Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41396 Publications

Concept of a compact gantry for laser based proton therapy.

Karsch, L.; Bussmann, M.; Enghardt, W.; Kroll, F.; Masood, U.; Pawelke, J.

  • Poster
    52th Particle Therapy Cooperative Group (PTCOG) Meeting, 02.-08.06.2013, Essen, Deutschland
  • Contribution to proceedings
    52th Particle Therapy Cooperative Group (PTCOG) Meeting, 02.-08.06.2013, Essen, Deutschland
    Proceedings of the 52th Particle Therapy Cooperative Group (PTCOG) Meeting, 312

Permalink: https://www.hzdr.de/publications/Publ-21528
Publ.-Id: 21528


Einfluss der Pulslänge auf die Sättigungskorrektur von Ionisationskammern in gepulsten Strahlungsfeldern.

Gotz, M.; Karsch, L.; Pawelke, J.

  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
  • Contribution to proceedings
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
    H. Treuer (Ed.): Medizinische Physik 2013, Deutsche Gesellschaft für Medizinische Physik e. V., ISBN 978-3-9816002-1-6, 318-321

Permalink: https://www.hzdr.de/publications/Publ-21527
Publ.-Id: 21527


Optimierung der Bestrahlungsplanungsstrategie für laserbeschleunigte Protonen.

Findeisen, A.; Karsch, L.; Masood, U.; Pawelke, J.

  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
  • Contribution to proceedings
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
    H. Treuer (Ed.): Medizinische Physik 2013, Deutsche Gesellschaft für Medizinische Physik e. V., ISBN 978-3-9816002-1-6, 714-715

Permalink: https://www.hzdr.de/publications/Publ-21526
Publ.-Id: 21526


Proton therapy in Dresden: present and future

Pawelke, J.

  • Invited lecture (Conferences)
    International Conference on the Future of Radiation Oncology: Imaging, Dosimetry, Biology and Therapy (7th Berder Workshop), 25.-28.09.2013, Berder Island, France

Permalink: https://www.hzdr.de/publications/Publ-21525
Publ.-Id: 21525


Review on radiobiological studies using laser driven particle beams:From in vitro experiments to human tumor irradiations on mice

Pawelke, J.

  • Invited lecture (Conferences)
    International Workshop on Microbeam Probes of Cellular Radiation Response (11th Microbeam Workshop), 03.-04.10.2013, Bordeaux, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-21524
Publ.-Id: 21524


Development of a compact particle therapy facility with laser- driven ion beams via novel pulse powered gantry systems

Masood, U.; Bussmann, M.; Baumann, M.; Cowan, T. E.; Enghardt, W.; Herrmannsdörfer, T.; Hofmann, K. M.; Kaluza, M.; Karsch, L.; Kroll, F.; Schramm, U.; Schürer, M.; Wilkens, J. J.; Pawelke, J.

  • Contribution to proceedings
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz
    Proceedings of the Joint Conference in Medical Physics, 27-28
  • Lecture (Conference)
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-21523
Publ.-Id: 21523


A treatment planning study to assess the feasibility and the limitations of laser-driven proton therapy

Hofmann, K. M.; Masood, U.; Pawelke, J.; Wilkens, J. J.

  • Contribution to proceedings
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz
    Proceedings of the Joint Conference in Medical Physics, 29
  • Lecture (Conference)
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-21522
Publ.-Id: 21522


Wechselwirkung langsamer hochgeladener Ionen mit Ionenkristalloberflächen und ultradünnen Kohlenstoffmembranen

Wilhelm, R. A.

In der vorliegenden Arbeit wurde die Strukturbildung durch Einzeleinschlag von langsamen hochgeladenen Ionen (v < 5·10^5 m/s, Q < 40) auf Ionenkristalloberflächen und freistehenden amorphen Kohlenstofffolien untersucht. Mittels experimenteller Methoden der Rasterkraft-, Transmissionselektronen- und Heliumionenmikroskopie wurden die in jüngster Zeit gewonnenen Modellbeschreibungen für Nanostrukturbildung an Oberflächen erweitert. Beim Auftreffen eines langsamen hochgeladenen Ions auf die (001)-Oberfläche von KCl können Nanostrukturen mit Ausdehnungen bis zu einigen 10nm entstehen. Die damit verknüpften Desorptionsausbeuten von bis zu 3000 Atomen pro Ion aus der Oberfläche werden vor allem durch die Deposition der potentiellen Energie in sehr oberflächennahe Schichten erklärt. Die kinetische Energie der Ionen wirkt jedoch unterstützend auf die Entstehung und Vergrößerung der Lochstrukturen. Die Entstehung der Strukturen durch die potentielle Energie kann konsistent im Bild der defektinduzierten Desorption erklärt werden.
Für die CaF2(111)-Oberfläche konnte gezeigt werden, dass auch unter ununterbrochenen Ultrahochvakuumbedingungen Nanohügel durch Ionenbeschuss erzeugt werden können. Die Größenverteilung beobachteter Nanohügel ist dabei jedoch um einen Faktor 3 kleiner im Vergleich zu atmosphärenexponierten Proben. Der Einfluss der Atmosphäre auf die beobachteten Strukturgrößen wird diskutiert. Für niedrigere Ladungszustände als nötig für Nanohügelerzeugung wurden ioneninduzierte Kristalldefekte durch nasschemisches Ätzen der Oberfläche nachgewiesen. Diese Tatsache verbindet die Beschreibung der Strukturbildung durch elektronische Anregungen in Alkali- und Erdalkalihaliden.
Für den Durchgang von hochgeladenen Ionen durch 1 nm dicke, freistehende und amorphe Kohlenstofffolien zeigte sich, dass Poren durch Einzelioneneinschlag entstehen, sobald ein Schwellwert von etwa Q = 25 in der Ionenladung überschritten wurde. Erstmalig konnte gezeigt werden, dass sich bei der Transmission der Ionen zwei unterschiedliche Ladungszustandsverteilungen bilden. Die Ausbildung der beiden Verteilungen wird durch einen stark stoßparameterabhängigen Ladungsaustausch beschrieben. Neben dem Einfluss der potentiellen Energie bei der Porenbildung ist auch der Einfluss der kinetischen Energie untersucht worden. Um den Anteil nuklearer und elektronischer kinetischer Energieverluste in Abhängigkeit des Ionenladungszustandes abzuschätzen, wurde ein Modell im Rahmen der Beschreibung statistischer Atome bzw. Ionen aufgestellt. Auf Basis dieses Modells wird der Einfluss der kinetischen Energiedeposition und die damit verbunde- ne Synergie aus potentieller und kinetischer Energie bei der Strukturbildung diskutiert.

The formation of nano-structures due to the impact of individual slow highly charged ions (v < 5 · 105 m/s, Q < 40) on surfaces of ionic crystals and 1 nm thick, freestanding and amorphous carbon membranes is investigated in this work. By an experimental approach using atomic force, transmission elec- tron and helium ion microscopy recent model descriptions for the formation processes of highly charged ion induced nano-structures are expanded. Upon impact of slow highly charged ions on the (001)-surface of KCl pit-like structures with sizes up to a few 10nm are found. The corresponding desorption yields of a few thousand atoms per ion are mainly attributed to the deposition of potential energy in a shallow region near the surface. The kinetic energy has only a minor effect on the formation processes. The structure formation due to potential energy deposition is described consis- tently in the framework of a defect induced desorption model.
For the CaF2(111) surface it is shown, that even without breaking the vac- uum between irradiation and analyses ion induced nano-hillocks are present. However, the sizes of the nano-hillocks are about a factor of 3 smaller than the sizes after exposure to atmosphere. The influence of the atmosphere conditions on the structure sizes is discussed. For lower charge states than needed for nano-hillock formation ion-induced defects are revealed by wet- chemical etching of the exposed surfaces. The existence of defects for lower charge states combines the model descriptions of nano-structure formation by strong electronic excitations for alkali and earth-alkali halide surfaces. Pore formation due to highly charged ion impact on 1 nm thick, freestanding and amorphous carbon films is observed for ions with a charge state above a threshold of about Q = 25. It has been shown for the first time that two distinct exit charge state distributions are formed upon transmission of the ions through the membrane. The formation of the distributions is explained
by a strongly impact parameter dependent charge exchange. Besides the influence of the potential energy on the pore formation also the importance of the kinetic energy is investigated. To distinguish between nuclear and electronic losses in the case of highly charged ions at low velocities a model for charge state dependent energy loss is proposed. Based on the descrip- tion of statistical atoms and ions, respectively, the synergy of potential and kinetic energy upon nano-structure formation is discussed.

Related publications

  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Prof. Jürgen Fassbender / Dr. Stefan Facsko
    149 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21521
Publ.-Id: 21521


In vivo dose response to laser driven electron beams

Oppelt, M.; Baumann, M.; Bergmann, R.; Beyreuther, E.; Brüchner, K.; Hartmann, J.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Lessmann, E.; Nicolai, M.; Reuter, M.; Sävert, A.; Schnell, M.; Schürer, M.; Pawelke, J.

  • Contribution to proceedings
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz
    Proceedings of the Joint Conference in Medical Physics, 191
  • Lecture (Conference)
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-21520
Publ.-Id: 21520


Laserbasierte Partikeltherapie.

Pawelke, J.

Laserbasierte Partikeltherapie.

  • Invited lecture (Conferences)
    Symposium “Innovationen in der Radioonkologie”, 24.09.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21519
Publ.-Id: 21519


Development of short-pulsed high-field electromagnetic dipoles for laser-based proton therapy

Schürer, M.; Herrmannsdörfer, T.; Karsch, L.; Kroll, F.; Masood, U.; Pawelke, J.

Introduction
During the last years, the new technology of laser based particle acceleration was developed at such a rate that medical application for cancer therapy becomes conceivable. Promising more compact and economic accelerators, the laser technology however generates intense ultra-short (~ ps) pulsed proton beams with large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of such pulsed proton beams is investigated including the development of a laser accelerator and a suitable beam transport.
Methods
A compact beam transport system was designed enabling an efficient transport of proton pulses from generation to treatment site. The initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and formed by quadrupole magnets, whereas the spectrum is shaped by adaptable lead apertures. For realization, electromagnetic dipoles with magnetic fields of up to 10 T are required to deflect up to 220 MeV protons. These field strengths are achieved by in-house developed non-ferrous dipoles that consist of 80 copper coils in 12 layers and are operated at peak currents of up to 20 kA. To handle the high currents and the generated heat the dipoles are externally cooled and operated in 1 ms short pulses synchronized with the laser repetition frequency.
Results
The prototype of a short-pulsed electromagnetic dipole magnet was designed and manufactured. Results of the experimental characterization and first performance tests at a conventional Tandem accelerator are under way.
Conclusion
Pulsed electromagnetic dipoles as crucial components of a compact beam line for laser-accelerated protons are engineered. Following validation of their suitability at a conventional accelerator the dipoles will be implemented and further tested at a laser accelerator. Together with improvement of the dipole the design of quadrupoles will start.

  • Open Access Logo Abstract in refereed journal
    Biomedical Engineering / Biomedizinische Technik 59(2014)Suppl 1, 891
    DOI: 10.1515/bmt-2014-5011
    Cited 1 times in Scopus
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, 08.-10.10.2014, Hannover, Deutschland
  • Poster
    48. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Hannover, Germany, 8-10 Oct 2014, 08.-10.10.2014, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21518
Publ.-Id: 21518


Development of laser-driven proton beam therapy

Masood, U.; Bussmann, M.; Cowan, T.; Enghardt, W.; Herrmannsdörfer, T.; Kaluza, M.; Krause, M.; Pawelke, J.; Sauerbrey, R.; Schramm, U.; Baumann, M.

  • Open Access Logo Abstract in refereed journal
    Annals of Oncology 25(2014)Suppl 4, iv546-iv547
    DOI: 10.1093/annonc/mdu358.3
  • Lecture (Conference)
    Congress of the European Society for Medical Oncology (ESMO) on “Precision Medicine in Cancer Care”, 26.-30.09.2014, Madrid, Spanien
  • Poster
    Congress of the European Society for Medical Oncology (ESMO) on “Precision Medicine in Cancer Care”, 26.-30.09.2014, Madrid, Spanien

Permalink: https://www.hzdr.de/publications/Publ-21517
Publ.-Id: 21517


Negative magneto- and electroresistance of silicon films with superconducting nanopreciptates - the role of inelastic cotunneling

Heera, V.; Fiedler, J.; Schmidt, B.; Hübner, R.; Voelskow, M.; Skrotzki, R.; Skorupa, W.

The electronic transport properties of insulating Si:Ga films with superconducting, Ga-rich nanopreciptates are investigated in dependence on temperature, current, and magnetic field. The large negative magnetoresistance, observed below the critical temperature, can be explained by Cooper pair breaking and subsequent tunneling of the fermionic quasiparticles. Localization due to quantum interferences of bosons or fermions, as recently discussed, seems not to be the reason for the insulating state and the large magnetoresistance. Cooper pair tunneling is blocked by the high Coulomb barrier. The quasiparticles can overcome the barrier by inelastic cotunneling that results in nonlinear current-voltage characteristics and negative electroresistance. Since the experimental results obtained for the Si:Ga film resemble that of many other films with superconducting nanoprecipitates the conclusions drawn here could be quite general.

Keywords: disordered films; superconducting precipitates; insulating state; magnetotransport measurement; negative magnetoresistance; inelastic cotunneling

Related publications

Permalink: https://www.hzdr.de/publications/Publ-21516
Publ.-Id: 21516


Comparison study of in vivo dose response to laser driven versus conventional electron beam.

Oppelt, M.; Baumann, M.; Bergmann, R.; Beyreuther, E.; Brüchner, K.; Hartmann, J.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Reuter, M.; Richter, C.; Sävert, A.; Schürer, M.; Schnell, M.; Woithe, J.; Kaluza, M.; Pawelke, J.

The long-term goal to integrate laser-based particle accelerators into radiotherapy clinics not only requires technological development of high-intensity lasers and new techniques for beam detection and dose delivery, but also characterization of the biological consequences of this new particle beam quality, i.e. ultra-short, ultra-intense pulses. In the present work, we describe successful in vivo experiments with laser-driven electron pulses by utilization of a small tumour model on the mouse ear for the human squamous cell carcinoma model FaDu. The already established in vitro irradiation technology at the laser system JETI was further enhanced for 3D tumour irradiation in vivo in terms of beam transport, beam monitoring, dose delivery and dosimetry in order to precisely apply a prescribed dose to each tumour in full-scale radiobiological experiments. Tumour growth delay was determined after irradiation with doses of 3 and 6 Gy by laser-accelerated electrons. Reference irradiation was performed with continuous electron beams at a clinical linear accelerator in order to both validate the dedicated dosimetry employed for laser-accelerated JETI electrons and above all review the biological results. No significant difference in radiation-induced tumour growth delay was revealed for the two investigated electron beams. These data provide evidence that the ultra-high dose rate generated by laser acceleration does not impact the biological effectiveness of the particles.

Permalink: https://www.hzdr.de/publications/Publ-21515
Publ.-Id: 21515


Scaling of TNSA-accelerated proton beams with laser energy and focal spot size

Obst, L.; Zeil, K.; Metzkes, J.; Kraft, S.; Schramm, U.

By focusing an ultra-short high-intensity laser pulse on a solid target, pulses of protons and other positively charged ions with energies of several 10 MeV per nucleon are generated. The properties of these particle beams such as their energy and absolute number are highly dependent on experimental conditions like laser and target parameters. In order to achieve principal comparability between different experimental campaigns at the Draco laser system at the Helmholtz-Zentrum Dresden-Rossendorf, a reference setup for the laser ion acceleration experiment was established. A configuration is sought in which proton beams of reproducible characteristics are generated. To ensure a high stability of the proton spectra, the application of longer focal length parabolas (f ~ 1000 mm) will be tested for this setup, according preparatory studies being presented in this paper.

Keywords: accelerators; laser-driven proton acceleration; high-intensity lasers; beams and electromagnetism

  • Open Access Logo Contribution to proceedings
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland
    IPAC2014 - Proceedings, TUPME033
  • Poster
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21514
Publ.-Id: 21514


Energetic stability of solute–carbon–vacancy complexes in bcc iron

Bakaev, A.; Terentyev, D.; Zhurkin, E. E.; van Neck, D.

The strong binding between a vacancy and carbon in bcc iron plays an important role in the evolution of radiation-induced microstructure. Our previous ab initio study points to the fact that the vacancy–carbon (V–C) pair can serve as a nucleus for the solute-rich clusters. Here, we continue the ab initio study by considering the interaction of mixed solute clusters (Mn, Ni and Si) with the V–C pair, and the interaction of typical alloying elements of Fe-based steels (i.e., Mn, Ni, Cu, Si, Cr and P) with di-carbon–vacancy pair (V–C2). We have identified the sequence of growth of Ni, Si and Mn solute-rich clusters nucleating on the V–C pair. The mixed-solute–V–C configurations are found to be less stable clusters than pure-solute–V–C clusters with the energy difference up to 0.22 eV per four atoms. The V–C2 pair is found to be as strong nucleation site for the solute-rich clusters as the V–C pair. Only Si solute atom stands out from the trend showing a weaker affinity to the V–C2 complex by 0.09 eV compared to the attraction to the V–C pair. The overall results point to the importance of taking into account the existence of both V–C and V–C2 complexes in studying the formation of solute-rich clusters in Fe-based steels for nuclear applications.

Keywords: Ferritic steels; Minor alloying elements; Carbon; Solute clusters; Ab initio calculations

Permalink: https://www.hzdr.de/publications/Publ-21513
Publ.-Id: 21513


The pH dependence of Am(III) complexation with acetate: an EXAFS study

Froehlich, D. R.; Skerencak-Frech, A.; Bauer, N.; Rossberg, A.; Panak, P. J.

The complexation of acetate with Am(III) is studied as a function of the pH (1–6) by extended X-ray absorption fine-structure (EXAFS) spectroscopy. The molecular structure of the Am(III)–acetate complexes (coordination numbers, oxygen and carbon distances) is determined from the raw k3-weighted Am LIIIedge EXAFS spectra. The results show a continuous shift of Am(III) speciation with increasing pH value towards the complexed species. Furthermore, it is verified that acetate coordinates in a bidentate coordination mode to Am(III) (Am—C distance: 2.82 0.03 A ° ). The EXAFS data are analyzed by iterative transformation factor analysis to further verify the chemical speciation, which is calculated on the basis of thermodynamic constants, and the used structural model. The experimental results are in very good agreement with the thermodynamic modelling.

Keywords: americium; acetate; coordination chemistry; EXAFS; ITFA

Related publications

Permalink: https://www.hzdr.de/publications/Publ-21512
Publ.-Id: 21512


A new look at the structural properties of trisodium uranate Na3UO4

Smith, A. L.; Raison, P. E.; Martel, L.; Prieur, D.; Charpentier, T.; Wallez, G.; Suard, E.; Scheinost, A. C.; Hennig, C.; Martin, P.; Kvashnina, K. O.; Cheetham, A. K.; Konings, R. J. M.

The crystal structure of the trisodium uranate, which forms following the interaction between sodium and hyperstoichiometric urania, has been solved for the first time using powder X-ray and neutron diffraction, X-ray Absorption Near-Edge Structure spectroscopy, and solid state 23Na Multi-Quantum Magic Angle Spinning Nuclear Magnetic Resonance. The compound, isostructural with Na3BiO4, has a monoclinic symmetry, in space group P2~c. Moreover, it has been shown that this structure can accommodate some cationic disorder, with up to 16(2)% sodium on the uranium site, corresponding to the composition -Na3(U1−x,Nax)O4 (0

Keywords: Sodium uranate; X-ray diffraction (XRD); Neutron diffraction; XANES; MQMAS NMR

Related publications

Permalink: https://www.hzdr.de/publications/Publ-21511
Publ.-Id: 21511


Pushing the Limits of Ferromagnetic Resonance: Detection of Single sub-100-nm Nanodots

Lenz, K.; Banholzer, A.; Narkowicz, R.; Grebing, J.; Stienen, S.; Lindner, J.; Fassbender, J.

Spintronic devices like MRAM, STNOs, or magnonic crystals are based on various types of magnetic nanostructures. Hence, it is crucial to know their magnetic properties, e.g., to allow for proper simulation for further development. The magnetic characterization in terms of magnetic damping, resonance modes, or magnetic anisotropy of single nanosized objects is very challenging, nevertheless of utmost importance, as otherwise bulk or film parameters need to be used for simulations.
Ferromagnetic resonance (FMR) is in principle the ultimate technique to measure such parameters. Unfortunately, conventional FMR based on resonant cavities and even modern broadband coplanar waveguide FMR lacks the sensitivity to measure single sub-micron-sized nano elements. Usually the detection limit of FMR, i.e. the minimum number of spins, which can be detected, is about 1012 spins for permalloy. Up to now, arrays of such elements had to be prepared to overcome this limit. However, great care on a homogeneous sample preparation has to be taken. For example, already slight inhomogeneities between the array's elements render the individual resonant modes of the nanostructures invisible, due to linewidth broadening.
For the analysis of single nanoobjects a much higher sensitivity is required. Using our recently developed microresonators [1,2] we show how single nanoelements down to sample diameters of 100 nm can be measured.
Taking the signal-to-noise ratio achieved so far into account, we extrapolate the detection limit to 105 spins. The uniform excitation mode as well as various localized modes like e.g. edge modes can be observed. Their state can be visualized with micromagnetic simulations.
References:
[1] A. Banholzer, et al., Nanotechnology 22, 295713 (2011).
[2] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).

Keywords: ferromagnetic resonance; nanostructures; damping; spinwaves; microresonators

Related publications

  • Lecture (Conference)
    59th Annual Magnetism and Magnetics Materials Conference, 04.-07.11.2014, Honolulu, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-21510
Publ.-Id: 21510


Light emitting diode based on (In,Ga)As/GaAs coaxial multi-shell nanowires monolithically integrated on silicon

Dimakis, E.; Jahn, U.; Ramsteiner, M.; Tahraoui, A.; Grandal, J.; Trampert, A.; Biermanns-Föth, A.; Pietsch, U.; Riechert, H.; Geelhaar, L.

We demonstrate the use of III-arsenide nanowires as light emitting diodes (LEDs) monolithically integrated on Silicon. LEDs made of (In,Ga)As/GaAs coaxial multi-shell nanowires were grown catalyst-free directly on Si(111) by molecular beam epitaxy (MBE). The active region consists of a single (In,Ga)As/GaAs quantum well in the radial direction (Fig. 1-a). Correlating the emission properties of the quantum wells (Fig. 1-b) with the growth kinetics on the ( ) side-walls, we were able to identify the optimal growth conditions for coherently strained quantum wells with high-quality interfaces and homogeneous structure (in terms of chemical composition and shell thicknesses) along the nanowire axes. Shell-doping methods were successfully employed for the realization of p- and n-type GaAs shells, while a planarization scheme with transparent ohmic contacts allowed massive biasing in parallel configuration of the free-standing nanowires on the Silicon substrate. Rectifying operation and room-temperature electroluminescence were obtained (Fig. 1-c), proving the great potential of this technology.

  • Invited lecture (Conferences)
    Nanowires 2013, 12.11.2013, Weizmann Institute of Science, Rehovot, Israel

Permalink: https://www.hzdr.de/publications/Publ-21509
Publ.-Id: 21509


Magnetostatics and Dynamics of Ion Irradiated NiFe/Ta Multilayer Films Studied by Vector Network Analyzer Ferromagnetic Resonance

Markó, D.

In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer lms have been investigated with the main objective of nding a way to determine their saturation magnetization. Both polar magneto-optical Kerr eect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine 0MS, circumventing the problem of the unknown eective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high uences.
Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and tting software.
With both increasing ion uence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10Py samples, an immediate decrease of 0MS already sets in at small ion uences. However, for the 1Py and 5Py samples, the saturation magnetization remains constant up to a certain ion uence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical uence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10{15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaected by the ion uence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter increases with both increasing number of Py/Ta interfaces and higher ion uences, with the former having a stronger in uence. The inhomogeneous linewidth broadening B0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion uences.

Keywords: ferromagnetic resonance; FMR; thin films; multilayers; ferromagnetism

Related publications

  • Doctoral thesis
    TU Dresden, 2010
    Mentor: Jürgen Fassbender
    107 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21508
Publ.-Id: 21508


From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media

Ball, D. K.

Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities for magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest.
The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation.
In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements.
Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics.
Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetization with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains.
From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetization aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived.

Keywords: Ferromagnetic resonance; VSM; ferromagnetism; MOKE; nanostructures; spin waves

Related publications

  • Doctoral thesis
    TU Dresden, 2013
    Mentor: Jürgen Fassbender
    132 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21507
Publ.-Id: 21507


Method for evaluation of upgrading by liberation and separation

Leißner, T.; Mütze, T.; Atanasova, P.; Bachmann, K.; Peuker, U. A.

A method is presented for the evaluation of mineral processing by liberation and upgrading. The method bases on the plot of recovery of valuables versus the recovery of gangue (Fuerstenau upgrading curve). The locking curve of a feed material was plotted together with the upgrading curve in a Fuerstenau diagram. The assessment of liberation and upgrading is done by a comparison of surfaces formed by the curves and some characteristic lines of the diagram. This plot allows the calculation of two new quantitative measures for liberation and upgrading.
Both parameters can be combined to a third parameter describing the quality of the whole technical setup for mineral processing by subtracting the upgrading parameter from the liberation parameter. The third parameter shows a positive value in cases of upgrading determined processes, a negative value in cases of liberation affected processes and about zero for processes affected equally by liberation and upgrading. Thus it is easily possible to distinguish between poor results in the mineral processing caused by insufficient liberation or poor results caused by insufficient upgrading. Preliminary results from two case studies, performed on two different ore types, are very promising illustrating the practical use of such an approach.

Keywords: flotation modeling; optimization; process development

  • Contribution to proceedings
    XXVII International Congress on Mineral Processing, 20.-24.10.2014, Santiago de Chile, Chile
    Proceedings of the XXVII International Mineral Processing Congress – IMPC 2014, 1-10

Permalink: https://www.hzdr.de/publications/Publ-21506
Publ.-Id: 21506


Morphology-Induced Magnetic Phenomena Studied by Broadband Ferromagnetic Resonance

Körner, M.

In the present work, the influence of the morphology of thin ferromagnetic films on their static as well as dynamic magnetic properties was investigated by means of broadband ferromagnetic resonance (FMR). Using an ion beam erosion process the surface of the substrates was periodically modulated (ripples), where the modulation wavelength is determined by the ion energy. In this way a well-controllable roughness profile evolves ranging from a few ten up to several hundreds of nanometers in wavelength. The substrate’s surface profile in turn is repeated by films grown on top offering an easy and fast approach to investigate morphology influences on the magnetic properties. This work aims on modifications of the magnetic anisotropy as well as the FMR linewidth of the magnetic relaxation process.
Prior to magnetic investigations the existing FMR setup was extended to measure FMR spectra at a fixed microwave frequency while sweeping the external magnetic field. Furthermore, a software toolbox was developed to perform the data processing and evaluation.
Starting with the morphology influence on the magnetic anisotropy 10 nm thin Fe, Co, and Ni81Fe19 (Permalloy Py) films were deposited on rippled Si substrates. Due to Si displacements during ion erosion and natural oxidation the rippled Si substrates exhibit an amorphous surface causing a polycrystalline material growth. This leads to a suppression of magneto-crystalline anisotropy leaving only morphology-induced anisotropy contributions.
Here, a uniaxial magnetic anisotropy (UMA) was observed that aligns its easy axis with the ripple ridges, whereas its strength decays with increasing ripple wavelength for all materials. From thickness-dependent measurements two characteristic regions were determined with competing uniaxial volume and surface anisotropy contributions. Underlined by micromagnetic simulations a dominant volume contribution was found in the thin region accompanied by magnetic moments nearly following the surface corrugation. In the thick region the UMA is controlled by dipolar stray fields at the surface.
In contrast to Si, ion eroded MgO keeps its crystal structure offering epitaxial growth of 10 nm thin single-crystalline Fe films. Consequently, a superposition of morphology-induced UMA and magneto-crystalline cubic anisotropy was observed. The direction of the ripple ridges is predetermined by the incident ion beam, which allows to freely orient the UMA’s direction with respect to the cubic anisotropy, offering a possibility for anisotropy engineering. In comparison to the planar reference case rippled magnetic films exhibit lower intrinsic and extrinsic relaxation contributions.
For the final part, 30 nm Py was grown on rippled Si covering modulation wavelengths l ranging from 27 to 432 nm. Using magnetic force microscopy and holography measurements the dipolar stray fields above and inside the magnetic layer were characterized. For l 222 nm, the stray fields act as scattering centers for spin waves triggering two-magnon scattering (TMS). This causes an apparent line broadening generating distinct peaks in the frequency-dependent linewidth whose position can be tuned by altering l. These effects are understood in the framework of a perturbation theory of spin waves in periodically perturbed films recently presented in the literature. Furthermore, the in-plane angular dependence of the linewidth revealed a two-fold symmetry, which is not present for vanishing TMS at small l.

Keywords: ferromagnetic resonance; ferromagnetism; FMR; thin films; spin waves

Related publications

  • Doctoral thesis
    TU Dresden, 2013
    Mentor: Jürgen Fassbender
    185 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21505
Publ.-Id: 21505


Polytypism in GaAs nanowires: determination of the interplanar spacing of wurtzite GaAs by X-ray diffraction

Köhl, M.; Schroth, P.; Minkevich, A. A.; Hornung, J.-W.; Dimakis, E.; Somaschini, C.; Geelhaar, L.; Aschenbrenner, T.; Lazarev, S.; Grigoriev, D.; Pietsch, U.; Baumbach, T.

In GaAs nanowires grown along the cubic [111]c direction, zinc blende and wurtzite arrangements have been observed in their stacking sequence, since the energetic barriers for nucleation are typically of similar order of magnitude. It is known that the interplanar spacing of the (111)c Ga (or As) planes in the zinc blende polytype varies slightly from the wurtzite polytype. However, different values have been reported in the literature. Here, the ratio of the interplanar spacing of these polytypes is extracted based on X-ray diffraction measurements for thin GaAs nanowires with a mean diameter of 18–25 nm. The measurements are performed with a nano-focused beam which facilitates the separation of the scattering of nanowires and of parasitic growth. The interplanar spacing of the (111)c Ga (or As) planes in the wurtzite arrangement in GaAs nanowires is observed to be 0.66% 0.02% larger than in the zinc blende arrangement.

Keywords: GaAs; nanowires; polytypism; X-ray diffraction; nanofocus

Permalink: https://www.hzdr.de/publications/Publ-21504
Publ.-Id: 21504


Analyse eines Messplatzes für frequenzaufgelöste magnetooptische Kerr-Effektmessungen (FR-MOKE) sowie dessen Ansteuerung auf der Basis von LabVIEW

Trache, M.

keines Vorhanden

Keywords: ferromagnetism; ferromagnetic resonance; MOKE; FR-MOKE

Related publications

  • Diploma thesis
    Wilhelm Büchner Hochschule, 2012
    Mentor: Kilian Lenz
    80 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21503
Publ.-Id: 21503


Untersuchung der elektrischen und magnetischen Eigenschaften von BiFeO3-Filmen

Noack, H.

keines vorhanden.

Keywords: ferromagnetism; ferromagnetic resonance; ferroelectrics

Related publications

  • Diploma thesis
    Wilhelm Büchner Hochschule, 2011
    Mentor: Kilian Lenz
    94 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21502
Publ.-Id: 21502


Magnetische Charakterisierung dünner Keilschichten mittels frequenzaufgelöstem magnetooptischen Kerr-Effekt

Hoffmann, S.

Im Rahmen dieser Arbeit wurden erstmalig ein Probensystem aus zwei ferromagnetischen Fe3Si Schichten und einer keilförmigen Magnesiumoxid (MgO) Zwischenschicht, mittels der Kombination von ferromagnetischer Resonanz (FMR) und magnetooptischer Detektion mit Hilfe des Kerr-Effekts (MOKE), am FR-MOKE Aufbau untersucht. An verschiedenen Stellen der Probe wurden frequenzabhängige Messungen durchgeführt, um daraus Rückschlüsse auf die magnetischen Eigenschaften des Materials zu ziehen. Durch den Vergleich mit Literaturwerten konnte gezeigt werden, dass mithilfe dieser Messmethode durchaus zuverlässige Messungen durchgeführt werden können. Anhand der aufgenommen Spektren wurde der Gradient in der Probe nachgewiesen, sowie die Abhängigkeit der Interlagenaustauschkopplung von der Zwischenschichtdicke verdeutlicht.

Keywords: magnetism; ferromagnetic resonance; MOKE; thin films

Related publications

  • Bachelor thesis
    TU Ilmenau, 2014
    Mentor: Kilian Lenz
    50 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21501
Publ.-Id: 21501


Impact of strain induced by polymer curing in benzocyclobutene embedded semiconductor nanostructures

Bussone, G.; Dimakis, E.; Grifone, R.; Biermanns, A.; Tahraoui, A.; Carbone, D.; Geelhaar, L.; Schülli, T. U.; Pietsch, U.

Polymers such as benzocyclobutene are commonly used as embedding materials for semiconductor nanostructures. During the curing process of the polymer up to 250 °C, a significant impact of strain can be induced on the embedded semiconductor material due to different thermal expansion coefficients. This strain has been revealed by X-ray diffraction in free-standing GaAs nanowires grown on a silicon substrate, embedded in a polymer matrix. It will be shown that this strain is released during the X-ray irradiation if additionally an external static electric field is applied.

Keywords: benzocyclobutene; polymer matrix; X-ray diffraction; embedded semiconductor nanostructures; GaAs nanowires; strain

Permalink: https://www.hzdr.de/publications/Publ-21499
Publ.-Id: 21499


Untersuchung der magnetischen Eigenschaften von Permalloy-Filmen mittels frequenzaufgelöstem magnetooptischen Kerr-Effekt (FR-MOKE)

Rupp, S.

Im Rahmen dieser Arbeit wurden dünne ferromagnetische Filme aus Permalloy (Ni80Fe20) mit eine Kombination aus ferromagnetischer Resonanz (FMR) und magnetooptischem Kerr-Effekt (MOKE) auf ihre dynamischen Eigenschaften hin untersucht. Das Hauptmerkmal dieser frequenzaufgelösten FR-MOKE Messung lag hierbei auf der Bestimmung der Linienbreite zur Charakterisierung der wirksamen Dämpfung der Magnetiserungspräzession und des g-Faktors für Permalloy. Die Ergebnisse im Einzelnen sind: 1. Die Linienbreite kann im Bereich von 1-25 GHz bestimmt werden. 2. Die Linienbreite steigt mit der Mikrowellenfrequenz f linear an und besitz einen geringen inhomogenen Anteil. 3. Die Amplitude der Lorentzkurve fällt mit 1/f ab. 4. Bestimmung des g-Faktors g=2,085(11), für Permalloy. 5.
Die Dämpfung ist konstant und beträgt alpha=0,007.

Keywords: ferromagnetism; ferromagnetic resonance; thin films; MOKE

Related publications

  • Bachelor thesis
    nta Naturwissenschaftlich-Technische Akademie Prof. Dr. Grübler gGmbH, 2014
    Mentor: Kilian Lenz
    54 Seiten

Permalink: https://www.hzdr.de/publications/Publ-21498
Publ.-Id: 21498


Role of liquid indium in the structural purity of wurtzite InAs nanowires that grow on Si(111)

Biermanns, A.; Dimakis, E.; Davydok, A.; Sasaki, T.; Geelhaar, L.; Takahasi, M.; Pietsch, U.

InAs nanowires that grow catalyst-free along the [111] crystallographic orientation are prone to wurtzite-zincblende polytypism, making the control of the crystal phase highly challenging. In this work, we explore the dynamic relation between the growth conditions and the structural composition of the nanowires using time-resolved X-ray scattering and diffraction measurements during the growth by molecular beam epitaxy. A spontaneous buildup of liquid indium is directly observed in the beginning of the growth process and associated with the simultaneous nucleation of InAs nanowires predominantly in the wurtzite phase. The highly arsenic-rich growth conditions that we used limited the existence of the liquid indium to a short time interval, which is defined as the nucleation phase. After their nucleation, the nanowires grow in the absence of liquid indium, and with a highly defective wurtzite structure. Complementary ex-situ diffuse X-ray scattering measurements and modeling revealed that this structural degradation is due to the formation of densely spaced stacking faults. Thus, high wurtzite phase purity is associated with the presence of liquid indium. This finding implies that pure wurtzite nanowires may be obtained only if the growth is performed under the continuous presence of liquid indium at the growth interface, that is, in the vapor–liquid–solid mode.

Keywords: nanowires; InAs; Si; molecular beam epitaxy (MBE); X-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-21497
Publ.-Id: 21497


Two-dimensional electron gas in monolayer InN quantum wells

Pan, W.; Dimakis, E.; Wang, G. T.; Moustakas, T. D.; Tsui, D. C.

We report in this letter experimental results that confirm the two-dimensional nature of the electron systems in a superlattice structure of 40 InN quantum wells consisting of one monolayer of InN embedded between 10 nm GaN barriers. The electron density and mobility of the two-dimensional electron system (2DES) in these InN quantum wells are 51015cm2 (or 1.251014cm2 per InN quantum well, assuming all the quantum wells are connected by diffused indium contacts) and 420 cm2/Vs, respectively. Moreover, the diagonal resistance of the 2DES shows virtually no temperature dependence in a wide temperature range, indicating the topological nature of the 2DES.

Permalink: https://www.hzdr.de/publications/Publ-21496
Publ.-Id: 21496


Evolution of polytypism in GaAs nanowires during growth revealed by time-resolved in situ x-ray diffraction

Schroth, P.; Köhl, M.; Hornung, J.-W.; Dimakis, E.; Somaschini, C.; Geelhaar, L.; Biermanns, A.; Pietsch, U.; Bauer, S.; Lazarev, S.; Baumbach, T.

In III-V nanowires the energetic barriers for nucleation in zinc blende or wurtzite arrangement are typically of similar order of magnitude. As a result, both arrangements can occur in a single wire. Here, we investigate the evolution of this polytypism in self-catalyzed GaAs nanowires on Si(111) grown by molecular beam epitaxy with time-resolved in situ X-ray diffraction. We interpret our data in the framework of a height dependent Markov model for the stacking in the nanowires. This way, we extract the mean sizes of faultless wurtzite and zinc blende segments -- a key parameter of polytypic nanowires -- and their temporal evolution during growth. Thereby, we infer quantitative information on the differences of the nucleation barriers including their evolution without requiring a model of the nucleus.

Permalink: https://www.hzdr.de/publications/Publ-21495
Publ.-Id: 21495


Status of the ELBE SRF Gun II

Arnold, A.

As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation, it turned out that the specified performance has not been achieved. However, to demonstrate the full potential of this new type of electron source, a second and slightly modified SRF gun II was built in collaboration with Thomas Jefferson National Accelerator Facility (TJNAF). We will report on commissioning and first results of the new gun, which includes in particular the characterization of the most important RF properties as well as their comparison with previous vertical test results.

Keywords: superconducting electron injector; SRF gun; ELBE

Related publications

  • Lecture (others)
    HOPE / SINEMP project meeting, 03.-04.11.2014, Siegen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21494
Publ.-Id: 21494


System Integration and Application of CdZnTe Detectors in a Compton Camera for Medical Use

Fiedler, F.; Enghardt, W.; Golnik, C.; Hueso-Gonzalez, F.; Kormoll, T.; Schumann, A.; Pausch, G.; Petzold, J.; Rohling, H.; Roemer, K.; Schoene, S.

Ion beams offer advantages over conventional treatment modalities, such as photons. Because of the way ions deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the collateral damage to the surrounding healthy tissue. However, the range of these particles is sensitive to small density changes in the irradiated volume. Deviations will lead to a misalignment of the deposited dose maximum and the tumor. It is therefore highly desirable to verify the particle range in-vivo and in realtime by means of a detector system independent from the treatment device. One approach is to monitor the prompt gamma-ray emissions from excited nuclei that originate in the interaction of projectile and target nuclei. A Compton camera could be one of the feasible technical solutions for such a monitoring system. To set up a clinical applicable device a comprehensive modelling of the creation of secondary radiation as well as of the detection process is required. Furthermore, a sophisticated reconstruction of the data is essential. This paper will present three different prototypes of such a detector system made of CdZnTe and scintillation detectors. Also we will show measurements on the detector performance as well as reconstructed images of the radiation sources.

Keywords: Compton camera; in-vivo dose imaging; proton therapy; CdZnTe detectors

  • Invited lecture (Conferences)
    IEEE NSS MIC, 21st Symposium on room-temperature Semiconductor and Gamma-Ray detectors, 08.-15.11.2014, Seattle, WA, USA

Permalink: https://www.hzdr.de/publications/Publ-21493
Publ.-Id: 21493


Broadband, diode pumped Yb-doped fused silica laser

Röser, F.; Loeser, M.; Albach, D.; Siebold, M.; Grimm, S.; Brand, D.; Schwuchow, A.; Langner, A.; Schötz, G.; Schönfeld, D.; Schramm, U.

We report on the fabrication, optical properties and lasing characteristics of Yb-doped fused silica in bulk volume. The glass rods were manufactured by sintering of Yb-doped fused silica granulates and subsequent homogenization. Samples of various thicknesses containing doping levels of 0.27 mol% and 0.39 mol%, respectively, were investigated. The glass shows a high optical quality with refractive index variations in the 10 ppm range. We successfully demonstrated cw lasing with a maximum optical to optical efficiency of 60 % and slope efficiencies of about 70 % with respect to absorbed pump power for all samples. The laser cavity could be tuned in a wavelength range of 100 nm. The large amplification bandwidth of fused silica was verified by gain distribution measurements in a double-pass amplifier configuration.

Keywords: Lasers, diode-pumped; Lasers, ytterbium; Lasers, solid-state; Laser materials

Permalink: https://www.hzdr.de/publications/Publ-21492
Publ.-Id: 21492


Comparison of a Separated Flow Response to Localized and Global type Disturbances

Monnier, B.; Williams, D.; Weier, T.; Albrecht, T.

POD modes and coefficients obtained from an inclined flat plate with Lorentz force actuator are compared to that of a pitching wing model (NACA 0009). The pitching wing model emulates an impulsive disturbance by pitching from 15 deg to 17 deg and then back to 15 deg in a very short time interval. There is also a negative pitching case, 15 deg to 13 then back to 15 deg. The Lorentz force actuator produced a spatially localized disturbance, whereas the pitching wing produces a spatially global disturbance. We found very close similarities in the POD modes and the time-varying coefficients. We also found that POD mode 2 tracks the negative of the lift force in both cases.

Keywords: active flow control; Lorentz force; pitching wing

  • Lecture (Conference)
    53rd AIAA Aerospace Sciences Meeting, 05.-09.01.2015, Kissimmee , Florida, USA
  • Contribution to proceedings
    53rd AIAA Aerospace Sciences Meeting, 05.-09.01.2015, Kissimmee, Florida, USA
    AIAA papers
    DOI: 10.2514/6.2015-1056
    Cited 1 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-21491
Publ.-Id: 21491


Critical exponents and intrinsic broadening of the field-induced transition in NiCl2 · 4SC(NH2)2

Wulf, E.; Hüvonen, D.; Schönemann, R.; Kühne, H.; Herrmannsdörfer, T.; Glavatskyy, I.; Gerischer, S.; Kiefer, K.; Gvasaliya, S.; Zheludev, A.

The field-induced ordering transition in the quantum spin system NiCl2 · 4SC(NH2)2 is studied by means of neutron diffraction, ac magnetometry, and relaxation calorimetry. The interpretation of the data is strongly influenced by a finite distribution of transition fields in the samples, which was present but disregarded in previous studies. Taking this effect into account, we find that the order-parameter critical exponent is inconsistent with the BEC universality class even at temperatures below 100 mK. All results are discussed in comparison with previous measurements and with recent similar studies of disordered Ni(Cl1−xBrx)2 · 4SC(NH2)2.

Permalink: https://www.hzdr.de/publications/Publ-21490
Publ.-Id: 21490


Multigap superconductivity in locally noncentrosymmetric SrPtAs: An 75As nuclear quadrupole resonance investigation

Brückner, F.; Sarkar, R.; Günther, M.; Kühne, H.; Luetkens, H.; Neupert, T.; Reyes, A. P.; Kuhns, P. L.; Biswas, P. K.; Stürzer, T.; Johrendt, D.; Klauss, H.-H.

We report detailed 75As nuclear quadrupole resonance investigations of the locally noncentrosymmetric superconductor SrPtAs. The spin-lattice relaxation studies prove weakly coupled multigap superconductivity. A retardation of the decay in 1/T1T evidences a nodeless (fully gapped) superconducting state on the complex multipocket Fermi surface, which is consistent with an anisotropic s-wave order parameter and with proposed unconventional f-wave and chiral d-wave symmetries. A quantitative analysis of these models favors the unconventional f-wave state.

Permalink: https://www.hzdr.de/publications/Publ-21489
Publ.-Id: 21489


Nanowire spin torque oscillator driven by spin orbit torques

Duan, Z.; Smith, A.; Yang, L.; Youngblood, B.; Lindner, J.; Demidov, V. E.; Demokritov, S. O.; Krivorotov, I. N.

Spin torque from spin current applied to a nanoscale region of a ferromagnet can act as negative magnetic damping and thereby excite self-oscillations of its magnetization. In contrast, spin torque uniformly applied to the magnetization of an extended ferromagnetic film does not generate self-oscillatory magnetic dynamics but leads to reduction of the saturation magnetization. Here we report studies of the effect of spin torque on a system of intermediate dimensionality—a ferromagnetic nanowire. We observe coherent self-oscillations of magnetization in a ferromagnetic nanowire serving as the active region of a spin torque oscillator driven by spin orbit torques. Our work demonstrates that magnetization selfoscillations can be excited in a one-dimensional magnetic system and that dimensions of the active region of spin torque oscillators can be extended beyond the nanometre length scale.

Permalink: https://www.hzdr.de/publications/Publ-21488
Publ.-Id: 21488


Calculation of Electronic Structure and Transport properties of Donor – Acceptor Polymers

Günther, F.; Gemming, S.; Seifert, G.

Donor-acceptor (DA) polymers have been found to be good materials for organic electronics since they provide interesting features like mechanical flexibility and high impact resistance.
Moreover, they offer the possibility to produce devises by low cost roll-to-roll printing techniques.
Thus, they are highly promising candidates for organic thin-film transistors and solar cells.
For applications, however, these materials should fulfill several demands such as ambient stability, good solubility, and good film-forming properties.
The charge carrier mobility is one of the most important quantities.
In order to analyse the influence of the molecular structure on these properties, we investigate DA polymers using first-principals methods as density functional theory (DFT).
In particular, density functional based tight binding (DFTB) is used to study large systems.

In our study we analyse the electronic structures of the isolated monomers which are the building blocks of the DA polymers, of finite oligomers up to a length of 20 conjugated units, and of infinite long polymers using periodic boundary conditions.
Furthermore, we investigate the morphological properties by studying systems of several polymer chains with different crossing angles and relative shifts.

Using Marcus transfer theory, we then calculated the electronic transport properties based on hopping processes.
Here, we focus on the coupling matrix elements and their dependence on the stacking configuration.
Using a Boltzmann-like approach for evaluating an average value of this quantity, we obtain good agreements to experimental trends.
Especially the dominating transport type is nicely reproduced by our approach.

  • Lecture (others)
    Arbeitsgruppenseminar der Professur für Theoretische Chemie, 20.11.2014, Dresden, Deutschland
  • Lecture (others)
    Seminar der Professur Theorie ungeordneter Systeme, 17.12.2014, Chemnitz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21487
Publ.-Id: 21487


Optical Synchronization and Electron Bunch Diagnostic at the CW-Linac ELBE

Kuntzsch, M.

no abstract submitted

Keywords: Synchronization ELBE BAM BCM Diagnostic

Related publications

  • Invited lecture (Conferences)
    DESY MSK Seminar, 09.01.2015, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-21486
Publ.-Id: 21486


Optimising the spatial structure of BLN protein models by means of "partial distortion''-quench cycles

Günther, F.; Möbius, A.; Schreiber, M.

The prediction of the spatial structure of a protein based on its amino acid sequence is a challenging problem.
Corresponding theoretical studies of the protein folding require highly efficient structure optimisation tools.
Here we investigate whether and to what extent the thermal cycling (TC) algorithm [1] is appropriate for determining low energy structures of the BLN protein model by J.D. Honeycutt and D. Thirumalai [2].
In our simulations for 46-, 58-, and 69-bead sequences, the TC algorithm reliably finds the global minimum within reasonable computing time.
In comparison to the multi-start local search and simulated annealing approaches, TC turns out to be far more efficient.

In the present work, the BLN model with rigid bonds is studied in detail for the first time.
Comparing these results to data for the extended model by Berry et al. [3], where stiff springs are substituted for the rigid bonds, we observe several level crossings when varying the spring constant, even for quite hard springs.

[1] A. Möbius et al. , Phys. Rev. Lett. 79 (1997) 4297.
[2] J.D. Honeycutt and D. Thirumalai, Biopolymers 32 (1992) 695.
[3] R.S. Berry et al. , Proc. Natl. Acad. Sci. USA 94 (1997) 9520.

  • Lecture (Conference)
    DPG Spring Meeting 2014, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21485
Publ.-Id: 21485


Handling Domain Decomposition in Massively Parallel Implementations of Stochastic Lattice Models

Kelling, J.; Ódor, G.; Gemming, S.

Nanopatterning of surfaces and bulk materials is very important from molecular electronics to photovoltaics. But, in order to understand the underlying physics of self-organization, large scale atomistic simulations are crucial. Only stochastic models can bridge the gap from nano to micro, enabling simulations of micron-sized volumes, billions of atoms and study long-time evolution. Random site-selection is essential but can be harmed by domain decomposition in GPGPU. We present solutions by example of a dimer-model for KPZ surface growth.

Keywords: Statistical Physics; Domain Decompostion

Permalink: https://www.hzdr.de/publications/Publ-21484
Publ.-Id: 21484


Mesoscale magnetism

Hoffmann, A.; Schultheiss, H.

Magnetic interactions give rise to a surprising amount of complexity due to the fact that both static and dynamic magnetic properties are governed by competing short-range exchange interactions and long-range dipolar coupling. Even though the underlying dynamical equations are well established, the connection of magnetization dynamics to other degrees of freedom, such as optical excitations, charge and heat flow, or mechanical motion, make magnetism a mesoscale research problem that is still wide open for exploration. Synthesizing magnetic materials and heterostructures with tailored properties will allow to take advantage of magnetic interactions spanning many length-scales, which can be probed with advanced spectroscopy and microscopy and modeled with multi-scale simulations. This review highlights some of the current basic research topics in mesoscale magnetism, which beyond their fundamental science impact are also expected to influence applications ranging from information technologies to magnetism based energy conversion.

Keywords: Magnetic soliton; Magnetomechanical coupling; Magnonics; Optical magnetization switching; Permanent magnet; Spin caloritronics; Spin Hall effect; Spin texture; Spin transfer torque

Related publications

Permalink: https://www.hzdr.de/publications/Publ-21483
Publ.-Id: 21483


Calculation of Electronic Structure and Transport in Polymers

Günther, F.; Seifert, G.; Luschtinetz, R.; Gemming, S.

Organic thin-film transistors producible by low-cost roll-to-roll manufacturing processes seem to be highly promising for flexible electronics. Therefore, high mobility semiconducting polymers with ambient stability, good solubility and film-forming properties are needed. Our study is turned to the calculation of the electronic transport properties through polymers consisting of conjugated thiophene based donor units and di-ketopyrrolo-pyrrol based acceptor units. The structure and electronic properties of thiophene-based molecular stacks is studied by means of quantum- mechanical calculations. We demonstrate how the functionalization of thiophenes can increase the dispersion interaction and promote the parallel- stacked arrangement of the molecules, which is essential to get efficient charge transport channels in the direction perpendicular to the plane of the thiophene rings. Moreover, we found that the π-π-stacking is the main driving force in the self-assembly of the molecules in the film. These results are the basis for further studies of the hopping transport properties of this promising organic semiconducting material.
For the description of the electronic transport we apply a Greens function method, including Coulomb and inelastic tunneling to a simple one-particle hopping Hamiltonian by calculating the matrix elements through overlap integrals of orbitals obtained from density-functional calculations.

  • Poster
    XXIII International Materials Research Congress, 17.-21.08.2014, Cancun, Mexico

Permalink: https://www.hzdr.de/publications/Publ-21482
Publ.-Id: 21482


Transport Calculations for Si4 Clusters with Gold single Atom Contacts

Kelling, J.; Kerbusch, J.; Erbe, A.; Dietsche, R.; Ganteför, G.; Scheer, E.; Zahn, P.; Gemming, S.

We present results for electronic transport through Si4 clusters contacted by single-atom gold contacts attached to <111> fcc-gold leads. The calculations were performed using density functional theory and the non-equilibrium Green's function approach for transport. The simulation setup mimics contacts in mechanically controllable break-junction experiments, which provide data for comparison.

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21481
Publ.-Id: 21481


Ab inito study on morphology of donor-acceptor polymers

Günther, F.; Gemming, S.; Seifert, G.

Donor-acceptor (DA) polymers have been found to be good materials for organic electronics since they provide interesting features like mechanical flexibility and high impact resistance.
Moreover, they offer the possibility to produce devises by low cost roll-to-roll printing techniques. Thus, they are highly promising candidates for organic thin-film transistors and solar cells. For applications, however, these materials should fulfill several demands such as ambient stability, good solubility, and good film-forming properties. The charge carrier mobility is one of the most important quantities.
In order to analyze the influence of the molecular structure on these properties, we investigate DA polymers using first-principals methods as density functional theory (DFT). In particular, density functional based tight binding (DFTB) is used to study large systems.
Starting from isolated monomers being the building blocks of the DA polymers the total energy, the atomic charges, the difference between highest occupied and lowest unoccupied molecular orbitals, and the reorganization energies are calculated.
Furthermore, oligomers up to a length of 100 conjugated units as well as infinite long polymers are considered. Finally, the morphological properties are investigated by studying systems of several polymer chains with different crossing angles and relative shifts.

  • Poster
    IHRS NanoNet Annual Workshop 2014, 29.-30.09.2014, Rathen, Sächsische Schweiz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21480
Publ.-Id: 21480


Structure optimization of BLN protein models combining local-search, evolutionary, and genetic approaches

Günther, F.; Möbius, A.; Schreiber, M.

Establishing relations between the amino acid sequence of a protein and its spatial structure is a very important and challenging task.
When analysing the forces affecting the protein folding, the investigation of the related free energy landscape is of central importance.
Thereby, to obtain the ground state and low-energy metastable states, highly effcient structure optimization tools are needed.
Here, we study the properties of genetic local-search type optimization approaches, in particular of thermal cycling (TC) [1] and systematic-crossover localsearch (SCLS) algorithms.
For this aim, we focus on the BLN protein model, designed by J.D. Honeycutt and D. Thirumalai [2]. We consider 46-, 58-, and 69-bead sequences from Refs. [2,3]; the 69-bead sequence seems to be the largest BLN model treated in the liteature up to now.
In all these cases, the TC and SCLS algorithms reliably find the global minimum within reasonable computing times.
Both algorithms proved to be far more effcient than multi-start local-search and simulated annealing approaches.
In the present work, to the best of our knowledge, the BLN model with rigid bond lengths is studied in detail for the first time.
We compare our results to the properties of the extended model by Berry et al. [4], in which stiff spring-like bonds are substituted for the rigid bonds:
The hardening of the spring constants causes several level crossings of the metastable states.
For the 46-bead model, this concerns even the ground state.

[1] A. Möbius, A. Neklioudov, A. Diaz-Sanchez, K.H. Hoffmann, A. Fachat, and M. Schreiber, Phys. Rev. Lett. 79 (1997) 4297.
[2] J.D. Honeycutt and D. Thirumalai, Biopolymers 32 (1992) 695.
[3] M.T. Oakley, D.J.Wales, and R.L. Johnston, J. Phys. Chem. B 115 (2011) 11525.
[4] R.S. Berry, N. Elmaci, J.P. Rose, and B. Vekhter, Proc. Natl. Acad. Sci. USA 94 (1997) 9520.

  • Poster
    Conference of Middle European Coorperation in Statistical Physics, 08.-10.04.2014, Coventry, England

Permalink: https://www.hzdr.de/publications/Publ-21479
Publ.-Id: 21479


Electronic Transport through Au-contacted PEEB

Kelling, J.; Gemming, S.

Transport through the organic molecule PEEB has been investigated using Density functional Theory (DFT) and the Non-Equilibrium Green's Function (NEGF) approach.

Keywords: electronic transport; molectular electronics; dft

  • Poster
    NanoNet Workshop, 29.-30.09.2014, Rathen, Sächsische Schweiz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21478
Publ.-Id: 21478


Calculation of electronic transport properties through polymeres

Günther, F.; Gemming, S.; Seifert, G.

Organic thin-film transistors producible by low-cost roll-to-roll manufacturing processes seem to be highly promising for flexible electronics.
Therefore, high mobility semiconducting polymers with ambient stability, good solubility and film-forming properties are needed.
Our study is turned to the calculation of the electronic transport properties through polymers consisting of conjugated thiophene based donor units and di-ketopyrrolo-pyrrol based acceptor units.
Therefore, we use empirical hopping equations such as Marcus transfer theory in order to determine the mobility of holes and electrons.
The parameters required for this are taken from first-principles calculations such as density functional theory and Hartree-Fock approaches.

  • Poster
    DPG Spring Meeting 2014, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21477
Publ.-Id: 21477


EcoMetals - innovative eco-efficient biohydrometallurgy process for the recovery of strategic and rare metals: primary and secondary resources

Kutschke, S.; Bodénan, F.; Schaefer, J.; Guezennec, A.-G.; Janneck, E.; Möckel, R.; Petiot, C.; Pollmann, K.

The German-French project EcoMetals focuses on metal production from base (copper) and rare metal- bearing primary and secondary resources in Europe. The main objectives are the development of alternative methods in mineral processing involving pretreatment steps, biohydrometallurgical and metal recovery processes, their up scaling and finally the determination of economic and sustainable performances through process integration, life cycle analysis and economic assessment.
German Kupferschiefer dumps and ores from Mansfeld and Lausitz region, Polish Kupferschiefer concentrates and French complex polymetallic deposits will be used as case studies for scientific breakthrough and integrated process demonstration activity.

Keywords: copper; rare metals; black shale; bioleaching

  • Lecture (Conference)
    Biohydrometallurgy '14, 09.-11.06.2014, Falmouth, United Kingdom and Ireland

Permalink: https://www.hzdr.de/publications/Publ-21476
Publ.-Id: 21476


Recyclingpotenziale von Galliumarsenid

Kutschke, S.; Zeidler, O.; Matys, S.; Pollmann, K.; Scharf, C.

Zusammenfassung zu Stand der Arbeiten zum Galiumarsenid-Recycling, Darstellung bilogischer und hydrometallurigischer Ansätze

  • Lecture (others)
    21. Kolloquium Abfall & Altlasten aktuell, 11.12.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21475
Publ.-Id: 21475


Stacked topological spin textures as emitters for multidimensional spin wave modes

Sluka, V.; Weigand, M.; Kakay, A.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.; Wintz, S.

In the present contribution we will show that in a vortex pair system with uniaxial magnetic anisotropy, spin waves of different symmetries and dimensionalities can be excited.

Keywords: vortex spin wave

  • Lecture (Conference)
    IEEE International Magnetics Conference (Intermag), 11.-15.05.2015, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-21474
Publ.-Id: 21474


Fast Timing with BGO (and other Scintillators) on Digital Silicon Photomultipliers for Prompt Gamma Imaging

Petzoldt, J.; Roemer, K.; Kormoll, T.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Hueso-Gonzalez, F.; Golnik, C.; Kirschke, T.; Wagner, A.; Pausch, G.

Particle therapy is supposed to be an advanced treatment modality compared to conventional radiotherapy because of the well-defined range of the ions. Prompt gamma rays, produced in nuclear reactions between ion and nuclei, can be utilized for real-time range verification to exploit the full potential of particle therapy. Several devices have been investigated in the field of Prompt Gamma Imaging (PGI), like Slit and Compton Cameras. The latter need very high detection efficiency as well as good time and energy resolution, requiring a versatile scintillation detector. In positron emission tomography (PET), LSO and LYSO are known for their good timing resolution, while the lower cost alternative BGO shows worse performance. In PGI however, where gamma rays have energies up to 10 MeV, the light output of a scintillator is up to 20 times larger compared to PET with E gamma = 511 keV. This reduces the statistical contribution of the time resolution, which is the dominant part in case of BGO. Thus, BGO could be a reasonable alternative to LSO/LYSO for applications in PGI. Hence, experiments at the ELBE accelerator at Helmholtz-Zentrum Dresden Rossendorf (Germany) were performed using digital silicon photomultiplier (dSiPM) from Philips with monolithic BGO and LYSO crystals and for completeness with GAGG and CeBr3. The time resolution of BGO compared to the faster scintillators will be presented for a wide range of trigger- and validation levels as well as validation lengths of the dSiPM. Timing resolutions below 300 ps were obtained for BGO, while LYSO and CeBr3 achieve about 170 ps.

Keywords: fast timing; digital silicon photomultiplier; particle therapy; range verification

Related publications

  • Lecture (Conference)
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
  • Contribution to proceedings
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
    Proceedings of 2014 NSS/MIC

Permalink: https://www.hzdr.de/publications/Publ-21473
Publ.-Id: 21473


In-Vivo Range Verification Based on Prompt Gamma-Ray Timing Measurements

Golnik, C.; Hueso-Gonzalez, F.; Enghardt, W.; Mueller, A.; Fiedler, F.; Kormoll, T.; Ostendorf, R.; Petzold, J.; Roemer, K.; Dendooven, P.; Pausch, G.

We present a novel approach for real time range verification in particle therapy based on prompt gamma ray timing (PGT) spectroscopy. The measurement approach relies on the fact that high-energy particles need, dependent on their range, a varying transit time through the irradiated material. This transit time is about 1-2 ns in the case of protons with a range of 5-20 cm. Timing spectroscopy of promptly emitted gamma rays, measured with an arrangement resembling a typical time-of-flight (TOF) setup, encode these transit times and thus give a real time access to the particle range. We show that statistical momenta of PGT distributions such as the center of gravity and the variance incorporate the information on the particle range with a millimeter precision, although measurement uncertainties may cover the described effect at first sight. Typical uncertainties are limited by the detector time resolution and the particle bunch spread, and are finally determined by the spectrum stability. In contrast to other prompt gamma imaging techniques, the PGT method is based on straight timing spectroscopy with a single scintillation detector. Therefore, neither passive nor electronic collimation is required. The proposed idea is verified by an analysis of experimental data taken during proton irradiation experiments at the AGOR facility at KVI-CART in Groningen (The Netherlands). The measurement results are in excellent agreement with Monte Carlo based modeling of the experimental setup. We conclude that precise range assessment is feasible within a few seconds of irradiation due to the direct measurement method.

Keywords: particle therapy; range verification; prompt gamma timing

  • Lecture (Conference)
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA

Permalink: https://www.hzdr.de/publications/Publ-21472
Publ.-Id: 21472


Particle Range Retrieval in Heterogeneous Phantoms with the Prompt Gamma Timing Method at a Clinical Proton Accelerator

Hueso-Gonzalez, F.; Golnik, C.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Heidel, K.; Janssens, G.; Kormoll, T.; Petzoldt, J.; Prieels, D.; Priegnitz, M.; Roemer, K. E.; Smeets, J.; Sobiella, M.; Vander Stappen, F.; Wagner, A.; Weinberger, D.; Pausch, G.

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potential of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment under development in several research centers, the prompt gamma ray timing method has been recently proposed. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies. From the resulting distributions, particle range differences of around 5 millimeters in heterogeneous phantoms were observed. In conclusion, we proved the feasibility of the prompt gamma ray timing method for range verification in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.

Keywords: particle therapy; range verification; prompt gamma timing

Related publications

  • Poster
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
  • Contribution to proceedings
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
    Proceedings of 2014 NSS/MIC

Permalink: https://www.hzdr.de/publications/Publ-21471
Publ.-Id: 21471


Vacancy controlled spontaneous pattern formation on semiconductor surfaces

Facsko, S.

In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instability, which is responsible for this kind of growth is caused by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms to cross terrace steps. The arriving atoms are trapped on a terraces and can again nucleate to form new terraces. An analogous mechanism is also observed on ion irradiated surfaces. However, ion sputtering leads to the erosion of the surfaces and at room temperature semiconductor surfaces become amorphous. At these conditions periodic patterns are observed which are oriented perpendicular or parallel to the ion beam direction or are isotropic dot or hole patterns for normal incidence of the ion beam.
At temperatures above the recrystallization temperature of the material, bulk defects are dynamically annealed and amorphization is prevented. Now, ion sputtering is creating vacancies on the crystalline surface and the surfaces morphology is determined primarily by vacancy kinetics. The diffusion of vacancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into a 3D erosion. The resulting structures are inverse pyramids which are growing into the surface. The symmetry of these patterns is given by the crystal symmetry. Hence, checkerboard patterns appear on the Ge (001) surface, oriented in the <100> directions (Fig. 1 left). On the other hand, on the Ge (111) surface facets with a three fold symmetry evolve (Fig. 1 right).
For the description of the pattern formation and evolution in reverse epitaxy a continuum equation can be used, which combines the effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By including also a conserved Kardar-Parisi-Zhang term a remarkable qualitative agreement to the experiments is achieved.

Keywords: reverse epitaxy; nanostructures; ion irradiation; self-organized patterning

Related publications

  • Lecture (others)
    Seminar, 12.11.2014, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21470
Publ.-Id: 21470


Faceting semiconductor surfaces by reverse epitaxy

Facsko, S.; Ou, X.; Helm, M.; Fassbender, J.

In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instability, which is responsible for this kind of growth is caused by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms to cross terrace steps. The arriving atoms are trapped on a terraces and can again nucleate to form new terraces. An analogous mechanism is also observed on ion irradiated surfaces. However, ion sputtering leads to the erosion of the surfaces and at room temperature semiconductor surfaces become amorphous. At these conditions periodic patterns are observed which are oriented perpendicular or parallel to the ion beam direction or are isotropic dot or hole patterns for normal incidence of the ion beam.
At temperatures above the recrystallization temperature of the material, bulk defects are dynamically annealed and amorphization is prevented. Now, ion sputtering is creating vacancies on the crystalline surface and the surfaces morphology is determined primarily by vacancy kinetics. The diffusion of vacancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into a 3D erosion. The resulting structures are inverse pyramids which are growing into the surface. The symmetry of these patterns is given by the crystal symmetry. Hence, checkerboard patterns appear for instance on the Ge (001) surface, oriented in the <100> directions. On the other hand, on the Ge (111) surface facets with a three fold symmetry evolve. For high ion fluences the patterns also exhibit facets, which correspond to low index crystal planes.
For the description of the pattern formation and evolution in reverse epitaxy a continuum equation can be used, which combines the effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By including also a conserved Kardar-Parisi-Zhang term a remarkable qualitative agreement to the experiments is achieved.

Keywords: reverse epitaxy; ion irradiation; nanopatterning; nanostructures

Related publications

  • Invited lecture (Conferences)
    16th International Conference on Thin Films, 13.-16.10.2014, Dubrovnik, Kroatien

Permalink: https://www.hzdr.de/publications/Publ-21467
Publ.-Id: 21467


Energy Loss and Charge Exchange of Highly Charged Ions in Carbon Nanomembranes

Facsko, S.; Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Aumayr, F.

During the interaction of highly charged ions with solids the ions potential energy, i.e. the stored ionization energy, is released via multiple charge exchanges on a fs time scale. Thus, HCIs reach charge equilibrium after passing only a few nanometers of the solid. The dependence of the charge state on the stopping force of the ions is therefore not accessible in irradiation experiments with bulk material. In order to investigate this pre-equilibrium regime films of just a few nanometers have to be used.
We examined the charge state and the energy loss of highly charged Xe ions after their passage through 1 nm thick carbon nanomembranes. Surprisingly, two distinct exit charge distributions were observed [1]. Part of the ions are passing the membrane with almost now charge loss, whereas the other part loose most of their charge. Apparently, the measured charge distribution reflects two different impact parameter regimes. Ions with trajectories far away of any C atom of the membrane can stabilize only few electrons and exit therefore in a high charge state, whereas ions with trajectories close to a C atom can capture enough electrons and exit the membrane in a low charge state. The different impact parameter regimes are also connected to different energy losses: ions with large impact parameters are practically not stopped, whereas ions in close collisions exhibit high stopping force which is strongly dependent on the incident charge state.
The charge distribution and energy loss of Xeq+ ions of different incident charge states up to q=30 will be presented and the implication for the formation of holes in these nanomembranes by the HCIs [2] will be discussed.

[1] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).
[2] R. Ritter, R.A. Wilhelm, M. Stöger-Pollach, R. Heller, A. Mücklich, U. Werner, H. Vieker, A. Beyer, S. Facsko, A. Gölzhäuser, F. Aumayr, Appl. Phys. Lett. 102, 063112 (2013).

Keywords: highly charged ions; nano membranes; energy loss

Related publications

  • Lecture (Conference)
    International Conference on Ion Beam Modification of Materials, 15.-19.09.2014, Leuven, Belgien

Permalink: https://www.hzdr.de/publications/Publ-21466
Publ.-Id: 21466


IBA on a Nanometer Scale by use of a Helium Ion Microscope - Challenges, Achievements and ongoing Progress

Klingner, N.; Heller, R.; von Borany, J.; Facsko, S.; Gnauk, P.

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of about 0.3 nm and the ultimate field of depth make them a unique tool in surface imaging. The imaging contrast in such devices is usually generated either by measuring the secondary electron emission yield (SE mode) or the backscattered He ion yield (RBI mode). So far there is no possibility to analyze target compositions (elements) in a quantitative manner.
In the present contribution we will show concepts as well as first preliminary studies on the capability, efficiency and the limits of applying (Rutherford) Backscattering Spectrometry (RBS) within a HIM device to image samples with target mass contrast and to analyze target compositions. In particular, the capability of different kind of particle detectors (Si detector, TOF-setup, electrostatic and magnetic analyzers) with respect to their use for IBA in a HIM will be discussed.
The basic considerations and design studies are accompanied by first He backscat- tering investigations for energies between 1-40 keV using a test facility equipped alternatively with a time-of-flight detector or a classical 70° ESA. For various projectile energies the energy resolution of both detection systems is measured and compared to theoretical estimations. Moreover, we will present an experimental setup which allows to perform quantitative measurements on the secondary electron yield, the absolute backscattering cross sections and the charge fraction of the backscattered particles for ions with low energies in the order from sub keV to 40 keV. These measurements will be one key point on the way to a quantitative IBA within the HIM.

Keywords: Helium Ion Microscope

Related publications

  • Lecture (Conference)
    21st Ion Beam Analysis, 23.-28.06.2013, Seattle, United States of America

Permalink: https://www.hzdr.de/publications/Publ-21465
Publ.-Id: 21465


Study of the relationship between zinnwaldite chemical composition and magnetic susceptibility

Chehreh Chelgani, S.; Leißner, T.; Rudolph, M.; Peuker, U. A.

This study investigates the relationship between chemical analyses and magnetic susceptibility of zinnwaldite through magnetic separation of various size fractions. Statistical analyses were used to increase information about magnetic properties of this mineral as a future source of lithium. Statistical modeling indicated that magnetic susceptibility (as a main factor of magnetic separation) accurately can be predicted based on cations content of zinnwaldite. However the size of particles had a significant effect on magnetic susceptibility. The small difference between the estimated and measured values for the non-linear relationship of this prediction (less than 1 (10−8 m3/kg)) shows that these accurate theoretical techniques can be also applied to estimate magnetic properties of zinnwaldite in other resources, and in-situ analysis.

Keywords: Zinnwaldite; Lithium; Magnetic Susceptibility; Statistical Analysis; Chemical Composition

Permalink: https://www.hzdr.de/publications/Publ-21464
Publ.-Id: 21464


Spontaneous pattern formation on Ge induced by ion irradiation

Facsko, S.; Ou, X.; Böttger, R.; Bischoff, L.; Liedke, B.; Heinig, K. H.

Ion irradiation of Ge surfaces leads to a variety of morphologies depending on the ion beam parameters. In the energy range of a few hundreds down to a few tens of keV swelling and the formation of sponge like structures is observed [1]. When lowering the energy these porous structures turn into self-organized periodic surface patterns. At off-normal incidence angles well-known ripple patterns with wave vector parallel or perpendicular to the ion beam direction appear, whereas at normal incidence angles hexagonally ordered dot [2] or hole patterns can be formed [3]. The structure size of the patterns is in the range of 10 - 100 nm and, occasionally, a remarkable high degree of ordering is achieved.
On materials which turn amorphous during ion irradiation the formation of periodic patterns relies on at least two inter-playing processes: ion induced surface roughening due to local variation of erosion rate and smoothing via diffusional processes [4]. In addition, atomic relocations on the surface and in the bulk resulting from the collision cascade have been identified as equally important or even dominant [5]. At the atomic level the creation of surface and bulk defects, sputtering, and the influence of the ion beam on kinetic processes in the surface play a decisive role in the morphology evolution.
At high temperature, when amorphization of the Ge surface is prevented, novel crystalline surface patterns are developing during ion irradiation. In this case, regular checkerboard patterns are evolving on the Ge (001) surface with structures oriented along the <100> direction [6]. Moreover, an additional mechanism for pattern formation on Ge has been discovered recently: by very heavy ion irradiation melt pools are induced at the Ge surface by the incident ions. These melt pools can also lead to a surface instability and thus to the formation of periodic dot patterns at normal incidence.
We will present an overview of the different morphologies induced by ion irradiation on Ge surfaces and analyze briefly the dominant formation mechanism.

References
[1] R. Böttger, K.-H. Heinig, L. Bischoff, B. Liedke, and S. Facsko, Appl. Phys. A (2013) 113, 53.
[2] R. Boettger, L. Bischoff, K.-H. Heinig, W. Pilz, and B. Schmidt, J. Vac. Sci. Technol. B (2012) 30, 06FF12.
[3] M. Fritzsche, A. Muecklich, and S. Facsko, Appl. Phys. Lett. (2012) 100, 223108.
[4] R.M. Bradley and J.M.E. Harper, J. Vac. Sci. Technol. A (1988) 6, 2390.
[5] C.S. Madi, E. Anzenberg, K.F. Ludwig, and M.J. Aziz, Phys. Rev. Lett. (2011) 106, 066101.
[6] X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. (2013) 111, 016101.

Keywords: reverse epitaxy; pattern formation; ion irradiation; Ge

Related publications

  • Lecture (Conference)
    26th International Conference on atomic collisions in solids, 14.-18.07.2014, Debrecen, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-21463
Publ.-Id: 21463


Spontaneous pattern formation in reverse epitaxy

Facsko, S.; Ou, X.

In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instability, which is responsible for this kind of growth is caused by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms to cross terrace steps [1]. The arriving atoms are trapped on a terraces and can again nucleate to form new terraces. This mechanism leads to the growth of pyramidal mounds on the surface with facets corresponding to energetically favored crystal planes. An analogous mechanism is also observed on ion irradiated surfaces. However, ion sputtering leads to the erosion of the surfaces and at room temperature semiconductor surfaces become amorphous. At these conditions periodic patterns are observed which are oriented perpendicular or parallel to the ion beam direction or are isotropic dot or hole patterns for normal incidence of the ion beam [2].
At temperatures above the recrystallization temperature of the material, bulk defects are dynamically annealed and amorphization is prevented. Now, ion sputtering is creating vacancies on the crystalline surface and the surfaces morphology is determined primarily by vacancy kinetics. The diffusion of vacancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into a 3D erosion. The resulting structures are inverse pyramids which are growing into the material [3]. The symmetry of these patterns is given by the crystal symmetry of the surface. Hence, checkerboard patterns appear for instance on the Ge (001) surface, oriented in the <100> directions. On the other hand, on the Ge (111) surface facets with a three fold symmetry evolve. For high ion fluences the patterns also exhibit facets, which correspond to low index crystal planes [3].
For the description of the pattern formation and evolution in reverse epitaxy a continuum equation can be used, which combines the effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By including also a conserved Kardar-Parisi-Zhang term a remarkable qualitative agreement to the experiments is achieved [3].
[1] P. Politi, G. Grenet, A. Marty, A. Ponchet, J. Villain, Phys. Rep. 324, 271 (2000).
[2] A. Keller, S. Facsko, Materials 3, 4811 (2010).
[3] X. Ou, A. Keller, M. Helm, J. Fassbender, S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).

Keywords: reverse epitaxy; pattern formation; nanostructures; ion irradiation

Related publications

  • Invited lecture (Conferences)
    5th International Conference on NANO-structures SElf-Assembly, 07.-11.07.2014, Marseille, France

Permalink: https://www.hzdr.de/publications/Publ-21462
Publ.-Id: 21462


Low energy ion irradiations in material research

Facsko, S.

The ion beam centre (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf is an European leading user facility primarily dedicated to research and application of ion beam techniques in materials science. The IBC comprises various ion beam facilities (accelerators, ion beam implanters, plasma-based ion beam equipment, focused / highly-charged ion facilities) which provide a wide energy range between 100 eV and 60 MeV. Besides these facilities, structural analysis (electron microscopy and spectroscopy, X-ray scattering techniques) and sample or device processing (under clean-room conditions) are part of the IBC to deliver a “complete” user service.
Special focus of the IBC is material research with low energy ions. Irradiations of surfaces with low energy ions can induce the formation of patterns with periodicities in the range of tens to hundreds of nanometers. At off-normal angle of incidence between 50° and 70° to the surface normal ripple patterns oriented perpendicular to the ion beam direction are observed. At normal incidence or for incidence angles smaller than 50° smoothing dominates on elemental materials, like Si and Ge. However, in contrast to irradiations at room temperature pattern formation is observed at normal ion incidence irradiations performed at temperatures above the recrystallization temperature of the material. Depending on the surface orientation checkerboard patterns with two-fold, three-fold, or six-fold symmetry reflecting the crystal structure of the irradiated surface are formed (Fig. 1).
Moreover, low energy highly charged ions are used to create nanostructures on surfaces and in thin membranes by single ion impacts. In this case the release of the potential energy of the ions leads to a local phase transformation of the material. Currently a new facility for highly charged ions is developed to enable controlled single ion implantation with a positioning accuracy of a few nanometers only.

Keywords: ion irradiation; highly charged ions; surface patterning; nanostructures

Related publications

  • Lecture (others)
    Seminar, 20.06.2014, Cork, Ireland

Permalink: https://www.hzdr.de/publications/Publ-21461
Publ.-Id: 21461


Energy Loss and Charge Exchange of Highly Charged Ions in Carbon Nanomembranes Nanomembranes

Facsko, S.; Wilhelm, R. A.; Gruber, E.; Heller, R.; Aumayr, F.

During the interaction of highly charged ions with solids the ions potential energy, i.e. the stored ionization energy, is released via multiple charge exchanges on a fs time scale. Thus, HCIs reach charge equilibrium after passing only a few nanometers of the solid. The dependence of the charge state on the stopping force of the ions is therefore not accessible in irradiation experiments with bulk material. In order to investigate this pre-equilibrium regime films of just a few nanometers have to be used.
We examined the charge state and the energy loss of highly charged Xe ions after their passage through 1 nm thick carbon nanomembranes. Surprisingly, two distinct exit charge distributions were observed [1]. Part of the ions are passing the membrane with almost now charge loss, whereas the other part loose most of their charge. Apparently, the measured charge distribution reflects two different impact parameter regimes. Ions with trajectories far away of any C atom of the membrane can stabilize only few electrons and exit therefore in a high charge state, whereas ions with trajectories close to a C atom can capture enough electrons and exit the membrane in a low charge state. The different impact parameter regimes are also connected to different energy losses: ions with large impact parameters are practically not stopped, whereas ions in close collisions exhibit high stopping force which is strongly dependent on the incident charge state.
The charge distribution and energy loss of Xeq+ ions of different incident charge states up to q=30 will be presented and the implication for the formation of holes in these nanomembranes by the HCIs [2] will be discussed.

[1] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).
[2] R. Ritter, R.A. Wilhelm, M. Stöger-Pollach, R. Heller, A. Mücklich, U. Werner, H. Vieker, A. Beyer, S. Facsko, A. Gölzhäuser, F. Aumayr, Appl. Phys. Lett. 102, 063112 (2013).

Keywords: highly charged ions; nano membranes; energy loss

Related publications

  • Lecture (others)
    Seminar an der Fakultät für Physik der Universität Bielefeld, 06.06.2014, Bielefeld, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21460
Publ.-Id: 21460


Ion Induced Surface Patterning - The Role of Surface Currents

Facsko, S.; Liedke, B.; Ou, X.; Heinig, K. H.

The formation of these periodic surface patterns during ion irradiation is generally ascribed to the interplay of a sur- face instability, i.e. ion induced roughening, and smoothing mechanisms [2]. Different mechanisms have been proposed for surface roughening: The Bradley-Harper (BH) mecha- nism describes the curvature dependent sputtering whereas the Carter-Vishnyakov (CV) mechanism accounts for mass drift by momentum transfer from the incoming ions. Sur- face smoothing is accomplished by surface diffusion, and surface viscous flow [2].
2.2. ReverseEpitaxy
At temperature above the dynamic recrystallization temper- ature of the material a new kind of pattern is formed on the surface during ion irradiation [3]. At these conditions the surface remains crystalline and an additional surface in- stability appears due to the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms or vacancies to cross terrace steps. The symmetry of the pattern is now given by the crystalline symmetry of the surface. In Figure 1 patterns on different crystalline Ge surfaces irradiated with 1 keV Ar+ at normal incidence are shown: a checkerboard pattern with four-fold symmetry on the Ge(100) surface ori- ented along h100i crystal directions is visible in the atomic force microscopy (AFM) in Fig. 1a). On the Ge(111) sur- face a pattern with three-fold symmetry is formed by ion irradiation (Fig. 2b).

Keywords: ion irradiation; self-organized patterning; ripples

Related publications

  • Lecture (Conference)
    20th International Workshop on Inelastic Ion-Surface Collisions, 16.-21.02.2014, Wirrina Cove, Australien

Permalink: https://www.hzdr.de/publications/Publ-21459
Publ.-Id: 21459


Ion Beam Analysis in a Helium Ion Microscope

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

Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of below 0.3 nm and the highest field of depth make them a unique tool in surface imaging. So far the possibilities to identify target materials (elements) are rather limited.
In the present contribution we will show concepts as well as preliminary studies on the capability, efficiency and the limits of applying (Rutherford) Backscattering Spectrometry (RBS) within a HIM device to image samples with target mass contrast and to analyze target compositions.
We will present different concepts of how to realize RBS in a HIM and point out mayor challenges and physical limitation.

Keywords: Helium Ion Microscope

Related publications

  • Poster
    AVS 61st International Symposium & Exhibition, 09.-14.11.2014, Baltimore, United States of America
  • Poster
    19th International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, Leuven, Belgium
  • Lecture (Conference)
    Ionenstrahlen & Nanostrukturen, 20.-22.07.2014, Paderborn, Deutschland
  • Lecture (Conference)
    Ionenstrahlen in Forschung und Anwendung, 13.-14.06.2013, Leipzig, Deutschland
  • Poster
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 18.03.2015, Berlin, Deutschland
  • Invited lecture (Conferences)
    ZEISS ORION User Meeting, 15.04.2015, Empoli, Italy
  • Poster
    3rd Dresden Nanoanalysis Symposium, 17.04.2015, Dresden, Deutschland
  • Lecture (others)
    PhD Seminar, 31.08.2015, Dresden, Deutschland
  • Lecture (others)
    Zeiss Meeting, 27.01.2015, Dresden, Deutschland
  • Lecture (others)
    Meeting at Ion Microscopy Innovation Center at Carl Zeiss Microscopy LLC, 20.11.2014, Peabody, United States of America
  • Lecture (others)
    Group Meeting at Rutgers University, 19.11.2014, Rutgers, United States of America
  • Poster
    9th PhD seminar, Altenberg, 26.09.2014, Altenberg, Deutschland
  • Lecture (others)
    FWI Internal Meeting, 14.06.2014, Weinböhla, Deutschland
  • Lecture (others)
    8th PhD Seminar, 08.10.2013, Bautzen, Deutschland
  • Lecture (others)
    Annual FWI PhD Seminar, 02.09.2013, Dresden, Deutschland
  • Lecture (others)
    Internal FWI Meeting "Statusklausur", 10.07.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21458
Publ.-Id: 21458


Bioleaching von Kupferschiefer- ecometals

Kutschke, S.; Dirlich, S.

Vorstellung des aktuellen arbeitsstands im Projekt Ecometals

  • Lecture (others)
    Treffen des TK Geobiotechnologie, 29.09.2014, Aachen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21457
Publ.-Id: 21457


Seltene Erden in Mikroorganismen

Kutschke, S.

Bisher galten die Seltenen Erden nicht als biologisch bedeutsam. Forscher des Max-Planck-Instituts für medizinische Forschung entdeckten in dem acidophilen und thermophilen Bakterium Methylacidiphilium fumarolicum kürzlich eine Methanol-Dehydrogenase, die Seltene Erden als Kofaktor benötigt (vgl. Journal Club, BIOspektrum 7/13, S. 762). M. fumarolicum ist dabei in der Lage mehr Seltene Erden aus der Umwelt aufzunehmen, als er zum Überleben benötigt. Möglicherweise speichert er die Metalls in der Zelle. Das könnte ihn für Biomining interessant machen. Seltene Erden sind zwar nicht selten, aber nur an wenigen Stelen existieren abbauwürdige Vorkommen.

  • BIOspektrum 20(2014)1, 99

Permalink: https://www.hzdr.de/publications/Publ-21456
Publ.-Id: 21456


Efficient and accurate identification of platinum group minerals by a combination of Mineral Liberation Analysis and Electron Probe Microanalyser with a new approach of offline overlap correction of Platinum Group Elements Concentrations

Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.

Identification and accurate characterisation of platinum group minerals (PGM) is a very cumbersome procedure due to their grain sizes that are mostly below 10 µm and a light microscopic appearance that is rather inconspicuous. A novel strategy for finding PGM and quantifying their composition was applied by combining a mineral liberation analyser (MLA), a point logging system and an electron probe microanalyser (EPMA).
As a first step the PGM are identified, using the MLA. Grains identified as PGM are then marked and coordinates recorded and transferred to the EPMA. Case studies illustrate that the combination of MLA, point logger and EPMA results in the identification of several times more PGMs than by careful reflected light microscopy. Wavelength dispersive spectrometer analyses of PGM by EPMA require considerable caution due to overlaps of X-rays on both peak and background of almost all PGE and associated elements. X-ray lines suitable for quantitative analyses need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight percent proportions has been developed and explained in detail. Results obtained with the procedure proposed in this study attain acceptable totals and atomic proportions, concluding that the applied corrections are appropriate.

Permalink: https://www.hzdr.de/publications/Publ-21455
Publ.-Id: 21455


Euler-Euler-Modelling of Segregated Flows and Flows with Transitions between Different Flow Morphologies

Höhne, T.

Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. Special flow characteristics as flow rate, pressure drop and flow regimes have always been of engineering interest. The numerical simulation of free surface flows can be performed using phase-averaged multi-fluid models, like the homogeneous and the two-fluid approaches, or non-phase-averaged variants. The approach shown in this paper within the two-fluid framework is the Algebraic Interfacial Area Density (AIAD) model. It allows the macroscopic blending between different models for the calculation of the interfacial area density and improved models for momentum transfer in dependence on local morphology. An approach for the drag force at the free surface was introduced. The model improves the physics of the existing two fluid approaches and is already applicable for a wide range of industrial two phase flows. A further step of improvement of modelling the turbulence was the consideration of sub-grid wave turbulence (SWT) that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. The new approach was verified and validated against horizontal two-phase slug flow data from the HAWAC channel and smooth stratified flow experiments of a different rectangular channel. The results approve the ability of the AIAD model to predict key flow features like liquid hold-up and free surface waviness. Furthermore an evaluation of the velocity and turbulence fields predicted by the AIAD model against experimental data was done. The results are promising and show potential for further model improvement.

Keywords: CFD; horizontal flow; AIAD; two-phase flow; HAWAC; HZDR

  • Book chapter
    Guan Heng Yeoh: Handbook of Multiphase Flow Science and Technology, Singapore: Springer, 2017, 978-981-4585-86-6
    DOI: 10.1007/978-981-4585-86-6_5-1
  • Book chapter
    Guan Heng Yeo,h Jyeshtharaj B. Joshi: Handbook of Multiphase Flow Science and Technology, Singapore: Springer Verlag, 2023, 978-981-287-091-9, 233-267
    DOI: 10.1007/978-981-287-092-6_5

Permalink: https://www.hzdr.de/publications/Publ-21454
Publ.-Id: 21454


Diffusion of Carbon Atoms at the Carbon-Nickel Interface During Graphitization

Wenisch, R.; Hübner, R.; Gemming, S.; Munnik, F.; Krause, M.

Interface dynamics play a crucial role in the Nickel catalyzed synthesis of carbon nanotubes, carbon nanoribbons and graphene. Interface dynamics are studied by deposition of atomic C on Ni at temperatures of 23−550°C.
The obtained films are characterized by transition electron microscopy, Ramanspectroscopy, nuclear reaction analysis and X-ray photoelectron spectroscopy. Bulk diffusion and carbon dissolution are found to be negligible under the chosen experimental conditions leaving surface/interface diffusion as the main graphitization mechanism.
Graphitic ordering starts at ~ 250°C and increases further at temperatures > 500°C. The initial graphitization occurs parallel to the Ni surface. As the growth continues, additional atomic planes turn perpendicular. First results are shown for the Si-Ag system processed under similar deposition conditions.

Related publications

  • Poster
    International Winterschool on Electronic Properties of Novel Materials, 08.-15.03.2014, Kirchber in Tirol, Österreich

Permalink: https://www.hzdr.de/publications/Publ-21453
Publ.-Id: 21453


Carbon-Nickel Interface Dynamics During Physical Vapor Deposition

Wenisch, R.; Krause, M.; Hübner, R.; Gemming, S.; Abrasonis, G.

Interface dynamics play a crucial role in Nickel catalyzed fabrication of carbon nanotubes, carbon nanowires and graphene. Interface dynamics are studied by deposition of atomic C on Ni at temperatures of 23–550°C. The obtained films are characterized by transition electron microscopy, Raman-spectroscopy, nuclear reaction analysis and X-ray photoelectron spectroscopy. Bulk diffusion and solubility are found negligible in the present experiments leaving surface diffusion as the main graphitization mechanism. The presented process may open new avenues for the fabrication of graphene on Ni at low temperatures (< 300°C).

Related publications

  • Poster
    DPG Früjahrstagung, 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21452
Publ.-Id: 21452


First experiences with SRF Gun II

Teichert, J.

The talk presents status and preliminary results of the ELBE SRF gun II.

Keywords: photo injector; superconducting RF; electron source

Related publications

  • Lecture (others)
    PITZ collaboration meeting, 02.-03.12.2014, Zeuthen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21451
Publ.-Id: 21451


α integrin targeting for radiosensitization of three-dimensionally grown human head and neck squamous cell carcinoma cells.

Steglich, A.; Vehlow, A.; Eke, I.; Cordes, N.

Integrin cell adhesion molecules play a crucial role in tumor cell resistance to radio- and chemotherapy and are therefore considered attractive targets for cancer therapy. Here, we assessed the role of β1 integrin-interacting α integrin subunits in more physiological three-dimensional extracellular matrix grown head and neck squamous cell carcinoma (HNSCC) cell cultures for evaluating cytotoxic and radiosensitizing potential. α2, α3, α5 and α6 integrins, which are overexpressed in HNSCC according to Oncomine database analysis, were coprecipitated with β1 integrin. More potently than α2, α5 or α6 integrin inhibition, siRNA-based α3 integrin targeting resulted in reduced clonogenic cell survival, induced apoptosis and enhanced radiosensitivity. These events were associated with diminished phosphorylation of Akt, Cortactin and Paxillin. Cell line-dependently, simultaneous α3 and β1 integrin inhibition led to higher cytotoxicity and radiosensitization than α3 integrin blocking alone. Stable overexpression of wild-type and constitutively active forms of the integrin signaling mediator focal adhesion kinase (FAK) revealed FAK as a key determinant of α3 integrin depletion-mediated radiosensitization. Our findings show that α3 integrin is essentially involved in HNSCC cell radioresistance and critical for a modified cellular radiosensitivity along with β1 integrins.

Keywords: FAK; Head and neck cancer; Radiosensitivity; α3 integrin; β1 integrin

Permalink: https://www.hzdr.de/publications/Publ-21450
Publ.-Id: 21450


Hyperbranched polyglycerols: Biodistribution and structure-compatibility relationships

Pant, K.; Stephan, H.; Bergmann, R.; Pietzsch, J.; Gröger, D.; Haag, R.; Spizzia, L.; Graham, B.

Dendritic polyglycerols (PG’s) are promising biocompatible scaffolds for drug delivery, targeting and other therapeutic applications due to their low polydispersity, multivalency and convenient large scale one-pot synthesis. In particular, the sulphated polyglycerol derivatives are potent candidates for, e.g., anti-inflammatory drugs due to their ability to inhibit the L & P Selectins [1]. It is therefore crucial to know the physiological fate of these scaffolds in order to establish their suitability for potential biomedical applications. The present work deals with the biodistribution studies of the dendritic polyglycerol sulphate derivatives (dPGS, 10 kDa) using 64Cu (t1/2 = 12.5 h) for tracking them with positron emission tomography (PET). Since PG’s do not have any metal binding sites, coupling of bifunctional chelators (BFCs) capable of binding 64Cu to PG’s is required. A prerequisite for achieving reliable biodistribution data is that the BFCs form stable complexes with 64Cu. For this reason, BFCs based on macrocyclic triazacyclononane containing two pendant pyridyl rings (DMPTACN) [2] (LogCu-L > 25) have been synthesized with maleimide and isothiocyanate coupling groups to enable conjugation to mercapto and amine groups of the polyglycerol derivatives. These conjugates form highly stable radiocopper complexes at room temperature within 5 minutes. The conjugates are resistant to transchelation and are stable in the presence of superoxide dismutase. The biodistribution of the dPGS has been studied in healthy Wistar rats for 72 h. Furthermore, in order to exploit the properties PG’s for further applications, the effect of size, charge and surface groups have been investigated. Cytotoxicity has been studied using a selection of cell lines. The results from these studies show that these polyglycerols are highly biocompatible and potential candidates for theranostics that combine multimodal imaging and drug targeting.

References:

[1] H. Türk et al, Bioconjug. Chem. 2004, 15, 162-167.
[2] G. Gasser et al, Bioconjug. Chem 2008, 19, 719-730

  • Poster
    7th Asian Biological Inorganic Chemistry Conference (AsBIC7), 30.11.-05.12.2014, Gold Coast, Australia

Permalink: https://www.hzdr.de/publications/Publ-21449
Publ.-Id: 21449


Synthesis and biodistribution of 64Cu and 68Ga radiolabelled dendritic polyglycerol sulfate derivatives

Pant, K.; Stephan, H.; Bergmann, R.; Steinbach, J.; Gröger, D.; Haag, R.

Dendrimers and their hyper-branched analogues, particularly highly biocompatible polyglycerols, claim an interesting area of research due to their multivalency, simplicity in preparation and large scale one-pot synthesis. They can be modified and functionalized using manifold strategies. Dendritic polyglycerol sulfates (dPGS) are potent substances that serve as candidates for anti-inflammatory drugs [1]. The presence of amino functionalities can be further exploited for the introduction of fluorescent dyes, drugs, radiolabels or any moiety of interest. To achieve detailed information about the in vivo fate of certain compounds, nuclear imaging techniques are the most reliable methodologies. Ex vivo imaging using 35S–isotopic labelling of these macromolecules has already been reported [2]. Positron emission tomography (PET) provides quantitative distribution data in vivo. The convenient detection of the emitted radiation from the radionuclides in combination with the high sensitivity underlines the utility of nuclear imaging techniques. If a metal is used as a radiolabel, the choice of an appropriate bifunctional chelator (BFC) is the crucial point. The BFCs shall permit an easy linkage to the polymers and rapid, unsophisticated, stable labelling.
Herein, protocols for the attachment of BFCs for the positron emitting radionuclides 64Cu (t1/2 = 12.7h) and 68Ga ((t1/2 = 68 min) on dPGS scaffolds are reported. For this reason, derivatives based on 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane (DMPTACN) and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) equipped with suitable linker groups have been applied. Efficient radiolabelling procedures have been established (>99% RCY). The stability of the radiolabelled bioconjugates has been studied in presence of strong competing chelators (EDTA/Cyclam) as well as in presence of HSA (human serum albumin), SOD[3] (for Cu-Conjugates) and transferrin (for Ga-conjugates). Furthermore, PET studies using Wistar rats have been performed and discussed.

References
[1] J. Demedde, A. Rausch, M.Weinhart, S. Enders, R. Tauber, K. Licha, M. Schimer, U. Zugel, A. von Bonin, R. Haag, Proc. Natl. Acad. Sci. 107, 19679 (2010).
[2] C. Holzhausen, D. Groger, L. Mundhenk, P. Welker, R. Haag, A. D. Gruber, Nanomed. 9,

  • Lecture (Conference)
    5th EuCheMS Chemistry Congress, 31.08.-04.09.2014, Istanbul, Turkey

Permalink: https://www.hzdr.de/publications/Publ-21448
Publ.-Id: 21448


Temporal changes in mantle wedge geometry and magma generation processes in the Central Andes: towards linking petrological data to thermomechanical models

Heistek, R.; Brandmeier, M.; Freymuth, H.; Wörner, G.

Temporal and spatial patterns of Neogene ignimbrite magmatism in the Central Andes were analyzed using GIS and geostatistical modeling. We compiled a comprehensive ignimbrite database using available literature, satellite imagery and geochemical data. 203 individual ignimbrite sheets were digitized in GIS, for which geochemical, isotopic (partly), and geochronological data are available from literature sources and own data (http://www.arcgis.com/home/item.html?id=47038ddc0628473f9f0ce67aa2eff8be). Based on this analysis, we estimate composition, volumes and sources of erupted ignimbrite magmas through space and time for five segments of the Central Andes.
The total erupted ignimbrite magma volume is estimated to be about 31,000 km3 for the past 30 Ma, with the highest average eruption rates (rm) for the northern Puna segment (3.4 km3 Ma-1 km (arc)-1), followed by 0.7 km3 Ma-1 km (arc)-1 for the Altiplano. For Southern Peru, rm is smaller (0.5 km3Ma-1km (arc)-1), which might be due to the lack of knowledge about intra-caldera volumes. Furthermore there is a clear N-S “younging” of ignimbrite pulses. Major pulses of high magma eruption rate occurred at 19-24 Ma (e.g. Oxaya, Nazca Group), 13-14 Ma (e.g. Huaylillas ignimbrites), 6-10 Ma (Altiplano and Puna ignimbrites, e.g. Vilama ignimbrite) and 3-6 Ma (e.g. Atana, Los Frailes, Toconao). In contrast, small volume young ignimbrites from 0-3 Ma (e.g. Lauca-Perez, Purico) do not show the spatio-temporal pattern of eruptions that are documented for the large- volume ignimbrite flare-ups.
Compositional and Sr-O isotopic data indicate that ignimbrite magmas are more crustally derived in younger flare-ups in the Southern Central Andes (up to 50 % crustal melts) compared to older ignimbrites in the north (only up to 20 % crustal melts). This suggests that thermal conditions, juvenile magma production in the mantle, thickness, and/or composition of the crust must have been different along the Central Andes at the time when ignimbrite flare up magmas formed.
The amount of juvenile magmas that entered the crust and the degree and volume of partial melting within the crust can thus in principle be constrained in time and space by these data. Such data are essential in order to understand the thermal evolution of the Andean crust in space and time.
The Miocene large-volume, plateau forming ignimbrites always overly a pronounced unconformity and occur after a time with no magmatism. They are followed, however, by andesitic arc magmatism characterized during the Late Miocene by low angle, large-volume (~2.2 km3 per lava flow) volcanic shields with long single lava flows up to 20 km. These shields are succeeded by younger and more evolved steeply-sided strato-cones that characterize much of the CVZ active volcanic front for Pliocene-Quaternary times. Andesites in such young stratovolcanoes (~0.7 km3 per lava flow) are often characterized by amphibole phenocrysts.
In principle, the transition between these andesite regimes could be due to:
(1) a change in the mantle melting regime from decompression (hot and dry?) to flux melting (wet and lower T?),
(2) different rates in magma production and effusion, and
(3) different P-T-regimes of magma evolution within the crust as is shown by the depletion in HREE and Y from Miocene to Pleistocene volcanic rock caused by a residual garnet after crustal assimilation in a thickened crust.

To understand the shift from andesite shields to stratovolcanoes we studied Miocene to modern Central Andean volcanic rocks that represent different ages but are similar in petrography and composition in order to test differences in processes of magma generation. Based on a survey of ~1300 chemical analyses of lava samples (http://andes.gzg.geo.uni-goettingen.de/) we selected three representative sample types: (1) most mafic samples (50-55 % SiO2), (2) intermediate andesites representing 63 % of the data (55-60 % SiO2), and (3) felsic samples (60-65 % SiO2), all of which were identified before as important endmember magma type in the Central Andes. Using a range of geothermometers, hygrometers and MELTS modelling we show that the P-T parameters at the time of eruption, for a given composition, remained surprisingly constant trough time and throughout the Central Andes (e.g. 975 °C to 985 °C for 2-px thermometry). Moreover, the depth of the last (phenocryst) crystallization of Miocene to Present magmas took place between 9 and 3.5 km throughout Andean history. These observations clearly indicate that estimated temperatures only reflect the late crystallization history at shallow levels and that any distinct regimes of magma formation in the mantle wedge that may have existed are entirely dampened out during the passage through the crust. Density, viscosity and degassing of andesite magmas control the latest stages of ascent and crystallization and these parameters are independent of crustal conditions, subduction geometry and mantle wedge conditions. Therefore, the thickened upper crust not only serves as a chemical filter for mantle wedge magmas but also controls (and synchronizes) P-T conditions of crystallization as recorded in erupted products.
Deep evolution at the level of the magma sources and lower crust, where assimilation and magmatic differentiation takes place, is thus completely decoupled from the shallow processes of late crystallization. Therefore only the rate of effusion, and by implication, magma production and upper crustal stress regime remain as primary factors that may have influenced differences between Miocene and Recent magmatic products.
Since the sequence of distinct magmatic regimes (plateau-ignimbrites, shield andesites and evolved stratovolcanoes) is diachronous during the past 26 Ma of Andean evolution with ages getting younger from N to S. This suggests control by “deeper” processes guided by the geometry of the slab and the thermal evolution of the upper plate during Andean orogeny. As patterns, timing of events, subduction parameters and magma production rates in the mantle wedge change regionally and temporally during ongoing thickening of the Central Andean crust, the upper plate reacts at any given location individually to these changes according to its present thermal state, crustal composition, magmatic history and tectonic stress conditions at that time and space.
We propose that large-volume ignimbrite eruptions occurred in the wake of subduction of the Juan-Fernandez ridge that passed below the Central Andes from N to S during the past 25 Ma. This event resulted in compression, uplift, low angle subduction (flat slab) and fluid release in a first stage, followed by massive inflow and melting of asthenospheric mantle after the passing of the ridge when the slab again steepened rapidly. This in turn caused massive melting within the crust aided by advective heat transport shortly after slab steepening. Differences in chemical and isotopic composition of the large-volume ignimbrites are related to changes in crustal thickness, and its “preconditioning” during the Anden orogeny over time.
The change in effusion rate during the Miocene to Pliocene/Quarternary may be the only parameter that relates to changing angles and/or convergence rates of the slab. Since only convergence rates changed during the last 26 Ma (Sérbier and Solar, 1991), this parameter likely controls magmatic activity (Cagnoicle et al., 2007). In southern Peru, Miocene voluminous magmatic activity correlates with high convergence rates, both decreasing in the last 10 Ma (Sébrier and Soler, 1991).
Previous model predictions for arc magmatism (Sobolev et al., 2006) follows from the comparison between the evolution of tectonic shortening and the evolution of the mantle temperature beneath the magmatic arc. Processing the delamination material throught the asthenospheric wedge by corner flow results in an increasing shortening rate. Simultaneously, the temperature of the asthenospheric wedge beneath the magmatic arc decreases, which in turn should lead to reduced magmatic activity. However, apart from the Puna (Kay and Kay, 1993) and Northern Altiplano (Back and Zandt., 2002; Yuan et al., 2002)) no evidence exists for mantle lithosphere delamination in the Central Andes. Therefore a new model based on our volumes, eruption rates, petrological constraints and the movement of the Juan Fernández ridge should give a better understanding of the controlling factors of arc magmatism.

Back SL, Zandt G (2002) The nature of orogenic crust in the Central Andes. J Geophys Res 107:n doi 10.1029/2000JB000124
Cagnioncle AM, Parmentier EM, Elkins-Tanton LT (2007) Effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries. J Geophys Res 112: B09402
de Silva, S., Gosnold, W.D. (2007) Episodic construction of batholiths: Insights from the spatiotemporal development of an ignimbrite flare-up. J. Volcanol. Geotherm. Res. 167: 320–335.
Kay RW, Kay SM (1993) delamination and delamination magmatism. Tectonophysics 219:177 - 189
Sébrier, M., Solar, P. 1991. Tectonics and magmatism in the Peruvian Andes from late Oligocene time to the Present. Geological Society of America 265, 259–278.
Sobolev SV, Babeyko AY, Koulakov I, Oncken O (2006) Mechanism of the Andean orogeny: insight from numerical modeling. In: Oncken O, Chong G, Franz G, Giese P, Götze H-J, Ramos VA, Strecker MR, Wigger P (eds) The Andes – active subduction orogeny. Frontiers in Earth Science Series, Vol 1. Springer-Verlag, Berlin Heidelberg New York, pp 513–536, this volume
Yáñez, G., Cembrano, J., Pardo, M., Ranero, C., Selles, D., 2002. The Challenger–Juan Fernández– Maipo major tectonic transition of the Nazca–Andean subduction system at 33–34 S: geodynamic evidence and implications. Journal of South American Earth Sciences 15, 23‐38.

  • Contribution to proceedings
    GeoMod 2014, 31.07.-05.09.2014, GFZ Potsdam, Germany

Permalink: https://www.hzdr.de/publications/Publ-21447
Publ.-Id: 21447


From basalt to ryholite: Uniform components and mixing regimes in magma systems of the Central Andes

Wörner, G.; Banaszak, M.; Brandmeier, M.; Heistek, R.

The major element most mafic compositions of Quaternary to Miocene magmatism in the Andean Central Volcanic Zone are rather variable but present throughout the evolution of the Central Andes in the past 20 Ma. Compositions encompass high-K to medium-K calc-alkaline basaltic andesites (52-55 SiO2 wt%) and have large ranges in major (3.6-9.4 wt% MgO, 4-7 wt% Na2O+K2O, 0.8-1.8 wt% TiO2) and trace element concentrations (9-197 ppm Ni, 501-1944 ppm Sr, 95-257 ppm Zr), as well as trace element ratios (LILE/HFSE: 93>Sr/Y>24; LREE/HREE: 8>La/Yb>63). Such a remarkable variability and the absence of truly primitive lavas in the CVZ since the onset of crustal thickening reflects distinct petrogenetic processes during ascent and evolution of mantle-derived melts traversing exceptionally thick continental crust (70 km).
Our statistical analysis (Polytopic Vector Analysis, PVA) on a on a subset of our large data base of Andean magmas (>1000 samples) which have complete major- and trace element data and isotope compositions shows that the entire compositional space of Central Andean magmas can be described by the three same endmembers: (1) a low-Mg high-Al calc-alkaline basaltic andesite (BA), (2) a incompatible trace element enriched basalt (EB), and 3) a high-K calc-alkaline rhyodacite (RD). A first mixing stage produces a range of hybrid baseline magmas consisting of the EB and BA. These represent typical recharge magmas into more evolved magma chambers at shallower crustal levels. There, a second mixing stage occurs with mixing between the already mixed, mafic (BA+EB) and the silicic RD component, which typically is crystal rich. Mixing proportions between these endmembers vary widely and magma compositions of endmembers and/or hybrids are overprinted by different degrees of magmatic differentiation and crustal assimilation.
These three endmember magmas enclose nearly all Quaternary CVZ lavas in a mixing triangle and accounts for the entire compositional variability of the Quaternary volcanic rocks in the CVZ. A first mixing stage produces hybrid baseline magmas consisting of the EB and BA. The second mixing stage represents shallow crustal magma mixing between the already mixed, mafic (BA+EB) and the silicic RD components. Mixing proportions between these endmembers vary widely and magma compositions of endmembers and/or hybrids are overprinted by different degrees of magmatic differentiation and up to 20% crustal assimilation.
A particular setting is required for andesite lava fields that occur throughout the Central Andes (Huambo, Andagua, Negrillar). These Quaternary lava fields are unrelated to stratovolcanoes and probably reflect direct differentiation of the mafic hybrids towards phenocryst poor pyroxene-andesites without interaction with crystal-rich shallow crustal magmas.
A survey of our data base including older (Pliocene and Miocene) andesites and dacites shows a surprisingly similar compositional pattern.
The BA, EB, and RD endmembers represent distinct magma sources: the mantle wedge, enriched lithospheric mantle, and the continental crust, respectively. Therefore, these endmembers are expected to be ubiquitous in the central Andes and have uniform geochemical character.
These mixed magmas give rise to and are genetically associated with large volume ignimbrite eruptions (ignimbrite “flare-ups” with >3000km3 erupted in 1 Ma) that are hybrids between 20 to 50% of a crustal melting endmember and a mantle component. Further evolution of these silicic magmas towards the thermal minimum results in rather uniform magma compositions smoothing out compositional diversity in the constituent magmas. A rigorous statistical analyses of the ignimbrite compositional data throughout the Central Andes identifies four groups that reflect the assembly of large magma volumes from slightly distinct sources at different P-T-X conditions.

  • Contribution to proceedings
    IMA2014 - 21st General Meeting of the International Mineralogical Association, 01.-05.09.2014, Sandton Convention Centre, Gauteng South Africa, South Africa

Permalink: https://www.hzdr.de/publications/Publ-21446
Publ.-Id: 21446


Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations

Szücs, T.; Bemmerer, D.; Reinhardt, T. P.; Schmidt, K.; Takács, M. P.; Wagner, A.; Wagner, L.; Weinberger, D.; Zuber, K.

The main background above 3MeV for in-beam nuclear astrophysics studies with g-ray detectors is caused by cosmic-ray induced secondaries. The two commonly used suppression methods, active and passive shielding, against this kind of background were formerly considered only as alternatives. In this work the study of the effects of active shielding against cosmic-ray induced events at a medium deep location is performed. Background spectra were recorded with two actively shielded HPGe detectors. The experiment was located at 148m below the surface of the Earth in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data with the same detectors at the Earth's surface, and at depths of 45m and 1400 m, respectively.

Keywords: Nuclear astrophysics; underground physics; active shielding; gamma-ray background; cosmic-ray induced background; germanium detectors

Permalink: https://www.hzdr.de/publications/Publ-21445
Publ.-Id: 21445


Migrating Ignimbrite Flares in the Central Andes, Implications for Crustal Evolution Based on Chemical, Isotopic, Geochronological, and GIS-Based Volumetric Data

Wörner, G.; Brandmeier, M.; Freymuth, H.; Heistek, R.

Temporal and compositional patterns of Neogene ignimbrites in the Central Andes were analysed using GIS and geostatistical modelling based on 203 digitized ignimbrite sheets for which geochronological, geochemical, and Sr-Nd-Pb-isotopic data on pumices as well as Sr-O isotopes on minerals from selected samples were compiled and compared to compositional and isotopic data from andesite lavas. Composition, timing, volumes and sources of erupted ignimbrite deposits are thus constrained and magma volumes through space and time are calculated. The total erupted ignimbrite magma volume of 31,000 km3 (minimum value) in the past 30 Ma indicate an average magmatic addition of 20-30 km3*Ma/km, similar to the basaltic “base”-flux for arc magmatism. Ignimbrite flare-ups are, however, rather punctuated, short-lived events well separated in space and time. There is a clear N-S “younging” of ignimbrite pulses from N to S at 19-24 Ma, 13-14 Ma, 6-10 Ma and 3-6 Ma. Ignimbrite eruptions occurred in the wake of subduction of the Juan-Fernandez ridge on the Nazca Plate passing below the Central Andes from N to S. Low angle subduction caused compression and fluid release is followed by massive inflow and melting of asthenospheric mantle when the slab steepened again after the passing of the ridge. This in turn caused massive melting within the crust aided by advective heat transport. Differences in chemical and isotopic composition of the large-volume ignimbrites are related to changes in crustal thickness, and different “preconditioning” during the Andean orogeny at a given space in time. Isotope data and whole rock compositional data suggest a higher degree of crustal assimilation for the younger Altiplano ignimbrites in the S (c. 50%) compared to the older (22-19 Ma) ignimbrites in the N were the crustal component is significantly less (20%). REE compositions reflect changes in crustal thickness with a "transition" at c. 13-9 Ma that can be related to accelerated crustal shortening and lower crustal heating at that time. There is no “single” ignimbrite flare up, we suggest a more dynamic scenario, with “flares” moving from N to S across the Central Andes during the past 25 Ma. Our database yield volumes of mantle and crustal magmas produced through time and space and should aid to constrain numerical models of Andean geodynamic processes.

  • Contribution to proceedings
    AGU Fall Meeting, 15.-19.12.2014, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-21444
Publ.-Id: 21444


Terahertz dephasing of intersublevel transitions in InAs/GaAs quantum dots

Schneider, H.; Teich, M.; Winnerl, S.; Stephan, D. R.; Wilson, L. R.; Helm, M.

Semiconductor quantum dots (QD) exhibit a discrete spectrum of bound electronic sublevels. While interband transitions in these synthetic quasi-atoms have been exploited intensively, much less attention has been devoted to excitation between sublevels within the same band. Only recently a systematic study of electron intersublevel relaxation has been reported at various energies below the longitudinal optical phonons [1]. In particular, very long electronic relaxation times up to >1 ns were observed. Therefore the question arises whether the associated dephasing time T2 has similar values.
We will report on THz four-wave mixing (FWM) in self-assembled InAs/GaAs QDs using the free-electron laser FELBE at HZDR. In these QDs, the s-p intersublevel transition has been reduced by interdiffusion to energies below the Reststrahlen band. Dephasing times up to 600 ps have been determined at 18 meV photon energy. By comparing pump-probe and four-wave mixing measurements, we find that dephasing is mainly caused by acoustic phonon scattering, and that there is no significant influence of any pure dephasing process at low temperature [2]. The latter property makes QDs promising for quantum optical applications at THz frequencies.
[1] E. A. Zibik et al., Nature Materials 8, 803 (2009).
[2] M. Teich et al., , Appl. Phy. Lett. 103, 252110 (2013).

Keywords: terahertz; intersublevel transitions; quantum dot; carrier relaxation

Related publications

  • Lecture (Conference)
    Fifth International Symposium on Terahertz Nanoscience (TeraNano V), 01.-05.12.2014, Fort-de-France, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-21443
Publ.-Id: 21443


Optimization and radiolabeling of ultrasmall upconverting nanoparticles for multimodal cancer imaging

Hesse, J.; Graham, B.; Geipel, G.; Grenzer, J.; Hübner, R.; Spiccia, L.; Steinbach, J.; Stephan, H.

In recent years, multimodal imaging has obtained increasing attention since it is an attractive strategy to combine the advantages of different imaging modalities, aiming to enhance the efficiency and sensitivity of disease diagnosis and imaging of treatment progress. In this context, nanoparticles come to the fore due to their diversity and versatility. Depending on the material used, nanoparticles themselves can already constitute an imaging probe because of magnetic and/or fluorescence properties which enable magnetic resonance (MR) or optical imaging. In addition, they offer the opportunity for multiple functionalization to introduce additional labels and biospecific molecules on their surface. Nanoparticles of particular interest are the so-called “upconverting nanophosphors” (UCNPs). With their exceptional ability to convert near-infrared to visible light (upconversion), these inorganic lanthanide-doped nanoparticles are very attractive for biomedical applications. Their excitation in an optical transparency window (the “biological window” between 700-1000 nm) enables deep penetration into tissue, as well as high contrast related to minimum autofluorescence in this spectral range. Furthermore, these materials have shown no inherent toxicity effects in both in vitro and in vivo studies. Known syntheses of UCNPs generate mainly hydrophobic particles. However, there are several possibilities to achieve biocompatibility by applying different coating strategies [1]. Here, we discuss the synthesis and photophysical properties of ultrasmall (<10 nm) UCNPs based on a host lattice of nanocrystalline NaYF4 doped with Yb3+ as a sensitizer, as well as Er3+ or Tm3+ as emitter ions with an excitation wavelength at 980 nm. Additionally, by insertion of Nd3+ as a primary sensitizer, the excitation wavelength can be changed to 795 nm, resulting in deeper tissue penetration and lower heating effects associated with water absorption in the range of 1000 nm. Furthermore, by using an active shell strategy, quenching effects can be reduced. The most appropriate UCNPs were coated with amphiphilic polymers in order to achieve highly colloidally-stable, water-dispersible systems suitable for biomedical applications. In this way, further functionalization with targeting vector molecules and the introduction of bifunctional chelators is possible. By way of demonstration, a dipicolyl derivative of 1,4,7-triazacyclononane has been coupled as a radiocopper chelator to allow for 64Cu-based positron emission tomography [2].

References
1. G. Chen, H. Qiu, P. N. Prasad and X. Chen, Chem. Rev. (2014), DOI: 10.1021/cr400425h.

2. K. Pombo-García, K. Zarschler, J. A. Barreto, J. Hesse, L. Spiccia, B. Graham and H. Stephan, RSC Adv. 3, 22443 (2013).

  • Lecture (Conference)
    5th EuCheMS Chemistry Congress, 31.08.-04.09.2014, Istanbul, Turkey

Permalink: https://www.hzdr.de/publications/Publ-21442
Publ.-Id: 21442


(Iminophosphoranyl)(thiophosphoranyl)methane Rare-Earth Borohydride Complexes: Synthesis, Structures and Polymerization Catalysis

Schmid, M.; Ona-Burgos, P.; Guillaume, S. M.; Roesky, P. W.

The (iminophosphoranyl)(thiophosphoranyl)methanide {CH(PPh2=NSiMe3)(PPh2=S)}- ligand has been used for the synthesis of divalent and trivalent rare-earth borohydride complexes. The salt metathesis of the potassium reagent [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Yb(BH4)2(THF)2] resulted in the divalent monoborohydride ytterbium complex [{CH(PPh2=NSiMe3)-(PPh2=S)}Yb(BH4)(THF)2]. The 2D 31P/171Yb HMQC-NMR spectrum clearly showed the coupling between both nuclei. The trivalent bisborohydrides [{CH(PPh2=NSiMe3)-(PPh2=S)}Ln(BH4)2(THF)] (Ln = Y, Sm, Tb, Dy, Er, Yb and Lu) were obtained by reaction of [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Ln(BH4)3(THF)3]. All new compounds were characterized by single X-ray diffraction. The divalent and trivalent compounds were next used as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) and trimethylene carbonate (TMC). All complexes afforded a generally well-controlled ROP of both of these cyclic esters. High molar mass poly(ε-caprolactone) diols (Mn,NMR < 101 300 g/mol, ÐM = 1.44) and α-hydroxy,ω-formate telechelic poly(trimethylene carbonate)s (Mn,NMR < 20 000 g/mol, ÐM = 1.61) were thus synthesized under mild operating conditions.

Permalink: https://www.hzdr.de/publications/Publ-21441
Publ.-Id: 21441


Multifunctionalization of Ultrasmall Upconverting Nanoparticles for Multimodal Cancer Imaging

Hesse, J.; Graham, B.; Geipel, G.; Grenzer, J.; Hübner, R.; Spiccia, L.; Stephan, H.

The design of multimodal imaging systems for disease diagnosis and imaging of treatment progress has been receiving increasing attention in recent years. The combination of two or more imaging modalities allows the limitations of each method to be overcome and ultimately provides the ability to enhance the sensitivity and efficiency of diagnosis. A promising platform for the development of targeted imaging agents are ultrasmall nanoparticles (< 10 nm) as they offer the opportunity for multifunctionalization of the particle surface with different labels and biospecific molecules. Additionally, the nanomaterials themselves can exhibit magnetic and/or fluorescence properties that enable their applications as magnetic resonance (MR) or optical imaging probes. So-called “upconverting nanoparticles” (UCNPs) represent an intriguing class of optical imaging agents, especially for biomedical applications. The attraction of these nanomaterials derives from their capacity for excitation in the biologically transparent window (700-1000 nm), exceptional ability to convert near infrared radiation into visible light (upconversion), and capability for deep tissue, high contrast imaging related to minimum autofluorescence in this spectral range [1]. Here, we discuss the design, synthesis and surface modification of ultrasmall (<10 nm) UCNPs with an excitation wavelength of 795 nm, which are based on a host lattice of crystalline NaYF4 doped with Nd3+ and Yb3+ as sensitizers, and Er3+ or Tm3+ as emitter ions. Established strategies for producing UCNPs yield mainly hydrophobic particles[1]. We report the conversion of these into water-soluble, colloidally-stable, biocompatible and multi-functionalized platforms using polymer coating and ligand exchange strategies, and the influence of the coating on the UCNPs’ photophysical properties. As a proof-of-concept, a radiocopper (64Cu) chelator has been coupled to produce a UCNP-based bimodal imaging agent for in vitro and PET (positron emission tomography) studies.

[1] G. Chen, H. Qiu, P. N. Prasad and X. Chen, Chem. Rev., 2014, DOI: 10.1021/cr400425h.

  • Poster
    7th Asian Biological Inorganic Chemistry Conference (AsBIC7), 30.11.-05.12.2014, Gold Coast, Australia

Permalink: https://www.hzdr.de/publications/Publ-21440
Publ.-Id: 21440


Backscattered helium spectroscopy in the helium ion microscope: Principles, resolution and applications

van Gastel, R.; Hlawacek, G.; Dutta, S.; Poelsema, B.

We demonstrate the possibilities and limitations for microstructure characterization using backscattered particles from a sharply focused helium ion beam. The interaction of helium ions with matter enables the imaging, spectroscopic characterization, as well as the nanometer scale modification of samples. The contrast that is seen in helium ion microscopy (HIM) images differs from that in scanning electron microscopy (SEM) and is generally a result of the higher surface sensitivity of the method. It allows, for instance, a much better visualization of low-Z materials as a result of the small secondary electron escape depth. However, the same differences in beam interaction that give HIM an edge over other imag- ing techniques, also impose limitations for spectroscopic applications using backscattered particles. Here we quantify those limitations and discuss opportunities to further improve the technique.

Keywords: Helium ion microscopy; Ion scattering; Rutherford backscattering spectroscopy

Related publications

Permalink: https://www.hzdr.de/publications/Publ-21439
Publ.-Id: 21439


Biotechnologische Konzepte zur Gewinnung von Rohstoffen

Pollmann, K.

Übersichtsvortrag

  • Lecture (others)
    Heraeus, Workshop, 24.10.2014, Hanau/Gellhausen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21438
Publ.-Id: 21438


High resolution UHV Helium Ion Microscopy of work function, step edges and crystal structure

Hlawacek, G.; Jankowski, M.; van Gastel, R.; Wormester, H.; Zandvliet, H. J. W.; Poelsema, B.

Helium Ion Microscopy—in particular under UHV conditions—is well know for it’s high resolution imaging capabilities and the exceptional surface sensitivity. Here, we utilize both of these outstanding characteristics of this technology to visualize step edges, minute changes in composition and structural properties of a Ag/Pt alloy layer grown on Pt(111). A work function contrast of only a few ten’s of meV allows to distinguish between areas of different Ag content in the alloy layer. As a result step edges on the Pt(111) crystal overgrown by the alloy layer become visible. Furthermore, the regular arrangement of FCC and HCP areas in the alloy layer could be revealed using fast Fourier image analysis and dechanneling image contrast. The measured spacing of 6nm agrees well with the expected value. Low energy electron microscopy has been used to cross check the results and further analyse the alloy layer.
This research is supported by the Dutch Technology Foundation STW, which is the applied science division of NWO, and the Technology Programme of the Ministry of Economic Affairs.

  • Poster
    AVS 61st International Symposium and Exhibition (AVS-61), 09.-14.11.2014, Baltimore, USA

Permalink: https://www.hzdr.de/publications/Publ-21437
Publ.-Id: 21437


Effect on microstructure and hardness of 1 MeV carbon ion implantation in Al, Co and W

Meunier, C.; Vives, S.; Munnik, F.; Berthout, G.; Mikhailov, S.

Carbon implantation is used to change the surface properties of materials without changing the bulk properties in various fields such as microelectronics, optics, tribology and biomaterials. While this implantation is usually performed at energies lower than 200 keV and thus in the low energy range of the stopping power curve, here we studied the effect of a 1 MeV ion beam which is in the medium energy range. The higher energies increase the modified depth range and thereby the load-carrying ability of metal surfaces. Light (Al), medium (Co) and heavy (W) metals were chosen as substrates. Three ion fluencies of 1016 ions/cm², 1017 ions/cm², and 1018 ions/cm² were used. Nuclear reaction analysis evidenced the presence of carbon at the samples surface and at a depth in accordance with Monte-Carlo (SRIM) simulations. Glancing incidence X-ray diffraction (GIXRD) allowed us to reveal the formation of aluminum carbide while no carbide was observed for Co and W. The modifications of the lattice parameters of Co and of W were studied by Rietveld refinements of X-ray diffraction patterns. For these metals the increase of the profile asymmetry of the diffraction peaks can result from the generation of dislocations induced by irradiation. The hardness measured by nano-indentation tests increases with the carbon ion dose, and the rise of hardness is larger for aluminum and tungsten than for cobalt.

Keywords: 1 MeV carbon implantation; Ion beam; Metals; Nano-indentation; Hardness; XRD

Related publications

Permalink: https://www.hzdr.de/publications/Publ-21436
Publ.-Id: 21436


Point defects in Helium Ion Microscopy: an ionoluminescence study

Hlawacek, G.; Veligura, V.; van Gastel, R.; Zandvliet, H. J. W.; Poelsema, B.

In Helium Ion Microscopy (HIM) [1] several signals are available to form an image and obtain information on sample properties. Besides secondary electrons and backscattered helium atoms also photons can be utilized. The latter phenomenon is referred to as ionoluminescence (IL). We show how the ion beam can be used to create sub surface luminescence patterns, that can be made visible using optical techniques [2]. The patterned areas are not visible in the obtained images of the sample surface.
Here, we use IL together with HIM to understand the creation of defects and their behaviour in ionic crystals. The emission of the created point defects has been analyzed in dependence of scanning parameters (pixel spacing and primary current). The fluence dependent results can be understood when the different diffusion behaviour of the identified defects is taken into account [3].
In a second step, single pixel exposures have been used to directly measure the surface projected interaction volume of the beam with sodium chloride. The results are compared to different theoretical calculations. We find that in the presented case a minimum density of 3 emission centers per nm^2 is needed for a detectable IL signal [2].
This research is supported by the Dutch Technology Foundation STW, which is the applied science division of NWO, and the Technology Programme of the Ministry of Economic Affairs.
References:
[1] Gregor Hlawacek, et al. Helium ion microscopy. J. Vac. Sci. Technol. B Microelectron. Nanom. Struct., 32(2):020801, 2014.
[2] Vasilisa Veligura, Gregor Hlawacek, Uwe Jahn, Raoul van Gastel, Harold J. W. Zandvliet, and Bene Poelsema. Creation and physical aspects of luminescent patterns using helium ion microscopy. J. Appl. Phys., 115(18):183502, 2014.
[3] Vasilisa Veligura, Gregor Hlawacek, R van Gastel, Harold J. W. Zandvliet, and Bene Poelsema. A high resolution ionoluminescence study of defect creation and interaction. J. Phys. Condens. Matter, 26(16):165401, 2014.

Related publications

  • Poster
    IBMM - 19th International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-21435
Publ.-Id: 21435


Helium Ion Microscopy: A high resolution tool for the nano-world

Hlawacek, G.; Veligura, V.; Bali, R.; van Gastel, R.; Poelsema, B.; Facsko, S.

Helium Ion Microscopy (HIM) [1] utilizes a subnanometer He+ beam to scan the sample surface. Besides the name giving helium also the heavier neon is available in the latest generation of tools. High-resolution imaging—also of uncoated insulating samples—has become a routine task in HIM. However, the combination of neon and helium also allows for efficient and precise milling of nano-structures. In HIM several signals are available to form an image and obtain information on sample properties. Besides secondary electrons and backscattered helium atoms also photons can be utilized. The latter phenomenon is referred to as ionoluminescence (IL).
We will present examples of high resolution imaging and nano-fabrication always highlighting the important physical aspects relevant for the contrast generation. Dechanneling contrast [2], subsurface imaging and the high surface sensitivity [3] of the method will be discussed. Particular emphasis will be given to the role of defects created by the energetic ion beam and how they can be exploited. We used IL together with HIM to understand the creation of defects and their behaviour in ionic crystals [4]. IL has also been used to directly measure the surface projected interaction volume of the beam with sodium chloride. The results are compared to different theoretical calculations. We find a minimum density of 3 emission centres per nm² is needed for a detectable IL signal [5].
Acknowledgements:
This research is supported by the Dutch Technology Foundation STW, which is the applied science division of NWO, and the Technology Programme of the Ministry of Economic Affairs.
References:
[1] Gregor Hlawacek, et al. Helium ion microscopy. J. Vac. Sci. Technol. B, 32(2):020801, (2014).
[2] Hlawacek, G. et al. Imaging ultra thin layers with helium ion microscopy: Utilizing the channeling contrast mechanism. Beilstein J. Nanotechnol. 3, 507–512 (2012).
[3] Hlawacek, G., Ahmad, I., Smithers, M. A. & Kooij, E. S. To see or not to see: Imaging surfactant coated nano-particles using HIM and SEM. Ultramicroscopy 135C, 89–94 (2013).
[4] Vasilisa Veligura, Gregor Hlawacek, R van Gastel, Harold J. W. Zandvliet, and Bene Poelsema. A high resolution ionoluminescence study of defect creation and interaction. J. Phys. Condens. Matter., 26(16):165401, (2014).
[5] Vasilisa Veligura, Gregor Hlawacek, Uwe Jahn, Raoul van Gastel, Harold J. W. Zandvliet, and Bene Poelsema. Creation and physical aspects of luminescent patterns using helium ion microscopy. J. Appl. Phys., 115(18):183502, (2014).

Related publications

  • Invited lecture (Conferences)
    Workshop Ionenstrahlen & Nanostrukturen, 20.-22.07.2014, Paderborn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21434
Publ.-Id: 21434


The dark side of Helium Ion Microscopy

Hlawacek, G.

Defects are an unavoidable side product of Helium Ion Microscopy (HIM). Several studies have investigated the creation and fluence dependence of the ion beam related damage to the specimen. Here, I want to present results of defect related investigations obtained with an ultra high vacuum HIM.
I will show examples of very small doses as low as 1×1012 cm−2. Such doses were used to investigated the quenching of ionoluminescence (IL) in semiconductors. It turns out that the quenching is not only material dependent but also sensitive to the size of the specimen.
IL has further been used to create luminescence bulk patterns and measure the surface projected interaction volume of the beam with ionic crystals.
At higher doses the well known bubble and blister formation is observed. We studied this effect for Gold and estimated He pressures from several 100MPA up to a few GPa. At even higher doses selforganized nanostructures are formed on metal surfaces. First results of a temperature and material dependent investigation with fluences up 1×1024 m2 will be shown.
This research is supported by the Dutch Technology Foundation STW, which is the applied science division of NWO, and the Technology Programme of the Ministry of Economic Affairs.

Related publications

  • Invited lecture (Conferences)
    Colloquium, 06.06.2014, Bielefeld, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21433
Publ.-Id: 21433


The He ion microscope—a high resolution tool for the nano–world

Hlawacek, G.

Invited presentation ANP retreat

Related publications

  • Invited lecture (Conferences)
    ANP retreat, 19.-20.06.2014, Tecklenburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-21432
Publ.-Id: 21432


Resistive Switching in Titanium dioxide: Comparison of thermally oxidized and magnetron sputtered films

Blaschke, D.; Cornelius, S.; Zahn, P.; Gemming, S.; Skorupa, I.; Scheumann, B.; Scholz, A.; Potzger, K.

Resistive RAM devices based on TiO2 are promising candidates for the next generation memory storage devices.
We compared TiO2 thin films from two different preparation methods with respect to crystallinity and resistive switching behavior.
While thermal oxidation of 100nm Ti on Pt/Ti/SiO2/Si substrates leads to polycrystalline rutile TiO2 layers, dc-magnetron sputter deposition of films on Nb:STO substrates leads to epitaxial anatase TiO2 structure.
In case of the rutile films, unipolar switching occurred, which points to a filamentary mechanism based on the formation of Magnéli phases [1]. The epitaxial anatase films, however, showed bipolar switching, which we correlated with the modification of the metal/oxide interface due to the drift of oxygen vacancies in the applied electric field [2].

The project is funded by the Initiative and Networking Fund of the Helmholtz Association (VI MEMRIOX, VH-VI-422).

[1] Deok-Hwang Kwon et al., “Atomic structure of conducting nanofilaments in TiO2 resistive switching memory”, Nature Nanotechnology 5, 148 – 153 (2010)

[2] J. Joshua Yang et al., “Memristive switching mechanism for metal/oxide/metal nanodevices”, Nature Nanotechnology 3, 429 – 433 (2008)

Keywords: resistive switching; Titanium dioxide; thermal oxidation; magnetron sputtering

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 30.03.-04.04.2014, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-21431
Publ.-Id: 21431


Beam transport and bunch compression at TARLA

Aksoy, A.; Lehnert, U.

The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) will operate two InfraRed Free Electron Lasers (IR-FEL) covering the range of 3–250 μm. The facility will consist of an injector fed by a thermionic triode gun with two-stage RF bunch compression, two superconducting accelerating ELBE modules operating at continuous wave (CW) mode and two independent optical resonator systems with different undulator period lengths. The electron beam will also be used to generate Bremsstrahlung radiation. In this study, we present the electron beam transport including beam matching to the undulators and the shaping of the longitudinal phase space using magnetic dispersive sections.

Keywords: Beam transport; Beam undulator matching; Bunch compression; FEL

Permalink: https://www.hzdr.de/publications/Publ-21430
Publ.-Id: 21430


5 years of Helium Ion Microscopy

Hlawacek, G.

Presentation at UTwente on Helium Ion Microscopy

  • Lecture (others)
    Colloquium PIN/UTwente, 17.04.2014, Enschede, Netherlands

Permalink: https://www.hzdr.de/publications/Publ-21429
Publ.-Id: 21429


Functionalization of nanoparticles for nanoelectronics

Teschome, B.; Facsko, S.; Kerbusch, J.; Hübner, R.; Keller, A.

Nowadays, DNA origami has become a key technique for designing well-defined nanostructures with any desired shape and for the controlled arrangement of nanostructures with few nanometer resolution. These unique features of DNA origami nanostructures make them promising candidates for use as a scaffolds in nanoelectronics and nanophotonics device fabrication. In recent years, a number of studies have shown the precise organization of functional nanoparticles on various shapes of DNA origami. Most of these studies used, however, homogeneous nanostructures such as either metallic or semiconducting nanoparticles. In this work, we demonstrate the assembly of heterogeneous nanostructures, i.e. 5 nm gold nanoparticles (AuNPs) and 10 nm semiconductor quantum dots (QDs), on a single DNA origami. First, a streptavidin-conjugated QD was assembled on the center of biotin functionalized and immobilized DNA origami nanotube, then DNA coated AuNPs were hybridized along the right and left side of the QD-modified nanotube. The high yield of AuNP assembly was achieved by careful control of the buffer concentration and the hybridization time on Si surface.

Keywords: DNA nanostructures; DNA origami; self-assembly; nanoparticles; nanoelectronics

Related publications

  • Poster
    IHRS NanoNet Annual Workshop 2014, 29.-30.09.2014, Lohmen, Germany

Permalink: https://www.hzdr.de/publications/Publ-21428
Publ.-Id: 21428


In Situ Observations during Chemical Vapor Deposition of Hexagonal Boron Nitride on Polycrystalline Copper

Kidambi, P. R.; Blume, R.; Kling, J.; Wagner, J. B.; Baehtz, C.; Weatherup, R. S.; Schloegl, R.; Bayer, B. C.; Hofmann, S.

Using a combination of complementary in situ X-ray photoelectron spectroscopy and X-ray diffraction, we study the fundamental mechanisms underlying the chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) on polycrystalline Cu. The nucleation and growth of h-BN layers is found to occur isothermally, i.e., at constant elevated temperature, on the Cu surface during exposure to borazine. A Cu lattice expansion during borazine exposure and B precipitation from Cu upon cooling highlight that B is incorporated into the Cu bulk, i.e., that growth is not just surface-mediated. On this basis we suggest that B is taken up in the Cu catalyst while N is not (by relative amounts), indicating element-specific feeding mechanisms including the bulk of the catalyst. We further show that oxygen intercalation readily occurs under as-grown h-BN during ambient air exposure, as is common in further processing, and that this negatively affects the stability of h-BN on the catalyst. For extended air exposure Cu oxidation is observed, and upon re-heating in vacuum an oxygen-mediated disintegration of the h-BN film via volatile boron oxides occurs. Importantly, this disintegration is catalyst mediated, i.e., occurs at the catalyst/h-BN interface and depends on the level of oxygen fed to this interface. In turn, however, deliberate feeding of oxygen during h-BN deposition can positively affect control over film morphology. We discuss the implications of these observations in the context of corrosion protection and relate them to challenges in process integration and heterostructure CVD.

Keywords: CVG; Graphene; Borazine

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Permalink: https://www.hzdr.de/publications/Publ-21427
Publ.-Id: 21427


Thickness-dependent metal-insulator transition in epitaxial SrRuO3 ultrathin films

Shen, X.; Qiu, X.; Su, D.; Zhou, S.; Li, A.; Wu, D.

Transport characteristics of ultrathin SrRuO3 films, deposited epitaxially on TiO2-terminated SrTiO3 (001) single-crystal substrates, were studied as a function of film thickness. Evolution from a metallic to an insulating behavior is observed as the film thickness decreases from 20 to 4 unit cells. In films thicker than 4 unit cells, the transport behavior obeys the Drude low temperature conductivity with quantum corrections, which can be attributed to weak localization. Fitting the data with 2-dimensional localization model indicates that electron-phonon collisions are the main inelastic relaxation mechanism. In the film of 4 unit cells in thickness, the transport behavior follows variable range hopping model, indicating a strongly localized state. Magnetoresistance measurements reveal a likely magnetic anisotropy with the magnetic easy axis along the out-of-plane direction.

Keywords: SrRuO3; metal-insulator transition

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Permalink: https://www.hzdr.de/publications/Publ-21426
Publ.-Id: 21426


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