Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31828 Publications
Phase Transitions in Two-Dimensional Transition Metal Dichalcogenides under Electron Beam
Kretschmer, S.ORC; Komsa, H.-P.ORC; Bøggild, P.; Krasheninnikov, A. V.ORC
Recently a phase transition from the hexagonal 1H to trigonal distorted 1T’-phase in two-dimensional (2D) MoS2 has been induced by electron irradiation [1]. Using density functional theory calculations, we study the energetics of these stable and metastable phases when electric charge, mechanical strain and vacancies are present. Based on the results of our calculations, we propose an explanation for this phenomenon which is likely promoted by charge redistribution in the monolayer combined with vacancy formation due to electron beam and associated mechanical strain in the sample. We further show that this mechanism can be extended to other 2D transition metal dichalcogenides.

[1] Y.-C. Lin, D. O. Dumcenco, Y.-S. Huang, and K. Suenaga, Nature Nanotechnology 9, 391 (2014)
Keywords: phase transition, two-dimensional, transition metal dichalcogenides, electron beam
  • Lecture (Conference)
    Towards Reality in Nanoscale Materials IX, 13.-16.02.2017, Levi, Finland
  • Lecture (Conference)
    MRS Spring Meeting, 17.-21.04.2017, Phoenix, USA
  • Lecture (others)
    Seminar, 15.-19.05.2017, Helsinki, Finland

Publ.-Id: 26872 - Permalink


Mechanosensing at the nanoscale: the influence of thermoplastic nanostructures on neural cells
Masciullo, C.; Tonazzini, I.; Dell’Anna, R.; Sonato, A.; Böttger, R.; Pepponi, G.; Romanato, F.; Cecchini, M.;
It is well established that the behavior of neural cells is influenced by geometrical patterns in the micrometric and sub-micrometric range. Here we present two different types of periodical patterns in the nanometric range (i.e. with a typical features having a lateral size ≤ 100 nm) and their impact on cell contact guidance. In the first case, hierarchical periodic nano-rippled structure (i.e. nano-ripples) made by ion-bombardment technique were replicated on top of polyethylene terephtalate (PET) films. We demonstrated that Schwann cells actively interact with these nanorippled surfaces, showing perpendicular contact guidance and improved adhesion and proliferation with respect to standard flat substrates. The second type of scaffolds here presented consist in cyclic-olefin-copolymer (COC) nanogratings with periodicity (down to 200nm -50% duty cycle), obtained by hot embossing from photoresist molds fabricated by interference lithography. In this case, we coupled the substrates with the PC12 neuronal cell line and measured the neurite alignment and focal adhesion (FA) morphometric parameters. We show optimal contact guidance in the case of periodicity > 400nm, while a progressive degradation of polarized alignment appears by further decreasingthe grating lateral dimensions, correlating with FA shaping. These results set for the first time a lower limit in grating periodicity for effective neurite contact guidance. Altogether thesestudies provide interesting elements for regenerative medicine applications and for developing artificial neural interfaces.
Keywords: Mechanobiology, Nanotechnology
  • Poster
    Nanoengineering for Mechanobiology, 26.-29.03.2017, Camogli, Genova, Italy

Publ.-Id: 26871 - Permalink


Ions irradiation on bi-layer coatings
Tessarolo, E.; Corso, A. J.; Böttger, R.; Martucci, A.; Pelizzo, M. G.;
Future space missions will operate in very harsh and extreme environments. Optical and electronics components need to be optimized and qualified in view of such operational challenges. This work focuses on the effect of low alpha particles irradiation on coatings. Low energy He+ (4 keV and 16 keV) ions have been considered in order to simulate in laboratory the irradiation of solar wind (slow and fast components) alpha particles. Mono- and proper bi-layers coatings have been investigated. The experimental tests have been carried out changing doses as well as fluxes during the irradiation sessions. Optical characterization in the UV-VIS spectral range and superficial morphological analysis have performed prior and after irradiation.
Keywords: ion Irradiation, coatings, space applications
  • Contribution to proceedings
    SPIE Optical Engineering + Applications, 06.-10.08.2017, San Diego, United States
    Proc. SPIE 10401, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems
    DOI: 10.1117/12.2274795

Publ.-Id: 26870 - Permalink


Curvature-induced asymmetry of spin-wave dispersion
Otálora, J. A.; Yan, M.; Schultheiss, H.; Lindner, J.; Fassbender, J.; Hertel, R.; Kákay, A.;
Spin waves (SWs), or magnons, are dynamic eigen-oscillations of spins in ferromagnetic materials. Analogous to the electron currents in electronics, spin-based currents are proposed to be used to carry, transport and process information in the research field of magnonics. Since SWs, with frequencies between GHz to THz range propagate over macroscopic distances without electron charges being displaced, information technologies based on magnon computation are expected to achieve low power consumption, fast operative rates and small packing sizes. Accordingly, remarkable progress has been made both theoretically and experimentally, leading to prototype building blocks of spin-wave-based logics.
Due the their stable magnetisation states and small sizes magnetic nanotubes are perfect candidates for magnonic waveguides. Such novel structures can nowadays be very well produced [1,2], motivated by the broad range of applications for magnetoresistive devices, optical metamaterials, cell-DNA separators, and drug delivery vectors [3,4]. The high stability of their equilibrium state [5,6] against external perturbations and their robust domain walls propagating with velocities faster than the SW phase velocity [7] promote MNTs as appealing candidates for racetrack memory devices [8,9] and information processing [7].
We show using micromagnetic simulations and analytical calculations that spin-wave propagation in ferromagnetic nanotubes is fundamentally different than in flat thin films. The dispersion relation is asymmetric regarding the sign of the wave vector for both the zeroth and first order azimuthal modes. This is a purely curvature induced effect and its origin is identified to be the classical dipole-dipole interaction. In certain cases the Damon-Eshbach modes in nanotubes behave as the volume-charge-free backward volume modes in flat thin films. Such non-reciprocal spin-wave propagation [10] is known for flat thin films with Dzyalonshiinsky-Moriya interaction, an antisymmetric exchange due to spin-orbit coupling. The analytical expression of the dispersion relation has the same mathematical form as in flat thin films with DMI. The influence of curvature on spin waves is thus equivalent to an effective dipole-induced Dzyalonshiinsky-Moriya interaction [11].
We also derive the dispersion relation for the limiting cases k=0 and k much larger than 1/R, where k is the wave vector of the spin wave and R the nanotube radius. For the first case, the mathematical formula of the dispersion relation resembles the well-known Kittel formula for the ferromagnetic resonance of a thin film with the in-plane magnetization parallel to the applied field, and both oriented perpendicularly to the in-plane easy axis of the shape anisotropy field. In the latter case the expression is identical to the exchange-dominated dispersion relation of a planar thin film in the Damon-Esbach configuration with the in-plane magnetization oriented perpendicularly to the in-plane easy axis.
Keywords: spin waves, dipole-induced DMI, broken inversion symmetry
  • Lecture (Conference)
    Hysteresis Modelling and Magnetism - HMM, 29.-31.05.2017, Barcelona, Spain

Publ.-Id: 26869 - Permalink


From plasma acceleration to accelerators ? Status of laser and plasma accelerator development in Dresden
Schramm, U.ORC
Seminar Talk on laser plasma accelerators
Keywords: Laser plasma acceleration, high power laser development
  • Invited lecture (Conferences)
    Plasmaphysik Seminar der GSI, 23.01.2018, Darmstadt, Deutschland

Publ.-Id: 26868 - Permalink


Curvature-Induced Asymmetry of Spin-Wave Dispersion in Nanotubes
Kakay, A.; Otalora, J. A.; Schultheiss, H.; Lindner, J.; Hertel, R.; Fassbender, J.;
Due the their stable magnetisation states and small sizes magnetic nanotubes are perfect candidates for magnonic waveguides. Such novel structures can nowadays be very well produced [1,2], motivated by the broad range of applications for magnetoresistive devices, optical metamaterials, cell-DNA separators, and drug delivery vectors [3,4].
The high stability of their equilibrium state [5,6] against external perturbations and their robust domain walls propagating with velocities faster than the SW phase velocity [7] promote MNTs as appealing candidates for racetrack memory devices [8,9] and information processing [7].
We show using micromagnetic simulations and analytical calculations that spin-wave propagation in ferromagnetic nanotubes is fundamentally different than in flat thin films. The dispersion relation is asymmetric regarding the sign of the wave vector.
As shown in figures 1 and 2, the spin-wave dispersion is asymmetric for both the zeroth and first order azimuthal modes. This is a purely curvature induced effect and its origin is identified to be the classical dipole-dipole interaction.
In certain cases the Damon-Eshbach modes in nanotubes behave as the volume-charge-free backward volume modes in flat thin films. Such non-reciprocal spin-wave propagation [10] is known for flat thin films with Dzyalonshiinsky-Moriya interaction (DMI), an antisymmetric exchange due to spin-orbit coupling. The analytical expression of the dispersion relation has the same mathematical form as in flat thin films with DMI. The influence of curvature on spin waves is thus equivalent to an effective dipole-induced Dzyalonshiinsky-Moriya interaction [11].
We also derive the dispersion relation for the limiting cases k=0 and k much larger than 1/R, where k is the wave vector of the spin wave and R the nanotube radius. For the first case, the mathematical formula of the dispersion relation resembles the well-known Kittel formula for the ferromagnetic resonance of a thin film with the in-plane magnetization parallel to the applied field, and both oriented perpendicularly to the in-plane easy axis of the shape anisotropy field. In the latter case the expression is identical to the exchange-dominated dispersion relation of a planar thin film in the Damon-Esbach configuration with the in-plane magnetization oriented perpendicularly to the in-plane easy axis.
Keywords: asymmetric dispersion, spin waves, DMI
  • Lecture (Conference)
    Intermag Dublin, 24.04.2017, Dublin, Ireland

Publ.-Id: 26867 - Permalink


Curvature-Induced Asymmetry of Spin-Wave Dispersion
Otalora, J. A.; Yan, M.; Lindner, J.; Schultheiss, H.; Fassbender, J.; Hertel, R.; Kakay, A.;
We show using micromagnetic simulations and analytical calculations that spin-wave propagation in ferromagnetic nanotubes is fundamentally different than in flat thin films. The dispersion relation is asymmetric regarding the sign of the wave vector. This is a purely curvatureinduced effect and its fundamental origin is identified to be the classical dipole-dipole interaction. In certain cases the Damon-Eshbach modes in nanotubes behave as the volume-charge-free backward volume modes in flat thin films. Such non-reciprocal spin-wave propagation [1] is known for flat thin films with Dzyalonshiinsky-Moriya interaction (DMI), an antisymmetric exchange due to spin-orbit coupling.
The analytical expression of the dispersion relation has the same mathematical form as in flat thin films with DMI. The influence of curvature on spin waves is thus equivalent to an effective dipole-induced Dzyalonshiinsky-Moriya interaction [2].
[1] K. Zakeri, et. al., Phys. Rev. Lett. 104, 137203 (2010).
[2] J.A. Otálora, et. al., Phys. Rev. Lett. 117, 227203 (2016).
Keywords: spin waves, asymmetric dispersion, broken inversion symmetry
  • Lecture (Conference)
    DPG Dresden, 19.-24.03.2017, Dresden, Germany

Publ.-Id: 26866 - Permalink


EGFR Amplification, Tumor Microenvironment and Gene Expression as potential Biomarkers for EGFR-directed Radiotherapy in HNSCC Xenograft Models
Koi, L.; Linge, A.; Löck, S.; Thurow, C.; Baumann, M.; Krause, M.; Gurtner, K.;
Fragestellung: Zur Etablierung neuer spezifischer Targets und Biomarker zur Evaluierung neuer Therapieansätze in Kombination mit der Strahlentherapie wurden insgesamt 10 verschiedene Plattenepithelkarzinomzelllinien des Kopf-/Halsbereiches in vivo und ex vivo untersucht. Die Ergebnisse der ersten 5 Tumormodelle wurden bereits publiziert (Gurtner et al., Radiother Oncol 2011 (99): 323–330). Die Wirkung einer Kombination von fraktionierter Bestrahlung und EGFR-Inhibition auf die lokale Tumorkontrolle wurde mit Parametern, wie z.B. EGFR-Amplifizierungsstatus und Tumormikromilieubedingungen, korreliert.
Methodik: Die Bestimmung der lokalen Tumorkontrolle 120 Tage nach Ende der Bestrahlung erfolgte nach alleiniger fraktionierter Strahlentherapie (30 f/6 Wo) oder nach simultaner Applikation des monoklonalen Antikörpers Cetuximab. Der Amplifikationsstatus wurde durch die Fluoreszenz-in situ-Hybridisierung (FISH) untersucht (EGFR-CEP-7 ratio) und mit dem Ansprechen auf eine EGFR-gerichtete Kombinationstherapie verglichen. Zusätzlich wurden unbehandelte und mit Cetuximab +/- Strahlentherapie behandelte Tumoren entnommen, die zur Untersuchung der Tumormikromilieueigenschaften (Hypoxie, Perfusion) sowie Genexpressionsanalysen verwendet wurden.
Ergebnisse: Von den insgesamt 10 untersuchten Tumormodellen wurde durch die Kombination mit dem molekularen Antikörper Cetuximab und fraktionierter Bestrahlung bei 6 Modellen eine signifikante Verbesserung der lokalen Tumorkontrolle im Vergleich zur alleinigen Bestrahlung erreicht. Bei drei dieser Responder konnte eine Amplifikation des EGF-Rezeptors nachgewiesen werden. Alle sechs Respondermodelle zeigten eine höhere Perfusionsrate im Vergleich zu den Tumormodellen, die nicht auf eine EGFR-gerichtete Therapie ansprachen. In Genexpressionsanalysen an unbehandelten Tumoren konnten signifikante Unterschiede sowohl zwischen Responder und Non-Responder als auch zwischen EGFR-amplifizierten und nicht EGFR-amplifizierten Tumoren nachgewiesen werden.
Schlussfolgerung: Tumoren mit einer guten Perfusion zeigten in diesen Experimenten ein besseres Ansprechen auf die EGFR-gerichtete Kombinationstherapie. Zudem scheinen neben der EGFR-Amplifikation auch spezielle Stammzellmarker eine vielversprechende Rolle bei der kombinierten Strahlentherapie zu spielen.
  • Open Access LogoAbstract in refereed journal
    Strahlentherapie und Onkologie 193(2017), S123-S124

Publ.-Id: 26864 - Permalink


Scaling laser plasma acceleration to the Petawatt level
Schramm, U.ORC
Invited talk on laser plasma acceleration
Keywords: laser plasma accelerators
  • Invited lecture (Conferences)
    International Conference on Extreme Light (ICEL), 06.-09.11.2017, Szeged, Ungarn
  • Invited lecture (Conferences)
    IBS Conference on Laser Plasma Accelerators 2017 (LPAW), 28.08.-01.09.2017, Jeju Island, Korea

Publ.-Id: 26863 - Permalink


High-field study of UCo2Si2 : Magnetostriction at metamagnetic transition and influence of Fe substitution
Andreev, A. V.; Skourski, Y.; Gorbunov, D. I.; Prokes, K.;
UCo2Si2 (tetragonal crystal structure) is antiferromagnet below TN = 83 K with ferromagnetic basal-plane layers of U magnetic moments oriented parallel to the c axis. The layers are coupled in +-+- sequence along this axis. In fields of 45 T applied along the c axis, UCo2Si2 exhibits very sharp metamagnetic transition to ++- uncompensated antiferromagnetic state. The transition is accompanied by pronounced magnetostriction effects. The crystal expands along the c axis by 1 * 10-4 and shrinks in the basal plane by 0.5 * 10-4 (at 1.5 K) resulting in negligible volume effect. Between 20 K and 40 K the transition changes from the first- to the second-order type. The Fe doping in UCo2Si2 reduces TN from 83 K to 80 K at x = 0.2 in U(Co1-xFe)2Si2. Metamagnetic transition shifts to higher fields (from 45 T at x = 0 - 56 T for x = 0.2). Magnetization jump over the transition remains practically the same which is in agreement with uranium magnetic moment determined by neutron diffraction on crystal with x = 0.1 as 1.29 μB, i.e. only slightly lower than that in UCo2Si2.

Publ.-Id: 26862 - Permalink


Transition from itinerant metamagnetism to ferromagnetism in UCo1-xOsxAl solid solutions
Andreev, A. V.; Sebek, J.; Shirasaki, K.; Danis, S.; Gorbunov, D. I.; Yamamura, T.; Vejpravova, J.; Havela, L.; de Boer, F. R.;
The influence of substitution of a small amount of Os (< 2 %) on the Co sublattice on the magnetism of the itinerant metamagnet UCoAl is studied on single-crystalline UCo1-xOsxAl compounds with x = 0.002, 0.005 and 0.01. For x = 0.002, the ground state is still paramagnetic, like in UCoAl. The metamagnetic-transition field is 0.37 T, twice lower than in UCoAl. The compound with x = 0.005 is at the border between the paramagnetic and the ferromagnetic ground state. At T = 2 K, it is ferromagnetic, at elevated temperatures a magnetic field is necessary to maintain the magnetic state. In zero field, the ferromagnetic state vanishes at T = 8 K. The compound with x = 0.01 is a ferromagnet with strong uniaxial magnetic anisotropy similar to the previously studied compounds with x = 0.02-0.20.

Publ.-Id: 26861 - Permalink


Magnetisation process in the rare earth tetraborides, NdB4 and HoB4
Brunt, D.; Balakrishnan, G.; Mayoh, D. A.; Lees, M. R.; Gorbunov, D.; Qureshi, N.; Petrenko, O. A.;
A field-induced magnetisation process in the frustrated antiferromagnets is often much richer compared to the materials without competing interactions. The applied field tends to stabilise unusual spin configurations which frequently results in the appearance of magnetisation plateaux. Here we report a study into the field-induced magnetisation of the two frustrated rare earth tetraborides, HoB4 and NdB4. NdB4 shows a fractional magnetisation plateau occurring at M/Msat ≈ 1/5 before saturating in a field of 33 kOe. On cooling down to 0.5 K the temperature dependent susceptibility of NdB4 shows an unconventional transition where the system returns to the zero field antiferromagnetic state from a higher-temperature ferrimagnetic state. We are able to reconstruct the magnetic phase diagram of NdB4 from the magnetisation, susceptibility and resistivity measurements for both H ‖ c and H ⊥ c. For HoB4, the most interesting behaviour is found at the lowest temperature of 0.5 K, where the field dependent magnetisation demonstrates a new fractional ½-magnetisation plateau. Further insight into the relations between the exchange interactions and single ion effects is gained through high-field magnetisation measurements in both HoB4 and NdB4.

Publ.-Id: 26860 - Permalink


Mechanical Properties of Metal Oxide Aerogels
Benad, A.; Jürries, F.; Vetter, B.; Klemmed, B.; Hübner, R.; Leyens, C.; Eychmüller, A.;
In this study we report on mechanical properties of molded, single component Al2O3, Ga2O3, Fe2O3, and ZrO2 as well as mixed aerogels, made from yttrium stabilized zirconia, yttrium aluminum garnet, and zinc aluminum spinel. Initially all aerogels were produced equally in molded bodies by a facile epoxy method and were annealed afterward at 300 °C. Then we performed uniaxial pressure tests on cylindrical aerogel monoliths to gain Young's modulus which depends on composition, density, and post-treatment. Already pure aerogels like ZrO2 show well-promising Young's modulus of 10.7 MPa, whereas most popular SiO2 materials display a modulus between 2 and 3 MPa at comparable densities. Moreover we focused on Al2O3 aerogels which exhibit high stability and interesting densification behavior depending on the annealing temperature. On the basis of this observation, we combined the toughness of the Al2O3 scaffold with the extraordinary hardness of ZrO2, by adding up to 20 atom % Zr, to increase the specific Young's modulus. For the mixed material with a Zr content of 20 atom %, we reach a record value for compressible aerogels of 125 MPa mL g-1.

Publ.-Id: 26859 - Permalink


Magnetic properties of DyFe5-xCoxAl7: Suppression of exchange interactions and magnetocrystalline anisotropy by Co substitution
Gorbunov, D. I.; Andreev, A. V.; Neznakhin, D. S.; Henriques, M. S.; Sebek, J.; Skourski, Y.; Danis, S.; Wosnitza, J.;
In 3d - 4f intermetallic compounds, a Co substitution for Fe usually strengthens the exchange interactions due to a shift of the Fermi energy to a region of the 3d band with higher density of states. Here, we study the influence of Co on the magnetism of ferrimagnetic DyFe5Al7 using magnetization measurements in static (up to 14 T) and pulsed (up to 58 T) magnetic fields. We find that the homogeneity range of DyFe5-xCoxAl7 is limited to x ≤ 2:5. The Co substitution for Fe produces a strong detrimental effect on the 3d - 3d intrasublattice exchange interactions, which leads to a pronounced decrease of the Curie temperature and of the 3d - 4f intersublattice exchange field. A reduction of the density of states at the Fermi level might occur due to a broadening of the 3d band. A decrease of the rare-earth contribution to the magnetic anisotropy energy is also observed with increasing Co content. This is attributed to a competition between the Fe and Co contributions to the crystal electric field at the Dy site.

Downloads:

  • Secondary publication expected

Publ.-Id: 26858 - Permalink


Research facility for radiobiological studies at the University Proton Therapy Dresden
Beyreuther, E.; Baumann, M.; Enghardt, W.; Helmbrecht, S.; Karsch, L.; Krause, M.; Pawelke, J.; Schreiner, L.; Schürer, M.; von Neubeck, C.;
Purpose: In order to take full advantage of proton radiotherapy the biological effect of protons in normal and tumor tissue as well as the interaction with concomitant therapies should be investigated and understood in detail. Dedicated and systematic in vitro trials are needed to resolve the underlying mechanisms and processes that are necessary to prepare the translation into the clinics. For this purpose, a setup for radiobiological studies and the corresponding dosimetry should be established that enables in vitro experiments at a horizontal proton beam and, as a reference, a clinical 6 MV photon linear accelerator (Linac).
Methods and results: The experimental proton beam is characterized by high beam availability and reliability throughout the day in parallel to patient treatment. For cell irradiation, a homogeneous 10 × 10 cm² proton field with an optional spread-out Bragg-peak can be formed. A water-filled phantom was installed that allows for precise positioning of different cell sample geometries along the proton path. The depth-dose profiles within the phantom and the dose homogeneity over different cell samples were characterized for the proton beam and the photon reference source. A daily quality assurance protocol was implemented that provides absolute dose information required for significant and reproducible in vitro trials.
Conclusion: In the experimental room of the University Proton Therapy Dresden, clinically relevant conditions for proton in vitro experiments have been realized. The established cell phantom and dosimetry, which facilitate irradiation in an aqueous environment, could easily be transferred to other proton, photon or even ion accelerators. Precise positioning and easy exchange of cell samples, monitor unit-based dose delivery, and high beam availability allow for systematic in vitro trials. The close vicinity to the radiotherapy and radiobiology departments provides access to a clinical linacs as well as the interdisciplinary basis for further translational steps.

Publ.-Id: 26857 - Permalink


Irradiation of mouse brains at University Proton Therapy Dresden (UPTD): Treatment planning, dose verification and biological assessment of radiation damage
Müller, J.; Suckert, T.; Beyreuther, E.; Tillner, F.; Krause, M.; Enghardt, W.; Dietrich, A.; Bütof, R.; Lühr, A.; von Neubeck, C.;
Proton therapy holds the potential to spare tumor-surrounding tissue and is therefore frequently used in brain tumor treatment. Clear indications from in vitro experiments show that the clinically applied relative biological effectiveness of 1.1 is higher towards the distal edge of the proton Bragg peak. Due to planning margins and range uncertainties the Bragg peak is typically placed in normal tissue and might increase neurological toxicities. Clinical evidence for radiation induced brain necrosis is yet scarce, nonetheless, needs critical evaluation. Sophisticated in vivo studies might be able to close this knowledge gap when designed to mirror the clinical exposure scenario.
Here, the setup for in vivo experiments together with the first results of mouse brain irradiation at the experimental beam line [1] of the UPTD will be presented. Absolute dosimetry in treatment position was done with ionization chambers and EBT3 radiochromic films. The anesthetized mice were fixed in an in-house developed multi-modality bed suitable for imaging and irradiation. Following CT for target delineation and proton radiography [2] for treatment positioning, mice were irradiated with a lateral collimated proton beam of 2 mm in diameter to the proximal hemisphere of the brain. Following radiation, mouse brains were excised and analyzed for DNA and tissue damage. Matching photon experiments with SAIGRT [3] are currently underway allowing in the future a direct comparison of treatment related side effects in the brain.
[1] Helmbrecht et al. J Instrum 2016
[2] Müller et al. Acta Oncologica 2017
[3] Tillner et al. Phys Med Biol 2016
  • Contribution to proceedings
    PTCOG 57 - 57th Annual Conference of the Particle Therapy Co-operative Group, 21.-26.05.2018, Cincinnati, USA

Publ.-Id: 26856 - Permalink


Establishment of small animal irradiation at University Proton Therapy Dresden
Müller, J.; Beyreuther, E.; Suckert, T.; Neubert, C.; Karsch, L.; von Neubeck, C.; Pawelke, J.; Schürer, M.; Krause, M.; Lühr, A.;
Introduction: It is a common practice to use a fixed relative biological effectiveness (RBE) of 1.1 when planning treatments and analyzing outcomes for proton therapy. In contrast, a multitude of in vitro experiments demonstrate variable RBE values. Also, some clinical evidence of RBE variability is emerging, especially at the distal edge of proton treatment fields, showing increased risk of normal tissue complications. However, only a limited number of in vivo trials have been performed to confirm such results. This contribution presents an irradiation setup to study adverse effects in mouse brains induced at proton field edges.
Methods: The mouse is fixated (teeth, ears) in a closed sterile 3D printed holder specifically designed for CT and MR imaging as well as for irradiation with X-rays and protons. Target delineation based on CT and MR imaging can be performed before irradiation. Image-guided positioning of the target volume is achieved by proton radiography [1] with the mouse in treatment position.
In a first brain toxicity study, the distal edge of a laterally collimated clinical proton field (150 MeV) will be positioned in the proximal hemisphere of the mouse brain by inserting polycarbonate plates in front of the mouse holder. For different beam settings, dose distributions in treatment position were obtained with radiochromic EBT3 films placed in plastic phantoms within the mouse holder. Variation of the proton beam range and lateral shape with the amount of decelerating material and collimator size, respectively, were analyzed and used to build a proton beam model. The beam intensity, measured with an ionization chamber, was correlated with the EBT3 film dose measurements at treatment position. This allows for a controlled irradiation of the brain volume with predefined and absolute dose values.
Results and Conclusion: All requirements for systematic proton irradiation experiments in vivo are established at the University Proton Therapy Dresden including target volume delineation, mouse positioning, and dosimetry. First experiments comparing brain toxicity after proton irradiation of one hemisphere relative to photon treatment are in progress.
Reference: [1] Müller et al. Acta Oncologica 2017
  • Lecture (Conference)
    Fourth Symposium on Precision Image-Guided Small Animal RadioTherapy, 12.-14.03.2018, Lisbon, Portugal

Publ.-Id: 26855 - Permalink


Ion beam based methods for materials research and investigation of pipe organ metallic materials
Skorupa, W.; Pelic, B.; Werner, H.; Eule, D.;
Pipe organ instruments contain mostly a considerable number of metallic pipes (flute and reed types), which are sometimes prone to heavy corrosion attack, resulting finally in a loss of their voice. Under certain conditions, the atmospheric corrosion of reed pipe tongues as well as flute pipe foots consisting of Cu-Zn alloys (brass) and PbSn-based alloys, respectively, is strongly enhanced by traces of volatile organic compounds (especially acetic acid vapor) and other corrosive gases.
Experiments have been undertaken to explore the corrosion resistance of CuZn and PbSn-based alloys against vapour from an aqueous solution containing high acetic acid concentration (2 – 5 v/v%), by deposition of protective films of either Al2O3 or Al on the nanoscale using pulsed laser deposition (PLD) and magnetron sputtering (MS). Afterwards, in order to improve the adhesion between the deposited layer and the substrate as well as to perform a kind of nitridation of the coatings, the samples were implanted with nitrogen ions using the plasma immersion ion implantation (PI3) process. Such a nanoscale coating (~50 nm) is then able to withstand stresses and vibrations due to sound generation in organ pipes. Moreover it produces a barrier to volatile organic acids and water vapour. The laboratory corrosion test of the applied protective treatment for lead-tin and brass samples were combined with the field work studies to approach the best conditions for the samples research in real environment.
Moreover, ion beam analysis with the Rossendorf external beam facility was used to determine corrosion products on extremely valuable organ pipes from the early 18th century of the famous organ builder Gottfried Silbermann.
Keywords: Ion beam based methods, pipe organ, brass, lead-tin-alloys, antocorrosive protection, plasma immersion ion implantation, nitridation, pulsed laser deposition, magnetron sputtering
  • Lecture (Conference)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisboa, Portugal

Publ.-Id: 26854 - Permalink


New approaches for studying radiobiological effects of kilovoltage X-rays in vivo and in vitro
Hunger, A.; Burger, K.; Porth, A.-K.; Dierolf, M.; Günther, B.; Bartzsch, S.; Achterhold, K.; Gleich, B.; Beyreuther, E.; Pfeiffer, F.; Combs, S. E.; Wilkens, J. J.; Schmid, T. E.;
Introduction: X-ray microbeam radiation therapy (MRT) as a novel tumor treatment strategy deposits high doses in spatially fractionated X-ray beamlets promising reduced normal tissue toxicity, compared to conventional irradiation, and a better tumor control. Radiobiological studies of MRT with kilovoltage X-rays are mainly performed at synchrotron radiation facilities with high costs and space requirements. The Munich Compact Light Source (MuCLS) is a laboratory-sized and cost-effective source based on inverse Compton scattering of infrared laser photons [1]. Currently the most widely accepted method for assessment of treatment efficiencies is tumor growth delay with subcutaneous tumors in the hind leg of small animals. However, a new model is required for MRT with kilovoltage X-ray beams which only allow for short penetration depths. Therefore, we successfully developed a setup for a growth delay study in a tumor-bearing mouse ear model for investigation of MRT at the MuCLS. In addition, we successfully established a protocol to isolate tumor cells from irradiated tumors for evaluation of radiobiological effect on cellular level.
Materials & Methods: The dose rate of the MuCLS was improved with the installation of a polycapillary collimation optic. A W-Air collimator was inserted to get a collimated X-ray beam with 50 μm wide microbeams and a center-to-center distance of 350 μm. We implemented the mouse ear tumor model with a human head and neck cancer cell line FaDu [2] suspended in extracellular matrix and subcutaneously injected into the right ear of NMRI (nu/nu) mice. After reaching a size of 2x2 mm2 tumors were irradiated using doses of either 3 and 5 Gy with 25 keV X-rays at the MuCLS. Tumor growth delay was determined with a caliper over a follow-up period of 30 days and compared between MRT, homogeneous and control mice. Animals were sacrificed when tumors reached the 15-fold initial volume. A single tumor cell suspension was prepared from excised tumors for in-vitro studies. The analysis of radiosensitivity by colony formation assay and stable chromosomal aberrations by two-color fluorescence in-situ hybridization is still on-going.
Results: We successfully installed a setup at the MuCLS which allows irradiation of tumors in small animals and implemented a xenograft tumor model in mouse ears. Homogeneously irradiated tumors showed a growth delay at 5 Gy compared to control mice. There was no tumor growth delay after MRT and homogeneous irradiation at 3 Gy. Tumor cells from irradiated tumors were successfully isolated and cultured. Preliminary data shows an increased radiosensitivity of tumor cells originating from homogeneously and MRT-irradiated tumors compared to control tumor cells.
Conclusion: This innovative approach allowed the irradiation of tumors in a mouse ear model at a novel laser-based X-ray source, the MuCLS. Homogeneous irradiation at MuCLS induced a tumor growth delay at 5 Gy. In addition, we successfully validated a protocol for tumor cell isolation for investigations of radiation-induced effects.
Supported by the DFG Cluster of Excellence: Munich-Centre for Advanced Photonics.
References:
[1] Eggl et al., J. Synchrotron Rad. (2016) 23: 1137
[2] Beyreuther et al., PLos One (2017)
  • Lecture (Conference)
    Fourth Symposium on Precision Image-Guided Small Animal RadioTherapy, 12.-14.03.2018, Lisbon, Portugal

Publ.-Id: 26853 - Permalink


Nanoscale anticorrosive protection of pipe organ metallic materials
Skorupa, W.; Pelic, B.; Werner, H.; Eule, D.;
Historical pipe organs with their unique sound and beautiful housing are important objects of the European cultural heritage dating back to the 15th century for the oldest ones being playable yet. But new instruments are built permanently up to the present time. The instruments contain mostly a considerable number of metallic pipes (flute and reed types), which are sometimes prone to heavy corrosion attack from their environment, resulting finally in a loss of their voice. Under certain conditions, the atmospheric corrosion of reed pipe tongues as well as flute pipe foots consisting of Cu-Zn alloys (brass) and PbSn-based alloys, respectively, is strongly enhanced by traces of volatile organic compounds (especially acetic acid vapor) and other corrosive gases.
Investigations have been undertaken to explore the corrosion resistance of CuZn and PbSn-based alloys against vapour from an aqueous solution containing high acetic acid concentration (2 – 5 v/v%), by deposition of protective films of either Al2O3 or Al on the nanoscale using pulsed laser deposition (PLD) and magnetron sputtering (MS). Afterwards, in order to improve the adhesion between the deposited layer and the substrate as well as to perform a kind of nitridation of the coatings, the samples were implanted with nitrogen ions using the plasma immersion ion implantation (PI3) process. Such a nanoscale coating (~50 nm) is then able to withstand stresses and vibrations due to sound generation in organ pipes. Moreover it produces a barrier to volatile organic acids and water vapour. The laboratory corrosion test of the applied protective treatment for lead-tin and brass samples were combined with the field work studies to approach the best conditions for the samples research in real environment. Some of the samples were exposed for 15 months in a small North-German church with a harmful (corrosive) indoor environment.
Modification and analysis of the surface of metals and thin film properties on the nanoscale using fundamental phenomena based on ion-solid interactions as well as standard conventional methods can create new technological applications in restoration and conservation to protect our historical and modern cultural heritage in regard to environmental attacks.
Keywords: nanoscale coating, anticorrosive protection, historical organs, pulsed laser deposition, magnetron sputtering, acetic acid, plasma immersion ion implantation, cultural heritage
  • Lecture (Conference)
    3rd International Conference NANOAPP (Nanomaterials & Application), 14.-18.06.2017, Bled, Slovenia

Publ.-Id: 26852 - Permalink


Infrared nanoscopy on Si-doped GaAs-InGaAs core-shell nanowires
Lang, D.; Balaghi, L.; Dimakis, E.; Hübner, R.; Kehr, S. C.; Eng, L. M.; Winnerl, S.; Schneider, H.; Helm, M.;
We present nanoscopic studies on MBE-grown GaAs-InGaAs core-shell nanowires (NWs) with various Si-doped shells. For higher dopings and charge carrier densities, the plasmonic resonance shifts into the mid-infrared wavelength range, that can be fully probed using IR radiation from the FELBE free-electron laser source at the Helmholtz-Center Dresden-Rossendorf. Exploring these plasmonic resonance peaks at different wavelengths allows mapping the local charge carrier density and distribution along the NW with a high spatial resolution of better than 50 nm. Preliminary results using a CO2 laser scanned from 9.7-11.4 μm indicated the resonant behavior for the highest shell doping, in clear contrast to lower or undoped NWs. In the resonant case, the near-field (NF) emerging from the NW is strongly increased as compared to the substrate, in accordance with theory. The NF profiles of particular NWs show characteristic modifications at different wavelengths, which indicate an inhomogeneous distribution of the charge carrier density.
Keywords: FEL, mid-infrared, nanowires, near-field microscopy, plasmonics
  • Poster
    WIRMS 2017 - 9th International Workshop on Infrared Microscopy and Spectroscopy with Accelerator Based Sources, 25.-28.09.2017, Oxford, United Kingdom
  • Lecture (Conference)
    DPG-Frühjahrstagung, 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 26851 - Permalink


Low-temperature scattering scanning near-field optical micropscopy (LT-s-SNOM)
Lang, D.; Döring, J.; Kuschewski, F.; Kehr, S. C.; Eng, L. M.; Winnerl, S.; Schneider, H.; Helm, M.;
We present a combination of a versatile low-temperature scattering-type near-field optical microscope (LT-s-SNOM [1]) with a tunable infrared free-electron laser (FEL [2]). Our s-SNOM operates over a broad temperature range from 15 - 300 K [1,3,4] and is unique in being tunable over a broad frequency range, thanks to the FEL. The overall LT-s-SNOM functionality down to lowest temperature was tested on both standard Au and structured Si-SiO2 samples, revealing net near-field contrasts and no topography cross-talk. Secondly, we investigated several ferroelectric phase transitions in barium titanate single crystals at 273 K [1] and 193 K [5], allowing to associate clear near-field resonances to every phase and each ferroelectric domain; here, the clear benefit of our LT-s- SNOM pays off, being able to record s-SNOM, PFM, KPFM and topographic data with one and the same tip from every sample surface spot. Thirdly, we used these piezoelectrics to quantify the local temperature increase under the AFM tip upon IR irradiation. [1] Döring et al., Appl. Phys. Lett. 105, 053109 (2014). [2] Kuschewski et al., Appl. Phys. Lett. 108, 113102 (2016). [3] Yang et al., Rev. Sci. Instrum. 84, 023701 (2013). [4] McLeod et al., Nature Phys. (2016); DOI: 10.1038/NPHYS3882. [5] Döring et al., J. Appl. Phys. 120, 084103 (2016).
Keywords: FEL, near-field micropscopy, mid-infrared, phase transition, low temperature
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 19.-24.03.2017, Dresden, Deutschland
  • Poster
    OTST2017 - Optical Terahertz Science and Technology, 02.-07.04.2017, London, United Kingdom

Publ.-Id: 26850 - Permalink


WP4 : Highly selective metal recovery techniques for complex metal mixtures including by-product and critical metals
Scharf, C.; Kelly, N.; Helbig, T.;
WP4 : Highly selective metal recovery techniques for complex metal mixtures including by-product and critical metals
  • Lecture (others)
    CHROMIC – M6 Meeting, 10.-11.05.2017, Freiberg, Deutschland

Publ.-Id: 26849 - Permalink


GA - WP4 meeting (M12)
Scharf, C.; Kelly, N.;
GA - WP4 meeting (M12)
  • Lecture (others)
    CHROMIC M12 General Assembly Meeting, 22.-23.11.2017, Orléans, Frankreich

Publ.-Id: 26848 - Permalink


Helmholtz Institute Freiberg for Resource Technology - FWGM - Metallurgy & Recycling
Scharf, C.; Kelly, N.;
Helmholtz Institute Freiberg for Resource Technology FWGM - Metallurgy & Recycling
  • Lecture (others)
    Université de Lorraine - FWGM, 25.-26.09.2017, Nancy, Frankreich

Publ.-Id: 26847 - Permalink


Exploring the Metabolism of (+)-[18F]Flubatine in vitro and in vivo: LC-MS/MS aided Identification of Radiometabolites in a Clinical PET Study
Ludwig, F.-A.; Fischer, S.; Smits, R.; Deuther-Conrad, W.; Hoepping, A.; Tiepolt, S.; Patt, M.; Sabri, O.; Brust, P.;
Both (+)-[18F]flubatine and its enantiomer (-)-[18F]flubatine are radioligands for the neuroimaging of a4ß2 nicotinic acetylcholine receptors (nAChRs) by positron emission tomography (PET). Within a clinical study in patients with early Alzheimer’s disease, (+)-[18F]flubatine ((+)-[18F]1) was examined regarding its metabolic fate, in particular by identification of degradation products detected in plasma and urine. The investigations included an in vivo study of (+)-flubatine ((+)-1) in pig and structural elucidation of formed metabolites by LC-MS/MS. Incubations of (+)-1 and (+)-[18F]1 with human liver microsomes were performed to generate in vitro metabolites as well as radiometabolites, which enabled an assignment of their structures by comparison of LC-MS/MS and radio-HPLC data. Plasma and urine samples taken after administration of (+)-[18F]1 into human were examined by radio-HPLC and, on the basis of results obtained in vitro and in vivo, formed radiometabolites were identified.
In pig, (+)-1 was monohydroxylated at different sites of the azabicyclic ring system of the molecule. Additionally, one intermediate metabolite underwent glucuronidation, as also demonstrated in vitro. In human, 95.9 ? 1.9% (N = 10) of unchanged tracer remained in plasma, 30 min after injection. However, despite the low metabolic degradation, both radiometabolites formed could be characterized as i.) a product of C-hydroxylation at the azabicyclic ring system and ii.) a glucuronide conjugate of previously N8-hydroxylated (+)-[18F]1.
Keywords: [18F]flubatine; NCFHEB; [18F]FLBT; radiometabolites; glucuronides; liquid chromatrography-tandem mass spectrometry (LC-MS/MS); liver microsomes; positron emission tomography (PET); nicotinic acetylcholine receptors (nAChRs)

Publ.-Id: 26846 - Permalink


A spectroscopic and computational study of Cm3+ incorporation in lanthanide phosphate rhabdophane (LnPO4·0.67H2O) and monazite (LnPO4)
Huittinen, N.; Scheinost, A. C.; Ji, Y.; Kowalski, P. M.; Arinicheva, Y.; Wilden, A.; Neumeier, S.; Stumpf, T.;
This study investigates the incorporation of the minor actinide curium (Cm3+) in a series of synthetic La1-xGdxPO4 (x = 0, 0.24, 0.54, 0.83, 1) monazite and rhabdophane solid solutions. To obtain information of the incorporation process on the molecular scale and to understand the distribution of the dopant in the synthetic phosphate phases, combined time-resolved laser fluorescence spectroscopy (TRLFS) and x-ray absorption fine structure (XAFS) spectroscopy investigations have been conducted and complemented with ab initio atomistic simulations. We found that Cm3+ is incorporated in the monazite endmembers (LaPO4 and GdPO4) on one specific, highly ordered lattice site. The intermediate solid solutions, however, display increasing disorder around the Cm3+ dopant as a result of random variations in nearest neighbor distances. In hydrated rhabdophane, and especially its La-rich solid solutions, Cm3+ is preferentially incorporated on non-hydrated lattice sites. This site occupancy is not in agreement with the hydrated rhabdophane structure, where two thirds of the lattice sites are associated with water of hydration (LnPO4·0.67H2O), implying that structural substitution reactions cannot be predicted based on the structure of the host matrix only.
Keywords: Cm3+, incorporation, monazite, rhabdophane, spectroscopy, ab initio simulations

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Publ.-Id: 26844 - Permalink


Thermodynamic evaluations using the law of mass action under consideration of the activity coefficients in the system NdCl₃-HCl (or NaOH)-H₂O-DEHPA-kerosene
Scharf, C.; Ditze, A.;
Rare earth elements, including neodymium, are in widespread use today. They serve, for example, as alloying elements in magnesium (WE 43, WE 54, AE44, AE42), in permanent magnets (neodymium-iron-boron) or as luminescent materials. In addition, they are amongst the most important commodities in Europe. The demand for their use is growing and the recycling of these elements is indispensable. Their recycling potential can be increased through detailed scientific studies and to this end this article presents a thermodynamic evaluation of equilibrium data in the system neodymium-chloride-hydrochloric acid (or sodium hydroxide)-water-di-(2-ethylhexyl) phosphoric acid (DEHPA)-kerosene. Considering the relationship between the activity coefficients γ(Nd³⁺(aq)), γ(Nd(org)) and γ((DEHPA)₂), which arise from the law of mass action, the deviations of the experimental results from the ideal behaviour can be explained. From the calculation of γ(Nd³⁺(aq)) with the expanded Debye-Hückel equation and from literature data for γ((DEHPA)₂), indications arise for the development of the functions of the activity coefficients of DEHPA and neodymium in the organic phase.
Keywords: Law of mass action; Thermodynamic evaluation

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Publ.-Id: 26843 - Permalink


Spectroscopic investigations of actinide incorporation in LnPO4 ceramic solid solutions
Huittinen, N.;
Introduction to luminescence spectroscopy will be presented using Eu3+ and Cm3+ as examples. Examples of how luminescence spectroscopy can be used to probe the local environment of lanthanide and actinide doped monazite ceramics will be given.
Keywords: incorporation, luminescence spectroscopy, lanthanides, actinides, monazite ceramics
  • Invited lecture (Conferences)
    ThUL School 2017, 16.10.2017, Forschungszentrum Jülich, Germany

Publ.-Id: 26842 - Permalink


Environmental radioactivity studies in Kabul and northern Afghanistan
Tanha, M. R.; Ikeda-Ohno, A.ORC; Schulze, M.; Khalid, F. R.; Storai, M. A.; Walther, C.
From earlier surveys conducted by soviet researchers, the Kabul area was identified as a region of high natural radioactivity. However, only fragmentary maps on dose rates (often only given in relative units) are available. No detailed information of, e.g., uranium and thorium distributions in the upper soil and rock exists. In recent years, residential houses have been built in some of these places known for their elevated radiation dose rate. In order to assess possible radiological risk, 51 soil and rock samples as well as 51 all-purpose water samples were collected and measured with regard to radioisotope content and contamination by other pollutants such as, e.g. heavy metals. For the rocks and soil samples, gamma spectroscopy was used as main technique, while ICP-MS and ICP-OES was used as main technique for water analysis. Furthermore, alpha spectroscopy, μ-XRF, PXRD, TOF-SIMS and LSC were used to verify the gamma spectroscopy and ICP-MS results. Activity concentrations in soil and rocks ranged between 160 to 28600 Bq/kg, 73 to 383000Bq/kg, and 270 to 24600 Bq/kg for uranium, thorium, and potassium, respectively. While none of the samples showed any anomalies of the radioactive equilibria some of the samples contained remarkably high levels of thorium and uranium (and their daughter nuclides). Thorium was bound in a cheralite mineral structure. Not all of the investigated waters are safe for drinking, exceeding the national and international recommended values.
Keywords: Radioecology, environmental radioactivity, natural samples, soils, rocks, drinking water

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  • Secondary publication expected from 06.10.2019

Publ.-Id: 26841 - Permalink


Magnetorotational instability in Taylor-Couette flows between cylinders with finite electrical conductivity
Rüdiger, G.; Schultz, M.; Stefani, F.; Hollerbach, R.;
The nonaxisymmetric azimuthal magnetorotational instability is studied for hydromagnetic Taylor-Couette flows between cylinders of finite electrical conductivity. We find that the magnetic Prandtl number Pm determines whether perfectly conducting or insulating boundary conditions lead to lower Hartmann numbers for the onset of instability. Regardless of the imposed rotation profile, for small Pm the solutions for perfectly conducting cylinders become unstable for weaker magnetic fields than the solutions for insulating cylinders. The critical Hartmann and Reynolds numbers form monotonic functions of the ratio sigma of the electrical conductivities of the cylinders and the fluid, such that sigma = O(10) provides a very good approximation to perfectly conducting cylinders, and sigma = O(0.1) a very good approximation to insulating cylinders. These results are of particular relevance for the super-rotating case where the outer cylinder rotates faster than the inner one; in this case the critical onset values are substantially different for perfectly conducting versus insulating boundary conditions. An experimental realization of the super-rotating instability, with liquid sodium as the fluid and cylinders made of copper, would require an electric current of at least 33.5 kA running along the central axis.
Keywords: astrophysical fluid dynamics; Taylor-Couette flow

Publ.-Id: 26840 - Permalink


Nanopatterning during ion sputtering: The reverse epitaxy mechanism on crystalline surfaces
Erb, D.; Malsch, G.; Engler, M.; Ou, X.; Facsko, S.;
Normal-incidence low energy ion irradiation is known to amorphize and smoothen semiconductor surfaces via ballistic redistribution of atoms by the impacting ions [1]. However, intriguing nanoscale surface patterns can form spontaneously, if the semiconductor substrate is heated above its recrystallization temperature during ion irradiation [2].

Above the recrystallization temperature the surface remains crystalline even under ion irradiation: On the one hand, bulk defects are annealed instantly. On the other hand, on a crystalline surface the diffusing surface vacancies and ad-atoms encounter the Ehrlich-Schwoebel barrier, the energy barrier for crossing terrace steps. In analogy to epitaxial growth, this can lead to the formation of well-defined faceted surface structures for ion irradiations performed in a specific energy and temperature range [2]. The resulting surface morphology is strongly dependent on the crystalline structure and surface orientation of the semiconductor substrate. For instance, Ge(001) exhibits inverse pyramids with a square base and Ge(111) shows inverse pyramids with a threefold symmetry, while GaAs(001) and InAs(001) develop regular ripple structures with a saw tooth profile [3]. The periodicity and the regularity of the surface pattern can be influenced by external process parameters such as substrate temperature, ion energy, and ion fluence.

In this contribution, we outline the reverse epitaxy mechanism, highlight the diversity of resulting surface patterns, and present possible applications, for instance in templated metal nanostructure growth or in the fabrication of semiconductor nanostructures.

[1] C S Madi et al., Physical Review Letters 106, 066101 (2011)
[2] X Ou et al., Physical Review Letters 111, 016101 (2013)
[3] X Ou et al., Nanoscale 7, 18928 (2015)
  • Poster
    IISC, 17.-22.09.2017, Dresden, Deutschland

Publ.-Id: 26839 - Permalink


Bottom-up fabrication of periodic nanostructure arrays based on reverse epitaxy
Erb, D.; Ou, X.; Dimakis, E.; Hübner, R.; Lenz, K.; Schlage, K.; Röhlsberger, R.; Lindner, J.; Facsko, S.;
Potential technological applications of periodic nanostructure arrays range from photovoltaics [1] to biomolecule detection using plasmonic signal enhancement [2] and information technology based on magnonic crystals [3]. Industrial-scale fabrication of such devices requires nanopatterning processes which are cost-effective, scalable, and highly reproducible. These demands can be met by a versatile bottom-up approach based on ion irradiation of semiconductor surfaces and well-established thin film deposition techniques.
Reverse epitaxy, i.e. the self-assembly of vacancies and ad-atoms under ion irradiation, leads to nanoscale surface patterning with well-defined lateral periodicity on semiconductor substrates [4]. Among these, GaAs(001) and InAs(001) surfaces exhibit regular faceting and thus lend themselves to transferring this pattern regularity to other materials. The nanofaceted surfaces can for instance be employed as substrates for molecular beam epitaxy under grazing incidence, producing periodic arrays of nanowires, periodically corrugated thin films, or combinations thereof by geometrical shading. They can also induce long-range chemical ordering in diblock copolymer thin films, which may then serve as highly ordered chemical templates for metal nanostructure growth in a variety of pattern morphologies [5]. Furthermore, separated semiconductor nanostructures can be fabricated by introducing an interlayer before ion irradiation.
In this contribution, we outline the reverse epitaxy mechanism and present examples of how it can be employed in the fabrication of large-area nanostructure arrays. We hope to stimulate discussion of further applications by emphasizing the simplicity and versatility of this bottom-up approach.
[1] H.A. Atwater and A. Polman, Nature Materials 9 (2010)
[2] J. Vogt et al., Phys. Chem. Chem. Phys. 17 (2015)
[3] D. Grundler, Nature Physics 11 (2015)
[4] X. Ou et al., Nanoscale 7 (2015)
[5] D. Erb et al., Science Advances 1 (2015)
  • Poster
    SMMIB17 - International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisboa, Portugal

Publ.-Id: 26838 - Permalink


Ion-induced nanopatterning of GaAs and InAs (001) surfaces and possible applications in bottom-up nanostructure fabrication
Erb, D.; Malsch, G.; Engler, M.; Ou, X.; Facsko, S.;
Periodic nanostructure arrays are sought-after for advanced photovoltaics, high-sensitivity biomolecule detection, and future information technology. One cost-effective bottom-up approach to fabricate such nanostructure arrays is templated growth on spontaneously nanopatterned surfaces, which can be achieved on semiconductors by low energy ion irradiation [1]. We studied the influence of process parameters such as ion energy and fluence, substrate temperature, and ion incidence angles on the resulting nanoscale morphologies of GaAs and InAs surfaces.

If the semiconductor surface is irradiated with low-energy ions above the recrystallization temperature of the material, the surface remains crystalline. In the so-called reverse epitaxy regime, the diffusion of the ion-induced vacancies and ad-atoms on the crystalline surface is subject to the Ehrlich-Schwoebel barrier, an energy barrier for crossing terrace steps. In analogy to epitaxial growth, for ion irradiations performed in a specific energy and temperature range this can lead to the formation of well-defined faceted surface structures [2]. The resulting surface morphology is strongly dependent on the crystalline structure of the semiconductor substrate. For instance, GaAs(001) and InAs(001) surfaces exhibit regular ripple structures with a saw tooth profile oriented along the [1-10] direction. For this pattern formation to take place, InAs must be kept in a temperature range between 160°C and 430 °C, while GaAs requires sample temperatures of at least 430 °C. Increasing the ion energy increases the ripple periodicity, and so does increasing the sample temperature at lower ion energies. The order of the pattern increases with increasing ion fluence and, for InAs, with increasing ion energy.

Such nanorippled surfaces can for example be employed as substrates for physical vapor deposition under various incidence angles, producing periodic arrays of nanowires, periodically corrugated thin films, or combinations thereof. Furthermore, epitaxial growth is expected on these crystalline surfaces for materials with low lattice mismatch.


[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou et al., Nanoscale 7 (2015).
  • Poster
    Nanopatterning / FOR3Nano Workshop, 26.-30.06.2017, Helsinki, Finnland

Publ.-Id: 26837 - Permalink


Bottom-up fabrication of periodic magnetic nanostructures based on ion-induced spontaneous surface nanopatterning
Erb, D.; Ou, X.; Schlage, K.; Lenz, K.; Röhlsberger, R.; Lindner, J.; Facsko, S.; Helm, M.; Fassbender, J.;
Large-area nanopatterning is a key requirement in diverse applications ranging from photovoltaics to computing and biomolecule detection. We present a simple and scalable bottom-up nanopatterning approach based on ion irradiation of semiconductor surfaces and wellestablished thin film deposition techniques: On crystalline semiconductor substrates, nanoscale surface patterns with well-defined lateral periodicity form via the mechanism of reverse epitaxy, i.e. the nonequilibrium self-assembly of vacancies and ad-atoms under ion irradiation [1]. The nanopatterned surfaces can for instance be employed as substrates for MBE under grazing incidence, producing periodic metal nanostructures by geometrical shading. They can also be the basis for metal nanostructure growth in a variety of pattern morphologies by hierarchical self-assembly [2]. In this contribution, we outline the reverse epitaxy mechanism and present examples of periodic magnetic nanostructures based on the resulting surface patterns. We hope to stimulate discussion of further applications in magnetism by emphasizing the simplicity and versatility of this bottom-up approach.
[1] Ou et al., Nanoscale 7 (2015); [2] Erb et al., Science Advances 1 (2015)
  • Poster
    DPG Frühjahrstagung Sektion Kondensierte Materie, 19.-24.03.2017, Dresden, Deutschland

Publ.-Id: 26836 - Permalink


Bottom-up fabrication of periodic nanostructure arrays based on reverse epitaxy
Erb, D.; Ou, X.; Dimakis, E.; Hübner, R.; Lenz, K.; Schlage, K.; Röhlsberger, R.; Lindner, J.; Facsko, S.;
Potential technological applications of periodic nanostructure arrays range from photovoltaics augmented by light trapping [1] to high-sensitivity biomolecule detection using plasmonic signal enhancement [2] and high-speed low-energy information technology based on magnonic crystals [3]. Industrial-scale fabrication of such devices requires nanopatterning processes which are cost-effective, scalable, and highly reproducible. These demands can be met by a versatile bottom-up approach based on ion irradiation of semiconductor surfaces and well-established thin film deposition techniques.
Reverse epitaxy, i.e. the non-equilibrium self-assembly of vacancies and ad-atoms under ion irradiation, leads to nanoscale surface patterning with well-defined lateral periodicity on semiconductor substrates [4]. The GaAs(001) and InAs(001) surfaces exhibit highly regular faceting and therefore lend themselves to transferring this pattern regularity to other materials. The nanofaceted surfaces with a sawtooth profile can for instance be employed as substrates for molecular beam epitaxy under grazing incidence, producing periodic arrays of nanowires, periodically corrugated thin films, or combinations thereof by geometrical shading. They can also induce long-range chemical ordering in diblock copolymer thin films, which may then serve as highly ordered chemical templates for metal nanostructure growth in a variety of pattern morphologies [5]. Furthermore, separated semiconductor nanostructures can be fabricated by introducing an interlayer before ion irradiation.

In this contribution, we outline the reverse epitaxy mechanism and present examples of how it can be employed in the fabrication of large-area nanostructure arrays. We hope to stimulate discussion of further applications by emphasizing the simplicity and versatility of this bottom-up approach.

[1] H.A. Atwater and A. Polman, Nature Materials 9 (2010); [2] J. Vogt et al., Phys. Chem. Chem. Phys. 17 (2015); [3] D. Grundler, Nature Physics 11 (2015); [4] X. Ou et al., Nanoscale 7 (2015); [5] D. Erb et al., Science Advances 1 (2015)
  • Poster
    Ionentagung 2017, 12.-15.02.2017, Göttingen, Deutschland

Publ.-Id: 26835 - Permalink


Inter-patient variations of radiation-induced normal-tissue changes in Gd-EOB-DTPA-enhanced hepatic MRI scans during fractionated proton therapy
Richter, C.; Andronesi, O.; Borra, R.; Voigt, F.; Löck, S.; Duda, D.; Guimaraes, A.; Hong, T.; Bortfeld, T.; Seco, J.;
Background and purpose
Previous MRI studies have shown a substantial decrease in normal-tissue uptake of a hepatobiliary-directed contrast agent 6–9 weeks after liver irradiation. In this prospective clinical study, we investigated whether this effect is detectable during the course of proton therapy.

Material and methods
Gd-EOB-DTPA enhanced MRI was performed twice during hypo-fractionated proton therapy of liver lesions in 9 patients (plus two patients with only one scan available). Dose-correlated signal changes were qualitatively scored based on difference images from the two scans. We evaluated the correlation between the MRI signal change with the planned dose map. The GTV was excluded from all analyses. In addition, were examined timing, irradiated liver volume, changes in liver function parameters as well as circulating biomarkers of inflammation.

Results
Strong, moderate or no dose-correlated signal changes were detected for 2, 3 and 5 patients, respectively. Qualitative scoring was consistent with the quantitative dose to signal change correlation. In an exploratory analysis, the strongest correlation was found between the qualitative scoring and pretreatment IL-6 concentration. For all patients, a clear dose-correlated signal decrease was seen in late follow-up scans.

Conclusion
Radiation-induced effects can be detected with Gd-EOB-DTPA enhanced MRI in a subgroup of patients within a few days after proton irradiation. The reason for the large inter-patient variations is not yet understood and will require validation in larger studies.
Keywords: Gd-EOB-DTPA, liver, MRI, radiation-induced changes, inflammatory response, in vivo verification

Publ.-Id: 26834 - Permalink


Evaluation of interfacial heat transfer models for flashing flow with two-fluid cfd
Liao, Y.; Lucas, D.;
The complexity of flashing flows is increased vastly by the interphase heat transfer as well as its coupling with mass and momentum transfers. A reliable heat transfer coefficient is the key in the modelling of such kinds of flows with the two-fluid model. An extensive literature survey on computational modelling of flashing flows has been given in previous work. The present work is aimed at giving a brief review on available theories and correlations for the estimation of interphase heat transfer coefficient, and evaluating them quantitatively based on computational fluid dynamics simulations of bubble growth in superheated liquid. The comparison of predictions for bubble growth rate obtained by using different correlations with the experimental as well as direct numerical simulation data reveals that the performance of the correlations is dependent on the Jakob number and Reynolds number. No generally applicable correlations are available. Both conduction and convection are important in cases of bubble rising and translating in stagnant liquid at high Jakob numbers. The correlations combining the analytical solution for heat diffusion and the theoretical relation for potential flow give the best agreement.

Publ.-Id: 26833 - Permalink


Neutron irradiation test of Hamamatsu, SensL and AdvanSiD UV-extended SiPMs
Cordelli, M.; Diociaiuti, E.; Donghia, R.; Ferrari, A.; Miscetti, S.; Müller, S.ORC; Sarra, I.
In this paper, we report the measurement of the neutron radiation hardness of custom Silicon Photomultipliers arrays (SiPMs) manufactured by three companies: Hamamatsu (Japan), AdvanSiD (Italy) and SensL (Ireland). These custom SiPMs consist of a 2 × 3 array of 6 × 6 mm^2 monolithic cells with pixel sizes of respectively 50 μm (Hamamatsu and SensL) and 30 μm (AdvanSid).
A sample from each vendor has been exposed to neutrons generated by the Elbe Positron Source facility (Dresden), up to a total fluence of ∼ 8.5 × 10^11 n 1MeV /cm 2 . Test results show that the dark current increases almost linearly with the neutron fluence.
The room temperature annealing was quantified by measuring the dark current two months after the irradiation test. The dependence of the dark current on the device temperature and on the applied bias have been also evaluated.
Keywords: SiPM, Neutron damage, annealing

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Publ.-Id: 26832 - Permalink


Annealing effect on ferromagnetic properties, hole concentration and electronic band structure of GaMnAs epitaxial layers
Zhu, J. J.; Li, L.; Chen, L.; Prucnal, S.; Grenzer, J.; Zhao, J. H.; Helm, M.; Zhou, S. Q.;
In this paper, we analyze the correlation of the magnetism and the carrier concentration with the shift of the spectroscopic critical points for low compensated GaMnAs samples with a high Curie temperature of around 150 K. The GaMnAs layers were grown by low-temperature molecular beam epitaxy. The low-temperature annealing leads to a reduction of Mn interstitials from 0.8 to 0.4% and an enhancement in the hole concentration. The saturation magnetization is 51 emu/cm and the Curie temperature is 150 K after post-growth annealing, while those of as-grown layers are 37 emu/cm and 80 K. The resistivity dropped significantly after the post-growth annealing, due to the fact that the number of Mn, which act as double donors and compensate holes, was significantly reduced by the low-temperature and long-time annealing. The electronic band structure is investigated by spectroscopic ellipsometry. The transition energies of critical points show redshift after post-growth annealing due to the annealing-induced enhancement of the hole concentration. Our results support the valence band picture (the Zener model) in ferromagnetic GaMnAs.
Keywords: GaMnAs, DMS, doping, magnetic properties

Publ.-Id: 26831 - Permalink


Structural Analysis of Germanium (Ge)-Containing Ferrous Calcium Silicate Magnesia Slag for Applications of Black Copper Smelting
Shuva, M. A. H.; Rhamdhani, M. A.; Brooks, G. A.; Masood, S. H.; Reuter, M. A.;
Ferrous-calcium-silicate (FCS) based slag has been used in the copper industry over the last two decades. The FCS slag has also been used in a secondary copper processing such as in black copper smelting which has different operation conditions compared to that of typical primary copper processing. In the process, a variety of copper bearing scraps from sources such as industrial waste, consumer waste and electronic waste (e-waste) are used. The valuable metals in these secondary resources are distributed in different phases during the process. Understanding the behaviour of the valuable elements at the relevant conditions is vital for optimizing the process and to maximize the recovery of the elements. In this study, we investigated the structure of Ge-containing FCS-based slag at different conditions (oxygen partial pressure and temperature) using Fourier-Transform Infrared (FTIR) spectroscopy to explore the effect of the polymerization on the behaviour of the valuable element Ge in the slag. It was found that experimental parameters significantly influence the slag structure, and therefore, the partitioning of Ge in the slag. A correlation between the distribution ratio of Ge and the slag structure has developed in the current study.
Keywords: Copper processing Slag structure Distribution ratio
  • Contribution to proceedings
    9th International Symposium on High-Temperature Metallurgical Processing organized in conjunction with the Annual Meeting and Exhibition - TMS 2018, 11.-15.03.2017, Phoenix, USA
    Minerals, Metals and Materials Series, Cham: Springer, 978-3-319-72137-8, 295-304
    DOI: 10.1007/978-3-319-72138-5_30

Publ.-Id: 26830 - Permalink


Diodengepumpte hochenergetische Laserverstärker für ultrakurze Laserpulse Das PENELOPE Lasersystem
Loeser, M.;
Öffentlicher Verteidigungsvortrag der Dissertation "Diode-Pumped High-Energy Laser Amplifiers for Ultrashort Laser Pulses - The PENELOPE Laser System" von Herrn Markus Löser.
  • Lecture (others)
    Öffentliche Verteidigung/Disputation, 16.11.2017, Dresden, Deutschland

Publ.-Id: 26829 - Permalink


Structural impact of chromium incorporation in as-grown and flash-lamp-annealed sputter deposited titanium oxide films
Gago, R.; Prucnal, S.; Perez-Casero, R.; Caretti, I.; Jimenez, I.; Lungwitz, F.; Cornelius, S.;
We address the impact of chromium (Cr) incorporation (< 15 at.%) in the structure of titanium dioxide (TiO2: Cr) films for as-grown and after flash-lamp-annealing (FLA) states. Samples were produced by DC magnetron sputtering on either unheated or heated (400 degrees C) substrates. Complementary medium-and local-order information was extracted by X-ray diffraction and absorption near-edge structure, respectively. TiO2: Cr grown on unheated substrates are amorphous with the major contribution from Cr3+ and progressive formation of Cr6+ with Cr. On heated substrates, anatase phase is dominant for low Cr levels (<= 7 at.%) and the structure evolves with Cr towards a disordered mixed-oxide with rutile structure. By tuning the FLA energy density, customized (single or mixed) phase formation is achieved from (initially amorphous) Cr-free TiO2. For amorphous TiO2: Cr with low Cr (<= 7 at.%), FLA induces a short-range rutile structure but structural ordering is not observed at higher Cr levels. Nonetheless, FLA annihilates Cr6+ sites and promotes Cr4+, which is associated to the mixed-oxide rutile. FLA also improves the pristine structure of anatase TiO2: Cr grown on heated substrates. These results provide relevant information about the atomic structure of mixed oxides and the use of FLA for the synthesis of band-gap engineered TiO2-based materials.
Keywords: TiO2, anatase, doping, flash lamp annealing, XRD

Publ.-Id: 26828 - Permalink


Doping of Ge via nonequilibrium processing
Prucnal, S.;
Here an overview of different doping techniques will be presented. Special attention will be focused on the use of ion implantation followed by flash-lamp (FLA) annealing for the fabrication of heavily doped Ge. In contrast to conventional annealing procedures, rear-side FLA leads to full recrystallization of Ge and dopant activation independently of pre-treatment. The maximum carrier concentration is well above 10^20 cm-3 for n-type and above 10^21 for p-type doping. The recrystallization mechanism and the dopant distribution during rear-side FLA are discussed in detail.
Keywords: ion implantation, flash lamp annealing, Ge, doping
  • Invited lecture (Conferences)
    18th AGATA week and 2nd Position Sensitive Germanium Detectors and Application Workshop, 11.-15.09.2017, Milano, Italy

Publ.-Id: 26827 - Permalink


Pulse-Resolved Data Acquisition at High Repetition Rates: Getting the Most Out of Modern Light Sources
Green, B.; Kovalev, S.; Golz, T.; Stojanovic, N.; Kampfrath, T.; Fisher, A. S.; Gensch, M.;
Sub cycle dynamics on THz driven Phenomena are an emerging class of experiments in ultra-fast science. Hence THz pump laser probe experiments are an essential class of experiments at the new TELBE THz facility. Even the most modern accelerators can be synchonised only down to 80 fs (peak to peak) by active feedbacks [1]. For that reason a unique high-rep-rate arrivaltime monitoring has been developed at TELBE that provides timing down to (in theory) 12 fs by post-mortem arrivaltime-jitter correction.
  • Poster
    XFEL User's Meeting, 26.01.2018, DESY, Deutschland

Publ.-Id: 26826 - Permalink


Bonding analysis of tetravalent actinide complexes with salen
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
The bonding situation of tetravalent actinide-complexes with salen is investigated by using tools of real-space bonding-analysis. These tools, involving plots of density-differences and non-covalent interactions (NCI), reveal covalent interactions of Th(IV) with the O-donor of salen. The contribution of the two f-electrons of U(IV) even enhance this interaction.
Keywords: bonding analysis, covalency, density difference, non-covalent interactions, actinides, salen, theoretical chemistry
  • Lecture (others)
    FENABIUM-Projekttreffen, 04.12.2017, Dresden-Rossendorf, Deutschland

Publ.-Id: 26825 - Permalink


Bonding analysis of tetravalent actinide complexes with N-/O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.;
By using real-space bonding-analysis tools, like non-covalent interactions and density-difference plots, the bonding situation in tetravalent actinide (Th(IV), U(IV)) complexes with salen is investigated.
Keywords: bonding analysis, theoretical chemistry, actinides, salen, non-covalent interactions
  • Lecture (Conference)
    Theoretical User-Lab (ThUL School), 16.-20.10.2017, Jülich, Deutschland

Publ.-Id: 26824 - Permalink


Defect engineering in SiC for quantum spintronics
Zhou, S.; Zhang, Z.; Liu, Y.; Hübner, R.; Gemming, S.; Helm, M.;
Silicon carbide (SiC) is a wide band-gap semiconductor (6H-SiC with Eg of 3.05 eV) with unique mechanical, electrical, and thermal properties, which make the material suitable for many demanding applications in extreme conditions, such as high temperature, high power, high frequency and high radiation exposure. Two recently reported phenomena related to the defects in SiC are opening the door for semiconductor spintronics and quantum computing:
(1) Room temperature ferromagnetism has been observed in neon ion or neutron irradiated both 4H- and 6H-SiC [1, 2]. This is somehow surprising since the materials are transition-metal free, which also gives rise to the term ‘‘d0 ferromagnetism’’.
(2) Some defect (including the neutral carbon–silicon divacancy) spin states in 4H-SiC can be optically addressed and coherently controlled up to room temperature [3]. These defect spin states are ideal information carriers for quantum computing.

Particle irradiation provides a way to engineer defects in crystalline materials regarding the defect concentration and type. In this contribution, we made a comprehensive investigation on the structural and magnetic properties of ion implanted and neutron irradiated SiC samples. In combination with X-ray absorption spectroscopy, high-resolution transmission electron microscopy and first-principles calculations, we try to understand the mechanism in a microscopic picture.

For neon or xenon ion implanted SiC, we identify a multi-magnetic-phase nature [2, 4]. The magnetization of SiC can be decomposed into paramagnetic, superparamagnetic and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. By combining X-ray magnetic circular dichroism and first-principles calculations, we clarify that p-electrons of the nearest-neighbor carbon atoms around divacancies are mainly responsible for the long-range ferromagnetic coupling [5]. Thus, we provide a correlation between the collective magnetic phenomena and the specific electrons/orbitals.

For neutron irradiated SiC, we observe a strong paramagnetism, scaling up with the neutron fluence [6]. A weak ferromagnetic contribution only occurs in a narrow fluence window or after annealing. The interaction between the nuclear spin and the paramagnetic defect can effectively tune the spin-lattice relaxation time (T1) as well as the nuclear spin coherent time (T2). For the sample with the largest neutron irradiation fluence, T1 and T2 are determined to be around 520 s and 1 ms at 2K, respectively.

[1] Y. Liu, et al., Phys. Rev. Lett. 106, 087205 (2011).
[2] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).
[3] W. Koehl, et al., Nature 479, 84 (2011).
[4] Y. Wang, et al., Phys. Rev. B 89, 014417 (2014).
[5] Y. Wang, et al., Scientific Reports, 5, 8999 (2015).
[6] Y. Wang, et al., Phys. Rev. B 92, 174409 (2015).
  • Lecture (Conference)
    Gadest2017: Gettering and Defect Engineering in Semiconductor Technology, 01.-06.10.2017, Lopota, Georgia

Publ.-Id: 26823 - Permalink


Tetravalent actinides – from polymeric complexes to nanoparticles
Hennig, C.;
Tetravalent actinides show a strong tendency towards hydrolysis. This forces the formation of polynuclear species. However, the polynuclear species undergo further polymerization and form colloids. One way to isolate polynuclear species is to introduce terminating groups which hinder further polymerization. We found that carboxylates are well suited for this task. Larger clusters can form either highly ordered nanoparticles, complete amorphous structures, or transitions between them. Nanoparticles with an ordered structure can be stabilized by the introduction of termination functions, whereas amorphous nanoparticles can be potentially stabilized by introducing ions that modify the surface charge. These modifications support the structure analysis of the species. The nanoparticles of tetravalent actinides can form colloid suspensions which are stable over years. Due to their low solubility, tetravalent actinides are considered as nearly immobile in the nature. The surface charge may significantly enhance their migration.
Keywords: tetravalent actinides, polynuclear species, nanoparticles, colloids
  • Invited lecture (Conferences)
    225th American Chemical Society Meeting, 18.-22.03.2018, New Orleans, USA

Publ.-Id: 26822 - Permalink


Tuning ferromagnetic semiconductors by ion irradiation
Zhou, S.; Yuan, Y.; Xu, C.; Rushforth, A.; Chen, L.; Sawicki, M.; Helm, M.;
Ion irradiation has been widely used to render a semiconductor layer highly resistive through the creation of carrier-trapping centers. In Mn doped III-V compound semiconductors, which are proposed for spintronic applications, free carriers play deterministic roles for the magnetic properties and material functionalities. However, by substituting the cation, Mn in III-V acts as an acceptor, resulting in the difficulty to independently change the local-moment and hole concentration. In this contribution, we show how the carrier concentration in (III,Mn)V and the consequent magnetic properties can be precisely tuned by ion irradiation [1, 2].
On one hand, we investigate fundamentally how magnetic properties change upon shifting the Fermi level by hole compensation via ion irradiation. We monitor the change of Curie temperature (TC) and conductivity. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC with carrier compensation over a wide temperature range while the conduction is changed from metallic to insulating. The existence of TC below 10 K is also confirmed in heavily compensated samples. Our experimental results are naturally explained by assuming that the Fermi level resides in the valence band being merged with the Mn-derived impurity band [2].
On the other hand, we explore the application potential of ion irradiation in semiconductor spintronics. We show that the magnetic easy axis of (Ga,Mn)(As,P) can be gradually changed between in-plane and out-of-plane directions [3]. Combined with the possibility of lateral patterning [4], such an approach allows for developing new concepts for spintronic devices.
[1] L. Li, S. Yao, S. Zhou, et al., J. Phys. D: Appl. Phys. 44, 099501 (2011).
[2] S. Zhou, et al., Phys. Rev. B 94, 075205 (2016).
[3] Y. Yuan, ..., S. Zhou, Phys. Rev. Mater. 1, 054401 (2017).
[4] L. Li, ..., S. Zhou, Nucl. Instr. Meth. B 269, 2469-2473 (2011).
  • Lecture (Conference)
    19th International Conferences on Radiation Effects in Insulators, 30.06.-07.07.2017, Versallies, France

Publ.-Id: 26821 - Permalink


Propagation of spin wave under time dependent magnetic fields
Nishida, N.; Matthies, P.;
The spin-wave dispersion relation strongly depends on the effective magnetic field acting on the magnetic moments. In order to investigate how spin waves behave if the magnetic field changes in time during their propagation, we applied pulsed magnetic fields changing on the nanosecond time scale.
Spin waves were excited in a NiFe micro stripe. A static bias magnetic field and a time dependent pulse field were applied to the stripe. The spin-wave intensity was measured by time-resolved Brillouin light scattering microscopy. We observed a frequency shift of spin waves at the rising edge of the pulse field. The change in frequency can be understood by the shift of the dispersion relation induced by the pulse field. We succeeded to manipulate the spin-wave frequency during their propagation by temporally inhomogeneous magnetic fields.
  • Poster
    Bad Honnef Physics School on Magnetism: From Fundamentals to Spin based Nanotechnology, 17.-22.09.2017, Bad Honnef, Germany

Publ.-Id: 26820 - Permalink


Defect induced magnetism in SiC characterized by magnetometry
Zhou, S.;
Silicon carbide (SiC) is a wide band-gap semiconductor with unique mechanical, electrical, and thermal properties, which make the material suitable for many demanding applications in extreme conditions, such as high temperature, high power, high frequency and high radiation exposure. The spin states related with defects in SiC can be optically addressed and coherently controlled up to room temperature [1] or can be ferromagnetically coupled [2, 3], opening the door for semiconductor spintronics and quantum computing.



In this contribution, we present a comprehensive investigation on defects in SiC by using magnetometry [2-6]. In combination with X-ray absorption spectroscopy, high-resolution transmission electron microscopy and first-principles calculations, we try to understand the mechanism of defect induced magnetism in SiC in a microscopic picture.



For neon or xenon ion implanted SiC, we identify a multi-magnetic-phase nature [3, 4]. The magnetization of SiC can be decomposed into paramagnetic, superparamagnetic and ferromagnetic contributions. The ferromagnetic contribution persists well above room temperature and exhibits a pronounced magnetic anisotropy. By combining X-ray magnetic circular dichroism and first-principles calculations, we clarify that p-electrons of the nearest-neighbor carbon atoms around divacancies are mainly responsible for the long-range ferromagnetic coupling [5]. Thus, we provide a correlation between the collective magnetic phenomena and the specific electrons/orbitals.



For neutron irradiated SiC, we observe a strong paramagnetism, scaling up with the neutron fluence [6]. A weak ferromagnetic contribution only occurs in a narrow fluence window or after annealing. The interaction between the nuclear spin and the paramagnetic defect can effectively tune the spin-lattice relaxation time (T1) as well as the nuclear spin coherent time (T2). For the sample with the largest neutron irradiation fluence, T1 and T2 are determined to be around 520 s and 1 ms at 2K, respectively.



[1] W. Koehl, et al., Nature 479, 84 (2011).

[2] Y. Liu, et al., Phys. Rev. Lett. 106, 087205 (2011).

[3] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).

[4] Y. Wang, et al., Phys. Rev. B 89, 014417 (2014).

[5] Y. Wang, et al., Scientific Reports, 5, 8999 (2015).

[6] Y. Wang, et al., Phys. Rev. B 92, 174409 (2015).
  • Lecture (Conference)
    2017 MRS SPRING MEETING, 17.-21.04.2017, Phoenix, US

Publ.-Id: 26819 - Permalink


Facile Preparation of Multifunctionalisable ‘Stealth’ Upconverting Nanoparticles for Biomedical Applications
Nsubuga, A.; Sgarzi, M.ORC; Zarschler, K.ORC; Kubeil, M.ORC; Hübner, R.; Steudtner, R.; Graham, B.; Joshi, T.; Stephan, H.ORC
Pure hexagonal (β-phase) NaYF4-based hydrophobic upconverting nanoparticles (UCNPs) were surface-modified with O-phospho-L-threonine (OPLT), alendronic acid, and PEG-phosphate ligands to generate water-dispersible UCNPs. Fourier-transform infrared (FTIR) spectroscopy was used to establish the presence of the ligands on the UCNP surface. These UCNPs exhibit great colloidal stability and a near-neutral surface at physiological pH, as confirmed by dynamic light scattering (DLS) and zeta potential (ζ) measurements, respectively. The particles also display excellent long-term stability, with no major adverse effect on the size of UCNPs when kept at pH 7.4. Upon exposure to human serum, PEG-phosphate- and alendronate-coated UCNPs showed no formation of biomolecular corona, as confirmed by SDS-PAGE analysis. The photophysical properties of water-dispersible UCNPs were investigated using steady-state as well as time-resolved luminescence spectroscopy, under excitation at ca. 800 nm. The results clearly show that the UCNPs demonstrate bright upconversion (UC) luminescence. Furthermore, the presence of reactive groups on the NPs, such as, free amine group in alendronate-coated UCNPs, enables further functionalisation of UCNPs with, for example, small molecules, peptides, proteins, and antibodies. Overall these protein corona resistant UCNPs show great biocompatibility and are worthy of further investigation as potential new biomaging probes.

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  • Secondary publication expected

Publ.-Id: 26818 - Permalink


Low energy dynamics in charge ordered R0.5Sr0.5MnO3 (R = Nd and Pr) manganite thin films
Rana, R.; Schmidt, J.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.;
Transition metal oxides represent an exotic class of correlated systems in which a complex interplay between the spin, charge, orbital and lattice degrees of freedom may result in colossal magnetoresistance, superconductivity; charge ordered (CO) phases, etc. The half-doped Pr0.5Sr0.5MnO3 manganite represents a unique stripe type CO-orbital order that induces transport and magnetic anisotropy whereas the CO in Nd0.5Sr0.5MnO3 is charge-exchange (CE)-type which is isotropic in nature.

We have systematically explored ~ 200nm epitaxial manganite thin films grown on (100), (110), and (111) oriented (LaAlO3)0.3(Sr2TaAlO6)0.7 substrates by pulsed laser deposition technique. Our Terahertz (THz) time-domain spectroscopic data reveal charge density wave (CDW) resonance centered around 5-6 meV for (110) oriented films and Drude-like conductivity for (100) and (111) oriented films. The CDW resonance in the optical conductivity spectra can be tuned from 4 meV to 6 meV for (110) oriented films and depends on the amount of ferromagnetic phase fraction in the CO matrix and corroborates well with the magnetization measurements. The nonlinear conductivity related to the sliding of the pinned CDW character makes the studied systems promising candidates for ultrafast coherent control of charge transport by resonant THz pumping.
Keywords: Manganites; charge order; terahertz
  • Poster
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Publ.-Id: 26817 - Permalink


Propagation of spin wave pulses during time dependent magnetic fields
Nishida, N.; Matthies, P.; Wagner, K.; Schultheiss, K.; Schultheiss, H.;
Spin wave dispersion relation depends on a magnetic field. The resonance frequency is higher for higher magnetic fields. While it was previously reported how spin waves adapt to spatially inhomogeneous magnetic fields [1], we investigated spin-wave propagation under the influence of nanosecond magnetic field pulses.
We fabricated a 2 µm-wide spin-wave waveguide from NiFe with an antenna for spin wave excitation and a dc line below the spin-wave conduit. An external magnetic field was applied perpendicular to the stripe. In order to modulate the internal magnetic field in the stripe, a dc pulse was injected into the dc line, because the dc pulse generates Oersted field. We measured a magnon density on the stripe using time-resolved Brillouin light scattering microscopy, and investigated spin-wave dynamics when the dc pulse came in. We succeeded to observe the temporal magnon density when the dc pulse came in and went out. For a fixed excitation frequency observed a decrease (increase) of the spin-wave frequency at the rising (falling) edge of the dc pulse. Since Oersted field is in the opposite direction to the external magnetic field, the internal magnetic field is lower than the external field while the dc pulse is on. The dispersion relation shifts to lower frequency, and it matches to the resonance magnetic field temporarily. At that time spin wave pulse is excited under the antenna. We also observed the position dependency of the excited spin wave pulse. The spin wave pulse propagated, and the frequency shifted lower at the rising edge of the dc pulse, or shifted higher at the falling edge of the dc pulse. We succeeded to observe the excited spin wave pulse following the change of the dispersion relation, and demonstrated the modulation of spin wave by the change of the magnetic field.

[1] V. E. Demidov et. al., Appl. Phys. Lett. 99, 082507 (2011).
  • Poster
    Magnonics 2017, 07.-10.08.2017, Oxford, United Kingdom

Publ.-Id: 26816 - Permalink


Magnetic anisotropy in antiferromagnetic hexagonal MnTe
Kriegner, D.; Reichlova, H.; Grenzer, J.; Schmidt, W.; Ressouche, E.; Godinho, J.; Wagner, T.; Martin, S.; Shick, A.; Volobuev, V.; Springholz, G.; Holy, V.; Wunderlich, J.; Jungwirth, T.; Vyborny, K.;
Antiferromagnetic hexagonal MnTe is a promising material for spintronic devices relying on the control of antiferromagnetic domain orientations. Here we report on neutron diffraction, magnetotransport, and magnetometry experiments on semiconducting epitaxial MnTe thin films together with density functional theory (DFT) calculations of the magnetic anisotropies. The easy axes of the magnetic moments within the hexagonal basal plane are determined to be along < 1-100 > directions. The spin-flop transition and concomitant repopulation of domains in strong magnetic fields is observed. Using epitaxially induced strain the onset of the spin-flop transition changes from similar to 2 to similar to 0.5 T for films grown on InP and SrF2 substrates, respectively.
Keywords: MOLECULAR-BEAM EPITAXY; NEUTRON-DIFFRACTION; MANGANESE TELLURIDE; THERMAL-EXPANSION; TEMPERATURE; BEHAVIOR; MEMORY; FILM

Publ.-Id: 26815 - Permalink


Synthesis and characterization of tetravalent actinide complexes with amidinates and guanidinates
Schöne, S.; März, J.; Kaden, P.;
Recent results of ongoing research of tetravalent actinde complexes with amidinates and guadinates is presented. Thereby the presentation fucuses on solid state characterisations with SC-XRD and paramagnetic NMR studies in organic solvents.
  • Lecture (others)
    FENABIUM Projekttreffen, 04.12.2017, Dresden-Rossendorf, Deutschland

Publ.-Id: 26814 - Permalink


Site-controlled Si quantum dots in buried SiO2 layer formed by ion-beam implantation and phase separation
Xu, X.ORC; Wolf, D.; Hlawacek, G.; Engler, M.; Hübner, R.; Bischoff, L.; Pruefer, T.; Heinig, K.-H.; von Borany, J.
The increased use of personal computing devices and the Internet of Things (IoT) is accompanied by a demand for a computation unit with extra low energy dissipation. The single electron transistor (SET), which uses a Coulomb island to manipulate the movement of single electrons, is a candidate device for future low power electronics. However, so far its success is hindered by low temperature requirements and the missing CMOS-compatible fabrication route. By combining standard top-down lithography with bottom-up self-assembly of Si nanodots we will overcome this barrier.
In this work, Si nanodots--suitable for RT operation of SETs--are formed in a CMOS compatible way inside a buried SiO2 layer, providing the basic structure of an SET. This is achieved via phase separation induced by ion beam mixing in a geometrical restricted volume, followed by a thermal treatment. Guided by 3DkMC and TRI3DYN simulations, we utilize Helium Ion Microscopy (HIM) to irradiate continuous layers with Ne+, and Si+ broad beam irradiation of pillars. Both attempts lead to a restriction of the size of the collision cascade and hence the mixed volume. The size and position of the formed Si nanodots are studied with transmission electron microscopy, SIMS, and various electrical characterization techniques.
  • Lecture (Conference)
    Ionenstrahltreffen 2017, 13.02.2017, Göttingen, Germany

Publ.-Id: 26813 - Permalink


Site-controlled formation of Si nanodots in a buried SiO2 layer via ion-beam implantation and phase separation
Xu, X.ORC; Wolf, D.; Hlawacek, G.; Hübner, R.; Gharbi, A.; Prüfer, T.; Bischof, L.; Heinig, K.-H.; Facsko, S.; von Borany, J.
The increased use of personal computing devices and the Internet of Things (IoT) is accompanied by a demand for a computation unit with extra low energy dissipation. The single electron transistor (SET), which uses a Coulomb island to manipulate the movement of single electrons, is a candidate device for future low power electronics. However, so far its success is hindered by low temperature requirements and the missing CMOS compatible fabrication route. By combining standard top-down lithography with bottom-up self-assembly of Si nanodots we will overcome this barrier.
In this work, Si nanodots--suitable for RT operation of SETs--are formed in a CMOS compatible way inside a buried SiO2 layer, providing the basic structure of an SET. This is achieved via phase separation induced by ion beam mixing in a geometrical restricted volume, followed by a thermal treatment. Guided by 3DkMC and TRI3DYN simulations, we utilize Helium Ion Microscopy (HIM) to irradiate continuous layers with Ne+, and Si+ broad beam irradiation of pillars. Both attempts lead to a restriction of the size of the collision cascade and hence the mixed volume. The size and position of the formed Si nanodots are studied with transmission electron microscopy, SIMS, and various electrical characterization techniques.
  • Lecture (Conference)
    81. DPG-Jahrestagung und DPG-Frühjahrstagung der Sektion Kondensierte Materie, 22.03.2017, Dresden, Germany

Publ.-Id: 26812 - Permalink


Site-controlled Si Nanodot Formation for a RT-SET via Ion Beam Mixing and Phase Separation
Xu, X.ORC; Wolf, D.; Prüfer, T.; Hlawacek, G.; Hübner, R.; Bischoff, L.; Perego, M.; Gharbi, A.; Heinig, K.-H.; von Borany, J.
The increased use of personal computing devices and the Internet of Things (IoT) is accompanied by a demand for a computation unit with extra low energy dissipation. The Single Electron Transistor (SET), which uses a Coulomb island to manipulate the movement of single electrons, is a candidate device for future low-power electronics. However, so far its development is hindered by low-temperature requirements and the absence of CMOS compatibility. By combining advanced top-down lithography with bottom-up self-assembly of Si nano dots (NDs) we will overcome this barrier.
In this work, Si NDs – suitable as RT Coulomb islands – are formed via ion beam mixing followed by thermally stimulated phase separation. Broad-beam Si+ and Ne+ beams followed by a rapid thermal annealing (RTA) treatment were utilized to create a layer of NDs, which are subsequently visualized by Energy-Filtered Transmission Electron Microscopy (EFTEM). The conditions for ND formation, namely the dependence on ion type, primary energy, irradiation fluence, layer thickness and thermal budget during RTA, are optimized based on an extensive survey of this multidimensional parameter space. The presented work is guided by TRIDYN simulations of the Si excess in a SiO2 layer due to ion beam mixing and 3D Kinetic Monte-Carlo (3DkMC) simulation for the phase separation during the thermal treatment. To tailor towards a single Si ND, the focused Ne+ beam from the Helium Ion Microscope (HIM) is utilized to create user defined patterns of NDs in planar layer stacks. This allows achieving a mixing volume small enough for restricted Ostwald ripening and successful single ND formation. The existence of the formation of spatially controlled single NDs with a diameter of only 2.2 nm is confirmed by comparing the EFTEM Si plasmon-loss intensity with simulated plasmon loss images.
In the future – by combining conventional lithography, direct self-assembly (DSA) and ion beam mixing – nanopillars with a single embedded ND will be integrated in a CMOS-compatible way. EFTEM and electrical characterization techniques will be used for realizing this novel pathway towards a room-temperature SET device.

This work has been funded by the European Union’s Horizon2020 research program ‘IONS4SET’ under Grant Agreement No. 688072.
  • Lecture (Conference)
    FOR3NANO: Formation of 3D Nanostructures by Ion Beams, 29.06.2017, Helsinki, Finnland

Publ.-Id: 26811 - Permalink


Site-controlled Si Nanodot Formation for a RT-SET via Ion Beam Mixing and Phase Separation
Xu, X.ORC; Hlawacek, G.; Wolf, D.; Prüfer, T.; Hübner, R.; Bischoff, L.; Perego, M.; Gharbi, A.; Engelmann, H.-J.; Facsko, S.; Heinig, K.-H.; von Borany, J.
The increased use of personal computing devices and the Internet of Things (IoT) is accompanied by a demand for a computation unit with extra low energy dissipation. The Single Electron Transistor (SET), which uses a Coulomb island to manipulate the movement of single electrons, is a candidate device for future low-power electronics. However, so far its development is hindered by low-temperature requirements and the absence of CMOS compatibility. By combining advanced top-down lithography with bottom-up self-assembly of Si nano dots (NDs) we will overcome this barrier.
In this work, Si NDs – suitable as RT Coulomb islands – are formed via ion beam mixing followed by thermally stimulated phase separation. Broad-beam Si+ and Ne+ beams followed by a rapid thermal annealing (RTA) treatment were utilized to create a layer of NDs, which are subsequently visualized by Energy-Filtered Transmission Electron Microscopy (EFTEM). The conditions for ND formation, namely the dependence on ion type, primary energy, irradiation fluence, layer thickness and thermal budget during RTA, are optimized based on an extensive survey of this multidimensional parameter space. The presented work is guided by TRIDYN simulations of the Si excess in a SiO2 layer due to ion beam mixing and 3D Kinetic Monte-Carlo (3DkMC) simulation for the phase separation during the thermal treatment. To tailor towards a single Si ND, the focused Ne+ beam from the Helium Ion Microscope (HIM) is utilized to create user defined patterns of NDs in planar layer stacks. This allows to achieve a mixing volume small enough for restricted Ostwald ripening and successful single ND formation. The existence of the formation of spatially controlled single NDs with a diameter of only 2.2 nm is confirmed by comparing the EFTEM Si plasmon-loss intensity with simulated plasmon loss images.
In the future – by combining conventional lithography, direct self-assembly (DSA) and ion beam mixing – nanopillars with a single embedded ND will be integrated in a CMOS-compatible way. EFTEM and electrical characterization techniques will be used for realizing this novel pathway towards a room-temperature SET device.
  • Lecture (Conference)
    AVS 64th International Symposium & Exhibition, 01.11.2017, Tampa, FL, USA

Publ.-Id: 26810 - Permalink


Junctionless Nanowire Transistors: Promising Devices for Biosensor Applications
Georgiev, Y. M.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. , , 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. , 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).
  • Lecture (Conference)
    NanoBioSensors Conference, 04.-05.09.2017, Dresden, Germany

Publ.-Id: 26809 - Permalink


High Resolution Nanofabrication
Georgiev, Y. M.ORC
Nanofabrication aims at creating structures and devices having minimum dimensions below 100 nm. This is possible to achieve in two main ways: bottom-up and top-down. In the former, the structures and devices are created from small to large in an additive fashion, which relies to a great extent on self-organisation processes. In the latter, the fabrication goes from large to small where nano-structures and devices are carved from a larger piece of material in a subtractive fashion. The top-down approach is much more mature than the bottom-up one and is based on two long-established processes: (i) nanolithography, where a stencil with the required pattern is created in a sacrificial layer called “resist”, deposited on the main working material (substrate), and (ii) pattern transfer through the resist stencil into the base material.
In this paper we will present results on high-resolution nanofabrication of structures and devices with critical dimensions (CD) below 10 nm on silicon (Si), silicon-on-insulator (SOI), germanium (Ge) and germanium-on-insulator (GeOI) substrates. The fabrication was mainly within the frames of the top-down approach and was based on electron beam lithography (EBL) with positive or negative resists followed by a pattern transfer with both additive (metal deposition and lift-off) and subtractive (dry etching) methods.[1-4] Moreover, high-end results on combination of bottom-up and top-down approaches will also be presented such as (i) contacting of bottom-up grown and randomly distributed nanostructures for their integration into functional devices [5] as well as (ii) pattern density multiplication by directed self assembly (DSA) of block-copolymers (BCP).[6,7] We believe that these results are showing some of the promising trends for future development of high-resolution nanofabrication.
References:
[1] Küpper, D., Küpper, D., Wahlbrink, T., Bolten, J., Lemme, M. C., Georgiev, Y. M., & Kurz, H. (2006). Megasonic-assisted development of nanostructures. Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 24(4), 1827.
[2] Georgiev, Y. M., Petkov, N., McCarthy, B., Yu, R., Djara, V., O’Connell, D., … Holmes, J. D. (2014). Fully CMOS-compatible top-down fabrication of sub-50nm silicon nanowire sensing devices. Microelectronic Engineering, 118, 47-53.
[3] Gangnaik, A., Georgiev, Y. M., McCarthy, B., Petkov, N., Djara, V., & Holmes, J. D. (2014). Characterisation of a novel electron beam lithography resist, SML and its comparison to PMMA and ZEP resists. Microelectronic Engineering, 123, 126-130.
[4] Gangnaik, A. S., Georgiev, Y. M., Collins, G., & Holmes, J. D. (2016). Novel germanium surface modification for sub-10 nm patterning with electron beam lithography and hydrogen silsesquioxane resist. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 34(4), 041603.
[5] Teschome, B., Facsko, S., Schönherr, T., Kerbusch, J., Keller, A., & Erbe, A. (2016). Temperature-Dependent Charge Transport through Individually Contacted DNA Origami-Based Au Nanowires. Langmuir, 32(40), 10159-10165.
[6] Cummins, C., Gangnaik, A., Kelly, R. A., Borah, D., O'Connell, J., Petkov, N., … Morris, M. A. (2015). Aligned silicon nanofins via the directed self-assembly of PS-b-P4VP block copolymer and metal oxide enhanced pattern transfer. Nanoscale, 7(15), 6712-6721.
[7] Cummins, C., Gangnaik, A., Kelly, R. A., Hydes, A. J., O’Connell, J., Petkov, N., … Morris, M. A. (2015). Parallel Arrays of Sub-10 nm Aligned Germanium Nanofins from an In Situ Metal Oxide Hardmask using Directed Self-Assembly of Block Copolymers. Chemistry of Materials, 27(17), 6091-6096.
  • Invited lecture (Conferences)
    5th International workshop “Nano-Fabrication, Devices & Metrology”, 19.-20.06.2017, Eindhoven, The Netherlands

Publ.-Id: 26808 - Permalink


Dopant Induced Single Electron Tunneling within the Sub-bands of Single Silicon NW Tri-gate Junctionless n-MOSFET
Uddin, W.; Georgiev, Y. M.ORC; Maity, S.; Das, S.
We report 1D electron transport of silicon functionless tri-gate n-type transistor at 4.2 K. The step like curve observed in the current voltage characteristic suggests 1D transport. Besides the current steps for 1D transport, we found multiple spikes within individual steps, which we relate to inter-band single electron tunnelling, mediated by the charged dopants available in the channel region. Clear Coulomb diamonds were observed in the stability diagram of the device. It is shown that a uniformly doped silicon nanowire can provide us the window for the single electron tunnelling. Back-gate versus front-gate color plot, where current is in a color scale, shows a crossover of the increased conduction region. This is a clear indication of the dopant–dopant interaction. It has been shown that back-gate biasing can be used to tune the coupling strength between the dopants.
Keywords: functionless transistor, 1D transport, single electron tunnelling, Coulomb blocked, dopant–dopant interaction

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Publ.-Id: 26807 - Permalink


Doping top-down e-beam fabricated germanium nanowires using molecular monolayers
Long, B.; Alessio Verni, G.; O’Connell, J.; Shayesteh, M.; Gangnaik, A.; Georgiev, Y. M.ORC; Carolan, P.; O’Connell, D.; Kuhn, K. J.; Clendenning, S. B.; Nagle, R.; Duffy, R.; Holmes, J. D.
This paper describes molecular layer doping of Ge nanowires. Molecules containing dopant atoms are chemically bound to a germanium surface. Subsequent annealing enables the dopant atoms from the surface bound molecules to diffuse into the underlying substrate. Electrical and material characterisation was carried out, including an assessment of the Ge surface, carrier concentrations and crystal quality. Significantly, the intrinsic resistance of Ge nanowires with widths down to 30 nm, doped using MLD, was found to decrease by several orders of magnitude.
Keywords: Molecular layer doping, Nanowires, Semiconductors, Germanium, Conformal, Non-destructive

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Publ.-Id: 26806 - Permalink


Frequency modulation of backward volume spin wave by electric current
Nishida, N.; Lee, S. W.; Lee, S. J.; Lee, K. J.; Schultheiss, H.; Sekiguchi, K.;
In the field of magnonics, spin waves are envisioned as a new candidate for information transport and processing. Since spin waves propagate without any charge displacement and are free from Joule heating, they offer significant reduction of energy consumption in devices. The spin transfer torque (STT) effect originating from conduction electrons is a powerful method for modulating spin waves. Here, we investigated the current induced Doppler shift of backward volume spin waves.
We fabricated a NiFe stripe with a width of 2 µm, which was magnetized in backward volume configuration. The antennas fabricated on top of the NiFe stripe were connected to a vector network analyzer for measuring the spin-wave spectra. We applied a dc current to the NiFe stripe. For a current density of 5 × 10^10 A/m^2 the spin-wave frequencies shifted +170 MHz compared to the spin-wave spectra without dc current. This frequency shift is 60 times larger than previous works reported for forward volume spin waves. Hence, we demonstrated giant frequency modulation of backward volume spin waves by a dc current.
  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Germany

Publ.-Id: 26805 - Permalink


Magnetotransport in Half-Metallic Manganese Ruthenium Gallium
Fowley, C.; Rode, K.; Borisov, K.; Atcheson, G.; Lau, Y.-C.; Thiyagarajah, N.; Coey, M.; Stamenov, P.; Gallardo, R.; Kampert, E.; Wang, Z.; Lindner, J.; Deac, A. M.;
The recently discovered fully-compensated half-metal, manganese ruthenium gallium (MRG), is a very promising material for spintronics. It possesses tunable magnetic moment, high magnetic anisotropy field and high spin polarisation. Here, we use the extraordinary Hall effect and longitudinal magnetoresistance to characterise the properties of MRG. Experiments are carried out in pulsed magnetic fields up to 60 T at the Dresden High Magnetic Field Laboratory (HLD). The spin-flop transition, as well as a large spontaneous Hall angle are observed. The spontaneous Hall angle is over 2% and is seen to be independent of temperature. The magneto-transport in MRG is shown to be dominated by one sublattice only, even at the magnetic compensation temperature (i.e. when the total magnetic moment is zero). MRG behaves magnetically an antiferromagnet and electrically as a normal ferromagnet with a sizeable spin-polarisation.
Keywords: anomalous Hall effect, half-metals, Heusler alloys, ferrimagnetism, high magnetic fields
  • Lecture (Conference)
    81. DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Germany
  • Lecture (Conference)
    Intermag 2017, 24.-28.04.2017, Dublin (Baile Átha Cliath), Ireland (Éire)

Publ.-Id: 26804 - Permalink


Phase stability of magnonic logic operation in the microfabricated ferromagnetic stripe
Nishida, N.; Lee, S. J.; Lee, S. W.; Lee, K. J.; Sekiguchi, K.; Schultheiss, H.;
Magnons, which are the quasi-particles of spin waves, have a great potential to realization of low-energy-dissipation devices, because the magnons deliver an angular momentum and the propagation of magnons is free from Joule heating. Magnons are expected as non-charged new information carriers[1], and logic operation of magnons is demonstrated in ferromagnetic thin film[2]. In order to apply to actual devices, miniaturization of logic circuits is essential for integration of circuits. However, in the micrometer-sized magnon waveguides a confinement of magnon emerges[3] and make magnon propagation complex.
In order to make clear the logic operation of magnon in the micro waveguides, we measured magnon densities of spin-wave interference in 2.5-µm-wide ferromagnetic stripe using microfocused Brillouin light scattering spectroscopy. Spatial mapping of the magnon density revealed that the interference pattern of spin wave is confined within a limited area because of contributions of transverse quantized modes. In the limited area the phase of interference pattern is able to be controlled by the spin-wave phase. A micromagnetic simulation revealed transverse 100 nm interference patterns, which affect a signal-to-noise ratio of logic operation. These results will be important to decide the design of integrated magnonic devices.

References
[1] A. V. Chumak et al., Nat. Commun. 5, 4700 (2014).
[2] N. Sato et al., Appl. Phys. Express 6, 063001 (2013).
[3] P. Pirro et al., Phys. Status Solidi B 248, 1404 (2011).
  • Poster
    633. WE-Heraeus-Seminar on `Spin Orbit Dynamics – Connecting timescales from nanoseconds to femtoseconds', 04.-06.01.2017, Bad Honnef, Germany

Publ.-Id: 26803 - Permalink


Incorporation of Europium(III) into Scheelite-Related Host Matrices ABO4 (A = Ca2+, Sr2+, Ba2+; B = W6+, Mo6+): Role of A- and B- Sites on the Dopant Site-Distribution and Photoluminescence
Xiao, B.; Schmidt, M.;
Calcium orthotungstates and -molybdates are naturally occurring minerals that have been studied extensively. The minerals are named scheelite (CaWO4) and powellite (CaMoO4), respectively. Scheelite is the most important economic W mineral. Powellite is actively studied in the nuclear waste management field. Powellite is one of the primary Mo crystalline phases expected to form in high-level nuclear waste (HLW) borosilicate glasses during waste processing.
Both scheelite and powellite have a large number of synthetic derivatives that are based on a general formula ABO4 (A = Ca2+, Sr2+, Ba2+; B = W6+, Mo6+). Recently, much of the interest in study of scheelite-type materials arises from their exceptional compositional variability. In the context of nuclear waste disposal, this compositional variability offers a potential pathway for the effective retention of highly radiotoxic actinides like Pu and Am in a powellite secondary phase. However, the thermodynamic stability of these solid solutions will depend on their structural deviation from the stoichiometric phases.
Investigations have shown that the presence of excess positive charge in scheelite-typed ABO4 materials upon incorporation of each trivalent ion is compensated via coupled substitution with a monovalent alkali cation. Single-crystal X-ray measurements demonstrate that the crystal structure of the resulting solid solutions is disordered, that is, the trivalent dopant and monovalent charge-compensating cation statistically occupy the same divalent A2+ site in ABO4 structure. However, the structural details behind such disordered substitution, such as specific ionic environment around dopants, number of non-equivalent doping species as well as spatial accommodation of doping centers, are difficult parameters to characterize from the crystallographic data, especially when the dopant is present at trace concentration levels.
Polarization-dependent site-selective time resolved laser-induced fluorescence spectroscopy (p-TRLFS) is unique in its capability to characterize the local environment of a fluorescent probe, here Eu3+, in a multi-species system with point-group accuracy at trace concentration levels. This work aims to clarify the impact of site effect on the local symmetry distortion from the bulk crystallographic site symmetry in scheelite-type ABO4 single crystals. This will improve our understanding of the formation of solid solutions on the molecular scale.
Keywords: TRLFS
  • Lecture (Conference)
    GeoBremen, 24.-29.09.2017, Bremen, Germany

Publ.-Id: 26801 - Permalink


Lattice location and electrical activation of tellurium in hyperdoped silicon
Wang, M.; Berencén, Y.; Prucnal, S.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Skorupa, W.; Helm, M.; Zhou, S.;
Silicon hyperdoped with chalcogens beyond the equilibrium solubility limit exhibits sub-band gap optical absorption, presenting a potential material for silicon-based optoelectronic applications [1-3]. In our work, tellurium hyperdoped silicon was obtained by ion implantation combined with pulsed laser melting. The crystallization of implanted layers and the lattice location of impurities in silicon matrix were determined by the Rutherford backscattering spectrometry / channeling (RBS/C). The chemical states of tellurium dopants in tellurium-hyperdoped silicon were probed by the tellurium K-edge X-ray absorption fine structure spectroscopy. The electrical transport reveals the insulator-to-metal transition (IMT) in tellurium-hyperdoped silicon, which is confirmed and understood by using calculations based on the density functional theory. However, the critical tellurium concentration for IMT is much higher than the calculated value. The lattice location results suggest that a significant fraction of the tellurium atoms form dimers, which are electrically deactivated. After considering this fraction, the critical concentration claimed from the DFT calculation is consistent with the number of electrically activated tellurium atoms.

[1] T. G. Kim, J.M. Warrender, M. J. Aziz, Applied Physics Letters 88(24), 2006, 1850.
[2] M. Tabbal, T. G. Kim, D. N. Woolf, et al. Applied Physics A 98(3), 2010, 589-594.
[3] Y. Berencén, S. Prucnal, L. Fang, et al. Scientific Reports 7, 2017, 43688.
Keywords: hyperdoped Si, Rutherford backscattering spectrometry, channeling (RBS/C),insulator-to-metal transition (IMT)
  • Lecture (Conference)
    The 23rd International Conference on Ion Beam Analysis, 08.-13.10.2017, Shanghai, China

Publ.-Id: 26800 - Permalink


GaAs-based core/shell nanowires with extremely large lattice mismatch grown on Si substrates
Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Grenzer, J.; Ghorbani Asl, M.; Krasheninnikov, A.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.;
The geometry and high surface-to-volume ratio of nanowires offer unique possibilities for strain engineering in epitaxial semiconductor heterostructures with large lattice mismatch. In addition, the possibility to grow nanowires of high crystal quality epitaxially on Si substrates adds to their technological significance. In this work, we have investigated the growth of free-standing GaAs/InxGa1-xAs and GaAs/InxAl1-xAs core/shell nanowires on Si(111) substrates by molecular beam epitaxy, the accommodation of the lattice mismatch therein, and its effect on the nanowire properties.
Very thin GaAs core nanowires (20-25 nm in diameter) were grown in the self-catalyzed mode with a sufficiently low number density (to avoid beam shadowing effects) on SiOx/Si(111) substrates, after an in situ treatment of the latter with Ga droplets. This resulted in zinc blende nanowires with their axis along the [111] crystallographic direction and six {1-10} sidewalls. Subsequently, conformal overgrowth of the InxGa1-xAs or InxAl1-xAs shell was obtained only under kinetically limited growth conditions that suppressed mismatch-induced bending phenomena.
The strain in the core and the shell was studied systematically as a function of the shell composition and thickness. To that end, we used Raman scattering spectroscopy, transmission electron microscopy and synchrotron X-ray diffraction, and compared the results with theoretical predictions based on continuum elasticity and density functional theories. Our results demonstrate that highly mismatched core/shell nanowires with defect-free interface can be obtained beyond what is possible in thin film heterostructures.
More interestingly, nanowires with strain-free shell and fully strained core can be grown under certain conditions. The large strain in the GaAs core is expected to have a strong effect on its fundamental properties. Here, we demonstrate a large shrinkage of the band gap, which can be as high as 35 % depending on the composition of the shell.
  • Lecture (Conference)
    Austrian MBE Workshop 2017, 28.-29.09.2017, Wien, Austria

Publ.-Id: 26799 - Permalink


Sub-band-gap optical response in Au-implanted silicon
Wang, M.; Berencén, Y.; Prucnal, S.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Skorupa, W.; Helm, M.; Zhou, S.;
Recently it was suggested that Au doping in Si can be realized by ion implantation and pulsed laser melting. The sub-band-gap optoelectronic response is observed and increases with the implanted Au concentration [1]. In our work, Au implanted Si was fabricated by ion-implantation with three different fluences of 7×1014 cm-2, 1.4×1015 cm-2 and 2.1×1015 cm-2, followed by pulsed laser melting. The Raman spectrum results confirm the high-quality recrystallization of the Au implanted layer. And the Rutherford backscattering spectrometry / Channeling reveal that Au atoms diffused to the near surface region. In addition the detailed angular scans along Si [001] reveal that Au atoms are mostly in the interstitial lattice sites. From the transport measurements, a p-type conductivity and an increasing carrier concentration are observed in the implanted layer. Moreover, the transmission and reflection were measured using near infrared spectroscopy (NIR) to quantify the sub-band-gap absorptance in the hyperdoped silicon. In the Au implanted layer the spectral response extends to wavelengths as long as 3.2 μm. However, the sub-band-gap absorptance has no dependence on the Au fluence or the carrier concentration.

[1] Mailoa, Jonathan P., et al., Nat. Commun. 5, 3011 (2014)
Keywords: Sub-band-gap optical response , Si, Au-implanted
  • Poster
    19th International Conference on Radiation Effects in Insulators, 02.-07.07.2017, Versailles, France

Publ.-Id: 26797 - Permalink


Compositional and strain analysis of In(Ga)N/GaN short period superlattices
Dimitrakopulos, G. P.; Vasileiadis, I. G.; Bazioti, C.; Smalc-Koziorowska, J.; Kret, S.; Dimakis, E.ORC; Florini, N.; Kehagias, T.; Suski, T.; Karakostas, T.; Moustakas, T. D.; Komninou, P.
Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising twodimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry, and strain. The high angle annular dark field Z-contrast observations were quantified for such layers, regarding the indium content of the QWs, and were correlated to their strain state using peak finding and geometrical phase analysis. Image simulations taking into thorough account the experimental imaging conditions were employed in order to associate the observed Z-contrast to the indium content. Energetically relaxed supercells calculated with a Tersoff empirical interatomic potential were used as the input for such simulations. We found a deviation from the tetragonal distortion prescribed by continuum elasticity for thin films, i.e., the strain in the relaxed cells was lower than expected for the case of 1 ML QWs. In all samples, the QW thickness and strain were confined in up to 2 ML with possible indium enrichment of the immediately abutting MLs. The average composition of the QWs was quantified in the form of alloy content.

Publ.-Id: 26796 - Permalink


Hyperdoping silicon with tellurium for optoelectronics
Wang, M.; Berencén, Y.; Prucnal, S.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.;
Chalcogen-hyperdoped silicon has been a topic of great interest due to its potential optoelectronic applications owing to the sub-band gap absorption [1-3]. In our work, tellurium hyperdoped Si was fabricated by ion-implantation with different fluences ranging from 1.09×1015 to 1.25×1016 cm-2 followed by pulsed laser melting (PLM). The Rutherford backscattering spectrometry / Channeling (RBS/C) results reveal the high-quality recrystallization of tellurium implanted silicon by PLM. From the transport measurements, an insulator-to-metal transition is observed with increasing tellurium concentration. Moreover, the ellipsometry measurements show that the band gap narrows with increasing tellurium doping concentration. And the Fourier transform infrared (FTIR) spectroscopy show that tellurium hyperdoped Si has strong infrared absorption. This gives us a signal that hyperdoped silicon with tellurium could enable silicon-based optoelectronics in the infrared band.
Keywords: Hyperdoping,pulsed laser melting (PLM),silicon,optoelectronics
  • Poster
    19th International Conference on Radiation Effects in Insulators, 02.-07.07.2017, Versailles, France

Publ.-Id: 26795 - Permalink


Asymmetric strip line electrodes for photoconductive terahertz emission
Singh, A.; Winnerl, S.; König-Otto, J. C.; Stephan, D. R.; Helm, M.; Schneider, H.;
Here we studied various combinations (two symmetric and two asymmetric designs) of stripline widths for stripline photoconductive emitters fabricated on semi-insulating GaAs. We found out that the THz emission efficiency depends strongly on the anode width. The wider the anode, the higher is the THz amplitude. Cathode width does not play a significant role in THz emission performance.
Keywords: Terahertz emitter, stripline, antenna, GaAs
  • Poster
    Optical Terahertz Science and Technology (OTST 2017), 02.-07.04.2017, London, UK

Publ.-Id: 26794 - Permalink


Short-time annealing for nanomaterials
Neubert, M.; Rebohle, L.; Berencen, Y.; Prucnal, S.; Hübner, R.; Böttger, R.; Georgiev, Y.; Erbe, A.; Helm, M.; Skorupa, W.;
Semiconductor structures with dimensions in the nanometer range become more and more important in microelectronics and other new emerging technologies. Thereby, the transition from bulk to nanomaterials often requires significant changes in the process technology, including the change from equilibrium to non-equilibrium processes. In this work, we investigate the modification of nanomaterials by flash lamp annealing with pulse lengths in the millisecond range [1]. In detail, we focus on two specific materials: (i) the annealing of thin ZnO layers and the impact of different process conditions on the materials properties, and (ii) the high-level doping of Si and Ge nanowires for sensor applications by ion implantation and flash lamp annealing.
Keywords: Semiconductor, hyperdoping, flash lamp annealing, nanomaterials
  • Lecture (Conference)
    NanoApp 2017, 14.-18.06.2017, Bled, Slovenia

Publ.-Id: 26793 - Permalink


How indium nitride senses water
Jovic, V.; Moser, S.; Ulstrup, S.; Goodacre, D.; Dimakis, E.ORC; Koch, R.; Katsoukis, G.; Moreschini, L.; Mo, S.-K.; Jozwiak, C.; Bostwick, A.; Rotenberg, E.; Moustakas, T. D.; Smith, K. E.
The unique electronic band structure of indium nitride InN, part of the industrially significant III−N class of semiconductors, offers charge transport properties with great application potential due to its robust n-type conductivity. Here, we explore the water sensing mechanism of InN thin films. Using angle-resolved photoemission spectroscopy, core level spectroscopy, and theory, we derive the charge carrier density and electrical potential of a two-dimensional electron gas, 2DEG, at the InN surface and monitor its electronic properties upon in situ modulation of adsorbed water. An electric dipole layer formed by water molecules raises the surface potential and accumulates charge in the 2DEG, enhancing surface conductivity. Our intuitive model provides a novel route toward understanding the water sensing mechanism in InN and, more generally, for understanding sensing material systems beyond InN.
Keywords: Sensor, two-dimensional electron gas (2DEG), ARPES, surface electronic potential, quantum well

Publ.-Id: 26792 - Permalink


Investigation of an 18F-labelled Imidazopyridotriazine for Molecular Imaging of Cyclic Nucleotide Phosphodiesterase 2A
Schröder, S.; Wenzel, B.; Deuther-Conrad, W.; Teodoro, R.; Kranz, M.; Scheunemann, M.; Egerland, U.; Höfgen, N.; Briel, D.; Steinbach, J.; Brust, P.;
Specific radioligands for in vivo visualization and quantification of cyclic nucleotide phosphodiesterase 2A (PDE2A) by positron emission tomography (PET) are increasingly gaining interest in brain research. Herein we describe the synthesis, the 18F-labelling as well as the biological evaluation of our latest PDE2A (radio-)ligand 9-(5-Butoxy-2-fluorophenyl)-2-(2-([18F])fluoroethoxy)-7-methylimidazo[5,1-c]pyrido[2,3-e][1,2,4]triazine (([18F])TA5). It is the most potent PDE2A ligand out of our series of imidazopyridotriazine-based derivatives so far (IC50 hPDE2A = 3.0 nM; IC50 hPDE10A > 1000 nM). Radiolabelling was performed in a one-step procedure starting from the corresponding tosylate precursor. In vitro autoradiography on rat and pig brain slices displayed a homogenous and non-specific binding of the radioligand. Investigation of stability in vivo by RP-HPLC and micellar liquid chromatography (MLC) analyses of plasma and brain samples obtained from mice revealed a high fraction of one main radiometabolite. Hence, we concluded that [18F]TA5 is not appropriate for molecular imaging of PDE2A neither in vitro nor in vivo. Our ongoing work is focusing on further structurally modified compounds with enhanced metabolic stability.
Keywords: Phosphodiesterase 2A (PDE2A), secondary messengers, PDE2A radioligands, positron emission tomography (PET), neuroimaging, metabolic stability, micellar liquid chromatography (MLC)

Publ.-Id: 26791 - Permalink


Theoretische und experimentelle Untersuchung des Wärmeübergangs an berippten Rohren unter Naturkonvektion
Thiele, J.;
In dieser Diplomarbeit werden experimentelle Untersuchungen zum Wärmeübergang an berippten Rohren unter Naturkonvektion bei unterschiedlichen Randbedingungen durchgeführt und ausgewertet. Kernthema dieser Arbeit ist der Einfluss des Rippenabstandes und des Neigungswinkels eines ovalen Rohres bei glatten Rippen und bei Stiftrippen. Untersucht werden Rippenrohre mit einem Rippenabstand von 6 mm, 11 mmund 16 mm. Der Einfluss des Neigungswinkels der Rohre wird bei 0° (horizontale Ausrichtung), 20°, 30° und 40° analysiert. Dafür wird die äußere Rippenrohroberfläche auf 30 °C bis 90 °C (in 10 °C Schritten) erwärmt. Die Oberflächentemperatur der Rippe wird durch Thermoelemente, die an verschiedenen Positionen befestigt sind, gemessen. Daraus lassen sich der Wärmeübergangskoeffizient und der Rippenwirkungsgrad als signifikante Parameter berechnen. In dieser Arbeit wurden folgende Erkenntnisse gewonnen. Das Anwinkeln des Rohres hat keine signifikanten Auswirkungen auf den Wärmeübergangskoeffizienten. Ein Neigungswinkel von 30°weist dabei die beste Performance auf. Eine Vergrößerung des Wärmeübergangskoeffizienten um 14% ist möglich. Die Verwendung von Stiftrippen zeigt keine größeren Werte für den Wärmeübergangskoeffizienten. Lediglich die Rippenrohre mit größeren Rippenabständen verbessern den konvektiven Wärmeübergang. Durch einen Abstand von 16mm kann der Wärmeübergangskoeffizient um bis zu 100 % gegenüber einem Rohr mit einem Rippenabstand von 6 mm gesteigert werden. Der Rippenwirkungsgrad ist am kleinsten, wenn der Rippenabstand am größten ist. Eine Verschlechterung um 25 % ist möglich. Die größten Rippenwirkungsgrade werden bei einem Neigungswinkel von 40° erreicht. Dies gilt sowohl für die Stiftrippe als auch die Glattrippe. Die Untersuchungen liefern einen Beitrag für das Verständnis von Auswirkungen geometrischer Veränderungen an Rippenrohren auf den luftseitigen Wärmeübergang. In Zukunft können diese Erkenntnisse genutzt werden, um die Effizienz von luftgekühlten Wärmeübertragern zu steigern.

This diploma thesis considers the natural convective heat transfer on finned tubes under different boundary conditions. Object of this study is the influence of the fin spacing and the angle of inclination of an oval tube with plain fins or with pin-fins. Finned tubes with a fin spacing of 6mm, 11 mm and 16 mmare examined. The inclination angle of the tubes is evaluated at 0°(horizontal alignment), 20°, 30° and 40°. For that purpose, the finned tubes are heated up between 30 °C and 90 °C in increments of 10 °C. At different position on the fins thermocouples are located to measure the surface temperature. The heat transfer coefficient and the fin efficiency are significant parameters, which can be calculated from the measured temperatures. The increase of the inclination angle has little effect on the heat transfer coefficient. The highest performance improvement has been observed at an inclination angle of 30°, which shows about 14 % enhanced heat transfer coefficient. Pin fins do not enhance the heat transfer coefficient. Finned tubes with larger fin spacing improve the convective heat transfer. The heat transfer coefficient can be enhanced up to 100 % for a spacing of 16mm compare to a tube with a fin spacing of 6 mm. Finned tubes with smaller fin spacing improve the fin efficiency, which can beenhanced up to 25% for a spacing of 6 mm compare to a tube with a fin spacing of 16 mm. The highest values for the fin efficiency have been observes at an inclination angle of40°. The research contributes to understand the effect of geometrical changes on the air-side heat transfer of finned oval tubes. These applications can be used to increase the efficiency of air-cooled heat exchangers in the future.
  • Diploma thesis
    TU Dresden, 2018
    Mentor: Sebastian Unger, Matthias Beyer
    103 Seiten

Publ.-Id: 26789 - Permalink


Investigating the structure of crosslinked polymer brushes (brush-gels) by means of Positron Annihilation Spectroscopy
Dehghani, E. S.; Aghion, S.; Anwand, W.; Consolati, G.; Ferragut, R.; Panzarasa, G.;
Polymer brushes can be useful as small-scale reactors for the controlled synthesis of nanoparticles, an approach which is gaining increasing interest. In this context, chemical crosslinking of polymer brushes could be considered as a viable approach to control the size and size distribution of the formed nanoparticles. Here we describe the application of Positron Annihilation Spectroscopy (PAS) for the characterization of crosslinked polymer brushes (brush-gels). Poly(hydroxyethyl methacrylate) (PHEMA) brushes were obtained on silicon substrates by means of a surface-initiated atom transfer radical polymerization (SI-ATRP). Crosslinking was achieved during the polymerization by adding different amounts of diethyleneglycol dimethacrylate (DEGDMA) as a difunctional monomer. The resulting brushes, both un- and crosslinked, were then post-modified with carboxylic acid groups, allowing the in situ synthesis of silver nanoparticles after ion exchange with silver nitrate and reduction with sodium borohydride. The detailed characterization of such systems is notoriously challenging and PAS proved to be an effective, non-invasive technique to acquire insight on the structure of the brushes and of their nanoparticle composites.
Keywords: Polymer brushes nanoparticles Positron Annihilation Spectroscopy

Publ.-Id: 26788 - Permalink


DFT-MD simulations of mixing properties in warm dense plastic
Vorberger, J.;
Mixtures of carbon and hydrogen at megabar conditions and at temperatures below one electronvolt can be found in a variety of planets of our solar system like Uranus and Neptune and are believed to feature prominently in extrasolar planets. The equation of state, transport and mixing properties of carbo-hydrates thus strongly influence the inner structure and evolution of these astrophysical objects.
We present results of density-functional molecular dynamics simulations for the structure and mixing properties of carbo-hydrates at such conditions in order to explain recent experimental results showing the demixing of carbon and hydrogen and the formation of nano-diamonds at double shock conditions.
Keywords: warm dense matter, plastic, CH, DFT-MD, x-ray scattering, planets, planetary interior
  • Lecture (Conference)
    38th Hirschegg meeting on High Energy Density Physics, 28.01.-02.02.2018, Hirschegg, Österreich

Publ.-Id: 26787 - Permalink


Rodare - Rossendorf Data Repository
Frust, T.ORC
Rodare (Rossendorf Data Repository) is the data publication platform at HZDR. Rodare is based on the Invenio framework (http://invenio-software.org) and is a fork of the popular data publication service Zenodo which is offered by CERN. Rodare allows HZDR researchers to publish their research data to make them citeable, discoverable and reusable.
Keywords: Rodare; Data repository; Open Science; Open Access
  • Software in external data repository
    Publication year 2018
    Programming language: Python, Javascript
    System requirements: Python 3, Elasticsearch, Postgresql, RabbitMQ, Redis, Nginx, HAproxy
    License: GPLv3 (Link to license text)
    Hosted on HZDR GitLab: Link to location

Publ.-Id: 26785 - Permalink


Comparison of tumour hypoxia measured by FMISO-PET and gene signatures for patients with HNSCC
Löck, S.; Linge, A.; Seidlitz, A.; Bandurska-Luque, A.; Großer, M.; Baretton, G. B.; Zöphel, K.; Zips, D.; Troost, E. G. C.; Krause, M.; Baumann, M.;
Purpose: Tumour hypoxia is well known to increase radio-resistance of tumours. In a recent prospective biomarker imaging trial, hypoxia has been measured by [18F]fluoromisonidazole positron emission tomography (FMISO-PET) scans [1,2]. Here, we compared hypoxia imaging with the expression of hypoxia-associated gene signatures for patients with locally advanced head and neck squamous cell carcinoma (HNSCC) treated by primary radiochemotherapy (RCHT).

Material and methods: FMISO-PET imaging and gene expression analyses were performed on the cohort of 50 HNSCC patients [1,2]. For this study, the FMISO-PET parameters tumour-to-background ratio (TBPpeak) and hypoxic tumour volume (HV1.6) analysed before RCHT were considered. Expressions of 15-, 26- and 30-gene hypoxia-associated signatures [3-5] were analysed from formalin-fixed paraffin-embedded (FFPE) tumour biopsies obtained before RCHT using the GeneChip® Human Transcriptome Array 2.0 (Affymetrix) and nanoString analysis. Gene expressions were compared between the two methods using the Pearson correlation coefficient. Linear regression was applied to relate TBRpeak and HV1.6 to the mean expression of the gene signatures, including the interaction with tumour volume which was assessed on the planning CT by an experienced radiation oncologist. The association of FMISO-PET parameters and gene expressions to loco-regional control (LRC) and progression-free survival (PFS) was assessed by Cox regression.

Results: The mean expressions of all hypoxia-associated gene signatures were highly correlated between Affymetrix and nanoString analyses (R>0.5). While TBRpeak and HV1.6 were weakly correlated with the expression of hypoxia-associated genes alone, significant correlations were observed if the interaction term of gene expression and tumour volume was included (R>0.5). Both FMISO-PET parameters were significantly correlated with LRC and PFS (p<0.01), while the combination of hypoxia-associated gene expressions and their interaction with tumour volume showed a significant but weaker correlation for the 30-gene signature to LRC and for the 15- and 30-gene signature to PFS (p<0.05). The figure shows patient stratifications using HV1.6 (p=0.02), the 30-gene signature (p=0.07) and their combination (p<0.01).

Conclusion: Hypoxia imaging correlates to the expression of hypoxia-associated genes if the interaction of gene expression and tumour volume is included. Interestingly, both methods may complement each other, which may be of advantage for identifying patients who are at high risk of treatment failure and may benefit from dose escalation. While FMISO-PET directly measures hypoxia, the gene signatures are also associated with other radiobiologic phenomena such stemness of cancer cells.
  • Lecture (Conference)
    ESTRO 36, 05.-09.05.2017, Wien, Österreich
  • Open Access LogoAbstract in refereed journal
    Radiotherapy and Oncology 127(2018), S136-S137
    DOI: 10.1016/S0167-8140(18)30579-6

Publ.-Id: 26784 - Permalink


Development of short-pulsed, high-field electromagnets for laser-based proton therapy
Schürer, M.; Herrmannsdörfer, T.; Karsch, L.; Kroll, F.; Masood, U.; Sobiella, M.; Pawelke, J.;
The new particle acceleration by high intensity laser promises more compact and economic accelerators for cancer treatment. However, the resulting particle beam is pulsed with an ultra-short pulse-duration (~ ps) and has a large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of laser-driven proton beams is investigated including the development of a laser accelerator and suitable beam transport. The designed magnets are intended for a compact beam transport system (gantry) which efficiently transports proton pulses (≤ 220 MeV) from generation to treatment site. For this purpose the initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and focussed by quadrupole magnets, while the energy window is selected by adjustable lead apertures. The implementation as short-pulsed (~ 1 ms) electromagnets allows to generate very high magnetic field strengths (up to 20 T) for short times, which enables the compact construction of both individual magnets and the whole gantry system. The pulse frequency of the magnets can be synchronized with that of the laser accelerator. The high field strengths demand high peak currents (up to 20 kA) and the resultant heating is dissipated by a cooling integrated into the magnets. The in-house developed pulsed magnets will enable a proton gantry 2-3 times smaller than those used in current clinical installations. Pulsed solenoids have been completely engineered and tested, and are routinely applied at laser particle accelerators. Two prototypes of a pulsed dipole and a first pulsed quadrupole were designed and manufactured, and their experimental characterization at the University Proton Therapy Dresden is in progress.
Pulsed electromagnets are crucial components of a compact gantry and after their extensive individual testing they will be combined step-by-step and used at the laser proton accelerator.
  • Poster
    Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland
    DOI: 10.1515/bmt-2017-5078
  • Open Access LogoAbstract in refereed journal
    Biomedical Engineering / Biomedizinische Technik 62(2017)Suppl. 1, S412
    DOI: 10.1515/bmt-2017-5078

Publ.-Id: 26783 - Permalink


Saturation correction in pulsed fields of high dose-per-pulse
Gotz, M.; Karsch, L.; Pawelke, J.;
Current developments in accelerator technology and beam application have the potential to bring pulsed radiation sources with very high dose-per-pulse into clinical application. In particular, laser-based particle accelerators and pencil beam scanning using synchro-cyclotrons provide intensely pulsed beams. Current methods to determine the saturation correction factor (ks) in ionization chambers are not intended for use at such high dose-per-pulse, possibly leading to an inaccurate dosimetry. We present a method based on the numerical approximation of the ionization, charge reaction and transport processes in an ionization chamber, which is able to overcome the limitations of current procedures used to calculate ks . This numerical work is supported by experimental data of a plane-parallel advanced Markus ionization chamber irradiated with a pulsed electron beam of a dose-per-pulse up to 600 mGy. At a low collection voltage of 100 V a satisfactory description of the saturation correction dependency on dose-per-pulse can be achieved using existing models and tuning their parameter values. However, at the reference voltage of 300 V this is not possible and the newly presented method shows marked improvements. Chief among the additional effects considered in the presented numerical method is the shielding of the electric field by the liberated charges, which alters the dose-per-pulse dependency of ks in a way that can not be replicated by existing approaches.
  • Poster
    Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland
    DOI: 10.1515/bmt-2017-5029
  • Open Access LogoAbstract in refereed journal
    Biomedical Engineering / Biomedizinische Technik 62(2017)Suppl. 1, S129
    DOI: 10.1515/bmt-2017-5029

Publ.-Id: 26779 - Permalink


Integration of Vessel‐Based Hyperspectral Scanning and 3D‐Photogrammetry for Mobile Mapping of Steep Coastal Cliffs in the Arctic
Salehi, S.; Lorenz, S.; Sørensen, E. V.; Zimmermann, R.; Fensholt, R.; Heincke, B. H.; Kirsch, M.; Gloaguen, R.;
Remote and extreme regions such as in the Arctic remain a challenging ground for geological mapping and mineral exploration. Coastal cliffs are often the only major well-exposed outcrops, but are mostly not observable by air/spaceborne nadir remote sensing sensors. Current outcrop mapping efforts rely on the interpretation of Terrestrial Laser Scanning and oblique photogrammetry, which have inadequate spectral resolution to allow for detection of subtle lithological differences. This study aims to integrate 3D-photogrammetry with vessel-based hyperspectral imaging to complement geological outcrop models with quantitative information regarding mineral variations and thus enables the differentiation of barren rocks from potential economic ore deposits. We propose an innovative workflow based on: 1) the correction of hyperspectral images by eliminating the distortion effects originating from the periodic movements of the vessel, 2) lithological mapping based on spectral information and 3) accurate 3D integration of spectral products with photogrammetric terrain data. The method is tested using experimental data acquired from near-vertical cliff sections in two parts of Greenland, in Karrat (Central West) and Søndre Strømfjord (South West). Root-Mean-Square Error of (6.7, 8.4) pixels for Karrat and (3.9, 4.5) pixels for Søndre Strømfjord in X and Y directions demonstrate the geometric accuracy of final 3D products and allow a precise mapping of the targets identified using the hyperspectral data contents. This study highlights the potential of using other operational mobile platforms (e.g. unmanned systems) for regional mineral mapping based on horizontal viewing geometry and multi-source and multi-scale data fusion approaches.
Keywords: Hyperspectral Remote Sensing; Digital Outcrop Models; Spectral Mobile Mapping; Scale Invariant Feature Transform Method; Multi-Source Data Integration; Near-Vertical Topography

Publ.-Id: 26778 - Permalink


Swift heavy ion shaping of oxide-structures at (sub)-micrometer scales
Ferhati, R.; Amirthapandian, S.; Fritzsche, M.; Bischoff, L.; Bolse, W.;
100 nm thin NiO-films on oxidized Si-substrates were pre-structured into small platelets of 100-5000 nm side-lengths utilizing the focused ion beam technique. The development of the individual platelets under grazing angle swift heavy ion irradiation was monitored using our "High Resolution In Situ Scanning Electron Microscope" installed in the beam line of the UNILAC ion accelerator at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt/Germany. This instrument allows us to in situ investigate the structural and compositional development of individual objects in the μm- and nm-range under swift heavy ion bombardment, from the very first ion impact up to fluences of some 1015 ions/cm-2. The sample is irradiated in small fluence steps and in between SEM-images (and EDX-scans) of one-and-the-same surface area are taken. Swift heavy ion irradiation at grazing incidence (tilt angle ≥80°) and continuous azimuthal sample rotation results in lateral shrinking and vertical growth of the platelets. At intermediate fluences additional rounding of edges and corners can be observed. At high fluences the deformation finally saturates. The deformation of the platelets is accompanied by huge sputtering of the exposed SiO2-layer, which due to the retracting edges of the platelets results in a pyramidal-like base underneath of the NiO-structures. In our presentation we will illustrate and discuss the reshaping mechanisms and underlying driving forces.
Keywords: Ion hammering, Ion shaping, NiO, Surface tension, Swift heavy ions

Downloads:

  • Secondary publication expected

Publ.-Id: 26777 - Permalink


Narrow-band Tunable Spintronic THz Emission from Ferrimagnetic Nanofilms
Awari, N.; Kovalev, S.; Fowley, C.; Rode, K.; Lau, Y.-C.; Betto, D.; Thiyagarajah, N.; Green, B.; Yildrim, O.; Lindner, J.; Fassbender, J.; Coey, M.; Deac, A.; Gensch, M.;
We report on narrow-band THz emission from ferrimagnetic Mn3-xGa nano-films based. The emission originates from coherently excited spin precession. The central frequency of the emitted radiation is determined by the anisotropy field, while the bandwidth relates to Gilbert damping. It is shown how THz emission can be used for the characterization of dynamic properties of ultra-thin magnetic films. We furthermore study the dependence of THz emission on laser power and applied external magnetic field.
Keywords: THz emission, Heusler alloys
  • Poster
    Ultrafast Magnetism Conference 2017, 09.-13.10.2017, Kaiserslautern, Germany

Publ.-Id: 26776 - Permalink


Frequency dependence of THz induced ultrafast demagnetization dynamics in amorphous ferromagnetic films
Awari, N.; Hudl, M.; Polley, D.; Kovalev, S.; Gensch, M.; Bonetti, S.;
The interaction between magnetism and light is receiving considerable interest in recent years, after the ground-breaking experiments that showed that ultrashort (~100 fs) infrared light pulses can be used to demagnetize [1] or even switch [2] the magnetization of thin film ferromagnets. However, the fundamental physical processes governing the ultrafast magnetization have proven to be challenging to understand. Two main mechanisms have been put forward as possible ways of absorbing spin angular momentum: dissipation of spins through the electronic system, via the creation of super diffusive spin-currents [3], or via the phonon bath, through spin- orbit scattering of Elliot-Yafet type [4]. Although experimental evidence for both mechanisms has been reported, their relative contributions to ultrafast demagnetization remain debated with the accurate modelling of the infrared fs laser-induced highly non-equilibrium state remaining a key obstacle.
Here, we represent our recent work on thin amorphous ferromagnetic films using unique multicycle, strong THz fields from the High-field THz user facility TELBE [5] to drive ultrafast magnetization dynamics. With the THz pulse duration of the order of the electronic and spin scattering events, it was possible to assess the influence of elementary scattering processes on the sample magnetization while a non-equilibrium current is flowing in the magnetic material. Preliminary result shows that ultrafast magnetization depends both on the lattice ordering and the frequency of THz pulses used. This effect was quadratic in the THz field strength and could be separated from the magnetization precession around the THz magnetic field. Complementary THz conductivity measurements allow us to relate these observations to defect-induced spin-lattice scattering processes of Elliot-Yafet type [6].

References:
[1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996).
[2] C. D. Stanciu et al., Phys. Rev. Lett. 99, 047601 (2007).
[3] M. Battiato et al., Phys. Rev. Lett. 105, 027203 (2010).
[4] B. Koopmans et al., Phys. Rev. Lett. 95, 267207 (2005).
[5] B. Green et. al., Sci. Rep. 5, 22256 (2016).
[6] B. Koopmans, et al. Nature Mat. 9, 259 (2010).
Keywords: ultrafast magnetization, Demagnetization, spin- orbit scattering of Elliot-Yafet type
  • Poster
    Ultrafast Magnetism Conference 2017, 09.-13.10.2017, Kaiserslautern, Germany

Publ.-Id: 26775 - Permalink


An activation database for materials used at high-intensity laser acceleration facilities
Fasso', A.; Ferrari, A.; Olsovcova, V.; Shetty, N.; Versaci, R.;
The ELI Beamlines facility will be the high-energy, high repetition-rate laser pillar of the Extreme Light Infrastructure (ELI). The goal of ELI Beamlines is to deliver ultra-short, high-energy laser pulses for the generation and applications of high-brightness X-ray sources and accelerated particles. Particle beams are expected to operate in an unprecedented energy range for laser-driven accelerators, going up to 10 GeV for electrons and 250 MeV for protons, with envisaged upgrade to higher energies (up to 50 GeV for electrons and to 3 GeV for protons). Depending on the experimental setup, the number of particles per laser shot is expected to be 109 -1011. The high energy and the large current per shot of the produced beams, together with the possibility to operate at 10 Hz laser repetition rate, require an adequate evaluation of activation in structural materials. Several radiation protection problems, such as minimization of residual dose rates and management of activated materials (short and long-term storage and eventual decommissioning), must be assessed.
A comprehensive database covering all the energies and materials of interest is being developed using FLUKA, a Monte Carlo transport code successfully benchmarked for the production of radioactive nuclides. Results for electrons and protons at different energies are presented. These results, although focused on the needs of laser-driven accelerators, are likely to be useful also when designing more conventional facilities.
  • Open Access LogoContribution to proceedings
    SATIF-13: 13th Meeting of the task- force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany
    Proceedings of SATIF-13, Paris: OECD/NEA, 422-429

Publ.-Id: 26774 - Permalink


Shielding and activation calculations around the reactor core for the MYRRHA ADS design
Ferrari, A.; Mueller, S.; Konheiser, J.; Castelliti, D.; Sarotto, M.; Stankovskiy, A.;
In the frame of the FP7 European project MAXSIMA, an extensive simulation study has been done to assess the main shielding problems in view of the construction of the MYRRHA accelerator-driven system at SCK·CEN in Mol (Belgium). An innovative method based on the combined use of the two state-of-the-art Monte Carlo codes MCNPX and FLUKA has been used, with the goal to characterize complex, realistic neutron fields around the core barrel, to be used as source terms in detailed analyses of the radiation fields due to the system in operation, and of the coupled residual radiation. The main results of the shielding analysis are presented, as well as the construction of an activation database of all the key structural materials. The results evidenced a powerful way to analyse the shielding and activation problems, with direct and clear implications on the design solutions.
Keywords: Shielding, ADS systems, Monte Carlo, FLUKA, MCNPX
  • Open Access LogoContribution to proceedings
    ICRS-13 & RPSD-2016, 13th International Conference on Radiation Shielding & 19th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society - 2016, 03.-06.10.2016, Paris, France
    EPJ Web Conferences, 153 (2017) 05001
    DOI: 10.1051/epjconf/201715305001
  • Lecture (Conference)
    ICRS-13 & RPSD-2016, 13th International Conference on Radiation Shielding & 19th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society - 2016, 03.-06.10.2016, Paris, France

Publ.-Id: 26773 - Permalink


Electromagnetically driven convection suitable for mass transfer enhancement in liquid metal batteries
Weber, N.; Nimtz, M.; Personnettaz, P.; Salas, A.; Weier, T.;
Liquid metal batteries (LMBs) were recently proposed as cheap large scale energy storage. Such devices are urgently required for balancing highly fluctuating renewable energies. During discharge, LMBs tend to form intermetallic phases. These do not only limit the up-scalability, but also the efficiency of the cells. Generating a mild fluid flow in the fully liquid cell will smoothen concentration gradients and minimise the formation of intermetallics. In this context we study electro-vortex flow numerically. We simulate a recent LMB related experiment and discuss how the feeding lines to the cell can be optimised to enhance mass
transfer. The Lorentz forces have to overcome the stable thermal stratification in the cathode of the cell; we show that thermal effects may reduce electro-vortex flow velocities considerable. Finally, we study the influence of the Earth magnetic field on the flow.

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  • Secondary publication expected from 17.07.2019

Publ.-Id: 26772 - Permalink


Residual activity evaluation: benchmark and intercomparison between ANITA, FISPACT, FLUKA and PHITS codes
Firpo, G.; Viberti, C. M.; Ferrari, A.; Frisoni, M.;
The activity of residual nuclides dictates the radiation fields in periodic inspections/repairs (maintenance periods) and dismantling operations (decommissioning phase) of accelerator facilities (i.e., medical, industrial, research) and nuclear reactors. Therefore, the correct prediction of the material activation allows for a more accurate planning of the activities, in line with the ALARA (As Low As Reasonably Achievable) principles. The scope of the present work is to show the results of a comparison between residual total specific activity versus a set of cooling time instants (from zero up to 10 years after irradiation) as obtained by two analytical (FISPACT and ANITA) and two Monte Carlo (FLUKA and PHITS) codes, making use of their default nuclear data libraries. A set of ~40 irradiating scenarios is considered, i.e. neutron and proton particles of different energies, ranging from zero to many hundreds MeV, impinging on pure elements or materials of standard composition typically used in industrial applications (namely, AISI SS316 and Portland concrete). In some cases, experimental results were also available for a more thorough benchmark.
Keywords: Activation, Monte Carlo, Benchmarks, Decommissioning
  • Open Access LogoContribution to proceedings
    ICRS-13 & RPSD-2016, 13th International Conference on Radiation Shielding & 19th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society - 2016, 03.-06.10.2016, Paris, France
    EPJ Web of Conferences 153, (2017), 02006
    DOI: 10.1051/epjconf/201715302006
  • Lecture (Conference)
    ICRS-13 & RPSD-2016, 13th International Conference on Radiation Shielding & 19th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society - 2016, 03.-06.10.2016, Paris, France
  • Poster
    SATIF-13: 13th Meeting of the task- force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany

Publ.-Id: 26771 - Permalink


Herstellung und Charakterisierung von Spin-Hall Effekt-basierten Nano-Mikrowellenoszillatoren
Hache, T.;
Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs. These are devices where the current density is increased locally due to lateral confinement. Hence, the spin current generated by the spin Hall effect can create well defined hot-spots for auto-oscillations.
We present BLS measurements of auto-oscillations in Co60Fe20B20(5 nm)/Pt(7 nm) based samples with two interacting, neighbouring nanoconstrictions.
The precession amplitude in these samples can be driven far from equilibrium, resulting in clear nonlinear signatures in the spinwave spectra. The spatial distributions of the observed modes and current dependencies are shown.
Keywords: spin Hall, spin Hall nano-oscillators, Spin-Hall Nanooszillatoren, spin current, auto-oscillations, Autooszillationen
  • Master thesis
    Westsächsische Hochschule Zwickau, 2017, 2017
    Mentor: Prof. Dr. Wieland Zahn, Dr. Helmut Schultheiss
    96 Seiten
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, TU Berlin, Deutschland

Publ.-Id: 26770 - Permalink


Shielding assessment for the HED Science Instrument at the European XFEL
Ferrari, A.; Nakatsutsumi, M.; Pelka, A.; Tschentscher, T.; Cowan, T.;
Interaction with plasma of high-power, high-intensity lasers of multi-TW and PW class always produces ‘hot’ electrons with a quasi-Maxwellian energy spectrum, with temperatures between about 10 keV and several MeV for intensities ranging from 1016 W/cm2 up to about 1022 W/cm2. Those electrons interact in turn with the target and the surrounding materials, producing Bremsstrahlung and possibly photo-neutrons. The resulting radiation field is present in all laser-plasma experiments, and drives the shielding design of every facility dedicated to high energy density research.
The proper definition of the radiation source term is a challenging aspect, and the shielding cannot therefore be designed with the conventional tools used in nuclear and accelerator physics. Different, complementary approaches are possible: relying only on analytical formulas, combining those predictions with experimental results to characterize source terms in input to established Monte Carlo codes, and/or interfacing those codes with specialized Particle-In-Cell programs. At the Helmholtz-Beamline of the European XFEL, the shielding design of the High Energy Density (HED) Physics Instrument has been evaluated by using analytical calculations, cross-checked with measurements done at the DRACO laser of the Helmholtz-Zentrum Dresden-Rossendorf. In this work the characterization of the radiation fields and the resulting shielding solutions are summarized.
Keywords: Shielding, Source Terms, HIBEF, HED Instrument
  • Open Access LogoContribution to proceedings
    SATIF-13, 13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany
    Proceedings of SATIF-13, Paris: OECD-NEA
  • Lecture (Conference)
    SATIF-13, 13th Meeting of the task- force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany

Publ.-Id: 26769 - Permalink


Magnetic e-skins enabled somatic and touchless interactive devices
Jin, G.; Xu, W.; Gilbert Santiago, C. B.; Changan, W.; Shengqiang, Z.; Jürgen, F.; Denys, M.;
Humans skin provide perceptions of the temperature of objects, strain and pressure on skin, friction for holding objects, which help humans interact very precisely with unstructured surroundings [1]. Electronic skins [2-4] allow for the realization of similar sensing functions and also having the possibility of integrating other sensing functions beyond humans, for example, touchless feeling. Very recently we demonstrated magnetosensitive e-skins, which is an important step towards the realization of artificial magnetoception for humans [5,6].
Here, we present a magnetic e-skin that not only has the ability to detect the position and movement of magnetic objects in a touchless mode but also is sensitive to mechanical forces. The magnetic skin is a stack of a magnetoresistive (MR) sensor layer and a surface-pyramid-structured magnetic foil. The MR sensor of the magnetic skin is sensitive to the surrounding magnetic field change. When the surface of the target object is fixed with a magnet, the magnetic e-skin will have the ability to detect the distance change between itself and the target object in a touchless mold. Furthermore, when a pressure is applied on the surface of the magnetic e-skin, the induced distance change between the MR sensor and the magnetic foil will also result in the resistance change of the MR sensor. As a result, this magnetic e-skin also has the ability to detect the pressure change applied on its surface in a touch mold (somatic interaction). This multi-functional magnetic e-skin will hold a great promise for the realization of advanced humanoid robots, biomedical prostheses, and surgical electronic gloves.

1. A. Zimmerman, et al. Science 346, 950 (2014).
2. T. Someya, et al. Proc. Natl. Acad. Sci. U.S.A. 101, 9966 (2004).
3. Z. Ma, et al. Science 333, 830 (2011).
4. Z. Bao, et al. Adv. Mater. 25, 5997 (2013).
5. M. Melzer, et al, Nat. Commun. 6, 6080 (2015).
6. D. Makarov, et al., Appl. Phys. Rev. 3, 011101 (2016).
Keywords: e-skin, pressure sensor, flexible, magnetic sensor, multi-functional
  • Lecture (Conference)
    2017 MRS Fall Meeting, 26.11.-01.12.2017, Boston, America

Publ.-Id: 26768 - Permalink


Bridging from Brain to Tumor imaging: (S)- and (R)-[18F]Fluspidine for investigation of Sigma-1 Receptors in Tumor-bearing Mice
Kranz, M.; Bergmann, R.; Kniess, T.; Belter, B.; Neuber, C.; Cai, Z.; Deng, G.; Fischer, S.; Steinbach, J.; Zhou, J.; Huang, H.; Brust, P.; Deuther-Conrad, W.; Pietzsch, J.;
Sigma-1-receptors (Sig1R) are highly expressed in various human cancer cells and hence imaging of this target with positron emission tomography (PET) can contribute to a better understanding of tumor pathophysiology and support the development of antineoplastic drugs. Two Sig1R-specific radiolabeled enantiomers (S)-(−)- and (R)-(+)-[18F]fluspidine were investigated in several tumor cell lines including melanoma, squamous cell/epidermoid carcinoma, prostate carcinoma and glioblastoma. Dynamic PET scans were performed in mice to investigate the suitability of both radiotracers for tumor imaging. The Sig1R expression in the respective mice tumors was confirmed by Western blot. Rather low radiotracer uptake was found in heterotopically implanted tumors. Therefore, a brain tumor model (U87-MG) with orthotopic implantation was chosen to investigate the suitability of the two Sig1R radiotracers for brain tumor imaging. A high tumor uptake as well as a favorable tumor-to background ratio was found. These results suggest that Sig1R PET imaging of brain tumors with [18F]fluspidine could be possible. Further studies with this tumor model will be performed to confirm specific binding and the integrity of the blood-brain barrier (BBB).
Keywords: : [18F]fluspidine, carcinoma, glioblastoma, melanoma, Sigma-1 receptor, dedicated small animal PET/CT

Publ.-Id: 26767 - Permalink


The timing of deglaciation on the northern Swiss Plateau inferred by cosmogenic 10Be surface exposure dating
Groos, A. R.; Struck, J.; Wüthrich, L.; Veit, H.; Gnägi, C.; Merchel, S.; Scharf, A.; Rugel, G.; Zech, R.;
During the Last Glacial Maximum (19-30 ka) extensive ice caps and large outlet glaciers covered the alpine valleys and forelands in the Swiss Alps (e.g. Ivy-Ochs, 2015). The former Rhône Glacier expanded onto the Swiss Plateau, was deflected and bounded by the Jura Mountain Range, and reached 'Wangen an der Aare' (Niederbipp Stade). Various studies have investigated respective glacial deposits, but the maximum extent of glaciation and the exact timing of deglaciation is still under discussion (Wüthrich et al. 2018, 2017). We investigated 18 additional samples from 15 erratic boulders from the region by cosmogenic 10Be surface exposure dating to constrain the timing of deglaciation. The 10Be exposure ages from seven different locations vary mainly between 17-30 ka. Five outliers show three younger ages (4 ka, 7 ka, and 10 ka, respectively) and two older ages (42 ka and 87 ka, respectively) than expected, proofing again that geomorphological processes and inheritance can affect the exposure ages of the erratic boulders.
Ivy-Ochs, S. (2015). Glacier variations in the European Alps at the end of the Last Glaciation. Cuadernos de Investigación Geográfica 41, 295–315.
Wüthrich, L., Brändli, C., Braucher, R., Veit, H., Haghipour, N., Terrizzano, C., Christl, M., Gnägi, C., Zech, R. (2018): 10Be depth profiles in glacial sediments on the Swiss Plateau: deposition age, denudation and (pseudo-)inheritance, E&G Quaternary Sci. J., 66, 57–68.
Wüthrich, L., Garcia Morabito, E., Zech, J., Gnägi, C., Trauerstein, M., Veit, H., Merchel, S., Scharf, A., Rugel, G., Christl, M., Zech, R. (under review, 2017): 10Be surface exposure dating of the last deglaciation in the Aare Valley, Switzerland. Swiss Journal of Geosciences.
Keywords: AMS, glaciation, LGM
  • Poster
    European Geosciences Union (EGU) General Assembly, 08.-13.04.2018, Wien, Österreich

Publ.-Id: 26766 - Permalink


Mesoscale Dzyaloshinskii-Moriya interaction in curvilinear geometries: one-dimensional and two-dimensional cases
Volkov, O.; Kravchuk, V.; Sheka, D.; Makarov, D.; Fassbender, J.; Gaididei, Y.; Roessler, U.; van den Brink, J.; Fuchs, H.; Fangohr, H.;
A broken chiral symmetry in a magnetic system manifests itself as the appearance of either periodical (e.g. helical or cycloid modulations [1]) or localized magnetization structures (e.g. chiral domain walls and skyrmions [2]). The origin of these magnetic textures is spin-orbit Dzyaloshinskii-Moriya interaction (DMI), which is observed in bulk magnetic crystals with low symmetry [3-4] or at interfaces between a ferromagnet and a nonmagnetic material with strong spin-orbit coupling [5]. This DMI is intrinsic to the crystal or layer stack. Recently, it was reported that geometrically-broken symmetry in curvilinear magnetic systems leads to the appearance of curvature-driven DMI-like chiral contribution in the energy functional [6]. This chiral term is determined by the sample geometry, e.g local curvature and torsion, and is therefore extrinsic to the crystal or layer stack. It reveals itself in the domain wall pinning at a localized wire bend and is responsible for the existence of magnetochiral effects in curvilinear magnetic
systems, e.g. in ferromagnetic Möbius rings, nanorings and helix wires [7].
The intrinsic and extrinsic DMI act at different length scales and, hence, their combination can be referred to as a mesoscale DMI. The symmetry and strength of this term are determined by the geometrical and material properties of the three-dimensional (3D) object. Although, intrinsic and extrinsic terms separately are broadly investigated, their synergistic impact is not known yet. Here, we study the properties of the mesoscale DMI in a 1D curvilinear wire and in 2D curvilinear shells. We derive the general expressions for the mesoscale DMI term and analyze the magnetization states which arise in a helix wire and in a thin spherical shell with intrinsic DMI.
[1] I. E. Dzyaloshinskii, Sov. Phys. JETP, vol. 19, pp. 964–971 (1964).
[2] N. Nagaosa and Y. Tokura, Nature Nanotechnology, vol. 8, pp. 899–911 (2013).
[3] I. E. Dzialoshinskii, Sov. Phys. JETP, vol. 5, pp. 1259–1272 (1957).
[4] T. Moriya, Phys. Rev. Lett., vol. 4, pp. 228–230 (1960).
[5] A. Fert, Materials Science Forum, vol. 59-60, pp. 439–480 (1990).
[6] Y. Gaididei, V. P. Kravchuk, and D. D. Sheka, Phys. Rev. Lett., vol. 112, p. 257203 (2014).
[7] R. Streubel, P. Fischer, F. Kronast, V. P. Kravchuk, D. D. Sheka, Y. Gaididei, O. G. Schmidt, and D. Makarov, Journal of Physics D: Applied Physics, vol. 49, p. 363001 (2016)
Keywords: Dzyaloshinskii-Moriya interaction, curved geometry, helical wire, magnetochirality, mesoscale, skyrmion
  • Lecture (Conference)
    TOP-SPIN 3: Spin and Topological Phenomena in Nanostructures - Towards Topological Materials Science, 25.-28.04.2017, Dresden, Germany

Publ.-Id: 26765 - Permalink


Mesoscale Dzyaloshinskii-Moriya interaction: one-dimensional and two-dimensional cases
Volkov, O.; Kravchuk, V.; Sheka, D.; Makarov, D.; Fassbender, J.; Gaididei, Y.; Roessler, U.; van den Brink, J.; Fuchs, H.; Fangohr, H.; Kosub, T.;
A broken chiral symmetry in a magnetic system manifests itself as the appearance of either periodical (e.g. helical or cycloid modulations [1-3]) or localized magnetization structures (e.g. chiral domain walls and skyrmions [3-6]). The origin of these magnetic textures is spin-orbit Dzyaloshinskii-Moriya interaction (DMI), which is observed in bulk magnetic crystals with low symmetry [7-8] or at interfaces between a ferromagnet and a nonmagnetic material with strong spin-orbit coupling [9]. This DMI is intrinsic to the crystal or layer stack. Recently, it was reported that geometrically-broken symmetry in curvilinear magnetic systems leads to the appearance of curvature-driven DMI-like chiral contribution in the energy functional [10-14]. This chiral term is determined by the sample geometry, e.g local curvature and torsion, and is therefore extrinsic to the crystal or layer stack. It reveals itself in the domain wall pinning at a localized wire bend [15] and is responsible for the existence of magnetochiral effects in curvilinear magnetic systems, e.g. in ferromagnetic Möbius rings [16], nanorings [11] and helix wires [12, 13, 17].
The intrinsic and extrinsic DMI act at different length scales and, hence, their combination can be reffered to as a mesoscale DMI. The symmetry and strength of this term are determined by the geometrical and material properties of a three-dimensional (3D) object. Although, intrinsic and extrinsic terms separately are broadly investigated, their synergistic impact is not known yet. Here, we study the properties of the mesoscale DMI in a 1D curvilinear wire and in 2D curvilinear shells. We derive the general expressions for the mesoscale DMI term and analyse the magnetization states which arise in a helix wire and in a thin spherical shell with intrinsic DMI.
The clear cut comparison a helix wire with a straight wire with homogeneous tangential intrinsic DMI reveals: (i) The magnetic states of a curved wire is governed by a single vector of magnetochirality — a vector of the mesoscale DMI — originating from the vector sum of the intrinsic and extrinsic DMI vectors; (ii) The symmetry and period of the chiral structures are determined by the strength and direction of the vector of the mesoscale DMI, which depends on both material and geometrical parameters of a curvilinear wire (Figure, panel a); (iii) Similarly to the case of the straight wire [18] both types of phase transitions (of the first and the second order) are found in the helix. The appearance of
each state can be determined by measuring of the average values of the magnetization components and/or by establishing space Fourier spectra of the coordinate-dependent magnetic signals from the helices.
In the case of 2D curvilinear magnetic shells, it’s shown the existence of a skyrmion solution on a thin magnetic spherical shell even without any additional intrinsic DMI [19]. Such skyrmions can be stabilized by curvature effects only, namely by the curvature-induced, extrinsic DMI (Figure, panel b). In addition to the striking difference to the case of a planar skyrmion, magnetic skyrmions on a spherical shell are topologically trivial. This is due to a shift of the topological index of the magnetization field caused by topology of the surface itself. As a result, a skyrmion on a spherical shell can be induced by a uniform external magnetic field. Further, the curvature stabilized skyrmions are very small, with a lateral extension of several nm only (Figure, panel b). The size of the skyrmion core can be tailored e.g. by an additional intrinsic DMI (Figure, panel c). One can note here, that the curvature stabilized skyrmions are always of Neel type (at least, for a surface of rotation). Due to their small sizes and ease in manipulating using homogeneous magnetic fields, we envision those topological objects to be relevant for the realization of on-demand tunable topological logic. Indeed, topological Hall effect can be digitally switched on or off by exposing a sample withferromagnetic spherical shells submerged by a nonmagnetic conductor.
References:
[1] I. E. Dzyaloshinskii, “Theory of helicoidal structures in antiferromagnets. i. nonmetals,” Sov. Phys. JETP, vol. 19, pp. 964–971 (1964).
[2] A. Bogdanov, U. Rössler, and C. Pfleiderer, “Modulated and localized structures in cubic helimagnets,” Physica B: Condensed Matter, vol. 359-361, pp. 1162–1164 (2005).
[3] S. Rohart and A. Thiaville, “Skyrmion confinement in ultrathin film nanostructures in the presence of dzyaloshinskii-moriya interaction,” Physical Review B, vol. 88, p. 184422 (2013).
[4] A. Thiaville, S. Rohart, É. Jué, V. Cros, and A. Fert, “Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films,” EPL (Europhysics Letters), vol. 100, p. 57002 (2012).
[5] A. Bogdanov and A. Hubert, “The stability of vortex-like structures in uniaxial ferromagnets,” Journal of Magnetism and Magnetic Materials, vol. 195, pp. 182–192 (1999).
[6] N. Nagaosa and Y. Tokura, “Topological properties and dynamics of magnetic skyrmions,” Nature Nanotechnology, vol. 8, pp. 899–911 (2013).
[7] I. E. Dzialoshinskii, “Thermodynamic theory of “weak” ferromagnetism in antiferromagnetic substances,” Sov. Phys. JETP, vol. 5, pp. 1259–1272 (1957).
[8] T. Moriya, “New mechanism of anisotropic superexchange interaction,” Phys. Rev. Lett., vol. 4, pp. 228–230 (1960).
[9] A. Fert, “Magnetic and transport properties of metallic multilayers,” Materials Science Forum, vol. 59-60, pp. 439–480 (1990).
[10] Y. Gaididei, V. P. Kravchuk, and D. D. Sheka, “Curvature effects in thin magnetic shells,” Phys. Rev. Lett., vol. 112, p. 257203 (2014).
[11] D. D. Sheka, V. P. Kravchuk, and Y. Gaididei, “Curvature effects in statics and dynamics of low dimensional magnets,” Journal of Physics A: Mathematical and Theoretical, vol. 48, p. 125202 (2015).
[12] D. D. Sheka, V. P. Kravchuk, K. V. Yershov, and Y. Gaididei, “Torsion-induced effects in magnetic nanowires,” Phys. Rev. B, vol. 92, p. 054417 (2015).
[13] O. V. Pylypovskyi, D. D. Sheka, V. P. Kravchuk, K. V. Yershov, D. Makarov, and Y. Gaididei, “Rashba torque driven domain wall motion in magnetic helices,” Scientific Reports, vol. 6, p. 23316 (2016).
[14] R. Streubel, P. Fischer, F. Kronast, V. P. Kravchuk, D. D. Sheka, Y. Gaididei, O. G. Schmidt, and D. Makarov, “Magnetism in curved geometries (topical review),” Journal of Physics D: Applied Physics, vol. 49, p. 363001 (2016).
[15] K. V. Yershov, V. P. Kravchuk, D. D. Sheka, and Y. Gaididei, “Curvature-induced domain wall pinning,” Phys. Rev. B, vol. 92, p. 104412 (2015).
[16] O. V. Pylypovskyi, V. P. Kravchuk, D. D. Sheka, D. Makarov, O. G. Schmidt, and Y. Gaididei, “Coupling of chiralities in spin and physical spaces: The Möbius ring as a case study,” Phys. Rev. Lett., vol. 114, p. 197204 (2015).
[17] K. V. Yershov, V. P. Kravchuk, D. D. Sheka, and Y. Gaididei, “Curvature and torsion effects in spin-current driven domain wall motion,” Phys. Rev. B, vol. 93, p. 094418 (2016).
[18] M. Heide, G. Bihlmayer, and S. Blügel, “Non-planar dzyaloshinskii spirals and magnetic domain walls in noncentrosymmetric systems with orthorhombic anisotropy,” Journal of Nanoscience and Nanotechnology, vol. 11,
pp. 3005–3015 (2011).
[19] V. P. Kravchuk, U. K. Rößler, O. M. Volkov, D. D. Sheka, J. van den Brink, D. Makarov, H. Fuchs, H. Fangohr, and Y. Gaididei, “Topologically stable magnetization states on a spherical shell: Curvature-stabilized skyrmions,” Phys. Rev. B, vol. 94, p. 144402 (2016).
Keywords: Dzyaloshinskii-Moriya interaction, curved geometry, helical wire, magnetochirality, mesoscale, skyrmion
  • Poster
    2017 IEEE International Magnetics Conference, 24.-28.04.2017, Dublin, Ireland

Publ.-Id: 26764 - Permalink


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