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35173 Publications

Scaling up the Synthesis of a Hydroxyquinoline-Functionalized p‑tert-Butylcalix[4]arene.

Roode-Gutzmer, Q. I.; Holderied, L. N.; Glasneck, F.; Kersting, B.; Fröhlich, P.; Bertau, M.

The optimization for an upscaled technical production of a lower rim-functionalized p-tert-butylcalix[4]arene, furnished with N₄O₄-donor ligands for superior solvent extraction separation between heavy and light lanthanides, is described. We demonstrate that reducing the polarity of the aprotic solvent in the (1,3)-distal esterification of p-tert-butylcalix[4]arene 1 does not compromise the quality or yield of product 2. It was possible to use the technical quality educt 1, that is, without prior crystallization in toluene, in conjunction with reductions in reaction time and solvent volume. The raw diester product 2 could be used, without prior recrystallization (which originally required 3 days) in the condensation reaction with hydrazine monohydrate to form hydrazide 3. Most importantly, the solvent volume required in the final condensation reaction of 3 with 8- hydroxyquinoline-2-carboxaldehyde could be reduced by an order of magnitude by using chloroform. Not only was the final disubstituted product yield improved but also the purity of the final product could be ensured by preventing the precipitation of the intermediate monosubstituted product during reaction. The filtration characteristics of the final product, as well as its solvation properties during solvent extraction of lanthanides were significantly improved.

Keywords: rare earths; lanthanides; actinides; solvent extraction; calixarene synthesis; scale up

Permalink: https://www.hzdr.de/publications/Publ-30484
Publ.-Id: 30484


Characterization of Goethe’s prisms by external ion beam

Munnik, F.; Mäder, M.; Heller, R.; Schreiber, A.; Müller, O.

Johann Wolfgang von Goethe is known the world over as a renowned writer. However, he was also involved in scientific studies and has written several scientific books, of which he considered the “Theory of colours” (“Farbenlehre”, 1400 pages published in 1810) his most important work overall. In this work, he characterises colours as arising from the interplay between light and dark. This is in contrast to Newton’s analytical treatment of colour from one century earlier, which is based on the observation that white light can be separated into colours with a prism, that Goethe opposed. Over the centuries, Goethe’s theory was discredited and Newton’s theory prevailed. However, Goethe performed systematic and accurate optical measurements.
For these experiments, he and his partner J. Ritter, who discovered UV-light, used water prisms and glass prisms ordered from a glassmaker in Jena. The aim of current research is to reconstruct these optical experiments and the observed spectra [1]. For this, detailed knowledge of the composition of the glass prisms is important. This knowledge is, for example, also important to evaluate how innovative his prisms were.
Therefore, eleven prisms from Goethe’s estate or from contemporary sources belonging to the Klassik Stiftung Weimar have been analysed at the external beam setup of the Ion Beam Center at the HZDR. A 4 MeV proton beam has been used to acquire PIXE, PIGE and RBS spectra, sometimes on several areas. Care had to be taken to minimise damage by using short measurement times and measuring on inconspicuous areas because the glass quickly showed dark spots under irradiation. The PIXE and PIGE spectra have been used for quantitative analysis in an iterative procedure and the RBS spectra have only been evaluated quantitatively. The results of this analysis and the interpretation are presented in this work.

  • Lecture (Conference)
    16th International Conference on Particle Induced X-ray Emission, 24.-29.03.2019, Caldas da Rainha, Portugal

Permalink: https://www.hzdr.de/publications/Publ-30483
Publ.-Id: 30483


Junctionless Nanowire Transistors: an Excellent Platform for Ultrasensitive Chemo/Biosensors

Georgiev, Y.

Junctionless nanowire transistors (JNTs) are gated resistors where the source, channel and drain have the same type of doping without any dopant concentration gradient. The JNT is the simplest transistor structure possible and probably the most scalable of all field effect transistor (FET) structures. It is easier to fabricate than standard metal-oxide-semiconductor FETs (MOSFETs) and has also a number of performance advantages over them. [1, 2, 3] Two of the advantages are especially important for the JNT application as sensors:

1. The current flow in JNTs is not controlled by a reverse biased p-n junction as in standard MOSFETs but entirely by the gate potential. Therefore, they are more sensitive to any change in the electrostatic potential on the channel surface acting as a gate potential.

2. JNTs demonstrate bulk conductance near the centre of the channel, in contrast to the conductance in a thin surface inversion or accumulation layer near the gate in the inversion mode or accumulation mode MOSFETs, which leads to higher drive currents. Moreover, this fact makes the conduction in JNTs less affected by the noise-inducing parasitic surface states than in the case of conventional MOSFETs, which is very important for achieving high signal-to-noise ratio and low detection limit.

In the presentation, these advantages will be discussed in detail followed by results of implementation of silicon (Si) JNTs as chemical and biological sensors. A series of experiments for sensing the ionic strength and the pH value of buffer solutions have proven the excellent sensitivity of these sensors. [4, 5] Moreover, sensing of the protein streptavidin at a concentration as low as 580 zM has been observed, which is by far the lowest concentration of this protein ever detected and corresponds to detection in the range of only few molecules.

The high sensitivity of JNT sensors, combined with their very simple structure and relaxed fabrication process, makes them promising candidates for cheap mass production by the conventional microelectronic technology. This can enable their numerous applications in various fields where fast, low-cost, label-free, low-volume and real-time detection of chemical and biological species at low detection levels is required.

REFERENCES:

[1]. J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nanowire transistors without junctions. Nature Nanotech. 5, 225 (2010).
[2]. J. P. Colinge, C. W. Lee, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, A. Kranti, R. Yu. Junctionless Transistors: Physics and Properties, in Semiconductor-On-Insulator Materials for Nanoelectronics Applications. (Eds: A. Nazarov, J. P. Colinge, F. Balestra, J.-P. Raskin, F. Gamiz, V. S. Lysenko), Springer-Verlag Berlin, Heidelberg, Germany, pp.187-200, Ch. 10 (2011).
[3]. J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Junctionless Nanowire Transistor (JNT): Properties and design guidelines. Solid State Electron. 65-66, 33 (2011).
[4]. Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices. Microelectron. Eng. 118, 47 (2014).
[5]. Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, In "Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting", (Eds: A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre), Springer International Publishing AG, Cham, Switzerland, pp. 367-388, Ch. 17 (2014).

Keywords: nanowires; biosensors; junctionless transistors; protein; streptavidin; single-molecule detection

  • Invited lecture (Conferences)
    IHRS NanoNet International Conference, 08.-11.10.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30482
Publ.-Id: 30482


Application of junctionless nanowire transistors as ultrasensitive biosensors

Georgiev, Y.; Petkov, N.; Yu, R.; Nightingale, A. M.; Buitrago, E.; Lotty, O.; Demello, J. C.; Ionescu, A. M.; Holmes, J. D.

Junctionless nanowire transistors (JNTs) have been recently proposed as a disruptive alternative of the conventional metal-oxide-semiconductor field-effect transistors (MOSFETs) [1]. They are gated resistors where the source, channel and drain have the same type of doping without any junctions and dopant concentration gradient. Thus JNT is the simplest possible transistor structure and probably the most scalable of all FET structures. It is easier to fabricate than standard MOSFETs and has also a number of performance advantages over them [1,2]. Therefore, JNTs have quickly attracted a vast interest. However, their application as sensors, although very appealing, has not yet been extensively studied.

Here we report on the fabrication of silicon JNTs and their implementation as chemical and biological sensors. The devices have been fabricated by a top-down approach mainly based on electron beam lithography and reactive ion etching (see Fig 1) [3]. The nanowire surfaces have been appropriately functionalised for the respective analytes of interest. A series of experiments (see Fig. 2) for sensing the ionic strength (see Fig. 3) and the pH value of buffer solutions have proven the excellent sensitivity of the fabricated sensors [3,4]. Moreover, sensing of the protein streptavidin at a concentration as low as 580 zM has been observed (see Fig. 4), which is by far the lowest concentration of this protein ever detected and corresponds to detection in the range of only few molecules.

To explain the ultrahigh sensitivity of JNT sensors, we will discuss in detail two advantages of JNTs over the classical MOSFETs [1-4], which are especially important for their application as sensors:

1. The current flow in JNTs is not controlled by a reverse biased p-n junction as in standard MOSFETs but entirely by the gate potential modulating the carrier density in the channel. Thus they are more sensitive to any change in the electrostatic potential on the channel surface acting as a gate potential.

2. JNTs demonstrate bulk conductance near the centre of the channel, in contrast to the conductance in a thin surface inversion or accumulation layer near the gate in the classical inversion mode or accumulation mode transistors, which leads to higher drive currents. Moreover, this fact makes the modulation of depletion and the conduction in JNTs less affected by the noise-inducing parasitic surface states than in the case of conventional MOSFETs, which is very important for achieving high signal-to-noise ratio and hence low detection limit [6,7].

The ultrahigh sensitivity of JNT sensors, combined with their very simple structure and relaxed fabrication process, makes them promising candidates for cheap mass production by the conventional microelectronic technology. This can enable their numerous applications in various fields where fast, low-cost, label-free, low-volume and real-time detection of chemical and biological species at low detection levels is required.

[1] J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nature Nanotech. 5 (2010) 225-229.
[2] J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Solid State Electron. 65-66 (2011) 33-37.
[3] Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Microelectron. Eng. 118 (2014) 47-53.
[4] Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, in A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre, eds., Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting, (Springer International Publishing AG, Cham, Switzerland, Ch. 17, 2014) 367-388.
[5] Y. M. Georgiev, N. Petkov, R. Yu, A. M. Nightingale, E. Buitrago, O. Lotty, J. De Mello, A. M. Ionescu, J. D. Holmes, Nanotechnology (2019), accepted, https://doi.org/10.1088/1361-6528/ab192c
[6] N. K. Rajan, D. Routenberg, M. Reed. Appl. Phys. Lett. 98 (2011) 264107.
[7] K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, R. L. Stoop, S. Rigante, J. Brunner, W. Fu, C. David, M. Calame, J. Gobrecht, C. Schönenberger. Sensor. Actuat. B-Chem. 191 (2014) 270.

Keywords: nanowires; biosensors; junctionless transistors; protein; streptavidin; single-molecule detection

  • Lecture (Conference)
    45th International Conference on Micro- and Nanofabrication and Manufacturing (MNE 2019), 23.-26.09.2019, Rhodes, Greece

Permalink: https://www.hzdr.de/publications/Publ-30481
Publ.-Id: 30481


Multi-direction channelling study of the Ag:YSZ nanocomposites prepared by ion implantation

Mikšová, R.; Jagerová, A.; Malinský, P.; Harcuba, P.; Veselý, J.; Holý, V.; Kentsch, U.; Macková, A.

The paper reports on implantation damage accumulation, Ag distribution and the interior morphology in different crystallographic orientations of implanted samples of cubic yttria-stabilised zirconia (YSZ). (100)-, (110)- and (111)-oriented YSZ was implanted with 400-keV Ag⁺ ions at ion fluences from 5 × 10¹⁴ to 5 × 10¹⁶ cm⁻². Rutherford backscattering spectrometry (RBS) in the channelling mode (RBS-C), as well as X-ray diffraction (XRD), were used for the quantitative measurement of the lattice disorder and Ag distribution. The defect propagation and Ag accumulation were observed using transmission electron microscopy (TEM) with the energy-dispersive X-ray spectroscopy (EDX). Although similar damage evolution trends were observed along with all channelling directions, the disorder accumulation is lower along the <110> direction than along the <100> and <111> direction. The damage extends much deeper than the theoretically predicted depths. It is attributed to long-range defect migration effects, confirmed by TEM. At the ion fluence of 5 × 10¹⁶ cm⁻², nanometre-sized Ag precipitates were identified in the depth of 30–130 nm based on the Ag concentration–depth profiles determined by RBS.

Keywords: Ag ion-implantation; Yttria-stabilized zirconia; Damage accumulation; Strain relaxation; Nanoparticles

Permalink: https://www.hzdr.de/publications/Publ-30480
Publ.-Id: 30480


Group IV Nanowires: Fabrication and Particular Applications

Georgiev, Y.; Khan, M. B.; Deb, D.; Echresh, A.; Ghamsari, S. J.; Prucnal, S.; Rebohle, L.; Erbe, A.; Helm, M.; Gangnaik, A. S.; Game, A. D.; Biswas, S.; Petkov, N.; Holmes, J. D.

Group IV semiconductor nanowires (NWs) are very attractive because of the variety of possible applications as well as of the good silicon (Si) compatibility, which is important for their integration into the existing semiconductor technology.

We will give an overview of our activities on fabrication and application of group IV NWs. These include top-down fabrication (based on electron beam lithography and reactive ion etching) of Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up (vapour-liquid-solid, VLS) growth of alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1 and diameters of 50-70 nm. We will also discuss the innovative nanoelectronic devices that we are working on: junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we will present results on Si JNTs for sensing application as well as on Ge and GeSn JNTs for digital logic. We will also show results on Si RFETs as well as preliminary data on SiGe and GeSn RFETs, which are expected to outperform the Si RFETs.

Keywords: semiconductor nanowires; top-down nanofabrication; electron beam lithography; reactive ion etching; bottom-up nanofabrication; nanoelectronic devices; junctionless nanowire transistors; reconfigurable field effect transistors; biosensors

  • Lecture (Conference)
    83d DPG Annual Conference and DPG Spring Conference, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30479
Publ.-Id: 30479


Fabrication and Particular Applications of Group IV Semiconductor Nanowires

Georgiev, Y.; Khan, M. B.; Deb, D.; Echresh, A.; Jazavandi Ghamsari, S.; Prucnal, S.; Rebohle, L.; Erbe, A.; Helm, M.; Gangnaik, A. S.; Game, A. D.; Biswas, S.; Petkov, N.; Holmes, J. D.; Knoch, J.

During the last 1-2 decades semiconductor nanowires (NWs) have received significant academic and commercial attention due to their attractive electrical and mechanical properties and large surface area to volume ratios. They have a variety of possible applications including nanoelectronics, nanophotonics, photovoltaics, sensorics, etc. Among all semiconductor NWs the ones based on group IV materials have the advantage of being the most silicon (Si) compatible. This is very important since their integration into the existing semiconductor technology platform can be relatively easy.

We will give a general overview of our activities on group IV nanowires. We will first present the NWs that we are working with, including top-down fabricated Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up grown alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1, diameters of 50-70 nm and lengths of 1 to 3 µm. We are currently working also on the fabrication of alloyed SiGe and SiGeSn NWs with varying content of the different materials.

Next, we will discuss the innovative nanoelectronic devices that we are working on, namely junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we are fabricating Si JNTs for sensing application as well as Ge and GeSn JNTs for digital logic. Concerning RFETs, we are currently working on Si RFETs and commencing activities on SiGe and GeSn RFETs, which are expected to outperform the Si RFETs.

Finally, we will briefly present a novel device concept that we recently invented: a specific group IV heterostructure band-to-band tunnel FET (TFET). The fabrication process of this device is scalable and fully CMOS compatible and should allow the achievement of high on-current Ion together with low off-current Ioff, hence steep subthreshold slope.

Keywords: semiconductor nanowires; top-down nanofabrication; bottom-up nanofabrication; nanoelectronic devices; junctionless nanowire transistors; reconfigurable field effect transistors; band-to-band tunnel field effect transistors; biosensors

  • Lecture (Conference)
    The 10th workshop “Towards Reality in Nanoscale Materials X”, 12.-14.02.2019, Levi, Finland

Permalink: https://www.hzdr.de/publications/Publ-30478
Publ.-Id: 30478


Vanishing influence of the band gap on charge exchange of slow highly charged ions in freestanding single layer MoS₂

Creutzburg, S.; Schwestka, J.; Niggas, A.; Inani, H.; Tripathi, M.; George, A.; Heller, R.; Kozubek, R.; Madauß, L.; Facsko, S.; Kotakoski, J.; Schleberger, M.; Turchanin, A.; Grande, P. L.; Aumayr, F.; Wilhelm, R. A.

Charge exchange and kinetic energy loss of slow highly charged xenon ions transmitted through freestanding monolayer MoS₂ are studied. Two distinct exit charge state distributions, characterized by low and high charge exchange, are observed. They are accompanied by smaller and larger kinetic energy losses, respectively. High charge exchange is attributed to two-center neutralization processes, which take place in close impact collisions with the target atoms. Experimental findings are compared to graphene as a target material and simulations based on a time-dependent scattering potential model. Independently of the target material, experimentally observed charge exchange can be modeled by the same electron capture and de-excitation rates for MoS₂ and graphene. A common dependence of the kinetic energy loss on the charge exchange for MoS₂ as well as graphene is also observed, which additionally underlines the common nature of the two-center Auger neutralization process. Considering the similarities of the zero band gap material graphene and the 1.9 eV direct band gap material MoS₂, we suggest that electron transport on the femtosecond time scale is dominated by the strong influence of the ion’s Coulomb potential in contrast to the dispersion
defined by the material’s band structure.

Permalink: https://www.hzdr.de/publications/Publ-30477
Publ.-Id: 30477


Adaptive Control of Meniscus Velocity in Continuous Caster Based on NARX Neural Network Model

Abouelazayem, S.; Glavinic, I.; Wondrak, T.; Hlava, J.

Meniscus velocity in continuous casting process is critical in determining the quality of the steel. Due to the complex nature of the various interacting phenomena in the process, designing model-based controllers can prove to be a challenge. In this paper a NARX neural network model is trained to describe the complex relationship between the applied magnetic field from an Electromagnetic Brake (EMBr) and the meniscus velocity. The data for the model is obtained using a laboratory scale continuous casting plant. The next step was to use Adaptive Model Predictive Control (MPC) to deal with the non-linearity of the model by adapting the prediction model to the different operating conditions. The controller will utilize the EMBr as an actuator to keep the meniscus velocity within the optimum range, and reject disturbances that occur during the casting process such as changing the casting speed.

Keywords: Mining; mineral and metal; Nonlinear system identification; Adaptive control design

  • Contribution to proceedings
    13th IFAC Workshop on Adaptive and Learning Control Systems - ALCOS 2019, 04.-06.12.2019, Winchester, United Kingdom
    IFAC-PapersOnLine 52(2019) 29, 222-227
    DOI: 10.1016/j.ifacol.2019.12.653

Permalink: https://www.hzdr.de/publications/Publ-30476
Publ.-Id: 30476


Control of Jet Flow Angle in Continuous Casting Process using an Electromagnetic Brake

Abouelazayem, S.; Glavinic, I.; Wondrak, T.; Hlava, J.

The flow pattern in the mould of the continuous casting is an important factor in determining the quality of the steel slabs that are produced in the end of the process. Hence it can heavily influence manufacturing costs due to the scrap percentage. Electromagnetic actuators are frequently used in the continuous casting process to stabilize the flow in the mould and therefore produce higher quality of steel slabs. Usually they are used in open loop but their effect on the flow pattern may be much better directed if they are used as a part of closed loop control based on real time measurements. In this paper, a closed loop controller is proposed that adjusts the magnetic field of an electromagnetic brake using the real time measurement of the angle of the jet flowing from the Submerged Entry Nozzle (SEN). The angle is kept within a specific range by the controller in order to prevent a deeper jet impingement into the mould; this allows us to achieve the desirable double roll flow pattern, and to avoid the entrapment of slugs. The controller is based on a model of the relationship between brake current and jet angle that was obtained using experimental data from a laboratory scale continuous casting plant.

Keywords: Flow Control; Tomography; Process Automation; Model Predictive Control

  • Contribution to proceedings
    Mining, Mineral and Metal Processing 2019, 28.-30.08.2019, Stellenbosch, South Africa
    Control of Jet Flow Angle in Continuous Casting Process using an Electromagnetic Brake
    DOI: 10.1016/j.ifacol.2019.09.169

Permalink: https://www.hzdr.de/publications/Publ-30475
Publ.-Id: 30475


Switched MPC Based on Clogging Detection in Continuous Casting Process

Abouelazayem, S.; Glavinic, I.; Wondrak, T.; Hlava, J.

Nozzle clogging contributes heavily to quality issues seen during the process of continuous casting. The presence of clogging in the Submerged Entry Nozzle (SEN) can significantly change the flow patterns in the mould and therefore impact the quality of the steel product. Also, there is a high risk of inclusions due to parts of the clogging material breaking off and entering the mould. In this paper, we propose a new sensor setup that allows us to detect clogging in the SEN by monitoring the angle of the exiting jet. Based on this clog detection setup, a switched MPC controller is used to keep the angle of the exiting jet between the optimum ranges using an Electromagnetic Brake. This allows the controller to keep the angle of the jet in the optimum range even when clogging occurs in the nozzle. Experimental data from a laboratory scale continuous caster is used to derive the models for the controller.

Keywords: Flow Control; Tomography; Switched MPC; Hammerstein-Wiener Model

  • Contribution to proceedings
    IFAC 2020 World Congress, 12.-17.07.2020, Berlin, Germany
    Switched MPC Based on Clogging Detection in Continuous Casting Process

Permalink: https://www.hzdr.de/publications/Publ-30474
Publ.-Id: 30474


Two new diffractometers at BM20/ESRF for single crystal, powder and surface diffraction

Hennig, C.; Schmidt, M.; Ikeda-Ohno, A.; Radoske, T.; Feig, M.; Findeisen, S.; Claußner, J.; Exner, J.; Naudet, D.; Baumann, N.; Scheinost, A.

The Institute of Resource Ecology / Helmholtz-Zentrum Dresden-Rossendorf is operating the Rossendorf Beamline (ROBL/BM20) at the European Synchrotron Radiation Facility (ESRF) for 20 years. We are constructing a second experimental hutch with two new diffractometers for single crystal, powder and surface diffraction. The single crystal diffractometer is foreseen for small and large molecule crystallography, mainly for structures with heavy metals. This diffractometer is equipped with a Pilatus3 X 2M detector mounted in a sturdy metal frame on a granite table. Sample-detector distances can be varied between 140 und 600mm. Three goniometers are available to mount single crystals: a Huber Kappa goniometer 512.410, an Arinax Kappa MK3, and a Huber uniaxial goniometer 410. The energy range of 5-35keV allows the application of anomalous dispersion. In-situ experiments on single crystals and powders are supported. Diffraction measurements can be combined simultaneously with XANES and XRF spectroscopy using a Vortex X90 CUBE silicon drift detector with a FalconX1 processor.
The second diffractometer will be used for surface diffraction and moderate high-resolution powder diffraction. This diffractometer is a 6-circle Huber diffractometer with Eulerian cradle geometry. Surface and powder diffraction techniques comprise specific setups. Both techniques will use a Pilatus 100k detector. The resolution for powder diffraction using the Pilatus 100k detector does not reach the resolution of synchrotron diffractometers with secondary analyzer crystals, but provides a magnitude better resolution than lab diffractometers. A specific support allows the installation of the Vortex X90 detector also on this diffractometer. The setup comprises a cryo cooler (80-400 K) and a heater (up to 1200 K) which can be installed at both diffractometers. The experimental hutch is equipped for the use of radioactive material.

Keywords: Single crystall diffraction; powder diffraction; surface diffraction; Rossendorf Beamline

  • Lecture (Conference)
    Joint Polish-German Crystallographic Meeting 2020, 24.-27.02.2020, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30473
Publ.-Id: 30473


Flow monitoring for continuous steel casting using Contactless Inductive Flow Tomography (CIFT)

Glavinic, I.; Ratajczak, M.; Stefani, F.; Wondrak, T.

The control of the liquid steel flow in the mould of a continuous caster based on real time flow measurements is a challenging task due to the lack of appropriate measurement techniques. The opaqueness, the high temperature of 1500 C and the chemical aggressiveness of the melt require non-optical contactless methods. In order to reconstruct the complex flow structure in the mould, the Contactless Inductive Flow Tomography (CIFT) is a promising candidate, since it allows the visualization of the flow structure in the melt by applying a magnetic field to the melt, measuring the flow induced perturbation of that field and solving subsequently a linear inverse problem. The combination of this new measurement technique with typical electromagnetic actuators like electromagnetic brakes used in continuous casting, pose a challenge to the CIFT measurement system, because the flow induced magnetic field is in the range of 100 nT and has to be measured robustly on the background of the static magnetic field with the amplitude of 300 mT generated by the brake. In this work we will show recent developments regarding this topic for a small model of a continuous caster in the lab.
Furthermore, we will present a new method on how the complex linear inverse problem can be solved in real time providing a time resolution of about 1 Hz.

Keywords: Tomography-based industrial process control; CIFT; Continuous casting; mini-LIMMCAST; Process tomography sensors

  • Contribution to proceedings
    IFAC 2020 World Congres, 12.-17.07.2020, Berlin, Deutschland
    Proceedings of the IFAC 2020 World Congres

Permalink: https://www.hzdr.de/publications/Publ-30472
Publ.-Id: 30472


Experimental study on the magnetic pulse welding process of large aluminum tubes on steel rods

Bellmann, J.; Schettler, S.; Dittrich, S.; Lueg-Althoff, J.; Schulze, S.; Hahn, M.; Beyer, E.; Tekkaya, A. E.

Solid state welding technologies enable dissimilar metal welding without critical intermetallic phase formation. Magnetic Pulse Welding (MPW) is a promising joining method for hybrid sheet connections in car body production or for manufacturing of dissimilar tube connections. Given a suitable MPW process design, the shear testing of MPW joints usually leads to failure in the weaker base material. This finding emphasizes the high strength level of the joining zone itself. Consequently, the transmission of higher forces or torques, respectively, requires stronger materials or adapted geometries. In the present experimental study, the diameter of an exemplary driveshaft was doubled to 80 mm at constant tube wall thickness to increase the load bearing capability. The characteristic impact flash was recorded at different positions around the tube’s circumference and it was used to adjust the most relevant process parameters, i.e. working length and acceleration gap, at the lower process boundary. In metallographic analysis, the final shapes of both joining partners were compared with the original driveshaft dummies on macroscopic and microscopic scale. The typical wavy interface between aluminum and steel was analyzed in detail. Doubling the tube diameter lead to four times higher torque levels of failure during quasistatic and cyclic torsion tests.

Permalink: https://www.hzdr.de/publications/Publ-30471
Publ.-Id: 30471


Near free-fall oscillatory velocities in liquid metal rotating convection

Vogt, T.; Horn, S.; Aurnou, J.

The geomagnetic field is induced by liquid metal ow inside Earths outer core as a self-excited dynamo. Buoyancy drives the liquid metal flow because the iron rich core is cooling from its primordial state through heat loss to the mantle. The rotation of the Earth and Lorentz forces alter the resulting convective flow. However, since a 3000 km thick rocky mantle hinders our ability to observe core dynamics, the detailed ow topology is still largely unknown. Here we will investigate the effect of rotation on a low Prandtl number thermal convection by means of laboratory experiments and DNS. Therefore, we consider a rotating Rayleigh-Bénard convection setup in an upright cylindrical vessel of aspect ratio Γ = D/H = 2. We investigate supercriticalities in the range of 1 < R < 20 and Ekman numbers 4x10^-4 < Ek < 5 x 10^-6 in liquid gallium at Pr = 0.03. We find that oscillatory convection generates velocity that appear to exceed predictions in steady convection. Multi-modal bulk oscillations dominate the vertical velocity field over the whole range of supercriticalities investigated. Additionally, coherent mean zonal flows and time-mean helicity is found in the rotating liquid metal convection. Thus, we show that these oscillatory flows can be relevant for dynamo action.

Keywords: Rotating convection; liquid metal; Rayleigh-Bénard convection

  • Lecture (Conference)
    72nd Annual Meeting of the American Physical Society’s Division of Fluid Dynamics (DFD), 23.-27.11.2019, Seattle, USA

Permalink: https://www.hzdr.de/publications/Publ-30469
Publ.-Id: 30469


Verminderung des Tumorwachstums durch Kombination von Radiotherapie, Decitabin und Abacavir in einem orthotopischen Gruppe-3-MB-Mausmodell

Gringmuth, M.; Patties, I.; Toussaint, M.; Kranz, M.; Böhme, L.; Kortmann, R.-D.; Glasow, A.

Fragestellung:
Medulloblastome (MBs) sind die häufigsten malignen Hirntumore im Kindesalter. Die derzeitige Therapie besteht aus Tumorresektion und Radio-Chemotherapie. Dennoch zeigen insbesondere Patienten mit SHH/p53-mutierten- sowie Gruppe-3-MBs eine schlechte Prognose mit einer 5-Jahres-Überlebensrate von nur 41 % sowie 45 %. Verbesserte Therapiestrategien stehen daher im Fokus der aktuellen Forschung.
Unser Projekt kombiniert Radiotherapie (RT) mit dem DNA-de-novo-Methyltransferase-Inhibitor Decitabin (5 Aza 2’-desoxycytidin) und dem Telomerase-Inhibitor Abacavir in einem orthotopischen MB Mausmodell, da in 70 % der primären MBs eine aberrante Hypermethylierung beziehungsweise erhöhte Telomeraseaktivitäten nachgewiesen wurden. Zudem konnten wir in vitro bereits zeigen, dass die Kombinationsbehandlung mit RT, Decitabin und Abacavir das klonogene Überleben signifikant verringert.
Methodik:
Alle Tierexperimente wurden durch die Landesdirektion Sachsen genehmigt (Reg.-Nr: TVV 30/14). NSG-Mäusen wurden Gruppe-3-MB-PDX-Zellen (DKFZ Heidelberg, Dr. Kool) stereotaktisch ins Cerebellum injiziert. Drei Wochen postoperativ wurde den Tieren täglich über 14 Tage Decitabin (0,1 mg/kg/Tag) und/oder Abacavir (50 mg/kg/Tag) intraperitoneal verabreicht. Die lokale Einzeit-Bestrahlung (2 Gy) erfolgte am Tag 8. Mit Erreichen der definierten Abbruchkriterien wurden die Mäuse euthanasiert (= Überlebenszeit) und die Gehirne kryokonserviert. Im Anschluss wurden Gefrierschnitte immunhistologisch angefärbt und die mittlere Anzahl proliferierender Zellen (Ki-67) sowie die Vaskularisierung (CD31) im Tumor ermittelt.
Die statistische Auswertung erfolgte mit n = 10 Tieren je Behandlungsgruppe mittels Mann-Whitney-Test (medianes Überleben) bzw. zweiseitigem T-Test (Ki-67; CD31) zur unbehandelten Kontrollgruppe.
Ergebnis:
Zum Behandlungsstart war eine Tumorgröße von 1 mm nicht überschritten, was durch wöchentliche MRT-Untersuchungen (1-Tesla-Kleintier-MRT/PET Gerät Mediso) nachgewiesen wurde. Die Überlebensanalyse zeigte eine signifikante Verlängerung des medianen Überlebens nach multimodaler Behandlung (RT, Decitabin, Abacavir; 66 ± 9 Tage) vs. der unbehandelten Kontrollgruppe (44 ± 2 Tage) und Bestrahlung (50 ± 1 Tage). Sowohl die Behandlung mit RT+Decitabin (55 ± 3 Tage), als auch mit RT+Abacavir (59 ± 6 Tage), zeigte eine signifikante Überlebenszeitverlängerung vs. Kontrolle, aber nicht vs. RT. Die Proliferation und die Vaskularisierung waren in den multimodal behandelten gegenüber den Kontrolltumoren signifikant (p ≤ 0,05) um 15 % bzw. 14 % verringert.
Schlussfolgerung:
Die multimodale Therapie mit Radiotherapie, Decitabin und Abacavir konnte das Überleben von Mäusen mit orthotopischem Gruppe-3-Medulloblastom signifikant verlängern. Die Therapie zeigt damit klinisch relevantes Potential, welches wir derzeit im Shh/p53-mutierten MB-Mausmodell evaluieren.
Fördermittel:
Das Projekt wird durch die Else Kröner-Fresenius-Stiftung (2016_A184) und die Janssen-Cilag GmbH (DEC-I-17-DEU-001-V01) unterstützt.

Keywords: Medulloblastome; Tri-Therapie; Radiotherapie; Decitabin; Abcavir

  • Poster
    26. Jahrestagung der Deutschen Gesellschaft für Radioonkologie, 25.-28.06.2020, Wiesbaden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30468
Publ.-Id: 30468


Imaging of current induced Néel vector switching in antiferromagnetic Mn2Au

Bodnar, S. Y.; Filianina, M.; Bommanaboyena, S. P.; Forrest, T.; Maccherozzi, F.; Sapozhnik, A. A.; Scurschii, I.; Kläui, M.; Jourdan, M.

The effects of current induced Néel spin-orbit torques on the antiferromagnetic domain structure of epitaxial Mn2Au thin films were investigated by x-ray magnetic linear dichroism–photoemission electron microscopy. We observed current induced switching of antiferromagnetic domains essentially corresponding to morphological features of the samples. Reversible as well as irreversible Néel vector reorientation was obtained in different parts of the samples and the switching of up to 30% of all domains in the field of view of 10 μm is demonstrated. Our direct microscopical observations are compared to and fully consistent with anisotropic magnetoresistance effects previously attributed to current induced Néel vector switching in Mn2Au.

Permalink: https://www.hzdr.de/publications/Publ-30467
Publ.-Id: 30467


Cubic symmetry and magnetic frustration on the fcc spin lattice in K2IrCl6

Khan, N.; Prishchenko, D.; Scurschii, I.; Mazurenko, V. G.; Tsurlin, A. A.

Cubic crystal structure and regular octahedral environment of Ir4+ render antifluorite-type K2IrCl6 a model fcc antiferromagnet with a combination of Heisenberg and Kitaev exchange interactions. High-resolution synchrotron powder diffraction confirms cubic symmetry down to at least 20 K, with a low-energy rotary mode gradually suppressed upon cooling. Using thermodynamic and transport measurements, we estimate the activation energy of Δ ≃ 0.7 eV for charge transport, the antiferromagnetic Curie-Weiss temperature of θCW ≃ −43 K, and the extrapolated saturation field of Hs ≃ 87 T. All these parameters are well reproduced ab initio using Ueff = 2.2 eV as the effective Coulomb repulsion parameter. The antiferromagnetic Kitaev exchange term of K ≃ 5 K is about one half of the Heisenberg term J ≃ 13 K. While this combination removes a large part of the classical ground-state degeneracy, the selection of the unique magnetic ground state additionally requires a weak second-neighbor exchange coupling J2 ≃ 0.2 K. Our results suggest that K2IrCl6 may offer the best possible cubic conditions for Ir4+ and demonstrates the interplay of geometrical and exchange frustration in a high-symmetry setting.

Permalink: https://www.hzdr.de/publications/Publ-30466
Publ.-Id: 30466


Electron spin resonance study of spin relaxation in the strong-leg spin ladder with nonmagnetic dilution

Krasnikova, Y. V.; Glazkov, V. N.; Ponomaryov, O.; Zvyagin, S.; Povarov, K. Y.; Galeski, S.; Zheludev, A.

We have studied electron spin resonance (ESR) absorption spectra for the nonmagnetically diluted strongleg spin ladder magnet (C7H10N)2Cu(1−x)ZnxBr4 (abbreviated as DIMPY) down to 450 mK. Formation of the clusters with nonzero net magnetization is confirmed; the cluster-cluster interaction is evidenced by the concentration dependence of ESR absorption. High-temperature spin-relaxation time was found to increase with nonmagnetic dilution. The ESR linewidth analysis proves that the Dzyaloshinskii-Moriya (DM) interaction remains the dominant spin-relaxation channel in diluted DIMPY. Experimental data indicate that the Dilution results in the weakening of the effective DM interaction, which can be interpreted as total suppression of DM interaction in the close vicinity of impurity atom.

Permalink: https://www.hzdr.de/publications/Publ-30465
Publ.-Id: 30465


Investigations on bubbly two-phase flow in a constricted vertical pipe

Neumann-Kipping, M.; Bieberle, A.; Hampel, U.

We report on an experimental investigation of adiabatic bubbly two-phase flow development in a DN50 pipe with a ring-shaped and a baffle-shaped constriction at different superficial velocities of gas (up to jg = 0.1400 m·s-1) and liquid (up to jl = 1.6110 m·s-1) using ultrafast electron beam X-ray computed tomography (UFXCT). From UFXCT images, cross-sectional gas holdup distributions were obtained with a temporal resolution of up to 2,500 frames per second in 18 scanning planes along the pipe. A sophisticated data processing approach was applied to extract gas holdup data immediately from the two-phase flow image stack. Based on that, time-averaged gas holdup of the cross-section and the axial center of the pipe were calculated. In addition, bubble sizes and velocities were determined.

Keywords: gas-liquid two-phase flow; bubbly flow; flow constriction; three-dimensional flow; computed tomography; experimental benchmark data

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  • Secondary publication expected from 21.05.2021

Permalink: https://www.hzdr.de/publications/Publ-30464
Publ.-Id: 30464


Influence of synthetic wastewater on the isotactic and atactic polypropylene microplastic surfaces

Nikpay, M.; Siamak, E.; Krebs, P.

The municipal wastewater collection system is recognized as an initial point of interaction between microplastics (MPs) and the urban wastewater matrix. The raw wastewater contains a wide variety of organic and inorganic substances including chemicals and heavy metals. However, the fate of MPs in urban sewer systems is not yet well understood. In this work two types of virgin polypropylene (PP) samples, isotactic (iPP) and atactic (aPP), were exposed to two synthetic wastewater solutions in order to study their effects on the physical properties of the hydrophobic polymer surfaces. Particular attention was paid to the pollution adhesion at the air-liquid-solid interfaces of the surface air pockets entrapped on the polymer surfaces. The first wastewater solution consists of mixed fat, oil and grease (FOG) - surfactant and another which is an exclusively contained wastewater surfactant. The interaction experiment over a period of 10 min between the polymer’s air pocket and solutions indicated that the size of the bubble in the mixed FOG-surfactant solution increased more pronouncedly for iPP (%152) in contrast to aPP (%31) and was also compared with the greater surface roughness of the polymers. The size variation of the spherical cap on the immersed polymer surfaces were measured between 17 µm and 85 µm using image processing techniques while the data was analyzed by the Young-Laplace equation. The corresponding technical surface roughness of the polymers, the surface tension of the liquids and their air/water contact angle on the flat polymer surfaces were also measured. The results of this study indicated that surface air pockets influence the adsorption capacity of MPs and thus their buoyancy and contamination potential.

Keywords: polypropylene (PP); surface roughness; air pockets; surfactant; FOG; wastewater

Permalink: https://www.hzdr.de/publications/Publ-30463
Publ.-Id: 30463


Atomic Scale Analysis of Ultra-Thin InxGa1-xN/GaN Quantum Wells by High Resolution HR(S)TEM

Vasileiadis, I. G.; Lymperakis, L.; Liebscher, C. H.; Dimakis, E.; Hübner, R.; Adikimenakis, A.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.

Short period superlattices (SPSs) of InxGa1-xN/GaN quantum wells (QW) with a thickness of one up to just a few atomic monolayers (MLs) are promising for bandgap and strain engineering towards advanced optoelectronics devices and novel topological insulators.

We have considered 5-period InxGa1-xN/GaN SPSs deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates under metal-rich conditions. The nominal QW thickness was 1 ML and the GaN barriers were 10 nm thick. The SPSs were grown at various growth temperatures keeping the same temperature for both QWs and GaN barriers.

Cs-corrected high resolution transmission electron microscopy (HRTEM), and probe-corrected scanning TEM (HRSTEM) observations were carried out in order to elucidate the effect of growth temperature on the structural quality, composition, and strain state of the QWs. Cross-sectional observations were conducted along the <11-20> and <1-100> projection directions. Atomic positions were identified on images using a peak finding algorithm and were employed in order to extract nanoscale strain maps. Furthermore, quantification of the Z-contrast of atomic columns on the HRSTEM observations was employed for the direct determination of the indium content in QWs. The thin foil relaxation phenomenon was considered in the analysis.

Composition dependent strain graphs were calculated theoretically in order to associate the experimental strain measurements to the indium content. For that purpose, a series of energetically relaxed InxGa1-xN/GaN supercells were constructed taking into account several indium contents, and the QW thickness limited to 1 ML. For the relaxation of the supercells a ternary empirical interatomic potential was utilized using molecular dynamics simulations.

  • Lecture (Conference)
    XXXIV Panhellenic Conference on Solid State Physics and Materials Science, 11.09.2019, Patras, Greece

Permalink: https://www.hzdr.de/publications/Publ-30462
Publ.-Id: 30462


Status and Applications TOF-SIMS in the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.

The helium ion microscope (HIM), well known for its highresolution
imaging and nanofabrication performance, suffered
from the lack of a well integrated analytic method that can
enrich the highly detailed morphological images with materials
contrast. Recently, a magnetic sector and a time-of-flight
secondary ion mass spectrometer (TOF-SIMS) have been developed
that can be retrofitted to existing microscopes [1,2].
We report on our time-of-flight setup using a straight secondary
ion extraction optics that has been designed and
optimized for highest transmission. The high efficiency is
the most crucial parameter to collect enough signal from
nanoparticles prior to their complete removal by ion sputtering.
As a major advantage the time-of-flight approach
inherently can measure all masses in parallel and thus provides
the complete picture of the sample composition. The
TOF-SIMS is a versatile add-on that helps the user to get
previously unknown details about his samples and is therefore
beneficial for many applications. At the end we will also
give an outlook on future developments.

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.;
Notte, J. A.; Huang, J. and Facsko, S.; Nanometer scale
elemental analysis in the helium ion microscope using time
of flight spectrometry, Ultramicroscopy 162(2016): 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von
Borany, J.; Time-of-flight secondary ion mass spectrometry
in the helium ion microscope, Ultramicroscopy 198(2019),
10-17

  • Lecture (Conference)
    Ion Beam Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30461
Publ.-Id: 30461


Strain Relaxation in In(Ga)N/GaN Short Period Superlattices

Vasileiadis, I. G.; Adikimenakis, A.; Dimakis, E.; Hübner, R.; Lymperakis, L.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.

Introduction/Purpose: Short period superlattices (SPSs) comprising ultrathin InGaN/GaN quantum wells (QW) with thicknesses ranging from one to few (0002) monolayers (MLs) are promising for novel applications ranging from band gap engineering in optoelectronic devices to topological insulators. The strain relaxation behavior of a range of samples grown by varying the growth temperatures for the QWs and GaN barriers has been considered.
Methods: In(Ga)N/GaN SPSs were deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates. Structural characterization was performed by high resolution transmission and scanning transmission electron microscopy (HRTEM/HRSTEM).
Results: Strain relaxation through formation of stacking fault domains was observed with decreasing growth temperature. For the quantification of strain versus composition, peak finding with a recently established approach was implemented. This involves quantification of Z-contrast from HRSTEM observations by comparison with calculated composition-dependent graphs of InxGa1-xN/GaN atomic column intensity ratios obtained from multislice image simulations of energetically relaxed supercells under the frozen lattice approximation. Energetical relaxation was performed by molecular dynamics using an empirical interatomic potential, considering the ordered, disordered, and island models of QW structure. Comparison to the experimental observations was performed along the a-type zone axis that is appropriate to deduce average values for the QW composition and strain.
Conclusions: The investigation concluded to the influence of growth temperature in the composition and structural properties of ultra-thin In(Ga)N/GaN QWs.

  • Lecture (Conference)
    EUROMAT 2019, 01.09.2019, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-30460
Publ.-Id: 30460


Nano-pillar evolution by FIB irradiation with heavy ions

Bischoff, L.; Heinig, K.-H.; Möller, W.; Klingner, N.; Pilz, W.; Borany, J.

The European H2020 project “ion4SET” is directed to the development of advanced computation and communication devices with significantly lower power consumption. The general objective is to demonstrate the manufacturability of single electron transistors (SETs) using CMOS compatible technology. The basic idea of this SET is a nano-pillar (NP) transistor having a single Si nanodot (ND) in the oxide layer separating source and drain. The ND is formed by ion beam mixing and post annealing from a Si top layer. The ion irradiation under normal incidence is a crucial process for the small nano-pillars which are only 10 to 30 nm in width and about 80 nm in height.
In this work the evolution nano-pillars shape is investigated under heavy ion irradiation from a mass separated focused ion beam (FIB) for different ion energies at RT and 400°C target temperature. In particular Si (60 keV), Pb (30 and 60 keV), Au (30 and 60 keV) ions as well as polyatomic projectiles Au2 and Au3 (Uacc = 30 kV) with a fluence of 5 x 1015 cm-2 were applied.
Whereas the Si ion irradiation of Si pillars at elevated temperatures only deforms the pillar tip, the heavy ion irradiation leads depending on the fluence up to a total removing of the pillar. The fluence variation was obtained on the slope of the beam profile. The irradiation at RT with Pb ions at 30 keV showed a more pronounced bending of the pillar due to the high energy deposition caused stress and viscous flow than that at 60 keV. The influence of the irradiation is also depending on the thickness and the distance of the pillars in different lithographic prepared fields. For a better comprehension of the irradiation results the experiments were simulated using the TRI3DYN code.

  • Lecture (Conference)
    Ion Beam Physics Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30459
Publ.-Id: 30459


Sub-50 keV helium ions as an imaging probe in transmission microscopy and secondary ion mass spectrometry

Mousley, M.; Eswara, S.; Bouton, O.; Audinot, J.-N.; Klingner, N.; Hlawacek, G.; Wirtz, T.

Transmission imaging with helium ions is expected to offer contrast not possible with electron beams. Whilst MeV helium ion transmission imaging is possible1, sub-50 keV helium ions are more widely available, for example, in helium ion microscope (HIM) machines. These HIM systems can perform high-resolution secondary electron imaging as well as secondary ion mass spectrometry (SIMS) elemental analysis2. Despite recent interest in the transmission imaging capabilities of low energy helium3, this method still requires detailed evaluation. Time of flight (TOF) spectroscopy for backscattered helium in a HIM has also been reported4 but transmission TOF energy spectroscopy with sub-50 keV energy helium remains unexplored. This technique should obtain information not accessible using solely transmission images.
This work focuses on the contrasts available using sub-50 keV He+ in a transmission-HIM (THIM). Our experiments used an in-house developed THIM utilising a duoplasmatron ion source operated below 50 kV. Powdered crystals of BN, NaCl and MgO were investigated in the THIM, using 10 keV He+ stationary beam illumination. A large scattering effect was visible (fig. 1B) and has been explained by sample charging, which will require consideration in all future THIM imaging experiments. Scanning THIM (STHIM) results will also be discussed, SE and STHIM images were recorded in parallel for a Cu mesh (fig. 1C ). As an additional mode, deflector plates can pulse the primary beam, allowing our THIM to record STHIM-TOF spectra (see fig. 1D) .We will also present selected recent results obtained using our in-house developed SIMS system, attached to a Zeiss Nanofab HIM2. Fig. 2 shows images from a CIGS photovoltaic solar cell active layer, containing Na, In and Cu. HIM-SIMS can efficiently analyse the nanometre scale distribution of Na, the presence of which can reduce the efficiency of the solar cell.
Funding from Luxembourg National Research Fund (FNR) project STHIM (C16/MS/11354626) and EU Horizon 2020 Grant No. 720964.

Figure 1 A) THIM image of MgO sample on Cu grid, hole width 108 µm bar width 19 µm (scale bar approx. 2.5 mrad), B) a spot pattern from MgO. C) SE and STHIM images of a Cu grid recorded in parallel, hole width approx. 90 µm. D) TOF spectrum of source emission for 10 keV He+.

Figure 2A) HIM-SE image and HIM-SIMS images showing the distributions of Na, In and Cu for an active layer of a CIGS solar cell. SE image recorded using 20 keV He+, SIMS images recorded, using 20 keV Ne+ ions, in a Zeiss Nanofab equipped with an in-house developed SIMS system. Field of view is 10 µm.

1. Watt, F. et al. Whole cell structural imaging at 20 nanometre resolutions using MeV ions. Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 306, 6–11 (2013).
2. Dowsett, D. & Wirtz, T. Co-Registered In Situ Secondary Electron and Mass Spectral Imaging on the Helium Ion Microscope Demonstrated Using Lithium Titanate and Magnesium Oxide Nanoparticles. Anal. Chem. 89, 8957–8965 (2017).
3. Wang, J. et al. Focussed helium ion channeling through Si nanomembranes. J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 36, 021203 (2018).
4. Klingner, N. et al. Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry. Ultramicroscopy 162, 91–97 (2016).

  • Lecture (Conference)
    Microscopy Conference 2019, 01.-05.09.2019, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30458
Publ.-Id: 30458


Controlled-growth and tuning of electronic properties in GaAs nanowires on Si substrates

Tauchnitz, T.; Balaghi, L.; Fotev, I.; Shan, S.; Pashkin, O.; Bussone, G.; Grifone, R.; Grenzer, J.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.

III-As semiconductors in the form of free-standing nanowires have exhibited new potentials for a wide variety of future applications in nanotechnology, ranging from energy-efficient electronic switches to entangled-photon-pair sources for quantum information technology, including the possibility for monolithic integration in the mainstream Si technology. Using molecular beam epitaxy, we developed an in situ procedure (substrate annealing – Ga deposition – substrate annealing) in order to modify the surface of Si substrates and, thus, to achieve highly synchronized nucleation of self-catalyzed GaAs nanowire ensembles with well controlled dimensions and number density. Specifically, the radius can be as low as 10 nm, the distribution of lengths can be sub-Poissonian (due to the so-called nucleation anti-bunching), and the number density can be varied from 10 ⁶ to 10 ⁹ cm-2.
Furthermore, the GaAs nanowires can be hydrostatically strained when they are overgrown all-around with lattice-mismatched shells. The high surface-to-volume ratios allow for growing highly mismatched combinations without dislocations, beyond to what is possible in thin-film heterostructures. Here, we show that the mismatch strain inside the GaAs core can be engineered via the composition and the thickness of an (In, Ga)As or (In, Al)As shell. As a result, the electronic properties of GaAs can be widely tuned; the band gap and the electron effective mass can be reduced down to 60% of the strain-free values, rendering GaAs nanowires suitable for photonic devices across the near-infrared (800 – 1400 nm) range or for high-speed transistors.

  • Poster
    2nd Scientific Workshop of the Program “From Matter to Materials and Life” (MML) in the Helmholtz Research Field “Matter”, 13.02.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30457
Publ.-Id: 30457


Complex three-dimensional heterostructures in III-As nanowires

Tauchnitz, T.; Balaghi, L.; Hübner, R.; Wolf, D.; Bussone, G.; Grifone, R.; Grenzer, J.; Pelekanos, N. T.; Schneider, H.; Helm, M.; Dimakis, E.

Free-standing nanowires are promising platforms for hosting three-dimensional heterostructures such as single quantum dots for quantum photonics, modulation doped heterostructures for gate-all-around high mobility transistors, etc. The peculiarity of heteroepitaxy in nanowires is the existence of multiple growth interfaces with different crystallographic orientations (usually one top- and six side-facets), where the growth can take place in different modes (e.g. vapor-liquid-solid on the top- and vapor-solid on the side-facets) and can be controlled independently. Furthermore, strained epilayers in nanowires can relax elastically both at the lateral free surface and by stretching the substrate, which in this case are the thin nanowires. All these features open up new possibilities for complex three-dimensional heterostructures with loose strain restrictions.
Here, we have investigated the growth of radial and axial heterostructures, as well as combinations of the two, within III-As nanowires. The radial ones consist of thin GaAs nanowires overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. In agreement with theory, the small volume of the core allows for strain engineering both in the core and the shell, and for realization of highly-mismatched/strained heterostructures (with misfits up to 4%) without dislocations. The manipulation of the growth kinetics is necessary in order to suppress strain-driven phenomena, such as the preferential shell-growth and In-incorporation on one side of the core. The axial heterostructures consist of single or multiple GaAs/AlxGa1-xAs quantum dots. The width and the thickness of these dots can be controlled independently. The AlxGa1-xAs segments were grown as digital alloys using pulsed epitaxy in order to achieve sharper interfaces and to avoid the formation of stacking faults. Finally, we realized complex heterostructures with single GaAs/AlxGa1-xAs quantum dots inside the core of core/shell nanowires, aiming at engineering the electronic properties of the dots depending on the composition and thickness of the shell.
Besides MBE experiments, our investigations involved transmission electron microscopy (HR-TEM, STEM, EDX, STEM tomography), X-ray diffraction, Raman scattering spectroscopy, and photoluminescence spectroscopy.

  • Lecture (Conference)
    20th European Workshop on Molecular Beam Epitaxy, 17.02.2019, Lenggries, Germany

Permalink: https://www.hzdr.de/publications/Publ-30456
Publ.-Id: 30456


TOF-SIMS with highest lateral resolution by pulsing the Ne-GFIS in a HIM

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.

The helium ion microscope (HIM), well known for its high-resolution imaging and nanofabrication performance, suffered from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. Recently, a magnetic sector and a time-of-flight secondary ion mass spectrometer (TOF-SIMS) have been developed that can be retrofitted to existing microscopes [1,2].
We report on our time-of-flight setup using a straight secondary ion extraction optics that has been designed and optimized for highest transmission. The high efficiency is the most crucial parameter to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. As a major advantage the time-of-flight approach inherently can measure all masses in parallel and thus provides the complete picture of the sample composition. The TOF-SIMS is a versatile add-on that helps the user to get previously unknown details about his samples and is therefore beneficial for many applications. At the end we will also give an outlook on future developments.

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and
Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018). Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.

  • Lecture (Conference)
    3rd EuFN Workshop 2019 of the European FIB Network, 12.-14.06.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30455
Publ.-Id: 30455


Complex quantum dots in III-As nanowires

Tauchnitz, T.; Balaghi, L.; Hübner, R.; Chatzarakis, N.; Pelekanos, N. T.; Bussone, G.; Grifone, R.; Grenzer, J.; Schneider, H.; Helm, M.; Dimakis, E.

Single quantum dots in the core of freestanding semiconductor nanowires is a promising scheme for the realization of on-demand sources of single photons or entangled photon pairs in quantum technology systems. Here, we demonstrate that complex quantum-dots can be grown in self-catalyzed III-As nanowires and their emission can be tuned in a wide range of wavelengths.
The quantum dots are formed inside self-catalyzed GaAs nanowires (grown on Si substrates by molecular beam epitaxy) by first growing an axial AlxGa1-xAs/GaAs/AlxGa1-xAs heterostructure in pulsed mode . The AlxGa1-xAs segments are grown as digital alloys with a precise control of the composition, the thickness, and the crystal structure (absence of stacking faults). Then, the nanowires are overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. Owing to the large lattice-mismatch with the shell, the thin core develops tensile hydrostatic strain and the emission from the dot is strongly red-shifted. Furthermore, distinct exciton-biexciton features are identified in photoluminescence measurements.

Keywords: self-catalyzed; strain engineering; bandgap tuning

  • Lecture (Conference)
    Nanowire Week 2019, 23.09.2019, Pisa, Italy

Permalink: https://www.hzdr.de/publications/Publ-30454
Publ.-Id: 30454


Imaging by Transmission Ion Microscopy and Secondary Ion Mass Spectrometry using sub-50 keV He+ ion beams

Eswara, S.; Mousley, M.; de Castro, O.; Bouton, O.; Audinot, J.-N.; Klingner, N.; Koch, C.; Hlawacek, G.; Wirtz, T.

The recent availability of high-brightness helium ion sources has enabled exciting new possibilities in the fields of microscopy and nanofabrication. When compared to electron beams of same energy, He+ ions have a smaller interaction volume and thus offer higher lateral resolution (< 0.5 nm) in the secondary electron (SE) imaging mode1. While the majority of the applications of the commercial Helium Ion Microscope - HIM (Zeiss Nanofab) have been in SE imaging and nanofabrication, the complete range of imaging possibilities is still not fully explored. In this context, transmission ion microscopy is expected to offer new contrast mechanisms (e.g. charge neutralization) which are not possible in a Transmission Electron Microscope (TEM). Transmission microscopy using MeV He+ ions has already been demonstrated2, but, they are not very widely available. With the increasing availability of HIM which operate at primary energies below 50 keV, the potential to use it for transmission ion microscopy and ion energy-loss spectroscopy still need to be fully explored. To address this, we developed a prototype Transmission Helium Ion Microscope (THIM) that can operate on both stationary full-field THIM mode as well as Scanning THIM (STHIM) mode with simultaneous SE imaging possibility. This prototype has a duoplasmatron ion source and offers full flexibility in terms of instrumental configurations. This is a significant advantage in comparison to using the commercial instrument in which space below the specimen plane is very limited and thus restrict the possible experimental configurations. We imaged BN, NaCl and MgO crystalline powders in the stationary full-field THIM imaging using 10 keV He+ and investigated the distribution of transmitted ion intensities. The scattered intensity form unexpected spot patterns that may be explained by sample charging and morphology. Furthermore, we have added electronics to pulse the primary ion beam in the prototype instrument. This allows us to perform Time-of-Flight (TOF) multispectral imaging in both THIM and STHIM modes in addition to the standard Bright-Field, Dark-Field and SE imaging modes. Our presentation will focus mainly on the transmission ion configuration. We will also briefly discuss the recent developments in the Secondary Ion Mass Spectrometers (SIMS) that we developed for Zeiss Nanofab instruments (HIM-SIMS) which allow direct chemical mapping at nanoscale.
1 G. Hlawacek and A. Gölzhäuser, editors , Helium Ion Microscopy, 1st ed. (Springer, 2016).
2 F. Watt et al, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 306, 6 (2013).

  • Lecture (Conference)
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS 2019, 13.-20.10.2019, Antibes, France

Permalink: https://www.hzdr.de/publications/Publ-30453
Publ.-Id: 30453


A TOF-SIMS nanoprobe with sub-10 nm lateral resolution

Klingner, N.; Heller, R.; Hlawacek, G.

The Helium Ion Microscopes (HIM) provides spot sizes up to 0.5 nm for Helium and 1.8 nm for Neon ion beams. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating.

We designed, implemented and reported on the first time-of-flight secondary ion mass spectrometry (TOF-SIMS) add-on that can be retrofitted to existing microscopes [1, 2, 3]. It is based on fast blanking electronics that chop the primary beam into pulses with a minimal length of 20 ns. An ion optic has been designed and optimized for high extraction and transmission efficiency of sputtered secondary ions. The high transmission is crucial to collect enough signal from nano-particles prior to their complete removal by ion sputtering. Currently the sample will be tilted towards the extraction optic and will be constantly biased to +/- 500 V to accelerate the ions into the extraction nozzle.

The setup can obtain SIMS data from a region of interest or can be used in imaging mode to obtain elemental line profiles and maps of the surface. The beam resolution has been evaluated to 8 nm using the knife edge method, and unpulsed beam and a 75%/25% criterion. We will show an outlook on adding a delayed secondary ion extraction.

References

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162, 91-97.

[2] Heller, R.; Klingner, N.; Hlawacek, G. (2016). Backscattering Spectrometry in the Helium Ion Microscope: Imaging Elemental Compositions on the nm Scale. In: Hlawacek, G. & Gölzhäuser, A. (Ed.), Helium Ion Microsc., Springer International.

[3] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2019) Time-of-flight secondary ion mass spectrometry in the helium ion microscope, Ultramicroscopy 198, 10-17

  • Poster
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS 2019, 13.-18.10.2019, Antibes, France

Permalink: https://www.hzdr.de/publications/Publ-30452
Publ.-Id: 30452


Visualisation and Chemical Characterisation of the Cathode Electrolyte Interphase in High Voltage Li-ion Battery Material LiCoPO4 using He-ion Microscopy and in-situ Time-of-Flight Secondary Ion Mass Spectroscopy

Wheatcroft, L.; Klingner, N.; Heller, R.; Hlawacek, G.; Ozkaya, D.; Cookson, J.; Inkson, B. J.

The development of high voltage Li-ion battery materials has been hindered by undesired reactions at the electrolyte-electrode interface. Here, the process of cathode electrolyte interphase (CEI) formation in high voltage cathode material, LiCoPO4, has been investigated for the first time using Helium Ion Microscopy (HIM), and in-situ Time-of-Flight (ToF) Secondary Ion Mass Spectrometry (SIMS). The combination of HIM and Ne-ion ToF-SIMS has been used to correlate the morphology and chemistry of the CEI layer on LiCoPO4 with local cathode microstructure. Helium ion microscopy was found to be capable of imaging the CEI layer with higher resolution than scanning electron microscopy (SEM), and at large fields of view. The CEI layer was found to grow on LiCoPO4 when the cathode was charged, and undergo partial dissolution on discharge. CEI layer coverage on LiCoPO4 was inhomogenous, and typically thinner on larger agglomerates. Ne-ion SIMS characterisation identified the presence of oxyfluorophosphates from HF attack by the electrolyte, and the presence of uncycled Li and potential Co dissolution on the surface. The variable thickness of the CEI layer with inactive Li on the surface of the LiCoPO4 electrodes led to severe degradation over the course of 10 cycles.

Permalink: https://www.hzdr.de/publications/Publ-30450
Publ.-Id: 30450


Energy cascades, coherent structures, and the arrow of time in turbulence

Kelley, D. H.; Tithof, J. R.; Horstmann, G. M.; Suri, B.; Aluie, H.; Schatz, M. F.; Grigoriev, R. O.

Energy cascades, coherent structures, and the arrow of time in turbulence

  • Invited lecture (Conferences)
    Physics seminar, 18.11.2019, Fayetteville, Arkansas, USA

Permalink: https://www.hzdr.de/publications/Publ-30448
Publ.-Id: 30448


Energy cascades & the asymmetric motion of coherent structures

Kelley, G. H.; Tithof, J. R.; Horstmann, G. M.; Suri, B.; Aluie, H.; Schatz, M. F.; Grigoriev, R. O.

Energy cascades, coherent structures, and the arrow of time in turbulence

  • Lecture (Conference)
    72nd Annual Meeting of the APS Division of Fluid Dynamics, 23.-26.11.2019, Seattle, Washington, USA

Permalink: https://www.hzdr.de/publications/Publ-30447
Publ.-Id: 30447


Flow regimes of Rayleigh-Bénard convection in a vertical magnetic field

Zürner, T.; Schindler, F.; Vogt, T.; Eckert, S.; Schumacher, J.

The effects of a vertical constant magnetic field on the flow structure and global transport properties of momentum and heat in liquid metal Rayleigh-Bénard convection are investigated. Experiments are conducted in a cylindrical convection cell of unity aspect ratio, filled with the alloy GaInSn at a low Prandtl number of Pr = 0.029. Changes of the large-scale velocity field structure with increasing magnetic field strength are probed using multiple ultrasound Doppler velocimetry sensors and thermocouples for a Rayleigh number range of 10^6 < Ra < 6x10^7 and Hartmann numbers Ha < 1000. Our simultaneous multi-probe temperature and velocity measurements demonstrate how the large-scale circulation is affected by an increasing magnetic field strength (or Hartmann number). Lorentz forces induced in the liquid metal first suppress the oscillations of the large-scale circulation, then transform the one-roll structure into a cellular large-scale pattern consisting of multiple up- and downwellings, before finally expelling any fluid motion out of the bulk leaving only a near-wall convective flow that persists even below Chandrasekhar's linear instability threshold. Our study thus proofs experimentally the existence of wall modes in confined magnetoconvection. The magnitude of the transferred heat remains nearly unaffected by the steady decrease of the velocity momentum over a large range of Hartmann numbers. Previous experiments and direct numerical simulations are consistent with our results.

Keywords: magnetoconvection Rayleig-Bénard convection; liquid metal

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-30445
Publ.-Id: 30445


Rayleigh-Bénard Convection in Liquid metal under Influence of Vertical Magnetic Fields

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

Conference (Lecture):

American Physics Society (APS) DFD meeting 2019 Seattle

In the presented Rayleigh-Bénard convection experiments the turbulent 3d-
flow of the liquid gallium-indium-tin alloy is investigated by use of ultrasound
Doppler velocimetry, temperature and contactless inductive flow tomography
measurements. We reconstruct for the first time near-wall as well as bulk
flow, momentum and heat transport as well as long-term behaviour of the large-scale liquid
metal flow at a low Prandtl number of 0.029 and high Rayleigh numbers up
to 6 · 10e7. Also the influence of a strong magnetic field on the turbulent liquid metal is investigated. The results of the
experiments are compared to direct numerical simulations and other experiments. These are also
considered for the interpretation of the measured turbulence statistics.
Our experiments aim to provide a deeper understanding of the turbulent
convection and its interaction with magnetic fields in turbulent low Prandtl number
flows as those in molten steel, aluminium or geo- and astrophysical flows.

Keywords: Rayleigh-Bénard convection; magnetohydrodynamics; low Prandtl number; liquid metal; ultrasound velocimetry

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-11-23
    DOI: 10.14278/rodare.231
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30444
Publ.-Id: 30444


Analysis, design and optimization of compact ultra-high sensitivity coreless induction coil sensors

Ratajczak, M.; Wondrak, T.

We require a compact magnetic field measurement system that is able to measure alternating magnetic flux densities in the nanotesla range on the background of signals with constant amplitudes of some hundred millitesla. The signal of interest has a frequency of a few Hertz and must be measured with an amplitude error smaller than 0.1% and a phase error no larger than 10⁻¹ deg. For this we present theoretical and experimental analyses of absolute and first order gradiometric induction coil sensors with sensitivities larger than 500 V/T/Hz and diameters of 28 mm. From their equivalent circuits, we derive the associated complex-valued transfer functions and fit these to calibration measurements, thereby determining the value of the equivalent circuit components. This allows us to compensate their non-linear frequency-dependent amplitude and phase behaviour. Furthermore, we demonstrate the optimization of coils based on Brooks' design of equal squares in the adaptation by Murgatroyd, which maximizes the inductance (and thereby most likely the sensitivity) of the coils. Finally, we design a new coil with a diameter of 74 mm and a sensitivity of 577 V/T/Hz with an analytically predicted equivalent magnetic field noise of around 40 pT/√Hz in the 1 Hz frequency range, which is then confirmed by measurements on the manufactured prototype.

Keywords: magnetic field measurement; induction coil; gradiometric coil; contactless inductive flow tomography

Permalink: https://www.hzdr.de/publications/Publ-30443
Publ.-Id: 30443


Rayleigh-Bénard Convection in a Vertical Magnetic Field at Low Prandtl Number

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

11th PAMIR International Conference- Fundamental and Applied MHD July 1-5, 2019, Reims, EVEM France

The present work shows the experimental realisation of three-dimensional
magnetoconvection studies at Rayleigh numbers between 10e6 and 6 · 10e7 and Hartmann
numbers up to 1000 in a Rayleigh-Bénard convection cell. The fluid in the cell is the
GaInSn metal alloy with a low Prandtl number of 0.029. The flow is investigated using
thermocouples and ultrasound-Doppler-velocimetry. The change of the Nusselt number
with increasing Hartmann number is studied and presented. Experimental results are
compared to other experiments and simulations.

Keywords: liquid metal; low Prandtl number; Rayleigh-Bénard magnetoconvection; vertical magnetic Field

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-07-01
    DOI: 10.14278/rodare.229
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30441
Publ.-Id: 30441


X-ray radiographic visualization of bubbly flows injected by a top submerged lance in a liquid metal layer

Akashi, M.; Keplinger, O.; Anders, S.; Reuter, M.; Eckert, S.

We report on laboratory experiments focusing on bubbling phenomena arising from gas injection through a top submerged lance (TSL) in a liquid metal layer. Visualization was performed in the eutectic alloy GaInSn using X-ray radiography. Argon bubbles were injected through the nozzle positioned at three different submergence depths. Essential parameters such as the bubble size, bubble shape, detachment frequency or the two-dimensional gas distribution in the flat vessel were obtained by image processing. The results show that the deep position of the submerged lance causes an asymmetric large-scale circulation inside the fluid vessel. Bubble detachment frequencies were calculated by Fast Fourier Transformation from fluctuations of the image intensity in the vicinity of the nozzle injection point. This frequency does not show strong variations with respect to changes of the gas flow rate and the submergence depth of the nozzle. An increasing gas flow rate results in an increasing two-dimensional projected bubble area and the occurrence of a significant number of small bubbles being trapped by the strong fluid flow in the liquid metal layer.

Keywords: Two phase flow; Liquid metal; Top submerged lance

  • Lecture (Conference)
    17th Multiphase Flow Conference and Short Course, 11.-15.11.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30440
Publ.-Id: 30440


Low Prandtl Number Rayleigh-Bénard Convection in a Vertical Magnetic Field

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

Lecture (Conference)

11th PAMIR International Conference- Fundamental and Applied MHD July 1-5, 2019, Reims, EVEM France

We are investigating turbulent Rayleigh-Bénard convection in liquid metal under the
influence of a vertical magnetic field. Utilizing a combination of thermocouple (TC) and
ultrasound-Doppler-velocimetry (UDV) measurements gives us the possibility to directly
determine the temperature and velocity field, respectively. Further this gives us the
possibility to observe changes in the large-scale flow structure.
By applying magnetic fields to the liquid metal convection, we quantified changes of heat
and momentum transport in the liquid metal alloy GaInSn. The experimental results of our
setup agree well with theory findings and direct numerical simulations of the dynamics in
our convection cell. The requirement of large computing power at these parameters makes
it hard to simulate long-term dynamics with time scales from minutes to several hours. Thus
to investigate slow developing dynamics like sloshing, rotation, or deformation of the large-
scale flow structure model experiments are indispensable.
We demonstrate the suppression of the convective flow by a vertical magnetic field in a
cylindrical cell of aspect ratio 1. In this setup Rayleigh numbers up to 6·107 are
investigated. The flow structure at low Hartmann numbers is a single roll large scale
circulation (LSC). Increasing the Hartmann number leads to a transition from the single-roll
LSC into a cell structure. An even stronger magnetic field supresses the flow in the center
of the cell completely and expels the flow to the side walls.
Even above the critical Hartmann numbers corresponding to the Chandrasekhar limit for
the onset of magnetoconvection in a fluid layer without lateral boundaries we still observe
remarkable flows near the side walls. The destabilising effect of the non-conducting side
walls was predicted by theory and simulations, and is here for the first time experimentally
confirmed.

Keywords: Rayleigh-Bénard-Convection; Magnetohydrodynamic; low Prandtl Number; liquid metal; Ultrasound velocimetry

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-07-01
    DOI: 10.14278/rodare.227
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30439
Publ.-Id: 30439


CFD Modeling of Top-Submerged-Lance Argon injection in liquid metal

Obiso, D.; Sebastian, K.; Akashi, M.; Eckert, S.; Reuter, M.

The present paper focuses on the application of CFD techniques to investigate the Top-Submerged-Lance (TSL) gas injection in liquid metal.
Previous works of the authors have shown that up- and down-scaling procedures based on the modi-fied Froude number have some shortcomings, as this approach does not take into account the interfa-cial and viscous forces. Indeed surface tension and dynamic viscosity of the smelting slags (σ = 0.4-0.5 N/m, μ = 0.2 Pa·s) are higher than the operating fluids that have been used in literature (water, par-affin oil), which have been used to study TSL injection in down-scaled furnaces.. In order to get closer to real systems, the authors study the TSL injection of Argon in a liquid metal.
An experimental campaign was carried out at the Magnetohydrodynamic Department of Helmholtz-Zentrum Dresden-Rossendorf (HZDR), where the eutectic alloy GaInSn was used as liquid phase. The alloy is liquid at room temperature, and X-Ray imaging is used to picture the multiphase flow in a qua-si-2D vessel (140x140x12 mm).
The aim of the present work is to demonstrate the applicability of CFD techniques to model multi-phase flows involving liquid metals, and validate the model using the data produced at HZDR. The commercial software ANSYS Fluent® was used together with the Volume of Fluid model to directly resolve the gas-liquid interphase. Some features of the flow, such as the void fraction distribution and bubble detachment frequency are tracked with CFD and compared to the experimental data. The ef-fect on the hydrodynamics of different operating conditions, such as the lance immersion depth is investigated.
The authors are currently extending the work to new geometries and operating conditions, in order to get a broader amount of data, useful for the validation of models and for the further understanding of the TSL injection.

Keywords: two phase flow; top submerged lance; liquid metal

  • Lecture (Conference)
    10th Copper International Conference (COPPER 2019), 18.-21.08.2019, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-30436
Publ.-Id: 30436


Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing

Xie, Y.; Yuan, Y.; Wang, M.; Xu, C.; Hübner, R.; Grenzer, J.; Zeng, Y.-J.; Helm, M.; Zhou, S.; Prucnal, S.

Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.

  • Open Access Logo Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 03.04.2019, Regensburg, Deutschland
    DOI: 10.1063/1.5057733

Permalink: https://www.hzdr.de/publications/Publ-30435
Publ.-Id: 30435


Experimental analysis of gas phase dynamics in a lab scale bubble column operated with deionized water and NaOH solution under uniform bubbly flow conditions

Kipping, R.; Kryk, H.; Hampel, U.

In this study we present an investigation on the impact of sparger configuration and fluid properties on the local gas phase dynamics for up to 17% total gas holdup. Experiments in a bubble column with 100 mm inner diameter were conducted with deionized water and NaOH solution of up to cNaOH = 32 mmol·l−1. Ultrafast X-ray computed tomography (UFXCT) was applied to obtain local hydrodynamic parameters, such as gas holdup distribution, bubble sizes and average bubble rise velocities. Radial gas holdup profiles show wall peaking, which is attributed to the uniform bubbly flow regime generated by the needle sparger used in this study. The addition of NaOH leads to similar gas holdup values but significant changes on local bubbly dynamics, such as bubble size distribution and axial gas phase velocity. The Sauter mean diameter was found to decrease with increasing concentration of NaOH, whereby the decrease is larger at higher gas flow rate.

Keywords: bubble column hydrodynamics; mono-dispersed bubbly flow; bubble size distribution; bubble rise velocity; electrolyte solutions; Ultrafast X-ray tomography

Related publications

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  • Secondary publication expected from 25.08.2021

Permalink: https://www.hzdr.de/publications/Publ-30434
Publ.-Id: 30434


Mmpxrt; X-ray spectrometer simulation code with a detailed support of mosaic crystals.

Smid, M.; Pan, X.; Falk, K.

This is a a newly developed ray tracing code called mmpxrt, dedicated to study and design x-ray crystal optics, with a special focus on mosaic crystal spectrometers. Its main advantage over other currently available ray tracing codes is that it includes detailed and benchmarked algorithm to treat mosaic crystals, especially HOPG and HAPG (Highly Oriented / Annealed Pyrolitic Graphite). The code is dedicated primarily to study crystal spectrometers, therefore their implementation is very straightforward, and the code has mostly automatic evaluation of their performance. It can, however, be used universally to study other crystal instruments, like monochromators, mirrors, and analyzers. The code is publicly available in HZDR's Gitlab, written in Python3 and is distributed as a Python library with test cases included.

Keywords: mosaic crystal; x-ray spectroscopy; ray tracing; Python3

Related publications

  • Software in the HZDR data repository RODARE
    Publication date: 2021-01-12
    DOI: 10.14278/rodare.740
    License: CC-BY-4.0

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30433
Publ.-Id: 30433


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.; Makarov, D.

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]
Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The 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 (λ = 450-490 nm). Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] 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 DOI: 10.1002/smll.201803613.
4. Wang, X., et al., Small 2018, 14, 1802537.

Keywords: Active Janus particles; exclusion interaction; passive beads; visible light‐driven micromotors

  • Lecture (Conference)
    DPG Spring Meetings 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30432
Publ.-Id: 30432


Programmed Magnetically-Triggered Ultrafast Soft Robots

Wang, X.; Ge, J.; Canon Bermudez, G. S.; Kosub, T.; Illing, R.; Wang, C.; Bischoff, L.; Faßbender, J.; Makarov, D.

Soft robots have been designed and developed to fulfil the demands of better deformability and adaptability to changing environment [1-2]. These soft robots could be made of various stimuli responsive materials that can be actuated by 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 the benefits stem from their long-range penetration, easy accessibility, and controllability [2]. Very recently, there are already impressive demonstrations of magnetically triggered millimetre- and centimetre- scaled soft robots performing multimodal locomotion [9] and complex 3D actuations [10]. However, their thick and bulky bodies [9-10] challenge themselves to reveal better performances for specific implantations which require more, for instance, high actuation speed, and reversible large-scale actuation amplitude by a rather low magnetic field.

Here, we present an ultrathin (7-100 μm) and lightweight (1.2-2.4 g/cm3) soft robot that can be actuated in a tiny magnetic field of 0.2 mT reaching full actuation amplitude with a reaction time of 10 ms only. By programming the foils into different geometries, these soft robots are readily used for multifunctional nature-mimicking motion with a magnetic coil or a permanent magnet, such as a quick fly gripping and releasing, complex fast human cross-clapping mimicking, etc.

[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., Nature materials 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nature Materials 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today, 10, 30 (2007)
[7] Q. Zhao et al., Nature communications 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)

Keywords: Soft robots; magnetic field; ultrafast actuation

  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibit, 22.-26.04.2019, Phoenix, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-30431
Publ.-Id: 30431


Investigation of particle dynamics and solidification in two phase system by neutron radiography

Baranovskis, R.; Sarma, M.; Ščepanskis, M.; Beinerts, T.; Gaile, A.; Eckert, S.; Räbiger, D.; Lehmann, E. H.; Thomsen, K.; Trtik, P.

We investigate directional solidification of the melt with solid inclusions by means of neutron radiography (NR). As NR is a non-invasive imaging technique, the results, for the first time, reveal the particle trapping in the solidifying melt at macro scale. It is shown that particle solidification in volume can be achieved when liquid and solid phases form mushy zone. Experiments were performed using a rectangular vessel containing tin which was electromagnetically stirred and directionally solidified. Information about the recirculating flow was gathered by tracing 355-500 μm gadolinium (Gd) particles which visualize the flow field and phase composition in any given time. The findings show that metallurgical challenges, e.g. stirring and homogenously dispersing ceramic reinforcement material in MMC, could be solved by applying electromagnetic treatment while melt is in semi-solidus state.

Keywords: Neutron radiography; particle trapping; directional solidification; mushy zone

  • Contribution to proceedings
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
  • Magnetohydrodynamics 56(2020)1, 43-50
    DOI: 10.22364/mhd.56.1.4

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Permalink: https://www.hzdr.de/publications/Publ-30430
Publ.-Id: 30430


Pulsed magnetic field, high pressure and FIB microstructures - a powerful combination for studies of unconventional metals

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

  • Invited lecture (Conferences)
    J-Physics Conference, 18.-21.09.2019, Kobe, Japan

Permalink: https://www.hzdr.de/publications/Publ-30428
Publ.-Id: 30428


FIB microstructures and experiments under extreme conditions

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

  • Invited lecture (Conferences)
    LNCMI - Solid State Physics Seminar, 18.04.2019, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-30427
Publ.-Id: 30427


Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys

Devi, P.; Salazar Mejia, C.; Caron, L.; Singh, S.; Nicklas, M.; Felser, C.

Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large thermal hysteresis at their firstorder martensitic phase transition which hinders a technological application in magnetic refrigeration. By optimizing the Cu content in Ni2CuxMn1.4−xIn0.6, we obtained a thermal hysteresis of the martensitic phase transition in Ni2Cu0.2Mn1.2In0.6 of only 6 K. We can explain this very small hysteresis by an almost perfect habit plane at the interface of martensite and austenite phases. Application of hydrostatic pressure does not reduce the hysteresis further, but shifts the martensitic transition close to room temperature. The isothermal entropy change does not depend on warming or cooling protocols and is pressure independent. Experiments in pulsed-magnetic fields on Ni2Cu0.21.2In0.6 find a reversible magnetocaloric effect with a maximum adiabatic temperature change of −13 K.

Permalink: https://www.hzdr.de/publications/Publ-30426
Publ.-Id: 30426


Fermi surface investigation of the filled skutterudite LaRu4As12

Klotz, J.; Götze, K.; Lorenz, V.; Prots, Y.; Rosner, H.; Harima, H.; Bochenek, L.; Henkie, Z.; Cichorek, T.; Sheikin, I.; Wosnitza, J.

Of all stoichiometric filled-skutterudite superconductors, LaRu4As12 has the highest critical field and temperature. Here we report on a detailed Fermi-surface investigation of LaRu4As12 by means of de Haas–van Alphen measurements and density-functional-theory calculations. We find evidence for a nearly spherical and a multiply connected Fermi-surface sheet. The different effective masses and mass enhancements for the two sheets support two-band superconductivity, which was inferred from previous specific-heat measurements. Furthermore, quantum oscillations persist as well in the superconducting phase. We use two models to describe the additional damping, yielding energy gaps differing by a factor of 5.

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-30424
Publ.-Id: 30424


Focused-ion-beam assisted micropatterning for experiments under extreme conditions

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzangabe vorgelegen.

  • Invited lecture (Conferences)
    Helmholtz MML-Workshop, 13.-15.02.2019, Dresden, Deutschland
  • Invited lecture (Conferences)
    EMFL User Meeting, 25.06.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30423
Publ.-Id: 30423


Topological Two-Dimensional Polymers

Springer, M.; Liu, T.-J.; Kuc, A. B.; Heine, T.

There are around 200 two-dimensional (2D) networks with different topologies. The structural topology of a 2D network defines its electronic structure. Including the electronic topological properties, it gives rise to Dirac cones, topological flat bands and topological insulators. In this Tutorial Review, we show how electronic properties of 2D networks can be calculated by means of a tight-binding approach, and how these properties change when 2nd-neighbour interactions and spin-orbit coupling are included. We explain how to determine whether or not the resulting electronic features have topological signatures by calculation of Chern numbers, Z2 invariants, and by the nanoribbon approach. This tutorial gives suggestions how such topological properties could be realized in explicit atomistic chemical 2D systems made of molecular frameworks, in particular in 2D polymers, where the edges and vertices of a given 2D net are substituted by properly selected molecular building blocks and stitched together in such a way that long-range π-conjugations is retained.

Permalink: https://www.hzdr.de/publications/Publ-30422
Publ.-Id: 30422


Unidirectional tilt and enhancement of the Walker limit for domain walls in stripes with Dzyaloshinskii-Moriya interaction

Pylypovskyi, O.; Kravchuk, V.; Volkov, O.; Faßbender, J.; Sheka, D.; Makarov, D.

Efficient manipulations of chiral textures like domain walls and skyrmions are crucial for the development of prospective spintronic devices [1-2]. Domain walls moving in stripes with perpendicular anisotropy and Dzyaloshinskii-Moriya interaction (DMI) exhibit a tilt resulting in a decrease of their maximal velocity [3]. Beside the direct current influence [3], the tilt is usually caused by in-plane fields [4] or an edge roughness [5]. In this work, we show that the domain wall tilt can appear as a result of competition of the in-plane anisotropy and DMI. We also describe the field-driven dynamics of the tilted domain wall.

We consider an infinitely long biaxial stripe with interfacing DMI (Fig. 1) and biaxial anisotropy. The first easy axis of anisotropy is perpendicular to the stripe plane and the second easy axis lies within the stripe plane and makes an angle α with the stripe axis. The shape anisotropy forces α=0, while α≠0 can appear due to other effects, e.g. exchange bias from underlying antiferromagnet. The second anisotropy rotates the in-plane magnetization inside the domain wall according to the in-plane easy axis direction. The optimum of the DMI energy is reached when the magnetization rotates perpendicularly to the domain wall plane. In stripes the energy balance between these two energy terms and the energy of the domain wall tension results in a unidirectional tilt by angle χ of the domain wall plane (χ=0 corresponds to the domain wall perpendicular to the stripe), determined by α. There is a metastable state of the wall, tilted into the opposite direction in a certain range of anisotropy and DMI values. This is related to the symmetry break between the two opposite directions of the magnetization rotation inside the domain wall due to the presence of a weak DMI. Furthermore, the dynamics of the domain wall in the presence of a biaxial anisotropy and DMI exhibits a symmetry break with respect to the magnetic field and the easy axis direction A. The domain wall reveals fast and slow motion regimes for the opposite signs of α. The slow regime is characterized by a smaller Walker field b and switch of the magnetization direction inside the domain wall in a certain field below b . The latter results in an increase of the domain wall speed. The velocity of the domain wall is inversely proportional to cos χ. The maximum of the Walker field corresponds to α≠0 (Fig. 2).

In conclusion, we describe a unidirectional tilt of a domain wall in a biaxial stripe with DMI, which appears at equilibrium without external magnetic field and demonstrate the enhancement of the Walker field and velocity [6]. The domain wall dynamics reveal fast and slow regimes depending on the orientation of the easy axis of the in-plane anisotropy and the applied magnetic field.

References: [1] K.-S. Ryu, L. Thomas, S.-H. Yang et al., Nat. Nanotech., Vol. 8, 527 (2013); [2] O. Pylypovskyi, D. Sheka, V. Kravchuk et al., Sci. Rep. Vol. 6, 23316 (2016); [3] O. Boulle, S. Rohart, L. Buda-Prejbeanu et al., Phys. Rev. Lett. Vol. 111, 217203 (2013); [4] C. Muratov, V. Slastikov, A. Kolesnikov et al., Phys. Rev. B. Vol. 96, 134417 (2017); [5] E. Martinez, S. Emori, N. Perez et al. J. Appl. Phys. Vol. 115, 213909 (2014); [6] O. Pylypovskyi, V. Kravchuk, O. Volkov et al., ArXiv, 2001.03408 (2020)

Keywords: magnetism; domain wall; Walker limit

  • Lecture (Conference)
    Intermag (Conference is cancelled due to COVID-19), 04.-08.05.2020, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-30421
Publ.-Id: 30421


Skyrmion states, engineered by curvature gradients

Pylypovskyi, O.; Makarov, D.; Kravchuk, V.; Gaididei, Y.; Saxena, A.; Sheka, D.

Skyrmions attract a special attention for spintronic and spinorbitronic devices by their unique static and dynamic properties [1]. The interplay between geometry and magnetization texture gives additional degrees of freedom in control of such topologically nontrivial patterns via geometry-induced anisotropy and Dzyaloshinskii-Moria interaction (DMI) in materials with easy-normal anisotropy [2-5]. It is sufficient for appearance of skyrmions and skyrmion lattices as a ground state on small curvilinear defects [6].

Here, we propose a new way to stabilize skyrmions and control their size via curvature gradient in a nanoindentation even without intrinsic DMI [7]. Our mathematical formalism also allows to describe planar films with inhomogeneous distribution of material parameters. We consider a thin membrane with easy-normal anisotropy and circular nanoindentation of a conic frustrum shape with inner and outer radii R and R , respectively. This geometry can be described by two principal curvatures, k and k , providing the whole information about geometry in the given point of the membrane. While k (r) is inversely proportional to the distance from origin r, k (r) has sharp peaks in points of the bend of the membrane. To compare textures in curved membranes and flat films we propose a projection of a surface of revolution to a plane, which reconstructs a skyrmion equation. The energy of the magnetic texture in projected coordinates obtains a curvature-modified anisotropy and two DMI terms, related to principal curvatures. In contrast to the planar case, the corresponding skyrmion equation is characterized not only by DMI coefficients itself, but also their spatial derivatives playing a role of the external driving force, proportional to d(k + k )/dr. The main consequences of the driving force are: (i) the ground state cannot be strictly normal to the membrane with nonconstant curvature; (ii) a gradient of k can result in stabilization of the Neel skyrmion of radius R or R (Fig. 1). Skyrmions, stabilized at the inner and outer bends, have the opposite chiralities. If the difference between R and R is large enough, both skyrmions can coexist forming a skyrmionium state with zero total winding number. In the limiting case of sharp bends, the minimal angle α of the indentation side for stabilizing topologically nontrivial textures equals 4L/R radians, with R being either R or R (α = 0 corresponds to a flat film) and L being a magnetic length. Numerical analysis of skyrmion stability is performed in a wide range of geometrical parameters (Fig. 2). It is shown that the strength and spatial localization of the DMI coefficient, associated with k , plays the main role in the pinning of topologically nontrivial textures and pinning strength is estimated to be hundredths of Kelvin for typical parameters of Co/Pt multilayers.

In conclusion, we propose a mathematical framework which allows us to describe magnetic nanomembranes with rotational symmetry and planar films with circular distribution of material parameters using the same apparatus. It uncovers two mechanisms of skyrmion stabilization, namely DMI-driven [8] and DMI gradient-driven [7]. The first one does not require the curvature gradients and lead to formation of small-radius skyrmions, while the second allows stabilization of large-radius skyrmions and skyrmionium states of the geometrically defined size.

References: [1] A. Fert, N. Reyren, V. Cros, Nat. Rev. Mater., Vol. 2, 17031 (2017); [2] R. Streubel, P. Fischer, F. Kronast et al., J. Phys. D: Appl. Phys. Vol. 49, 363001 (2016); [3] O. Pylypovskyi, V. Kravchuk, D. Sheka et al., Phys. Rev. Lett. Vol. 114, 197204 (2015); [4] Y. Gaididei, V. Kravchuk, D. Sheka, Phys. Rev. Lett. Vol. 112, 257203 (2014); [5] Y. Gaididei, A. Goussev, V. Kravchuk et al., J. Phys. A: Mat. and Theor. Vol. 50, 385401 (2017); [6] V. Kravchuk, D. Sheka, A. Kákay et al., Phys. Rev. Lett. Vol. 120, 067201 (2018); [7] O. Pylypovskyi, D. Makarov, V. Kravchuk et al., Phys. Rev. Appl. Vol. 10, 064057 (2018); [8] V. Kravchuk, U. Roessler, O. Volkov et al., Phys. Rev. B, Vol. 94, 144402 (2016).

Keywords: curvature; nanoindentation; magnetism

  • Lecture (Conference)
    Intermag (Conference is cancelled due to COVID-19), 04.-08.05.2020, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-30420
Publ.-Id: 30420


Exploring the applications of advanced geomorphic indices in statistically based landslide susceptibility models: a case study from Tajik Tien Shan and Pamir

Barbosa Mejia, L. N.; Andreani, L.; Gloaguen, R.

The identification of areas prone to landslides is essential to adapt the response and reduce the negative impact in affected regions. This is usually done using landslide susceptibility models, which give the likelihood of a landslide occurring in an area depending on the local terrain conditions and the location of known past events. Detailed databases covering different thematic groups such as geomorphology, hydrology, geology and land use are paramount in order to produce a reliable identification of susceptible areas. However, thematic data from developing countries are scarce and the situation is even worse in mountainous regions which are yet highly vulnerable to natural disasters such as landslides. As a result, susceptibility models often rely heavily on geomorphic parameters derived from DEMs. The three dominantly used variables include slope, aspect and curvature. While these variables are simple to compute and can be obtained from any GIS software, the geomorphological significance of the last two of them is often poorly justified as the window of observation (3×3 pixels) is too small to capture the morphometric signature of landslides or the overall morphology of an entire slope profile.

This study explores the use of advanced geomorphic indices as the main input for landslide susceptibility models. These indices have been often used in tectonic geomorphology to understand the relationship between surface processes and landscape evolution and can provide a useful way to characterize the topography in mountainous regions. Tested indices include surface roughness, local relief, topographic position index, elevation relief ratio, surface index and Eigen-based analysis of the landscape. The test area encompasses the mountainous areas in Tajikistan (SW Tien Shan and Western Pamir), where large magnitude historical landslides have been reported and studied. Landslide susceptibility maps with good predictive capabilities are obtained using different statistically based approaches such as logistic regression and random forest. First, we explored the spatial association between the variables and the landslide catalog. Then, the input variables are recursively selected for each model based on the spatial associations and the improvement in model performance. The best model is chosen based on its predictive capability, measured by the receiver operator curve (ROC) and its dispersion from the cross-validation. Our results suggest that landslide susceptibility modeling using advanced geomorphic indices as the primary source of thematic information is a viable approach. Measures of the relative importance of geomorphic variables used in the best models show that indices such as eigenvalues, local relief, surface roughness, slope, topographic position index and surface index contributed significantly to the models while commonly used aspect and curvatures had a limited impact. Also, the methodology we used is low cost and built on free and open source programs (R and Python), making it easily available for developing countries.

Keywords: Landslide susceptibility; morphometric indices; digital elevation model

  • Poster
    EGU2019, 10.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30417
Publ.-Id: 30417


Publishing - Licensing - Financing : 1. EU-Day at HZDR

Reschke, E.

What should you know about publishing within an EC project? Which license is the best for your publication? The presentation gives information about Open Access and financing of Articles Processing Charges (APC), licencing and the HZDR repositories ROBIS and RODARE.

Keywords: Open Access; Articles Processing Charges (APC); ROBIS; RODARE; Publishing; European Commission; Project publications; Licensing; Copyright; Hybrid journals; DEAL

  • Open Access Logo Lecture (others)
    1. EU-Day at Helmholtz-Zentrum Dresden-Rossendorf, 09.12.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30416
Publ.-Id: 30416


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.1 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 as templates 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. In order to investigate the transport properties of the fabricated nanostructures, the wires are contacted using top-down methods. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K.2 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.

  • Poster
    MML meeting From Matter to Materials and Life, 15.01.2019, Dreikönigskirche Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30415
Publ.-Id: 30415


Morphology Modification of Si Nanopillars under Ion Irradiation at Elevated Temperatures

Xu, X.; Heinig, K.-H.; Möller, W.; Engelmann, H.-J.; Klingner, N.; Gharbi, A.; Tiron, R.; Facsko, S.; Hlawacek, G.; Borany, J.

Ion beam irradiation of vertical nanopillar structures may be utilized to fabricate a vertical gate-all-around (GAA) single electron transistor (SET) device in a CMOS-compatible way. After irradiation of Si nanopillars (with a diameter of 35 nm and a height of 70 nm) by either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) at room temperature and a fluence of 2e16 ions/cm2, strong deformation of the nanopillars has been observed which hinders further device integration. This is attributed to ion beam induced amorphization of Si allowing plastic flow due to the ion hammering effect, which, in connection with surface capillary forces, dictates the final shape. However, plastic deformation can be suppressed under irradiation at elevated temperatures (investigated up to 672 K). Then, as confirmed by bright-field transmission electron microscopy, the substrate and the nanopillars remain crystalline and are continuously thinned radially with increasing fluence down to a diameter of 10 nm. This is attributed to enhanced forward sputtering through the sidewalls of the pillar and found in reasonable quantitative agreement with the predictions from 3D ballistic computer simulation using the TRI3DYN program.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

  • Lecture (Conference)
    10th International Workshop on Nanoscale Pattern Formation at Surfaces (NanoPatterning 2019), 07.-10.07.2019, Surrey, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30414
Publ.-Id: 30414


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

Reschke, E.; Konrad, U.

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

Downloads:

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.; Heinig, K.-H.; Engelmann, H.-J.; Möller, W.; Klingner, N.; Gharbi, A.; Tiron, R.; Facsko, S.; Hlawacek, G.; 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.; Kaden, P.; 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.; 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, N.

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, S.

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

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


The distribution bias of direct sampling with continues variables

van den Boogaart, K. G.; Selia, S. R. R.; Tolosana Delgado, R.

In direct sampling for the conditional simulation of random fields with continues distributions the probablity of finding exact matches of the local conditions in the training image is zero. We thus need to take samples with similar but different patterns. The maximum permissible difference is an algorithmic threshold parameter t controlling the speed, the reliability and the correctness of the simulation.

The contribution describes the effect that simulations sampled with this algorithm follow a conditional distribution, which is systematically biased with respect to the conditional distribution represented by the training images. This sampling bias is create by the fact that it is more likely to find conditioning events deviating from the observed conditioning shifted in the direction of the gradient of the marginal density of the conditioning events. These conditioning events however also typically have a conditional distribution shifted accordingly. The implicitly generated distribution of the conditional simulation is thus just not only (as it was always understood) a little smoothness with respect to the true distribution, but systematically biased. This sampling bias can be easily demostrated in simple Gaussian examples, where it introduces a regression to the mean type effect into a conditional simulation. The effect of the bias accumulates along the simulation path. The size of the sampling bias depends on the choosen tolerance, the choosen neighbourhood, the choosen iteration limit, and the local conditioning events.

The contribution will also discuss strategies to limit and control the effect of this sampling bias, by selecting appropriate algorithmic parameters, and by quantifying the DS sampling bias.

Keywords: Multipoint Geostatistics; Direct Sampling

  • Lecture (Conference)
    Geostats 2020, 17.-21.08.2020, Toronto, Canada

Permalink: https://www.hzdr.de/publications/Publ-30403
Publ.-Id: 30403


Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction

Pylypovskyi, O.; Kravchuk, V. P.; Volkov, O.; Faßbender, J.; Sheka, D.; Makarov, D.

The orientation of a chiral magnetic domain wall in a racetrack determines its dynamical properties. In equilibrium, magnetic domain walls are expected to be oriented perpendicular to the stripe axis. We demonstrate the appearance of a unidirectional domain wall tilt in out-of-plane magnetized stripes with biaxial anisotropy and Dzyaloshinskii--Moriya interaction (DMI). The tilt is a result of the interplay between the in-plane easy-axis anisotropy and DMI. We show that the additional anisotropy and DMI prefer different domain wall structure: anisotropy links the magnetization azimuthal angle inside the domain wall with the anisotropy direction in contrast to DMI, which prefers the magnetization perpendicular to the domain wall plane. Their balance with the energy gain due to domain wall extension defines the equilibrium magnetization the domain wall tilting. We demonstrate that the Walker field and the corresponding Walker velocity of the domain wall can be enhanced in the system supporting tilted walls.

Keywords: magnetism; doman wall; anisotropy; Dzyaloshinskii-Moriya interaction; Walker field; Walker velocity

Permalink: https://www.hzdr.de/publications/Publ-30401
Publ.-Id: 30401


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.; 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 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.; Makarov, D.

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.; Makarov, D.

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.; Makarov, D.

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.; Makarov, D.

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.; Makarov, D.

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.; Makarov, D.

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.; Makarov, D.

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.

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.

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


Tunable magnetic vortex dynamics in ion-implanted permalloy disks

Ramasubramanian, L.; Kákay, A.; Fowley, C.; Yildirim, O.; Matthes, P.; Sorokin, S.; Titova, A.; Hilliard, D.; Böttger, R.; Hübner, R.; Gemming, S.; Schulz, S. E.; Kronast, F.; Makarov, D.; Faßbender, J.; Deac, A. M.

Nanoscale, low-phase noise, tunable transmitter-receiver links are key for enabling the progress of wireless communi-cation. We demonstrate that vortex-based spin-torque nano-oscillators, which are intrinsically low-noise devices due to their topologically-protected magnetic structure, can achieve frequency tunability when submitted to local ion im-plantation. In the experiments presented here, the gyrotropic mode is excited with spin-polarized alternating currents and anisotropic magnetoresistance measurements yield discreet frequencies from a single device. Indeed, chromium-implanted regions of permalloy disks exhibit different saturation magnetisation than the surrounding, non-irradiated areas, and thus different resonance frequency, corresponding to the specific area where the core is gyrating. Our study proves that such devices can be fabricated without the need of further lithographical steps, suggesting ion irradiation can be a viable and cost-effective fabrication method for densely-packed networks of oscillators.

Keywords: electrical detection; vortex dynamics; frequency tunability; ion implantation; reduced saturation magnetisation

Permalink: https://www.hzdr.de/publications/Publ-30380
Publ.-Id: 30380


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

Titova, A.; Fowley, C.; Lau, Y.-C.; Borisov, K.; Atcheson, G.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Faßbender, J.; 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.; Arekapudi, S. S. P. K.; Cansever, H.; Böttger, R.; Hlawacek, G.; Hellwig, O.; Lindner, J.; Faßbender, J.; 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

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

Downloads:

  • Secondary publication expected

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.; Makarov, D.

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

Downloads:

  • Secondary publication expected

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.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

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

Downloads:

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.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

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.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

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


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