Helmholtz-Zentrum Berlin Research Articles

Gamma-ray emission in alpha-particle reactions with C, Mg, Si, Fe

Cross sections for the strongest γ-ray emission lines produced in α-particle reactions with C, Mg, Si, Fe have been measured in the range E α = 50-90 MeV at the center for protontherapy at the Helmholtz-Zentrum Berlin. Data for more than 60 different γ-ray lines were determined, with particular efforts for lines that are in cross section compilations/evaluations with astrophysical purpose, and where data exist at lower projectile energies. The data are compared with predictions of a modern nuclear reaction code and cross-section curves of the latest evaluation for gamma-ray line emission in accelerated-particle interactions in solar flares.

New approach for an industrial low-temperature roll-to-roll CI(G)Se hybrid sputter coevaporation deposition process

A new industrial approach for the production of CuInSe2 (CISe) absorber layers in a roll-to-roll process is described. This process is used by Sunplugged GmbH and combines magnetron sputtering with thermal coevaporation. A CISe-based device with a conversion efficiency of more than 10% has been fabricated from absorbers grown on polyimide at low temperature. The characteristic properties of a copper-poor ([Cu]/[In] = 0.73) CISe layer, deposited by Sunplugged's industrial process, are compared to those of a state-of-the-art, more copper-rich ([Cu]/[In] = 0.93) layer, grown in a molecular beam epitaxy system at Helmholtz-Zentrum Berlin. The presence of a so called vacancy-compound in low [Cu]/[In] CISe devices exhibiting an increased bandgap energy is visible by external quantum efficiency measurements, Raman scattering, and scaps simulations.

Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain.

Invited for the cover of this issue is the group of Michał Rams at Jagiellonian University (Kraków, Poland) and colleagues at Christian-Albrechts-Universität zu Kiel, Friedrich-Schiller-Universität Jena, and Helmholtz-Zentrum Berlin. The image represents a 1D coordination polymer with Co(II) spins that are flipped by photons during an EPR experiment. Read the full text of the article at 10.1002/chem.201903924.

First neutron data recorded at the V20 Test Instrument utilizing prototype chopper systems and beam monitors planned for ESS

The main objective of the European Spallation Source (ESS) is to perform consistently high impact neutron scattering science using the highest neutron flux of any facility in its class. This ambition is naturally accompanied by operational challenges related to the vertical integration of the instruments' hardware and software shared between collaborators from 13 European countries. The present work will detail integration tests performed at the V20 Test Instrument at Helmholtz-Zentrum Berlin in Germany. An ESS chopper prototype was successfully controlled through the ESS Chopper Integration Controller (CHIC) and Experimental Physics and Industrial Control System (EPICS). Neutron data were successfully collected and timestamped using neutron beam monitors, the ESS prototype detector readout electronics and the Data Management Software Center (DMSC) data acquisition (DAQ) software. Chopper rotation events were timestamped and the chopper disk showed excellent stability and neutron absorption characteristics. The test resulted in i) the expected time-of-flight (TOF) response, ii) collected data that compared well with instrument reference data and iii) revealing the diagnostic power of the performed integration tests. The results of this integration test validate the ESS chopper and detector DAQ architecture choices.

Simulation of Quench Detection Algorithms for Helmholtz Zentrum Berlin SRF Cavities

The Helmholtz Zentrum Berlin is carrying out two accelerator projects which make use of high gradient Continuous Wave (CW) Superconducting Radiofrequency (SRF) cavities: bERLinPro and BESSY-VSR. In both projects, a prompt detection of a quench is crucial to avoid damages in the cryomodules and cavities themselves. In this paper, the response of real time estimation of the cavity parameters using the transmitted and forward RF signals is simulated, in order to perform the quench detection. The time response of the estimated half bandwidth is compared with the dissipated energy in the cavity walls for the different type of SRF cavities used in both projects, i.e., bERLinPro's photoinjector, booster and linac, and BESSY-VSR 1.5 GHz and 1.75 GHz cavities. As an intermediate step prior to the implementation in an mTCA.4 system together with the LLRF control and test with a real cavity, the algorithm has been implemented using a National Instruments FPGA board to check its proper behavior.

Simulation of quench detection algorithms for Helmholtz Zentrum Berlin SRF cavities

The Helmholtz Zentrum Berlin is carrying out two accelerator projects which make use of high gradient Continuous Wave (CW) Superconducting Radiofrequency (SRF) cavities: bERLinPro and BESSY-VSR. In both projects, a prompt detection of a quench is crucial to avoid damages in the cryomodules and cavities themselves. In this paper, the response of real time estimation of the cavity parameters using the transmitted and forward RF signals is simulated, in order to perform the quench detection. The time response of the estimated half bandwidth is compared with the dissipated energy in the cavity walls for the different type of SRF cavities used in both projects, i.e., bERLinPro’s photoinjector, booster and linac, and BESSY-VSR 1.5 GHz and 1.75 GHz cavities. As an intermediate step prior to the implementation in an mTCA.4 system together with the LLRF control and test with a real cavity, the algorithm has been implemented using a National Instruments FPGA board to check its proper behavior.

Incorporation of a MESA linac module into bERLinPro

bERLinPro is an Energy Recovery Linac (ERL) project, currently being set up at the Helmholtz-Zentrum Berlin fur Materialien und Energie, Berlin, Germany. bERLinPro is designed as - and for - experiments in accelerator physics and as a test bed for novel ERL components. MESA is an ERL project under construction at the Johannes Gutenberg- Universitt, Mainz, Germany. MESA is designed as a user facility to perform experiments in dark matter physics and precision measurements of natural constants. Despite the diverse goals, the main linac, providing the larger part of the particles energy, is fairly compatible. It is planned to test and run the MESA linac module in bERLinPro, prior to its usage in MESA. The goals and benefits of this unique cooperation for both projects are outlined in this paper. The necessary adaptions in bERLinPro, including hardware aspects, the new optics, and the scope of performance are described.

Spatially resolved time-of-flight neutron imaging using a scintillator CMOS-camera detector with kHz time resolution.

We herein report on using a compact and low cost scintillator-camera based neutron detection system for quantitative time-of-flight imaging applications. While powerful pulsed neutron sources emerge and enable unprecedented scientific achievements, one bottleneck is the availability of suitable detectors that provide high count- and high frame- rate capabilities. For imaging applications the achievable spatial resolution/pixel size is obviously another key characteristic. While major effort was so far directed towards the development of neutron counting type imaging detectors, this work demonstrates that a camera based detector system as commonly employed at steady state sources can also be used if a suitable camera is utilized. This is demonstrated at the ESS test beamline (V20) at Helmholtz-Zentrum Berlin by recording the time-of-flight transmission spectrum of steel samples using a CMOS camera at 1 kHz frame rate, revealing the characteristic Bragg edge pattern. This 'simple' setup in the current state presents a useful option of neutron detection and has the potential to overcome many of the existing limitations and could provide a reliable alternative for neutron detector technology in general, given that the camera and scintillator technology keep up the current development speed.

Visualization of Liquid Water in a Metal Foam Flow-Field Based Polymer Electrolyte Fuel Cell Via Neutron Radiography

Polymer electrolyte fuel cells (PEFCs) have shown significant advances in terms of performance, efficiency and durability for a wide range of applications. Flow-fields are crucial components that affect the water management and performance of PEFCs. The existence of gas channel and land configurations in the conventional flow-field designs render gas and water distribution highly non-uniform. Such issue can lead to a series of events detrimental to PEFC performance and longevity [1]. As an alternative, new type of flow-field such as metal foam has been introduced. In-depth understanding of water management in metal foam flow-field based PEFC is indispensable for the optimisation of performance and durability. Here, liquid water formation and transport across the 25 cm2 metal foam flow-field based PEFC is evaluated using neutron radiography. A nickel foam was put on cathode aluminium plate and a silicone gasket was then placed around the foam to seal in gases. A vertical single-channel serpentine was used for the anode aluminium flow-field, as shown in Fig. 1 (a). All experiments were conducted at the cold neutron radiography (CONRAD) beamline facility at Helmholtz-Zentrum Berlin (HZB). The setup for neutron imaging has been described in [2]. The result showed the enhancement of mass transport and cell performance in the metal foam flow-field compared to the conventional triple-serpentine design. Correlation of performance to neutron radiography reveals that the performance deviation in the mass transport region is likely due to flooding issues. The metal foam flow-field based PEFC exhibits less flooding and better uniformity in the local water distribution compared with that of serpentine flow-field design (Fig. 1 (b)). [1] Wu, Y., et al. "Effect of serpentine flow-field design on the water management of polymer electrolyte fuel cells: An in-operando neutron radiography study." Journal of Power Sources 399 (2018): 254-263. [2] Wu, Y., et al. "Effect of compression on the water management of polymer electrolyte fuel cells: An in-operando neutron radiography study." Journal of Power Sources 412 (2019): 597-605. Figure 1

Structure of plastic-munching enzyme solved

Plastic bottles and packaging made from poly(ethylene terephthalate) (PET) are ubiquitous, and plastic litter is a global problem, from the great Pacific garbage patch to the air we breathe. PET can be broken down and reused, but the process is not widely employed. In 2016, researchers discovered a bacterium that partially feeds on PET. The bacterium uses two enzymes: PETase converts PET to mono(2-hydroxyethyl) terephthalate (MHET) and then MHETase breaks that product into terephthalic acid and ethylene glycol. Researchers at the University of Greifswald and Helmholtz-Zentrum Berlin have now solved the crystal structure of MHETase (Nat. Commun. 2019, DOI: 10.1038/s41467-019-09326-3), showing how the enzyme closes around the substrate when it docks. After determining the active-site structure, the team made mutants that work at higher substrate concentrations and can break down another substrate, taking another step in the journey toward plastics biorecycling.

Laue three dimensional neutron diffraction

This article presents a measurement technique and data analysis tool to perform 3D grain distribution mapping and indexing of oligocrystalline samples using neutrons: Laue three-dimensional neutron diffraction (Laue3DND). The approach builds on forward modelling used for correlation and multiple fitting of the measured diffraction spots relative to individual grains. This enables not only to identify individual grains, but also their position and orientation in the sample. The feasibility and performance of the Laue3DND approach are tested using multi-grain synthetic datasets from cubic (α-Fe) and tetragonal (YBaCuFeO5) symmetries. Next, experimental results from two data sets measured at the FALCON instrument of Helmholtz-Zentrum Berlin are presented: A cylindrical alpha iron (α-Fe) reference sample with 5 mm diameter and 5 mm height, as well as a 2 mm3 layered perovskite (YBaCuFeO5). Using Laue3DND, we were able to retrieve the position and orientation of 97 out of 100 grains from a synthetic α-Fe data set, as well as 24 and 9 grains respectively from the α-Fe and YBaCuFeO5 sample measured at FALCON. Results from the synthetic tests also indicate that Laue3DND is capable of indexing 10 out of 10 grains for both symmetries in two extreme scenarios: using only 6 Laue projections and using 360 projections with extremely noisy data. The precision achieved in terms of spatial and orientation resolution for the current version of the method is 430 μm and 1° respectively. Based on these results obtained, we are confident to present a tool that expands the capabilities of standard Laue diffraction, providing the number, position, orientation and relative size of grains in oligocrystalline samples.

On the characterization of a 1 m long, ultra-precise KB-focusing mirror pair for European XFEL by means of slope measuring deflectometry.

Recently, the European X-Ray Free Electron Laser (XFEL) has successfully produced its first X-ray photon pulse trains. This unique photon source will provide up to 27 000 photon pulses per second for experiments in different fields of science. In order to accomplish this, ultra-precise mirrors of dedicated shape are used to guide and focus these photons along beamlines of up to 930 m in length from the source in the undulator section to the desired focal point at an experimental station. We will report on a Kirkpatrick-Baez-mirror pair designed to focus hard-X-rays in the energy range from 3 to 16 keV to a 100 nm scale at the SPB/SFX instrument of the European XFEL. Both mirrors are elliptical cylinder-like shaped. The figure error of these 1 m long mirrors was specified to be better than 2 nm pv in terms of the height domain; this corresponds to a slope error of about 50 nrad rms (at least a best effort finishing is requested). This is essential to provide optimal experimental conditions including preservation of brilliance and wavefront. Such large and precise optics represents a challenge for the required deterministic surface polishing technology, elastic emission machining in this case, as well as for the metrology mandatory to enable a precise characterization of the topography on the mirror aperture. Besides the slope errors, the ellipse parameters are also of particular interest. The mirrors were under inspection by means of slope measuring deflectometry at the BESSY-NOM slope measuring profiler at the Helmholtz Zentrum Berlin. The NOM measurements have shown a slope error of 100 nrad rms on a aperture length of 950 mm corresponding to a residual figure deviation ≤20 nm pv for both mirrors. Additionally we found a strong impact of the mirror support conditions on the mirror shape finally measured. We will report on the measurement concept to characterize such mirrors as well as to discuss the achieved results.

10th ISSE Workshop on Sample Environment at Scattering Facilities at the Helmholtz-Zentrum Berlin

10th ISSE Workshop on Sample Environment at Scattering Facilities at the Helmholtz-Zentrum Berlin

Transverse resonance island buckets for synchrotron-radiation based electron time-of-flight spectroscopy.

At the Metrology Light Source (MLS), the compact electron storage ring of the Physikalisch-Technische Bundesanstalt (PTB) with a circumference of 48 m, a specific operation mode with two stable closed orbits for stored electrons was realized by transverse resonance island buckets. One of these orbits is closing only after three turns. In combination with single-bunch operation, the new mode was applied for electron time-of-flight spectroscopy with an interval of the synchrotron radiation pulses which is three times the revolution period at the MLS of 160 ns. The achievement is of significant importance for PTB's future programs of angular-resolved electron spectroscopy with synchrotron radiation and similar projects at other compact electron storage rings. The scheme applied here for selecting the photons originating from a particular orbit by optical imaging has been used before in fs slicing applications and may be relevant for the BESSY VSR project of the Helmholtz-Zentrum Berlin.

Measuring Aging Stability of Perovskite Solar Cells

Michael Saliba is a Group Leader at the Adolphe Merkle Institute in Fribourg, Switzerland. His group studies novel materials focusing on perovskites for a sustainable energy future. Michael was a Marie Curie Fellow at EPFL. He obtained his PhD at Oxford University, an MSc with the Max Planck Institute for Solid State Research, and BSc degrees in mathematics and physics from Stuttgart University. Michael was awarded the Young Scientist Award of the German University Association, was named one of the World's 35 Innovators Under 35 by the MIT Technology Review, and is a Member of the Global Young Academy. Martin Stolterfoht is a postdoctoral research fellow in the Soft Matter Physics group at the University of Potsdam, Germany. He completed his Master degree in Physics at the University of Graz and obtained his PhD at the University of Queensland Australia in 2016 before moving to Potsdam. His research is focused on improving device efficiency through a fundamental understanding of charge transport and recombination processes in perovskite and organic solar cells. Christian M. Wolff obtained an MSc in Physics from Ludwig-Maximilians- Universitat Munchen with a focus on spectroscopy on semiconductor nanomaterials for solar-to-fuel conversion with Prof. J. Feldmann. He joined Prof. Neher's group in 2015 investigating halide perovskites and loss mechanisms in single and multijunction solar cells. Dieter Neher is a full professor of Soft Matter Physics at the University of Potsdam, Germany. He received his Diploma in Physics and his PhD in Chemical Physics at the Johannes Gutenberg University in Mainz, Germany. He worked as a postdoctoral research fellow at the Optical Science Center in Tuscon and the CREOL in Orlando, US. His current research focuses on the understanding and improvement of the electrical and optoelectronic properties of organic conjugated materials, hybrid organic/inorganic systems and organometallic perovskite semiconductors, and the implementation of such materials into highly efficient devices. Antonio Abate is a group leader at the Helmholtz-Zentrum Berlin in Germany and Visiting Professor at Fuzhou University in China. His group is currently researching novel active materials and interfaces to make stable perovskite solar cells. Before his move to the Helmholtz, Antonio was leading the solar cell research at the Adolphe Merkle Institute in Switzerland. After his PhD in Politecnico di Milano in Italy, he was a Marie Sklodowska-Curie Fellow at Ecole Polytechnique Federale de Lausanne and postdoctoral researcher at the University of Oxford.

Advanced characterization and in-situ growth monitoring of Cu(In,Ga)Se2 thin films and solar cells

The continuous improvement of Cu(In,Ga)Se2 (CIGSe) solar cells relies considerably on advanced characterization of individual layers in the solar-cell stacks as well as of completed CIGSe devices. The present contribution provides an overview of corresponding efforts performed by various research groups at Helmholtz-Zentrum Berlin für Materialien und Energie GmbH. In-situ growth monitoring of CIGSe absorber layers by means of energy-dispersive X-ray spectrometry and light scattering is described, as well as structural analyses by means of X-ray and neutron diffraction. In addition, the characterization of surfaces and interfaces by soft X-ray and electron spectroscopy, the microscopic analysis by means of correlative electron microscopy, and optoelectronic characterization by optical spectroscopy are highlighted. The present contribution shows which substantial efforts in a research network are necessary in order to obtain deeper insight into materials properties and potentially limiting factors for the device performance, as well as to be able to control these factors during the solar-cell production.

Salvage proton beam therapy for recurrent iris melanoma: outcome and side effects.

This study aims to analyze the effect of salvage proton beam therapy for the treatment of recurrent iris melanoma. In this clinical case series, we retrospectively analyzed the data of eight patients who underwent proton beam therapy of the whole anterior segment as salvage therapy between 2000 and 2016 for recurrent iris melanoma after resection, ruthenium brachytherapy, or sector proton beam therapy. Two patients received salvage proton beam therapy for repeated tumor relapse. All patients were observed and prepared for proton beam therapy at the Charité and irradiated at the Helmholtz-Zentrum Berlin where they received 50 cobalt Gray equivalents (CGE) in four daily fractions. We investigated survival rates and ocular outcome. Median follow-up after salvage proton beam therapy was 39months. No local recurrence was detected during follow-up. One patient died from hepatic metastases 5.5years after salvage therapy. Secondary glaucoma occurred in seven out of eight patients during follow-up. Two patients had chronic corneal erosion and two other patients presented with corneal decompensation, necessitating Descemet membrane endothelial keratoplasty (DMEK), and perforating keratoplasty. Median visual acuity was 0.2 logMAR before salvage proton beam therapy and 0.7 logMAR at the end of follow-up. Whole anterior segment salvage proton beam therapy has effectively controlled recurrent iris melanoma in our patients, but has been associated with a high incidence of radiation-induced corneal impairment and secondary glaucoma requiring extensive secondary treatment.

Gratings for synchrotron and FEL beamlines: aproject for the manufacture of ultra-precise gratings at Helmholtz Zentrum Berlin.

Blazed gratings are of dedicated interest for the monochromatization of synchrotron radiation when a high photon flux is required, such as, for example, in resonant inelastic X-ray scattering experiments or when the use of laminar gratings is excluded due to too high flux densities and expected damage, for example at free-electron laser beamlines. Their availability became a bottleneck since the decommissioning of the grating manufacture facility at Carl Zeiss in Oberkochen. To resolve this situation a new technological laboratory was established at the Helmholtz Zentrum Berlin, including instrumentation from Carl Zeiss. Besides the upgraded ZEISS equipment, an advanced grating production line has been developed, including a new ultra-precise ruling machine, ion etching technology as well as laser interference lithography. While the old ZEISS ruling machine GTM-6 allows ruling for a grating length up to 170 mm, the new GTM-24 will have the capacity for 600 mm (24 inch) gratings with groove densities between 50 lines mm-1 and 1200 lines mm-1. A new ion etching machine with a scanning radiofrequency excited ion beam (HF) source allows gratings to be etched into substrates of up to 500 mm length. For a final at-wavelength characterization, a new reflectometer at a new Optics beamline at the BESSY-II storage ring is under operation. This paper reports on the status of the grating fabrication, the measured quality of fabricated items by ex situ and insitu metrology, and future development goals.

Professor Michael H. Foerster: update of the option for treatment of intraocular tumors

Being more than 19 years head of the Eye Clinic, Charite-Campus Benjamin Franklin, Prof. Dr. Michael Foerster ( Figure 1 ) is a leading expert in the field of eye tumors in the ocular fundus. These tumors are the result of an extremely malicious disease, which not only menace the ability to see, but also but a patient in mortal danger. Patients with eye tumors are being treated with proton beams since June 1998 by the Universitatsklinikum Benjamin Franklin of the Freie Universitat Berlin (now: Charite, Universitatsmedizin Berlin, Campus Benjamin Franklin) together with the Hahn-Meitner-Institut (now: Helmholtz-Zentrum Berlin fur Materialien und Energie) in Berlin.

Effects of doxorubicin on the structural and morphological characterization of solid lipid nanoparticles (SLN) using small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS)

Cancer is still a major public health problem. Leaving detection of early stages of tumors and other issues aside, minimizing unwarranted side effects, for example after clinical usage of a liposomal anticancer drug doxorubicin (Dox) formulation, is an unmet clinical problem and the focus of many studies. Using compounds typically used in the preparation of food and/or cosmetics to prepare drug carrier systems, we observed that sodium tetradecyl sulfate (STS) containing and soybean-oil based carriers are more efficient in reducing the viability of HeLa cells tumor cells in comparison to their respective counterparts. Here, we probe the doxorubicin (Dox) loading on structural properties of either soybean oil or coconut oil (Mygliol 812) formulations. Small angle neutron scattering (SANS) assays were performed using V16 instrument at Helmholtz-Zentrum Berlin (HZB) at 25, 37 and 40 °C with two or 11 m distance between detector and sample to assess a wide range in scattering vector Q. Combined with previous measurement using small angle X-ray scattering (SAXS), our results show that the Dox has different influence in the surface structure of the solid lipid nanoparticles (SLN) and also affects the fractality in the vesicle aggregates when the concentration of the drug is altered, for Mygliol and soybean oil SLN drug delivery carrier systems.