Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33403 Publications

Integriertes Management und Publikation von wissenschaftlichen Artikeln, Software und Forschungsdaten am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) : 1.Sächsische FDM-Tagung 2019, Dresden

Reschke, E.ORC; Konrad, U.ORC
Mit dem Ziel, das Publizieren von Artikeln, Forschungsdaten und wissenschaftlicher Software gemäß den FAIR-Prinzipien (https://www.go-fair.org/fair-principles/) zu unterstützen, wurde am HZDR ein integriertes Publikationsmanagement aufgebaut. Insbesondere Daten- und Softwarepublikationen erfordern die Entwicklung bedarfsgerechter organisatorischer und technischer Strukturen ergänzend zu bereits sehr gut funktionierenden Services im Publikationsmanagement. In der Zusammenarbeit mit Wissenschaftlern des HZDR und internationalen Partnern in ausgewählten Projekten wurde der Bedarf an Unterstützung im Forschungsdatenmanagement analysiert. Darauf aufbauend wurde schrittweise ein integriertes System von Infrastrukturen und Services entwickelt und bereitgestellt. In einer seit Mai 2018 gültigen Data Policy wurden die Rahmenbedingungen und Regelungen sowohl für wissenschaftliche Mitarbeiter als auch für externe Messgäste definiert. Im Vortrag wird auf die Erfahrungen im integrierten Publikationsmanagement für Artikel, Forschungsdaten und Forschungssoftware eingegangen und daraus resultierend werden die nächsten Aufgaben und Ziele entwickelt
Keywords: ROBIS, RODARE, Publikationsmanagement, Forschungsdaten, Forschungssoftware, publication management, research data, research software, FAIR, Open Access
  • Open Access Logo Invited lecture (Conferences)
    1. Sächsische FDM-Tagung, 19.09.2019, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-30413
Publ.-Id: 30413


Towards a vertical nanopillar-based single electron transistor – a high-temperature ion beam irradiation approach

Xu, X.ORC; Heinig, K.-H.; Engelmann, H.-J.; Möller, W.; Klingner, N.ORC; Gharbi, A.; Tiron, R.; Facsko, S.ORC; Hlawacek, G.ORC; Borany, J.
The usage of ion beam irradiation on vertical nanopillar structures is a prerequisite for fabricating a CMOS-compatible, vertical gate-all-around(GAA) SET device. After either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) irradiation of the nanopillars (with diameter of 35 nm and height of 70 nm) at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the program TRI3DYN. We assume that it is the result from the ion beam induced amorphization of Si accompanied by the ion hammering effect. The amorphous nano-structure behaves viscously and the surface capillary force dictates the final shape. To confirm such a theory, ion irradiation at elevated temperatures (up to 672 K) has been performed and no plastic deformation was observed under these conditions. Bright-field transmission electron microscopy micrographs as well as Electron Beam Diffraction confirmed the crystallinity of the substrate and nanopillars after HT-irradiation. In addition, a steady thinning process of the nanopillars to a diameter of 10 nm has been observed at higher fluencies. As the original pillar diameter is comparable to the size of the collision cascade, instead of direct knock-on sputtering, enhanced forward sputtering through the sidewalls of the pillar is responsible for this effect. The relation between ion beam energy, flux and temperature with the observed thinning of the nanopillars has been studied experimentally and compared to TRI3DYN simulations. Such a reliable and CMOS-compatible process could serve as a potential downscaling technique for large-scale fabrication of nanopillar-based electronics.
  • Lecture (Conference)
    The Second International Workshop of the PicoFIB Network, 13.02.2019, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30412
Publ.-Id: 30412


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Eychmüller, A.; Samano, E.; Seidel, R.; Erbe, A.
The DNA origami method provides a programmable bottom-up
approach for creating nanostructures of any desired shape, which can
be used as scaffolds for nanoelectronics and nanophotonics device
fabrications. Based on this technique, the precise positioning of
metallic and semiconducting nanoparticles along DNA nanostructures
can be achieved. In this study, various DNA origami nanostructures
(nanomolds, nanotubes and nanosheets) are used for the fabrication of
nanoelectronic devices. To this end, gold nanoparticles, semiconductor
quantum dots/rods are used in/on the DNA origami structures to create
nanowires and transistor-like devices. The DNA origami nanowires
and transistors were electrically characterized from room temperature
(RT) down to 4.2K. Temperature-dependent characterizations of
wires were performed in order to understand the dominant conduction
mechanisms. Some nanowires showed pure metallic behavior.
Transistor like devices showed Coulomb blockade behavior at RT.
The study shows that self-assembled DNA structures can be used for
nanoelectronic patterning and single electron devices.
  • Lecture (Conference)
    DPG Spring Meeting, 31.03.-05.04.2019, Universität Regensburg, Germnay

Permalink: https://www.hzdr.de/publications/Publ-30411
Publ.-Id: 30411


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Martinez-Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.
  • Lecture (Conference)
    IHRS NanoNET International Conferance, 08.-11.10.2019, Dresden, Germnay

Permalink: https://www.hzdr.de/publications/Publ-30410
Publ.-Id: 30410


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.
The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade behavior at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.
  • Open Access Logo Poster
    Nucleic Acid Nanotechnology: from algorithmic design to biochemical applications, 27.-29.05.2019, Aalto University, Finland

Permalink: https://www.hzdr.de/publications/Publ-30409
Publ.-Id: 30409


A Spectroscopic Study of the Interactions of Trivalent f-Elements with α-Chitin and its Constituents

Kammerlander, K.; Huittinen, N. M.ORC; Kaden, P.ORC; Stumpf, T.; Brunner, E.
A Spectroscopic Study of the Interactions of Trivalent f-Elements with α-Chitin and its Constituents
  • Lecture (Conference)
    GdCH Jahrestagung der Fachgruppe Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30408
Publ.-Id: 30408


Sorption of Trivalent f-Elements by Materials of Biological Origin: NMR and Luminescence Spectroscopic Studies

Kammerlander, K.; Köhler, L.; Huittinen, N. M.ORC; Stumpf, T.; Brunner, E.
Sorption of Trivalent f-Elements by Materials of Biological Origin: NMR and Luminescence Spectroscopic Studies
  • Lecture (Conference)
    Migration 2019, 15.-20.09.2019, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-30407
Publ.-Id: 30407


Radiochemistry and the radioactive nuclear waste management

Mayordomo Herranz, N.ORC
This invited lecture gives an overview to students of chemistry at Universidad de Alcalá (Spain) about radiochemistry and the ways to tackle radioactive waste
  • Invited lecture (Conferences)
    Lectures about chemistry (Lecciones de química), 06.02.2020, Alcalá de Henares, Spain

Permalink: https://www.hzdr.de/publications/Publ-30406
Publ.-Id: 30406


Commercial applications of research institute Tandem accelerators: the Rossendorf example

Akhmadaliev, Shavkat
The Ion Beam Center (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a unique user facility with decades of experience applying ion beams for materials analysis and modification. The IBC provides ion beams of nearly all stable elements in an unique energy range from some tens of eV up to 60 MeV using tandem accelerators and electrostatic ion implanters, focused ion beam systems, a helium ion microscope, highly-charged ions systems, as well as an accelerator mass spectrometer (AMS) and a secondary ion spectrometer combined with a tandem accelerator. Annually, the IBC offers more than 16.000 hours of beam time for research and industrial purposes to users across the globe. Continuous access to the IBC is permitted via an online proposal procedure [1, 2]. In addition to the beam time, the IBC provides numerous add-on services including sample preparation, clean-room processing, surface and thin film metrology, optical and electron-beam lithography, thermal processing, thin-film deposition, optical and electrical characterization, electron microscopy and spectroscopy, X-ray investigations, as well as simulation of ion-related processes and data evaluation.
Since 2011, the spin-off HZDR Innovation GmbH [3] shares the IBC equipment and offers fast and direct access to the IBC for commercial services. The activity of the spin-off is focused on the high-energy ion implantation mostly for doping and defect engineering of semiconductors. Up to 8 inch wafers are handled (semi-)automatically at accelerators of IBC under clean room conditions. Many leading international microelectronic companies are customers of HZDR Innovation GmbH. HZDR Innovation GmbH provides an important contribution to the development and production of novel techniques for micro and power electronics, making semiconductor devices more effective and climate-friendly.

[1] http://www.hzdr.de/db/Cms?pNid=3249
[2] https://gate.hzdr.de/user/
[3] http://hzdr-innovation.de/2/
  • Invited lecture (Conferences)
    NUSPRASEN Workshop on Nuclear Science Applications, 25.-27.11.2019, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-30405
Publ.-Id: 30405


Structural and compositional modification of graphene oxide by means of medium and heavy ion implantation

Malinský, P.; Cutroneo, M.; Sofer, Z.; Szőkölová, K.; Böttger, R.; Akhmadaliev, S.; Macková, A.
Graphene and its allotropes belong to the new generation of materials. Due to their extraordinary electrical, mechanical and other properties, their application possibilities are vast. In this work, a study on interactions of graphene oxide (GO) layers using Au and Ga ions with energy of 40 keV was realized. Very shallow layers of GO are modified as low energy ions are depositing energy mostly in the upper layer due to the low projected ion ranges at most of 50 nm. The ion irradiation fluences of 5.0 × 1014 cm−2, 5.0 × 1015 cm−2 and 5.0 × 1016 cm−2 were used. Upon irradiation, the modified GO foils were characterised using nuclear analytical methods – Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA) and various conventional analytical methods such as Raman spectroscopy, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and 2-point conductivity measurements. Oxygen species removal was evidenced as the increasing function of the ion implantation fluence and oxygen depth profiles exhibited complex behaviour connected to implanted ion specie. The deep oxygen depletion in the broad surface layer accompanied by Ga diffusion into the depth was observed in Ga irradiated GO compared to Au irradiated samples which exhibited a narrow oxygen depleted layer at GO surface. XPS evidenced strong increase of C=C bonds compared to C-O bonds on the irradiated GO surface with increasing ion fluence, which was comparable for both ion species. Raman spectroscopy shows the modification of main phonon modes identified in GO. The D peak slight decrease and broadening was observed for GO irradiated with ion fluence above 5 × 1015 cm−2 and mainly for Au ion irradiation. FTIR analysis proved the oxygen containing functional group release with the increased ion fluence, mainly C-O group release after Au ion irradiation was observed. Simultaneously H-O stretching absorption peak is in FTIR spectrum reduced more significantly for Ga irradiated GO which is in accordance with RBS elemental analysis exhibiting the more pronounced hydrogen depletion. Electrical conductivity measurement shows the linear I-V characteristics for the GO irradiated using both ion species and all ion fluences; the surface layer exhibited conductive behaviour comparing to pristine GO non-linear I-V characteristics.
Keywords: Chemical properties Electrical properties Graphene oxide Ion Irradiation

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Permalink: https://www.hzdr.de/publications/Publ-30404
Publ.-Id: 30404


Materials science for information technology

Helm, M.
Research at the Institute of Ion Beam Physics and Materials Research
Keywords: ion implanation, materials science, information technology
  • Lecture (others)
    talk at UESTC, 15.10.2019, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-30400
Publ.-Id: 30400


Tunable plasmonics in heavily doped GaAs via ion implantation and sub-second annealing

Duan, J.; Wang, M.ORC; Helm, M.; Skorupa, W.; Zhou, S.ORC; Prucnal, S.
Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that either the millisecond range flash lamp annealing (solid phase epitaxy) or nanosecond range pulsed laser annealing (liquid phase epitaxy) is able to recrystallized the implanted layers and electrically activate the dopants.The carrier concentration in the heavily doped p- and n-type GaAs with sub-second annealing treatment is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained ultra-highly GaAs films display a room-temperature plasma frequency above 2200 cm-1, which enables to exploit the plasmonic properties of GaAs for sensing in the mid-infrared spectral range.
Keywords: heavily doped GaAs, plasmonic, sub-second annealing
  • Lecture (Conference)
    2019 DPG, 31.03.-05.04.2019, Regensbrug, Germany

Permalink: https://www.hzdr.de/publications/Publ-30399
Publ.-Id: 30399


Tunable plasmonics in heavily doped GaAs fabricated by ion implantation and sub-second annealing

Juanmei, D.; Helm, M.; Skorupa, W.; Zhou, S.; Prucnal, S.
Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low electron effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that both the millisecond range flash lamp annealing (solid phase epitaxy) and nanosecond range pulsed laser annealing (liquid phase epitaxy) are able to recrystallize the implanted layers and electrically activate dopants. The carrier concentration in the heavily doped p- and n-type GaAs is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained GaAs films display a room-temperature plasma frequency above 2200 cm-1, which makes GaAs attractive for sensing in the mid-infrared spectral range.
Keywords: Heavily doped GaAs, mid-infrared plasmonic, sub-second annealing
  • Poster
    2019 Spring Meeting of the European Materials Research Society, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30398
Publ.-Id: 30398


Experimental and Theoretical Studies of Exchange-driven Chiral Effects

Volkov, O.
Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I review the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. At the first switching event, a domain wall pinned by the curvature induced exchange-driven DMI is expelled leading to a magnetisation state homogeneous along the parabola's long axis. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. The magnitude of the effect can be tuned by the parabola's curvature. It is found that the strength of the exchange-induced DMI interaction for the experimentally realised geometries is remarkably strong, namely $\approx 0.4~$mJ/m$^2$, compared the surface induced DMI. The presented study legitimates the predictive power of full-scale micromagnetic simulations to design the properties of ferromagnets through their geometry, thus stabilising chiral textures.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)
Keywords: Micromagnetism, curvilinear effects
  • Invited lecture (Conferences)
    Seminar at the Advanced Materials and Microsystems Laboratory, 05.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30397
Publ.-Id: 30397


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U.; Faßbender, J.ORC; Makarov, D.ORC
Magnetoelectric materials are of the great interest due to their unique coupling of the magnetic and electrical order parameters. In these materials magnetic states can be manipulated via electric field and vice versa, offering exciting prospectives for energy efficient memory, logic and sensor devices. However, a sizeable magnetoelectric coupling for technologically relevant applications is obtained for a limited set of single-phase bulk materials. Typically, this restriction can be removed by using two-phase materials, containing strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers. Although the concept is promising, there is a clear limitation regarding the fact that strain-induced changes result in the modification of all intrinsic magnetic parameters, in particular anisotropic couplings. Ideally, it would be advantageous that electric field control of magnetic state is achieved without change of global intrinsic magnetic parameters.

We propose a novel type of artificial magnetoelectric material [1], which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters. The proposal refers to geometrically curved helimagnets [2,3] embedded in a piezoelectric matrix or sandwiched between two piezoelectric layers. In contrast to typical strain-coupled magnetoelectric heterostructures, we exploit the geometric coupling between the piezoelectric matrix and curvilinear helimagents. Namely, a small geometrical deformation causes a drastic modification of magnetic state of the helimagnet through a magnetic phase transition between a homogeneous magnetic state and a periodical one. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical “1” and “0”. This paves the way towards the realization of novel magnetoelectric devices with geometrically tunable and deterministically switchable magnetic states.

We provide not only the general concept but also show analytical validation for a prototypical example of torsional nanospring helimagnets. Furthermore, we put forth a discussion on the feasibility of the experimental realization of the concept including the choice of materials and fabrication approaches.

[1] O. M. Volkov et al., J. Phys. D: Appl. Phys. (2019). doi:10.1088/1361-6463/ab2368.
[2] O. M. Volkov et al., Scientific Reports 8, 866 (2018).
[3] R. Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).
Keywords: Micromagnetism, curvilinear effects, magnetoelectric materials
  • Lecture (Conference)
    2019 MRS Fall meeting & Exhibit, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30396
Publ.-Id: 30396


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U.; Faßbender, J.ORC; Makarov, D.ORC
Magnetoelectric materials are of the great interest due to their unique coupling of the magnetic and electrical order parameters, offering exciting prospectives for energy efficient memory, logic and sensor devices. However, a sizeable magnetoelectric coupling for technologically relevant applications is obtained for a limited set of single-phase bulk materials. Typically, this restriction can be removed by using two-phase materials, containing strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers. Although the concept is promising, there is a clear limitation regarding the fact that strain-induced changes result in the modification of all intrinsic magnetic parameters, in particular anisotropic couplings. Ideally, it would be advantageous that electric field control of magnetic state is achieved without change of global intrinsic magnetic parameters.

We propose a novel type of artificial magnetoelectric material [1], which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters. The proposal refers to geometrically curved helimagnets [2,3] embedded in a piezoelectric matrix or sandwiched between two piezoelectric layers. In contrast to typical strain-coupled magnetoelectric heterostructures, we exploit the geometric coupling between the piezoelectric matrix and curvilinear helimagents. Namely, a small geometrical deformation causes a drastic modification of magnetic state of the helimagnet through a magnetic phase transition between a homogeneous magnetic state and a periodical one. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical “1” and “0”. This paves the way towards the realization of novel magnetoelectric devices with geometrically tunable and deterministically switchable magnetic states.

We provide not only the general concept but also show analytical validation for a prototypical example of torsional nanospring helimagnets. Furthermore, we put forth a discussion on the feasibility of the experimental realization of the concept including the choice of materials and fabrication approaches.

[1] O. M. Volkov et al., J. Phys. D: Appl. Phys. (2019). doi:10.1088/1361-6463/ab2368.
[2] O. M. Volkov et al., Scientific Reports 8, 866 (2018).
[3] R. Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).
Keywords: Micromagnetism, curvilinear effects, magnetoelectric materials
  • Lecture (Conference)
    2019 Conference on Magnetism and Magnetic Materials (MMM), 04.-08.11.2019, Las Vegas, USA

Permalink: https://www.hzdr.de/publications/Publ-30395
Publ.-Id: 30395


Theoretical and Experimental Study of Curvature Effects in Nanomagnetism

Volkov, O.
Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)
Keywords: Micromagnetism, curvilinear effects
  • Invited lecture (Conferences)
    Advanced Training Course “Spintronics Radar Detectors”, 14.-18.10.2019, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-30394
Publ.-Id: 30394


Experimental observation of exchange-driven chiral effects in parabolic nanostripes

Volkov, O.
Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I review the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. At the first switching event, a domain wall pinned by the curvature induced exchange-driven DMI is expelled leading to a magnetisation state homogeneous along the parabola's long axis. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. The magnitude of the effect can be tuned by the parabola's curvature. It is found that the strength of the exchange-induced DMI interaction for the experimentally realised geometries is remarkably strong, namely $\approx 0.4~$mJ/m$^2$, compared the surface induced DMI. The presented study legitimates the predictive power of full-scale micromagnetic simulations to design the properties of ferromagnets through their geometry, thus stabilising chiral textures.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)
Keywords: Micromagnetism, curvilinear effects
  • Invited lecture (Conferences)
    International Workshop “Curvilinear Magnetism”, 23.-24.05.2019, Kyiv, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-30393
Publ.-Id: 30393


Mesoscale Dzyaloshinskii-Moriya interaction: geometrical tailoring of the magnetochiralit

Volkov, O.; Sheka, D.; Gaididei, Y.; Kravchuk, V.; Rößler, U.; Faßbender, J.ORC; Makarov, D.ORC
Magnetic crystals with broken chiral symmetry possess intrinsic spinorbit driven Dzyaloshinskii-Moriya interaction (DMI). Geometrically broken symmetry in curvilinear magnetic systems also leads to the appearance of extrinsic to the crystal exchange driven effective DMI [1,2]. The interplay between the intrinsic and geometrical-induced DMI paves the way to a mesoscale DMI, whose symmetry and strength depend on the geometrical and material parameters [3]. We demonstrate this approach on the example of a helix with intrinsic DMI. Adjusting the helical geometry allows to create new artificial chiral nanostructures with defined properties from standard magnetic materials. For instance, we propose a novel approach towards artificial magnetoelectric materials, whose state is controlled by means of the geometry.
[1] Y. Gaididei et. al, Phys. Rev. Lett. 112, 257203 (2014).
[2] R. Streubel et. al, J. Phys. D: Applied Physics 49, 363001 (2016).
[3] O. Volkov et. al, Scientific Reports 8, 866 (2018).
Keywords: Micromagnetism, curvilinear effects
  • Open Access Logo Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30392
Publ.-Id: 30392


High-motility visible light-driven Ag/AgCl Janus microswimmers interacting with passive beads

Wang, X.; Baraban, L.; Misko, V. R.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Faßbender, J.ORC; Makarov, D.ORC
Visible light driven nano/micro swimmers are promising candidates for potential biomedical and environmental applications. However, the previously reported mean squared displacement (MSD) values are low, typically in the range of up to 200 µm2 (when measured over 10 s), even under the favourable UV light illumination.[1,2] This is a severe drawback for the applications where the efficient transport of micromotors within a vessel is demanded.

Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The proper design of an Ag/AgCl-based micromotor can boost the MSD to a remarkable value of 3000 µm2 (over 10 s) in pure H2O, even when activated with blue light (excitation λ = 450-490 nm). The revealed propulsion of micromotors owns a dependence of the intensity of visible light, which is contributed by the couple plasmonic light absorption of Ag/AgCl and the efficient photochemical decomposition of AgCl. With the motion comparisons of individual Janus particle, small cluster, and large cluster, the effect of suppressed rotational diffusion has been revealed experimentally and in numerical simulations. Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] The exclusion efficiency is controlled by the number of single Janus PS/Ag/AgCl particles that compose a cluster. Using numerical simulations of the Langevin equations, we gain a fundamental understanding not only the diffusion constants, but also the system-specific interaction parameter between Janus motors and passive beads.

1. Ibele, M., et al., Angew. Chem. Int. Ed. 2009, 48, 3308.
2. Simmchen, J., et al., ChemNanoMat 2017, 3, 65.
3. Wang, X., et al., Small 2018, 14, 1803613.
4. Wang, X., et al., Small 2018, 14, 1802537.
Keywords: Active Janus particles, exclusion interaction, passive beads, visible light‐driven micromotors
  • Lecture (Conference)
    Materials Research Society Fall Meeting, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30391
Publ.-Id: 30391


Experimental confirmation of exchange-driven DMI

Volkov, O.; Kakay, A.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Faßbender, J.ORC; Makarov, D.ORC
Dzyaloshinskii-Moriya interaction (DMI) is a key ingredient which allows to obtain chiral non-collinear magnetic textures, e.g. chiral domain walls and skyrmions. The conventional spin-orbit induced DMI emerges in gyrotropic crystals or at the interfaces. Therefore, tailoring of DMI is done by optimizing materials. A viable alternative to the material screening approach relies on the use of geometrically broken symmetries of conventional materials, where local geometrical curvatures generate effective exchange-induced DMI.
Here, we provide the very first experimental confirmation of the existence of the curvature-induced DMI in a Permalloy parabolic nanostripe. By analyzing the evolution of transversal domain wall (DW) [1] under the influence of external field we correlate the depinning field of the DW with the curvature-induced DMI field. We put forth a framework to analyze this field and assess the strength of the effective DMI.
[1] O. Volkov et. al, Physica Status Solidi – Rapid Research Letters, 1800309 (2018).
Keywords: Micromagnetism, curvilinear effects
  • Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30390
Publ.-Id: 30390


Magnetically-triggered ultrafast soft robots with embedded magnetic cognition and feedback control

Wang, X.; Canon Bermudez, G. S.; Faßbender, J.ORC; Makarov, D.ORC
In the last years, soft robots have been designed and developed to fulfil demands of better malleability and adaptability to changing environment [1-2]. They can be made of various stimuli responsive materials, which respond to magnetic field [3], light [4], temperature [5], electric fields [6], chemicals [7], pressure [8], etc. In contrast to other actuation mechanisms, magnetic fields are appealing for numerous application scenarios (e.g. environmental, biological, medical), where their long-range penetration, easy accessibility, and controllability [2, 9, 10] offer exciting advantages. Despite the significant advances in soft magnetic actuators, real-time monitoring and precise feedback control [11-13] remain a challenge for magnetic soft robots.

Here, we present a soft robotic system capable of precisely controlling its deformation degree by means of embedded highly compliant, high-performance magnetic sensors. Our ultrathin (7-100 μm) and ultrafast soft robots that can be actuated by in external magnetic fields pulsating at rates of up to 200 Hz. The high-performance magnetic field sensor is based on the giant magnetoresistive effect and is prepared on ultrathin polymeric foils [14-17] to assure its high mechanical stability combined with mechanical imperceptibility. The latter is crucial to avoid any disturbance of the soft actuator due to the presence of magnetic sensing device. The self-sensing function is realized by monitoring the change of the sensor signal upon approaching it to a magnetic patch applied to the soft robot. This concept of an entirely soft and integrated sensor-actuator system enables contactless self-tracking of motion for magnetic soft robots and can be readily extended to other stimuli-driven soft actuators. These developments will pave the way towards intelligent soft robots, autonomous and reactive soft devices, and new types of human-robot interaction.


[1] D. Rus et al., Nature 521, 467 (2015)
[2] L. Hines et al., Adv. Mater. 29, 13 (2017)
[3] J. Y. Kim et al., Nat Mat. 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nat Mat. 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today 10, 30 (2007)
[7] Q. Zhao et al., Nat Commun 5 (2014)
[8] SA. Morin et al., Science 337, 828 (2012)
[9] W. Hu et al., Nature 554, 81(2018)
[10] Kim. Y, et al., Nature 558, 274 (2018)
[11] T. G. Thuruthel et al., Sci Robot. 4, eaav1488 (2019)
[12] J. A. Lewis et al., Adv. Mater. 30, 1706383 (2018)
[13] W. Zhang et al., Adv Funct Mater. 29, 1806057 (2019)
[14] M. Melzer et al., Adv. Mater. 27, 1274 (2015)
[15] G. S. C. Bermúdez et al., Nat Electron. 1, 589 (2018)
[16] G. S. C. Bermúdez et al., Sci Adv., 4, eaao2623 (2018)
[17] P. N. Granell et al., npj Flexible Electronics, 3, 3 (2018)
Keywords: Soft robot, magnetic sensor, feedback control
  • Lecture (Conference)
    Materials Research Society Fall Meeting, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30389
Publ.-Id: 30389


Experimental and theoretical study of curvature effects in parabolic nanostripes

Volkov, O.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Kakay, A.; Faßbender, J.ORC; Makarov, D.ORC
Curvilinear magnetic objects are in the focus of intensive research due to the possibility to obtain new fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. The physics in these systems is driven by the interplay between exchange and magnetostatic interactions, which contain spatial derivatives in their energy functionals. This makes both interactions sensitive to the appearance of bends and twists in the physical space.
Here, we address experimentally and theoretically curvature-induced effects in parabolic nanostripes with different geometrical parameters [2]. We show that two different magnetic states can appear: the homogeneous magnetic distribution along the parabolic stripe and a state with a transversal domain wall pinned at the vertex of the parabola. The analytical calculation, based on local magnetostatic model, showed its validity and applicability in a wide range of geometrical parameters.
[1] R. Streubel et al., J. Phys. D: Applied Physics 49, 363001 (2016).
[2] O. Volkov et al., Physica Status Solidi – Rapid Research Letters, 1800309 (2018).
Keywords: Micromagnetism, curvilinear effects
  • Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30388
Publ.-Id: 30388


Magnetic and Magnetothermal Properties of Hydrogenated Materials Based on Rare Earths and Iron

Paukov, M. A.; Ivanov, L. A.; Gorbunov, D.; Tereshnina, I. S.
Iron-rich rare-earth compounds are the basis for high-energy permanent magnets. These include the R(Fe,T)12, R2Fe17, and R2FeB intermetallics (R = rare earth; T = Ti, V, Mo, Si) that readily absorb hydrogen, which changes their fundamental and functional characteristics. In this letter, we investigate the stability of the magnetic properties of some hydrides with maximum hydrogen content (namely, TmFe11TiH1 and Tm2Fe17H5.5) in a wide temperature range using high magnetic fields. The magnetic phase transition from the ferrimagnetic to the ferromagnetic state was studied immediately after hydrides were obtained, as well as after one year of storage of the samples at ambient temperature. Only the TmFe11TiH hydride is stable over time. The effect of hydrogen on the magnetothermal properties of the Nd2Fe14B and Nd1Pr1Fe14B compounds and a range of magnetic phase transitions were also investigated. Hydrogenation leads to a decrease in the magnetocaloric effect in all investigated compounds as a result of an increase in the distance between magnetically active ions due to the lattice expansion. A magnetic phase diagram is constructed.

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Permalink: https://www.hzdr.de/publications/Publ-30387
Publ.-Id: 30387


Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe2

Ranjith, K. M.; Luther, S.; Reimann, T.; Schmidt, B.; Schlender, P.; Sichelschmidt, J.; Yasuoka, H.; Strydom, A. M.; Scurschii, I.; Wosnitza, J.; Kühne, H.; Doert, T.; Baenitz, M.
High-quality single crystals of NaYbSe2, which resembles a perfect triangular-lattice antiferromagnet without intrinsic disorder, are investigated by magnetization and specific heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance. The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the H⊥c direction, a field-induced magnetic phase transition is observed above 2 T from the CP(T ) data, agreeing with a clear Ms/3 plateau of M(H), which is associated with an up-up-down spin arrangement. For the H ǀǀ c direction, a field-induced transition could be evidenced at a much higher field range (9–21 T). The 23Na NMR measurements provide microscopic evidence of field-induced ordering for both directions. A reentrant behavior of TN, originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions J ≃ 4.7 K and Jz ≃ 2.33 K are extracted from the modified bond-dependent XXZ model for the spin- 1/2 triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond frustration, arising from the complex spin-orbit entangled 4 f ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin- 1/2 triangular-lattice antiferromagnets.

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Permalink: https://www.hzdr.de/publications/Publ-30386
Publ.-Id: 30386


Microscopic insights into the disorder induced phase transition in FeRh thin films

Eggert, B.; Schmeink, A.; Potzger, K.; Lindner, J.; Fassbender, J.; Ollefs, K.; Keune, W.; Bali, R.; Wende, H.
By employing 57Fe conversion electron Mössbauer spectroscopy, we qualitatively determined the changes of the microscopic Fe moment of chemical disordered epitaxial B2-FeRh(001) thin films, where the chemical disorder has been induced by ion irradiation with Ne+. Apart from the initial magnetic splitting at 25.4 T an additional sextet contribution arises with an hyperfine field of 27.4 T. A comparison between the structural disorder and the temperature induced phase transition shows a similar change of the 57Fe hyperfine field as a function of the macroscopic magnetisation. This gives an indirect indication, that the metamagnetic phase transition proceeds via a defect-driven domain nucleation of ferromagnetic domains in the antiferromagnetic matrix, as it was suggested based on XPEEM and nano-XRD measurements along the phase transition [1]. We would like to thank the Ion Beam Center at Helmholtz-Zentrum Dresden-Rossendorf for providing the necessary facilities and acknowledge the financial support by DFG (WE2623/17-1).
D. Keavney et al. Scientific Reports 8 1778 (2018)
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 31.03.-05.04.2019, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30385
Publ.-Id: 30385


Frustrated and low-dimensional magnetic materials in high magnetic fields

Wosnitza, J.
es liegt keine inhaltliche Kurzfassung des Vortrages vor
  • Invited lecture (Conferences)
    VII European-Asian Symposium “Trends in MAGnetism”, EASTMAG 2019,, 08.-13.09.2019, Ekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-30384
Publ.-Id: 30384


Materials research in high magnetic fields

Wosnitza, J.
es liegt keine inhaltliche Kurzfassung des Vortrages vor
  • Invited lecture (Conferences)
    HFML-FELIX User Meeting, 08.-10.07.2019, Nijmegen, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30383
Publ.-Id: 30383


Modulated Order Parameter in the FFLO State of Layered Organic Superconductors

Wosnitza, J.
es liegt keine inhaltliche Kurzfassung des Vortrages vor
  • Invited lecture (Conferences)
    Gordon Research Conference on Superconductivity, 12.-18.05.2019, Les Diablerets, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-30382
Publ.-Id: 30382


Microscopic evidence for the FFLO state in layered organic superconductors

Wosnitza, J.
es liegt keine inhaltliche Kurzangabe vor
  • Invited lecture (Conferences)
    3rd International Symposium of the SFB/TR 49 on “Novel states in correlated con-densed matter – from model systems to real materials”, 18.-20.03.2019, Bad Neuenahr, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30381
Publ.-Id: 30381


Spin-transport in magnetic tunnel junctions with a zero-moment half-metallic electrode

Titova, A.; Fowley, C.ORC; Lau, Y.-C.; Borisov, K.; Atcheson, G.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Faßbender, J.ORC; Deac, A. M.
The Big Data revolution has spurred the social need for transmitting ever-larger amounts of data and increasing data transmission speed. Mobile data speeds operating in the low GHz band will not be sufficient in the years to come, and society and researchers, therefore, look towards THz frequencies for next-generation wireless communication. To be successful, cheap and compact THz-transmitters/receivers have to be created. From the field of spintronics, spin-transfer-torque nano-oscillators (STNOs) may offer a solution for this demand, provided that their output frequency can be increased. In such devices, a spin-polarized current induces magnetization dynamics at frequencies of the same order of magnitude as their resonance frequencies. The operating frequencies for current STNOs based on typical transition metal-based ferromagnets and their derivatives lie in the GHz range, as a consequence of their low magnetic anisotropy and high magnetization. On the other hand, ferrimagnetic materials with ultra-high effective anisotropy fields are very promising, as they exhibit magnetic resonances of several hundred GHz, with antiferromagnetic modes in the THz. By integrating such materials into STNOs, sub-THz and even THz wireless emission may be achieved. In order to obtain high output power, the multilayer stacks have to exhibit high magnetoresistive effects: giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR). High spin polarization is a necessary condition for strong magnetoresistive and spin-transfer effects. Therefore half-metals, which are metallic for one spin direction and semiconducting for the other, appear as the ideal choice. The focus of the work presented here is high anisotropy compensated ferrimagnetic half-metals (CFHMs) – a class of materials predicted in 1995 by van Leuken and de Groot. CFHMs behave like antiferromagnets (AFMs) with respect to external magnetic fields, since the magnetic moments of the two sublattices compensate, while simultaneously exhibiting half-metallic electron transport behavior. Many attempts had been made to fabricate such materials. Currently, MnGa-based alloys, where high anisotropy is coupled with low magnetization, attract intense attention and some have already been integrated into magnetic tunnel junctions (MTJs). Complete magnetic compensation in such alloys is, however, difficult to obtain. This was first realized in 2014 in Mn2RuxGa (MRG), which is a material that combines ideal properties like low magnetization, high magnetic anisotropy, and large spin polarization.

Here, the first demonstration of successful integration of MRG in the perpendicular magnetic tunnel junction stack is presented. The magnitude of TMR obtained in the stacks where the MgO barrier was used, although high, can still be improved. The main reason for TMR ratios being lower than what theory predicts is the presence of impurities in the tunnel barrier. In order to enhance the device's performance, different insertion layers between MgO and MRG were incorporated. These layers are diffusion barriers which stop Mn diffusion into the tunnel barrier. The highest TMR to-date (40 % at 10 K) was achieved in MgO-based stacks where a layer of Al 0.6 nm is incorporated. Within this thesis it was demonstrated that the TMR is insensitive to the compensation of the ferromagnetic MRG electrode, thereby, highlighting the fundamental difference between an antiferromagnet and a compensated half-metallic ferrimagnet. Furthermore, another tunnel barrier – Al2O3 (which is expected to be less sensitive to contamination than MgO) – has been integrated into MRG-based MTJ stacks. The current work provides a detailed study of the annealing, the bias voltage applied across the tunnel barrier and the external temperature influence on the performance of MRG-based MTJs. The stacks were analyzed not only via magnetotransport measurements, but also from the point of view of their structural and magnetic properties. This work contributes to the better understanding of spin transport in MRG-based MTJs and shows that these devices exhibit sufficient tunneling magnetoresistance ratios to observe current-induced magnetization dynamics, and, hence, establish a cornerstone of future spintronics devices.

Part of this work was carried out under the EU Project TRANSPIRE - DLV-737038.
Keywords: Magnetic tunnel junctions, Heusler compound, Ferrimagnet, Half-metal
  • Invited lecture (Conferences)
    11th International Workshop on nanomagnetism and its novel applications SpinS-2019, 02.-04.10.2019, Duisburg/Mülheim an der Ruhr, Germany

Permalink: https://www.hzdr.de/publications/Publ-30379
Publ.-Id: 30379


Ion Irradiation Induced Cobalt/Cobalt Oxide Heterostructures: From Materials to Devices

Hilliard, D.; Yildirim, O.; Fowley, C.ORC; Arekapudi, S. S. P. K.; Cansever, H.ORC; Böttger, R.; Hlawacek, G.ORC; Hellwig, O.ORC; Lindner, J.; Faßbender, J.ORC; Deac, A. M.
The demand on high data transfer and storage capacities requires smaller devices to transmit or save data. Forming well-defined ferromagnetic and electrically conducting volumes in a non-magnetic and insulating matrix in nanometer dimensions can pave a way to the production of such small devices. Oxygen reduction in Co3O4/Pd multilayers is possible by local proton irradiation resulting in ferromagnetic and conducting Co embedded in a nonmagnetic and insulating Co3O4 matrix [1].
To understand the mechanism behind this, we analysed in-plane single- and out-of-plane multilayer cobalt oxide films after H+ irradiation. We also confined irradiated areas on films in the range of microns to sub-micron to ascertain the lateral distribution of displaced oxygen, while establishing vertical Co/CoO interfaces which would lead to exchange bias across said interfaces.
Irradiated films were characterized by SQUID magnetometry to estimate the effective O removal. Figure 1 (a) shows hysteresis loops for single layers irradiated with various doses and (b) multilayer systems irradiated with a fixed dose. In (a) we see that irradiating single layer films results in minimal O removal by measuring the saturation magnetization Ms. Geometrical confinement of the irradiated region indeed increases the Ms suggesting lateral O displacement, although this value is still only about 10% of bulk Co metal ((a) inset). The effect is much more pronounced in 0.8 nm CoO multilayers as indicated by the presence of perpendicular magnetic anisotropy (b).
Figure 2 shows a loop shift for the multilayer (green) after field cooling demonstrating the formation of vertical Co/CoO interfaces post irradiation. This result is not seen in a single layer system (orange) as the layer is too thick to maintain a well-defined interface. These findings present new opportunities of device fabrication in single and bilayer systems.
Keywords: ion, irradiation, proton, cobalt oxide, CoO, Co3O4, paramagnetic, ferromagnetic, reduction, removal, oxygen, displacement, exchange, bias, magnetization, antiferromagnetic, perpencular, magnetic, anisotropy
  • Lecture (Conference)
    2019 Joint MMM-Intermag Washington DC, 14.-18.01.2019, Washington DC, USA

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Permalink: https://www.hzdr.de/publications/Publ-30378
Publ.-Id: 30378


Comparison of STED, confocal and optical microscopy of ultra-short pitch cholesterics

Pišljar, J.; Posnjak, G.; Pajk, S.; Godec, A.; Podlipec, R.; Kokot, B.; Muševič, I.
The goal of this work is to compare experimentally achievable resolution limits of three different optical microscopy techniques in chiral nematic liquid crystals: (i) standard optical polarisation microscopy, (ii) confocal optical microscopy using fluorescently labelled liquid crystal and (iii) Stimulated Emission Depletion (STED) microscopy using custom synthesised fluorescent dyes. The microscopy experiments on micrometre thin LC samples reveal that the lateral resolution better than ~90 nm can be achieved using STED technique in thin layers of liquid crystals. The standard optical microscopy with index matching between the objective and the sample cover glass in combination with short-wavelength narrow-band optical illumination is quite competitive to STED technique and optical details as small as ~150 nm could be resolved using aberration limited microscope.
Keywords: Sections, STED, optical microscopy, confocal microscopy, lateral resolution, short pitch cholesteric, fingerprint texture

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Permalink: https://www.hzdr.de/publications/Publ-30376
Publ.-Id: 30376


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U. K.; Faßbender, J.ORC; Makarov, D.ORC
A novel type of artificial magnetoelectric material, which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters, is proposed. It refers to three dimensional curvilinear helimagnets, e.g. torsion springs, embedded in a piezoelectric matrix. In contrast to conventional strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers, we exploit the geometrical coupling of the matrix to the curvilinear helimagnet with intrinsic chiral Dzyaloshinskii–Moriya interactions. Namely, the magnetic state is modified due to the change of geometrical parameters of the curved nanomagnet. Theoretically, the essence of the proposal is analysed for a deformable torsional spring made of helimagnetic material. In response to the geometrical change magnetic phase transition between the homogeneous and a periodically modulated state can be driven in a wide range of geometrical parameters. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical ‘1’ and ‘0’. As the chiral magnetic properties are easier to control by mechanical distortion than effective anisotropies, our concept should lead to a robust design of novel magnetoelectric devices.
Keywords: Curvilinear magnetism, Helimagnet, Magnetoelectric material, Converse magnetoelectric effect

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  • Secondary publication expected from 21.06.2020

Permalink: https://www.hzdr.de/publications/Publ-30375
Publ.-Id: 30375


Gas-liquid two-phase flow in a centrifugal pump mock-up with swirling gas flow injection at 1600 rpm

Bieberle, A.ORC; Schäfer, T.

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1600 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-01-07
    DOI: 10.14278/rodare.223

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Permalink: https://www.hzdr.de/publications/Publ-30374
Publ.-Id: 30374


Gas-liquid two-phase flow in a centrifugal pump mock-up with swirling gas flow injection at 1480 rpm

Bieberle, A.ORC; Schäfer, T.

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 10 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1480 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-01-10
    DOI: 10.14278/rodare.221

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30373
Publ.-Id: 30373


Gas-liquid two-phase flow in a centrifugal pump mock-up with swirling gas flow injection at 1300 rpm

Bieberle, A.ORC; Schäfer, T.

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1300 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-01-07
    DOI: 10.14278/rodare.219

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30372
Publ.-Id: 30372


Gas-liquid two-phase flow in a centrifugal pump mock-up with disperse gas flow injection at 1600 rpm

Bieberle, A.ORC; Schäfer, T.

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1600 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-01-07
    DOI: 10.14278/rodare.217

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30371
Publ.-Id: 30371


Gas-liquid two-phase flow in a centrifugal pump mock-up with disperse gas flow injection at 1480 rpm

Bieberle, A.ORC; Schäfer, T.

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1480 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-01-10
    DOI: 10.14278/rodare.214

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30370
Publ.-Id: 30370


Gas-liquid two-phase flow in a centrifugal pump mock-up with disperse gas flow injection at 1300 rpm

Bieberle, A.ORC; Schäfer, T.

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1300 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2020-01-10
    DOI: 10.14278/rodare.212

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30369
Publ.-Id: 30369


Visualisation of melt flow effects on dendritic solidification

Shevchenko, N.ORC; Keplinger, O.; Eckert, S.ORC
X-ray radioscopic studies have been performed to improve the understanding of the complex interrelation between melt flow and the evolution of dendritic structures during solidification of Ga-In alloys. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. Within this work special interest was focused on dendrite fragmentation and segregation phenomena. Melt convection alters the solutal field near the solidification front, leading to different microstructures or even to the formation of freckle defects. Essential process parameters such as flow patterns, solute concentration, the mushy zone morphology and permeability, dendrite growth velocities were quantified by image analysis. Particular attention is paid to the development of segregation structures and to the “self-healing” process of segregation zones. The observations indicate that if the local melt flow near the solidification front is destabilized, the Indium-rich melt flows inside the channel. The consequence is the “self-healing” process, i.e. the channel is filled in a short time by new dendrites and finally disappears. Eventual mechanisms that destabilize the channel formation are discussed so that the freckle defect can be eliminated by electromagnetic stirring on early stage of solidification. Moreover, our experiments demonstrate how the melt flow contributes to grain refinement, the CET (columnar to equiaxed transition) and dendrite fragments transport, which are discussed intensively in the literature.
Keywords: Solidification; Ga-In alloy; Convection; Freckle defects
  • Lecture (Conference)
    5th International Conference on Advances in Solidification Processes (ICASP-5) & 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5), 17.-21.06.2019, Salzburg, Austria

Permalink: https://www.hzdr.de/publications/Publ-30365
Publ.-Id: 30365


Quantum radiation in dielectric media with dispersion and dissipation

Lang, S.ORC; Schützhold, R.; Unruh, W.
By a generalization of the Hopfield model, we construct a microscopic Lagrangian describing a dielectric medium with dispersion and dissipation. This facilitates a well-defined and unambiguous ab initio treatment of quantum electrodynamics in such media, even in time-dependent backgrounds. As an example, we calculate the number of photons created by switching on and off dissipation in dependence on the temporal switching function. This effect may be stronger than quantum radiation produced by variations of the refractive index Δn(t) since the latter are typically very small and yield photon numbers of order (Δn)². As another difference, we find that the partner particles of the created medium photons are not other medium photons but excitations of the environment field causing the dissipation (which is switched on and off).

Permalink: https://www.hzdr.de/publications/Publ-30364
Publ.-Id: 30364


Off-shell Ward identities for N-gluon amplitudes

Ahmadiniaz, N.ORC; Schubert, C.
Off-shell Ward identities in non-abelian gauge theory continue to be a subject of active research, since they are, in general, inhomogeneous and their form depends on the chosen gauge-fixing procedure. For the three-gluon and four-gluon vertices, it is known that a relatively simple form of the Ward identity can be achieved using the pinch technique or, equivalently, the background-field method with quantum Feynman gauge. The latter is also the gauge-fixing underlying the string-inspired formalism, and here we use this formalism to derive the corresponding form of the Ward identity for the one-loop N - gluon amplitudes.

Permalink: https://www.hzdr.de/publications/Publ-30361
Publ.-Id: 30361


Waves in the magnetized spherical Couette problem.

Garcia Gonzalez, F.ORC; Seilmayer, M.ORC; Giesecke, A.ORC; Stefani, F.ORC
Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. This allows us to carefully investigate the time-scales of the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. In addition, modulated rotating waves, obtained at secondary bifurcations, are exhaustively studied by means of direct numerical simulations, with main focus on their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    Alexander von Humboldt Colloquium “Research without Borders – Alexander von Humboldt’s Legacy Today”, 11.-13.04.2019, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-30360
Publ.-Id: 30360


Experiments and simulations on the magnetized spherical Couette problem

Garcia Gonzalez, F.ORC; Seilmayer, M.ORC; Giesecke, A.ORC; Stefani, F.ORC
Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. Bifurcation diagrams for modulated rotating waves and chaotic flows, obtained by means of DNS, are presented as well. This allows us to carefully investigate the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. The main focus is on studing their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    Bursting the Bubble: Connecting Thermonuclear Burst Research to a Wider Community 2019, 24.-28.06.2019, Leiden, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30359
Publ.-Id: 30359


The Hämmerlein skarn-greisen deposit in the Erzgebirge (Germany) - Analysis, geometallurgy and pre-concentration of a compositionally complex and fine-grained ore deposit

Kern, M.ORC
The polymetallic Hämmerlein skarn-greisen deposit, located in the central portion of the Erzgebirge (Germany), is one of the most promising and prominent tin exploration targets in the world, with indium and zinc as potential by-products. The deposit has been discovered 50 years ago but has never been exploited, primarily because of the challenging beneficiation process. Currently, tin is mainly extracted from placer deposits in the Southeast Asian tin belt and in hydrothermal greisen deposit in China. Economic concentrations of tin are also found in metasomatically altered calc-silicate rocks called tin skarn, which is the predominant rock type at Hämmerlein. The exploitation of such deposits is usually challenging because of their complex mineralogy and fine-grained textures. As the currently mined easy-accessible and high-grade tin deposits are getting fewer, complex tin skarn orebodies have recently become the prime focus of tinexploration. The aim of this thesis is to characterize the ores from the Hämmerlein deposit and to evaluate the success of beneficiation experiments. This is achieved by developing an analytical procedure allowing for deportment analysis of complex ores, by combining geological and geometallurgical understanding of the Hämmerlein orebody, and by developing a novel data-driven approach to determine the optimal sensor that can be used for sensor-based sorting. A newly developed approach for the analysis of fine-grained complex ores combines mineralogical and chemical analysis using a Mineral Liberation Analyzer (MLA), electron probe microanalysis, X-ray powder diffraction, inductively-coupled plasma optical emission spectroscopy and X-ray fluorescence analysis to crushed and uncrushed samples. For MLA analysis, the conventional approach of creating a mineral reference list containing energy-dispersive X-ray (EDX) spectra and information about elemental concentrations and mineral densities did not achieve accurate results for the characterization of some of the samples analyzed. The fine-grained texture of the ore and the presence of a variety of tin-bearing minerals necessitate adding mineral references with manually mixed EDX-spectra, calculated elemental concentrations and calculated densities. Modal mineralogy and calculated assay data obtained by this modified approach for evaluating and processing MLA data is in very good agreement with results from bulk geochemistry and X-ray powder diffraction. The new approach can be adapted to calculate complex metal deportment of other mineralogically complex ore types containing a multitude of ore minerals. Quantitative MLA data from bulk samples and hand specimens are used to interpret the orebody from a geological and geometallurgical perspective. Analyzed samples exhibit considerable variability in modal mineral content and Sn deportment within the different lithounits of the deposit. The systematic differences between lithounits are VIII attributed to several stages of ore formation. The so-called MAMA ratio — a mineral association parameter that is calculated from automated mineralogy data — captures the cassiterite-chlorite-fluorite-sulfide assemblage. This assemblage is identified as the major source of tin in the deposit. It forms stockwork mineralization in greisen-type ores of the footwall and replaces pre-existing skarn lithologies in the hanging wall. These findings provide insight into the genesis of Sn mineralization and also yield important clues for beneficiation. Sensor-based sorting is the most promising technology to separate coarse barren particles from ore particles in the size range between 1 and 10 cm. A newly developed simulation-based approach is applied to find the optimal sensor for sensor-based sorting. Cassiterite is the single most important ore mineral, yet, it is only a very minor constituent (< 4 vol. %), which is heterogeneously distributed and fine-grained, ranging in size from 5 μm to 3 mm. Quantitative mineralogical and textural data from more than 100 thin sections acquired by MLA were taken to capture mineralogical and textural variability of the skarn ore and Schiefererz. Parameters from MLA datasets, such as mineral grain size distribution, modal mineralogy, mineral area and mineral density distribution are used to simulate the prospects of sensor-based sorting using different sensors. The results illustrate that the abundance of rock-forming chlorite and/or density anomalies may well be used as proxies for the abundance of cassiterite. Synchronization of MLA data and analysis of the same material with commercially available sensors illustrates excellent correspondence. Sorting of the Hämmerlein ore may well be achieved by using a shortwavelength infrared detector — to quantify the abundance of chlorite — or a dual-energy X-ray transmission detector to determine the abundance dense components. In summary, this thesis uses MLA data to assess the beneficiation potential of the Hämmerlein deposit by distinguishing between recoverable and unrecoverable Sn, evaluating processing strategies and by determining optimal sensors for sensor-based sorting. The presented approaches, beneficiation strategies and analytical procedures can be adapted for other ore types and have the potential to become standard technologies for the assessment of complex deposits.
  • Doctoral thesis
    TU Bergakademie Freiberg, 2019

Permalink: https://www.hzdr.de/publications/Publ-30358
Publ.-Id: 30358


Convection and magnetohydrodynamics in rotating spherical geometry: Simple models and their application to astrophysics

Garcia Gonzalez, F.ORC
Spherical geometry and rotation are key factors for the study of many geophysical and astrophysical phenomena. In addition, strong temperature gradients develop in planetary and stellar fluid interiors. The Boussinesq approximation is a basic step for understanding flow dynamics in such environments. The formulation and numerical approach to this approximation in the context of thermal convection in rapidly rotating thin shells will be presented together with the main parameters describing the problem. The application to several geophysical (planetary atmospheres or cores) and astrophysical (white dwarfs, neutron stars...) contexts will be outlined.

As an example of simple magnetohydrodynamics problem, the magnetised spherical Couette system will be considered. Some interesting applications to the astrophysical community and advanced experiments of this problem will be commented.
  • Invited lecture (Conferences)
    Bursting the Bubble: Connecting Thermonuclear Burst Research to a Wider Community 2019, 24.-28.06.2019, Leiden, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30357
Publ.-Id: 30357


Die Auswahl eines optimalen Sensors zur sensor-basierten Sortierung unter Anwendung automatisierter Mineralogie in Kombination mit Maschinellem Lernen

Kern, M.ORC; Tusa, L.; Khodadadzadeh, M.ORC; Leißner, T.; van den Boogaart, K. G.ORC; Gloaguen, R.ORC; Gutzmer, J.ORC
Sensor-basierte Sortierung ist eine Technologie, die in zunehmendem Maße zur Aufbereitung von Primärrohstoffen verwendet wird. Um beurteilen zu können, ob der Einsatz sensor-basierter Sortierung zur Anreicherung eines bestimmten Erzes wirtschaftlich eingesetzt werden kann, werden nach Stand der Technik zeitaufwändige und teure empirische Teststudien durchgeführt. Mit dem hier vorgestellten innovativen simulations-basierten Ansatz ist es möglich, die Auswahl eines Sensors auf Grundlage von quantitativen mineralogischen und texturellen Daten zu treffen. Solche Daten können mit verfügbaren Methoden der automatisierten Mineralogie rasch und kostengünstig erhoben werden. Das dokumentierte Fallbeispiel basiert auf Daten aus mehr als 100 Dünnschliffen von zwei verschiedenen Erztypen aus der Sn-In-Zn Lagerstätte Hämmerlein, Erzgebirge. Die Proben wurden ausgewählt, um die mineralogische und texturelle Variabilität zu erfassen. Parameter wie Mineralkorngrößenverteilung, modale Mineralogie, Mineralflächen- und Mineraldichteverteilung wurden verwendet, um die Erfolgsaussichten einer sensorgestützten Sortierung mit verschiedenen Sensoren zu simulieren. Die Ergebnisse zeigen, dass die Häufigkeit von gesteinsbildendem Chlorit und/oder Dichteanomalien als Proxy für die Häufigkeit von Kassiterit, dem Haupterzmineral, verwendet werden können. Dies deutet darauf hin, dass die Sortierung des Hämmerlein-Erzes entweder mit einem Kurzwellen-Infrarotdetektor zur Quantifizierung des Chloritgehalts oder einem Dual-Energy-Röntgentransmissionsdetektor zur Abschätzung des Kassiteritgehalts erreicht werden kann. Die Abschätzung des Kassiteritgehalts einer Probe wurde durch Maschinelles Lernen optimiert, indem die Daten des Kurzwellen-Infrarot-Detektors mit den mineralogischen Daten integriert wurden. Dies führt zu einer weiteren, wichtigen Verbesserung der simulierten Ergebnisse. Empirische Tests mit handelsüblichen Sensorsystemen wurden genutzt, um die Vorhersagen der Simulationen experimentell zu validieren. Der entwickelte Ansatz kann sehr einfach auf andere Rohstofftypen angepasst werden; er birgt damit großes Potenzial, eine Schlüsseltechnologie zur Optimierung von Aufbereitungsprozessen zu werden.
  • Contribution to proceedings
    Tagung Aufbereitung und Recycling, 07.-8.11.2019, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30356
Publ.-Id: 30356


Experiments and simulations on the magnetized spherical Couette problem

Garcia Gonzalez, F.ORC; Seilmayer, M.ORC; Giesecke, A.ORC; Stefani, F.ORC
Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. Bifurcation diagrams for modulated rotating waves and chaotic flows, obtained by means of DNS, are presented as well. This allows us to carefully investigate the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. The main focus is on studing their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.
  • Poster
    11th pamir International Conference Fundamental and Applied MHD 2019., 01.-05.07.2019, Reims, France

Permalink: https://www.hzdr.de/publications/Publ-30355
Publ.-Id: 30355


Correction to. The inherent link between ore formation and geometallurgy as documented by complex tin mineralization at the Hämmerlein deposit (Erzgebirge, Germany)

Kern, M.ORC; Kästner, J.; Tolosana Delgado, R.; Jeske, T.; Gutzmer, J.ORC
We noticed that the presented formula for calculation of the MAMA ratio requires clarification in two places.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30354
Publ.-Id: 30354


Pair production in temporally and spatially oscillating fields

Kohlfürst, C.ORC; Aleksandrov, I. A.
Electron-positron pair production for inhomogeneous electric and magnetic fields oscillating in space and time is investigated. By employing accurate numerical methods (Furry-picture quantization and quantum kinetic theory), final particle momentum spectra are calculated and analyzed in terms of effective models. Furthermore, criteria for the applicability of approximate methods are derived and discussed. In this context, special focus is placed on the local density approximation, where fields are assumed to be locally homogeneous in space. Eventually, we apply our findings to the multiphoton regime. Special emphasis is on the importance of linear momentum conservation and the effect of its absence in momentum spectra within approximations based on local homogeneity of the fields.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-30353
Publ.-Id: 30353


Chaotic and oscillatory flows in the magnetized spherical Couette system.

Garcia Gonzalez, F.ORC; Seilmayer, M.ORC; Stefani, F.ORC
Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for modulated rotating waves and chaotic flows are obtained for investigating the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies.
  • Invited lecture (Conferences)
    9th International Congress on Industrial and Applied Mathematics, ICIAM 2019, 15.-19.07.2019, Valencia, Spain

Permalink: https://www.hzdr.de/publications/Publ-30352
Publ.-Id: 30352


The MAMA ratio: An index that quantifies genetic and geometallurgic relationships

Kern, M.ORC; Kästner, J.; Tolosana Delgado, R.; Jeske, T.; Gutzmer, J.ORC
A comprehensive quantitative mineralogical study on the Hämmerlein tin deposit in the Erzgebirge, Germany, yields not only insights into the genesis of Sn mineralization but provides also important clues for beneficiation. The lithological units of the skarn and greisen deposit show significant differences in modal mineralogy and Sn deportment. These systematic differences are attributed to several stages of ore formation. Of greatest significance is a paragenetically late cassiterite-chlorite-fluorite-sulfide assemblage. This assemblage replaces pre-existing skarn lithologies and also forms stockwork mineralization in greisen-type ores developed at the expense of mica schist that surrounds the skarn. The co-genetic formation of the cassiterite-chlorite-fluorite-sulfide assemblage is captured by the mineral association parameter – a parameter that can be easily quantified from data acquired during automated mineralogy studies. To document the preferred mineral association a ratio is introduced that illustrates how closely cassiterite – the only Sn mineral of economic relevance – is associated with chlorite, fluorite and sulfides. This so-called MAMA ratio illustrates the strongly preferred association between cassiterite and chlorite. The same data can also be used to deduce constraints and opportunities for beneficiation. The case study illustrates the inherent link between ore genesis and process mineralogy – a link that should be considered in any geometallurgical assessment.
  • Contribution to proceedings
    GOOD Meeting 2019, 22.-24.01.2019, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30351
Publ.-Id: 30351


On the effect of time-dependent inhomogeneous magnetic fields on the particle momentum spectrum in electron-positron pair production

Kohlfürst, C.ORC
Electron-positron pair production in spatially and temporally inhomogeneous electric and magnetic fields is studied within the Dirac-Heisenberg-Wigner formalism (quantum kinetic theory) through computing the corresponding Wigner functions. The focus is on discussing the particle momentum spectrum regarding signatures of Schwinger and multiphoton pair production. Special emphasis is put on studying the impact of a strong dynamical magnetic field on the particle distribution functions. As the equal-time Wigner approach is formulated in terms of partial integro-differential equations an entire section of the manuscript is dedicated to present numerical solution techniques applicable to Wigner function approaches in general.

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  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-30350
Publ.-Id: 30350


On self-created and self-creating dynamos

Stefani, F.ORC
The lecture gives an overview about recent and future (self-created) liquid metal experiments on dynamo action and magnetically triggered flow instabilities. Some aspects of non-linear (self-creating) dynamos, in which induction and flow instabilities conspire to provide self-excitation, are also discussed.
  • Invited lecture (Conferences)
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France

Permalink: https://www.hzdr.de/publications/Publ-30349
Publ.-Id: 30349


Measure where protons stop in the patient: Verification of proton therapy by means of prompt gamma rays

Khamfongkhruea, C.; Nenoff, L.; Priegnitz, M.; Barczyk, S.; Berthold, J.; Vander Stappen, F.; Petzoldt, J.; Smeets, J.; Enghardt, W.ORC; Pausch, G.ORC; Richter, C.ORC
Introduction
Proton therapy is the most advanced radiotherapeutic technique. For the same dose in the tumor, the dose in the surrounding normal tissue is substantially lower than in classical radiation therapy using photon beams. Protons stop in the patient and no dose is deposited behind that position. However, the resulting dose deposition is more sensitive to anatomical changes during treatment and to uncertainties in the CT-based range calculation. Therefore, monitoring of the proton range during treatment would substantially improve proton therapy. Prompt gamma radiation, which is emitted in nuclear reactions of the proton beam with the patient’s tissue, can be used to conclude on the proton range. The most translational advanced approach is prompt-gamma imaging (PGI) using a so-called slit camera [1]. A one-dimensional projection of the prompt-gamma distribution is acquired through a slit collimator onto a spatially resolved detector (Fig.1). The system, developed by IBA, is evaluated concerning its clinical benefit.

Materials and Methods
The PGI slit-camera was first enabled for routine clinical use by developing dedicated calibration and QA procedures as well as a clinical workflow and setting up a clinical study. In 2015, we were able to perform the first in-man PGI-based range verification [2], 13 years after the idea was initially proposed. In addition, the sensitivity and accuracy of the PGI slit-camera to detect different types of treatment deviations were evaluated for pencil-beam-scanning (PBS) proton therapy in an anthropomorphic phantom [3]. Following, a 2nd generation system was developed to improve positioning accuracy and reproducibility. Clinical application of this system in PBS proton therapy started in 2018.

Results
In the first in-man applications, detected inter-fractional global range variations were below ±2 mm, and thereby within the overall measurement uncertainties. This was verified with independent control CTs acquired directly before treatment. The phantom study revealed, that global and local range shifts can be detected with high sensitivity. Shift detection accuracy was better than 2 mm under clinical conditions. With the 2nd generation system, positioning uncertainty could be reduced to about 1 mm, potentially allowing a first in-man validation of the absolute range prediction as the measurement uncertainty is below the range prediction uncertainty.

Conclusion
With the translation from basic physics experiments into clinical operation, we were able to demonstrate the applicability of PGI-based range verification for improving the accuracy of proton therapy. Currently, we systematically evaluate the clinical benefit of the approach aiming for an automated detection of clinical relevant treatment deviation and classification of the underlying error source.
  • Poster
    1. German Cancer Research Congress - GCRC, 04.-05.02.2019, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30348
Publ.-Id: 30348


Polar Waves and Chaotic Flows in Thin Rotating Spherical Shells

Garcia Gonzalez, F.ORC; Chambers, F.; Watts, A.
Convection in rotating spherical geometries is an important physical process in planetary and stellar systems. Using continuation methods at a low Prandtl number, we find both strong equatorially asymmetric and symmetric polar nonlinear rotating waves in a model of thermal convection in thin rotating spherical shells with stress-free boundary conditions.
For the symmetric waves, convection is confined to high latitude in both hemispheres but is only restricted to one hemisphere close to the pole in the case of asymmetric waves. This is in contrast to what is previously known from studies in the field. These periodic flows, in which the pattern is rotating steadily in the azimuthal direction, develop a strong axisymmetric component very close to onset. Using stability analysis of periodic orbits, the regions of stability are determined and the topology of the stable/unstable oscillatory flows bifurcated from the branches of rotating waves is described. By means of direct numerical simulations of these oscillatory chaotic flows, we show that these three-dimensional convective polar flows exhibit characteristics, such as force balance or mean physical properties, which are similar to flows occurring in planetary atmospheres.
We show that these results may open a route to understanding unexplained features of gas giant atmospheres, particularly in the case of Jupiter. These include the observed equatorial asymmetry with a pronounced decrease at the equator (the so-called dimple), and the coherent vortices surrounding the poles recently observed by the Juno mission.
Keywords: Astrophysical fluid dynamics, Bifurcations, Convection, Geophysical fluid dynamics, Rotating geophysical flows

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Permalink: https://www.hzdr.de/publications/Publ-30347
Publ.-Id: 30347


Dual-energy computed tomography for improved proton therapy treatment planning

Peters, N.; Wohlfahrt, P.ORC; Möhler, C.; Greilich, S.; Richter, C.ORC
Purpose/Objective:
Cancer treatment with protons requires an accurate prediction of the particle’s range in tissue. In cCurrently clinical practice, computed tomography (CT) images are used to voxelwise translate the CT number into the tissue’s stopping power relative to water (SPR) via heuristic relations (HLUT). However, the general validity of this approach is limited due to the different physical interaction processes of photons and ions. The resulting range uncertainty is taken into account in the treatment plan by adding a safety margin around the tumor, effectively limiting the potential benefits of particle therapy over conventional radiotherapy. The use of dual-energy CT (DECT) allows for a direct derivation of tissue parameters, resulting in a better characterization of the tissue. The potential of a DECT-based,and ultimately allows a patient-individualized range prediction (DirectSPR) has been shown in previous work. In 2015, we were first to introduce DECT scans for routine clinical treatment planning, still using a generic HLUT. Here, we portray the next steps towards the full clinical implementation of DirectSPR, namely its validation and assessment of its clinical benefit.

Material and Methods:
To validate the method for realistic clinical scenarios, its accuracy was investigated in an anthropomorphic head phantom as well as in porcine biological tissue. Furthermore, intra- and inter-patient variabilities in CT-based SPR prediction were investigated in a retrospective analysis of 102 brain-tumor and 25 prostate-cancer patients. The clinical HLUT was then refined by performing a step-wise weighted linear fit of the resulting SPR distribution in different tissue regionsusing the DirectSPR information of the investigated patient cohort. To assess the effect of this refinement on the proton range within the patient, treatment plans were recalculated using the clinical HLUT, the refined HLUT as well as the DirectSPR approach.

Results:
In the complex head geometry, DirectSPR showed an improved accuracy compared to the clinical HLUT approach. For biological tissues in a simple geometry, an accuracy below 0.2% could be achieved. Between clinical HLUT and DirectSPR, mean range differences (±1SD) of (1.2±0.7)% for brain-cancer and (1.7±0.5)% for prostate-tumor patients were determined. By refining the HLUT, they were significantly reduced (p≪0.001, two-sample t-test) below 0.3%. HoweverMoreover, an observed intra-patient soft-tissue diversity of 6% as well as an inter-patient bone diversity of 5%, underline an additional benefit of the DirectSPR approach, as such variabilities cannot be considered by any generic HLUT-based range prediction.

Conclusions:
The clinical feasibility of DirectSPR for proton range prediction as well as its advantage over the HLUT approach has been demonstrated. A retrospective application on patient data allowed for a reduction of systematic deviations found in clinical HLUT. The refined HLUT was implemented at our institution as a step towards the currently ongoing full integration of DirectSPR. The Its higher precision accuracy in range prediction is reflected in a potentially allows a reduction of the safety margin, which is currently under investigation.
  • Poster
    1. German Cancer Research Congress GCRC, 04.-05.02.2019, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30346
Publ.-Id: 30346


A model for tidal synchronization and modulation of the solar dynamo

Stefani, F.ORC; Giesecke, A.ORC; Weier, T.
We present a solar dynamo model of Tayler-Spruit type with an Omega-effect that is conventionally produced by solar-like differential rotation, while its alpha-effect is periodically modulated by planetary tidal forcing. The underlying resonance builds upon the tendency of the Tayler instability to generate helicity oscillations which can be synchronized by periodic tidal forces. We focus on the 11.07 years alignment periodicity of the planets Venus, Earth, and Jupiter and analyze its synchronization with the solar dynamo. The typically emerging dynamo modes are dipolar or quadrupolar fields, oscillating with a 22.14 years period or pulsating with a 11.07 years period. When starting from a conventional alpha-Omega-dynamo, the addition of the periodic alpha-part can lead to entrainment of the entire dynamo via parametric resonance. Phase coherent transitions between dipoles and quadrupoles are discussed, too.
  • Lecture (Conference)
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
  • Contribution to proceedings
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
    Proceedings of the 11th PAMIR International Conference - Fundamental and Applied MHD, Reims, France: University of Reims Champagne-Ardenne, 43-47

Permalink: https://www.hzdr.de/publications/Publ-30345
Publ.-Id: 30345


Dual Energy - Stopping Power Ratio: Facilitating clinical implementation of Dual Energy CT-based stopping power prediction – What‘s the benefit?

Richter, C.ORC; Möhler, C.
Facilitating clinical implementation of Dual Energy CT-based stopping power prediction – What‘s the benefit?
  • Invited lecture (Conferences)
    Siemens Healthineers Lunch Symposium at ESTRO 38, 29.04.2019, Milano, Italia

Permalink: https://www.hzdr.de/publications/Publ-30344
Publ.-Id: 30344


CT-based delineation: What can we gain from state-of-the-art CT image acquisition and reconstruction techniques?

Richter, C.ORC; Negwer, F.; Troost, E. G. C.ORC; Wohlfahrt, P.ORC
X-ray computed tomography (CT) has been the standard imaging modality in radiation oncology for both, treatment planning and delineation of targets and organs at risk for decades. For further improvement, especially for delineation, magnetic resonance imaging (MRI) and positron emission tomography (PET) are being extensively investigated and more often included into clinical routines. They can provide better soft tissue contrast and functional information. Still, also in the field of CT imaging relevant improvements have been made, that are not so much in the spotlight. Hence, this talk will focus on novel CT image acquisition and reconstruction techniques and their potential benefit for radiation oncology applications.
First, the potential value of dual-energy CT (DECT) for delineation will be discussed. DECT has already been proven to allow for a more accurate treatment planning, especially in particle therapy. It provides additional tissue information compared to conventional CT imaging. Furthermore, DECT enables the reconstruction of different CT datasets with varying image contrasts. Currently, it is unproven whether this additional information translates into improvement of the segmentation and delineation quality. The exploration of this benefit in combination with machine learning approaches is envisioned. First studies will be presented.
Second, the potential of iterative CT reconstruction methods will be highlighted. They allow for a substantial reduction of imaging dose to reach a similar noise level as conventional filtered back projection. Hence, iterative reconstruction is of high relevance for adaptive protocols as it reduces the dose burden from more frequent CT imaging during treatment.
Third, the value and challenges of metal artefact reduction algorithms will be covered. It has been shown that the visual image impression can be substantially improved for regions suffering from metal artefacts in conventional CT reconstruction, suggesting a direct benefit for delineation purposes. However, as these algorithms can also quantitatively alter the image in regions not influenced by metal artefacts, great care should be taken – especially in particle therapy planning.
In summary, state-of-the-art CT imaging can provide additional value for radiation oncology purposes. This talk aims to increase awareness of this potential. By revisiting the institutional imaging protocol, one can potentially improve the image quality for delineation and/or safe dose to patients.
  • Invited lecture (Conferences)
    ESTRO 38, 26.-30.04.2019, Milano, Italia
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 133(2019), S361-S361
    DOI: 10.1016/S0167-8140(19)31118-1

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Permalink: https://www.hzdr.de/publications/Publ-30343
Publ.-Id: 30343


Translational medical physics research: Increasing accuracy in particle therapy towards its physical limit

Richter, C.ORC
Translational medical physics research: Increasing accuracy in particle therapy towards its physical limit
  • Invited lecture (Conferences)
    Sino-German Round Table Symposium on Cancer Precision Medicine in the Era of Big Data, 19.-20.06.2019, Tianjin, China

Permalink: https://www.hzdr.de/publications/Publ-30342
Publ.-Id: 30342


Bildgeführte Teilchentherapie und Bestrahlungs-Verifizierung

Richter, C.ORC
Bildgeführte Teilchentherapie und Bestrahlungs-Verifizierung
  • Invited lecture (Conferences)
    Fachkundekurs und Aktualisierungskurs für die Partikeltherapie, 07.-09.11.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30341
Publ.-Id: 30341


Dual-Energy CT for particle therapy planning and beyond

Richter, C.ORC
Dual-Energy CT for particle therapy planning and beyond
  • Invited lecture (Conferences)
    ESTRO School: Imaging for Physicists, 29.09.-03.10.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30340
Publ.-Id: 30340


CT-based in-room imaging

Richter, C.ORC
CT-based in-room imaging
  • Invited lecture (Conferences)
    ESTRO School: Imaging for Physicists, 29.09.-03.10.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30339
Publ.-Id: 30339


CT for radiotherapy planning

Richter, C.ORC
CT for radiotherapy planning
  • Invited lecture (Conferences)
    ESTRO School: Imaging for Physicists, 29.09.-03.10.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30338
Publ.-Id: 30338


Clinical implementation of TPS-independent DECT-based patient-individual SPR prediction and its way into Raystation

Richter, C.ORC; Wohlfahrt, P.ORC
Clinical implementation of TPS-independent DECT-based patient-individual SPR prediction and its way into Raystation
  • Invited lecture (Conferences)
    Raysearch Particle Premeeting at PTCOG, 12.06.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30337
Publ.-Id: 30337


The DRESDYN Project at HZDR

Stefani, F.ORC; Eckert, S.ORC; Gerbeth, G.; Giesecke, A.ORC; Seilmayer, M.ORC; Vogt, T.ORC
We discuss the background and the recent status of the DRESDYN project at HZDR. Special focus is laid on the relation with sodium flow problems specific to SFR's.
  • Lecture (Conference)
    ESFR-SMART workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30336
Publ.-Id: 30336


Bubble Generation at Micro-Orifices with Application to Wastewater Treatment

Mohseni, E.ORC; Reinecke, S. F.; Hampel, U.
Many chemical, biochemical and environmental processes are characterized by inefficient mass transfer and mixing. This hold particularly for aeration and ozonisation in waste water treatment. Therefore, technologies for efficient fine gas dispersion and creation of small gas bubbles are of interest. One way to achieve finer gas dispersion is to scale-down the opening at which the gas bubbles are generated. At very small openings, the bubble formation process is highly influenced by high capillary pressure and gas kinetic energy. So far, the leverage of small orifices, especially smaller than 1 mm, to the final gas bubble size is not well understood. In the current investigation, we experimentally studied the dynamics of gas bubble formation from submerged orifices ranging between 0.04 and 0.8 mm in a wide range of gas flow rates. We observed different mechanisms of bubble formation at micro-orifices compared to millimetre orifices. Moreover, we present a bubbling regime map to describe the dynamic behaviour of forming bubbles. Finally, to evaluate the performance of micro-orifice spargers, we compared them with industrial rubber membrane diffusers with respect to the Sauter mean bubble diameter.
Keywords: Bubble Generation; Micro-orifices; Aeration; Biological Wastewater Treatment; Rubber Membrane Diffusers
  • Poster
    LET2019- The 16th IWA Leading Edge Conference on Water and Wastewater Technologies, 10.-14.06.2019, Edinburgh, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30335
Publ.-Id: 30335


Planetary dynamos in the lab

Stefani, F.ORC
Magnetic fields of planets are known to be generated by the homogeneous dynamo effect in moving liquid metals, such as iron or metallic hydrogen. For a long time, hydromagnetic dynamos have been the subject of purely theoretical and numerical research. This situation changed in 1999 when the threshold of magnetic-field self-excitation was crossed in the two large-scale liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced key processes of geophysical interest such as reversals and excursions. Further liquid metal experiments in Grenoble, Madison, Maryland, Perm, Princeton, Perm, Queretaro, and Socorro have contributed important findings to dynamo research. After giving an overview about those recent achievements, the talk will delineate the present status of the DRESDYN precession experiment at HZDR. A few further issues connected with the experimental demonstration of magnetically triggered flow instabilities, such as magnetorotational and Tayler instability, are also discussed.
  • Invited lecture (Conferences)
    8th Joint Workshop on High Pressure, Plnaetary and Plasma Physics (HP4), 09.-11.10.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30334
Publ.-Id: 30334


Schwabe, Gleissberg, Suess-de Vries: A simple model for synchronizing solar cycles by planetary forces

Stefani, F.ORC; Giesecke, A.ORC; Seilmayer, M.ORC; Stepanov, R.; Weier, T.
Aiming at a simple and consistent planetary synchronization model of both short-term and long-term solar cycles we analyze Schove's data of the cycle minima and maxima. Their residuals from the average cycle duration of 11.07 years show a high degree of regularity, comprising a dominant period of 200 years (Suess-de Vries cycle), and a few periods around 90 years (Gleissberg cycle). Based on Dicke's ratio between the mean square of the residuals to the mean square of the difference of two consecutive residuals, we conjecture that the Schwabe cycle is synchronized, very likely via a helicity-mediated parametric resonance, by the 11.07 years alignment cycle of the tidally dominant planets Venus, Earth and Jupiter. In an attempt to explain the rather regular long-term behaviour, we enhance our Parker-type solar dynamo model by a modulation of the field-storage capacity of the tachocline with the 19.86 years periodicity of the movement of the sun around the barycenter of the solar system, which results basically from the Jupiter-Saturn synodes. Not surprisingly, this modulation leads to a 193-year beat period of dynamo activity which is indeed close to the observed 200 years Suess-de Vries cycle. In cases, the model produces also additional peaks at typical Gleissberg frequencies, which might be interpreted as beat periods of the Schwabe cycle with the Jupiter-Uranus (13.81-year) or the Jupiter-Neptune (12.78-year) synodes.
  • Invited lecture (Conferences)
    4th Dynamo Thinkshop, 25.-26.11.2019, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-30333
Publ.-Id: 30333


Sustaining turbulence in spectrally stable shear flows – interplay of linear transient growth and nonlinear transverse cascade

Gogichaishvili, D.; Mamatsashvili, G.; Horton, W.; Chagelishvili, G.
We analyze the sustaining mechanism of nonlinear perturbations/turbulence in spectrally stable smooth shear flows. The essence of the sustenance is a subtle interplay of linear transient growth of Fourier harmonics and nonlinear processes. In spectrally stable shear flows, the transient growth of perturbations is strongly anisotropic in spectral (k-)space. This, in turn, leads to anisotropy of nonlinear processes in k-space and, as a result, the main (new) nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that nonlinear state is sustained owing to the interplay of the linear nonmodal growth and the transverse cascade. The possibility of such course of events has been described in k-space by G. Chagelishvili, J.-P. Zahn, A. Tevzadze and J. Lominadze, A&A, 402, 401 (2003) that reliably exemplifies the well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. We present selected results of the simulations performed in different (HD and MHD; 2D and 3D; plane and Keplerian) shear flows to demonstrate the transverse cascade in action.
Keywords: nonmodal growth, turbulence, magnetorotational instability, MHD, self-sustaining process, transverse cascade
  • Contribution to proceedings
    Astro Fluid: An International Conference in Memory of Professor Jean-Paul Zahn's Great Scientific Achievements, 27.06.2016, Paris, Frankreich
    EAS Publications Series, volume 82, 2019, pp.423 - 434
    DOI: 10.1051/eas/1982037

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Permalink: https://www.hzdr.de/publications/Publ-30332
Publ.-Id: 30332


Nonlinear transverse cascade – a key factor of sustenance of subcritical turbulence in shear flows

Gogichaishvili, D.; Mamatsashvili, G.ORC; Chagelishvili, G.; Horton, W.
We analyze the essence of nonlinear processes that underlie turbulence sustenance in spectrally stable shear flows. In these flows, the strong anisotropy of velocity shear-induced nonmodal growth phenomenon in spectral (k-)space, in turn, entails the anisotropy of nonlinear processes in this space. Consequently, the main novel nonlinear process is transverse, or angular redistribution of modes in Fourier space referred to as the nonlinear transverse cascade rather than a mere direct/inverse cascade. It is demonstrated that nonlinear coherent as well as turbulent states are sustained via a subtle interplay of the linear nonmodal growth (that has transient nature) and the nonlinear transverse cascade. This course of events exemplifies the well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. In this proceedings paper, we present selected results of our simulations of hydrodynamic and MHD 2D plane shear flows to demonstrate the transverse cascade in action.
Keywords: nonmodal growth, instabilities, turbulence, MHD, transverse cascade, self-sustaining process
  • Contribution to proceedings
    Turbulent Cascades II, 05.12.2017, Lyon, Frankreich
    Turbulent Cascades II -- Proceedings of the Euromech-ERCOFTAC Colloquium 589
    DOI: 10.1007/978-3-030-12547-9_12

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Permalink: https://www.hzdr.de/publications/Publ-30331
Publ.-Id: 30331


MHD turbulence in Keplerian disks – specific anisotropy of nonlinear processes, active modes, dynamical balances and sustenance

Mamatsashvili, G.
We investigate MHD turbulence in Keplerian disk flows threaded by a non-zero net azimuthal magnetic flux. In order to gain a deeper insight into the underlying dynamical balances and sustaining mechanism, we performed a set of numerical simulations in the shearing box model and based on the simulation data, analyzed in detail the turbulence dynamics in Fourier/wavenumber space. In the case of a net azimuthal field, classical exponential/modal instabilities are absent in the disk flow and linear growth of perturbations (shearing waves) is transient, also referred to as nonmodal growth. Namely, in the presence of disk rotation, radial shear and azimuthal field, the magnetorotational instability (MRI), being only available source of energy for turbulence, takes on transient character and, therefore, by itself, cannot ensure a long-term sustenance of the perturbations, i.e., it is “imperfect” in this sense. A necessary positive nonlinear feedback is required to regenerate nonmodally growing modes. In other words, the role of nonlinearity becomes crucial in this case: it lies at the heart of the sustenance of turbulence. The detailed analysis of the dynamics in Fourier space, allows us to demonstrate existence of the positive feedback. Specifically, the main novelties of our findings are the following:
1. The nonmodal MRI growth process is strongly anisotropic in Fourier space that, in turn, leads to anisotropy of nonlinear processes in this space. As a result, the main nonlinear process appears to be not a usual and well-known direct/inverse, but rather a new type of transverse/angular redistribution of perturbation modes in Fourier space, when their wavevector changes mostly its orientation (and not its magnitude) during nonlinear interactions. We refer to this angular transfer as the nonlinear transverse cascade.
2. Both the linear nonmodal growth of MRI and nonlinear transverse cascade mainly operate/dominate at large length scales, comparable to the box/system size. Consequently, the corresponding central, small wavenumber area of Fourier space is crucial in the turbulence sustenance process and is thus called the vital area.
3. We demonstrate that the turbulence in disks with net azimuthal field is sustained by a subtle interplay of the linear nonmodal growth of MRI and the nonlinear transverse cascade. Analyzing this interplay, we revealed the basic subcycle of the sustenance scheme that clearly shows synergy of the linear and nonlinear processes in the self-organization of the magnetized flow system.
Keywords: nonmodal growth, magnetorotational instability, turbulence, MHD
  • Open Access Logo Lecture (Conference)
    Turbulence & magnetic fields - from the early universe to late-type stars, 01.04.2019, Tuusula, Finland

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Permalink: https://www.hzdr.de/publications/Publ-30330
Publ.-Id: 30330


A new type of double-diffusive helical magnetorotational instability in rotational flows with positive shear

Mamatsashvili, G.ORC; Stefani, F.ORC; Hollerbach, R.; Rüdiger, G.
We revealed a novel type of linear axisymmetric helical magnetorotational instability in viscous and resistive rotating flows with radially increasing angular velocity, or positive shear, exposed to a helical magnetic field. It operates for a broad range of positive shear, provided that magnetic Prandtl number is not unity. This instability can play an important role in the magnetic activity of the equatorial parts of the solar tachocline, where the shear of differential rotation is positive.
Keywords: magnetorotational instability, liquid metals, MHD, solar tachocline
  • Open Access Logo Lecture (Conference)
    11th Pamir International Conference on Fundamental and Applied MHD, 01.07.2019, Reims, France
  • Open Access Logo Lecture (Conference)
    8-th International Symposium on Bifurcations and Instabilities in Fluid Dynamics, 16.07.2019, Limerick, Ireland

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Permalink: https://www.hzdr.de/publications/Publ-30329
Publ.-Id: 30329


Implantation experiments to check the Plasma Immersion Ion Implantation quality

Yankov, R.; Julin, J. A.ORC; Munnik, F.ORC; Skorupa, W.
Projekttreffen-relevanter Vortrag zur ERDA-Untersuchung von Fluor in Nickel-basierten Legierungen nach Plasma-Immersions-Implantation
Keywords: ERDA-Untersuchung, Fluor, Nickel-basierte Legierungen, Plasma-Immersions-Implantation
  • Lecture (others)
    Projektausschußsitzung "Nickelbasierte Legierungen", 04.06.2019, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30326
Publ.-Id: 30326


Hochtemperaturoxidationsschutz für Nickelwerkstoffe durch Fluorimplantation

Donchev, A.; Yankov, R.; Skorupa, W.; Galetz, M.
Projekttreffen-relevanter Vortrag zur Korrosions- und mikrostrukturellen Untersuchung von Nickel-basierten Legierungen nach Plasma-Immersions-Implantation mit Fluor
Keywords: Fluor, Nickel-basierte Legierungen, Plasma-Immersions-Implantation, Korrosionsunterdrückung, Mikrostruktur
  • Lecture (others)
    Projektausschußsitzung "Nickelbasierte Legierungen", 04.06.2019, Braunschweig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30325
Publ.-Id: 30325


Hochtemperaturoxidationsschutz für Nickelwerkstoffe durch Fluorimplantation

Donchev, A.; Yankov, R.; Skorupa, W.; Galetz, M.
Projekttreffen-relevanter Vortrag zur Korrosions- und mikrostrukturellen Untersuchung von Nickel-basierten Legierungen nach Plasma-Immersions-Implantation mit Fluor
Keywords: Fluor, Nickel-basierte Legierungen, Plasma-Immersions-Implantation, Korrosionsunterdrückung, Mikrostruktur
  • Lecture (others)
    Projektausschußsitzung "Nickelbasierte Legierungen", 03.12.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30324
Publ.-Id: 30324


ERDA for more Fluorine in Nickel-based alloys

Yankov, R.; Julin, J. A.ORC; Munnik, F.ORC; Skorupa, W.
Projekttreffen-relevanter Vortrag zur ERDA-Untersuchung von Fluor in Nickel-basierten Legierungen nach Plasma-Immersions-Implantation
Keywords: ERDA-Untersuchung, Fluor, Nickel-basierte Legierungen, Plasma-Immersions-Implantation
  • Lecture (others)
    Projektausschußsitzung "Nickelbasierte Legierungen", 03.12.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30323
Publ.-Id: 30323


The Nam Xe REE-Project in Vietnam - From Mineralogy to Possible Processing Routes

Möckel, R.ORC; Heinig, T.; Cardenas Vera, A. F.; Merker, G.; Quang, V. P.; Gutzmer, J.ORC
The Nam Xe deposit in northern Vietnam is a promising REE prospect. A German-Vietnamese cooperative project included massive pre-mining environmental monitoring, detailled mineralogical investigation and processing experiments. Outcomes were detailled mapping results of radioactive elements and a first suggestion for a processing route of the REE ore, including sensor sorting and a two stage flotation scheme.
Keywords: Nam Xe, rare earth elements, flotation, sensor sorting
  • Lecture (Conference)
    HiTech AlkCarb and SoS RARE celebratory and results launch event, 26.-27.11.2019, London, UK

Permalink: https://www.hzdr.de/publications/Publ-30322
Publ.-Id: 30322


Antikorrosive Wirkung nanoskaliger Schichten auf metallischen Legierungen im Orgelbau

Skorupa, W.; Quade, A.; Schäfer, J.; Schumann, T.; Eule, D.
Der Vortrag beschäftigt sich mit den Ergebnissen von zwei durch die Sächsische Aufbaubank in Kombination zu EU-EFRE geförderten Projekten, an denen der Hermann Eule Orgelbau, das Helmholtz-Zentrum Dresden-Rossendorf (HZDR) und das Leibniz-Institut INP Greifswald beteiligt waren bzw. noch sind. Im Mittelpunkt des Interesses standen die Erzeugung von nanoskaligen Schichten (30-100 nm Schichtdicke) durch plasma-gestützte Abscheideverfahren unter Vakuum sowie bei Atmosphärendruck auf Blei- und Messing-Materialien. Diese Schichten wurden hinsichtlich ihrer antikorrosiven Wirkung gegenüber essigsäurehaltiger Atmosphäre untersucht.
Keywords: Plasma-gestützte Abscheideverfahren, Plasmaimmersions-Ionenimplantation, atmosphärische Plasma-CVD, antikorrosive Behandlung, Messing, Blei-Zinn-Legierung, Korrosion, Essigsäure,
  • Invited lecture (Conferences)
    BDO-Workshop Bleikorrosion (BDO-Bund Deutscher Orgelbaumeister e.V.), 24.-25.10.2019, Ludwigsburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30320
Publ.-Id: 30320


Using deep learning for object recognition on hyperspectral data

Sudharshan, V.
Benefitting from the rapid expansion of consumer electronics (CE), plenty of new electronic products are introduced into the market annually. At the same time, due to the short life span of such products and the rapid emergence of new generations, large quantities of electronic waste are produced. The objective of this thesis is obtaining information on printed circuit boards (PCB) composition through non-invasive analysis using RGB (red, green and blue) and hyperspectral data to aid in recycling precious metals from recycled PCBs. The obtained information will be useful in more efficient processing of E-waste by harnessing deep learning networks. The goal of the thesis is to identify the surface mounted devices of a PCB such as the integrated circuits, connectors, capacitors, resistors etc. through the spatial information available in RGB images. The information obtained will be used in conjunction with HSI (Hyperspectral Images) to localise the detection area to recognise the composition of the PCB. We utilize spectral signatures of materials derived from HSI's and combining the spectral and spatial information to obtain a more precise recognition of the composition of a PCB. While hyperspectral data finds its use mostly in the remote sensing community to aid geological exploration, the application of this technology in the area of PCB recycling shows promise. The RGB images and HSI are collected by the multi-sensor system at the Helmholtz Institute Freiberg for Resource Technology (HIF) and supplements the training of the neural networks with the public data sets available from analogous research to localize the area of analysis for HSI based recognition. The neural network chosen for the application is the Faster Regional Convolutional Networks (Faster-RCNN) and we propose a guided anchoring method that utilizes Hyperspectral data to further improve the detection accuracy of the RGB based Faster RCNN, thereby including both spatial and spectral information of the PCBs. The results are then shown in comparison to demonstrate that the cross modal guided anchoring has a pronounced effect on the detection accuracy of the object detection network.
  • Master thesis
    TU Chemnitz, 2019

Permalink: https://www.hzdr.de/publications/Publ-30319
Publ.-Id: 30319


Antikorrosive Behandlungen metallischer Legierungen für den Orgelbau mittels Nanotechnologie

Quade, A.; Schumann, T.; Schäfer, J.; Kumpe, C.; Eule, D.; Skorupa, W.
Neben dem Problem des Schimmelpilzbefalls in Orgel-Instrumenten existiert das Problem der Korrosion von metallischen Orgelbestandteilen aus Blei/Zinn- sowie Kupfer/Zink (Messing)-Legierungen. Dabei werden die labialen Orgelpfeifen aus den Blei/Zinn-Legierungen gefertigt, während Messingteile für die Tonerzeugung in Zungenpfeifen verwendet werden. Die Korrosion erfolgt vor allem durch Ausdiffusion von Gerb-bzw. Ameisensäure aus dem in Orgeln verbauten Holz, wobei die Luftfeuchtigkeit der Umgebung eine katalytisch verstärkende Wirkung hat. Legierungen mit hohem Bleigehalt (>95%) sind dabei besonders gefährdet. Unsere Experimente konzentrierten sich auf Laborexperimente zur Korrosion entsprechender Legierungsproben aus dem Orgelbau mittels verdünnter Essigsäure (2–5 v/v%). Zuvor waren die Proben mit zwei verschiedenen Verfahren zur Erzeugung einer nanoskaligen Schutzschicht behandelt worden: (1) Gepulste Laserabscheidung bzw. Sputtern von Al2O3 -oder Al-Schichten gefolgt von Stickstoffbestrahlung mittels Plasmaimmersion, und (2) plasma-gestützte chemische Dampfphasenabscheidung (CVD) von SiOx. Während das erstere Verfahren ein Vakuumprozess ist, erfolgt das zweitgenannte Verfahren bei Atmosphärendruck. Die Barriere-Schichten wurden erfolgreich im Labor erprobt. Messing-Proben, beschichtet nach Verfahren 1, wurden in einem Feldexperiment in einer Mecklenburger Kirche mit besonders hohem Korrosionspotential für 15 Monate nach Einbau in reale Pfeifen ebenso erfolgreich getestet.
Keywords: pipe organ, atmospheric corrosion, acetic acid, volatile organic compounds, CuZn-alloy, brass, PbSn-alloy, plasma immersion ion implantation,
  • Invited lecture (Conferences)
    5. Mykologisches Kolloquium „Technische Maßnahmen zur Vermeidung von Schimmelpilzbefall in Kirchenorgeln“, 09.-10.05.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30318
Publ.-Id: 30318


Kreuz + Quer – Denken: …erlaubt? (…oder: Ist Innovation lehrbar?)

Skorupa, W.
Vortrag anläßlich der Inauguration von Prof. Thoralf Gebel an der Hochschule Mittweida - (University of Applied Science), Fakultät Wirtschaftsingenieurwesen, Lehrstuhl Industrial Management mit den Schwerpunkten Innovationsmanagement und Consulting
Keywords: Inauguration, Hochschule Mittweida, Prof. Thoralf Gebel
  • Invited lecture (Conferences)
    Vortrag zur Inauguration, Prof. Thoralf Gebel, Hochschule Mittweida, 10.04.2019, Mittweida, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30317
Publ.-Id: 30317


Nanoscale anticorrosive protection of pipe organ metallic materials

Quade, A.; Schumann, T.; Schäfer, J.; Kumpe, C.; Eule, D.; Skorupa, W.
Pipe organs with their unique musical sound are important objects of the cultural heritage. Such instruments consist of a number of pipes (flute and reed), which are prone to heavy corrosion attack, getting finally voiceless. The atmospheric corrosion of reed (CuZn alloys) and flute pipes (PbSn alloys) is strongly enhanced by traces of volatile organic compounds (VOCs) and the alloy’s instability. Moreover, there is a strong impact of humidity in the corrosion process. Experiments have been undertaken to explore the suppression of an aqueous corrosion with acetic acid concentration (2–5 v/v%) of CuZn and PbSn alloys, by deposition of nanocoating using two different methods: (i) Pulsed laser- or Magnetron sputtering deposition of Al2O3 or Al followed by plasma immersion ion implantation of nitrogen as a vacuum technology, and (ii) Plasma enhanced CVD of SiOx films at atmospheric pressure. The nanocoating is then able to withstand acoustic vibrations of organ pipes, and it produces a barrier to VOCs and water vapor. The laboratory corrosion tests were combined with field studies to approach environmental conditions. Some of the samples were exposed for 15 months to harmful indoor environment in North-German church. Surface modification of metallic alloys based on ion-solid interactions as well as plasma-based processing creates new paths in restoration and conservation technologies to protect our historical and modern cultural heritage against environmental attacks.
Keywords: pipe organ, atmospheric corrosion, acetic acid, volatile organic compounds, CuZn-alloy, brass, PbSn-alloy, plasma immersion ion implantation,
  • Lecture (Conference)
    EMRS Spring Mtg., Symposium.BB „Cultural heritage – science, materials and technologies“, Nizza – May 27-31, 2019, 27.-31.05.2019, Strasbourg, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-30316
Publ.-Id: 30316


Fractional Abundance Estimation of Mixed and Compound Materials by Hyperspectral Imaging

Koirala, B.; Zahiri, Z.; Khodadadzadeh, M.ORC; Scheunders, P.
The mechanical and chemical properties of a compound material are determined by the fractional abundances of its components. In this work, we present a spectral unmixing technique to estimate the fractional abundances of the components of mixed and compound materials from hyperspectral images. The estimation of fractional abundances in mixed materials faces the main challenge of intimate mixing. In compound materials, the mixing with water causes changes in chemical properties resulting in spectral variability and non-linearity. To address these challenges, a supervised method is proposed that learns a mapping from the hyperspectral data to spectra that follow the linear mixing model. Then, a linear unmixing technique is applied on the mapped spectra to estimate the fractional abundances. To demonstrate the potential of the proposed method, experiments are conducted on hyperspectral images from mixtures of red and yellow clay powders and hardened mortar samples with varying water to cement ratios.
  • Contribution to proceedings
    2019 10th Workshop on Hyperspectral Imaging and Signal Processing: Evolution in Remote Sensing (WHISPERS), 24.-26.09.2019, Amsterdam, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30315
Publ.-Id: 30315


Abundance-Indicated Subspace for Hyperspectral Classification With Limited Training Samples

Xu, S.; Li, J.; Khodadadzadeh, M.ORC; Marinoni, A.; Gamba, P.; Li, B.
The imbalance between the (often limited) number of available training samples and the high data dimensionality, together with the presence of mixed pixels, often complicates the classification of remotely sensed hyperspectral data. In this paper, we tackle these problems by developing a new method that combines spectral unmixing and classification techniques in a subspace-based approach. The proposed method is developed under the assumption that the spectral signature of a land cover class is associated with a given set of pure spectral signatures (called endmembers in spectral unmixing terminology), which define a low-dimensional subspace with clear physical meaning. We aim to exploit this relationship to learn the class-dependent subspaces and integrate them with a multinomial logistic regression procedure. Experiments on synthetic datasets and real hyperspectral images show that our method is able to obtain competitive performances in comparison with other approaches, particularly when very limited training sets are available.
Keywords: Hyperspectral image classification , mixed pixels , mutinomial logistic regression (MLR) , spectral unmixing , subspace learning
  • IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 12(2019)4, 1265-1278
    DOI: 10.1109/JSTARS.2019.2903940

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Permalink: https://www.hzdr.de/publications/Publ-30314
Publ.-Id: 30314


Cationic Porphyrin-Graphene Oxide Hybrid: Donor-Acceptor Composite for Efficient Photoinduced Electron Transfer

Larowska, D.; Lindner, A. A.; Mazurkiewicz-Pawlicka, M.; Malolepszy, A.; Stobiński, L.; Marciniak, B.; Lewandowska-Andralojc, A.
Non-covalent nanohybrids composed of cationic 5,10,15,20-tetra(4-trimethylammoniophenyl)porphyrintetra(p-toluenesul-fonate) (TMAP) and the graphene oxide sheets were prepared under two pH values (6.2 vs. 1.8).The TMAP molecule was positively charged, regardless of the pH value during preparation. However, protonation of the iminonitrogens increased the overall charge of the porphyrin molecule from +4 to +6 (TMAP4+ and TMAP6+). It was found that at acidic pH,interaction of TMAP6+ with GO was largely suppressed. On the other hand,results of FTIR, Raman spectroscopy, thermogravimetric analysis, atomic force microscopy (AFM) and elemental analysis confirmed effective non-covalent functionalization of graphene oxide with cationic porphyrinat pH 6.2. The TMAP4+-GO hybrids exhibited well defined structure with a monolayer of TMAP4+ on the GO sheets as confirmed by AFM.Formation of the ground-stateTMAP4+-GO complex in solution was monitored by the red-shift of the porphyrin Soret absorption band.This ground-state interaction between TMAP4+ and GO is responsible for the static quenching of the porphyrin emission.Fluorescence was not detected for the nanohybrid which indicated that a very fast deactivation process had to take place.Ultrafast time-resolved transient absorption spectroscopy clearly demonstrated the occurrence of electron transfer from the photoexcited TMAP4+ singlet state to GO sheets,as proven by the formation of a porphyrin radical cation.
Keywords: Porphyrin, graphene oxide, hybrid, photoinduced electron transfer

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  • Secondary publication expected from 28.03.2020

Permalink: https://www.hzdr.de/publications/Publ-30313
Publ.-Id: 30313


Self-created and self-creating dynamos: Some inspirations drawn from Axel Brandenburg’s works

Stefani, F.ORC; Gerbeth, G.; Giesecke, A.ORC; Gundrum, T.; Seilmayer, M.ORC; Vogt, T.ORC; Weier, T.
A theoretician of the first water, Axel Brandenburg has always been interested in experimental MHD as well. Anecdotal evidence has it that he is the only person who witnessed in operation the three successful dynamo experiments in Riga, Karlsruhe and Cadarache. Axel’s theoretical work, in turn, has inspired experimentalists more often than not. One case in point is his early work on nonlinear and highly supercritical dynamos which has motivated investigations into the common mechanism underlying the field reversals of the geodynamo and the VKS dynamo. These efforts lead to the complementary explanations of reversals in terms of spectral exceptional points of non-selfadjoint dynamo operators, or via saddle-node bifurcations. In this context, we shortly report the construction progress of the DRESDYN precession driven dynamo, the set-up of which was partly motivated by the signature of Milankovic cycles in the reversal statistics of the geodynamo.
The second part of the talk refers to Axel’s work on massively non-linear, “self-creating” dynamos, such as the MRI dynamo or the Tayler-Spruit dynamo. Here we summarize some previous experiments on the magnetorotational instability (MRI) and the Tayler instability (TI), and present some recent results on double-diffusive instabilities for rotating flows with positive shear. The talk will close with a highly speculative idea which connects the oscillatory behaviour of the TI-related alpha-effect to the persistent synchronization of the solar dynamo with the 11.07 years periodic alignments of the tidally dominant planets Venus, Earth and Jupiter.
  • Lecture (Conference)
    Turbulence and magnetic fields - from the early universe to late-type stars, 01.-05.04.2019, Tuusula, Finland

Permalink: https://www.hzdr.de/publications/Publ-30312
Publ.-Id: 30312


A Supervised Method for Nonlinear Hyperspectral Unmixing

Koirala, B.; Khodadadzadeh, M.ORC; Contreras Acosta, I. C.; Zahiri, Z.; Gloaguen, R.ORC; Scheunders, P.
Due to the complex interaction of light with the Earth’s surface, reflectance spectra can be described as highly nonlinear mixtures of the reflectances of the material constituents occurring in a given resolution cell of hyperspectral data. Our aim is to estimate the fractional abundance maps of the materials from the nonlinear hyperspectral data. The main disadvantage of using nonlinear mixing models is that the model parameters are not properly interpretable in terms of fractional abundances. Moreover, not all spectra of a hyperspectral dataset necessarily follow the same particular mixing model. In this work, we present a supervised method for nonlinear spectral unmixing. The method learns a mapping from a true hyperspectral dataset to corresponding linear spectra, composed of the same fractional abundances. A simple linear unmixing then reveals the fractional abundances. To learn this mapping, ground truth information is required, in the form of actual spectra and corresponding fractional abundances, along with spectra of the pure materials, obtained from a spectral library or available in the dataset. Three methods are presented for learning nonlinear mapping, based on Gaussian processes, kernel ridge regression, and feedforward neural networks. Experimental results conducted on an artificial dataset, a data set obtained by ray tracing, and a drill core hyperspectral dataset shows that this novel methodology is very promising.
Keywords: hyperspectral unmixing; spectral mixing models; machine learning algorithms

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Permalink: https://www.hzdr.de/publications/Publ-30310
Publ.-Id: 30310


Noncovalent Porphyrin–Graphene Oxide Nanohybrids: The pH-Dependent Behavior

Gacka, E.; Lindner, A. A.; Mazurkiewicz-Pawlicka, M.; Malolepszy, A.; Stobiński, L.; Kubas, A.; Hug, G. L.; Marciniak, B.; Lewandowska-Andralojc, A.
Noncovalent nanohybrids between meso-(p-hydroxyphenyl)porphyrin (TPPH) and graphene oxide (GO)sheets were studied as a function of pH. The overall charge of theTPPH molecule changes between negative (−4), neutral, and positive (+2) depending on the pH of the solution. Results of Fourier transform infrared spectroscopy, thermogravimetricanalysis, and elemental analysis confirm successful noncovalent functionalization of GO sheets with TPPH. We applied a numberof methods to probe the ground-state as well as the excited-state interaction between the components of the new material. The experimental results were additionally supported by theoretical calculations that included optimizations of the ground-state structures of TPPH and TPPH2+and their complexes with amolecular model of GO. It was demonstrated that both TPPHand TPPH2+molecules can be assembled onto the surface of GO, but it was clearly shown that the stronger interaction with GO occurs for TPPH2+. The stronger interaction in the acidic environment can be rationalized by the electrostatic attraction between positively charged TPPH2+ and negatively charged GO, whereas the interaction between TPPH4−and GO at basic pH was largely suppressed. Our comprehensive analysis of the emission quenching led to the conclusion that it was solely attributed to static quenching of the porphyrin by GO. Surprisingly,fluorescence was not detected for the nanohybrid, which indicates thata very fast deactivation process must take place. Ultrafast time-resolved transient absorption spectroscopy demonstrated that although the singlet excited-state lifetime of TPPH2+adsorbed on the GO sheets was decreased in the presence of GO from 1.4ns to 12 ps, no electron-transfer products were detected. It is highly plausible that electron transfer takes place and is followed by fast back electron transfer.
Keywords: graphene oxide, porphyrin, nanohybrid

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Permalink: https://www.hzdr.de/publications/Publ-30309
Publ.-Id: 30309


Dense storage of alkali metals between graphene and MoS2 bilayers: a computational study

Ghorbani Asl, M.ORC; Chepkasov, I.; Krasheninnikov, A.ORC
We study the intercalation of alkali metals, namely lithium and sodium, between graphene and MoS2 sheets using density functional theory calculations with the van der Waals correction. The structures and energetics of a different number of alkali layers with closed packed structures have been investigated for various stacking sequences of bilayer graphene. The intercalation energies suggested that the AA stacking is more favorable for the single-layer intercalation but it has no considerable effect on multilayer storage. Our calculations showed that there is a clear correlation between the intercalation energy and the electron transfer between alkali atoms and layered material. While the higher values of charge transfer observed for the single-layer intercalation, the charge transfer is noticeable only for the outer alkali layers in the multi-layer case. As a result, the intercalation energy reduces with increasing the number of the lithium and sodium layers but reduces for potassium. In the case of lithium intercalation between MoS2 bilayers, a 2H-1T phase transition was observed due to the
significant charge transfer. The present study can shed light on the design of high storage alkali batteries using two-dimensional layered materials as reported recently.
Keywords: Alkali metals, graphene, intercalation
  • Lecture (Conference)
    Atomic structure of nanosystems from first-principles simulations and microscopy experiments (AS-SIMEX 2019), 28.-30.05.2019, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-30308
Publ.-Id: 30308


Ion beam modification of single-layer transition metal dichalcogenides

Ghorbani Asl, M.ORC; Kretschmer, S.ORC; Krasheninnikov, A.ORC
Ion irradiation techniques have been extensively used for material modification, post-synthesis engineering and imaging purposes. Although the response of bulk targets to ion irradiation has been studied at length, including simulations, much less is known about the effects of ion bombardment on two-dimensional (2D) materials. 2D transition metal dichalcogenides (TMDs) have shown outstanding physical properties which make them intriguing candidates for various nanoelectronic and optoelectronic applications. We have studied the effects of ion irradiation on freestanding and supported 2D TMDs by using analytical potential molecular dynamics combined with Monte Carlo simulations. We characterized the types and assess the abundance of point defects in our structures as a function of ion energy, mass and incident angle. Furthermore, we studied the irradiation with highly charged ions (HCIs) for the fabrication of well-defined pores in MoS2 monolayer. The simulations indicated a dependence of the pore size on the potential energy of the projectile and suggested enrichment in molybdenum in the vicinity of the pore edges. These findings help to understand the fundamental physical mechanisms underlying ion irradiation of low-dimensional materials and finding optimum parameters for defect engineering of 2D TMDs with optimized properties
Keywords: Ion irradiation, transition metal dichalcogenides, monolayer
  • Lecture (Conference)
    Towards Reality in Nanoscale Materials X, 12.-14.02.2019, Levi, Finland

Permalink: https://www.hzdr.de/publications/Publ-30307
Publ.-Id: 30307


Calculation of defect- and interface-induced electronic states in 2D materials

Wagner, C.ORC; Gemming, S.ORC
Two-dimensional (2D) materials feature exceptional electronic and optoelectronic properties controlled by the strong confinement in the third dimension. Here, we present calculations within the framework of density functional theory (DFT) to assess the change of 2D materials and their properties under the influence of deviations from the purely 2D nature.
Significant changes to the electronic and optical properties have been monitored already in free-standing 2D layers when comparing structurally perfect monolayers and slightly thicker multilayer structures of the same material, although the multilayer still obeys the same ideal 2D periodicity as the monolayer does. This effect becomes more pronounced once the in-plane symmetry is reduced by rotational stacking faults between the layers of a single 2D material, in van-der-Waals bound heterostructures with other 2D materials, or in the proximity of the substrate. If the adjacent 2D crystal lattices are (nearly) commensurate, such structures still obey periodic boundary conditions in-plane, but with larger superlattice vectors. In that case, the electronic structure undergoes additional modulations within the supercell, which are then periodically repeated in 2D. From a symmetry point of view, the decoration of 2D materials with two-dimensionally periodic assembled organic films may lead to very similar lateral superlattice features, although the interaction of the 2D layer and the individual molecules of the film is local. That provides the possibility to use molecular functionalization for enhancing or suppressing such superlattice features in a predefined way. Finally, decoration can also be employed to heal local structural and electronic defects, which occur depending on the synthesis conditions and break the ideal 2D periodicity of realistic samples. Electronic confinements along 1D boundary lines or localized states at intrinsic defects on the faces cause rather strong local and non-periodic changes of the 2D properties. Calculations suggest that in the limit of low defect density, i.e., below the percolation threshold, the long-range properties of such systems still maintain their 2D nature, but additional effects, such as scattering may result from the interaction with the defects.
Molybdenum sulfide is a well-studied binary 2D material, which exhibits all those effects without the need to add additional elements, e.g. hydrogen, to saturate dangling bonds at termination sites. The implications for other, electronically more complex materials such as graphene will be discussed.
Keywords: 2D materials, DFT, Bethe-Salpeter, Density-functional perturbation theory, MoS2, GaSe, bilayer, van-der-Waals heterostructure, interlayer exciton
  • Invited lecture (Conferences)
    International Symposium on Epi-Graphene, 25.-28.08.2019, Chemnitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30306
Publ.-Id: 30306


In-situ GISAXS for morphological characterization of ion-induced nanopatterning on the crystalline Ge(001) surface

Erb, D.; Myint, P.; Evans-Lutterodt, K.; Ludwig, K.; Facsko, S.ORC
Grazing Incidence Small Angle X-ray Scattering (GISAXS) has been established as a versatile tool for comprehensive morphological characterization of surfaces on the nanometer scale. As a contact-less technique it lends itself especially to in-situ monitoring of surface nanopattern development or the growth of supported nanostructures under various conditions such as reactive atmospheres, high temperatures, applied fields, or ion irradiation. A GISAXS intensity pattern is a representation of the shapes, sizes, as well as lateral and vertical arrangements of three-dimensional structures in reciprocal space, in dependence of the direction of the incident X-ray beam. Complementary to local imaging techniques such as atomic force microscopy (AFM), it provides information on the average surface morphology of the extended area covered by the footprint of the X-ray beam. We implemented an in-situ ultra-high vacuum setup at the ISR beamline of the NSLS-II synchrotron combining GISAXS with low-energy broad-beam ion irradiation, providing sample rotation as well as heating to several hundred degrees Celsius. This setup allows us to observe the nanoscale pattern formation kinetics on crystalline semiconductors in-situ under ion irradiation. We studied the pattern formation on Ge(001) surfaces, where the crystallinity of the surface under ion irradiation is ensured by heating the sample above its recrystallization temperature. The Ge(001) surface is known to develop a pit-and-mound pattern of faceted pyramidal structures under irradiation with 1 keV Ar+ ions. The edges of the pyramidal structures are aligned along the <100> and <010> direction, while their sidewall facets have a uniform polar tilt from the <001> direction. Such a regular surface morphology results in a distinct GISAXS intensity pattern. From the development of the GISAXS pattern features with ion fluence, we can conclude on the corresponding development of the surface morphology. Using this technique, we monitor the lateral correlation length as well as the polar facet angle and the azimuthal pattern orientation as indicators of the kinetics of this ion-induced self-assembly process.
  • Lecture (Conference)
    IISC23, 17.-22.11.2019, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-30305
Publ.-Id: 30305


Interlayer excitons in van-der-Waals heterostructures from ab initio perspective - the case of MoS2 on GaSe

Wagner, C.ORC; Rahaman, M.; Zahn, D. R. T.; Gemming, S.ORC
The talk investigates the formation of interlayer excitons as a function of heterostack composition for MoS2 and GaSe.
The composition of the stack has a large influence of the exciton binding energy.
As experimentally fabricated stacks are large, theoretical data need to be extrapolated slightly.
This finally results in a theoretical prediction closer to experimental observations of the interlayer excitons.
Keywords: 2D materials, DFT, Bethe-Salpeter, Density-functional perturbation theory, MoS2, GaSe, bilayer, van-der-Waals heterostructure, interlayer exciton, heterostack
  • Invited lecture (Conferences)
    Holzhau-2019 meeting, 25.-27.09.2019, Holzhau, Tschechei

Permalink: https://www.hzdr.de/publications/Publ-30303
Publ.-Id: 30303


Morphology, density, and temporal evolution of topological defects in reverse epitaxy

Erb, D.; Malsch, G.; Facsko, S.ORC
Low-energy ion-irradiation of semiconductors above their recrystallization temperature has been shown to induce regular nanoscale patterning of the crystalline surface. The mechanism is called reverse epitaxy in analogy to epitaxy in growth: ion-induced mobile vacancies and ad-atoms on the crystalline surface encounter the Ehrlich-Schwoebel energy barrier for crossing terrace steps and exhibit preferential diffusion along specific in-plane directions. This can lead to the formation of well-defined faceted surface structures with morphologies strongly dependent on crystalline structure and surface orientation. For instance, GaAs(001) and InAs(001) develop periodic ripple structures with a saw tooth profile.
We have studied the topological defects in ion-induced patterns on GaAs(001) and InAs(001), i.e. ripple junctions, and present results from both experiments and simulations on the following aspects:
-- defect morphology and the influence of polar and azimuthal ion incidence angles thereon
-- dependence of the defect density on sample temperature and ion energy
-- temporal evolution of the defect density
-- defect motion and annihilation processes
We find strong dependencies on the easily controllable external process parameters, which is crucial information when preparing ion-induced surface patterns for specific applications.
  • Poster
    Nanopatterning Workshop 2019, 07.-10.07.2019, Surrey, England

Permalink: https://www.hzdr.de/publications/Publ-30302
Publ.-Id: 30302


High field Terahertz user facility TELBE: extremely efficient nonlinear THz light control in Dirac materials

Kovalev, S.ORC; Hafez, H.; Chen, M.ORC; Green, B. W.ORC; Bawatna, M.ORC; Germanskiy, S.ORC; Awari, N.ORC; Wang, Z.ORC; Deinert, J.-C.ORC; Ilyakov, I.ORC; Turchinovich, D.; Gensch, M.
Terahertz (THz) frequency range contains wave-lengths between 3 mm to 30 µm that corresponds to the energies between 0.4 meV to 40 meV. Spectroscopy in this range plays very important role in an understanding the solid state physics as there are multiple low energy excitations (phonons, magnons, Higgs mode etc.) that determine numerous physical parameters of the matter. Not only to perform THz spectroscopy but to coherently manipulate the phase of matter through these excitations it is required to develop high field narrow band THz radi-ation sources with very sensitive probing techniques.
THz user facility TELBE at Helmholtz-Zentrum Dresden-Rossendorf provides quasi CW SRF accelerator based narrowband THz radiation at high repetition rates. The source is based on superradiant principle that ena-bles high degree of CEP stability, operation in deep THz frequencies tunable between 100 GHz to 3 THz and rep-etition rates up to MHz range [1]. The bandwidth of radi-ation is 10-15 % with pulse energies up to 2-3 µJ in a fundamental band (up to 100 µJ as design parameter) that results in few 100 kV/cm peak field strength. Using pulse-resolved technique we can reach few femto-second synchronization with ultra-fast laser system that is crucial for studying ultrafast dynamics [2]. The listed above parameters outperform state of the art high repeti-tion rates laser based THz sources and are important for observing novel high field THz phenomena. In this con-tribution we present concept of superradiant THz sources and our recent results on observing novel high field te-rahertz phenomena making use of such sources. Among the experimental results we will present THz high har-monic generation in Dirac materials, Higgs spectroscopy of high TC superconductors and spintronic based THz oscillators.
  • Invited lecture (Conferences)
    VII International Conference “Frontiers of Nonlinear Physics”, 28.06.-04.07.2019, Nizhny Novgorod, Russia

Permalink: https://www.hzdr.de/publications/Publ-30300
Publ.-Id: 30300


Role of contacts in carbon nanotube giant piezoresistive sensors

Böttger, S.; Wagner, C.ORC; Lorkowski, F.; Hartmann, M.; Heldt, G.; Reuter, D.; Schuster, J.; Hermann, S.
From the perspective of wafer-level integration technologies, this work presents theoretical and experimental insights on fundamental device properties of single-walled carbon nanotubes (SWCNTs) based giant piezoresistive transducers. The role of contacts in such devices and their contribution to a significant tunneling-related sensitivity enhancement is demonstrated. The origin of this phenomenon is the strain dependence of the effective Schottky barrier (SB) width which is modulated by a drain-source voltage (VDS) dependent large built-in electric field F at the Schottky-barrier (SB), which defines the effective SB width and can be controlled via VDS. Moreover, perspectives for forthcoming sensor generations exposing operation regimes beyond intrinsic sensitivity are revealed.
Keywords: carbon nanotube, SWCNT sensor, giant piezoresistivity, sensitivity enhancement, transport modeling, contact tunneling, Schottky barrier
  • Poster
    TRANSDUCERS 2019, 23.-26.06.2019, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30299
Publ.-Id: 30299


Engineering and coherent control of defect qubits in SiC at room temperature

Astakhov, G.ORC
Quantum bit or qubit is a two-level system, which builds the foundation for quantum computation, simulation, communication and sensing. Quantum states of higher dimension, i.e., qutrits (D = 3) and especially qudits (D = 4 or higher), offer significant advantages. Particularly, they can provide noise-resistant quantum cryptography, simplify quantum logic and improve quantum metrology. Flying and solid-state qudits have been implemented on the basis of photonic chips and superconducting circuits, respectively. However, there is still a lack of room-temperature qudits with long coherence time and high spectral resolution. The silicon vacancy centers in silicon carbide (SiC) with spin S = 3/2 are quite promising in this respect. Here, we report a two-frequency protocol to excite and image multiple qudit modes in a SiC spin ensemble under ambient conditions. Strikingly, their spectral width is about one order of magnitude narrower than the inhomogeneous broadening of the corresponding spin resonance. By applying Ramsey interferometry to these spin qudits, a spectral selectivity of 600 kHz and a spectral resolution of 30 kHz are achieved. As a practical consequence, we demonstrate absolute DC magnetometry insensitive to thermal noise and strain fluctuations.
  • Invited lecture (Conferences)
    1st Sino-German Symposium: Defect Engineering in SiC Device Manufacturing, 14.11.2019, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-30298
Publ.-Id: 30298


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