Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33272 Publications

Stability criterion for the magnetic separation of rare-earth ions

Lei, Z.ORC; Fritzsche, B.; Eckert, K.ORC
The stability criterion for the magnetic separation of rare-earth ions is studied, taking dysprosium Dy(iii) ions as an example. Emphasis is placed on quantifying the factors that limit the desired high enrichment. During magnetic separation, a layer enriched in Dy(iii) ions is generated via the surface evaporation of an aqueous solution which is levitated by the Kelvin force. Later, mass transport triggers instability in the enriched layer. The onset time and position of the instability is studied using an interferometer. The onset time signals that an advective process which significantly accelerates the stratification of enrichment is taking place, although the initial phase is quasi-diffusion-like. The onset position of the flow agrees well with that predicted with a generalized Rayleigh number (Ra∗=0) criterion which includes the Kelvin force term acting antiparallel to gravity. Further three-dimensional analysis of the potential energy, combining magnetic and gravitational terms, shows an energy barrier that has to be overcome to initiate instability. The position of the energy barrier coincides well with the onset position of the instability.
Keywords: Evaporation, Flow instability, Instability control, Optical interferometry, Transport phenomena

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Permalink: https://www.hzdr.de/publications/Publ-30582
Publ.-Id: 30582


Renewable Methanol Synthesis

Roode-Gutzmer, Q. I.ORC; Kaiser, D.; Bertau, M.
Renewable methanol production is an emerging technology that bridges the gap in the shift from fossil fuel to renewable energy. Two thirds of the global emission of CO₂ stems from humanity’s increasing energy need from fossil fuels. Renewable energy, mainly from solar and wind energy, suffers from supply intermittency, which current grid infrastructures cannot accommodate. Excess renewable energy can be harnessed to power the electrolysis of water to produce hydrogen, which can be used in the catalytic hydrogenation of waste CO₂ to produce renewable methanol. This review considers methanol production in the current context, regionally for Europe, which is dominated by Germany, and globally by China. Appropriate carbon-based feedstock for renewable methanol production is considered, as well as state-of-the-art renewable hydrogen production technologies. The economics of renewable methanol production necessitates the consideration of regionally relevant methanol derivatives. The thermodynamics, kinetics, catalytic reaction mechanism, operating conditions and reactor design are reviewed in the context of renewable methanol production to reveal the most up to date understanding.
Keywords: Catalysis, Energy storage, Hydrogenation of CO₂, Renewable methanol, Waste CO₂

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Permalink: https://www.hzdr.de/publications/Publ-30575
Publ.-Id: 30575


The role of gas impurities on the optical properties of sputtered Ti(Al)N coatings

Bohovičová, J.; Meško, M.; Méndez, Á.; Julin, J. A.ORC; Munnik, F.ORC; Hübner, R.; Grenzer, J.; Čaplovič, Ľ.; Krause, M.ORC
In this study, we investigated the role of impurities, such as H, C, and O on the optical properties of the Ti(Al)N coatings. For comparison, coatings were prepared by direct-current magnetron sputtering (DC-MS) and high-power impulse magnetron sputtering (HiPIMS) at the same average power. The elemental composition of the thin films was measured by elastic recoil detection analysis. Regardless of the deposition technique used, no significant difference in H and C concentrations were found. The analysis showed, that HiPIMS coatings contain less O impurities than the corresponding DC-MS films, despite the lower deposition rate. The reduced residual O content in HiPIMS coatings can be explained by the cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. Given the reduced O content, HiPIMS films showed higher optical reflectance for the entire measured spectral range.
  • Lecture (Conference)
    The 15th International Symposium on Sputtering and Plasma Processes, ISSP 2019, 11.-14.06.2019, Kanazawa, Japan
  • Poster
    The 15th International Symposium on Sputtering and Plasma Processes, ISSP 2019, 11.-14.06.2019, Kanazawa, Japan
  • Contribution to proceedings
    The 15th International Symposium on Sputtering and Plasma Processes, ISSP 2019, 11.-14.06.2019, Kanazawa, Japan

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Permalink: https://www.hzdr.de/publications/Publ-30572
Publ.-Id: 30572


Ultrafast Mid-Infrared and Terahertz Phenomena in Graphene

Winnerl, S.;
Graphene, the first atomically thin 2D material that was intensely investigated since its discovery in 2014, is a gapless semiconductor or semimetal with linear dispersion. Consequently, graphene absorbs light at all energies, in particular also at low photon energies in the THz frequency range. Here we show that pump-probe experiments at low photon energies can provide deep insights into the carrier dynamics. In particular, electron-phonon scattering can be disentangled from Coulomb scattering processes [1, 2]. Coulomb scattering in graphene is responsible for a number of unusual effects like strong Auger scattering under Landau quantization [3].
With respect to applications we present a graphene based detector with ultrafast response time of 40 ps. It operates in the very broad frequency range from visible to THz radiation [4].
[1] S. Winnerl, M. Orlita, P. Plochocka, P. Kossacki, M. Potemski, T. Winzer, E. Malic, A. Knorr, M. Sprinkle, C. Berger, W. A. de Heer, H. Schneider und M. Helm, Phys. Rev. Lett. 107, 237401 (2011).
[2] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm und S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).
[3] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm und S. Winnerl, Nature Phys. 11, 75 (2015).
[4] M. Mittendorff, J. Kamann, J. Eroms, D. Weiss, C. Drexler, S. D. Ganichev, J. Kerbusch, A. Erbe, R. J. Suess, T. E. Murphy, S. Chatterjee, K. Kolata, J. Ohser, J. C. König-Otto, H. Schneider, M. Helm, S. Winnerl, Optics Express 23, 28728 (2015).
Keywords: graphene, terahertz, ultrafast
  • Invited lecture (Conferences)
    Sino-German Bilateral Symposium on Low Dimensional Semiconductors and Opto-electronics Integration, 14.-17.11.2019, Changsha, China

Permalink: https://www.hzdr.de/publications/Publ-30568
Publ.-Id: 30568


Ge-based photoconductive emitters producing gapless broadband THz spectra

Singh, A.; Pashkin, A.; Winnerl, S.; Helm, M.; Schneider, H.;
We present photoconductive emitters
based on Ge featuring gapless
broadband spectra up to 13 THz. Thus they can fill the gap in the 5 – 10 THz range and can be excited
with fiber lasers.
Keywords: terahertz, broadband, photoconductive emitters
  • Lecture (Conference)
    CLEO/Europe-EQEC 2019, 23.-27.06.2019, Munich, Germany

Permalink: https://www.hzdr.de/publications/Publ-30567
Publ.-Id: 30567


Nonlinear THz resoponse of graphene plasmonic structures

Winnerl, S.; Jadidi, M. M.; Chin, M.; Seidl, A.; Schneider, H.; Helm, M.; Drew, H. D.; Murphey, T. E.; Mittendorff, M.;
Ribbons and discs based on doped graphene feature strong tunable plasmonic resonances. We show that excitation with THz radiation results in strong changes of transmission, even at moderate pump fluences. The response is due to a broadening and redshift for the plasmonic absorption line as charge carriers are heated. The response time is determined by the cooling of carriers, which is of the order of 10 ps.
Keywords: graphene, plasmonics, nonlinear terahertz spectroscopy
  • Invited lecture (Conferences)
    META 2019, the 10th International Conference on Metamaterials, Photonic Crystals and Plasmonics, 23.-26.07.2019, Lisbon, Portugal

Permalink: https://www.hzdr.de/publications/Publ-30566
Publ.-Id: 30566


Nonlinear THz spectroscopy in low-dimensional semiconductors using a free-electron laser

Winnerl, S.; Schmidt, J.; König-Otto, J. C.; Mittendorff, M.; Schneider, H.; Helm, M.;
Sources for intense THz pulses allow one to investigate interesting nonlinear effects in various solid-
state systems in a time-resolved manner. Here we discuss perturbative and non-perturbative nonlinear
effects in graphene-based systems and GaAs/AlGaAs quantum wells, respectively, which are excited by
intense, tunable, narrowband THz pulses from a free-electron laser (FEL).
For the graphene-based samples we have pursued two strategies to resonantly enhance the linear
and nonlinear response. One way is to apply a magnetic field perpendicular to the graphene layer.
This splits the linear band structure into a set of non-equidistant Landau levels. Four-wave mixing
experiments on the lowest Landau levels reveal a strong nonlinearity and a rapid dephasing of the
microscopic polarization on sub-ps timescales [1]. The second path for resonant enhancement is the
fabrication of ribbons and discs of doped graphene that feature a strong plasmonic response [2]. The
nonlinearity corresponding to the plasmonic response is based on a red-shift and broadening of the
absorption line caused by carrier heating.
While the previously discussed phenomena are perturbative nonlinear effects, FEL pulses are also
well suited to generate non-perturbative effects such as the intraexcitonic Autler-Townes effect and
double dressing of polaritons in microcavities [3, 4]. Here we present novel results on the dressing of
subbands in a single GaAs/AlGaAs quantum well by THz photons. To this end, the transition between
the second and third subband was resonantly pumped with the FEL. Broadband probing by THz time-
domain spectroscopy using GaP crystals for optical rectification enabled us to observe the THz-dressing
of the electronic states. Namely Autler-Townes splitting occurs at the transition between the first and
second subband while the transition from the second to the third subband is split into a Mollow triplet.
We are grateful to our collaborators M. M. Jadidi, T. E. Murphy, A. Belyanin, and E. Malic.
REFERENCES
1. König-Otto, J. C., Wang, Y., Belyanin, A., Berger, C. de Heer, W. A., Orlita, M., Pashkin, A.,
Schneider, H., Helm, M., Winnerl, S. "Four-wave mixing in Landau-quantized graphene," Nano
Lett., Vol. 17, 2184-2188, 2017.
2. Jadidi, M. M., Daniels, K. M., Myers-Ward, R. L., Gaskill, D. K., Konig-Otto, J. C., Winnerl, S.,
Sushkov, A. B., Drew, H. D., Murphy, T. E., Mittendorff, M. "Optical control of plasmonic hot
carriers in graphene," ACS Photonics, Vol. 6, 302307, 2019.
3. Wagner, M., Schneider, H., Stehr, D., Winnerl, S., Andrews, A. M., Schartner, S., Strasser, G.,
Helm, M. "Observation of the intraexciton Autler-Townes effect in GaAs=AlGaAs semiconductor
quantum wells," Phys. Rev. Lett., Vol. 105, 167401, 2010.
4. Pietka, B., Bobrovska, N., Stephan, D., Teich, M., Krol, M., Winnerl, S., Pashkin, A., Mirek, R.,
Lekenta, K., Morier-Genoud, F., Schneider, H., Deveaud, B., Helm, M., Matuszewski, M.,
Szczytko, J. "Doubly dressed bosons: exciton polaritons in a strong terahertz field," Phys. Rev.
Lett., Vol. 119, 077403, 2017.
Keywords: Free-electron laser, terahertz, nonlinear spectroscopy, low-dimensional semiconductors
  • Invited lecture (Conferences)
    Photonics & Electromagnetics Research Symposium (PIERS), 17.-20.06.2019, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-30565
Publ.-Id: 30565


THz nonlinear optics in graphene ribbons

Jadidi, M. M.; Daniels, K. M.; Myers-Ward, R.; Gaskill, D. K.; König-Otto, J.; Winnerl, S.; Sushkov, A.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.;
Graphene plasmonics is an emerging field due the unique combination of spectral tunability, strong plasmonic resonance and low losses. Here we study the nonlinear optical properties of graphene bilayer ribbons, featuring a plasmonic resonance at 3.9 THz, in time resolved experiments. A redshift of the plasmonic resonance is observed upon excitation with picosecond THz pulses. The unconventional nonlinear effect is explained by the optical response of hot carriers. Already at fairly low fluences in the µJ/cm2 range strong changes in transmission in the 10 % range can be induced. This strong response, together with the fast recovery determined by the electron cooling time (∼10 ps), makes the system promising for optical switching applications.
Keywords: graphene, plasmonics, nonlinear optics
  • Lecture (Conference)
    DPG-Frühjahrstagung, 31.03.-05.04.2019, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30564
Publ.-Id: 30564


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

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

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


Emergence of nanoscale patterns under ion induced non-equilibrium conditions

Facsko, S.ORC
Various self-organized nanoscale patterns emerge on surfaces which are irradiated by low- or medium-energy ion beams [1]. Depending on the irradiation conditions, hexagonally ordered dot or pit patterns, checkerboard patterns, as well as periodic ripple patterns are formed spontaneously due to the non-equilibrium conditions induced by continuous ion irradiation. In the collision cascade induced by an ion impact several defects, including interstitials, vacancies, ad-atoms and more complex defects are created. Below the recrystallization temperature, the surface is thus quickly amorphized by continuous ion irradiation and massive mass-transport takes place due to momentum-transfer from the ions to the near-surface atoms. Furthermore, ion sputtering is eroding the material non-homogeneously inducing a roughening instability.
On amorphous or amorphized surfaces, the formation of periodic patterns at high ion fluences results from an interplay of different roughening mechanisms, e.g. curvature dependent sputtering, ballistic mass redistribution, or altered surface stoichiometry on binary materials, and smoothing mechanisms, e.g. surface diffusion or viscous flow. Therefore, the patterns obey the symmetry given by the ion beam direction, i.e. hexagonal near order at normal incidence and two-fold symmetry with the ripple direction oriented perpendicular or parallel to the ion beam direction at off-normal incidence.
If the temperature during ion irradiation is above the recrystallization temperature of the material, ion induced defects are dynamically annealed and amorphization is prevented. The diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is now additionally affected by the Ehrlich-Schwoebel barrier, like in molecular beam epitaxy. Vacancies and ad-atoms are trapped on terraces and can nucleate to form pits or terraces, respectively. Patterns formed in this regime exhibit the symmetry of the crystal structure of the irradiated surface and often have inverse pyramidal shapes with well-defined facets [2,3]. Therefore, this mechanism is called “reverse epitaxy”.
1.1. Ion induced patterns on Ge and GaAs
In Fig. 1 examples of ion irradiation induced pattern are shown for amorphized Ge surface (a, b) and for Ge (001) (c) and GaAs (001) (d) irradiated above their respective recrystallization temperatures of 250° and 200°C.
1.2. Modelling pattern formation by continuum equations
Pattern formation on ion irradiated surfaces can be modelled my atomistic simulation methods, such as molecular dynamics (MD) and Monte-Carlo (kMC), or by continuum equations. Due to the large area and high fluences, MD and MC cannot cover the large dynamic range, however, they can provide valuable insight into defect generation and ion induced mass transport. Continuum equations on the other hand are coarse grain approximations, which can cover much larger spatial and temporal regimes. Information from MD or MC can furthermore be used as input for predictive modelling of new materials and irradiation conditions.
Keywords: ion beams, ion-surface interaction, nanopattering
  • Invited lecture (Conferences)
    23rd International Workshop on Inelastic Ion-Surface Collisions, 17.-22.11.2019, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-30562
Publ.-Id: 30562


Ion beam modification and ion beam analysis in current materials research

Facsko, S.ORC; Heller, R.; Munnik, F.ORC; Klingner, N.ORC; Hlawacek, G.ORC
Introduction to the IOne Beam Cneter and Current Research.
Keywords: Ion beam analysis, ion beam modification
  • Lecture (Conference)
    NATO Advanced Training Course: “Spintronics Radar Detectors”, 14.-18.10.2019, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-30561
Publ.-Id: 30561


Comparison of Si and Ge surface patterns produced by ion irradiation in the reverse epitaxy regime

Facsko, S.ORC; Xin, O.; de Schultz, R.; Erb, D.
In addition to sputtering, ion irradiation is often also leading to restructuring of the surface and a plethora of surface patterns can appear. At irradiation temperatures high enough to dynamically anneal defects induced by the collision cascades the surface remains crystalline. Still, a high density of ion-induced surface vacancies and adatoms remains and their diffusion is affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. These defects are therefore trapped on terraces, nucleate and form pits or mounds [1]. In this way three dimensional, faceted nanostructures are formed, reflecting the underlying crystal lattice. Due to the similarity to growth of three-dimensional structures in molecular beam epitaxy this mechanism is called reverse epitaxy.
We will present patterns on Si and Ge surface induced by low energy, normal incidence, high fluence ion irradiation at temperatures above the recrystallization temperature. Patterns with very different symmetry can result, depending on the surface orientation: pyramidal structures with four-fold symmetry on the (001) surface, with three-fold and six-fold symmetry on the (111) surface and elongated structures with two-fold symmetry on the (011) surface [2].
Although Si and Ge have the same diamond crystal lattice, the resulting patterns and facets are different: on Ge(001) predominantly (105) facets are formed, whereas (115) facets are found on Si(001). Similarly, on Si(111) the pattern exhibits a six-fold symmetry with (123) facets, whereas on Ge(111) the patterns are formed by (356) facets and exhibit a three-fold symmetry. The formation mechanism and possible effects leading to these differences on Ge and Si surfaces will be presented and discussed.
Keywords: ion beams, nanopatterning, ion-surface interaction
  • Lecture (Conference)
    10th International Workshop on Nanoscale Pattern Formation at Surfaces (NanoPatterning 2019), 07.-10.07.2019, Surrey, England

Permalink: https://www.hzdr.de/publications/Publ-30560
Publ.-Id: 30560


Interaction of low-energy ions with surfaces and 2D materials

Facsko, S.ORC
The ion beam centre (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf is a user facility primarily dedicated to research and application of ion beam techniques in materials research. The IBC comprises various ion beam facilities (accelerators, ion beam implanters, plasma-based ion beam equipment, focused / highly-charged ion facilities) which provide a wide energy range between 10 eV and 60 MeV. Besides these facilities, structural analysis (electron microscopy and spectroscopy, X-ray scattering techniques) and sample or device processing (under clean-room conditions) are part of the IBC to deliver a “complete” user service.
Special focus of the IBC is material research with low energy ions. Irradiations of surfaces with low energy ions can induce the formation of patterns with periodicities in the range of tens to hundreds of nanometers. At off-normal angle of incidence between 50° and 70° to the surface normal ripple patterns oriented perpendicular to the ion beam direction are observed. At normal incidence or for incidence angles smaller than 50° smoothing dominates on elemental materials, like Si and Ge. However, in contrast to irradiations at room temperature pattern formation is observed at normal ion incidence irradiations performed at temperatures above the recrystallization temperature of the material. Depending on the surface orientation checkerboard patterns with two-fold, three-fold, or six-fold symmetry reflecting the crystal structure of the irradiated surface are formed (Fig. 1).
Moreover, single impacts of low energy ions are used to create nanostructures and in thin membranes and for doping of 2D materials, like graphene and MoS2. In this case of highly charged ions the release of the potential leads to a local phase transformation of the material and subsequently to the formation of dots, pits or holes. Currently, a new facility for low energy ion nanoengineering is commissioned comprising a 100 keV accelerator for ion irradiations and MEIS, thin film deposition system, and different analytic tools for nanoscale analysis and characterization.
Keywords: ion beams, ion surface interaction, 2D materials
  • Lecture (others)
    Physics Seminar, 26.05.2019, Uppsala, Schweden

Permalink: https://www.hzdr.de/publications/Publ-30558
Publ.-Id: 30558


Advancing laser plasma accelerators by means of femto-scale diagnostics

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

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


Joining of two different ceramic nanomaterials for bottom-up fabrication of heterojunction devices

Rajbhar, M.; Das, P.; Satpati, B.; Möller, W.; Facsko, S.ORC; Böttger, R.; Ramgir, N.; Chatterjee, S.
Fabrication of device though bottom-up approach and using nanowires as building blocks has received significant attention as one can build flexible electronics which can handle stress better than thin film based device. However successful joining of the nanowires for fabrication of such device remains a challenge till date. While several well researched joining techniques are available for metal based nanowires, the same for ceramic nanowires is scarce at present. In this work we explore ion beam induced formation of heterojunction between two metal oxide nanowires, namely hydrogen titanate (H2Ti3O7) and cuprous oxide (Cu2O). The electron microscopy studies reveal detailed structural modifications at the joining sections. The ion beam modifications are explained using state-of-the-art TRI3DYN simulations, which details about migration of atoms, defects, sputtering, redeposition and atomic mixing between the two nanowires and emphasize that such junction formation is caused mainly due to atomic collisional effects.
Keywords: Ceramic nanomaterials; Metal oxides; Welding; Heterojunction; Ion-surface interaction; Nanowires

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Permalink: https://www.hzdr.de/publications/Publ-30556
Publ.-Id: 30556


Neoadjuvant Radiochemotherapy Significantly Alters the Phenotype of Plasmacytoid Dendritic Cells and 6-Sulfo LacNAc

Wagner, F.; Hölig, U.; Wilczkowski, F.; Plesca, I.; Sommer, U.; Wehner, R.; Kießler, M.; Jarosch, A.; Flecke, K.; Arsova, M.; Tunger, A.; Bogner, A.; Reißfelder, C.; Weitz, J.; Schäkel, K.; Troost, E. G. C.ORC; Krause, M.ORC; Folprecht, G.; Bornhäuser, M.; Bachmann, M.ORC; Aust, D.; Baretton, G.; Schmitz, M.
Neoadjuvant radiochemotherapy (nRCT) can significantly influence the tumor immune architecture that plays a pivotal role in regulating tumor growth. Whereas, various studies have investigated the effect of nRCT on tumor-infiltrating T cells, little is known about its impact on the frequency and activation status of human dendritic cells (DCs). Plasmacytoid DCs (pDCs) essentially contribute to the regulation of innate and adaptive
immunity and may profoundly influence tumor progression. Recent studies have revealed that higher pDC numbers are associated with poor prognosis in cancer patients. 6-sulfo LacNAc-expressing monocytes (slanMo) represent a particular proinflammatory subset of human non-classical blood monocytes that can differentiate into DCs. Recently, we have reported that activated slanMo produce various proinflammatory cytokines and
efficiently stimulate natural killer cells and T lymphocytes. slanMo were also shown to accumulate in clear cell renal cell carcinoma (ccRCC) and in metastatic lymph nodes from cancer patients. Here, we investigated the influence of nRCT on the frequency of rectal cancer-infiltrating pDCs and slanMo. When evaluating rectal cancer tissues obtained from patients after nRCT, a significantly higher density of pDCs in comparison to pre-nRCT
tissue samples was found. In contrast, the density of slanMo was not significantly altered by nRCT. Further studies revealed that nRCT significantly enhances the proportion of rectal cancer-infiltrating CD8+ T cells expressing the cytotoxic effector molecule granzyme B. When exploring the impact of nRCT on the phenotype of rectal cancer-infiltrating pDCs and slanMo, we observed that nRCT markedly enhances the percentage of inducible nitric oxide synthase (iNOS)- or tumor necrosis factor (TNF) alpha-producing slanMo. Furthermore, nRCT significantly increased the percentage
of mature CD83+ pDCs in rectal cancer tissues. Moreover, the proportion of pDCs locally expressing interferon-alpha, which plays a major role in antitumor immunity, was significantly higher in post-nRCT tissues compared to pre-nRCT tumor specimens. These novel findings indicate that nRCT significantly influences the frequency and/or phenotype of pDCs, slanMo, and CD8+ T cells, which may influence the clinical response of rectal
cancer patients to nRCT.
Keywords: plasmacytoid dendritic cells, 6-sulfo LacNAc+ monocytes, CD8+ T cells, tumor immune architecture, radiochemotherapy, rectal cancer

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Permalink: https://www.hzdr.de/publications/Publ-30553
Publ.-Id: 30553


DDR1 (discoidin domain receptor tyrosine kinase 1) drives glioblastoma therapy resistance by modulating autophagy

Vehlow, A.; Cordes, N.;
Therapy resistance of tumor cells is a major obstacle for efficient anticancer treatment approaches and has been attributed to tumor heterogeneity as well as genetic and epigenetic changes. Accumulating evidence demonstrates that tumor cell adhesion to the extracellular matrix acts as an additional essential factor conferring tumor cell resistance to both radio- and chemotherapeutic intervention.
Our recent study demonstrates that DDR1 (discoidin domain receptor tyrosine kinase 1) elicits therapy resistance of glioblastoma multiforme (GBM) stem-like and bulk cells through its adhesion to extra-cellular matrix and the subsequent modulation of macroautophagy/autophagy. Mechanistically, DDR1 associates with a YWHA/14–3-3-BECN1-AKT1 multiprotein complex favoring pro-survival/anti-autophagic and resistance-mediating AKT-MTOR signaling. In turn, inhibition of DDR1 sensitizes glioblastoma cells to radio- and chemotherapy by inducing autophagy. Collectively, our study suggests that DDR1 may be a potential target for sensitizing glioblastoma cells to combination therapies through its efficient induction of autophagic cell death.
Keywords: Autophagy; discoidin domain receptor tyrosine kinase 1; glioblastoma; radiochemotherapy; therapy resistance

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  • Secondary publication expected from 23.05.2020

Permalink: https://www.hzdr.de/publications/Publ-30552
Publ.-Id: 30552


Interaction of Discoidin Domain Receptor 1 with a 14-3-3-Beclin-1-Akt1 Complex Modulates Glioblastoma Therapy Sensitivity

Vehlow, A.; Klapproth, E.; Jin, S.; Hannen, R.; Hauswald, M.; Bartsch, J. W.; Nimsky, C.; Temme, A.; Leitinger, B.; Cordes, N.;
Glioblastoma (GBM) is highly refractory to therapy and associated with poor clinical outcome. Here, we reveal a critical function of the promitotic and
adhesion-mediating discoidin domain receptor 1 (DDR1) in modulating GBM therapy resistance. In GBM cultures and clinical samples, we show a
DDR1 and GBM stem cell marker co-expression that correlates with patient outcome. We demonstrate that inhibition of DDR1 in combination with
radiochemotherapy with temozolomide in GBM models enhances sensitivity and prolongs survival superior to conventional therapy. We identify a 14-
3-3-Beclin-1-Akt1 protein complex assembling with DDR1 to be required for prosurvival Akt and mTOR signaling and regulation of autophagy-associated therapy sensitivity. Our results uncover a mechanism driven by DDR1 that controls GBM therapy resistance and provide a rationale target for the development of therapy-sensitizing agents.

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Permalink: https://www.hzdr.de/publications/Publ-30551
Publ.-Id: 30551


Photons or protons for reirradiation in (non-)small cell lung cancer: Results of the multicentric ROCOCO

Troost, E. G. C.ORC; Wink, K. C. J.; Roelofs, E.; Simone, C. B.; Makocki, S.; Löck, S.; van Kollenburg, P.; Dechambre, D.; Minken, A. W. H.; van der Stoep, J.; Avery, S.; Jansen, N.; Solberg, T.; Bussink, J.; de Ruysscher, D.
objective: Locally recurrent disease is of increasing concern in (non-)small cell lung cancer [(N)SCLC] patients. Local reirradiation with photons or particles may be of benefit to these patients. In this multicentre in silico trial performed within the Radiation Oncology Collaborative Comparison (ROCOCO) consortium, the doses to the target volumes and organs at risk (OARs) were compared when using several photon and proton
techniques in patients with recurrent localised lung cancer scheduled to undergo reirradiation.
Methods: 24 consecutive patients with a second primary (N)SCLC or recurrent disease after curative- intent, standard fractionated radio(chemo)therapy were included in this study. The target volumes and OARs were centrally contoured and distributed to the participating ROCOCO sites. Remaining doses to the OARs were calculated on an individual patient’s basis. Treatment planning was performed by the
participating site using the clinical treatment planning system and associated beam characteristics.
results: Treatment plans for all modalities (five photon and two proton plans per patient) were available for 22 patients (N = 154 plans). 3D-conformal photon therapy and double-scattered proton therapy delivered significantly lower doses to the target volumes. The highly conformal techniques, i.e., intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), CyberKnife, TomoTherapy and intensity-modulated proton therapy (IMPT), reached the highest doses in the target volumes. Of these, IMPT was able to statistically significantly decrease the radiation doses to the OARs.
conclusion: Highly conformal photon and proton beam techniques enable high-dose reirradiation of the target volume. They, however, significantly differ in the dose deposited in the OARs. The therapeutic options, i.e., reirradiation or systemic therapy, need to be carefully weighed and discussed with the patients.
advances in knowledge: Highly conformal photon and proton beam techniques enable high-dose reirradiation of the target volume. In light of the abilities of the various highly conformal techniques to spare specific OARs, the therapeutic options need to be carefully weighed and patients included in the decision-making process.

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  • Secondary publication expected from 20.12.2020

Permalink: https://www.hzdr.de/publications/Publ-30550
Publ.-Id: 30550


Impact of Cancer-Associated Fibroblast on the Radiation-Response of Solid Xenograft Tumors

Steer, A.; Cordes, N.; Jendrossek, V.; Klein, D.;
Increasing evidence indicates that the heterogeneous tumor stroma supports therapy
resistance at multiple levels. Fibroblasts, particularly cancer-associated fibroblasts (CAFs) are critical components of the tumor stroma. However, the impact of CAFs on the outcome of radiotherapy (RT) is poorly understood. Here, we investigated if and how fibroblasts/CAFs modulate the radiation response of malignant tumors by altering cancer cell radiosensitivity or radioresistance in vitro and in vivo. The influence of fibroblasts on cancer cell proliferation, cell death induction and long-term survival after RT was studied using different sets of fibroblasts and cancer cells in an indirect co-culture (2D) system to analyse potential paracrine interactions or a 3D model to study direct interactions. Paracrine signals from embryonic NIH-3T3 fibroblasts promoted MPR31.4 prostate and Py8119 breast cancer cell proliferation. Indirect co-culture with L929 skin fibroblasts induced higher levels of apoptosis in irradiated MPR31.4 cells, while they promoted proliferation of irradiated Py8119 cells. In addition, NIH-3T3 fibroblasts
promoted long-term clonogenic survival of both tumor cell types upon irradiation in the 3D co-culture system when compared to non-irradiated controls. Also in vivo, co-implantation of cancer cells and fibroblasts resulted in different effects depending on the respective cell combinations used: co-implantation of MPR31.4 cells with NIH-3T3 fibroblasts or of Py8119 cells with L929 fibroblasts led to increased tumor growth and reduced radiation-induced tumor growth delay when compared to the respective tumors without co-implanted fibroblasts. Taken together, the impact of fibroblasts on cancer cell behavior and radiation sensitivity largely depended on the respective cell types used as they either exerted a pro-tumorigenic and radioresistance-promoting effect, an anti-tumorigenic effect, or no effect. We conclude that the plasticity of fibroblasts allows
for such a broad spectrum of activities by the same fibroblast and that this plasticity is at least in part mediated by cancer cell-induced fibroblast activation toward CAFs.
Keywords: cancer-associated fibroblast, fibroblast, cancer therapy, radiation therapy, radiation resistance, tumor stoma, tumor microenvironment

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Permalink: https://www.hzdr.de/publications/Publ-30549
Publ.-Id: 30549


Network-based analysis of prostate cancer cell lines reveals novel marker gene candidates associated with radioresistance and patient relapse

Seifert, M.; Peitzsch, C.; Gorodetska, I.; Börner, C.; Klink, B.; Dubrovska, A.ORC
Radiation therapy is an important and effective treatment option for prostate cancer, but high-risk patients are prone to relapse due to radioresistance of cancer cells. Molecular mechanisms that contribute to radioresistance are not fully understood. Novel computational strategies are needed to identify radioresistance driver genes from hundreds of gene copy number alterations. We developed a network-based approach based on lasso regression in combination with network propagation for the analysis of prostate cancer cell lines with acquired radioresistance to identify clinically relevant marker genes associated with radioresistance in prostate cancer patients. We analyzed established radioresistant cell lines of the prostate cancer cell lines DU145 and LNCaP and compared their gene copy number and expression profiles to their radiosensitive parental cells. We found that radioresistant DU145 showed much more gene copy number alterations than LNCaP and their gene expression profiles were highly cell line specific. We learned a genome-wide prostate cancer-specific gene regulatory network and quantified impacts of differentially expressed genes with directly underlying copy number alterations on known radioresistance marker genes. This revealed several potential driver candidates involved in the regulation of cancer-relevant processes. Importantly, we found that ten driver candidates from DU145 (ADAMTS9, AKR1B10, CXXC5, FST, FOXL1, GRPR, ITGA2, SOX17, STARD4, VGF) and four from LNCaP (FHL5, LYPLAL1, PAK7, TDRD6) were able to distinguish irradiated prostate cancer patients into early and late relapse groups. Moreover, in-depth in vitro validations for VGF (Neurosecretory protein VGF) showed that siRNA-ediated gene silencing increased the radiosensitivity of DU145 and LNCaP cells. Our computational approach enabled to predict novel radioresistance driver gene candidates. Additional preclinical and clinical studies are required to further validate the role of VGF and other candidate genes as potential biomarkers for the prediction of radiotherapy responses and as potential targets for radiosensitization of prostate cancer.

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Permalink: https://www.hzdr.de/publications/Publ-30548
Publ.-Id: 30548


Impact of prophylactic cranial irradiation on overall survival of patients with advanced non-small-cell lung cancer

Schmidt, J.; Appold, S.; Troost, E. G. C.ORC
Hintergrund In einer randomisierten Phase-III-Studie sollte untersucht werden, ob eine prophylaktische Ganzhirnbestrahlung bei kurativ-intendiert behandelten Patienten mit einem nicht-kleinzelligen Bronchialkarzinom (NSCLC) im Stadium III Einfluss auf das Auftreten von symptomatischen Hirnmetastasen hat.

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  • Secondary publication expected from 21.02.2020

Permalink: https://www.hzdr.de/publications/Publ-30547
Publ.-Id: 30547


Proton beam electron return effect: Monte Carlo simulations and experimental verification

Lühr, A.ORC; Burigo, L. N.; Gantz, S.; Schellhammer, S.; Hoffmann, A. L.
Proton therapy (PT) is expected to benefit from integration with magnetic resonance (MR) imaging. However, the magnetic field distorts the dose distribution and enhances the dose at tissue-air interfaces by the electron return effect (ERE). The objectives were (a) to provide experimental
evidence for the ERE in proton beams and (b) to systematically characterise the dependence of the dose enhancement ratio (DER) on magnetic field strength, orientation, proton energy and voxel size by computer simulations. EBT3 films were irradiated with 200 MeV protons with and without a 0.92 T transverse field of a permanent magnet to determine the DER at effective measurement depths of 0.156 and 0.467 mm from an air interface. High-resolution Monte Carlo simulations were performed to reproduce the irradiation experiments and to calculate the DER for proton energies between 50–200 MeV and magnetic field strengths between 0.35–3 T as function of distance from the air interface. Voxel sizes of
0.05, 0.5 and 1 mm were analysed. DERs of (2.2 ± 0.4)% and (0.5 ± 0.6)% were measured at 0.156 and 0.467 mm from the air interface, respectively. Measurements and simulations agreed within 0.15%. For a 200 MeV proton beam, the maximum DER in 0.05 mm voxels increased with magnetic field strength from 2.6% to 8.2% between 0.35 and 1.5 T, respectively. For a 1.0 T magnetic field, maximum DER increased
from 3.2% to 7.6% between 50 and 200 MeV, respectively. Voxel sizes of 0.5 and 1 mm resulted in maximum DER values of 2.6% and 1.4%, respectively.
The ERE for proton beams in transverse magnetic fields is measurable. The local dose enhancement is significant, well predictable, decreases rapidly with distance from the air interface, and is negligible beyond 1 mm depth. Its impact on air-filled ionisation chambers and porous tissues
(e.g. lung) needs to be considered.
Keywords: proton therapy, MRI, MR-guided radiotherapy, dosimetry, magnetic field, electron return effect, EBT3 film

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  • Secondary publication expected from 29.01.2020

Permalink: https://www.hzdr.de/publications/Publ-30546
Publ.-Id: 30546


Can Local Ablative Radiotherapy Revert Castration-resistant Prostate Cancer to an Earlier Stage of Disease

Lohaus, F.; Zöphel, K.; Löck, S.; Wirth, M.; Kotzerke, J.; Krause, M.ORC; Baumann, M.; Troost, E. G. C.ORC; Hölscher, T.
In prostate cancer, disease progression after primary treatment and subsequent andro-
gen deprivation therapy is common. Intensification of systemic treatment is the stan-
dard of care. Recently, 68[16_TD$DIFF]Ga prostate-specific membrane antigen positron emission
tomography (PSMA-PET) imaging was introduced to identify oligometastatic prostate
cancer patients. In this retrospective, exploratory study, we report on the efficacy of
PSMA-PET-guided local ablative radiotherapy (aRT) in 15 oligometastatic castration-
resistant prostate cancer (CRPC) patients, selected from our prospective institutional
database and treated between 2013 and 2016. After multidisciplinary discussion, aRT
was delivered with two different schedules. Androgen deprivation therapy remained
unchanged. Prostate-specific antigen (PSA) response and time to PSA progression were
analysed. For comparison, individual time to PSA progression without aRT was estimated
by individual PSA doubling time (PSADT). PSA response was observed in 11 patients
(73%). Mean time to PSA progression or last follow-up was 17.9 mo, as opposed to 2.9 mo
estimated from the PSADT without aRT (p <0.001). A relevant subset of CRPC patients
had a PSA response with aRT to PET-positive lead metastases. A prospective trial is in
preparation.
Patient summary: In selected patients with prostate-specific antigen (PSA) increase
during androgen deprivation, metastases were detected with prostate-specific mem-
brane antigen positron emission tomography imaging. Fifteen patients with three or
fewer metastases were treated with high-dose radiotherapy. Subsequently, PSA values
dropped in 11 patients and in six patients no PSA progression was detected for >12 mo.
Keywords: Castration-resistant prostate cancer Ablative radiotherapy Stereotactic ablative body radiotherapy Oligometastatic prostate cancer Prostate-specific membrane antigen positron emission tomography

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Permalink: https://www.hzdr.de/publications/Publ-30545
Publ.-Id: 30545


Independent validation of tumour volume, cancer stem cell markers and hypoxia-associated gene expressions for HNSCC after primary radiochemotherapy

Linge, A.; Schmidt, S.; Baumann, M.; Krenn, C.; Bandurska-Luque, A.; Platzek, I.; Neubeck, V. C.; Appold, S.; Nowak, A.; Gudziol, V.; Buchholz, F.; Baretton, B. B.; Lohaus, F.; Löck, S.; Krause, M.ORC
Objective: To independently validate the impact of tumour volume, p16 status, cancer stem cell (CSC) marker expression and hypoxia-associated gene signatures as potential prognostic biomarkers for patients with locally advanced head and neck squamous cell carcinoma (HNSCC), who underwent primary radiotherapy or radiochemotherapy (RCTx). These markers have previously been reported in a study of the German Cancer Consortium Radiation Oncology Group (DKTK-ROG) (Linge et al., 2016).
Materials and methods: In this retrospective monocentric study, 92 patients with locally advanced HNSCC were included. Univariable and multivariable logistic regressions and Cox models presented in the study of the DKTK-ROG were validated using the area under the curve (AUC) and the concordance index (ci), respectively. The primary endpoint of this study was loco-regional tumour control (LRC) after primary RCTx.
Results: Although both cohorts significantly differed in the proportion of the tumour subsites, the parameters tumour volume, p16 status and N stage could be validated regarding LRC and overall survival (OS) using multivariable Cox regression (LRC ci: 0.59, OS ci: 0.63). These models were slightly improved by combination with the putative CSC marker CD44 (LRC ci: 0.61, OS ci: 0.69). The logistic regression model for 2-year LRC based on tumour volume, p16 status and CD44 protein was validated with an AUC of 0.64. The patient stratification based on hypoxia-associated gene signatures status was similar to the original study but without significant differences in LRC and OS.
Conclusions: In this validation study, the inclusion of the putative CSC marker CD44 slightly improved the prognostic performance of the baseline parameters tumour volume, p16 status and N stage. No improvement was observed when including expressions of the hypoxia-associated gene signatures. Prospective validation on a larger cohort is warranted to assess the clinical relevance of these markers.
Keywords: Biomarker HNSCC Cancer stem cells HPV Hypoxia Primary radiochemotherapy

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Permalink: https://www.hzdr.de/publications/Publ-30543
Publ.-Id: 30543


In-situ Investigations of Solid-Liquid Interfaces by means of RBS

Baghban Khojasteh Mohammadi, N.; Apelt, S.; Bergmann, U.; Facsko, S.ORC; Heller, R.
Solid-liquid interfaces are of crucial significance since their presence in nature is ubiquitous. They play a fundamental role in diverse fields as biology, fluid physics, radiation physics, geological and environmental research, surface science and electro-chemistry. Binnig and Rohrer (Nobel Price 1986) considered the significance of the solid-liquid interface as:

"The solid-liquid interface is, in our opinion, the interface of the future." [1]

Investigating phenomena at the interface of a solid and an aqueous solution, where chemical reactions, oxidation, corrosion, adhesion, dissolution and ion exchange may take place, represents a challenging task. The techniques applied should not influence any of these processes, they should be able to access the interface (through the liquid or through the solid) and simultaneously deliver quantitative information on the interface properties.

A new versatile experimental setup for in-situ Rutherford backscattering spectrometry at solid-liquid interfaces enabling direct and quantitative measurements with highest sensitivity is presented [2]. An electro-chemical liquid cell with a three-electrode arrangement was mounted at the IBCs 2MV Van-de-Graaff accelerator. A thin Si3N4 window (thickness down to 150 nm) separates the vacuum of the detector chamber from the electrolyte in the cell.

In a first study, we investigated the attachment of Ba onto the Si3N4 surface as a function of contact time and pH value of the electrolyte solution (see Fig. 1). From these measurements, we can deduce the evolution of the double layer with sub-monolayer sensitivity in a direct and quantitative manner.

Despite focusing on a particular system as presented here, the setup allows to conduct a large variety of in-situ investigations at solid-liquid interfaces such as monitoring of electro-chemical reactions, segregation, adsorption, dissolution and corrosion processes.

Details of the setup, its capabilities and limitations are presented and the results of first measurements are discussed in detail.


[1] G. Binnig and H. Rohrer, Reviews of Modern Physics 71 (1999), 324.
[2] N. B. Khojasteh, S. Apelt, U. Bergmann, S. Facsko and R. Heller, Review of Scientific Instruments (2019), submitted.
Keywords: Ion beam analysis, Rutherford backscattering, RBS, elemental analysis, solid-liquid interface, electric double layer
  • Lecture (Conference)
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS, 13.-18.10.2019, ANTIBES, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-30542
Publ.-Id: 30542


Modern Ion Beam Techniques for Elemental Analysis of Surfaces and Interfaces at the nm Scale

Heller, R.;
The general trend in technology and science to create, process and analyze small structures on the nm scale leads to new challenges in modern ion beam analysis (IBA). This is accompanied by higher demands on the lateral resolution as well as on high precision determination of elemental compositions on an atomic depth scale.

Thinner layer structures are closely related to an increased sensitivity on external impacts. Even the transport of a sample to the place of analysis under ambient conditions can lead to unwanted (chemical) modifications at the surface. Furthermore, in technological developments not only the state of a system after processing but the process itself may be of particular interest. “Online” IBA under process conditions is thus highly desired.

Classical IBA methods like RBS (Rutherford Backscattering Spectrometry), ERD (Elastic Recoil Detection Analysis), PIXE (Particle Induced X-Ray Emission) or PIGE (Particle Induced Gamma Emission), either applied as broad beam or as a micro probe, can therefore quickly reach their limits.

In the present contribution, we give an overview on recent and ongoing developments of new IBA techniques and approaches at the HZDR Ion Beam Center (IBC) addressing the above-mentioned difficulties. These developments include in particular

- the implementation of IBA in a helium ion microscope enabling elemental mapping on the nm scale,
- the unification of different IBA techniques in complex experimental chambers including in-situ capabilities,
- a new setup for in-operando, online and quantitative analysis of solid-liquid interfaces with sub mono-layer sensitivity,
- A new low-energy ion laboratory equipped with a Medium Energy Ion Scattering (MEIS) chamber for quantitative elemental depth profiling on the nm scale.

We will give an overview on these techniques and their capabilities. Since the IBC is an international user facility all presented techniques are available for external users experiments.
Keywords: Ion beam analysis, elemental composition, imaging, materials analysis, nano scale, backscattering
  • Poster
    18th European Conference on Applications of Surface and Interface Analysis, 15.-20.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30541
Publ.-Id: 30541


Efficacy and safety of carbon-ion radiotherapy for locally recurrent rectal cancer: results of the J-CROS Study 1404 Rectum

Jentsch, C.; Troost, E. G. C.ORC
Hintergrund In dieser retrospektiven Arbeit untersuchten die Autoren die Wirksamkeit und Sicherheit einer Kohlenstoffionentherapie lokal rezidivierter Rektumkarzinome.

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  • Secondary publication expected from 02.05.2020

Permalink: https://www.hzdr.de/publications/Publ-30540
Publ.-Id: 30540


Photocatalytic biocidal effect of copper doped TiO2 nanotube coated surfaces under laminar flow, illuminated with UVA light on Legionella pneumophila

Oder, M.; Koklič, T.; Umek, P.; Podlipec, R.; Štrancar, J.; Dobeic, M.;
Legionella pneumophila can cause a potentially fatal form of humane pneumonia (Legionnaires’ disease), which is most problematic in immunocompromised and in elderly people. Legionella species is present at low concentrations in soil, natural and artificial aquatic systems and is therefore constantly entering man-made water systems. The environment temperature for it’s ideal growth range is between 32 and 42°C, thus hot water pipes represent ideal environment for spread of Legionella. The bacteria are dormant below 20°C and do not survive above 60°C. The primary method used to control the risk from Legionella is therefore water temperature control. There are several other effective treatments to prevent growth of Legionella in water systems, however current disinfection methods can be applied only intermittently thus allowing Legionella to grow in between treatments. Here we present an alternative disinfection method based on antibacterial coatings with Cu-TiO2 nanotubes deposited on preformed surfaces. In the experiment the microbiocidal efficiency of submicron coatings on polystyrene to the bacterium of the genus Legionella pneumophila with a potential use in a water supply system was tested. The treatment thus constantly prevents growth of Legionella pneumophila in presence of water at room temperature. Here we show that 24-hour illumination with low power UVA light source (15 W/m2 UVA illumination) of copper doped TiO2 nanotube coated surfaces is effective in preventing growth of Legionella pneumophila. Microbiocidal effects of Cu-TiO2 nanotube coatings were dependent on the flow of the medium and the intensity of UV-A light. It was determined that tested submicron coatings have microbiocidal effects specially in a non-flow or low-flow conditions, as in higher flow rates, probably to a greater possibility of Legionella pneumophila sedimentation on the coated polystyrene surfaces, meanwhile no significant differences among bacteria reduction was noted regarding to non or low flow of medium.

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Permalink: https://www.hzdr.de/publications/Publ-30539
Publ.-Id: 30539


A Monte Carlo based radiation response modelling framework to assess variability of clinical RBE in proton therapy

Eulitz, J.; Lutz, B.ORC; Wohlfahrt, P.ORC; Dutz, A.; Enghardt, W.ORC; Karpowitz, C.; Krause, M.ORC; Troost, E. G. C.ORC; Lühr, A.ORC
he clinical implementation of a variable relative biological effectiveness (RBE) in proton therapy is currently controversially discussed. Initial clinical evidence indicates a variable proton RBE, which needs to be verified. In this study, a radiation response modelling framework for assessing clinical
RBE variability is established. It was applied to four selected glioma patients (grade III) treated with adjuvant radio(chemo)therapy and who developed late morphological image changes on T1-weighted contrast-enhanced (T1w-CE) magnetic resonance (MR) images within approximately
two years of recurrence-free follow-up. The image changes were correlated voxelwise with dose and linear energy transfer (LET) values using univariable and multivariable logistic regression analysis.
The regression models were evaluated by the area-under-the-curve (AUC) method performing a leave-one-out cross validation. The tolerance dose TD50 at which 50% of patient voxels experienced toxicity was interpolated from the models. A Monte Carlo (MC) model was developed to simulate
dose and LET distributions, which includes variance reduction (VR) techniques to decrease computation time. Its reliability and accuracy were evaluated based on dose calculations of the clinical treatment planning system (TPS) as well as absolute dose measurements performed in the
patient specific quality assurance.
Morphological image changes were related to a combination of dose and LET. The multivariable models revealed cross-validated AUC values of up to 0.88. The interpolated TD50 curves decreased with increasing LET indicating an increase in biological effectiveness. The MC model reliably
predicted average TPS dose within the clinical target volume as well as absolute water phantom dose measurements within 2% accuracy using dedicated VR settings.
The observed correlation of dose and LET with late brain tissue damage suggests considering RBE variability for predicting chronic radiation-induced brain toxicities. The MC model simulates radiation fields in patients precisely and time-efficiently. Hence, this study encourages and enables
in-depth patient evaluation to assess the variability of clinical proton RBE.
Keywords: proton therapy, clinical RBE, Monte Carlo, passive scattering

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Permalink: https://www.hzdr.de/publications/Publ-30538
Publ.-Id: 30538


Correlation between FMISO-PET based hypoxia in the primary tumour and in lymph node metastases in locally advanced HNSCC patients

Bandurska-Luque, A.; Löck, S.; Haase, R.; Richter, C.ORC; Zöphel, K.; Perrin, R.; Appold, S.; Krause, M.ORC; Steinbach, J.; Kotzerke, J.; Hofheinz, F.ORC; Zips, D.; Baumann, M.; Troost, E. G. C.ORC
Purpose: This secondary analysis of the prospective study on repeat [18F]fluoromisonidazole (FMISO)-PET in patients with locally advanced head and neck squamous cell carcinoma (HNSCC) assessed the correlation of hypoxia in the primary tumour and lymph node metastases (LN) prior to and during primary radiochemotherapy.
Methods: This analysis included forty-five LN-positive HNSCC patients having undergone FMISO-PET/CTs at baseline, and at week 1, 2 and 5 of radiochemotherapy. The quantitative FMISO-PET/CT parameters maximum standardised uptake value (SUVmax, corrected for partial volume effect) and peak tumour-to-background ratio (TBRpeak) were estimated in the primary tumour as well as in index and large LN, respectively. Statistical analysis was performed using the Spearman correlation coefficient q.
Results: In 15 patients with large LN (FDG-PET positive volume >5 ml), there was a significant correlation between the hypoxia measured in the primary tumour and the large LN at three out of four time-points using the TBRpeak (baseline: q= 0.57, p = 0.006; week 2: q= 0.64, p = 0.003 and week 5: q= 0.68, p = 0.001). For the entire cohort (N = 45) only assessed prior to the treatment, there was a statistically significant, though weak correlation between FMISO-SUVmax of the primary tumour and the index LN (q= 0.36, p = 0.015).
Conclusions: We observed a significant correlation between FMISO-based hypoxia in the primary tumour and large lymph node(s) in advanced stage HNSCC patients. However, since most patients only had relatively small hypoxic lymph node metastases, a comprehensive assessment of the primary tumour and lymph node hypoxia is essential.
Keywords: Hypoxia FMISO PET Primary tumour Lymph node metastases Locally advanced HNSCC Radiochemotherpy

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Permalink: https://www.hzdr.de/publications/Publ-30537
Publ.-Id: 30537


Morphology Modification of Si Nanopillars under Ion Irradiation at Elevated Temperatures

Xu, X.ORC; Heinig, K.-H.; Möller, W.; Engelmann, H.-J.; Klingner, N.ORC; Gharbi, A.; Tiron, R.; Borany, J.; Hlawacek, G.ORC
Ion beam irradiation of vertical nanopillar structures can be utilized to fabricate a vertical gate-all-around (GAA) single electron transistor (SET) device in a CMOS-compatible way. After irradiation of Si nanopillars (with a diameter of 35 nm and a height of 70 nm) by either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) at room temperature and a fluence of 2e16 ions/cm2, strong deformation of the nanopillars has been observed which hinders further device integration. This is attributed to ion beam induced amorphization of Si allowing plastic flow due to the ion hammering effect, which, in connection with surface capillary forces, dictates the final shape. However, plastic deformation can be suppressed under irradiation at elevated temperatures (investigated up to 672 K). Then, as confirmed by bright-field transmission electron microscopy, the substrate and the nanopillars remain crystalline and are continuously thinned radially with increasing fluence down to a diameter of 10 nm. This is attributed to enhanced forward sputtering through the sidewalls of the pillar, and found in reasonable quantitative agreement with the predictions from 3D ballistic computer simulation using the TRI3DYN program.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.
  • Poster
    AVS 66th International Symposium & Exhibition, 24.10.2019, Columbus, USA

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


Realization of wafer-scale nanogratings with sub-50 nm period through vacancy epitaxy

Huang, Q.; Jia, Q.; Feng, J.; Huang, H.; Yang, X.; Grenzer, J.; Huang, K.; Zhang, S.; Lin, J.; Zhou, H.; You, T.; Yu, W.; Facsko, S.; Jonnard, P.; Wu, M.; Giglia, A.; Zhang, Z.; Liu, Z.; Wang, Z.; Wang, X.; Ou, X.;
Gratings, one of the most important energy dispersive devices, are the fundamental building blocks for the majority of optical and optoelectronic systems. The grating period is the key parameter that limits the dispersion and resolution of the system. With the rapid development of large X-ray science facilities, gratings with periodicities below 50 nm are in urgent need for the development of ultrahigh-resolution X-ray spectroscopy. However, the wafer-scale fabrication of nanogratings through conventional patterning methods is difficult. Herein, we report a maskless and high-throughput method to generate wafer-scale, multilayer gratings with period in the sub-50 nm range. They are fabricated by a vacancy epitaxy process and coated with X-ray multilayers, which demonstrate extremely large angular dispersion at approximately 90 eV and 270 eV. The developed new method has great potential to produce ultrahigh line density multilayer gratings that can pave the way to cutting edge high-resolution spectroscopy and other X-ray applications.
Keywords: GRATINGS; SCATTERING; ARRAYS

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Permalink: https://www.hzdr.de/publications/Publ-30535
Publ.-Id: 30535


High resolution materials modification with low fluence Helium Ion Microscopy

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

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


Focused ion beam materials modification with noble gas ions

Hlawacek, G.ORC
I will present results obtained using Helium Ion Microscopy
(HIM) [1] in various nanostructuring projects. The common
goal of the research is to change the electronic or magnetic
properties of the target material at the nano-scale in a con-
trolled way to achieve new functionality. Where applicable
this new functionality will be measured in-situ during the
nanostructure fabrication process.
For all presented examples the critical length scale of the
nanostructure is smaller or in the range of collision cascade.
This size regime can not easily be accessed with traditional
broad beam based ion irradiation and holds many promises
but also challenges that need to be overcome to enable new
device concepts and new functional materials on the nano-
scale.
  • Invited lecture (Conferences)
    IISC23, 20.11.2019, Matsue, Japan

Permalink: https://www.hzdr.de/publications/Publ-30532
Publ.-Id: 30532


Nanostructure characterization with ions

Hlawacek, G.ORC
Helium Ion Microscopy (HIM) is best known for its high resolution imaging capabilities of both
conductive as well as insulating samples. Over the last decade several efforts have been made to also
add high spatial resolution analytic capabilities to the instrument. In many cases the starting point for
these efforts was given by existing high energy ion beam analysis techniques. In particular TOF-RBS,
magnetic sector SIMS and TOF-SIMS have successfully been realized. In addition in-situ probing, and
in-operando methods are used to evaluate directly the effect of ion beam irradiation on nanostructures.
New developments aim at the improving of magnetic sector SIMS and the implementation of scanning
transmission ion microscopy.
This work is supported by European Union’s H-2020 research project ‘npSCOPE’ under Grant Agree-
ment No. 720964 and the FNR STHIM project under grant number I7748, and by the German BMWi
via Grant 03ET7016 and 03THW12F01.
Keywords: HIM, SIMS, STIM
  • Invited lecture (Conferences)
    8th EU Korea Nanoworkshop, 25.11.2019, Brüssel, Belgien

Permalink: https://www.hzdr.de/publications/Publ-30531
Publ.-Id: 30531


Tailoring magnetic nanostructures with a He-Ne ion microscope

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

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


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

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

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


Analytic approaches for Helium Ion Microscopy

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

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


In-situ experiments and characterization in the Helium Ion Microscope

Hlawacek, G.ORC
In-situ experiments in the HIM
Keywords: HIM
  • Open Access Logo Invited lecture (Conferences)
    Ion beams for future technologies 2019, 2.4.2019, Dubrovnik, Kroatien

Permalink: https://www.hzdr.de/publications/Publ-30526
Publ.-Id: 30526


Avoiding amorphization in silicon nano structures

Hlawacek, G.ORC; Xu, X.ORC; Engelmann, H.-J.; Heinig, K.-H.; Möller, W.; Ahmed, G.; Raluca, T.; Bischoff, L.ORC; Prüfer, T.; Hübner, R.; Facsko, S.ORC; Borany, J.
Helium Ion Microscopy (HIM) [1, 2] is best known for its high resolution imaging capabilities of both
conductive as well as insulating samples. However, since the introduction of Ne as an imaging gas for the
gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized. While
the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV
Ne compared to 0.5 nm for 30 keV He) the user usually benefits from the much higher cross section for
nuclear stopping. The latter results in a larger number of sputtered atoms and bonds broken directly
by small impact parameter collisions.
After a brief introduction of the technique I will present results obtained using direct write milling low
fluence ion beam irradiation and ion beam based mixing. In all three cases the electronic or magnetic
properties of the target material will be altered at the nano-scale in a controlled way to achieve new
functionality. The examples comprise
∙ The fabrication of semiconducting graphene nano-ribbons by direct milling [3]
∙ The fabrication of a lateral spin valve structure using low fluence ion irradiation [4]
∙ The formation of individual 3 nm Si clusters for a room temperature single electron transistor [5]
For all presented examples the critical length scale of the nanostructure is smaller or in the range of
collision cascade. This size regime can not be accessed with traditional broad beam based ion irradiation
and holds many promises but also challenges that need to be overcome to enable new device concepts
and new functional materials on the nano-scale.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant
Agreement No. 688072
Keywords: HIM, modification
  • Lecture (Conference)
    DPG Frühjahrstagung, 3.4.2019, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30525
Publ.-Id: 30525


Spatially resolved materials modification using Helium Ion Microscopy

Hlawacek, G.ORC
Helium Ion Microscopy (HIM) [1, 2] is best known for its high resolution imaging capabilities of both
conductive as well as insulating samples. However, since the introduction of Ne as an imaging gas for the
gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized. While
the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV
Ne compared to 0.5 nm for 30 keV He) the user usually benefits from the much higher cross section for
nuclear stopping. The latter results in a larger number of sputtered atoms and bonds broken directly
by small impact parameter collisions.
After a brief introduction of the technique I will present results obtained using direct write milling low
fluence ion beam irradiation and ion beam based mixing. In all three cases the electronic or magnetic
properties of the target material will be altered at the nano-scale in a controlled way to achieve new
functionality. The examples comprise
∙ The fabrication of semiconducting graphene nano-ribbons by direct milling [3]
∙ The fabrication of a lateral spin valve structure using low fluence ion irradiation [4]
∙ The formation of individual 3 nm Si clusters for a room temperature single electron transistor [5]
For all presented examples the critical length scale of the nanostructure is smaller or in the range of
collision cascade. This size regime can not be accessed with traditional broad beam based ion irradiation
and holds many promises but also challenges that need to be overcome to enable new device concepts
and new functional materials on the nano-scale.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant
Agreement No. 688072
Keywords: Helium ion microscopy, materials modification
  • Lecture (others)
    Institutsseminar, 31.01.2019, Strassbourg, Frankreich
  • Invited lecture (Conferences)
    EIPBN, 30.5.2019, Minneapolis, USA

Permalink: https://www.hzdr.de/publications/Publ-30524
Publ.-Id: 30524


Mapping of Magnetic Metastable States in Synthetic Antiferro- and Ferrimagnets with Perpendicular Magnetic Anisotropy

Salikhov, R.; Samad, F.; Koch, L.; Böhm, B.; Hellwig, O.;
Magnetic multilayers (MLs) with perpendicular magnetic anisotropy (PMA), such as Co/Pt or
Co/Pd, are the host materials for a variety of metastable magnetic configurations, e.g. aligned or labyrinth
stripe domains, bubble domains and their mixtures. The magnetic morphology at remanence mostly depends
on the specific demagnetization routine using an external magnetic field [1], whereas the characteristic size of
the magnetic objects (domain period or bubble radius) is mostly determined by the design parameters of the
magnetic MLs (e.g. the thickness of Co layer, periodicity and the number of repeats X) [1,2]. Interleaving the
Co/Pt blocks by Ru or Ir layers, which promote antiferromagnetic (AF) interlayer coupling between PMA ML
blocks, results in a class of artificial magnetic structures, known as synthetic antiferromagnets (SAFs) with
PMA. The AF interlayer exchange energy alters the typical energy balance, thus modifying the morphology
and characteristic size of magnetic domain states in PMA SAFs [1]. Stabilisation of magnetic bubble domain
states in SAFs is of particular practical interest [3], whereas other new magnetic configurations are of interest
for fundamental research. Here we present the mapping of magnetic states in SAFs for different
demagnetization protocols and ML parameters by means of monitoring the remanent magnetization Mr during
the AC or DC demagnetization process itself and performing magnetic force microscopy (MFM) imaging at the
intermediate states of interest (Fig. 1). The aligned stripe domain state is characterised by almost zero Mr,
whereas bubble domains [4] and mixed states (Fig. 1) manifest themselves by an enhanced Mr. The magnetic
states for SAFs with tunable parameters such as Co thickness and repetition number X will be presented. We
will also discuss the magnetic behaviour in synthetic ferrimagnets, where the two ML block sub-lattices have
different magnetic moments.
References: [1] O. Hellwig, A. Berger, J. B. Kortright, JMMM, Vol. 319, p.13-55 (2007)
[2] I. Lemesh, F. Büttner, G. S. D. Beach, Phys. Rev. B, Vol. 95, p.174423 (2017)
[3] K. Chesnel, A. S. Westover, C. Richards, Phys. Rev. B, Vol. 98, p.224404 (2018)
[4] A. Hubert, R. Schäfer, Magnetic Domains, Springer Berlin (2009)
  • Lecture (Conference)
    64th Annual Conference on Magnetism and Magnetic Materials (MMM 2019), 04.-08.11.2019, Las Vegas, Nevada, USA

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Permalink: https://www.hzdr.de/publications/Publ-30523
Publ.-Id: 30523


ESUO - The European Synchrotron and FEL User Organisation: Aims and activities

Arčon, I.; Arikan, P.; Bittencourt, C.; Boscherini, F.; Braz Fernandes, F. M.; Brooks, N.; Casu, B.; D'Astuto, M.; Feiters, M.; Froideval, A.; Granroth, S.; Gross, S.; Gutt, C.; Hase, T.; Jablonska, K.; Jergel, M.; Khan, A.; Kirm, M.; Kokkinidis, M.; Kövér, L.; Lamba, D.; Larsen, H. B.; Lechner, R. T.; Le Hir, R.; Logan, D. T.; López, O.; Lorentz, K.; Mariani, C.; Marinkovic, B.; Mcguinness, C.; Meedom Nielsen, M.; Micetic, M.; Mickevicius, S.; Mikulík, P.; Petukhov, A.; Pietsch, U.; Pokroy, B.; Purans, J.; Renault, L.; Santoro, G.; Shivachev, B.; Stangl, J.; Tromp, M.; Vankó, G.; Blasetti, C.; Freire Anselmo, A. S.; Grobosch, M.; Helm, M.; Schramm, B.; Vollmer, A.;
The European Synchrotron and free-electron laser User Organisation (ESUO) established in 2010 represents about 22.000 users. It is composed of 30 member countries. Our vision is to support a thriving (European) synchrotron and FEL user community with equal opportunities of access and participation for all scientists, based solely on the scientific merit of their ideas.
  • Poster
    EMFL User Meeting 2019, 25.06.2019, Faculty of Physics of the University of Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30521
Publ.-Id: 30521


Exploiting Hysteresis in a Multicaloric Cooling Cycle

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

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


Multicaloric materials and their characterization

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

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


The activities of the European Synchrotron and FEL User Organisation for even brighter European Photon Science

Pietsch, U.; Arčon, I.; Arikan, P.; Bittencourt, C.; Boscherini, F.; Braz Fernandes, F. M.; Brooks, N.; Casu, B.; D'Astuto, M.; Feiters, M.; Froideval, A.; Granroth, S.; Gross, S.; Gutt, C.; Hase, T.; Jablonska, K.; Jergel, M.; Khan, A.; Kirm, M.; Kokkinidis, M.; Kövér, L.; Lamba, D.; Larsen, H. B.; Lechner, R. T.; Le Hir, R.; Logan, D. T.; López, O.; Lorentz, K.; Mariani, C.; Marinkovic, B.; Mcguinness, C.; Meedom Nielsen, M.; Micetic, M.; Mickevicius, S.; Mikulík, P.; Petukhov, A.; Pokroy, B.; Purans, J.; Renault, L.; Santoro, G.; Shivachev, B.; Stangl, J.; Tromp, M.; Vankó, G.; Blasetti, C.; Freire Anselmo, A. S.; Grobosch, M.; Helm, M.; Schramm, B.; Vollmer, A.;
The European Synchrotron and FEL User Organisation (ESUO) represents about 22 000 users of the European synchrotron radiation (SR) and Free-Electron Laser (FEL) facilities, which offer various kinds of experiments ranging from physics over life sciences up to cultural heritage. Established in 2010, ESUO is composed of national delegates from 30 European member states and associated countries and is headed by an executive board of eight members. Our vision is to support a thriving (European) synchrotron and FEL user community with equal opportunities of access and participation for all scientists, based solely on the scientific merit of their ideas.
  • Invited lecture (Conferences)
    ESUO Regional Workshop at PHOTONICA 2019 conference, 28.08.2019, SASA and University of Belgrade, Serbia

Permalink: https://www.hzdr.de/publications/Publ-30518
Publ.-Id: 30518


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

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

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


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

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

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


ESUO - The European Synchrotron and FEL User Organisation

Arčon, I.; Arikan, P.; Bittencourt, C.; Boscherini, F.; Braz Fernandes, F. M.; Brooks, N.; Casu, B.; D'Astuto, M.; Feiters, M.; Froideval, A.; Granroth, S.; Gross, S.; Gutt, C.; Hase, T.; Jablonska, K.; Jergel, M.; Khan, A.; Kirm, M.; Kokkinidis, M.; Kövér, L.; Lamba, D.; Larsen, H. B.; Lechner, R. T.; Le Hir, R.; Logan, D.; López, O.; Lorentz, K.; Mariani, C.; Marinkovic, B.; Mcguinness, C.; Meedom Nielsen, M.; Micetic, M.; Mickevicius, S.; Mikulík, P.; Petukhov, A.; Pietsch, U.; Pokroy, B.; Purans, J.; Renault, L.; Santoro, G.; Shivachev, B.; Stangl, J.; Tromp, M.; Vankó, G.; Freire Anselmo, A. S.; Blasetti, C.; Grobosch, M.; Helm, M.; Schramm, B.; Vollmer, A.;
The European Synchrotron and free-electron laser User Organisation (ESUO) established in 2010 represents about 22.000 users. It is composed of 30 member countries. Our vision is to support a thriving (European) synchrotron and FEL user community with equal opportunities of access and participation for all scientists, based solely on the scientific merit of their ideas.
  • Poster
    11th Joint BER II and BESSY II User Meeting, 04.-06.12.2019, HZB, Germany

Permalink: https://www.hzdr.de/publications/Publ-30514
Publ.-Id: 30514


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

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

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


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

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

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


Acoustic signatures of the phase transitions in the antiferromagnet U2Rh2Sn

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

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  • Secondary publication expected

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


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

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

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


Wayforlight: The Catalogue of European Light Sources

Blasetti, C.; Andrian, I.; Billè, F.; Coghetto, E.; Deiuri, S.; Favretto, D.; Turcinovich, M.; Pugliese, R.; Osmenaj, E.; Appleby, G.; Froideval, A.; Pietsch, U.; Sanchez, A.; Valls Vidal, N.; Mitchell, E.; Rabhi, N.; Aogaki, S.; Kasik, Z.; Canova, F.; Gliksohn, F.; Stozno, D.; Michel, J.; Normand, D.; Brancaleon, R.; Paro, G.; Zotti, M. T. &. D.;
Wayforlight.eu is the gateway to finding the most suitable instruments for experiments with synchrotron, FEL, and laser light sources. The portal's main asset is a detailed searchable catalogue of facilities, beamlines, and instrumentation available at European light sources. Thanks to its advanced search tools, a visitor can filter beamlines by scientific discipline, by technique, but also by energy range or sample type.

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Permalink: https://www.hzdr.de/publications/Publ-30507
Publ.-Id: 30507


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

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

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


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

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

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


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

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

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


Theory and simulation on nonlinear spin-wave dynamics in magnetic vortices

Körber, L.ORC; Schultheiß, K.ORC; Hula, T.ORC; Verba, R.; Kakay, A.; Hache, T.ORC; Ivanov, B.; Faßbender, J.ORC; Schultheiß, H.ORC
One of the fascinating qualities of spin waves (or magnons), which are the elementary excitations in magnetically ordered substances, is their nonlinear behavior at moder- ate excitation powers. This makes spin waves not only an attractive model system to study general nonlinear systems, but it also provides a way to utilize nonlinear dynamics in possible technical applications. In a ferromagnetic nano disk which is magnetized in the vortex state, the spin-wave modes meet strict boundary conditions and therefore inherit a discrete spectrum. When driven with a large enough excitation field, they can decay into other spin-wave modes within well-defined channels due to a nonlinear process called three-magnon scattering [1]. The aim of this project is to explore this phenomenon within nonlinear spin-wave theory and by means of micromagnetic simulations.
For this purpose, first the linear dynamics are mapped out and the possible scattering channels are predicted. The stability of these channels with respect to static external fields is studied. Within this context, exotic spin-wave modes which arise in a broken cylindrical symmetry are found. Moreover, a model to predict the temporal evolution of the spin-wave modes is developed within the classical Hamiltonian formalism for nonlinear spin-wave dynamics. Together with micromagnetic simulations, this model is applied in order to study the power-dependence of three-magnon scattering as well as to uncover a phenomenon called stimulated three-magnon scattering, which may allow for an integration of this nonlinear pro- cess in magnonics circuits. The results are compared with Brillouin light-scattering experiments which were conducted prior to this thesis or were motivated by it. Financial support of within DFG programme SCHU 2922/1-1 and KA 5069/1-1 is acknowledged.
Keywords: nonlinear, spin wave, magnon, vortex, three-magnon scattering, BLS, micromagnetic simuations, micromagnetism
  • Poster
    710. WE-Heraeus-Seminar: Spin Transport in Complex Magnetic Structures, 07.-10.01.2020, Physikzentrum Bad Honnef, Germany

Permalink: https://www.hzdr.de/publications/Publ-30502
Publ.-Id: 30502


Integration of 1D and 2D Materials into Functional Structures and Devices

Georgiev, Y.ORC
In this talk I will make a brief overview of our activities for integration of different 1D and 2D materials into functional structures and devices.

I will first present the work on fabrication, processing and application of group IV semiconductor nanowires (NWs). These include top-down fabricated Si, SiGe and Ge NWs as well as bottom-up grown Si, Ge1-xSnx with x = 0.07-0.1 and GaAs/In0.45Ga0.55As NWs. I will also consider the innovative devices that we are targeting: junctionless nanowire transistors (JNTs), reconfigurable field effect transistors (RFETs) and band-to-band tunnel FETs (TFETs).

I will next discuss our activities for fabrication and characterisation of FETs based on 2D heterostructures. As examples I will show FETs fabricated on hBN-encapsulated InSe, a material with attractive properties but very unstable in ambient atmosphere, as well as TFETs fabricated on hBN/MoS2/WSe2/graphene heterostructures.

Finally, I will pay some attention to our work on using DNA origami templates for the fabrication of functional structures with the outlook to the application of DNA origami for self-assembly of electronic circuits. In particular, I will show fabrication of conducting metallic NWs using templates of DNA nanotubes, nanosheets and nanomoulds as well as incorporation into them of molecules and semiconducting nanoparticles for enhanced electronic functionality.
Keywords: 1D materials, 2D materials, semiconductor nanowires, DNA origami, transition metal dichalcogenides, top-down nanofabrication, bottom-up nanofabrication, junctionless nanowire transistors, reconfigurable field effect transistors, band-to-band tunnel field effect transistors
  • Invited lecture (Conferences)
    Meeting at the Advanced Microelectronic Centre Aachen (AMICA), AMO gGmbH, 02.-03.12.2019, Aachen, Germany

Permalink: https://www.hzdr.de/publications/Publ-30499
Publ.-Id: 30499


Ion beam implanted Germanium nanowires

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

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

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

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


Phosphorous doped Germanium nanowires

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

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


Ion beam implanted Germanium nanowires fabricated by using electron beam lithography

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

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


Implementation of a cryogenic hydrogen jet target at the DRACO PW laser

Rehwald, M.ORC; Bernert, C.; Curry, C.; Cowan, T.ORC; Gauthier, M.; Glenzer, S.; Goede, S.; Kim, J.; Kluge, T.ORC; Kraft, S.ORC; Obst-Hübl, L.ORC; Schoenwaelder, C.; Schlenvoigt, H.-P.ORC; Schramm, U.ORC; Ziegler, T.ORC; Zeil, K.ORC
As high power laser systems producing high repetition rate pulses become interesting for applications in e.g.
radiation therapy, there is a high demand for rapid and controlled target delivery at the high power laser focus.
Due to their continuous and debris-free operation, cryogenic target systems producing renewable jets of
hydrogen [1] or other species proved to be very beneficial. Furthermore, the low plasma density of solid single
species hydrogen of only 30nc@800nm and the availability of different jet geometries allowed for gaining
deeper understanding of the laser proton acceleration process [2,3,4]. In this talk we focus on the
implementation of a hydrogen jet target at the Petawatt (PW) beam line of the high power laser source DRACO
at HZDR. The laser system delivers pulses with energies of up to 23J and pulse durations of about 30 fs on
target. We present significant improvements of the operation robustness of the cryogenic target with respect to
the harsh environment around the interaction zone and thereby leading to substantial increase in stability of the
laser accelerated proton beams. Prior and during experiments, characterization of the jet target was conducted
with a synchronized off-harmonic optical probe laser. It allowed for on-shot study of the onset of ionization
induced by the leading edge of the main laser pulse prior to its intensity maximum with sub-picosecond time
resolution. Also, by adding artificial pre-pulses the initial shape and size of the target can be engineered for
optimal interaction conditions with the high intensity laser pulse.
  • Lecture (Conference)
    4th Targetry for High Repetition Rate Laser-Driven Sources Workshop, 09.-12.06.2019, Milano, Italien

Permalink: https://www.hzdr.de/publications/Publ-30494
Publ.-Id: 30494


Hybrid LWFA-PWFA staging; from concept to proof-of-principle experiments

Irman, A.ORC; Bussmann, M.ORC; Chang, Y.-Y.; Corde, S.; Couperus Cabadağ, J. P.ORC; Debus, A.ORC; Ding, H.; Döpp, A.; Heinemann, T.; Hidding, B.; Gilljohann, M. F.; Götzfried, J.; Karsch, S.; Kononenko, O.; Kurz, T.ORC; Köhler, A.ORC; Martinez De La Ossa, A.; Pausch, R.ORC; Raj, G.; Schindler, S.; Schöbel, S.; Zarini, O.ORC; Assmann, R. W.; Schramm, U.ORC
Beam-driven plasma wakefield accelerators (PWFAs) offer a unique regime for the generation and acceleration of high-quality electron beams to multi-GeV energies. Here we present an innovative hybrid staging approach, deploying electron beams generated in a laser-driven wakefield accelerator(LWFA) as drivers for a PWFA, integrated in a particularly compact setup. This scenario exploits the capability of LWFAs to deliver shortest, high peak-current electron bunches [1] with the prospects for high-quality witness beam generation in PWFAs [2]. The feasibility of the concept is presented through exemplary particle-in-cell simulations, before describing experimental results from extensive campaigns performed at high-power laser facilities; ATLAS (LMU, Munich), SALLE-JAUNE (LOA, Paris) and DRACO (HZDR, Dresden). Using few-cycle optical probing we captured clear images of beam-driven plasma waves in a dedicated plasma stage, allowing us to identify a non-linear plasma-wave excitation regime. Trailing the plasma waves, the impact of ion motion to the transverse modulation of the plasma density was observed over many picoseconds [3]. Furthermore, we demonstrate for the first time the acceleration of distinct witness beams in such LWFA-driven PWFA (LPWFA) setup, showcasing an accelerating gradient on the order of 100 GV/m. These milestones pave the way towards compact sources of energetic ultra-high brightness electron beams as well as a miniature model for large scale PWFA facilities.
Keywords: laser wakefield acceleration, plasma wakefield acceleration
  • Open Access Logo Lecture (Conference)
    European Advanced Accelerator Concept (EAAC), 20.09.2019, ELBA, Italia

Permalink: https://www.hzdr.de/publications/Publ-30492
Publ.-Id: 30492


Field driven recovery of the collective spin dynamics of the chiral soliton lattice

Trindade Goncalves, F. J.; Shimamoto, Y.; Sogo, T.; Paterson, G. W.; Kousaka, Y.; Togawa, Y.;
We investigate the magnetic field dependence of the spin excitation spectra of the chiral soliton lattice (CSL) in the helimagnet CrNb₃S₆, by means of microwave resonance spectroscopy. The CSL is a prototype of a noncollinear spin system that forms periodically over a macroscopic length scale. Following the field initialisation of the CSL, we found three collective resonance modes over an exceptionally wide frequency range. With further reducing the magnetic field towards 0 T, the spectral weight of these collective modes was disrupted by the emergence of additional resonances whose Kittel-like field dependence was linked to coexisting field polarised magnetic domains. The collective behaviour at a macroscopic level was only recovered upon reaching the helical magnetic state at 0 T. The magnetic history of this non collinear spin system can be utilized to control microwave absorption, with potential use in magnon driven devices.

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Permalink: https://www.hzdr.de/publications/Publ-30491
Publ.-Id: 30491


Laser-proton acceleration from a cryogenic hydrogen jet at the DRACO PW laser

Rehwald, M.ORC; Bernert, C.; Curry, C.; Cowan, T.ORC; Gauthier, M.; Glenzer, S.; Goede, S.; Kim, J.; Kluge, T.ORC; Kraft, S.ORC; Obst-Hübl, L.ORC; Schoenwaelder, C.; Schlenvoigt, H.-P.ORC; Schramm, U.ORC; Ziegler, T.ORC; Zeil, K.ORC
Demanding applications like radiation therapy of cancer have pushed the development of laser proton accelerators and defined necessary proton beam properties as well as levels of control and stability.
The presentation will give an overview of the recent experiments for laser driven proton acceleration employing a cryogenic target system which is capable of producing a renewable and debris free jet target. The micrometer sized pure hydrogen jet is characterized by a low plasma density of 30 times the critical density at 800 nm and was irradiated at the Petawatt (PW) amplifier stage of the high power laser source DRACO at the HZDR. The Ti:sapphire system delivers laser pulses with energies of up to 23 J and pulse durations of 30 fs on target.
In this talk we present substantially improvements of the target system leading to an increase in stability of the accelerated protons as well as the long-term operations. Evaluation of different target geometries (cylindrical with a diameter of 5µm and planar with up to 4x20 µm²) demonstrating the capabilities in terms of size and shape of available hydrogen jets.
We report on the laser contrast dependencies of the proton beam properties by introducing artificial pre-pulses and describe their influence on the target shape at the interaction time by using a synchronized optical probe beam.
Furthermore different ion diagnostics reveal mono-species proton acceleration in the laser incidence plane from the jet target, reaching foil-like proton cut-off energies in target normal direction.
  • Lecture (Conference)
    Laser Plasma Accelerator Workshop 2019, 06.05.2019, Split, Kroatien

Permalink: https://www.hzdr.de/publications/Publ-30489
Publ.-Id: 30489


Using XFELs to Probe Extreme Magnetic Fields Inside Solid Targets Driven by Optical High Power Lasers at HiBEF

Huang, L.; Schlenvoigt, H.-P.ORC; Takabe, H.; Cowan, T.ORC
In this talk, we will firstly present a systematic study of the bulk magnetic field generation using particle-in-cell simulations, that we observe the effect of varying the laser and target parameters, including laser intensity, focal size, incident angle, preplasma scale length, target thickness and material, and experimental geometry. The simulation results suggest that the strongest magnetic field is generated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency. The simulations have also shown that the collisional ionization potential and model are critical to determining the structure and diffusion time of the self-generated magnetic fields. Then we will propose to probe the bulk magnetic fields inside the solid density plasmas by X-Ray polarimetry via Faraday rotation using an X-Ray free electron lasers (XFEL), taking its advantage of simultaneous high spatial-temporal resolution and several tens of micrometers attenuation length in solid. The synthetic simulations predict that the XFEL polarization is rotated by a few hundred micro-radians after penetrating through solid density plasmas which is feasible to be measured with X-Ray polarimetry.
With the results of this work, we are in an excellent position to maximize our chances of measuring laser generated magnetic fields using Faraday rotation at high power laser beamlines at XFELs. One of the first examples of this will be at the European XFEL-HED endstation, in the frame of Helmholtz International Beamline for Extreme Fields at the European XFEL (HiBEF) project, where a 7.5J/300TW high power laser has already installed as a permanent instrument. A dedicated beamtime at the European XFEL-HED endstation to investigate the performance of ultra-high purity X-ray polarimeters under the conditions of European XFEL source has already been scheduled in the end of May, 2019. This is expected to become the basis to probe the laser-driven ultra-strong magnetic fields inside the solid-density targets, accessed via plasma Faraday rotation and imaging polarimetry.
Keywords: magnetic field,X-Ray polarimetry,Faraday rotation, XFEL
  • Invited lecture (Conferences)
    The 4th International Conference on Matter and Radiation at Extremes (ICMRE 2019), 29.05.-02.06.2019, Hefei, China

Permalink: https://www.hzdr.de/publications/Publ-30488
Publ.-Id: 30488


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

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

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


Characterization of Goethe’s prisms by external ion beam

Munnik, F.ORC; Mäder, M.; Heller, R.; Schreiber, A.; Müller, O.
Johann Wolfgang von Goethe is known the world over as a renowned writer. However, he was also involved in scientific studies and has written several scientific books, of which he considered the “Theory of colours” (“Farbenlehre”, 1400 pages published in 1810) his most important work overall. In this work, he characterises colours as arising from the interplay between light and dark. This is in contrast to Newton’s analytical treatment of colour from one century earlier, which is based on the observation that white light can be separated into colours with a prism, that Goethe opposed. Over the centuries, Goethe’s theory was discredited and Newton’s theory prevailed. However, Goethe performed systematic and accurate optical measurements.
For these experiments, he and his partner J. Ritter, who discovered UV-light, used water prisms and glass prisms ordered from a glassmaker in Jena. The aim of current research is to reconstruct these optical experiments and the observed spectra [1]. For this, detailed knowledge of the composition of the glass prisms is important. This knowledge is, for example, also important to evaluate how innovative his prisms were.
Therefore, eleven prisms from Goethe’s estate or from contemporary sources belonging to the Klassik Stiftung Weimar have been analysed at the external beam setup of the Ion Beam Center at the HZDR. A 4 MeV proton beam has been used to acquire PIXE, PIGE and RBS spectra, sometimes on several areas. Care had to be taken to minimise damage by using short measurement times and measuring on inconspicuous areas because the glass quickly showed dark spots under irradiation. The PIXE and PIGE spectra have been used for quantitative analysis in an iterative procedure and the RBS spectra have only been evaluated quantitatively. The results of this analysis and the interpretation are presented in this work.
  • Lecture (Conference)
    16th International Conference on Particle Induced X-ray Emission, 24.-29.03.2019, Caldas da Rainha, Portugal

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


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

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

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

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

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

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


REFERENCES:

[1]. J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nanowire transistors without junctions. Nature Nanotech. 5, 225 (2010).
[2]. J. P. Colinge, C. W. Lee, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, A. Kranti, R. Yu. Junctionless Transistors: Physics and Properties, in Semiconductor-On-Insulator Materials for Nanoelectronics Applications. (Eds: A. Nazarov, J. P. Colinge, F. Balestra, J.-P. Raskin, F. Gamiz, V. S. Lysenko), Springer-Verlag Berlin, Heidelberg, Germany, pp.187-200, Ch. 10 (2011).
[3]. J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Junctionless Nanowire Transistor (JNT): Properties and design guidelines. Solid State Electron. 65-66, 33 (2011).
[4]. Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices. Microelectron. Eng. 118, 47 (2014).
[5]. Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, In "Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting", (Eds: A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre), Springer International Publishing AG, Cham, Switzerland, pp. 367-388, Ch. 17 (2014).
Keywords: nanowires, biosensors, junctionless transistors, protein, streptavidin, single-molecule detection
  • Invited lecture (Conferences)
    IHRS NanoNet International Conference, 08.-11.10.2019, Dresden, Germany

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


Application of junctionless nanowire transistors as ultrasensitive biosensors

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

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

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

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

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

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

[1] J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nature Nanotech. 5 (2010) 225-229.
[2] J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Solid State Electron. 65-66 (2011) 33-37.
[3] Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Microelectron. Eng. 118 (2014) 47-53.
[4] Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, in A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre, eds., Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting, (Springer International Publishing AG, Cham, Switzerland, Ch. 17, 2014) 367-388.
[5] Y. M. Georgiev, N. Petkov, R. Yu, A. M. Nightingale, E. Buitrago, O. Lotty, J. De Mello, A. M. Ionescu, J. D. Holmes, Nanotechnology (2019), accepted, https://doi.org/10.1088/1361-6528/ab192c
[6] N. K. Rajan, D. Routenberg, M. Reed. Appl. Phys. Lett. 98 (2011) 264107.
[7] K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, R. L. Stoop, S. Rigante, J. Brunner, W. Fu, C. David, M. Calame, J. Gobrecht, C. Schönenberger. Sensor. Actuat. B-Chem. 191 (2014) 270.
Keywords: nanowires, biosensors, junctionless transistors, protein, streptavidin, single-molecule detection
  • Open Access Logo Lecture (Conference)
    45th International Conference on Micro- and Nanofabrication and Manufacturing (MNE 2019), 23.-26.09.2019, Rhodes, Greece

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


Group IV Nanowires: Fabrication and Particular Applications

Georgiev, Y.ORC; Khan, M. B.; Deb, D.; Echresh, A.; Ghamsari, S. J.; Prucnal, S.; Rebohle, L.; Erbe, A.; Helm, M.; Gangnaik, A. S.; Game, A. D.; Biswas, S.; Petkov, N.; Holmes, J. D.
Group IV semiconductor nanowires (NWs) are very attractive because of the variety of possible applications as well as of the good silicon (Si) compatibility, which is important for their integration into the existing semiconductor technology.

We will give an overview of our activities on fabrication and application of group IV NWs. These include top-down fabrication (based on electron beam lithography and reactive ion etching) of Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up (vapour-liquid-solid, VLS) growth of alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1 and diameters of 50-70 nm. We will also discuss the innovative nanoelectronic devices that we are working on: junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we will present results on Si JNTs for sensing application as well as on Ge and GeSn JNTs for digital logic. We will also show results on Si RFETs as well as preliminary data on SiGe and GeSn RFETs, which are expected to outperform the Si RFETs.
Keywords: semiconductor nanowires, top-down nanofabrication, electron beam lithography, reactive ion etching, bottom-up nanofabrication, nanoelectronic devices, junctionless nanowire transistors, reconfigurable field effect transistors, biosensors
  • Open Access Logo Lecture (Conference)
    83d DPG Annual Conference and DPG Spring Conference, 31.03.-05.04.2019, Regensburg, Germany

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


Fabrication and Particular Applications of Group IV Semiconductor Nanowires

Georgiev, Y.ORC; Khan, M. B.; Deb, D.; Echresh, A.; Jazavandi Ghamsari, S.; Prucnal, S.; Rebohle, L.ORC; Erbe, A.; Helm, M.; Gangnaik, A. S.; Game, A. D.; Biswas, S.; Petkov, N.; Holmes, J. D.; Knoch, J.
During the last 1-2 decades semiconductor nanowires (NWs) have received significant academic and commercial attention due to their attractive electrical and mechanical properties and large surface area to volume ratios. They have a variety of possible applications including nanoelectronics, nanophotonics, photovoltaics, sensorics, etc. Among all semiconductor NWs the ones based on group IV materials have the advantage of being the most silicon (Si) compatible. This is very important since their integration into the existing semiconductor technology platform can be relatively easy.

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

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

Finally, we will briefly present a novel device concept that we recently invented: a specific group IV heterostructure band-to-band tunnel FET (TFET). The fabrication process of this device is scalable and fully CMOS compatible and should allow the achievement of high on-current Ion together with low off-current Ioff, hence steep subthreshold slope.
Keywords: semiconductor nanowires, top-down nanofabrication, bottom-up nanofabrication, nanoelectronic devices, junctionless nanowire transistors, reconfigurable field effect transistors, band-to-band tunnel field effect transistors, biosensors
  • Lecture (Conference)
    The 10th workshop “Towards Reality in Nanoscale Materials X”, 12.-14.02.2019, Levi, Finland

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


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

Abouelazayem, S.; Glavinic, I.ORC; Wondrak, T.; Hlava, J.
The flow pattern in the mould of the continuous casting is an important factor in determining the quality of the steel slabs that are produced in the end of the process. Hence it can heavily influence manufacturing costs due to the scrap percentage. Electromagnetic actuators are frequently used in the continuous casting process to stabilize the flow in the mould and therefore produce higher quality of steel slabs. Usually they are used in open loop but their effect on the flow pattern may be much better directed if they are used as a part of closed loop control based on real time measurements. In this paper, a closed loop controller is proposed that adjusts the magnetic field of an electromagnetic brake using the real time measurement of the angle of the jet flowing from the Submerged Entry Nozzle (SEN). The angle is kept within a specific range by the controller in order to prevent a deeper jet impingement into the mould; this allows us to achieve the desirable double roll flow pattern, and to avoid the entrapment of slugs. The controller is based on a model of the relationship between brake current and jet angle that was obtained using experimental data from a laboratory scale continuous casting plant.
Keywords: Flow Control, Tomography, Process Automation, Model Predictive Control
  • Contribution to proceedings
    Mining, Mineral and Metal Processing 2019, 28.-30.08.2019, Stellenbosch, South Africa
    Control of Jet Flow Angle in Continuous Casting Process using an Electromagnetic Brake
    DOI: 10.1016/j.ifacol.2019.09.169

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


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

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

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Publ.-Id: 30471


Near free-fall oscillatory velocities in liquid metal rotating convection

Vogt, T.ORC; Horn, S.; Aurnou, J.
The geomagnetic field is induced by liquid metal ow inside Earths outer core as a self-excited dynamo. Buoyancy drives the liquid metal flow because the iron rich core is cooling from its primordial state through heat loss to the mantle. The rotation of the Earth and Lorentz forces alter the resulting convective flow. However, since a 3000 km thick rocky mantle hinders our ability to observe core dynamics, the detailed ow topology is still largely unknown. Here we will investigate the effect of rotation on a low Prandtl number thermal convection by means of laboratory experiments and DNS. Therefore, we consider a rotating Rayleigh-Bénard convection setup in an upright cylindrical vessel of aspect ratio Γ = D/H = 2. We investigate supercriticalities in the range of 1 < R < 20 and Ekman numbers 4x10^-4 < Ek < 5 x 10^-6 in liquid gallium at Pr = 0.03. We find that oscillatory convection generates velocity that appear to exceed predictions in steady convection. Multi-modal bulk oscillations dominate the vertical velocity field over the whole range of supercriticalities investigated. Additionally, coherent mean zonal flows and time-mean helicity is found in the rotating liquid metal convection. Thus, we show that these oscillatory flows can be relevant for dynamo action.
Keywords: Rotating convection, liquid metal, Rayleigh-Bénard convection
  • Lecture (Conference)
    72nd Annual Meeting of the American Physical Society’s Division of Fluid Dynamics (DFD), 23.-27.11.2019, Seattle, USA

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


Imaging of current induced Néel vector switching in antiferromagnetic Mn2Au

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

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Publ.-Id: 30467


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

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

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Publ.-Id: 30466


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

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

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


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

Vasileiadis, I. G.; Lymperakis, L.; Liebscher, C. H.; Dimakis, E.ORC; Hübner, R.; Adikimenakis, A.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.
Short period superlattices (SPSs) of InxGa1-xN/GaN quantum wells (QW) with a thickness of one up to just a few atomic monolayers (MLs) are promising for bandgap and strain engineering towards advanced optoelectronics devices and novel topological insulators.

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

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

Composition dependent strain graphs were calculated theoretically in order to associate the experimental strain measurements to the indium content. For that purpose, a series of energetically relaxed InxGa1-xN/GaN supercells were constructed taking into account several indium contents, and the QW thickness limited to 1 ML. For the relaxation of the supercells a ternary empirical interatomic potential was utilized using molecular dynamics simulations.
  • Lecture (Conference)
    XXXIV Panhellenic Conference on Solid State Physics and Materials Science, 11.09.2019, Patras, Greece

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


Status and Applications TOF-SIMS in the Helium Ion Microscope

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

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.;
Notte, J. A.; Huang, J. and Facsko, S.; Nanometer scale
elemental analysis in the helium ion microscope using time
of flight spectrometry, Ultramicroscopy 162(2016): 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von
Borany, J.; Time-of-flight secondary ion mass spectrometry
in the helium ion microscope, Ultramicroscopy 198(2019),
10-17
  • Lecture (Conference)
    Ion Beam Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

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


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

Vasileiadis, I. G.; Adikimenakis, A.; Dimakis, E.ORC; Hübner, R.; Lymperakis, L.; Georgakilas, A.; Karakostas, T.; Komninou, P.; Dimitrakopulos, G. P.
Introduction/Purpose: Short period superlattices (SPSs) comprising ultrathin InGaN/GaN quantum wells (QW) with thicknesses ranging from one to few (0002) monolayers (MLs) are promising for novel applications ranging from band gap engineering in optoelectronic devices to topological insulators. The strain relaxation behavior of a range of samples grown by varying the growth temperatures for the QWs and GaN barriers has been considered.
Methods: In(Ga)N/GaN SPSs were deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates. Structural characterization was performed by high resolution transmission and scanning transmission electron microscopy (HRTEM/HRSTEM).
Results: Strain relaxation through formation of stacking fault domains was observed with decreasing growth temperature. For the quantification of strain versus composition, peak finding with a recently established approach was implemented. This involves quantification of Z-contrast from HRSTEM observations by comparison with calculated composition-dependent graphs of InxGa1-xN/GaN atomic column intensity ratios obtained from multislice image simulations of energetically relaxed supercells under the frozen lattice approximation. Energetical relaxation was performed by molecular dynamics using an empirical interatomic potential, considering the ordered, disordered, and island models of QW structure. Comparison to the experimental observations was performed along the a-type zone axis that is appropriate to deduce average values for the QW composition and strain.
Conclusions: The investigation concluded to the influence of growth temperature in the composition and structural properties of ultra-thin In(Ga)N/GaN QWs.
  • Lecture (Conference)
    EUROMAT 2019, 01.09.2019, Stockholm, Sweden

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


Nano-pillar evolution by FIB irradiation with heavy ions

Bischoff, L.ORC; Heinig, K.-H.; Möller, W.; Klingner, N.ORC; Pilz, W.; Borany, J.
The European H2020 project “ion4SET” is directed to the development of advanced computation and communication devices with significantly lower power consumption. The general objective is to demonstrate the manufacturability of single electron transistors (SETs) using CMOS compatible technology. The basic idea of this SET is a nano-pillar (NP) transistor having a single Si nanodot (ND) in the oxide layer separating source and drain. The ND is formed by ion beam mixing and post annealing from a Si top layer. The ion irradiation under normal incidence is a crucial process for the small nano-pillars which are only 10 to 30 nm in width and about 80 nm in height.
In this work the evolution nano-pillars shape is investigated under heavy ion irradiation from a mass separated focused ion beam (FIB) for different ion energies at RT and 400°C target temperature. In particular Si (60 keV), Pb (30 and 60 keV), Au (30 and 60 keV) ions as well as polyatomic projectiles Au2 and Au3 (Uacc = 30 kV) with a fluence of 5 x 1015 cm-2 were applied.
Whereas the Si ion irradiation of Si pillars at elevated temperatures only deforms the pillar tip, the heavy ion irradiation leads depending on the fluence up to a total removing of the pillar. The fluence variation was obtained on the slope of the beam profile. The irradiation at RT with Pb ions at 30 keV showed a more pronounced bending of the pillar due to the high energy deposition caused stress and viscous flow than that at 60 keV. The influence of the irradiation is also depending on the thickness and the distance of the pillars in different lithographic prepared fields. For a better comprehension of the irradiation results the experiments were simulated using the TRI3DYN code.
  • Lecture (Conference)
    Ion Beam Physics Workshop 2019, 24.-26.06.2019, Dresden, Deutschland

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


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

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

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

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


1. Watt, F. et al. Whole cell structural imaging at 20 nanometre resolutions using MeV ions. Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 306, 6–11 (2013).
2. Dowsett, D. & Wirtz, T. Co-Registered In Situ Secondary Electron and Mass Spectral Imaging on the Helium Ion Microscope Demonstrated Using Lithium Titanate and Magnesium Oxide Nanoparticles. Anal. Chem. 89, 8957–8965 (2017).
3. Wang, J. et al. Focussed helium ion channeling through Si nanomembranes. J. Vac. Sci. Technol. B, Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 36, 021203 (2018).
4. Klingner, N. et al. Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry. Ultramicroscopy 162, 91–97 (2016).
  • Lecture (Conference)
    Microscopy Conference 2019, 01.-05.09.2019, Berlin, Deutschland

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


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

Tauchnitz, T.; Balaghi, L.ORC; Fotev, I.ORC; Shan, S.; Pashkin, O.ORC; Bussone, G.; Grifone, R.; Grenzer, J.; Hübner, R.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC
III-As semiconductors in the form of free-standing nanowires have exhibited new potentials for a wide variety of future applications in nanotechnology, ranging from energy-efficient electronic switches to entangled-photon-pair sources for quantum information technology, including the possibility for monolithic integration in the mainstream Si technology. Using molecular beam epitaxy, we developed an in situ procedure (substrate annealing – Ga deposition – substrate annealing) in order to modify the surface of Si substrates and, thus, to achieve highly synchronized nucleation of self-catalyzed GaAs nanowire ensembles with well controlled dimensions and number density. Specifically, the radius can be as low as 10 nm, the distribution of lengths can be sub-Poissonian (due to the so-called nucleation anti-bunching), and the number density can be varied from 10 ⁶ to 10 ⁹ cm-2.
Furthermore, the GaAs nanowires can be hydrostatically strained when they are overgrown all-around with lattice-mismatched shells. The high surface-to-volume ratios allow for growing highly mismatched combinations without dislocations, beyond to what is possible in thin-film heterostructures. Here, we show that the mismatch strain inside the GaAs core can be engineered via the composition and the thickness of an (In, Ga)As or (In, Al)As shell. As a result, the electronic properties of GaAs can be widely tuned; the band gap and the electron effective mass can be reduced down to 60% of the strain-free values, rendering GaAs nanowires suitable for photonic devices across the near-infrared (800 – 1400 nm) range or for high-speed transistors.
  • Poster
    2nd Scientific Workshop of the Program “From Matter to Materials and Life” (MML) in the Helmholtz Research Field “Matter”, 13.02.2019, Dresden, Germany

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


Complex three-dimensional heterostructures in III-As nanowires

Tauchnitz, T.; Balaghi, L.ORC; Hübner, R.; Wolf, D.; Bussone, G.; Grifone, R.; Grenzer, J.; Pelekanos, N. T.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC
Free-standing nanowires are promising platforms for hosting three-dimensional heterostructures such as single quantum dots for quantum photonics, modulation doped heterostructures for gate-all-around high mobility transistors, etc. The peculiarity of heteroepitaxy in nanowires is the existence of multiple growth interfaces with different crystallographic orientations (usually one top- and six side-facets), where the growth can take place in different modes (e.g. vapor-liquid-solid on the top- and vapor-solid on the side-facets) and can be controlled independently. Furthermore, strained epilayers in nanowires can relax elastically both at the lateral free surface and by stretching the substrate, which in this case are the thin nanowires. All these features open up new possibilities for complex three-dimensional heterostructures with loose strain restrictions.
Here, we have investigated the growth of radial and axial heterostructures, as well as combinations of the two, within III-As nanowires. The radial ones consist of thin GaAs nanowires overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. In agreement with theory, the small volume of the core allows for strain engineering both in the core and the shell, and for realization of highly-mismatched/strained heterostructures (with misfits up to 4%) without dislocations. The manipulation of the growth kinetics is necessary in order to suppress strain-driven phenomena, such as the preferential shell-growth and In-incorporation on one side of the core. The axial heterostructures consist of single or multiple GaAs/AlxGa1-xAs quantum dots. The width and the thickness of these dots can be controlled independently. The AlxGa1-xAs segments were grown as digital alloys using pulsed epitaxy in order to achieve sharper interfaces and to avoid the formation of stacking faults. Finally, we realized complex heterostructures with single GaAs/AlxGa1-xAs quantum dots inside the core of core/shell nanowires, aiming at engineering the electronic properties of the dots depending on the composition and thickness of the shell.
Besides MBE experiments, our investigations involved transmission electron microscopy (HR-TEM, STEM, EDX, STEM tomography), X-ray diffraction, Raman scattering spectroscopy, and photoluminescence spectroscopy.
  • Lecture (Conference)
    20th European Workshop on Molecular Beam Epitaxy, 17.02.2019, Lenggries, Germany

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


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

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

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and
Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018). Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.
  • Lecture (Conference)
    3rd EuFN Workshop 2019 of the European FIB Network, 12.-14.06.2019, Dresden, Germany

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


Complex quantum dots in III-As nanowires

Tauchnitz, T.; Balaghi, L.ORC; Hübner, R.; Chatzarakis, N.; Pelekanos, N. T.; Bussone, G.; Grifone, R.; Grenzer, J.; Schneider, H.ORC; Helm, M.; Dimakis, E.ORC
Single quantum dots in the core of freestanding semiconductor nanowires is a promising scheme for the realization of on-demand sources of single photons or entangled photon pairs in quantum technology systems. Here, we demonstrate that complex quantum-dots can be grown in self-catalyzed III-As nanowires and their emission can be tuned in a wide range of wavelengths.
The quantum dots are formed inside self-catalyzed GaAs nanowires (grown on Si substrates by molecular beam epitaxy) by first growing an axial AlxGa1-xAs/GaAs/AlxGa1-xAs heterostructure in pulsed mode . The AlxGa1-xAs segments are grown as digital alloys with a precise control of the composition, the thickness, and the crystal structure (absence of stacking faults). Then, the nanowires are overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. Owing to the large lattice-mismatch with the shell, the thin core develops tensile hydrostatic strain and the emission from the dot is strongly red-shifted. Furthermore, distinct exciton-biexciton features are identified in photoluminescence measurements.
Keywords: self-catalyzed, strain engineering, bandgap tuning
  • Lecture (Conference)
    Nanowire Week 2019, 23.09.2019, Pisa, Italy

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


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

Eswara, S.; Mousley, M.; de Castro, O.; Bouton, O.; Audinot, J.-N.; Klingner, N.ORC; Koch, C.; Hlawacek, G.ORC; Wirtz, T.
The recent availability of high-brightness helium ion sources has enabled exciting new possibilities in the fields of microscopy and nanofabrication. When compared to electron beams of same energy, He+ ions have a smaller interaction volume and thus offer higher lateral resolution (< 0.5 nm) in the secondary electron (SE) imaging mode1. While the majority of the applications of the commercial Helium Ion Microscope - HIM (Zeiss Nanofab) have been in SE imaging and nanofabrication, the complete range of imaging possibilities is still not fully explored. In this context, transmission ion microscopy is expected to offer new contrast mechanisms (e.g. charge neutralization) which are not possible in a Transmission Electron Microscope (TEM). Transmission microscopy using MeV He+ ions has already been demonstrated2, but, they are not very widely available. With the increasing availability of HIM which operate at primary energies below 50 keV, the potential to use it for transmission ion microscopy and ion energy-loss spectroscopy still need to be fully explored. To address this, we developed a prototype Transmission Helium Ion Microscope (THIM) that can operate on both stationary full-field THIM mode as well as Scanning THIM (STHIM) mode with simultaneous SE imaging possibility. This prototype has a duoplasmatron ion source and offers full flexibility in terms of instrumental configurations. This is a significant advantage in comparison to using the commercial instrument in which space below the specimen plane is very limited and thus restrict the possible experimental configurations. We imaged BN, NaCl and MgO crystalline powders in the stationary full-field THIM imaging using 10 keV He+ and investigated the distribution of transmitted ion intensities. The scattered intensity form unexpected spot patterns that may be explained by sample charging and morphology. Furthermore, we have added electronics to pulse the primary ion beam in the prototype instrument. This allows us to perform Time-of-Flight (TOF) multispectral imaging in both THIM and STHIM modes in addition to the standard Bright-Field, Dark-Field and SE imaging modes. Our presentation will focus mainly on the transmission ion configuration. We will also briefly discuss the recent developments in the Secondary Ion Mass Spectrometers (SIMS) that we developed for Zeiss Nanofab instruments (HIM-SIMS) which allow direct chemical mapping at nanoscale.
1 G. Hlawacek and A. Gölzhäuser, editors , Helium Ion Microscopy, 1st ed. (Springer, 2016).
2 F. Watt et al, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 306, 6 (2013).
  • Lecture (Conference)
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS 2019, 13.-20.10.2019, Antibes, France

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


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

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

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

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

References

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

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

[3] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2019) Time-of-flight secondary ion mass spectrometry in the helium ion microscope, Ultramicroscopy 198, 10-17
  • Poster
    24TH INTERNATIONAL CONFERENCE ON ION BEAM ANALYSIS 2019, 13.-18.10.2019, Antibes, France

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


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

Kelley, D. H.; Tithof, J. R.; Horstmann, G. M.ORC; Suri, B.; Aluie, H.; Schatz, M. F.; Grigoriev, R. O.
Energy cascades, coherent structures, and the arrow of time in turbulence
  • Invited lecture (Conferences)
    Physics seminar, 18.11.2019, Fayetteville, Arkansas, USA

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


Energy cascades & the asymmetric motion of coherent structures

Kelley, G. H.; Tithof, J. R.; Horstmann, G. M.ORC; Suri, B.; Aluie, H.; Schatz, M. F.; Grigoriev, R. O.
Energy cascades, coherent structures, and the arrow of time in turbulence
  • Lecture (Conference)
    72nd Annual Meeting of the APS Division of Fluid Dynamics, 23.-26.11.2019, Seattle, Washington, USA

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


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

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

Conference (Lecture):

American Physics Society (APS) DFD meeting 2019 Seattle

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

 

Keywords: Rayleigh-Bénard convection, magnetohydrodynamics, low Prandtl number, liquid metal, ultrasound velocimetry
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-11-23
    DOI: 10.14278/rodare.231
    License: CC-BY-4.0

Downloads:

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


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

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

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

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

 

Keywords: liquid metal, low Prandtl number, Rayleigh-Bénard magnetoconvection, vertical magnetic Field
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-07-01
    DOI: 10.14278/rodare.229
    License: CC-BY-4.0

Downloads:

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


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

Akashi, M.; Keplinger, O.; Anders, S.ORC; Reuter, M.ORC; Eckert, S.ORC
We report on laboratory experiments focusing on bubbling phenomena arising from gas injection through a top submerged lance (TSL) in a liquid metal layer. Visualization was performed in the eutectic alloy GaInSn using X-ray radiography. Argon bubbles were injected through the nozzle positioned at three different submergence depths. Essential parameters such as the bubble size, bubble shape, detachment frequency or the two-dimensional gas distribution in the flat vessel were obtained by image processing. The results show that the deep position of the submerged lance causes an asymmetric large-scale circulation inside the fluid vessel. Bubble detachment frequencies were calculated by Fast Fourier Transformation from fluctuations of the image intensity in the vicinity of the nozzle injection point. This frequency does not show strong variations with respect to changes of the gas flow rate and the submergence depth of the nozzle. An increasing gas flow rate results in an increasing two-dimensional projected bubble area and the occurrence of a significant number of small bubbles being trapped by the strong fluid flow in the liquid metal layer.
Keywords: Two phase flow, Liquid metal, Top submerged lance
  • Lecture (Conference)
    17th Multiphase Flow Conference and Short Course, 11.-15.11.2019, Dresden, Germany

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


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

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

Lecture (Conference)

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

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

 

Keywords: Rayleigh-Bénard-Convection, Magnetohydrodynamic, low Prandtl Number, liquid metal, Ultrasound velocimetry
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2019-07-01
    DOI: 10.14278/rodare.227
    License: CC-BY-4.0

Downloads:

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


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

Obiso, D.; Sebastian, K.; Akashi, M.; Eckert, S.ORC; Reuter, M.ORC
The present paper focuses on the application of CFD techniques to investigate the Top-Submerged-Lance (TSL) gas injection in liquid metal.
Previous works of the authors have shown that up- and down-scaling procedures based on the modi-fied Froude number have some shortcomings, as this approach does not take into account the interfa-cial and viscous forces. Indeed surface tension and dynamic viscosity of the smelting slags (σ = 0.4-0.5 N/m, μ = 0.2 Pa·s) are higher than the operating fluids that have been used in literature (water, par-affin oil), which have been used to study TSL injection in down-scaled furnaces.. In order to get closer to real systems, the authors study the TSL injection of Argon in a liquid metal.
An experimental campaign was carried out at the Magnetohydrodynamic Department of Helmholtz-Zentrum Dresden-Rossendorf (HZDR), where the eutectic alloy GaInSn was used as liquid phase. The alloy is liquid at room temperature, and X-Ray imaging is used to picture the multiphase flow in a qua-si-2D vessel (140x140x12 mm).
The aim of the present work is to demonstrate the applicability of CFD techniques to model multi-phase flows involving liquid metals, and validate the model using the data produced at HZDR. The commercial software ANSYS Fluent® was used together with the Volume of Fluid model to directly resolve the gas-liquid interphase. Some features of the flow, such as the void fraction distribution and bubble detachment frequency are tracked with CFD and compared to the experimental data. The ef-fect on the hydrodynamics of different operating conditions, such as the lance immersion depth is investigated.
The authors are currently extending the work to new geometries and operating conditions, in order to get a broader amount of data, useful for the validation of models and for the further understanding of the TSL injection.
Keywords: two phase flow, top submerged lance, liquid metal
  • Lecture (Conference)
    10th Copper International Conference (COPPER 2019), 18.-21.08.2019, Vancouver, Canada

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


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

Xie, Y.; Yuan, Y.; Wang, M.ORC; Xu, C.ORC; Hübner, R.; Grenzer, J.; Zeng, Y.-J.; Helm, M.; Zhou, S.ORC; Prucnal, S.
Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.
  • Open Access Logo Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 03.04.2019, Regensburg, Deutschland
    DOI: 10.1063/1.5057733

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


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

Wang, X.; Baraban, L.; Misko, V. R.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Faßbender, J.ORC; Makarov, D.ORC
Visible light driven nano/micro swimmers are promising candidates for potential biomedical and environmental applications. However, the previously reported mean squared displacement (MSD) values are low, typically in the range of up to 200 µm2 (when measured over 10 s), even under the favourable UV light illumination.[1,2]
Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The Ag/AgCl-based micromotor can boost the MSD to a remarkable value of 3000 µm2 (over 10 s) in pure H2O, even when activated with blue light (λ = 450-490 nm). Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] Using numerical simulations of the Langevin equations, we gain a fundamental understanding not only the diffusion constants, but also the system-specific interaction parameter between Janus motors and passive beads.
1. Ibele, M., et al., Angew. Chem. Int. Ed. 2009, 48, 3308.
2. Simmchen, J., et al., ChemNanoMat 2017, 3, 65.
3. Wang, X., et al., Small DOI: 10.1002/smll.201803613.
4. Wang, X., et al., Small 2018, 14, 1802537.
Keywords: Active Janus particles, exclusion interaction, passive beads, visible light‐driven micromotors
  • Lecture (Conference)
    DPG Spring Meetings 2019, 31.03.-05.04.2019, Regensburg, Germany

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


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