Bernd Schmitt

Understanding structure at the atomic scale is fundamental for understanding the functioning and the development of materials with improved properties. Compared with other probes providing atomic resolution, electrons offer the strongest interaction in combination with minimal radiation damage, which makes them an ideal tool for investigating very small and radiation-sensitive samples [Henderson (1995), Q. Rev. Biophys. 28 , 171–193]. However, these benefits are often offset by the laborious preparation of nanometre-sized samples that are not visible using a light microscope, and the fact that experiments are largely restricted to ultra-high vacuum [Duyvesteyn et al. (2018), Proc. Natl Acad. Sci. USA 115 , 9569–9573; Gruene et al. (2021), Nat. Rev. Chem. 5 , 660–668]. Here, we report the successful implementation of MeV electron diffraction for ab initio 3D structure determination of the quasi-2D material muscovite and the quantum material 1 T -TaS ₂ at atomic resolution. By employing ultrashort electron pulses from the REGAE (Relativistic electron gun for atomic exploration) accelerator, we obtained high-quality diffraction datasets suitable for structural refinements based on dynamical scattering theory, enabling precise localization of even hydrogen atoms. The increased penetration depth of MeV electrons significantly expands the applicable thickness range of samples, overcoming previous restrictions associated with traditional electron diffraction. These findings establish MeV electron diffraction as a viable approach for investigating a broad range of materials, including nanostructures and radiation-sensitive compounds, and open up new opportunities for in situ and time-resolved experiments [Chao et al. (2023), Chem. Rev. 123 , 8347–8394; Filippetto et al. (2022), Rev. Mod. Phys. 94 , 045004].

A Jungfrau-1M detector has undergone testing at Diamond Light Source. The Jungfrau series of detectors from PSI use integration and adaptive gain, to offer very high frame rate and dynamic range, suitable for high-flux and time-resolved measurements. They are becoming more widely used, to take advantage of increasing light source brightness. We report on our experiences in testing the performance of a Jungfrau-1M without illumination, with a laboratory X-ray tube and on a microfocus beamline. The Jungfrau-1M was found to be able to resolve single photons in the laboratory and on the beamline. It was confirmed that range switching from high to intermediate gain is associated with a discontinuity in the detector response. Two methods of dark frame subtraction were compared for their effect on minimizing this discontinuity. The Jungfrau-1M was found to be very effective for recording macromolecular crystallography diffraction patterns, with no apparent detriment from the discontinuity. The Diamond machine will be upgraded in 2028–9 and will operate at significantly higher flux than at present, necessitating increased use of integrating detectors, such as Jungfrau, in the future.

Electrons have emerged as an important complement to X-rays in crystallography, particularly for compounds that present challenges in growing crystals sufficiently large for synchrotron radiation (5–10 µm) or laboratory diffractometers (∼50 µm). Given the nature of electron-matter interactions, electron diffraction (ED) provides a way to experimentally determine the electrostatic potential of compounds. To fully harness the power of ED, we have integrated a fast, low-noise and radiation-hard 1 Megapixel JUNGFRAU detector with a modern JEOL transmission electron microscope (TEM). JUNGFRAU is a charge-integrating hybrid pixel detector, with a dynamic range of 120 MeV/pixel/frame and a maximum frame rate of 2.2 kHz in continuous mode. It can detect up to 1.3 million 200 keV electrons per pixel per second before saturation. To handle the resulting 5 GB/s raw data stream (fiberoptic; 4×10 Gbps), our system features an FPGA-based backend, Jungfraujoch , which converts raw ADC values into deposited energy and enables on-the-fly frame summation. Additionally, we developed a software package with an intuitive graphical user interface that integrates detector and microscope control. This solution provides partly automated data acquisition and post-processing, with data stored in compressed HDF5 files with comprehensive metadata. This work assesses the performance of JUNGFRAU across multiple electron energies by analyzing energy deposition and pixel spread. The complete data pipeline — from detector to user interface — is validated through an ED experiment yielding structural insights.

With the evolution of synchrotron light sources to fourth generation (diffraction-limited storage rings), the brilliance is increased by several orders of magnitude compared to third generation facilities. For example, the Swiss Light Source (SLS) has been upgraded to SLS 2.0, promising a horizontal emittance reduced by a factor of 40, and a brilliance up to two orders of magnitude (three at higher energies). A key challenge arising from the increased flux is the heightened accumulated dose in silicon sensors, which leads to a significant increase in radiation damage. This translates into an increase of both noise and dark current, as well as a reduction in the dynamic range for long exposure times, thus affecting the performance of the detector, in particular, for charge-integrating detectors. We have designed sensors with a 4 × 4 mm² pixel array featuring 16 design variations of 25 µm pitch pixels with different implant and metal sizes and tested them bump-bonded to MÖNCH 0.3, a charge integrating hybrid pixel detector readout ASIC. Following a first assessment of the functionality and performance of the different pixel designs, the assembly has been irradiated with X-rays. The variation in the tested parameters was characterized at different accumulated doses up to 100 kGy at the sensor entrance window side. The annealing dynamics at room temperature have also been measured. The results show that the default pixel design is currently not optimal and can benefit from layout changes (reduction in the inter-pixel gap area with full metal coverage of the implant). Further studies on the metal coverage over large implants could be conducted. The layout changes are, however, not sufficient for future full-sized sensors, requiring improved radiation hardness and long-term stability, and additional strategies such as focusing on detector cooling and changes in sensor technologies would be required.

The JUNGFRAU 4-megapixel (4M) charge-integrating pixel-array detector, when operated at a full 2 kHz frame rate, streams data at a rate of 17 GB s⁻¹. To operate this detector for macromolecular crystallography beamlines, a data-acquisition system called Jungfraujoch was developed. The system, running on a single server with field-programmable gate arrays and general-purpose graphics processing units, is capable of handling data produced by the JUNGFRAU 4M detector, including conversion of raw pixel readout to photon counts, compression and on-the-fly spot finding. It was also demonstrated that 30 GB s⁻¹ can be handled in performance tests, indicating that the operation of even larger and faster detectors will be achievable in the future. The source code is available from a public repository.

Monitoring crustal movements is essential to volcanic hazard assessment in areas of active volcanism. These surface movements occur on a wide range of time scales and wavelengths. However, the origin of crustal movements is not always associated with volcanic activities, particularly in areas with rigorous human activities (i.e., ground water extraction). It is challenging yet critical to distinguish between the ongoing volcanic and anthropogenic activities. In this study, we focus on the East Eifel Volcanic Field, which consists of multiple active Quaternary volcanoes. We report areas of uplift and subsidence 2-3 km away from each other near the Laacher See volcanic crater (2-3 km distance), and investigate the mechanisms responsible for the reversed deformation in such close proximity.PS-InSAR measurements by the BodenBewegungsdienst Deutschland (BBD) show notable ground displacements in this area for the period between 2014 and 2019. The deformation is clearly mapped by three different tracks of the Sentinel-1 satellite – two ascending and one descending, which confirms the robustness of the signal being detected by PS-InSAR. The main deformation is round in shape, and the rates peak up to 10 mm per year in line-of-sight (LOS) for the uplift area near the village Glees and reach down to -4 mm LOS for the subsidence zone in the vicinity of the village Wehr. To investigate the likely mechanism responsible for the ground displacements, we model the crustal movements with two spherical pressure point sources (i.e., the Mogi sources) simultaneously using a combined global and local optimization scheme. In the inversion, we search for the optimal combinations for a set of four parameters (latitude, longitude, depth and volume) for each Mogi source. The global optimization is achieved by Multi-Level Single-Linkage algorithm and we use the PRAXIS algorithm to find the local minimum. We include all three tracks of data, of which the different satellite viewing geometries help stabilize the inversion.Our results show that the uplift trend in Glees can be explained by an additional volume of 13000 m³ per year at 530 m depth. The subsidence near Wehr can be best fitted by a decrease in volume of 1700 m³ per year at 340 m depth. The modelling results show a trade-off between depth and volume, however, the uncertainties are smaller for the subsidence source near Wehr. Residuals trending in SW-NE direction are observed at the Glees uplift area, and the relatively large parameter uncertainties for Glees uplift zone are likely due to sparse persistent scatters there. Given the shallow depth of the Mogi sources, we interpret the Glees uplift being predominantly associated with fluid refilling in the respective volume caused by former CO2 extraction. The subsidence around Wehr is linked to ongoing industrial CO2 extraction. Our study identifies anthropogenic factors that may cause ground deformation in an active volcanic region, and has implications for future volcanic hazard assessment.

Speed, dynamic range, and radiation hardness make hybrid pixel detectors suitable image detectors for diffraction experiments. At synchrotrons and X-ray free electron lasers they are ubiquitous. However, for electron microscopy their spatial resolution is limited by multiple scattering in the sensor layer. In this paper we examine the use of two high Z sensor materials: CdTe and GaAs, as a way to mitigate this problem. The sensors were bonded to a JUNGFRAU readout chip which is a charge integrating hybrid pixel detector developed for use at X-ray free electron lasers. Using in-pixel gain switching, it can detect single particles down to 2 keV while maintaining a dynamic range of 120 MeV/pixel/frame. The characteristics of JUNGFRAU, besides being a capable detector, make it a good tool for sensor characterization since we can measure dark current and energy deposition per pixel. The high Z material shows better spatial resolution than silicon at 200 and 300 keV, however, their practical use with integrating detectors is still limited by material defects.