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38996 Publications

Terahertz free carrier absorption to modulate the optical properties of nanometer-thick van der Waals semiconductors

Venanzi, T.; Selig, M.; Pashkin, O.; Winnerl, S.; Katzer, M.; Arora, H.; Erbe, A.; Patane, A.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Baldassarre, L.; Knorr, A.; Helm, M.; Schneider, H.

Free carriers in doped semiconductors absorb terahertz radiation when the frequency of the electromagnetic field is lower or comparable to the plasma frequency of the system. This phenomenon can be used to manipulate the optical response of the material. We present here the results of two different experiments performed at the infrared free-electron laser FELBE on atomically-thin van der Waals semiconductors. In MoSe2 monolayers, we observe a terahertz-induced redshift of the trion resonance. Terahertz absorption induces an average high momentum to the carriers and this momentum gets transferred during the trion formation, resulting in a net redshift in the absorption. In few-layer InSe, the terahertz pulses induce a transient quenching of the photoluminescence emission. In both cases, a microscopic study of the hot carrier distribution cooling is also presented.

Keywords: 2D materials; photoluminescence; terahertz; MoSe2; InSe

Related publications

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 04.-09.09.2022, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36441
Publ.-Id: 36441


Time-resolved nanospectroscopy on Si-doped GaAs-InGaAs core-shell nanowires

Luferau, A.; Obst, M.; Winnerl, S.; Kehr, S. C.; Dimakis, E.; Pashkin, O.; Klopf, J. M.; Eng, L. M.; Helm, M.

High-quality epitaxial nanowires (NWs) based on III–V semiconductors such as (In)GaAs offer the possibility to fabricate ultrafast optical devices due to their direct bandgap and the high electron mobility. Contactless investigation of the charge carrier concentration and mobility in NWs is enabled by terahertz time-domain spectroscopy [1]. The determination of these properties locally on individual NWs can be carried out by scattering-type scanning near-field optical microscopy (s-SNOM), which provides spatial resolution far beyond the diffraction limit. In optical-pump THz-probe experiments the response of photogenerated carriers has been investigated on the 10 nm and 10 fs scale [2].
Time-resolved studies are still missing in both far-field and near-field spectroscopy for doped nanowires excited by far-infrared (FIR) radiation via free-carrier absorption. Here we report on FIR-pump MIR-probe s-SNOM studies on highly-doped GaAs/InGaAs core-shell NWs utilizing intense narrowband FIR radiation from the free-electron laser (FEL) FELBE.
The samples under study are Si-doped GaAs-InGaAs core-shell NWs grown by molecular beam epitaxy. They consist of a 25-nm-thick GaAs core and a 80-nm-thick In0.44Ga0.56As shell that is homogeneously doped with Si at a concentration of 9 × 1018 cm-3. For s-SNOM studies these NWs are transferred to a (100) Si substrate and dispersed randomly over the substrate.
The experiment was carried out with the s-SNOM setup from Neaspec GmbH equipped with difference-frequency generation (DFG) source (5 – 15 µm; 83 – 248 meV). For the pump-probe measurements the laser oscillator of the DFG source was synchronized to FEL and the time delay between the pulses was varied by an optical delay line. A low-pass filter suppress the scattered FIR radiation from FELBE going into the nano-FTIR unit (Fig 1,a).
In the unpumped case, a sharp plasma edge around 130 meV is observed. Upon below-bandgap pumping with 23 µm FEL radiation (pulse duration 2 – 5 ps, average power 15 mW), the near-field response of plasma resonance changes dramatically. The spectrally integrated pump-probe signal exhibits a small negative component followed by a stronger positive signal that decays with the longest time constant (1/e) of ≈7 ps (Fig. 1,b, Insert). The nano-FTIR studies reveal strong red shift and flattening of plasma resonance of spectra (Fig.1,b). We assign this effect to a substantial heating of the electrons in the conduction band and subsequent increase of the effective mass in the nonparabolic Γ-valley due to high peak electric field strengths up to several 10 kV cm−1 of pulsed FEL radiation [3]. Power-dependent and nanoimaging pump-probe studies are performed to conclude the nature of observed effects. In particular, the experiments should reveal if there is a contribution of carrier transfer to side valleys at high excitation fields.
[1] P. Parkinson, et al., Nano Lett. 7, 2162 (2007).

Keywords: core-shell nanowires; terahertz; near-field microscopy; time-resolved nanoscopy

Related publications

  • Lecture (Conference)
    9th International Conference on Optical Terahertz Science and Technology (OTST 2022), 19.-24.06.2022, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-36437
Publ.-Id: 36437


Pump-induced terahertz anisotropy in graphene

Seidl, A.; Anvari, R.; Dignam, M. M.; Richter, P.; Seyller, T.; Schneider, H.; Helm, M.; Winnerl, S.

Nonlinear optical properties of graphene have been discussed for a more than a decade [1]. Experimentally, the most prominent nonlinear effect is high harmonic generation in the THz range [2]. This phenomenon is caused by a reduced conductivity of hot thermalized electrons. In our study, we investigate an effect beyond the response of thermalized hot carriers, which by nature is isotropic. We observe anisotropic THz-induced bleaching related to a change in effective mass of charge carriers under strong THz excitation.
We investigated monolayer and bilayer graphene on SiC with carrier concentrations of 1.0 x 10^13 cm-2 and 6.5 × 10^12 cm−2, respectively. In degenerate pump-probe experiments at 3.4 THz utilizing linearly polarized radiation, the differential transmission was recorded for co- and cross-polarized probe beams. For bilayer graphene, co-polarized probing yields signals that are about two times larger as compared to the cross-polarized case (cf. Fig. 1) [3]. Since the response of thermalized carriers is isotropic, it cannot explain the observed anisotropic bleaching. We describe the physical origin of the anisotropic nonlinear response using a simple semiclassical model: In essence, the change in effective mass in x-direction differs strongly for carriers excited along or perpendicular to the direction of the probe field. For a quantitative comparison, modelling based on the density matrix formalism with a phenomenological scattering time was performed. For a momentum scattering time of 50 fs good agreement with the experimental data is obtained. The monolayer sample shows qualitatively similar behavior, however, the scaling of the induced transmission with the pump electric field is different. In summary, time-resolved THz nonlinear spectroscopy turns out as a powerful method to explore nonlinearities directly related to the bandstructure of Dirac materials.
[1] S. A. Mikhailov and K. Ziegler, J. Phys.: Condens. Matter 20, 384204 (2008).
[2] H. A. Hafez et al., Nature 561, 507 (2018).
[3] A. Seidl et al., Phys. Rev. B. 105, 085404 (2022).

Keywords: graphene; terahertz; nonlinear response

Related publications

  • Lecture (Conference)
    9th International Conference on Optical Terahertz Science and Technology (OTST 2022), 19.-24.06.2022, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-36436
Publ.-Id: 36436


Data publication: Ab initio Computation of the Static Exchange--Correlation Kernel of Real Materials: From Ambient Conditions to Warm Dense Matter

Moldabekov, Z.; Böhme, M.; Vorberger, J.; Blaschke, D.; Dornheim, T.

This repository contains the DFT simulation results presented in the article "Ab Initio Static Exchange-Correlation Kernel across Jacob's Ladder without Functional Derivatives"

Downloads

Permalink: https://www.hzdr.de/publications/Publ-36423
Publ.-Id: 36423


Advancing laser accelerated proton beam performance for dose controlled irradiation studies and beyond the 100 MeV frontier

Schramm, U.

Advancing laser accelerated proton beam performance for
dose controlled irradiation studies and
beyond the 100 MeV frontier

  • Invited lecture (Conferences)
    John D Lawson Lecture, 08.12.2022, Oxford, UK

Permalink: https://www.hzdr.de/publications/Publ-36404
Publ.-Id: 36404


Establishing Laser Accelerated Proton Beam Performance for Dose Controlled and High Dose Rate Irradiation Studies

Schramm, U.

Establishing Laser Accelerated Proton Beam Performance
for Dose Controlled and High Dose Rate Irradiation Studies

  • Invited lecture (Conferences)
    Plasma Physics Seminar GSI, 14.06.2022, Darmstadt, Deutschland
  • Invited lecture (Conferences)
    Laserlab Europe V JRA Meeting, 13.06.2022, Darmstadt, Deutschland
  • Invited lecture (Conferences)
    Euronnac EAAC, 19.09.2022, La Biodola Elba, Italien
  • Invited lecture (Conferences)
    Laserlab Europ General Assembly, 03.10.2022, Lausanne, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-36400
Publ.-Id: 36400


Science and Applications of Plasma‐Based Accelerators - Health and industrial applications

Schramm, U.

Talk on Science and Applications of Plasma‐Based Accelerators - Health and industrial applications

  • Invited lecture (Conferences)
    767. WE-Heraeus-Seminar, 16.-18.05.2022, Bad Honnef, Deutschland
  • Invited lecture (Conferences)
    CASUSCON, 11.07.2022, Breslau, Polen

Permalink: https://www.hzdr.de/publications/Publ-36399
Publ.-Id: 36399


Highly Altered State of Proton Transport in Acid Pools in Charged Reverse Micelles

Hao, H.; Adams, E.; Funke, S.; Schwaab, G.; Havenith, M.; Head-Gordon, T.

Transport mechanisms of solvated protons of 1 M HCl acid pools,
confined within reverse micelles (RMs) containing the negatively charged surfactant
sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) or the positively charged
cetyltrimethylammonium bromide (CTABr), are analyzed with reactive force field
simulations to interpret dynamical signatures from TeraHertz absorption and dielectric
relaxation spectroscopy. We find that the forward proton hopping events for NaAOT are
further suppressed compared to a nonionic RM, while the Grotthuss mechanism ceases
altogether for CTABr. We attribute the sluggish proton dynamics for both charged RMs
as due to headgroup and counterion charges that expel hydronium and chloride ions
from the interface and into the bulk interior, thereby increasing the pH of the acid pools
relative to the nonionic RM. For charged NaAOT and CTABr RMs, the localization of
hydronium near a counterion or conjugate base reduces the Eigen and Zundel
configurations that enable forward hopping. Thus, localized oscillatory hopping
dominates, an effect that is most extreme for CTABr in which the proton residence time increases dramatically such that even
oscillatory hopping is slow.

Keywords: Counterions; Interfaces; Ions; Micelles; Oscillation

  • Open Access Logo Journal of the American Chemical Society 145(2023)3, 1826-1834
    Online First (2023) DOI: 10.1021/jacs.2c11331

Permalink: https://www.hzdr.de/publications/Publ-36397
Publ.-Id: 36397


Flexible and printed magnetic field sensors

Zabila, Y.; Makushko, P.; Oliveros Mata, E. S.; Kosub, T.; Illing, R.; Volkov, O.; Faßbender, J.; Mönch, J. I.; Xu, R.; Pylypovskyi, O.; Makarov, D.; Cañón Bermúdez, G. S.; Milkin, P.; Ionov, L.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Schmidt, N.; Albrecht, M.; Vladymyrskyi, I.; Varvaro, G.; Ha, M.; Wang, Y.

Work with spintronic functional elements for flexible magnetic field sensors, we was interested
in improving their performance, relying on new materials and metrological approaches. We
employ novel fabrication technics as an alternating magnetic field activation of self-healing of
percolation network [1]. It allows to fabricate printable magnetoresistive sensors revealing an
enhancement in sensitivity of more than one and two orders of magnitude, relative to previous
reports. Printed electronics are attractive due to their low-cost and large-area processing
features, which have been successfully extended to magnetoresistive sensors and devices [2].
This technology was enabled initially, by thin films magnetic field sensors, embedded in a soft
and flexible format to constitute magntosensitive electronic skin (e-skins). But now we
demonstrate what interactive electronics, based on flexible spin valve switches [3] or printed
and stretchable Giant Magnetoresistive Sensors, could act also as a logic elements, namely
momentary and permanent (latching) switches. All this printing technology aspects are yet to
be developed to comply with requirements to mechanical conformability of on-skin appliances.
Due to the fact that the metallic layer is subjected to unsteady mechanical stresses, deposition
of the magnetic sensor onto few microns thick non-rigid substrate creates a numerous
problems, and the strain sensitivity is the first effect which have to be discussed. The
thermoelectric effect is the second effect that also have to be considered in order to minimize
thermal errors. These aspects will be discussed more detailed in this contribution.

References

[1] R. Xu, Nature Communications 13, 6587 (2022)
[2] E. S. Oliveros Mata, Applied Physics A 127, 280 (2021)
[3] P. Makushko, Adv. Funct. Mater. 31, 2101089 (2021)
[4] M. Ha, Adv. Mater. 33, 2005521 (2021)

Keywords: Flexible; Magnetic; Sensor

  • Poster
    776. WE-Heraeus-Seminar, 04.-06.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36393
Publ.-Id: 36393


Homogenization and Chemical Ordering in Co-Pt Thin Films

Pedan, R.; Makushko, P.; Dubikovskyi, O.; Bodnaruk, A.; Burmak, A.; Makarov, D.; Vladymyrskyi, I.

Binary alloys based on CoPt are attractive as a materials for spintronics, permanent magnets applications and data storage devices due to the high and tunable coercivity combined as well as an excellent corrosion resistance [1].
The formation of chemically ordered CoPt magnetic phases is intensively studied both in thin films and in nanoparticles [2, 3]. In Co-Pt alloys, a large coercive field and magnetic anisotropy can be achieved even in chemically disordered alloys due to short-range order [4]. We have implemented a systematic structural and magnetometry study of the diffusion-controlled formation of a homogeneous CoPt alloy by vacuum heat treatment of Pt/Co stacks, where diffusion processes are driven by diffusion-induced grain boundary migration mechanism.
Layered stacks of Pt(14 nm)/Co(13 nm)/Ta(3 nm) were magnetron sputter deposited and annealed in vacuum of 10‑6 mbar in the temperature range of 200 °С – 550 °С. The structure, chemical composition and magnetic properties of the films were analyzed by X-ray diffraction, secondary ion mass spectrometry, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and VSM magnetometry.
We demonstrate that a Co‑Pt alloy with a homogeneous structure is formed after annealing at temperature above 500 °C. Despite the fact that long-range chemical order in CoPt film was not formed, thermal treatment leads to an increase of the coercive field. We attribute the short-range chemical ordering as a mechanism responsible for the formation of a local anisotropy in Co‑Pt alloy. In this respect, our study suggests that the diffusion mechanism relying on grain boundary migration can be used to promote short-range ordering in binary magnetic alloys. These results will motivate further studies of diffusion processes and the formation of hard magnetic chemical

  • Lecture (Conference)
    IEEE 12th International Conferenfe "Nanomaterials: Applications & Properties", 11.-16.09.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-36392
Publ.-Id: 36392


Effect of a Discontinuous Ag Layer on Optical and Electrical Properties of ZnO/Ag/ZnO Structures

Vitanov, P.; Ivanova, T.; Dikov, H.; Terziyska, P.; Ganchev, M.; Petkov, N.; Georgiev, Y.; Asenov, A.

ZnO/Ag/ZnO nanolaminate structures were deposited by consecutive RF sputtering at room temperature.The optical transparency, sheet resistance, and figure of merit are determined in relation to the deposition time of Ag and to the film thickness of the ZnO top layer. An improved transmittance has been found in the visible spectral range of the ZnO/Ag/ZnO structure compared to ZnO multilayers without Ag. High transmittance of 98% at 550 nm, sheet resistance of 8 W/sq, and figure of merit (FOM) of 111.01x10-3 Ω-1 are achieved for an optimized ZnO/Ag/ZnO nanolaminate structure. It is suggested that the good optical and electrical properties are due to the deposition of the discontinuous Ag layer. The electrical metallic type conductivity is caused by planar located silver metal granules. The deposition of a discrete layer of Ag nano-granules is confirmed by atomic force microscopy (AFM) and cross-section high-resolution transmission electron microscopy (HRTEM) observations.

Keywords: transparent conductive oxide (TCO) transparent conducting nanolam; magnetron sputtering; ZnO/Ag/ZnO; transparent conducting nanolaminate structures; discontinuous Ag layer; oxide/metal/oxide

Permalink: https://www.hzdr.de/publications/Publ-36373
Publ.-Id: 36373


Surface magnetization of Cr2O3 (104) quantified via scanning NV magnetometry

Lehmann, P.; Wagner, K.; Pylypovskyi, O.; Weber, S.; Hedrich, N.; Makushko, P.; Shields, B.; Kosub, T.; Veremchuk, I.; Sheka, D.; Spaldin, N.; Makarov, D.; Maletinsky, P.

Magneto-electric antiferromagnets are candidate materials for future spintronic
devices. While antiferromagnets offer high speed, low power consumption and
robustness to external fields, magneto-electrics allow manipulation of the magnetic
order parameter not only via magnetic signals, but also via electric signals [1, 2].
Readout and manipulation of the antiferromagnetic order on the nanoscale typically
relies on local probes sensitive to the surface magnetization. Therefore, its optimization
is key challenge in device engineering. Here we investigate the surface magnetization
of an oblique cut of single crystal Cr 2 O3 using scanning probe nitrogen-vacancy center
magnetometry. The (104) surface normal is at an angle of 38.5° to the uniaxial
anisotropy axis of Cr 2 O3. By magneto-electric annealing [3], a homogeneous
antiferromagnetic order is initialized. We then measure the stray magnetic fields
produced by topographic steps fabricated by ICP etching. The steps have various
angles with respect to the c-axis in-surface component, allowing us to probe different
`cuts` of the magnetization. We finally consider a simple model based on a
homogenous surface magnetization strength and orientation for the various crystal
facets. We find good agreement between this model and the recorded stray fields for
a magnetization aligned with the bulk c-axis orientation. The predicted magnitude
agrees with previous results of measurements on (001) surfaces [4]. We hope that
these findings may aid in understanding the relation between surface and bulk
magnetic order in antiferromagnets and aid in the development of antiferromagnetic
spintronic devices.

Keywords: antiferromagnetism; Cr2O3

  • Lecture (Conference)
    WE-Heraeus-Seminar “Re-thinking Spintronics: From Unconventional Materials to Novel Technologies”, 03.-06.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36372
Publ.-Id: 36372


Magnetic field-induced textures and phase transitions in antiferromagnetic spin chains: geometry-induced effects

Borysenko, Y.; Sheka, D.; Yershov, K.; Faßbender, J.; van den Brink, J.; Makarov, D.; Pylypovskyi, O.

Easy axis antiferromagnets (AFMs) are robust against external magnetic fields of a moderate strength. Spin reorientation transitions in strong fields can provide an insight into more subtle properties of antiferromagnetic materials, which are often hidden by their high ground state symmetry. In curved intrinsically achiral AFM spin chains geometrical bends and twists provide helimagnetic responses, characterized as effective anisotropic and Dzyaloshinskii–Moriya-like (DMI) interactions [1]. Here, we address theoretically effects of curvature in achiral anisotropic ring-shaped AFM spin chains with even number of spins exposed to strong magnetic fields using the methodology of curvilinear magnetism. We identify the geometry-governed helimagnetic phase transition enabled in the spin-flop phase, which separates locally homogeneous (vortex) and periodic (onion) AFM textures [2, 3]. The curvature-induced Dzyaloshinskii–Moriya interaction results in the spin-flop transition being of the first- or second-order depending on the ring curvature. Spatial inhomogeneity of the Néel vector in the spin-flop phase generates the weakly ferromagnetic response in the plane perpendicular to the applied magnetic field [3]. In AFM spin chains possesing torsion, e.g. helices, these effects are enhanced by the inhomogeneity of local texture in the ground state. Our work provides further insights in the physics of curvilinear AFMs in static magnetic fields and guides prospective experimental studies of geometrical effects in the spin-chain nanomagnets.

Keywords: antiferromagnetism; curvilinear spin chains

  • Lecture (Conference)
    WE-Heraeus-Seminar “Re-thinking Spintronics: From Unconventional Materials to Novel Technologies”, 03.-6.01.2023, Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-36371
Publ.-Id: 36371


Nanoscale studies of antiferromagnetic spin-textures

Wagner, K.; Lehmann, P.; Pylypovskyi, O.; Hedrich, N.; Makushko, P.; Shields, B.; Kosub, T.; Sheka, D.; Makarov, D.; Maletinsky, P.

Magneto-electric antiferromagnets hold promise for future spintronic devices, as they offer magnetic field hardness, high switching speeds and both electric and magnetic control of their order parameters, owing to the magneto-electric coupling [1]. As information and functionality is encoded in the antiferromagnetic order parameter, its manipulation, read-out and nanoscale textures are paramount for device operation, as well as interesting from a fundamental point of view. For applications the surface plays a key-role as the interface often dictates the read/write functionalities and gains importance as thin film devices are targeted. Using scanning nitrogen vacancy magnetometry [2] we study a ‘textbook’, single crystal magneto-electric antiferromagnet Cr 2O3 and perform nanoscale imaging of its surface magnetization, which is directly linked to its magnetic order parameter. We first confirm magneto-electric poling [3] of a homogeneous antiferromagnetic order and study the stray field polarity at the surface depending on the used field configuration. Our results are consistent with a theoretically predicted topmost disordered layer [4]. In the next step local electrodes are utilized to nucleate individual single domain walls. Manipulation of the domain wall path is demonstrated both by local laser heating, as well as the creation of an energy landscape for the domain wall position via topographic structuring [2]. Analysing the domain wall path yields further information about the boundary conditions for the order parameter at topographic edges and an estimate of the full 3D-profile of the texture based on minimizing the domain walls surface energy. A Snell like refraction of the domain wall path is found, that can be represented in an analytical approximation as a ‘refractive index’ for a given island dimension as demonstrated for a range of incidence angles. The demonstrated pinning and control of the domain wall position constitutes the main ingredients for logic devices based on domain walls in magneto-electric antiferromagnets and their fundamental study. Understanding the intrinsic properties and stability of the magnetic order at the direct surfaces may aid in exploring their functionality in spintronic devices that often rely on spin-scattering mechanisms at the interface.

Keywords: antiferromagnetism; Cr2O3; domain walls

  • Lecture (Conference)
    MMM 2022, 31.10.-4.11.2022, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-36370
Publ.-Id: 36370


Domain walls in Cr2O3

Pylypovskyi, O.

Presentation about our recent achievements on the domain wall studies in Cr2O3.

Keywords: antiferromagnetism; Cr2O3

  • Invited lecture (Conferences)
    Ukrapro workshop, 01.06.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36369
Publ.-Id: 36369


Skin-conformal magnetoreceptors for human-machine interaction

Makushko, P.; Oliveros Mata, E. S.; Canon Bermundez, G. S.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Zabila, Y.; Faßbender, J.; Vladymyurskyi, I.; Albrecht, M.; Varvaro, G.; Xu, R.; Makarov, D.

Artificial magnetoception, i.e., electronically expanding human perception to detect magnetic fields, is a new and yet unexplored route for interacting with our surroundings. This technology relies on thin, soft, and flexible magnetic field sensors, dubbed magnetosensitive electronic skins (e-skins) [1]. These devices enable reliable and obstacle insensitive proximity, orientation and motion tracking features [2, 3] as well as bimodal touchless-tactile interaction [4].
Although, basic interactive functionality has been demonstrated, the current on-skin magnetoreceptors are not yet employed as advanced spintronics-enabled switches and logic elements for skin compliant electronics. The major limitation remains primarily due to the use of in-plane magnetized layer stacks. The predominant in-plane sensitivity prevents these devices from becoming intuitive switches or logic elements for interactive flexible electronics, as the natural actuation axis of switches is out-of-plane.
Here, we will introduce current technologies towards realization of skin-conformal magnetoelectronics for touchless and tactile interactivity in virtual and augmented reality. The focus will be put on the fabrication of on-skin spin valve switches with out-of-plane sensitivity to magnetic fields [5]. The device is realized on a flexible foil relying on Co/Pd multilayers with perpendicular magnetic anisotropy and synthetic antiferromagnet as a reference layer. Owing to the intrinsic tunability, these interactive elements can provide fundamental logic functionality represented by momentary and permanent (latching) switches and reliably discriminate the useful signals from the magnetic noise. The flexible device retain its performance upon bending down to 3.5 mm bending radii withstand more than 600 bending cycles.
We showcase the performance of our device as on-skin touchless human-machine interfaces, which allows interactivity with a virtual environment, based on external magnetic fields. We envision that this technology platform will pave the way towards magnetoreceptive human-machine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances.

  • Lecture (Conference)
    MMM 2022 Conference, 31.10.-04.11.2022, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-36368
Publ.-Id: 36368


Flexible Magnetoreceptive Switch for On-Skin Touchless Human-Machine Interaction

Makushko, P.; Oliveros Mata, E. S.; Cañón Bermúdez, G. S.; Hassan, M.; Laureti, S.; Rinaldi, C.; Fagiani, F.; Barucca, G.; Schmidt, N.; Zabila, Y.; Kosub, T.; Illing, R.; Volkov, O.; Vladymyrskyi, I.; Faßbender, J.; Albrecht, M.; Varvaro, G.; Makarov, D.

Artificial magnetoception, i.e., electronically expanding human perception to detect magnetic fields, is a new and yet unexplored route for interacting with our surroundings. This technology relies on thin, soft, and flexible
magnetic field sensors, dubbed magnetosensitive electronic skins (e-skins) [1]. These devices enable reliable and obstacle insensitive proximity, orientation and motion tracking features [2, 3] as well as bimodal touchless-tactile
interaction [4].
Although, basic interactive functionality has been demonstrated, the current on-skin magnetoreceptors are not yet employed as advanced spintronics-enabled switches and logic elements for skin compliant electronics. The
major limitation remains primarily due to the use of in-plane magnetized layer stacks, sensitive mainly to the magnetic fields oriented within the sensor plane. This prevailing in-plane sensitivity has prevented them from becoming intuitive switches or logic elements for interactive flexible electronics, as the natural actuation axis of switches is out-of-plane. Flexible Hall effect sensors [5, 6] could provide out-of-plane sensitivity, but not intrinsic logic functionality.
In this work, we present the very first tunable magnetoreceptive platform for on-skin touchless interactive electronics based on flexible spin valve switch elements with dedicated out-of-plane sensitivity to magnetic fields [5]. The device is realized on a flexible polyethylene naphthalate (PEN) foil relying on Co/Pd multilayers with perpendicular magnetic anisotropy and synthetic antiferromagnet as a reference layer. Owing to the intrinsic tunability, these interactive elements can provide fundamental logic functionality represented by momentary and permanent (latching) switches and reliably discriminate the useful signals from the magnetic noise. The flexible
device retain its performance upon bending down to 3.5 mm bending radii and withstand more than 600 bending cycles.
We showcase the performance of our device as on-skin touchless human-machine interfaces, which allows interactivity with a virtual environment, based on external magnetic fields. Depending on the material properties of the on-skin switch used, the virtual functions can be impervious to (latching) or controlled by (momentary) ambient
magnetic stimuli. We envision that this technology platform will pave the way towards magnetoreceptive humanmachine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances.

  • Lecture (Conference) (Online presentation)
    2022 IEEE 12th International Conference "Nanomaterials: Applications & Propertie", 11.-16.09.2022, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-36362
Publ.-Id: 36362


Characterization of Tri- and Tetravalent Actinide Complexes with Amidinate Ligands

Hong, B.; Fichter, S.; Näder, A.; März, J.; Kaden, P.; Patzschke, M.; Schmidt, M.; Stumpf, T.

Understanding the physical and chemical properties of radionuclides interacting with organic ligands is fundamental for a reliable evaluation of the migration behaviour of radionuclides in the environment. In this context, our group has been conducting research with a particular emphasis on the complexation of early actinides with relatively soft N-donor ligands, and recently, the tetravalent actinide complexes with the chiral benzamidinate ((S)-PEBA) have been successfully synthesized. The present study is inspired by these precedent studies to synthesize a new series of amidinate compounds with An(III) and An(IV) to provide and expand a comprehensive understanding of the electronic properties of actinide complexes.

In this study, we succeeded to obtain a series of tetravalent actinide amidinate chloro complexes [AnClx(amid)y] (An= Th, U, and Np; amid= iPr2BA, (S)-PEBA, and Cy2TA). The crystal structures of the benzamidinate complexes were determined by single-crystal XRD, all showing three amidinates and one halide ligand coordinated to the actinide metal center in a mono-capped distorted octahedral coordination geometry. In the case of the Cy2TA ligand with a sterically bulky tert-butyl substituent, only the complex with a metal-to-ligand ratio of 1:2 [UCl2(Cy2TA)2] was obtained. The paramagnetic effects of these actinide complexes were investigated extensively in solution with NMR spectroscopy. Furthermore, the reduction of An(IV) to An(III) afforded the corresponding homoleptic amidinate complexes [An(amid)3] (An= U and Np; amid= iPr2BA and (S)-PEBA), allowing the comparison of structural and chemical bonding situations with isostructural Ln(III) complexes via paramagnetic NMR studies.

Keywords: actinides; lanthanides; coordination chemistry; SC-XRD; NMR; amidinate; N-donor ligands

  • Poster
    ATAS-AnXAS 2022, 17.-21.10.2022, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-36355
Publ.-Id: 36355


Thermal Performance Study of a Heat-Pipe in Comparison with Experiments Using CFD

Höhne, T.

Heat pipes are playing a more important role in many industrial applications, particularly in improving the thermal performance of heat exchangers and increasing energy savings in applications with commercial use. In this paper, a Computational Fluid Dynamics (CFD) model was built to simulate the details of the steam/water two-phase flow and heat transfer phenomena during the operation of a heat pipe. The homogeneous model in ANSYS CFX was used for the simulation. The evaporation, condensation and phase change processes were modelled. The 3D simulations could reproduce the heat and mass transfer processes in comparison with experiments from the literature. Reasonable good agreement was not only observed between CFD temperature profiles in relation with experimental data but also in comparing the thermal performance of the heat-pipe. It was found that the heating power should not increase above 1000 W for the analyzed type of TPCT using copper material.

Keywords: Two-phase flow; Boiling; CFD; Condensation; Heat-pipe

Permalink: https://www.hzdr.de/publications/Publ-36353
Publ.-Id: 36353


Synthesis and Characterization of Tetravalent Actinide Amidinate Halide Complexes

Hong, B.; Fichter, S.; März, J.; Kaden, P.; Patzschke, M.; Schmidt, M.; Stumpf, T.

Amidinate ligands have attracted considerable attention in the field of coordination chemistry over the last decades as versatile soft N-donor ligands to stabilize the transition metal complexes in various oxidation states. The additional advantages of employing amidinates over other ligand systems are their high modularity and easy access to a variety of analogs by altering the substitution patterns through straightforward synthetic procedures. There have been a number of studies on the transition metal amidinate complexes including lanthanides, and even some early actinides. Still, these studies are mainly limited to thorium(Th) and high valent(V,VI) uranium(U) complexes. Here we focused on the interaction of An(IV) complexes (An= Th, U, and Np) with benzamidinate ligands to provide a comprehensive understanding of the electronic properties of actinide compounds.

In this study, we successfully synthesized a series of tetravalent actinide tris-benzamidinate chloro complexes [AnCl(amid)3] (An= Th, U, and Np; amid= iPr2BA and (S)-PEBA). Furthermore, we also obtained additional halide complex series (F, Br) by halogen exchange reactions on chloro complexes as precursors to investigate the conformational stability of the complex. The crystal structures of the model actinide complexes were determined by SC-XRD, showing three benzamidinates and one halide ligand coordinated to the actinide metal center in a mono-capped distorted octahedral coordination geometry, resulting in a propeller-like shape with the halide lying on the rotation axis. The actinide complexes were also
characterized in solution by using paramagnetic NMR spectroscopy to elucidate structural and chemical bonding situations with an increasing number of unpaired electrons along the 5f series.

Keywords: actinides; coordination chemistry; NMR; SC-XRD; N-donor ligands; amidinate; halogen

  • Open Access Logo Lecture (Conference)
    19th Radiochemical Conference, 15.-20.05.2022, Marianske Lazne, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-36352
Publ.-Id: 36352


Synthesis and complexation of nitrogen donor ligands with tetravalent uranium

Duckworth, T.; Schwarz, N.; März, J.; Patzschke, M.; Schmidt, M.; Stumpf, T.

The knowledge of complexation reactions of early actinides with nitrogen donor ligands serves not only as fundamental research in this underrepresented field of chemistry but also contributes to a deeper understanding of their reactivity and coordination chemistry. In contrast to the lanthanides, with the dominating oxidation state of + III, actinides, especially the early actinides up to Plutonium, can exist in a variety of different oxidation states ranging from +II to +VI.
The coordination chemistry of tri- and tetravalent actinides with selective soft nitrogen donor ligands is of special interest, with a potential use as extraction and/or decontamination agents.
In order to understand the bonding trends and electronic structure, the nitrogen donor ligand 2,6-bis(1-(4-bromo-2,6-dimethylphenyl)-1H-1,2,3-triazol-4-yl)pyridine, a BPTP-type ligand, was used as the compound of choice in this contribution. BPTP-type ligands are based on the commonly known BTP-ligand, a tridentate chelating ligand which was designed for the purpose of separating lanthanides from actinides.[1] The BPTP ligand was synthesized by a copper mediated click reaction of 2,6-diethynylpyridine with the corresponding azide.
Within this ongoing study, we focus on the synthesis and characterization of tetravalent actinides, which are readily available for all of the early actinides from Thorium up to Plutonium.
The obtained U(IV) complex was characterized by single crystal X-ray diffraction (SC-XRD). Further characterization of the novel coordination complex using NMR, IR, and EPR, as well as an expansion to the transuranic elements will complete this study.

  • Lecture (Conference)
    19th Radiochemical Conference - RadChem 2022, 15.-20.05.2022, Mariánské Lázně, Tschechien

Permalink: https://www.hzdr.de/publications/Publ-36348
Publ.-Id: 36348


Synthesis and Coordination Chemistry of N-Donor Ligands with early Actinides

Duckworth, T.; März, J.; Kaden, P.; Patzschke, M.; Schwarz, N.; Greif, G.; Stumpf, T.

Understanding the subtle differences between lanthanide and actinide complexation chemistry with different ligand systems is an ongoing field of resarch. Soft donor ligands, especially ligands containing nitrogen, have shown to be promising for the investigation of the small differences in bonding behavior of actinides compared to lanthanides particularly with regards to the covalent contribution within the bond.

BTP type ligands have been used as an extacting ligand for the separation of lanthanides from actinides.1 Therefore, new soft nitrogen donor ligands based on the BTP type ligand (2,6-Bis(1,2,4-Triazin-3-yl)Pyridine) or Schiff base lig-ands have been synthesized to explore the fundamental chemistry of the early 5f-elements. In order to investigate the coordination environment, ligand selectivity, bonding trends and electronic properties a series of actinide complexes ranging from thorium to plutonium has been characterized in solid state as well as in solution.

In the present study the synthesis of the new soft donor ligand L1 was carried out via a copper mediated click reaction of the corresponding alkyne and azide. The bipyridine based ligand L2 was obtainend in a three step synthesis starting from bipyridine via the corresponding N-oxide and cyanide to give the tetrazine.
Both ligands L1 and L2 were succesfully applied in the complexation reaction with trivalent lanthanides e.g. Er and Sm. In this contribution the investigation of the coordination chemistry of these soft N-donor ligands is exended to the early actinides in their tri- and tetravalent oxidation state.

First experimental results show the formation of a 3:1 complex in the case of trivalent Er. In contrast, the same ligand system L1 forms a 2:1 complex with U(IV) including methanolato and iodo ligands for charge compensation. Further results including first structural characterization as well as results from quantum chemical calculations to elucidate the binding situation, will be presented in this contribution.

  • Poster
    Actinides revisited 2022, 21.-23.09.2022, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36347
Publ.-Id: 36347


Quantitative assessment of separation quality, using neural networks and multivariate stochastic modeling

Kirstein, T.; Furat, O.; Leißner, T.; Bachmann, K.; Gutzmer, J.; Peuker, U. A.; Schmidt, V.

The quality and behavior of application specific industrial materials, such as those used for the production of coatings, membranes and electrodes, are influenced by the properties of particles within the materials, for example, particle size, flatness and sphericity. To fabricate materials with desired properties, particle systems may undergo processes such as fractionation or magnetic separation for quality adjustment. X-ray computed tomography (CT) can image large volumes of given particle systems with a sufficiently good resolution to allow for the analysis of individual particles. However, methods to efficiently analyze such image data and model the observed particle properties are still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the classic watershed algorithm, struggle to recognize particles with satisfying accuracy. Therefore, more advanced methods of machine learning can be utilized for such image segmentation tasks to improve the validity of further subsequent analyzes.

In this talk, experimentally measured three-dimensional CT images of a zinnwaldite-quartz composite material are considered before and after a magnetic separation process is applied to enrich valuable mineral ores. Therefore, an image segmentation method using a deep convolutional neural network (CNN), specifically an adaptation of the U-net architecture, is used. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. In addition, a fully parametric vine copula based model is designed to determine multivariate probability distributions of particle size/shape/textural/composititional characteristics—allowing for the estimation and interpretable characterization of highly-dimensional interdependencies of particle characteristics. The described methodology is then applied to describe image data of particle systems before and after magnetic separation, to quantitatively evaluate the separation success.

  • Lecture (Conference)
    5th International Conference Hybrid 2022 - Materials and Structures, 20.-22.07.2022, Leoben, Austria

Permalink: https://www.hzdr.de/publications/Publ-36345
Publ.-Id: 36345


Coordination chemistry of N-Donor Ligands with early Actinides

Duckworth, T.; März, J.; Kaden, P.; Schmidt, M.; Stumpf, T.

The development and investigation of N-donor ligands e.g. for actinide / lanthanide separation is an ongoing field of study, in particular with respect to understanding the structure-property-relationship.
In this context we have been exploring the coordination chemistry of the early actinides (Th – Am) with tridentate chelating ligands containing pyridine and bipyridine moieties.
Ligands 1 and 2 were successfully used for complexation with trivalent lanthanides.
Encouraged by these results, we have been focusing on their coordination chemistry with tri- and tetravalent early actinides. We aim to understand the reactivity of these ligands that exploit the unique electronic structure of the early 5f-elements.
The synthesis of such complexes was carried out in acetonitrile with recrystallization from methanol.
For instance, the synthesized U(IV) complex of 1a which was characterized by single crystal XRD revealed a nine-fold coordinated uranium center. In contrast to the nine-fold Ln(III) complex which exhibits a ligand to metal ratio of 3:1 the U(IV) complex shows a 2:1 ratio with additional methanolato and iodo ligands for charge compensation.
Expanding the series to the tri- and tetravalent transuranic metals and characterizing the obtained complexes both structurally and spectroscopically will help to elucidate the differences between the coordination behavior of the lanthanides compared to the actinides.

  • Poster
    Plutonium Futures – The Science 2022, 26.-29.09.2022, Avignon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-36344
Publ.-Id: 36344


Quantitative assessment of separation quality, using neural networks and multivariate stochastic modeling

Kirstein, T.; Furat, O.; Leißner, T.; Bachmann, K.; Peuker, U. A.; Schmidt, V.

Particle properties such as size, shape and composition are key for many products and in many processes. For example, in order to enrich minerals in a targeted manner, an ore must be crushed, classified and sorted so that high grades are achieved with a high recovery at the same time. To describe and optimize the processes, the influence of particle properties on the process result must be determined. X-ray computed tomography (CT) can image large volumes of given particle systems with a sufficiently good resolution to allow for the analysis of individual particles. However, methods to efficiently analyze such image data and model the observed particle properties are still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the classic watershed algorithm, struggle to recognize particles with satisfying accuracy. Therefore, more advanced methods of machine learning can be utilized for such image segmentation tasks to improve the validity of further analyzes. In this talk, experimentally measured three-dimensional CT images of a zinnwaldite-quartz composite material are considered before and after a magnetic separation process is applied to enrich valuable minerals. Therefore, an image segmentation method using a deep convolutional neural network (CNN), specifically an adaptation of the 3D U-net architecture, is used. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. In addition, a fully parametric vine copula based model is designed to determine multivariate probability distributions of particle size/shape/textural/composititional characteristics—allowing for the estimation and interpretable characterization of highly-dimensional interdependencies of particle characteristics. The described methodology is then applied to characterize the particle systems before and after
magnetic separation, to quantitatively evaluate the separation success.

  • Lecture (Conference) (Online presentation)
    IMPC Asia-Pacific 2022, 21.-23.08.2022, Melbourne, Australien

Permalink: https://www.hzdr.de/publications/Publ-36343
Publ.-Id: 36343


Application of mineral liberation analysis to determine the spatial association of accessory minerals with biotite in granitic rocks

Bachmann, K.; Gilbricht, S.; Renno, A.; Hamilton, D. C.; Clarke, D. B.

We apply mineral liberation analysis (MLA) to resolve and automate highly specific petrological questions. In this study, we quantify the spatial association of more than 15,000 grains of accessory apatite, monazite, xenotime, and zircon with essential biotite, and clustered with themselves, in a peraluminous biotite granodiorite from the South Mountain Batholith in Nova Scotia (Canada). A random distribution of accessory minerals demands that the proportion of accessory minerals in contact with biotite is identical to the proportion of biotite in the rock, and the binary touching factor (percentage of accessory mineral touching biotite divided by modal proportion of biotite) would be ~1.00. Instead, the mean binary touching factors for the four accessory minerals in relation to biotite are: apatite (5.06 for 11168 grains), monazite (4.68 for 857 grains), xenotime (4.36 for 217 grains), and zircon (5.05 for 2876 grains). Shared perimeter factors give similar values. Monazite and zircon have approximately log-normal grain-size distributions, but apatite is strongly skewed toward larger grain sizes, and xenotime is skewed toward smaller grain sizes. Accessory mineral grains that straddle biotite grain boundaries are larger than completely locked, or completely liberated, accessory grains. Only apatite-monazite clusters are significantly more abundant than expected for random distribution. The high, and statistically significant, binary touching factors and shared perimeter factors suggest a strong physical or chemical control on their spatial association. We discuss several petrogenetic processes that may lead to this spatial association. This study is an example of how modern methods of automated mineralogy, combined with powerful statistical methods, allow petrographic observations defined as "well known" and "given" to be transformed into viable scientific statements that are verifiable and falsifiable.

  • Poster
    Geoanalysis 2022, 06.-12.08.2022, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36341
Publ.-Id: 36341


Prediction of mineralogical particle composition using CT data and R-vine copulas

Furat, O.; Kirstein, T.; Leißner, T.; Bachmann, K.; Gutzmer, J.; Peuker, U. A.; Schmidt, V.

Computed tomography (CT) can capture volumes large enough to measure a statistical meaningful number of micron-sized particles with a sufficiently good resolution to allow for the analysis of individual particles. However, the development of methods to efficiently investigate such image data and interpretably model the observed particle features is still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the watershed algorithm, struggle to recognize particles with satisfying accuracy. Thus, more advanced methods of machine learning must be utilized for image segmentation to improve the validity of subsequent analyzes. Moreover, CT data does not include information about the mineralogical composition of particles and, therefore, additional SEM-EDS image data must be acquired. Here, micro-CT data of a particle system mostly composed of zinnwaldite-quartz composites is considered. First, an image segmentation method is applied which uses deep convolutional neural networks (CNN), namely a U-net. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. Then, parameterized models based on vine copulas are designed to determine multivariate probability distributions of descriptor vectors for the size, shape, texture and composition of particles. For model fitting, the segmented three-dimensional CT data and co-registered two-dimensional SEM-EDS data are used. The models are applied to predict the mineralogical composition of particles, solely on the basis of particle descriptors observed in CT data. The power of the introduced prediction models for estimating the mineralogical composition of particles by means of CT-based descriptor vectors, are evaluated with respect to the prediction of the zinnwaldite volume fraction of particles. Results obtained for the goodness of fit and the predictive power are quantitatively assessed.

  • Lecture (Conference)
    WCPT9 - World Congress on Particle Technology, 18.-22.09.2022, Madrid, Spanien

Permalink: https://www.hzdr.de/publications/Publ-36338
Publ.-Id: 36338


Antiferromagnetic spin chains: ground states and phase transitions in static magnetic field of arbitrary direction

Borysenko, Y.; Sheka, D.; Yershov, K.; Faßbender, J.; van den Brink, J.; Makarov, D.; Pylypovskyi, O.

While easy axis antiferromagnets (AFMs) are robust against external magnetic fields of a moderate strength, spin reorientations in strong fields provide an insight into subtle properties of materials, which are usually hidden by the high symmetry of the ground state [1]. In absence of external magnetic fields, they reveal geometry-driven chiral and anisotropic responses supplemented by weak ferromagnetism [2]. Here, we address theoretically the effects of curvature in achiral anisotropic ring-shaped AFM spin chains exposed to strong magnetic fields using the methodology of curvilinear magnetism [3]. We identify the geometry-governed helimagnetic phase transition enabled in the spin-flop phase, separating locally homogeneous (vortex) and periodic (onion) AFM textures (Fig. 1). The curvature-induced Dzyaloshinskii–Moriya interaction results in the spin-flop transition being of the first- or second-order depending on the ring curvature. Spatial inhomogeneity of the Néel vector in the spin-flop phase generates the weakly ferromagnetic esponse in the plane perpendicular to the applied magnetic field, which is inherent to curved systems. In AFM spin chains possesing torsion, e.g. helices, these effects are enhanced by the inhomogeneity of local texture in the ground state. Our work provides further insights in the physics of curvilinear AFMs in static magnetic fields and guides prospective experimental studies of geometrical effects in the spin-chain nanomagnets.

Keywords: antiferromagnetism; curvilinear spin chains

  • Lecture (Conference)
    AIM 2023 Advances in Magnetics, 15.-18.01.2023, Moena, Italy, 15.-18.01.2023, Moena, Italy

Permalink: https://www.hzdr.de/publications/Publ-36331
Publ.-Id: 36331


A Contribution to a Better Understanding of Lithium-Ion Battery Recycling by Using Automated Mineralogy

Vanderbruggen, A.; Bachmann, K.; Rudolph, M.; Gutzmer, J.

Recycling is a potential solution to narrow the gap between the supply and demand of battery materials such as Co, Ni, Mn and graphite. However, increasing the efficiency of the recycling of lithium ion batteries (LIB) remains a challenge. This paper evaluates the influence of the recycling routes on the liberation of LIB components and on the joint recovery of lithium metal oxides and spheroidized graphite particles using froth flotation. The products of the two different recycling routes – mechanical, and thermomechanical – were analyzed using a particle-based method, namely scanning electron microscopy (SEM)-based automated image analysis. The mechanical process enabled the delamination of active materials from the foils. However, binder preservation hinders active materials liberation as indicated by their aggregation. In contrast, the thermo-mechanical process showed a preferential liberation of individual anode active particle thus identified as an upstream route for flotation. However, this thermal treatment led to a lack of liberation of cathode material and to the oxidation of aluminium foil resulting in its distribution in all size fractions. Among the two, the thermo-mechanical black mass showed the highest flotation selectivity due to the removal of the binder thereby producing liberated active particles.

  • World of Metallurgy - Erzmetall 75(2022)3, 144-152

Permalink: https://www.hzdr.de/publications/Publ-36330
Publ.-Id: 36330


Statistical characterization of the interfacial behavior captured by a novel image processing algorithm during the gas/liquid counter-current two-phase flow in a 1/3 scaled down of PWR hot leg

Astyanto, A. H.; Nugroho, A. N. A.; Indarto; Catrawedarma, I. G. N. B.; Lucas, D.; Deendarlianto

This study addresses a statistical characterization of the interfacial behaviors during gas/liquid counter-current flow in a large scale of pressurized water reactor’s hot leg typical geometry on the basis of both time and frequency domain analyses. Here, the visualizations were captured by high-speed cameras. Furthermore, the image processing algorithm on the basis of pixel identification was developed to identify the time-series interfacial dynamics of the liquid holdup fluctuations, comprising the wave growth and its movement. The obtained data were further analyzed by using various advanced statistical tools comprising the probability density function, power spectral density function, and also discrete wavelet transform. Additionally, chaotic levels of the flow were obtained through the Kolmogorov-entropy analysis.
Particular results reveal that a typical mechanism of flooding begins with the appearance of a wavy interface which further develops into either a roll or large wave, and later blocks the entire cross-sectional area of the conduit around the bend region. This later stage indicates the inception of flooding which is characterized by the increase of the water level close to the bend region. Next, the higher the pressure of system, the higher the frequency occurrence of slugging, while the injected gas flow rate obtained a different trend. However, the Kolmogorov entropy enables to correlate the stabilizing effect due to the fluid resistance which corresponds to either the pressure of the system or the physical properties of the fluid. In addition, there were no significant differences between the flooding mechanisms for both the air/water and steam/water flows.

Keywords: Counter-Current Flow Limitation; stratified flow

Permalink: https://www.hzdr.de/publications/Publ-36322
Publ.-Id: 36322


Matrix-Matched Reference Materials for the Analysis of Tungsten-Minerals for Trace Elements with Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Krause, J.; Berndt, J.

Scheelite (CaWO4) and wolframite-group minerals (Fe,Mn)WO4 represent the economically most important W-ore minerals. In order to constrain the processes responsible for the formation and overprint of W-ores knowledge of trace element concentrations including Mo, Sr, As, Nb, Ta and REE are necessary. In some cases, these ores are also associated with Au-mineralization.

Accuracy of quantitative analysis with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is improved by the use of matrix matched reference materials (RMs). In addition to matrix effects, the analysis of W-minerals involves analytical challenges such as abundance sensitivity of W on Ta and Re and molecular interferences of W-oxides and -nitrides on Au.

A gem-quality scheelite (Scheelite S) from a late-stage alpine vein in the Felbertal tungsten mine, Austrian Alps, is free of Ta and Re and therefore provides the opportunity to determine correction factors for abundance sensitivity of W on Ta and Re. For an exemplary set of samples from the Felbertal tungsten mine, the uncorrected data yield fairly constant Re concentrations of ~5-6µg/g and 0.99-2.14 µg/g for Ta respectively. After correction for abundance sensitivity, Re is below the lower limit of quantification and Ta ranges from 0.07-1.09 µg/g.

For Au the uncorrected concentrations range from 0.14 to 0.38 µg/g. After the correction for molecular interferences by W-oxides and -nitrides the concentrations varied between 0 and 0.32 µg/g.

Preliminary data from wolframite-group minerals indicate similar effects of the abundance sensitivity of W on Ta and Re, as well as the molecular interferences of W-oxides an –nitrides on Au.

Our study demonstrates significantly improved analyses of some important trace elements in W-minerals when matrix-matched RMs are used for the correction of the abundance sensitivity and molecular interferences.

  • Lecture (Conference)
    Geoanalysis 2022, 06.-11.08.2022, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36321
Publ.-Id: 36321


Atom Probe Tomography: Basics and applications on complex sulphides

Krause, J.

Atom Probe Tomography combines the three dimensional reconstruction of the lattice in real space with a time–of–flight mass spectrometer. The result is a tomographic image of the chemical composition of a solid sample making it a powerful technique to determine the chemical composition of nanostructures in 3-D with sub-nanoscale spatial resolution. It is a powerful technique to study processes on the near-atomic scale such as diffusion, exsolution, or the formation of nano-scale inclusions.

  • Invited lecture (Conferences)
    Vortragsreihe der Österreichischen Mineralogischen Gesellschaft, 17.03.2022, Universität Innsbruck, Österreich

Permalink: https://www.hzdr.de/publications/Publ-36320
Publ.-Id: 36320


Atom Probe Tomography: Basics and applications on complex sulphides

Krause, J.

Atom Probe Tomography combines the three dimensional reconstruction of the lattice in real space with a time–of–flight mass spectrometer. The result is a tomographic image of the chemical composition of a solid sample making it a powerful technique to determine the chemical composition of nanostructures in 3-D with sub-nanoscale spatial resolution. It is a powerful technique to study processes on the near-atomic scale such as diffusion, exsolution, or the formation of nano-scale inclusions.

  • Invited lecture (Conferences)
    Vortragsreihe der Österreichischen Mineralogischen Gesellschaft, 16.03.2022, Montanuniversität Leoben, Österreich

Permalink: https://www.hzdr.de/publications/Publ-36319
Publ.-Id: 36319


Atom Probe Tomography: Basics and applications on complex sulphides

Krause, J.

Atom Probe Tomography combines the three dimensional reconstruction of the lattice in real space with a time–of–flight mass spectrometer. The result is a tomographic image of the chemical composition of a solid sample making it a powerful technique to determine the chemical composition of nanostructures in 3-D with sub-nanoscale spatial resolution. It is a powerful technique to study processes on the near-atomic scale such as diffusion, exsolution, or the formation of nano-scale inclusions.

  • Invited lecture (Conferences)
    Vortragsreihe der Österreichischen Mineralogischen Gesellschaft, 14.03.2022, Universität Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-36318
Publ.-Id: 36318


Helmholtz AI: Diversity in Teaching Machine Learning supports democratising AI

Cea, D.; Hoffmann, H.; Weiel, M.; Steinbach, P.; Kesselheim, S.

“Democratising AI” – that is the motto for the Helmholtz AI consultants. With our scientific consulting, we enable Helmholtz researchers from all domains to leverage AI for their datasets by providing comprehensive support with AI methods, tools, and software engineering. And this does not only apply to scientists working on their own research projects. We also offer courses, workshops, lectures, and challenges on various AI-related topics. On our poster, you can find an overview of past teaching experiences from the different consultant teams. These include an in-depth introductory course to deep learning using the flipped classroom approach, advanced courses on AutoML and explainable AI with multiple hands-on sessions, data challenges introducing the learners to domain adaptation tasks and making them experiment and search for personal solutions to complex and current problems, and crash courses on AI for a broader and less technical audience.
You are curious to learn more? Then drop by our poster and let’s have a chat.

Keywords: machine learning; community; learning; diversity; inclusion

  • Open Access Logo Poster
    TEACH2, 09.11.2022, zoom, Germany

Downloads

Permalink: https://www.hzdr.de/publications/Publ-36317
Publ.-Id: 36317


Neptunium(V) and uranium(VI) sorption onto the zircaloy corrosion product zirconia (ZrO₂)

Jessat, I.

The interactions of long-lived radionuclides, such as uranium and the transuranium element
neptunium, with corroded phases in the near-field of a repository are crucial processes that
have to be taken into account in the safety assessment of a repository. Neptunium(V) and
uranium(VI) were chosen as representatives of pentavalent and hexavalent actinides,
respectively. Zirconia (ZrO₂) is the main corrosion product of the zircaloy cladding material of
spent nuclear fuel rods and constitutes as one of the first barriers encountered by mobilized
radionuclides. A comprehensive, multi-method approach was pursued to obtain a detailed
understanding of the Np(V)/U(VI) interactions at the zirconia-water interface. pH-dependent
batch sorption studies and isotherm experiments as well as spectroscopic techniques (EXAFS,
IR) were employed to gain information on the macroscopic and the molecular scale,
respectively. The derived information about Np(V)/U(VI) binding sites as well as number and
structure of the formed surface species were then used to constrain the parametrization of a
thermodynamic surface complexation model. The results of this work will contribute to more
reliable predictions about the environmental fate of Np(V)/U(VI) surrounding the near-field of
a repository.

Keywords: uranium(VI); neptunium(V); zirconia; ZrO₂; EXAFS; IR; sorption

  • Lecture (others)
    Presentation PhD topic, 09.11.2022, Veldhoven, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-36313
Publ.-Id: 36313


Introduction to kernel methods and Gaussian processes

Schmerler, S.

Introduction to kernel methods and Gaussian processes

  • Open Access Logo Lecture (others) (Online presentation)
    Institute Seminar, 08.11.2022, Görlitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-36308
Publ.-Id: 36308


Radiative particle-in-cell simulations of the beam hosing instability -- an analysis by components

Lebedev, A.; Pausch, R.; Widera, R.; Bastrakov, S.; Bussmann, M.; Schramm, U.; Debus, A.

We present first results and analyses of radiation spectra expected to be produced by highly relativistic particle beams propagating through a plasma medium experiencing the hosing instability. We determine these spectra in particle-in-cell simulations by in-situ computation of coherent and incoherent radiation based on Liénard-Wiechert potentials, emitted by all simulated particles (>10^9) of the beam and plasma for over 160 distinct detectors distributed across half a solid angle. Our code allows us to distinguish radiation emitted by plasma particles from that of the bunch, thereby enabling us to infer the origin of the spectral features.
In the simulation campaign, conducted at the JUWELS Booster cluster at JSC, we considered linear and non-linear regimes of the instability for highly relativistic electron beams of varying emittance impacting a homogeneous electron plasma.
We further show a preliminary analysis of the data relating observed characteristics of the spectra to the characteristics of the instability.
A goal of these studies is to open up new experimental avenues for better understanding the beam instability evolution by identifying quantitative radiation signatures of the instability that can be measured in experiments.

Keywords: Firehose Instability; PIConGPU; High-Performance Computing; Plasma-Wakefield Accelerators; Plasma Instabilities; Radiation Signatures

  • Lecture (Conference) (Online presentation)
    DPG Spring Meeting of the Divisions Hadronic and Nucleonic Physics, Plasma Physics and the Working Group Accelerator Physics, 28.03.-1.04.2022, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36307
Publ.-Id: 36307


Radiative particle-in-cell simulations of the beam hosing instability

Lebedev, A.; Pausch, R.; Bastrakov, S.; Widera, R.; Bussmann, M.; Schramm, U.; Steiniger, K.; Debus, A.

We present the results and analyses of radiation spectra expected to be
produced by highly relativistic particle beams propagating through a
plasma medium and experiencing the hosing instability.
Coherent and incoherent contributions to the spectra are determined
in-situ for all simulated particles (>10^9) of the particle cloud and
ambient plasma for a lage assembly of detectors.
With the help of our particle-in-cell code we are able to distinguish
radiation emitted by plasma particles from that of the bunch.
In the simulation campaign, conducted at the JUWELS Booster cluster at
JSC, we consider linear and non-linear regimes of the instability for
highly relativistic electron beams impacting a homogeneous electron plasma.
We show an updated analysis of the data relating observed
characteristics of the spectra to the features of the bunch and ambient
plasma, thereby identifying first features indicative of the hosing
instability in PWFA.
A goal of these studies is to open up new experimental avenues for
better understanding the beam instability evolution by identifying
quantitative radiation signatures of the instability that can be
measured in experiments.

Keywords: Firehose Instability; High-Performance Computing; PIConGPU; Plasma-Wakefield Accelerator

  • Open Access Logo Lecture (Conference)
    8th Annual Matter and Technologies Student Retreat, 27.-28.09.2022, DESY Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36306
Publ.-Id: 36306


Precipitation stripping of nanometrical particles for the recovery of metal vanadates

Sánchez-Loredo, M. G.; Ebert, D.; Chekhonin, P.; Labrada Delgado, G. J.; Kelly, N.

Transition metal vanadates have shown potential in applications as sensors, in photocatalysis, and recently, because of their high theoretical capacity, safety, easy preparation, and low cost, as electrode materials for primary and rechargeable batteries. Motivated by these relevant applications, much research work has been done on the synthesis and electrochemical studies of various 1D transition metal vanadates. Metal vanadates are normally synthesized by hydrothermal methods at high temperatures and pressures, making the synthesis expensive, and the control of the microstructure and composition difficult to achieve.
Vanadium can currently be found in the slag by-products of certain steel production processes, and the development of hydrometallurgical processes for the recovery and purification is relevant, mostly from alkaline media. Various methods are being investigated for separation of the metal value from alkaline leach feeds, including solvent extraction.
In case of the recovery of vanadium an interesting modification of the conventional solvent extraction process is the addition of a crystallization operation (precipitation stripping). In this work, the extraction was carried out using an Aliquat 336 solution in n-octanol/kerosene as extractant. Precipitation stripping was carried out using several metal salts dissolved in a concentrated chloride solution. For some experiments, polyvinylpyrrolidone was used as stabilizer in order to avoid agglomeration and to control growth. The structural characteristics of the crystallized products were studied. From the results, the synthesis of nanostructured vanadates is a simple and versatile method for the fabrication of valuable vanadium compounds.

  • Poster
    Jahrestreffen der ProcessNet Fachgruppen Extraktion, Phytoextrakte und Membrantechnik, 23.-24.05.2022, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36305
Publ.-Id: 36305


The Extraction of HREES and LREES with Primene JM-T in Sulphate Media

Bastürkcü, E.; Kelly, N.; Stelter, M.; Yüce, A. E.; Timur, S. İ.

The number of studies on the separation process of rare earth elements (REEs) has been studied intensively because REEs are playing a very critical role of high-tech products. Due to the restriction of export from China which has a dominating position in terms of reserve and production of REEs, other countries have investigated potential reserves and production techniques of rare earths. In case of Turkiye a high potential REE deposit is located in Eskisehir-Beylikova. In the presented study, the separation of heavy rare earth elements (HREEs) from light rare earth elements (LREEs) from the model solution was studied with solvent extraction. The solution was produced based on dissolution of pre-concentrate of Eskisehir-Beylikova ore by water leaching after acid baking. Primene JM-T was selected as an extractant which has not been studied in the separation of HREEs and LREEs. The key parameters pH, extractant concentration and A/O ratio were optimized. The optimum conditions were determined to be 10% concentration of extractant, pH 1 and A:O ratio, 1:1. The extraction for LREEs was 75-80% while HREEs had lower extraction rates of only 45-70%.

Keywords: REE; PrimeneJM-T; solvent extraction; sulphate media

  • Lecture (Conference)
    International Mineral Processing Symposium, 15.-17.12.2022, Istanbul, Türkiye
  • Contribution to proceedings
    International Mineral Processing Symposium, 15.-17.12.2022, Istanbul, Türkiye

Permalink: https://www.hzdr.de/publications/Publ-36304
Publ.-Id: 36304


Precipitation stripping of V(V) as a novel approach for the preparation of transition metal vanadates

Kelly, N.; Ebert, D.; Möckel, R.; Labrada-Delgado, G. J.; Sánchez-Loredo, M. G.

Transition metal vanadates, and particularly copper vanadates (CVO), have shown potential in applications as sensors, in photocatalysis, and recently, because of their high theoretical capacity, safety, easy preparation, and low cost, as electrode materials for primary and rechargeable lithium-ion batteries (LIBs). During discharge, the Cu2+ is reduced, and, more than one lithium ion per vanadium react, giving a high theoretical discharge capacity. Motivated by this relevant application, much research work has been done on the synthesis and electrochemical studies of various 1D transition metal vanadates. Among them, particularly Cu3V2O7(OH)2.2H2O has been studied as an electrode for primary lithium batteries with a high storage capacity. CVO and other metal vanadates are normally synthesized by hydrothermal methods at high temperatures and pressures, making the synthesis expensive, and the control of the microstructure and composition difficult to achieve.
An interesting modification of the conventional solvent extraction process is the addition of a crystallization operation, where low-solubility metal salts such as oxalates, oxides, or sulfides can be precipitated (precipitation stripping). In this work, copper vanadate nanoparticles have been synthesized by a simple synthetic route by solvent extraction and precipitation stripping. The extraction was carried out by ion exchange using a 20% (v/v) Aliquat 336 solution in n-octanol/kerosene as extractant, and an alkaline aqueous solution (0.1 M NaOH) prepared using vanadium pentoxide (V(V) concentration 2 g/L). Precipitation stripping was carried out using copper sulphate (0.01, 0.05 and 1 mol/L) dissolved in a concentrated chloride solution (4 mol/L). For some experiments, polyvinylpyrrolidone (PVP, Sigma Aldrich, ~44,000 g/mol) was used as stabilizer in order to avoid agglomeration and control growth. The prepared materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), and X-Ray Fluorescence (XRF). The obtained diffractograms could be indexed to the Cu3V2O7(OH)2.2H2O phase, space group: C2/m(12), JCPDS Card No. 46-1443, corresponding to volborthite, an uncommon secondary mineral formed in the oxidized zone of vanadium-bearing hydrothermal mineral deposits, monoclinic or pseudohexagonal and forms normally rosette-like aggregates of scaly crystals. The copper vanadate particles are nanometrical in size, with morphologies varying from nanowires to spherical particles (in presence of PVP)

  • Lecture (Conference)
    International solvent extraction conference (ISEC), 26.-30.09.2022, Göteborg, Sweden

Permalink: https://www.hzdr.de/publications/Publ-36303
Publ.-Id: 36303


Selektive Extraktion von Molybdän mit Cyanex 272 und Cyanex 600: Charakterisierung der organischen Phase zur optimierten Prozessführung

Helbig, T.; Tasker, P.; Kaden, P.; Foerstendorf, H.; Lehmann, F.; Kelly, N.

Der steigende Bedarf an Metallen für moderne technische Anwendungen erfordert die Entwicklung und Optimierung von Verfahren zur Rückgewinnung und zum Recycling dieser wertvollen Metalle. Die Bedeutung hydrometallurgischer Verfahren, z. B. unter Einsatz der Flüssig-Flüssig-Extraktion, aus Rohstoffquellen mit niedrig konzentrierten Wertelementen nimmt dabei stetig zu. Sie ermöglichen eine effiziente Rückgewinnung von Metallen sowohl aus industriellen Abwässern oder aber auch aus festen Sekundärrohstoffen und tragen zudem zu einer Reduzierung der Umweltbelastung durch alte Haldenmaterialien bei. Ein typisches Beispiel für diese Materialien stellt der Theisenschlamm dar, welcher bis 1990 im Rahmen der Aufbereitung von Kupferschiefer im Schachtofen als Abfallprodukt (220000 t) anfiel. Dieser enthält neben Elementen wie Kupfer und Zink auch signifikante Mengen an anderen Wertmetallen (Molybdän, Rhenium, Cobalt). Die komplexe Zusammensetzung des Materials, die Anwesenheit von umweltrelevanten Störelementen und der hohe Anteil an organischen Verbindungen erfordert ein mehrstufiges Verfahren, um die Metalle aufzukonzentrieren und mit notwendiger chemischer Reinheit zu gewinnen.
Im vorliegenden Beitrag wird die selektive Extraktion von Molybdän aus sauren Lösungen unter Einsatz der kommerziellen Extraktionsmittel Cyanex 272 und Cyanex 600 betrachtet. Dabei werden die in der organischen Phase gebildeten Komplexe durch vielseitige moderne, analytische Methoden (NMR, FTIR, Raman, MS) charakterisiert und diskutiert. Ein besseres Verständnis für diese bisher unzureichend untersuchten Extraktionssysteme ist ebenso hinsichtlich des Auftretens dritter Phasen hilfreich. In Kombination mit den optimierten technischen Parametern zur selektiven Abtrennung und Anreicherung des Molybdäns erfolgt eine Übertragung in einen kontinuierlich geführten Prozess.

  • Lecture (Conference)
    Jahrestreffen der ProcessNet Fachgruppen Extraktion, Phytoextrakte und Membrantechnik, 23.-24.05.2022, Frankfurt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36302
Publ.-Id: 36302


Synthetic shadowgrams of laser-plasma accelerators computed by a PIConGPU in-situ plugin

Carstens, F.-O.; Steiniger, K.; Pausch, R.; Chang, Y.-Y.; Schöbel, S.; Couperus Cabadağ, J. P.; Irman, A.; Lehmann, M.; Widera, R.; Bussmann, M.; Schramm, U.; Cowan, T.; Debus, A.

Few-cycle shadowgraphy is a valuable diagnostic for laser-plasma accelerators to obtain insight into the µm- and fs-scale relativistic plasma dynamics. To enhance the understanding of experimental shadowgrams we developed a synthetic shadowgram diagnostic within the fully relativistic particle-in-cell code PIConGPU.

In an initial version of the synthetic shadowgraphy diagnostic, the probe laser is propagated through the plasma using PIConGPU, and then extracted and propagated onto a virtual CCD using a post-processing code based on Fourier optics. However, the latter step requires 3D-FFTs, which results in performance and scaling limitations in large-scale simulations. To circumvent this, we develop an in-situ plugin for PIConGPU, in which we extract the probe laser slice-wise to obtain the synthetic shadowgrams during the simulation without post-processing.

In this talk, we present the development of the PIConGPU plugin and show preliminary results of synthetic shadowgrams for laser and plasma wakefield accelerators.

Keywords: Shadowgraphy; Synthetic Diagnostics; PIConGPU; Laser-Electron Acceleration

  • Lecture (Conference) (Online presentation)
    Virtuelle DPG-Frühjahrstagung, 28.03.-01.04.2022, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36299
Publ.-Id: 36299


Dissipation losses limiting first-order phase transition materials in cryogenic caloric cooling: A case study on all-d-metal Ni(-Co)-Mn-Ti Heusler alloys

Beckmann, B.; Koch, D.; Pfeuffer, L.; Gottschall, T.; Taubel, A.; Adabifiroozjaei, E.; Miroshkina, O. N.; Riegg, S.; Niehoff, T.; Kani, N. A.; Gruner, M. E.; Molina-Luna, L.; Skokov, K. P.; Gutfleisch, O.

Ni-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are highly promising materials for energy-efficient solid-state refrigeration as large multicaloric effects can be achieved across their magnetostructural martensitic transformation. However, no comprehensive study on the crucially important transition entropy change Δs exists so far for Ni(-Co)-Mn-Ti. Here, we present a systematic study analyzing the composition and temperature dependence of Δst. Our results reveal a substantial structural entropy change contribution of approximately 65 J(kgK)-1, which is compensated at lower temperatures by an increasingly negative entropy change associated with the magnetic subsystem. This leads to compensation temperatures Tcomp of 75 K and 300 K in Ni35Co15Mn50-yTiy and Ni33Co17Mn50-yTiy, respectively, below which the martensitic transformations are arrested. In addition, we simultaneously measured the responses of the magnetic, structural and electronic subsystems to the temperature- and field-induced martensitic transformation near Tcomp, showing an abnormal increase of hysteresis and consequently dissipation energy at cryogenic temperatures. Simultaneous measurements of magnetization and adiabatic temperature change ΔTad in pulsed magnetic fields reveal a change in sign of ΔTad and a substantial positive and irreversible ΔTad up to 15 K at 15 K as a consequence of increased dissipation losses and decreased heat capacity. Most importantly, this phenomenon is universal, it applies to any first-order material with non-negligible hysteresis and any stimulus, effectively limiting the utilization of their caloric effects for gas liquefaction at cryogenic temperatures.

Downloads

Permalink: https://www.hzdr.de/publications/Publ-36298
Publ.-Id: 36298


From laser-plasma accelerator experiments to digital twins

Debus, A.

Building high-fidelity digital twins through start-to-end models to better understand and control advanced laser-plasma accelerators, as well as compact free-electron laser beamlines, requires direct comparison to experimental data. We highlight recent results in start-to-end simulations and developments with a focus on their connection to experiment, such as by synthetic diagnostics and experimental data reconstruction analyses.

Keywords: digital twins; machine learning; laser-plasma accelerators; free-electron laser

  • Invited lecture (Conferences)
    8. Annual MT meeting, 26.-27.9.2022, DESY, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36296
Publ.-Id: 36296


PIConGPU: Getting Particle-in-cell Plasma Simulations Ready for Exascale

Debus, A.; Widera, R.; Lebedev, A.; Bastrakov, S.; Pausch, R.; Steiniger, K.; Pöschel, F.; Stephan, J.; Bussmann, M.

No official abstract here. We present an overview talk on laser-particle acceleration research with the challenges of modeling laser-plasma interactions using PIConGPU on latest exascale machines (JUWELS BOOSTER, Perlmutter,Summit and early-access systems for Frontier).We show the softwarestack of the particle-in-cell code PIConGPU (alpaka,openPMD, ...) with an emphasis on performance-portability and I/O at exascale. Furthermore we showed in an example how detailed performance benchmarking and profiling (together with JSC) helped improving code performance.

Keywords: particle-in-cell code; PIConGPU

  • Invited lecture (Conferences) (Online presentation)
    10 Year Anniversary Workshop of NVIDIA Application Lab at Jülich, 21.-22.6.2022, Jülich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36295
Publ.-Id: 36295


Traveling-wave electron accelerators -- Getting PIConGPU simulations ready for exascale

Debus, A.; Chandrasekaran, S.; Steiniger, K.; Widera, R.; Bastrakov, S.; Meyer, F.; Pausch, R.; Garten, M.; Kluge, T.; Kelling, J.; Hernandez Arreguin, B.; Leinhauser, M.; Young, J.; Pöschel, F.; Hübl, A.; Rogers, D.; Juckeland, G.; Bussmann, M.

Traveling-wave electron acceleration (TWEAC) is an advanced laser-plasma accelerators scheme, which is neither limited by dephasing, nor by pump depletion or diffraction. Such accelerators are scalable to energies beyond 10 GeV without the need for staging and are candidates for future compact electron-positron colliders.

TWEAC simulations to high energies require exascale compute resources. Within the early-access program (CAAR) for the upcoming exascale Frontier cluster at ORNL, we prepare PIConGPU, a 3D3V particle-in-cell code, for large-scale TWEAC simulations, including tuning and refining PIConGPU to run on the latest AMD GPUs. In this talk we present progress in TWEAC simulations and the technical advances in PIConGPU that enable running on Frontier.

Keywords: Traveling-wave electron acceleration; TWEAC; exascale; Laser-plasma accelerator; PIConGPU; particle-in-cell code

  • Lecture (Conference) (Online presentation)
    Virtuelle DPG-Frühjahrstagung in "Mainz" 2022, 28.03.-01.04.2022, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36294
Publ.-Id: 36294


Influence of Underlayer Quality and Sputter Gas Pressure on Structural and Magnetic Properties of Co/Pt Multilayers

Ehrler, R.; Uhlig, T.; Hellwig, O.

Influence of Underlayer Quality and Sputter Gas Pressure on Structural and Magnetic Properties of Co/Pt Multilayers

  • Lecture (Conference)
    AVS 68th International Symposium & Exhibition, 07.-11.11.2022, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-36292
Publ.-Id: 36292


Exploring Magnetic Reversal Behavior and Domain Structure in Perpendicular Anisotropy Layered Synthetic Antiferromagnets

Hellwig, O.

Exploring Magnetic Reversal Behavior and Domain Structure in Perpendicular Anisotropy Layered Synthetic Antiferromagnets

  • Lecture (Conference)
    AVS 68th International Symposium & Exhibition, 07.-11.11.2022, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-36291
Publ.-Id: 36291


Designing Antiferromagnetic Domain Landscapes via Focused Ion Beam Irradiation

Samad, F.; Hlawacek, G.; Koch, L.; Hellwig, O.; Xu, X.

Designing
Antiferromagnetic Domain Landscapes
via
Focussed Ion Beam Irradiation

  • Lecture (Conference)
    AVS 68th International Symposium & Exhibition, 09.11.2022, Pittsburgh, USA

Permalink: https://www.hzdr.de/publications/Publ-36290
Publ.-Id: 36290


Orthotopic Glioblastoma Models for Evaluation of the Clinical Target Volume Concept 

Bütof, R.; Hönscheid, P.; Aktar, R.; Sperling, C.; Tillner, F.; Rassamegevanon, T.; Dietrich, A.; Meinhardt, M.; Aust, D.; Krause, M.; Troost, E. G. C.

 In times of high‐precision radiotherapy, the accurate and precise definition of the primary tumor localization and its microscopic spread is of enormous importance. In glioblastoma, the 
microscopic tumor extension is uncertain and, therefore, population‐based margins for Clinical Target Volume (CTV) definition are clinically used, which could either be too small—leading to 
increased risk of loco‐regional recurrences r too large, thus, enhancing the probability of normal tissue toxicity. Therefore, the aim of this project is to investigate an individualized definition of the CTV in preclinical glioblastoma models based on specific biological tumor characteristics. The microscopic tumor extensions of two different orthotopic brain tumor models (U87MG_mCherry; G7_mCherry) were evaluated before and during fractionated radiotherapy and correlated with corresponding histological data. Representative tumor slices were analyzed using Matrix‐Assisted Laser Desorption/Ionization (MALDI) and stained for putative stem‐like cell markers as well as invasion markers. The edges of the tumor are clearly shown by the MALDI segmentation via unsupervised clustering of mass spectra and are consistent with the histologically defined border in H&E staining in both models. MALDI component analysis identified specific peaks as potential markers for normal brain tissue (e.g., 1339 m/z), whereas other peaks demarcated the tumors very well (e.g., 1562 m/z for U87MG_mCherry) irrespective of treatment. MMP14 staining revealed only a few positive cells, mainly in the tumor border, which could reflect the invasive front in both 
models. The results of this study indicate that MALDI information correlates with microscopic tumor spread in glioblastoma models. Therefore, an individualized CTV definition based on 
biological tumor characteristics seems possible, whereby the visualization of tumor volume and protein heterogeneity can be potentially used to define radiotherapy sensitive and resistant areas.

Keywords: glioblastoma; CTV; orthotopic model; MALDI; invasion

Permalink: https://www.hzdr.de/publications/Publ-36288
Publ.-Id: 36288


Positrons in Material Sciences: Intense Beams for Defect Characterizations and Porosimetry

Wagner, A.

The Helmholtz-Center Dresden - Rossendorf operates a superconducting electron linear accelerator as a driver for secondary radiation sources, which include two IR-FEL, a broadband high-field THz radiation source, high-energy X-rays, neutrons and positrons. The accelerator runs in continuous-wave (CW) mode and in a 24/7 regime serving an international user community.
Electron-bremsstrahlung is being converted into an intense beam of positrons by means of pair production. After moderation to thermal energies, positrons are re-accelerated to form a mono-energetic positron beam with variable kinetic energies ranging from 0.5 to 18 keV for depth profiling of atomic defects and porosities on nm-scales in thin films. High timing resolutions ( < 100 ps) at high average rates (105 s-1) and adjustable beam repetition rates allow performing high-throughput experiments of positron annihilation lifetimes.
The accelerator-based positron source is complemented by a several radioisotope-driven setups for conventional annihilation lifetime measurements (defect characterizations) and Doppler-broadening spectroscopy, which is sensitive to the defect’s chemical surroundings.
In my presentation, I will highlight some of the unique features of the experimental facilities and I will show various experimental results obtained with positrons in defect characterizations of materials and porosimetry due to their sensitivity on open-volume defects ranging from sub-nm to µm scales.

Keywords: material sciences; positron; positron annihilation spectroscopy; positron lifetime spectroscopy

Related publications

  • Invited lecture (Conferences)
    Department seminar, 12.01.2023, Bowling Green, Ohio, USA
  • Invited lecture (Conferences)
    Materials Science Laboratory Seminar, 19.01.2023, Los Alamos, New Mexico, USA

Permalink: https://www.hzdr.de/publications/Publ-36287
Publ.-Id: 36287


Out-of-field measurements and simulations of a proton pencil beam in a wide range of dose rates using a Timepix3 detector: Dose rate, flux and LET

Oancea, C.; Granja, C.; Marek, L.; Jakubek, J.; Solc, J.; Bodenstein, E.; Gantz, S.; Pawelke, J.; Pivec, J.

Stray radiation produced by ultra-high dose-rates (UHDR) proton pencil beams is characterized using ASIC-chip semiconductor pixel detectors. A proton pencil beam with an energy of 220 MeV was utilized to deliver dose rates (DR) ranging from conventional radiotherapy DRs up to 270 Gy/s. A MiniPIX Timepix3 detector equipped with a silicon sensor and integrated readout electronics was used. The chip-sensor assembly and chipboard on water-equivalent backing were detached and immersed in the water-phantom. The deposited energy, particle flux, DR, and the linear energy transfer (LET(Si)) spectra were measured in the silicon sensor at different positions both laterally, at different depths, and behind the Bragg peak. At low-intensity beams, the detector is operated in the event-by-event data-driven mode for high-resolution spectral tracking of individual particles. This technique provides precise energy loss response and LET(Si) spectra with radiation field composition resolving power. At higher beam intensities a rescaling of LET(Si) can be performed as the distribution of the LET (Si) spectra exhibits the same characteristics regardless of the delivered DR. The integrated deposited energy and the absorbed dose can be thus measured in a wide range. A linear response of measured absorbed dose was obtained by gradually increasing the delivered DR to reach UHDR beams. Particle tracking of scattered radiation in data-driven mode could be performed at DRs up to 0.27 Gy/s. In integrated mode, the saturation limits were not reached at the measured out-of-field locations up to the delivered DR of over 270 Gy/s. A good agreement was found between measured and simulated absorbed doses.

Keywords: Out-of-field proton therapy; Timepix3; Particle tracking; LET(Si) spectra; UHDpulse; Flash radiotherapy

Permalink: https://www.hzdr.de/publications/Publ-36286
Publ.-Id: 36286


Non-linearity induced contrast degradation in high-power lasers

Bock, S.; Oksenhendler, T.; Püschel, T.; Gebhardt, R.; Helbig, U.; Ziegler, T.; Zeil, K.; Pausch, R.; Toncian, T.; Nishiuchi, M.; Kiriyama, H.; Schramm, U.

The characteristics of high power lasers applied for relativistic plasma experiments are a matter of constant research and improvement for supporting highest possible performance. Especially the temporal contrast is crucial, while different mechanisms can lead to its degradation. One prominent effect is the non-linear B-integral induced pulse coupling from a post pulse generating a pre-pulse, generally described by Didenko, et.al. [1]. Recent measurements showed a more complex behavior with delayed pre-pulse generation and complex temporal shapes [2]. We applied an improved SRSI-ETE [3] setup to measure the non-linear pulse coupling at the DRACO Petawatt facility [4], revealing the spectral-temporal structure of the generated pulses. To assist the understanding of the observed non-linear effects a model was developed [5], covering the principle B-integral induced pulse generation, as well as the generation of the additional pulse structures, by means of non-resonant and resonant non-linear optical effects. The performed study allows a full understanding of the non-linear processes generating the pre-pulse and subsequent structures.

  • Lecture (Conference)
    ICUIL 2022, 19.-23.09.2022, Jeju Island, Korea

Permalink: https://www.hzdr.de/publications/Publ-36284
Publ.-Id: 36284


High-content multi-spectral fluorescence microscopy sample preparation artefacts

Sharma, V.; Yakimovich, A.

Sample preparation artefacts represent a significant source of errors in high-content screening datasets leading to misinterpretation of results in drug discovery. To address this we have created a multispectral high-content imaging dataset with typical sample preparation artefacts added to the samples. This dataset consists of high-content images of cultured HeLa ATCC cells in the presence of typical sample preparation artefacts. The aim of this dataset. HeLa cells imaged in this dataset were cultured in a black 96-well (rows A to H and columns 1 to 12) polystyrene imaging plate (Corning, Sigma).

To obtain a dataset similar to the experimental setup of a high-content image-based screening we have used a 96-well (rows A to H and columns 1 to 12) black polystyrene imaging plate (Corning, Sigma). HeLa cells were seeded a day prior to the experiment in 200 µL volume (per well) containing 250000 cells per mL in Dulbecco’s Modified Eagle’s Medium (Sigma) containing 10% fetal calf serum (Sigma) 4500 mg/L glucose (Sigma), sodium bicarbonate (Sigma), L-glutamine (Sigma), sodium pyruvate (Sigma), and non-essential amino acids (Sigma). To obtain a gradient of cell density, the cell suspension was stepwise diluted at 1:2 ratio during seeding (columns 2 to 12). The first column was reserved as no-cells control. Upon seeding, the HeLa cells were incubated overnight at 37° C in a 5% CO2 atmosphere with humidity control. The next day after seeding, cells were fixed with 4% paraformaldehyde (Sigma) solution prepared in phosphate buffer saline (PBS, Sigma). Upon fixation, HeLa cell nuclei were stained with Hoechst 33342 dye (Sigma) at 40 µg/mL concentration prepared in PBS. Row A was kept unstained as the control without Hoechst dye. Upon preparation of the bona fide artefact-free experimental plate, we have collected samples of dust across the approximately 100 m2 laboratory and prepared a suspension of these dust samples in PBS. Next, we added this suspension to rows A to G of the 96-well plate, leaving row H as an artefact-free control.

The dataset consists of images obtained with 4x and 10x objectives using fluorescence cube assemblies for DAPI, CFP, GFP, TRITC and Cy5 channels. For hardware reasons, images with the CFP filter cube were obtained separately from images with DAPI, CFP, GFP, TRITC and Cy5 filter cubes. Furthermore, CFP images (and in some cases DAPI images) were obtained with varying exposure times corresponding to “_w1”, “_w2” and so on filename suffixes. Images were obtained using ImageXpress Micro XL high-content microscope (Molecular Devices). Images are organised into the following folders:

  1. 4x-cfp

  2. 4x-dapi-gfp-tritc-cy5

  3. 10x-6cfp

  4. 10x-6dapi

  5. 10x-cfp

  6. dapi-gfp-tritc-cy5

  7. filters_spectra

Here, folders A and B correspond to 4x magnification and contain images obtained with the CFP (folder A) and the other filter cubes respectively (folder B). Each folder contains “TimePoint_1” subfolder containing the raw images. In the case of 4x images, each field of view (“site” designed with “_s1”, “_s2” etc. suffixes) corresponds to a nearly perfect quarter of a 96-well plate well. In addition to the raw images in the “TimePoint_1”, a subfolder “Stitched” contains images of the entire wells. In the case of folder B containing all other fluorescence channels, “_w1”, “_w2”, “_w3”, and “_w4” correspond to a single optimal exposure time of DAPI, GFP, TRITC and Cy5 filters respectively.

Similarly, folders C - F correspond to 10x magnification and contain images of multiple exposures of CFP and DAPI (folders C and D) and single exposures of CFP and other channels (folders E and F). In the case of CFP and DAPI multiple exposures folders, varying exposure times correspond to “_w1”, “_w2” etc. Finally, folder G contains metadata on filter cubes used in the dataset, including the emission and excitation filters spectra for each filter cube.

Keywords: fluorescence microscopy; high-content microscopy; sample preparation artefacts

Downloads

Permalink: https://www.hzdr.de/publications/Publ-36282
Publ.-Id: 36282


Catalytic Activity of Defect-Engineered Transition Metal Dichalcogenides Mapped with Atomic Scale Precision by Electrochemical Scanning Tunneling Microscopy

Lunardon, M.; Kosmala, T.; Ghorbani Asl, M.; Krasheninnikov, A.; Kolekar, S.; Durante, C.; Batzill, M.; Agnoli, S.; Granozzi, G.

Unraveling structure–activity relationships is a key objective of catalysis. Unfortunately, the intrinsic complexity and structural heterogeneity of materials stand in the way of this goal, mainly because the activity measurements are area-averaged and therefore contain information coming from different surface sites. This limitation can be surpassed by the analysis of the noise in the current of electrochemical scanning tunneling microscopy (EC-STM). Herein, we apply this strategy to investigate the catalytic activity toward the hydrogen evolution reaction of monolayer films of MoSe₂. Thanks to atomically resolved potentiodynamic experiments, we can evaluate individually the catalytic activity of the MoSe₂ basal plane, selenium vacancies, and different point defects produced by the intersections of metallic twin boundaries. The activity trend deduced by EC-STM is independently confirmed by density functional theory calculations, which also indicate that, on the metallic twin boundary crossings, the hydrogen adsorption energy is almost thermoneutral. The micro- and macroscopic measurements are combined to extract the turnover frequency of different sites, obtaining for the most active ones a value of 30 s⁻¹ at −136 mV vs RHE.

Keywords: green hydrogen; two-dimensional materials; transition metal dichalcogenides; catalyst; hydrogen evolution reaction; defect; scanning tunneling microscopy

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Permalink: https://www.hzdr.de/publications/Publ-36281
Publ.-Id: 36281


Generalized Gelfand-Dikii equation for fermionic Schwinger pair production

Ahmadiniaz, N.; Pyo Kim, S.; Schubert, C.

Generalized Gelfand-Dikii equation for fermionic Schwinger pair production

Keywords: Schwinger pair production; Gelfand-Dikii equation

  • Open Access Logo Contribution to proceedings
    29th annual International Laser Physics Workshop (LPHYS'21), 19.-23.07.2022, virtual, virtual
    Journal of Physics: Conference Series 2249 (2022), 012020
    DOI: 10.1088/1742-6596/2249/1/012020
    arXiv: https://arxiv.org/pdf/2205.15945.pdf

Permalink: https://www.hzdr.de/publications/Publ-36280
Publ.-Id: 36280


Generalized Gelfand-Dikii equation and solitonic electric fields for fermionic Schwinger pair production

Ahmadiniaz, N.; Fedotov, A. M.; Gelfer, E. G.; Pyo Kim, S.; Schubert, C.

Schwinger pair creation in a purely time-dependent electric field can be reduced to an effective quantum mechanical problem using a variety of formalisms. Here we develop an approach based on the Gelfand-Dikii equation for scalar QED, and extent it to spinor QED. We discuss some solvable special cases from this point of view. It was previously shown how to use the well-known solitonic solutions of the KdV equation to construct “solitonic” electric fields that do not create scalar pairs with an arbitrary fixed momentum. We show that this construction can be adapted to the fermionic case in two inequivalent ways, both leading to the vanishing of the pair-creation rate at certain values of the P ̈oschl-Teller like index of the associated Schr ̈odinger equation. Thus for any given momentum, we can construct electric fields that create scalar particles but not spinor particles, and also the other way round. Therefore, while often spin is even neglected in Schwingerpair creation, in such cases it becomes decisive.

Keywords: Schwinger mechanism; Pair production; Gelfand-Dikii equation

Permalink: https://www.hzdr.de/publications/Publ-36279
Publ.-Id: 36279


Summing Feynman diagrams in the worldline formalism

Ahmadiniaz, N.; Edwards, J. P.; Lopez-Arcos, C.; Lopez-Lopez, M. A.; Moctezuma Mata, C.; Nicasio, J.; Schubert, C.

The worldline formalism shares with string theory the property that it allows one to write down master integrals that effectively combine the contributions of many Feynman diagrams. While at the one-loop level, these diagrams differ only by the position of the external legs along a fixed line or loop, at multiloop they generally involve different topologies. Here we summarize various efforts that have been made over the years to exploit this property in a computationally meaningful way. As a first example, we show how to generalize the Landau-Khalatnikov-Fradkin formula for the non-perturbative gauge transformation of the fermion propagator in QED to the general2𝑛- point case by pure manipulations at the path-integral level. At the parameter-integral level, we show how to integrate out individual photons in the low-energy expansion and then sketch a recently introduced general framework for the analytical evaluation of such worldline integrals involving a reduction to quantum mechanics on the circle and the relation between inverse derivatives and Bernoulli polynomials

Keywords: Woldline formalism; Feynman diagrams; QED

  • Open Access Logo Contribution to proceedings
    Loops and Legs in Quantum Field Theory - LL2022, 25.-30.04.2022, Ettal, Germany
    Proceedings of Science (LL2022), 052
    DOI: 10.22323/1.416.0052
    arXiv: https://arxiv.org/pdf/2208.06585.pdf

Permalink: https://www.hzdr.de/publications/Publ-36277
Publ.-Id: 36277


Spin-wave study of magnetic perpendicular surface anisotropy in single crystalline MgO/Fe/MgO films

Solano, J.; Gladii, O.; Kuntz, P.; Henry, Y.; Halley, D.; Bailleul, M.

Broadband ferromagnetic resonance is measured in single crystalline Fe films of varying thickness sandwiched between
MgO layers. An exhaustive magnetic characterization of the films (exchange constant, cubic, uniaxial and surface
anisotropies) is enabled by the study of the uniform and the first perpendicular standing spin wave modes as a function of
applied magnetic field and film thickness. Additional measurements of nonreciprocal spin-wave propagation allow us to
separate each of the two interface contributions to the total surface anisotropy. The results are consistent with the model of a
quasi-bulk film interior and two magnetically different top and bottom interfaces, a difference ascribed to different oxidation
states

Keywords: Interface states; spin wave; Magnetic anisotropy; Broadband ferromagnetic resonance

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Permalink: https://www.hzdr.de/publications/Publ-36276
Publ.-Id: 36276


Coupled thermo-fluid-mechanical FEM simulations for thermoelastic harvesting of low-grade waste heat

Neumann, B.; Eckert, K.; Fähler, S.

COMSOL-Multiphysics file for the FEM-Simulations of the paper. The attached version was used to generate plot data. The extracted plot data is attached as well.

Keywords: Energy; FEM; Thermoelastic Energy Harvesting; Simulation

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Permalink: https://www.hzdr.de/publications/Publ-36275
Publ.-Id: 36275


Field-assisted birefringent Compton scattering

Ahmadiniaz, N.; Cowan, T.; Ding, M.; Lopez Lopez, M. A.; Sauerbrey, R.; Shaisultanov, R.; Schützhold, R.

Motivated by experimental initiatives such as the Helmholtz International Beamline for ExtremeFields (HIBEF), we study Compton scattering of x-rays at electrons in a strong external field (e.g., a strong optical laser) with special emphasis on the polarization-changing (i.e., birefringent) contribution on the amplitude level. Apart from being a potential background process for the planned vacuum birefringence experiments, this effect could be used for diagnostic purposes. Since the birefringent signal from free electrons (i.e., without the external field) vanishes in forward direction, the ratio of the birefringent and the normal (polarization conserving) contribution yields information about the field strength at the interaction point.

Keywords: Vacuum birefringent; Compton scattering; HIBEF

Permalink: https://www.hzdr.de/publications/Publ-36274
Publ.-Id: 36274


Solid-Phase Parallel Synthesis of Dual Histone Deacetylase-Cyclooxygenase Inhibitors

Bachmann, L. M.; Hanl, M.; Feller, F.; Sinatra, L.; Schöler, A.; Pietzsch, J.; Laube, M.; Hansen, F. K.

Multi-target drugs (MTDs) are emerging alternatives to combination therapies. Since both his-tone deacetylases (HDACs) and cyclooxygenase-2 (COX-2) are known to be overexpressed in several cancer types, we herein report the design, synthesis, and biological evaluation of a li-brary of dual HDAC-COX inhibitors. The designed compounds were synthesized via an efficient parallel synthesis approach using preloaded solid-phase resins. Biological in vitro assays demon-strated that several of the synthesized compounds possess pronounced inhibitory activities against HDAC and COX isoforms. The membrane permeability and inhibition of cellular HDAC activity of selected compounds were confirmed by whole-cell HDAC inhibition assays and western blot experiments. The most promising dual inhibitors C3 and C4 evoked antiprolifera-tive effects in the low micromolar concentration range and caused a significant increase in apoptotic cells. In contrast to previous reports, the simultaneous inhibition of HDAC and COX activity by dual HDAC-COX inhibitors or combination treatment with vorinostat and celecoxib did not result in additive or synergistic anticancer activities.

Keywords: COX; HDAC; multi-target drugs; cancer; solid-phase synthesis

Permalink: https://www.hzdr.de/publications/Publ-36271
Publ.-Id: 36271


Data publication: Core-shell structured MCM-48-type silica-polymer hybrid material synthesis and characterization

Yismaw, S.; Wenze, M.; Attallah, A. G.; Zaleski, R.; Matysik, J.; Poppitz, D.; Gläser, R.; Ebbinghaus, S. G.; Enke, D.

In the current study, a core-shell structured material of MCM-48-type mesoporous silica nanoparticles (MSNs) and cross-linked poly(N-isopropylacrylamide) homopolymer and its copolymer with methacrylic acid was synthesized. The polymer was preferentially grafted on the outer surface of silane linker-functionalized MSNs based on free radical polymerization. The successful chemical grafting of the polymer on the silica surface was confrmed by FTIR, NMR, TG, and elemental analyses. The polymer contents of the hybrid particles vary from 18 to 40 % as determined by thermogravimetric and elemental analyses. The polymer content was tailored by varying diferent reaction parameters including monomer concentration, linker content/type, and reaction time. Well-defned uniform core-shell structured spherical particles with an average particle size of 367 ± 25 nm and shell thickness of 29 ± 8 nm were observed in TEM analysis. According to XRD and nitrogen physisorption studies, the ordered mesopore structure of the core MCM-48-type MSNs was maintained after an extended polymer grafting process and surface coverage with a high content of polymer. No signifcant pore blockage was observed in porosimetry analysis. More than 75% of specifc surface area, 68% of total pore volume, and the mean mesopore diameter were retained after successful grating of polymer on the outer silica surface. The pore volume thus can provide enough space to encapsulate high contents of cargo molecules for applications. The narrow pore width distribution of the main mesopores of silica determined by PALS analysis corresponds to the N2 sorption analysis and further confrms the uniformity of the mesopores.

Keywords: MCM-48-type mesoporous silica nanoparticles; Hybrid material; Core-shell structure; Polymer; Grafting; Synthesis

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Permalink: https://www.hzdr.de/publications/Publ-36269
Publ.-Id: 36269


Modelling based approach for the identification of germanium- and indium - binding siderophores

Hintersatz, C.; Tsushima, S.; Jain, R.; Pollmann, K.

Density functional theory was used in order to screen for siderophores selective for gallium, indium, and germanium, respectively.

  • Lecture (Conference) (Online presentation)
    BioCuInGe Workshop on Waste to Wealth, 25.-26.11.2022, Delhi, Indien

Permalink: https://www.hzdr.de/publications/Publ-36265
Publ.-Id: 36265


Selection and production of siderophores suitable germanium-, indium and gallium - recovery

Hintersatz, C.; Rojas, L. A.; Kutschke, S.; Jain, R.; Tsushima, S.; Pollmann, K.

Siderophores are a diverse group of small iron-chelating molecules that are synthesized by a vast number of bacteria, fungi and graminaceous plants in order to sequester the essential metal under iron-limited conditions. Their capability to complex other metals as well makes them possibly suited compounds for the usage in bio-based recycling technologies.
The aim of this work is to find siderophores, which selectively bind the critical elements indium, gallium and germanium. Due to the vast number of different known siderophores the complete experimental evaluation is impractical, though. Hence, density functional theory (DFT) is used to simulate the chelation reaction in order to estimate the affinities of various siderophores towards gallium and indium as well as the stability of the resulting coordination complexes. Additionally, environmental samples from lagoons of the Atacama Desert are screened for novel siderophore-producing organisms. The siderophores excreted by those organisms might possess unique binding abilities due to the highly saline and alkaline conditions of the isolation sites. Siderophores selected via DFT as well as those produced by isolated microorganisms are tested experimentally for their affinity towards the metals of interest.
Proving the applicability of siderophores in the recovery of indium and gallium from low concentrated waste waters would create a vast amount of further possible applications of the biomolecules to aid securing the future supply of not just said energy-critical elements, but all strategic metals.

  • Lecture (Conference) (Online presentation)
    ACS Spring 2022, 20.-24.03.2022, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-36263
Publ.-Id: 36263


Spaceborne GNSS-Receiver Evolution – From Classical HiRel to NewSpace Constellation

Schütz, M.; Zehetmayer, S.; Zajac, K.; Laabs, M.; Borany, J.; Zangl, R.; Sust, M.

Spaceborne Global Navigation Satellite System (GNSS) receivers have become indispensable components of satellites, in particular for real-time navigation as part of the attitude and orbit control system and for precise orbit determination in support of highly accurate earth observation instruments. In cooperation with the project partners TU Dresden and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Beyond Gravity (formerly RUAG Space) has developed a flexible GNSS receiver platform targeting NewSpace applications but leveraging the performance of the current gold standards with respect to spaceborne GNSS-receiver technology. A novel radiation test environment was introduced, and selected components were radiation tested to ensure a consistent reliability.

  • Lecture (Conference)
    Deutscher Luft- und Raumfahrtkongress (DLRK 2022), 27.-29.09.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36256
Publ.-Id: 36256


Using mini-CT specimens for the fracture characterization of ferritic steels within the ductile to brittle transition range: a review

Sánchez, M.; Cicero, S.; Kirk, M.; Altstadt, E.; Server, W.; Yamamoto, M.

The use of mini-CT specimens for the fracture characterization of structural steels is currently a topic of great interest from both scientific and technical points of view, mainly driven by the needs and requirements of the nuclear industry. In fact, the long-term operation of nuclear plants requires accurate characterization of the reactor pressure vessel materials and evaluation of the embrittlement caused by neutron irradiation without applying excessive conservatism. However, the amount of material placed inside the surveillance capsules used to characterize the resulting degradation is generally small. Consequently, in order to increase the reliability of fracture toughness measurements and reduce the volume of material needed for the tests, it is necessary to develop innovative characterization techniques, among which the use of mini-CT specimens stands out. In this context, this paper provides a review of the use of mini-CT specimens for the fracture characterization of ferritic steels, with particular emphasis on those used by the nuclear industry. The main results obtained so far, revealing the potential of this technique, together with the main scientific and technical issues will be thoroughly discussed. Recommendations for several key topics for future research are also provided.

Keywords: mini-CT; ductile-to-brittle transition range; reference temperature; master curve

Permalink: https://www.hzdr.de/publications/Publ-36253
Publ.-Id: 36253


PIConGPU -- High-Fidelity Plasma Simulations on Desktop Computers up to Exascale Compute Systems and a View on its Recent Applications

Debus, A.; Steiniger, K.; Bastrakov, S.; Bastrakova, K.; Bussmann, M.; Carstens, F.-O.; Chandrasekaran, S.; Garten, M.; Gruber, B. M.; Hernandez Arreguin, B.; Hübl, A.; Juckeland, G.; Kelling, J.; Lebedev, A.; Leinhauser, M.; Marre, B. E.; Meyer, F.; Ordyna, P.; Pausch, R.; Pöschel, F.; Rogers, D.; Schramm, U.; Sprenger, L.; Starke, S.; Thévenet, M.; Trojok, J.; Wang, M.; Widera, R.; Young, J.

PIConGPU’s latest release 0.6.0 in December 2021 brought a number of new features. Among these are an arbitrary-order Maxwell solver, the Higuera-Cary pusher, collisions, and incident field generation via the total field/scattered field technique enhancing its numerical stability and predictive capabilities.
Furthermore, there are various technical advances, most notably support of the HIP computational backend allowing to run on AMD GPUs. These advances are mainly driven by our participation in OLCF’s Frontier Center for Accelerated Application Readiness providing access to the hardware platform of the Frontier exascale supercomputer scheduled for deployment in 2022. We show performance data and present recent applications of PIConGPU profiting from these developments. To these applications belongs the advanced laser-plasma accelerator scheme Traveling-wave electron acceleration (TWEAC), providing scalability to energies beyond 10 GeV while avoiding staging. We further present simulation campaigns modeling and delivering valuable insight into the micrometer and femtosecond plasma dynamics of existing experimental
campaigns.

Keywords: particle-in-cell code; TWEAC; PIConGPU; performance portable

  • Poster
    767. WE-Heraeus-Seminar: Science and Applications of Plasma‐Based Accelerators, 15.-18.05.2022, Physikzentrum, Bad Honnef, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36252
Publ.-Id: 36252


minterpy: Multivariate Interpolation in Python

Schreiber, J.; Wicaksono, D. C.; Thekke Veettil, S. K.; Hajizade, A.; Zavalani, G.; Suarez Cardona, J. E.; Hernandez Acosta, U.; Hecht, M.

Many solutions to the computational challenges arising in the fields of computational science and engineering rely on solving interpolation tasks of highly-varying sparse and scattered data. The tasks include surrogate modeling, sparse data regression, global black-box optimization, model inference, as well as solutions for partial differential equations (PDE) on complex geometries.

Interpolation tasks in multi-dimensional space typically suffer from the curse of dimensionality in which the computational cost of interpolation scales exponentially with the number of dimensions.

The open-source Python package minterpy developed and maintained by the Hecht-Lab, CASUS, aims to lift the curse of dimensionality from a brand field of interpolation tasks arising across scientific disciplines.

Keywords: interpolation; multivariate interpolation; surrogate modeling; sparse data regression; global black-box optimization; model inference; partial differential equations (PDE)

  • Open Access Logo Poster
    Big data analytical methods for complex systems, 06.-07.10.2022, Wroclaw, Poland

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Permalink: https://www.hzdr.de/publications/Publ-36251
Publ.-Id: 36251


Transverse Emittance Measurements and Optimization for a Superconducting RF Photon Injector

Ma, S.

As one of the most promising continuous wave (CW) injectors for high brightness electron
beams, ELBE superconducting radio-frequency (SRF) gun has been developed and optimized.
This gun can provide beams with good quality for the ELBE user facility. One important
aspect is to measure the transverse emittance accurately and efficiently. This thesis contributes
to the progress in this field and focuses on measuring and optimizing the transverse emittance
for ELBE SRF gun. The slit-scan, quadrupole scan, and an advanced thermal emittance
measurement method, called single shot cathode transverse momentum imaging, have been
studied and applied at this SRF gun.
A fast slit-scan emittance measurement system consisting of a continuously moving slit and
a yttrium aluminium garnet (YAG) screen has been developed. During the beamlet image
processing, the machine learning (ML) algorithms have been integrated in order to improve
the signal-to-noise ratio effectively. This is the first time to successfully apply the ML in such
diagnostic methods. The measurement speed is improved about ten times and accuracy is also
better than before. The errors of slit-scan emittance measurement, arising from slit position,
beamlet intensity, center position and root mean square (RMS) width uncertainties, have been
analyzed. The quadrupole scan emittance measurement method has been studied too. The
influence of the space charge effect on quadrupole scan results has been revealed. The error of
the quadrupole scan measurement has also been analyzed.
To compensate the transverse emittance due to space charge effect, a superconducting (SC)
solenoid is placed as close as possible to the exit of the SRF cavity. Another important part in
this thesis is the investigation and optimization of the SC solenoid. The spherical aberration
of the SC solenoid has been analyzed. In order to decrease it, a new yoke geometry of SC
solenoid for the next generation SRF gun has been designed. The multipole transverse field
modes of the solenoid caused by an axis tilt have bean analyzed by means of simulations and
experimental investigations using a formalism fitting method. The influences of the multipole
modes, especially the quadrupole and sextupole fields on transverse emittance have been
calculated. A pair of a normal quadrupole and a skew quadrupole, called correctors, have been
adopted to compensate the influence of the quadrupole field on the emittance.
The cathode intrinsic emittance can contribute a non-negligible part to the transverse emittance.
So in this thesis the cathode intrinsic emitttance is measured too. The single shot transverse
momentum imaging method has been used to measure the cathode intrinsic emittance. A
further advantage is that this method allows to determine the transverse momentum locally at
different positions on the cathode.

Keywords: accelerator; superconducting RF photo injector; beam dynamic; emittance measurement

Related publications

  • Doctoral thesis
    Universität Hamburg, 2022
    125 Seiten

Permalink: https://www.hzdr.de/publications/Publ-36250
Publ.-Id: 36250


Tracer diffusion in proton-exchanged congruent LiNbO3 crystals as a function of hydrogen content

Dörrer, L.; Heller, R.; Schmidt, H.

The proton-exchange process is an effective method of fabricating low-loss waveguides based on
LiNbO3 crystals. During proton-exchange, lithium is replaced by hydrogen and Li1 xHxNbO3 is formed.
Currently, mechanisms and kinetics of the proton-exchange process are unclear, primarily due to a lack
in reliable tracer diffusion data. We studied lithium and hydrogen tracer diffusion in proton-exchanged
congruent LiNbO3 single crystals in the temperature range between 130–230 1C. Proton-exchange was
done in benzoic acid with 0, 1, 2, or 3.6 mol% lithium benzoate added, resulting in micrometre thick
surface layers where Li is substituted by H with relative fractions between x = 0.45 and 0.85 as
determined by Nuclear Reaction Analysis. For the diffusion experiments, ion-beam sputtered isotope
enriched 6LiNbO3 was used as a Li tracer source and deuterated benzoic acid as a H tracer source.
Isotope depth profile analysis was carried out by secondary ion mass spectrometry. From the
experimental results, effective diffusivities governing the lithium/hydrogen exchange as well as individual
hydrogen and lithium tracer diffusivities are extracted. All three types of diffusivities can be described by
the Arrhenius law with an activation enthalpy of about 1.0–1.2 eV and increase as a function of hydrogen
content nearly independent of temperature. The effective diffusivities and the lithium tracer diffusivities
are identical within a factor of two to five, while the hydrogen diffusivities are higher by three orders of
magnitude. The results show that the diffusion of Li is the rate determining step governing the protonexchange
process. Exponential dependencies between diffusivities and hydrogen concentrations are
determined. The observed increase of Li tracer diffusivities and effective diffusivities as a function of
hydrogen concentration is attributed to a continuous reduction of the migration enthalpy of diffusion by
a maximum factor of about 0.2 eV. Simulations based on the determined diffusivities can reproduce the
step-like profile of hydrogen penetration during proton-exchange.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36243
Publ.-Id: 36243


Investigation of matrix independent calibration of oxygen in glow discharge optical emission spectrometry

Hoffmann, V.; Gebel, B.; Heller, R.; Gemming, T.

The performance of glow discharge optical emission spectrometry for matrix independent oxygen determination was
investigated using the spectral lines of atomic oxygen at 130 nm and 777 nm and standard conditions for dc discharge with a
4 mm anode (700 V, 20 mA). Using hot-pressed calibration samples of Cu-, Al- and Mg-powder mixed with their oxides, at
130 nm the dependence of the emission yield on these matrices was confirmed. However, at 777 nm oxygen has the same
emission yield in these matrices. In order to compare the emission yield of oxygen with the emission yield in iron a thick 43
μm FeO-layer was prepared and characterized by Rutherford backscattering spectrometry, X-ray diffraction and glow
discharge optical emission spectrometry. At 130 nm, the emission yield of oxygen in FeO is most similar to that in an Almatrix.
At 777 nm, the calibration revealed a higher emission yield of oxygen in FeO in comparison to the common emission
yield of oxygen in Cu-, Al- and Mg-matrices. © 2022 The Royal Society of Chemistry

Keywords: glow discharge; optical emission spectroscopy; material science

Related publications

Permalink: https://www.hzdr.de/publications/Publ-36241
Publ.-Id: 36241


Survey of spatio-temporal couplings throughout high-power ultrashort lasers

Jeandet, A.; Jolly, S. W.; Borot, A.; Bussière, B.; Dumont, P.; Gautier, J.; Gobert, O.; Goddet, J.-P.; Gonsalves, A.; Irman, A.; Leemans, W. P.; Lopez-Martens, R.; Mennerat, G.; Nakamura, K.; Ouillé, M.; Pariente, G.; Pittman, M.; Püschel, T.; Sanson, F.; Sylla, F.; Thaury, C.; Zeil, K.; Fabien Quéré, A.

The investigation of spatio-temporal couplings (STCs) of broadband light beams is
becoming a key topic for the optimization as well as applications of ultrashort laser systems.
This calls for accurate measurements of STCs. Yet, it is only recently that such complete
spatio-temporal or spatio-spectral characterization has become possible, and it has so far mostly
been implemented at the output of the laser systems, where experiments take place. In this survey,
we present for the first time STC measurements at different stages of a collection of high-power
ultrashort laser systems, all based on the chirped-pulse amplification (CPA) technique, but with
very different output characteristics. This measurement campaign reveals spatio-temporal effects
with various sources, and motivates the expanded use of STC characterization throughout CPA
laser chains, as well as in a wider range of types of ultrafast laser systems. In this way knowledge
will be gained not only about potential defects, but also about the fundamental dynamics and
operating regimes of advanced ultrashort laser systems.

Permalink: https://www.hzdr.de/publications/Publ-36238
Publ.-Id: 36238


Characterization of the plasma mirror system at the J-KAREN-P facility

Kon, A.; Nishiuchi, M.; Fukuda, Y.; Kondo, K.; Ogura, K.; Sagisaka, A.; Miyasaka, Y.; Dover, N. P.; Kando, M.; Pirozhkov, A. S.; Daito, I.; Chang, L.; Woo Choi, I.; Hee Nam, C.; Ziegler, T.; Schlenvoigt, H.-P.; Zeil, K.; Schramm, U.; Kiriyama, H.

We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai
Photon Science Institute, National Institutes for Quantum Science and Technology. The reflectivity of the single plasma
mirror system exceeded 80%. In addition, the temporal contrast was improved by two orders of magnitude at 1 ps before
the main pulse. Furthermore, the laser near-field spatial distribution after the plasma mirror was kept constant at plasma
mirror fluence of less than 100 kJ/cm2. We also present the results of investigating the difference and the fluctuation in
energy, pulse width and pointing stability with and without the plasma mirror system.

Permalink: https://www.hzdr.de/publications/Publ-36237
Publ.-Id: 36237


High energy proton acceleration at DRACO-PW and radio-biological applications

Zeil, K.

Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power laser driven compact plasma accelerators can generate short, high-intensity pulses of high energy ions with special beam properties. By that they may expand the portfolio of conventional machines in many application areas. The maturation of laser driven ion accelerators from physics experiments to turn-key sources for these applications will rely on breakthroughs in both, generated beam parameters (kinetic energy, flux), as well as increased reproducibility, robustness and scalability to high repetition rate.
Recent developments at the high-power laser facility DRACO-PW enabled the production of polychromatic proton beams with unprecedented stability [1]. This allowed the first in vivo radiobiological study to be conducted using a laser-driven proton source [2]. Yet, the ability to achieve energies beyond the 100 MeV frontier is matter of ongoing research, mainly addressed by exploring advanced acceleration schemes like the relativistically induced transparency (RIT) regime.
In this talk we report on experimental proton acceleration studies at the onset of relativistic transparency using pre-expanded plastic foils. Combined hydrodynamic and 3D particle-in-cell (PIC) simulations helped to identify the most promising target parameter range matched to the prevailing laser contrast conditions carefully mapped out in great detail beforehand. A complex suite of particle and optical diagnostics allowed characterization of spatial and spectral proton beam parameters and the stability of the regime of best acceleration performance, yielding cut-off energies larger than 100 MeV in the best shots.

  • Invited lecture (Conferences)
    20th Advanced Accelerator Concepts Workshop (AAC’22), 07.11.2022, Long Island, USA

Permalink: https://www.hzdr.de/publications/Publ-36236
Publ.-Id: 36236


Laser-plasma ion accelerators for radio-biological research

Zeil, K.

Particle accelerators have always been fundamental engines of discovery and drivers of innovations in industry, basic research, and life sciences. Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power laser-driven compact plasma accelerators can generate short, high-intensity pulses of high energy electrons and ions with special beam properties. By that they may expand the portfolio of conventional machines in many application areas.

For laser-driven ion accelerators, the full application in ultra-high dose rate radiotherapy (RT) research marks one of the most important research objectives and is perfectly timed with the emerging interest on ultra-high dose rate RT. Laser proton accelerators are ideal instruments to investigate ultra-high dose rate effects, yet their ability to provide radiobiological in-vivo data comparable in quality to a clinical reference standard has called for demonstration for a long time.

The talk will introduce the concept of laser-driven ion accelerators and challenges of this technology. For the example of the high power laser source DRACO operated at HZDR, key developments for the production of reliable polychromatic proton beams with maximum energies of around 60 MeV are presented. Most recently, these achievements enabled the first successful small animal pilot study on radiation-induced tumor growth delay in mice using a laser-driven proton source and a clinical reference.

  • Invited lecture (Conferences) (Online presentation)
    Virtual DPG Spring Meeting - Symposium Plasma Induced Accelerators, 31.03.2022, Mainz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36235
Publ.-Id: 36235


Laser driven proton accelerators with solid hydrogen jets for application

Zeil, K.

Laser plasma-based particle accelerators attract great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. However, despite the fact that first principles particle in cell simulations have predicted several advantageous ion acceleration schemes,
laser accelerators have not yet reached their full potential in producing simultaneous high-radiation
doses at high particle energies. The most stringent limitation is the lack of a suitable high-repetition
rate target that also provides a high degree of control of the plasma conditions which is required
to access these advanced regimes. Here, we demonstrate that the interaction of petawatt-class laser
pulses with a pre-formed micrometer-sized cryogenic hydrogen jet plasma overcomes these limitations. Controlled pre-expansion of the initially solid target by low intensity pre-pulses allowed for tailored density scans from the solid to the underdense regime. Our experiment demonstrates that
the near-critical plasma density profile produces proton energies of 80 MeV. This energy presents
more than a factor of two increase compared to the solid hydrogen target. Our three-dimensional
particle in cell simulations show the transition between different acceleration mechanisms and suggest enhanced proton acceleration at the relativistic transparency front for the optimal case.

  • Invited lecture (Conferences)
    13th International Particle Accelerator Conference (IPAC’22), 15.06.2022, Bangkok, Thailand

Permalink: https://www.hzdr.de/publications/Publ-36234
Publ.-Id: 36234


High energy proton detection in Draco PW experiments

Zeil, K.; Assenbaum, S.; Bernert, C.; Brack, F.-E.; Cowan, T.; Garten, M.; Gaus, L.; Göthel, I.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Reimold, M.; Rehwald, M.; Schlenvoigt, H.-P.; Umlandt, M. E. P.; Vescovi Pinochet, M. A.; Ziegler, T.; Schramm, U.

Exploiting the strong electromagnetic fields that can be supported by a plasma, high-power
laser driven compact plasma accelerators can generate short, high-intensity pulses of high
energy ions with special beam properties interesting for many application areas. The transition
of laser driven ion accelerators from physics experiments to turn-key sources for these
applications relies on improvement of generated beam parameters (kinetic energy, flux), as
well as increased reproducibility, robustness and scalability to high repetition rate.
Recent developments at the high-power laser facility DRACO-PW enabled the production
of polychromatic proton beams with unprecedented stability [1] which enabled the first in vivo
radiobiological study to be conducted using a laser-driven proton source [2]. Yet, the ability to
achieve highest energies around or even beyond the 100 MeV frontier is matter of ongoing
research, mainly addressed by exploring advanced acceleration schemes.
In parallel to the testing of these schemes an important challenge is to provide convincing
evidence that these very high energies could be reached at all for a significant number of
particles. Occurring complications are due to the nature of the multi-species beams with
typically exponentially decaying spectra and low shot statistics of laser-plasma experiments
at the necessary laser pulse energy levels. The latter is in particular complicated for highly
non-linear acceleration regimes with intrinsically low reproducibility.
In this talk we summarize our approaches for the spatial and spectral characterization of our
proton beam parameters with cut-off energies larger than 80 MeV. Key is the combination of
a multitude of different methods based on different detection principles established for single
shot measurements. Time-of-flight methods are discussed for energy cross-calibration of our
Thomson parabola spectrometers and the use of different screen types for on-shot particle
number calibration is presented.

  • Lecture (Conference)
    BLIN5 Workshop 2022, 14.10.2022, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36233
Publ.-Id: 36233


Preliminary results from the x-ray spectrometers at Draco PW laser facility

Stefanikova, R.; Pan, X.; Smid, M.; Schlenvoigt, H.-P.; Prencipe, I.; Gaus, L.; Umlandt, M. E. P.; Vescovi Pinochet, M. A.; Reimold, M.; Ziegler, T.; Kroll, F.; Kraft, S.; Schramm, U.; Zeil, K.; Metzkes-Ng, J.; Falk, K.

A large amount of complex processes within laser-produced plasmas put a huge demand for precise diagnostics methods. For example, x-ray emission spectroscopy can be used to study atomic physics and plasma conditions. Here, we introduce two new x-ray spectrometers installed in the Ion acceleration lab at the Draco PW laser facility. Availability of such diagnostics at the Draco PW Ti:sapphire 30 fs laser system (i.e. ultra-short pulse system) allows not only for studying unique plasma conditions driving the ion acceleration, but also exploring new possibilities for x-ray backlighters suitable for high energy density experiments.
Both spectrometers are utilized for acquisition of Ti spectral lines, but offer different spectral resolution and range. Quartz crystal spectrometer has wider spectral range, including Ti K-α and He-α emission lines in the spectrum, whereas Ge crystal spectrometer focuses on K-α emission lines and offers 1D spatial imaging. We present first results demonstrating the capabilities of both spectrometers.
The first spectroscopic measurements include the emission spectra measurements from flat Ti targets used for proton acceleration calibration and optimization with and without laser pre-pulse and the use of structured targets for enhanced x-ray emission as well as tailoring of the electron spectra for optimization of the proton acceleration process.

Keywords: x-ray spectrometer; laser-produced plasma; characteristic emission lines

  • Poster
    17th International Conference on the Physics of Non-Ideal Plasmas, 22.09.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36232
Publ.-Id: 36232


Fabrication of highly n-type-doped germanium nanowires and Ohmic contacts using ion implantation and flash lamp annealing

Echresh, A.; Prucnal, S.; Li, Z.; Hübner, R.; Ganss, F.; Steuer, O.; Bärwolf, F.; Jazavandi Ghamsari, S.; Helm, M.; Zhou, S.; Erbe, A.; Rebohle, L.; Georgiev, Y.

Accurate control of doping and fabrication of metal contacts on n-type germanium nanowires (GeNWs) with low resistance and linear characteristics remain a major challenge in germanium-based nanoelectronics. Here, we present a combined approach to fabricate Ohmic contacts on n-type-doped GeNWs. Phosphorus (P) implantation followed by millisecond rear-side flash lamp annealing was used to produce highly n-type doped Ge with an electron concentration in the order of 10^19 − 10^20 cm^(−3). Electron beam lithography, inductively coupled plasma reactive ion etching, and nickel (Ni) deposition were used to fabricate GeNW-based devices with symmetric Hall bar configuration, which allows detailed electrical characterization of the NWs. Afterward, rear-side flash lamp annealing was applied to form Ni germanide at the Ni-GeNWs contacts to reduce the Schottky barrier height. The two-probe current-voltage measurements on n-type-doped GeNWs exhibit linear Ohmic behavior. Also, the size-dependent electrical measurements showed that carrier scattering near the NW surfaces and reduction of the effective NW cross-section dominate the charge transport in the GeNWs.

Keywords: Germanium nanowires; ion implantation; flash lamp annealing; n-type doped; Ohmic contacts; Hall bar configuration

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  • Secondary publication expected from 02.11.2023

Permalink: https://www.hzdr.de/publications/Publ-36230
Publ.-Id: 36230


Impact of pre-plasma tailoring on K-ɑ emission and proton acceleration

Stefanikova, R.; Pan, X.; Smid, M.; Gaus, L.; Kraft, S.; Kroll, F.; Kozlová, M.; Prencipe, I.; Reimold, M.; Schlenvoigt, H.-P.; Umlandt, M. E. P.; Schramm, U.; Zeil, K.; Metzkes-Ng, J.; Falk, K.

Laser-produced plasmas are widely studied complex systems. In order to get better understanding of their inner processes, advanced diagnostics methods have to be used to get a valuable insight – for example, x-ray emission spectroscopy has the capability to unfold atomic processes and plasma conditions and reveal information about the hot electron population.
Recently, two x-ray crystal spectrometers were installed in the Ion Acceleration Lab at Draco PW laser facility, which allows to acquire characteristic emission spectra including Ti K-α and He-α lines from Ti targets. While quartz spectrometer offers wide spectral range and excellent spectral resolution of ∼ 0.3 eV, Ge spectrometer focuses on Ti K-α emission lines and provides 1D spatial imaging with resolution below 10 μm.
Here, we present the first results from the x-ray spectroscopic measurements from proton acceleration targets at the DRACO PW laser facility uncovering the plasma conditions and electron dynamics for various target and laser configurations including inclusion artificial pre-pulse or the use of reduced mass targets.

  • Poster (Online presentation)
    The 48th European Conference on Plasma Physics (2022), 01.07.2022, Maastricht (online), Netherlands

Permalink: https://www.hzdr.de/publications/Publ-36229
Publ.-Id: 36229


Clarifying space use concepts in ecology: range vs. occurrence distributions

Alston, J.; Fleming, C.; Noonan, M.; Tucker, M.; Silva, I.; Folta, C.; Akre, T.; Ali, A.; Belant, J.; Beyer, D.; Blaum, N.; Boehning-Gaese, K.; Cunha De Paula, R.; Dekker, J.; Drescher-Lehman, J.; Farwig, N.; Fichtel, C.; Fischer, C.; Ford, A.; Janssen, R.; Jeltsch, F.; Kappeler, P.; Lapoint, S.; Markham, A.; Medici, P.; Morato, R.; Nathan, R.; Olson, K.; Patterson, B.; Petroelje, T.; Ramalho, E.; Roesner, S.; Santos, L.; Schabo, D.; Selva, N.; Sergiel, A.; Spiegel, O.; Ullman, W.; Zieba, F.; Zwijacz-Kozica, T.; Wittemyer, G.; Fagan, W.; Mueller, T.; Calabrese, J.

Quantifying animal movements is necessary for answering a wide array of research questions in ecology and conservation biology. Consequently, ecologists have made considerable efforts to identify the best way to estimate an animal’s home range, and many methods of estimating home ranges have arisen over the past half century. Most of these methods fall into two distinct categories of estimators that have only recently been described in statistical detail: those that measure range distributions (methods such as Kernel Density Estimation that quantify the long-run behavior of a movement process that features restricted space use) and those that measure occurrence distributions (methods such as Brownian Bridge Movement Models and the Correlated Random Walk Library that quantify uncertainty in an animal movement path during a specific period of observation). In this paper, we use theory, simulations, and empirical analysis to demonstrate the importance of applying these two classes of space use estimators appropriately and distinctly. Conflating range and occurrence distributions can have serious consequences for ecological inference and conservation practice. For example, in most situations, home-range estimates quantified using occurrence estimators are too small, and this problem is exacerbated by ongoing improvements in tracking technology that enable more frequent and more accurate data on animal movements. We encourage researchers to use range estimators to estimate the area of home ranges and occurrence estimators to answer other questions in movement ecology, such as when and where an animal crosses a linear feature, visits a location of interest, or interacts with other animals.

Permalink: https://www.hzdr.de/publications/Publ-36228
Publ.-Id: 36228


Study of x-ray emission from proton acceleration targets at Draco PW laser facility

Stefanikova, R.; Pan, X.; Meckel, N.; Smid, M.; Schlenvoigt, H.-P.; Prencipe, I.; Kozlová, M.; Gaus, L.; Umlandt, M. E. P.; Vescovi Pinochet, M. A.; Reimold, M.; Ziegler, T.; Kroll, F.; Kraft, S.; Schramm, U.; Zeil, K.; Metzkes-Ng, J.; Falk, K.

Laser plasma-based ion accelerators are very promising candidates for many applications. In order to ensure the reliability of such accelerators a comprehensive set of diagnostics is required. X-ray emission spectroscopy allows us to directly measure the plasma conditions of the laser-plasma interaction and also provides information about the hot electron population through the cold K-α emission production.
Here, we present preliminary results from two new x-ray spectrometers used to study interaction regimes relevant for laser-driven ion acceleration at ultra-short pulse PW-class laser facility. We acquired the emission spectra from flat Ti targets for a range of target thicknesses and laser energies. Additionally, artificial laser pre-pulses were added to alter the laser absorption efficiency.

Keywords: x-ray spectroscopy; laser-produced plasma; characteristic emission lines; laser-plasma ion acceleration

  • Lecture (Conference) (Online presentation)
    DPG-Frühjahrstagung, 28.03.2022, Mainz, online, Germany

Permalink: https://www.hzdr.de/publications/Publ-36227
Publ.-Id: 36227


Study of the influence of various pre-plasma conditions on laser-proton acceleration via x-ray spectroscopy

Stefanikova, R.; Pan, X.; Smid, M.; Gaus, L.; Kozlová, M.; Kraft, S.; Kroll, F.; Prencipe, I.; Reimold, M.; Schlenvoigt, H.-P.; Umlandt, M. E. P.; Schramm, U.; Zeil, K.; Metzkes-Ng, J.; Falk, K.

Laser driven ion acceleration is a fast growing field, where understanding of the internal processes of laser-plasma interaction is crucial for optimization of such ion sources. Namely, x-ray spectroscopy offers a unique in-situ view at plasma conditions and electron signatures from within the target, which can help to identify important parameters for optimization of the laser-driven acceleration process.
Here, we present an x-ray spectroscopy platform installed at the Draco PW laser facility (Ti:sapphire 30 fs laser system) and how the addition of x-
ray spectroscopy reveals the suprathermal electron population, which provides insight into the energy conversion from laser to the proton-accelerating sheath.
As an example, we study the impact of pre-plasma tailoring on characteristic x-ray emission and proton acceleration via controlled introduction of various pre-pulses on the Ti 2 μm thick target that precede the arrival of the main laser pulse by 2.5 − 30 ps. Based on our data from x-ray spectroscopy combined with proton diagnostics we then gain understand-
ing of the underlying processes in proton acceleration and the influence of pre-plasma formation.

Keywords: x-ray spectrometer; laser-produced plasma; characteristic emission lines

  • Lecture (Conference) (Online presentation)
    64th Annual Meeting of the APS Division of Plasma Physics, 20.10.2022, Spokane, USA

Permalink: https://www.hzdr.de/publications/Publ-36226
Publ.-Id: 36226


The relationship between controllability, optimal testing resource allocation, and incubation-latent period mismatch as revealed by COVID-19

Demers, J.; Fagan, W.; Potluri, S.; Calabrese, J.

The severe shortfall in testing supplies during the initial phases of the COVID-19 pandemic and ensuing struggle to control disease spread have affirmed the need to plan rigorous optimized supply-constrained resource allocation strategies for the next inevitable novel disease epidemic. To address the challenge of optimizing limited resource usage in the face of complicated disease dynamics, we develop an integro partial differential equation disease model which incorporates realistic latent, incubation, and infectious period distributions along with limited testing supplies for identifying and quarantining infected individuals, and we analyze the influence of these ele- ments on controllability and optimal resource allocation between two testing strategies, ‘clinical’ targeting symptomatic individuals and ‘non-clinical’ targeting non-symptomatic individuals, for reducing total infection sizes. We apply our model to not only the original, delta, and omicron COVID-19 variants, but also to generic diseases which have different offsets between latent and incubation period distributions which allow for or prevent varying degrees of presymptomatic transmission or preinfectiousness symptom onset. We find that factors which reduce control- lability generally call for reduced levels of non-clinical testing, while the relationship between symptom onset, controllability, and optimal strategies is complicated. Although greater degrees of presymptomatic transmission reduce disease controllability, they may enhance or reduce the role of non-clinical testing in optimal strategies depending on other disease factors like overall transmissibility and latent period length. Our model allows a spectrum of diseases to be com- pared under the same lens such that the lessons learned from COVID-19 can be adapted to resource constraints in the next emerging epidemic and analyzed for optimal strategies under a consistent mathematical framework.

Permalink: https://www.hzdr.de/publications/Publ-36225
Publ.-Id: 36225


Characterization of low-density rear-driven collisional plasma jets from thin foil targets

Perez-Martin, P.; Smid, M.; Hronová, L.; Bouffetier, V.; Brack, F.-E.; Cagas, P.; Červenák, M.; Gajdos, P.; He, Z.; Holec, M.; Kagan, G.; Kaniz, K.; Kozlová, M.; Kroll, F.; Liu, H.; Pan, X.; Prencipe, I.; Schaumann, G.; Singh, S.; Sobiella, M.; Srinivasan, B.; Stafford, J.; Xie, Z.; Xiong, J.; Suzuki-Vidal, F.; Krůs, M.; Ren, L.; Kang, N.; Falk, K.

Magnetized low density, collisional plasma jets are found in astrophysical systems, such as accretion
discs or polars, and they also show potential as a platform to study transport properties in
astrophysical plasmas. However, no systematic study of their properties has been conducted yet.
Through experiments in kilojoule laser facilities, we aim to benchmark a range of rear-driven
jets from foils of different thicknesses and materials.
We studied free propagation of jets, their collisions with a static object and the collisions
between two counterpropagating jets. The setup was also placed inside a split pair coil, which
provides an external magnetic field of 5-10 T. A streak camera was used to track jet velocity
and density was measured with 4-frame interferometry and x-ray radiography.
The results can be used to plan experiments with focus on specific jet properties, as well as
providing a benchmark for hydrodynamic codes. The data on collisions and magnetized jets
provides insight into compression waves and the effects of strong external magnetic fields,
which are used for the study of transport properties of plasmas.

Keywords: Plasma flows; Laboratory astrophysics; Magnetized plasma; High magnetic fields; Interferometry

  • Lecture (Conference) (Online presentation)
    48th EPS Conference on Plasma Physics, 28.06.-01.07.2022, Online, N/A

Permalink: https://www.hzdr.de/publications/Publ-36224
Publ.-Id: 36224


Modeling of magnetized astrophysical objects through the study of magnetized rear-driven plasma jets from thin foil targets

Perez-Martin, P.; Smid, M.; Hronová, L.; Bouffetier, V.; Bott, A.; Brack, F.-E.; Červenák, M.; Donat, F.; Gajdoš, P.; Kozlová, M.; Kroll, F.; Manuel, M.; Pan, X.; Prencipe, I.; Singh, S.; Sobiella, M.; Krus, M.; Falk, K.

Plasma jets can be found in astrophysical systems (Accretion disks[1][2], Polars [3] or Young
Stellar Objects [4]), but they are also useful as a platform to study plasma properties and transport
effects. On a experiment at the PALS facility, we have studied the formation and propagation
of rear-driven, collisional plasma jets from different foil thicknesses and materials when
subject to an intense external magnetic field.
Magnetic fields were generated using a pair of Helmholtz coils that provide 5-10 T in the
direction perpendicular to the jet propagation. The diagnostics used were the streaked optical
self-emission as a measurement of jet velocity, and 4-frame interferometry as a measurement of
the jet density.
With the right scaling factors, this data can help model the accretion of matter into magnetized
astrophysical systems, such as the surface of Young Stellar Objects, as well as the role that
instabilities play in this process [4].
The work was supported by the Helmholtz Association under Grant No. VH-NG-1338
[1] G. Revet et al., Science Advances 3, 11 (2017)
[2] Kulkarni, A. K. & Romanova, M. M. , Monthly Notices RAS 386, (2008)
[3] E. Falize, et al., Astrophysics and Space Science 336, 81 (2011)
[4] Burdonov, K. et al., A&A 657, A112 (2022)

Keywords: Plasma flows; Laboratory astrophysics; Magnetized plasma; High magnetic fields; Magnetosphere physics; Young Stellar Objects

  • Lecture (Conference)
    64th Annual Meeting of the APS Division of Plasma Physics, 16.-21.10.2022, Spokane, United States of America

Permalink: https://www.hzdr.de/publications/Publ-36223
Publ.-Id: 36223


Atomic Layer Etching of Nanowires Using Conventional RIE Tool

Khan, M. B.; Shakeel, S.; Richter, K.; Ghosh, S.; Erbe, A.; Georgiev, Y.

Innovative material and processing concepts are needed to further enhance the performance of complementary metal-oxide-semiconductor (CMOS) transistors-based circuits as the scaling limits are being reached. To achieve that, we report on the development of an atomic layer etching (ALE) [1] process to fabricate smooth and thin nanowires using a conventional dry etching tool. Firstly, a negative tone resist (hydrogen silsesquioxane) is spin-coated on SiGe-on-insulator (SiGeOI) samples and electron beam lithography performed to create nano-patterns. These patterns act as an etch mask and are transferred into the SiGeOI layer using an inductively-coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, an SF6 and Ar+ based ALE process is employed to smoothen the nanowires and reduce their widths. SF6 modifies the surface of the samples, while in the next step Ar+ removes the modified surface. The ALE cycle sequence is surface modification with 60 sccm SF6 for 20 s, 60 sccm Ar purge for 15 s, removal of the layer with 60 sccm Ar for 10 s at 25 W platen power, and 40 sccm Ar purge for 10 s.
To investigate the effect of ALE on the nanowire roughness and width, several ALE cycles are performed. The surface of the etched features is studied using scanning electron microscopy and atomic force microscopy. With the increasing number of ALE cycles, a reduction in the width of the nanowires, as well as surface roughness, is observed. The roughness reduced from ca. 6 nm to 1 nm (the resolution of the AFM tip) as the number of ALE cycles is increased from 78 to 102.
An etch per cycle of 1.1 Å is obtained. Sub-12 nm nanowires with smooth sidewalls were achieved after performing 63 ALE cycles. This process, developed on a conventional ICP-RIE tool, can be used to further down-scale semiconductor nanowires.

1. Kanarik, Keren J., et al. "Overview of atomic layer etching in the semiconductor industry." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 33.2 (2015): 020802.

Related publications

  • Lecture (Conference)
    14th EBT 2022 International conference, 26.06.-01.07.2022, Varna, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-36222
Publ.-Id: 36222


Partial Reduction in BRCA1 Gene Dose Modulates DNA Replication Stress Level and Thereby Contributes to Sensitivity or Resistance

Classen, S.; Rahlf, E.; Jungwirth, J.; Albers, N.; Hebestreit, L.; Zielinski, A.; Poole, L.; Groth, M.; Koch, P.; Liehr, T.; Kankel, S.; Cordes, N.; Petersen, C.; Rothkamm, K.; Pospiech, H.; Borgmann, K.

BRCA1 is a well-known breast cancer risk gene, involved in DNA damage repair via homologous recombination (HR) and replication fork protection. Therapy resistance was linked to loss and amplification of the BRCA1 gene causing inferior survival of breast cancer patients. Most studies have focused on the analysis of complete loss or mutations in functional domains of BRCA1. How mutations in non-functional domains contribute to resistance mechanisms remains elusive and was the focus of this study. Therefore, clones of the breast cancer cell line MCF7 with indels in BRCA1 exon 9 and 14 were generated using CRISPR/Cas9. Clones with successful introduced BRCA1 mutations were evaluated regarding their capacity to perform HR, how they handle DNA replication stress (RS), and the consequences on the sensitivity to MMC, PARP1 inhibition, and ionizing radiation. Unexpectedly, BRCA1 mutations resulted in both increased sensitivity and resistance to exogenous DNA damage, despite a reduction of HR capacity in all clones. Resistance was associated with improved DNA double-strand break repair and reduction in replication stress (RS). Lower RS was accompanied by increased activation and interaction of proteins essential for the S phase-specific DNA damage response consisting of HR proteins, FANCD2, and CHK1.

Keywords: Breast cancer; BRCA1; DNA repair

Permalink: https://www.hzdr.de/publications/Publ-36221
Publ.-Id: 36221


Chemical Vapor Deposition and High-Resolution Patterning of a Highly Conductive Two-Dimensional Coordination Polymer Film

Rubio-Giménez, V.; Arnauts, G.; Wang, M.; Oliveros Mata, E. S.; Huang, X.; Lan, T.; Tietze, M. L.; Kravchenko, D. E.; Smets, J.; Wauteraerts, N.; Khadiev, A.; Novikov, D. V.; Makarov, D.; Dong, R.; Ameloot, R.

Crystalline coordination polymers with high electrical conductivities and charge carrier mobilities might open new opportunities for electronic devices. However, current solvent-based synthesis methods hinder compatibility with microfabrication standards. Here, we describe a solvent-free chemical vapor deposition method to prepare high-quality films of the two-dimensional conjugated coordination polymer Cu-BHT (BHT = benzenehexanothiolate). This approach involves the conversion of a metal oxide precursor into Cu-BHT nanofilms with a controllable thickness (20–85 nm) and low roughness (<10 nm) through exposure to the vaporized organic linker. Moreover, the restricted metal ion mobility during the vapor–solid reaction enables high-resolution patterning via both bottom-up lithography, including the fabrication of micron-sized Hall bar and electrode patterns to accurately evaluate the conductivity and mobility values of the Cu-BHT films.

  • Open Access Logo Journal of the American Chemical Society 145(2023)1, 152-159
    Online First (2022) DOI: 10.1021/jacs.2c09007

Permalink: https://www.hzdr.de/publications/Publ-36220
Publ.-Id: 36220


Defect-assisted ion transport in magneto-ionic nitrides probed by positrons

Liedke, M. O.; Butterling, M.; de Rojas, J.; Quintana, A.; Lopeandía, A.; Menéndez, E.; Costa-Krämer, J. L.; Hirschmann, E.; Elsherif, A. G. A.; Sort, J.; Wagner, A.

Magneto-ionics deals with a class of spintronic materials where the external electrical field induces ion migration and leads to a raise of magnetization, a consequence of magnetic species local segregations or increased magnetic interactions between them. Since this ion transport is activated by the voltage actuation, no large electrical currents are required and heat dissipation processes are mostly negligible. In addition, simply reversing the direction of the voltage bias, the generated ferromagnetic state returns to its original magnetic configuration, which realizes the magnetic switch concept. Using magnetometry and electron microscopy supported with positron annihilation spectroscopy techniques different nitrides (CoN, FeN, NiN) have been investigated. CoN and FeN are promising candidates for fast magneto-ionic switching, whereas NiN clearly underperforms. Positron annihilation spectroscopy provides a unique probe of open volume defects, e.g. dislocations, vacancies and their agglomerations at grain boundaries, and it was successfully utilized to study the defect nanostructure here. As a reference, we first present electrolyte-gated and defect-mediated oxygen migration in single-layer, paramagnetic Co3O4 at room temperature, which allows voltage-controlled ON-OFF magnetic switching via internal reduction/oxidation processes [1]. Here, the bias-induced motion of oxygen ions was caused by dominant vacancy clusters, with oxygen motion promoted at grain boundaries and assisted by the development of O-rich diffusion channels and Co-rich grain inner regions. In the case of nitrides, on the other hand, nitrogen transport is found to occur uniformly throughout the film, creating a plane-wave-like migration front (Fig. 1), without assistance of diffusion channels [2,3]. Using positrons as a probe, we will show that the initial average open volume is larger in nitrides compared to oxides, which likely governs the migration process and allows for enhanced switching rates and cyclability as well as lowers threshold voltages. We will try to propose factors playing a role in case of hindered ionic migration in NiN, too.

Figure 1: Depth profile of the S-parameter as a function of increasing electrical field.

[1] A. Quintana, E. Menéndez, M. O. Liedke et al., ACS Nano, 12, 10291 (2018)
[2] J. de Rojas, A. Quintana, A. Lopeandía et al., Nature Communications, 11, 5871 (2020)
[3] J. de Rojas, J. Salguero, F. Ibrahim et al. ACS Appl. Mater. Interfaces, 13, 30826 (2021)

Keywords: magneto-ionics; Co3O4; CoN; NiN; positron annihilation spectroscopy; defects

Related publications

  • Poster (Online presentation)
    ICPA-19 (International Conference on Positron Annihilation), 22.-26.08.2022, Helsinki, Finnland

Permalink: https://www.hzdr.de/publications/Publ-36219
Publ.-Id: 36219


Defect-assisted ion transport in magneto-ionic functional oxides and nitrides probed by positrons

Liedke, M. O.; Butterling, M.; de Rojas, J.; Quintana, A.; Lopeandía, A.; Menéndez, E.; Costa-Krämer, J. L.; Hirschmann, E.; Sort, J.; Wagner, A.

Magneto-ionics deals with a class of spintronic materials where the external electrical field induces ion migration and leads to a raise of magnetization as a consequence of magnetic species local segregations or increased magnetic interactions between them. Since this ion transport is activated by the voltage actuation, no large electrical currents are required and heat dissipation processes are mostly negligible. Moreover, by simply reversing the direction of the voltage bias, the generated ferromagnetic state is brought back to its original magnetic configuration, which realizes the magnetic switch concept. Using magnetometry and electron microscopy supported with positron annihilation spectroscopy techniques, oxides (Co3O4) and different nitrides (CoN and FeN) have been investigated, which are promising candidates for fast magneto-ionic switching. Positron annihilation spectroscopy provides a unique probe of open volume defects, e.g. dislocations, vacancies within crystal and at interfaces, vacancy agglomerations at grain boundaries, macro- and mesopores and it was successfully utilized to study the defect nanostructure here. We first present electrolyte-gated and defect-mediated oxygen migration in single-layer, paramagnetic Co3O4 at room temperature, which allows voltage-controlled ON-OFF magnetic switching via internal reduction/oxidation processes [1]. Here, the bias-induced motion of oxygen ions is caused by dominant vacancy clusters, with oxygen motion promoted at grain boundaries and assisted by the development of O-rich diffusion channels and Co-rich grain inner regions. In the case of nitrides, on the other hand, nitrogen transport is found to occur uniformly throughout the film, creating a plane-wave-like migration front, without assistance of diffusion channels [2,3]. Using positrons as a probe, we will show that the initial average open volume is larger compared to oxides, which likely governs the migration process and allows, moreover, for enhanced switching rates and cyclability as well as lower threshold voltages.
[1] A. Quintana, E. Menéndez, M. O. Liedke et al., ACS Nano, Vol. 12, p. 10291 (2018)
[2] J. de Rojas, A. Quintana, A. Lopeandía et al., Nature Communications, Vol. 11, p. 5871 (2020)
[3] J. de Rojas, J. Salguero, F. Ibrahim et al. ACS Appl. Mater. Interfaces Vol. 13, p. 30826 (2021)

Keywords: magneto-ionics; Co3O4; CoN; FeN; positron annihilation spectroscopy; defects

Related publications

  • Lecture (Conference)
    E-MRS Fall Meeting 2022, 19.-22.09.2022, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-36218
Publ.-Id: 36218


Data publication : Tailoring crosstalk between localized 1D spin-wave nanochannels using focused ion beams

Iurchuk, V.; Pablo-Navarro, J.; Hula, T.; Narkowicz, R.; Hlawacek, G.; Koerber, L.; Kakay, A.; Schultheiss, H.; Fassbender, J.; Lenz, K.; Lindner, J.

This dataset contains raw data (SEM images, AFM, FMR, BLS, TetraX) used to study the dynamical edge modes in closely spaced permalloy microstrips.

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-36217
Publ.-Id: 36217


Investigation of laser reflectivity and transmissivity of laser-plasma interaction with thin foil targets

Umlandt, M. E. P.; Ziegler, T.; Bernert, C.; Garten, M.; Gaus, L.; Göthel, I.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Prencipe, I.; Rehwald, M.; Reimold, M.; Schlenvoigt, H.-P.; Vescovi Pinochet, M. A.; Zeil, K.; Schramm, U.

Ion acceleration by compact laser-plasma sources promises a variety of applications ranging from medical relevance to fusion experiments.Reaching the required beam quality parameters for those applications demands a very high level of understanding and control over the laserplasma interaction process. Central components in this context are the absorption of the electromagnetic laser field by the plasma and the quality of the resulting acceleration field structure.
Measuring and analyzing unabsorbed light - as transmitted and/or specularly reflected parts - thus allows insight into properties of the underlying laser-plasma interaction. We experimentally investigate these interactions for high and low-contrast laser pulses with thin solid density foil targets at the Draco PW laser system (HZDR). The results of spectral, spatial, and energy analysis of transmitted and reflected light indicate changes in the plasma interaction and will be presented.

Keywords: laser plasma; laser proton acceleration; high power laser

  • Lecture (Conference) (Online presentation)
    DPG-Frühjahrstagung 2022, 28.03.-01.04.2022, Mainz / virtuell, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-36216
Publ.-Id: 36216


Data publication: Underground hyperspectral outcrop scanning for automated mine-face mapping — the Lithium deposit of Zinnwald/Cínovec

Kirsch, M.; Mavroudi, M.; Thiele, S. T.; Lorenz, S.; Tusa, L.; Booysen, R.; Herrmann, E.; Fatihi, A.; Möckel, R.; Dittrich, T.; Gloaguen, R.

As part of a project on the development of hyperspectral scanning to support geological mapping in underground mines, we acquired hyperspectral data from three adjacent outcrops of Sn-W-Li greisen rocks in the visitor’s mine of Zinnwald, Germany. The hyperspectral scans were pre-processed and then back-projected onto photogrammetric, three-dimensional digital outcrop models resulting in so-called "hyperclouds". The here presented hyperclouds from the three outcrops (Z1, Z2, and Z3) contain the following attributes:

ZX_Absorbance.ply
RGB colours: Mica/clay-zinnwaldite-topaz abundance based on absorbance (1 – hull-corrected reflectance) at 2200 nm (red), 2250 nm (green), and 2085 nm (blue)
Scalars: Absorbance at 2086.88 nm, 2160.69 nm, 2197.53 nm, 2209.8 nm, 2252.7 nm, and 2338.31 nm

ZX_Iron.ply
RGB colours: Composite (Fe3+ Fe2+ FeOH) iron index (red: 600/570 nm, green:(920 nm + 1650 nm)/ (1035 nm 1230 nm), blue: (2230 nm 2290 nm)/(2245 nm + 2260 nm)
Scalars: Fe3+ = 600/570 nm, Fe2+ = (920 nm + 1650 nm)/ (1035 nm + 1230 nm), FeOH = (2230 nm + 2290 nm)/(2245 nm + 2260 nm)

ZX_MNF.ply
RGB colours: Minimum noise fraction false colour (red: band 4, green: band 7, blue: band 5)
Scalars: Minimum noise fraction bands 4, 7, 5)

ZX_RGB_mineralogy_Li.ply
RGB colours: True colour RGB from photogrammetric outcrop model
Scalars: Mineral abundances derived by combining sample mineralogy from quantitative XRD measurements and hyperspectral unmixing approaches: Quartz/Feldspar, Zinnwaldite, Muscovite/Illite, Kaolinite, Topaz, Lithium (by multiplying the zinnwaldite abundance by its average lithium content of 1.7%)

Keywords: hyperspectral; underground mining; point cloud; lithium; mineral mapping

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Permalink: https://www.hzdr.de/publications/Publ-36215
Publ.-Id: 36215


Wild herbivores enhance resistance to invasion by exotic cacti in an African savanna

Wells, H. B. M.; Crego, R. D.; Alston, J.; Ndungu, S. K.; Khasoha, L. M.; Reed, C. G.; Hassan, A. A.; Kurukura, S.; Ekadeli, J.; Namoni, M.; Stewart, P. S.; Kimuyu, D. M.; Wolf, A. A.; Young, T. P.; Kartzinel, T. R.; Palmer, T. M.; Goheen, J. R.; Pringle, R. M.

Whether wild herbivores confer biotic resistance to invasion by exotic plants remains a key question in ecology. There is evidence that wild herbivores can impede invasion by exotic plants, but it is unclear whether and how this generalises across ecosystems with varying wild herbivore diversity and functional groups of plants, particularly over long-term (decadal) time frames. Using data from three long-term (13- to 26-year) exclosure experiments in central Kenya, we tested the effects of wild herbivores on the density of exotic invasive cacti, Opuntia stricta and O. ficus-indica (collectively, Opuntia), which are among the worst invasive species globally. We also examined relationships between wild herbivore richness and elephant occurrence probability with the probability of O. stricta presence at the landscape level (6150 km2). Opuntia densities were 74% to 99% lower in almost all plots accessible to wild herbivores compared to exclosure plots. Opuntia densities also increased more rapidly across time in plots excluding wild herbivores. These effects were largely driven by megaherbivores (≥1000 kg), particularly elephants. At the landscape level, modelled Opuntia stricta occurrence probability was negatively correlated with estimated species richness of wild herbivores and elephant occurrence probability. On average, O. stricta occurrence probability fell from ~0.56 to ~0.45 as wild herbivore richness increased from 6 to 10 species and fell from ~0.57 to ~0.40 as elephant occurrence probability increased from ~0.41 to ~0.84. These multi-scale results suggest that any facilitative effects of Opuntia by wild herbivores (e.g. seed/vegetative dispersal) are overridden by suppression (e.g. consumption, uprooting, trampling). Synthesis. Our experimental and observational findings that wild herbivores confer resistance to invasion by exotic cacti add to evidence that conserving and restoring native herbivore assemblages (particularly megaherbivores) can increase community resistance to plant invasions. © 2022 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.

Keywords: biotic resistance; elephants; invasion ecology; long-term exclosure experiments; megaherbivores; multi-trophic interactions; Opuntia stricta; prickly pear

Permalink: https://www.hzdr.de/publications/Publ-36214
Publ.-Id: 36214


Foam Targets as Extreme Magnetic Field Drivers

Laso García, A.; Toncian, T.; Habibi, M.; Prencipe, I.; Cowan, T.; Rinderknecht, H. G.; Wei, M. S.; Bruhaug, G.; Arefiev, A.; Wang, T.; Doria, D.; Crăciun, V.; Ghenuche, P.; Năstasă, V.

Structured foam targets are of great interest for the laser-plasma community. Recent studies have shown how low density foams could be used to generate extreme magnetic fields in the MegaTesla range. A result of the interaction of the fields with the accelerated electrons in the foam is a large increase in the electron kinetic energy, and the generation of bright flashes of synchrotron radiation in the MeV range.

In this talk we introduce experimental results obtained at HED/HiBEF at the European XFEL on the structural changes and homogenization of the foam during the laser interaction. Then we will show results on synchrotron emission at Texas Petawatt. Finally we will provide an overview of our roadmap towards implementing foam experiments at the 10 PW level at ELI-NP

Keywords: laser-plasma; foams; HiBEF; XFEL; ELI-NP; texas PW; synchrotron; bright gamma flashes

  • Invited lecture (Conferences)
    Foam Target Workshop, 02.11.2022, Dolní Břežany, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-36213
Publ.-Id: 36213


Towards High-Field Experiments in Existing and Upcoming Laser Facilities

Laso García, A.; Toncian, T.; Habibi, M.; Prencipe, I.; Rinderknecht, H. G.; Wei, M. S.; Bruhaug, G.; Arefiev, A.; Wang, T.; Doria, D.; Crăciun, V.; Ghenuche, P.; Năstasă, V.; Cernăianu, M.; Dreghici, D.-B.; Talposi, A.-M.; Quevedo, H.; Ditmire, T.; Schlenvoigt, H.-P.; Smid, M.; Cowan, T.

The Helmholtz International Beamline for Extreme Fields is a user consortium providing drivers for high-energy density and high-field science at the HED station of EuXFEL. This presentation will give an overview of the current implementation and commissioning results as well as future plans and exemplary science cases.
In parallel, new exciting opportunities for high-field science are opening with the first user call at the ELI facilities. Here, we will discuss first results on Megatesla magnetic field generation in overdense plasmas. We will also discuss future plans to exploit the high intensities, up to 10 PW, to be delivered at ELI-NP.

Keywords: Extreme fields; Laser-plasmas; HiBEF; XFEL; bright gamma flashes; high energy density

  • Invited lecture (Conferences)
    QED Laser Plasmas, 26.-30.09.2022, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-36212
Publ.-Id: 36212


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