Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33168 Publications

On self-created and self-creating dynamos

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

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


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

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

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

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

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

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


Polar Waves and Chaotic Flows in Thin Rotating Spherical Shells

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

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


Dual-energy computed tomography for improved proton therapy treatment planning

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

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

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

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

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


A model for tidal synchronization and modulation of the solar dynamo

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

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


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

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

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


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

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

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


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

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

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


Bildgeführte Teilchentherapie und Bestrahlungs-Verifizierung

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

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


Dual-Energy CT for particle therapy planning and beyond

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

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


CT-based in-room imaging

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

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


CT for radiotherapy planning

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

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


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

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

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


The DRESDYN Project at HZDR

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

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


Planetary dynamos in the lab

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

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


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

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

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


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

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

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


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

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

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


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

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

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


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

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

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


Implantation experiments to check the Plasma Immersion Ion Implantation quality

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

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


Hochtemperaturoxidationsschutz für Nickelwerkstoffe durch Fluorimplantation

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

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


Hochtemperaturoxidationsschutz für Nickelwerkstoffe durch Fluorimplantation

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

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


ERDA for more Fluorine in Nickel-based alloys

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

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


Antikorrosive Wirkung nanoskaliger Schichten auf metallischen Legierungen im Orgelbau

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

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


Antikorrosive Behandlungen metallischer Legierungen für den Orgelbau mittels Nanotechnologie

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

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


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

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

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


Nanoscale anticorrosive protection of pipe organ metallic materials

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

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


Fractional Abundance Estimation of Mixed and Compound Materials by Hyperspectral Imaging

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

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


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

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

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  • Secondary publication expected from 28.03.2020

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


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

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

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


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

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

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  • Secondary publication expected from 25.01.2020

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


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

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

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


Ion beam modification of single-layer transition metal dichalcogenides

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

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


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

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

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


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

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

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


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

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

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


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

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

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


Role of contacts in carbon nanotube giant piezoresistive sensors

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

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


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

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

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


Room temperature coherent control of spin qudit modes in SiC

Astakhov, G.ORC
One of the challenges in the field of quantum sensing and information processing is to selectively address and coherently manipulate highly homogeneous qubits subject to external perturbations. Here, we present room-temperature coherent control of high-dimensional quantum bits, the so-called qudits, associated with vacancy-related spins in silicon carbide enriched with nuclear spin-free isotopes. In addition to the excitation of a spectrally narrow qudit mode at the pump frequency, several other modes are excited in the electron spin resonance spectra. We demonstrate selective quantum control of homogeneous spin packets with sub-MHz spectral resolution. Furthermore, we perform two-frequency Ramsey interferometry to demonstrate absolute DC magnetometry, which is immune to thermal noise and strain inhomogeneity.
  • Invited lecture (Conferences)
    Colloquium on Quantum Technology: Quantum Sensing, Quantum-IT, Quantum Computing, Simulation, Industrialization., 09.10.2019, Esslingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-30297
Publ.-Id: 30297


Electron-doped SiGe Quantum Well Terahertz Emitters pumped by FEL pulses

Ciano, C.; Montanari, M.; Persichetti, L.; Di Gaspare, L.; Virgilio, M.; Bagolini, L.; Capellini, G.; Zoellner, M.; Skibitzki, O.; Stark4, D.; Scalari, G.; Faist, J.; Rew, K.; Paul, D. J.; Grange, T.; Birner, S.; Pashkin, O.ORC; Helm, M.; Baldassarre, L.; Ortolani, M.; de Seta, M.
We explore saturable absorption and terahertz photoluminescence emission in a set of n-doped Ge/SiGe asymmetric coupled quantum wells, designed as three-level systems (i.e., quantum fountain emitter). We generate a non-equilibrium population by optical pumping at the 1→3 transition energy using picosecond pulses from a free-electron laser and characterize this effect by measuring absorption as a function of the pump intensity. In the emission experiment we observe weak emission peaks in the 14-25 meV range (3-6 THz) corresponding to the two intermediate intersubband transition energies. The results represent a step towards silicon-based integrated terahertz emitters.
Keywords: Quantum cascade lasers, Mathematical model, Silicon, Optical pumping, Photonics
  • Open Access Logo Contribution to proceedings
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 01.-06.09.2019, Paris, France
    2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), IEEE Xplore: IEEE
    DOI: 10.1109/IRMMW-THz.2019.8873894

Permalink: https://www.hzdr.de/publications/Publ-30295
Publ.-Id: 30295


Cavity enhanced third-harmonic generation in Si:B pumped with intense terahertz pulses

Meng, F.; Thomson, M. D.; Klug, B.; Ul-Islam, Q.; Pashkin, O.ORC; Schneider, H.ORC; Roskos, H. G.
We report third-harmonic generation (THG) of terahertz free-electron laser (FEL) pulses in Si:B at cryogenic temperatures. The physical mechanism of THG is attributed to the free-carrier χ(3) nonlinearity due to the non-parabolicity of the valence band. The value of χ(3) increases as a function of the carrier density, which are generated via impact ionization of the boron dopants under irradiation by the FEL pulses. By positioning the Si:B in a one-dimensional photonic crystal (1D PC) cavity, the measured THG intensity increases by a factor of about 200.
Keywords: Cavity resonators, Impact ionization, Semiconductor device measurement, Power harmonic filters, Silicon, Harmonic analysis
  • Open Access Logo Contribution to proceedings
    44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 01.-06.09.2019, Paris, France
    2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), IEEE Xplore
    DOI: 10.1109/IRMMW-THz.2019.8874582

Permalink: https://www.hzdr.de/publications/Publ-30294
Publ.-Id: 30294


Transmission of highly charged xenon ions through a monolayer of molybdenum disulfide

Creutzburg, S.; Schwestka, J.; Grande, P. L.; Inani, H.; Tripathi, M. K.; Heller, R.; Niggas, A.; Kozubek, R.; Madauß, L.; Facsko, S.ORC; Kotakoski, J.; Schleberger, M.; Aumayr, F.; Wilhelm, R. A.ORC
The modification of solids by ion irradiation is a longstanding research objective driven by the urge for controlled defect engineering. By incorporating defects in a host material, the electronic, optical and magnetic properties of a solid can be modified. Especially in low-dimensional materials, like 2D layers, the presence of defects may significantly change their performance in applications. Highly charged ions (HCIs) are an effective tool for nanostructure formation on surfaces [1,2]. For HCI impact on a surface, nanostructure formation is driven by the deposition of the potential energy in very shallow depths in the order of nanometers. Recently, pore formation in 2D materials, like carbon nanomembranes [1] or MoS₂ [2], was observed by HCI impact despite the fact that their atomic thickness is limiting the amount of energy, which can be deposited. By measuring the charge exchange of HCIs transmitted through a monolayer of MoS₂, we can provide an upper estimate for the energy transferred to the layer available for pore formation in MoS₂. Additionally, we can gain insights into non equilibrium charge state effects, i.e. the neutralization behavior of the projectile and the charge state dependent kinetic energy loss.
The exit charge state of the ions transmitted through a suspended monolayer of MoS₂ placed on a TEM grid is measured simultaneously with their time-of-flight (TOF) [3].
A two-dimensional charge state and scattering angle resolved spectrum is measured. Two distinct exit charge state distributions at high and low charge states are observed. The distribution at high charge states is accompanied by small scattering angles, which indicates collision events taking place at large impact parameters. On the contrary, the distribution at low charge states is characterized by larger scattering angles pointing to collisions occurring at small impact parameters. We can associate both exit charge state distributions with two well separated peaks in the TOF signal corresponding to slow and fast transmitted ions, i.e. high and low energy loss, respectively. The low exit charge state distribution was already observed for HCI interaction with graphene. Neutralization times of a few femtoseconds were determined previously [4], which could only be explained by ion de-excitation via an Interatomic Coulombic Decay process. This common neutralization behavior for graphene and MoS₂ implies a common de-excitation mechanism for HCI interaction for both target materials. The additional high exit charge state distribution for MoS₂ is interpreted as a feature related to the different crystalline structure of the material in contrast to graphene. Our experimental results are supported by computer simulations using the Monte-Carlo code TDPot [5], which also reveals two distinct interaction regimes of the incident ions within the unit cell of MoS₂.
[1] R. A. Wilhelm et al., 2D Mater. 2, 035009 (2015).
[2] R. Kozubek et al., J. Phys. Chem. Lett. 10, 904-910 (2019).
[3] J. Schwestka et al., Rev. Sci Instrum. 89, 085101 (2018).
[4] R. A. Wilhelm et al., Phys. Rev. Lett. 119, 103401 (2017).
[5] R. A. Wilhelm and P. L. Grande, Commun. Phys. 2, 89 (2019).
  • Lecture (Conference)
    23rd International Workshop on Inelastic Ion-Surface Collisions (IISC-23), 18.11.2019, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-30293
Publ.-Id: 30293


Energy deposition of highly charged ions transmitted through single layer MoS₂

Creutzburg, S.; Schwestka, J.; Inani, H.; Tripathi, M. K.; Grande, P. L.; Heller, R.; Klingner, N.ORC; Niggas, A.; Kozubek, R.; Madauss, L.; Facsko, S.ORC; Kotakoski, J.; Schleberger, M.; Aumayr, F.; Wilhelm, R. A.ORC
Highly charged ions (HCIs) are an efficient tool for the perforation of suspended 2D materials. Only a fraction of their potential energy is transferred to the atomically thin target during the very short interaction time and is available for pore formation. Charge exchange spectra were measured for highly charged xenon ions transmitted through suspended, single layer MoS₂ in order to determine the deposited potential energy available for pore formation. Additionally, charge exchange dependent ion stopping responsible for kinetic sputtering was measured simultaneously.
  • Poster
    XXXI International Conference on Photonic, Electronic, and Atomic Collisions, 29.07.2019, Deauville, République française

Permalink: https://www.hzdr.de/publications/Publ-30292
Publ.-Id: 30292


High energy ion beams as a powerful tool for the surface analysis of the elemental composition of almost any sample

Munnik, F.ORC; Heller, R.
High energy ion beams as a powerful tool for the surface analysis of the elemental composition of almost any sample.
Keywords: Ion Beam Analysis
  • Lecture (others)
    Vortrag am Helmholtz-Zentrum für Umweltforschung GmbH - UFZ, 17.12.2019, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30291
Publ.-Id: 30291


Charge exchange of heavy ions transmitted through a single layer of molybdenum disulfide

Creutzburg, S.; Schwestka, J.; Grande, P. L.; Inani, H.; Tripathi, M. K.; Heller, R.; Niggas, A.; Kozubek, R.; Madauß, L.; Facsko, S.ORC; Kotakoski, J.; Schleberger, M.; Aumayr, F.; Wilhelm, R. A.ORC
2D materials offer extraordinary optical, electronic and mechanical properties, which make them interesting for future applications. Modification techniques, like ion irradiation, allow to alter their properties to specific applications. However, because of their atomic thickness applied techniques have to address mainly the surface region. Highly charged ions are a novel tool for nanostructure formation. They carry potential energies up to tens of keV, which trigger the process of nanostructure formation due to the energy deposition in shallow depths in close vicinity of the surface region. Recently, HCI impact induced nanoholes in carbon nanomembranes [1] and in suspended monolayer MoS₂ [2] have been observed despite their atomic thickness limiting the amount of potential energy to be transferred. Here, we investigate the charge exchange of highly charged xenon ions passing a monolayer of MoS₂, from which we can obtain an upper estimate of the deposited energy. The exit charge states of transmitted ions are measured simultaneously with their scattering angle as well as with their time-of-flights [3]. Two distinct distributions at high and low charge states are visible. The different scattering angles indicate the existence of two impact parameter regimes leading to two (exit charge state) distributions. Our experimental results are supported by computer simulations using the Monte-Carlo code TDPot [4].
Keywords: [1] R. A. Wilhelm et al., 2D Mater. 2, 035009 (2015). [2] R. Kozubek et al., J. Phys. Chem. Lett. 10, 904-910 (2019). [3] J. Schwestka et al., Rev. Sci Instrum. 89, 085101 (2018). [4] R. A. Wilhelm and P. L. Grande, Commun. Phys. 2, 89 (2019).
  • Poster
    1st Symposium on electron, photon, and ion collisions on molecular & atomic nanostructures, 22.07.2019, Caen, République française

Permalink: https://www.hzdr.de/publications/Publ-30290
Publ.-Id: 30290


Energy deposition of heavy ions in freestanding 2D materials

Creutzburg, S.; Schwestka, J.; Inani, H.; Tripathi, M. K.; Heller, R.; Klingner, N.ORC; Niggas, A.; Lehnert, T.; Leiter, R.; Kozubek, R.; Facsko, S.ORC; Kaiser, U.; Kotakoski, J.; Schleberger, M.; Aumayr, F.; Wilhelm, R. A.ORC
2D materials are promising candidates for electronic and photonic applications in future devices. Their properties can be tailored by surface sensitive modification techniques, like ion irradiation. Usually single charged ions are used, which deposit the main part of their kinetic energy in depths well below the surface. Only a tiny fraction is converted into the sputtering of target atoms. In contrast, highly charged ions (HCIs) carry additional potential energy in the keV regime, which may even exceed their kinetic energy. The deposition of the potential energy causes intense excitation and ionization of the electronic system of the target atoms in a shallow surface region. The high density of electronic excitations may lead to local temperatures above the sublimation point and finally to the creation of nanostructures. Even for freestanding 2D materials, like carbon nanomembranes, which consist of only a few atomic layers, pore formation induced by HCIs was observed. The small thickness of 2D materials enables spectroscopic measurements of the HCIs after transmission with respect to their charge state and kinetic energy. From our data we can estimate the amount of energy deposited in the material and therefore available for pore formation. In the present study, the influence of target properties on the charge exchange and on the neutralization dynamics is investigated. Spectroscopic measurements of the charge state of transmitted ions were performed using monolayers consisting of graphene, MoS₂ and hBN, which show different band gap energies between 0 and 6 eV, conductance properties (semi-metallic, semi-conducting and insulating) and layer structures.
  • Poster
    ECAMP13, 13th European Conference on Atoms, Molecules and Photons, 11.04.2019, Firenze, Italia

Permalink: https://www.hzdr.de/publications/Publ-30287
Publ.-Id: 30287


Charge exchange between highly charged ions and 2D materials

Creutzburg, S.; Schwestka, J.; Tripathi, M. K.; Inani, H.; Heller, R.; Klingner, N.ORC; Niggas, A.; Lehnert, T.; Leiter, R.; Kozubek, R.; Facsko, S.ORC; Kaiser, U.; Kotakoski, J.; Schleberger, M.; Aumayr, F.; Wilhelm, R. A.ORC
The neutralisation of ions due to their interaction with matter deals with fundamental aspects of ion-solid interaction, e.g.: How does the kinetic energy loss depend on the charge exchange? In order to investigate the neutralisation behaviour, classical ion beam foil experiments were performed using ultimately thin 2D materials as target. Because of their low thickness, an ion with a sufficiently high incident charge state does not reach charge equilibrium, which enables the measurement of the non-equilibrium exit charge state distribution. The influence of target material properties on the charge exchange is investigated for 2D materials consisting of graphene, MoS₂ and hBN, which show different band gap energies between 0 and 6 eV, conductance properties (metallic, semi-conducting and insulating) and layer structures.
  • Lecture (Conference)
    Verhandlungen der Deutschen Physikalischen Gesellschaft, Regensburg 2019, 03.04.2019, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30286
Publ.-Id: 30286


Experimental Observation of Exchange-Driven Chiral Effects in Curvilinear Magnetism

Volkov, O.; Kakay, A.; Florian, K.; Mönch, J. I.; Mohamad-Assaad, M.; Faßbender, J.ORC; Makarov, D.ORC
The main origin of the chiral symmetry breaking and, thus, for the magnetochiral effects in magnetic materials is associated with an antisymmetric exchange interaction, the intrinsic Dzyaloshinskii-Moriya interaction (DMI). Recently, numerous inspiring theoretical works predict that the bending of a thin film to a curved surface is often sufficient to induce similar chiral effects. However, these originate from the exchange or magnetostatic interactions and can stabilize noncollinear magnetic structures or influence spin-wave propagation. Here, we demonstrate that curvature-induced chiral effects are experimentally observable rather than theoretical abstraction and are present even in conventional soft ferromagnetic materials. We show that, by measuring the depinning field of domain walls in the simplest possible curve, a flat parabolic stripe, the effective exchange-driven DMI interaction constant can be quantified. Remarkably, its value can be as high as the interfacial DMI constant for thin films and can be tuned by the parabola’s curvature.
Keywords: Domain walls, Exchange interaction, Ferromagnetism, Magnetiyation switching

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-30285
Publ.-Id: 30285


Thermodynamics and determination of the exchange stiffness of asymmetrically sandwiched ultrathin ferromagnetic films with perpendicular anisotropy

Iastremskyi, I.; Volkov, O.; Kopte, M.; Kosub, T.; Stienen, S.; Lenz, K.ORC; Lindner, J.; Faßbender, J.ORC; Ivanov, B. A.ORC; Makarov, D.ORC
Thermodynamic properties, in particular, the temperature dependencies of magnetization of asymmetrically sandwiched ultrathin cobalt films with perpendicular anisotropy are investigated. The experimental results are described theoretically in the frame of magnon thermodynamics consistently accounting for the finite thickness of the films. The analysis includes both three-dimensional (Bloch’s T3/2 law) and two-dimensional (the 2D Bloch law) theories as limiting cases. By fitting the experimental temperature dependencies of magnetization to the theoretical model, the exchange stiffness parameter is extracted. This approach provides access to the exchange stiffness without the need to know the strength of the Dzyaloshinskii-Moriya interaction in the stack. The exchange stiffness of sub-nm-thick Co films is found to be about three times smaller compared to the case of bulk cobalt. In the temperature range T<170±30 K the temperature dependencies of magnetization follow the 2D Bloch law. The applicability of Bloch’s T3/2 law and analysis of the Curie temperature (two-dimensional and three-dimensional pictures) to extract the exchange stiffness for sub-nm-thick Co films are tested as well. The closest value of the exchange stiffness to the magnon thermodynamics turned out to be within the analysis of the Curie temperature in the three-dimensional picture.
Keywords: Exchange interaction, Ferromagnetism, Magnetic anisotropy, Micromagnetism, Skyrmions, Spintronics, Thermodynamics, Magnetic multilayers

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Permalink: https://www.hzdr.de/publications/Publ-30278
Publ.-Id: 30278


Radioimmunotherapy in Combination with Reduced-Intensity Conditioning for Allogeneic Hematopoietic Cell Transplantation in Patients with Advanced Multiple Myeloma

Fasslrinner, F.; Stölzel, F.; Kramer, M.; Teipel, R.; Brogsitter, C.; Morgner, A.; Arndt, C.; Bachmann, M.ORC; Hänel, M.; Röllig, C.; Kotzerke, J.; Schetelig, J.; Bornhäuser, M.
Radioimmunotherapy (RIT) has the potential to reduce the incidence of relapse after allogeneic hematopoietic cell transplantation (allo-HCT) in patients with advanced-stage multiple myeloma (MM). In this study, we evaluated the efficacy of RIT in combination with chemotherapy-based reduced-intensity conditioning (RIC). RIT was based on the coupling of an anti-CD66 antibody to the beta emitter 188-rhenium (188-re) for targeted bone marrow irradiation. Between 2012 and 2018, 30 patients with MM, most of them heavily pretreated with various therapies including proteasome inhibitors, immunomodulatory drugs, anti-CD38 antibodies, and autologous hematopoietic cell transplantation (auto-HCT), were treated with a RIT-RIC combination before allo-HCT. In addition to a fludarabine plus melphalan- or treosulfan-based RIC, a median dose of 18.1 Gy (interquartile range [IQR], 14.6 to 24.1 Gy) was applied to the bone marrow. After a median duration of follow-up for surviving patients of 2.1 years (IQR, 1.3 to 3.0 years), the 2-year progression-free survival and overall survival rates were 43% (95% confidence interval [CI], 26% to 73%) and 55% (95% CI, 38% to 79%), respectively. The 2-year nonrelapse mortality and cumulative incidence of progression were 17% (95% CI, 3% to 30%) and 46% (95% CI, 25% to 67%), respectively. Renal toxicity and mucositis were the most frequent extramedullary side effects. In conclusion, the addition of RIT to RIC was safe and feasible and resulted in promising outcomes compared with those previously reported for RIC-based allo-HCT without the addition of RIT in patients with relapsed/refractory MM. Nevertheless, despite the addition of RIT, relapse after allo-HCT remained a major determinant of therapeutic failure. Therefore, the development of novel RIT strategies (eg, dual targeting strategies or combinations with adapter chimeric antigen receptor T cell-based therapies) is needed.
  • Biology of Blood and Marrow Transplantation (2019)

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Permalink: https://www.hzdr.de/publications/Publ-30276
Publ.-Id: 30276


Combination of short-lived and extended half-life target modules for optimized UniCAR T cell therapy

Arndt, C.; Loureiro, L.; Feldmann, A.; Koristka, S.; Mitwasi, N.; Jureczek, J.; Hoffmann, A.; Berndt, N.; Bergmann, R.; Bachmann, M.;
Background: Chimeric antigen receptor (CAR) T cells are powerful living drugs to fight against cancer. However, they also possess the capacity to elicit moderate to severe toxicities that might be even fatal. Thus, one major issue of CAR T cell engineering is to reduce the risk for side effects while maintaining high anti-tumor activity. In order to improve the safety profile of CAR, we developed the so-called UniCAR system. In this modular platform technology, soluble, tumor-specific target modules (TM) act as molecular switches of per se inactive universal (Uni)CAR T cells. TM consist of tumor-specific binding domains fused to the E5B9 peptide epitope that is recognized by the UniCAR. All so far developed TMs have a low molecular weight and are therefore rapidly eliminated. This allows to specifically and repeatedly turn on/off UniCAR T cell activity via TM dosing.
Aims: Tumor patients with bulky disease present the highest risk for CAR T cell-related toxicities. At this stage, a high level of safety and therefore controllability of (Uni)CAR T cells is required. However, for convenient treatment of patients with lower tumor burden, we intended to develop extended half-life TM to foster anti-tumor responses and to ease the clinical TM administration at later stages of tumor therapy.
Methods: Based on the human IgG4 Fc-domain, we engineered a set of novel extended half-life TM each consisting of tumor-specific single-chain fragments variable (scFv), the IgG4 hinge and Fc domain as well as the E5B9 peptide epitope. Functionality of these IgG4-based TMs was analyzed in vitro and in vivo in comparison to originally developed scFv-based TM. Pharmacokinetic properties were studied in experimental mice.
Results: In presence of extended half-life TM, UniCAR T cells are able to efficiently mediate tumor cell lysis in vitro and in vivo. Anti-tumor responses are comparable or even improved in comparison to smaller TM, whereas bioavailability and plasma half-life are prolonged.
Summary: Overall, combination of both short-lived and longer lasting (IgG4-based) TM is a highly promising approach for redirection of UniCAR T cells to various cancer cells. At the beginning of tumor treatment, rapidly eliminated TM should be chosen to provide a fast safety switch. After significant reduction in tumor burden, IgG4-based TM with increased serum half-lives could be administered to avoid continuous TM infusions and to improve the elimination of residual tumor cells. This strategy might allow a more convenient, individualized and safe treatment of cancer patients.
  • Open Access Logo Invited lecture (Conferences)
    34th Annunal Meeting and Pre-Conference Programs of the Society for Immunotherapy of Cancer (SITC) / World Immunotherapy Council´s 3rd Young Investigator Symposium, 06.-10.11.2019, National Habor, MD, USA

Permalink: https://www.hzdr.de/publications/Publ-30273
Publ.-Id: 30273


Engaging UniCAR T cells via short-lived and longer lasting target modules

Arndt, C.; Loureiro, L.; Feldmann, A.; Koristka, S.; Mitwasi, N.; Jureczek, J.; Hoffmann, A.; Berndt, N.; Bergmann, R.; Bachmann, M.;
Background: Chimeric antigen receptor (CAR) T cell therapy has demonstrated impressive clinical efficiency, but can also cause moderate to severe adverse effects that might be even fatal. Thus, preventing or managing CAR T cell toxicity is still an important issue for successful treatment of tumor patients. In order to provide a novel CAR technology platform with an improved safety profile, we established the switchable UniCAR system. This platform consists of (I) universal CAR (UniCAR) T cells that are per se inactive. Their anti-tumor activity can be specifically and repeatedly turned on/off in dependence of soluble tumor-binding target modules (TM).e.g.1-4 TMs are constructed by fusing an antigen-specific binding moiety with the E5B9 peptide epitope recognized by UniCARs. As these molecules are rapidly eliminated, UniCAR T cells can be easily controlled by TM dosing.
Aims: As the risk for CAR T cell-related toxicities will also decrease with reduction of tumor burden, we intended to develop TMs with prolonged half-life that might ease clinical application and improve elimination of residual tumor cells in late phase of tumor therapy.
Methods: We constructed a set of novel, longer lasting TMs by fusion of different tumor-specific single-chain fragment variables (scFv) and the E5B9 peptide epitope to the Fc domain of human IgG4 antibodies. The resulting IgG4-based TMs were functionally compared with smaller, scFv-based TMs in vitro and characterized for their pharmacokinetic properties in experimental mice.
Results: The novel IgG4-based TMs are able to efficiently activate UniCAR T cells for killing of various tumor cell lines. In comparison to short-lived TMs, they are characterized by a comparable or increased efficiency at low TM concentrations. Pharmacokinetic studies in tumor-bearing mice further revealed that IgG4-based TM have a prolonged plasma half-life and enhanced bioavailability.
Summary: Our data demonstrate that IgG4-based TMs in combination with smaller TMs are highly promising tools for redirection of UniCAR T cells to various cancer cells. Once the tumor burden is reduced, UniCAR T cells can be combined with IgG4-based TMs instead of small TMs. This is more convenient for patients as IgG4-based TM have not to be continuously infused due to their prolonged serum half-lives. Overall, the combination of UniCAR T cells with TMs of different size and specificity should allow a more convenient, individualized and safe treatment regimen of cancer patients.
  • Open Access Logo Lecture (Conference)
    Tumorimmunology meets Oncology (TIMO) XV, 25.-27.04.2019, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30271
Publ.-Id: 30271


What we can learn from the ’f’ in f-elements

Drobot, B.ORC; Steudtner, R.; Raff, J.ORC; Brendler, V.ORC; Bauer, A.; Bok, F.ORC; Patzschke, M.ORC; Tsushima, S.ORC
An introduction of spectroscopy with f-elements (actinides/lanthanides)
  • Invited lecture (Conferences)
    14. PhD seminar Kompetenzverbundes für Kerntechnik Ost, 05.12.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30270
Publ.-Id: 30270


Gilbert damping in NiFeGd compounds: Ferromagnetic resonance versus time-resolved spectroscopy

Salikhov, R.; Alekhin, A.; Parpiiev, T.; Pezeril, T.; Makarov, D.ORC; Abrudan, R.; Meckenstock, R.; Radu, F.; Farle, M.; Zabel, H.; Temnov, V. V.
Engineering the magnetic properties (Gilbert damping, saturation magnetization, exchange stiffness, and
magnetic anisotropy) of multicomponent magnetic compounds plays a key role in fundamental magnetism
and its applications. Here, we perform a systematic study of (Ni81Fe19 )100−xGdx films with x = 0%, 5%, 9%,
and 13% using ferromagnetic resonance (FMR), element-specific time-resolved x-ray magnetic resonance, and
femtosecond time-resolved magneto-optical pump-probe techniques. The comparative analysis of field and
time domain FMR methods, with complimentary information extracted from the dynamics of high-frequency
exchange magnons in ferromagnetic thin films, is used to investigate the dependence of Gilbert damping on the
Gd concentration.
Keywords: Gilbert damping; Ferromagnetic resonance

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Permalink: https://www.hzdr.de/publications/Publ-30263
Publ.-Id: 30263


A review on stretchable magnetic field sensorics

Melzer, M.; Makarov, D.ORC; Schmidt, O. G.
The current establishment of stretchable electronics to form a seamless link between soft or
even living materials and the digital world is at the forefront of multidisciplinary research
efforts, bridging physics, engineering and materials science. Magnetic functionalities can
provide a sense of displacement, orientation or proximity to this novel formulation of
electronics. This work reviews the recent development of stretchable magnetic field sensorics
relying on the combination of metallic thin films revealing a giant magnetoresistance effect
with elastomeric materials. Stretchability of the magnetic nanomembranes is achieved
by specific morphologic features (e.g. wrinkles or microcracks), which accommodate the
applied tensile deformation while maintaining the electrical and magnetic integrity of the
sensor device. The entire development, from the demonstration of the world’s first elastically
stretchable magnetic sensor to the realization of a technology platform for robust, ready-touse
elastic magnetosensorics is described. Soft giant magnetoresistive elements exhibiting the
same sensing performance as on conventional rigid supports, but with fully strain invariant
properties up to 270% stretching have been demonstrated. With their unique mechanical
properties, these sensor elements readily conform to ubiquitous objects of arbitrary shapes
including the human skin. Stretchable magnetoelectronic sensors can equip soft and epidermal
electronic systems with navigation, orientation, motion tracking and touchless control
capabilities. A variety of novel technologies, like electronic skins, smart textiles, soft robotics
and actuators, active medical implants and soft consumer electronics will benefit from these
new magnetic functionalities.
Keywords: shapeable magnetic field sensors, stretchable electronics

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Permalink: https://www.hzdr.de/publications/Publ-30262
Publ.-Id: 30262


Neutron Fluence Calculations for the Dismantling and Decommissioning of a German PWR

Rachamin, R.; Konheiser, J.; Barkleit, A.; Marcus, S.;
Presentation at AAA Workshop 02.12.2019
Keywords: Decommissioning studies, Neutron fluence, Monte-Carlo
  • Open Access Logo Lecture (Conference)
    AAA Workshop, GRS GmbH, 02.12.2019, Garching, Germany

Permalink: https://www.hzdr.de/publications/Publ-30261
Publ.-Id: 30261


Curvilinear magnetic nanomembranes: fundamentals and technologies

Makarov, D.ORC
Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films and nanowires where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system [1-3]. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics [4] for automotive but also virtual and augmented reality appliances [5-8]. The balance between the fundamental and applied inputs stimulates even further the development of new theoretical methods and novel fabrication/characterization techniques [9-11].
In this talk, recent fundamental and technological advancements in this exciting research field will be reviewed.

[1] R. Streubel et al., Magnetism in curved geometries. J. Phys. D: Appl. Phys. (Review) 49, 363001 (2016).
[2] D. Sander et al., The 2017 magnetism roadmap. J. Phys. D: Appl. Phys. (Review) 50, 363001 (2017).
[3] O. M. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism. Phys. Rev. Lett. 123, 077201 (2019).
[4] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Review) 3, 011101 (2016).
[5] G. S. Cañón Bermúdez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
[6] G. S. Cañón Bermúdez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[7] P. N. Granell et al., Highly compliant planar Hall effect sensor with sub 200 nT sensitivity. npj Flexible Electronics 3, 3 (2019).
[8] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[9] R. Streubel et al., Retrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies. Nature Communications 6, 7612 (2015).
[10] T. Kosub et al., All-electric access to the magnetic-field-invariant magnetization of antiferromagnets. Phys. Rev. Lett. 115, 097201 (2015).
[11] T. Kosub et al., Purely antiferromagnetic magnetoelectric random access memory. Nature Communications 8, 13985 (2017).
Keywords: shapeable magnetoelectronics, curved magnetic nanomembranes
  • Lecture (others)
    Seminar at the Key Lab of Magnetic Materials and Devices, 01.11.2019, Ningbo, China

Permalink: https://www.hzdr.de/publications/Publ-30260
Publ.-Id: 30260


Fundamentals and applications of curved magnetic thin films

Makarov, D.ORC
Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films and nanowires where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system [1-3]. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics [4] for automotive but also virtual and augmented reality appliances [5-8]. The balance between the fundamental and applied inputs stimulates even further the development of new theoretical methods and novel fabrication/characterization techniques [9-11].
In this talk, recent fundamental and technological advancements in this exciting research field will be reviewed.

[1] R. Streubel et al., Magnetism in curved geometries. J. Phys. D: Appl. Phys. (Review) 49, 363001 (2016).
[2] D. Sander et al., The 2017 magnetism roadmap. J. Phys. D: Appl. Phys. (Review) 50, 363001 (2017).
[3] O. M. Volkov et al., Experimental observation of exchange-driven chiral effects in curvilinear magnetism. Phys. Rev. Lett. 123, 077201 (2019).
[4] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Review) 3, 011101 (2016).
[5] G. S. Cañón Bermúdez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
[6] G. S. Cañón Bermúdez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[7] P. N. Granell et al., Highly compliant planar Hall effect sensor with sub 200 nT sensitivity. npj Flexible Electronics 3, 3 (2019).
[8] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[9] R. Streubel et al., Retrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies. Nature Communications 6, 7612 (2015).
[10] T. Kosub et al., All-electric access to the magnetic-field-invariant magnetization of antiferromagnets. Phys. Rev. Lett. 115, 097201 (2015).
[11] T. Kosub et al., Purely antiferromagnetic magnetoelectric random access memory. Nature Communications 8, 13985 (2017).
Keywords: curvilinear magentism, magnetic field sensors, shapeable magnetoelectronics
  • Lecture (others)
    Seminar at the Department of Materials Science, 11.11.2019, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-30259
Publ.-Id: 30259


Flexible electronics: from interactive on-skin devices to bio/medical applications

Makarov, D.ORC
Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study fundamentals of 3D curved magnetic thin films [1] and explore their application potential for flexible electronics, eMobility and health. We put forth the concept of shapeable magnetoelectronics [2] for various applications ranging from automotive [3] through consumer electronics to virtual and augmented reality [4-7] applications. These activities impact several emerging research fields of smart skins, soft robotics and human-machine interfaces.
Highly compliant functional elements are exceptionally suited for bio/medical applications. Very recently we realized an implantable, multifunctional and highly compliant device for targeted thermal treatment of cancer [8]. We fabricated a flexible light weight diagnostic platform based on highly sensitive Si nanowire field effect transistors revealing remarkable limit of detection at 40 pM for Avian Influenza Virus (AIV) subtype H1N1 DNA sequences [9].
For the emerging field of biosensing technologies, we developed droplet-based magnetofluidic platforms encompassing integrated novel functionalities [10] including analytics in a flow cytometry format [11], magnetic barcoding and sorting of magnetically encoded emulsion droplets using flexible microfluidic devices [12]. These features are crucial to address the needs of modern medical research, e.g. drug discovery.

[1] R. Streubel et al., J. Phys. D: Appl. Phys. (Review) 49, 363001 (2016)
[2] D. Makarov et al., Appl. Phys. Rev. (Review) 3, 011101 (2016).
[3] M. Melzer et al., Adv. Mater. 27, 1274 (2015).
[4] G. S. Cañón Bermúdez et al., Science Advances 4, eaao2623 (2018).
[5] G. S. Cañón Bermúdez et al., Nature Electronics 1, 589 (2018).
[6] P. N. Granell et al., npj Flexible Electronics 3, 3 (2019).
[7] J. Ge et al., Nature Communications 10, 4405 (2019).
[8] G. S. Cañón Bermúdez et al., Adv. Eng. Mater. 21, 1900407 (2019).
[9] D. Karnaushenko et al., Adv. Healthcare Mater. 4, 1517 (2015).
[10] G. Lin, D. Makarov et al., Lab Chip (Review) 17, 1884 (2017).
[11] G. Lin, D. Makarov et al., Small 12, 4553 (2016).
[12] G. Lin, D. Makarov et al., Lab Chip 14, 4050 (2014).
Keywords: flexible electronics, magentic field sensors
  • Invited lecture (Conferences)
    Workshop on Active and Passive Materials for Tissue Engineering and Biomedical Applications, 30.10.2019, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-30258
Publ.-Id: 30258


Thermal Stability of Defect-Enhanced Ge on Si Quantum Dot Luminescence upon Millisecond Flash Lamp Annealing

Spindlberger, L.; Prucnal, S.; Aberl, J.; Brehm, M.;
The intentional merging of epitaxial Ge on Si(001) quantum dots with optically active defect sites promises low-cost applications such as room temperature (RT)light emitters in Si photonics. Despite recent progress in this field, important benchmarks, for example, the thermal stability of such a combination of low-dimensional nanosystems, as well as the curing of parasitic charge-carrier recombination channels, have been barely investigated thus far. Herein, the structural robustness of defect-enhanced quantum dots (DEQDs) is examined under millisecond flash lamp annealing (FLA), carried out at sample temperatures up to 800oC. Changes in the optical DEQD properties are investigated using photoluminescence spectroscopy performed in a sample temperature range from10 to 300 K. It is demonstrated that FLA—in contrast to in situ thermal annealing—leads to only negligible modifications of the electronic band alignment. Moreover, upon proper conditions of FLA, the RT emission intensity of DEQDs is improved by almost 50% with respect to untreated reference samples.
Keywords: Ge QDs, MBE, FLA, PL

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Permalink: https://www.hzdr.de/publications/Publ-30256
Publ.-Id: 30256


Modification of optical, electrical and structural properties of two-dimensional materials using millisecond range flash lamp annealing

Prucnal, S.; Juanmei, D.; Tsai, H.-S.; Chia-Nung, K.; Chin, S. L.; Zhou, S.;
The two-dimensional materials with direct band gap are attractive for optoelectronics operated in the visible and near infrared spectral range. The number of new van der Waals crystals increases systematically but the doping and the modification of their optoelectronic properties remain challenging. Here we present the tuning of the fundamental properties of different 2D mono- and dichalcogenides using millisecond range flash lamp annealing (FLA) in the controlled atmosphere. Those investigated 2D flakes are made by mechanical exfoliation onto the SiN/Si substrates. The change of internal properties of 2D chalcogenides is monitored by micro-Raman, photoluminescence and photoreflectance spectroscopies as well as conductive atomic force microscope (c-AFM). Using ms-range FLA in N2 ambient the transition metal dichalcogenides are stable up to the annealing at 1200 oC, while upon high temperature annealing the group IV-dichalcogenides can be reduced to monochalcogenides which opens new route for the fabrication of heterostructures. The formation of SnSe/SnSe2 heterostructures is proven by micro-Raman spectroscopy and current-voltage characteristic obtained by c-AFM measurements.
Keywords: 2D materials, MoSe2, MnPS3, FLA, ion implantation, Raman spectroscopy
  • Lecture (Conference)
    EMRS Fall Meeting 2019, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30255
Publ.-Id: 30255


Tuning of the photocatalytic efficiency in anatase-TiO2 using millisecond range flash lamp annealing

Prucnal, S.; Gago, R.; Esteban-Mendoza, D.; Jiménez, I.; Aktas, O. C.; Faupel, F.; Zhou, S.;
Semiconducting metal oxides often exhibit high photocatalytic efficiency (PE) and, among them, the anatase-TiO2 (A-TiO2) is the most promising material for the water splitting under sun light illumination. The PE of TiO2-based materials mainly depends on the surface state density, Fermi level position, band gap and crystalline structure (anatase, rutile, brookite). Here, we present the optical, electrical and structural properties of A-TiO2 thin films made by RT magnetron sputtering followed by ms-range flash lamp annealing (FLA) in N2 ambient. X-ray diffraction (XRD), X-ray absorption near-edge structure, and Raman spectroscopies reveal the transformation from amorphous to single-phase A-TiO2 during FLA for 20 ms. The FLA energy density was in the range of 65 to 110 Jcm-2, corresponding to peak temperatures in the range of 500oC to 1100 oC, respectively. XRD and scanning electron microscopy shows that with increasing FLA energy the average crystal size of the A-TiO2 increases from a few nm?s up to ~200 nm after annealing at energy density of 110 Jcm-2. On the other hand, the optical band-gap, as determined by spectroscopic ellipsometry, remains at ~3.4 eV. The bleaching of methylene blue under irradiation with a high-intensity light-emitting-diode (4.5 W/cm2) at 365 nm has been used to test the photoactivity of the samples after FLA. The PE of the samples is enhanced with increasing the annealing temperature, which we assign to the engineering of surface states and carrier lifetime upon FLA in N2 ambient.
Keywords: TiO2, doping, FLA,
  • Poster
    EMRS Fall Meeting 2019, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30254
Publ.-Id: 30254


Band gap renormalization in n-type Ge and GeSn alloys made by millisecond range flash lamp annealing

Prucnal, S.; Berencen, Y.ORC; Wang, M.ORC; Rebohle, L.ORC; Kudrawiec, R.; Polak, M.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Grenzer, J.; Turek, M.; Droździel, A.; Pyszniak, K.; Zuk, J.; Helm, M.; Skorupa, W.; Zhou, S.ORC
The last missing piece of puzzle for the full functionalization of group IV optoelectronic devices is the direct band gap semiconductor made by CMOS compatible technology. Here we report on the fabrication of GeSn alloys with a Sn concentration of up to 6 % using ion implantation followed by ms-range explosive solid phase epitaxy. The n-type single crystalline GeSn alloys are made by co-doping of Sn and P into Ge. Both the activation of P and the formation of GeSn are performed during a single-step flash lamp annealing for 3 ms. The band gap engineering in ultra-doped n-type Ge and GeSn alloys is theoretically predicted by density functional theory and experimentally verified using ellipsometric spectroscopy. We demonstrate that both the diffusion and the segregation of Sn and P atoms in Ge are fully supressed by ms-range non-equilibrium thermal processing.
Keywords: Ge, GeSn, ion implantation, FLA, Raman
  • Poster
    EMRS Fall Meeting 2019, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30253
Publ.-Id: 30253


Evolution of donor-vacancy clusters in Ge, GeSn and SiGeSn during ms-range FLA monitored by positron annihilation spectroscopy

Prucnal, S.; Liedke, M. O.; Wang, X.; Posselt, M.ORC; Knoch, J.; Berencen, Y.ORC; Rebohle, L.ORC; Napolitani, E.; Frigerio, J.; Ballabio, A.; Isella, G.; Hübner, R.; Wagner, A.; Zuk, J.; Turek, M.; Helm, M.; Zhou, S.ORC
The n-type doping of Ge and Ge-based alloys is a self-limiting process due to the formation of vacancy-donor complexes (DnV with n ≤ 4) that deactivate the donors. This work clearly demonstrates that the dissolution of the DnV clusters in a heavily n-doped Ge, GeSn and SiGeSn layers can be achieved by millisecond-flash lamp annealing. This DnV cluster dissolution results in a considerable increase of the electrical activation together with a suppression of donor diffusion. Using electrical measurements and positron annihilation lifetime spectroscopy, combined with theoretical calculations, it is possible to address, understand and solve the fundamental problem of achieving ultra-high doping level in Ge, that has hindered so far the full integration of Ge and Ge-based alloys with complementary-metal-oxide-semiconductor technology.
Keywords: Ge, GeSn alloy, defects, flash lamp annealing, ion implantation
  • Lecture (Conference)
    EMRS Fall Meeting 2019, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30251
Publ.-Id: 30251


Dissolution of donor-vacancy clusters in heavily doped n-type germanium via millisecond annealing

Prucnal, S.; Liedke, M. O.; Butterling, M.; Posselt, M.; Wang, X.; Knoch, J.; Windgassen, H.; Hirschmann, E.; Berencén, Y.; Napolitani, E.; Frigerio, J.; Ballabio, A.; Isella, G.; Hübner, R.; Wagner, A.; Helm, M.; Zhou, S.;
The n-type doping of Ge is self-limiting process due to formation of the vacancy-donor complexes (Dn V with n≤4). Here we report on experiments and density functional theory (DFT) calculations solving the basic problem of donor deactivation in heavily doped Ge. The self-healing process of heavily doped n-type Ge is achieved by rear-side flash lamp annealing (r-FLA) for 20 ms with the peak temperature of about 1050 K. The positron-annihilation lifetime spectroscopy (PALS) reveals that the P4V clusters are main defects in the as-grown Ge:P samples. Millisecond range high-temperature treatment dissociates the phosphorus-vacancy cluster (P4V) and, as shown by SIMS, fully supress the P diffusion. The electrochemical capacitance-voltage (ECV) profiling shows that the effective carrier concentration in P doped Ge (P concentration - 1×1020 cm-3) increases from about 3×1019 cm-3 in as-grown sample to above 8×1019 cm-3 after r-FLA. For the first time using structural (PALS, SIMS) and electrical (ECV) characterization combined with DFT calculations we were able to addressed, explained and solved the fundamental problem hindering the full integration of Ge with CMOS technology.
Keywords: ion implantation, germanium, FLA, defects
  • Lecture (Conference)
    Gettering and Defect Engineering in Semiconductor Technology, 22.-27.09.2019, Zeuthen, Germany

Permalink: https://www.hzdr.de/publications/Publ-30249
Publ.-Id: 30249


Range Verification in Particle Therapy – From Physics in the Lab Towards Clinical Applications

Kögler, T.ORC
Reichweiteverifikation ist ein wesentlicher Baustein zur Reduzierung der Sicherheitssäume in der Partikeltherapie. Da eine direkte Messung der Reichweite schwerer geladener Teilchen im menschlichen Gewebe schwierig ist, ist man derzeit auf den Informationsgehalt von Sekundärstrahlung angewiesen, die bei der Abbremsung der primären Teilchen im Körper entstehen.
Die durch Kernwechselwirkungen entstehende prompte Gammastrahlung ist hierfür ein vielversprechende Sonde.
Mehrere Ansätze zur Verifikation der Reichweite von therapeutischen Protonen mittels prompter Gammastrahlung wurden in den vergangenen Jahren untersucht. Bisher wurde erst eine, das Prompt Gamma Ray Timing, erfolgreich am Patienten angewendet. Andere Methoden befinden sich kurz vor den ersten klinischen Anwendungen.
Auf dem Weg von der Idee eines Reichweiteverifikationsverfahrens bis hin zu dessen klinischer Implementierung ist es jedoch ein langer und schwieriger Weg. Dieser Beitrag zeigt welche Schwierigkeiten bei der erfolgreichen Einführung eines derartigen Systems in den klinischen Alltag existieren und geht dabei auf mehrere konkrete Beispiele ein.
Keywords: Range verification, proton therapy, prompt gamma rays
  • Invited lecture (Conferences)
    Young Investigator's Workshop on Photon Detection in Medicine and Medical Physics, 02.-03.12.2019, Siegen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30248
Publ.-Id: 30248


The role of microlayer for bubble sliding in nucleate boiling: A new view point for heat transfer enhancement via surface engineering

Ding, W.ORC; Zhang, J.; Sarker, D.; Hampel, U.
In an experimental study with a stainless steel heater (surface with maximum roughness Rt = 0.82 µm and contact angle hysteresis θhys = 53°), we investigated the bubble growth and motion during nucleation and departure. Complementary to that we analysed the formation of microlayer during the bubble growth and motion with computational fluid dynamics (CFD) simulation. From the simulations we found that the bubble motion leads to an expansion of the microlayer. From the experiments we obtained the drag coefficient on the bubble during bubble growth with an assumption of the absence of the wall surface tension force. From the comparison of this drag coefficient and the proposed values from the literature, we conclude that the vapour bubble does not directly contact the solid wall during the sliding. Using well-known mechanistic bubble growth models for further analysis of available microlayer area with the experimental data we conclude that a microlayer exists and the bubble must slide completely on this microlayer after leaving its originating cavity. From the change of microlayer size we can also explain the bubble regrowth after departure.
Keywords: Wall boiling; Bubble sliding; Microlayer; Nucleation;

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  • Secondary publication expected from 01.03.2021

Permalink: https://www.hzdr.de/publications/Publ-30246
Publ.-Id: 30246


Cerebral Oxygen Metabolism in Adults with Sickle Cell Disease

Václavů, L.; Petr, J.ORC; Petersen, E. T.; Mutsaerts, H. J. M. M.; Majoie, C. B. L.; Wood, J. C.; Vanbavel, E.; Nederveen, A. J.; Biemond, B. J.
In sickle cell disease (SCD), oxygen delivery is impaired due to anemia, especially during times of increased metabolic demand, and cerebral blood flow (CBF) must increase to meet changing physiologic needs. But hyperemia limits cerebrovascular reserve (CVR) and ischemic risk prevails despite elevated CBF. The cerebral metabolic rate of oxygen (CMRO 2 ) reflects oxygen supply and consumption so may be more insightful than flow-based CVR measures for ischemic risk in SCD. We hypothesized that adults with SCD have impaired CMRO 2 at rest and that a vasodilatory challenge with acetazolamide would improve CMRO 2 . CMRO 2 was calculated from CBF and oxygen extraction fraction (OEF), measured with arterial spin labeling and T 2 -prepared tissue relaxation with inversion recovery (T 2 -TRIR) MRI. We studied 36 adults with SCD without a clinical history of overt stroke and 9 healthy controls. As expected, CBF was higher in patients with SCD versus controls (mean ± standard deviation: 74±16 vs 46±5 mL/100g/min, P<.001), resulting in similar oxygen delivery (SCD: 377±67 vs controls: 368±42 μmol O 2 /100g/min, P=.69). OEF was lower in patients versus controls (27±4 vs 35±4 %, P<.001), resulting in lower
CMRO 2 in patients versus controls (102±24 vs 127±20 μmol O 2 /100g/min, P=.002). After acetazolamide, CMRO 2 declined further in patients (P<.01) and did not decline significantly in controls (P=.78), indicating that forcing higher CBF worsened oxygen utilization in SCD patients. This lower CMRO 2 could reflect variation between healthy and unhealthy vascular beds in terms of dilatory capacity and resistance whereby dysfunctional vessels become more oxygen-deprived, hence increasing the risk of localized ischemia.

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Permalink: https://www.hzdr.de/publications/Publ-30245
Publ.-Id: 30245


Ferromagnetic writing on B2 Fe50Rh50 thin films using ultra-short laser pulses

Schmeink, A. H.ORC; Eggert, B.; Ehrler, J.; Mawass, M.; Hübner, R.; Potzger, K.; Lindner, J.; Fassbender, J.; Kronast, F.; Wende, H.; Bali, R.
The chemically ordered B2 Fe50Rh50 alloy is antiferromagnetic. By
inducing chemical disorder its structure can be changed to the ferromagnetic
A2 structure. Following the laser writing method published
here [1] we used a pulsed laser to induce ferromagnetism locally in
Fe50Rh50 thin films of 10, 20, and 30nm thickness. XMCD measurements
on the laser-treated region revealed the formation of an annulus
of FM contrast and a non-FM center. Transmission electron microscopy
(TEM) on a section through the annulus found the FM region to be
A2 and the enclosed non-contrast region of the fcc A1 structure. The
surrounding untreated region remained in the B2 structure.
  • Poster
    DPG Frühjahrstagung Regensburg, 31.03.-05.04.2019, Regensburg, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-30244
Publ.-Id: 30244


Supervised machine learning for the quantification of mineral phases in drill-core hyperspectral data

Tusa, L.; Khodadadzadeh, M.ORC; Contreras Acosta, I. C.; Fuchs, M.; Gloaguen, R.ORC; Gutzmer, J.ORC
Discovery and delineation of new ore deposits require substantial investment into diamond-drilling. Traditionally, the extracted drill-cores are visually analysed by site geologists and subjected to geochemical analyses for metal grade evaluation. Frequently, the geochemical information is insufficient for the evaluation of the mineralization and system morphology, mineralogical information being therefore required. Traditional mineralogical analyses such as optical microscopy, scanning electron microscopy, and X-ray diffraction are time consuming, require extensive sample preparation and deliver non-continuous point information. Due to its fast acquisition time, low sample handling requirements, and non-invasive character hyperspectral drill-core scanning has recently become an efficient tool for lithological / alteration drill core logging. Most commonly used for drill core scanning are visible to near-infrared (VNIR) and short-wave infrared (SWIR) hyperspectral sensors. These sensors allow the identification of mineral groups that show a specific signature as they absorb parts of the incoming light between 400 and 2500 nm. Many of the spectrally active minerals such as white micas, chlorites, epidotes or gypsum play an important role in exploration mapping as they have specific associations with the ore minerals and strong zonality in their distribution within the deposit. They can, therefore, be used as proxies for exploration vectoring and ore deposit modelling. Their compositional analysis and quantification has thus become an important tool for exploration. Commonly used methods for mineral abundance estimation from hyperspectral data consist in unmixing algorithms, which strongly rely on endmember extraction techniques. However, the obtained endmembers in hyperspectral drill-core data using conventional tools usually consist of mineral mixtures due to the spatial resolution of most hyperspectral sensors; the unmixing results will thus only define abundances of mixed compositions.
We propose a supervised machine learning-based methodology that uses the abundance of SWIR active mineral groups in selected representative known areas of the drill-core samples for predicting the content of these groups at the drill-core scale.
The training data consists of high-resolution scanning electron microscopy-based mineral maps resampled to the resolution of the hyperspectral image. As a result, the resampled image contains in each pixel the abundance of each selected mineral or mineral group. An artificial neural network-based regression is used in order to upscale the mineral abundances from the training set to the entire drill-core sample. Preliminary results show a great potential for automation and allow for the evaluation of the individual abundance of each mineral or mineral group.
  • Contribution to proceedings
    EGU General Assembly, 07.-12.04.2019, Vienna, Austria
    Supervised machine learning for the quantification of mineral phases in drill-core hyperspectral data
  • Poster
    EGU General Assembly, 07.-12.04.2019, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-30243
Publ.-Id: 30243


Evaluating the performance of hyperspectral short-wave infrared sensors for the pre-sorting of complex ores using machine learning methods

Tusa, L.; Kern, M.ORC; Khodadadzadeh, M.ORC; Blannin, R.; Gloaguen, R.ORC; Gutzmer, J.ORC
Sensor-based sorting is increasingly used for the concentration of ores. To assess the sorting performance for a specific ore type, the raw materials industry currently conducts trial-and-error batch tests. In this study, a new methodology to assess the potential of hyperspectral visible to near-infrared (VNIR) and short-wave infrared (SWIR) sensors, combined with machine-learning routines to improve the sorting potential evaluation, is pre- sented. The methodology is tested on two complex ores. The first is a tin ore in which cassiterite—the target mineral—is variable in grain size, heterogeneously distributed and has no diagnostic response in the VNIR-SWIR range of the electromagnetic spectrum. However, cassiterite is intimately associated with SWIR active minerals, such as chlorite and fluorite, which can be used as proxies for its presence. The second case study consists of a copper-gold porphyry, where copper occurs mainly in chalcopyrite, bornite, covellite and chalcocite, while gold is present as inclusions in the copper minerals and in pyrite. Machine-learning techniques such as Random Forest and Support Vector Machine applied to the hyperspectral data predict excellent sorting results in terms of grade and recovery. The approach can be adjusted to optimize sorting for a variety of ore types and thus could increase the attractivity of VNIR-SWIR sensor sorting in the minerals industry.
Keywords: Sensor-based sorting, Hyperspectral imaging, SWIR, Machine learning, Complex ores
  • Minerals Engineering 146(2020)
    DOI: 10.1016/j.mineng.2019.106150
  • Contribution to proceedings
    MEI Physical Separation, 13.-14.06.2019, Fallmouth, United Kingdom
  • Lecture (Conference)
    MEI Physical Separation, 13.-14.06.2019, Fallmouth, United Kingdom

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  • Secondary publication expected from 15.01.2021

Permalink: https://www.hzdr.de/publications/Publ-30242
Publ.-Id: 30242


Mineral Mapping and Vein Detection in Hyperspectral Drill-Core Scans: Application to Porphyry-Type Mineralization

Tusa, L.; Andreani, L.ORC; Khodadadzadeh, M.ORC; Contreras Acosta, I. C.; Ivascanu, P.; Gloaguen, R.ORC; Gutzmer, J.ORC
The rapid mapping and characterization of specific porphyry vein types in geological
samples represent a challenge for the mineral exploration and mining industry. In this paper, a
methodology to integrate mineralogical and structural data extracted from hyperspectral drill-core
scans is proposed. The workflow allows for the identification of vein types based on minerals
having significant absorption features in the short-wave infrared. The method not only targets
alteration halos of known compositions but also allows for the identification of any vein-like
structure. The results consist of vein distribution maps, quantified vein abundances, and their
azimuths. Three drill-cores from the Bolcana porphyry system hosting veins of variable density,
composition, orientation, and thickness are analysed for this purpose. The results are validated using
high-resolution scanning electron microscopy-based mineral mapping techniques. We demonstrate
that the use of hyperspectral scanning allows for faster, non-invasive and more efficient drill-core
mapping, providing a useful tool for complementing core-logging performed by on-site geologists.
Keywords: hyperspectral imaging; drill-core; mineral mapping; short-wave infrared; porphyry-type veins

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Permalink: https://www.hzdr.de/publications/Publ-30241
Publ.-Id: 30241


Ligand-Exchange-Mediated Fabrication of Gold Aerogels Containing Different Au(I) Content with Peroxidase-like Behavior

Fan, X.; Cai, B.; Du, R.; Hübner, R.; Georgi, M.; Jiang, G.; Li, L.; Samadi Khoshkhoo, M.; Sun, H.; Eychmüller, A.;
Noble-metal aerogels are emerging functional porous materials that have been applied in diverse fields. Among them, gold (Au) aerogels have displayed grand potentials in a wide range of catalytic processes. However, current fabrication methods fall short in obtaining Au gels with small ligament sizes and controlled surface valence states, which hinder the study of the underlying catalytic mechanisms. Here, a new approach of producing Au aerogels is reported. Via a two-phase ligand exchange, the long-chain ligands (oleylamine) of the as-prepared Au nanoparticles were replaced by short sulfide ions and subsequently self-assembled into three-dimensional gels. As a result, Au aerogels with small ligament sizes (ca. 3−4 nm) and tunable surface valence states are acquired. Taking the application for peroxidase mimics as an example, by correlating the surface valence with the catalytic properties, Au(I) is found to be the active site for H2O2 and substrate-binding site for 3,3′,5,5′-tetramethylbenzidine, paving a new avenue for on-target devising Au-based catalysts.

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Permalink: https://www.hzdr.de/publications/Publ-30240
Publ.-Id: 30240


Linear stability analysis of magnetized relativistic rotating jets

Bodo, G.; Mamatsashvili, G.; Rossi, P.; Mignone, A.;
We carry out a linear stability analysis of a magnetized relativistic rotating cylindrical jet flow using the approximation of zero thermal pressure. We identify several modes of instability in the jet: Kelvin-Helmholtz, current-driven and two kinds of centrifugal-buoyancy modes - toroidal and poloidal. The Kelvin-Helmholtz mode is found at low magnetization and its growth rate depends very weakly on the pitch parameter of the background magnetic field and on rotation. The current-driven mode is found at high magnetization, the values of its growth rate and the wavenumber, corresponding to the maximum growth, increase as we decrease the pitch parameter of the background magnetic field. This mode is stabilized by rotation, especially, at high magnetization. The centrifugal-buoyancy modes, arising due to rotation, tend also to be more stable when magnetization is increased. Overall, relativistic jet flows appear to be more stable with respect to their non-relativistic counterpart.
Keywords: instabilities; MHD; galaxies: jets; Astrophysics - High Energy Astrophysical Phenomena

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-30239
Publ.-Id: 30239


Application of Flash Lamp Annealing for Controlled Nickel Silicidation of Silicon Nanowires

Khan, M. B.; Deb, D.; Prucnal, S.; Erbe, A.; Georgiev, Y.ORC
Silicon (Si) nanowires (NWs) have potential applications in various areas including electronics, opto-electronics and biochemical sensing. These wires are used to fabricate electronic devices with new architectures to complement the scaling down of electronic circuits. Our work focuses on one such architecture called Reconfigurable field effect transistors (RFET). An RFET is a Nickel(Ni)Si2-Si-NiSi2 Schottky junctions based device, which has an intrinsic Si channel. To fabricate an RFET, SiNWs are silicided at both ends to form Schottky junctions with the Si channel. Typically, it has two gates placed on each of the two Schottky junctions. It can be tuned to p- or n- polarity by applying appropriate electrostatic potential at one of the gates. Therefore, functional complexity and performance of electronic circuits can be enhanced using such FETs. Formation of NiSi2 is a pre-requisite for proper operation of these devices because metal work function of NiSi2 aligns itself near the mid-bandgap of Si. This enables band bending by application of an appropriate electrostatic potential for the operation of devices either as p- or as n- FET. We report our results on Ni silicidation using flash lamp annealing. By optimizing the silicidation process, control over the diffusion of Ni into the nanowire and proper silicide phase formation is achieved.
  • Open Access Logo Lecture (Conference)
    DPG-Frühjahrstagung, Regensburg, 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30238
Publ.-Id: 30238


Fabrication and Characterization of Reconfigurable Field Effect Transistors

Khan, M. B.; Prucnal, S.; Hübner, R.; Erbe, A.; Georgiev, Y.ORC
To complement scaling of field effect transistors, new device concepts were introduced recently. One such concept is the reconfigurable field effect transistor (RFET). These transistors are based on nickel silicide-Si-nickel silicide Schottky junctions and their polarity can be switched between p- and n- type at runtime by the application of an electrostatic potential [1]. Control over silicide length and phase is important for scaling and proper functioning of these devices [2]. NiSi2 is the desirable silicide phase as its metal work function aligns itself near mid bandgap of Si, which enables reconfigurability of the device [1, 3].
We report on fabrication and electrical characterization results of RFETs. Si nanowires (SiNWs) are fabricated on undoped silicon-on-insulator (SOI) substrates by a top-down process based on electron beam lithography and inductively coupled plasma etching. Then, Ni is placed at both ends of the SiNWs by metal evaporation and lift-off processes. Afterwards, flash lamp annealing (FLA) is performed for silicidation of the NWs.
FLA has enabled better control over silicidation length since flash times are much shorter (of the order of milli-seconds) than rapid thermal annealing (RTA) times. Transmission electron microscopy (TEM) shows the formation of the desired NiSi2 phase near the silicide-Si interface. Electrical characterization of the devices with back gating shows ambipolar behaviour. For unipolar behaviour, top gates need to be fabricated, results of which will be presented at the conference.
Keywords: Schottky junction; reconfigurability; field effect transistors; nickel silicide; annealing
  • Open Access Logo Poster
    45th International Conference on Micro and Nano Engineering (MNE), 23.09.-26.12.2019, Rhodes, Greece

Permalink: https://www.hzdr.de/publications/Publ-30237
Publ.-Id: 30237


Understanding the role of carbon in active trap centre formation in porous alumina for ion beam dosimetry

Bhowmick, S.; Pal, S.; Das, D.; Singh, V.; Khan, S.; Hübner, R.; Roybarman, S.; Kanjilal, D.; Kanjilal, A.;
In recent days, due to increased use of hadron therapy for cancer and tumor treatment, precise online dose monitoring is an important issue for safety purpose. Regarding hadron therapy, recently carbon ion beam with high Linear Energy Transfer (LET) is found to be more effective than the photon beams. Among several known TL/OSL oxides phosphors, C-doped alumina (Al2O3) is favorable for radiation dosimetry, especially in medical field due to its tissue equivalent in terms of radiation absorption, simple glow curve, and high sensitivity. A facile approach to improve thermoluminescence sensitivity of electrochemically anodized porous Al2O3 (AAO) is presented by introducing carbon ions for ion beam dosimetry. Initially, ion implantation technique has been carried out for Carbon doping in AAO in controlled manner. HAADF-STEM, EDS mapping, SEM studies reveal the evolution of a porous structure followed by the carbon distribution up to 200 nm. However, the evolution of optically active F+ centres with increasing ion fluence has been examined by photoluminescence investigation at room temperature and thermoluminescence (TL) measurement while the chemical nature of such defect centres has been extracted by depth dependent XPS analysis.
  • Lecture (Conference)
    APS March Meeting 2019, 04.-08.03.2019, Boston, MA, USA

Permalink: https://www.hzdr.de/publications/Publ-30236
Publ.-Id: 30236


Ion beams for information technology

Zhou, S.ORC
Taking the advancing of accelerator technologies, a variety of ions (all stable elements and some radioactive elements) in a wide energy range from eV to GeV can be produced and injected into targets. Using the chemical effect of injected ions, “ion implantation" has been well established to dope semiconductors and integrated into the standard microelectronics production line in Si-chip technology. Ion irradiation refers to using other effects rather than the doping effect in materials and has been used for defect (or lifetime) engineering in microelectronics. Moreover, ion beams are also instrument for the analysis of solid state surfaces to get the information about the composition and impurity lattice location. In this talk, I will give some examples for the application of ion beams in information technologies. The following topics will be included: (1) Doping semiconductors well above the solid solidity limits: by doing so the semiconductors can be ferromagnetic or superconducting [1-5]. (2) Defect engineering in SiC: defects can carry magnetic moments giving possibilities for ferromagnetic coupling in SiC as well as for manipulating single defect center for quantum technology [6, 7]. (3) Defect engineering in oxides: it can introduce uniaxial strain and change the properties rather than by choosing different growth substrates [8, 9]. It is worthy to note that ion beam technology has been well developed for applications at wafer (450 mm) scale. Once the proof-of-concept is done, these applications mentioned above can be easily transferred to industries.

[1] M. Khalid, et al., Phys. Rev. B 89, 121301(R) (2014).
[2] S. Zhou, J. Phys. D: Appl. Phys. 48, 263001(2015).
[3] Y. Yuan, et al., Phys. Rev. Materials 1, 054401 (2017).
[4] M. Wang, et al., Phys. Rev. Applied. 11, 054039 (2019).
[5] S. Prucnal, et al., Phys. Rev. Materials 3, 054802 (2019).
[6] S. Zhou, X. Chen, J. Phys. D: Appl. Phys. 52, 393001 (2019).
[7] C. Kasper, et al., arXiv:1908.06829v1 (2019).
[8] P. Pandey, et al., APL Materials 6, 066109 (2018).
[9] C. Wang, et al., Topological Hall effect in single thick SrRuO3 layers induced by defect engineering, submitted (2019).
  • Lecture (others)
    Invited seminar at Institute of Semiconductors, CAS, 14.11.2019, Beijing, China
  • Lecture (others)
    Invited seminar at Tsinghua Univ., 15.11.2019, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-30233
Publ.-Id: 30233


Extended room-temperature infrared photoresponse in hyperdoped Si by ion implantation

Zhou, S.ORC
Presently, silicon photonics requires photodetectors that are sensitive in a broad infrared range, can operate at room temperature, and are suitable for integration with the existing Si technology process. Here, we demonstrate strong room-temperature sub-bandgap photoresponse of photodiodes based on Si hyperdoped with chacolgen ions. The epitaxially recrystallized hyperdoped Si layers are developed by ion implantation combined with pulsed laser melting and incorporate Se/Te dopant concentrations several orders of magnitude above the solid solubility limit. With increasing the impurity concentration, the hyperdoped Si is changed from insulating to quasi-metallic with a finite conductivity as the temperature tends to zero. The optical absorptance is found to increase monotonically with increasing dopant concentration and extends well into the mid-infrared range. Temperature-dependent optoelectronic photoresponse unambiguously demonstrates that the extended infrared photoresponsivity from hyperdoped Si p-n photodiodes is mediated by an impurity band within the upper half of the Si bandgap. This work contributes to pave the way towards establishing a Si-based broadband infrared photonic system operating at room temperature.
References: Sci. Reports 7, 43688 (2017), Phys. Rev. Appl. 10, 024054 (2018) and Adv. Mater. Inter. 5, 1800101 (2018), Phys. Rev. Applied 11, 054039 (2019).
  • Invited lecture (Conferences)
    14TH NATIONAL CONFERENCE ON LASER TECHNOLOGY AND OPTOELECTRONICS, 17.-20.03.2019, Shanghai, China
  • Invited lecture (Conferences)
    2nd International Conference on Radiation and Emission in Materials, 15.-18.12.2019, Bangkok, Thailand

Permalink: https://www.hzdr.de/publications/Publ-30232
Publ.-Id: 30232


Ion irradiation effect in complex oxides: Another degree of freedom or complexity?

Zhou, S.ORC; Wang, C.ORC; Pandey, P.; Chang, C. H.; Ganesh, R.; Chen, D.; Gemming, S.ORC; Chu, Y.-H.; Helm, M.
Inter-relations among charge, spin, orbital and lattice parameters are largely demonstrated in multi-functional oxide materials, which exhibit a variety of exotic properties, ranging from superconductivity, insulator-metal transition, colossal magnetoresistance, charge ordering, and orbital ordering, etc. In particular, tilting a delicate energy balance in lattice interactions and kinetics, achieved by temperature, pressure or chemical control, may result in exotic phenomena in these systems. However, fine-tailoring such interactions has proven difficult. In this context, defect engineering by ion irradiation, which can introduce strain and electronic disorder, has emerged as a powerful technique to fine tune complex phases of oxide thin films. In this contribution, we show that ion irradiation can modify the magnetic and electrical transport properties in a broad variety of materials, including spinel NiCo2O4, perovskite BiFeO3, SrRuO3 and LaNiO3 [1-4]. Diverse magnetic, structure and magneto-transport modifications, which are inaccessible by conventional film growth methods, have been obtained. For instance, the transport in LaNiO3 can be driven from metallic phase into an Anderson insulator by directly tuning the electronic mean free path via irradiation-induced disorder [4]. In BiFeO3, we have obtained a super-tetragonal phase with the largest c/a ratio ~ 1.3 that has ever been experimentally achieved in BiFeO3 [2]. This may lead to strong polarization enhancement. By comparing the effect in different materials, we will also point out the complexity in understanding the tailoring of oxides by ion beams.

Reference
[1] P. Pandey, Y. Bitla, M. Zschornak, M. Wang, C. Xu, J. Grenzer, D. C. Meyer, Y. Y. Chin, H. J. Lin, C. T. Chen, S. Gemming, M. Helm, Y. H. Chu, S. Zhou, Enhancing the Magnetic Moment of Ferrimagnetic NiCo2O4 via Ion Irradiation driven Oxygen Vacancies, APL Materials 6, 066109 (2018)
[2] C. Chen, C. Wang, X. Cai, C. Xu, C. Li, J. Zhou, Z. Luo, Z. Fan, M. Qin, M. Zeng, X. Lu, X. Gao, U. Kentsch, P. Yang, G. Zhou, N. Wang, Y. Zhu, S. Zhou, D. Chen, J. Liu, Controllable defect driven symmetry change and domain structure evolution in BiFeO3 with enhanced tetragonality, Nanoscale 11, 8110 (2019)
[3] C. Wang, C. Chen, C.-H. Chang, H.-S. Tsai, P. Pandey, C. Xu, R. Böttger, D. Chen, Y.-J. Zeng, X. Gao, M. Helm, S. Zhou, Defect-induced exchange bias in a single SrRuO3 layer, ACS Appl. Mater. Interfaces, 27472 (2018).
[4] C. Wang, C.-H. Chang, A. Huang, P.-C. Wang, P.-C. Wu, L. Yang, C. Xu, P. Pandey, M. Zeng, R. Böttger, H.-T. Jeng, Y.-J. Zeng, M. Helm, Y.-H. Chu, R. Ganesh, S. Zhou, Tunable disorder and localization in the rare-earth nickelates, Phys. Rev. Materials 3, 053801 (2019)
  • Lecture (Conference)
    64th Annual Conference on Magnetism and Magnetic Materials, 03.-08.11.2019, Las Vegas, US
  • Lecture (others)
    Seminar talk at DESY, 06.-07.05.2019, Hamburg, DE

Permalink: https://www.hzdr.de/publications/Publ-30231
Publ.-Id: 30231


Ferromagnetism and Anisotropic Spinodal Phase Separation in (In,Fe)As

Yuan, Y.; Hübner, R.; Birowska, M.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.ORC
We report on the experimental observation and theoretical studies of a self-assembled Fe-rich (In,Fe)As nano-lamellar structure that is driven by anisotropic spinodal decomposition at the growth front during laser heating-induced recrystallization of Fe-implanted InAs [1]. Pseudomorphically embedded in the InAs lattice, those Fe-rich nano-lamellae are perpendicular to the (001) surface and parallel to the in-plane [110] crystallographic direction. The Fe atoms are substitutionally incorporated at the indium sites. Magnetic measurements indicate a typical blocked superparamagnetic behavior suggesting strong ferromagnetic orderings inside the Fe-rich nanostructures, but weak coupling between the nano-lamellae. Our findings explain the surprisingly high apparent Curie temperatures and unexpected eight-fold symmetry of crystalline anisotropic magnetoresistance found previously in Be-doped n-type (In,Fe)As grown by molecular beam epitaxy [2]. Prompted by these results we discuss how a different d-level electronic configuration of Fe in InAs and Mn in GaAs [3] affects the magnetic ion incorporation and spatial distribution and, thus, magnetism and anisotropy. Our results also indicate that the directional distribution of impurities or alloy components setting in during the growth may account for the observed nematicity in other classes of correlated systems.

Reference
[1] Y. Yuan, R. Hübner, M. Birowska, C. Xu, M. Wang, S. Prucnal, R. Jakiela, K. Potzger, R. Böttger, S. Facsko, J.A. Majewski, M. Helm, M. Sawicki, S. Zhou, T. Dietl, Nematicity of correlated systems driven by anisotropic chemical phase separation, in Phys. Rev. Materials 2, 114601 (2018).
[2] Pham Nam Hai, D. Sasaki, Le Duc Anh, and M. Tanaka, Crystalline anisotropic magnetoresistance with twofold and eight-fold symmetry in (In,Fe)As ferromagnetic semiconductor, Appl. Phys. Lett. 100, 262409 (2012).
[3] M. Birowska, C. Śliwa, J. A. Majewski, and T. Dietl, Origin of Bulk Uniaxial Anisotropy in Zinc-Blende Dilute Magnetic Semiconductors, Phys. Rev. Lett. 108, 237203 (2012).
  • Lecture (Conference)
    64th Annual Conference on Magnetism and Magnetic Materials, 03.-08.11.2019, Las Vegas, US

Permalink: https://www.hzdr.de/publications/Publ-30230
Publ.-Id: 30230


Near-Surface Cobalt Implantation Into Amorphous Carbon Films: Observation Of Complex Magnetic Nanostructures And Multiple Magnetic Phases

Suschke, K.; Gupta, P. G. S.; Williams, G. V. M.; Hübner, R.; Kennedy, J.; Markwitz, A.;
Magnetic nanoclusters in amorphous carbon have promising applications for highly responsive magnetic sensors, where decreasing the size of the nanoclusters can lead to superparamagnetism and therefore low remanence. The insulating properties (wide bandgap) of amorphous carbon are also potentially useful for designing high frequency components. Both these properties are crucial to achieve ultra-high density magnetic data storage.

High fluence (1.2×1017 Co/cm2) near-surface implantation of 30 keV Co ions into amorphous carbon results in the formation of complex magnetic nanostructures and multiple magnetic phases. Next to small segregated cobalt carbide nanoclusters, starting forming at a depth of 25 nm within the amorphous carbon film, a nearly continuous network of cobalt carbide thin nanocrystalline regions can be observed at a depth of 8 nm. On the surface a 3 nm thin cobalt oxide nanostructured layer is seen separated from the cobalt carbide by a 1 nm thin Co-depleted region. TEM and magnetic measurements show superparamagnetic nanoclusters with a blocking temperature of 5 K. However, a small proportion of larger cobalt carbide nanoclusters exhibits magnetic hysteresis even at room-temperature. The magnetic saturation moment is as high as 0.51 µB/Co at 2 K and 0.32 µB/Co at room temperature - ten times larger than previously reported on hydrogenated amorphous carbon [1]. The structural disorder of the nanoparticles results in a spin glass behaviour with a range of transition temperatures below ~70 K, suggesting a spin disordered shell model [2]. Thus high fluence Co-implantation into amorphous carbon at room temperature created complex magnetic nanostructures consisting of cobalt oxide and cobalt carbide. Multiple magnetic phases such as superparamagnetism, spin glass, ferromagnetism and also antiferromagnetism can be observed.

References:
1. P.G. Sridhar Gupta, G.V.M. Williams and A. Markwitz, Journal of Physics D: Applied Physics, 2016, 49, 5, 055002.
2. T. Prakash, G.V.M. Williams, J. Kennedy and S. Rubanov, Materials Research Express, 2016, 3, 12, 126102.
  • Lecture (Conference)
    9th International Conference on Advanced Materials and Nanotechnology, AMN9, 10.-14.02.2019, Wellington, New Zealand

Permalink: https://www.hzdr.de/publications/Publ-30228
Publ.-Id: 30228


Probing the role of bound excitons in optical properties of titanium dioxide anatase from first principles

Sruthil, L. S. B.; Devaraj, M.; Posselt, M.ORC; Alok, S.
The electronic structure and optical spectra of anatase titanium dioxide is computed by combining state-of-the-art density functional theory (DFT) and many-body perturbation theory (MBPT). Excitonic optical spectra is computed by solving Bethe-SalpeterEquation (BSE). From the solution of BSE and also from the analysis of charge distribution the photo-generated excitons in anatase is shown to be strongly bound and localized. Such typical behavior of intrinsic excitons in bulk anatase makes it a material which shows superior performance in photo catalysis, photovoltaics, optoelectronics and in nonlinear optical regime.
Keywords: Excitons, optical properties, titanium dioxide, first-principle calculations
  • Poster
    64th DAE Solid State Physics Symposium, 18.-22.12.2019, Jodhpur, Rajasthan, India

Permalink: https://www.hzdr.de/publications/Publ-30225
Publ.-Id: 30225


Correlative microscopy of relevant ex-vivo and in-vitro biological systems by multimodal optical and high resolution ion/electron based techniques

Podlipec, R.; Klingner, N.; Heller, R.; Kriselj, A.; Pelicon, P.; Strancar, J.; von Borany, J.;
Correlative microscopy combining light and electron microscopy (CLEM) has become one of the important and unmissable tools in various investigations of complex biological systems revealing high-resolution structural and highly-specific functional information [1]. In the last years more combinations of other advanced techniques have been developed, such as combining optical microscopy with atomic force spectroscopy/microscopy (AFM) or with magnetic resonance imaging, etc [2] whereas in our study multimodal optical microscopy has been correlated with ion and electron based techniques such as is helium ion microscopy (HIM) [3]. The purpose for using combination of the complementary techniques was to elucidate or better interpret specific biological problems which could not be explained just by one technique lacking of whether resolution, sensitivity of specificity. We focused on toxicology related scientific questions of how inhaled nanoparticles interact with lung epithelial cells/tissue once get into direct contact and why interactions can eventually lead to diseases and potentially persistent inflammation [4,5]. In order to better understand the interaction on nanometer scales we first developed proper lung in-vitro model which was followed by proper sample preparation for efficient correlative microscopy using multimodal optical microscopy and high resolution HIM microscopy. By latter we managed to image single metal oxide nanoparticles on cell surfaces interacting with cell membranes, while functional information of the same events was prior measured with confocal and super-resolution optical microscopy. Besides, we implemented described correlative microscopies also for scientific problem related to rejection of hip implants where material debris is found everywhere in the surrounding periprosthetic tissue with lack of knowledge what happens on a molecular scale. The latest findings of both ongoing studies will be presented.

References:

1. P. de Boer, JP Hoogenboom, BNG Giepmans, Nature Methods 12, 503-513 (2015).
2. T Ando, et. Al, Journal of Physics D: Applied physics 44, (2018)
3. G Hlawacek. et Al. Helium Ion Microscopy. J. Vac. Sci. Technol. 32, (2014)
4. Li, X., Jin, L. & Kan, H. Air pollution: a global problem needs local fixes. Nature 570, 437–439 (2019).
5. E Underwood. The polluted brain. Science 355, 342–345 (2017).
Keywords: CLEM, Helium Ion Microscopy, FLIM microscopy, lung epithelium, TiO2 nanotubes, hip implants, periprosthetic tissue, metal debris
  • Invited lecture (Conferences)
    Seminar of Croatian Biophysical Society, 16.12.2019, Zagreb, Croatia

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Permalink: https://www.hzdr.de/publications/Publ-30224
Publ.-Id: 30224


Upscaling High-Resolution Mineralogical Analyses to Estimate Mineral Abundances in Drill Core Hyperspectral Data

Khodadadzadeh, M.ORC; Gloaguen, R.ORC
In this paper, we propose a supervised learning method for estimating mineral quantities in drill core hyperspectral data. Our proposed method links the high-resolution mineralogical analyses and hyperspectral data to learn a dictionary. The learned dictionary is then used for linear unmixing and estimating mineral abundances of the entire drill core sample. To evaluate the performance of the proposed method, we use a drill core data set, which is composed of the VNIR-SWIR hyperspectral data and high-resolution mineralogical analyses performed by a Scanning Electron Microscopy (SEM) instrument equipped with the Mineral Liberation Analysis (MLA) software. The quantitative and qualitative analysis of the experimental results shows that the proposed method provides reliable mineral quantity estimates.
Keywords: Hyperspectral drill core data, highresolution mineralogical analysis, upscaling, dictionary learning
  • Contribution to proceedings
    IGARSS 2019-2019 IEEE International Geoscience and Remote Sensing Symposium, 28.07.-02.08.2019, Yokohama, Japan, Japan

Permalink: https://www.hzdr.de/publications/Publ-30223
Publ.-Id: 30223


Zustandsüberwachung von Transport- und Lagerbehältern für abgebrannte Brennelemente und wärmeentwickelnde HAW bei verlängerter Zwischenlagerung – strahlungsbasierte, thermographische und akustische Messverfahren

Wagner, M.; Fiß, D.; Schmidt, S.; Reinicke, S.; Kratzsch, A.; Hampel, U.;
Bis ein Endlager in tiefen geologischen Formationen zur Verfügung steht, besteht in Deutschland Bedarf für die sichere Zwischenlagerung abgebrannter Brennelemente an den Kraftwerksstandorten. Es wird davon ausgegangen, dass erhebliche Zeiträume von mehr als 50 Jahren zu berücksichtigen sind. Dadurch ergeben sich verschiedene regulatorische und sicherheitstechnische Fragestellungen. Eine davon ist die nach der Langzeitintegrität der Brennelemente in den Behältern. Ihre Beantwortung hat direkte Relevanz für den späteren Transport zum Endlager und die Umladung des abgebrannten Kernbrennstoffs in andere Behälter. Im Rahmen des vom BMWi geförderten Vorhabens DCS-MONITOR untersuchen wir Potenziale und Grenzen von nichtinvasiven Verfahren zur Überwachung des Zustands des radioaktiven Inventars von Trockenlagerbehältern. Als solche betrachten wir die Thermographie, strahlungsbasierte Messverfahren sowie akustische Messverfahren.
  • Invited lecture (Conferences)
    Fachworkshop Zwischenlagerung, 22.-23.10.2019, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30222
Publ.-Id: 30222


Development of novel α-CEA target modules (RevTMs) for the switchable RevCAR system

González Soto, K. E.;
Cancer is one of the main causes of death and represents a worldwide health problem. Most
of the cancer-related deaths are associated with the appearance and progression of a solid
tumor. Even though effective conventional treatments exist, they share a common drawback,
which is their incapacity to strictly distinguish between malignant and healthy cells. Since it
was observed that immune cells are capable to eliminate cancer cells, extensive research
has been made to retarget immune cells towards malignant cells without damaging healthy
tissue. This type of approach is termed as immunotherapy and involves diverse strategies
ranging from the use of Abs to engineered immune cells. One of the most attractive
immunotherapeutic strategies is based on the engineering of T cells to express chimeric
antigen receptors (CARs), which can recognize specific antigens localized on the surface of
cancer cells, leading to an activation of the CAR T cells and a subsequently killing of the
malignant cells. Even though CAR technology has shown a strong potential in targeting
cancer cells during pre-clinical and clinical studies, numerous clinical trials have also
revealed that once they are infused into the patient, the activity of the modified T cells
becomes uncontrollable, which represents the main safety problem from the system. For this
reason, a novel modular and switchable CAR platform, termed as RevCAR system, was
developed in the group of Prof. Bachmann. A crucial element of mentioned system is the
design of the RevCAR. In contrast to conventional CARs, RevCARs lack an extracellular
binding moiety and comprise only a short peptide epitope instead. Thus, RevCAR T cells are
per se inert because they cannot bind to any antigen. Only in the presence of target modules
(RevTMs), which bind on the one hand to the peptide epitope of RevCARs and on the other
hand simultaneously to tumor targets, RevCAR T cells can be redirected and consequently
activated against tumor cells. An attractive tumor-associated antigen (TAA) for the
development of immunotherapies is the carcinoembryonic antigen (CEA), because it is highly
overexpressed on certain cancer types associated with solid tumor formation, such as breast
and lung cancer. In order to show the proof of concept that CEA is an optimal TAA to redirect
the RevCAR system, two different formats of RevTMs (scFv- or IgG-based) were produced
and tested for their functionality. Here we have shown, that both RevTMs were able to
efficiently redirect RevCAR T cells to eliminate CEA-expressing tumor cells in an antigenand
epitope-specific as well as TM-dependent manner. Moreover, here, the IgG4-based
RevTM worked more efficient than the scFv-based RevTM.
  • Master thesis
    HZDR, 2019

Permalink: https://www.hzdr.de/publications/Publ-30213
Publ.-Id: 30213


Off-harmonic optical probing of high intensity laser interaction with cryogenic hydrogen jet target

Bernert, C.; Kraft, S.ORC; Löser, M.ORC; Metzkes-Ng, J.ORC; Obst-Hübl, L.ORC; Rehwald, M.ORC; Schlenvoigt, H.-P.ORC; Siebold, M.; Zeil, K.ORC; Ziegler, T.ORC; Schramm, U.ORC
High-intensity short-pulse lasers in the Petawatt regime offer the possibility to study new compact accelerator schemes by utilizing high-density targets for the generation of energetic ion beams. The optimization of the acceleration process demands comprehensive exploration of the plasma dynamics involved, for example via optical probing. In particular, experiments using low density cryogenic hydrogen jet targets with µm-scale transverse size are well suited to deliver new results which can then be compared to predictive particle-in-cell simulations. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and complicates data analysis. Here, we present a stand-alone probe laser system operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm and its implementation into an experiment dedicated to laser-proton acceleration from the hydrogen jet target irradiated by the DRACO PW laser at Helmholtz-Zentrum Dresden – Rossendorf. We show that the plasma self-emission in the probe images is significantly suppressed and we are able to measure the pre-expansion of the target by the DRACO PW laser for intrinsic and for plasma mirror enhanced laser contrast. The influence of the plasma pre-expansion on the measured proton acceleration performance is presented.
Keywords: optical probing, laser, laser particle acceleration
  • Lecture (Conference)
    European Advanced Accelerator Concepts Workshop, 15.-20.09.2019, Isola d'Elba, Italy

Permalink: https://www.hzdr.de/publications/Publ-30212
Publ.-Id: 30212


Antigen-specific redirection of immune effector cells against GD2-expressing tumors

Metwasi, N.;
Extensive research in the last decades has revealed the dynamic role of the immune system in surveillance, recognition and elimination of cancer cells. However, resistant variants can rise and overcome these immune responses by various escape mechanisms. Therefore, huge efforts have been invested in developing of immunotherapies that can overcome these hurdles and allow the specific activation and retargeting of immune cells toward tumor cells. Immunotherapy includes diverse strategies ranging from cytokines to antibodies and their derivatives reaching to engineered immune cells.
One of the very promising immunotherapeutic approaches is based on the engineering of T cells to express chimeric antigen receptors (CARs) which can redirect immune cells to specific antigens leading to T cell activation and subsequent killing of target cells. The CAR technology has shown a strong therapeutic potential in targeting of cancer both in preclinical as well as clinical studies, especially with hematological malignancies, which lead to FDA approval of CD19-specific CAR T cells for the treatment of leukemia. Despite the success of CAR T cells, clinical trials have also revealed various toxicities and adverse events that can be life-threatening for patients. Moreover, the CAR technology still faces many hurdles to achieve an effective targeting of solid tumors due to the structure, immunosuppressive microenvironment and heterogeneity of the disease. Therefore, a novel modular and switchable CAR platform, called the UniCAR system, was developed in the group of Prof. Bachmann in order to address these obstacles. The UniCAR system consists of UniCAR T cells that cannot bind surface antigens. Instead, UniCARs recognize an epitope (E5B9) which is derived from the nuclear protein La-SS/B. Therefore, UniCAR T cells can only be redirected via target modules (TMs) that have the E5B9 tag on one hand and an antigen-binding domain on the other hand. These TMs provide a bridge with tumor cells that allow the activation of UniCAR T cells. Once these TMs are eliminated, the UniCAR T cells can no more be activated, and thus they are switched off. This approach provides not only a safety switch but also a flexible platform for multi-targeting of diverse antigens by using various TMs with different antigen specificities. Alternatively, the UniCAR system can be applied on NK cells or NK cell lines, which have a natural anti-tumor response. Cell lines like NK-92 are of especial interest because they can be used allogenically, and thus provide an off-the-shelf therapy that might reduce the cost and time of therapy development.
For my thesis work, disialoganglioside GD2 was selected as a target for the UniCAR system. GD2 is overexpressed on many tumors including neuroblastoma, Ewing’s sarcoma, melanoma, osteosarcoma and others. In fact, GD2 is considered as one of the priority antigens to be targeted for cancer therapy according to a pilot project of the national cancer institute. Moreover, targeting GD2 with CAR T cells has shown very positive clinical outcome in previously published clinical trials. However, as other tumor-associated antigens, GD2 has also some limited expression on normal tissues including some regions of the central nervous system and peripheral nerves. Therefore, using a safety switch like the UniCAR system emerges as a necessary step to assure better controlling of any on-target/off-tumor side effects.
Driven by these facts, several formats of anti-GD2 TMs were developed in order to redirect UniCAR T cells to GD2-expressing tumors. Three TMs were designed based on a single chain fragment variable (scFv) connected to the E5B9 epitope. However, they differed in the orientation of the variable light and variable heavy chain domains and their linker components in order to find the best functional conformation. In vitro functional assays showed that all of the three TMs were able to redirect UniCAR T cells toward tumor cells leading to efficient tumor cell killing and release of cytokines in an antigen-specific and TM-dependent manner. Furthermore, the TMs showed dose-dependent killing with half-maximal effective concentration (EC50) in the picomolar range. As all the TM formats showed comparable results in vitro, further in vivo studies were restricted to one TM. This anti-GD2 TM was able to activate UniCAR T cells to eradicate GD2-positive tumor cells in experimental mice. Furthermore, the TM was modified and radiolabeled with 64Cu, in order to investigate its pharmacokinetic properties and biodistribution in tumor-bearing mice. PET analysis of the radiolabeled anti-GD2 TM showed enrichment in the GD2-expressing tumors with blood elimination half-life of less than one hour, which makes it a suitable key for a fast safety switch of UniCAR T cells.
In contrast to UniCAR T cells, the UniCAR NK-92 cell line provides an-off-the shelf therapy that can be expanded for allogenic use. Since these cells are usually irradiated before infusion into patients, their life-span as well as the possibility of side effects is reduced. Therefore, we have further created an IgG4-based anti-GD2 TM with an extended half-life that fits to the life-span of irradiated NK-92 cells. PET imaging of the radiolabeled IgG4-based TM showed an increase in the half-life of about 24 folds in comparison to the scFv TM format. Further testing has shown that UniCAR NK-92 cells are functional with both scFv- and IgG4-based TM formats leading to specific killing of GD2-expressing tumor cells as well as secretion of pro-inflammatory cytokines in vitro. In addition, UniCAR NK-92 showed specific killing of tumor cells in vivo when combined with the anti-GD2 TM.
In summary, we have shown that the UniCAR system can be used to redirect both T cells and NK-92 cells against GD2-expressing tumors in vitro as well as in vivo in an antigen-specific and TM-dependent manner. The UniCAR system allows an on/off safety switch as well as fine controlling of the activity of UniCAR T/NK-92 cells via titration (dosing) of the anti-GD2 TMs. Furthermore, it provides a flexible platform that allows the use of several antibody formats for an effective and safe targeting of cancer.
  • Doctoral thesis
    HZDR, 2019

Permalink: https://www.hzdr.de/publications/Publ-30211
Publ.-Id: 30211


Off-harmonic optical probing of high intensity laser interaction with hydrogen targets using a stand-alone probe laser system

Bernert, C.; Kraft, S.ORC; Löser, M.ORC; Metzkes-Ng, J.ORC; Obst-Hübl, L.ORC; Rehwald, M.ORC; Schlenvoigt, H.-P.ORC; Siebold, M.; Zeil, K.ORC; Ziegler, T.ORC; Schramm, U.ORC
The development of high-intensity short-pulse lasers in the Petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets for the generation of ion beams with multiple 10 MeV energy per nucleon. The optimization of the acceleration process demands comprehensive exploration of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly sensible in the case of cryogenic hydrogen jet targets. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronized probe laser system for off-harmonic probing at the DRACO laser operated at the Helmholtz-Zentrum Dresden–Rossendorf showed promising performance.
Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating (Optigrate Corp) is used as a hybrid stretcher and compressor unit. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ. By deploying the upgraded probe laser system in the laser-proton acceleration experiment with the renewable cryogenic hydrogen jet target, the plasma self-emission could be significantly suppressed while studying the temporal evolution of the expanding plasma jet. Recorded probe images resemble those of z-pinch experiments with metal wires and indicate a sausage-like instability along the jet axis, which will be discussed.
Keywords: optical probing, laser, laser particle acceleration
  • Lecture (Conference)
    SPIE Optics + Optoelectronics 2019, 01.-04.04.2019, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-30210
Publ.-Id: 30210


Stand-alone laser system for off-harmonic optical probing of high intensity laser interaction with cryogenic hydrogen jet targets

Bernert, C.; Kraft, S.ORC; Löser, M.ORC; Metzkes-Ng, J.ORC; Obst-Hübl, L.ORC; Rehwald, M.ORC; Schlenvoigt, H.-P.ORC; Siebold, M.; Zeil, K.ORC; Ziegler, T.ORC; Schramm, U.ORC
The availability of high-intensity short-pulse lasers in the Peta-Watt regime drives the development of new and compact accelerator schemes like for example the generation of multiple 10 MeV proton beams from high-density targets. To optimize the acceleration performance and to pave the way towards medical applications of these particle beams both target and diagnostic development are of great importance. Particularly cryogenic hydrogen jet-targets offer the benefit of being debris-free and capable of high-repetition rate applications. Together with spatially and temporally resolved optical probing techniques this target is most suitable for a comparison to numerical particle-in-cell simulations. However, the strong plasma self-emission often masks the laser-target interaction point and thus complicates the data analysis. Recently, the development of a synchronized stand-alone probe-laser-system operating off the harmonics of the driver laser showed promising performance.
Here we show the performance of an upgraded probe-laser-system operating at a central wavelength of 1030nm far off the fundamental wavelength of the drive laser at 800nm. It consists of a synchronized fs-oscillator and a novel and robust CPA system based on a chirped volume Bragg grating as a hybrid stretcher and compressor unit, chirped mirrors for GDD compensation and a regenerative amplifier with Yb.CaF2 as laser medium. The system delivers 160fs pulse duration together with 0.9mJ energy at a repetition rate of 200Hz.
The application of the upgraded probe-laser-system in an experimental campaign dedicated to laser-proton acceleration together with cryogenic hydrogen jet-targets showed a significant improvement of imaging quality for the laser-target interaction concerning the plasmas self-emission. The recorded probe-images resemble those of z-pinch experiments with metal wires and indicate a sausage-like instability along the hydrogen jet axis.
Keywords: optical probing, laser, particle acceleration
  • Open Access Logo Lecture (Conference)
    DPG Frühjahrstagung, 17.-22.03.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30209
Publ.-Id: 30209


Introducing a novel switchable CAR platform with reduced CAR size for immunotherapy of tumors

Hoffmann, A.; Feldmann, A.ORC; Kittel-Boselli, E.; Bergmann, R.ORC; Koristka, S.; Berndt, N.; Arndt, C.; Rodrigues Loureiro, L. R.; Bachmann, M.ORC
1. Introduction
Recently the use of chimeric antigen receptor (CAR) modified T cells in the immunotherapy of tumors has become a promising approach. CAR T cells are able to recognize tumor-associated antigens (TAAs) in a major histocompatibility-complex (MHC)-independent manner. Although highly efficient, the inability to regulate the activity of CAR T cells can cause severe side effects and thus needs to be considered in future developments. Here, we introduce the RevCAR system – a novel switchable modular universal CAR system having a minimal size to overcome the obstacles of conventional CAR therapy.
2. Objectives
In order to improve the controllability of CAR T cells a modular CAR system, which allows switching the activity of CAR T cells repeatedly “ON” and “OFF”, was generated. Furthermore, to avoid unspecific side effects and minimize tonic signaling of conventional CAR T cells, the extracellular single chain variable fragment (scFv) was removed. Thus, resulting RevCARs have a smaller size allowing “gated” targeting strategies, e.g. by facilitating simultaneous transduction of two independent CARs with different specificities and split motifs, which could further improve the safety of CAR T cells.
3. Materials & methods
In order to reduce the size of the artificial receptor the original idea was to replace the extracellular scFv domain of a conventional CAR with a small peptide epitope and to engage the resulting RevCAR
T cell via a bispecific target module which we termed RevTM. For proof of concept two small peptide epitopes were selected and the respective RevCARs constructed. In addition, a series of different RevTMs was generated. On the one hand the RevTM recognizes one of the two peptide epitopes on the other hand the RevTM can be directed to any potential TAA.
4. Results
Until now a series of RevTMs was constructed and functionally analyzed. RevCAR T cells armed via the respective RevTM were able to efficiently lyse their respective target cells in a peptide epitope and target specific, as well as target module dependent manner. These data are supported by the analysis of cytokine secretion from RevCAR T cells which was only observed in the presence of both target cells and the respective RevTM.
5. Conclusion
Taken together these results demonstrate the high anti-tumor efficiency of the novel RevCAR platform which is characterized by a small size, an improved safety, easy controllability as well as high flexibility.
  • Abstract in refereed journal
    EUROPEAN JOURNAL OF IMMUNOLOGY 49(2019), 266-267
  • Poster
    Annual Meeting of the German Society for Immunology (DGfI 2019), 10.-13.09.2019, München, Deutschland

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  • Secondary publication expected from 12.09.2020

Permalink: https://www.hzdr.de/publications/Publ-30208
Publ.-Id: 30208


Convective and Surface Tension Sub-Filter Scale Models

Meller, R.; Klein, M.ORC; Lucas, D.ORC; Schlegel, F.
Industrial applications feature a huge variety of different flow patterns, such as bubbly flow, slug flow or annular flow. Thereby the issue of a big range of different physical scales is involved. With the objective of reproduction of occurring phenomena with one single multifluid solver, we present an Euler-Euler-approach, which combines a number of different methods for treatment of the partial aspects. The implementation into OpenFOAM is always with focus on sustainable research. A segregated approach is used for treatment of the phase momentum equations, phase fraction equations and the pressure equation, featuring a consistent momentum interpolation scheme (Cubero et al., 2014). To fulfill the kinematic condition at resolved interfaces between different continuous phases, the latter may be coupled by an isotropic drag (Strubelj and Tiselj, 2011). In this case, the immensely strong phase coupling requires an adapted numerical method. The overall objective is to take interactions between the all different aspects, such as disperse phases, resolved interfaces and turbulence with effects on momentum and mass transfer into account.
  • Lecture (others)
    Seminar des Instituts für Mathematik und Rechneranwendungen der Universität der Bundeswehr München, 05.11.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30207
Publ.-Id: 30207


A-Posteriori Assessment of Sub-Filter Scale Models for Turbulence-Interface Interaction with the Two-Fluid Formulation Considering a Single Rising Gas Bubble in Liquid

Meller, R.; Klein, M.ORC; Lucas, D.ORC; Schlegel, F.
Gas-liquid flows are of great importance for a large number of different industrial applications, e.g. in energy sector or metal processing industry. From there arises a strong need for numerical tools, which help to predict dynamics of two-phase flows in technical facilities with high predictive accuracy, reasonable computational expense and without any need for initial knowledge of the present flow regime. A big challenge in investigations of such problems is the large range of interfacial and turbulent scales, which need to be accounted for in numerical simulations. A typical approach to capture all these dynamics and their interactions are multi-scale multi-regime methods, which make use of coupling of different individual modeling concepts.
The overall aim is to adopt the hybrid approach of H ̈ ansch et al. (2012), which combines an Eulerian-Eulerian approach with a volume-of-fluid(VOF)-like method in a two-fluid model in order to represent interfacial structures on subgrid-scale and on grid-scale, respectively. In situations, where transitions between different morphologies occur, interfacial structures appear to be too large for an Eulerian-Eulerian model approach and, at the same time, too small for the flow dynamics to be fully resolved in a VOF-like model. In other words, in the range of mesh scale and slightly above, interfacial and turbulent structures need to be simulated in an under-resolved manner. For this to deliver physically reasonable results, modeling of subgrid-scale (SGS) dynamics becomes necessary.
  • Lecture (Conference)
    Direct and Large Eddy Simulation 12 (DLES12), 05.-07.06.2019, Madrid, Spanien

Permalink: https://www.hzdr.de/publications/Publ-30205
Publ.-Id: 30205


On the enstrophy in a precessing cylinder

Pizzi, F.; Giesecke, A.ORC; Stefani, F.ORC
Within the project DRESDYN (DREsden Sodium facility for DYNnamo and thermohy-
draulic studies) a precession driven a fluid flow of liquid sodium will be examined with regard
to the possibility of serving as source for magnetic field generation. Hydrodynamic studies
and simulations are essential to understand the behaviour of the fluid flow. Here we present
the direct numerical simulations of a fluid flow forced by precession conducted in a cylindrical
domain, with the focus on the relation between dissipation and enstrophy.
Keywords: Precessing Cylinder, enstrophy, flow field
  • Open Access Logo Invited lecture (Conferences)
    9th European Postgraduate Fluid Dynamics Conference, 16.-19.07.2019, Ilmenau, Germany

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Permalink: https://www.hzdr.de/publications/Publ-30204
Publ.-Id: 30204


The Dresdyn Precession Dynamo Experiment

Pizzi, F.; Giesecke, A.ORC; Gundrum, T.; Vogt, T.ORC; Stefani, F.ORC
In the most ambitious experiment of DRESDYN (DREsden Sodium facility
for DYNnamo and thermohydraulic studies) a fluid flow of liquid sodium, solely driven
by precession, will be considered as a possible source for magnetic field generation. Here,
after the description of the experimental facility, we are going to present the results (in
particular the hydrodynamic ones) from the direct numerical simulation conducted in a
cylindrical domain. We will discuss the dynamics of the system and show that the m = 1
Kelvin mode is crucial for the dynamo action. The second part will be dedicated to the
influence of the nutation angle; finally we will quantify the dissipation and the role of
turbulent fluctuations on the flow.
Keywords: cylinder, dissipation, dynamo, precession, turbulence
  • Contribution to proceedings
    11 th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
  • Invited lecture (Conferences)
    11 th PAMIR International Conference - Fundamental and Applied MHD, 01.07.2019, Reims, France

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Permalink: https://www.hzdr.de/publications/Publ-30202
Publ.-Id: 30202


Start-to-end simulations of L|PWFA hybrid accelerator experiments using PIConGPU

Pausch, R.ORC; Debus, A.ORC; Steiniger, K.ORC; Garten, M.ORC; Hübl, A.ORC; Widera, R.ORC; Kurz, T.ORC; Schöbel, S.; Couperus Cabadağ, J. P.ORC; Chang, Y.-Y.; Köhler, A.ORC; Zarini, O.ORC; Heinemann, T.; Gilljohann, M. F.; Ding, H.; Götzfried, J.; Döpp, A.; Kononenko, O.; Raj, G.; Martines De La Ossa, A.; Assmann, R.; Hidding, B.; Karsch, S.; Code, S.; Irman, A.ORC; Schramm, U.ORC; Bussmann, M.ORC
The poster gives an overview of the LPWFA experimental setup and explains in detail the accompanying simulation campaign.
Keywords: LPWFA, hybrid, PIConGPU, ISAAC, alpaka
  • Poster
    CASUS Eröffnungsworkshop, 26.-28.08.2019, Görlitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30200
Publ.-Id: 30200


Current status of the L|PWFA start-to-end simulations using PIConGPU

Pausch, R.ORC; Debus, A.ORC; Steiniger, K.ORC; Garten, M.ORC; Widera, R.ORC; Bussmann, M.ORC
A summary of the LPWFA simulations of the last half year as performed within the hybrid collaboration.
Keywords: PIConGPU, LPWFA, hybrid
  • Lecture (others)
    LPWFA hybrid-collaboration meeting, 04.-05.07.2019, Glasgow, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30199
Publ.-Id: 30199


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