Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33168 Publications

High Power Lasers for Advanced Accelerator Development at the ELBE Center Dresden

Schramm, U.ORC
Presentation of High Power Lasers Activities for
Advanced Accelerator Development
at the ELBE Center Dresden
Keywords: high power lasers
  • Invited lecture (Conferences)
    Helmholtz Laser and Photonics Meeting 2019, 03.-04.12.2019, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30563
Publ.-Id: 30563


Advancing laser plasma accelerators by means of femto-scale diagnostics

Schramm, U.ORC
Invited talk on the role of femtoscale probing on laser plasma particle acceleration
Keywords: laser plasma accelerator
  • Invited lecture (Conferences)
    Conference on High Intensity and Attosecond Laser Science CHILI, 09.-11.12.2019, Tel Aviv, Israel

Permalink: https://www.hzdr.de/publications/Publ-30557
Publ.-Id: 30557


Morphology Modification of Si Nanopillars under Ion Irradiation at Elevated Temperatures

Xu, X.ORC; Heinig, K.-H.; Möller, W.; Engelmann, H.-J.; Klingner, N.ORC; Gharbi, A.; Tiron, R.; Borany, J.; Hlawacek, G.ORC
Ion beam irradiation of vertical nanopillar structures can 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.
  • Poster
    AVS 66th International Symposium & Exhibition, 24.10.2019, Columbus, USA

Permalink: https://www.hzdr.de/publications/Publ-30536
Publ.-Id: 30536


High resolution materials modification with low fluence Helium Ion Microscopy

Hlawacek, G.ORC
Helium Ion Microscopy (HIM) is best known for its high resolution imaging capabilities of both
conductive as well as insulating samples. However, since the introduction of Ne as a source gas for the
gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized. While
the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV Ne +
compared to 0.5 nm for 30 keV He + ) the user usually benefits from the much higher cross section for
nuclear stopping. The latter results in a larger number of sputtered atoms, vacancies, interstitials and
chemical bonds broken directly by small impact parameter collisions.
After a brief introduction of the technique I will present results obtained using direct write milling, low
fluence ion beam irradiation and ion beam based mixing. In all cases the electronic, optical or magnetic
properties of the target material will be altered at the nano-scale in a controlled way to achieve new
functionality. The examples comprise
∙ Irradiation of 2D materials including a discussion on the achievable resolution
∙ The fabrication of a lateral spin valve and other magnetic structures using low fluence focused ion
beam irradiation
∙ Irradiation of Si nanostructures at elevated temperatures to avoid amorphization
∙ Irradiation of SiC with very low fluencies
For many of the presented examples the critical length scale of the nanostructure is smaller or in the
range of collision cascade. This size regime can not easily be accessed with traditional broad beam based
ion irradiation and holds many promises but also challenges that need to be overcome to enable new
device concepts and new functional materials on the nano-scale. The use of in-situ instrumentation to
characterize and influence the irradiated material during the irradiation is a key element for the above
examples.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant
Agreement No. 688072.
Keywords: HIM , modification
  • Invited lecture (Conferences)
    1st Sino-German Symposium on "Defect Engineering in SiC Device Manufacturing - Atomistic Simulations, Characterization and Processing" DESiC 2019, 12.11.2019, Peking, China

Permalink: https://www.hzdr.de/publications/Publ-30534
Publ.-Id: 30534


Tailoring magnetic nanostructures with a He-Ne ion microscope

Hlawacek, G.ORC; Bali, R.; Lenz, K.ORC; Samad, F.; Peter, D.
Tailoring magnetic nanostructures with a He-Ne ion microscope
Keywords: HIM, magnetism
  • Lecture (Conference)
    Spins, Waves and Interactions 2019, 5.9.2019, Greifswald, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30529
Publ.-Id: 30529


Avoiding amorphization during ion beam irradiation and critical dimension reduction of nanostructures

Xu, X.ORC; Hlawacek, G.ORC; Engelmann, H.-J.; Bischoff, L.ORC; Heinig, K.-H.; Borany, J.
Ion beam induced collateral damage is becoming an issue in FIB processing, as it limits the
application of ion beams for nanostructure fabrication. This is of special importance for the
application of focused ion beams for nanostructure fabrication.
Here, we present an approach to mitigate the ion beam induced damage inflicted on semi -
conductor nanostructures during ion beam irradiation. Nanopillars (with a diameter of
35 nm and a height of 70 nm) have been irradiated with both, a 50 keV Si + broad beam and
a 25 keV focused Ne + beam from a helium ion microscope (HIM). Upon irradiation of the
nanopillars at room temperature with a medium fluence (2x10 16 ions/cm2), strong plastic
deformation has been observed which hinders further device integration. The shape and
crystallinity has been studied by HIM and TEM. This differs from predictions made by
Monte-Carlo based simulations using the TRI3DYN. However, irradiation at elevated tem-
peratures with the same fluence not only preserves the shape of the nanopillars but allows
for controlled diameter reduction by as much as 50 % without significant change in pillar
height.
It is well known that above a critical temperature amorphization of silicon is prevented in-
dependent of the applied fluence. At high enough temperatures and for not too high flux
this prevents the ion beam hammering and viscous flow of the nanostructures. These two
effects are responsible for the shape change observed at low temperature. We find that ir-
radiation above 650 K preserves the crystalline nature of the pillars and prevents viscous
flow. In addition, a steady thinning process of the nanopillars to a diameter of 10 nm with-
out a significant change in height is observed for higher fluencies at elevated temperatures.
As the original pillar diameter is smaller than the size of the collision cascade, enhanced
forward sputtering through the sidewalls of the pillar is responsible for this pillar-thinning
effect. Results for various ion beam energies, fluencies, fluxes and temperatures will be
presented and compared to TRI3DYN simulations. Such a reliable and CMOS-compatible
process could serve as a potential down scaling technique for large-scale fabrication of
nanostructure based electronics and many other FIB based milling applications.
Keywords: HIM
  • Lecture (Conference)
    EU-F-N 2019, 14.6.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30528
Publ.-Id: 30528


Analytic approaches for Helium Ion Microscopy

Hlawacek, G.ORC; Klingner, N.ORC; Veligura, V.; Xu, X.ORC; Serralta Hurtado De Menezes, E.ORC; Schmeink, A. H.ORC; Borany, J.; Facsko, S.ORC
Helium Ion Microscopy (HIM) utilizes a Gas Field Ion Source (GFIS) to create a Helium or Neon
ion beam with a diameter better than 0.5 nm and 1.8 nm, respectively. The method is well known
for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for
conducting but also insulating samples without the need for a conductive coating. However, the existing
GFIS based focused ion beam (FIB) tools suffer from the lack of a well integrated analytic method that
can enrich the highly detailed morphological images with material properties contrast. While HIM
technology is relatively young several efforts have been made to add such an analytic capability to
the technique. So far, ionoluminescence, secondary electron spectroscopy, backscattering spectrometry
(BS), and secondary ion mass spectrometry (SIMS) using a magnetic sector or time of flight (TOF)
setup have been demonstrated. In addition in-situ experiments can be performed that allow to directly
and in real time investigate the effect of the focused ion beam on the materials under various conditions.
I will present our efforts to perform in-situ experiments in the Helium Ion Microscope and enhance its
analytic capabilities. In the first part of my presentation I will give an overview of the in-situ characteri-
zation capabilities of the HZDR Orion NanoFab including in-situ heating and electrical characterization.
In the second part of the talk I will focus on different analytic approaches tested in the past. I will
briefly give an overview on ionoluminescence in the HIM and than present our newly developed TOF-BS
and TOF-SIMS setup which allow to obtain information on the composition of the sample. They both
utilize the same cost efficient and minimal invasive pulsing scheme for the primary ion beam. The lateral
resolution reached for TOF-BS is approximately 50 nm while for TOF-SIMS a value of 8 nm could be
reached. First images will be presented and the performance of the TOF-SIMS spectrometer will be
discussed.
Keywords: HIM, SIMS
  • Invited lecture (Conferences)
    Zakopane School of Physics, 24.5.2019, Zakopane, Polen

Permalink: https://www.hzdr.de/publications/Publ-30527
Publ.-Id: 30527


Exploiting Hysteresis in a Multicaloric Cooling Cycle

Gottschall, T.ORC
für den Vortrag hat keine inhaltliche Kurzfassung vorgelegen
  • Invited lecture (Conferences)
    Annual Conference on Magnetism and Magnetic Materials 2019, 04.-08.11.2019, Las Vegas, USA

Permalink: https://www.hzdr.de/publications/Publ-30520
Publ.-Id: 30520


Multicaloric materials and their characterization

Gottschall, T.ORC
für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen
  • Invited lecture (Conferences)
    Ruhr Symposium 2019, 09.10.2019, Duisburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30519
Publ.-Id: 30519


Preparation and Characterization of Solar Thermal Absorbers by Nanoimprint Lithography and Sputtering

Mitteramskogler, T.; Haslinger, M. J.; Wennberg, A.; Fernandez Martínez, I.; Muehlberger, M.; Krause, M.ORC; Guillén, E.
Selective solar absorbers comprised of plasmonic materials offer great flexibility in design
along with a highly promising optical performance. However, the nanopattern generation,
typically done with electron beam writing, is a very time-intensive process. In this work, we
present a fast, scalable, and flexible method for the fabrication of plasmonic materials by the
combination of a deposition mask prepared by nanoimprint lithography and thin film
deposition by magnetron sputtering. The fabrication process was first performed on silicon
wafer substrates using AFM and SEM measurements to calibrate the deposition time,
determine maximal deposition height, and characterize samples. Afterwards, the process was
transferred to polished Inconel NiCr-alloy substrates used in high temperature solar
absorbers. To investigate the adhesion properties of the nanostructure on the substrate, two
different deposition methods were investigated: DC magnetron sputtering and High Power
Impulse Magnetron Sputtering (HiPIMS).
Keywords: Solar absorbers, nanoimprint lithography, HiPIMS
  • Contribution to proceedings
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA
    MRS Advances: Cambridge
    DOI: 10.1557/adv.2019.285
  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Pheonix, USA

Permalink: https://www.hzdr.de/publications/Publ-30516
Publ.-Id: 30516


High temperature in-air stability of solar absorber coatings based on aluminium titanium oxynitride nanocomposites

Heras, I.; Krause, M.ORC; Rincón, G.; Guillén, E.; Azkona, I.; Lungwitz, F.; Munnik, F.ORC; Escobar Galindo, R.
One of the major challenges in Concentrating Solar Power (CSP) implies an increase of the working temperature of the solar receiver. In particular, current central tower systems operate at maximum temperatures of 550 ºC mainly due to the severe degradation that the state of the art absorber paints (i.e. Pyromark®) suffer at higher temperatures. In previous works [1,2] aluminum titanium oxynitrides AlyTi1-y(OxN1-x) were shown to be excellent candidate materials for solar selective coatings (SSC). These results confirmed that the designed SSCs based on materials withstand breakdown at 600 ºC in air after 900 hours of thermal cycling.
In this paper we discuss the high temperature (up to 700ºC) stability in air of a solar absorber coating based on AlyTi1-y(OxN1-x) deposited by cathodic vacuum arc (CVA) at higher working pressure (P = 2.1 Pa) than those discussed in [1] and [2]. The composition, morphology and microstructure of the films were characterized by ion beam analysis, scanning and transmission electron microscopy and X-ray diffraction. The optical properties were determined by ellipsometry and spectrophotometry (UV-Vis-NIR, FTIR). The microstructural and morphological characterization shows the formation of a solid solution of AlTiN crystalline nanoparticles embedded in an amorphous Al2(O, N)3 matrix. This particular microstructure results in a coating with a high absorption coefficient within the whole wavelength range of interest (0,3 to 25 um) as modeled by spectroscopic ellipsometry. Hence, this single layer absorber shows a solar absorptance, α, of 92% and an emissivity, εRT, of 70%. The addition of an antireflective Al2O3 layer and post deposition thermal treatments improved the optical properties of the absorber to better values (α=96% and εRT=60%) than those of Pyromark®. The thermal stability in air of the absorber was firstly analyzed by cyclic heating tests, showing no degradation after 300h of cycles in air at 700ºC. Subsequently, the samples were tested in a solar furnace at 650 °C and 800 ºC for 12 hours at environmental conditions. Therefore, this absorber coating can be a feasible alternative to absorber paints for next generation of concentrated solar power plants operating at high temperature.
[1] I. Heras et al., Sol. Energy Mat. Solar Cells, 176, 81-92 (2018)
[2] R. Escobar-Galindo et al., Sol. Energy Mat. Solar Cells, 185, 183-191 (2018)
Keywords: Solar selective coatings, thermal stability, optical properties, concentrated solar power, optical simulation, oxynitrides
  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-30515
Publ.-Id: 30515


High temperature in-air stability studies of SnO2:Ta thin films used as solar-selective transmitter in CSP

Méndez Fernández, Á.; Fernández Martínez, I.; Wennberg, A.; Muñoz Piña, S.; Carlos Rodriguez, J.; Lungwitz, F.; Janke, D.; Escobar Galindo, R.; Krause, M.ORC
The importance of finding more effective and cleaner ways of producing energy other than fossil fuels is growing fast in order to reduce
CO2 emissions that contribute to the greenhouse effect. Concentrating solar power (CSP) uses reflectors to redirect and concentrate the solar radiation onto a receiver, where it is transformed into heat. Downstream heat exchangers and gas turbines are the final responsibles of transforming the heat into electricity. Current CSP plants are operated at a maximum of 550 °C, but an increase of the operation temperature to 800 °C, in combination with solar-selective coatings, would significantly improve their efficiency by more than 10 %. In order to approach this issue, a transparent conductive oxide (TCO) thin film based on SnO2 doped with Ta was developed and optimized by reactive magnetron sputtering [1]. This material was shown resisting 800 °C in vacuum for 4 hours, transmitting incident sunlight and blocking infrared emission from the underlaying blackbody absorber. As such, it exhibits all properties required of a solar-selective transmitter for hightemperature CSP usage. In this work, thermal stability tests were carried out in air using an electric furnace for a total of 12 hours at 650 °C and 800 °C, respectively, for laboratory samples and industrially produced coatings. These results will be shown and discussed. In addition, the coatings were tested under environmental conditions at 650 °C and 800 °C in a solar furnace, again for a total of 12 hours each, providing information about their behaviour and performance in a situation much closer to the final application. Spectrophotometry, Rutherford backscattering spectrometry and conductivity measurements, among other techniques, were used to track the evolution of the properties and performance of SnO2 :Ta thin films under these conditions.
[1] F. Lungwitz et al., submitted to Sol. Energy Mat. Solar Cells (2018)
This work was supported by the EU H2020 RISE project “Framework of Innovation for Engineering of New Durable Solar Surfaces” (FRIENDS ,
GA-645725).
Keywords: concentrated solar power, solar thermal electricity, solar-selective transmitter, transparent conductive oxide, cluster tool, high-temperature in situ procesing and analysis
  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Pheonix, USA

Permalink: https://www.hzdr.de/publications/Publ-30513
Publ.-Id: 30513


Cluster tool for in situ processing and comprehensive characterization of energy materials at high temperatures

Krause, M.ORC; Wenisch, R.; Lungwitz, F.; Heras, I.; Janke, D.; Azkona, I.; Escobar Galindo, R.; Gemming, S.ORC
In situ processing and comprehensive characterization is essential for design and development of materials used and processed at high-temperatures. Here, a new cluster tool for processing and depth-resolved compositional, structural and optical characterization of layered
materials with thicknesses ranging from sub-nm to 1 μm at temperatures of -100 to 1000 °C is described [1]. The implemented techniques comprise
magnetron sputtering, ion irradiation, Rutherford backscattering spectrometry, Raman spectroscopy and spectroscopic ellipsometry. The combination of techniques enables sample processing by scalable, clean, waste-free, and industry-relevant technologies, quantitative depth-profiling for elements with Z ≥ 6, structural and chemical characterization, sensitivity and nm-precise thickness and optical information for single layers, multilayers and composites. In this study, the cluster tool was used for i) metal-induced crystallization with layer-exchange of a-Si/ Ag layer stacks, and ii) for hightemperature characterization of two types of solar-selective coatings for concentrated solar power (CSP), namely Al Ti (O N )-based single and multilayers [2, 3] and an n-type doped solar-selective transparent conductive oxide [4]. Starting with an a-Si/ Ag bilayer stack, metal-induced silicon crystallization with partial layer exchange occurs at 540 °C. The final stack is approximately described by the sequence crystalline Si (c-Si)/ Ag/ c-Si. All the layers contain minor fractions of the other element. Moreover, the Si volume fraction comprises approximately 10 % of amorphous Si. For the CSP coatings, no compositional and structural changes were found up to a maximum temperature of 840 °C in vacuum. Both types of solar-selective coatings thus represent promising materials for the next generation of CSP technology.
[1] R. Wenisch et al., Anal. Chem. 90, 7837-7824 (2018)
[2] I. Heras et al., Sol. Energy Mat. Solar Cells, 176, 81-92 (2018)
[3] R. Escobar-Galindo et al., Sol. Energy Mat. Solar Cells, 185, 183-191 (2018)
[4] F. Lungwitz et al., submitted (2018)
Financial support by the EU, grant No. 645725, project FRIENDS , and the HGF via the W3 program (S.G.) is gratefully acknowledged.
Keywords: Cluster tool, in situ processing and analysis, high temperature, Rutherford backscattering, Raman spectroscopy, ellipsometry, metal-induced crystallization
  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-30511
Publ.-Id: 30511


Acoustic signatures of the phase transitions in the antiferromagnet U2Rh2Sn

Gorbunov, D.; Andreev, A. V.; Ishii, I.; Prokes, K.; Suzuki, T.; Zherlitsyn, S.ORC; Wosnitza, J.
We report on ultrasound measurements in a single crystal of the antiferromagnet U2Rh2Sn as a function of temperature and magnetic field. We find pronounced anomalies in the sound velocity at the Néel temperature, 25 K, and at the field-induced spin-flop-like transition at 22.5 T, which points to a strong magnetoelastic coupling. Additionally, we find that in the paramagnetic regime the temperature dependence of the magnetic susceptibility and the field dependences of the magnetization and sound velocity of transverse acoustic waves can be well described assuming a localized character of the 5 f electrons. Using this premise, the crystal-electric-field scheme of U2Rh2Sn has been determined.

Downloads:

  • available with HZDR-Login
  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-30510
Publ.-Id: 30510


Easy-plane magnetic anisotropy in layered GdMn2Si2 compound with easy-axis magnetocrystalline anisotropy

Gerasimov, E. G.; Terentev, P. B.; Gubkin, A. F.; Fischer, H. E.; Gorbunov, D.; Mushnikov, N. V.;
Magnetic properties and magnetic structures of layered GdMnSi2 compound were studied using quasisingle crystal, high magnetic fields up to 520 kOe, and neutron powder diffraction experiment designed for high absorbent systems. It was shown that GdMn2Si2 has strong easy plane type magnetic anisotropy at temperatures TGd < 52 K at which Gd atoms are magnetically ordered. At temperatures 52 K < T < 453 K, the compound has antiferromagnetic ordering of Mn layers and easy axis type magnetic anisotropy with the easy axis directed along the tetragonal c-axis. The exchange-induced in-plane magnetic anisotropy of layered GdMn2Si2 at low temperatures arises to prevent magnetic frustration in Gd layers. Magnetic properties of GdMn2Si2 at temperatures below 52 K can be described within a threesublattice model based on the Yafet-Kittel approximation.

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  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-30509
Publ.-Id: 30509


REELS and Auger spectroscopy study of layers exchange in C/Ni-bilayer system

Vretenár, V.; Janke, D.; Vanco, L.; Krause, M.;
New experimental methods for synthesis of low dimensional carbon structures still attract considerable attention, many of them based on catalytically driven processes.
In this contribution we present REELS and Auger spectroscopy study of Ni-induced
layer exchange in Ni/C-bilayer thin film system. EELS spectroscopy in reflected
mode (REELS) and Auger electron spectroscopy (AES) were employed to characterize
the structure, homogeneity and quality of carbon and nickel film (each having
thickness around 50 nm) and their interface between, before and after thermal annealing
at 700 °C. AES mapping and depth profiling revealed a layer exchange
between the layers after thermal annealing, accompanied by partial nickel diffusion
into MgO substrate. REELS analysis showed successful structural transformation
of initially amorphous carbon layer into compact graphitic one. The transformed carbon
layer has a slightly rippled surface as confirmed by topological backscattered
electron imaging.
Keywords: Metal-induced crystallization, turbostratic carbon, electron spectroscopy
  • Poster
    International Winterschool on Electronic Properties of Novel Materials - Molecular Nanostructures, 09.-16.03.2019, Kirchberg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30506
Publ.-Id: 30506


Time- and temperature-resolved in situ investigation of the metal-induced crystallization of amorphous carbon thin films

Janke, D.; Julin, J.; Hübner, R.; Gemming, S.; Rafaja, D.; Krause, M.;
The graphitization of amorphous carbon in thin film stacks with Ni was investigated in situ as a function of the initial stacking order, temperature and time by Rutherford backscattering spectrometry and Raman spectroscopy. Four different bilayer and triple layer stacks were exposed to heating ramps up to 700 °C. The graphitization occurred simultaneously with a layer exchange (LE) and was completed during the applied heating ramp. The temperature-resolved measurements allowed the determination of the onset temperatures and transition rates for the respective stacking order. Finally, the activation energies for the graphitization of the amorphous carbon were estimated for both LE directions. In combination with thermodynamic calculations,
this in situ study allowed to identify metal-induced crystallization with LE via wetting and diffusion along grain boundaries as mechanism responsible for the graphitization of amorphous carbon thin films in contact with Ni, instead of bulk dissolution/precipitation. The proposed model can potentially be used to estimate the catalytic transformation of group 14 elements in contact with transition metals.
Keywords: Cluster Tool, in situ processing and analysis, layer exchange, turbostratic carbon
  • Poster
    International Winterschool on Electronic Properties of Novel Materials - Molecular Nanostructures, 09.-16.03.2019, Kirchberg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30505
Publ.-Id: 30505


Directionality and energetics of the metal-induced crystallization of amorphous carbon thin films

Janke, D.; Wüstefeld, C.; Julin, J.; Hübner, R.; Grenzer, J.; Gemming, S.; Rafaja, D.; Krause, M.;
The catalytic graphitization with layer exchange (LE) of amorphous carbon in thin
film stacks with Ni was investigated as a function of the initial stacking order. Bilayer
and triple layer stacks were exposed to heating ramps up to 700 °C. Raman spectroscopy
showed the formation of a layered graphitic structure after the annealing.
During outwards LE, as C is transported towards the sample surface, a smooth layer
with graphitic planes parallel to the interface with the substrate has formed through
a 2D growth. A significant restructuring of the Ni layer appeared during inwards LE,
as C is transported towards the substrate. Here, the fragmentation of the Ni layer,
as well as the regions with turbulence-like and folding defects indicated a 3D growth.
The degree of LE, quantified by ion beam analysis, is 95 % and 80 % for the outand
inwards direction, respectively. Based on the calculation of surface and interface
energies of the initial and final states, thermodynamic estimations pointed to
the wetting of Ni grain boundaries by C atoms as the initial driving force for the LE
and allowed a consistent understanding of the LE directionality and of the final thin
film microstructure.
  • Poster
    International Winterschool on Electronic Properties of Novel Materials - Molecular Nanostructures, 09.-16.03.2019, Kirchberg, Österreich
  • Lecture (Conference)
    MRS Spring Meeting & Exhibition, 22.-26.04.2019, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-30503
Publ.-Id: 30503


Ion beam implanted Germanium nanowires

Echresh, A.; Xie, Y.; Prucnal, S.; Rebohle, L.ORC; Georgiev, Y.ORC
Germanium (Ge) is a promising high mobility channel material for future nanoelectronics. Materials with high carrier mobility can enable increased integrated circuit functionality or reduced power consumption. Hence, Ge based nanoelectronic devices could offer improved performance at reduced power consumption compared to Si electronics [1].

The introduction of impurity atoms allows the tuning of the electrical properties of the semiconductor material. Ion beam implantation is an industrial standard for semiconductor's doping as it can incorporate single ion species with a single energy in a highly controlled fashion. However, the destructive nature of ion beam implantation requires a crystal recovery step such as an annealing process [2].

In this work, Germanium-on-insulator (GeOI) substrates were doped with phosphorous (P) using ion beam implantation followed by flash lamp annealing (FLA). During FLA process the implanted layer recrystallized and P was electrically activated. Then Ge nanowires were fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. Raman spectra showed the amorphisation of Ge structure after implantation and good recovery after FLA (Fig. 1). Rutherford backscattering spectrometry (RBS) measurement in random (R) and channeling (C) modes (Fig. 2) were used to verify the crystal quality of Ge layer before and after FLA. As one can see, the yield intensity of the channeling mode was increased after implantation, which can be related to amorphisation of the top Ge layer. Also, the yield peak of flashed GeOI has a good match with unimplanted counterpart, which shows the good recrystallization during FLA. Moreover, we designed Hall effect measurement configuration for single Ge nanowires (Fig. 3) to determine the carrier mobility and carrier concentration. The results of these measurements will be shown at the conference [3,4]. The goal is to fabricate p-n junction along the Ge nanowires and use it as an infrared sensor.
Keywords: Ion beam implantation; Flash lamp annealing; Doping; p-n junction; Infrared sensor
  • Poster
    45th International Conference on Micro & Nano Engineering (MNE), 23.-26.09.2019, Rhodes, Greece
  • Poster
    NanoNet International Conference 2019, 08.-11.10.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30498
Publ.-Id: 30498


Phosphorous doped Germanium nanowires

Echresh, A.; Jazavandi Ghamsari, S.; Georgiev, Y.ORC; Rebohle, L.ORC
Germanium (Ge) is a promising high mobility channel material for future nanoelectronic devices with a lower effective charge carrier mass than Silicon (Si) and higher electron and hole mobility. Materials with high carrier mobility can enable increased integrated circuit functionality. Hence, Ge based nanoelectronic devices could offer improved performance at reduced power consumption compared to Si electronics. In this work, Ge nanowires were fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. Then ion beam implantation was used to introduce phosphorous (P) dopant atoms into the Ge nanowires. Afterwards, flash lamp annealing (FLA) was applied to recover the crystal structure of the Ge nanowires and activate the dopant atoms. Micro-Raman spectroscopy spectra showed that by increasing the fluence of ion implantation, the peak of optical phonon mode in Ge was broadened asymmetrically which shows that dopant atoms are electrically activated. Moreover, we are designing Hall Effect measurement configurations for single Ge nanowires to determine their mobility and carrier concentrations.
  • Poster
    DPG Spring Meeting 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30497
Publ.-Id: 30497


Ion beam implanted Germanium nanowires fabricated by using electron beam lithography

Echresh, A.; Jazavandi Ghamsari, S.; Helm, M.; Rebohle, L.ORC; Georgiev, Y.ORC
Germanium (Ge) is a promising high mobility channel material for future nanoelectronic devices with a lower effective charge carrier mass than Silicon (Si), which results in a higher electron (×2) and hole (×4) mobility. Materials with high carrier mobility can enable increased integrated circuit functionality or reduced power consumption. Hence, Ge based nanoelectronic devices could offer improved performance at reduced power consumption compared to Si electronics. Doping or the introduction of impurity atoms allows the tuning of the electrical properties of the semiconductor material. Ion beam implantation is an industrial standard for semiconductor's doping as it can incorporate single ion species with a single energy in a highly controlled fashion. The destructive nature of ion implantation doping due to the deposited energy and resultant cascade of recoils within the nanowire volume requires a crystal recovery step such as an annealing process. In this work, Ge nanowires were first fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. Then ion beam implantation was used to introduce phosphorous (P) dopant atoms into Ge nanowires. Afterwards, flash lamp annealing (FLA) was applied to recover the crystal structure of Ge nanowires and activate the dopant atoms. Micro-Raman spectroscopy spectra showed that, by increasing the fluency of ion implantation, the optical phonon mode of Ge peak was broadened asymmetrically. This is related to the Fano effect and shows that dopant atoms are placed in substitutional positions and are electrically activated. Moreover, we are designing three- and four-probe Hall Effect measurement configurations for single Ge nanowires to determine their mobility and carrier concentrations.
  • Poster
    Towards Reality in Nanoscale Materials X, 14.-16.02.2019, Levi, Finland

Permalink: https://www.hzdr.de/publications/Publ-30495
Publ.-Id: 30495


Characterization of Goethe’s prisms by external ion beam

Munnik, F.ORC; 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


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

Abouelazayem, S.; Glavinic, I.ORC; 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


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.

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


Near free-fall oscillatory velocities in liquid metal rotating convection

Vogt, T.ORC; 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


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.

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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.

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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.ORC; 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.

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


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.ORC; 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.ORC; Heller, R.; Hlawacek, G.ORC
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.ORC; 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.ORC; Heinig, K.-H.; Möller, W.; Klingner, N.ORC; 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.ORC; Hlawacek, G.ORC; 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.ORC; Fotev, I.ORC; Shan, S.; Pashkin, O.ORC; Bussone, G.; Grifone, R.; Grenzer, J.; Hübner, R.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC
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.ORC; Hübner, R.; Wolf, D.; Bussone, G.; Grifone, R.; Grenzer, J.; Pelekanos, N. T.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC
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.ORC; Heller, R.; Hlawacek, G.ORC; Facsko, S.ORC
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.ORC; Hübner, R.; Chatzarakis, N.; Pelekanos, N. T.; Bussone, G.; Grifone, R.; Grenzer, J.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC
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.ORC; Koch, C.; Hlawacek, G.ORC; 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


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

Kelley, D. H.; Tithof, J. R.; Horstmann, G. M.ORC; 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


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

Schindler, F.; Zürner, T.; Vogt, T.ORC; Eckert, S.ORC; 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

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


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

Schindler, F.; Zürner, T.; Vogt, T.ORC; Eckert, S.ORC; 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.ORC; Reuter, M.ORC; Eckert, S.ORC
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.ORC; Eckert, S.ORC; 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.ORC; Reuter, M.ORC
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.ORC; Xu, C.ORC; Hübner, R.; Grenzer, J.; Zeng, Y.-J.; Helm, M.; Zhou, S.ORC; 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 Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 03.04.2019, Regensburg, Germany
    DOI: 10.1063/1.5057733

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


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

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

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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.ORC
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.ORC
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.

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


Fermi surface investigation of the filled skutterudite LaRu4As12

Klotz, J.ORC; 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.
  • Physical Review B 100(2019), 205106

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  • Secondary publication expected

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


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

Helm, T.ORC
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


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.ORC; Gloaguen, R.ORC
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.ORC
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

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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


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

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

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


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.
  • Open Access Logo Lecture (Conference)
    IHRS NanoNET International Conferance, 08.-11.10.2019, Dresden, Germnay

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


Functionalized DNA Origami Nanostructures for Molecular Electronics

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

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


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

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

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


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

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

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


Commercial applications of research institute Tandem accelerators: the Rossendorf example

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

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

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


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

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

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  • available with HZDR-Login

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


Materials science for information technology

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

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


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

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

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


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

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

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


Experimental and Theoretical Studies of Exchange-driven Chiral Effects

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

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

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


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

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

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

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

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

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


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

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

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

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

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

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


Theoretical and Experimental Study of Curvature Effects in Nanomagnetism

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

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

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


Experimental observation of exchange-driven chiral effects in parabolic nanostripes

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

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

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


Mesoscale Dzyaloshinskii-Moriya interaction: geometrical tailoring of the magnetochiralit

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

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


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

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

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

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

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


Experimental confirmation of exchange-driven DMI

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

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


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

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

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


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

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


Experimental and theoretical study of curvature effects in parabolic nanostripes

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

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


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

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

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


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

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

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


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


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

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

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


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

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

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  • Secondary publication expected from 21.06.2020

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


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

Bieberle, A.ORC; Schäfer, T.

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

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

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

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


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

Bieberle, A.ORC; Schäfer, T.

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

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

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

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


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

Bieberle, A.ORC; Schäfer, T.

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

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

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

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


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

Bieberle, A.ORC; Schäfer, T.

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

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

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

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


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

Bieberle, A.ORC; Schäfer, T.

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

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

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

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


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

Bieberle, A.ORC; Schäfer, T.

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

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

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

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


Visualisation of melt flow effects on dendritic solidification

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

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


Quantum radiation in dielectric media with dispersion and dissipation

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

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


Off-shell Ward identities for N-gluon amplitudes

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

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


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

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

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


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

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

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


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

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

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


Pair production in temporally and spatially oscillating fields

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

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


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

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

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


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

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

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


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