic graphite that, as a mosaic crystal, combines high integral reflectivity with a very low mosaicity of typically less than 0.1°. When used as dispersive X-ray optics, a high resolving power has been observed, rendering HAPG very suitable for applications in high-resolution X-ray spectroscopy, which conventionally relies on ideal crystals. For the design and modelling of HAPG crystals in applications requiring high spectral resolution, the diffraction properties must be known very accurately. To close this gap, a comprehensive characterization of HAPG crystals was performed that allows for modelling of the diffraction properties in different diffraction orders over a broad spectral range. The crystal properties under investigation are the mosaic spread, the peak reflectivity and the intrinsic reflection width. The investigations were carried out for different thickness crystal films, which were mounted adhesively on a substrate. It is shown that the diffraction properties are strongly correlated to the grade of adhesion, which depends crucially on the substrate material and its surface properties. The investigations were performed using monochromated tunable synchrotron radiation of high spectral purity with a high-precision experimental setup and calibrated detection devices at the electron storage ring BESSY II.

Overview of nanoscale NEXAFS performed with soft X-ray microscopes.

Today, in material science nanoscale structures are becoming more and more important. Not only for the further miniaturization of semiconductor devices like carbon nanotube based transistors, but also for newly developed efficient energy storage devices, gas sensors or catalytic systems nanoscale and functionalized materials have to be analysed. Therefore, analytical tools like near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has to be applied on single nanostructures. Scanning transmission X-ray microscopes (STXM) as well as full-field transmission X-ray microscopes (TXM) allow the required spatial resolution to study individual nanostructures. In the soft X-ray energy range only STXM was used so far for NEXAFS studies. Due to its unique setup, the TXM operated by the Helmholtz-Zentrum Berlin (HZB) at the electron storage ring BESSY II is the first one in the soft X-ray range which can be used for NEXAFS spectroscopy studies which will be shown in this review. Here we will give an overview of the different microscopes used for NEXAFS studies and describe their advantages and disadvantages for different samples.

Fundamental parameters of Zr and Ti for a reliable quantitative X‐ray fluorescence analysis

Employing characterized beamlines as well as radiometrically calibrated detection systems in the Physikalisch‐Technische Bundesanstalt laboratory at the electron storage ring BESSY II in Berlin, fundamental parameters of the Zr (L subshells) and the Ti (K shell) have been experimentally determined and compared to available literature data. This study is mainly focused on the provision of a reliable uncertainty budget based on the calibrated instrumentation. Using a reference‐free X‐ray fluorescence approach and an advanced evaluation procedure without any input from databases, fundamental parameters, such as Coster–Kronig probabilities as well as fluorescence yields, are determined with both decreased and reliable uncertainties. Copyright © 2015 John Wiley & Sons, Ltd.

New reference and test materials for the characterization of energy dispersive X-ray spectrometers at scanning electron microscopes.

Checking the performance of energy dispersive X-ray spectrometers as well as validation of the results obtained with energy dispersive X-ray spectrometry (EDX) at a scanning electron microscope (SEM) involve the use of (certified) reference and dedicated test materials. This paper gives an overview on the test materials mostly employed by SEM/EDX users and accredited laboratories as well as on those recommended in international standards. The new BAM reference material EDS-CRM, which is currently in the process of certification, is specifically designed for the characterization of EDS systems at a SEM through calibration of the spectrometer efficiency in analytical laboratories in a simple manner. The certification of the spectra by means of a reference EDS is described. The focus is on the traceability of EDS efficiency which is ensured by measurements of the absolute detection efficiency of silicon drift detectors (SDD) and Si(Li) detectors at the laboratory of the PTB using the electron storage ring BESSY II as a primary X-ray source standard. A new test material in development at BAM for testing the performance of an EDS in the energy range below 1keV is also briefly presented.

Experimental verification of the individual energy dependencies of the partial L-shell photoionization cross sections of Pd and Mo.

An experimental method for the verification of the individually different energy dependencies of L(1)-, L(2)-, and L(3)- subshell photoionization cross sections is described. The results obtained for Pd and Mo are well in line with theory regarding both energy dependency and absolute values, and confirm the theoretically calculated cross sections by Scofield from the early 1970 s and, partially, more recent data by Trzhaskovskaya, Nefedov, and Yarzhemsky. The data also demonstrate the questionability of quantitative x-ray spectroscopical results based on the widely used fixed jump ratio approximated cross sections with energy independent ratios. The experiments are carried out by employing the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin; the obtained fluorescent intensities are thereby calibrated at an absolute level in reference to the International System of Units. Experimentally determined fixed fluorescence line ratios for each subshell are used for a reliable deconvolution of overlapping fluorescence lines. The relevant fundamental parameters of Mo and Pd are also determined experimentally in order to calculate the subshell photoionization cross sections independently of any database.

Characterization of an in-vacuum PILATUS 1M detector.

A dedicated in-vacuum X-ray detector based on the hybrid pixel PILATUS 1M detector has been installed at the four-crystal monochromator beamline of the PTB at the electron storage ring BESSY II in Berlin, Germany. Owing to its windowless operation, the detector can be used in the entire photon energy range of the beamline from 10 keV down to 1.75 keV for small-angle X-ray scattering (SAXS) experiments and anomalous SAXS at absorption edges of light elements. The radiometric and geometric properties of the detector such as quantum efficiency, pixel pitch and module alignment have been determined with low uncertainties. The first grazing-incidence SAXS results demonstrate the superior resolution in momentum transfer achievable at low photon energies.

Broad-band efficiency calibration of ITER bolometer prototypes using Pt absorbers on SiN membranes

The energy resolved efficiency of two bolometer detector prototypes for ITER with 4 channels each and absorber thicknesses of 4.5 μm and 12.5 μm, respectively, has been calibrated in a broad spectral range from 1.46 eV up to 25 keV. The calibration in the energy range above 3 eV was performed against previously calibrated silicon photodiodes using monochromatized synchrotron radiation provided by five different beamlines of Physikalische Technische Bundesanstalt at the electron storage rings BESSY II and Metrology Light Source in Berlin. For the measurements in the visible range, a setup was realised using monochromatized halogen lamp radiation and a calibrated laser power meter as reference. The measurements clearly demonstrate that the efficiency of the bolometer prototype detectors in the range from 50 eV up to ≈6 keV is close to unity; at a photon energy of 20 keV the bolometer with the thick absorber detects 80% of the photons, the one with the thin absorber about 50%. This indicates that the detectors will be well capable of measuring the plasma radiation expected from the standard ITER scenario. However, a minimum absorber thickness will be required for the high temperatures in the central plasma. At 11.56 keV, the sharp Pt-L3 absorption edge allowed to cross-check the absorber thickness by fitting the measured efficiency to the theoretically expected absorption of X-rays in a homogeneous Pt-layer. Furthermore, below 50 eV the efficiency first follows the losses due to reflectance expected for Pt, but below 10 eV it is reduced further by a factor of 2 for the thick absorber and a factor of 4 for the thin absorber. Most probably, the different histories in production, storage, and operation led to varying surface conditions and additional loss channels.

Nanoscale spectroscopy and tomography with the HZB X-ray microscope: Applications in materials and life sciences

The full-field transmission X-ray microscope at the electron storage ring BESSY II allows nanoscale spectroscopy as well as correlative fluorescence and nanoscale tomographic imaging of frozen-hydrated adherent cells. Reconstructions of tilt series permit the visualization of the sub-cellular structures in mammalian cells and plant cells. Quantitative information about package densities of cell organelles in the cytoplasm is possible. We present an overview of recent results in materials and life sciences obtained with the HZB X-ray microscope.

Electronic structure of copper halides CuI and CuCl: A comparative X-Ray photoelectron and absorption spectroscopy study

The energy distributions of the occupied and unoccupied electronic states for copper halides CuCl and CuI have been investigated using X-ray photoemission and absorption spectroscopy with a highenergy resolution on the equipment of the Russian-German beamline for outlet and monochromatization of synchrotron radiation from the electron storage ring BESSY II. A quasi-molecular analysis of the obtained experimental spectra has revealed that there is a fundamental similarity of the energy structures of the valence band and the conduction band of copper halides CuX (X = Cl, I) due to the identical atomic structure of the studied compounds. The differences in the positions of individual energy subbands in the valence band and the conduction band of CuX and in their intensities in the spectra are associated with different degrees of hybridization of the Cu 3d, 4s and X(n + 1)s, np valence states, as well as with different sizes of structural units (CuCl4 and CuI4 quasi-molecules) of the studied crystals.

Measurement of the mass energy-absorption coefficient of air for x-rays in the range from 3 to 60 keV

For the first time the absolute photon mass energy-absorption coefficient of air in the energy range of 10 to 60 keV has been measured with relative standard uncertainties below 1%, considerably smaller than those of up to 2% assumed for calculated data. For monochromatized synchrotron radiation from the electron storage ring BESSY II both the radiant power and the fraction of power deposited in dry air were measured using a cryogenic electrical substitution radiometer and a free air ionization chamber, respectively. The measured absorption coefficients were compared with state-of-the art calculations and showed an average deviation of 2% from calculations by Seltzer. However, they agree within 1% with data calculated earlier by Hubbell. In the course of this work, an improvement of the data analysis of a previous experimental determination of the mass energy-absorption coefficient of air in the range of 3 to 10 keV was found to be possible and corrected values of this preceding study are given.

L-subshell fluorescence yields and Coster-Kronig transition probabilities with a reliable uncertainty budget for selected high- and medium-Zelements

Photon-in/photon-out experiments at thin specimens have been carried out to determine $L$-subshell fluorescence yields as well as Coster-Kronig transition probabilities of Au, Pb, Mo, and Pd using radiometrically calibrated instrumentation in the Physikalisch-Technische Bundesanstalt (PTB) laboratory at the electron storage ring BESSY II in Berlin. An advanced approach was developed in order to derive the fluorescence line intensities by means of line sets of each subshell that were corrected for self-absorption and broadened with experimentally determined detector response functions. The respective photoelectric cross sections for each subshell were determined by means of transmission measurements of the same samples without any change in the experimental operating condition. All values derived were compared to those of earlier works. A completely traceable uncertainty budget is provided for the determined values.

Synchrotron-based ultrafast x-ray diffraction at high repetition rates

We present a setup for ultrafast x-ray diffraction (UXRD) based at the storage ring BESSY II, in particular, a pump laser that excites the sample using 250 fs laser-pulses at repetition rates ranging from 208 kHz to 1.25 MHz. We discuss issues connected to the high heat-load and spatio-temporal alignment strategies in the context of a UXRD experiment at high repetition rates. The spatial overlap between laser pump and x-ray probe pulse is obtained with 10 μm precision and transient lattice changes can be recorded with an accuracy of δa/a(0) = 10(-6). We also compare time-resolved x-ray diffraction signals from a laser excited LSMO/STO superlattice with phonon dynamics simulations. From the analysis we determine the x-ray pulse duration to 120 ps in standard operation mode and below 10 ps in low-α mode.

A survey of the Italian research in solid state physics by infrared spectroscopy with electron-beam sources

Two beamlines for the use of InfraRed Synchrotron Radiation (IRSR) are presently working in Italy, at the ELETTRA storage ring in Trieste, and at the collider DAFNE in Frascati. A third facility, SPARC in Frascati, has been equipped for the extraction of Terahertz radiation with the aim to perform pump-probe time-domain experiments. Here we describe those apparata and we review the main results that the Italian groups have obtained therein, in recent years, in solid-state physics. We also describe the experiments performed in collaboration with the storage ring BESSY in Berlin, for the exploitation of Coherent Synchrotron Radiation, and the terahertz beam line recently implemented at SPARC, the Free Electron Laser of Laboratori Nazionali di Frascati

Characterization of the resolving power and contrast transfer function of a transmission X-ray microscope with partially coherent illumination

The achievable spatial resolution and the contrast transfer function (CTF) are key parameters characterizing an X-ray microscope. We measured the spatial resolution and the contrast transfer function of the transmission X-ray microscope (TXM) at the electron storage ring BESSY II. The TXM uses the radiation of an undulator source and operates under partially coherent illumination conditions. For spatial resolutions down to 25 nm, our measurements of the CTF's are in good agreement with theoretical CTF data for partial coherence. With higher resolution zone plate objectives, we measured a spatial resolution (half-pitch) of 11 nm in 1st and 3rd order of diffraction. However, with these objectives the stray light level increases significantly.