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41421 Publications

Chiral Skyrmion and Skyrmionium States Engineered by the Gradient of Curvature

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

Curvilinear nanomagnets can support magnetic skyrmions stabilized at a local curvature without any intrinsic chiral interactions. Here, we propose an alternative mechanism to stabilize chiral Neel skyrmion states relying on the gradient of curvature. We illustrate our approach with an example of a magnetic thin film with perpendicular magnetic anisotropy shaped as a circular indentation. We show that in addition to the topologically trivial ground state, there are two skyrmion states with winding numbers +/- 1 and a skyrmionium state with a winding number 0. These chiral states are formed due to the pinning of a chiral magnetic domain wall at a bend of the nanoindentation due to spatial inhomogeneity of the curvature-induced Dzyaloshinskii-Moriya interaction. The latter emerges due to the gradient of the local curvature at the bend. While the chirality of the skyrmion is determined by the sign of the local curvature, its radius can be varied in a broad range by engineering the position of the bend with respect to the center of the nanoindentation. We propose a general method, which enables us to reduce the magnetic problem for any surface of revolution to the common planar problem by means of proper modification of constants of anisotropy and Dzyaloshinskii-Moriya interaction.

Permalink: https://www.hzdr.de/publications/Publ-28636
Publ.-Id: 28636


Predictive Geometallurgy: The Role of SEM Based Automated Mineralogy and Statistical Assesment for Mineral Processing

Birtel, S.; Büttner, P.; Bachmann, K.; Kern, M.; Gutzmer, J.

SEM-based image analyses is widely used as major analytical tool to improve the recovery of those constituents (ore minerals) that contain the major products (metals) of existing or planned mining operations and processing plants. Here three very different case studies are presented where SEM based automated mineralogical and microstructural data is combined with complementary analytical data and statistically assessed in order to predict the material behaviour during mineral processing. This approach is applied (1) on the recovery of Sn from a historic flotation tailings storage facility; (2) on by-product recovery from a chromite ore deposit; and (3) on simulated sensor based sorting. The studies were performed by interdisciplinary teams in resource characterization, minerals processing and statistical modelling.

Keywords: SEM-based image analysis; MLA; statistical assesment; geometallury

  • Invited lecture (Conferences)
    Conference in Minerals Engineering 2019, 05.-06.02.2019, Luleå, Sweden
  • Contribution to proceedings
    Conference in Minerals Engineering 2019, 05.-06.02.2019, Luleå, Sweden
    Conference in Minerals Engineering, Luleå: LTU

Permalink: https://www.hzdr.de/publications/Publ-28635
Publ.-Id: 28635


Improved accuracy of prompt-gamma-based range verification system enabling validation of CT-based stopping-power prediction

Berthold, J.; Khamfongkhruea, C.; Petzoldt, J.; Thiele, J.; Hölscher, T.; Wohlfahrt, P.; Pausch, G.; Janssens, G.; Smeets, J.; Richter, C.

Objective:

To improve the accuracy of range verification with prompt-gamma-ray imaging (PGI), enabling the validation of CT-based stopping-power prediction in patients.
Material & Methods:
A PGI-slit-camera system was modified to enhance its positioning accuracy, now using a floor-based docking station. The camera position is calibrated with orthogonal X-rays and its reproducibility was validated with X-ray measurements at two different days with ten repositioning iterations each. To determine the PGI simulation accuracy, the camera position derived with the X-Ray system and PGI-based range shift determination in a PMMA phantom (measured vs. simulated PGI profiles) was correlated.
Subsequently, the PGI system was clinically applied to monitor absolute proton ranges for a 1.5Gy field during eight fractions of a hypo-fractionated prostate-cancer treatment using pencil beam scanning (Fig.1). For all monitored fractions, in-room control CT scans were acquired in treatment position, enabling PGI-based range analysis for the actual patient anatomy.
Results:
The reproducibility of the camera position in beam direction was ±0.55mm (1σ) over different days. A 1.1mm offset in absolute range determination was found. It can be directly identified as simulation accuracy and is corrected in subsequent clinical application. The overall PGI range measurement uncertainty of about 2mm (averaging over multiple spots for global-shift determination) is well below the range prediction uncertainty (3.5%∙Range+2mm). Evaluation of the clinical slit-camera application and the verification of the applied stopping-power prediction using dual-energy CT is ongoing.
Conclusion:
The accuracy of PGI-based range verification was improved to enable the verification of CT-based stopping-power prediction in patients, potentially allowing for a future reduction of currently used range uncertainties.

  • Lecture (Conference)
    PTCOG58 - 58th Annual Conference of the Particle Therapy Co-operative Group, 10.-15.06.2019, Manchester, Großbritannien

Permalink: https://www.hzdr.de/publications/Publ-28634
Publ.-Id: 28634


Dual-energy computed tomography improves delineation in primary brain-tumor patients

Wohlfahrt, P.; Agolli, L.; Krause, M.; Pilz, K.; Richter, C.; Troost, E.

Purpose/Objective:

Dual-energy CT (DECT) improves the accuracy in proton therapy compared to single-energy CT (SECT). Since delineation of tumors and organs-at-risk (OARs) is gaining importance, we assessed whether DECT reduces the intra- and inter-observer delineation variability.
Material/Methods:
Two cohorts of 10 primary brain-tumor patients (adjuvant radio(chemo)therapy) each, receiving either 120kVp SECT or 80/140kVp DECT with identical dose, were evaluated. Four different pseudo-monoenergetic CT (MonoCT) datasets, representing several contrasts, were derived from DECT. Three radiation oncologists delineated the postoperative tumor bed volume (TBV) and several OARs. Delineations on SECT datasets were repeated once to assess intra-observer variability. Finally, delineations were performed on T1/T2-weighted MR scans as clinical reference.
The contour conformity was quantified by Jaccard index (JI) and Hausdorff distance (HD) between the contour intersection and union (Fig.1).
Results:
The median inter-observer TBV conformity (Fig.2A) was almost independent from CT acquisition (HD=6-9mm/JI=61-66%) and comparable to MR (HD=6-7mm/JI = 66-67%). The consistency of brainstem contours (Fig.2B) was best at the lowest energy (median HD=2.8mm/JI=81%). The conformity of parotid glands (Fig.2C) gained slightly from higher energies (0.6mm median HD reduction, 1% JI increase) and led to better results as MR. Smaller inter-observer variations were mostly achieved using the most suitable MonoCT instead of SECT.
The intra-observer TBV variability did not depend on clinical experience. However, less-experienced clinicians are more affected by different tissue contrasts (Fig.2D).
Conclusion:
For primary brain-tumor patients, DECT-derived MonoCT datasets improve intra- and inter-observer delineation conformity compared to SECT. Moreover, they in part led to similar or better results as the gold standard MR.

  • Lecture (Conference)
    PTCOG58 - 58th Annual Conference of the Particle Therapy Co-operative Group, 10.-15.06.2019, Manchester, Großbritannien

Permalink: https://www.hzdr.de/publications/Publ-28633
Publ.-Id: 28633


Chemistry first, Accelerator Mass Spectrometry (AMS) second

Merchel, S.; Rugel, G.; Dreams-Users; Dreams-Friends

Accelerator mass spectrometry (AMS) is the most sensitive analytical method to measure long-lived radionuclides. The detection limits are generally several orders of magnitude better, i.e. as low as 10-16 (radionuclide/stable nuclide), than any other mass spectrometry or decay counting method. AMS needs smaller sample sizes and measurements are finished within a few minutes to hours; though after performing chemical separation of the radionuclide from the sample matrix (ice, snow, rain, ground water, marine sediments, soil, meteorites, deep-sea nodules, lava, rocks). Hence, AMS is right from the start, from sample taking over chemistry and measurements to data interpretation, true interdisciplinary research. Users at the DREAMS (DREsden AMS) facility (www.dresden-ams.de) apply AMS to most diverse projects from astrophysics to Earthquake studies.

Keywords: AMS; radionuclide

Related publications

  • Invited lecture (Conferences)
    52nd annual conference of the German Society for Mass Spectrometry (DGMS), 10.-13.03.2019, Rostock, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-28632
Publ.-Id: 28632


Drastic Fermi-surface reconstruction in Nd-doped CeCoIn5

Green, E.

  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields, 24.-28.06.2018, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-28631
Publ.-Id: 28631


A novel multicaloric cooling cycle that exploits thermal hysteresis

Gottschall, T.

  • Invited lecture (Conferences)
    9th JEMS Conference 2018 (Joint European Magnetic Symposia), 03.-07.09.2018, Mainz, Germany
  • Invited lecture (Conferences)
    Thermag VIII, 16.-20.09.2018, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-28630
Publ.-Id: 28630


Glacial evolution of the Pamir mountains: insights from geomorphology and cosmogenic radionuclide dating

Stübner, K.; Bookhagen, B.; Merchel, S.; Rugel, G.; Aminov, J.

The Pamir mountains at the western end of the Himalaya-Karakorum-Tibet mountain belt are characterized by landscape extremes: The western Pamir has an extreme local relief of >2000 m. The eastern Pamir plateau is a low-relief orogenic plateau at ~4100 m. In most of the Pamir, modern glaciers are small and often are rock glaciers restricted to the north sides of the crests but significant ice caps occur in the eastern Pamir (Muztagh Ata, Kongur Shan) and in the northwestern Pamir, where the Fedchenko glacier is the longest glacier outside the polar regions. Glaciation of the Pamir contrasts with the strong glaciation of the Karakorum ranges farther south reflecting differences in annual precipitation between the Monsoon-influenced Karakorum and the arid, Westerlies-controlled Pamir.
Glacial and glaciogenic sediments that have been mapped throughout the Pamir suggest much more widespread glaciation during the Pleistocene. Cosmogenic radionuclide (CRN) dates indicate that one or several glacial maxima occurred > 100 ka, but the extent of the mid-Pleistocene ice cover is currently not known. While CRN exposure ages of glacially polished bedrock in the west-Pamir valleys suggest that these may have been formed by mid-late Pleistocene Alpine glaciers there is little record of the glacial advances on the east-Pamir plateau. We present new CRN exposure ages that elucidate the glacial and post-glacial history of the Pamir. We also present a geomorphological analysis focusing on the strong east-west difference in topography and on morphological evidence of glaciation in the eastern Pamir. Our analysis sheds light on the landscape evolution and on the competing effects of fluvial and glacial erosion and mass-wasting processes in an arid mountain environment.

Keywords: ANS; TCN; dating; CRN; glacier

Related publications

  • Poster
    European Geosciences Union (EGU) General Assembly 2019, 07.-12.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-28629
Publ.-Id: 28629


Solid oxygon in ultrahigh magnetic fields

Nomura, T.

  • Invited lecture (Conferences)
    CC2018 - 12th International Conference on Cryocrystals and Quantum Crystals, 26.-31.08.2018, Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-28628
Publ.-Id: 28628


Body size-dependent energy storage causes Kleiber’s law scaling of the metabolic rate in planarians

Thommen, A.; Werner, S.; Frank, O.; Philipp, J.; Knittelfelder, O.; Quek, Y.; Fahmy, K.; Shevchenko, A.; Friedrich, B. M.; Jülicher, F.; Rink, J. C.

Kleiber’s law, or the 3/4 -power law scaling of the metabolic rate with body mass, is considered one of the few quantitative laws in biology, yet its physiological basis remains unknown. Here, we report Kleiber’s law scaling in the planarian Schmidtea mediterranea. Its reversible and life history-independent changes in adult body mass over 3 orders of magnitude reveal that Kleiber’s law does not emerge from the size-dependent decrease in cellular metabolic rate, but from a size-dependent increase in mass per cell. Through a combination of experiment and theoretical analysis of the organismal energy balance, we further show that the mass allometry is caused by body size dependent energy storage. Our results reveal the physiological origins of Kleiber’s law in planarians and have general implications for understanding a fundamental scaling law in biology.

Keywords: calorimetry; metabolism; growth

Permalink: https://www.hzdr.de/publications/Publ-28627
Publ.-Id: 28627


Surface Exposure Dating on Waterfalls to Reconstruct the Landscape Evolution of South Central Africa

Olivotos, S.; Niedermann, S.; Mouslopoulou, V.; Merchel, S.; Cotterill, F.; Flugel, T.; Gärtner, A.; Rugel, G.; Scharf, A.; Bookhagen, B.

Northern Zambia and south-eastern Katanga Province (D.R. Congo) comprise a tectonically dynamic landscape, which lies within the southwest extension of the East African Rift System. The seismotectonic research in the area has been minimal, despite the fundamental importance of neotectonics, which controls all landscapes southwest of the Tanganyika graben. Two major sets of fault systems (Mweru and Upemba) were revealed by preliminary Google Earth mapping. The recorded seismicity patterns of both systems, during the last 35 years, indicate their current active behavior.
The novelty of our interdisciplinary project is to combine methods, such as DNA sequencing of selected fish groups to define molecular clocks with surface exposure dating of key landforms using cosmogenic nuclides (CNs). Quartz-rich samples were collected from selected waterfalls with the aim of quantifying exposure ages and erosion rates.
Combined analyses of radionuclides ¹⁰Be and ²⁶Al and stable ²¹Ne are necessary, due to the complex exposure scenarios involving surface erosion or retreat of waterfalls. First results from Northern Zambia indicate burial of a large area for an extended period of time. This specific burial may confirm the existence of a significantly deeper Paleo-Lake Mweru before the modern drainage evolved (Dixey, 1943).
²¹Ne and ¹⁰Be-²⁶Al measurements took place at the GFZ Noble Gas Laboratory and at the Accelerator Mass Spectrometry facility of the HZDR, respectively. ¹⁰Be and ²⁶Al targets were prepared at the CN laboratories of University of Potsdam and HZDR. More results from Northern Zambia will be presented.
References
Dixey F. 1943. South African Geographical Journal 25: 20-41.

Keywords: AMS; DNA; geomorphology; TCN; noble gas; dating

Related publications

  • Poster
    PhD Seminar Geosciences University Potsdam, 25.01.2019, Golm, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28626
Publ.-Id: 28626


Static and dynamic properties of modulated phases in Co/Pt multilayers and their dependence on the total magnetic thickness

Fallarino, L.; Oelschlägel, A.; Arregi, J. A.; Bashkatov, A.; Stienen, S.; Lindner, J.; Gallardo, R.; Landeros, P.; Schneider, T.; Chesnel, K.; Lenz, K.; Hellwig, O.

Ferromagnetic (FM) / non-magnetic multilayers with perpendicular magnetic anisotropy provide an efficient route for controlling magnetism, with highly tunable magnetic properties by changing the individual layer thicknesses or the number of repetitions [1]. During the past years, an extensive work effort has led to an apparently complete understanding of those structures. The majority of these studies, though, utilized very thin FM layers since an in-plane reorientation of the magnetization is expected for larger individual thicknesses. However, for sufficiently thick individual FM layers, the system undergoes a second transition back to out-of-plane orientation [2]. Consequently, we present a study of magnetic properties of [Co(t )/Pt(0.7nm)] multilayers as a function of t thicknesses and Co/Pt bilayer repetitions N. Studying in more detail the influence of the magnetic history on the remanent domain pattern, we determine the range of material properties and magnetic fields where, instead of the typical maze-like domains, a lattice of bubbles is stabilized with extraordinary high density, as depicted in Fig. 1 [3]. The dynamic response of such modulations of the ferromagnetic order parameter is further investigated by ferromagnetic resonance spectroscopy (FMR). We find that the observed FMR modes have a direct correlation to the magnetic phase of the samples and its evolution under the application of a magnetic field, as depicted in Fig.2. Using both micromagnetic modeling and analytical calculations, we are able to quantitatively reproduce our experimental observations, which suggest the existence of localized spin-wave and FMR modes that are dependent on the modulation period as well as on the type of modulation itself [4]. Lastly, we show that such modulations resemble magnonic crystals, where tuning of the band-gap is enabled by the specific magnetic field history.
References: [1] M. T. Johnson et al. Rep. Prog. Phys. 59, 1409 (1996).
[2] L. Fallarino et al. Phys. Rev. B 94, 064408 (2016).
[3] K. Chesnel et al. Phys. Rev. B 98, 224404 (2018).
[4] L. Fallarino et al., accepted in Phys. Rev. B (03/01/2019).

Keywords: Ferromagnetic multilayers; PMA; FMR; VSM; magnetic domains; not collinear spin textures

  • Lecture (Conference)
    2019 Joint MMM-Intermag, 14.-18.01.2019, Washington D.C., United states of America

Permalink: https://www.hzdr.de/publications/Publ-28625
Publ.-Id: 28625


Controlled coexcitation of direct and indirect ultrafast demagnetization in Co/Pd multilayers with large perpendicular magnetic anisotropy

Pan, S.; Hellwig, O.; Barman, A.

Ever since its discovery in 1996, ultrafast demagnetization has ignited immense research interest due to its scientific rigor and technological potential. A flurry of recent theoretical and experimental investigations has proposed direct and indirect excitation processes in separate systems. However, it still lacks a unified mechanism and remains highly debatable. Here, we demonstrate that instead of either direct or indirect interaction, simultaneous and controlled excitation of both direct and indirect mechanisms of demagnetization is possible in multilayers composed of repeated Co/Pd bilayers. Moreover, we are able to modulate demagnetization time (from ∼350 to ∼750 fs) by fluence and thickness-dependent indirect excitation due to heat current flowing vertically downward from top layers, which is combined with an altogether different scenario of direct irradiation. Finally, by regulating the pump wavelength, we can effectively control the contribution of indirect process, which gives a confirmation to our understanding of the ultrafast demagnetization process.

Keywords: ultrafast demagnetization; Co/Pd multilayers

Permalink: https://www.hzdr.de/publications/Publ-28624
Publ.-Id: 28624


Rohstoffe für die Energiewende: Systemische Effekte

van den Boogaart, K. G.; Weigelt, A.

Ziel des Projektteils am Helmholz Institut Freiberg für Resourchentechnologie war ein grundsätzliches Verständnis zu entwickeln für den Zusammenhang zwischen der Endlichkeit prim"arer Rohstoffquellen und dem erh"ohten Rohstoffbedarf der Erneuerbaren Energien und Energiespeicher. Dazu wurden Modelle verwendet, welche basierend auf Datenstrukturen der Lebenszyklusanalyse eine weitere Zeitdimension hinzufügen und so große transiente Veränderungen, wie beispielsweise die Erschöpfung bestimmter Rohstoffquellen zu erfassen. Als besondere Schwierigkeit hat sich herausgestellt, dass diese Beschreibung nur im globalen Kontext sinnvoll wird und dafür bisher nicht genügend Daten vorliegen. Trotz eines quantitativen Modellansatzes konnten daher bisher nur qualitative Ergebnisse erzielt werden: Aufgrund der begrenzten Lebensdauern der Systeme und der unvollständigen Rückgewinnung der Materialien in Recyclingprozessen sind auch erneuerbare Energien nicht vollständig erneuerbar. Die globale Rohstoffverfügbarkeit kann für Technologien, die auf seltenen Metallen (z. B. Dünnschichtsolarzellen, direct-drive Windturbinen) begrenzend wirken. Nur eine gute Mischung verschiedener Technologien kann sicherstellen, dass nicht einzelne Rohstoffquellen überfordert werden. Durch den erhöhten Bedarf an Rohstoffen und Recycling erzeugt das Energiesystem einen sekundären Bedarf an Energie und Landnutzung, welcher aufgrund eine Rückkopplunseffekts erheblich ansteigen kann, wenn einzelne Rohstoffe sich verknappen. Der primäre Rohstoffbedarf steht durch die Änderung der Energiesysteme und die Einführung der Elektromobilität und das Verzögerte des Rücklaufs aus Recycling vor erheblichen Änderungen und Schwankungen in den nächsten Jahrzehnten. Zusammenfassen kann gesagt werden, dass eine Planung der Energiewende immer global gedacht werden muss und immer auch den Rohstoffbedarf und die dadurch generierten sekundären Auswirkungen mitbedenken muss.

Keywords: Energiewende; Rohstoffwirtschaft

  • Lecture (others)
    Arbeitsgruppentreffen Topic 4, Energiesysteme 2050, 16.-17.01.2019, Frankfurt, Deutschlad

Permalink: https://www.hzdr.de/publications/Publ-28623
Publ.-Id: 28623


Ion-trap analog of particle creation in cosmology

Fey, C.; Schätz, T.; Schützhold, R.

We consider the transversal modes of ions in a linear radio-frequency trap where we control the time-dependent axial confinement to show that we can excite quanta of motion via a two-mode squeezing process. This effect is analogous to phenomena predicted to occur in the early universe, in general out of reach for experimental investigation. As a substantial advantage of this proposal in comparison to previous ones we propose to exploit the radial and axial modes simultaneously to permit experimental access of these effects based on state-of-the-art technology. In addition, we propose to create and explore entanglement between the two ions.

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Permalink: https://www.hzdr.de/publications/Publ-28622
Publ.-Id: 28622


Nanoscale Imaging of Antiferromagnetic Order using Single-spin Magnetometry

Shields, B.; Appel, P.; Kosub, T.; Hedrich, N.; Fassbender, J.; Huebner, R.; Makarov, D.; Maletinsky, P.

Nitrogen vacancy microscopy is used to detect tiny magnetic stray fields from antiferromagnetic Cr2O3 thin films. Domains and domain dynamics are reported.

Related publications

  • Poster
    International Conference on Magnetism, 15.-20.7.2018, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-28621
Publ.-Id: 28621


Granularity Effects in Antiferromagnetic Spintronics Devices

Kosub, T.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Lindner, J.; Fassbender, J.; Makarov, D.

thin films of antiferromagnets are notably different than bulk crystals.

Related publications

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 11.-16.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28620
Publ.-Id: 28620


Discrete worldline instantons

Schneider, C.; Torgrimsson, G.; Schützhold, R.

The semiclassical approximation of the worldline path integral is a powerful tool to study non-perturbative electron-positron pair creation in spacetime-dependent background fields. Finding solutions of the classical equations of motion, i.e., worldline instantons, is possible analytically only in special cases, and a numerical treatment is nontrivial as well. We introduce a completely general numerical approach based on an approximate evaluation of the discretized path integral that easily and robustly gives the full semiclassical pair production rate in nontrivial multidimensional fields, and apply it to some example cases.

Permalink: https://www.hzdr.de/publications/Publ-28619
Publ.-Id: 28619


Interaction of a Bose-Einstein condensate with a gravitational wave

Schützhold, R.

Partly motivated by recent proposals for the detection of gravitational waves, we study their interaction with Bose-Einstein condensates. For homogeneous condensates at rest, the gravitational wave does not directly create phonons (to lowest order) but merely affects existing phonons or indirectly creates phonon pairs via quantum squeezing-an effect which has already been considered in the literature. For inhomogeneous condensate flows such as a vortex lattice, however, the impact of the gravitational wave can directly create phonons. This more direct interaction can be more efficient and could perhaps help bring such a detection mechanism for gravitational waves a step closer towards experimental realizability-even though there is still a long way to go. Finally, we argue that super-fluid helium might offer some advantages in this respect.

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Permalink: https://www.hzdr.de/publications/Publ-28618
Publ.-Id: 28618


The CD98 heavy chain is a marker and regulator of head and neck squamous cell carcinoma radiosensitivity

Digomann, D.; Kurth, I.; Tyutyunnykova, A.; Chen, O.; Löck, S.; Gorodetska, I.; Peitzsch, C.; Skvortsova, I.; Negro, G.; Aschenbrenner, B.; Eisenhofer, G.; Richter, S.; Heiden, S.; Porrmann, J.; Klink, B.; Schwager, C.; Dowle, A.; Hein, L.; Kunz-Schughart, L.; Abdollahi, A.; Lohaus, F.; Krause, M.; Baumann, M.; Linge, A.; Dubrovska, A.

Purpose: The heavy chain of the CD98 protein (CD98hc) is encoded by the SLC3A2 gene. Together with the light subunit LAT1, CD98hc constitutes a heterodimeric transmembrane amino acid transporter. High SLC3A2 mRNA expression levels are associated with poor prognosis in patients with head and neck squamous cell carcinoma (HNSCC) treated with radiochemotherapy. Little is known regarding the CD98hc protein mediated molecular mechanisms of tumor radioresistance.
Experimental Design: CD98hc protein expression levels were correlated with corresponding tumor control dose 50 (TCD50) in HNSCC xenograft models. Expression levels of CD98hc and LAT1 in HNSCC cells were modulated by siRNA or CRISPR/Cas9 gene editing. HNSCC cell phenotypes were characterized by transcription profiling, plasma membrane proteomics, metabolic analysis and signaling pathway activation.
Expression levels of CD98hc and LAT1 proteins were examined by immunohistochemical analysis of tumor tissues from patients with locally advanced HNSCC treated with primary radiochemotherapy (RCTx). Primary endpoint was locoregional tumor control (LRC).
Results: High expression levels of CD98hc resulted in an increase in mTOR pathway activation, amino acid metabolism and DNA repair as well as downregulation of oxidative stress and autophagy. High expression levels of CD98hc and LAT1 proteins were significantly correlated and associated with an increase in radioresistance in HNSCC in vitro and in vivo models. High expression of both proteins identified poor prognosis subgroup in patients with locally advanced HNSCC after RCTx.

Keywords: radiotherapy; radiosensitivity; CD98; SLC3A2; LAT1; head and neck squamous cell carcinoma; HNSCC

Permalink: https://www.hzdr.de/publications/Publ-28617
Publ.-Id: 28617


Small samples, nearly no chemistry and a big accelerator: Beryllium‑7 measurements as low as 1 mBq

Merchel, S.; Bemmerer, D.; Querfeld, R.; Steinhauser, G.; Rugel, G.; Scharf, A.; Tiessen, C.

Introduction
Beryllium-7 (T1/2 = 53.22 d), mainly measured via gamma-spectrometry, is used as a (natural) radiotracer for educational and scientific purposes. For samples with lower activities (<0.1 Bq) and especially for natural samples containing both ⁷Be and the longer-lived ¹⁰Be (T1/2 = 1.387 Ma), accelerator mass spectrometry (AMS) is the method-of-choice. Here, we demonstrate that ⁷Be- and ¹⁰Be-AMS can be performed at the Dresden AMS facility (DREAMS) [1,2] on the same chemically prepared BeO from rain water samples collected in Germany.

Results
Detection limits for ⁷Be are as low as 0.6 mBq, which is one-to-two orders of magnitude better than “standard/ordinary” and “sophisticated” decay counting (e.g. in an underground laboratory). Validation measurements by gamma-counting of two larger rainwater samples were in excellent agreement with our AMS results. Uncertainties are usually 6-7% for small samples.
Sample sizes as small as tens of milliliters of rain water can be chemically processed to BeO within a few hours without the need for more expensive, time-consuming and labor-intense methods like ion exchange. Basic steps are: Acidification (of utmost importance), filtration, ⁹Be carrier addition, hydroxide precipitation, washing, drying, ignition, and mixing with Nb. Isobar (⁷Li) suppression by chemistry and AMS is sufficient.

Conclusion and outlook
Both the detection limit and uncertainty can be improved by more precise decay counting measurements of the calibration material (high ⁷Be activities from p-activated Li), the removal of so-called “dummy” steps currently required by the AMS machine software, and better tuning conditions. Our study qualifies AMS at DREAMS for being an ultrasensitive, cheap, and fast detection method for ⁷Be allowing high sample throughput.
Our ⁷Be and ¹⁰Be data clearly showed the very first rain (<5 min) collected being enriched in particulate matter (Fig. 1). Hence, AMS analyzing small samples can be used for time evolution studies of rain. The low detection limit and the high sample throughput will also enable future studies of small timescale phenomena where high-precision measurements of small sample volumes are needed. Further information is given by Tiessen et al. [3].

Figure 1: ⁷Be concentrations of rainwater water samples from Dresden (Drs) and Hannover (Hann). Drs 05_05, Drs 05_06, Drs 2, and Drs 3 were collected at the start of rainfall containing a larger amount of dust. Drs 5 was also from the start of rainfall but after long rain the night before, likely depleting the air of particulate matter. *Both Hannover samples are depleted in ⁷Be due to long collection times and partially missing acidification (Hann only).

Acknowledgements
Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association. We appreciate support of Dominik Güttler, René Ziegenrücker and the DREAMS operator team during AMS-measurements, of Gyürky György (Hungarian Academy of Sciences) for providing ⁷Be for the calibration material, and of BMBF (05K16MG1) and DAAD-RISE Professional (HZDRPH-456) for funding. It was a pleasure to discuss ⁷Be-AMS with Andrew Smith (ANSTO).

References
[1] S. Akhmadaliev et al., Nucl. Instr. Meth. B 294 (2013) 5-10.
[2] G. Rugel et al., Nucl. Instr. Meth. B 370 (2016) 94-100.
[3] C. Tiessen et al., Accelerator mass spectrometry (AMS) for beryllium-7 measurements in smallest rainwater samples, JRNCh, 2018, doi: 10.1007/s10967-018-6371-6.

Keywords: AMS; rain

Related publications

  • Poster
    27th Seminar on Activation Analysis and Gamma Spectrometry (SAAGAS 27), 24.-27.02.2019, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28616
Publ.-Id: 28616


BRCA1 and EZH2 cooperate in regulation of prostate cancer stem cell phenotype

Gorodetska, I.; Lukiyanchuk, V.; Peitzsch, C.; Kozeretska, I.; Dubrovska, A.

Prostate cancer is the second most common malignancy and the sixth leading cause of cancer-related death among men worldwide. Prostate carcinogenesis is driven by the accumulation of genetic and epigenetic aberrations, which regulate cancer cell Transition between a stem- and non-stem-cell state and accelerate tumor evolution. Elevated expression of enhancer of zeste homolog 2 (EZH2) histone methyltransferase, a core member of the Polycomb Repressive Complex 2 (PRC2), results in cancer progression through histone methylation-driven tumor cells de-differentiation. Previous studies demonstrated that Tumor suppressor BRCA1 (breast cancer 1) is a negative regulator of PRC2-dependent H3K27 methylation and that loss of BRCA1 induces population of breast cancer stem cells (CSCs) and enhances aggressiveness of breast tumors. Our recent studies revealed that inhibition of EZH2-mediated histone methylation radiosensitizes prostate CSC population. However, the link between BRCA1 and EZH2 in regulation of prostate CSCs remains elusive. Present study demonstrated that BRCA1 and EZH2 are co-regulated in patients’ tumors and prostate cancer cell lines and cooperate in regulation of CSC phenotype and properties. Knockdown of BRCA1 expression significantly increases the number and the size of tumor spheres. Inhibition of BRCA1 and EZH2 expression leads to enrichment of ALDH (aldehyde dehydrogenase) positive cell population that is, at least partially, attributed to the upregulation of ALDH1A3 protein, whereas treatment with a global histone methylation regulator DZNeP (3-Deazaneplanocin A) abrogates this regulation. We found that EZH2/BRCA1 signaling mechanisms play an important role in the maintenance of prostate CSC properties and may be a promising target for tumor treatment.

Keywords: BRCA1; EZH2; cancer stem cells; prostate cancer; DZNeP

Permalink: https://www.hzdr.de/publications/Publ-28615
Publ.-Id: 28615


BRCA genes: the role in genome stability, cancer stemness and therapy resistance

Gorodetska, I.; Kozeretska, I.; Dubrovska, A.

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were associated with genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.

Keywords: BRCA1; BRCA2; genomic instability; cancer stem cells; cancer treatment

Permalink: https://www.hzdr.de/publications/Publ-28614
Publ.-Id: 28614


Graphene Oxide Functional Nanohybrids with Magnetic Nanoparticles for Improved Vectorization of Doxorubicin to Neuroblastoma Cells

Lerra, L.; Farfalla, A.; Sanz, B.; Cirillo, G.; Vittorio, O.; Voli, F.; Le Grand, M.; Curcio, M.; Pasquale Nicoletta, F.; Dubrovska, A.; Hampel, S.; Iemma, F.; Goya, G.

With the aim to obtain a site-specific doxorubicin (DOX) delivery in neuroblastoma SH-SY5Y cells, we designed an hybrid nanocarrier combining graphene oxide (GO) and magnetic iron oxide nanoparticles (MNPs), acting as core elements, and a curcumin–human serum albumin conjugate as functional coating. The nanohybrid, synthesized by redox reaction between the MNPs@GO system and albumin bioconjugate, consisted of MNPs@GO nanosheets homogeneously coated by the bioconjugate as verified by SEM investigations. Drug release experiments showed a pH-responsive behavior with higher release amounts in acidic (45% at pH 5.0) vs. neutral (28% at pH 7.4) environments. Cell internalization studies proved the presence of nanohybrid inside SH-SY5Y cytoplasm. The improved efficacy obtained in viability assays is given by the synergy of functional coating and MNPs constituting the nanohybrids: while curcumin moieties were able to keep low DOX cytotoxicity levels (at concentrations of 0.44–0.88 µM), the presence of MNPs allowed remote actuation on the nanohybrid by a magnetic field, increasing the dose delivered at the target site.

Keywords: graphene oxide; iron oxide nanoparticles; magnetic targeting; nanohybrids; synergism

Permalink: https://www.hzdr.de/publications/Publ-28613
Publ.-Id: 28613


Subspace Multinomial Logistic Regression Ensemble for Classification of Hyperspectral Images

Khodadadzadeh, M.; Ghamisi, P.; Contreras, C.; Gloaguen, R.

Exploiting multiple complementary classifiers in an ensemble framework has shown to be effective for improving hyperspectral image classification results, especially when the training samples are limited. With a different principle and based on this assumption that hyperspectal feature vectors effectively lie in a low-dimensional subspace, the subspace-based techniques have shown great classification performance. In this work, we propose a new ensemble method for accurate classification of hyperspectral images, which exploits the concept of subspace projection. For this purpose, we extend the subspace multinomial logistic regression classifier (MLRsub) to learn from multiple random subspaces for each class. More specifically, we impose diversity in constructing MLRsub by randomly selecting bootstrap samples from the training set and subsets of the original hyperspectral feature space, which leads to generate different class subspace features. Experimental results, conducted on two real hyperspectral data sets, indicate that the proposed method provides significant classification results in comparison with other state-of-the-art approaches.

Keywords: Hyperspectral images; classification; ensemble-based approaches; subspace multinomial logistic regression; remote sensing

  • Contribution to proceedings
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 22.-27.07.2018, Valencia, Spain

Permalink: https://www.hzdr.de/publications/Publ-28612
Publ.-Id: 28612


Tuning of electrocatalytic properties of MoS2 by chalcogenide ion implantation

Luxa, J.; Mazánek, V.; Mackova, A.; Malinsky, P.; Akhmadaliev, S.; Sofer, Z.

MoS2 is one of the most explored and promising material for electrocatalytic water splitting by hydrogen evolution reaction (HER). However, in its bulk form, MoS2 possesses only poor activity towards HER. Therefore, appropriate treatment has to be employed to tune its catalytic properties. In this study, we report the influence of ion bombardment (S, Se and Te ions) with medium ion energy (400 keV) and various ion fluences (1 × 1014–1 × 1016 ions/cm2) on the electrocatalytic properties of bulk MoS2 crystals. Our results showed that upon irradiation, sulfur vacancies were created. Upon exposure to ambient atmosphere, sulfur vacancies were partially replaced by oxygen, which led to surface oxidation. Nevertheless, samples irradiated using the higher range of ion fluences have generally showed enhanced catalytic HER performance in comparison with untreated MoS2 crystals. Furthermore, we have also demonstrated that ion irradiation/implantation can serve as a tool for doping of MoS2 crystals with Se and Te which can also influence the HER performance. The reported results demonstrate that ion beam irradiation can be used for doping as well as creation of sulfur vacancies in bulk MoS2 crystals which is fundamental for the HER performance.

Keywords: Electrocatalysis; Hydrogen evolution reaction; Ion implantation; MoS2

Related publications

Permalink: https://www.hzdr.de/publications/Publ-28611
Publ.-Id: 28611


Probing plutonium dioxide nanoparticles with various synchrotron methods

Gerber, E.; Romanchuk, A.; Pidchenko, I.; Hennig, C.; Trigub, A.; Weiss, S.; Scheinost, A.; Rossberg, A.; Kalmykov, S.; Kvashnina, K.

Plutonium is one of the most complicated element among actinides. It can exist in four different oxidation states (III, IV, V, VI) under environmental conditions. Due to the small value of standard electrode potentials among these linked oxidation states plutonium can change its oxidation state easily. Moreover, plutonium may exist in several oxidation states simultaneously, which makes its chemistry even more complex.
It was previously shown that plutonium migrates in colloidal form in the subsurface environment with the distance of several kilometers. It turned out that so called “colloidal Pu(IV) polymers” are in fact aggregates of PuO2 nanoparticles with diameters ~ 2 nm. However, the certain structure and stoichiometry of these colloids, as well as presence of other oxidation states but Pu(IV) is still debated.

This contribution will show results of plutonium oxide nanoparticle studies at the large-scale facility – The European Synchrotron (ESRF) by complementary methods that used X-rays in different regimes to probe the Pu oxide nanoparticles. Samples were prepared by rapid chemical precipitation using precursors in the different oxidation states (Pu(III), Pu(IV), Pu(V) and Pu(VI)). These precursors were obtained by chemical reduction or oxidation of Pu stock solution. The obtained nanoparticles were characterized at the different beamlines at the ESRF. It gives the opportunity to study our samples with various techniques: X-ray diffraction (XRD), pair distribution function analysis (PDF), and several types of spectroscopies: high energy resolution fluorescence detection (HERFD) at L3 and M5-edges, X-ray emission spectroscopy (XES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The applying multifold synchrotron methods benefits to discover features, which may be unclear or even indistinguishable, these approach is also crucial to confirm results, obtained with individual methods.
It was found that small (2 nm) nanoparticles are formed from the Pu(III), Pu(IV), Pu(V) aqueous solutions, with the crystal structure close to PuO2, without any other Pu-O contributions or oxidation states of Pu except Pu(IV).

Related publications

  • Lecture (Conference)
    RAD 2019 Conference, 10.-14.06.2019, Herceg Novi, Montenegro

Permalink: https://www.hzdr.de/publications/Publ-28610
Publ.-Id: 28610


Subspace clustering algorithms for mineral mapping

Khodadadzadeh, M.; Contreras, C.; Tusa, L.; Gloaguen, R.

The application of drill core hyperspectral data in exploration campaigns is receiving great interest to obtain a general overview of a mineral deposit. However, the main approach to the investigation of such data is by visual interpretation, which is subjective and time-consuming. To address this issue, recently, the use of machine learning techniques is proposed for the analysis of this data. For drill core samples that for which only very little prior knowledge is often available, applying classification algorithms which are supervised learning methods is very challenging. In this paper, we suggest to use clustering (unsupervised) methods for mineral mapping, which are similar to classification but no predefined class labels are needed. To handle mapping of the very highly mixed pixels in drill core hyperspectral data, we propose to use advanced subspace clustering methods, in which pixels are assumed to lie in a union of low-dimensional subspaces. We conduct a comparative study and evaluate the performance of two well-known subspace clustering methods, i.e., sparse subspace clustering (SSC) and low-rank representation (LRR). For the experiments, we acquired VNIR-SWIR hyperspectral data and applied scanning electron microscopy based Mineral Liberation Analysis (MLA) for two drill core samples. MLA is a high-resolution imaging technique that allows detailed mineral characterization. We use the high-resolution MLA image as a reference to analyze the clustering results. Qualitative analysis of the obtained clustering maps indicates that the subspace clustering methods can accurately map the available minerals in the drill core hyperspectral data, especially in comparison to the traditional k-means clustering method.

Keywords: Mineral mapping; drill core; hyperspectral data; subspace clustering; remote sensing

  • Contribution to proceedings
    SPIE Image and Signal Processing for Remote Sensing XXIV, 10.-13.09.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28609
Publ.-Id: 28609


High-precision image-guided proton irradiation of mouse brain sub-volumes

Suckert, T.; Müller, J.; Beyreuther, E.; Bütof, R.; Dietrich, A.; Gotz, M.; Haase, R.; Schürer, M.; Tillner, F.; Krause, M.; Lühr, A.; von Neubeck, C.

Purpose:

Proton radiotherapy offers the potential to reduce normal tissue toxicity. However, clinical safety margins, range uncertainties and varying relative biological effectiveness (RBE) may result in a critical dose in tumor-surrounding normal tissue. To assess potential adverse effects in preclinical studies, we established stereotactic proton mouse brain irradiation and a cell-based analysis of radiation damage repair.
Material and methods:
A setup to shape a proton beam with 7 mm range in water and 3 mm in diameter was built and dosimetrically characterized. Cone-beam computed tomography (CBCT) and orthogonal X-ray imaging were used to delineate the right hippocampus (target) and to position the mice, respectively. For two mouse strains (C57BL/6 and C3H), brains were irradiated with 4 Gy or 8 Gy and excised after 30 min or 3 h. Brain sections (3 µm) were cut every 100 µm and DNA double-strand break (DSB) repair kinetics was visualized by staining for cell nuclei and H2AX. Imaged sections were analyzed with an automated and validated processing pipeline to provide a quantitative, spatially-resolved damage indicator.
Results:
Twenty mice underwent the treatment workflow including imaging, target delineation, positioning, and irradiation. The analyzed DNA damage pattern clearly visualized the radiation effect and could be mapped onto the measured dose distribution. For all evaluated C3H mice, the proton beam hit the right hippocampus and stopped in the brain. Damage pattern became spatially more extended and diffuse for 8 Gy and 3 h after irradiation, respectively. C57BL/6 mice showed comparable damage distributions, however, with larger spatial variation of the beam alignment relative to the hippocampus.
Conclusion:
We established and biologically validated stereotactic proton irradiation of mouse brains. The clinically-oriented workflow facilitates (back-) translational studies. Geometric accuracy and cell-based assessment enable a biologically and spatially resolved analysis of radiation response and RBE.

Keywords: Relative biological effectiveness (RBE); H2AX; particle therapy; small animal irradiation; normal tissue toxicity

Permalink: https://www.hzdr.de/publications/Publ-28608
Publ.-Id: 28608


Tonic signaling and its effects on lymphopoiesis of CAR-armed hematopoietic stem and progenitor cells

Albert, S.; Koristka, S.; Gerbaulet, A.; Cartellieri, M.; Arndt, C.; Feldmann, A.; Berndt, N.; Loureiro, L.; von Bonin, M.; Ehninger, G.; Eugster, A.; Bonifacio, E.; Bornhäuser, M.; Bachmann, M.; Ehninger, A.

Long-term survival of adoptively transferred chimeric antigen receptor (CAR) T cells is often limited. Transplantation of hematopoietic stem cells (HSCs) transduced to express CARs could help to overcome this problem as CAR-armed HSCs can continuously deliver CAR+ multi-cell lineages (e.g. T cells, NK cells). In dependence on the CAR construct a variable extent of tonic signaling in CAR T cells was reported, thus, effects of CAR-mediated tonic signaling on the hematopoiesis of CAR-armed HSCs is unclear. To assess effects of tonic signaling two CAR constructs were established and analyzed: (i) A signaling CAR inducing a solid antigen-independent tonic signaling termed CAR-28/, and (ii) a non-stimulating control CAR construct lacking intracellular signaling domains termed CAR-Stop. Bone marrow (BM) cells from immunocompetent mice were isolated, purified for HSC-containing Lin-cKit+ (LK) cells or the LK Sca-1+ subpopulation (Lin Sca 1+cKit+, LSK) and transduced with both CAR constructs. Subsequently, modified BM cells were transferred into irradiated mice where they successfully engrafted and differentiated into hematopoietic progenitors. HSCs expressing the CAR-Stop sustained normal hematopoiesis. In contrast, expression of the CAR-28/ led to elimination of mature CAR+ T and B cells suggesting that the CAR-mediated tonic signaling mimics autorecognition via the newly recombined immune receptors in the developing lymphocytes.

Keywords: Chimeric antigen receptors; tonic signaling; HSC transplantation; hematopoiesis; HSC engraftment; immunotherapy; adaptive immune system

Permalink: https://www.hzdr.de/publications/Publ-28607
Publ.-Id: 28607


Multidimensional fluid mixing capabilities of ATHLET 3.1A during an overcooling transient in a generic PWR KONVOI

Diaz Pescador, E.

In the presented work, a simulation of a 10% main steam line break (MSLB) in steam generator (SG) 1 in a generic German PWR KONVOI model is carried out and investigated by means of the system code ATHLET 3.1A. The accident analysis is focused first, on a thermal-hydraulic transient characterization, in order to subsequently study the multidimensional fluid mixing in the reactor pressure vessel (RPV), and further verification against suitable experimental data. With this aim, in the ATHLET simulation, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions from the test PKL G3.1. The obtained results show an increase in the heat removal through the U-tubes of SG 1during boil-off, giving rise to an asymmetric overcooling in the reactor coolant system. At the arrival of the overcooled water to the RPV, the cold water stream mixes with the ambient coolant in the downcomer and eventually spreads across the whole region. In the core region, the overcooled water propagates from the periphery towards the core centre. The obtained behavior is in good agreement with the experimental results from the ROCOM and PKL test facilities.

  • Poster
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Germany

Permalink: https://www.hzdr.de/publications/Publ-28606
Publ.-Id: 28606


Integration of drone-borne hyperspectral and geomagnetic data. A combined approach in geologic remote sensing. A test from the Siilinjärvi carbonatite, Finland.

Jackisch, R.; Zimmermann, R.; Lorenz, S.; Saartenoja, A.; Pirttijärvi, M.; Heincke, B.; Gloaguen, R.

The worlds need for critical materials sees a surge since the last two decades. Most of Europe’s larger mineral deposits have been discovered and exploited by now. A rising need to include formerly unattractive or inaccessible prospects is apparent. Here, using drones for detailed prospecting of small areas comes in handy. Drones have the advantage of being cost-efficient, easily deployable and having a short turn-around time for high resolution data.
With this study, we introduce a novelty approach for non-invasive mineral exploration based on the integration of remote sensing applications. In particular, we combine the advantage of light-weight drone technology with a snapshot hyperspectral camera and a magnetometer. The platform delivers specified, integrated measurements of spectrometric high-resolution surface images fused with data of the earth’s magnetic field. This allows us to identify surficial rock exposures and the estimation of the subsurface proportions of the aforesaid target.
The sensor system is attached to an octocopter platform with a flight endurance of around 30 minutes. A fixed-wing drone is used to acquire magnetic data of the same target with a larger area. The combined data is processed through a framework of correction software and projected on digital elevation models (DEMs) from the target area. The DEMs are acquired via Structure-from-Motion Multi-View Stereo photogrammetry. Hyperspectral data is corrected for topographic effects and automatically georeferenced using the MEPHYSTo toolbox. Magnetic data is calibrated for orientation effects and corrected for diurnal and external induced field fluctuations via base station recordings. We validate the measurements with a field-tested assembly of different techniques, e.g., mineralogical and geochemical analysis, in-situ ground spectroscopy and geomagnetic readings.
The results are promising and we demonstrate that drone-based exploration becomes more affordable, intuitive and accessible to the mining sector and the geoscientific community.

Keywords: UAS; UAV; remote sensing; mineral exploration; hyperspectral; geomagnetic; fluxgate

Permalink: https://www.hzdr.de/publications/Publ-28605
Publ.-Id: 28605


Investigations on the thermal-hydraulic behavior of a generic PWR KONVOI during a 1% cold leg small-break loss of coolant accident using the system code ATHLET

Diaz Pescador, E.; Schäfer, F.; Wilhelm, P.; Kliem, S.

In the presented paper, a simulation of a small-break loss of coolant accident (SBLOCA) with a 1% break in the cold leg 1 in a generic German PWR KONVOI model is carried out and investigated by means of the thermal-hydraulic system code ATHLET 3.1A. The accident analysis is focused first on a thermal-hydraulic characterization of the SBLOCA, and a subsequent qualitative comparison with the test PKL H1.1. With this aim, in the simulation with ATHLET 3.1A, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions of the test PKL H1.1.
The test PKL H1.1 reproduces a SBLOCA superposed by additional system failures, such as unavailability of the high-pressure safety injection and the automatic secondary-side cool-down. The test was conducted in the framework of the OECD/PKL3 project in the large-scale test facility PKL (“Primärkreislauf”), operated by Framatome Germany, as a counterpart test of LSTF/ROSA SB-CL-32.
The second part of the paper is devoted to the study of the boron dilution into the steam generators, and the subsequent transport and fluid mixing phenomena in the reactor pressure vessel. The results in the simulation, show how the implementation of a 200 K/h cool-down through the steam generators, initiated at a peak cladding temperature (PCT) of 500°C, is able to eventually achieve a long-term safe stable condition, due to the injection of cold water, first from the hydro-accumulators at a pressure of 26 bar, and then the actuation of the low pressure safety injection at a pressure of 10 bar.
This outcome is also observed in the test H1.1. Nevertheless, unlike the results obtained in the test, the implementation of the 200 K/h cool-down during the SBLOCA in the simulation cannot avoid core damage, fact strongly influenced by the initial pressure differences between the KONVOI model and the PKL test facility, being the latter limited by design constraints to a maximum pressure of 50 bar.

Keywords: KONVOI; small-break loss of coolant accident; cool-down procedure; emergency core cooling systems; ATHLET 3.1A

  • Lecture (Conference)
    ICONE 27. 27th International Conference on Nuclear Engineering, 19.-24.05.2019, Ibaraki, Japan
  • Contribution to proceedings
    ICONE 27. 27th International Conference on Nuclear Engineering, 19.-24.05.2019, Ibaraki, Japan, Mechanical Engineering Journal (JSME): The Japan Society of Mechanical Engineers

Permalink: https://www.hzdr.de/publications/Publ-28604
Publ.-Id: 28604


Atomistic Simulations to Design a Room-Temperature Single Electron Transistor

Prüfer, T.; Möller, W.; von Borany, J.; Heinig, K. H.

For future low power-consumption nanoelectronics, a room-temperature single-electron transistor may be configured by placing a small (few nm diam.) Si nanodot in a thin (<10 nm) SiO2 interlayer in Si. This can be achieved by ion-irradiation induced interface mixing, which turns the oxide layer into metastable SiOx, and subsequent high-temperature thermal decomposition which leaves, for a sufficiently small mixed volume, a single Si nanodot in the SiO2 layer. Corresponding ion mixing simulations have been performed using the binary collision approximation (BCA)[1], followed by kinetic Monte-Carlo (KMC) simulations[2] of the decomposition process, with good qualitative agreement with the structures observed in related experiments. Quantitatively, however, the BCA simulation appears to overestimate the mixing effect. This is attributed to the neglect of the positive entropy of mixing of the Si-SiO2 system, i.e. the immiscibility counteracts the collisional mixing by “up-hill diffusion” [3]. Consequently, intermitting KMC diffusion steps have been introduced into the BCA mixing simulation, resulting in an excellent predictive power for the irradiation step of the production process. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

  • [1] W. Möller et al., NIM B, 322, 23–33
  • [2] M. Strobel et al., PRB 64, 245422
  • [3] B. Liedke et al., NIM B 316 (2013) 56–61

Related publications

  • Lecture (Conference)
    E-MRS 2018 Fall Meeting, 17.-21.09.2018, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-28603
Publ.-Id: 28603


Si Quantum Dots for Single Electron Transistor: Synthesis, Characterization and Theoretical Comparison

Prüfer, T.; Wolf, D.; Engelmann, H.-J.; Hübner, R.; Bischoff, L.; Hlawacek, G.; Heinig, K.-H.; Facsko, S.; Xu, X.; von Borany, J.

The appearance of quantum effects makes nanoparticles (NPs) more and more important in semiconductor physics and especially in nanoelectronics. One very promising application is the single electron transistor (SET). Common field effect transistors (FET) could be outperformed by SETs in many applications because of their ultra-low power consumption (~100 times). Important for the fabrication of SETs operating at room temperature is the control of position and size of nano dots (<5nm). Our CMOS-compatible approach to manufacture SETs follows a two-step synthesis of NPs: (i) Producing tiny SiOx volumes by ion beam irradiation of ultrathin buried SiO2 layers (<10nm) and (ii) self-organizing single Si nanodots by phase separation during thermal treatment.
Energy-filtered transmission electron microscopy (EFTEM) is an advanced technique for the structural analysis of Si NPs in buried SiO2 layers. Although the NPs in the SiO2 layer superimpose in 2-dimentional projections from cross-sectional TEM samples, we managed to characterize the density and size distribution of the formed nanoclusters using the knowledge of the electron mean free path length to convert the Si-plasmon-loss filtered TEM image into a Si-thickness map. Here we will present the characterization and a comparison with theory to show a significant overestimation of the mixing effect by BCA simulation. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

Related publications

  • Lecture (Conference)
    European Materials Research Society Fall Meeting, 17.-21.09.2018, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-28602
Publ.-Id: 28602


A sizeable change in the electronic properties of GaAs via strain engineering in lattice-mismatched core/shell nanowires

Schneider, H.; Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Helm, M.; Dimakis, E.

III-V compound semiconductors have fueled many breakthroughs in physics and technology owing to their direct band gap and high electron mobility. It has also been very important that these fundamental properties can be tailored in ternary or quaternary alloys by selecting the chemical composition appropriately. Here we explore the great possibilities for strain engineering in core/shell nanowires as an alternative route to tailor the properties of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InₓGa₁₋ₓAs or GaAs/InₓAl₁₋ₓAs core/shell nanowires can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic properties. Core/shell nanowires were grown in the self-catalyzed mode on SiOₓ/Si(111) substrates by molecular beam epitaxy. Strain analysis was performed using synchrotron X-ray diffraction and Raman scattering spectroscopy, and showed that for a thin enough core, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness, we obtain a heavily tensile-strained core and an almost strain-free shell. The tensile strain of the core exhibits a predominantly-hydrostatic character and causes the reduction of the GaAs band gap energy in accordance with our theoretical predictions using deformation-potential theory and first-principle calculations. For 7 % of strain (x = 0.54), the band gap energy was reduced to 0.87 eV at 300 K, i.e. a remarkable reduction of 40 %. Signatures of valence-band splitting were also identified in polarization-resolved photoluminescence measurements, as a result of the strain anisotropy in GaAs. Presuming a reduced effective mass of electrons in the tensile-strained core of GaAs/InₓAl₁₋ₓAs nanowires (core diameter = 22 nm, x = 0.39 - 0.49), the corresponding electron mobility was measured by time-domain terahertz spectroscopy to be in the range of 4000 cm²/V·s at 300 K. These values are the highest reported, even in comparison to GaAs/AlₓGa₁₋ₓAs nanowires with double the core thickness. Our results demonstrate that strained GaAs in core/shell nanowires can resemble the electronic properties of InₓGa₁₋ₓAs, surmounting issues with phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the device performance.

Keywords: core/shell III-V semiconductor nanowires; molecular eam epitaxy; MBE; strain; effective mass

Related publications

  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-28601
Publ.-Id: 28601


Squeezing information about ThO2 nanoparticles’ size and shape from high resolution XANES

Amidani, L.; Rossberg, A.; Romanchuk, A.; Plakhova, T.; Kvashnina, K.

Extracting information on the size and shape of very small nanoparticles (NPs) is not a trivial task and it is fundamental to push the analysis of the available techniques to extract as much in-formation as possible from the available data. In this perspective we present a detailed modelling of Th L3 edge high resolution XANES collected on ThO2 NPs showing how the size and shape of the NP impacts the spectral shape.
Nanoparticles of ThO2 with average size between 2 and 35 nm were synthesized by chemical precipitation and measured at Th L3 edge with High-Energy Resolution Fluorescence Detected (HERFD) XANES. The HERFD-XANES spectrum of NPs with diameter above 2.5 nm are all very similar, while for NPs below 2.5 nm the first post edge feature is missing. In order to un-derstand what this absence could be correlated to, we performed a series of simulations with the FDMNES code on particles of different shape and with size close to 2 – 2.5 nm. We considered three possible shapes and cut the structures from ThO2 bulk. As a first approximation we did not consider disorder at the surface, but only the effects induced by size and shape. After cutting the NPs from the bulk, the symmetry of the crystal is lowered and different Th atoms have different local environment. We set the cutoff radius of our simulations to 6 Å and identified the groups of equivalent Th atoms by comparing the local environment of each Th up to 6 Å. To fully characterize the XANES of the NP under study, a separate simulation per equivalent Th atom was performed with the FDMNES code.
By comparing the simulations of Th atoms at the surface and inside the NP it clearly emerges that the first post edge feature is particularly sensitive to the number of Th second nearest neigh-bors. The spectrum of a specific shape is given by the weighted average of all the different Th in the NP. Considering that the shape determines how many Th with a specific local environment will be present, each shape results in a different final spectrum. By comparing the data and the simulations we suggest that the ThO2 NP with diameter below 2.5 nm have octahedral shape.

Related publications

  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Permalink: https://www.hzdr.de/publications/Publ-28600
Publ.-Id: 28600


Mineral mapping of drill core hyperspectral data with extreme learning machines

Contreras, C.; Khodadadzadeh, M.; Ghamisi, P.; Gloaguen, R.

Hyperspectral scanners are increasingly being used in the mining industry as a non-destructive and non-invasive technique to efficiently map minerals in drill core samples. Hyperspectral data allows the characterization of different mineral assemblages, structural features and alteration patterns based on reflectance spectrum profiles. Traditional methods to analysis drill core hyperspectral data include the use of reference spectral libraries by visual analysis or a well established software. However, although these approaches produce good results, they are time-consuming and prone to errors. Therefore, in this paper, we take advantage of the latest and advanced machine learning techniques proposed in different scientific fields and explore the use of extreme learning machines (ELM) to map minerals in drill core hyperspectral data. This is a supervised technique that provides fast and automatic means to characterize hyperspectral data. To be able to implement this technique, a reference map was generated from the drill core hyperspectral data. The obtained results indicate that ELM can successfully map minerals in drill core hyperspectral data producing better quantitative and qualitative results than a typical RF classifier.

Keywords: Drill cores; hyperspectral data; mineral mapping; extreme learning machine; random forest

  • Open Access Logo Contribution to proceedings
    2019 IEEE International Geoscience and Remote Sensing Symposium., 28.07.-02.08.2019, Yokohama, Japan
    IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium

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Permalink: https://www.hzdr.de/publications/Publ-28599
Publ.-Id: 28599


The Structural and Compositional Changes of Graphene Oxide Induced by Irradiation With 500 keV Helium and Gallium Ions

Malinsky, P.; Macková, A.; Florianová, M.; Cutroneo, M.; Hnatowicz, V.; Bohácová, M.; Szokölová, K.; Böttger, R.; Sofer, Z.

Structural and compositional modification of 2D materials as graphene or graphene oxide (GO) are topical objects of nowadays due to their many technological applications. Ion irradiation of graphene based materials, as a method for improvement of their surface properties started recently. Ion mass, energy, and fluence are crucial for forming of GO electrical, optical, and mechanical properties. In this work, the GO films are irradiated with 500 keV He and Ga ions to different fluences. The ions with different masses and electronic/nuclear stopping power ratios, are chosen with the aim to examine mechanisms of radiation defect creation. The elemental composition of the GO is investigated using Rutherford back-scattering (RBS) and elastic recoil detection analysis (ERDA) techniques. The structural and chemical changes are characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy and the electrical properties are determined by two-point method. The RBS and ERDA analyses indicate deoxygenation and dehydrogenation of the irradiated GO surface. The thickness and the degree of O and H depletion depend on the ion mass. XPS and Raman spectroscopy show removal of oxygen functionalities and structural modifications leading to a decrease in the surface resistivity.

Keywords: graphene oxide; ion Irradiation; Helium; Gallium; structure; composition

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Permalink: https://www.hzdr.de/publications/Publ-28598
Publ.-Id: 28598


A Machine Learning Technique for Drill Core Hyperspectral Data analysis

Contreras, C.; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.

Hyperspectral data are increasingly being used to map minerals in drill core samples allowing a non-invasive and non-destructive characterization of the mineral assemblages, and therefore, the mineralogical composition of a system, its variability, and structural features. The analysis of drill core hyperspectral data is traditionally carried out by a visual interpretation of the spectra and a comparison with reference libraries using spectral similarity measures. Although this approach produces good results it is time-consuming and subjective. In this work, we introduce, for the first time, an innovative automatic mineral mapping technique for drill core hyperspectral data by using a machine learning approach. More specifically, we propose to exploit detailed information coming from the Scanning Electron Microscopy (SEM)-based Mineral Liberation Analysis (MLA) to train a supervised classifier. For the extraction of input features, a traditional technique is explored, i.e., Principal Component Analysis (PCA). For the classification step, we suggest to use Random Forest (RF) because of its significant performance when there are few training samples available. Experimental results conducted on a VNIR-SWIR drill core hyperspectral dataset, show accurate classification results.

Keywords: Drill core hyperspectral data; Mineral Liberation Analysis; Random Forest; mineral mapping

Permalink: https://www.hzdr.de/publications/Publ-28597
Publ.-Id: 28597


Comparison of pancreatic respiratory motion management with three abdominal corsets for particle radiation therapy

Dolde, K.; Schneider, S.; Stefanowicz, S.; Alimusaj, M.; Flügel, B.; Saito, N.; Troost, E. G. C.; Pfaffenberger, A.; Hoffmann, A. L.

Background and Purpose: Abdominal organ motion seriously compromises the targeting accuracy for particle therapy in patients with pancreatic adenocarcinoma. This study compares three different abdominal corsets regarding their ability to reduce pancreatic motion and their potential usability in particle therapy.

Materials and Methods: A patient-individualized polyurethane (PU), a semi-individualized polyethylene (PE), and a patient-individualized 3D-scan based polyethylene (3DPE) corset were manufactured for one healthy volunteer. Time-resolved volumetric magnetic resonance imaging (4D-MRI) and single-slice 2D cine-MRI scans were acquired on two consecutive days to compare free-breathing motion patterns with and without corsets. The corset material properties, such as thickness variance, material homogeneity in Hounsfield units (HU) on CT scans, and manufacturing features were compared. The water equivalent ratio (WER) of corset material samples was measured using a multi-layer ionization chamber for proton energies of 150 MeV and 200 MeV.

Results: All corsets reduced the pancreatic motion on average by 9.6 mm in inferior-superior and by 3.2 mm in anterior-posterior direction. With corset, the breathing frequency was approximately doubled and the day-to-day motion variations were reduced. The WER measurements showed an average value of 0.993 and 0.956 for the PE and 3DPE corset, respectively, and of 0.298 for the PU corset. The PE and 3DPE corsets showed a constant thickness of 2.8 ± 0.2 mm and 3.8 ± 0.2 mm, respectively and a homogeneous material composition with a standard deviation (SD) of 31 HU and 32 HU, respectively. The PU corset showed a variable thickness of 4.2−25.6 mm and a heterogeneous structure with air inclusions with an SD of 113 HU.

Conclusion: Abdominal corsets are effective devices to reduce pancreatic motion. For particle therapy, PE-based corsets are preferred over PU-based corset due to their material homogeneity and constant thickness.

Keywords: Motion management; pancreatic cancer; abdominal corset; image-guided radiotherapy; 4DMRI; particle therapy

Permalink: https://www.hzdr.de/publications/Publ-28596
Publ.-Id: 28596


Non-classical Liquid Metal Ion Sources for advanced FIB nano-patterning

Mazarov, P.; Bischoff, L.; Pilz, W.; Klingner, N.; Nadzeyka, A.; Stodolka, J.; Gierak, J.

Focused Ion Beam (FIB) processing has been developed into a well-established and still promising technique for direct patterning and proto-typing on the nm scale. Exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represents a promising alternative to expand the global FIB application fields. Especially, Ion Beam Lithography (IBL) as direct, resistless and three-dimensional patterning enables a simultaneous in-situ process control by cross-sectioning and inspection. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources to an alternative technology feasible for nano-patterning challenges, e.g. to tune electrical, optical, magnetic or mechanical properties.

In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source.

L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Appl. Phys. Rev. 3, 021101 (2016).

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  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-28594
Publ.-Id: 28594


The race against time: TOF-SIMS in the HIM

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

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

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

Related publications

  • Lecture (Conference)
    Advances in Gas-Ion Microscopy - The Second International Meeting of The PicoFIB Network, 13.02.2019, London, Großbritanien

Permalink: https://www.hzdr.de/publications/Publ-28593
Publ.-Id: 28593


A Time-of-Flight Secondary Ion Mass Spectrometer Add-on for the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Facsko, S.

In a Helium Ion Microscopes (HIM) a Gas Field Ion Source (GFIS) is used to create a Helium or Neon ion beam with a diameter smaller than 0.5 nm and 1.8 nm, respectively. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating.

However, the existing HIM tools suffered from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. Recently, we designed, implemented and reported on the first time-of-flight secondary ion mass spectrometry (TOF-SIMS) add-on that can be retrofitted to existing microscopes [1,2,3].

After a brief introduction to the HIM, I will focus on the new time-of-flight setup. It is based on fast blanking electronics that chop the primary beam into pulses with a minimal length of 20 ns. In combination with a MCP based stop detector this enables TOF backscattering spectrometry with 54 nm lateral resolution [1,2] - the world record for spatially resolved backscattering spectrometry. In order to extend the TOF setup for SIMS an ion optic has been designed and optimized for high transmission by ion transport simulations and an evolutionary algorithm. The high transmission is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering.

The setup can obtain SIMS data from a region of interest or can be used in imaging mode to obtain elemental line profiles and maps of the surface. For m/q ≤ 80 u a m/∆m > 200 has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g. C, N). The lateral resolution has been evaluated to 8 nm using the knife edge method and a 75%/25%. The results will be compared to the theoretical achievable lateral resolution and the limiting experimental and physical constraints of this approach will be reviewed.

References

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Heller, R.; Klingner, N.; Hlawacek, G. (2016). Backscattering Spectrometry in the Helium Ion Microscope: Imaging Elemental Compositions on the nm Scale. In: Hlawacek, G. & Gölzhäuser, A. (Ed.), Helium Ion Microsc., Springer International.
[3] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018) Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.

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  • Lecture (Conference)
    SIMS Europe 2018, 16.-18.09.2018, Münster, Germany

Permalink: https://www.hzdr.de/publications/Publ-28592
Publ.-Id: 28592


Compositional analysis and in-situ experiments in the HIM

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Serralta, E.; Facsko, S.

The HIM is well known for its imaging with spot sizes below 0.5 nm, its nano-fabrication capabilities, the small energy spread of less than 1 eV and the extremely high brightness. However, it still suffers from the lack of instruments for in-situ studies as well as capabilities for a well integrated material analysis. In the first part a plug and socket system for sample holders will be shown with up to six freely customizable high-voltage electrical connections Additionally time-of flight spectrometry has been implemented for compositional analysis [1]. New results, drawbacks and derive conclusions for the practical use of time-of-flight SIMS will be presented [2]. Our setup delivers a mass resolution delta m < 0.3 u (for m/q < 80 u) and a lateral resolution of 8 nm.

[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J.A. Notte, J. Huang, S. Facsko. Ultramicroscopy 162 (2016), pp 91-97
[2] N. Klingner, R. Heller, G. Hlawacek, S. Facsko, J. von Borany (2018), submitted

Related publications

  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-28591
Publ.-Id: 28591


High Resolution in 3 dimensions – TOF-SIMS in the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.

Ongoing miniaturization in semiconductor industry, nanotechnology and life science requirement further improvements for high-resolution imaging, fabrication and analysis of the produced nanostructures. Continuously shrinking object dimensions lead to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques. Secondary ion mass spectrometry (SIMS), as one of the most powerful techniques for surface analysis, performed on the nanometer scale may comply with this demands. The direct determination of the sputtered ions mass provides elemental and molecular information and even allows to measure isotope concentrations.

During the last decades, primary ion species used in SIMS have been optimized in terms of best ionization probabilities and less molecular fragmentation. Thereby, highest mass-resolution has been one of the biggest design goals in the development of new SIMS spectrometers. In contrast to former developments, our approach aims for ultimate lateral resolution.

In recent years helium ion microscopy has been developed as a valuable tool for nanofabrication and high-resolution imaging. Helium ion microscopy (HIM) utilizes a gas field ion source to form a helium or neon ion beam with a diameter of less than 0.5 nm and 1.8 nm, respectively. This is not only possible for conducting but also for insulating samples without the need for a conductive coating. However, the existing tools suffer from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. While the technology is relatively young several efforts have been made to add such an analytic capability. Past and ongoing activities of various labs for in situ analysis will be summarized.

Recently, we implemented time-of-flight (TOF) spectrometry to measure the energy of backscattered particles, the mass of sputtered ions [1, 2]. In future activities we intent to determine the energy loss of transmitted particles as well. Based on the findings obtained with this first approachof integrating a TOF SIMS setup, a dedicated extraction optics for secondary ions has been designed and tested (see figure 1).

The focus of this presentation will be on the technical realization of the significantly improved setup. The setup can be operated in spot mode to obtain local mass spectra or in imaging mode to obtain element maps of the specimen surface (see figure 2).

New results, drawbacks and derived conclusions for the practical use of this promising technique will be presented [4]. Similarities and differences to the also recently developed system using a sophisticated magnetic sector field analyzer will be shown [5]. We will reveal that SIMS can be performed with unprecedented lateral resolutions.

First experiments revealed a very high relative transmission which is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. For m / q <= 80 u a mass resolution of delta m <= 0.3 u has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g.: C, N). The lateral resolution of 8 nm has been evaluated using the knife edge method and a 75 % / 25 % criterion and represents a world record for spatially resolved secondary ion mass spectrometry.

The results will be compared to the theoretical limit of achievable lateral and depth resolution and the experimental and physical constraints of this approach will be reviewed.

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  • Invited lecture (Conferences)
    HRDP 9 - 9th International Workshop on High-Resolution Depth Profiling, 25.-29.06.2018, Uppsala, Sweden

Permalink: https://www.hzdr.de/publications/Publ-28590
Publ.-Id: 28590


Application of a new model for bubble-induced turbulence to bubbly flows in containers and vertical pipes

Liao, Y.; Ma, T.; Krepper, E.; Lucas, D.; Fröhlich, J.

The present paper extends the baseline model for the CFD-simulation of turbulent poly-disperse bubbly flows in the Euler-Euler framework by improving the modelling of bubble-induced turbulence. The closure terms in the transport equations of the k-ω SST model are revisited and replaced with a new model recently proposed by Ma et al. (Ma et al., Physical Review Fluids 2, 034301, 2017) which is based on an analysis of the turbulent kinetic energy budget obtained from direct numerical simulation data. Detailed validation results for various flow configurations with a wide range of gas and liquid volumetric fluxes are presented. In case of vertical pipe flow significant improvements in the predicted gas volume fraction and velocity profiles are obtained, especially in high gas volume fraction cases where bubble-induced turbulence is dominant. Simulations of other configurations, such as uniform and non-uniform bubble columns, show that the new model results in an also for these cases overall improvement. Therefore, the baseline model is now updated to include the new model for bubble-induced turbulence.

Keywords: Bubbly flow; Bubble-induced turbulence; Euler-Euler modelling; Baseline model

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Permalink: https://www.hzdr.de/publications/Publ-28589
Publ.-Id: 28589


Verification of ATHLET against TRACE on Superphenix start-up tests

Di Nora, V. A.; Fridman, E.; Mikityuk, K.

The thermal-hydraulics (TH) code ATHLET has been upgraded to be capable of sodium flow modeling. Its new extension is under verification and validation phase. The presented study aimed to demonstrate ATHLET capability in Sodium-cooled Fast Reactor (SFR) transient predictions, through the comparison against TRACE TH code, this last being more established and tested for SFR applications. Calculations were performed on a set of start-up tests on Superphénix (SPX) SFR, and compared with TRACE results, which were used as a reference. It has been shown that given a specific set of reactivity coefficients, ATHLET and TRACE give consistent and close results.

Keywords: Superphénix start-up tests; Benchmarking ATHLET against TRACE; ATHLET for SFRs

  • Lecture (others)
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28588
Publ.-Id: 28588


Time-lapse imaging of particle invasion and deposition in porous media using in situ X-ray radiography

Da Assuncao Godinho, J. R.; Chellappah, K.; Collins, I.; Ng, P.; Smith, M.; Withers, P. J.

This paper introduces time-lapse radiography as an in situ technique to image and quantify changes in the internal structure of a porous medium with sub-second temporal resolution. To demonstrate the technique’s potential, an experiment was performed using a model system involving flow of a suspension containing ground marble particles through a porous bed of compacted glass beads housed within a pressurized flow rig. During the experiment, particle deposition occurred both within the internal porous structure and on its surface (forming a filter cake). The volume of particles deposited was derived from changes in the grey scale of the radiographs. At the initial stages of the experiment, the volume of particles deposited internally was seen to increase linearly with time. The subsequent growth and compaction of an external filter cake decreased the rate of internal particle deposition. The filter cake’s structure was observed to fail owing to increasing stress at higher pressures. The demonstrative experiment illustrates the potential of time-lapse radiography as a new tool to elucidate mechanisms underpinning formation damage, and to optimize drilling fluids and enhanced oil recovery (EOR). A critical assessment of the technique’s advantages and limitations to characterise particulate behaviour within porous media is included.

Keywords: Permeability; formation damage; fines migration; filter cake; EOR; computed tomography

Permalink: https://www.hzdr.de/publications/Publ-28586
Publ.-Id: 28586


Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment

Mohseni, E.; Herrmann-Heber, R.; Reinecke, S. F.; Hampel, U.

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers.

Keywords: Bubble Generation; Micro-orifices; Aeration; Biological Wastewater Treatment; Rubber Membrane Diffusers; Oxygen Transfer

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Permalink: https://www.hzdr.de/publications/Publ-28585
Publ.-Id: 28585


Ion-induced surface patterning and its application in nanofabrication via templated growth

Erb, D.; Malsch, G.; de Schultz, R.; Facsko, S.

Low-energy ion irradiation of surfaces can lead to nanoscale pattern formation with a wide variety of morphologies, resulting from a number of interacting ballistic and diffusive mechanisms which govern the mass redistribution under ion irradiation. The choice of process parameters such as sample temperature or ion incidence angle determines the relative influence of these mechanisms and thereby the pattern morphology.
After briefly outlining the patterning mechanisms and discussing the resulting morphologies on semiconductor surfaces, we present our approaches at templated nanostructure growth based on these ion-induced surface patterns. They include epitaxial nanowires via geometric shading, long-range chemical ordering in diblock-copolymer thin films, and engineering of magnetic anisotropy in topographically modulated thin films.
The required technologies of low-energy ion irradiation, polymer chemistry, and physical vapor deposition are well-established and can readily be implemented at industrially relevant scales. Thus, nanostructured materials fabricated in such bottom-up manner have the potential to make substantial contributions to solving our society’s present challenges: They can increase the sensitivity of diagnostical tools in medicine, lead to novel information technology, or enhance the efficiency of energy harvesting from renewable sources.

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  • Poster
    SNI2018 - Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at Large Facilities, 17.-19.09.2018, Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28584
Publ.-Id: 28584


Nanostructure arrays via templated growth

Erb, D.; Schlage, K.; Röhlsberger, R.; Facsko, S.

Nanostructured materials have the potential to make substantial contributions to solving our society’s present challenges, e.g. in the fields of medicine, information technology, or energy harvesting from renewable sources. The possibility to fabricate them at industrially relevant scales will maximize the impact of such materials.
We present bottom-up nanopatterning approaches which promise easy implementation and scale-up by combining well-established techniques and effects:
(a) spontaneous nanopatterning of crystalline surfaces upon heating,
(b) suface nanopatterning induced by low-energy ion irradiation,
(c) diblock copolymer self-assembly
(d) physical vapor deposition with selective wetting,
(e) physical vapor deposition with geometrical sha-ding.
Combinations of these techniques and effects can result in highly regular nanostructure arrays of various morphologies and are applicable to a wide range of materials. The versatility of these approaches enables creative research and may lead to beneficial applications in diverse fields, ranging from optics and magnetism to catalysis.

Related publications

  • Invited lecture (Conferences)
    NAP2018 - 8th International Conference on Nanomaterials: Applications & Properties, 09.-14.09.2018, Zatoka, Ukrajina

Permalink: https://www.hzdr.de/publications/Publ-28583
Publ.-Id: 28583


Surface nanopatterning induced by low-energy ion irradiation: Experimental investigations of non-equilibrium pattern formation

Erb, D.; de Schultz, R.; Malsch, G.; Facsko, S.

Irradiating a surface with low-energy ions of about 100 to 1000 eV activates a number of different processes: the surface is eroded by sputtering; the ion impacts create vacancies and ad-atoms; mass redistribution of the mobile species proceeds via both diffusive and ballistic effects; anisotropies in mass redistribution can be induced both by the ion beam and the structure of the surface on the atomic scale. Some mechanisms destabilize the surface height while others lead to surface smoothing. The simultaneous presence of such counteracting effects can result in the formation of periodic nanoscale surface patterns. Depending on factors such as temperature, ion energy, or the incidence orientation of the ion beam, the individual surface processes are enhanced or suppressed, yielding different pattern morphologies. The fact that the patterning can be influenced by various readily accessible external parameters offers a way toward deeper understanding of the underlying processes and their interactions. Furthermore, it enables large-scale production of novel templates for bottom-up fabrication of nanostructures or nanostructured materials for future applications in diverse fields, ranging from optics and magnetism to catalysis.
We discuss our experimental studies of ion-induced pattern formation on different semiconductor surfaces in dependence of external process parameters and with regard to temporal evolution, pattern symmetry and morphology, and patterning defects. Further, we present our approaches to employing these patterned surfaces for nanostructure fabrication, especially by means of physical vapor deposition.

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  • Lecture (Conference)
    CAARI 2018 - 25th Conference on Application of Accelerators in Research and Industry, 12.-17.08.2018, Grapevine, USA

Permalink: https://www.hzdr.de/publications/Publ-28582
Publ.-Id: 28582


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

Erb, D.; Malsch, G.; Facsko, S.

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.

Related publications

  • Poster
    Ion Beam Workshop 2018 - MAT Science Week, 24.04.2018, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28581
Publ.-Id: 28581


A route to epitaxial growth of periodic metal nanostructure arrays

Erb, D.; Malsch, G.; Hübner, R.; Lenz, K.; Lindner, J.; Facsko, S.; Helm, M.; Fassbender, J.

Epitaxial thin film growth on planar substrate surfaces is well-established for many materials. We present a novel bottom-up approach showing that it can also be feasible to grow nanostructures in an oriented manner on nanopatterned crystalline surfaces. Produced by a scalable procedure on large surface areas, such nanostructure arrays may find diverse applications in research and technology, e.g. in the fields of magnetism or catalysis.
On semiconductor substrates, nanoscale surface patterns with well-defined lateral periodicity form under low-energy ion irradiation via non-equilibrium self-assembly of vacancies and ad-atoms [1]. For appropriate process temperatures, the crystallinity of the substrate is retained during ion irradiation. When a material is then deposited onto the substrate by PVD under non-normal incidence, shadowing effects give rise to the formation of separated nanostructures [2], while a suitable lattice matching can induce epitaxial growth.
In this contribution, we outline the patterning and growth procedure. As an example, we will present periodic Fe/Au nanostructure arrays and discuss their strongly anisotropic optical and magnetic properties.

[1] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender,
S. Facsko, Nanoscale 7, 18928 (2015)
[2] Q. Jia, X. Ou, M. Langer, B. Schreiber, J. Grenzer, P. F. Siles, R. D. Rodriguez,
K. Huang, Y. Yuan, A. Heidarian, R. Hübner, T. You, W. Yu, K. Lenz, J. Lindner,
X. Wang, and S. Facsko, Nano Research 15, 1 (2017)

Related publications

  • Poster
    DPG Frühjahrstagung 2018 - Sektion Kondensierte Materie, 11.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28580
Publ.-Id: 28580


Ion-induced nanopatterning of crystalline surfaces for applications in bottom-up nanostructure fabrication

Erb, D.; Hübner, R.; Malsch, G.; de Schultz, R.; Grenzer, J.; Lenz, K.; Lindner, J.; Facsko, S.

Nanostructured materials will be key components in future technological solutions of our society’s present challenges: They can enhance the efficiency of energy harvesting from renewable sources, increase the sensitivity of diagnostical tools in medicine, or enable novel information technology. For making substantial contributions to these fields by applying nanostructured materials, we must be able to fabricate them easily and reproducibly on industrially relevant scales. This can be achieved by the bottom-up approach of templated growth on substrates nanopatterned by ion irradiation: The required technologies of low-energy ion irradiation, polymer chemistry, and physical vapor deposition are well-established.
In this contribution, we outline the mechanism of self-assembly of vacancies and adatoms on crystalline semiconductor surfaces induced by low-energy ion irradiation [1,2]: At temperatures above the material’s recrystallization temperature, the substrate crystallinity is retained. Thus, diffusion of vacancies and adatoms on the surface is highly anisotropic, which leads to the formation of surface nanopatterns reflecting the crystal symmetry of the substrate material. The various resulting pattern morphologies and the influence of external process parameters will be presented. We hope to initiate discussion and collaboration by highlighting potential applications based on these ion-induced nanopatterns, such as growing epitaxial nanowire arrays by shadowing effects at oblique incidence deposition, or inducing long-range order in copolymer thin films to fabricate chemically nanopatterned templates for nanostructure growth [3].

Acknowledgement
We thank K. Potzger and A. Henschke (HZDR) for their support in MBE for templated nanowire growth.

References
[1] X. Ou et al., Nanoscale 7, 18928 (2015)
[2] Q. Jia et al., Nano Research 15, 1 (2017)
[3] D. Erb et al., Science Advances 1, e1500751 (2015)

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  • Lecture (Conference)
    SHIM-ICACS 2018 - 10th InternationaL Symposium on Swift Heavy Ions in Matter & 28th International Conference on Atomic Collisions in Solids, 01.-06.07.2018, Caen, France

Permalink: https://www.hzdr.de/publications/Publ-28579
Publ.-Id: 28579


Ex situ n+ doping of GeSn alloys via non-equilibrium processing

Prucnal, S.; Berencén, Y.; Wang, M.; Rebohle, L.; Böttger, R.; Fischer, I. A.; Augel, L.; Oehme, M.; Schulze, J.; Voelskow, M.; Helm, M.; Skorupa, W.; Zhou, S.

Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p- and n-type doped regions for both planar and tri-dimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1 × 10^19 cm−3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3 × 10^15 cm−2 and electron concentration of about 4 × 10^19 cm−3. The optical and structural properties of ion-implanted GeSn layers are comparable with the in situ doped MBE grown layers.

Keywords: Ge; GeSn; MBE; n-type doping; flash lamp annealing; ion implantation

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Permalink: https://www.hzdr.de/publications/Publ-28578
Publ.-Id: 28578


Structural and electrical properties of Se-hyperdoped Si via ion implantation and flash lamp annealing

Liu, F.; Prucnal, S.; Yuan, Y.; Heller, R.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

We report on the hyperdoping of silicon with selenium obtained by ion implantation followed by flash lamp annealing. It is shown that the degree of crystalline lattice recovery of the implanted layers and the Se substitutional fraction depend on the pulse duration and energy density of the flash. While the annealing at low energy densities leads to an incomplete recrystallization, annealing at high energy densities results in a decrease of the substitutional fraction of impurities. The electrical properties of the implanted layers are well-correlated with the structural properties resulting from different annealing processing.

Keywords: Silicon; hyperdoping; Se; flash lamp annealing; ion implantation

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Permalink: https://www.hzdr.de/publications/Publ-28577
Publ.-Id: 28577


Prophylactic cranial irradiation in stage IV small cell lung cancer: 5 Selection of patients amongst European IASLC and ESTRO experts

Putora, P. M.; Glatzer, M.; Belderbos, J.; Besse, B.; Blackhall, F.; Califano, R.; Cappuzzo, F.; de Marinis, F.; Dziadziuszko, R.; Felip, E.; Faivre-Finn, C.; Früh, M.; Garrido, P.; Le Pechoux, C.; Mcdonald, F.; Nestle, U.; Novello, S.; O‘Brien, M.; Paz Ares, L.; Peeters, S.; Pöttgen, C.; Ramella, S.; Reck, M.; Slotman, B.; Troost, E. G. C.; Houtte, P. V.; Westeel, V.; Widder, J.; Mornex, F.; de Ruysscher, D.

Background: Due to conflicting results between major trials the role of prophylactic cranial irradiation (PCI) in stage IV small cell lung cancer (SCLC) is controversial. Methods: We obtained a list of 13 European experts from both the European Society for Therapeutic Radiation Oncology (ESTRO) and the International Association for the Study of Lung Cancer (IASLC). The strategies in decision making for PCI in stage IV SCLC were collected. Decision trees were created representing these strategies. Analysis of consensus was performed with the objective consensus methodol-ogy.
Results: The factors associated with the recommendation for the use of PCI included the fitness of the patient, young age and good response to chemotherapy. PCI was recommended by the majority of experts for non-elderly fit patients who had at least a partial response (PR) to chemotherapy (for complete remission (CR): 85% of radiation oncologists and 69% of medical oncologists, for partial remission: 85% of radiation oncol- ogists and 54% of medical oncologists). For patients with stable disease after chemotherapy, PCI was rec- ommended by 6 out of 13 (46%) radiation oncologists and only 3 out of 13 medical oncologists (23%). For elderly fit patients with CR, a majority recommended PCI (62%) and no consensus was reached for patients with PR. Conclusion: European radiation and medical oncologists specializing in lung cancer recommend PCI in selected patients and restrict its use primarily to fit, non-elderly patients who responded to chemotherapy.

Keywords: Small cell lung cancer; PCI; Stage IV; Expert opinion; ESTRO; IASLC

Permalink: https://www.hzdr.de/publications/Publ-28576
Publ.-Id: 28576


Oxygen Exchange Kinetics of SrTiO3 Single Crystals: A Non-Destructive, Quantitative Method

Stoeber, M.; Cherkouk, C.; Leisegang, T.; Schelter, M.; Zosel, J.; Walter, J.; Hanzig, J.; Zschornak, M.; Prucnal, S.; Boettger, R.; Meyer, D. C.

The time-resolved oxygen exchange rate of strontium titanate (SrTiO3) single crystals is studied by means of oxygen solid electrolyte coulometry (OSEC) and compared to model calculations. Experiments are performed on pure, ion implanted (Ni, Ag, O and N ions) and partially covered crystals with silver layer. In this work, a theoretical model is used, which is based on defect chemistry under equilibrium conditions. It is applied as a fit in order to determine the effective rate constants and activation energy of the oxygen exchange reaction on the crystal surface. OSEC is used for the first time to characterize kinetic parameters of oxygen exchange on single crystalline surfaces. Transmission electron microscopy and sputter X-ray photoelectron spectroscopy are performed to determine structural and chemical changes after ion implantation.

Keywords: strontium titanate; ion implantation; oxygen exchange reaction; X-ray photoelectron spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-28575
Publ.-Id: 28575


Ion Beam Modification of ZnO Epilayers: Sequential Processing

Turos, A.; Ratajczak, R.; Mieszczynski, C.; Jozwik, P.; Stonert, A.; Prucnal, S.; Heller, R.; Skorupa, W.; von Borany, J.; Guziewicz, E.

Defect agglomeration in ion-implanted compound semiconductors produces lattice stress eventually causing plastic deformation at sufficiently high fluence. Consequently, a dislocations tangle is formed which can hardly be completely removed by thermal annealing. To solve this problem, a new method of sequential processing has been developed consisting of low fluence ion implantation followed by subsequent annealing. The procedure can be then repeated until the required impurity concentration has been reached without producing excessive damage. Epitaxial ZnO layers are grown using the atomic layer deposition (ALD) technique. Structural changes in ZnO epilayers due to Yb-ion implantation and subsequent annealing are analyzed by Rutherford backscattering/channeling (RBS/c) and photoluminescence (PL). Correlation between defect transformations and PL efficiency is determined. Increased Yb-atom optical activation upon sequential processing as compared to the standard single-step annealing is observed.

Keywords: ZnO; ALD; Defects; ion implantation; RBS

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Permalink: https://www.hzdr.de/publications/Publ-28574
Publ.-Id: 28574


Fractionwise verification of delivered proton dose to prostate cancer patients based on daily in-room CT imaging

Stützer, K.; Valentini, C.; Agolli, L.; Hölscher, T.; Thiele, J.; Dutz, A.; Löck, S.; Krause, M.; Baumann, M.; Richter, C.

Purpose: Retrospective proton dose calculation based on a unique dataset of daily CT images to confirm our prostate patient positioning and immobilization protocol for counterbalancing interfractional motion.
Material/Methods: For 12 prostate cancer patients treated to 74GyE with double-scattered lateral or anterior oblique proton fields, daily (27-37, median 32) in-room control CTs (cCT) were acquired. Patient preparation includes a drink protocol, water-filled endorectal balloon insertion, bony anatomy alignment by orthogonal X-Ray imaging, and CT-based verification of prostate location via implanted fiducial marker positions. Fraction doses were calculated on all manually delineated cCTs and accumulated on the planning CT by a deformable image registration (DIR) in RayStation 5.99. DVH parameters of iCTVs, bladder, rectum, femoral heads, bladder and rectal wall were analyzed fractionwise prior and after DIR and values from the cumulated and planned dose distributions were compared.
Results: Fig.1 shows the fractionwise assessed DVH parameters for one patient. 275 fraction doses were analyzed in total without finding trends for improving or worsening DVH parameters over treatment time. Intended target coverage, D98%(iCTV)>95%, was missed in 29 cCTs (10.5%) due to suboptimal bladder filling, endorectal balloon position or delineation variation. No overdosage was observed (D2%(iCTV)<105%). DIR led partly to notable changes of DVH parameters (Fig.1). No alarming differences exist between planned and cumulated doses (Fig.2), but significant changes (p<0.05, Wilcoxon signed rank test) were found for D2%(iCTV), V75%(bladder) and V30Gy(bladder wall).
Conclusion: Despite some suspicious fractions, the total delivered doses to prostate cancer patients are accurate with the applied positioning and immobilization protocol.

  • Lecture (Conference)
    58th annual conference of the particle therapy co-operative group, 10.-15.06.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-28573
Publ.-Id: 28573


Interplay between localization and magnetism in (Ga,Mn)As and (In,Mn)As

Yuan, Y.; Xu, C.; Hübner, R.; Jakiela, R.; Böttger, R.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.

Ion implantation of Mn combined with pulsed laser melting is employed to obtain two representative compounds of dilute ferromagnetic semiconductors (DFSs): Ga1−xMnxAs and In1−xMnxAs. In contrast to films deposited by the widely used molecular beam epitaxy, neither Mn interstitials nor As antisites are present in samples prepared by the method employed here. Under these conditions the influence of localization on the hole-mediated ferromagnetism is examined in two DFSs with a differing strength of p-d coupling. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1−xMnxAs compared to Ga1−xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Furthermore, the findings support strongly the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions even on the insulator side of the metal-insulator transition.

Keywords: electronic-structure; magnetotransport properties; curie-temperature; coulomb gap; (ga,mn)as; ga1-xmnxas; semiconductors; ferromagnetism

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  • Poster
    DPG-Jahrestagung und DPG-Frühjahrstagung, 13.03.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28572
Publ.-Id: 28572


Luminescence in the Visible Region from Annealed Thin ALD-ZnO Films Implanted with Different Rare Earth Ions

Ratajczak, R.; Guziewicz, E.; Prucnal, S.; Łuka, G.; Böttger, R.; Heller, R.; Mieszczynski, C.; Wozniak, W.; Turos, A.

Epitaxial ZnO thin films grown by atomic layer deposition on GaN/Al2O3 substrates are implanted with Yb, Dy, and Pr ions to a fluence of 5e14 atcm-2 and subsequently anneals at 800 C using a rapid thermal annealing (RTA) system. Structural properties of implanted and annealed ZnO films and the optical response are evaluated by channeling Rutherford backscattering (RBS/c) and photoluminescence spectroscopy (PL), respectively. RTA leads to a partial removal of the post-implantation defects with simultaneous native defects transformation and optical activation of RE ions. It is found that two groups of defects: defects formed during implantation process and native defects, play an important role in the luminescence in the visible region. The room temperature PL spectra obtained from annealed ZnO:RE films do not show sharp PL lines from transitions within the RE 4f shell, but show near band gap emission and defect related emission, which energy emission is controlled by the RE atoms. It suggests a presence of RE-related complexes that are formed during hightemperature annealing in oxygen atmosphere. The excitonic and defect emission modified by RE ions create an optical response of the system resulting in a specific color of the emitted light.

Keywords: ZnO; flash lamp annealing; PL; ion implantation; rare earth

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Permalink: https://www.hzdr.de/publications/Publ-28571
Publ.-Id: 28571


Strain and Band-Gap Engineering in Ge-Sn Alloys via P Doping

Prucnal, S.; Berencén, Y.; Wang, M.; Grenzer, J.; Voelskow, M.; Hübner, R.; Yamamoto, Y.; Scheit, A.; Bärwolf, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Żuk, J.; Turek, M.; Droździel, A.; Pyszniak, K.; Kudrawiec, R.; Polak, M. P.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge−Sn alloys. The heavily doped n-type Ge−Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge−Sn layers and to modify the lattice parameter of P-doped Ge−Sn alloys. The strain engineering in heavily-P-doped Ge−Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge−Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1 × 10^20 cm the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology.

Keywords: Ge; GeSn; n-type doping; ion implantation; x-ray diffraction; Raman spectroscopy; strain

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Permalink: https://www.hzdr.de/publications/Publ-28570
Publ.-Id: 28570


Advanced doping of Ge and GeSn

Prucnal, S.; Berencén, Y.; Hübner, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Wang, M.; Helm, M.; Zhou, S.

One of the main obstacles towards wide application of Ge in nanoelectronics is the indirect band gap of Ge and the lack of an efficient doping method with well controlled junction depth. Heavily n-type doped Ge becomes a quasi-direct bandgap semiconductor [1] which makes it very attractive for modern optoelectronics but n-type Ge doped above 5×10^19 cm-3 is metastable and thus difficult to be achieved [2]. In contrast to Ge, the GeSn alloy with direct band gap is the most promising semiconductor material for light emitters integrated with CMOS technology [3]. Here an overview of different doping techniques of Ge and fabrication methods to form GeSn will be presented. Special attention will be focused on the use of ion implantation followed by flash-lamp (FLA) annealing for the fabrication of heavily doped n-type Ge and GeSn with direct band gap [4]. In contrast to conventional annealing procedures, rear-side FLA leads to full recrystallization of Ge and GeSn, and simultaneously the Sn segregation and diffusion of n-type dopants are supressed. The maximum electron concentration is well above 10^20 cm-3 both in Ge and in GeSn with Sn concentration up to 6%. Due to the ultra-high n-type doping, Ge becomes a quasi-direct band gap semiconductor showing room-temperature photoluminescence from G-HH transitions [4]. The recrystallization mechanism and the dopant distribution in Ge and GeSn alloy synthesized by ion implantation during rear-side FLA are discussed in detail.
Moreover, we report on the strong mid-IR plasmon absorption in heavily n-type doped Ge and GeSn thin films in the wavelength range from 3000 nm to 10 000 nm.

[1] R. E. Camacho-Aguilera et al., Optics Express 20, 11316-11320 (2012)
[2] S. Prucnal et al., Sci. Rep. 6, 27643 (2016).
[3] S. Wirths et al., Nat. Photon., 9, 88–92 (2015)
[4] S. Prucnal et al., Semicond. Sci. Technol. 32, 115006 (2017).

Keywords: Ge; GeSn; ion implantation; flash lamp annealing; n-type doping

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  • Lecture (Conference)
    34th International Conference on the Physics of Semiconductors, 29.07.-03.08.2018, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-28569
Publ.-Id: 28569


Robust intensity-modulated proton therapy with dose-escalated simultaneous integrated boost reduces the low-dose to surrounding tissues in pancreatic cancer patients

Stefanowicz, S.; Zschaeck, S.; Troost, E. G. C.

Purpose
This in-silico study on simultaneous integrated boost dose-escalation in non-metastatic pancreatic cancer patients dosimetrically compared robust multi-field optimized intensity-modulated proton therapy (IMPT) with volumetric modulated arc therapy (VMAT).

Material and Methods
For five patients, both treatment plans were optimized on free-breathing CTs using RayStation. For VMAT, at least 95% of the prescribed doses of 66Gy and 51Gy to the boost (GTV) and PTV (CTV+5mm), respectively, were to cover 95% of the targets. For IMPT, robust optimization with a setup uncertainty of 5mm and a density uncertainty of 3.5% was applied to the GTV and CTV, with the aforementioned dose levels (RBE) again covering 95% of the targets. The OAR dose constraints adhered to local guidelines and QUANTEC.

Results
All treatment plans reached the prescribed doses to the targets. Doses to the bowel, stomach and/or liver exceeded at least one constraint in all treatment plans, since those OARs were next to or within the targets. While VMAT reduced the median V50Gy of the stomach, doses to the remaining gastrointestinal organs, e.g. liver and kidneys, were lower for IMPT (Fig. 1). Overall, IMPT deposited less low dose outside the CTV (Fig. 2, median integral V20Gy: 1483.4ccm vs. 756.2ccm).

Conclusion
Disregarding inter- and intra-fractional organ motion, dose escalation with IMPT and VMAT is possible. IMPT reduced the dose to surrounding normal tissues, except for OARs overlapping with the target volume, in which the dose was higher due to the robust optimization approach. Additional patients will be included in this study.

  • Poster
    PTCOG 58, 10.-15.06.2019, Manchaster, UK

Permalink: https://www.hzdr.de/publications/Publ-28568
Publ.-Id: 28568


Abnormal lattice location and electrical activation in chalcogen-hyperdoped Si

Wang, M.; Prucnal, S.; Debernardi, A.; Heller, R.; Yuan, Y.; Xu, C.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Hyperdoping has emerged as a promising method for designing semiconductors with unique physical properties. In general, these properties are primarily determined by the lattice location of the impurity atoms in the host material. In this contribution, the lattice location of implanted chalcogens in Si was experimentally determined by means of Rutherford backscattering/channeling (RBS/C). The implication on the electrical activation of chalcogens in Si will be discussed with respect to the Hall effect results. The obtained carrier concentration and the RBS angular scans across the <100> and <110> axis reveal that the electrically active/inactive concentration of Te correlates with the concentration of substitutional/interstitial site Te atoms. Surprisingly, contrary to the general belief, we find that the interstitial fraction decreases with increasing impurity concentration. This abnormal dependence of lattice location and electrical activation on impurity concentration suggests that the formation energy for the substitutional Te or Te-Te dimers in Si is lower than for the interstitial Te. This assumption is theoretically verified by the first-principles calculations.

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  • Lecture (Conference)
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 28.06.2018, San Antonio, USA

Permalink: https://www.hzdr.de/publications/Publ-28567
Publ.-Id: 28567


Extended infrared photoresponse in room-temperature Si hyperdoped with Te

Wang, M.; Berencén, Y.; Prucnal, S.; García-Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.

Presently, room-temperature infrared sub-band-gap photoresponse in Si is of great interest for the development of on-chip complementary-metal-oxide-semiconductor (CMOS)-compatible photonic platforms [1]. One of the most promising approaches to further extend the photoresponse of Si to the mid- and far-infrared (MIR/FIR) ranges consists of introducing deep-level dopants into the Si band gap at concentrations in excess of the solid solubility limit [2]. In this work, we demonstrate strong room-temperature sub-band-gap photoresponse of photodiodes based on Si hyperdoped with tellurium [3]. A CMOS-compatible approach of combining ion implantation with pulsed laser melting was applied to synthesize single-crystalline and epitaxial Te-hyperdoped Si layers with a Te concentration five orders of magnitude above the solid solubility limit. Driven by increasing Te concentration, both the insulator-to-metal transition and a band-gap renormalization are observed. The sub-band optical absorptance in the resulting Te-hyperdoped Si layers is found to increase monotonically with increasing Te concentration and extends well into the MIR/FIR ranges (1.4 to 25 μm). Importantly, the MIR/FIR optoelectronic response from Te-hyperdoped Si photodiodes is demonstrated to be related with known Te deep-energy levels into the Si band-gap. This work contributes to pave the way towards establishing a Si-based broadband infrared photonic system operating at room temperature.

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  • Lecture (Conference)
    ION 2018 - XII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 19.06.2018, Kazimierz Dolny, Poland
  • Poster
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 25.06.2018, San Antonio, USA
  • Poster
    ICPS-2018 - 34th International Conference on the Physics of Semiconductors, 30.07.2018, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-28566
Publ.-Id: 28566


Towards room-temperature extended infrared Si-based photoresponse: A case study of Te-hyperdoped Si

Wang, M.; Berencén, Y.; García Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.

Presently,room-temperature broadband Si-based photodetectors are required for Si photonic systems.Here,we demonstrate roomtemperature sub-band gap photoresponse of photodiodes based on Si hyperdoped with Te.The epitaxially recrystallized Te-hyperdoped Si layers are developed by ion implantation combined with pulsed laser melting and incorporate Te concentrations beyond the solid solubility limit.An insulator-to-metal transition driven by increasing Te concentration accompanied with a band gap renormalization is observed.The optical absorptance is found to increase monotonically with increasing Te concentration and extends well into the mid- and far- infrared regions.This work contributes to establish room temperature Si-based broadband infrared photonic system.

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  • Lecture (Conference)
    DPG-Frühjahrstagung 2018, 12.03.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28565
Publ.-Id: 28565


Mid- to far-infrared localized surface plasmon resonance in chalcogen-hyperdoped Si

Wang, M.; Prucnal, S.; Berencén, Y.; Rebohle, L.; Schönherr, T.; Yuan, Y.; Xu, C.; Khan, M. B.; Böttger, R.; Skorupa, W.; Helm, M.; Zhou, S.

Mid-infrared plasmonic sensing allows the direct targeting of molecules relevance in the so-called “vibrational fingerprint region”. Presently, heavily doped semiconductors exhibiting the potential to replace and outperform metals in the mid- infrared frequency range to revolutionize plasmonic devices. In this work, we demonstrate the occurrence of localized surface plasmon resonances (LSPR) in Te heavily-doped Si layers developed by ion implantation combined with flash lamp annealing. We fabricate micrometer-sized antennas out of the Te-hyperdoped Si layers by electron-beam lithography and reactive ion etching processes. The optical response characterized by Fourier-transform infrared (FTIR) spectroscopy demonstrates the enhancement of localized plasmon resonances in antennas, from mid- to far- infrared frequency range. Our results set a new path toward integration of plasmonic sensors with the one-chip CMOS platform.

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  • Poster
    DPG-Frühjahrstagung 2018, 14.03.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28564
Publ.-Id: 28564


Towards a Vertical Nanopillar-Based Single Electron Transistor – A High-Temperature Ion Beam Irradiation Approach

Xu, X.; Heinig, K.; Möller, W.; Gharbi, A.; Tiron, R.; Engelmann, H.; Bischoff, L.; Prüfer, T.; Hübner, R.; Facsko, S.; Hlawacek, G.; von Borany, J.

We propose an ion irradiation based method to fabricate a single Si nanocrystal embedded in a Si(001)/SiO2/Si nanopillar layer stack as a prerequisite for manufacturing a CMOS-compatible, room-temperature Si single electron transistor. After either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) irradiation of the nanopillars (with diameter of 35 nm and height of 70 nm) at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the program TRI3DYN. We assume that it is the result from the ion beam induced amophisation of Si accompanied by the ion hammering effect. The amorphous nano-structure behaves viscously and the surface capillary force dictates the final shape. To confirm such a theory, ion irradiation at elevated temperatures (up to 672 K) has been performed and no plastic deformation was observed under these conditions. Bright-field transmission electron microscopy micrographs confirmed the crystallinity of the substrate and nanopillars after HT-irradiation.
When a semiconductor material such as silicon is heated above its amorphisation critical temperature during ion irradiation, it stays crystalline due to an interplay between ion damage and dynamic annealing process. Viscous flow does not occur for the crystalline nano-structures and the shape remains intact. This effect has been observed previously mainly for swift heavy ions and energies higher than 100 keV. Such high-temperature irradiation, when carried out on a nanopillar with Si/SiO2/Si layer stack, would induce ion beam mixing without suffering from the plastic deformation of the nanostructure. Due to a limited mixing volume, single Si-NCs would form in a subsequent rapid thermal annealing process via Oswald ripening and serve as a basic structure of a gate-all-around single electron transistor device.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

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  • Lecture (Conference)
    2018 MRS Fall Meeting & Exhibit, 25.11.2018, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-28563
Publ.-Id: 28563


Synthesis and characterization of transition-metal germanides

Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Helm, M.; Zhou, S.; Prucnal, S.

Si was sufficient to fulfil the requirements of microelectronic industry for more than five decades. Further progress based on the miniaturisation of transistors is challenging. Therefore new materials and concepts are considered for the next generation of nanoelectronics. In this work, we present the formation of transition-metal germanides epitaxially grown on Ge wafer. Those materials have great promise for both the ohmic contacts to n-type Ge with extremely low specific contact resistivity and spintronics. The transition-metal germanides are synthesized by metal sputtering on Ge followed by millisecond range flash lamp annealing which is suitable for larger-area fabrication and compatible with CMOS technology. On one hand, orthorhombic NiGe whose contact resistivity is only around 1.2×10-6 Ω cm2, is beneficial for achieving high-performance Ge-based nano-electronic devices. On the other hand, cubic FeGe with B20 phase is a Skyrmion-carrier material attractive for spintronics. In summary, the epitaxial transition-metal germanides materials can be obtained by a novel epitaxial approach which provides insight to their technological usage.

Keywords: transition-metal germanides; spintronics

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  • Poster
    2018 DPG Spring Meeting Berlin, 12.03.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28562
Publ.-Id: 28562


Ultra-fast solid phase epitaxy of Mn5Ge3 on (001) Ge substrate

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

In the present work, we report on epitaxial growth of ferromagnetic Mn5Ge3 thin films on (001) Ge substrates induced by Mn in-diffusion during non-equilibrium flash lamp annealing for 20 ms. The ferromagnetic Mn5Ge3/Ge samples with very sharp interface between the Mn5Ge3 layer and the Ge substrate can be used to fabricate spintronic devices. Temperature-dependent magnetization reveals a Curie temperature of 282 K which can be tuned much above room temperature by strain engineering and/or co-doping with C. The microstructural properties of the fabricated films were investigated by X-ray diffraction, cross-sectional TEM and Rutherford backscattering spectrometry. Both used material and technology are highly compatible with complementary metal-oxide-semiconductor (CMOS) technology and can be used for spintronics.

Keywords: Epitaxial growth; ferromagnetic; flash lamp annealing

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  • Poster
    2018 EMRS Spring Meeting Strasbourg, 18.06.2018, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-28561
Publ.-Id: 28561


Challenges of the Circular Economy: A Material, Metallurgical, and Product Design Perspective

Reuter, M.; van Schaik, A.; Gutzmer, J.; Bartie, N.; Abadías-Llamas, A.

Circular economy’s (CE) noble aims maximize resource efficiency (RE) by among others extending product life cycles and using wastes as resources. Modern society’s vast and increasing amounts of waste and consumer goods, their complexity and functional material combinations is challenging the viability of the CE in spite of various alternative business models promising otherwise. The metallurgical processing of CE enabling technologies requires in the end a sophisticated and agile metallurgical infrastructure. The challenges of reaching a CE will among others be highlighted in terms thermodynamics, transfer processes, technology platforms, digitalization of the processes of the CE stakeholders, design for recycling (DfR) based on a product (mineral)-centric approach, challenging material centric considerations. Integrating product centric considerations into the water, energy, transport, heavy industry, and other smart grid systems will maximize the RE of future smart sustainable cities, providing the fundamental detail for realizing and innovating the United Nation’s Sustainability Development Goals.

Keywords: Circular economy; Process metallurgy; Thermoeconomics; Exergy; Design for Recycling

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Permalink: https://www.hzdr.de/publications/Publ-28559
Publ.-Id: 28559


The Geo-metallurgy of the circular economy: Fairphone

Reuter, M. A.

tools - HSC Sim & GaBi LCA
Particle description of recycling systems inclusive of exergy & energy
Recycling
Analysis of systems: Rock, residue, recyclate to refined metal
Copper production system: Irreversibility analysis of system & Footprint of complete system
Bill-of-Materials & Full Material Declaration linked to metallurgy, alloy and materials production

Keywords: HSC Sim; GaBi LCA; recycling systems; exergy; energy; Recycling

  • Invited lecture (Conferences)
    International Mineral Processing Congress, 17.-21.09.2018, Moskau, Russland

Permalink: https://www.hzdr.de/publications/Publ-28558
Publ.-Id: 28558


Thermodynamic evaluation using the law of mass action under consideration of the activity coefficients in the system NdCl3-HCl (or NaOH)-H2O-DEHPA-kerosene

Scharf, C.; Ditze, A.

For the recovery of neodymium, an important rare earth metal, solvent extraction using DEHPA as extractant is a possible process for winning and recycling. A preceding study by the authors has provided extensive experimental data of the system neodymium-chloride-hydrochloric acid (or sodium hydroxide)-water-di-(2-ethylhexyl)phosphoric acid (DEHPA)-kerosene. It was found that the description of the reaction Nd3+ + 3 (DEHPA)2 <=> Nd(DEHP·DEHPA)3 + 3 H+ by an ideal mass action law is only partly satisfactory. This article investigates the contribution of several parameters to non-ideality. On this basis, expressions for activity coefficients of neodymium in the aqueous phase as well as DEHPA and neodymium in the organic phase are derived. The resulting equations are shown to represent the system with considerably better accuracy than previously possible.

Keywords: thermodynamic evaluation; solvent extraction; neodymium; DEHPA

Permalink: https://www.hzdr.de/publications/Publ-28557
Publ.-Id: 28557


CIRCULAR ECONOMY STRATEGIES - Responsible Business Practices // Process Model Based Footprints Using HSC Chemistry Software

Reuter, M. A.; Roine, A.

SusCritMat aims to educate people from Master’s student level up, both in industry and academia about important aspects of Sustainable critical raw materials. In a novel concept, it introduces courses on these complex and interdisciplinary topics in a modula structure, adaptable to a variety of different formats and accessible to both students and managers in industry. These courses will develop new skills which will help participants to better understand the impact and role of critical raw materials in the whole value chain; enabling them to identify and mitigate risks. Understanding the bigger picture and the interconnected nature of global business and society is increasingly necessary to and valued by industry. SusCritMat is an EU-funded project that brings together the technical and pedagogical expertise of leading educational institutions and business partners. It uses and creates teaching materials which can be combined into different course formats. Multi-media education materials will be made available to participants of summer and winter schools so that they can work with state-of-the-art techniques and data.

Keywords: Circular Economy; resource efficiency; sustainability; Digitalization; Simulation

  • Lecture (others)
    SusCritMat Autumn School for Professionals 2018, 24.-26.10.2018, Delft, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-28556
Publ.-Id: 28556


Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

Schramm, A.; Bock, B.; Schmidt, A.; Zienert, T.; Ditze, A.; Scharf, C.; Aneziris, C. G.

To investigate possible reactions between differently coated carbon-bonded alumina filters and an AZ91 magnesium alloy melt, immersion tests were carried out. Uncoated as well as MgAl2O4-, Al2O3-, nano- (carbon nano tubes/alumina nano sheets) and MgO-C-coated filters were tested. Thermodynamic calculations showed that only magnesia (MgO) and carbon are stable against molten magnesium; alumina (Al2O3) and spinel (MgAl2O4) will be reduced under the formation of magnesia. Optical and scanning electron microscopy as well as EDX analysis were performed near and at the filter-magnesium alloy-interface of the cooled and sectioned filter samples after their immersion into the AZ91 melt. The results of the thermodynamic calculations were confirmed by the experiments. The MgO-C-coated filter was the only one that did not show an in situ-formed layer on its surface after being in contact with the magnesium alloy melt. The alumina- or spinel-containing filter surfaces displayed platelet-like in situ layers after their contact with the molten AZ91. The results of the EDX analysis of these layers suggest their composition of MgO, since notable respective Mg and O contents were detected, as predicted by the calculations.

Keywords: Ceramic Foam Filter; Interfaces; Al2O3; MgO

Permalink: https://www.hzdr.de/publications/Publ-28555
Publ.-Id: 28555


Semi-Solid remelting of Magnesium-Chips

Ohmann, S.; Ditze, A.; Scharf, C.

Compact and loose magnesium chips were processed by means of remelting. The remelting was successfully performed using the new method of semi-solid melting, without the addition of flux, at temperatures between 580°C and 600°C. In this temperature range, the exothermic reaction between magnesium and the oxygen present in the surrounding atmosphere is avoided; in addition, the oxygen layer of the chips is stripped off by the particles of the semi-solid melt. Results show that more than 95% of the magnesium chips can be recovered as metal. Experiments were performed on different scales to obtain production parameters for the recycling process. Larger particle sizes of magnesium chips can be remelted faster than smaller ones. The ability to remelt at temperatures in the semi-solid region of alloys demonstrates the possibility of recovering virtually all of the metal from the chips.

Permalink: https://www.hzdr.de/publications/Publ-28554
Publ.-Id: 28554


System integration, Environmental impact and Business models

Reuter, M. A.

Determine economic feasibility (OPEX and CAPEX) for industrial scale pretreatment based on different energy sources and their integration with existing industrial production of Mn-alloys for different cases;
Prepare a business plan for implementation of pretreatment technology at the project partners;
Prepare a strategy for future exploitation of the developed technology outside the project consortium and identify how this will reduce CO2 emissions also by including the embodied energy of the system;
Assess environmental impact on manganese alloy production, especially effect on CO2 emission and energy consumption of industrial scale pretreatment in separate unit integrated with existing industrial Mn-alloy production. This will be estimated by linking system simulation with environmental footprint using LCA and Life Cycle Cost analysis tools; and
Maximize the resource efficiency of manganese production by optimising the processing and the infrastructure of the system of technologies. This will be based on applied scales for mass flows and production processes. Both energy and exergy efficiency will be maximized.

Keywords: energy efficiency; exergy efficiency; resource efficiency

  • Lecture (others)
    PreMa Project Meeting, 22.-23.10.2018, Trondheim, Norwegen
  • Lecture (others)
    PreMa Projekt Meeting, 13.-14.11.2019, Oberursel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28553
Publ.-Id: 28553


Multi-source hyperspectral imaging of carbonatite-hosted REE-Nb-Ta mineralization at Marinkas Quellen, Namibia

Booysen, R.; Zimmermann, R.; Lorenz, S.; Gloaguen, R.; Nex, P. A. M.

The demand for mineral and metalliferous resources needs to match the continued global rise in population and global economic growth. Rare Earth Elements (REEs), Niobium (Nb) and Tantalum (Ta) are such deposits in high demand. This global rise makes it difficult to meet the growing demand using only the currently available resources, such as recycled REEs and known REE deposits. Although the concept of a purely circular economy is very attractive through the use of recyclable REE-Nb-Ta, this model is not completely sustainable due to the increased energy needed to bolster such a model. Therefore, a renewed focus on the exploration of REE-Nb-Ta deposits is imperative to ensure the future development of this commodity.
Traditional exploration techniques are mainly based on extensive field work supported by geophysical surveying. Restrictions such as field accessibility, financial status, area size and climate can hinder these traditional exploration techniques. Hence, we suggest to increase the use of multi-source and multi-scale hyperspectral remote sensing in order to decrease conventional restrictions in the exploration of minerals through the use of aerial and ground-based methods. The multi-scale, multi-source approach will consist of a downscaling procedure, moving from low spatial resolution to high spatial resolution. Firstly, satellite data (Sentinel-2) will be used to identify the study area, then hyperspectral airborne data (HyMap) will be used to refine the area of interest. Subsequently, a snapshot hyperspectral camera will be attached to a UAV to acquire drone-borne data for the investigation of the deposit in more detail. We further argue that the addition of drone-borne hyperspectral data can also vastly improve the accuracy of field mapping in future mineral exploration. Drone-borne measurements can supplement and direct geological observation immediately in the field and therefore allow better integration with in-situ ground investigations. In particular, in inaccessible and remote areas with little infra-structure, such systems are an excellent reconnaissance tool because it allows a systematic, dense and completely non-invasive surveying, which is often not possible using ground-based techniques. Additionally, spectral and spatial information will be integrated by combining drone-borne hyperspectral and Light Detection And Raging (LiDAR) data to provide more accurate classification results.
Ultimately, the corrected drone-borne data provide information on the spectral signatures of outcropping lithologies to the exploration teams. This is achieved by using end-member modelling and classification techniques such as non-linear machine learning algorithms, e.g., Neural Networks and decision tree based methods. The drone based data are integrated in a comprehensive workflow including in-situ acquisitions and results in an hypercloud. The validation of the resulting digital outcrop is performed via field spectroscopy, portable XRF and representative geochemical whole-rock analysis.
The area of interest for this study is the massive carbonatite intrusion at Marinkas Quellen, Namibia. The location is in a remote environment and characterized by difficult terrains and a complete carbonatite suite (e.g. calsio-, ferro- and magnesio-carbonatites). The first two factors would normally impede or restrict traditional field surveying. Preliminary results indicate that drone-borne surveying has a very high potential to directly detect REE-concentrations and indicator minerals for Nb and Ta, in fundamentally lowering the acquisition costs and increasing the information potential of data captured in the field.

Keywords: REEs; Multis-source; Hyperspectral; Exploration; Marinkas Quellen

  • Poster
    WHISPERS - Hyperspectral Image and Signal Processing Workshop, 23.-26.09.2018, Amsterdam, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-28552
Publ.-Id: 28552


Experimental study of the natural convection heat transfer performance for finned oval tubes at different tube tilt angles

Unger, S.; Beyer, M.; Thiele, J.; Hampel, U.

The natural convection heat transfer of finned oval tubes was studied for different tube tilt angles (0° to 40°), fin spacing (6 mm to 16 mm) and Rayleigh numbers (11000 to 130000). Fin efficiency was determined by temperature measurements along the fin surface and temperature gradient calculations. Nusselt number and volumetric heat flux density were chosen as assessment parameters for the thermal performance. A comparison of the experimental data with correlations from literature was made and good agreement was found. Furthermore, the uncertainty by the measurements was evaluated. In the horizontal tube orientation (0°) the Nusselt number increases with fin spacing, however the fin efficiency and the volumetric heat flux density reduce. The tilt angle of the longitudinal tube axis was found to have an essential impact on the thermal performance, in particular when the fin spacing is high. For the higher fin spacing values the horizontal orientation gives highest Nusselt number and volumetric heat flux density. At tube tilt angle of 40° the thermal performance becomes lowest for all fin spacing values. When the fin spacing is low, the effect of tube tilt angle is minor. From the experimental results correlations between Nusselt number, Rayleigh number, fin spacing and tube tilt angle are proposed to assist the future design of heat exchanger with tilted finned oval tubes.

Keywords: Finned oval tubes; Natural convection; Heat transfer; Tube tilt angle; Heat transfer correlation

Permalink: https://www.hzdr.de/publications/Publ-28551
Publ.-Id: 28551


Stoffkreislauf der Metalle – von der Gewinnung bis zum Recycling

Reuter, M. A.; Stelter, M.

In der heutigen Zeit bestimmen Metalle unser tägliches Leben. Im Bereich der Mobilität – sei es beim Auto mit Verbrennungsmotor oder bei Elektrofahrzeugen – sind immer Metalle die wesentlichen Bestandteile, ohne die unsere Welt nicht funktionieren würde. Im Bereich der Kommunikation, der Unterhaltungselektronik, aber auch in der Medizin sind sie ebenfalls unverzichtbar. Ihre herausragenden Eigenschaften – wie Härte, Duktilität, Umformbarkeit, Korrosionsbeständigkeit – machen sie zu idealen Werkstoffen für fast alle Anwendungen. Besonders zeichnet sie aber die Recyclingfähigkeit aus, denn Metalle können prinzipiell zu 100 % nach ihrer Nutzung zurückgewonnen werden.
Dass wir dies bisher nur eingeschränkt tun, hat verschiedene Ursachen. In der Arbeitsgruppe sollen die Aspekte der Kreislaufwirtschaft beleuchtet werden. So werden technologische Möglichkeiten und Grenzen in Beziehung zu den ökonomischen Bezügen gestellt. Gibt es eine optimale Kreislaufführung und, wenn ja, wie sieht sie aus? Welche Faktoren beeinflussen die dafür notwendigen unangewandten Prozesse? Ist es sinnvoll, in jedem Fall zu versuchen, eine Recyclingrate von 100 % zu erreichen? Und ist dies überhaupt möglich?
Eine differenzierte Betrachtung bezüglich unterschiedlicher Stoffgruppen ist dabei erforderlich. Eine weiter in die Details eindringende Betrachtung soll am Beispiel der Metalle den Teilnehmenden der Arbeitsgruppe Chancen und Risiken der Stoffkreislaufführung vermitteln. In Gesprächsrunden und Diskussionen sollen die Vor- und Nachteile von technologischen Prozessen herausgearbeitet und deren Nutzen für die Kreislaufführung der Werkstoffe bewertet werden.

Keywords: Recyclingfähigkeit; Metalle; optimale Kreislaufführung

  • Lecture (others)
    Workshop - Sommerakademie der Studienstiftung, 19.-30.08.2018, St. Johann, Italien

Permalink: https://www.hzdr.de/publications/Publ-28550
Publ.-Id: 28550


Circular Economy engineering - Recycling 4.0 - Challenges of the circular economy

Reuter, M. A.

The last hundred years have brought an unprecedented increase in natural resource use. This trend is likely to continue in the coming decades. Global resource use is expected to double by 2030. For Europe, these developments raise major concerns . Europe's economy depends on an uninterrupted flow of natural resources , metals, minerals, energy carriers and other raw materials , with imports providing a substantial proportion of these materials in many cases. Increasingly, this dependence will be a source of vulnerability, as growing global competition for natural resources has contributed to marked increases in price levels and volatility. Uncertain and unstable prices disrupt the industrial sectors that are dependent on these resources. At the same time, rapid increases in extraction and exploitation of natural resources are having a wide range of negative environmental impacts, particularly in Europe. Air, water and soil pollution, acidification of ecosystems, biodiversity loss, climate change and waste generation put economic and social well-being at risk. Creating a circular economy in Europe can help to address many of these challenges, and further improve the efficiency of resource use. It will have obvious economic benefits, reducing costs and risks while enhancing competitiveness. European leadership in the transition to a circular economy also offers opportunities securing first-mover advantages in the global economy.

The conference will address the issues impacting the transition from the linear take-make-consume-dispose economic model that currently dominates to a circular model that represents a fundamental alternative and explore the huge challenges and business opportunities in a circular economy. The conference will include presentations and panel discussions featuring renowned researchers within circular economy and leading Polish businesses presenting relevant projects and views on why and how the circular economy is introduced in their factories. It will bring together industry leaders, authorities and city planners, technology providers, business consultants, researchers and inventors, all with the common goal of driving innovation in new materials and better, more economic products and services and securing first-mover advantages in the global economy.

Recycling 4.0: digitalizing the system
Recycling 4.0: physics of separation
Recycling 4.0: industrial applications
Recycling 4.0 digital platforms

Keywords: Recycling 4.0

  • Invited lecture (Conferences)
    European Technology Forum 2018 / From Waste to Resources, 26.-27.09.2018, Katowice, Polen
  • Invited lecture (Conferences)
    THM-Kolloquim, 08.10.2018, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28549
Publ.-Id: 28549


SOCRATES 3nd Network-Wide Event

Reuter, M. A.

What have we done so far?
Current Status of SOCRATES projects
Communication, Dissemination and Exploitation progress
What are we going to do? Our contribution to SOCRATES

Keywords: SOCRATES; Copper production process; HSC Sim

  • Lecture (others)
    SOCRATES 3nd Network-Wide Event, 13.-16.02.2018, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28548
Publ.-Id: 28548


Numerical Studies of Normal Conducting Deflecting Cavity Designs for the ELBE Accelerator

Hallilingaiah, T. G.; van Rienen, U.; Arnold, A.; Lehnert, U.; Michel, P.

Currently, in the electron linac ELBE there is a single beam line. Therefore, at any given time only single user can use the beam. Moreover, as different user experiments require distinct beam intensity settings, not all the experiments fully utilize the 13 MHz CW beam capability of the facility. To utilize the full beam capacity, multiple beam lines can be established by using an array of transverse deflecting structures. For that, an RF cavity was the design choice due to its inherent advantages with respect to repeatability of the kick voltage amplitude and phase, and the possibility of CW operation in the MHz range. Potential design candidates are the CEBAF RF separator, the three proposed crab cavities for the HL-LHC upgrade project, and a novel NC deflecting cavity design. In this comparative study, the figures of merit of the cavities are computed from electromagnetic field simulations for a transverse voltage of 300 kV. This comparative study supported our selection of the deflecting cavity design for ELBE.

Keywords: normal conducting; RF cavity; RF kicker; beam spreader

Related publications

  • Open Access Logo Contribution to proceedings
    9th International Particle Accelerator Conference, 29.04.-04.05.2018, Vancouver, British Columbia,, Canada
    Proceedings of the 9th International Particle Accelerator Conference: JACoW, ISBN 978-3-95450-184-7, 3824-3827
    DOI: 10.18429/JACoW-IPAC2018-THPAL074

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Permalink: https://www.hzdr.de/publications/Publ-28547
Publ.-Id: 28547


Sub-threshold production of K0s mesons and Λ hyperons in Au(1.23A GeV)+Au

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.; Leifels, Y.

We present first data on sub-threshold production of K0 s mesons and Λ hyperons in Au+Au collisions at √sNN = 2.4 GeV. We observe an universal scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their part> scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable χ2 values.

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Permalink: https://www.hzdr.de/publications/Publ-28546
Publ.-Id: 28546


Mixed-valent neptunium oligomer complexes based on cation-cation interactions

Schöne, S.; März, J.; Stumpf, T.; Ikeda-Ohno, A.

Mixed-valent tri- and tetranuclear complexes of neptunium, [{NpIVCl4}{NpVO2Cl(THF)3}2]·THF and [{NpIVCl3}{NpVO2(μ2-Cl)(THF)2}3{μ3-Cl}] (THF = tetrahydrofuran), were synthesised and characterised. Both the complexes are formed via the cation-cation interactions between the Np(IV) centre and the axial oxygens of the neptunyl(V) unit (i.e. transdioxo NpO2+ cation), demonstrating the potential of cation-cation interactions for further exploring the oligomer/cluster chemistry of actinides.

Keywords: actinides; neptunium; mixed-valence; oligomers; polymers; coordination; structure characterisation; cation-cation interactions

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Permalink: https://www.hzdr.de/publications/Publ-28545
Publ.-Id: 28545


Strong absorption of hadrons with hidden and open strangeness in nuclear matter

Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Chernenko, S.; Chlad, L.; Chudoba, P.; Ciepal, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kornas, F.; Kotte, R.; Kubos, J.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Linev, S.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Malige, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowsk, K.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Prozorov, A. P.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Smyrski, J.; Spataro, S.; Spies, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Ungethüm, C.; Vazquez Doce, O.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.

We present the first observation of K- and φabsorption within nuclear matter by means of π- -induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K-/K+)W / (K-/K+)C is found to be 0.319 \pm 0.009(stat)+0.014-0.012 (syst) indicating a larger absorption of K- in heavier targets as compared to lighter ones. The measured φ/K- ratios in π-+C and π^- +W reactions within the HADES acceptance are found to be equal to 0.55±0.03(stat)+0.06−0.07 (syst) and to 0.63±0.05(stat)−0.11+0.11 (syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the φmeson in nuclear medium is strongly coupled to the K- dynamics. The large difference in the φ production off C and W nuclei is discussed in terms of a strong \phiN in-medium coupling.

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Permalink: https://www.hzdr.de/publications/Publ-28544
Publ.-Id: 28544


Observation of multiple magnetic phases and complex nanostructures in Co implanted amorphous carbon films

Suschke, K.; Gupta, P.; Williams, G. V. M.; Hübner, R.; Markwitz, A.; Kennedy, J.

Room temperature implantation of 30 keV Co ions into an amorphous carbon film with a high fluence of 1.2×1017 Co/cm2 results in formation of magnetic nanostructures displaying multiple magnetic phases. Cross-sectional TEM images show formation of Co containing nanoparticles at the surface and near-surface regions of the implanted films. EDXS measurements suggest the nanoparticles to be composed primarily of Co and O at the surface and Co and C in deeper regions. These nanoparticles with differing compositions were observed to be segregated by a thin layer devoid of Co. Magnetic measurements reveal the presence of superparamagnetic behavior from small CoxC nanoclusters with a blocking temperature of 5 K. There is a small fraction of larger CoxC nanoclusters that show magnetic hysteresis even at room temperature. The saturation magnetic moment is as high as 0.51 μB/Co at 2 K and 0.32 μB/Co at room temperature. Spin-disorder is seen with a range of spin glass temperatures below ∼70 K. Our high fluence Co implantation into amorphous carbon has resulted in the formation of complex magnetic nanostructures composed of cobalt, oxygen, and carbon. These nanostructures give rise to multiple magnetic phases such as superparamagnetism, spin glass, ferromagnetism, and possibly antiferromagnetism.

Keywords: a-C; DLC; Ion implantation; Superparamagnetic; Magnetization; Cobalt oxide; Cobalt carbide

Related publications

  • Journal of Physics and Chemistry of Solids 127(2019), 158-163

Permalink: https://www.hzdr.de/publications/Publ-28543
Publ.-Id: 28543


On a spectral problem in magnetohydrodynamics and its relevance for the geodynamo

Stefani, F.; Tretter, C.

One of the most remarkable features of the geodynamo is the irregular occurrence of magnetic field reversals. Starting with the operator theoretical treatment of a non-selfadjoint dynamo operator, we elaborate a dynamical picture of those reversals which relies on the existence of exceptional spectral points.

Keywords: geodynamo; magnetohydrodynamics

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Permalink: https://www.hzdr.de/publications/Publ-28542
Publ.-Id: 28542


Laser Plasma Based Accelerators for Radiobiological Applications - From Research Field MATTER to HEALTH

Metzkes-Ng, J.; Levy, Dan

Laser Plasma Based Accelerators for Radiobiological Applications - From Research Field MATTER to HEALTH

  • Invited lecture (Conferences)
    Festive Symposium on the occasion of the inaugruation of the Helmholtz Tel Aviv Office, 22.10.2018, Tel Aviv, Israel

Permalink: https://www.hzdr.de/publications/Publ-28541
Publ.-Id: 28541


Response of the QED(2) Vacuum to a Quench: Long-term Oscillations of the Electric Field and the Pair Creation Rate

Otto, A.; Graeveling, D.; Kämpfer, B.

We consider -- within QED(2) -- the backreaction to the Schwinger pair creation in a time dependent, spatially homogeneous electric field. Our focus is the depletion of the external field as a quench and the subsequent long-term evolution of the resulting electric field. Our numerical solutions of the self consistent, fully backreacted dynamical equations exhibit a self-sustaining oscillation of both the electric field and the pair number depending on the coupling strength.

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Permalink: https://www.hzdr.de/publications/Publ-28540
Publ.-Id: 28540


Probing Interlayer Excitons in a Vertical van der Waals p-n Junction using Scanning Probe Microscopy Technique

Rahaman, M.; Wagner, C.; Mukherjee, A.; Lopez-Rivera, A.; Gemming, S.; Zahn, D. R. T.

Two dimensional (2D) semiconductors feature exceptional optoelectronic properties controlled by strong confinement in one dimension. In this contribution, we studied interlayer excitons in a vertical p-n junction made of bilayer n-type MoS2 and few layers p-type GaSe using current sensing atomic force microscopy (CSAFM). The p-n interface is prepared by mechanical exfoliation onto highly ordered pyrolytic graphite (HOPG). Thus the heterostructure creates an ideal layered system with HOPG serving as the bottom contact for the electrical characterization. Home-built Au tips are used as the top contact in CSAFM mode. During the basic diode characterization, the p-n interface shows strong rectification behavior with a rectification ratio of 104 at ±1 V. The I-V characteristics reveal pronounced photovoltaic effects with a fill factor of 0.55 by excitation below the band gap. This phenomenon can be explained by means of the dissociation of interlayer excitons at the interface. The possibility of the interlayer exciton formation is indicated by density functional theory (DFT) calculations on this heterostructure: the valence band of GaSe and the conduction band of MoS2 contribute to an excitonic state at an energy of about 1.5 eV. The proof of such excitonic transition is provided by photoluminescence measurement at the p-n interface. Finally, photocurrent mapping at the interface under 785 nm excitation provides evidence of efficient extraction of such excitons. Our results demonstrate two dimensional device for future optoelectronics and light harvesting assisted by interlayer excitons in van der Waals heterostructure.

Keywords: van der Waals heterojunction; interlayer exciton; MoS2; GaSe; p-n junction; optoelectronics; density functional theory

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Publ.-Id: 28539


Damage formation and Er structural incorporation in m-plane and a-plane ZnO

Macková, A.; Malinský, P.; Jagerová, A.; Mikšová, R.; Nekvindová, P.; Cajzl, J.; Rinkevičiūtė, E.; Akhmadaliev, S.

The various crystallographic orientations in semiconductors as ZnO exhibit different resistivity under the ion beam irradiation/implantation. Study of the various crystallographic orientations is mandatory for nano-structured semiconductor system development. This paper reports on the implantation damage build-up, structural modification and Er dopant position in a-plane and m-plane ZnO implanted with Er+ 400 keV ions at the ion fluences 5 × 1014, 2.5 × 1015, 5 × 1015 cm-2 and subsequently annealed at 600 °C in O2 atmosphere using Rutherford Back-Scattering spectrometry (RBS) in channelling mode as well as using Raman spectroscopy. Strongly suppressed surface damage formation was observed in both crystallographic orientations compared to the deep damage growth with the increased ion implantation fluence. More progressive damage accumulation appeared in m-plane ZnO compared to a-plane ZnO. Simultaneously, the strong Er out-diffusion depth profile in m-plane ZnO accompanied by the damage accumulation at the surface was observed after the annealing. Contrary, the surface recovery accompanied by Er concentration depth profiles keeping a normal distribution with a small maximum shift to the surface was observed in a-plane ZnO. Different structure recovery and Er behaviour was evidenced in a-plane and m-plane ZnO by RBS-C, moreover Raman spectroscopy proved a lower damage at higher ion fluences introduced in a-plane ZnO compared to m-plane. The structure modifications were discussed in connection with a damage accumulation and Er concentration depth profile shape in various ZnO crystallographic orientations in as-implanted and as-annealed samples.

Keywords: a-Plane and m-plane ZnO doped; Damage accumulation asymmetry; Er ion implantation in ZnO; RBS channelling; Damage depth profiling

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Permalink: https://www.hzdr.de/publications/Publ-28538
Publ.-Id: 28538


Defects in hydrogen implanted SiC

Zhang, X.; Li, Q.; Wang, M.; Zhang, Z.; Akhmadaliev, S.; Zhou, S.; Wu, Y.; Guo, B.

SiC is a widely used wide-bandgap semiconductor. Ion implantation is often employed in SiC for doping, defect engineering and transferring of SiC thin films on different substrates. To transfer SiC or to get freestanding thin SiC films by "smart-cut" [Appl. Phys. Lett. 112 (2018) 192102], a large fluence of hydrogen (proton) ion implantation will be applied. Here, we show the structure and defect properties in 6H-SiC single crystals after hydrogen implantation up to a fluence of 5 x 1016 cm-2 at different energies of ions. We present the characterization by Rutherford Backscattering/Channeling spectrometry, Raman spectroscopy and electron spin resonance. Upon H+ ion implantation, point defects are mainly created and cause the lattice vibration softening. Our analysis also suggests that H+ ion implantation induces less lattice disorder than heavy ions at fluences producing the same number of displacements per atom. We also discuss the possible nature of the point defects and their influence on the electrical properties.

Keywords: SiC; Defects; Ion implantation; Raman-Spectroscopy; Damage formation; Ion; Surface; Neutron

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Permalink: https://www.hzdr.de/publications/Publ-28537
Publ.-Id: 28537


Thermocapillary convection during hydrogen evolution at microelectrodes

Massing, J.; Mutschke, G.; Baczyzmalski, D.; Hossain, S. S.; Yang, X.; Eckert, K.; Cierpka, C.

The origin of strong electrolyte flow during water electrolysis is investigated, that arises at the interface between electrolyte and hydrogen bubbles evolving at microelectrodes. This Marangoni convection was unveiled only recently (Yang et al., PCCP, 2018, [1]) and is supposed to be driven by shear stress at the gas-liquid interface caused by thermal and concentration gradients. The present work firstly allows a quantification of the thermocapillary effect and discusses further contributions to the Marangoni convection which may arise also from the electrocapillary effect. Hydrogen gas bubbles were electrolytically generated at a horizontal Pt microelectrode in a 1MH2SO4 solution. Simultaneous measurements of the velocity and the temperature field of the electrolyte close to the bubble interface were performed by means of particle tracking velocimetry and luminescent lifetime imaging. Additionally, corresponding numerical simulations of the temperature distribution in the cell and the electrolyte flow resulting from thermocapillary stress only were performed. The results confirm significant Ohmic heating near the micro-electrode and a strong flow driven along the interface away from the microelectrode. The results further show an excellent match between simulation and experiment for both the velocity and the temperature field within the wedge-like electrolyte volume at the bubble foot close to the electrode, thus indicating the thermocapillary effect as the major driving mechanism of the convection. Further away from the microelectrode, but still below the bubble equator, however, quantitative differences between experiment and simulation appear in the velocity field, whereas the temperature gradient still matches well. Thus, additional effects must act on the interface, which are not yet included in the present simulation. The detailed discussion tends to rule out solution-based effects, generally referred to as solutal effects, whereas electrocapillary effects are likely to play a role. Finally, the thermocapillary effect is found to exert a force on the bubble which is retarding its departure from the electrode.

Keywords: Water electrolysis; Thermocapillary convection; Microbubbles; Fluorescence lifetime imaging; Numerical simulation; Hydrogen evolution

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Permalink: https://www.hzdr.de/publications/Publ-28536
Publ.-Id: 28536


Messung der Marangoniströmung an elektrochemisch erzeugten Wasserstoffblasen

Massing, J.; Baczyzmalski, D.; Yang, X.; Mutschke, G.; Eckert, K.; Cierpka, C.

Bei der Wasserstoffelektrolyse kann es aufgrund von Gradienten in der Konzentration und der Temperatur zu Gradienten in der Oberflächenspannung an der Phasengrenzfläche der Wasserstoffblase kommen. Die dadurch angetriebene Marangoniströmung konnte erstmals an einer Mikroelektrode für verschiedene Potentiale gemessen werden. Die Strömungsgeschwindigkeit korreliert eindeutig mit dem elektrischen Strom. Für die vorgestellte Untersuchung werden sowohl der Einfluss des Konzentrationsgradienten als auch der Einfluss des Temperaturgradienten diskutiert und eine Größenordnungsabschätzung zur Beschreibung des Phänomens durchgeführt. Erste Ergebnisse zu Temperaturmessungen auf der Basis von temperatursensitiven Partikeln an der Wasserstoffblase ergänzen die in der Größenordnungsabschätzung gemachten Annahmen und zeigen die lokale Erwärmung am Blasenfuß.

Keywords: Elektrolyse; Gasentwicklung; Wasserstoff; Mikroelektrode; PIV; Temperaturmessung

  • Lecture (Conference)
    26. Fachtagung "Experimentelle Strömungsmechanik", 04.-06.09.2018, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28535
Publ.-Id: 28535


Longitudinal modulation of electron-cooled C-12(6+) and O-16(8+) ion beams at heavy ion storage ring CSRe

Wang, H.; Wen, W.; Huang, Z.; Zhang, D.; Hai, B.; Bussmann, M.; Winters, D.; Zhao, D.; Zhu, X.; Li, J.; Li, X.; Mao, L.; Mao, R.; Zhao, T.; Yin, D.; Wu, J.; Yang, J.; Yuan, Y.; Ma, X.

The longitudinal dynamics of electron-cooled and radio-frequency (RF)-bunched C-12(6+) and O-16(8+) ion beams have been investigated at a heavy-ion experimental cooler storage ring CSRe. An rf-buncher was employed to longitudinally modulate the ion beams. A new resonant Schottky pick-up was applied to monitor the intensities and longitudinal dynamics of stored and electron-cooled ion beams. Using electron-cooling, the separated Schottky noise signals of the C-12(6+) and O-16(8+) ions were clearly observed in the Schottky spectrum. The storage times and the particle numbers of both ion beams were measured by Schottky noise, which demonstrated the ability to perform Schottky mass spectrometry measurements and also the measurement of highly charged ions at the CSRe. In addition, an enhancement of the Schottky noise signals was observed for rf-bunched ion beams, which could be used to diagnose the intensity ion beams at storage rings. Finally, a broadly longitudinal manipulation of the ion beams by scanning the bunching frequency was realized. The investigation of electron-ion recombination experiment at ultra-low collision energies by scanning the bunching frequency of the ion beams at the storage ring CSRe is proposed.

Keywords: electron cooloing; schottky; ion beam

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Permalink: https://www.hzdr.de/publications/Publ-28534
Publ.-Id: 28534


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