Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31869 Publications
Synthesis and Reactivity of Tetravalent Actinide Amidinates
Schöne, S.ORC; März, J.; Kaden, P.
A series of tetravalent actinide amidinates was synthesized and characterized in solution and in solid state. Quantum chemical calculations support findings based on bonding analysis. Furthermore the reactivity of the complexes is presented.
  • Lecture (others)
    FENABIUM Projekttreffen März 2019, 27.02.2019, Dresden, Deutschland

Publ.-Id: 29371 - Permalink

Enantiopure Tetravalent Actinide Amidinates – Synthesis and Reactivity
Schöne, S.ORC; Kloditz, R.; März, J.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.
In contrast to the dominant trivalent state for the lanthanide series (Ln(III)), a wide variety of oxidation states (from II to VII) of actinides (An) makes their chemistry intricate but attractive. Especially the early An thorium (Th), uranium (U), neptunium (Np), and plutonium (Pu) form highly charged cations with the oxidation state +IV (An4+), which are of particular interest for coordination chemistry due to their strong interaction with ligands.
The focus of our investigations lies in the comprehensive characterization of An(IV) complexes with ligands bearing soft donor atoms, such as nitrogen (N), both in the solid state and in solution. The present study focuses particularly on the interaction of An(IV) (Th, U, Np) with N-donor ligands of amidinate type, which could be considered as a simplified model of naturally occurring N-donor organic compounds.
Recently, the trivalent lanthanide complexes with the chiral benzamidine, (S,S)-N,N‘-Bis-(1-phenylethyl)-benzamidine ((S)-HPEBA), have been successfully synthesized.[1,2] Mono- and bis-amidinate complexes of the later lanthanides (Er, Yb, Lu) were obtained using a salt metathesis approach. Only for the larger samarium(III) a homoleptic tris-amidinate was accessible.
We have extended this approach to the tetravalent An, and successfully synthesized the first transuranic amidinate complexes. Moreover, we have obtained the first enantiopure amidinate complexes of An(IV) [AnCl((S)-PEBA)3] (An = Th, U, and Np) as well as the analogous Ce(IV) compound, a chemical analog of An(IV). The tris-amidinate complexes have been structurally characterized in solid state and in solution showing a comparable complex geometry.
Due to the presence of a Cl- ligand in the An coordination sphere, it could be speculated that the complex should be reactive. Thus, the reactivity of the complexes has been demonstrated by successful reduction with potassium graphite to homoleptic trivalent actinide amidinates [An((S)-PEBA)3] (An = U, Np).
  • Lecture (Conference)
    Journées des Actinides 2019, 14.-18.04.2019, Erice, Italien

Publ.-Id: 29370 - Permalink

Comprehensive real space bonding analysis of tetravalent f-element complexes with Schiff-base ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
The contribution of the f-orbitals to chemical bonding leads to the rich chemistry of the actinides. This is in contrast to the lanthanides, where it is known that this contribution is less important. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands reflecting natural binding motifs.
This study compares the different bonding behavior of tetravalent actinides and lanthanides with the Schiff base salen (see Fig. 1, left) by means of real-space bonding analysis. Our approach makes use of the quantum theory of atoms in molecules (QTAIM), plots of the non-covalent interactions (NCI) and density differences complemented by natural population analysis (NPA). Especially the local properties at the bond critical points (Fig. 1, right), for instance charge, density, ellipticity and others, can be used to characterize a bond’s order, strength, and covalent contribution. In addition, thermodynamic calculations on the stability of these complexes are presented since the difference in stability is a direct consequence of the different interaction strengths of the f elements.
First results reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the interaction between the actinides and the nitrogen of salen is much weaker. The delocalization index, density and Laplacian reveal a significant increase of covalency for Pa to Pu compared to Th and Ce being an indicator of the contribution of the f-electrons. Tetravalent Ce as a lanthanide analogue of Th is expected to show a similar bonding behavior, but, surprisingly, this is not the case for all investigated bonding properties.
Such a detailed analysis of the electronic properties of actinide compounds will help to improve understanding of their behavior in the environment as well as in technical processes and leads to the possibility to predict properties of unknown complexes.
Keywords: Actinides, Quantum chemistry, DFT, Bonding, Covalency
  • Lecture (Conference)
    Journees des Actinides, 14.-18.04.2019, Erice, Italien

Publ.-Id: 29369 - Permalink

Hybrid LWFA–PWFA staging as a beam energy and brightness transformer: conceptual design and simulations
Martinez De La Ossa, A.; Assmann, R. W.; Bussmann, M.; Corde, S.; Couperus Cabadağ, J. P.; Debus, A.; Döpp, A.; Ferran Pousa, A.; Gilljohann, M. F.; Heinemann, T.; Hidding, B.; Irman, A.; Karsch, S.; Kononenko, O.; Kurz, T.; Osterhoff, J.; Pausch, R.; Schöbel, S.; Schramm, U.ORC
We present a conceptual design for a hybrid laserdriven
plasma wakefield accelerator (LWFA)
to beam-driven plasma wakefield accelerator
(PWFA). In this set-up, the output beams from
an LWFA stage are used as input beams of a
new PWFA stage. In the PWFA stage, a new
witness beam of largely increased quality can be
produced and accelerated to higher energies. The
feasibility and the potential of this concept is shown
through exemplary particle-in-cell simulations.
In addition, preliminary simulation results for
a proof-of-concept experiment in Helmholtz-
Zentrum Dresden-Rossendorf (Germany) are shown.
Keywords: laser plasma accelerator, LWFA, PWFA


  • Secondary publication expected from 25.06.2020

Publ.-Id: 29368 - Permalink

Bakterien als Alleskönner
Lederer, F.;
Bakterien sind Lebewesen, die unser tägliches Leben ganz entscheidend prägen. Ob Käse, Sauerkraut oder Wein - viele Delikatessen werden für uns durch diese kleinen Alleskönner produziert. Obwohl Bakterien häufig als Krankheitserreger verschrien sind, sind viele von ihnen wichtige Unterstützer unserer Gesundheit - was wir oft erst dann merken, wenn sie weg sind. Eine gesunde Darmflora aus Millionen von Bakterien ist entscheidend für die Produktion und Aufnahme vieler Vitamine in unserem Körper und für unser körperliches Wohlbefinden.
Auch in der Forschung werden Bakterien mit ihren vielen Eigenschaften gerne eingesetzt. Am Helmholtz-Zentrum Dresden-Rossendorf studiert man unter anderem ihre Fähigkeiten, sich fehlende Metalle aus der Umgebung zu besorgen und nutzt diese mikrobiellen Komplexbildner zur Rohstoffrückgewinnung aus Industrieabwässern.
Der Vortrag wird Bakterien als Alleskönner aus verschiednen Perspektiven beleuchten.
Keywords: Bakterien
  • Lecture (others)
    Seniorenakademie, 11.4.2019, Dresden, Deutschland

Publ.-Id: 29356 - Permalink

Ultrafast X-ray tomography raw-data of bubbly two-phase pipe flow around a ring shaped obstacle
Neumann, M.ORC; Hampel, U.ORC

For the investigation of bubbly two-phase flow, which should serve as a future benchmark experiment for CFD code validation, an experimental study has been conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) using ultrafast electron beam X-ray tomography (UFXRAY). In this study, flow obstacles were installed into a pipe to create a generic three-dimensional flow field as an advanced test case for CFD codes. UFXRAY provide valueable data of the gas phase dynamics with high temporal and spatial resolution.

The provided data set contains tomography raw-data for the experimental series L30 that uses a ring shaped flow obstacle with a blockage ratio of 0.5. 

For visualization, the data might be opend with Fiji. Therefore choose Import->Raw... In the following window specify "Image type" as 16-bit Unsigned, "Width" as 288 pixels and "Height" as 500 pixels for 2x1000Hz measurement or 200 pixels for 2x2500Hz measurement. Make sure that "Little-endian byte order" is checked. A data set contains image frames of both scvanning planes in alternating order. Therefore, if only a single scanning plane is required, the offset and gap parameters need to be set to 288000 bytes for 2x1000Hz measurement or 115200 bytes for 2x2500Hz measurement.

Keywords: ultrafast X-ray computed tomography; bubbly two-phase flow; three-dimensional flow field; two-phase pipe flow
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-18
    DOI: 10.14278/rodare.124
    License: CC-BY-4.0


Publ.-Id: 29354 - Permalink

Ultrafast X-ray tomography raw-data of bubbly two-phase pipe flow around a semi-circular obstacle
Neumann, M.ORC; Hampel, U.ORC

For the investigation of bubbly two-phase flow, which should serve as a future benchmark experiment for CFD code validation, an experimental study has been conducted at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) using ultrafast electron beam X-ray tomography (UFXRAY). In this study, flow obstacles were installed into a pipe to create a generic three-dimensional flow field as an advanced test case for CFD codes. UFXRAY provide valueable data of the gas phase dynamics with high temporal and spatial resolution.

The provided data set contains tomography raw-data for the experimental series L30 that uses a semi-circular flow obstacle with a blockage ratio of 0.5. 

For visualization, the data might be opend with Fiji. Therefore choose Import->Raw... In the following window specify "Image type" as 16-bit Unsigned, "Width" as 288 pixels and "Height" as 500 pixels for 2x1000Hz measurement or 200 pixels for 2x2500Hz measurement. Make sure that "Little-endian byte order" is checked. A data set contains image frames of both scvanning planes in alternating order. Therefore, if only a single scanning plane is required, the offset and gap parameters need to be set to 288000 bytes for 2x1000Hz measurement or 115200 bytes for 2x2500Hz measurement.

Keywords: ultrafast X-ray computed tomography; bubbly two-phase flow; three-dimensional flow field; two-phase pipe flow
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-06-26
    DOI: 10.14278/rodare.122
    License: CC-BY-4.0


Publ.-Id: 29353 - Permalink

Scalable, Data Driven Plasma Simulations with PIConGPU
Huebl, A.ORC; Widera, R.ORC; Garten, M.ORC; Pausch, R.ORC; Steiniger, K.ORC; Bastrakov, S.ORC; Meyer, F.; Bastrakova, K.; Debus, A.ORC; Kluge, T.ORC; Ehrig, S.ORC; Werner, M.; Worpitz, B.; Matthes, A.ORC; Rudat, S.; Starke, S.ORC; Bussmann, M.ORC
PIConGPU is an open source, multi-platform particle-in-cell code scaling to the fastest supercomputers in the TOP500 list. We present the architecture, novel developments, and workflows that enable high-precision, fast turn-around computations on Exascale-machines. Furthermore, we present our strategies to handle extreme data flows from thousands of GPUs for analysis with in situ processing and open data formats (openPMD). PIConGPU is since recently furthermore natively controlled by a Python Jupyter interface and we research just-in-time kernel generation for C++ with our Cling-CUDA extensions.
Keywords: LPA, laser-plasma, particle-in-cell, HPC, manycore, GPU, simulation, interactive, big data
Related publications
Scalable, Data Driven Plasma Simulations with PIConGPU (Id 29351) is a supplement to this publication
  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference (PASC19), 12.-14.06.2019, Zürich, Schweiz
    DOI: 10.14278/rodare.131


Publ.-Id: 29350 - Permalink

Heavy ion irradiation damage in Zr2AlC MAX phase
Qarra, H. H.; Knowles, K. M.; Vickers, M. E.; Akhmadaliev, S.; Lambrinou, K.;
Zr2AlC MAX phase-based ceramic material with 33 wt% ZrC has been irradiated with 22 MeV Au7+ ions between room temperature and 600 °C, achieving a maximum nominal midrange dose of 3.5 displacements per atom. The response of the material to irradiation has been studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Under room temperature irradiation, the ions caused a partial amorphisation of the MAX phase. At high temperatures, irradiated Zr2AlC remained crystalline, but developed an increased density of dislocations and stacking faults in the (0001) basal planes. The irradiated material also exhibited a temperature-dependent microcracking phenomenon similar to that previously reported in other MAX phase materials.

Publ.-Id: 29346 - Permalink

Advanced characterization methods for electrical and sensoric components and devices at the micro and nanoscale
Sheremet, E.ORC; Meszmer, P.ORC; Blaudeck, T.ORC; Hartmann, S.; Wagner, C.ORC; Ma, B.; Hermann, S.; Wunderle, B.; Schulz, S. E.; Hietschold, M.; Rodriguez, R. D.; Zahn, D. R. T.
This feature article covers the nano-analysis methods for four key material characteristics: electrical and electronic properties, optical, stress and strain, and chemical composition. With the downsizing of the geometrical dimensions of electronic, optoelectronic, and electromechanical devices from the micro to the nanoscale at the one hand and the increase of functionality density at the other, the previous generation of micro-analysis methods is no longer sufficient. Therefore, the metrology of materials’ properties with nanoscale resolution has become prerequisite in materials research and development. The article shortly reviews the standard analysis methods and focuses on advanced methods with a nanoscale spatial resolution based on atomic force microscopy (AFM): current-sensing AFM (CSAFM), Kelvin probe force microscopy (KPFM), and hybrid optical techniques coupled with AFM including tip-enhanced Raman spectroscopy (TERS), photothermal-induced resonance (PTIR) characterization methods (nano-Vis, nano-IR), photo-induced force microscopy (PIFM) and photothermal microspectroscopy (PTMS). The simultaneous acquisition of multiple parameters (topography, charge and conductivity, stress and strain, chemical composition) at the nanoscale is a key for exploring new research on structure-property relationships of nanostructured materials such as carbon nanotubes (CNTs) and nano/microelectromechanical systems (N/MEMS). Advanced nanocharacterization techniques foster the design and development of new functional materials for flexible hybrid and smart applications.
Keywords: Scanning probe microscopy, Kelvin probe force microscopy, nanoanalysis, Raman spectroscopy, atomic force microscopy

Publ.-Id: 29345 - Permalink

Entwicklung induktiver Strömungs- und Füllstandssensoren für flüssige Metalle
Krauter, N.;
In dieser Arbeit werden die Weiterentwicklung bestehender und die Entwicklung neuer Sensoren für die induktive Strömungs- und Füllstandsmessung in flüssigen Metallen sowie die zugehörigen Simulations- und Messergebnisse vorgestellt: Dabei handelt es sich um die Entwicklung und Charakterisierung eines miniaturisierten Eddy Current Flow Meters, das z.B. als Bestandteil der Sicherheitstechnik in flüssigmetallgekühlten Reaktoren zur Überwachung der Kühlmittelströmung bei hohen Umgebungstemperaturen eingesetzt werden kann. Außerdem wird das im Rahmen dieser Arbeit entwickelte Immersed Transient Eddy Current Flow Meter vorgestellt, welches eine direkte und kalibrierungsfreie Fließgeschwindigkeitsmessung ermöglicht und damit einen entscheidenden Vorteil gegenüber herkömmlichen induktiven Strömungssensoren besitzt. Anschließend werden neue Konzepte und ein Sensor für die Füllstandsüberwachung bei industriellen Prozessen, hier am Beispiel der Aluminium-Elektrolyse bei Temperaturen bis zu 1000 °C und der Titanherstellung vorgestellt.
Keywords: Induktive Messverfahren, Fließgeschwindigkeitsmessung, Füllstandsmessung
  • Doctoral thesis
    TUDpress, 2019
    Mentor: Prof. Dr. Uwe Hampel und Dr. Frank Stefani
    248 Seiten

Publ.-Id: 29336 - Permalink

Local inductive flow measurements
Krauter, N.; Stefani, F.;
An overview of current research on inductive local flow rate measurement techniques in liquid metals at the HZDR.
Keywords: Inductive Flow Measurements, Eddy Current Flow Meter, Immersed Transient Eddy Current Flow Meter
  • Lecture (Conference)
    ESFR-SMART European Workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Deutschland

Publ.-Id: 29335 - Permalink

Inductive Level Sensors
Krauter, N.; Stefani, F.; Zürner, T.; Wondrak, T.; Ratajczak, M.;
An overview of current research on inductive level measurement techniques in liquid metals at the HZDR.
Keywords: Eddy Current Level Sensor, Free Surface Detection, Look-Up-Table Method
  • Lecture (Conference)
    ESFR-SMART European Workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Deutschland

Publ.-Id: 29334 - Permalink

I-BEAT: Ultrasonic method for online measurement of the energy distribution of a single ion bunch
Haffa, D.; Yang, R.; Bin, J.; Lehrack, S.; Brack, F.-E.; Ding, H.; Englbrecht, F.; Gao, Y.; Gaus, L.; Gebhard, J.; Gilljohann, M.; Götzfried, J.; Hartmann, J.; Herr, S.; Hilz, P.; Kraft, S.; Kreuzer, C.; Kroll, F.; Lindner, F. H.; Metzkes-Ng, J.; Ostermayr, T. M.; Ridente, E.; Rösch, T. F.; Schilling, G.; Schlenvoigt, H.-P.; Speicher, M.; Taray, D.; Würl, M.; Zeil, K.; Schramm, U.ORC; Karsch, S.; Parodi, K.; Bolton, P.; Schreiber, J.; Assmann, W.
the shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens’ principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. this novel method, which we refer to as Ion-Bunch energy Acoustic tracing (I-BeAt), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BeAt is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches
Keywords: laser ion acceleration, ion spectrometer


Publ.-Id: 29332 - Permalink

Direct Observation of Plasma Waves and Dynamics Induced by Laser-Accelerated Electron Beams
Gilljohann, M. F.; Ding, H.; Döpp, A.; Götzfried, J.; Schindler, S.; Schilling, G.; Corde, S.; Debus, A.; Heinemann, T.; Hidding, B.; Hooker, S. M.; Irman, A.; Kononenko, O.; Kurz, T.; Martinez De La Ossa, A.; Schramm, U.ORC; Karsch, S.
Plasma wakefield acceleration (PWFA) is a novel acceleration technique with promising prospects for both particle colliders and light sources. However, PWFA research has so far been limited to a few large-scale accelerator facilities worldwide. Here, we present first results on plasma wakefield generation using electron beams accelerated with a 100-TW-class Ti:sapphire laser. Because of their ultrashort duration and high charge density, the laser-accelerated electron bunches are suitable to drive plasma waves at electron densities in the order of 1019  cm−3. We capture the beam-induced plasma dynamics with femtosecond resolution using few-cycle optical probing and, in addition to the plasma wave itself, we observe a distinctive transverse ion motion in its trail. This previously unobserved phenomenon can be explained by the ponderomotive force of the plasma wave acting on the ions, resulting in a modulation of the plasma density over many picoseconds. Because of the scaling laws of plasma wakefield generation, results obtained at high plasma density using high-current laser-accelerated electron beams can be readily scaled to low-density systems. Laser-driven PWFA experiments can thus act as miniature models for their larger, conventional counterparts. Furthermore, our results pave the way towards a novel generation of laser-driven PWFA, which can potentially provide ultralow emittance beams within a compact setup.
Keywords: laser wakefield, plasma wakefield electron acceleration, high power laser, advanced accelerator


Publ.-Id: 29331 - Permalink

A new method for the production of CeO2-base nanograined high capacity absorbent
Bonani, W.; Walter, O.; Cologna, M.; Prieur, D.; Beck, A.; Vitova, T.; Martin, P.; Störmer, H.; Popa, K.;
Due to the broad range of applications (e.g.: catalyst, polishing agents, in fuel cells, pollutant adsorbed, in medicine), ceria is one of the most engineered oxides at nano- and micro-scale. The present research demonstrates highly reactive, nearly mono-dispersed metal oxides NPs with very large specific surface area (>300 m /g). The size of the NPs can be tailored by controlling the temperature and the pressure of the process. This research project explores applications of high quality CeO nanomaterials towards safe management of liquid radioactive wastes contributing to the environmental protection, resources, energy consumption optimisation, and circular economy.
  • Poster
    Nano Today Conference, 17.-21.06.2019, Lisbon, Portugal

Publ.-Id: 29330 - Permalink

Instant kit preparation of 68Ga-radiopharmaceuticals via the hybrid chelator DATA: clinical translation of [68Ga]Ga-DATA-TOC
Sinnes, J. P.; Nagel, J.; Waldron, B. P.; Maina, T.; Nock, B. A.; Bergmann, R. K.; Ullrich, M.; Pietzsch, J.ORC; Bachmann, M.; Baum, P. B.; Rösch, F.
The widespread use of 68Ga for positron emission tomography (PET) relies on the development of radiopharmaceutical precursors that can be radiolabelled and dispensed in a simple, quick, and convenient manner. The DATA (6-amino-1,4-diazapine-triacetate) scaffold represents a novel hybrid chelator architecture possessing both cyclic and acyclic character that may allow for facile access to 68Ga-labelled tracers in the clinic. We report the first bifunctional DATA chelator conjugated to [Tyr3]octreotide (TOC), a somatostatin subtype 2 receptor (SST2)-targeting vector for imaging and functional characterisation of SSTR2 expressing tumours.

The radiopharmaceutical precursor, DATA-TOC, was synthesised as previously described and used to complex natGa(III) and 68Ga(III). Competition binding assays of [natGa]Ga-DATA-TOC or [natGa]Ga-DOTA-TOC against [125I-Tyr25]LTT-SS28 were conducted in membranes of HEK293 cells transfected to stably express one of the hSST2,3,5 receptor subtypes (HEK293-hSST2/3/5 cells). First in vivo studies were performed in female NMRI-nude mice bearing SST2-positive mouse phaeochromocytoma mCherry (MPC-mCherry) tumours to compare the in vivo SST2-specific tumour-targeting of [68Ga]Ga-DATA-TOC and its overall pharmacokinetics versus the [68Ga]Ga-DOTA-TOC reference. A direct comparison of [68Ga]Ga-DATA-TOC with the well-established PET radiotracer [68Ga]Ga-DOTA-TOC was additionally performed in a 46-year-old male patient with a well-differentiated NET (neuroendocrine tumour), representing the first in human administration of [68Ga]Ga-DATA-TOC.

DATA-TOC was labelled with 68Ga with a radiolabelling efficiency of > 95% in less than 10 min at ambient temperature. A molar activity up to 35 MBq/nmol was achieved. The hSST2-affinities of [natGa]Ga-DATA-TOC and [natGa]Ga-DOTA-TOC were found similar with only sub-nanomolar differences in the respective IC50 values. In mice, [68Ga]Ga-DATA-TOC was able to visualise the tumour lesions, showing standardised uptake values (SUVs) similar to [68Ga]Ga-DOTA-TOC. Direct comparison of the two PET tracers in a NET patient revealed very similar tumour uptake for the two 68Ga-radiotracers, but with a higher tumour-to-liver contrast for [68Ga]Ga-DATA-TOC.

[68Ga]Ga-DATA-TOC was prepared, to a quality appropriate for in vivo use, following a highly efficient kit type process. Furthermore, the novel radiopharmaceutical was comparable or better than [68Ga]Ga-DOTA-TOC in all preclinical tests, achieving a higher tumour-to-liver contrast in a NET-patient. The results illustrate the potential of the DATA-chelator to facilitate the access to and preparation of 68Ga-radiotracers in a routine clinical radiopharmacy setting.
Keywords: DATA-TOC; DOTA-TOC; Gallium-68; Molecular imaging; NET; PET-CT; Somatostatin receptor

Publ.-Id: 29328 - Permalink

High-field magnetoresistance of graphite revised
Barzola-Quiquia, J.; Esquinazi, P. D.; Precker, C. E.; Stiller, M.; Zoraghi, M.; Förster, T.; Herrmannsdörfer, T.; Coniglio, W. A.;
A detailed magnetoresistance (MR) study of bulk and microflake samples of highly oriented pyrolytic graphite in a broad temperature 240 ≳ T ≳ 1 K and magnetic field μ0H ≼ 62 T range, reveals the existence of three independent phenomena, the contributions of which are observed at different temperatures and fields. The identification of the three phenomena was possible by studying the MR of samples with thickness of 25 μm to 23 nm. At temperatures T ≳ 100 K the MR is mainly given by the semiconducting stacking order regions. At lower temperatures the contribution of the internal interfaces of graphite to its MR is clearly observable. These interfaces are the origin of the commonly observed electronic phase transitions at fields 35 ≲ μ0H ≲ 55 T at T ≲ 10 K as well as a background MR in the whole field range that resembles the MR measured in granular superconductors.

Publ.-Id: 29327 - Permalink

Extremely high conductivity observed in the triple point topological metal MoP
Kumar, N.; Sun, Y.; Nicklas, M.; Watzmann, S. J.; Young, O.; Leermakers, I.; Hornung, J.; Klotz, J.; Gooth, J.; Manna, K.; Süß, V.; Guin, S. N.; Förster, T.; Schmidt, M.; Muechler, L.; Yan, B.; Werner, P.; Schnelle, W.; Zeitler, U.; Wosnitza, J.; Parkin, S. S. P.; Felser, C.; Shekhar, C.;
Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Here, we report ultra-high electrical conductivity in MoP at low temperature, which has recently been established as a triple point fermion material. We show that the electrical resistivity is 6 nΩ cm at 2 K with a large mean free path of 11 microns. de Haas-van Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to noble metals with similar conductivity and number of carriers, the magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the momentum relaxing time of the electrons is found to be more than 15 times larger than the quantum coherence time. This difference between the scattering scales shows that momentum conserving scattering dominates in MoP at low temperatures.

Publ.-Id: 29325 - Permalink

Cytocompatible, Injectable, and Electroconductive Soft Adhesives with Hybrid Covalent/Noncovalent Dynamic Network
Xu, Y.; Patsis, P. A.; Hauser, S.; Voigt, D.; Rothe, R.; Günther, M.; Cui, M.; Yang, X.; Wieduwild, R.; Eckert, K.; Neinhuis, C.; Akbar, T. F.; Minev, I. R.; Pietzsch, J.ORC; Zhang, J.
Synthetic conductive biopolymers have gained increasing interest in tissue engineering, as they can provide a chemically defined electroconductive and biomimetic microenvironment for cells. In addition to low cytotoxicity and high biocompatibility, injectability and adhesiveness are important for many biomedical applications but have proven to be very challenging. Recent results show that fascinating material properties can be realized with a bioinspired hybrid network, especially through the synergy between irreversible covalent crosslinking and reversible noncovalent self-assembly.
Herein, a polysaccharide-based conductive hydrogel crosslinked through noncovalent and reversible covalent reactions is reported. The hybrid material exhibits rheological properties associated with dynamic networks such as self-healing and stress relaxation. Moreover, through fine-tuning the network dynamics by varying covalent/noncovalent crosslinking content and incorporating electroconductive polymers, the resulting materials exhibit electroconductivity and reliable adhesive strength, at a similar range to that of clinically used fibrin glue. The conductive soft adhesives exhibit high cytocompatibility in 2D/3D cell cultures and can promote myogenic differentiation of myoblast cells. The heparin-containing electroconductive adhesive shows high biocompatibility in immunocompetent mice, both for topical application and as injectable materials. The materials could have utilities in many biomedical applications, especially in the area of cardiovascular diseases and wound dressing.
Keywords: 3D cell culture, adhesion, biocompatibility, PEDOT, small animal magnetic resonance imaging

Publ.-Id: 29323 - Permalink

Exciton localization in MoSe₂ monolayer induced by adsorbed gas molecules
Venanzi, T.; Arora, H.; Erbe, A.; Pashkin, A.; Winnerl, S.; Helm, M.; Schneider, H.;
Lattice defects and dielectric environment play a crucial role for 2D materials. Gas molecules can get physisorbed easily on the surface through van der Waals forces and can modify dramatically the electronic and optical properties. In this work we investigate the impact of the physisorbed gas molecules on the optical properties of MoSe₂ monolayers by means of low-temperature photoluminescence (PL). More specifically we focus on the physics of excitons localized by gas molecules. The associated PL peak is observed to show a systematic and large red-shift with temperature and a blue-shift with laser irradiation. Both energy shifts are explained in terms of thermal instability of the localization in combination with hopping effects. Finally a model is presented which can reproduce the experimental data with excellent agreement.
Keywords: MoSe2, photoluminescence, localized excitons, TMD, physisorption


  • Secondary publication expected

Publ.-Id: 29321 - Permalink

XAFS Spectroscopy Study of Microstructure and Electronic Structure of Heterosystems Containing Si/GeMn Quantum Dots
Erenburg, S. B.; Trubina, S. V.; Zvereva, A.; Zinoviev, A.; Katsyuba, V.; Dvurechenskii, V.; Kvashnina, K. O.; Voelskow, M.;
Using X-ray absorption near edge structure spectroscopy, extended X-ray absorption fine structure spectroscopy, atomic force microscopy, and Rutherford backscattering spectroscopy, the features of the microstructure and elemental composition of Si/GeMn magnetic systems obtained by molecular beam epitaxy and containing quantum dots are studied. Intense mixing of Ge and Si atoms is found in all samples. The degree of mixing (diffusion) correlates with the conditions of synthesis of Si/GeMn samples. For these systems, direct contacts of germanium atoms with manganese atoms are characterized and the presence of interstitial manganese with tetrahedral coordination and substitution of manganese for germanium and silicon in the lattice sites is found. The presence of stoichiometric phases Ge8Mn11, Ge3Mn5 is not detected. The correlations of the Ge, Si, and Mn coordination numbers in the Ge environment are determined both with the Mn flux value (evaporator temperature) and with the temperature at which quantum dots are grown, as well as with other synthesis conditions. The manganese concentration in the samples is determined.


Publ.-Id: 29320 - Permalink

Viscosity measurements in pulsed magnetic fields by using a quartz-crystal microbalance
Nomura, T.; Zherlitsyn, S.; Kohama, Y.; Wosnitza, J.;
Viscosity measurements in combination with pulsed magnetic fields are developed by use of a quartz-crystal microbalance (QCM). When the QCM is immersed in liquid, the resonant frequency, f0, and the quality factor, Q, of the QCM change depending on (pn)0.5, where p is the mass density and n the viscosity. During the magnetic-field pulse, f0 and Q of the QCM are simultaneously measured by a ringdown technique. The typical resolution of (pn)>sup>0.5 is 0.5%. As a benchmark, the viscosity of liquid oxygen is measured up to 55 T.


  • Secondary publication expected

Publ.-Id: 29319 - Permalink

A model of a tidally synchronized solar dynamo
Stefani, F.; Giesecke, A.; Weier, T.;
We discuss 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 has its rationale in the tendency of the current-driven Tayler instability to undergo intrinsic helicity oscillations which, in turn, 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 persistent synchronization with the solar dynamo is briefly touched upon. 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 sub-critical nature of this Tayler–Spruit type dynamo. The resulting amplitude of the alpha oscillation that is required for dynamo action turns out to lie in the order of 1 m/s, which seems not implausible for the Sun. When starting with a more classical, non-periodic part of alpha, even less of the oscillatory alpha part is needed to synchronize the entire dynamo. Typically, the dipole solutions show butterfly diagrams, although their shapes are not convincing yet. Phase coherent transitions between dipoles and quadrupoles, which are reminiscent of the observed behavior during the Maunder minimum, can easily be triggered by long-term variations of dynamo parameters, but may also occur spontaneously even for fixed parameters. Further interesting features of the model are the typical second intensity peak and the intermittent appearance of reversed helicities in both hemispheres.


  • Secondary publication expected from 22.05.2020

Publ.-Id: 29317 - Permalink

Micro-scale isotopic variability of low-temperature pyrite in fractured crystalline bedrock ― A large Fe isotope fractionation between Fe(II)aq/pyrite and absence of Fe-S isotope co-variation
Yu, C.; Drake, H.; Lopez-Fernandez, M.; Whitehouse, M.; Dopson, M.; Åström, M. E.;
This study assessed Fe-isotope ratio (56Fe/54Fe, expressed as δ56Fe relative to the IRMM-014 standard) variability and controls in pyrite that has among the largest reported S-isotope variability (maximum δ34S: 140‰). The pyrite occurs as fine-grained secondary crystals in fractures throughout the upper kilometer of granitoids of the Baltic Shield, and was analyzed here for δ56Fe by in situ secondary ion mass spectrometry (SIMS). Part of these pyrite crystals were picked from borehole instrumentation at depths of >400 m below sea level (m.b.s.l.), and thus are modern (known to have formed within 17 years) and can be compared with the δ56Fe of the source dissolved ferrous iron. The δ56Fe values of the modern pyrite crystals (−1.81‰ to +2.29‰) varied to a much greater extent than those of the groundwaters from which they formed (−0.48‰ to +0.13‰), providing strong field evidence for a large Fe isotope fractionation during the conversion of Fe(II)aq to FeS and ultimately to pyrite. Enrichment of 56Fe in pyrite relative to the groundwater was explained by equilibrium Fe(II)aq-FeS isotope fractionation, whereas depletion of 56Fe in pyrite relative to the groundwater was mainly the result of sulfidization of magnetite and kinetic isotopic fractionation during partial transformation of microsized FeS to pyrite. In many pyrite crystals, there is an increase in δ34S from crystal center to rim reflecting Rayleigh distillation processes (reservoir effects) caused by the development of closed-system conditions in the micro-environment near the growing crystals. A corresponding center-to-rim feature was not observed for the δ56Fe values. It is therefore unlikely that the groundwater near the growing pyrite crystals became progressively enriched in the heavy Fe isotope, in contrast to what has been found for the sulfur in sulfate. Other pyrite crystals formed following bacterial sulfate reduction in the time period of mid-Mesozoicum to Quaternary, had an almost identical Fe-isotope variability (total range: −1.50‰ to +2.76‰), frequency-distribution pattern, and relationship with δ34S as the recent pyrite formed on the borehole instrumentation. These features suggest that fundamental processes are operating and governing the Fe-isotope composition of pyrite crystals formed in fractured crystalline bedrock over large time scales.
Keywords: Pyrite Iron isotopes Equilibrium Fe-isotope fractionation Magnetite sulfidization Partial pyritization Fractured crystalline bedrock


  • Secondary publication expected from 28.05.2020

Publ.-Id: 29315 - Permalink

Horizon-2020 ESFR-SMART project on SFR safety: status after first 15 months
Mikityuk, K.; Girardi, E.; Krepel, J.; Bubelis, E.; Fridman, E.; Rineiski, A.; Girault, N.; Payot, F.; Buligins, L.; Gerbeth, G.; Chauvin, N.; Latge, C.; Guidez, J.;
Devoted to the Generation-IV European Sodium Fast Reactor safety, the Horizon-2020 ESFR-SMART project was launched in September 2017. Selected results and milestones achieved during the first fifteen months of the project are briefly reviewed in the paper, including 1)proposal of new safety measures for ESFR; 2)evaluation of ESFR core performance; 3) benchmarking of codes; 4) experimental programs; and 5) education and training.
  • Contribution to proceedings
    27th International Conference on Nuclear Engineering - ICONE27, 19.-24.05.2019, Ibaraki, Japan

Publ.-Id: 29314 - Permalink

Benchmarking KENO-VI against MCNP/Serpent using a simplified SFR pin cell problem
Fridman, E.; Jiménez-Carrascosa, A.; García-Herranz, N.; Alvarez-Velarde, F.; Romojaro, P.; Bostelmann, F.;
  • Lecture (Conference)
    OECD/NEA UAM Workshop 2019, 13.-17.05.2019, Oak Ridge National Laboratory, USA

Publ.-Id: 29313 - Permalink

Initial solution of the SFR-UAM Exercises I-1 and I-2 with Serpent
Fridman, E.;
Initial solution of the SFR-UAM Exercises I-1 and I-2 with Serpent
  • Lecture (Conference)
    OECD/NEA UAM Workshop 2019, 13.-17.05.2019, Oak Ridge National Laboratory, USA

Publ.-Id: 29312 - Permalink

About the impact of the Unresolved Resonance Region in Monte Carlo simulations of Sodium Fast Reactors
Jiménez-Carrascosa, A.; Fridman, E.ORC; García-Herranz, N.; Alvarez-Velarde, F.; Romojaro, P.; Bostelmann, F.
In the last few years, and within the framework of different European projects, KENO-VI code from SCALE system has been employed to perform detailed continuous-energy Monte Carlo transport calculations for advanced fast reactors. The core characterization of both the sodium-cooled ASTRID and the lead-cooled ALFRED reactors was performed during the FP7 cross-cutting ESNII+ project; more recently, core calculations for the sodium-cooled Superphénix reactor and the improved European Sodium Fast Reactor design were performed within the HORIZON2020 ESFR-SMART project. In all cases, the effective multiplication factor predicted by KENO-VI was systematically higher (around 400-500 pcm) than the values computed by MCNP and Serpent Monte Carlo codes, using the same nuclear data library.

In order to provide insight into the origin of the observed discrepancies, a simplified 2D MOX-fueled SFR pin-cell benchmark has been launched. The multiplication factor, as well as 1-group and VITAMINJ 175-group cross-sections computed by KENO-VI, Serpent and MCNP codes employing ENDF/B-VII.1 data library, have been compared.

Significant differences between KENO-VI and the other codes have been found in the unresolved resonance regions of 239Pu and 241Pu capture and production cross sections, while negligible differences appeared outside those energy ranges. On the other hand, calculations without using probability tables have shown very good agreement. Quantita-tive comparison is presented and analyzed, along with a discussion of the impact of the probability-table treatment in the three codes for MOX-fueled systems with typical SFR spectrum.
Keywords: Unresolved Resonance Region, Probability Tables, Monte Carlo simulations of SFR
  • Contribution to proceedings
    ICAPP 2019 – International Congress on Advances in Nuclear Power Plants, 12.-15.05.2019, Juan-les-pins, France
    Proceedings of ICAPP 2019

Publ.-Id: 29311 - Permalink

In-house reference materials for the determination of low titanium concentration in SiO2 by secondary ion mass spectrometry
Ziegenrücker, R.ORC; Belokonov, G.; Böttger, R.; Couffignal, F.; Munnik, F.; Renno, A. D.; Wiedenbeck, M.; Wu, H. S.
Secondary ion mass spectrometry (SIMS) is routinely used for geochemical and mineralogical applications, but quantification is still the major challenge of this method. Each analysed matrix needs its own matrix-matched reference material (RM). However, the list of available reference materials is short compared to the needs.

One approach for the production of suitable RMs is the use of ion implantation to introduce a known amount of an isotope into a matrix-matched material. This is widely used for SIMS applications in materials science, but rarely for geochemical problems. Bumett et al. (2014) [1] demonstrated the principal appropriateness and ways to calibrate nominal implant fluence. We choose the more elaborate way of implanting a box profile to allow an effectivly homogeneous distribution of the respective isotope in all three dimensions.

Silicon dioxide SiO2, a “simple” mineralogical and chemical system, can record scientificly important data e.g. the Ti-in-quartz geothermometer [2, 3]. 47Ti respectively 48Ti were implanted into synthetic ultra-high purity silica glass. Box profiles with concentrations between 10 and 1000 ppm and a maximum depth of homogeneous 47/48Ti distribution between 200 and 500 nm were produced at the Ion Beam Center in Dresden-Rossendorf. Single implantation steps with different ion-energies and –doses were simulated with the SRIM (Stopping and Range of Ions in Matter) software [4] and optimized to the target concentrations, implantation-depths and technological limitations of the implanter.

Several different implanted test-samples were characterized by means of SIMS, atomic force microscopy (AFM) and other analytical techniques. These showed that Ti is homogeneously distributed in the glass structure within ± 5% uncertainty in all 3 dimensions, while the surface-roughness remains suitable for SIMS depth profiling.

Such reference materials are also very promising for the quantification of Super-SIMS measurements [5].

[1] Bumett, D.S., et al. (2014). Ion Implants as Matrix-Appropriate Calibrators for Geochemical Ion Probe Analyses. Geostandards and Geoanalytical Research, 39(3), 265-276.
[2] Wark, D. A., Watson E. B. (2006). TitaniQ: a titanium-in-quartz geothermometer. Contributions to Mineralogy and Petrology, 152(6), 743-754.
[3] Thomas, J. B., Watson E. B., et al. (2010). TitaniQ under pressure: the effect of pressure and temperature on the solubility of Ti in quartz. Contributions to Mineralogy and Petrology, 160(5), 743–759.
[4] Ziegler, J. F. (2004). SRIM-2003. Nuclear Instruments and Methods in Physics Research Section B, 219-220, 1027-1036.
[5] Rugel, G., et al, this conference.
Keywords: Implantation, SIMS, Titanium, Quartz, Quarz, Reference material, Referenz Material
  • Poster
    Ion Beam Physics Workshop 2019, 24.-26.06.2019, Dresden, Germany

Publ.-Id: 29310 - Permalink

Preparation of non-oxidized Ge quantum dot lattices in amorphous Al2O3, Si3N4 and SiC matrices
Nekić, N.; Šarić, I.; Salamon, K.; Basioli, L.; Sancho-Parramon, J.; Grenzer, J.; Hübner, R.; Bernstorff, S.; Petravić, M.; Mičetić, M.;
The preparation of non-oxidized Ge quantum dot (QD) lattices embedded in Al2O3, Si3N4, SiC matrices by self-assembled growth was studied. The materials were produced by magnetron sputtering deposition, using different substrate temperatures. The deposition regimes leading to the self-assembled growth type and the formation of three-dimensionally ordered Ge QD lattices in different matrices were investigated and determined. The oxidation of the Ge QDs in different matrices was monitored and the best conditions for the production of non-oxidized Ge QDs were found. The optical properties of the Ge QD lattices in different matrices show a strong dependence on the Ge oxidation and the matrix type.
Keywords: Ge QD lattices, Ge oxidation, self-assembled growth, influence of matrix

Publ.-Id: 29309 - Permalink

The magnetic structure of L10 ordered MnPt at room temperature determined using polarized neutron diffraction
Solina, D.; Schmidt, W.; Kaltofen, R.; Krien, C.; Lai, C.-H.; Schreyer, A.;
Neutron scattering studies have been carried out on single crystal films of [001] orientated L10 ordered MnPt grown epitaxially onMgO(001) usingDCmagnetron sputtering. Polarized neutron diffraction studies at room temperature show that the moments in ordered MnPt are aligned perpendicular to the [001] axis with a tilt of 45° to the [100] axis and not parallel to [100] as inferred from previous powder neutron diffraction measurements.
Keywords: antiferromagnetic, neutron diffraction, platinum alloys

Publ.-Id: 29308 - Permalink

Detection of ultra-low protein concentrations with the simplest possible field effect transistor
Georgiev, Y. M.ORC; Petkov, N.; Yu, R.; Nightingale, A. M.; Buitrago, E.; Lotty, O.; Demello, J. C.; Ionescu, A.; Holmes, J. D.
Silicon nanowire (Si NW) sensors have attracted great attention due to their ability to provide fast, low-cost, label-free, real-time detection of chemical and biological species. Usually configured as field effect transistors (FETs), they have already demonstrated remarkable sensitivity with high selectivity (through appropriate functionalisation) towards a large number of analyses in both liquid and gas phases. Despite these excellent results, Si NW FET sensors have not yet been successfully employed to detect single molecules of either a chemical or biological target species. Here we show that sensors based on silicon junctionless nanowire transistors (JNTs), the simplest possible transistors, are capable of detecting the protein streptavidin at a concentration as low as 580 zM closely approaching the single molecule level. This ultrahigh detection sensitivity is due to the intrinsic advantages of junctionless devices over conventional FETs.

Apart from their superior functionality, JNTs are much easier to fabricate by standard microelectronic processes than transistors containing p-n junctions. The ability of JNT sensors to detect ultra-low concentrations (in the zeptomolar range) of target species, and their potential for low-cost mass production, will permit their deployment in numerous environments, including life sciences, biotechnology, medicine, pharmacology, product safety, environmental monitoring and security.
Keywords: Si nanowire biosensor, junctionless nanowire transistor, ultrahigh detection sensitivity, protein, streptavidin, single-molecule detection


  • Secondary publication expected from 08.05.2020

Publ.-Id: 29306 - Permalink

Development of nuclear and optical dual-labelled agents for cancer imaging
Stephan, H.;
For the past decade, nuclear and optical dual-labelled imaging agents have attracted enormous attention. Applied to cancer imaging, tumours can be tracked down by nuclear techniques such as single-photon emission tomography (SPECT) and positron emission tomography (PET), and subsequently resected using image-guided surgery with the appropriate fluorophores. Moreover, the high spatial resolution of fluorescence imaging permits the elucidation of cell-biological events and thereby gaining a deeper insight into in vitro and in vivo processes. The development of dual imaging probes can be achieved using sophisticated low-molecular compounds that combine moieties for the desired imaging modalities, e.g. dyes for fluorescence optical imaging, and appropriate bifunctional chelator agents (BFCAs) for radiometals enabling SPECT or PET. We have developed BFCAs based on bis(2-pyridylmethyl)-1,4,7-triazacyclononane (DMPTACN) and 3,7-diazabicyclo[3.3.1]nonane (bispidine) that rapidly form stable 64CuII complexes under mild conditions. These BFCAs are well-suited for in vivo application in cancer imaging. Since they are also relatively easy to functionalize with multiple modalities, they are ideal chelators for the design of targeted dual-labelled imaging agents (PET, fluorescence imaging). Moreover, these chelating agents can be easily grafted on the surface of nanomaterials that are equipped with a multitude of different functionalities, such as targeting units, solubility enhancer and fluorescent tags. Hence, higher sensitivity can be achieved compared to small molecules, and there is an almost infinite variability regarding the surface functionalization.
Examples of target-specific peptides and bio(nano)materials equipped with DMPTACN/bispidine ligands for labelling with 64Cu as an ideal positron emitter are discussed. This enables tumour imaging and the biodistribution of materials can be studied over a period of days via positron emission tomography (PET). The additional introduction of fluorescence labels allows for optical imaging with high spatial resolution, and offers the possibility to visualize cellular processes by fluorescence microscopy.
  • Lecture (Conference)
    Seventh International Conference on Radiation in Various Fields of Research, 10.-14.06.2019, Herceg Novi, Montenegro

Publ.-Id: 29305 - Permalink

Prompt-gamma based range verification in proton therapy: Can we do better? Shall we do better?
Pausch, G.ORC
Prompt gamma-ray imaging (PGI) with a knife-edge slit camera has proven to be useful for range monitoring in proton therapy (PT). It is meanwhile applied in a prostate patient study at OncoRay. Together with an improved range prediction based on dual-energy CT and robust planning methods it could finally allow reducing the range margins, thus saving normal tissue in PT treatments. Translating these emerging techniques in clinical routine is a long but important process that will require considerable efforts.
Nevertheless we are also dealing with the far end of the translational conveyer, asking if and how in-vivo range verification could be improved. So far, PGI does not allow measuring range deviations of single pencil beams with the necessary precision. The reason is the short delivery time of such a beam spot, and the poor event statistics that can be accessed in this period. It is obvious to exploit not only spatial, but also spectroscopic and timing information of the gamma rays registered for range verification. The prompt gamma-ray spectroscopy method developed at MGH in Boston and the prompt gamma-ray timing technique explored at OncoRay in Dresden represent reasonable alternatives to PGI; but can these approaches be combined in a single, preferable simple and light-weight, clinically applicable system distinguished by minimum interference with beam and patient couch? Could such a combination improve the accuracy and allow single-spot range verification, maybe even for the non-distal spots comprising much less protons?
The talk will present our thoughts and approaches to answer this question. This includes recent results concerning prompt gamma-ray timing (PGT) and single-plane Compton imaging (SPCI). Part of the research performed in this context could also affect gamma-ray imaging in nuclear medicine.
Keywords: PGI, PGT, prompt gamma ray, proton therapy, range verification, treatment verification
  • Lecture (others)
    Medizinphysik-Seminar, 12.06.2019, Heidelberg, Deutschland

Publ.-Id: 29293 - Permalink

THEREDA - Achievements, present activities, and future developments
Moog, H. C.; Altmaier, M.; Bok, F.; Brendler, V.; Freyer, D.; Gaona, X.; Marquardt, C.; Richter, A.; Scharge, T.; Seher, H.; Thoenen, T.; Voigt, W.;
Five institutions are actively maintaining the thermodynamic reference database THEREDA aiming at the calculation of solubilities in high-saline solutions. The database is designed for applications in the context of the disposal of radioactive waste in rock salt formations and clay formations featuring solutions with a higher ionic strength [1]. The project is striving to provide an internally consistent set of data, formatted for the use by several widely-used geochemical codes. With the focus on high ionic strength systems, THEREDA complements other database projects focussing on low-saline solutions, such as THERMOCHIMIE [2] or the PSI/Nagra Chemical Thermodynamic Data Base [3].
In practical terms, work for THEREDA comprises several aspects. Most importantly, the database is continuously maintained and extended, based on annual contributions to the project. Other aspects concern the implementation of internal calculation routines, export functions and measures for quality assurance.

Data releases
In 2018 a new release (R-12) was issued covering phosphate in high-saline solutions [4-5]. Pitzer interaction coefficients were optimized using osmotic coefficients, activity coefficients, and solubility data in binary and ternary systems. To test the obtained database, experimental data from quaternary systems were successfully modelled.
Supplementary to the phosphate release, an earlier uranium release was upgraded by adding several solid phases with phosphate (R-09.1). Available experimental data for respective aqueous complexes with phosphate in high-saline solution are currently under inspection.

Data releases
THEREDA is working on new thermodynamic data sets, in part as extensions to existing releases, and in part representing new systems, hitherto not covered by THEREDA. In short, the systems currently in preparation are:
• Solubility of molecular oxygen (polythermal)
• Se(+VI,+IV,0,-II) – Na, K, Mg, Ca – Cl, SO4 – H2O (partially polythermal)
• Solubility of carbonates up to 100°C (upgrade for R-03)
• Extensions for the systems Na, Mg, Cl, OH- - H2O (Sorel phases)
• Cs – K, Na, Mg, Ca, – Cl, SO4 – H2O (polythermal upgrade for R-05)
• Rb - K, Na, Mg, Ca, – Cl, SO4 – H2O (25°C)
• U(VI) hydrolysis and solubility in NaCl, KCl and MgCl2 systems (25°C, upgrade of R-09.1)
• Implementation of CEMDATA 18 [8]; will not work with GWB and TOUGHREACT as they cannot handle solid solutions yet.

Preparation of new release mode
THEREDA ensures that all issued parameter files yield the results as laid out in the release papers available at the project website. To optimize the workload, we will abstain from producing release papers in the future and establish a new procedure for data releases, which ensures a high quality of issued parameter files. Future data releases will move along the following steps.
• 1. addition and modification of data sets in THEREDA;
• 2. “feature freeze” of the database: no new data sets are added, and no existing data sets modified;
• 3. All test calculations (at present 192) are automated for all supported codes, producing (at present 1131) individual results to be compared with the ones from previous releases;
• 4. If significant deviations occur, “debugging” and repetition of test calculations is started.
5. Release of one cumulative parameter file (covering all supported systems) for each supported code.

Supported codes
Due to a significantly decreasing number of downloads, the support for EQ3/6 has been abandoned. GEM-Selektor [9] is now able to import the generic JSON-export from THEREDA. As to GWB beside the traditional “Oct84” the “Jul17” format is supported.
At present we are working on the support for TOUGHREACT [10].

Assessment of current state of THEREDA
By the end of the year the management board of THEREDA is required to submit an assessment as to whether the database, related to supported systems, still represents the state-of-the-art, or to which extent updates are appropriate.

THEREDA aims for implementing additional thermodynamic data (Pitzer) for radionuclides and key matrix elements in future data releases. While THEREDA is particularly focusing on Germany, it is open for international exchange and exploiting synergies with the international scientific/technical community.

THEREDA is funded by the German “Bundesgesellschaft für Endlagerung (BGE)”, contract number 45162393 (8998-3).

1. H. C. MOOG et al.: Disposal of Nuclear Waste in Host Rock formations featuring high-saline solutions - Implementation of a Thermodynamic Reference Database (THEREDA). Appl. Geochem., 55, 72-84 (2015).
2. E. GIFFAUT et al.: Andra thermodynamic data for performance assessment: ThermoChimie. Appl. Geochem., 49, 225–236 (2014).
3. T. THOENEN et al.: The PSI/Nagra Chemical Thermodynamic Database 12/07. PSI Bericht Nr. 14-04, Paul Scherrer Institut, ISSN 1019-0643 (2014).
4. T. SCHARGE et al.: Thermodynamic modelling of high salinary phosphate solutions. I. Binary systems. J. Chem. Thermodynamics, 64, 249–256 (2013).
5. T. SCHARGE et al.: Thermodynamic modeling of high salinary phosphate solutions II. Ternary and higher systems. J. Chem. Thermodynamics, 80, 172-183 (2015).
6. A. P. SOLOV’JEV et al.: Rastvorimost‘ v ctevernych vzainych vodnych sistemach iz chloridov i fosfatov natrija i kalija pri 25°C, Sb. Naucn. Tr. Jarosl. Gos. Ped. Inst., 164, 136-142 (1977).
7. G. BRUNISHOLZ et al.: Contribution à L'étude du système quinaire H+-Na+-K+-Cl--PO43--H2O II. Le diagramme de solubilité du système quaternaire Na+-K+-Cl--H2PO4--H2O, Helv. Chim. Acta, 46, 2575-2587 (1963).
8. B. LOTHENBACH et al.: Cemdata18: A chemical thermodynamic database for hydrated Portland cements and alkali-activated materials. Cem. Concr. Res., 115, 472-506 (2019).
9. D. A. KULIK et al.: GEM-Selektor geochemical modeling package: revised algorithm and GEMS3K numerical kernel for coupled simulation codes. Comp. Geosc., 17, 1-24 (2013).
10: TIANFU XU et al.: TOUGHREACT—A simulation program for non-isothermal multiphase reactive geochemical transport in variably saturated geologic media: Applications to geothermal injectivity and CO2 geological sequestration. Comp.Geosc., 32, 145-165 (2006).
Keywords: THEREDA, Database, Geochemical Modelling, Thermodynamic, Nuclear Waste Repository, Pitzer
  • Lecture (Conference)
    Actinide Brine Chemistry (ABC-Salt) VI Workshop 2019, 25.-26.06.2019, Karlsruhe, Deutschland

Publ.-Id: 29292 - Permalink

Band gap renormalization in n-type GeSn alloys made by ion implantation and flash lamp annealing
Prucnal, S.; Berencén, Y.; Wang, M.; Rebohle, L.; Kudrawiec, R.; Polak, M.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Grenzer, J.; Turek, M.; Droździel, A.; Pyszniak, K.; Zuk, J.; Helm, M.; Skorupa, W.; Zhou, S.;
The last missing piece of the puzzle for the full functionalization of group IV optoelectronic devices is a direct bandgap semiconductor made by CMOS compatible technology. Here, we report on the fabrication of GeSn alloys with Sn concentrations up to 4.5% using ion implantation followed by millisecond-range explosive solid phase epitaxy. The n-type single crystalline GeSn alloys are realized by coimplantation of Sn and P into Ge. Both the activation of P and the formation of GeSn are performed during a single-step flash lamp annealing for 3 ms. The bandgap engineering in GeSn as a function of the doping level and Sn concentration is theoretically predicted by density functional theory and experimentally verified using ellipsometric spectroscopy. We demonstrate that both the diffusion and the segregation of Sn and P atoms in Ge are fully suppressed by millisecond-range nonequilibrium thermal processing.
Keywords: ion implantation, flash lamp annealing, Ge, GeSn, n-type doping


  • Secondary publication expected from 30.05.2020

Publ.-Id: 29290 - Permalink

Benchmarking ATHLET against TRACE as applied to Superphénix start-up tests
Di Nora, V. A.; Fridman, E.; Mikityuk, K.;
ATHLET is a thermal-hydraulic (TH) system code developed at the GRS for the modeling of Light Water Reactors (LWRs). To extend the applicability of ATHLET to the analyses of Sodium Fast Reactors (SFRs), the code was recently upgraded with the thermal-physical properties of the liquid sodium. The new extension is still under verification and validation phases. The present work contributes to the verification efforts. This study investigated the perfor-mance of the extended version of ATHLET as applied to the transient analysis of a set of start-up tests conducted at the Superphénix SFR. The specifications of the corresponding tests such as the simplified SPX reactor core models and the set of reactivity coefficients were adopted primarily from a previous dedicated study performed at PSI and at KIT. The reactivity effects accounted for by ATHLET included fuel Doppler effect and thermal expansion effects of sodium, fuel, diagrid, control rods driveline, strongback, and reactor vessel. The results obtained by ATHLET for main stationary TH parameters, power evolutions, and reactivity feedback components were benchmarked against the reference solutions provided by TRACE. Employing an identical set of reactivity coefficients, either in steady-state or transient calculations, the codes produce consistent and close results.
Keywords: ATHLET against TRACE; ATHLET verification; Superphénix start-up tests;
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants - ICAPP2019, 12.-15.05.2019, Juan-les-Pins, France

Publ.-Id: 29289 - Permalink

Photon diagnostics at the FLASH THz beamline
Pan, R.; Zapolnova, E.; Golz, T.; Krmpot, A. J.ORC; Rabasovic, M. D.; Petrovic, J.; Asgekar, V.ORC; Faatz, B.; Tavella, F.; Perucchi, A.; Kovalev, S.; Green, B.ORC; Geloni, G.; Tanikawa, T.ORC; Yurkov, M.; Schneidmiller, E.; Gensch, M.; Stojanovic, N.
The THz beamline at FLASH, DESY, provides both tunable (1–300 THz) narrow-bandwidth (∼10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.
Keywords: Electro-optic, FLASH, FTIR, Intense THz, THz diagnostic

Publ.-Id: 29288 - Permalink

Cross section of 3He(α , γ)7Be around the 7Be proton separation threshold
Szücs, T.ORC; Kiss, G. G.; Gyürky, G.; Halász, Z.; Szegedi, T. N.; Fülöp, Z.
Background: The 3He(α,γ)7Be reaction is a widely studied nuclear reaction; however, it is still not understood with the required precision. It has a great importance both in Big Bang nucleosynthesis and in solar hydrogen burning. The low mass number of the reaction partners makes it also suitable for testing microscopic calculations.

Purpose: Despite the high number of experimental studies, none of them addresses the 3He(α,γ)7Be reaction cross sections above 3.1-MeV center-of-mass energy. Recently, a previously unobserved resonance in the 6Li(p,γ)7Be reaction suggested a new level in 7Be, which would also have an impact on the 3He(α,γ)7Be reaction in the energy range above 4.0 MeV. The aim of the present experiment is to measure the 3He(α,γ)7Be reaction cross section in the energy range of the proposed level.

Method: For this investigation the activation technique was used. A thin window gas-cell target confining 3He gas was irradiated using an α beam. The 7Be produced was implanted into the exit foil. The 7Be activity was determined by counting the γ rays following its decay by a well-shielded high-purity germanium detector.

Results: Reaction cross sections have been determined between Ecm=4.0and4.4 MeV with 0.04-MeV steps covering the energy range of the proposed nuclear level. One lower-energy cross-section point was also determined to be able to compare the results with previous studies.

Conclusions: A constant cross section of around 10.5 μb was observed around the 7Be proton separation energy. An upper limit of 45 neV for the strength of a 3He(α,γ)7Be resonance is derived.
Keywords: Nuclear Astrophysics, alpha induced reaction, light element nucleosynthesis

Publ.-Id: 29287 - Permalink

Electromagnetic forcing of a flow with the azimuthal wavenumber m=2 in cylindrical geometry
Stepanov, R.; Stefani, F.;
In this paper, we consider a liquid metal flow generated in a cylindrical volume by AC currents in various coil configurations. The final aim of this study is to design and optimize a Rayleigh-Bénard experiment with a large scale circulation, the helicity oscillation of which is synchronized by a periodically modulated tide-like m=2 perturbation.
Keywords: Rayleigh-Bénard


  • Secondary publication expected from 10.05.2020

Publ.-Id: 29286 - Permalink

Incorporation of Europium into GaN Nanowires by Ion Implantation
Faye, D. N. A.; Biquard, X. B.; Nogales, E. C.; Felizardo, M. A.; Peres, M. A.; Redondo-Cubero, A. A.; Auzelle, T. B.; Daudin, B.; Tizei, L. H. G.; Kociak, M.; Ruterana, P.; Möller, W.; Méndez, B.; Alves, E.; Lorenz, K.;
Rare earth (RE)-doped GaN nanowires (NWs), combining the well-defined and controllable optical emission lines of trivalent RE ions with the high crystalline quality, versatility, and small dimension of the NW host, are promising building blocks for future nanoscale devices in optoelectronics and quantum technologies. Europium doping of GaN NWs was performed by ion implantation, and structural and optical properties were assessed in comparison to thin film reference samples. Despite some surface degradation for high implantation fluences, the NW core remains of high crystalline quality with lower concentrations of extended defects than observed in ion-implanted thin films. Strain introduced by implantation defects is efficiently relaxed in NWs and the measured deformation stays much below that in thin films implanted in the same conditions. Optical activation is achieved for all samples after annealing, and while optical centers are similar in all samples, Eu 3+ emission from NW samples is shown to be less affected by residual implantation damage than for the case of thin films. The incorporation of Eu in GaN NWs was further investigated by nano-cathodoluminescence and X-ray absorption spectroscopy (XAS). Maps of the Eu-emission intensity within a single NW agree well with the Eu-distribution predicted by Monte Carlo simulations, suggesting that no pronounced Eu-diffusion takes place. XAS shows that 70-80% of Eu is found in the 3+ charge state while 20-30% is 2+ attributed to residual implantation defects. A similar local environment was found for Eu in NWs and thin films: for low fluences, Eu is mainly incorporated on substitutional Ga-sites, while for high fluences XAS points at the formation of a local EuN-like next neighbor structure. The results reveal the high potential of ion implantation as a processing tool at the nanoscale.

Publ.-Id: 29285 - Permalink

Electron Paramagnetic Resonance in Ge/Si Heterostructures with Mn-Doped Quantum Dots
Zinovieva, A. F.; Zinovyev, V. A.; Stepina, N. P.; Katsuba, A. V.; Dvurechenskii, A. V.; Gutakovskii, A. K.; Kulik, L. V.; Bogomyakov, A. S.; Erenburg, S. B.; Trubina, S. V.; Voelskow, M.;
Ge/Si quantum dot (QD) structures doped with Mn have been tested by the EPR method to find the optimal conditions for formation of the diluted magnetic semiconductor (DMS) phase inside QDs. The effect of Mn doping has been studied for two series of samples: series A with QDs grown at 450 degrees C and varied Mn concentration and series B with QDs grown at different temperature with Mn concentration x = 0.02. Several effects of modification of the EPR spectra due to Mn presence in the samples have been obtained. These effects are related to (i) strain reduction due to GeSi intermixing, (ii) QD enlargement and change in QD shape, (iii) presence of an additional magnetic field produced by Mn atoms incorporated in QDs. The data obtained allow us to understand the reasons for irreproducibility of the results available in the literature on the creation of magnetic Ge1 - xMnx quantum dots.

Publ.-Id: 29283 - Permalink

Numerical modelling of air-breathing PEMFC
Weber, N.; Chaparro, A.; Ferreira-Aparicio, P.;
Übersicht über die Simulation von Luft atmenden Brennstoffzellen mit OpenFOAM
  • Lecture (others)
    Vortrag am IEK3 des Forschungszentrums Jülich, 22.05.2019, Jülich, Deutschland

Publ.-Id: 29279 - Permalink

Improved 242Pu(n,γ) thermal cross section combining activation and prompt gamma analysis
Lerendegui-Marco, J.; Guerrero, C.; Belgya, T.; Maróti, B.; Eberhardt, K.; Düllmann, C. E.; Junghans, A. R.; Mokry, C.; Quesada, J. M.; Runke, J.; Thörle-Pospiech, P.;
A good knowledge of the radiative capture cross section of 242Pu is required for innovative nuclear reactor studies, especially for MoX fuel reactors. However, the experimental data available show discrepancies in the energy regions of interest: the thermal point and the keV region. Previous experimental results of the thermal cross section deviate from each other by 20% and these discrepancies are reflected also in the evaluated libraries, each of them giving more credit to different data sets. A recent measurement by Genreith et al. did not succeed to solve the existing discrepancy due to the large uncertainties and correction factors in the analysis. This work presents a new measurement of the thermal capture cross section of 242Pu carried out in the Budapest Research Reactor using the same thin targets of a previous measurement at n_TOF-EAR1, each containing 30mg of 99.995% pure 242Pu . The combined analysis of the full prompt γ-ray spectrum and the 243Pu decay has led to three compatible values for the thermal cross section. Their average value, 18.9(9)b, has an improved accuracy compared to recent measurements. Leaving aside the activation value of Genreith using an outdated intensity value for the 84 keV decay line of 243Pu , our average result is in very good agreement with the JEFF-3.2 evaluation and all the previous measurements, with the exception of the highest value 22.5(11)b reported by Marie et al., which has a strong influence in the ENDF evaluation.242
Keywords: neutron capture cross section, 242Pu, thermal neutron spectrum

Publ.-Id: 29278 - Permalink

Analysis of studies and research projects regarding the detection of nanomaterials in different environmental compartments and deduction of need for action regarding method development
Hildebrand, H.; Franke, K.; Fischer, C.; Schymura, S.;
Exertengespräch und Präsentation der Ergebnisse aus der Literaturstudie zum Nachweis von Nanomaterialien in den verschiedenen Umweltkompartimenten, Projekt NanoExperte
Keywords: nanomaterials in environemtal media, detection, quantification
  • Invited lecture (Conferences)
    Abschlusspräsentation des Sachverständigengutachtens „NanoExperte“, 17.04.2019, Dessau-Roßlau, Deutschland

Publ.-Id: 29277 - Permalink

Specific ion effects directed noble metal aerogels: Versatile manipulation for electrocatalysis and beyond
Du, R.; Hu, Y.; Hübner, R.; Joswig, J.-O.; Fan, X.; Schneider, K.; Eychmüller, A.;
Noble metal foams (NMFs) are a new class of functional materials featuring properties of both noble metals and monolithic porous materials, providing impressive prospects in diverse fields. Among reported synthetic methods, the sol-gel approach manifests overwhelming advantages for versatile synthesis of nanostructured NMFs (i.e., noble metal aerogels) under mild conditions. However, limited gelation methods and elusive formation mechanisms retard structure/composition manipulation, hampering on-demand design for practical applications. Here, highly tunable NMFs are fabricated by activating specific ion effects, enabling various single/alloy aerogels with adjustable composition (Au, Ag, Pd, and Pt), ligament sizes (3.1 to 142.0 nm), and special morphologies. Their superior performance in programmable self-propulsion devices and electrocatalytic alcohol oxidation is also demonstrated. This study provides a conceptually new approach to fabricate and manipulate NMFs and an overall framework for understanding the gelation mechanism, paving the way for on-target design of NMFs and investigating structure-performance
relationships for versatile applications.

Publ.-Id: 29276 - Permalink

Radiobiology of high dose-rate particle beams
Beyreuther, E.; Karsch, L.; Pawelke, J.;
In the past few years, the normal tissue protecting effect of Flash electron irradiation was shown for several endpoints and in different species [1], [2]. Contrary to conventional, clinical beam delivery over minutes, the therapeutic dose is administered within less than 0.5 s by Flash irradiation. Hence, this treatment regime is linked to high mean dose rates of ~100 Gy/s and high pulse dose rates of ≥105 Gy/s, clearly exceeding the parameters of a few Gy/min on time average and of ~ 102 Gy/s within one pulse of conventional, clinical Linacs. Of note, tumors were cured by electron Flash as efficient as by conventional electron beam treatment over minutes [1]. Moreover, the protecting Flash effect was recently validated for photons [3], which promises a general validity of this effect also for other types of clinically used radiation.
First attempts testing the feasibility of proton Flash were conducted at clinical proton beam facilities in France [4] and at the University Proton Therapy Dresden (UPTD), Germany. At UPTD, a setup was established that allows for the irradiation of zebrafish embryo either with dose rates of 100 Gy/s for Flash or of 5 Gy/min for conventional reference. The zebrafish embryo were treated with graded doses up to 40 Gy and embryonic survival as well as the manifestation of morphological abnormalities were followed for up to four days. However, analysing the different endpoints, a clear dependency on dose but no significant dependence on proton dose rate was revealed.
This unexpected result implies, that more studies are needed to resolve the influence on beam time structure for the induction of a protective Flash effect. Here, research facilities like FAIR with a broader parameter space regarding ion species, particle fluence, LET, pulsing and beam time structure provide the possibility to study the physical limits of Flash in more detail. Therewith also questions on a potential influence or interaction of high dose-rate particle beam, high LET and oxygen level of the irradiated tissue could be investigated systematically. The results obtained therein could help to further develop dedicated clinical accelerators, like superconducting or heavy ion synchrotrons, to make clinical use of the Flash effect.

[1] V. Favaudon et al., “Ultrahigh dose-rate FLASH irradiation increases the differential response between normal and tumor tissue in mice,” Sci. Transl. Med., vol. 6, no. 245, p. 245ra93, Jul. 2014.
[2] P. Montay-Gruel et al., “Irradiation in a flash: Unique sparing of memory in mice after whole brain irradiation with dose rates above 100Gy/s,” Radiother. Oncol. J. Eur. Soc. Ther. Radiol. Oncol., vol. 124, no. 3, pp. 365–369, 2017.
[3] P. Montay-Gruel et al., “X-rays can trigger the FLASH effect: Ultra-high dose-rate synchrotron light source prevents normal brain injury after whole brain irradiation in mice,” Radiother. Oncol. J. Eur. Soc. Ther. Radiol. Oncol., vol. 129, no. 3, pp. 582–588, Dec. 2018.
[4] A. Patriarca et al., “Experimental Set-up for FLASH Proton Irradiation of Small Animals Using a Clinical System,” Int. J. Radiat. Oncol. Biol. Phys., vol. 102, no. 3, pp. 619–626, Nov. 2018.
  • Contribution to proceedings
    International Biophysics Collaboration Meeting, 20.-22.05.2019, Darmstadt, Deutschland
    DOI: 10.15120/GSI-2019-00596

Publ.-Id: 29270 - Permalink

Multi-Sensor Spectral Imaging of Geological Samples: A Data Fusion Approach using Spatio-Spectral Feature Extraction
Lorenz, S.; Seidel, P.; Ghamisi, P.; Zimmermann, R.; Tusa, L.; Khodadadzadeh, M.; Contreras, I. C.; Gloaguen, R.;
Spectral imaging or hyperspectral reflectance mapping for mineral exploration sample analysis has evolved rapidly in the recent decade. A wide range of deployable sensors is available nowadays, providing high flexibility in spectral as well as in spatial resolution and coverage. However, the fusion of data from different customized setups and sensors is challenging and usually not conducted. In the following study, the integration of such multi-sensor datasets is demonstrated on data acquired from five commercially available hyperspectral sensors and a pair of RGB cameras. We present a workflow for the integrated image analyses using advanced machine learning methods and evaluate the procedure on a representative set of geological samples. Detailed mineralogical and spectral validation affirms the approach. The suggested workflow provides a new way for the integration of multi-source data, e.g., it allows a straight-forward integration of visible/near-infrared (VNIR), short-wave infrared (SWIR) and long-wave infrared (LWIR) data for sensors with highly different spatial and spectral resolution. Finally, we evaluate the benefits of different multi-sensor combinations for potential applications in mineral exploration.
Keywords: hyperspectral; spectral imaging; multi-sensor data; data fusion; feature extraction; Support Vector Machine (SVM); Orthogonal Total Variation Component Analysis (OTVCA); mineral exploration

Publ.-Id: 29268 - Permalink

Superconductivity in single-crystalline aluminum- and gallium-hyperdoped germanium
Prucnal, S.; Heera, V.; Hübner, R.; Wang, M.; Mazur, G. P.; Grzybowski, M. J.; Qin, X.; Yuan, Y.; Voelskow, M.; Skorupa, W.; Rebohle, L.; Helm, M.; Sawicki, M.; Zhou, S.;
Superconductivity in group IV semiconductors is desired for hybrid devices combining both semiconducting and superconducting properties. Following boron-doped diamond and Si, superconductivity has been observed in gallium-doped Ge; however, the obtained specimen is in polycrystalline form [Phys. Rev. Lett. 102, 217003 (2009)]. Here we present superconducting single-crystalline Ge hyperdoped with gallium or aluminum by ion implantation and rear-side flash lamp annealing. The maximum concentration of Al and Ga incorporated into substitutional positions in Ge is 8 times higher than the equilibrium solid solubility. This corresponds to a hole concentration above 1021 cm−3. Using density functional theory in the local-density approximation and pseudopotential plane-wave approach, we show that the superconductivity in p-type Ge is phonon mediated. According to the ab initio calculations, the critical superconducting temperature for Al- and Ga-doped Ge is in the range of 0.45 K for 6.25at.% of dopant concentration, being in qualitative agreement with experimentally obtained values.
Keywords: superconductivity, ion implantation, Germanium, flash lamp annealing


Publ.-Id: 29266 - Permalink

Monolithic waveguide laser mode-locked by embedded Ag nanoparticles operating at 1 μm
Li, R.; Pang, C.; Li, Z.; Dong, N.; Wang, J.; Ren, F.; Akhmadaliev, S.; Zhou, S.; Chen, F.;
Monolithic waveguide laser devices are required to achieve on-chip lasing. In this work, a new design of a monolithic device with embedded Ag nanoparticles (NPs) plus the Nd:YAG ridge waveguide has been proposed and implemented. By using Ag+ ion implantation, the embedded Ag NPs are synthesized on the near-surface region of the Nd:YAG crystal, resulting in the significant enhancement of the optical nonlinearity of Nd:YAG and offering saturable absorption properties of the crystal at a wide wavelength band. The subsequent processing of the O5+ ion implantation and diamond saw dicing of crystal finally leads to the fabrication of monolithic waveguide with embedded Ag NPs. Under an optical pump, the Q-switched mode-locked waveguide lasers operating at 1 μm is realized with the pulse duration of 29.5 ps and fundamental repetition rate of 10.53 GHz, owing to the modulation of Ag NPs through evanescent field interaction with waveguide modes. This work introduces a new approach in the application of monolithic ultrafast laser devices by using embedded metallic NPs.

Publ.-Id: 29264 - Permalink

Laser-driven proton beam profiles in ultra-high fields
Obst-Hübl, L.ORC; Bernert, C.; Brack, F.-E.; Branco, J.; Bussmann, M.; Cochran, G.; Cowan, T. E.; Curry, C. B.; Gaus, L.; Fiuza, F.; Garten, M.; Gauthier, M.; Glenzer, S. H.; Göde, S.; Huebl, A.; Irman, A.; Kim, J. B.; Kluge, T.; Kraft, S.; Kroll, F.; Macdonald, M. J.; Metzkes-Ng, J.; Mishra, R.; Pausch, R.; Poole, P.; Prencipe, I.; Rehwald, M.; Rödel, C.; Ruyer, C.; Schlenvoigt, H.-P.; Sommer, P.; Schoenwalder, C.; Schumaker, W.; Ziegler, T.; Schramm, U.; Schumacher, D. W.; Zeil, K.
Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact multi-MeV proton accelerators with unique bunch characteristics. Protons are accelerated in TV/m fields that are established within the micrometer-scale vicinity of the high-power laser focus. This initial acceleration phase is followed by ballistic proton bunch propagation with negligible space-charge effects over millimeters to hundreds of centimeters to the particle detector or a proton target at a dedicated irradiation site. The detected proton emission distribution can be influenced by the spatio-temporal intensity distribution in the laser focus, electron transport through the target, potential plasma instabilities, as well as local and global target geometry and surface properties.
Substantially extending this picture, our recent results show a critical influence of the milimeter scale vacuum environment on the accelerated proton bunch, where residual gas molecules are ionized by the remnant laser light that is not absorbed into the target plasma but reflected or transmitted. In an experiment with µm-sized hydrogen jet targets, this effect lead to the counter-intuitive observation of laser near-field feature imprints in the detected proton beam profiles. Our results show that the remnant laser pulse induces a quasi-static deflecting field map in the ionized residual background gas that serves as a memorizing medium and allows for asynchronous information transfer to the naturally delayed proton bunch. Occurring under typical experimental laser, target and vacuum conditions, all-optical imprinting needs to be taken into account for sensible interpretation of modulated proton beam profiles.
Keywords: laser-driven plasmas, high-power lasers, novel accelerator concepts, laser-ion acceleration, plasma mirrors
  • Invited lecture (Conferences)
    Laser Plasma Accelerator Workshop 2019, 05.-10.05.2019, Split, Kroatien

Publ.-Id: 29261 - Permalink

Synthetic radiation diagnostics as a pathway for studying plasma dynamics from advanced accelerators to astrophysical observations
Pausch, R.;
PhD defense talk
Keywords: PhD defense
  • Lecture (others)
    Disputation, 25.03.2019, Dresden, Deutschland

Publ.-Id: 29259 - Permalink

Modeling hybrid plasma accelerator experiments with PIConGPU
Pausch, R.; Bussmann, M.; Garten, M.; Huebl, A.; Steiniger, K.; Widera, R.; Kurz, T.; Schöbel, S.; Chang, Y.-Y.; Couperus Cabadağ, J.; Köhler, A.; Zarini, O.; Heinemann, T.; Ding, H.; Döpp, A.; Gilljohann, M. F.; Kononeko, O.; Raj, G.; Corde, S.; Hidding, B.; Karsch, S.; Martinez De La Ossa, A.; Irman, A.; Schramm, U.; Debus, A.;
Utilizing laser-wakefield accelerated (LWFA) electrons to drive aplasma-wakefield accelerator (PWFA) holds great promise for realizingcentimeter-scale electron accelerators providing ultra-high brightnessbeams. Recent experiments at HZDR could demonstrate for the first timesuch an electron acceleration in a nonlinear PWFA plasma wakefield. Fordriving this compact hybrid accelerator setup, high-charge electronbunches from LWFA self-truncated ionization injection were used.In this talk, we present recent results of the accompanying simulationcampaign performed with the 3D3V particle-in-cell code PIConGPU. Thesesimulations model the geometry, density distributions, laser modes, andgas dopings as determined in the experiments. The simulation conditionsresemble the experiment to a very high degree and thus provide goodcomparability between experiment and simulation. Additionally, thewealth of information provided by the in-situ data analysis of PIConGPU provides insight into the plasma dynamics, otherwise inaccessible inexperiments.From an algorithmic and computational perspective, we modeled the hybridaccelerator from start to end in a single simulation scenario. Wediscuss the associated challenges in maintaining numerical stability andexperimental comparability of these long-duration simulations.
Keywords: LPWFA, hybrid, PIConGPU
  • Lecture (Conference)
    Laser-Plasma AcceleratorWorkshop 2019, 05.-10.05.2019, Split, Croatia

Publ.-Id: 29258 - Permalink

Hybrid plasma accelerators - LWFA-PWFA simulations with PIConGPU
Pausch, R.; Debus, A.; Garten, M.; Huebl, A.; Steiniger, K.; Widera, R.; Kurz, T.; Schöbel, S.; Couperus Cabadağ, J.; Irman, A.; Schramm, U.; Bussmann, M.;
Utilizing laser-wakefield accelerated (LWFA) electrons to drive a plasma-wakefield accelerator (PWFA) holds great promise for realizing centimeter-scale electron accelerators providing ultra-high brightness beams. Recent experiments at HZDR could demonstrate for the first time such an electron acceleration in a nonlinear PWFA plasma wakefield using this compact setup.

On this poster, we show recent results of the accompanying simulation campaign performed with the 3D3V particle-in-cell code PIConGPU. These simulations model the geometry, density distributions, laser modes, and gas dopings as determined in the experiments. The simulation conditions resemble the experiment to a very high degree and thus provide precise comparability between experiment and simulation. Additionally, the wealth of information provided by the in-situ data analysis of PIConGPU provides insight into the plasma dynamic, otherwise inaccessible in experiments. Algorithmic and computational challenges essential for the numerical stability of these long-duration simulations will be presented as well.
Keywords: PIConGPU, LPWFA, hybrid, ISAAC
  • Poster
    The fifth annual meeting of the programme "Matter and Technologies", 05.-07.03.2019, Jena, Deutschland

Publ.-Id: 29257 - Permalink

Approaching predictive capabilities for LWFA experiments with PIConGPU
Pausch, R.; Couperus Cabadağ, J.; Garten, M.; Huebl, A.; Köhler, A.; Kurz, T.; Schöbel, S.; Schramm, U.; Steiniger, K.; Widera, R.; Zarini, O.; Irman, A.; Bussmann, M.; Debus, A.;
State-of-the-art particle-in-cell simulations are becoming faster in terms of time to solution by utilizing modern hardware accelerators like GPUs and more accurate by improving the underlying algorithms. However, in order to model experiments, methods to include realistic laser pulses and gas distributions as well as efficient techniques to predict experimental observables, so-called synthetic diagnostics, need to be included in these simulations.

In this talk, we present extensions to the particle-in-cell code PIConGPU that were essential to accurately model LWFA experiments based on self-truncated ionization injection performed at HZDR. We discuss the significant impact of the implementation of higher order laser modes on the plasma dynamics and the resulting acceleration process. Furthermore, we discuss in detail the advantage of efficient in situ data analysis on the example of studying electron phase space evolution and of predicting spectrally and directionally radiation emission by all particles.

These improvements set the stage for quantitatively predicting the results of experiments in the near future.
Keywords: PIConGPU, LWFA, radiation, synthetic diagnostics
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Materie und Kosmos (SMuK), 18.-22.03.2019, München, Deutschland

Publ.-Id: 29256 - Permalink

Radiation imprint of ultra-intense laser heating of solids
Garten, M.ORC; Huebl, A.; Widera, R.; Goethel, I.; Obst-Huebl, L.; Ziegler, T.; Zeil, K.; Cowan, T.; Schramm, U.; Bussmann, M.; Kluge, T.
Laser-accelerated ions are increasingly recognized as a promising alternative to conventionally accelerated ion beams. Possible applications range from fast ignition in laser fusion to ion tumor therapy as well as studies of transient high-current and high-field phenomena in laboratory astrophysics and material science. A combination of ultra-short duration and very high charge density is the most sought-after characteristic of these beams which are produced in the violent interaction of an ultra-intense short pulse laser with a solid target. We have performed the – to our knowledge – very first full 3D particle-in-cell simulations of this interaction that includes the picosecond time span prior to the arrival of the main laser pulse. This time period is thought to be decisive for the following main pulse interaction, yet it is poorly explored – partly due to the immense computational needs to resolve the plasma kinetically with full precision. Here, we bridge scales hitherto inaccessible, from attosecond plasma oscillations over few-femtosecond laser oscillations and transient, non-equilibrium plasma dynamics on the tens of femtosecond laser duration to picosecond pre-plasma development. We study the influence of pre-pulse laser conditions and material on the ion acceleration performance. Additionally, we aim to infer radiative signatures of the plasma dynamics and link them to isochoric heating, instability development, and other complex dynamics. Beyond gaining a fundamental understanding of the governing fundamental principle plasma dynamics, the results will be used in the ongoing development of novel diagnostics analyzing the bremsstrahlung and synchrotron radiation in order to experimentally probe the sub-ps interaction. The simulations have been performed at Piz Daint at CSCS, Switzerland, using the 3D particle-in-cell code PIConGPU developed at HZDR.
Keywords: laser ion acceleration, laser-driven proton sources, particle-in-cell, PIConGPU, openPMD, HPC, throughput, PRACE, CSCS, Piz Daint
  • Invited lecture (Conferences)
    EuroHPC Summit Week 2019 / PRACEdays19, 13.-17.05.2019, Poznań, Polska


Publ.-Id: 29255 - Permalink

Synthetic radiation simulations as a path to study the relativistic Kelvin-Helmholtz instability in interstellar jets
Pausch, R.; Bussmann, M.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Debus, A.;
The relativistic Kelvin-Helmholtz instability (KHI) is expected in shear flow regions of astrophysical plasma jets originating from AGNs and SNR. It generates magnetic fields that influence the jet dynamics significantly.

We present 3D3V particle-in-cell simulations of unprecedented resolution and extent that not only allow studying the plasma dynamics during the KHI but also making quantitative predictions on the emitted radiation. We present a diagnostic method that allows identifying the linear phase of the instability via a polarization anisotropy observable light years away on Earth and to quantify the growth rate of the instability.

A microscopic model, that describes the fundamental origin of the radiation signature, will be covered in detail during the talk. Technical aspects relevant for performing these large-scale simulations with the particle-in-cell code PIConGPU and for making quantitative predictions with synthetic radiation diagnostics, based on Liénard-Wiechert potentials, will be discussed, and observation limits both for interstellar jets and in lab astrophysics experiments will be covered.
Keywords: KHI, PIConGPU, radiation, synthetic diagnostics, polarization, AGN, SNR
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Materie und Kosmos (SMuK), 18.-22.03.2019, München, Deutschland

Publ.-Id: 29254 - Permalink

Large-scale simulations of plasma acceleration
Pausch, R.; Huebl, A.; Bastrakov, S.; Debus, A.; Garten, M.; Matthes, A.; Steiniger, K.; Schramm, U.; Widera, R.; Zenker, E.; Bussmann, M.;
A brief presentation of the MuT/DMA activities of the Computational radiation group and solutions that might be of interest for the Matter in the Universe community.
Keywords: DMA, MUT, ARD, PIConGPU, alpaka
  • Lecture (Conference)
    "Matter and the Universe" Days 2019, 14.-15.02.2019, Hamburg, Deutschland

Publ.-Id: 29253 - Permalink

From studying the self-truncated ionization injection during LWFA to hybrid LPWFA simulations
Pausch, R.; Debus, A.; Bussmann, M.; Couperus Cabadag, J.; Garten, M.; Heinemann, T.; Huebl, A.; Martinez De La Ossa, A.; Irman, A.; Kurz, T.; Schöbel, S.; Steiniger, K.; Schramm, U.;
This talk gives a brief summary of the current status of the start-to-end simulations of the hybrid LPWFA setup using PIConGPU.
Keywords: PIConGPU, hybrid, LPWFA, LWFA, PWFA
  • Lecture (others)
    hybrid collaboration meeting, 09.-11.01.2019, Hamburg, Deutschland

Publ.-Id: 29252 - Permalink

Investigations on stationary measurements at COSMEA-I facility - CT part
Bieberle, A.ORC; Beyer, M.; Pietruske, H.; Hampel, U.ORC; Boden, S.ORC

This repository contains reconstructed and analysed CT data obtained from the COSMEA-I test facility that is operated under stationary operating conditions. Furthermore, a full CAD drawing set is provided.

Keywords: Passive Heat Transfer; Stream Condensation; Heat Flux Probe; Process Computed Tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-05-20
    DOI: 10.14278/rodare.126


Publ.-Id: 29250 - Permalink

Breaking the Doping Limit in Silicon by Deep Impurities
Wang, M.ORC; Debernardi, A.; Berencén, Y.; Heller, R.; Xu, C.; Yuan, Y.; Xie, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Prucnal, S.; Zhou, S.
n-type doping in Si by shallow impurities, such as P, As, and Sb, exhibits an intrinsic limit due to the Fermi-level pinning via defect complexes at high doping concentrations. Here, we demonstrate that doping Si with the deep chalcogen donor Te by nonequilibrium processing can exceed this limit and yield higher electron concentrations. In contrast to shallow impurities, the interstitial Te fraction decreases with increasing doping concentration and substitutional Te dimers become the dominant configuration as effective donors, leading to a nonsaturating carrier concentration as well as to an insulator-to-metal transition. First-principles calculations reveal that the Te dimers possess the lowest formation energy and donate two electrons per dimer to the conduction band. These results provide an alternative insight into the physics of deep impurities and lead to a possible solution for the ultrahigh electron concentration needed in today’s Si-based nanoelectronics.


Publ.-Id: 29247 - Permalink

Nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films for in-plane asymmetric micro-supercapacitors with ultrahigh energy density
He, Y.; Zhang, P.; Wang, M.ORC; Wang, F.; Tan, D.; Li, Y.; Zhuang, X.; Zhang, F.; Feng, X.
In-plane micro-supercapacitors (MSCs) with high power density, remarkable rate capability, and long cycling stability, exhibit promising application potential in modern electronic devices. To satisfy the fast-growing energy demands for the next-generation advanced micro-devices, increasing the energy density of MSCs is urgently desirable but still remains a great challenge. In this work, a series of in-plane asymmetric MSCs (AMSCs) are rationally constructed using a family of nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films with interdigital patterns. The voltage output window of the resultant AMSCs is able to reach up to 1.8 V, delivering superior areal capacitances of up to 19.84 mF cm-2, and ultrahigh energy density of 44.6 mW h cm-3 which is among the best performances of the state-of-the-art MSCs. Moreover, the achieved AMSCs show outstanding mechanical flexibility and integration capability. Thus, this work will promote the development of novel high-performance AMSCs.


Publ.-Id: 29246 - Permalink

Interface stability, mechanical and corrosion properties of AlCrMoNbZr/(AlCrMoNbZr)N high-entropy alloy multilayer coatings under helium ion irradiation
Zhang, W.; Wang, M.ORC; Wang, L.; Liu, C. H.; Chang, H.; Yang, J. J.; Liao, J. L.; Yang, Y. Y.; Liu, N.
High entropy alloy (HEA) coatings are promising for use as accident-tolerant fuel cladding due to their outstanding high-temperature corrosion resistance. In this work, we investigated the interface stability, mechanical properties and corrosion resistance of AlCrMoNbZr/(AlCrMoNbZr)N multilayer coatings with individual layer thickness of 5 nm, 10 nm and 50 nm, subjected to helium (He) ion irradiations: 400 keV He+ ions with fluences of 8×1015 ion/cm2 and 8×1016 ion/cm2. We determined that He bubbles are not observed in any of the multilayer coatings after a helium ion irradiation process with 400 keV He ions and a fluence as high as 8×1016 ion/cm2. Although intermixing and chemical reaction in the peak damage region of the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with 5 nm monolayer thickness are induced by the high fluence He ion irradiation, the FCC structure remained, and no intermetallic compounds are detected. Moreover, we found that the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with the monolayer thickness of 50 nm has better interface stability during the irradiation process. Nanoindentation tests reveal that the hardness of all multilayer coatings decreased for low and high fluences, which is mainly due to the thermal effect caused by irradiation. In addition, the electrochemical corrosion test show that AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating 50 nm coatings has better corrosion resistance than AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating 5 nm coatings under high fluence He irradiation. The corrosion resistance of the multilayer coating depends on the stability of the multilayer interface. Our results show that the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with a monolayer thickness of 50 nm had better interface stability, mechanical properties and corrosion resistance than the AlCrMoNbZr/(AlCrMoNbZr)N multilayer coating with a per layer thickness of 5 nm under high fluence He irradiation. This work reveals that high-entropy alloy multilayer coatings have potential applications as an accident-tolerant fuel cladding coating in light water reactors.
Keywords: AlCrMoNbZr/(AlCrMoNbZr)N, Multilayer coating, High-entropy alloy, Ion irradiation, Interfaces, Nanoindentation, Electrochemical corrosion, Accident-tolerant fuel (ATF)


Publ.-Id: 29245 - Permalink

Targeting Cyclooxygenase-2 in Pheochromocytoma and Paraganglioma: Focus on Genetic Background
Ullrich, M.ORC; Richter, S.; Seifert, V.; Hauser, S.; Calsina, B.; Martínez-Montes, A. M.; Ter Laak, M.; Ziegler, C. G.; Timmers, H.; Eisenhofer, G.; Robledo, M.; Pietzsch, J.ORC
Cyclooxygenase 2 (COX-2) is a key enzyme of the tumorigenesis-inflammation interface and can be induced by hypoxia. A pseudohypoxic transcriptional signature characterizes pheochromocytomas and paragangliomas (PPGLs) of the cluster I, mainly represented by tumors with mutations in von Hippel-Lindau (VHL), endothelial PAS domain-containing protein 1 (EPAS1), or succinate dehydrogenase (SDH) subunit genes. The aim of this study was to investigate a possible association between underlying tumor driver mutations and COX-2 in PPGLs. COX-2 gene expression and immunoreactivity were examined in clinical specimens with documented mutations as well as in spheroids and allografts derived from mouse pheochromocytoma (MPC) cells. COX-2 in vivo imaging was performed in allograft mice. We observed significantly higher COX-2 expression in cluster I, especially in VHL-mutant PPGLs, however, no specific association between COX-2 mRNA levels and a hypoxia-related transcriptional signature was found. COX-2 immunoreactivity was present in about 60 % of clinical specimens as well as in MPC spheroids and allografts. A selective COX-2 tracer specifically accumulated in MPC allografts. This study demonstrates that, although, pseudohypoxia is not the major determinant for high COX-2 levels in PPGLs, COX-2 is a relevant molecular target. This potentially allows for employing selective COX-2 inhibitors as targeted chemotherapeutic agents and radiosensitizers. Moreover, available models are suitable for preclinical testing of these treatments.
Keywords: VHL; NF1; EPAS1; hypoxia-inducible factor; inflammation; radiosensitization; succinate dehydrogenase; mouse pheochromocytoma cells; immunohistochemistry; fluorescence imaging

Publ.-Id: 29242 - Permalink

Damage accumulation and implanted Gd and Au position in a- and c-plane GaN
Macková, A.; Malinský, P.; Jagerová, A.; Mikšová, R.; Sofer, Z.; Klímová, K.; Mikulics, M.; Böttger, R.; Akhmadaliev, S.; Oswald, J.;
(0001) c-plane and (11−20) a-plane GaN epitaxial layers were implanted with 400 keV Au+ and Gd+ ions using ion implantation fluences of 5×1014, 1×1015 and 5×1015 cm-2. Rutherford Back-Scattering spectrometry in channelling mode (RBS/C) was used to follow the dopant depth profiles and the introduced disorder; the angular dependence of the backscattered ions (angular scans) in c- and a-plane GaN was measured to get insight into structural modification and dopant position in various crystallographic orientations. Defect-accumulation depth profiles exhibited differences for a- and c-plane GaN, with a-plane showing significantly lower accumulated disorder in the buried layer, accompanied by the shift of the maximum damage accumulation into the deeper layer with respect to the theoretical prediction, than c-plane GaN. Angular scans showed channelling preservation in as-implanted samples and better channelling recovery in the annealed a-plane GaN compared to cplane GaN. The angular scan widths were simulated by FLUX code as well as the half-width modifications of angular scans were discussed in connection to the damage accumulation. Photoluminescence measurement followed in detail yellow band and band edge luminescence decline after the implantation and the recovery of luminescence spectra features after annealing.
Keywords: Implanted (0001) and (11–20) GaN, Damage accumulation asymmetry in GaN, Ion implantation in semiconductors, RBS channelling, Damage-depth profiling

Publ.-Id: 29240 - Permalink

Surface nanobubbles on the rare earth fluorcarbonate mineral synchysite
Owens, C. L.ORC; Schach, E.; Heinig, T.; Rudolph, M.ORC; Nash, G. R.
Surface nanobubbles have been identified to play an important role in a range of industries from mineral processing to food science. The formation of surface nanobubbles is of importance for mineral processing in the extraction of complex ores, such as those containing rare earth elements. This is due to the way minerals are extracted utilising froth flotation. In this study, surface nanobubbles were imaged using non-contact atomic force microscopy on a polished cross section containing rare earth minerals. Nanobubbles were found on synchysite under reagent conditions expected to induce hydrophobicity in rare earth minerals, which is required for efficient processing.

Synchysite –(Ce) is a rare earth fluorcarbonate mineral containing over 30% rare earth elements. Relatively little research has been conducted on synchysite, with only a few papers on its surface behaviour and flotation. The resulting nanobubbles were analysed and showed an average contact angle of 24 degrees± 8. These are in line with contact angles found on dolomite and galena by previous studies.
Keywords: non-contact atomic force microscopy; synchysite; bastnäsite; rare earth elements; fluorcarbonate; surface nanobubbles; carbonatite


Publ.-Id: 29231 - Permalink

Synthesis of Mg and Zn diolates and their use in metal oxide deposition
Frenzel, P.; Preuß, A.; Bankwitz, J.; Georgi, C.; Ganss, F.; Mertens, L.; Schulz, S.; Hellwig, O.; Mehring, M.; Lang, H.;
The synthesis of complexes [M(OCHMeCH₂NMeCH₂)₂] (5, M = Mg; 7, M = Zn) is described. Treatment of MeHNCH2CH2NMeH (1) with 2-methyloxirane (2) gave diol (HOCHMeCH₂NMeCH₂)₂ (3), which upon reaction with equimolar amounts of MR₂ (4, M = Mg, R = Bu; 6, M = Zn, R = Et) gave 5 and 7. The thermal behavior and vapor pressure of 5 and 7 were investigated to show whether they are suited as CVD (= chemical vapor deposition) and/or spin-coating precursors for MgO or ZnO layer formation. Thermogravimetric (TG) studies revealed that 5 and 7 decompose between 80–530 °C forming MgO and ZnO as evidenced by PXRD studies. In addition, TG-MS-coupled experiments were carried out with 7 proving that decomposition occurs by M–O, C–O, C–N and C–C bond cleavages, as evidenced from the detection of fragments such as CH𔔢N+, C₂H𔔢N+, C₂H₅N+, CH₂O+, C₂H₂O+ and C₂H₃O+. The vapor pressure of 7 was measured at 10.4 mbar at 160 °C, while 5 is non-volatile. The layers obtained by CVD are dense and conformal with a somewhat granulated surface morphology as evidenced by SEM studies. In addition, spin–coating experiments using 5 and 7 as precursors were applied. The corresponding MO layer thicknesses are between 7–140 nm (CVD) or 80 nm and 65 nm (5, 7; spin-coating). EDX and XPS measurements confirm the formation of MgO and ZnO films, however, containing 12–24 mol% (CVD) or 5–9 mol% (spin-coating) carbon. GIXRD studies verify the crystalline character of the deposited layers obtained by CVD and the spin-coating processes.

Publ.-Id: 29229 - Permalink

Residual gammaH2AX foci in head and neck squamous cell carcinomas as predictors for tumour radiosensitivity: Evaluation in pre-clinical xenograft models and clinical specimens
Meneceur, S.; Löck, S.; Gudziol, V.; Hering, S.; Bütof, R.; Rehm, M.; Baumann, M.; Krause, M.; von Neubeck, C.;
Background and purpose: Predictive biomarkers can be instrumental to treatment individualisation of cancer patients and improve therapy outcome. Residual γH2AX foci represent a promising biomarker to predict tumour radiosensitivity. In this pre-clinical study, the slope of the dose–response curve was evaluated for its predictive relevance in head and neck squamous cell carcinoma xenografts (HNSCC). Additionally, the feasibility of the translated assay was tested in a clinical setting in patient derived HNSCC samples, and associations between residual γH2AX foci and clinical parameters were analysed. Materials and methods: Seven HNSCC xenografts models (FaDu, SAS, SKX, UT-SCC-5, UT-SCC-14, UT-SCC-45, XF354)were used. Tumour bearing NMRI nude mice were randomly distributed to five treatment arms (0–8 Gy). Residual γH2AX foci (24 h post irradiation)were counted by visual scoring in a micromilieu dependent manner (assessed with BrdU and pimonidazole). The local tumour control values measured as TCD 50 (tumour control dose 50%)have previously been published. Patient derived HNSCC biopsies were cultivated ex vivo for 24 h including 4 h of pimonidazole and BrdU treatment, subsequently irradiated with 0–8 Gy and fixed after 24 h. Results: In the pre-clinical study, the dose–response curve slopes negatively correlated with the tumour control dose after fractionated irradiation (TCD 50,fx , R 2 = 0.63, p = 0.032)and after single dose irradiation under homogeneous hypoxia (TCD 50,SD,clamp , R 2 = 0.66, p = 0.027). The γH2AX assay in clinical HNSCC samples showed a dose–response relationship, with the values of the slopes ranging from 0.099 Gy −1 to 0.920 Gy −1 (coefficient of variation = 52.8%). Slopes derived from patients were in the same ranges as the sensitive, moderate and resistant models of the pre-clinical study. Statistical analysis revealed a significant negative correlation between the slope and the patients’ age (R 2 = 0.65, p = 0.001). Conclusion: These results further support the promise of the slope of the residual γH2AX foci dose–response as a biomarker for radiosensitivity. In the clinical samples, the variation in the slopes reveals patients’ specific repair capacities, which could hold potential value for treatment individualisation. © 2019 Elsevier B.V.
Keywords: Clinical specimens, HNSCC, Predictive biomarker, Radiosensitivity, Xenograft modelsγH2AX

Publ.-Id: 29228 - Permalink

Advanced Methods for Temporal Reconstruction of Modulated Electron Bunches
Zarini, O.; Köhler, A.; Couperus, J.; Pausch, R.; Kurz, T.; Schöbel, S.; Meißner, H.; Bussmann, M.; Schramm, U.; Irman, A.; Debus, A.;
We describe optimizations of phase-retrieval algorithms for the reconstruction of the temporal structure of highly modulated electron bunches from coherent transition radiation (CTR) spectra. Synthetic data is used to quantitatively analyze capabilities and limitations of the approach taking into account realistic bandwidth constraints of ultra-broadband spectrometers. Established algorithms are combined with information from independent channels as charge calibrated electron spectra and absolute intensity calibration of the spectrometer. With this set of data, in principle available in experiments, we demonstrate a promising fidelity for the detailed analysis of substructured laser wakefield accelerated electron bunches.
Keywords: Electron bunch duration, reconstruction algorithm, transition radiation
  • Contribution to proceedings
    Advanced Accelerator Concepts Workshop (AAC2018), 12.-17.08.2018, Breckenridge, Colorado, USA: IEEE, 978-1-5386-7721-6
    DOI: 10.1109/AAC.2018.8659388

Publ.-Id: 29225 - Permalink

Measuring sub-femtosecond temporal structures in multi-ten kiloampere electron beams
Zarini, O.ORC
In laser wakefield acceleration, an ultra-short high-intensity laser pulse excites a plasma wave, which can sustain accelerating electric fields of several hundred GV/m.
This scheme advances a novel concept for compact and less expensive electron accelerators, which can be hosted in a typical university size laboratory. Furthermore, laser wakefield accelerators (LWFA) feature unique electron bunch characteristics, namely micrometer size with duration ranging from several fs to tens of fs. Precise knowledge of the longitudinal profile of such ultra-short electron bunches is essential for the design of future table-top X-ray light-sources and remains a big challenge due to the resolution limit of existing diagnostic techniques.

Spectral measurement of broadband coherent and incoherent transition radiation (TR) produced when electron bunches passing through a metal foil is a promising way to analyze longitudinal characteristics of these bunches. Due to the limited reproducibility of the electron source this measurement highly requires single-shot capability.
An ultra-broadband spectrometer combines the TR spectrum in UV/NIR (200-1000 nm), NIR (0.9-1.7 µm) and mid-IR (1.6-12 µm). A high spectral sensitivity, dynamic bandwidth and spectral resolution are realized by three optimized dispersion and detection systems integrated into a single-shot spectrometer.
A complete characterization and calibration of the spectrometer have been done concerning wavelengths, relative spectral sensitivities, and absolute photometric sensitivities, also taking into account for the light polarization.
The TR spectrometer is able to characterize electron bunches with charges as low as 1pC and can resolve time-scales of 0.4 fs. Electron bunches up to 16 fs (rms width) can be reconstructed from their TR spectrum.

In the presented work, the self-truncated ionization induced injection (STII) scheme has been explored to study the relevant beam parameters especially its longitudinal bunch profile and the resulting peak current.
Proper focusing of a high power laser pulse into a supersonic gas-jet target and tailoring the conditional laser and plasma density and taking advantage of the relativistic self-focusing effects are investigated in this PhD thesis in order to study the final beam parameters as well as the consequent beam loading effects by producing nC-class mono-energetic electron beams.

In the experiment at HZDR, the DRACO 100TW Ti:Sa based laser system is used in conjunction with a He-N₂ mixed, supersonic gas-jet target. Under optimized conditions, mono-energetic electron bunches are accelerated, which are massively loaded up to several 100 pC at 300 MeV peak energy with a narrow energy spread of a few 10 MeV. Reconstruction results of TR spectra, measured by TR spectrometer, show that the shortest electron bunch duration is at about 13 fs FWHM corresponding to a peak current as high as 20 kA.
Such peak current is about one order of magnitude higher than those generated by conventional RF linear accelerator. This landmarks a significant finding of this thesis.
Keywords: Laser wakefield acceleration, laser plasma accelerator, self-truncated ionization injection, high peak current, high bunch charge, beam loading, bunch duration measurement, coherent transition radiation, broadband spectrometer, infrared spectrometer, prism spectrometer, echelle spectrometer, phase reconstruction algorithm, Foldwrap reconstruction algorithm, PIConGPU
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-100 2019


Publ.-Id: 29222 - Permalink

Recent application of the solid targetry system
Alexander, M.; Karsten, F.;
The solid targetry system was used both, at port 4 directly mounted at the yoke and at the beamline at port 3. We will give an overview about the purification or separation of n.c.a. radionuclides like Sr-85, V-48, Cu-64, Cr-51, Co-56, Y-88, La-135, Zr-89, Ce-139 and Pb-203.
  • Lecture (Conference)
    14th CYCLEUR workshop 2019, 08.-10.05.2019, Dresden, Germany

Publ.-Id: 29221 - Permalink

Competence Center for Ion Beams in Materials Research and Medicine
Fassbender, J.;
Competence Center for Ion Beams in Materials Research and Medicine
Keywords: ion beams, high-energy, materials research, user facility
  • Invited lecture (Conferences)
    Competence Center for Ion Beams in Materials Research and Medicine, 02.05.2019, München, Deutschland

Publ.-Id: 29220 - Permalink

Improvement of UniCAR T cell effectiveness against EGFR+ tumor cells by using different αEGFR targeting module formats
Jureczek, J.; Feldmann, A.; Albert, S.; Bergmann, R.; Berndt, N.; Arndt, C.; Koristka, S.; Bachmann, M.;
Since epithelial growth factor receptor (EGFR) mutations or overexpression is linked with variety of malignancies, including lung, breast, stomach, colorectal, head and neck, and pancreatic carcinomas as well as glioblastomas it is an attractive target for tailored treatment of solid cancer. Thus over the last twenty years many strategies targeting EGFR were developed and even clinically approved, including disrupting intracellular signalling involving tyrosine kinase inhibitors (TKIs) or the inhibition of ligand binding using therapeutic monoclonal antibodies like e.g. Cetuximab, Panitumumab or Necitumumab. Unfortunately, cancers treated with these targeted drugs commonly become resistant to them. These limitations justify the need of more efficient therapy options. As chimeric antigen receptor (CAR) engineered T cells highly effectively eliminate hematological malignancies already in the clinics, one idea is to redirect CAR T cells also against EGFR expressing solid cancers. However, CAR T cell therapy can lead to severe even life-threatening side effects and its effectiveness against solid tumors is still limited. Particular worrying is that EGFR is a widespread antigen commonly expressed also on healthy tissues bearing a high risk of severe on-target/off-tumor side effects due to EGFR-targeted therapies, which cannot be controlled in patients. In order to overcome these challenges our UniCAR technology might be an appropriate answer combining high anti-tumor effectiveness, tumor specificity, flexibility, and safety control mechanisms. In contrast to conventional CARs, UniCAR T cells are per se inert because UniCARs are directed against a small peptide epitope, which is not present on living cells. The redirection of UniCAR T cells to tumor cells occurs only in the presence of a tumor specific targeting module (TM). TMs, on one hand carry the specificity for a certain tumor antigen and on the other hand contain the UniCAR peptide epitope recognized by UniCARs mediating the cross-linkage of UniCAR T cells and antigen presenting tumor cells. As TMs have a very short half-life in vivo they can be used as a switch to control UniCAR T cell activity on demand in patients. In detail, UniCAR T cells are only switched on in the presence of antigen specific TMs realized by permanent TM infusion, but could be rapidly switched off when the application of the TM is stopped and the TM is eliminated. Meanwhile we successfully generated a series of different TMs against different tumor antigens and entities. Interestingly, TMs can be made of different molecules showing various structures and can flexible be exchanged in order to target any tumor antigen and overcome tumor escape variants. Commonly our TMs consist of a humanized single-chain variable fragment (scFv) derived from the variable heavy and light chain domains of a murine monoclonal antibody. In addition, we successfully generated TMs based on different monovalent and bivalent antibody derivatives, nanobodies derived from one variable camelid antibody domain, affibodies and even small peptide molecules.
Recently we demonstrated proof-of-concept for the redirection of UniCAR T cells to EGFR expressing tumor cells by a nanobody based αEGFR TM derived from the camelid αEGFR antibody 7C12. Considering that the affinity and anti-tumor efficiency of the eucaryotically expressed αEGFR nanobody based TM was limited, we therefore asked the question, whether we could further improve the therapeutic effect against EGFR positive tumor cells using the UniCAR technology. In order to answer this question, we generated a novel TM based on a scFv derived from the clinically used chimeric monoclonal antibody Cetuximab (IMC C-225). In detail, we designed a murine and humanized αEGFR scFv TM, successfully expressed them in mammalian cell lines and compared their functionality with the eucaryotic αEGFR nanobody-based TM in vitro and in vivo. In principle, we observed that both TM formats, the αEGFR nanobody as well as the scFv-based TM, are able to redirect UniCAR T cells eliminate EGFR-expressing tumor cells in an antigen-specific and TM-dependent manner. As both the murine and humanized scFv TM variants worked equally well, obviously humanization of the αEGFR scFv does not affect its functionality. However most interestingly, the tumor killing efficiency of the αEGFR scFv TM was significantly superior in comparison to the αEGFR nanobody based TM. Here, the half maximal effective TM concentration (EC50) value of scFv based TM was improved 1000-fold, from nM to pM range. Consequently, UniCAR T cells in combination with the scFv based TM efficiently eliminate also target cells expressing a low EGFR density level, while UniCAR T cells redirected by the nb based TM clearly attack only highly EGFR expressing tumor cells. Furthermore, the high anti-tumor efficacy of the αEGFR scFv TM over nb TM was manifested in experimental mice.
In summary, we successfully established different αEGFR TM formats that are able to redirect UniCAR T cells to eliminate EGFR-positive tumor cells. However, the analysed αEGFR TM formats differ with respect to their anti-tumor efficiency, which might decide whether UniCAR T cells attack target cells showing different EGFR density levels.
  • Poster
    Tumor immunology meets oncology (TIMO XV), 25.-27.04.2019, Halle, Deutschland

Publ.-Id: 29214 - Permalink

Engineering human T cells with a novel switchable CAR technology for tumor immunotherapy
Hoffmann, A.; Feldmann, A.; Kittel-Boselli, E.; Bergmann, R.; Koristka, S.; Berndt, N.; Arndt, C.; Bachmann, M.;
With the first approvals of chimeric antigen receptor (CAR) T cell therapies by the FDA the use of genetically modified T cells in the immunotherapy of tumors has recently become a very promising approach. CAR T cells are able to recognize tumor-associated antigens (TAAs) via specific single-chain variable fragments (scFvs) in a major histocompatibility-complex (MHC)-independent manner. Although highly efficient, the inability to regulate the activity of CAR T cells can cause severe even
life-threatening side effects such as cytokine-release syndrome (CRS) and on-target, off-tumor toxicities. Modular CAR systems may overcome these limitations allowing to switch the activity of CAR T cells repeatedly “ON” and “OFF”. Alternatively or in addition, the safety of CAR T cells could also be improved by “gated” targeting strategies e.g. by splitting the signaling and costimulatory motifs to independent CARs of different specificities. Theoretically, the idea of gated targeting could be extended to include further e.g. inhibitory signals. However, the size of current CARs limit the number of specificities that can be simultaneously transduced into a T cell. We therefore developed a novel switchable modular universal artificial receptor having a minimal size. The platform was termed RevCAR system.
In order to reduce the size of the artificial receptor the original idea was to replace the extracellular scFv domain of a conventional CAR with a small peptide epitope and to engage the resulting RevCAR T cell via a bispecific target module which we termed RevTM. For proof of concept two small peptide epitopes were selected and the respective RevCARs constructed. In addition, a series of different RevTMs were constructed. On the one hand the RevTM recognized one of the two peptide epitopes on the other hand the RevTM was directed to a potential tumor associated antigen (TAA). Until now a series of such pairs of RevTMs were constructed and functionally analyzed. RevCAR T cells armed via the respective RevTM were able to specifically lyse their respective target cell in a peptide epitope specific and target specific as well as target dependent manner. These data are supported by analysis of cytokine secretion. We only observed a specific cytokine release from RevCAR T cells in the presence of both target cells and the respective RevTM. Released cytokines detected were IFN-gamma, GM-CSF, TNF, and IL-2.
Taken together these results demonstrate the high anti-tumor efficiency of the novel RevCAR platform which is characterized by a small size, an improved safety, easy controllability as well as high flexibility.
  • Poster
    Tumor immunology meets oncology (TIMO XV), 25.-27.04.2019, Halle, Deutschland

Publ.-Id: 29213 - Permalink

Thermal expansion of magnetron sputtered TiCxN1-x coatings studied by high-temperature X-ray diffraction
Saringer, C.; Kickinger, C.; Munnik, F.; Mitterer, C.; Schalk, N.; Tkadletz, M.;
The coefficient of thermal expansion (CTE) of TiCxN1-x can be adjusted by changing the value x between 0 (i.e. pure TiN) and 1 (pure TiC), which makes this material exceptionally useful as base layer to adapt the mismatch between the CTEs of substrate and coating. However, no comprehensive data on the CTE of sputtered TiCxN1-x has been reported up to now. Thus, in this work eleven coatings with compositions ranging from pure TiN to pure TiC were deposited using non-reactive magnetron sputtering. The elemental and phase composition were obtained by elastic recoil detection analysis and Raman spectroscopy, respectively. Powders of the coating material were analyzed using high-temperature X-ray diffraction between room temperature and up to 1000 °C to determine the temperature dependent lattice parameters. Subsequently, these lattice parameters were fitted using second order polynomials with coefficients linearly depending on the carbon content. Thus, a formula for the CTE of TiCxN1-x valid between 25 and 1000 °C was deduced which showed that at room temperature TiN has the highest CTE of 8.12 × 10-6 K-1. The CTE gradually decreases with increasing carbon content to 7.55 × 10-6 K-1 for pure TiC. While the value for TiC only shows a small increase with temperature, the CTE of TiN increases strongly up to 11.1 × 10-6 K-1 at 1000 °C. The presented formula for the temperature dependent CTE of sputtered TiCxN1-x coatings allows to calculate the required composition for TiCxN1-x base layers, in order to tune their thermal expansion for the use in complex multilayered coatings.
Keywords: Thermal expansion; Titanium carbonitride; High-temperature X-ray diffraction; Physical vapor deposition; Hard coatings

Publ.-Id: 29211 - Permalink

The UniCAR system: A modular CAR T cell approach to improve the safety of CAR T cells
Bachmann, M.;
The idea to eliminate tumor cells via our own immune system is more than a hundred years old. However, a real break through came first with the development of check point inhibitors, bispecific antibodies (bsAbs) and T cells genetically modified to express Chimeric Antigen Receptors (CARs). Eventhough the clinical application of T cells equipped with CARs can lead to a complete remission, unfortunately, their application can also cause severe or even life threatening side effects as their activity can no more be adjusted once given to the patient. For targeting of tumor cells expressing tumor associated antigens (TAAs) which are not limited to tumor cells but also accessible on healthy tissues CAR T cells should not be permanently in a killing mode but be equipped with some kind of a switch whereby the activity of CAR T cells can reversely be turned “on and off “. Moreover, in case of cytokine release syndrome (CRS), tumor lysis syndrome (TLS), or other deadly side effects the possibility of an emergency shut down of the CAR T cell activity should exist. Modular CAR variants such as the UniCAR system may fulfill these requirements.
Keywords: Immunotherapy, Chimeric antigen receptor, T cells, UniCAR, BiTE, Bispecific antibody

Publ.-Id: 29209 - Permalink

Bulk analysis of meteorites using INAA at FRM II
Li, X.; Merchel, S.ORC; Lierse Von Gostomski, C.
In March 2017, the 49th German meteorite was found lying on top of a rock pile on the side of a potato field, near the city of Cloppenburg, Lower Saxony, Germany [1,2]. With two other meteorites (Oldenburg (fall in 1930), Benthullen (find in 1948 or 1951)) from the same region and meteorites from other countries, we started a program to analyze extraterrestrial samples in 2017. We have analyzed in total three chondrites, three achondrites of the HED
group (Howardite-Eucrite-Diogenite) (Dhofar 1675, NWA 2690, NWA 2698), a lunar and a Martian meteorite (NWA 7986, NWA 4925), two iron meteorites (Gibeon, yet unnamed new find from Libya/Chad in 2019) and six potential micrometeorites. The bigger samples (10-20 mg) were normally irradiated twice: for 3-5 min and for a long time up to 1 h in the rabbit position. The much smaller micrometeorites (9-38 μg) were irradiated for 24 h in the high-flux capsule irradiation position (Φth>1E14 cm-2s-1). We used the k0-method for the analysis [3].
With the high and pure thermal neutron flux at the FRM II, up to 45 elements could be determined in most samples [3]. According to the element compositions, the meteorites could be classified or earlier classifications could be confirmed. Although, the sample weights of the micrometeorites are very small and manipulating them was challenging, we could determine up to 16 elements. All of them show a rather high Fe concentration, i.e. 55-70 weight-%. However, for Ni and Ir, we can only give a detection limit of about 0.4% and 2 ng/g, respectively. Their potential origin are under discussion.
We thank A. Muszynski and M. Szyszko (Poznan, PL), A. Bischoff (Uni. Münster), D. Heinlein, J. Feige (TU Berlin) and A. Gärtner (Senckenberg Dresden) for providing and preparation of samples and the TUM-Kolleg program for financial supports.
1. J. Gattacceca et al., Meteorit. Planet. Sci., 2019, 54, 469-471.
2. J. Storz et al., (Jan. 2019)
3. X. Li et al., J. Radioanal. Nucl. Chem. 2014, 300, 457-463.
Keywords: INAA, k0-method, meteorite, micrometeorite
  • Lecture (Conference)
    2nd International Conference on Radioanalytical and Nuclear Chemistry (RANC 2019), 05.-10.05.2019, Budapest, Hungary

Publ.-Id: 29206 - Permalink

Preliminary Report on the Study of Beam-induced Background Effects at a Muon Collider
Bartosik, N.; Bertolin, A.; Casarsa, M.; Collamati, F.; Ferrari, A.; Ferrari, A.ORC; Gianelle, A.; Lucchesi, D.; Mokhov, N.; Mueller, S.ORC; Pastrone, N.; Sala, P.; Sestini, L.; Striganov, S.
Physics at a multi-TeV muon collider needs a change of perspective for the detector design due to the large amount of background induced by muon beam decays. Preliminary studies, based on simulated data, on the composition and the characteristics of the particles originated from the muon decays and reaching the detectors are presented here. The reconstruction performance of the physics processes H→bb¯ and Z→bb¯ has been investigated for the time being without the effect of the machine induced background. A preliminary study of the environment hazard due to the radiation induced by neutrino interactions with the matter is presented using the FLUKA simulation program.
Keywords: Detectors in high-intensity environments, future accelerators, muon beams, neutrino-induced radiation
  • Open Access LogoarXiv:1905.03725 (2019)


Publ.-Id: 29205 - Permalink

Vertical Organic Thin-Film Transistors with an Anodized Permeable Base for Very Low Leakage Current
Dollinger, F.; Lim, K.-G.; Li, Y.; Guo, E.; Formánek, P.; Hübner, R.; Fischer, A.; Kleemann, H.; Leo, K.;
The organic permeable base transistor (OPBT) is currently the fastest organic transistor with a transition frequency of 40 MHz. It relies on a thin aluminum base electrode to control the transistor current. This electrode is surrounded by a native oxide layer for passivation, currently created by oxidation in air. However, this process is not reliable and leads to large performance variations between samples, slow production, and relatively high leakage currents. Here, for the first time it is demonstrated that electrochemical anodization can be conveniently employed for the fabrication of high-performance OPBTs with vastly reduced leakage currents and more controlled process parameters. Very large transmission factors of 99.9996 % are achieved, while excellent on/off ratios of 5 × 105 and high on-currents greater than 300 mA cm−2 show that the C60 semiconductor layer can withstand the electrochemical anodization. These results make anodization an intriguing option for innovative organic transistor design.
Keywords: aluminum oxide, anodization, organic permeable base transistors (OPBTs), organic transistors, organic thin-film transistors (OTFTs), vertical transistors

Publ.-Id: 29204 - Permalink

Wave-shaped polycyclic hydrocarbons with controlled aromaticity
Ma, J.ORC; Zhang, K.; Schellhammer, K. S.; Fu, Y.ORC; Komber, H.ORC; Xu, C.ORC; Popov, A. A.ORC; Hennersdorf, F.ORC; Weigand, J. J.ORC; Zhou, S.ORC; Pisula, W.ORC; Ortmann, F.; Berger, R.ORC; Liu, J.ORC; Feng, X.ORC
Controlling the aromaticity and electronic properties of curved π-conjugated systems has been increasingly attractive for the development of novel functional materials for organic electronics. Herein, we demonstrate an efficient synthesis of two novel wave-shaped polycyclic hydrocarbons (PHs) 1 and 2 with 64 π-electrons. Among them, the wave-shaped π-conjugated carbon skeleton of 2 is unambiguously revealed by single-crystal X-ray crystallography analysis. The wave-shaped geometry is induced by steric congestion in the cove and fjord regions. Remarkably, the aromaticity of these two structural isomers can be tailored by the annulated direction of cyclopenta[b]fluorene units. Isomer 1 (Eoptg = 1.13 eV) behaves as a closed-shell compound with weakly antiaromatic feature, whereas its structural isomer 2 displays a highly stable tetraradical character (y0 = 0.23; y1 = 0.22; t1/2 = 91 days) with a narrow optical energy gap of 0.96 eV. Moreover, the curved PH 2 exhibits remarkable ambipolar charge transport in solution-processed organic thin-film transistors. Our research provides a new insight into the design and synthesis of stable functional curved aromatics with multiradical characters.

Publ.-Id: 29201 - Permalink

Measurement-Protocol Dependence of the Magnetocaloric Effect in Ni-Co-Mn-Sb Heusler Alloys
Salazar-Mejia, C.; Kumar, V.; Felser, C.; Skourski, Y.; Wosnitza, J.; Nayak, A. K.;
Ni-Co-Mn-Sb-based Heusler shape-memory alloys that undergo a martensitic-structural transition around room temperature are well known for exhibiting large magnetic entropy change and elastocaloric effect. Here, we report the observation of a large adiabatic temperature change of −11 K in a Ni-Co-Mn-Sb system by using direct adiabatic temperature-change measurements in pulsed magnetic fields. We show that a large magnetic cooling can be achieved in a wide temperature range spanning from 120 to 270 K by purposefully varying the chemical composition. The temperature- and field-dependent irreversibility of the effect is analyzed through a detailed experimental study of the protocol-dependent magnetocaloric effect. The present study is an important contribution towards the understanding of irreversible magnetocaloric effects in materials with magnetostructural transition.


Publ.-Id: 29199 - Permalink

Magnetocaloric effect of gadolinium in high magnetic fields
Gottschall, T.; Kuz'Min, M. D.; Skokov, K. P.; Skourski, Y.; Fries, M.; Gutfleisch, O.; Ghorbani Zavareh, M.; Schlagel, D. L.; Mudryk, Y.; Pecharsky, V.; Wosnitza, J.;
The magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to 62 T. The maximum observed adiabatic temperature change is ΔTad = 60.5 K, the initial temperature T0 being just above 300 K. The field dependence of ΔTad is found to follow the usual H2/3 law, with a small correction in H4/3. However, as H is increased, a radical change is observed in the dependence of ΔTad on T0, at H = const. The familiar caret-shaped peak situated at T0 = TC becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, μ0H ≥ 140 T, calculations predict a complete disappearance of the maximum near TC and an emergence of a new very broad maximum far above TC.


Publ.-Id: 29198 - Permalink

Field-induced instability of the quantum spin liquid ground state in the Jeff = 1/2 triangular-lattice compound NaYbO2
Ranjith, K. M.; Dmytriieva, D.; Khim, S.; Sichelschmidt, J.; Luther, S.; Ehlers, D.; Yasuoka, H.; Wosnitza, J.; Tsirlin, A. A.; Kühne, H.; Baenitz, M.;
Polycrystalline samples of NaYbO2 are investigated by bulk agnetization and specific-heat measurements, as well as by nuclear magnetic resonance (NMR) and electron spin resonance (ESR) as local probes. No signatures of long-range magnetic order are found down to 0.3 K, evidencing a highly frustrated spin-liquid-like ground state in zero field. Above 2 T, signatures of magnetic order are observed in thermodynamic measurements, suggesting the possibility of a field-induced quantum phase transition. The 23Na NMR relaxation rates reveal the absence of magnetic order and persistent fluctuations down to 0.3 K at very low fields and confirm the bulk magnetic order above 2 T. The H-T phase diagram is obtained and discussed along with the existing theoretical concepts for layered spin- 1/2 triangular-lattice antiferromagnets.


Publ.-Id: 29197 - Permalink

Ion Sources for Focused Ion Beams – Present Status and Prospective Developments
Bischoff, L.ORC; Mazarov, P.; Pilz, W.; Klingner, N.; Gierak, J.
Focused Ion Beam (FIB) processing has been developed into a well-established, irreplaceable and still promising technique in nearly all fields of nano-technology in particular for direct patterning and proto-typing on the μm scale and well below as well as sample preparation for further investigations, using SEM or TEM.
At the moment nearly exclusively gallium Liquid Metal Ion Sources (LMIS) are used for ion beam generation. Therefore, the Liquid Metal Alloy Ion Sources (LMAIS) represent a promising new alternative research area to expand the global FIB application fields. Here, especially, IBL (Ion Beam Lithography) - a direct, resistless and threedimensional patterning - enables a simultaneous in-situ process control by crosssectioning and inspection. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years [1]. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources as an alternative technology feasible for nano patterning challenges e.g. to tune electrical, optical, magnetic or mechanic properties. In this contribution the operation principle, the preparation and testing
technology as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions, obtained with a VELION FIB/SEM system (Raith GmbH), as well as heavy Bi ions or polyatomic clusters, all coming from one ion source [2]. Additionally, also new ion source developments based on gas field emission (GFIS), on ionic liquids (ILIS), on magneto-optical traps (MOTIS) or on ICP or ECR high current sources for Xe-FIB are presented. Combined with an optimized FIB optics design they can open a bright field of new employments. These alternative ion sources will be introduced and briefly described.
[1] L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Liquid Metal Alloy Ion Sources - An Alternative
for Focused Ion Beam Technology, Appl. Phys. Rev. 3 (2016) 021101.
[2] W. Pilz, N. Klingner, L. Bischoff, P. Mazarov, and S. Bauerdick, Lithium Ion Beams from Liquid Metal
Alloy Ion Sources, J. Vac. Sci. Technol. B 37 (2019) 021802-1.
Keywords: Ion sources, Focused Ion Beam, Nanopatterning
  • Invited lecture (Conferences)
    European FIB Network, 3rd EuFN Workshop 2019, 12.-14.06.2019, Dresden, Germany

Publ.-Id: 29190 - Permalink

Geometry description in the FLUKA MC transport code
Mueller, S. E.ORC
Geometry description in the FLUKA MC transport code
Keywords: FLUKA, MU2E, CLFV
  • Lecture (others)
    MU2E SimWG meeting, 11.04.2019, Fermilab, Batavia, USA

Publ.-Id: 29187 - Permalink

Ultrafast Anisotropic Disordering in Graphite Driven by Intense Hard X-ray Pulses
Hartley, N. J.ORC; Grenzer, J.; Lu, W.; Huang, L. G.; Inubushi, Y.; Kamimura, N.; Katagiri, K.; Kodama, R.; Kon, A.; Lipp, V.; Makita, M.; Matsuoka, T.; Medvedev, N.; Nakajima, S.; Ozaki, N.; Pikuz, T.; Rode, A. V.; Rohatsch, K.; Sagae, D.; Schuster, A. K.; Tono, K.; Vorberger, J.; Yabuuchi, T.; Kraus, D.
We present results from the SPring-8 Angstrom Compact free electron LAser (SACLA) X-ray free electron laser (XFEL) facility, using an X-ray pump, X-ray probe scheme to observe ultrafast changes in the structure of heated graphite. The 9.8 keV XFEL beam was focused to give an intensity on the order of 10^19 W/cm2, and the evolution of the diffraction pattern observed up to delays of 300 fs. The interplanar diffraction peaks weaken significantly within 10s of femtoseconds, but in-plane diffraction orders i.e. those with Miller Index (hk0), persist up to 300 fs, with the observed signal increasing. We interpret this as nonthermal damage through the breaking of interplanar bonds, which at longer timescales leads to ablation by removal of intact graphite sheets. Post-experiment examination of the graphite samples shows damage which is comparable in size to the range of the excited photoelectrons. These results highlight the challenges of accurately modelling X-ray driven heating, as it becomes a routine approach to generating high energy density states.

Publ.-Id: 29186 - Permalink

Tunable disorder and localization in the rare-earth nickelates
Wang, C.; Chang, C.-H.; Huang, A.; Wang, P.-C.; Wu, P.-C.; Yang, L.; Xu, C.; Pandey, P.; Zeng, M.; Böttger, R.; Jeng, H.-T.; Zeng, Y.-J.; Helm, M.; Chu, Y.-H.; Ganesh, R.; Zhou, S.;
We demonstrate that transport in metallic rare-earth nickelates can be engineered by directly tuning the electronic mean free path. Using irradiation as a tool to induce disorder, we drive this system from a metallic phase into an Anderson insulator. This proceeds via an intermediate regime which shows a thermal crossover from insulating to metallic behavior. We argue that this phase falls within the paradigm of weak localization in three dimensions. We develop a theoretical model for the temperature dependence of resistivity which shows good agreement with our data. The three-dimensional weak localization picture is supported by magnetoconductivity, which scales as ∼B2 up to several tesla. Interestingly, our data indicate that this phase lies in the Mott-Ioffe-Regel regime with the mean free path approaching the lattice constant. Upon further increasing disorder, the charge carriers are localized, leading to insulating behavior at all temperatures. Our results show that irradiation provides a “clean” tuning knob for the mean free path, without altering other system parameters. This suggests promising directions for studies of Anderson localization.
Keywords: Anderson localization; Metal-insulator transition; Weak localization; Magnetoresistance


Publ.-Id: 29185 - Permalink

AMS at Big Accelerators: 53Mn and 60Fe in Meteorites
Rugel, G.; Faestermann, T.; Fimiani, L.; Korschinek, G.; Leya, I.; Ludwig, P.; Pavetich, S.; Smith, T.; Wallner, A.;
The poster describes that big tandem accelerators are essential to measure 53Mn and 60Fe in meteorites.
Keywords: AMS Accelerator Fe-60 Mn-53 Meteorites
  • Poster
    KIMM Workshop 2019, 02.05.2019, München, Deutschland

Publ.-Id: 29179 - Permalink

Magnetic Orders and Origin of Exchange Bias in Co Clusters Embedded Oxide Nanocomposite Films
Li, H.; Wang, C.; Li, D.-Y.; Pereira, L. M. C.; Homm, P.; Menghini, M.; Locquet, J.-P.; Temst, K.; Vantomme, A.; van Haesendonck, C.; van Bael, M. J.; Ruan, S.; Zeng, Y.-J.;
Magnetic nanoparticles embedded oxide semiconductors are interesting candidates for spintronics in view of combining ferromagnetic (FM) and semiconducting properties. Co-ZnO and Co-V2O3 nanocomposite thin films are synthesized by Co ion implantation in crystalline thin films. Magnetic order varies with the implantation fluence in Co-ZnO, where the superparamagnetic (SPM) order appears in the low-fluence films (2×1016 and 4×1016 ions/cm2) while the FM order coexists with the SPM phase in high-fluence ones (1×1017 ions/cm2). The exchange bias (EB) effect is evident in high-fluence films, which gives an EB field of about 100 Oe at 2 K and a blocking temperature of around 100 K. In parallel, 3.5×1016 ions/cm2 Co-V2O3 hybrid thin film exhibits a clear antiferromagnetic (AFM) coupling at low temperature with a weak EB effect. The different magnetic behaviors in the two Co-implanted systems lead us to believe on one hand, that the observed EB effect in the Co-ZnO system is the result of the FM/AFM coupling between large Co nanoparticles and their CoO/Co3O4 surroundings in the (Zn,Co)O matrix. While, on the other hand, the EB effect in Co-V2O3 system originates from the interaction between FM Co nanoparticles and AFM V2O3 matrix. Detailed studies of magnetic orders as well as EB effect in magnetic nanocomposite semiconductors pave the way for their application in spintronics.
Keywords: nanocomposite, exchange bias, antiferromagnetic, superparamagnetic


Publ.-Id: 29176 - Permalink

Thermal stability of Te-hyperdoped Si: Atomic-scale correlation of the structural, electrical, and optical properties
Wang, M.; Hübner, R.; Xu, C.; Xie, Y.; Berencén, Y.; Heller, R.; Rebohle, L.; Helm, M.; Prucnal, S.; Zhou, S.;
Si hyperdoped with chalcogens (S,Se,Te) is well known to possess unique properties such as an insulator-tometal transition and a room-temperature sub-band-gap absorption. These properties are expected to be sensitive to a postsynthesis thermal annealing, since hyperdoped Si is a thermodynamically metastable material. Thermal stability of the as-fabricated hyperdoped Si is of great importance for the device fabrication process involving temperature-dependent steps such as Ohmic contact formation. Here, we report on the thermal stability of the as-fabricated Te-hyperdoped Si subjected to isochronal furnace anneals from 250 to 1200 °C. We demonstrate that Te-hyperdoped Si exhibits thermal stability up to 400 °C for 10 min, which even helps to further improve the crystalline quality, the electrical activation of Te dopants, and the room-temperature sub-band-gap absorption. At higher temperatures, however, Te atoms are found to move out from the substitutional sites with a maximum migration energy of EM = 2.3 eV forming inactive clusters and precipitates that impair the structural, electrical, and optical properties. These results provide further insight into the underlying physical state transformation of Te dopants in a metastable compositional regime caused by postsynthesis thermal annealing. They also pave the way for the fabrication of advanced hyperdoped Si-based devices.


Publ.-Id: 29175 - Permalink

Controllable defect driven symmetry change and domain structure evolution in BiFeO3 with enhanced tetragonality
Chen, C.; Wang, C.; Cai, X.; Xu, C.; Li, C.; Zhou, J.; Luo, Z.; Fan, Z.; Qin, M.; Zeng, M.; Lu, X.; Gao, X.; Kentsch, U.; Yang, P.; Zhou, G.; Wang, N.; Zhu, Y.; Zhou, S.; Chen, D.; Liu, J.;
Defect engineering has been a powerful tool to enable the creation of exotic phases and the discovery of intriguing phenomena in ferroelectric oxides. However, the accurate control of the concentration of defects remains a big challenge. In this work, ion implantation, which can provide controllable point defects, allows us to produce a controlled defect driven true super-tetragonal (T) phase with a single-domain-state in ferroelectric BiFeO3 thin films. This point-defect engineering is found to drive the phase transition from the as-grown mixed rhombohedral-like (R) and tetragonal-like (MC) phase to true tetragonal (T) symmetry and induce the stripe multi-nanodomains to a single domain state. By further increasing the injected dose of the He ion, we demonstrate an enhanced tetragonality super-tetragonal (super-T) phase with the largest c/a ratio of ∼1.3 that has ever been experimentally achieved in BiFeO3. A combination of the morphology change and domain evolution further confirms that the mixed R/MC phase structure transforms to the single-domain-state true tetragonal phase. Moreover, the re-emergence of the R phase and in-plane nanoscale multi-domains after heat treatment reveal the memory effect and reversible phase transition and domain evolution. Our findings demonstrate the reversible control of R-Mc-T-super T symmetry changes (leading to the creation of true T phase BiFeO3 with enhanced tetragonality) and multidomain-single domain structure evolution through controllable defect engineering. This work also provides a pathway to generate large tetragonality (or c/a ratio) that could be extended to other ferroelectric material systems (such as PbTiO3, BaTiO3 and HfO2) which might lead to strong polarization enhancement.


  • Secondary publication expected from 05.04.2020

Publ.-Id: 29174 - Permalink

Absorption edge, Urbach tail, and electron-phonon interactions in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3
Zhu, JiajunORC; Xia, Y.; Li, G.; Zhou, S.ORC; Wimmer, S.; Springholz, G.ORC; Pashkin, A.ORC; Helm, M.; Schneider, H.ORC
We employ infrared transmission spectroscopy to explore the temperature-dependent absorption edge and electron-phonon (e-ph) interaction in topological insulator Bi2Se3 and band insulator (Bi0.89In0.11)2Se3 films. Upon heating from 5 K to 300 K, the absorption edge shifts from 262 to 249 meV for Bi2Se3 and from 367 to 343 meV for (Bi0.89In0.11)2Se3. By analyzing the temperature dependence of the Urbach tail, the significant role of Raman-active phonon mode E2g in e-ph interaction is identified, which agrees well with the ab initio calculation.


Publ.-Id: 29170 - Permalink

Electron-Beam-Driven Structure Evolution of Single-Layer MoTe2 for Quantum Devices
Lehnert, T.; Ghorbani-Asl, MahdiORC; Köster, J.; Lee, Z.; V. Krasheninnikov, A.ORC; Kaiser, U.
40 kV high-resolution transmission electron microscopy (TEM) experiments are performed to understand defect formation and evolution of their atomic structure in single-layer 2H MoTe2 under electron beam irradiation. We show that Te vacancies can agglomerate either in single Te-vacancy lines or in extended defects composed of column Te vacancies, including rotational trefoil-like defects, with some of them being never reported before. The formation of inversion domains with mirror twin boundaries of different types, along with the islands of the metallic T’ phase was also observed. Our first-principles calculations provide insights into the energetics of the transformations as well as the electronic structure of the system with defects and point out that some of the observed defects have localized magnetic moments. Our results indicate that various nano-scale structures, including metallic quantum dots consisting of T’-phase islands and one-dimensional metallic quantum systems such as vacancy lines and mirror twin boundaries embedded into a semiconducting host material can be realized in single-layer 2H MoTe2, and defect-associated magnetism can also be added, which may allow prospective control of optical and electronic properties of two-dimensional materials.
Keywords: Defects, 2D MoTe2, transmission electron microscopy, transition metal dichalcogenide, DFT, quantum devices


  • Secondary publication expected from 26.04.2020

Publ.-Id: 29169 - Permalink

Impact of Extrinsic and Intrinsic Hypoxia on Catecholamine Biosynthesis in Absence or Presence of Hif2α in Pheochromocytoma Cells
Bechmann, N.; Poser, I.; Seifert, V.; Greunke, C.; Ullrich, M.ORC; Qin, N.; Walch, A.; Peitzsch, M.; Robledo, M.; Pacak, K.; Pietzsch, J.ORC; Richter, S.; Eisenhofer, G.
Abstract: Pheochromocytomas and paragangliomas (PPGLs) with activated pseudohypoxic pathways are associated with an immature catecholamine phenotype and carry a higher risk for metastasis. For improved understanding of the underlying mechanisms we investigated the impact of hypoxia and pseudohypoxia on catecholamine biosynthesis in pheochromocytoma cells naturally lacking Hif2α (MPC and MTT) or expressing both Hif1α and Hif2α (PC12). Cultivation under extrinsic hypoxia or in spheroid culture (intrinsic hypoxia) increased cellular dopamine and norepinephrine contents in all cell lines. To distinguish further between Hif1α- and Hif2α-driven effects we expressed Hif2α in MTT and MPC-mCherry cells (naturally lacking Hif2α). Presence of Hif2α resulted in similarly increased cellular dopamine and norepinephrine under hypoxia as in the control cells. Furthermore, hypoxia resulted in enhanced phosphorylation of tyrosine hydroxylase (TH). A specific knockdown of Hif1α in PC12 diminished these effects. Pseudohypoxic conditions, simulated by expression of Hif2α under normoxia resulted in increased TH phosphorylation, further stimulated by extrinsic hypoxia. Correlations with PPGL tissue data led us to conclude that catecholamine biosynthesis under hypoxia is mainly mediated through increased phosphorylation of TH, regulated as a short-term response
(24–48 h) by HIF1α. Continuous activation of hypoxia-related genes under pseudohypoxia leads to a HIF2α-mediated phosphorylation of TH (permanent status).
Keywords: hypoxia; pseudohypoxia; spheroids; HIF; EPAS1; catecholamine; pheochromocytoma and paraganglioma; phosphorylation tyrosine hydroxylase

Publ.-Id: 29168 - Permalink

Silver Particles with Rhombicuboctahedral Shape and Effective Isotropic Interactions with Light
Steiner, A. M.; Mayer, M.; Schletz, D.; Wolf, D.; Formanek, P.; Hübner, R.; Dulle, M.; Förster, S.; König, T. A. F.; Fery, A.;
Truly spherical silver nanoparticles are of great importance for fundamental studies including plasmonic applications, but their direct synthesis in aqueous media is not feasible. Using the commonly employed copper-based etching processes, an isotropic plasmonic response can be achieved by etching well-defined silver nanocubes. Whilst spherical-like shape is typically prevailing in such processes, we established that there is a preferential growth toward silver rhombicuboctahedra, which is the thermodynamically most stable product of this synthesis. The rhombicuboctahedral morphology is further evidenced by comprehensive characterization with small-angle X-ray scattering in combination with transmission electron microscopy (TEM) tomography and high-resolution TEM. We also elucidate the complete reaction mechanism based on UV-vis kinetic studies, and the postulated mechanism can also be extended to all copper-based etching processes.

Publ.-Id: 29167 - Permalink

Carboranyl analogues of ketoprofen with cytostatic activity against human melanoma and colon cancer cell lines
Buzharevski, A.; Paskas, S.; Laube, M.ORC; Lönnecke, P.; Neumann, W.; Murganic, B.; Mijatovic, S.; Maksimovic-Ivanic, D.; Pietzsch, J.ORC; Hey-Hawkins, E.
Ketoprofen is a widely used nonsteroidal anti-inflammatory drug (NSAID) that also exhibits cytotoxic activity against various cancers. This makes ketoprofen an attractive structural lead for the development of new NSAIDs and cytotoxic agents. Recently, the incorporation of carboranes as phenyl mimetics in structures of established drugs has emerged as an attractive strategy in drug design. Herein, we report the synthesis and evaluation of four novel carborane-containing derivatives of ketoprofen, two of which are prodrug esters with an nitric oxide-releasing moiety. One of these prodrug esters exhibited high cytostatic activity against melanoma and colon cancer cell lines. The most pronounced activity was found in cell lines that are sensitive to oxidative stress, which was apparently induced by the ketoprofen analogue.

Publ.-Id: 29166 - Permalink

Thermal Transport in MoS2 from Molecular Dynamics using Different Empirical Potentials
Xu, K.; Gabourie, A. J.; Hashemi, A.; Fan, Z.; Wei, N.; Farimani, A. B.; Komsa, H.-P.; Krasheninnikov, A. V.ORC; Pop, E.; Ala-Nissila, T.
Thermal properties of molybdenum disulfide (MoS2) have recently attracted attention related to fundamentals of heat propagation in strongly anisotropic materials, and in the context of potential applications to optoelec- tronics and thermoelectrics. Multiple empirical potentials have been developed for classical molecular dynamics (MD) simulations of this material, but it has been unclear which provides the most realistic results. Here, we calculate lattice thermal conductivity of single- and multilayer pristine MoS2 by employing three different thermal transport MD methods: equilibrium, nonequilibrium, and homogeneous nonequilibrium ones. We mainly use the Graphics Processing Units Molecular Dynamics code for numerical calculations, and the Large-scale Atomic/Molecular Massively Parallel Simulator code for crosschecks. Using different methods and computer codes allows us to verify the consistency of our results and facilitate comparisons with previous studies, where different schemes have been adopted. Our results using variants of the Stillinger-Weber potential are at odds with some previous ones and we analyze the possible origins of the discrepancies in detail. We show that, among the potentials considered here, the reactive empirical bond order (REBO) potential gives the most reasonable predictions of thermal transport properties as compared to experimental data. With the REBO potential, we further find that isotope scattering has only a small effect on thermal conduction in MoS2 and the in-plane thermal conductivity decreases with increasing layer number and saturates beyond about three layers. We identify the REBO potential as a transferable empirical potential for MD simulations of MoS2 which can be used to study thermal transport properties in more complicated situations such as in systems containing defects or engineered nanoscale features. This work establishes a firm foundation for understanding heat transport properties of MoS2 using MD simulations.
Keywords: 2D materials; thermal transport; atomistic simulations


Publ.-Id: 29163 - Permalink

Tomonaga-Luttinger liquid in a box: electrons confined within MoS2 mirror twin boundaries
Jolie, W.; Murray, C.; Weiß, P. S.; Hall, J.; Portner, F.; Atodiresei, N.; Krasheninnikov, A. V.ORC; Busse, C.; Komsa, H.-P.; Rosch, A.; Michely, T.
Two- or three-dimensional metals are usually well described by weakly interacting, fermionic quasiparticles. This concept breaks down in one dimension due to strong Coulomb interactions. There, low-energy electronic excitations are expected to be bosonic collective modes, which fractionalize into independent spin- and charge-density waves. Experimental research on one-dimensional metals is still hampered by their difficult realization, their limited accessibility to measurements, and by competing or obscuring effects such as Peierls distortions or zero bias anomalies. Here we overcome these difficulties by constructing a well-isolated, one-dimensional metal of finite length present in MoS2 mirror-twin boundaries. Using scanning tunneling spectroscopy we measure the single-particle density of the interacting electron system as a function of energy and position in the 1D box. Comparison to theoretical modeling provides unambiguous evidence that we are observing spin-charge separation in real space.
Keywords: 2D materials, Tomonaga-Luttinger liquid, First-principles calculations


Publ.-Id: 29162 - Permalink

Room temperature ferromagnetism in MoTe2 by post-growth incorporation of vanadium impurities
Coelho, P. M.; Komsa, H.-P.; Lasek, K.; Kalappattil, V.; Karthikeyan, J.; Phan, M.-H.; Krasheninnikov, A. V.ORC; Batzill, M.
Post-synthesis doping of 2D materials is demonstrated by incorporation of vapor-deposited transition metals into a MoTe2 lattice. Using this approach, vanadium doping of 2H-MoTe2 produces a 2D ferromagnetic semiconductor with a Curie temperature above room temperature (RT). Surprisingly, ferromagnetic properties can be induced with very
low vanadium concentrations, down to ≈0.2%. The vanadium species introduced at RT are metastable, and annealing to above ≈500 K results in the formation of a thermodynamically favored impurity configuration that, however, exhibits reduced ferromagnetic properties. Doping with titanium, instead of vanadium, shows a similar incorporation behavior, but no ferromagnetism is induced in MoTe2. This indicates that the type of impurities in addition to their atomic configuration is responsible for the induced magnetism. The interpretation of the experimental results is consistent with ab initio calculations, which confirm that the proposed vanadium impurity configurations exhibit magnetic moments, in contrast to the same configurations with titanium impurities. This study illustrates the possibility to induce ferromagnetic properties in layered van der Waals semiconductors by controlled magnetic impurity doping and thus to add magnetic functionalities to 2D materials.
Keywords: 2D materials; STM; electronic structure calculations; doping


  • Secondary publication expected from 01.04.2020

Publ.-Id: 29161 - Permalink

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