Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31483 Publications
Two-Dimensional Kagome Lattices Made of Hetero Triangulenes Are Dirac Semimetals or Single-Band Semiconductors
Jing, Y.; Heine, T.ORC
Here we discuss, based on first-principles calculations, two-dimensional (2D) kagome lattices composed of polymerized heterotriangulene units, planar molecules with D3h point group containing a B, C, or N center atom and CH2, O, or CO bridges. We explore the design principles for a functional lattice made of 2D polymers, which involves control of π-conjugation and electronic structure of the knots. The former is achieved by the chemical potential of the bridge groups, while the latter is controlled by the heteroatom. The resulting 2D kagome polymers have a characteristic electronic structure with a Dirac band sandwiched by two flat bands and are either Dirac semimetals (C center), or single-band semiconductors—materials with either exclusively electrons (B center) or holes (N center) as charge carriers of very high mobility, reaching values of up to ∼8 × 103 cm2 V–1 s–1, which is comparable to crystalline silicon.
Keywords: DFT, kagome, 2D polymers, 2D COFs
  • Journal of the American Chemical Society 141(2019)2, 743-747
    Online First (2018) DOI: 10.1021/jacs.8b09900

Publ.-Id: 28890 - Permalink

Testing halophilic bacteria for their potential as pyrite biodepressants in Cu-Mo bioflotation
Luque Consuegra, G.;
Presentation outlining work up to June 2018 in the screening of halophilic bacteria as pyrite biodepressants in Cu-Mo bioflotation processes delivered in the BHT conference in TUBAF, Freiberg.
Keywords: Bioflotation, Pyrite, Halophilic bacteria, Adhesion, M.A.T.H
  • Lecture (Conference)
    BHT – Freiberger Universitätsforum, 08.06.2018, Freiberg, Deutschland

Publ.-Id: 28884 - Permalink

Characterization of Continuous Wave Laser-Induced ThermalGradients in Magnetic Tunnel Junctions Integrated IntoMicroresonators via COMSOL Simulations
Cansever, H.; Lindner, J.; Huebner, T.; Niesen, A.; Reiss, G.; Fassbender, J.; Deac, A. M.;
Spin caloritronics investigates static and dynamic effects on magnetic structures due to spin-currents generated by thermalgradients. Here, we present COMSOL simulation results using a 2-D heat transfer module applied to Co2FeAl/MgO/CoFeB magnetictunnel junctions (MTJs) integrated into microcavity resonators. Microresonators are used in order to study the effects of temperaturegradients on single micro-/nano-objects. We find that the thermal conductivity of the insulating barrier (MgO) plays a crucialrole, influencing the overall temperature, as well as the thermal gradient over the barrier. Taking into account the microresonatorstructure around the MTJ, which is mainly made from copper, strongly affects the uniform heating of the overall stack. Nevertheless,the gradient over the barrier is relatively unaffected by the surrounding conditions. The simulation results provide insight intothe temperature profile of the whole structure and show how modifying the structure of the surrounding materials may tune andoptimize the thermal gradient magnitude and ultimately provide a path for quantifying spin-transfer torques induced by thermalgradients.
Keywords: COMSOL simulation, ferromagnetic resonance (FMR), magnetic tunnel junction (MTJ), microresonator


  • Secondary publication expected from 05.02.2020

Publ.-Id: 28879 - Permalink

Fast-neutron-induced fission cross section of Pu(242) measured at the neutron time-of-flight facility nELBE
Kögler, T.ORC; Junghans, A. R.ORC; Beyer, R.ORC; Dietz, M.; Düllmann, C. E.ORC; Eberhardt, K.; Lorenz, C.; Müller, S. E.ORC; Nolte, R.; Reinhardt, T. P.; Schmidt, K.; Runke, J.; Schwengner, R.ORC; Takacs, M.; Vascon, A.; Wagner, A.ORC
The fast-neutron-induced fission cross section of ²⁴²Pu was measured at the neutron time-of-flight facility nELBE. A parallel-plate fission ionization chamber with novel, homogeneous, large-area ²⁴²Pu deposits on Si-wafer backings was used to determine this quantity relative to the IAEA neutron cross-section standard ²³²U(n, f ) in the energy range of 0.5 to 10 MeV. The number of target nuclei was determined from the measured spontaneous fission rate of ²⁴²Pu. This helps to reduce the influence of the fission fragment detection efficiency on the cross section. Neutron transport simulations performed with GEANT 4, MCNP 6, and FLUKA 2011 are used to correct the cross-section data for neutron scattering. In the reported energy range the systematic uncertainty is below 2.7% and on average the statistical uncertainty is 4.9%. The determined results show an agreement within 0.67(16)% to recently published data and a good accordance to current evaluated data sets.
Keywords: neutron-induced fission, plutonium, parallel plate fission ionization chambers, cross section measurements, neutron transport simulations, nuclear reactions, nucleon induced nuclear reactions, nELBE
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Die Bestimmung des neutroneninduzierten Spaltquerschnitts… (Id 26338) HZDR-primary research data are used by this publication


Publ.-Id: 28878 - Permalink

Carboranyl Analogues of Celecoxib with Potent Cytostatic Activity against Human Melanoma and Colon Cancer Cell Lines
Buzharevski, A.; Paskas, S.; Sárosi, M. B.; Laube, M.; Lönnecke, P.; Neumann, W.; Mijatovic, S.; Maksimovic-Ivanic, D.; Pietzsch, J.ORC; Hey-Hawkins, E.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most common way of treating inflammatory disorders. Their widespread use helped reveal their other modes of action as pharmaceuticals, such as a profound effect on various cancers. Celecoxib has proven to be a very prominent member of this group with cytostatic activities. On the other hand, the highly dynamic field of drug design is constantly searching for new ways of modifying known structures to obtain more powerful and less harmful drugs. A very interesting development is the implementation of carboranes in pharmacologically active structures, mostly as phenyl mimetics. Herein we report the synthesis of three carborane-containing derivatives of the COX-2-selective NSAID celecoxib. The new compounds proved to have promising cytostatic potential against various melanoma and colorectal adenocarcinoma cell lines. Inhibited proliferation accompanied by caspase-independent apoptotic cell death was found to be the main cause of decreased cell viability upon treatment with the most efficient celecoxib analogue, 3 b (4-[5-(1,7-dicarba-closo-dodecaboranyl)-3-trifluoromethyl-1H-pyrazol-1-yl]-1-methylsulfonylbenzene).
Keywords: cancer; carboranes; celecoxib; cytotoxicity; drug discovery


Publ.-Id: 28874 - Permalink

Fluorine-18 labeling of S100 proteins for small animal positron emission tomography
Laube, M.; Kniess, T.; Neuber, C.; Haase-Kohn, C.; Pietzsch, J.ORC
The interaction of S100 proteins (S100s), a multigenic family of Ca2+-binding and Ca2+-modulated proteins, with pattern recognition receptors, e.g., Toll-like receptors (TLRs), the receptor for advanced glycation end products (RAGE), or scavenger receptors (SR), is hypothesized to be of high relevance in the pathogenesis of various diseases. This includes chronic inflammatory conditions, atherosclerosis, cardiomyopathies, neurodegeneration, and progression of cancers. However, data concerning the role of circulating S100s in these pathologies are scarce. One reason for this is the shortage of suitable radiolabeling methods for direct assessment of the metabolic fate of circulating S100s in vivo. We report a radiotracer approach using radiolabeling of recombinant human S100s with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB). The methodological radiochemical part focuses on an optimized and automated synthesis of [18F]SFB comprising HPLC purification to achieve higher chemical purity. The respective radioligands, [18F]fluorobenzoylated S100s ([18F]FB-S100s), were obtained with appropriate radiochemical purities, yields, and effective molar activities. Biological applications comprise cell and tissue binding experiments in vitro, biodistribution and metabolite studies in rodents in vivo/ex vivo, and dynamic positron emission tomography studies using dedicated small animal PET systems. Radiolabeling of S100s with 18F and, particularly, the use of small animal PET provide novel probes to delineate both their metabolic fate and the functional expression of their specific receptors under normal and pathophysiological conditions in rodent models of disease.
Keywords: Bolton-Hunter-type reagent; in vivo imaging; radiopharmacological characterization; 18F building block; module-assisted radiosynthesis; S100 proteins; calcium; EF-hand
  • Book chapter
    Claus W. Heizmann: Calcium-Binding Proteins of the EF-Hand Superfamily: From Basics to Medical Applications, New York, NY: Humana Press, 2019, 978-1-4939-9029-0, 461-485
    DOI: 10.1007/978-1-4939-9030-6_29
  • Methods in Molecular Biology 1929(2019), 461-485
    DOI: 10.1007/978-1-4939-9030-6_29


  • Secondary publication expected from 02.02.2020

Publ.-Id: 28872 - Permalink

The Inverse Trans Effect in Uranium complexes containing N-heterocyclic Carbenes
Köhler, L.; März, J.; Patzschke, M.; Kloditz, R.; Stumpf, T.;
Aim of this work was to investigate the inverse trans influence (ITI) in uranium complexes containing soft-donor ligands. Uranium(IV) and (V) complexes were synthesized by using the N-heterocylic carbene ligand iPrIm (L¹ ) and lithium bis(trimethylsilyl)amide (TMSA) as a base. The structural characterization by SC-XRD and geometry optimization of the resulting compounds [U(IV)(L¹ )₂(TMSA)Cl₃] (1) and (HL¹ )₂ [U(V)(TMSI)Cl₅] (2) (TMSI = trimethylsilylimide) confirmed the occurrence of an inverse trans influence (ITI) by means of the silylamido- or silylimido ligand.
Keywords: inverse trans influence, ITI, uranium complex, actinides
  • Lecture (others)
    Bilaterales Treffen mit AK Roesky (KIT), 10.-11.01.2019, Karlsruhe, Deutschland

Publ.-Id: 28869 - Permalink

Reversible adiabatic temperature change in the shape memory Heusler alloy NiMn0.8Ga: An effect of structural compatibility
Devi, P.; Ghorbani Zavareh, M.; Salazar Mejia, C.; Hofmann, K.; Albert, B.; Felser, C.; Nicklas, M.; Singh, S.;
The large magnetocaloric effect (MCE) observed in Ni-Mn based shape memory Heusler alloys put them forward to use in magnetic refrigeration technology. It is associated with a first-order magnetostructural (martensitic) phase transition.We conducted a comprehensive study of the MCE for the off-stoichiometric Heusler alloy Ni2.2Mn0.8Ga in the vicinity of its first-order magnetostructural phase transition. We found a reversible MCE under repeated magnetic field cycles. The reversible behavior can be attributed to the small thermal hysteresis of the martensitic phase transition. Based on the analysis of our detailed temperature dependent x-ray diffraction data, we demonstrate the geometric compatibility of the cubic austenite and tetragonal martensite phases. This finding directly relates the reversible MCE behavior to an improved geometric compatibility condition between cubic austenite and tetragonal martensite phases. The approach will help to design shape memory Heusler alloys with a large reversible MCE taking advantage of the first-order martensitic phase transition.

Publ.-Id: 28868 - Permalink

Focusing of multi-MeV, subnanosecond proton bunches from a laser-driven source
Jahn, D.; Schumacher, D.; Brabetz, C.; Kroll, F.; Brack, F.-E.; Ding, J.; Leonhardt, R.; Semmler, I.; Blazevic, A.; Schramm, U.; Roth, M.;
We report on our latest transverse focusing results of subnanosecond proton bunches achieved with a laser-driven multi-MeV ion beamline. In the frame of the LIGHT collaboration, a target normal sheath acceleration (TNSA) source based 6 m long beamline was installed. In the past years, the laser-driven proton beam was transported and shaped by this beamline. The particle beam is collimated with a pulsed high-field solenoid and rotated in longitudinal phase space with a radio-frequency cavity which leads to an energy compression with an energy spread of (2.7 +/- 1.7)% (Delta E/E-0 at FWHM) or a time compression to the subnanosecond regime. Highest peak intensities in the subnanosecond regime open up an interesting field for several applications, e.g., proton imaging, as injectors in conventional accelerators or precise stopping power measurements in a plasma. We report on achieving highest peak intensities using an installed second solenoid as a final focusing system in our beamline to achieve small focal spot sizes. We measured a focal spot size of 1.1 x 1.2 mm leading to 5.8 x 10(19) protons per s cm(2) at a central energy bin of (9.55 +/- 0.25) MeV, which can be combined with a bunch duration below 500 ps at FWHM.


Publ.-Id: 28866 - Permalink

4He irradiation of zircon, ZrSiO4, using a micro-patterned, Si-based energy filter
Nasdala, L.; Akhmadaliev, S.; Chanmuang N., C.; Zowalla, A.; Csato, C.; Rüb, M.;
The quantitative evaluation of alpha-particle damage in the mineral zircon, ZrSiO4, using 4He irradiation experiments is difficult because the vast majority of atomic knock-ons in the target are concentrated in a narrow depth range near the ends of the He-ion trajectories. Here we present a new concept to overcome this problem, namely, tailoring the depth profile of damage by means of a micromechanically fabricated “energy filter”. Lamellae of 1.5 μm thickness, prepared from ZrSiO4 using the focused-ion-beam technique, were subjected to irradiation with 8.8 MeV 4He ions. Five irradiations with ion fluences in the range 2.5 × 1015–1 × 1017 cm-2 have resulted in mild to severe damage, as monitored by the broadening and downshift of SiO4-stretching Raman bands. Our results may provide a means for quantifying the contribution of alpha particles to the total self-irradiation damage in zircon.
Keywords: Radiation damage, Helium irradiation, Energy filter, Focused ion beam, Raman spectroscopy

Publ.-Id: 28865 - Permalink

Software in the context of luminescence dating: status, concepts and suggestions exemplified by the R package Luminescence
Kreutzer, S.; Burow, C.; Dietze, D.; Fuchs, M. C.; Fischer, M.; Schmidt, C.;
The relevance of luminescence dating is re- flected by the steadily growing quantity of published data. At the same time, the amount of data available for analysis has increased due to technological and methodological advances. Routinely, luminescence data are analysed using a mixture of commercially available soft- ware, self-written tools and specific solutions. Based on a luminescence dating literature screening we show how rarely articles report on the software used for the data analysis and we discuss potential problems arising from this. We explore the growing importance of the statistical programming language R in general and especially its reflection in recent software developments in the context of lu- minescence dating. Specifically, for the R package ‘Luminescence’ we show how the transparency, flexibility and reliability of tools used for the data analysis have been improved. We finally advocate for more transparency if unvalidated software solutions are used and we emphasise that more attention should be paid to the tools used for analysing the data.
Keywords: R, Software, Luminescence dating, Data analysis
  • Open Access LogoAncient TL 35(2017)2, 1-11


Publ.-Id: 28863 - Permalink

The Need for Multi-Source, Multi-Scale Hyperspectral Imaging to Boost Non-Invasive Mineral Exploration
Gloaguen, R.; Ghamisi, P.; Lorenz, S.; Kirsch, M.; Zimmermann, R.; Booysen, R.; Andreani, L.; Jackisch, R.; Hermann, E.; Tusa, L.; Unger, G.; Contreras, C.; Khodadadzadeh, M.; Fuchs, M.;
The high demand for raw materials in our post-industrial societies contrasts the increasing difficulties to find new mineral deposits. In Europe, accessible and high-grade deposits are mostly exhausted or currently mined. Hence, future exploration must focus on the remaining, more remote locations or penetrate much deeper into the Earth's crust. Sustaining mining activities in Europe would allow the development of key technologies but also sustainable and ethical production of technological metals. Thus, we suggest to focus research on advances in multi-scale and multi-sensor remote sensing-based Earth integration techniques. The scale should range from satellite to air- and drone-borne systems and include ground validation. Multi-sensor downscaling methods involving SAR and optical data are particularly promising. We demonstrate that the integration with other sensors and/or measures such as geophysical/geochemical data as well as non-conventional remote sensing features such as textures and geometries are of interest. Thus, ultimately, our objective is to boost the competitiveness, growth, sustainability and attractiveness of the raw material sector in Europe. While we focus on the raw material sector as it is currently of strategic importance, the required methods are transferable to most environmental studies.
Keywords: Hyperspectral Imaging, Mineral Exploration
  • Open Access LogoContribution to proceedings
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 22.-27.09.2018, Valencia, Spain
    Proceedings of IGARSS 2018

Publ.-Id: 28859 - Permalink

Heavy Metal Binding Peptides – Design and Construction of new Biosorbents
Braun, R.ORC; Schönberger, N.; Bachmann, S.; Matys, S.ORC; Lederer, F.ORC; Pollmann, K.ORC
Heavy metal contaminations in both industrial and environmental waters are widely occurring. However, removal is both challenging and cost-intensive. In this study, we identified metal-binding peptide sequences using phage surface display (PSD). Fusion proteins with PSD-derived sequences were construced for further recombinant production, future scale-up and as alternative to chemical synthesis. The construction of the fusion proteins included usage of inteins and affinity tags for simplified expression and purification. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used for further characterization of the peptide-metal interaction. The system developed in this study provides metal-binding peptides with high specificity and sensitivity. Being biodegradable, the constructed peptides can be used in multiple applications. The identified motifs can furthermore provide a deeper understanding of peptide-metal interaction, leading to the discovery of novel metal-interacting biomolecules and better prediction of involved amino acids.
  • Poster
    8th Peptide Engineering Meeting, 08.-10.11.2018, Berlin, Deutschland

Publ.-Id: 28858 - Permalink

Multivariate Data Assimilation for Resource Model Updating
Prior, A.; Benndorf, J.; Tolosana-Delgado, R.; van den Boogaart, K. G.;
This is just a presentation in the COSMO Day. I did not submit an abstract since I was invited speaker
  • Invited lecture (Conferences)
    COSMO Day 2018, 05.07.2018, Montreal, Canada

Publ.-Id: 28856 - Permalink

Multivariate Ensemble Based Sequential Update Of The Resource Model For Real Time Mine Settings
Prior, A.; Tolosana-Delgado, R.; Prior-Arce, A.;
Mining industry is continuously monitoring key performance indicators (KPI), and geo-metallurgical properties such as grade, fragmentation or tonnage and reconciling estimates to online capture production performance parameters. New technology is looking for monitoring also other properties as grain size.
Relevant information is obtained from sensors installed at different mining production process stages, as in a Block Evaluation or Schedule and Blending.
This study aims to develop an efficient updating framework based on Sequential Ensemble Filtering by using compositional data statistics that will be able to cope with the non-linearities of the system.
  • Poster
    POF Evaluation, 28.02.-02.03.2018, Dresden, Germany

Publ.-Id: 28855 - Permalink

Resource model updating for underground mining production settings
Prior, A.; Benndorf, J.; Mariz, C.;
This research is part of the European Union funded 'Real Time Mining' project, which aims to develop a new framework to reduce uncertainties during the extraction process in highly selective underground mining settings. A continuously self-updating resource/grade control model concept is presented and aims to improve the raw material quality control and process efficiency of any type of mining operation. Applications in underground mines include the improved control of different components of the mineralogy and geochemistry of the extracted ore utilizing available “big data” collected during production. The development of the methodology is based on two full scale case study, the copper-zinc mine Neves-Corvo in Portugal and Reiche-Zeche mine in Germany. These serve for both, for the definition of method requirements and also as a basis for defining a Virtual Asset Model (VAM), which serves for artificial sampling as benchmark for performance analysis. This contribution introduces to the updating concept, provides a brief description of the method, explains details of the test cases and demonstrates the value added by an illustrative case study.
Keywords: Underground Mining, Data Assimilation, Geostatistitcs
  • Open Access LogoContribution to proceedings
    REAL TIME MINING - Conference on Innovation on Raw Material Extraction Amsterdam 2017, 10.-11.10.2017, Amsterdam, The Netherlands

Publ.-Id: 28854 - Permalink

Tissue-type mapping of gliomas.
Raschke, F.; Barrick, T. R.; Jones, T.; Yang, G.; Ye, X.; Howe, F. A.;

To develop a statistical method of combining multimodal MRI (mMRI) of adult glial brain tumours to generate tissue heterogeneity maps that indicate tumour grade and infiltration margins.


We performed a retrospective analysis of mMRI from patients with histological diagnosis of glioma (n = 25). 1H Magnetic Resonance Spectroscopic Imaging (MRSI) was used to label regions of "pure" low- or high-grade tumour across image types. Normal brain and oedema characteristics were defined from healthy controls (n = 10) and brain metastasis patients (n = 10) respectively. Probability density distributions (PDD) for each tissue type were extracted from intensity normalised proton density and T2-weighted images, and p and q diffusion maps. Superpixel segmentation and Bayesian inference was used to produce whole-brain tissue-type maps.


Total lesion volumes derived automatically from tissue-type maps correlated with those from manual delineation (p < 0.001, r = 0.87). Large high-grade volumes were determined in all grade III & IV (n = 16) tumours, in grade II gemistocytic rich astrocytomas (n = 3) and one astrocytoma with a histological diagnosis of grade II. For patients with known outcome (n = 20), patients with survival time < 2 years (3 grade II, 2 grade III and 10 grade IV) had a high-grade volume significantly greater than zero (Wilcoxon signed rank p < 0.0001) and also significantly greater high grade volume than the 5 grade II patients with survival >2 years (Mann Witney p = 0.0001). Regions classified from mMRI as oedema had non-tumour-like 1H MRS characteristics.


1H MRSI can label tumour tissue types to enable development of a mMRI tissue type mapping algorithm, with potential to aid management of patients with glial tumours.
Keywords: Glioma; Magnetic resonance spectroscopy (MRS); Multimodal MRI; Nosologic imaging; Pattern recognition

Publ.-Id: 28845 - Permalink

Dynamics of the magnetoelastic phase transition and adiabatic temperature change in Mn1.3Fe0.7P0.5Si0.55
Fries, M.; Gottschall, T.; Scheibel, F.; Pfeuffer, L.; Skokov, K. P.; Skourski, I.; Acet, M.; Farle, M.; Wosnitza, J.; Gutfleisch, O.;
The adiabatic temperature change ΔTad of a Mn1.3Fe0.7P0.5Si0.55 Fe2P-type alloy was measured under different magnetic field-sweep rates from 0.93 Ts−1 to 2870 Ts−1. We find a field-sweep-rate independent magnetocaloric effect due to a partial alignment of magnetic moments in the paramagnetic region overlapping with the magnetocaloric effect of the first-order phase transition. Additionally, the first-order phase transition is not completed even in fields up to 20 T leading to a non-saturating behavior of ΔTad. Measurements in different pulsed fields reveal that the first-order phase transition cannot follow the fast field changes as previously assumed, resulting in a distinct field-dependent hysteresis in ΔTad.

Publ.-Id: 28844 - Permalink

Enzymes Immobilized on Carbon Nitride (C3N4) Cooperating with Metal Nanoparticles for Cascade Catalysis
Wang, Y.; Zhang, N.; Hübner, R.; Tan, D.; Löffler, M.; Facsko, S.; Zhang, E.; Ge, Y.; Qi, Z.; Wu, C.;
The exploration of effective platforms for immobilizing chemo- and biocatalysts to develop biohybrid catalysts is an attractive subject of practical interest. In this work, carbon nitride (C3N4) is used for the first time as a platform for the immobilization of metal catalyst (Pd nanoparticles) and biocatalyst (Candida antarctica lipase B, CalB) in a facile manner to prepare biohybrid catalyst. The optimal biohybrid catalyst inherits the intrinsic performance of both Pd nanoparticles and CalB, and shows high activity in the one-pot cascade reaction converting benzaldehyde to benzyl hexanoate at room temperature. With this proof of concept, it is expected that C3N4 can be utilized for immobilizing more types of chemo- and biocatalysts for perspective applications.
Keywords: biohybrid catalysts, CalB, carbon nitride, cascade reactions, Pd nanoparticles

Publ.-Id: 28842 - Permalink

Technical Note: Experimental verification of magnetic field-induced beam deflection and Bragg peak displacement for MR-integrated proton therapy.
Schellhammer, S. M.; Gantz, S.; Lühr, A.; Oborn, B. M.; Bussmann, M.; Hoffmann, A. L.;
Purpose: Given its sensitivity to anatomical variations, proton therapy is expected to benefit greatly from integration with magnetic resonance imaging for online anatomy monitoring during irradiation.
Such an integration raises several challenges, as both systems mutually interact. The proton beam will experience quasi-continuous energy loss and energy-dependent electromagnetic deflection at the same time, giving rise to a deflected beam trajectory and an altered dose distribution with a displaced Bragg peak. So far, these effects have only been predicted using Monte Carlo and analytical models, but no clear consensus has been reached and experimental benchmark data are lacking. We measured proton beam trajectories and Bragg peak displacement in a homogeneous phantom placed inside a magnetic field and compared them to simulations.
Methods: Planar dose distributions of proton pencil beams (80–180 MeV) traversing the field of a 0.95 T NdFeB permanent magnet while depositing energy in a PMMA slab phantom were measured using EBT3 radiochromic films and simulated using the Geant4 toolkit. Deflected beam trajectories and the Bragg peak displacement were extracted from the measured planar dose distributions and compared against the simulations.
Results: The lateral beam deflection was clearly visible on the EBT3 films and ranged from 1 to 10 mm for 80 to 180 MeV, respectively. Simulated and measured beam trajectories and Bragg peak displacement agreed within 0.8 mm for all studied proton energies.
Conclusions: These results prove that the magnetic field-induced Bragg peak displacement is both measurable and accurately predictable in a homogeneous phantom at 0.95 T, and allows Monte Carlo simulations to be used as gold standard for proton beam trajectory prediction in similar frameworks for MR-integrated proton therapy.
Keywords: magnetic field induced Bragg peak displacement, Monte Carlo simulation, MR guidance, proton dosimetry, proton therapy

Publ.-Id: 28841 - Permalink

SDF-1/CXCR4 expression is an independent negative prognostic biomarker in patients with head and neck cancer after primary radiochemotherapy
De-Colle, C.; Menegakis, A.; Mönnich, D.; Welz, S.; Boeke, S.; Sipos, B.; Fend, F.; Mauz, P. S.; Tinhofer, I.; Budach, V.; Abu, J. J.; Stuschke, M.; Balermpas, P.; Rödel, C.; Grosu, A. L.; Abdollahi, A.; Debus, J.; Belka, C.; Ganswindt, U.; Pigorsch, S.; Combs, S. E.; Lohaus, F.; Linge, A.; Krause, M.; Baumann, M.; Zips, D.;
Introduction: Preclinical and clinical data suggest that the chemokine pathway governed by SDF-1 and CXCR4 contributes to a resistant phenotype. This retrospective biomarker study aims to explore the specific prognostic value of SDF-1 and CXCR4 expression in locally advanced head and neck squamous cell carcinomas (HNSCC) treated with primary radiochemotherapy (RT-CT).
Material and methods: Biopsies from 141 HNSCC tumours of the oral cavity, oropharynx and hypopharynx were evaluated for SDF-1 and CXCR4 expression by immunofluorescence. SDF-1 and CXCR4 expression was correlated with clinico-pathological characteristics and outcome after RT-CT.
Results: Patients with tumours exhibiting overexpression of intracellular SDF-1 and CXCR4 have a higher risk for loco-regional relapse and a worse overall survival after RT-CT (multivariate analysis, hazard ratio 2.33, CI [1.18–4.62], p = 0.02 and hazard ratio 2.02, CI [1.13–3.59], p = 0.02, respectively). Similar results were observed when only the subgroup of HPV DNA negative patients were analysed (hazard ratio 2.23 and 2.16, p = 0.02 and p = 0.01, respectively).
Conclusions: Our data support the importance of SDF-1 and CXCR4 expression for loco-regional control and overall survival in HNSCC after primary radiochemotherapy. Prospective multivariate validation and further studies into CXCR4 inhibition to overcome radiation resistance are warranted.
Keywords: SDF-1 CXCR4 Head and neck cancer Prognostic Biomarker Primary radiochemotherapy

Publ.-Id: 28840 - Permalink

Improved effectiveness of stereotactic radiosurgery in large brain metastases by individualized isotoxic dose prescription: an in silico study
Zindler, J. D.; Schiffelers, J.; Lambin, P.; Hoffmann, A. L.;
Introduction In large brain metastases (BM) with a diameter of more than 2cm there is an increased risk of radionecrosis (RN) with standard stereotactic radiosurgery (SRS) dose prescription, while the normal tissue constraint is exceeded. The tumor control probability (TCP) with a single dose of 15Gy is only 42%. This in silico study tests the hypothesis that isotoxic dose prescription (IDP) can increase the therapeutic ratio (TCP/Risk of RN) of SRS in large BM.
Materials and methods A treatment-planning study with 8 perfectly spherical and 46 clinically realistic gross tumor volumes (GTV) was conducted. The effects of GTV size (0.5–4cm diameter), set-up margins (0, 1, and 2mm), and beam arrangements (coplanar vs non-coplanar) on the predicted TCP using IDP were assessed. For single-, three-, and five-fraction IDP dose–volume constraints of V12Gy = 10cm3, V19.2 Gy = 10cm3, and a V20Gy = 20cm3, respectively, were used to maintain a low risk of radionecrosis.
Results In BM of 4cm in diameter, the maximum achievable single-fraction IDP dose was 14Gy compared to 15Gy for standard SRS dose prescription, with respective TCPs of 32 and 42%. Fractionated SRS with IDP was needed to improve the TCP. For three- and five-fraction IDP, a maximum predicted TCP of 55 and 68% was achieved respectively (non-coplanar beams and a 1mm GTV-PTV margin).
Conclusions Using three-fraction or five-fraction IDP the predicted TCP can be increased safely to 55 and 68%, respectively, in large BM with a diameter of 4cm with a low risk of RN. Using IDP, the therapeutic ratio of SRS in large BM can be increased compared to current SRS dose prescription.
Keywords: Radiotherapy · Stereotactic · Dose prescription · Normal tissue tolerance · Large brain metastases

Publ.-Id: 28839 - Permalink

Impaired DNA damage response signaling by FUS-NLS mutations leads to neurodegeneration and FUS aggregate formation
Naumann, M.; Pal, A.; Goswami, A.; Lojewski, X.; Japtok, J.; Vehlow, A.; Naujock, M.; Günther, R.; Jin, M.; Stanslowsky, N.; Reinhardt, P.; Sterneckert, J.; Frickenhaus, M.; Pan-Montojo, F.; Storkebaum, E.; Poser, I.; Freischmidt, A.; Weishaupt, J. H.; Holzmann, K.; Troost, D.; Ludolph, A. C.; Boeckers, T. M.; Liebau, S.; Petri, S.; Cordes, N.; Hyman, A. A.; Wegner, F.; Grill, S. W.; Weis, J.; Storch, A.; Hermann, A.;
Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease. Cytoplasmic fused in sarcoma (FUS) aggregates are pathological hallmarks of FUS-ALS. Proper shuttling between the nucleus and cytoplasm is essential for physiological cell function. However, the initial event in the pathophysiology of FUS-ALS remains enigmatic. Using human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs), we show that impairment of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling due to mutations in the FUS nuclear localization sequence (NLS) induces additional cytoplasmic FUS mislocalization which in turn results in neurodegeneration and FUS aggregate formation. Our work suggests that a key pathophysiologic event in ALS is upstream of aggregate formation. Targeting DDR signaling could lead to novel therapeutic routes for ameliorating ALS.

Publ.-Id: 28837 - Permalink

Differential effects of α-catenin on the invasion and radiochemosensitivity of human colorectal cancer cells
Förster, S.; Hehlgans, S.; Rödel, F.; Otto, B.; Cordes, N.;
Driven by genetic and epigenetic alterations, progression, therapy resistance and metastasis are frequent events in colorectal cancer (CRC). Although often speculated, the function of cell-cell contact for radiochemosensitivity, particularly associated with E-cadherin/catenin complex, warrants further clarification. In this study, we investigated the role of the E-cadherin/catenin complex proteins under more physiological three-dimensional (3D) cell culture conditions in a panel of CRC cell lines. In contrast to floating spheroids and growth in the laminin-rich matrix, collagen type 1 induced the formation of two distinct growth phenotypes, i.e., cell groups and single cells, in 5 out of the 8 CRC cell lines.
Further characterization of these subpopulations revealed that, intriguingly, cell-cell contact proteins are important for invasion, but negligible for radiochemosensitivity, proliferation and adhesion. Despite the generation of genomic and transcriptomic data, we were unable to elucidate the mechanisms through which α-catenin affects collagen type 1 invasion. In a retrospective analysis of patients with rectal carcinoma, a low α-catenin expression trended with overall survival, as well as locoregional and distant control. Our results suggest that the E-cadherin/catenin complex proteins forming cell-cell contacts are mainly involved in the invasion, rather than the radiochemosensitivity of 3D grown CRC cells. Further studies are warranted in order to provide a better understanding of the molecular mechanisms controlling cell-cell adhesion in the context of radiochemoresistance.
Keywords: colorectal cancer, α-catenin, radiochemotherapy, E-cadherin

Publ.-Id: 28836 - Permalink

Pretherapeutic FDG–PET total metabolic tumor volume predicts response to induction therapy in pediatric Hodgkin’s lymphoma
Rogasch, J.; Hundsdoerfer, P.; Hofheinz, F.; Wedel, F.; Schatka, I.; Amthauer, H.; Furth, C.;

Standardized treatment in pediatric patients with Hodgkin’s lymphoma (HL) follows risk stratification by tumor stage, erythrocyte sedimentation rate and tumor bulk. We aimed to identify quantitative parameters from pretherapeutic FDG-PET to assist prediction of response to induction chemotherapy.


Retrospective analysis in 50 children with HL (f:18; m:32; median age, 14.8 [4–18] a) consecutively treated according to EuroNet-PHL-C1 (n = 42) or -C2 treatment protocol (n = 8). Total metabolic tumor volume (MTV) in pretherapeutic FDG-PET was defined using a semi-automated, background-adapted threshold. Metabolic (SUVmax, SUVmean, SUVpeak, total lesion glycolysis [MTV*SUVmean]) and heterogeneity parameters (asphericity [ASP], entropy, contrast, local homogeneity, energy, and cumulative SUV-volume histograms) were derived. Early response assessment (ERA) was performed after 2 cycles of induction chemotherapy according to treatment protocol and verified by reference rating. Prediction of inadequate response (IR) in ERA was based on ROC analysis separated by stage I/II (1 and 26 patients) and stage III/IV disease (7 and 16 patients) or treatment group/level (TG/TL) 1 to 3.


IR was seen in 28/50 patients (TG/TL 1, 6/12 patients; TG/TL 2, 10/17; TG/TL 3, 12/21). Among all PET parameters, MTV best predicted IR; ASP was the best heterogeneity parameter. AUC of MTV was 0.84 (95%-confidence interval, 0.69–0.99) in stage I/II and 0.86 (0.7–1.0) in stage III/IV. In patients of TG/TL 1, AUC of MTV was 0.92 (0.74–1.0); in TG/TL 2 0.71 (0.44–0.99), and in TG/TL 3 0.85 (0.69–1.0). Patients with high vs. low MTV had IR in 86 vs. 0% in TG/TL 1, 80 vs. 29% in TG/TL 2, and 90 vs. 27% in TG/TL 3 (cut-off, > 80 ml, > 160 ml, > 410 ml).


In this explorative study, high total MTV best predicted inadequate response to induction therapy in pediatric HL of all pretherapeutic FDG-PET parameters – in both low and high stages as well as the 3 different TG/TL.
Keywords: Pediatric Hodgkin’s lymphoma Early response assessment FDG-PET Metabolic tumor volume Asphericity

Publ.-Id: 28835 - Permalink

Enhancement of the effective mass at high magnetic fields in CeRhIn5
Jiao, L.; Smidman, M.; Kohama, Y.; Wang, Z. S.; Graf, D.; Weng, Z. F.; Zhang, Y. J.; Matsuo, A.; Bauer, E. D.; Lee, H.; Kirchner, S.; Singleton, J.; Kindo, K.; Wosnitza, J.; Steglich, F.; Thompson, J. D.; Yuan, H. Q.;
The Kondo-lattice compound CeRhIn5 displays a field-induced Fermi surface reconstruction at B* ≈ 30 T, which occurs within the antiferromagnetic state, prior to the quantum critical point at Bc0 ≈ 50 T. Here, in order to investigate the nature of the Fermi surface change, we measured the magnetostriction, specific heat, and magnetic torque of CeRhIn5 across a wide range of magnetic fields. Our observations uncover the field-induced itineracy of the 4f electrons, where above Bonset ≈ 17 T there is a significant enhancement of the Sommerfeld coefficient, and spin-dependent effective cyclotron masses determined from quantum oscillations. Upon crossing Bonset , the temperature dependence of the specific heat also shows distinctly different behavior from that at low fields. Our results indicate that the Kondo coupling is remarkably robust upon increasing the magnetic field. This is ascribed to the delocalization of the 4f electrons at the Fermi surface reconstruction at B*.

Publ.-Id: 28834 - Permalink

Concise Review: Prostate Cancer Stem Cells: Current Understandin
Skvortsov, S.; Skvortsova, I. I.; Tang, D. G.; Dubrovska, A.;
Prostate cancer (PCa) is heterogeneous, harboring phenotypically diverse cancer cell types. PCa cell heterogeneity is caused by genomic instability that leads to the clonal competition and evolution of the cancer genome and by epigenetic mechanisms that result in subclonal cellular differentiation. The process of tumor cell differentiation is initiated from a population of prostate cancer stem cells (PCSCs) that possess many phenotypic and functional properties of normal stem cells. Since the initial reports on PCSCs in 2005, there has been much effort to elucidate their biological properties, including unique metabolic characteristics. In this Review, we discuss the current methods for PCSC enrichment and analysis, the hallmarks of PCSC metabolism, and the role of PCSCs in tumor progression.
Keywords: Prostate • Cancer • Cancer stem cells • Heterogeneity • Metabolism

Publ.-Id: 28833 - Permalink

Field-induced phases in a heavy-fermion U(Ru0.92Rh0.08)2Si2 single crystal
Prokes, K.; Förster, T.; Huang, Y.-K.; Mydosh, J. A.;
We report the high-field-induced magnetic phases and phase diagram of a high quality U(Ru0.92Rh0.08 )2Si2 single crystal prepared using a modified Czochralski method. Our paper, that combines high-field magnetization and electrical resistivity measurements, shows for fields applied along the c-axis direction three field-induced magnetic phase transitions at μ0Hc1 = 21.60, μ0Hc2 = 37.90, and μ0Hc3 = 38.25 T, respectively. In agreement with a microscopic up-up-down arrangement of the U magnetic moments the phase above Hc1 has a magnetization of about one-third of the saturated value. In contrast the phase between Hc2 and Hc3 has a magnetization that is a factor of 2 lower than above the Hc3 where a polarized Fermi-liquid state with a saturated moment Ms ≈ 2.1μB/U is realized. Most of the respective transitions are reflected in the electrical resistivity as sudden drastic changes. Most notably, the phase between Hc1 and Hc2 exhibits substantially larger values. As the temperature increases, transitions smear out and disappear above ≈15 K. However, a substantial magnetoresistance is observed even at temperatures as high as 80 K. Due to a strong uniaxial magnetocrystalline anisotropy, a very small field effect is observed for fields applied perpendicular to the c-axis direction.

Publ.-Id: 28832 - Permalink

Jahn-Teller effect problems via ultrasonic experiments. Application to the impurity crystal CdSe:Cr
Averkiev, N. S.; Bersuker, I. B.; Gudkov, V. V.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y. V.; Surikov, V. T.;
Based on the data analysis of ultrasonic experiments, a novel approach has been developed to explore Jahn-Teller effect (JTE) problems in non-cubic crystals with JT centers without involving additional experimental data beyond the information about the electronic term and crystal symmetry. Distinguished from cubic crystals, the axis of symmetry of the bulk non-cubic crystal do not necessarily coincide with those of the local impurity center, thus complicating the relation between the distortions produced by the ultrasound wave and the JTE active modes. We analysed the problem with corresponding calculations for the wurtzite-type hexagonal crystal CdSe:Cr2+, in which the chromium ion substitutes the cadmium one in the tetrahedral environment, resulting in its electronic ground state 5T2(e2t2). Experimental investigation of this system by ultrasound at frequencies of 28-105 MHz in the temperature range of 4-180 K, yields a peak in the attenuation of the ultrasound below 40 K for the normal modes related to the c 11, c 44, c 55, c 55, and c 66 elastic moduli. The peak has been interpreted as the manifestation of the JTE, similar to the one, observed in cubic crystals doped with 3d ions. However, no anomalies of attenuation have been detected for the mode related to the c 33 elastic modulus, in contradiction to the theoretical predictions based on the previous method, worked out for cubic crystals. In the new method we obtained direct relations between the deformations, related to the crystal moduli, and the local JT modes, calculated the partition functions for each of the three possible JTE problems for systems with an electronic T term, T⊗e, T⊗t2 and T⊗(e + t2) revealed how these deformations alter the vibronic energy levels responsible for the relaxations in the JT centers. It emerged that in the wurtzite crystal under consideration, only in the T⊗e problem the deformation related to the elastic moduli c 33 displaces all the vibronic energy level uniformly, without relaxation possibilities, thus supporting the new method and explaining the experimental observations.

Publ.-Id: 28831 - Permalink

Changing the properties of GaAs via strain engineering in core/shell nanowires
Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Schneider, H.; Helm, M.; Dimakis, E.;
III-V compound semiconductors have fueled many breakthroughs in photonics owing to their direct optical band gap and the possibility to tailor it in ternary or quaternary alloys by selecting the chemical composition appropriately. More recently, III-V semiconductors in the form of free-standing nanowires have found new strengths for a wide range of future applications in nanotechnology, including nano-photonics. Here we explore the great possibilities for strain engineering in core/shell nanowires as an alternative route to tailor the optical band gap of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InxGa1-xAs or GaAs/InxAl1-xAs core/shell nanowires can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic proper-ties.

Core/shell nanowires were grown in the self-catalyzed mode on SiOx/Si(111) substrates by molecular beam epitaxy [1, 2]. Strain analysis was performed using synchrotron X-ray diffraction and Raman scat-tering spectroscopy, and showed that for a thin enough core, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness, we obtain a heavily tensile-strained core and an almost strain-free shell. The tensile strain of the core exhibits a predominantly-hydrostatic character and causes the reduction of the GaAs band gap energy (Figure 1) in accordance with our theoretical predictions using deformation-potential theory and first-principle calculations. For 7 % of strain (x = 0.54), the band gap energy was reduced to 0.87 eV at 300 K, i.e. a remarkable reduction of 40 %. This is particularly important for ap-plications in optical fiber telecommunications because the emission from strained GaAs nanowires can now cover the O-band and potentially the S-band of telecommunication wavelengths.

Besides the optical band gap, a similar reduction is expected for the effective mass of free electrons in tensile-strained GaAs. The corresponding electron mobility was estimated by time-domain terahertz spectroscopy to be in the range of 4000 – 5000 cm2/V·s at 300 K (core diameter = 22 nm, x = 0.39–0.49). These values are the highest reported, even in comparison to GaAs/AlxGa1-xAs nanowires with double the core thickness. This means that high-mobility transistors could now be possible with strained GaAs nanowires.

All in all, our results demonstrate that strained GaAs in core/shell nanowires can resemble the electronic properties of InxGa1-xAs, which makes it suitable for near-infrared nano-photonics. The use of a binary alloy instead of a ternary one would be advantageous because phenomena like phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the performance of photonic or electronic devices, become now irrelevant.
  • Invited lecture (Conferences)
    Nanostructures for Photonics, 07.05.2018, Saint Petersburg, Russia

Publ.-Id: 28829 - Permalink

Broadband photo-excited coherent acoustic frequency combs and mini-Brillouin-zone modes in a MQW-SESAM structure
Li, C.; Gusev, V.; Dimakis, E.; Dekorsy, T.; Hettich, M.;
A multiple quantum-well semiconductor saturable absorber mirror (MQW-SESAM) structure has been investigated by femtosecond pump-probe laser spectroscopy at a central wavelength of around 1050 nm. Coherent acoustic phonons are generated and detected over a wide frequency range from ~15 GHz to ~800 GHz. In the optical absorption region, i.e., in the multiple quantum wells (In0.27Ga0.73As), acoustic frequency combs centered at ~365 GHz, with a comb spacing of ~33 GHz, are generated. Most importantly, in the transparent region, i.e., in the distributed Bragg reflector, which is formed by a non-doped long-period semiconductor GaAs/Al0.95Ga0.05As superlattice, the mini-Brillouin-zone center, as well as zone-edge acoustic modes, are observed. The mini-zone-center modes with a fundamental frequency of 32 GHz can be attributed to the spatial modulation of the pump optical interference field with a period very close to that of the distributed Bragg reflector, in combination with the periodic spatial modulation of the electrostriction coefficient in the distributed Bragg reflector. The excitation of mini-zone-edge modes is attributed to the stimulated subharmonic decay of the fundamental center modes. Their subsequent back-folding to the mini-Brillouin-zone center makes them Raman active for the probe light.
Keywords: coherent acoustic phonons; pump-probe spectroscopy; quantum well; semiconductor superlattice; mini-Brillouin-zone; high-speed asynchronous optical sampling
  • Open Access LogoApplied Sciences 9(2019), 289

Publ.-Id: 28828 - Permalink

Structural and optical properties of pulsed-laser deposited crystalline β-Ga2O3 thin films on silicon
Berencén, Y.; Xie, Y.; Wang, M.; Prucnal, S.; Rebohle, L.; Zhou, S.;
Crystalline β-Ga2O3 thin films on (100)- and (111)-oriented Si substrates are produced by pulsed laser deposition. The as-deposited thin films are demonstrated to be polycrystalline and contain a slight deficit of oxygen atoms as measured by x-ray diffraction spectroscopy and Rutherford backscattering spectrometry, respectively. The crystallographic orientation of the Si substrate is found to play no role on the ultimate properties of the films. A direct optical band gap of 4.8 eV is determined by temperature-dependent photoluminescence excitation (PLE). Temperature-dependent PLE spectra reveal the existence of a deep acceptor level of around 1.1 eV with respect to the valence band related to self-trapped holes. We experimentally demonstrate that point defects in O-poor β-Ga2O3 thin films act as deep donors and the optical transitions are found to take place via recombination of electrons from one of the intrinsic deep donor levels with self-trapped holes located at 1.1 eV above the valence band. The 3.17 eV ultraviolet photoluminescence is proven to be related to self-trapped holes in a small polaron state between two O(II)-s sites, whereas the two blue (2.98, 2.72 eV) and the green (2.39 eV) luminescence bands are mainly originated from gallium-oxygen vacancy pairs in the (1-) charge state, gallium vacancies in the (2-) charge state and neutral oxygen interstitials, respectively.
Keywords: β-Ga2O3 thin film on Si, pulsed laser deposition, photoluminescence, substrate orientation


Publ.-Id: 28824 - Permalink

[11C]-Methionine-PET/MRI is superior to MRI alone for detecting residual tumor burden in glioblastoma multiforme undergoing radical radiochemotherapy – analysis of a prospective trial
Beuthien-Baumann, B.; Seidlitz, A.; Platzek, I.; Petr, J.; Kotzerke, J.; Jentsch, C.; Löck, S.; Zessin, J.; Krex, D.; Zöphel, K.; Schackert, G.; van den Hoff, J.; Baumann, M.; Krause, M.;
kein Abstrakt vorhanden
Keywords: [11C]Methionin, Glioblastoma, Positronen-Emissions-Tomographie
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 45(2018)S1, OP-088

Publ.-Id: 28817 - Permalink

Tissue-type mapping of gliomas
Raschke, F.; Barrick, T. R.; Jones, T. L.; Yang, G.; Ye, X.; Howe, F. A.;
Purpose: To develop a statistical method of combining multimodal MRI (mMRI) of adult glial brain tumours to generate tissue heterogeneity maps that indicate tumour grade and infiltration margins. Materials and methods: We performed a retrospective analysis of mMRI from patients with histological diagnosis of glioma (n = 25). 1H Magnetic Resonance Spectroscopic Imaging (MRSI) was used to label regions of “pure” low- or high-grade tumour across image types. Normal brain and oedema characteristics were defined from healthy controls (n = 10) and brain metastasis patients (n = 10) respectively. Probability density distributions (PDD) for each tissue type were extracted from intensity normalised proton density and T2-weighted images, and p and q diffusion maps. Superpixel segmentation and Bayesian inference was used to produce whole-brain tissue-type maps. Results: Total lesion volumes derived automatically from tissue-type maps correlated with those from manual delineation (p < 0.001, r = 0.87). Large high-grade volumes were determined in all grade III & IV (n = 16) tumours, in grade II gemistocytic rich astrocytomas (n = 3) and one astrocytoma with a histological diagnosis of grade II. For patients with known outcome (n = 20), patients with survival time < 2 years (3 grade II, 2 grade III and 10 grade IV) had a high-grade volume significantly greater than zero (Wilcoxon signed rank p < 0.0001) and also significantly greater high grade volume than the 5 grade II patients with survival >2 years (Mann Witney p = 0.0001). Regions classified from mMRI as oedema had non-tumour-like 1H MRS characteristics. Conclusions: 1H MRSI can label tumour tissue types to enable development of a mMRI tissue type mapping algorithm, with potential to aid management of patients with glial tumours. © 2019 The Authors
Keywords: Glioma, Magnetic resonance spectroscopy (MRS), Multimodal MRI, Nosologic imaging, Pattern recognition

Publ.-Id: 28815 - Permalink

Predictive Geometallurgy
Gutzmer, J.; Birtel, S.; Büttner, P.; Bachmann, K.; Kern, M.; Frenzel, M.;
For centuries the German proverb “Vor der Hacke ist es duster” has aptly described the lack of knowledge about ore volumes, grades and beneficiation characteristics during the incremental progress of mining operations. Although much progress has been made constraining ore volumes and grades by following rigorous exploration drilling programs and applying appropriate geostatistical and spatial modelling tools, there still remains considerable technical risk when exploration turns into exploitation. This is illustrated by the observation that ca. 70% of mines perform below the prediction of their feasibility study (Wood, 2018). This underperformance is usually attributed to deficiencies in the collection of tangible geoscientific data needed to design the mine and the minerals processing plant (Wood, 2018).
Geometallurgy is an interdisciplinary approach that aims to connect the data available from geosciences with the information required to predict the performance of technologies used for ore extraction and mineral beneficiation. Tangible resource characteristics – beyond grade and tonnage - are quantified to create a model that links the geology of an ore deposit with the performance achieved during mining, mineral processing and extractive metallurgy. Successful geometallurgical programs may thus be used to mitigate the risk of production planning and plant design. However, the tools of geometallurgy have thus far mostly been used by the mining industry to improve metal recoveries and to monitor process efficiency of mineral processing plants only.
Present research goes beyond these current applications of geometallurgy. Predictive geometallurgical models for complex ore bodies and even anthropogenic raw materials are being developed by interdisciplinary teams including expertise in exploration, resource characterization, minerals processing, geostatistics and spatial modelling. Case studies will be presented in this contribution that illustrate the approach taken. These examples include (1) the recovery of Sn from a historic flotation tailings storage facility; (2) the recovery of PGE as a by-product of chromite exploitation; and (3) the intelligent use of quantitative mineral abundance and mineral association data to predict the prospects of success of sensor-based sorting.
Results obtained in the three case studies illustrate the prospects of increasing resource and energy efficiency in the mining industry. Innovative approaches are of general applicability and can be easily extended to other metals and ore deposit types. The results clearly illustrate the value of conducting comprehensive geometallurgical assessments already during the latter stages of exploration; the initial process of constructing a predictive geometallurgical model will, of course, benefit greatly from regular follow-up during the phase of active exploitation.
Keywords: geometallurgy, geosciences, minerals processing, metallurgy
  • Invited lecture (Conferences)
    4th GOOD Meeting, 23.-25.01.2019, Bremen, Germany
  • Contribution to proceedings
    4th GOOD Meeting, 23.-25.01.2019, Bremen, Germany
    4th GOOD Meeting Abstract Volume, Bremen

Publ.-Id: 28808 - Permalink

Corrigendum to “Synchrotron tomographic quantification of the influence of Zn concentration on dendritic growth in Mg-Zn alloys” [Acta Mater. 156 (2018) 287-296]
Phillion, A.; Shuai, S.; Guo, E.; Wang, J.; Jing, T.; Ren, Z.; Neumann-Heyme, H.; Beckermann, C.; Lee, P.;
In solidification science, the solid-liquid interfacial area density is a key metric that characterizes the overall semi-solid morphology in a general sense. This interfacial area density can be defined in two different ways... [Abstract not available for Corrigenda]


Publ.-Id: 28807 - Permalink

Geometric reconstruction of 3D dendrite evolution from 2D transmission radiography data by a simple phase-field method
Neumann-Heyme, H.;
For the in-situ observation of dynamical processes radiographic imaging possess significant advantages over tomographic reconstruction in terms of e.g. time resolution and data handling. However, on the other hand essential spatial information is lost in the projected 2D image. The proposed method demonstrates, how in the case of continuously growing, coherent structures such as dendrites their time evolution can be utilized in recovering the 3D morphology. In addition, the reconstruction incorporates some prior knowledge including the smoothness and preferential growth directions of the interface. The capabilities of the method are assessed for different situations based on simulated experiments of dendritic growth. Finally, the reconstruction of evolving dendrites from flat sample synchrotron experiments is shown.
  • Lecture (Conference)
    55th Annual Technical Meeting of the Society of Engineering Science (SES2018), 10.-12.10.2018, Madrid, Spain

Publ.-Id: 28806 - Permalink

4D particle tracking velocimetry to analyze bubble-particles collisions and flotation recovery at low Stokes numbers
Sommer, A.-E.ORC; Heitkam, S.; Eckert, K.ORC
Froth flotation is a fundamental technique to separate minerals. Hydrophobized target particles attach to the fluidic interface of gas bubbles rising in a suspension. The success of the process depends on both the surface chemistry for the hydrophobization of particles and the hydrodynamics for an encounter between bubble and particle. In the first part of the talk on overview about flotation research and modeling is given.
The second part of the talk is devoted to own research on the hydrodynamics in model cells. To quantify this performance in terms of recovery, the number of target particles at various times in a reference volume is measured. One of the remaining challenges in this field is the flotation of fine particles with a size below 10 µm. Caused by their small inertia, the particles follow the streamlines around the bubble and no collision occurs [1]. This work focuses on the measurement of the collision probability of particles with a small inertia at the bubble surface to advance our understanding of relevant microprocesses and its influence on the flotation recovery. With a 4D particle tracking velocimetry device the particle and bubble trajectories were measured simultaneously with a high temporal (1000 fps) and spatial resolution (0.03 mm/pixels). We developed an algorithm to evaluate the flotation recovery based on the collision and attachment probability [2]. The three-phase flow within a rectangular bubble column consisted of fluorescent polystyrene particles (33 µm, 1.05 g/cm3), a bubble chain (1-7 mm) and deionized water with methanol. The variation of the bubble diameter and methanol concentration led to a change of the fluid flow around the bubble (Re = 100 - 1200) and the particle hydrophobization. The results show the preferred collision of the particles at the rear of the bubble due to a higher acceleration within the vortices in the wake.

[1] Yoon and Luttrell, Mineral Processing and Extractive Metallurgy Review 5, 101 (1989).
[2] AE Sommer, M Nikpay, S Heitkam, M Rudolph, K Eckert, Minerals Engineering 124, 116-122 (2018)
Keywords: flotation, particle image velocimetry
  • Invited lecture (Conferences)
    Permsker Wissenschaftliche Lesung, 24.-28.9.2018, Perm, Rusland

Publ.-Id: 28805 - Permalink

Coarsening and refinement phenomena in dendritic solidification
Neumann-Heyme, H.; Eckert, K.; Beckermann, C.;
Curvature-driven interface motion plays an important role in the formation of the final microstructure during dendritic solidification. Usually, such motion results in a coarser microstructure via coalescence or retraction of dendrite sidebranches \cite{ref1}. Under certain conditions, however, the microstructure can be refined due to curvature-driven pinching events that lead to dendrite fragmentation. Such pinching events are a strong function of the size and shape of the initial dendrite structure \cite{ref2}. In the present study, two- and three-dimensional phase-field simulations are performed to investigate coarsening and refinement phenomena during directional solidification of alloys. The phase-field model is solved using a finite element library that permits adaptive mesh refinement and exhibits wide parallel scalability on supercomputing facilities. A semi-implicit time integration scheme is used to allow for adaptive time stepping, which is important in particular, since curvature-driven interface motion occurs on significantly larger time scales than the initial growth. The present talk will focus on some characteristics of the applied model and physical insights that were obtained.
  • Lecture (Conference)
    5th GAMM Workshop on Phase-Field Modeling, 08.-09.02.2018, TU Dresden, Germany

Publ.-Id: 28804 - Permalink

Evaluation of Brain Nuclear Medicine Imaging Tracers in a Murine Model of Sepsis-Associated Encephalopathy
Szöllősi, D.; Hegedűs, N.; Veres, D. S.; Futó, I.; Horváth, I.; Kovács, N.; Martinecz, B.; Dénes, Á.; Seifert, D.; Bergmann, R.; Lebeda, O.; Varga, Z.; Kaleta, Z.; Szigeti, K.; Máthé, D.;
Purpose: The purpose of this study was to evaluate a set of widely used nuclear medicine imaging agents as possible methods to study the early effects of systemic inflammation on the living brain in a mouse model of sepsis-associated encephalopathy (SAE). The lipopolysaccharide (LPS)-induced murine systemic inflammation model was selected as a model of SAE.
Procedures: C57BL/6 mice were used. A multimodal imaging protocol was carried out on each animal 4 h following the intravenous administration of LPS using the following tracers: [99mTc][2,2-dimethyl-3-[(3E)-3-oxidoiminobutan-2-yl]azanidylpropyl]-[(3E)-3-hydroxyiminobutan-2-yl]azanide ([99m
Tc]HMPAO) and ethyl-7-[125I]iodo-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]ben-zodiazepine-3-carboxylate ([125I]iomazenil) to measure brain perfusion and neuronal damage, respectively; 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) to measure cerebral glucose uptake.
We assessed microglia activity on another group of mice using 2-[6-chloro-2-(4-[125I]iodo-phenyl)-imidazo[1,2-a]pyridin-3-yl]-N-ethyl-N-methyl-acetamide ([125I]CLINME). Radiotracer uptakes were measured in different brain regions and correlated. Microglia activity was also assessed using immunohistochemistry. Brain glutathione levels were measured to investigate oxidative stress.
Results: Significantly reduced perfusion values and significantly enhanced [18F]FDG and [125I]CLINME uptake was measured in the LPS-treated group. Following perfusion compensation, enhanced [125I]iomazenil uptake was measured in the LPS-treated group’s hippocampus and cerebellum. In this group, both [18F]FDG and [125I]iomazenil uptake showed highly negative correlation to perfusion measured with ([99mTc]HMPAO uptake in all brain regions. No significant differences were detected in brain glutathione levels between the groups. The CD45 and P2Y12 double-labeling immunohistochemistry showed widespread microglia activation in the LPS-treated group.
Conclusions: Our results suggest that [125I]CLINME and [99mTc]HMPAO SPECT can be used to detect microglia activation and brain hypoperfusion, respectively, in the early phase (4 h post injection) of systemic inflammation. We suspect that the enhancement of [18F]FDG and [125I]iomazenil uptake in the LPS-treated group does not necessarily reflect neural hypermetabolism and the lack of neuronal damage. They are most likely caused by processes emerging during neuroinflammation, e.g., microglia activation and/or immune cell infiltration.
Keywords: Systemic infection, Neuroinflammation, Microglia activation, LPS, [99mTc]HMPAO, [18F]FDG, [125I]iomazenil, [125I]CLINME, SPECT/CT, PET/MRI


  • Secondary publication expected from 07.05.2019

Publ.-Id: 28803 - Permalink

Effects of electron beam generated lattice defects on the periodic lattice distortion structure in 1T-TaS2 and 1T-TaSe2 thin layers
Kinyanjui, M. K.; Björkman, T.; Lehnert, T.; Köster, J.; Krasheninnikov, A.ORC; Kaiser, U.
We have investigated the influence of electron beam generated defects on the structure of periodic lattice distortions (PLDs) which accompany charge density wave modulations in 1T -TaS2 and 1T -TaSe2 . Lattice defects were generated through irradiation with high-energy electrons in a transmission electron microscope (TEM). Using atomically resolved high-resolution TEM imaging, we investigate the PLD structure and the changes in this structure with prolonged exposure to the electron beam. We observe the formation of dislocationlike topological defects in the PLD structure. Prolonged exposure to the electron beam also leads to an increase in density of these defects. This is also accompanied by an increase in structural disorder of the PLD. Density functional theory calculations were also performed in order to understand sulfur (S) and selenium (Se) vacancy defect formation in 1T -TaSe2 and 1T -TaS2 and their effects on the PLD structure. The formation energy of Se/S vacancies was calculated to be lowest for the highly displaced S/Se atoms in the vicinity of PLD maxima. Vacancies formed at the less displaced sites near the PLD minima were found to have lower formation energy. The calculations also showed that an increase in the S/Se vacancies leads to the formation of dislocations and an increase in disorder in the PLD structures. This supports the experimental observations.
Keywords: TEM, 2D materials, first-principles calculations


Publ.-Id: 28802 - Permalink

Characterization of continuous wave laser-induced thermal gradients in magnetic tunnel junctions integrated into microresonators via COMSOL simulations
Cansever, H.ORC; Lindner, J.; Huebner, T.; Niesen, A.; Reiss, G.; Fassbender, J.; Deac, A. M.
Spin caloritronics still is a vivid field and aims to investigate static and dynamic effects on magnetic structures due to spin-currents generated by thermal gradients [1]. In magnetic tunnel junctions, magnetization dynamics can be induced by bias voltage as well as thermal gradients [2]. In most research, COMSOL simulations are used to estimate the overall temperature of the magnetic tunnel junction as well as the thermal gradient over the insulating barrier [3-5]. Here, we perform COMSOL simulations using the 2D heat transfer module for specific Co2FeAl/MgO(2nm)/CoFeB magnetic tunnel junctions which are integrated into so-called microresonators [6]. Microresonators have been recently used as alternative approach to investigate the magnetization dynamics of the free-layer within magnetic tunnel junctions, induced by a thermal gradient by means of its ferromagnetic resonance response [6]. Utilizing microresonators for ferromagnetic resonance detection allow for the detection of signals from micron/nano-sized object under laser heating in terms of linewidth and resonance field and thus provide the possibility to detect influences of a thermal gradient on the magnetization dynamics far below the threshold of magnetic switching. The heat diffusion over all layers are modeled by starting with a 2D (vertical) rectangular shape in which we consider the MTJ stack with the MgO-substrate and backside metallization as part of the microresonators shown in Fig 1. Moreover, we consider an air ‘layer’ and the metal-contacts defining the microresonator on top of the MgO-substrate. Upon rotation of this two-dimensional shape around the central vertical z-axis of the MTJ, we obtain a 3D cylinder in which the heat profile is simulated (see Fig 2). The simulation parameters for the materials were chosen similar to those in [3,4]. In the simulation, the fundamental properties of layers i.e. thermal conductivity, heat capacity and material density are used to obtain a temperature profile of the magnetic structure. According to the simulation results, the thermal conductivity of the insulating barrier (MgO) and top metal thicknesses influence the thermal gradient, while uniform heating is strongly affected by the surrounding material of the microresonator which is mainly made from copper (high thermal conductivity). The simulation results provide insight into the heat profile of the whole structure and in particular demonstrate that not only changing the magnetic object itself but also modifying the structure of the surrounding materials yields a handle to tune and optimize the thermal gradient.
Figure 1. 2D sketch of MTJ structure integrated into a microresonator for COMSOL modelling. Heat source, i.e. cw- laser is applied to magnetic layers through the top-metal. The temperature of the bottom of the whole structure is set to 293.15 K.
Figure 2. (a) Temperature profile across the MTJ integrated in a microresonator with the applied power of 145 mW inset (b) 3D cylindrical image of MTJ structure.

[1] Bauer G E W, Saitoh E and van Wees B J 2012 Nat. Mater. 11 391
[2] Jia X, Xia K and Bauer G E W 2011 Phys. Rev. Lett.107 176603
[3] Walter M et al 2011 Nat. Mater. 10 742
[4] Huebner T, Boehnke A, Martens U, Thomas A, Schmalhorst J M, Reiss G, Münzenberg M and Kuschel T 2016 Phys. Rev. B 93 224433
[5] T Huebner et al 2018 J. Phys. D: Appl. Phys. 51 224006
[6] H Cansever et al 2018 J. Phys. D: Appl. Phys. 51 224009
Keywords: COMSOL Simulation, magnetic tunnel junction, microresonator, ferromagnetic resonance
  • Lecture (Conference)
    Joint MMM-Intermag Conference 2019 Washington D.C., 14.-18.01.2019, Washington D.C., The United States of America

Publ.-Id: 28800 - Permalink

The new Felsenkeller 5 MV underground accelerator: Status and Program
Bemmerer, D.;
Experimental nuclear astrophysics aims to study, in the laboratory, the nuclear reactions taking place in stars. However, at the energies relevant to stellar burnings, the relevant cross sections are strongly reduced by the repulsive Coulomb barrier. As a result, ion beam experiments in underground laboratories shielded from cosmic ray effects are needed in order to gain precise data. The Felsenkeller 5 MV accelerator, below 45 m rock in Dresden, is the first such accelerator on the MV scale in Europe. The laboratory was jointly built by HZDR and TU Dresden and opened in 2018. Both an internal and an external ion source have already been tested successfully underground. The accelerator itself is under commissioning, as well as a high-sensitivity radioactivity counting setup by TU Dresden. The talk will summarise the science case and the status for the new laboratory.
Keywords: Nuclear Astrophysics
  • Invited lecture (Conferences)
    Institutsseminar (Kolloquium), 24.01.2019, Dresden, Deutschland

Publ.-Id: 28797 - Permalink

Felsenkeller 5 MV underground ion accelerator status December 2018
Bemmerer, D.;
I review the status of the Felsenkeller 5 MV underground accelerator in view of the CELLAR network of underground labs.
Keywords: Nuclear Astrophysics Low-Level Radioactivity Measurements
  • Lecture (Conference)
    CELLAR / JEILORA Meeting, 05.-07.12.2018, Monaco, Monaco

Publ.-Id: 28796 - Permalink

Nuclear Astrophysics: Nucleosynthesis and Chemical Evolution Studies
Bemmerer, D.;
I review Nuclear Astrophysics: Nucleosynthesis and Chemical Evolution Studies.
Keywords: Nuclear Astrophysics
  • Invited lecture (Conferences)
    Astroparticle Physics in Germany: Status and Perspectives, 19.09.2018, Mainz, Deutschland

Publ.-Id: 28795 - Permalink

Felsenkeller 5 MV underground accelerator at the 5th International Solar Neutrino Conference
Bemmerer, D.;
I review the status of the 5 MV underground accelerator at Felsenkeller, Dresden/Germany.
Keywords: Underground physics Nuclear Astrophysics
  • Invited lecture (Conferences)
    5th International Solar Neutrino Conference, 13.06.2018, Dresden, Deutschland

Publ.-Id: 28794 - Permalink

Felsenkeller 5 MV underground ion accelerator for nuclear astrophysics
Bemmerer, D.; Cowan, T. E.; Grieger, M.; Hensel, T.; Junghans, A. R.; Koppitz, M.; Ludwig, F.; Rimarzig, B.; Reinicke, S.; Schwengner, R.; Stöckel, K.; Szücs, T.; Takács, M. P.; Turkat, S.; Wagner, A.; Zuber, K.;
A 5 MV Pelletron accelerator with both an internal and an external ion source providing for intensive 1H+, 4He+, and 12C+ beams is being installed in the Felsenkeller underground site in Dresden, shielded from cosmic rays by 45 m rock overburden. Civil construction has recently been completed. The technical features of the new laboratory, test results, and the scientific program will be summarized. In addition to in-house research by HZDR and TU Dresden, the new accelerator will be open for outside users, both from Germany and worldwide.
Keywords: Nuclear astrophysics Felsenkeller
  • Lecture (Conference)
    Frühjahrstagung Hadronen und Kerne, 26.02.2018, Bochum, Deutschland

Publ.-Id: 28793 - Permalink

Improved astrophysical rate for the 18O(p,α)15N reaction by underground measurements
Bruno, C. G.; Aliotta, M.; Descouvemont, P.; Best, A.; Davinson, T.; Bemmerer, D.; Boeltzig, A.; Broggini, C.; Caciolli, A.; Cavanna, F.; Chillery, T.; Ciani, G. F.; Corvisiero, P.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Lugaro, M.; Marigo, P.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Stöckel, K.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.;
The 18O(p,α)15N reaction affects the synthesis of 15N, 18O and 19F isotopes, whose abundances can be used to probe the nucleosynthesis and mixing processes occurring deep inside asymptotic giant branch (AGB) stars. We performed a low-background direct measurement of the 18O(p,α)15N reaction cross-section at the Laboratory for Underground Nuclear Astrophysics (LUNA) from center of mass energy E_CM= 340 keV down to E_CM = 55 keV, the lowest energy measured to date corresponding to a cross-section of less than 1 picobarn/sr. The strength of a key resonance at center of mass energy E_r = 90 keV was found to be a factor of 10 higher than previously reported. A multi-channel R-matrix analysis of our and other data available in the literature was performed. Over a wide temperature range, T=0.01-1.00 GK, our new astrophysical rate is both more accurate and precise than recent evaluations. Stronger constraints can now be placed on the physical processes controlling nucleosynthesis in AGB stars with interesting consequences on the abundance of 18O in these stars and in stardust grains, specifically on the production sites of oxygen-rich Group II grains.
Keywords: Stellar hydrogen burningHydrostatic stellar nucleosynthesis

Publ.-Id: 28791 - Permalink

Hyperspectral Feature Extraction Using Sparse and Smooth Low-Rank Analysis
Rasti, B.; Ghamisi, P.; Ulfarsson, M. O.;
In this paper, we develop a hyperspectral feature extraction method called sparse and smooth low-rank analysis (SSLRA). First, we propose a new low-rank model for hyperspectral images (HSIs) where we decompose the HSI into smooth and sparse components. Then, these components are simultaneously estimated using a nonconvex constrained penalized cost function (CPCF). The proposed CPCF exploits total variation penalty, ℓ1 penalty, and an orthogonality constraint. The total variation penalty is used to promote piecewise smoothness, and, therefore, it extracts spatial (local neighborhood) information. The ℓ1 penalty encourages sparse and spatial structures. Additionally, we show that this new type of decomposition improves the classification of the HSIs. In the experiments, SSLRA was applied on the Houston (urban) and the Trento (rural) datasets. The extracted features were used as an input into a classifier (either support vector machines (SVM) or random forest (RF)) to produce the final classification map. The results confirm improvement in classification accuracy compared to the state-of-the-art feature extraction approaches.


Publ.-Id: 28790 - Permalink

The IR-truncated PT-symmetric V = ix3 model and its asymptotic spectral scaling graph
Günther, U.ORC; Stefani, F.
The PT-symmetric V = ix3 model over the real line is infra-red (IR) truncated and considered as Sturm-Liouville problem over a finite interval. Structures hidden in the Airy function setup of the V = ix3 model are combined with WKB techniques developed by Bender and Jones in 2012 for the derivation of the real part of the spectrum of theV = ix3 model. Via WKB and Stokes graph analysis, the location of the complex spectral branches of the ix3 model as well as those of more general V = -(ix)2n+1 models over finite intervals are obtained. Splitting the related action functions into purely real scale factors and scale invariant integrals allows to extract underlying asymptotic spectral scaling graphs. These (structurally very simple) scaling graphs are geometrically invariant and cutoff-independent so that the IR limit can be formally taken. Moreover an increasing length scale can be associated with a spectral UV-IR renormalization group flow on this scaling graph. It is shown that the eigenvalues of the IR-complete V = ix3 model can be bijectively mapped onto a finite segment of the scaling graph asymptotically approaching a (scale invariant) PT phase transition region. In this way, a simple heuristic picture and complementary explanation for the unboundedness of projector norms and C-operator for the ix3 model are provided and the lack of quasi-Hermiticity of the ix3 Hamiltonian over the real line appears physically plausible. Possible directions of further research are briefly sketched.
Keywords: PT Quantum Mechanics, PT phase transition, spectral branch points, exceptional points, ix3 model, WKB techniques, IR truncation, IR completion, asymptotic spectral scaling graphs, spectral UV-IR renormalization group flow
  • Invited lecture (Conferences)
    Discrete-18, organized by CERN and the Austrian Academy of Sciences, 26.-30.11.2018, Wien, Österreich

Publ.-Id: 28787 - Permalink

The IR-truncated PT-symmetric V = ix3 model and its asymptotic spectral scaling graph
Günther, U.ORC; Stefani, F.
The PT-symmetric quantum mechanical V = ix3 model over the real line is infra-red (IR) truncated and considered as Sturm-Liouville problem over a finite interval of the real line. Via WKB and Stokes graph analysis, the location of the complex spectral branches of the V = ix3 model as well as those of more general V = -(ix)2n+1 models over finite intervals are obtained. Underlying asymptotic spectral scaling graphs are extracted which are scale-invariant so that the IR completion can be performed. Implications for the V = ix3 model over the full real line are discussed.
Keywords: PT Quantum Mechanics, PT phase transition, spectral branch points, exceptional points, ix3 model, WKB techniques, IR truncation, asymptotic spectral scaling graphs
  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics XV, 10.-13.09.2018, Prague, Czech Republic

Publ.-Id: 28786 - Permalink

The IR-truncated PT-symmetric V=ix3 model and its asymptotic spectral scaling graph
Günther, U.ORC; Stefani, F.
The PT-symmetric V=ix3 model over the real line is IR truncated and considered as Sturm-Liouville problem over a finite interval. Combining structures hidden in the Airy function setup of the V=ix model with WKB techniques developed by Bender and Jones in 2012 for the derivation of the real part of the spectrum of the ix3 model, a WKB and Stokes graph analysis for the complex spectral branches of the ix3 model as well as those of more general V=-(ix)2n+1 models over finite intervals is performed. Complementary insights into the spectra of these models are obtained by splitting the spectral branch-structure into purely real scale factors and asymptotic spectral scaling graphs. It turns out that the corresponding (structurally very simple) scaling graphs are geometrically invariant and cutoff-independent so that the infra-red (IR) limit can be formally taken. These graphs have invariantly existing PT phase transition regions. In this way, a simple heuristic picture and complementary explanation for the unboundedness of the C-operator and the lack of quasi-Hermiticity of the ix3 Hamiltonian over the real line is provided.
Keywords: PT-symmetric Quantum Mechanics, PT phase transition, spectral branch points, exceptional points, ix3 model, WKB techniques, IR truncation, C-operator, unboundedness, quasi-Hermiticity
  • Invited lecture (Conferences)
    Pseudo-Hermitian Hamiltonians in Quantum Physics (PHHQP) XVIII, 04.-13.06.2018, Bangalore, India

Publ.-Id: 28785 - Permalink

Curing processes in ultra low-k materials by positron annihilation spectroscopy
Liedke, M. O.ORC; Köhler, N.; Butterling, M.; Hirschmann, E.; Attallah, A. G.; Krause-Rehberg, R.; Schulz, S. E.; Wagner, A.
The first results on in-situ investigations of pore formation in ultra low-k dielectrics during a curing process, i.e., a porogen removal by vacuum annealing will be presented. The main focus is to obtain insight into initial stages of pore networks formation up to their full development. The in-situ annealing and Doppler broadening positron annihilation spectroscopy measurements have been conducted on our Apparatus for In-situ Defect Analysis (AIDA) - the end-station of a slow positrons beamline at HZDR. In addition, positron lifetime spectroscopy has been utilized, where mono-energetic pulsed positron beam (MePS) serves as a probe to evaluate pore sizes, their concentration and distribution as a function of curing temperature and time. The MePS facility has partly been funded by the Federal Ministry of Education and Research (BMBF) with the grant PosiAnalyse (05K2013). The AIDA system was funded by the Impulse- und Networking fund of the Helmholtz-Association (FKZ VH-VI-442 Memriox) and through the Helmholtz Energy Materials Characterization Platform (03ET7015)
Keywords: positron, low-k, curing, AIDA, defects, pores
  • Lecture (Conference)
    DPG Frühjahrstagung Berlin, 11.03.2018, Berlin, Deutschland

Publ.-Id: 28784 - Permalink

Vacancy-mediated magnetic phase-transitions
Liedke, M. O.ORC; Butterling, M.; Quintana, A.; Menéndez, E.; Ehrler, J.; Bali, R.; Hirschmann, E.; Sireus, V.; Nogués, J.; Sort, J.; Wagner, A.
Two thin film systems exhibiting vacancy mediated magnetic phase transitions will be discussed in detail, i.e., Co3O4 and Fe60Al40.
In applications, substituting electric currents, which are nowadays used to operate spintronic devices, with electric fields, would result in a reduction of both the energy consumption and cost [1]. Co3O4 is a candidate for a tunable, non-volatile energy-efficient functional material whose magnetic properties can be controlled by electric voltage. In our current investigations the as-grown Co3O4 films consist of a paramagnetic (PM) phase only, which is transformed to a ferromagnetic (FM) state by electrolyte-gated and defect-mediated O and Co transport. A negative voltage reduces Co3O4 to Co (FM: ON), resulting in a phase separated material with Co- and O-rich regions. Applying a positive bias, the process is reversed oxidizing Co back to Co3O4 (PM: OFF). We will show that atoms migration is driven by rather complex vacancy states and a clear increase of the grain boundaries volume after negative biasing assists to O transport. Moreover, concomitantly with the PM phase transition due to the positive biasing the structural defects picture reverses to a large extent as well, which manifests as reduction in volume of both vacancy clusters and grain boundaries.
B2-Fe60Al40 phase is paramagnetic, and strong ferromagnetism can be induced via disordering to the A2-Fe60Al40 phase [2]. Disordering implies the formation of anti-site defects [3], which correlates with an increased Fe coordination. The concentration and size of open volume defects can play an important role in reordering kinetics. Three different initial order states have been investigated: (i) as-grown, partially disordered Fe60Al40, (ii) the as-grown films after Ne+ irradiation, and (iii) Ne-irradiated B2-Fe60Al40. Since, reordering directly affects magnetization saturation; the extent of the diffusion process can be traced via magnetometry at slightly elevated temperature of 400 K. We show that immobile large vacancy clusters with a high thermal activation barrier are dominant in the as-grown film and hinder ordering. Ion irradiation breaks down these pinning sites, thereby strongly accelerating thermal diffusion and reordering. These results provide insights into thermal reordering processes in binary alloys, and the consequent effect on magnetic properties. Doppler broadening and positron annihilation lifetime spectroscopy have been used as a probe for both electric field driven ionic transport of Co and O via different type of defects in Co3O4 systems as well as vacancy-mediated ordering in Fe60Al40.
[1] Y. Shiota, et al. Nature Mater. 11, 39 (2012). [2] M.O. Liedke, et al., J. Appl. Phys. 117, 163908 (2015).
[3] R. Bali, et al., Nano Lett. 14, 435 (2014).
Keywords: magnetism, positron, ion, irradiation, phase transitions, defects, electrical fields
  • Invited lecture (Conferences)
    18th International Conference on Positron Annihilation (ICPA-18), 19.08.2018, Orlando, USA

Publ.-Id: 28783 - Permalink

Magnetic ordering and open volume defects – phase transitions in ion irradiated Fe60Al40 thin films
Liedke, M. O.ORC; Ehrler, J.; Bali, R.; Butterling, M.; Hirschmann, E.; Wagner, A.
Fe60Al40 exhibit the so-called disorder induced ferromagnetism, where anti-site disorder (ASD) promotes ferromagnetic A2-phase (disordered) over paramagnetic B2-phase (ordered). Both phases can be - in a controllable fashion - driven by ion irradiation or annealing, respectively. The main physical origin correlates strongly with ASD [R. Bali, et al., Nano Lett. 14, 435 (2014)]. Nevertheless, the concentration and size of open volume defects can be of crucial importance in determining the kinetics of the reordering processes. To unravel the influence of vacancy clusters, three different initial order states have been investigated: (i) as-sputtered, (ii) as-grown irradiated with Ne+ and (iii) B2 ordered films, obtained via 773 K annealing and Ne-irradiated. Open volume defects in the treated samples were investigated with Doppler broadening and positron annihilation lifetime spectroscopy. Furthermore, since the reordering directly affects Ms, the extent of the diffusion process can be traced via magnetometry at slightly elevated temperature of 400 K. We show that immobile large vacancy clusters are dominant in the as-grown films; these complexes present only in the as-sputtered film possess a high thermal activation barrier and hinder ordering. Ion irradiation breaks down these pinning defects strongly accelerating thermal diffusion and reordering. These results provide insights into thermal reordering processes in binary alloys, and the consequent effect on magnetic behavior.
Keywords: magnetism, positron, ordering, ion, irradiation, phase transition, defects
  • Lecture (Conference)
    9th Joint European Magnetic Symposia (JEMS-9), 03.09.2018, Mainz, Deutschland

Publ.-Id: 28782 - Permalink

On the use of stacks of fission-like targets for neutron capture experiments
Guerrero, C.; Lerendegui-Marco, J.; Eberhardt, K.; Düllmann, C. E.; Junghans, A.; Lommel, B.; Mokry, C.; Quesada, J. M.; Runke, J.; Thörle-Pospiech, P.; The N_Tof Collaboration;
The measurement of neutron induced reactions on unstable isotopes is of interest in many fields, from nuclear energy to astrophysics or applications; in particular transuranic isotopes are essential for the development of innovative nuclear reactors and for the management of the radioactive waste. In such measurements, the quality of the associated radioactive target is crucial for the success of the experiment, but in many cases the geometry, amount of mass and encapsulation of the target are not optimal, leading to limited results. In this work we propose to produce high quality radioactive targets for capture as a stack of thin targets using the techniques usually employed for fission measurements. In particular, we have succeeded in making a 242Pu target of nearly 100 mg by combining seven thin (~1 mg/cm2) fission-like targets with 45 mm in diameter achieving a total backing thickness of only 70 m of aluminum. The target has been shown to perform successfully in experiments at both a neutron time-of-flight facility (n_TOF at CERN) and a thermal neutron beam (BRR at KFKI), providing the most accurate data from thermal up to 250 keV to date.

Publ.-Id: 28781 - Permalink

Strahlenschutzaspekte bei der Errichtung und Inbetriebnahme des kanadischen Zyklotrons TR-FLEX im Helmholtz-Zentrum Dresden-Rossendorf
Preusche, S.; Naumann, B.; Kaspari, W.;
  • Invited lecture (Conferences)
    Strahlenschutz in Medizin, Forschung und Industrie, 11.-12.12.2018, Aschaffenburg, Deutschland

Publ.-Id: 28779 - Permalink

Universal Limits of Thermopower and Figure of Merit from Transport Energy Statistics
Zahn, P.ORC
The search for new thermoelectric materials aims at improving their power and efficiency, as expressed by thermopower S and figure of merit ZT.
By considering a very general transport spectral function w(ε), expressions for the S and ZT can be derived, which contain the statistical weights of an effective distribution function only, see Ref. [1]. The assumption of a Lorentzian shape with width kBT resulting from the electron-phonon coupling allows to estimate an upper limit of S and ZT regardless the microscopic mechanisms of the transport process.
The limit of |S| is given by 1.88 in units of kB/e, which is about 160 μV/K, and the limit for ZT is about 1.11 (red dots in the figure).
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, International Helmholtz Research School NanoNet (VH-KO-606), the Helmholtz Exzellenznetzwerk cfaed (ExNet-0026), and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2). We thank S. Gemming for helpful discussions.
Keywords: Thermoelectrics, Thermopower, Figure of Merit, universal limit, transport spectral function
  • Poster
    667. WE-Heraeus-Seminar 'System-oriented approach to thermoelectrics: Materials – Interfaces – Devices', 08.-11.04.2018, Bad Honnef, Deutschland

Publ.-Id: 28776 - Permalink

Burning in the Tail: Implications for a Burst Oscillation Model
Chambers, F.; Watts, A.; Keek, L.; Cavecchi, Y.; Garcia Gonzalez, F.;
Accreting neutron stars (NSs) can exhibit high-frequency modulations, known as burst oscillations, in their light curves during thermonuclear X-ray bursts. Their frequencies can be offset from the spin frequency of the NS (known independently) by several Hz, and can drift by 1-3 Hz. One plausible explanation for this phenomenon is that a wave is present in the bursting ocean that decreases in frequency (in the rotating frame) as the burst cools. The strongest candidate is the buoyant r-mode; however, models for the burning ocean background used in previous studies over-predict frequency drifts by several Hz. Using new background models (which include shallow heating, and burning in the tail of the burst) the evolution of the buoyant r-mode is calculated. The resulting frequency drifts are smaller, in line with observations. This illustrates the importance of accounting for the detailed nuclear physics in these bursts.

Publ.-Id: 28775 - Permalink

Experiments and Simulations of the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
The magnetized spherical Couette system models experiments that are being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal is confined within two differentially rotating spheres and immersed in a magnetic field parallel to the axis of rotation. Preliminary simulations of periodic and quasiperiodic flows, arising at the first bifurcations, will be presented. The aim is to study in detail the instabilities observed in the experiments and previous numerical studies. This study will reveal how the flow patterns depend on control parameters, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    Fifty years after Roberts' MHD: Dynamos and planetary flows today, 16.-17.11.2017, London, United Kingdom

Publ.-Id: 28774 - Permalink

Experiments and Simulations of the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
The magnetized spherical Couette system models experiments that are being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal is confined within two differentially rotating spheres and immersed in a magnetic field parallel to the axis of rotation. Preliminary simulations of periodic and quasiperiodic flows, arising at the first bifurcations, will be presented. The aim is to study in detail the instabilities observed in the experiments and previous numerical studies. This study will reveal how the flow patterns depend on control parameters, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    GDRI Dynamo meeting 2017, 27.-29.11.2017, Paris, France

Publ.-Id: 28773 - Permalink

New axisymmetric helical magnetorotational instability in dissipative rotating flows with positive shear
Mamatsashvili, G.; Stefani, F.; Hollerbach, R.; Rüdiger, G.;
We present a new type of axisymmetric magnetorotational instability which is capable of destabilizing viscous and resistive magnetized flows with radially increasing angular velocity. Using short-wavelength WKB approach, supported by 1D linear stability calculations in Taylor-Couette flow, we show that this instability works only when a combination of axial and azimuthal magnetic fields is applied and when the magnetic Prandtl number is different from one. It might have grave consequences for the stability of the equator-near parts of the solar tachocline, and for the dynamo action in this region
  • Lecture (Conference)
    MHD Days and GdRI Dynamo Meeting, 26.-28.11.2018, Dresden, Germany

Publ.-Id: 28772 - Permalink

Experiments and Simulations of the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
The magnetized spherical Couette system models experiments that are being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal is confined within two differentially rotating spheres and immersed in a magnetic field parallel to the axis of rotation. Preliminary simulations of periodic and quasiperiodic flows, arising at the first bifurcations, will be presented. The aim is to study in detail the instabilities observed in the experiments and previous numerical studies. This study will reveal how the flow patterns depend on control parameters, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    Alexander von Humboldt Foundation Network Meeting 2018, 19.-21.02.2018, Potsdam, Deutschland

Publ.-Id: 28771 - Permalink

A Tayler-Spruit type model of a tidally synchronized solar dynamo
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.;
We consider a solar dynamo model of Tayler-Spruit type whose Omega-effect is conventionally produced by a solar-like differential rotation but whose alpha-effect is assumed to be periodically modulated by planetary tidal forcing. This resonance-like effect relies on the tendency of the current-driven Tayler instability to produce intrinsic helicity oscillations which can be synchronized by periodic tidal perturbations. Specifically, we focus on the 11.07 years alignment periodicity of the tidally dominant planets Venus, Earth, and Jupiter, whose empirical synchronization with the solar dynamo is illustrated. The typically emerging dynamo modes are dipolar fields, oscillating with a 22.14 years period or pulsating with a 11.07 years period, but also quadrupolar fields with corresponding periodicities. In the absence of any constant part of alpha, we prove the subcritical nature of this periodic Tayler-Spruit type dynamo. Phase coherent transitions between dipoles and quadrupoles, which are reminiscent of the observed behaviour during the Maunder minimum, can be easily triggered by long-term variations of dynamo parameters. Further interesting features of the model are the typical second intensity peak and the intermittent appearance of reversed helicities in both hemispheres
  • Poster
    MHD Days and GdRI Dynamo Meeting, 26.-28.11.2018, Dresden, Germany

Publ.-Id: 28770 - Permalink

Rotating Waves in Spherical Geometry: Thermal Convection in Thin Rotating Shells and the Magnetized Spherical Couette System
Garcia Gonzalez, F.; Sánchez, J.; Net, M.; Chambers, F.; Watts, A.; Stefani, F.;
Fluid dynamics plays an important role in many geophysical and astrophysical objects such as planets and stars. For instance, convection can occur in neutron stars' oceans formed by very thin layers of helium or hydrogen, which are subject to the influence of strong temperature gradients and rotation. In addition, instabilities observed in differentially rotating flows in the presence of a magnetic field (magnetized spherical Couette flows) were attributed to the magnetorotational instability (MRI), which is presently considered the most promising candidate to explain the transport mechanism of angular momentum in accretion disks around black holes and protostars. In this study, bifurcation diagrams of the first instabilities occurring in the two mentioned set-ups will be presented. They were obtained by means of continuation techniques. The arising flow patterns will be described. In both cases, pseudo-spectral high order methods as well as high order time integration methods are used for the time evolution of the Navier-Stokes equations.
  • Lecture (Conference)
    International Conference on Spectral and High-Order Methods ICOSAHOM'18., 09.-13.07.2018, London, United Kingdom

Publ.-Id: 28769 - Permalink

The DRESDYN project: Liquid metal experiments on dynamo action and magnetorotational instability
Stefani, F.;
The dynamo effect in moving electrically conducting fluids is at the root of magnetic field generation in planets and stars. Yet, cosmic magnetic fields play also an active role in the formation of central objects, such as protostars and black holes, by destabilizing accretion disks that would be hydrodynamically stable. While often studied separately, dynamo action and magnetically triggered instabilities may also occur together in such highly non-linear processes as the MRI dynamo or the Tayler-Spruit dynamo.

The DRESDYN project at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) serves as a platform for continuing the liquid metal experiments of the last two decades which were related to dynamo action and magnetically triggered flow instabilities. After a short survey of the dynamo experiments in Riga, Karlsruhe and Cadarache, and the various MRI experiments at the PROMISE facility at HZDR, I discuss the preparatory status of a large-scale precession experiment and a Taylor-Couette experiment for investigating various forms of the MRI and their combinations with the Tayler instability. Special focus will be laid on the numerical predictions of both experiments, as well as on some recent findings concerning the relation of non-modal growth in rotating flows with dissipation-induced instabilities, such as helical and azimuthal MRI for negative and positive shear.
  • Invited lecture (Conferences)
    Waves, Turbulence, and Large-scale Structures in Rotating Magnetic Fluids: Above & Beyond Geophysical Fluid Dynamics, 10.-14.09.2018, Boulder, USA

Publ.-Id: 28768 - Permalink

A tidally synchronized Tayler-Spruid type model of the solar dynamo
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.;
We present a solar dynamo model of the Tayler-Spruit type whose Omega-effect is produced, as usual, by differential rotation but whose alpha-effect is assumed as being periodically modulated by planetary tidal forcing. This resonance-like effect has its rationale in the tendency of the current-driven Tayler instability to undergo intrinsic helicity oscillations which can be synchronized by periodic tidal perturbations. Specifically, we focus on the 11.07 years periodicity of the alignment of the tidally dominant planets Venus, Earth, and Jupiter. In the framework of a simple one-dimensional numerical model we prove the subcritical character of this Tayler-Spruit type dynamo. The typical dynamo modes are dipole fields, oscillating with a 22.14 year period, but also quadrupole fields pulsating with an 11.07 years period. Transitions between these field topologies are reminiscent of the observed behavior during the Maunder minimum. Further interesting features of the model are the emergence of mid-term fluctuations, and the intermittent appearance of reversed helicities in both hemispheres. With minor model modifications, the correct direction of the butterfly diagram comes out as a robust feature, too.
  • Lecture (Conference)
    Third Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russia

Publ.-Id: 28767 - Permalink

Experiments and Simulations on the Magnetized Spherical Couette Problem
Garcia Gonzalez, F.; Stefani, F.;
Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. This allows us to carefully investigate the time-scales of the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. In addition, modulated rotating waves, obtained at secondary bifurcations, are exhaustively studied by means of direct numerical simulations, with main focus on their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.
  • Lecture (Conference)
    MHD Days and GdRI Dynamo Meeting, 2018, 26.-28.11.2018, Dresden, Deutschland

Publ.-Id: 28766 - Permalink

A Tayler-Spruit model of the solar dynamo with tidal synchronization
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.;
We present a solar dynamo model of the Tayler-Spruit type whose Omega-effect is coventionally produced by differential rotation but whose alpha-effect is assumed as being periodically modulated by planetary tidal forcing. This resonance-like effect has its rationale in the tendency of the current-driven Tayler instability to undergo intrinsic helicity oscillations which can be synchronized by periodic tidal perturbations. Specifically, we focus on the 11.07 years periodicity of the alignment of the tidally dominant planets Venus, Earth, and Jupiter. In the framework of a simple one-dimensional numerical model we prove the subcritical character of this Tayler-Spruit type dynamo. The typical dynamo modes are dipole fields, oscillating with a 22.14 year period, but also quadrupole fields pulsating with an 11.07 years period. Transitions between these field topologies are reminiscent of the observed behavior during the Maunder minimum. Further interesting features of the model are the emergence of mid-term fluctuations, and the intermittent appearance of reversed helicities in both hemispheres. With minor model modifications, the correct direction of the butterfly diagram comes out as a robust feature, too.
  • Invited lecture (Conferences)
    Planetary-Stellar Connection: The Sun's Lesson, 07.-09.05.2018, Freiburg im Breisgau, Germany

Publ.-Id: 28765 - Permalink

Thermal convection in rotating spherical shells: Temperature-dependent internal heat generation using the example of triple-𝛼 burning in neutron stars
Garcia Gonzalez, F.; Chambers, F.; Watts, A.;
We present an extensive study of Boussinesq thermal convection including a temperature-dependent internal heating source, based on numerical three-dimensional simulations. The temperature dependence mimics triple-α nuclear reactions and the fluid geometry is a rotating spherical shell. These are key ingredients for the study of convective accreting neutron star oceans. A dimensionless parameter Raₙ, measuring the relevance of nuclear heating, is defined. We explore how flow characteristics change with increasing Raₙ and give an astrophysical motivation. The onset of convection is investigated with respect to this parameter and periodic, quasiperiodic, chaotic flows with coherent structures, and fully turbulent flows are exhibited as Raₙ is varied. Several regime transitions are identified and compared with previous results on differentially heated convection. Finally, we explore (tentatively) the potential applicability of our results to the evolution of thermonuclear bursts in accreting neutron star oceans.


Publ.-Id: 28764 - Permalink

Self-excitation in a helical liquid metal flow: the Riga dynamo experiments
Gailitis, A.; Gerbeth, G.; Gundrum, T.; Lielausis, O.; Lipsbergs, G.; Platacis, E.; Stefani, F.;
The homogeneous dynamo effect is at the root of magnetic field generation in cosmic bodies, including planets, stars and galaxies. While the underlying theory had increasingly flourished since the middle of the 20th century, hydromagnetic dynamos were not realized in the laboratory until 1999. On 11 November 1999, this situation changed with the first observation of a kinematic dynamo in the Riga experiment. Since that time, a series of experimental campaigns has provided a wealth of data on the kinematic and the saturated regime. This paper is intended to give a comprehensive survey about these experiments, to summarize their main results and to compare them with numerical simulations.


Publ.-Id: 28763 - Permalink

Continuation and stability of rotating waves in the magnetized spherical Couette system: secondary transitions and multistability
Garcia Gonzalez, F.; Stefani, F.;
Rotating waves (RW) bifurcating from the axisymmetric basic magnetized spherical Couette (MSC) flow are computed by means of Newton–Krylov continuation techniques for periodic orbits. In addition, their stability is analysed in the framework of Floquet theory. The inner sphere rotates while the outer is kept at rest and the fluid is subjected to an axial magnetic field. For a moderate Reynolds number Re = 10^3 (measuring inner rotation), the effect of increasing the magnetic field strength (measured by the Hartmann number Ha) is addressed in the range Ha ∈ (0, 80) corresponding to the working conditions of the HEDGEHOG experiment at Helmholtz-Zentrum Dresden-Rossendorf. The study reveals several regions of multistability of waves with azimuthal wavenumber m = 2, 3, 4, and several transitions to quasi-periodic flows, i.e modulated rotating waves. These nonlinear flows can be classified as the three different instabilities of the radial jet, the return flow and the shear layer, as found in the previous studies. These two flows are continuously linked, and part of the same branch, as the magnetic forcing is increased. Midway between the two instabilities, at a certain critical Ha, the non-axisymmetric component of the flow is maximum.


  • Secondary publication expected from 12.12.2019

Publ.-Id: 28762 - Permalink

The DRESDYN project: liquid metal experiments on dynamo action and magnetorotational instability
Stefani, F.; Gailitis, A.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Rüdiger, G.; Seilmayer, M.; Vogt, T.;
Magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, magnetic fields can play an active role in cosmic structure formation by destabilising rotational flows that would be otherwise hydro-dynamically stable. For a long time, both hydromagnetic dynamo action as well as magnetically triggered flow instabilities had been the subject of purely theoretical research. Meanwhile, however, the dynamo effect has been observed in large-scale liquid sodium experiments in Riga, Karlsruhe and Cadarache. In this paper, we summarise the results of liquid metal experiments devoted to the dynamo effect and various magnetic instabilities such as the helical and the azimuthal magnetorotational instability and the Tayler instability. We discuss in detail our plans for a precession-driven dynamo
experiment and a large-scale Tayler–Couette experiment using liquid sodium, and on the prospects to observe magnetically triggered instabilities of flows with positive shear.

Publ.-Id: 28761 - Permalink

Numerical simulation of multicomponent flows with the presence of density gradients for the upgrading of advanced turbulence models
Huang, M.; Höhne, T.;
The turbulence effects during the buoyancy-driven mixing was investigated at a vertical mixing (VeMix) test facility, which was developed to investigate the mixing of high borated and low borated coolant in nuclear reactor. Additional buoyancy terms are included in buoyancy-modified turbulence models, which have been implemented in the CFD code ANSYS CFX and validated with experimental data captured by optical methods and conductivity measurement technology. The physicality of the flow phenomena and the vortical oscillations analyzed by Fourier tranformation in both the experiments and simulations show good agreement under different flow conditions. The influence of different buoyancy models were investigated in detail and optimal models for simulations at similar flow conditions have been selected.
Keywords: Multicomponent flow, CFD, turbulence models, SBES, RANS, LES


  • Secondary publication expected from 01.04.2020

Publ.-Id: 28760 - Permalink

FDG-PET/MRI in patients with pelvic recurrence of rectal cancer: first clinical experiences
Plodeck, V.; Rahbari, N.; Weitz, J.; Radosa, C.; Laniado, M.; Hoffmann, R.; Zoephel, K.; Beuthien-Baumann, B.; Kotzerke, J.; Hoff, J. van den; Platzek, I.;
To determine the value of 18F-FDG-PET/MRI in the diagnosis and management of patients with pelvic recurrence of rectal cancer.

Forty-four patients (16 women, 28 men) with a history of rectal cancer who received FDG-PET/MRI between June 2011 and February 2017 at our institution were retrospectively enrolled. Three patients received two FDG-PET/MRIs; thus a total of 47 examinations were included. Pelvic recurrence was confirmed either with histology (n = 27) or imaging follow-up (n = 17) (> 4 months). Two readers (one radiologist, one nuclear medicine physician) interpreted the images in consensus. Pelvic lesions were assessed regarding FDG uptake and morphology. Sensitivity, specificity, positive and negative predictive values as well as accuracy of PET/MRI in detecting recurrence were determined.

In 47 FDG-PET/MRIs 30 suspicious pelvic lesions were identified, 29 of which were malignant. Two patients underwent resection and had histologically proven pelvic recurrence without showing suspicious findings on FDG-PET/MRI. Changes in management due to FDG-PET/MRI findings had been implemented in eight patients. Eighty per cent (16/20) of resected patients had histologically negative resection margins (R0), one patient had uncertain resection margins. Sensitivity of FDG-PET/MRI in detecting recurrence was 94%, specificity 94%, positive/negative predictive value and accuracy were 97%, 90% and 94%, respectively.

FDG-PET/MRI is a valuable tool in the diagnosis and staging of pelvic recurrence in patients with rectal cancer.
Keywords: Positron-emission tomography, Magnetic resonance imaging, Rectal cancer, local Neoplasm Recurrence

Publ.-Id: 28748 - Permalink

Investigation of the ion induced magnetization in FeRh
Semisalova, A.; Barton, C.; Bali, R.; Böttger, R.; Thomson, T.; Potzger, K.; Lenz, K.; Lindner, J.; Fassbender, J.;
Structurally B2-ordered equiatomic FeRh thin films are known for unique properties such as a temperature, magnetic field, and spin polarized current driven phase transition from the antiferro- to the ferromagnetic state. The strain and structural disorder also influences the magnetic properties of FeRh, which opens a new way for controllable modification of properties at the micro- and nanoscale. Namely, structural modification by ion beam irradiation was shown to be an effective tool for tuning the phase transition temperature in FeRh as well as the saturation magnetization [1-3]. Here, we present a detailed study of magnetic properties of ion irradiated 40 nm thick FeRh films using magnetometry and broadband ferromagnetic resonance technique. The structurally ordered films were deposited epitaxially on MgO(001) substrates using magnetron sputtering. The irradiation was performed with 25 keV Ne ions at fluences of 0.1 – 4 ions/nm2 leading to a controllable reduction of the order parameter. The ion beam induced magnetization of FeRh at room temperature was shown to be as high as 1300 kA/m. Ferromagnetic resonance measurements performed at frequencies up to 40 GHz show that the Gilbert damping in structurally disordered ferromagnetic FeRh films is comparable to Py films. Such a relatively low damping in combination with the highly tunable saturation magnetization appears promising for further experiments on magnetization dynamics and spin wave propagation in FeRh thin films and nanostructures fabricated using ion beam irradiation.
[1] N. Fujita et al., J. Appl. Phys. 107 (2010) 09E302
[2] A. Heidarian et al., Nucl. Instr. Meth. B 358 (2015) 251-254
[3] S.P. Bennett et al., Mater. Res. Lett. 6 (2018) 106-112
Keywords: FeRh; disorder; FMR; Gilbert damping; ion irradiation
  • Lecture (Conference)
    21st International Conference on Ion Beam Modification of Materials IBMM 2018, 24.-29.06.2018, San Antonio, Texas, USA

Publ.-Id: 28747 - Permalink

Probing the exchange coupling in the complex modified Ho-Fe-B compounds by high-field magnetization measurements
Tereshina, I. S.; Pyatakov, A. P.; Tereshina-Chitrova, E. A.; Gorbunov, D. I.; Skourski, Y.; Law, J. M.; Paukov, M. A.; Havela, L.; Doerr, M.; Zvezdin, A. K.; Andreev, A. V.;
By examining the Ho2Fe14B case, we explored the influence of substitution and absorption atoms on the high-field behavior of magnetization of rare-earth (R)-Fe intermetallics. The value of the first critical field shows that the inter-sublattice exchange interactions remain practically unchanged when the substitution takes place in the R sublattice (replacement of up to 50 % of Ho by Nd). On the contrary, hydrogen absorption by Ho2Fe14B and Ho1Nd1Fe14B of the maximum possible hydrogen concentration 5.5 at./f.u. decreases the strength of the R-Fe Exchange by 30%. Remarkably, the influence of hydrogenation is stronger in the compound modified by substitution.

Publ.-Id: 28746 - Permalink

2D Materials Under Ion Irradiation: In-situ Experiments and the Role of the Substrate
Hlawacek, G.; Kretschmer, S.; Maslov, M.; Ghaderzadeh, S.; Ghorbani-Asl, M.; Krasheninnikov, A. V.;
Helium ion Microscopy (HIM) is frequently used for the fabrication of 2D nanostructures in graphene, MoS 2 and other materials. While some of the experiments are carried out with freestanding materials most of the work is done on supported material. While the defect production is understood for the former case, it is not fully understood in the latter setup. We used a combination of analytical potential molecular dynamics and Monte Carlo simulations to elucidate the role of the different damage channels, namely primary ions, backscattered atoms and sputtered substrate atoms.
Using this approach we looked at the defect production by helium and neon ions in MoS 2 and graphene supported by SiO 2 at typical energies used in HIM. We show that depending on ion species and energy defect production for supported 2D materials can be dominated by sputtered atoms from the support, rather than direct damage induced by the primary ion beam. We also evaluated the consequences of these additional damage mechanisms on the achievable lateral resolution for HIM based defect engineering and nano-fabrication in 2D materials. The obtained results agree well with experimental results obtained by in-situ and ex-situ characterization of defects in graphene and MoS 2 .
Keywords: him, 2D, Simulations
  • Lecture (Conference)
    AVS International Symposium & Exhibition, 21.-26.10.2018, Long Beach, USA

Publ.-Id: 28744 - Permalink

Organized Single Si Quantum Dots in tiny SiO2 volumes: Self-alignment for Single Electron Transistors
Heinig, K.-H.; von Borany, J.; Prüfer, T.; Xu, X.; Möller, W.; Ahmed, G.; Tiron, R.; Gregor, H.; Bischoff, L.; Engelmann, H.-J.; Facsko, S.;
Room temperature (RT) operation of Single Electron Transistors (SETs) is based on two conditions: (i) The Coulomb blockade energy of charging a dot must be smaller than kT, i.e. a Si quantum dot must be <5nm. (ii) The electron tunneling distance from the Si dot embedded in SiO2 to an electrode must be <1.5nm. Such dimensions are beyond the limits of top-down processes like Electron Beam Lithography (EBL) and Reactive Ion Etching (RIE).
As we demonstrate by atomistic computer simulations, a functional nanostructure for RT-SETs can be achieved by bottom-up processes, self-organization and self-alignment: Phase separation in a tiny volume ~(10nm)3 of metastable SiOx results in the formation of a single Si precipitate in SiO2 . And, if this SiOx volume is bordered at two sides by an Si/SiOx interface, the Si dot becomes self-aligned (isolated) by an SiO2 layer (SiOx denuted by excess Si).
The tiny SiOx volume has been formed by top-down processes: From a bulk Si/7nm SiO2/a-Si layer stack nanopillars of <20nm diameter have been fabricated by EBL and RIE. Then, the SiO2 layer embedded in the nanopillar was transformed into SiOx by 50keV Si+ ion irradiation. During subsequent annealing the single Si dot is expected to form. Two nanoscale phenomena not observed so far have to be overcome to get a reliable RT-SET fabrication.
This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.
Keywords: HIM, nanostructures
  • Lecture (Conference)
    E-MRS Fall meeting, 16.-20.09.2018, Warsaw, Poland

Publ.-Id: 28742 - Permalink

Manufacturability of Single Si Quantum Dots for Single Electron Transistors operating at Room Temperature
Heinig, K.-H.; von Borany, J.; Prüfer, T.; Xu, X.; Möller, W.; Gharbi, A.; Tiron, R.; Hlawacek, G.; Bischoff, L.; Engelmann, H.-J.; Facsko, S.;
Single Electron Transistors (SETs) are an extremely low power consuming alternative to Field Effect Transistors (FETs). Their room temperature operation is based on two conditions:
(i) The Coulomb energy of charging the dot with an electron must exceed kT. That requires dot sizes <5 nm. (ii) The tunneling distance between dot and electrodes through SiO2 must be <1.5nm.
These requirements are beyond top-down approaches. Thus, we follow a bottom-up approach: (i) A single Si dot forms by self-organization during phase separation of a tiny metastable SiOx volume into a Si precipitate and a SiO2 matrix. (ii) If the tiny SiOx volume is sandwiched between Si, then the single dot becomes self-aligned, i.e. two tunnel barriers form due to condensation of excess Si of SiOx onto the Si/SiO2 interfaces.
Here, a CMOS compatible manufacturabilty of vertical-nanowire-based SETs will be presented. Regular arrays of Si nanowires with diameters down to 20nm are fabricated by top-down processes. A SiO2 layer of 7nm thickness is sandwiched between Si of the wire. This SiO2 is transformed to SiOx(x<2) by ion beam mixing. During subsequent thermal activation (RTA) the dot structure should evolve as described above. Experimental and computer simulation results will be presented, critical fundamental issues of the nanofabrication will be discussed.
This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.
Keywords: HIM, nanostructures
  • Lecture (Conference)
    E-MRS Fall meeting, 16.-20.09.2018, Warsaw, Poland

Publ.-Id: 28741 - Permalink

HeFIB 2018: Helium and emerging focused ion beams
Hlawacek, G.; Facsko, S.; Bischoff, L.; Klingner, N.; Xu, X.; Serralta, E.; Ghaderzadeh, S.;
Gas field ion sources (GFIS) using helium and neon as ion species are new and rapidly growing ion beam techniques.
However, GFIS based focused ion beams (FIB) are not the only new ion beam techniques offering new capabilities that go
beyond what classic Ga based FIB can do. Based on the contributions to the recently held meeting on Helium and
Emerging Focused Ion Beams (HeFIB) I will report on the newest developments in this field.
I will try to highlight new technological developments in the field of GFIS based FIBs, but also present new and emerging
alternative FIB source techniques such as Laser cooled sources, liquid metal alloy source, or Xe plasma FIBs. However,
such new techniques also open up many new application fields. I will present selected examples of in which focused ion
beams have been used for imaging, localized materials modification as well as classical FIB based fabrication of nano-
Keywords: HIM
  • Invited lecture (Conferences)
    CAARI 2018 - The Conference on Application of Accelerators in Research and Industry, 13.-17.08.2018, Fort Worth, USA

Publ.-Id: 28739 - Permalink

Molecular Dynamics simulations of 30 keV He impacts on gold nano-clusters
Ghaderzadeh, S.; Hlawacek, G.; Krasheninnikov, A.;
At the Helmholtz-Zentrum Dresden-Rossendorf, molecular dynamics computer simulations are employed to study the sputtering yield and channeling effects in Gold nano-clusters of different sizes. Primary ion energy and crystal orientation are varied to obtain a holistic image of the possible effects relevant for scanning transmission ion microscopy. Our results show that ion-channeling occurs not only in the principal low-index, but also in other directions in between. The strengths of different channels are specifed, and their correlations with sputtering yield and damage production is addressed. The figure below shows sputtering under 30 keV He ion irradiation of 5 nm Gold nano-clusters.
Keywords: HIM, nanostructures, simulations, channeling

Publ.-Id: 28738 - Permalink

Imaging and analytic possibilities in the Helium Ion Microscope
Hlawacek, G.; Klingner, N.; Heller, R.; Veligura, V.; van Gastel, R.; Poelsema, B.; von Borany, J.; Facsko, S.;
Helium Ion Microscopy (HIM) utilizes a Gas Field Ion Source (GFIS) to create a Helium or Neon ion beam with a diameter better than 0.5 nm and 1.8 nm, respectively. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating. The latter specimens are typically found in the fields of biosciences, MEMS/NEMS technology, catalyst research and many others. The availability of He and Ne ions with either low or moderate sputter yields, allow direct write nano-structuring with a precision below 10 nm in the HIM [1, 2]. However, the existing GFIS based focused ion beam (FIB) tools suffer from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. While HIM technology is relatively young several efforts have been made to add such an analytic capability to the technique. So far, ionoluminescence [1, 3], backscattering spectrometry (BS) [1, 4], and secondary ion mass spectrometry (SIMS) using a magnetic sector [5] or time of flight (TOF) setup have been demonstrated [4].
I will present results obtained using the above mentioned methods beginning with iono-luminescence and its application to various materials systems. The method is in particular suited for the analysis of various defects present in the sample and the behaviour of defects under ion beam irradiation. In the second part of the talk I will present our newly developed TOF-BS and TOF-SIMS setup which allow to obtain information on the composition of the sample. They both utilize the same cost efficient and minimal invasive pulsing scheme for the primary ion beam. The lateral resolution reached for TOF-BS is approximately 50 nm while for TOF-SIMS a value of 8 nm could be reached. First images will be presented and the performance of the TOF-SIMS spectrometer will be discussed.
Keywords: HIM,nanostructures, analytic, SIMS
  • Invited lecture (Conferences)
    Imaging 2020 Workshop, 06.04.2018, Sønderborg, Denmark
  • Lecture (others)
    PNNL Seminar, 19.10.2018, Richland, USA

Publ.-Id: 28737 - Permalink

Dispersion relation of interlayer exchange coupled tailored ferrimagnets
Sorokin, S.; Gallardo, R.; Fowley, C.; Atcheson, G.; Dennehy, G. S.; Rode, K.; Stamenov, P.; Lindner, J.; Fassbender, J.; Deac, A. M.;
Different ferromagnetic resonance (FMR) modes in micron-sized antiferromagnetically interlayer exchange coupled SiO2/Ta(5nm)/Py(t)/Ru(0.85 nm)/Py(3nm)/Ru(3nm) structures, with t = 3, 6 and 9 nm, were studied by means of the electrically detected ferromagnetic resonance (ED-FMR).
The main magnetoresistance effect used in ED-FMR was anisotropic magnetoresistance (AMR). Bilinear and biquadratic coupling strengths for each sample were determined by fitting SQUID-VSM measurements on 4×4 mm² thin films, using equilibrium total energy minimization. The existence of two different resonance modes (in-phase (acoustic) and out-of-phase (optic)) is shown for asymmetric samples. For the symmetric sample only the acoustic mode was observed, due to the compensation of AMR response from Py layers for the out-of-phase mode. The obtained dispersion relations show a clear dependence of the acoustic mode frequency minimum on the bilinear coupling strength.
Keywords: FMR, ED-FMR, Synthetic Antiferromagnets, Dispersion relation.
  • Poster
    The European School on Magnetism, 17.09.2018, Krakow, Poland

Publ.-Id: 28736 - Permalink

Dispersion relation of the interlayer exchange coupled tailored ferrimagnets
Sorokin, S.; Fowley, C.; Atcheson, G.; Dennehy, G.; Duan, J.; Khudorozhkov, A.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A.; Stamenov, P.;
Here we present a study of different ferromagnetic resonance (FMR) modes in micron-sized antiferromagnetically interlayer exchange coupled SiO2/Ta(5nm)/Py(t)/Ru(0.85 nm)/Py(3nm)/Ru(3nm) structures, with t = 3, 6 and 9 nm, by means of the electrically detected ferromagnetic resonance (ED-FMR).
The main magnetoresistance effect used in ED-FMR was anisotropic magnetoresistance (AMR). Bilinear and biquadratic coupling strengths for each sample were determined by fitting SQUID-VSM measurements on 4×4 mm² thin films, using equilibrium total energy minimization. The existence of two different resonance modes (in-phase (acoustic) and out-of-phase (optic)) is shown for asymmetric samples. For the symmetric sample only the acoustic mode was observed, due to the compensation of AMR response from Py layers for the out-of-phase mode. The obtained dispersion relations show a clear dependence of the acoustic mode frequency minimum on the bilinear coupling strength. For asymmetric samples, mode intermixing occurs for certain resonance fields, accompanied by abrupt jumps in both mode frequencies. Such behavior is not observed for symmetric samples, in accordance with predictions based on VNA-FMR experiments and simulations performed elsewhere.
Keywords: FMR, ED-FMR, Synthetic antiferromagnets, Dispersion relation.
  • Lecture (Conference)
    JEMS 2018 - The Joint European Magnetic Symposia, 03.09.2018, Mainz, Germany

Publ.-Id: 28735 - Permalink

Magneto-transport measurements in para- and ferromagnetic Fe60Al40 wires
Liersch, V.; Schmeink, A.; Eggert, B.; Warnatz, T.; Wintz, S.; Ehrler, J.; Böttger, R.; Hlawacek, G.; Potzger, K.; Lindner, J.; Faßbender, J.; Wende, H.; Bali, R.;
Certain alloys (Fe60Al40, Fe50Rh50, Fe65V35) have stable, chemically ordered, B2 and metastable, chemically dis-ordered, A2 crystal structures with different magnetic properties.
B2 Fe60Al40 is paramagnetic (PM), A2 Fe60Al40 is ferromagnetic (FM).
Possible applications are in phase change memories and sensors.
We investigate change of resistivity 𝜌 during A2 ↔ B2 transitions in Fe60Al40 wires.
Keywords: HIM, magnetic structures, nanopatterning
  • Poster
    DPG-Frühjahrstagung 2018, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 28734 - Permalink

Luminescence spectroscopy of uranium in environmental systems
Steudtner, R.; Drobot, B.; Zabelt, D.; Bader, M.; Hilpmann, S.; Großmann, K.;
Luminescence spectroscopy is a powerful tool to study the chemistry of uranium in trace concentration. Manifold operating mode, e.g. steady state, time-resolved, laser-induced, site-selective, cryogenic, etc. were used to investigate the environmental behavior of uranium in various geological and biological systems.
Hydrolysis is the basis for more complex aquatic systems and thus a deep understanding of those systems is indispensable. In case of U(VI) we demonstrated that a combination of luminescence spectroscopic methods together with state of the art data analysis (parallel factor analysis – PARAFAC) and quantum chemical calculations is a powerful setup to gain information on that system. We were able to extract thermodynamic constants for the mononuclear hydrolysis species using optimized data processing. Furthermore, advanced deconvolution of individual luminescence spectra demonstrates the correlation of luminescence spectroscopy and vibrational spectroscopy.
For kinetic studies of geological or biological sorption phenomena, different microscopic or flow-through cell techniques are useable. For online monitoring and characterization of U(VI) sorption species we develop a new technical in situ luminescence spectroscopy setup in comparability to the well established in situ time resolved ATR FT-IR spectroscopy. For biological systems, we combined microscopy with luminescence spectroscopic measurements for localization, visualization and chemical characterization of uranium complexes. This approach enables us to distinguish between biosorption, intracellular uptake or biomineralization as dominant retention process for uranium in biological samples.
Under reducing conditions expected in the near field of nuclear waste repository, the tetravalent uranium should be the major oxidation state. We studied the U(IV) luminescence characteristics in presence of various inorganic ligands (ClO4–, Cl–, SO42–). By using cryo-TRLFS at 77 K the speciation analysis limit for U(IV) was determined with 5·10–6 M and this corresponds to uranium concentrations occurring in the environment.
  • Lecture (Conference)
    8. RCA-Workshop, 12.-14.06.2018, Dresden, Germany

Publ.-Id: 28732 - Permalink

Towards an understanding of U(VI) interaction with Boom Clay dissolved organic matter by TRLFS
Buchatskaya, Y.; Salah, S.; Durce, D.; Steudtner, R.; Devillers, M.;
Uranium represents the most abundant radionuclide in nuclear waste and its behavior is a major concern for geological waste disposal. The speciation of Uranium in solution affects its mobility in porous media and must in consequence be well understood. The dissolved organic matter (DOM) present in pore waters of geological formations can change the speciation and the geochemical behavior of uranium [1]. DOM present in the potential host rock formation Boom Clay in Belgium differs in size (from hundreds to thousands of Da), solubility at different pH (humic and fulvic acids) and functionality. Due to DOM polydispersity and polyfunctionality, its interaction with U(VI) could involve various mechanism which need to be studied in details. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a well-known technique used to characterize U(VI) speciation and complex formation with inorganic and organic ligands. This method was already successfully applied to derive complex stability constants of U(VI) and humic acids [2]. The objective of the present work is to perform a systematic and multi-parametric study on the U(VI) complexation with BC DOM fractions using TRLFS.
Two DOM fractions different in molecular size were separated, concentrated and purified from natural Boom Clay organic matter: one “colloidal” (100 kDa – 0.45 µm) and one “small” (< 1 kDa). The separation and concentration were performed using ultrafiltration and solid phase extraction methods. The size distribution and reactivity of final fractions were characterized using size-exclusion chromatography, X-ray photoelectron spectroscopy and potentiometric titrations. Complex formation of U(VI) with different DOM fractions was studied using TRLFS in presence and absence of carbonates in 0.1 M NaClO4 for a pH range 4-12.5.
  • Lecture (Conference)
    International conference Uranium biogeochemistry, 21.-26.10.2018, Ascona, Switzerland

Publ.-Id: 28731 - Permalink

Mechanistic understanding for biochemical and biological processes of uranium(VI) by time-resolved laser-induced fluorescence spectroscopy (TRLFS)
Steudtner, R.; Hilpmann, S.; Bader, M.; Jessat, J.; Sachs, S.; Cherkouk, A.;
The transfer of radionuclides into the food chain is of central concern for the safety assessment of both nuclear waste repositories and radioactive contaminated areas, such as legacies of the former uranium mining. The interaction of radionuclides, here in this particular case uranium(VI), with microorganism or plants is mostly described by transfer factors without knowing the underlying processes. In two examples we want present that luminescence spectroscopy is a powerful tool to study these unknowing processes of uranium(VI) on a molecular level.
Rock salt formations are considered as potential host rocks for the long-term storage of highly radioactive waste in a deep geological repository. Extremely halophilic archaea, e.g. Halobacterium species, dominate this habitat. We studied and compared the interactions of different extremely halophilic Halobacterium species with uranium(VI) by classical chemical and biological, by multi-spectroscopic and microscopic and by molecular biological methods. Depending on the used initial uranium(VI) concentration the different Halobacterium species showed a different bioassociation behaviour of uranium(VI). By using TRLFS the formation of uranium(VI) phosphate minerals, such as meta-autunite, as well as the complexation with carboxylate groups was observed as a function of the uranium(VI) concentration and the Halobacterium species.
In a second example, we studied the interaction of uranium(VI) with canola cells (Brassica napus) focusing on the concentration dependent impact of uranium(VI) on the cell metabolism. Previous studies showed, for instance, a speciation dependent influence of radionuclide uptake and translocation in plants [1]. Heavy metal stress induces the synthesis of metal-binding metabolites, storage of metal chelates in vacuoles or the secretion into the rhizosphere [2], which changes the plant cell metabolism. To study the interaction of lanthanides with Brassica napus on a cellular level, callus and suspension cells were exposed to uranium(VI). Besides the kinetics of the bio-association, the amount of associated uranium(VI) and its effect on cell growth and viability was determined. TRLFS was used as direct speciation technique to determine the uranium(VI) species on callus cells and the supernatant. In combination with high performance liquid chromatography (HPLC) experiments the metabolic answer of the callus cells during the presence of uranium(VI) will be investigated.
  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 06.-09.11.2018, Nice, France

Publ.-Id: 28730 - Permalink

Perforating Freestanding Molybdenum Disulfide Monolayers with Highly Charged Ions
Kozubek, R.; Tripathi, M.; Ghorbani-Asl, M.ORC; Kretschmer, S.; Madauß, L.; Pollmann, E.; O'Brien, M.; Mcevoy, N.; Ludacka, U.; Susi, T.; Duesberg, G. S.; Wilhelm, R. A.; Krasheninnikov, A. V.ORC; Kotakoski, J.; Schleberger, M. Y.
Porous single-layer molybdenum disulfide (MoS2) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS2. Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process, and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies. Analysis of the irradiated samples with atomic resolution scanning transmission electron microscopy reveals a clear dependence of the pore size on the potential energy of the projectiles, establishing irradiation with highly charged ions as an effective method to create pores with narrow size distributions and radii between ca. 0.3 and 3 nm.
Keywords: ion irradiation, highly charged ions, molybdenum disulfide, 2D material, STEM, MD simulation, perforation

Publ.-Id: 28727 - Permalink

Site-controlled Si Nanodot Formation for a RT-SET via Ion Beam Mixing and Phase Separation
Xu, X.; Prüfer, T.; Wolf, D.; Hübner, R.; Bischoff, L.; Engelmann, H.-J.; Gharbi, A.; Heinig, K.-H.; Hlawacek, G.; von Borany, J.;
CMOS-compatible formation of Si nanodots (NDs) as Coulomb islands is a prerequisite for an RT Single Electron Transistor operation. In this work, Si NDs are formed via ion beam mixing and thermally stimulated phase separation. Broad-beam Si+ and Ne+ beams followed by a rapid thermal annealing treatment were utilized to create a layer of NDs and visualized by Energy-Filtered Transmission Electron Microscopy (EFTEM). The conditions for ND formation are optimized based on an extensive survey of the parameter space. The work is guided by TRIDYN simulations during the ion beam mixing and 3D Kinetic Monte-Carlo simulation for the phase separation during the thermal treatment. To tailor towards a single Si ND, the focused Ne+ beam from the Helium Ion Microscope (HIM) is utilized to create patterns of NDs in planar layer stacks. The formation of site-controlled single NDs with a diameter of 2.2 nm is confirmed by comparing the EFTEM Si plasmon-loss intensity with simulated intensity.
  • Lecture (Conference)
    HeFIB2018 Helium and emerging Focused Ion Beams, 11.06.2018, Dresden, Deutschland

Publ.-Id: 28724 - Permalink

Avoiding Amorphization Related Shape Changes of Nanostructures during Medium Fluence Ion Beam Irradiation of Semiconductor Materials
Xu, X.; Hlawacek, G.; Engelmann, H.-J.; Heinig, K.-H.; Möller, W.; Gharbi, A.; Tiron, R.; Bischoff, L.; Prüfer, T.; Hübner, R.; Facsko, S.; von Borany, J.;
We present an approach to mitigate the ion beam induced damage inflicted on semiconductor nano-structures during ion beam irradiation. Nanopillars (with diameter a of 35 nm and height of 70 nm) have been irradiated with both, a 50 keV Si+ broad beam and a 25 keV focused Ne+ beam from a helium ion microscope (HIM). Upon irradiation of the nanopillars at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the TRI3DYN. However, irradiation at elevated temperatures with the same fluence would preserve the shape of the nanopillars.
It is well known that a critical temperature exists for silicon above which it will recrystallize during ion beam irradiation. This prevents the amorphization of the target material independent of the applied fluence. At high enough temperatures and not for too high flux this prevents the ion beam hammering and viscous flow of the nano-structures. These two effects are responsible for the shape change observed at low temperature. This has been observed previously mainly for swift heavy ions and energies higher than 100 keV. We used HIM and transmission electron microscopy to follow the morphological evolution of the pillars and their crystallinity. While irradiation at room temperature results in amorphization and the related destruction of the nanopillars, irradiation above 650 K preserves the crystalline nature of the pillars and prevents viscous flow. This effect has been observed previously mainly for swift heavy ions and energies higher than 100 keV. Such high-temperature irradiation, when carried out on a nanopillar with Si/SiO2/Si layer stack, would induce ion beam mixing without suffering from the plastic deformation of the nanostructure. Due to a limited mixing volume, single Si-NCs would form in a subsequent rapid thermal annealing process via Oswald ripening and serve as a basic structure of a gate-all-around single electron transistor device.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.
  • Lecture (Conference)
    AVS 65th International Symposium & Exhibition, 22.10.2018, Long Beach, USA

Publ.-Id: 28723 - Permalink

Tuneable vortex dynamics with ion implantation
Ramasubramanian, L.; Kákay, A.; Fowley, C.; Yildirim, O.; Matthes, P.; Lindner, J.; Deac, A. M.;
The fundamental oscillation mode of magnetic vortices in thin-film elements has been proposed as working principle for spin-torque-driven nano-oscillators [Nat. Phys., 3:498, 2007].
Commercial applications require tuning of the output frequency by external parameters, such as spin-polarized currents. The tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design. The fundamental frequency is determined by the saturation magnetisation, Ms, as well as the geometrical confinement of the magnetisation i.e. the diameter and height of a magnetic disk. Our micromagnetic simulations have shown that if regions with different Ms can be induced in a magnetic disk, multiple precession frequencies can be generated. Here, we show that ion implantation [Phys. Rev. B 73, 184410, 2006] is a novel route to fabricate such devices.
Permalloy (Py) disks of various diameters and thicknesses were patterned and contacted to study the interaction of an applied AC current with the magnetic vortex. Using a conventional lock-in technique, the resonance frequencies are measured based on the anisotropic magnetoresistance (AMR) effect. Regions of different Ms are induced in single disks by ion implantation, yielding different resonance frequencies corresponding to the specific area where the core is precessing. The work represents a novel way to obtain multiple oscillation frequencies from a single disk.
Keywords: magnetic vortex, ion implantation, frequency tunability
  • Lecture (Conference)
    9th JEMS Conference 2018, 03.-07.09.2018, Mainz, Germany

Publ.-Id: 28722 - Permalink

Magnetic vortex dynamics and frequency tunability in Cr-implanted permalloy disks
Ramasubramanian, L.; Kákay, A.; Fowley, C.; Yildirim, O.; Matthes, P.; Böttger, R.; Lindner, J.; Fassbender, J.; Gemming, S.; Schulz, S. E.; Deac, A. M.;
The fundamental oscillation mode of magnetic vortices in thin-film elements has recently been proposed for designing spin-torque-driven nano-oscillators [1]. Commercial applications require tuning of the output frequency by external parameters, such as applied fields or spin-polarized currents. However, the tunability of vortex-based devices is limited, since the gyrotropic frequency is specific to the individual sample design. Indeed, the fundamental frequency is known to be determined by the saturation magnetisation, M_s , as well as the geometrical confinement of the magnetisation, i.e. the diameter and height of the magnetic disk [2, 3]. Micromagnetic simulations [4] have shown that if regions with different saturation magnetisation can be induced in a magnetic disk, multiple precession frequencies can be generated. We show that ion implantation [5] is a novel route to fabricate such devices.
Permalloy (Py) disks of various diameters and thicknesses were prepared using electron beam lithography followed by electron beam evaporation. Individual disks were contacted by gold leads to study the interaction of spin-polarized current with the magnetic vortex. The presence of vortex is verified by magneto optic Kerr effect (MOKE), X-ray magnetic circular dichroism (XMCD) and magnetotransport measurements. The magnetic field dependence of the vortex position can be tuned by the disk size as shown by XMCD (Figure 1 (a)). Higher magnetic stability due to larger annihilation fields can be achieved by smaller disk diameters, whereas larger field sensitivity is present in larger disks (Figure 1 (b)). Magnetotransport measurements on electrically contacted disks show the presence of anisotropic magnetoresistance (AMR) in different disks with varying thickness (Figure 1 (c)).
Using a conventional lock-in technique, the resonance frequencies are measured for disks with different radii as shown in Figure 2 (a), with the inset showing the scanning electron microscope image of an electrically contacted disk. In order to modify the magnetisation within a single disk and to achieve two different oscillation frequencies, we implant chromium in different regions of the disk (inner and outer). Cr-implantation leads to a decrease in the Curie temperature and thus a reduction in the magnetic moment [6]. The reduction of M_s as a function of Cr fluence was optimised on extended Py films using a vibrating sample magnetometer – superconducting quantum interference device (VSM-SQUID), see figure 2 (b). A clear drop in M_s with increasing the chromium ion fluence is observed. Concentric donut-like structures were then implanted with Cr and the modification of dynamics as a function of magnetic field was investigated. An example of Cr implantation in a 3 µm radius disk at 30 keV with a fluence of 1.2×〖10〗^16 ions/cm^2 is shown in Figure 2 (c). The vortex core is shifted between the two different magnetisation regions by applying an external in-plane field. The vortex nucleates in the irradiated region at – 2.281 mT, leading to a resonance frequency of 30.2 MHz (shown in orange in Figure 2 (c)). Further increasing the external field pushes the vortex core to the non-irradiated region where the resonance frequency is 42.3 MHz (shown in green), corresponding to a field of + 1.597 mT. The results show that ion implantation is a novel way to obtain multiple frequencies from a single disk.
Keywords: magnetic vortex, ion implantation, frequency tunability
  • Lecture (Conference)
    INTERMAG 2018 - The IEEE International Magnetics Conference (INTERMAG, 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 28720 - Permalink

Effect of insertion layer on the properties of Mn₂RuₓGa in magnetic tunnel junctions
Titova, A.; Fowley, C.; Clifford, E.; Lau, Y.-C.; Borisov, K.; Betto, D.; Atcheson, G.; Hübner, R.; Xu, C.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Fassbender, J.; Deac, A. M.;
The choice of proper materials for magnetic tunnel junctions (MTJs) for storage and communication applications (like MRAM or spin-transfer-torque nano-oscillators (STNOs)) is always an issue. On the one hand, the magnetic layers should exhibit as little stray field as possible and be mostly insensitive to the external magnetic field. On another hand, in order to maximize the tunneling magnetoresistance (TMR) ratio, these materials should provide high spin polarization, or even ideally possess half-metallic properties. An option which satisfies both criteria are the compensated half metallic ferrimagnets (CHFMs) — a class of materials predicted in 1995 by van Leuken and de Groot. CHFMs are materials which behave as antiferromagnets (AFMs) with respect to external magnetic fields, since the magnetic moments of the two sublattices compensate, while simultaneously exhibiting half-metal behavior from the point of view of magnetotransport. Experimentally, the first identified zero-moment half-metal was Mn₂RuₓGa (MRG) in 2014. It was already known that Mn-based Heusler compounds possess huge uniaxial anisotropy fields (exceeding tens of teslas); this, together with their vanishing magnetization, lead to resonance frequencies of several hundred GHz in such materials, making them very attractive candidates for STNOs in the sub-THz range. Such devices, due to the much higher bandwidth accessible, are expected to open the way for remote hospitals, 3-D remote meetings and much more.
Earlier MRG studies have already shown that these materials exhibit tunable magnetic properties. Indeed, the compensation temperature varies between 2 and 450K, depending on the Ru concentration. They also yield giant spontaneous Hall angle (7.7%). MRG has also been successfully integrated into perpendicular MRG/MgO/CoFeB MTJs, with low-bias TMR reaching up to 40 % at 10 K and 7 % at 300 K.
As the low value of TMR was attributed to diffusion of Mn atoms inside the MgO barrier, here, we investigate the effect of different insertion layers introduced between MRG and MgO on the magnetic properties and transport of MTJs. Mn₂Ruₓ Ga (23)/insertion layer(t)/MgO(1.7)/CoFeB(1)/Ta(0.3)/CoFeB(0.9)MgO(0.7)/Ta(3)/Ru(4) multilayers were deposited using a “Shamrock” fully automated sputter deposition tool (thickness given in nm). Mn₂RuₓGa was grown by co-sputtering from a Mn₂Ga and a Ru target. Different MRG compositions (Mn₂Ru1.1Ga, Mn₂Ru0.9Ga, Mn₂Ru0.75Ga, and Mn₂Ru0.65Ga) have been obtained by varying the sputtering power of Mn₂Ga while keeping the sputtering power of Ru constant. Changing Ru concentration in MRG allows adjusting the compensation temperature Tcomp from 2 to 450 K.
We fabricated MTJs without insertion layers, as well as stacks with Ta (0.3 nm, 0.6 nm, 0.9 nm) and Al (0.3 nm, 0.6 nm, 0.9 nm) insertion layers. The switching properties of MTJs were analyzed through magnetotransport measurements as a function of applied bias voltage at room temperature. Al 0.6 nm acts as the best diffusion barrier. Magnetic properties of the multi-layers were characterized by the quantum design superconducting quantum interference device (SQUID) with a maximal applied field of 7n T at the range of temperatures from 60 K to 300 T.
The magnetometry data was extracted from the typical out-of-plane hysteresis loop of the investigated MTJs (Fig.1). As the magnetic field is swept from +7 T to – 7 T, the magnetic moment of CoFeB starts to rotate first and switches close to 0 T. The sharp jump observed at -0.4 T is attributed to the reversal of MRG magnetization. With conducting the same measurements at different temperatures, it is possible to detect the compensation temperature of MRG, which will lead to a decrease of its magnetic moment and a divergence of the coercive field. The temperature with zero magnetic moment and extremely high Hc corresponds to the compensation point of MRG. In Fig.2 the temperature dependence of magnetic properties of MTJs with the same MRG composition, but different diffusion barriers, is presented. For different insertion layers, Tcomp can shift over a large range, showing that the choice of insertion layer can have a dramatic effect on the properties of MRG. For instance, in MTJs with no insertion layer 100 K < Tcomp < 160 K; the shift to the higher temperatures is observed for Ta 0.3 nm insertion (140 K < Tcomp < 200 K), and to the lower temperatures with Al 0.6 nm insertion (Tcomp < 120 K). Moreover, we demonstrate that Tcomp can also be altered by post-annealing, as a 20 K shift is observed after annealing at 325°C for 1 hour.
Mn₂RuₓGa integrated into MTJs demonstrates a low magnetic moment, high coercivity, and thereby high immunity to the applied magnetic field over a broad temperature range (60 K – 300 K). At the same time, these MTJs show TMR even at the compensation temperature, highlighting a fundamental difference between an AFM and a CHFM. All these make MRG extremely attractive for spintronics applications, and for the excitation of magnetic resonances in STNOs.
Keywords: Ferrimagnetism, Half-metals, Magnetic Tunnel Junctions, Heusler Alloy
  • Lecture (Conference)
    The IEEE International Magnetics Conference (INTERMAG), 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 28719 - Permalink

Running Status of SRF Gun-II at ELBE Center
Xiang, R.; Arnold, A.; Lu, P.; Murcek, P.; Schaber, J.; Teichert, J.; Vennekate, H.; Zwartek, P.;
As a new electron source with higher brilliance, the second version of the superconducting RF photoinjector (SRF Gun-II) has been successfully commissioned at the ELBE Center for high power radiation sources since 2014. SRF Gun-II features an improved 3.5-cell niobium cavity as well as a superconducting solenoid in the same cryomodule. With Mg photocathode SRF Gun-II can provide high current beam with bunch charge up to 300 pC at 100 kHz repetition rate. For user operation the SRF Gun-II successfully generated stable beam with 200 pC in CW mode and sub-ps bunch length. In this presentation the gun's status and beam parameters will be presented.
Keywords: photoinjector, SRF Gun, Mg photocathode, CW mode, sub-ps
  • Open Access LogoContribution to proceedings
    29th Linear Accelerator Conference, 16.-21.09.2018, Beijing, China
    Proceedings of the 29th Linear Accelerator Conference, ISBN 978-3-95450-194-6

Publ.-Id: 28718 - Permalink

Robust Cs2Te and Mg photocathodes in SRF gun at ELBE center successful for CW IR FEL and THz radiation
Xiang, R.; Teichert, J.;
Quality of photocathodes is one of the critical issues for the stability and reliability of the light source facility. In 2014, SRF gun-I with Cs2Te provided stable electron beams successfully for IR FEL at HZDR. Cs2Te worked in SRF gun for more than one year without degradation. Currently, Mg photocathodes with QE up to 0.5% are applied in SRF Gun II, which is able to generate e- beam with bunch charges up to 200 pC in CW mode with sub-ps bunch length for the high power THz radiation facility for the ELBE users.
Keywords: Photocathode, SRF gun
  • Lecture (Conference)
    Photocathode Physics for Photoinjectors 2018, 15.-17.10.2018, Santa Fe, NM, USA

Publ.-Id: 28717 - Permalink

Development and characterization of novel anti-GD2 target modules for retargeting of Universal CAR T cells toward GD2 expressing tumors
Mitwasi, N.; Feldmann, A.; Bergmann, R.; Berndt, N.; Rössig, C.; Bachmann, M.;
Although chimeric antigen receptor (CAR) engineered T cells demonstrated promising therapeutic effect against cancer, they are still associated with adverse side effects which could be life threatening in some cases. Therefore, in our group we have developed a switchable universal CAR T cell platform “UniCAR”, which can be repeatedly switched on and off. This system consists of CAR T cells that cannot bind tumor antigens directly but instead they are redirected with a target module (TM). Such TMs are mainly composed of an epitope on one side, which is recognized by the UniCAR T cells, and on the other side a tumor antigen-binding domain. Once the TM is eliminated, the UniCAR T cells are no more activated. Disialoganglioside GD2 was shown previously to be a very promising target for several tumors such as neuroblastoma and Ewing’s sarcomas. Therefore, anti-GD2 TMs were developed and evaluated regarding their functionality. They were shown to be functional in activating the UniCARs to secrete important pro-inflammatory cytokines and to kill GD2+ tumor cells both in vivo and in vitro. To further characterize the anti-GD2 TM with PET imaging, it was labeled with radioactive Cu64 . The TM showed a specific enrichment at the site of the GD2+ growing tumor, and it was mainly eliminated through the kidneys within half an hour due to its small size. Such short half-life, provides the UniCAR system with the fast safety switch in case any complications occurred in patients treated with the UniCAR T cells.
  • Poster
    The International Conference on Lymphocyte Engineering, 13.09.2018, Madrid, Spain
  • Abstract in refereed journal
    Human Gene Therapy 29(2018)11, A9

Publ.-Id: 28716 - Permalink

Automated Target Model Determination from MEIS Spectra Utilizing an Evolutionary Algorithm
Heller, R.;
To extract chemical compositions and layer thicknesses of layered samples from back scattering spectra experimentalists usually have to take the following approach: Simulation of a theoretical spectrum for an initial target configuration and comparison to the measured data followed by the successive re-adjustment of the target model iteratively, until simulation result and experimental spectrum fit together. For multi-layer samples this procedure can get rather time consuming, especially when a series of similar samples with varying layer thickness and/or stoichiometry has to be analyzed.

Although modern IBA spectrum simulation software like SimNRA[1] or WINDF[2] have become quite powerful and handy tools, the analysis of the spectra consumes still a significant fraction of an IBA scientist’s working time. SimNRA offers therefore the opportunity to partially fit layer thicknesses and/or elemental ratios for a given layer within a certain region of a spectrum. WINDF goes a step further and implements an automated spectrum fitting based on a simulated annealing algorithm. However, it takes the user quite some time to set up the boundary conditions and fit parameters until the actual fit procedure can be initiated. Furthermore, the outcome of the fit procedure in some cases contains non-physical artifacts and requires multiple re-adjustments of the boundary conditions / fit parameters.

An approach that came up in the past (and is still being applied for particular tasks) is the application of artificial neural networks (ANN) to derive sample information from IBA spectra [3,4]. In a nut-shell this method basically trains an algorithm how the shape of a spectrum is correlated to the sample’s target model without introducing any physics (numerical calculations) to the code. Therefore, the ANN is fed with many (typically several 10 thousand) training spectra with a known target model. After this training procedure (which can be quite time consuming) the ANN spits out the target model of any unknown spectra in almost zero time. However, the spectra must be of the same type as all the training spectra since an ANN can only interpolate and not extrapolate, which is for sure one of the mayor drawbacks of this approach. However, all these efforts are justified in some special scenarios e.g. if a large series of spectra of similar type has to be evaluated.

In this contribution, we present a new approach of automated IBA spectra fitting applying an evolutionary algorithm (EA). We show that EA is well suited and robust for complete and fast IBA spectrum fitting with minimum input of boundary conditions. The benefits of this algorithm and the particular differences to simulated annealing and ANN are pointed out. Special emphasis is put on the adoption of this algorithm to the analysis of MEIS spectra, since there is a couple of differences to classical IBA methods that needs to be considered.

Based on this algorithm a platform independent software package has been developed that comprises a clean and easy-to-use graphical user interface. We will introduce this software in a basic overview.
Keywords: Ion beam analysis, evaluation software, evolutionary algorithm
  • Invited lecture (Conferences)
    9th International Workshop on High-Resolution Depth Profiling (HRDP-9), 25.-29.06.2018, Uppsala, Schweden

Publ.-Id: 28715 - Permalink

Structural and magnetic properties of epitaxial Mn–Ge films grown on Ir/Cr buffered MgO(0 0 1)
Dash, S.; Schleicher, B.; Schwabe, S.; Reichel, L.; Heller, R.; Fähler, S.; Neu, V.; Patra, A. K.;
Epitaxial Mn–Ge films with varying composition have been prepared on Ir/Cr buffered MgO(0 0 1) substrates using DC magnetron sputtering. The effect of composition on phase formation, texture and magnetic properties of Mn–Ge films has been investigated. These films grow epitaxially on Ir/Cr buffered MgO(0 0 1) with a tetragonal D022 type structure. From the pole figure analysis the epitaxial relationship is determined to be: D022 Mn–Ge [1 0 0] (0 0 1)||Ir [1 0 0] (0 0 1)||Cr [1 1 0] (0 0 1)||MgO [1 0 0] (0 0 1). Mn–Ge films close to stoichiometric composition (Mn77.5Ge22.5) exhibit perpendicular magnetic anisotropy with crystallographic c-axis being the easy axis of magnetization. The room temperature measured values of coercivity µ 0 H c, saturation magnetization M S and anisotropy field µ 0 H A for Mn77.5Ge22.5 are 2.86 T, 90 kA m−1 and 9.6 T, respectively. Mn–Ge films with low and high Mn concentration possess high coercivity but extremely low magnetization and that can be ascribed to the presence of secondary phases of non-magnetic/low magnetic nature, possible interdiffusion, and especially partial substitution of excess Mn atoms into the Ge site.
Keywords: epitaxial growth, magnetron sputtering, ion beam analysis, Mn, Ge, magnetic propoerties

Publ.-Id: 28714 - Permalink

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