Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

25840 Publications
Investigation of thermal spin transfer torque in MgO-based magnetic tunnel junctions using FMR microresonators
Cansever, H.; Kowalska, E.; Fowley, C.; Aleksandrov, Y.; Yildirim, O.; Narkowicz, R.; Lenz, K.; Lindner, J.; Fassbender, J.; Deac, A.
Abstract: MgO-based magnetic tunnel junctions are commonly used in spintronic device applications, such as recent spin transfer torque random access memory (STT-RAM) because of their non-volatility, fast switching and high storage capacity. Spin transfer torque is defined as a spin polarized current flowing through a ferromagnet exerting a torque on the local magnetization. With thermal spin transfer torque (T-STT), thermally excited electron transport is used instead of spin polarized charge current and provides an interesting way of using thermoelectric effects in magnetic storage applications. Our study focuses on fundamental experimental research aimed at demonstrating that thermal gradients can generate spin-transfer torques in MgO-based magnetic tunnel junctions (MTJs). We use microresonators in order to analyze how the ferromagnetic resonance signal corresponding to the free layer of an in-plane MgO-based tunnel junction device is modified in the presence of a temperature gradient across the barrier.
This work is supported by DFG-SPP1538
  • Poster
    DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Germany
Registration No. 23712 - Permalink

Ionizing Radiation Measurements from Interaction of MEC Laser (0.7 J, 10^19 W/cm2) with Cu and Ni Targets
Liang, T.; Bauer, J.; Blaha, J.; Cimeno, M.; Ferrari, A.; Liu, J.; Rokni, S.; Woods, M.
Abstract: Laser system upgrades at SLAC Matter in Extreme Conditions (MEC) have increased the potential dose levels generated from laser-matter interactions at LCLS Hutch 6. In July 2014, the 800 nm Ti:sapphire MEC laser operated at 0.7 J with an intensity of 1.0 10^18 W/cm2, and shots were taken on Cu foils and a Ni nanowire target. In August 2014, MEC scientists utilized a deformable mirror improve the laser spot size to achieve an intensity of 1.0 10^19 W/cm2 with 0.7 J, and laser shots were again taken on Cu foil and Ni nanowire. During both experiments, passive (nanoDot, RADOS, 2 mR PIC) and active (Victoreen 451, BF3) detectors were deployed inside and outside the target chamber to measure ionizing radiation from laser shots on Cu and Ni targets, and measurements from active and passive detectors agree. No local cone shielding was in place at MEC during radiation measurements.
Keywords: laser induced ionizing radiation
  • Other report
    SLAC National Accelerator Laboratory, USA: SLAC RADIATION PHYSICS NOTE RP-14-23, 2014
    23 Seiten
Registration No. 23706 - Permalink

Shielding and activation studies for MYRRHA in critical and sub-critical mode
Ferrari, A.; Mueller, S.; Konheiser, J.
Abstract: This work has been performed in the framework of the FP7 European project MAXSIMA (“Methodology, Analysis and eXperiments for the Safety In MYRRHA Assessment”), which has the goal to support the design of the accelerator-driven system MYRRHA (“Multi-purpose hYbrid Research Reactor for High-Tech Applications”) at SCK-CEN in Mol (Belgium), in view of the licensing of the facility.
The aim of the MAXSIMA Work Package 2 is to provide solid safety analyses for the Belgian safety authorities in view of the licensing process.
The main goal of the Task 2.1 is to support these analyses on one side by providing the needed neutronic parameters as input (see Deliverable D2.1), and on the other side by performing shielding and activation studies using the up-to-date MYRRHA core models.
These studies are the object of the present Deliverable, D2.2.

Keywords: Shielding, accelerator driven systems, MYRRHA, spallation sources
  • Other report
    Report for EU Commission: Deliverable D2.2 of the MAXSIMA EU Project, 2015
    496 Seiten
Registration No. 23705 - Permalink

An activation database for materials used at high-intensity laser acceleration facilities
Ferrari, A.; Fasso', A.; Olsovcova, V.; Versaci, R.
Abstract: The ELI-Beamlines facility, which is expected to start operation in 2017, will be the high-energy, high repetition-rate laser pillar of the Extreme Light Infrastructure (ELI). The goal of the project is to deliver ultra-short, high-energy laser pulses for generation and applications of high-brightness X-ray sources and accelerated particles. Particle beams are expected to operate in an unprecedented energy range for laser-driven accelerators, going from 1 GeV up to 50 GeV for electrons and from 100 MeV up to 3 GeV for protons. The number of particles per laser shot is estimated to be 10^9-10^10 for electron beams and 10^10-10^12 for proton beams. The high energy and the large current per shot of the produced beams, together with the potentiality to operate at 10 Hz laser repetition rate, require an adequate evaluation of activation in structural materials in order to assess several radiation protection problems, such as minimization of residual dose rates close to and inside the experimental chambers and management of active materials (short and long-term storage and eventual decommissioning).
A large database covering all the energies and materials of interest is being developed using FLUKA, a Monte Carlo code successfully benchmarked for the production of radioactive nuclides. Results for electrons and protons at intermediate energies are presented. These results, although focused on the needs of laser-driven accelerators, are likely to be useful also when designing more conventional facilities.

Keywords: activation, laser induced ionizing radiation
  • Lecture (Conference)
    ARIA 2015 - Workshop on Accelerator Radiation Induced Activation, 15.-17.04.2015, Knoxville, Tennessee, United States
Registration No. 23704 - Permalink

Activation calculations for the MYRRHA accelerator-driven system design
Ferrari, A.; Castelliti, D.; Konheiser, J.; Mueller, S.; Sarotto, M.; Stankovskiy, A.
Abstract: The MYRRHA facility at SCK-CEN in Mol (Belgium), which is at present in an advanced phase of the design, aims to demonstrate efficient transmutation of high level waste and associated Accelerator-Driven System (ADS) technology. The system is based on a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and in sub-critical operation modes. Neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV, < 4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core. The use of a high energy/high current proton beam, coupled with a nuclear reactor operating in subcritical mode, presents many challenges for various aspects of the design, being minimization of the induced activation a key point. In order to assess the main activation and shielding problems, a method based on the combined use of the two Monte Carlo codes MCNPX and FLUKA has been developed, with the goal to perform detailed analyses of both the radiation fields due to the system in operation, and the coupled residual radiation due to the activated materials. Activation has been then evaluated for typical irradiation patterns and key structural materials, from the spallation target to the structure above the core, the reactor cover and critical points along the proton beamline.
The results of this simulation work are presented, with some implications on the design solutions.

Keywords: Activation, shielding, accelerator driven systems, spallation sources
  • Lecture (Conference)
    ARIA 2015 - Workshop on Accelerator Radiation Induced Activation, 15.-17.04.2015, Knoxville, Tennessee, United States
Registration No. 23703 - Permalink

Source term determination for shielding assessment of high-power laser-plasma experiments
Ferrari, A.; Cowan, T.; Pelka, A.; Nakatsutsumi, M.; Tschentscher, T.; Rokni, S.; Liu, J.; Bauer, J.; Liang, T.; Fasso’, A.; Margarone, D.; Versaci, R.
Abstract: In an increasing number of experiments, high-power, high-intensity lasers hit targets and create plasma. The laser-plasma interaction will produce hot electrons with a Maxwellian energy spectrum and an electron temperature ranging from about 10 keV to 10 MeV for irradiance between 10^16 and 10^21 W/cm2. The electrons interact in turn with the target, producing bremsstrahlung and possibly photoneutrons, resulting in a radiation field that must be contained by shielding. Since the physics of plasmas is very different from that of the common phases of matter, the shielding design cannot be carried out with only conventional tools.
Different, complementary approaches are possible: to use analytical formulas, to experimentally evaluate source terms to be used as input to established Monte Carlo codes, or to interface those codes with specialized Particle-In-Cell programs, which describe the generation and transport of particles in plasma.
At the Helmholtz-Beamline, which will operate as laser facility at the European XFEL, the shielding design of the High Energy Density (HED) Physics Instrument has been evaluated by using analytical calculations, cross-checked with measurements at the DRACO laser at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). On the other hand an extensive experimental campaign is planned at SLAC, where dedicated radiation measurements will be performed at the Matter in Extreme Conditions (MEC) short-pulse laser facility.
  • Poster
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States
Registration No. 23702 - Permalink

Radiation field calculations around the spallation target and the reactor core for the MYRRHA ADS design
Ferrari, A.; Castelliti, D.; Fernandez, R.; Konheiser, J.; Mueller, S.; Sarotto, M.; Stankovskiy, A.
Abstract: The MYRRHA facility at SCK·CEN in Mol (Belgium), which should enter the construction phase in 2015, aims to demonstrate efficient transmutation of high level waste and associated Accelerator-Driven Systems (ADS) technology. The system is based on a lead-bismuth eutectic (LBE) cooled reactor, working both in critical and in sub-critical operation modes. The neutrons needed to sustain fission in the sub-critical mode are produced via spallation processes by a 600 MeV,  4 mA proton beam, which is provided by a linear accelerator and hits a LBE spallation target located inside the reactor core. In order to assess the main shielding problems, a method based on the combined use of the two Monte Carlo codes MCNPX and FLUKA has been developed, with the goal to perform detailed analyses of both the radiation fields due to the system in operation, and the coupled residual radiation due to the activated materials. The results of this simulation work are presented, with the implications on the design solutions.
Keywords: Accelerator driven systems, spallation targets, shielding
  • Poster
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States
Registration No. 23701 - Permalink

Shielding and activation studies for the ELI-Beamlines project
Fasso, A.; Ferrari, A.; Korn, G.; Versaci, R.
Abstract: ELI-beamlines is one of the four pillars of the Extreme Light Infrastructure, a European ESFRI Project, for the next generation of high-energy and high-intensity lasers. It aims at the development of high-brightness sources of X-rays and the acceleration of proton, electron, and ion beams, to be used both for pure research and practical applications.
Aiming at a proper radiation protection assessment, for both shielding and activation, extensive FLUKA simulations have been performed, taking into account the laser high repetition rates. The present work, which is the continuation of the calculations presented at SATIF-10, is the first one based on the design of the facility being constructed and on the updated experimental set-up.

Keywords: Shielding, Monte Carlo calculations, FLUKA
  • Contribution to proceedings
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States
    Workshop Proceedings: OECD, Nuclear Science NEA/NSC/R(2015)3, 105-111
Registration No. 23700 - Permalink

Measurements of high-intensity laser induced ionising radiation at SLAC
Liang, T.; Bauer, J.; Cimeno, M.; Ferrari, A.; Galtier, E.; Granados, E.; Liu, J.; Nagler, B.; Prinz, A.; Rokni, S.; Tran, H.; Woods, M.
Abstract: A systematic study of measurements of photon and neutron radiation doses generated in high-intensity laser-target interactions is underway at SLAC National Accelerator Laboratory using a femtosecond pulsed Ti:sapphire laser (800 nm, 40 fs, up to 1 J and 25 TW) at the Linac Coherent Light Source’s (LCLS) Matter in Extreme Conditions (MEC) facility. Preliminary results from recent measurements with the laser-optic-target system (peak intensity 1.8x1018 W/cm2) are presented and compared with results from calculations based on analytical models and FLUKA Monte Carlo simulations.
Keywords: Laser induced ionising radiation, source terms measurements, shielding
  • Contribution to proceedings
    SATIF-12 Shielding aspects of Accelerators, Targets and Irradiation Facilities, 28.-30.04.2014, Fermilab, Batavia, Illinois, United States
    Workshop Proceedings: OECD, Nuclear Science NEA/NSC/R(2015)3, 40-53
Registration No. 23699 - Permalink

Data-driven model for evaluation of cerebrovascular-reserve measurement with hypercapnia BOLD
Vondráčková, L.; Krukowski, P.; Gerber, J.; Linn, J.; Kybic, J.; Petr, J.
Abstract: Hypercapnia BOLD with the breath-holding task is a technically easier and more clinically available alternative to cerebrovascular reserve (CVR) mapping than administration of CO enriched air using an air-tight mask. The disadvantage is complicated data evaluation in case the subject does not adhere to the breathing protocol completely. Here, a data-driven approach for evaluation is presented that is more robust to protocol deviations and produces a reasonable CVR map in most cases where the standard model-driven approach fails. This is demonstrated on randomized evaluation of CVR maps of a group of 86 subjects with stenosis or vessel occlusion.
  • Contribution to proceedings
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore
    Proceedings of the 24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
Registration No. 23698 - Permalink

Deformation and resolution issues in partial volume correction of 2D arterial spin labeling data
Petr, J.; Mutsaerts, H. J.; de Vita, E.; Maus, J.; van den Hoff, J.; Asllani, I.
Abstract: Partial volume (PV) effects are a well-recognized confounder in arterial spin labeling due to its limited spatial resolution. Several algorithms exist to correct for these errors. Nevertheless, PVcorrection is rarely used, mainly because the PV maps obtained from segmented T1-weighted images are regarded as not being suficiently reliable when transformed into ASL space. Here, we show the impact of spatial deformation and resolution in the PV-maps used for PV-correction in the calculation of mean total gray matter (GM) cerebral blood flow (CBF). We also show how the deformations affect the calculation of PV-uncorrected mean GM CBF.
  • Contribution to proceedings
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore
    Proceedings of the 24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
Registration No. 23697 - Permalink

Addressing multi-centre image registration of 3T arterial spin labeling images from the GENetic Frontotemporal dementia Initiative (GENFI)
Mutsaerts, H.; Thomas, D.; Petr, J.; de Vita, E.; Cash, D.; van Osch, M.; Groot, P.; van Swieten, J.; Laforce Jr, R.; Tagliavini, F.; Borroni, B.; Galimberti, D.; Rowe, J.; Graff, C.; Frisoni, G.; Finger, E.; Sorbi, S.; Mendonça, A.; Rossor, M.; Rohrer, J.; Masellis, M.; Macintosh, B.
Abstract: One obstacle in multi-centre arterial spin labeling (ASL) studies is the variability attributed to differences between vendor- or site-specific ASL implementations. This multi-centre study compares spatial registration methods from ASL to 3D-T1, to reduce the between-subject variability of cerebral blood flow (CBF) maps. Our results demonstrate that choices of image registration have profound effects on ASL data collected using different pulse sequences and/or sites. A rigid-body registration of CBF images to segmented gray matter images produced the most robust similarity outcome as a standard approach across the different ASL implementations.
  • Contribution to proceedings
    24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 07.05.2016, Singapore, Singapore
    Proceedings of the 24th Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine
Registration No. 23696 - Permalink

Perfusion decrease in healthy tissue following radiochemotherapy in glioblastoma patients
Petr, J.; Platzek, I.; Seidlitz, A.; Hofheinz, F.; Maus, J.; Beuthien-Baumann, B.; Krause, M.; van den Hoff, J.
Abstract: Ziel/Aim:
Decrease of perfusion as a side-effect of radio-chemotherapy was observed in several organs (1). However, the relation between the decrease and the radiation dose was not yet extensively studied. Non-invasive measurement of perfusion is now possible with a native MRI sequence called arterial spin labeling (ASL) (2) which offers a semi-quantitative alternative to [O-15]H2O PET measurement. The ASL measurement was used to study the regional perfusion changes in healthy tissue of glioblastoma patients undergoing radiochemotherapy.
Methodik/Methods:
Twenty-five patients (age 55.0±14.2 years) with glioblastoma multiforme were scanned in two (n=25) or three (n=13) sessions with interval 4.8 and 8.1 months from the first session, respectively. The ASL scan was co-registered with the treatment-planning CT and the dose plan. Perfusion changes between sessions were calculated in the hemisphere contralateral to the tumor. The perfusion changes were evaluated also in regions created by categorizing the individual dose maps into 10 Gy steps.
Ergebnisse/Results:
The relative perfusion decrease between the first two sessions was not significant (-2.4% and -7.5%) for the low dose regions 0 and 20 Gy. For the high-dose regions, the change was statistically significant and a decrease of -13.3% (20-30 Gy), -18.0% (30-40 Gy), -16.2% (40-50 Gy), and -16.8% (50-60 Gy) was observed. No further decrease of perfusion was observed on the third session. The mean regional changes were between -1.4% and 3.0% and the results were not statistically significant for any dose.
Schlussfolgerungen/Conclusions:
Global decrease of perfusion was observed in healthy tissue 3 months after the radiochemotherapy. The decrease was correlated with the dose received. No further decrease of perfusion was observed 6 months after the therapy.
  • Contribution to proceedings
    54. Jahrestagung der DGN, 20.04.2016, Dresden, Germany
    Perfusion decrease in healthy tissue following radiochemotherapy in glioblastoma patients
Registration No. 23695 - Permalink

Bestimmung der zerebrovaskulären Reserve mit BOLDMRT unter Atemanhalten bei Patienten mit Stenosen der hirnversorgenden Gefäße
Krukowski, P.; Petr, J.; Puetz, V.; Abramyuk, A.; Linn, J.; Gerber, J.
Abstract: Die Autoregulation der zerebralen Perfusion ist wichtiger Mechanismus der Homöostase. Hyperkapnie führt im gesunden Gefäßbett zur Dilatation präkapillärer Gefäße und zur Aktivierung der zerebralen Perfusionsreserve (CVR). BOLD (Blood Oxygen Level Dependent)-MRT unter Atemanhalten stellt die Veränderungen dar. Bei Patienten mit Stenosen hirnversorgender Arterien akquirierten wir prospektiv ein BOLD-MRT unter Atemanhalten, evaluierten die Machbarkeit und korrelierten die Zielstenose mit den BOLD-Veränderungen. Wir werteten das BOLD-MRT modell-basiert (Block-Design gefaltet mit der hämodynamischen Antwortfunktion) aus. Die maximale Kreuzkorrelation des Modells mit der durchschnittlichen Signalantwort des Patienten ergab die individuelle Antwort-Verzögerung des BOLD-Signals zum Stimulus Atemanhalten. Least-square fittings des modellierten Signalverlaufs mit den gemessenen Daten ergaben statistische Parameterkarten, die mit einer T1-gewichteten MRT registriert wurden. Wir werteten keine oder negative BOLDAntworten als pathologisch. Wir beurteilten die Parameterkarten im 3-Leser-Konsensus.
Bei 48 von 58 Patienten (82,8 %) waren die Parameterkarten beurteilbar. 36 Patienten hatten eine symptomatische, 12 hatten eine asymptomatische Stenose. 28 Patienten (58 %) hatten Veränderungen der CVR im Stromgebiet der Zielstenose (bei 21 symptomatischen und 7 asymptomatischen). Die Häufigkeit von BOLD-Veränderungen war bei Patienten mit symptomatischen und asymptomatischen Stenosen gleich (58,3 %).
In der Mehrzahl der Patienten sind BOLD-CVR-Veränderungen im Stromgebiet der stenosierten Arterie nachweisbar. Die Lesbarkeit sollte durch alternative Auswerte-Algorithmen verbessert werden.
  • Contribution to proceedings
    50. Jahrestagung der Deutschen Gesellschaft für Neuroradiologie, 15.10.2015, Gürzenich, Köln, Deutschland
    Clinical Neuroradiology: Springer
    DOI-Link: http://dx.doi.org/10.1007/s00062-015-0445-4
Registration No. 23694 - Permalink

Reducing in-core zinc borate precipitation after LOCA in pressurized water reactors
Kryk, H.; Harm, U.; Hampel, U.
Abstract: During the sump recirculation phase after loss-of-coolant accidents (LOCAs) in pressurized water reactors (PWRs), coolant spilling from the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by residual-heat removal pumps as part of the emergency core cooling system (ECCS).
Lab-scale studies within previous research projects have shown that the long-term contact of the boric acid containing coolant with hot-dip galvanized steel containment internals may cause corrosion of the corresponding materials influencing the cooling water chemistry due to dissolution of the zinc coat. Generic experimental investigations regarding the solubility of Zn corrosion products in boric acid solutions resulted in a decreasing solubility with increasing temperature. Thus, precipitation of solid corrosion products (zinc borates) cannot be ruled out if zinc containing coolant is heated up due to its recirculation into hot zones.
Consequently, generic corrosion experiments were carried out in a lab-scale corrosion test facility aiming at the development and test of water-chemical measures to prevent zinc corrosion and zinc borate precipitation in boric acid containing coolants.
The experimental results showed a decreasing corrosion rate with increasing pH value of the coolant. Thus, the risk of zinc borate precipitation can be reduced by addition of alkalizing media to the coolant after a LOCA. However, by adding of a moderate amount of alkalizing media to enhance the coolant pH into the neutral region, the zinc borate precipitation rate can be reduced only to about one third but not fully prevented. Extensive suppression of zinc corrosion and zinc borate precipitation is only achievable from a coolant pH of 7.5 resulting in a lithium concentration of 125 ppm if LiOH is used as alkalizing additive. Furthermore, foaming of the coolant cannot be ruled out if the coolant pH is increased into the slightly alkaline region.

Keywords: pressurized water reactor, loss-of-coolant accidents, corrosion, zinc, zinc borate, downstream effects
  • Lecture (Conference)
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Germany
Registration No. 23690 - Permalink

Tunable Picosecond Laser Pulses via the Contrast of Two Reverse Saturable Absorption Phases in a Waveguide Platform
Tan, Y.; Chen, L.; Wang, D.; Chen, Y.; Akhmadaliev, S.; Zhou, S.; Hong, M.; Chen, F.
Abstract: How to enhance the optical nonlinearity of saturable absorption materials is an important question to improve the functionality of various applications ranging from the high power laser to photonic computational devices. We demonstrate the saturable absorption (SA) of VO2 film attributed to the large difference of optical nonlinearities between the two states of the phase-transition materials (VO2). Such VO2 film demonstrated significantly improved performance with saturation intensity higher than other existing ultrathin saturable absorbers by 3 orders due to its unique nonlinear optical mechanisms in the ultrafast phase change process. Owing to this feature, a Q-switched pulsed laser was fabricated in a waveguide platform, which is the first time to achieve picosecond pulse duration and maintain high peak power. Furthermore, the emission of this VO2 waveguide laser can be flexibly switched between the continuous-wave (CW) and pulsed operation regimes by tuning the temperature of the VO2 film, which enables VO2-based miniature laser devices with unique and versatile functions. Registration No. 23686 - Permalink

Synthesis, Morphological, and Electro-optical Characterizations of Metal/Semiconductor Nanowire Heterostructures
Glaser, M.; Kitzler, A.; Johannes, A.; Prucnal, S.; Potts, H.; Conesa-Boj, S.; Filipovic, L.; Kosina, H.; Skorupa, W.; Bertagnolli, E.; Ronning, C.; Fontcuberta I. Morral, A.; Lugstein, A.
Abstract: In this letter, we demonstrate the formation of unique Ga/GaAs/Si nanowire heterostructures, which were successfully implemented in nanoscale light-emitting devices with visible room temperature electroluminescence. Based on our recent approach for the integration of InAs/Si heterostructures into Si nanowires by ion implantation and flash lamp annealing, we developed a routine that has proven to be suitable for the monolithic integration of GaAs nanocrystallite segments into the core of silicon nanowires. The formation of a Ga segment adjacent to longer GaAs nanocrystallites resulted in Schottky-diode-like I/V characteristics with distinct electroluminescence originating from the GaAs nanocrystallite for the nanowire device operated in the reverse breakdown regime.
The observed electroluminescence was ascribed to radiative band-to-band recombinations resulting in distinct emission peaks and a low contribution due to intraband transition, which were also observed under forward bias. Simulations of the obtained nanowire heterostructure confirmed the proposed impact ionization process responsible for hot carrier luminescence. This approach may enable a new route for on-chip photonic devices used for light emission or detection purposes.

Keywords: Nanowires, flash lamp annealing, ion implantation, GaAs, Si, liquid phase epitaxy Registration No. 23679 - Permalink

The effect of millisecond flash lamp annealing on electrical and structural properties of ZnO:Al/Si structures
Lindberg, P. F.; Lipp Bregolin, F.; Wiesenhütter, K.; Wiesenhütter, U.; Riise, H. N.; Vines, L.; Prucnal, S.; Skorupa, W.; Svensson, B. G.; Monakhov, E. V.
Abstract: The effect of millisecond flash lamp annealing (FLA) on aluminum doped ZnO (AZO) films and their interface with Si have been studied. The AZO films were deposited by magnetron sputtering on Si (100) substrates. The electrical and structural properties of the film and AZO/Si structures were characterized by current–voltage, capacitance–voltage, and deep level transient spectroscopy measurements, X-ray diffraction, and secondary ion mass spectrometry. The resistivity of the AZO film is reduced to a close to state-of-the-art value of 2x10-4Ohmcm after FLA for 3ms with an average energy density of 29 J/cm2. In addition, most of the interfacial defects energy levels are simultaneously annealed out, except for one persisting shallow level, tentatively assigned to the vacancy-oxygen complex in Si, which was not affected by FLA. Subsequent to the FLA, the samples were treated in N2 or forming gas (FG) (N2/H2, 90/10%mole) ambient at 200–500 C. The latter samples maintained the low resistivity achieved after the FLA, but not the former ones. The interfacial defect level persisting after the FLA is removed by the FG treatment, concurrently as another level emerges at ~0.18 eV below the conduction band. The electrical data of the AZO films are discussed in term of point defects controlling the resistivity, and it is argued that the FLA promotes formation of electrically neutral clusters of Zink vacancies (VZn’s) rather than passivating/compensating complexes between the Al donors and VZn’s.
Keywords: AZO, flash lamp annealing, magnetron sputtering, doping, Registration No. 23678 - Permalink

Structural modification of Ga+ and N+ ion implanted ta-C films
Berova, M.; Sandulov, M.; Tsvetkova, T.; Karashanova, D.; Boettger, R.; Bischoff, L.
Abstract: Thin-film samples (d ~ 40 nm) of tetrahedral amorphous carbon (ta-C) deposited by filtered cathodic vacuum arc (FCVA) were implanted with Ga+ at ion energy E = 20 keV and ion fluences D = 3×10^14÷3×10^15 cm-2 and N+ with the same energy and a dose D = 3×1014 cm-2. The Ga+ ion beam induced a structural modification of the implanted material. This resulted in a considerable change of its structural properties, manifested as the formation of a new phase under non-equilibrium conditions, which could be accompanied by considerable changes in the ta-C films optical properties. The N+ implantation also resulted in a modification of the surface structure. These effects were explored using transmission (TEM) and scanning (SEM) electron microscopy.
Keywords: ta-C, ion implantation Registration No. 23669 - Permalink

Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium
Radek, M.; Bracht, H.; Johnson, B. C.; Mccallum, J. C.; Posselt, M.; Liedke, B.
Abstract: We report experimental studies on atomic mixing of matrix atoms during solid-phase epitaxy (SPE). For this purpose isotopically enriched germanium (Ge) multilayer structures were amorphized by Ge ion implantation up to a depth of 1.5 um. Recrystallization of the amorphous structure was performed at temperatures between 350°C and 450°C. By means of secondary-ion-mass-spectrometry (SIMS) the concentration-depth profiles of the Ge isotope before and after the SPE process were determined. Analyses of the experimental depth profiles reveal an upper limit of 0.5 nm for the displacement length of the Ge matrix atoms induced by the SPE process. This small displacement length confirms theoretical models and atomistic simulations of SPE, indicating that the SPE mechanism consists of bond-switching with nearest-neighbours at the amorphous-crystalline (a/c) interface.
Keywords: Solid-phase epitaxial recrystallization, germanium, atom transport
  • Lecture (Conference)
    E-MRS Spring Meeting, Symposium K: Group IV semiconductors materials research - growth, characterization and applications to electronics and spintronics, 02.-06.05.2016, Lille, France
Registration No. 23668 - Permalink

Investigation of ion-beam mixing in silicon at temperatures below 500°C and the role of mobile extended defects
Radek, M.; Bracht, H.; Posselt, M.; Liedke, B.
Abstract: Implantation of germanium (Ge), gallium (Ga), or arsenic (As) ions into crystalline and preamorphized isotopically enriched silicon (Si) multilayer structures at temperatures between 20°C and 500°C was performed to study the mechanisms contributing to atomic mixing. Secondary-ion-mass-spectrometry (SIMS) was applied to determine the concentration-depth profiles of the Si isotopes after ion implantation. In contrast to Ge multilayer structures [1] a radiation enhanced self-diffusion (RESD), as well as a dopant dependence of RESD is observed in Si. The contribution of cascade mixing (thermal spike mixing) to the overall atomic mixing is estimated by means of molecular dynamics simulations leaving the contribution due to RESD. Continuum theoretical calculations reveals that the magnitude of RESD can not be described by the diffusion of isolated native defects in supersaturation. Instead RESD is successfully modelled assuming highly mobile di-interstials that form during annealing of the implantation damage.
[1] M. Radek et al.: Temperature dependence of ion-beam induced atomic mixing in germanium isotope structures, Appl. Phys. Lett. 115, 023506 (2015)

Keywords: Ion-beam mixing, silicon isotope multilayers
  • Lecture (Conference)
    E-MRS Spring Meeting, Symposium K: Group IV semiconductors materials research - growth, characterization and applications to electronics and spintronics, 02.-06.05.2016, Lille, France
Registration No. 23667 - Permalink

Self-diffusion in amorphous silicon: An experimental and theoretical study
Kirschbaum, J.; Teuber, T.; Radek, M.; Bracht, H.; Posselt, M.; Bougeard, D.
Abstract: Amorphous silicon (a-Si) is a widely used material, especially for solar cells and thin-film-transistors. Measuring the self-diffusion coefficient of a-Si is experimentally demanding since recrystallization during diffusion annealing must be suppressed. We used Si on insulator (SOI) structures to stabilize the amorphous state during annealing. Isotopically enriched Si multilayers with a thickness per layer of about 10 nm were grown by means of molecular beam epitaxy on top of SOI wafers. Subsequently the whole top crystalline Si layer was amorphized by means of Si ion implantation. Before and after annealing the distribution of the Si isotopes within the isotope structure was measured with SIMS. The observed broadening suggests a significantly higher self-diffusion in the amorphous compared to the crystalline state. Molecular dynamics simulations are employed to gain information about the mechanism of self-diffusion. We used an adjusted Stillinger-Weber potential, as the original Stillinger-Weber parametrization for Si overestimates the mobility of the matrix atoms. The parameters were chosen to simulate the experimentally observed diffusion in a-Si. The coordination numbers and radial-distribution-function were analyzed to confirm the assumption of bond switching as the dominant mechanism of self-diffusion.
Keywords: amorphous silicon, diffusion
  • Poster
    E-MRS Spring Meeting, Symposium K: Group IV semiconductors materials research - growth, characterization and applications to electronics and spintronics, 02.-06.05.2016, Lille, France
Registration No. 23666 - Permalink

Fractional Quantum Hall States in a Ge Quantum Well
Mironov, O. A.; D'Ambrumenil, N.; Dobbie, A.; Leadley, D. R.; Suslov, A. V.; Green, E.
Abstract: Measurements of the Hall and dissipative conductivity of a strained Ge quantum well on a SiGe/(001)Si substrate in the quantum Hall regime are reported. We analyze the results in terms of thermally activated quantum tunneling of carriers from one internal edge state to another across saddle points in the long-range impurity potential. This shows that the gaps for different filling fractions closely follow the dependence predicted by theory. We also find that the estimates of the separation of the edge states at the saddle are in line with the expectations of an electrostatic model in the lowest spin-polarized Landau level (LL), but not in the spin-reversed LL where the density of quasiparticle states is not high enough to accommodate the carriers required. Registration No. 23665 - Permalink

Tos-Nos-Mos: Synthesis of different aryl sulfonate precursors for the radiosynthesis of the alpha7 nicotinic acetylcholine receptor radioligand [18F]NS14490
Rötering, S.; Scheunemann, M.; Günther, R.; Löser, R.; Hiller, A.; Peters, D.; Brust, P.; Fischer, S.; Steinbach, J.
Abstract: Radiopharmacological investigations of [18F]NS14490 have proven that this radiotracer could be a potential PETradiotracer for imaging of alpha7 nicotinic acetylcholine receptor particularly with regard to vulnerable plaques of diseased vessels. For further optimisation of the previously automated one-pot radiosynthesis of [18F]NS14490 using a tosylate precursor, precursors with other leaving groups (nosylate and mosylate) were synthesized and compared with the tosylate with respect to their reactivities towards [18F]fluoride. The use of these different precursors resulted in comparable labelling yields of [18F]NS14490. A novel mosylate precursor was synthesized and evaluated, which has revealed a higher stability during a storage period of five months compared to the corresponding tosylate and nosylate.
Keywords: Alpha7 nAChR ligand; PET; Synthesis of precursor; Reactivity of precursor; Tosylate; Nosylate; Mosylate Registration No. 23661 - Permalink

Electrochemical behavior of nanocrystalline Ta/TaN multilayer on 316L stainless steel: Novel bipolar plates for proton exchange membrane fuel-cells
Alishahi, M.; Mahboubi, F.; Mousavi Khoie, S. M.; Aparicio, M.; Hübner, R.; Soldera, F.; Gago, R.
Abstract: Insufficient corrosion resistance and surface conductivity are two main issues that plague large-scale application of stainless steel (SS) bipolar plates in proton exchange membrane fuel cells (PEMFCs). This study explores the use of nanocrystalline Ta/TaN multilayer coatings to improve the electrical and electrochemical performance of polished 316L SS bipolar plates. The multilayer coatings have been deposited by (reactive) magnetron sputtering and characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The electrochemical behavior of bare and coated substrates has been evaluated in simulated PEMFC working environments by potentiodynamic and potentiostatic polarization tests at ambient temperature and 80 °C. The results show that the Ta/TaN multilayer coating increases the polarization resistance of 316L SS by about 30 and 104 times at ambient and elevated temperatures, respectively. The interfacial contact resistance (ICR) shows a low value of 12 µOhm cm-2 before the potentiostatic test. This ICR is significantly lower than for the bare substrate and remains mostly unchanged after potentiostatic polarization for 14 h. In addition, the high contact angle (92 °) with water for coated substrates indicates a hydrophobic character, which can improve the water management within the cell in PEMFC stacks.
Keywords: PEMFC, Bipolar plate, Magnetron sputtering, Multilayer coating, Interfacial contact resistance, Corrosion
  • Journal of Power Sources 322(2016), 1-9
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Registration No. 23659 - Permalink

Tailoring the magnetic anisotropy of (Ga,Mn)(As,P) by ion irradiation
Yuan, Y.; Rushforth, A.; Sawicki, M.; Dietl, T.; Helm, M.; Zhou, S.
Abstract: The rich phenomena in the magnetic anisotropy of diluted ferromagnetic semiconductors (DFS) have opened new concepts for spintronics beyond conventional electronic logic devices [1]. As an example, the magnetic anisotropy of (Ga,Mn)(As,P) can be changed from in-plane to out-of-plane by low temperature annealing [2, 3]. In this work, we demonstrate another flexible approach to tune the magnetic anisotropy by He+ ion irradiation, which is a well-developed chip-technology. For the as-prepared (Ga,Mn)(As,P), the low-temperature long-time annealing suppresses the compensation from Mn interstitials, resulting in a higher carrier concentration and the switching of the magnetic easy axis from the in-plane [100] to the out-of-plane [001] direction [3]. By He+ irradiation, we can turn the magnetic easy axis gradually back to the out-of-plane direction. Therefore, ion irradiation combined with low-temperature long-time annealing boosts the prospects of flexible tailoring of the magnetic anisotropy of DFS material, allowing for the development of new concepts for spintronic devices.

[1] T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014).
[2] M. Sawicki et al., Phys. Rev. B 70, 245325 (2004).
[3] A. Casiraghi et al., Appl. Phys. Lett. 97, 122504 (2010).
  • Poster
    EMRS 2016 Spring, 02.-06.05.2016, Lille, France
Registration No. 23658 - Permalink

Multiscale Self-Assembly of Silicon Quantum Dots into an Anisotropic Three-Dimensional Random Network
Ilday, S.; Ilday, F. O.; Hübner, R.; Prosa, T. J.; Martin, I.; Nogay, G.; Kabacelik, I.; Mics, Z.; Bonn, M.; Turchinovich, D.; Toffoli, H.; Toffoli, D.; Friedrich, D.; Schmidt, B.; Heinig, K.-H.; Turan, R.
Abstract: Multiscale self-assembly is ubiquitous in nature but its deliberate use to synthesize multifunctional three-dimensional materials remains rare, partly due to the notoriously difficult problem of controlling topology from atomic to macroscopic scales to obtain intended material properties. Here, we propose a simple, modular, noncolloidal methodology that is based on exploiting universality in stochastic growth dynamics and driving the growth process under far-from-equilibrium conditions toward a preplanned structure. As proof of principle, we demonstrate a confined-butconnected solid structure, comprising an anisotropic random network of silicon quantum-dots that hierarchically self-assembles from the atomic to the microscopic scales. First, quantum-dots form to subsequently interconnect without inflating their diameters to form a random network, and this network then grows in a preferential direction to form undulated and branching nanowire-like structures. This specific topology simultaneously achieves two scale-dependent features, which were previously thought to be mutually exclusive: good electrical conduction on the microscale and a bandgap tunable over a range of energies on the nanoscale.
Keywords: Si, random network, hierarchical, multiscale, self-assembly, stochastic deposition
  • Nano Letters 16(2016), 1942-1948
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Registration No. 23654 - Permalink

Defect studies of Mg films deposited on various substrates
Hruška, P.; Čížek, J.; Anwand, W.; Bulíř, J.; Drahokoupil, J.; Stráská, J.; Melikhova, O.; Procházka, I.; Lančok, J.
Abstract: In the present work the structure of Mg films deposited by RF magnetron sputtering was characterized using variable energy positron annihilation spectroscopy combined with scanning electron microscopy and X-ray diffraction. The effect of deposition parameters, namely temperature, type of substrate and deposition rate, on the microstructure was examined. All Mg films studied grow with the basal (0001) plane parallel with the substrate and exhibit only negligible in-plane stress. Films deposited at room temperature are characterized by nanocrystalline structure with high volume fraction of grain boundaries. and positrons are preferentially trapped in open volume defects present at grain boundaries. In these films positrons are trapped predominantly in open-volume defects present at grain boundaries. With increasing deposition temperature the mean grain size increases and the volume fraction of grain boundaries decreases. Hence, in Mg films prepared at elevated temperatures positrons are trapped mainly at misfit dislocations compensating different atomic spacing in the films and the substrate. Moreover, it was found that slow deposition rate leads to higher density of defects compared to fast deposition rate. By annealing of Mg film with thin 20 nm Pd over-layer at 300°C for 1 hour Pd layer is mixed with Mg film forming a Mg-Pd compound. The Mg-Pd phase likely contains structural open-volume defects which trap positrons.
Keywords: defect studies, Mg films, positron annihilation

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Registration No. 23651 - Permalink

Ferromagnetism in 5f-band metamagnet UCoAl induced by Os doping
Andreev, A. V.; Shirasaki, K.; Sebek, J.; Vejprovova, J.; Gorbunov, D. I.; Havela, L.; Danis, S.; Yamamura, T.
Abstract: UCoAl is a 5f-band metamagnet with a uniquely low paramagnetic-to-ferromagnetic transition field, 0.7 T, extremely sensitive to any perturbation such as elemental substitution. Here, we study variations of magnetic properties in the UCoAl-UOsAl system on single- and polycrystalline samples with different concentration of Os. We found that osmium can substitute Co in UCoAl up to 20%, while preserving the ZrNiAl structure type. Pure UOsAl was identified as a hexagonal Laves phase, MgZn2 type. It is a weak Pauli paramagnet. Even a 2%-substitution of Os for Co in the 5f band metamagnet stabilizes ferromagnetism with the Curie temperature TC = 26 K and uranium magnetic moment µ = 0.4 µB and shifts the critical metamagnetic field to zero. Higher Os concentrations enhance both TC and µ. All magnetic response is concentrated into the c-axis; the susceptibility for magnetic field perpendicular to c is low and practically temperature-independent. Our study reflects the decisive role of the 5f-5d hybridization in the magnetism of the UCoAl-UOsAl system. This work completes the study of the alloying of UCoAl with late transition metals and indicates that the non-magnetic phase exhibiting band metamagnetism is very limited in the concentration range. Registration No. 23650 - Permalink

Guided-wave second harmonics in Nd:YCOB ridge waveguides produced by combination of carbon ion irradiation and precise diamond blade dicing
Li, R.; Nie, W.; Shang, Z.; Cheng, C.; Akhmadaliev, S.; Zhou, S.; Lu, Q.; Chen, F.
Abstract: We report on the fabrication of Nd:YCa4O(BO3)3 (Nd:YCOB) ridge waveguides by combining carbon ion irradiation and precise diamond blade dicing. The guiding and spectroscopic properties of the planar as well as ridge waveguides are investigated. The second harmonic generation (SHG) at 532 nm has been realized through the waveguide structures. With nearly the same input power, the maximum average output powers are 0.56 mW and 0.62 mW, and the maximum conversion efficiencies reach 0.3%W−1 and 0.5%W−1, for planar and ridge waveguides, respectively.
Keywords: Optical waveguides; Nd:YCOB crystal; Second harmonic generation Registration No. 23646 - Permalink

Universality of 2+1 dimensional RSOS models
Kelling, J.; Ódor, G.; Gemming, S.
Abstract: Extensive dynamical simulations of Restricted Solid on Solid models in D=2+1 dimensions have been done using parallel multisurface algorithms implemented on graphics cards. Numerical evidence is presented that these models exhibit KPZ surface growth scaling, irrespective of the step heights N. We show that by increasing N the corrections to scaling increase, thus smaller step sized models describe better the asymptotic, long wave scaling behavior. Registration No. 23645 - Permalink

A possible new origin of long absorption tail in Nd-doped yttrium aluminum garnet induced by 15 MeV gold-ion irradiation and heat treatment
Amekura, H.; Akhmadaliev, S.; Zhou, S.; Chen, F.
Abstract: When ion irradiation introduces point-defects in semiconductors/insulators, discrete energy levels can be introduced in the bandgap, and then optical transitions whose energies are lower than the bandgap become possible. The electronic transitions between the discrete level and the continuous host band are observed as a continuous tail starting from the fundamental edge. This is the well-known mechanism of the absorption tail close to the band-edge observed in many semiconductors/insulators. In this paper, we propose another mechanism for the absorption tail, which is probably active in Nd-doped yttrium aluminum garnet (Nd:YAG) after ion irradiation and annealing. A Nd:YAG bulk crystal was irradiated with 15 MeV Au5+ ions to a fluence of 8 × 1014 ions/cm2. The irradiation generates an amorphous layer of ∼3 μm thick with refractive index reduction of Δn = −0.03. Thermal annealing at 1000 °C induces recrystallization to randomly aligned small crystalline grains. Simultaneously, an extraordinarily long absorption tail appeared in the optical spectrum covering from 0.24 to ∼2 μm without fringes. The origin of the tail is discussed based on two models: (i) conventional electronic transitions between defect levels and YAG host band and (ii) enhanced light scattering by randomly aligned small grains. Registration No. 23644 - Permalink

Systematic investigation of projectile fragmentation using beams of unstable B and C isotopes
Thies, R.; Heinz, A.; Adachi, T.; Aksyutina, Y.; Alcantara-Núñes, J.; Altstadt, S.; Alvarez-Pol, H.; Ashwood, N.; Aumann, T.; Avdeichikov, V.; Barr, M.; Beceiro-Novo, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C. A.; Boretzky, K.; Borge, M. J. G.; Burgunder, G.; Camaño, M.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkäll, J.; Chakraborty, S.; Chartier, M.; Chulkov, L. V.; Cortina-Gil, D.; Crespo, R.; Datta, U.; Díaz Fernández, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estradé, A.; Farinon, F.; Fraile, L. M.; Freer, M.; Freudenberger, M.; Fynbo, H. O. U.; Galaviz, D.; Geissel, H.; Gernhäuser, R.; Göbel, K.; Golubev, P.; Gonzalez Diaz, D.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Henriques, A.; Holl, M.; Ickert, G.; Ignatov, A.; Jakobsson, B.; Johansson, H. T.; Jonson, B.; Kalantar-Nayestanaki, N.; Kanungo, R.; Knöbel, R.; Kröll, T.; Krücken, R.; Kurcewicz, J.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lepyoshkina, O.; Lindberg, S.; Machado, J.; Marganiec, J.; Maroussov, V.; Mostazo, M.; Movsesyan, A.; Najafi, A.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Prochazka, A.; Rahaman, A.; Rastrepina, G.; Reifarth, R.; Ribeiro, G.; Ricciardi, M. V.; Rigollet, C.; Riisager, K.; Röder, M.; Rossi, D.; Sanchez Del Rio, J.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Stoica, V.; Streicher, B.; Taylor, J. T.; Tengblad, O.; Terashima, S.; Togano, Y.; Uberseder, E.; van de Walle, J.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Wheldon, C.; Wilson, G.; Wimmer, C.; Winfield, J. S.; Woods, P.; Yakorev, D.; Zhukov, M. V.; Zilges, A.; Zuber, K.
Abstract: Background: Models describing nuclear fragmentation and fragmentation fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool for reaching the most neutron-rich nuclei, creating a need for models to describe also these reactions.
Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes.
Method: We have measured projectile fragments from C10,12−18 and B10−15 isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent data set. We compare our data to model calculations.
Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic C10,12−18 and B10−15 isotopes impinging on a carbon target. Comparing model calculations to the data, we find that the epax code is not able to describe the data satisfactorily. Using abrabla07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease abrabla07 describes the data surprisingly well.
Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data has allowed a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.

Keywords: nuclear fragmentation fission radioactive ion beam facilities C10 C12−18 B10−15 isotope

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Registration No. 23640 - Permalink

Remote Sensing-Based Exploration of Structurally-Related Mineralizations around Mount Isa, Queensland, Australia
Jakob, S.; Gloaguen, R.; Laukamp, C.
Abstract: Hyperspectral imaging is a powerful tool for mineral mapping and increasingly used in poorly-accessible areas. It only requires a limited amount of validation sample points, but can fail to discriminate spectrally-similar features. In this manuscript, we show that we improve the identification of interesting targets by including geomorphological data in the spectral mapping scheme. We jointly use geomorphic and spectral features to locate gossanous ironstone ridges as an indicator for possible Pb-Zn-Ag-mineralization and provide an application around Mount Isa and George Fisher/Hilton mine, Queensland, Australia. We combine hyperspectral HyMap data using mixture tuned matched filtering with topographical indices, such as maximum curvature and the topographical position index. As it is often the case with structurally-controlled mineralization, the amount of training sites is limited, and supervised classification methods cannot be implemented. Therefore, we implement expert knowledge in a decision tree to take advantage of the relationship between mineralization, alteration and structure. Optimized rock sampling and spectral measurements provided data for validation. We are able to map sets of gossanous ridges with a minimum of validation points, not only within the Mount Isa mining area itself, but also outside the commonly-accepted host rocks. The ridges are parallel to north-south trending geomorphological features and probably associated with the Paroo fault zone. Similarities between the ridges were confirmed by field observations, spectral measurements and a qualitative rock sample analysis. We identified new mineralized ridges that we could subsequently attribute to a poorly-known and sub-economic deposit known as the Mount Novit Pb-Zn-deposit.
Keywords: HyMap, hyperspectral, mineral mapping, geomorphological features, alteration mapping

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Registration No. 23639 - Permalink

JRQ and JPA irradiated and annealed reactor pressure vessel steels studied by positron annihilation
Slugen, V.; Gokhman, O.; Pecko, S.; Sojak, S.; Bergner, F.
Abstract: The paper is focused on a comprehensive study of JRQ and JPA reactor pressure vessel steels from the positron annihilation lifetime spectroscopy (PALS) point of view. Based on our more than 20 years’ experience with characterization of irradiated reactor steels, we confirmed that defects after irradiation start to grow and/or merge into bigger clusters. Experimental results shown that JPA steel is more sensitive to the creation of irradiation-induced defects than JRQ steel. It is most probably due to high copper content (0.29 wt.% in JPA) and copper precipitation has a major impact on neutron-induced defect creation at the beginning of the irradiation. Based on current PALS results, no large vacancy clusters were formed during irradiation, which could cause dangerous embrittlement concerning operation safety of nuclear power plant. The combined PALS, small angle neutron
scattering and atomic probe tomography studies support the model for JRQ and JPA steels describing the structure of irradiationinduced clusters as agglomerations of vacancy clusters (consisting of 2–6 vacancies each) and are separated from each other by a distribution of atoms.

Keywords: Nuclear materials; positron annihilation spectroscopy; RPV steel; irradiation; ion beam implantation Registration No. 23638 - Permalink

The inhibitory potency of polyoxometalates at P2X receptors
Spanier, C.; Abdelrahman, A.; Tang, J.; Hausmann, R.; Kortz, U.; Schmalzin, G.; Stephan, H.; Wang, W.; Müller, C. E.
Abstract: P2X receptors are trimeric ligand-gated ion channels activated by ATP and permeable for cations such as Na+, K+ and Ca2+. Seven different subunits exist, assembled as homo- or heterotrimers of various stoichiometry.1 Polyoxometalates (POMs) are polynuclear metal-oxo anions of early transition metals in high oxidation states (e. g. W6+, Mo6+, V5+). This class of inorganic metal cluster compounds exhibits great variability with respect to shape, size, charge and composition.2 POMs bear several negative charges and in this respect resemble ATP, which binds to P2X receptors in its negatively charged state. We previously found that certain POMs can inhibit ATP-hydrolyzing ectonucleotidases.2-4 In the present study we investigated whether tungsten-containing POMs can interact with P2X receptors. A series of POMs was investigated for their ability to inhibit ATP-induced calcium influx in recombinant 1321N1 astrocytoma cells stably transfected with P2X receptor subtypes. Several POMs were found to be highly potent inhibitors of P2X receptors exhibiting low nanomolar potency. PEGylation of POMs to increase their metabolic stability was tolerated by the receptors. Structure-activity relationships at P2X receptor subtypes differed from those observed for ecto¬nucleotidases. The majority of POMs were found to be non-cytotoxic at pharmacologically active concentrations.
  • Poster
    Frontiers in Medicinal Chemistry (FiMC) Meeting 2016, 13.-16.03.2016, Bonn, Deutschland
Registration No. 23622 - Permalink

Small, but hitting the target – towards novel nanoparticle platforms for diagnostic cancer imaging
Zarschler, K.
Abstract: For effective localization of functionalized nanoparticles at diseased tissues such as solid tumours or metastases through biorecognition, appropriate targeting vectors directed against selected tumour biomarkers are a key prerequisite. The diversity of such vector molecules ranges from proteins, including antibodies and fragments thereof, through aptamers and glycans to short peptides and small molecules.
The presented work focusses on the epidermal growth factor receptor (EGFR) acting as a model receptor, since it is overexpressed and/or deregulated in a variety of solid tumours. Thus, bioconjugation of EGFR-specific single-domain antibodies (sdAbs) to different nanomaterials and characterization of sdAb-conjugates covering in vitro cancer cell imaging, cell proliferation as well as EGFR phosphorylation and signalling are described. The specificity of the sdAb-conjugates is investigated by way of receptor RNA silencing techniques with increasing complexity in vitro by introducing increasing concentrations of human or bovine serum. The results show that sdAb-functionalised nanomaterials can effectively target the EGFR, even in more complex bovine and human serum conditions where targeting specificity is largely conserved for increasing serum concentration. For highly affine targeting ligands such as sdAbs, targeting a receptor such as EGFR with low serum competitor abundance, receptor recognition function can still be partially realised in complex conditions. Moreover, sdAb-mediated biorecognition of EGFR is not restricted to particular nanomaterials, but was observed to work efficiently in combination with a variety of materials.
  • Lecture (others)
    Eingeladener Vortrag am Institut für Chemie der Universität Zürich, Schweiz, 29.01.2015, Zürich, Schweiz
Registration No. 23620 - Permalink

Small, but hitting the target – towards novel nanoparticle platforms for diagnostic cancer imaging
Zarschler, K.
Abstract: For effective localization of functionalized nanoparticles at diseased tissues such as solid tumours or metastases through biorecognition, appropriate targeting vectors directed against selected tumour biomarkers are a key prerequisite. The diversity of such vector molecules ranges from proteins, including antibodies and fragments thereof, through aptamers and glycans to short peptides and small molecules.
The presented work focusses on the epidermal growth factor receptor (EGFR) acting as a model receptor, since it is overexpressed and/or deregulated in a variety of solid tumours. Thus, bioconjugation of EGFR-specific single-domain antibodies (sdAbs) to different nanomaterials and characterization of sdAb-conjugates covering in vitro cancer cell imaging, cell proliferation as well as EGFR phosphorylation and signalling are described. The specificity of the sdAb-conjugates is investigated by way of receptor RNA silencing techniques with increasing complexity in vitro by introducing increasing concentrations of human or bovine serum. The results show that sdAb-functionalised nanomaterials can effectively target the EGFR, even in more complex bovine and human serum conditions where targeting specificity is largely conserved for increasing serum concentration. For highly affine targeting ligands such as sdAbs, targeting a receptor such as EGFR with low serum competitor abundance, receptor recognition function can still be partially realised in complex conditions. Moreover, sdAb-mediated biorecognition of EGFR is not restricted to particular nanomaterials, but was observed to work efficiently in combination with a variety of materials.
  • Lecture (others)
    Eingeladener Vortrag am Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Australia, 27.11.2014, Melbourne, Australien
Registration No. 23619 - Permalink

In vivo demonstration of an active tumor pretargeting approach with peptide nucleic acid bioconjugates as complementary system
Leonidova, A.; Foerster, C.; Zarschler, K.; Schubert, M.; Pietzsch, H.-J.; Steinbach, J.; Bergmann, R.; Metzler-Nolte, N.; Stephan, H.; Gasser, G.
Abstract: Aim
The ability of early-stage diagnosis of tumor malignancies and personalized treatment ultimately relies on the availability of highly tumor-affine compounds with purposeful pharmacological profile. Although monoclonal antibodies (mAbs) specifically bind to tumor-associated epitopes, the conventional concept of directly radiolabeled tumor-specific mAb has several drawbacks most prominently the prolonged radiation exposure of non-cancerous tissue. However, the concept of tumor pretargeting allows for the rational use of long-circulating high-affinity mAbs for non-invasive cancer radioimmunodetection and therapy. Our work describes a successful tumor pretargeting utilizing an EGFR-specific mAb and peptide nucleic acid (PNA) derivatives as the complementary system for specific radionuclide delivery to pretargeted tumor tissue.

Methods
After chemical synthesis, purification and detailed characterization of the individual components including antibody-PNA conjugates and different PNA oligomers, biodistribution studies were carried out using healthy Wistar rats. Finally, the pretargeting approach was evaluated in murine A431 tumor xenografts by single photon emission computed tomography.

Results
After optimizing the pharmacokinetic properties of PNA oligomers and investigating their hybridization properties, we elaborated a versatile conjugation protocol based on coupling a cysteine-functionalized PNA oligomer to a maleimido-functionalized mAb. The in vivo studies demonstrated a rapid and efficient accumulation of activity at the tumor site with a tumor-to-muscle ratio of > 8 and clearly distinguishable tumor visualization.

Conclusion
This successful tumor pretargeting study has demonstrated the high potential of this concept by applying radiolabeled complementary PNA strands as an alternative in vivo recognition and radionuclide transporting system. The next step involves the translation of these results to the application of therapeutic relevant radionuclides.
  • Lecture (Conference)
    NuklearMedizin 2016 - 54. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin e.V., 20.-23.04.2016, Dresden, Deutschland
Registration No. 23616 - Permalink

Single-domain antibodies for specific nanoparticle targeting of the EGF-receptor
Zarschler, K.
Abstract: For effective localization of functionalized nanoparticles at diseased tissues such as solid tumours or metastases through biorecognition, appropriate targeting vectors directed against selected tumour biomarkers are a key prerequisite. The diversity of such vector molecules ranges from proteins, including antibodies and fragments thereof, through aptamers and glycans to short peptides and small molecules.
The presented work focusses on the epidermal growth factor receptor (EGFR) acting as a model receptor, since it is overexpressed and/or deregulated in a variety of solid tumours. Thus, bioconjugation of EGFR-specific single-domain antibodies (sdAbs) to different nanomaterials and characterization of sdAb-conjugates covering in vitro cancer cell imaging, cell proliferation as well as EGFR phosphorylation and signalling are described. The specificity of the sdAb-conjugates is investigated by way of receptor RNA silencing techniques with increasing complexity in vitro by introducing increasing concentrations of human or bovine serum. The results show that sdAb-functionalised nanomaterials can effectively target the EGFR, even in more complex bovine and human serum conditions where targeting specificity is largely conserved for increasing serum concentration. For highly affine targeting ligands such as sdAbs, targeting a receptor such as EGFR with low serum competitor abundance, receptor recognition function can still be partially realised in complex conditions. Moreover, sdAb-mediated biorecognition of EGFR is not restricted to particular nanomaterials, but was observed to work efficiently in combination with a variety of materials.
  • Invited lecture (Conferences)
    Scientific Symposium "Targeting tumor angiogenesis with antibody-based technologies", 08.06.2015, Madrid, Spanien
Registration No. 23615 - Permalink

Diagnostic and therapeutic targeting of EGF-receptor positive cancer cells using single-domain antibodies
Zarschler, K.
Abstract: Single-domain antibodies (sdAbs) provide several advantages over classical antibodies and fragments thereof. Due to their small size and strict monomeric appearance combined with other important properties such as high solubility and stability as well as high specificity and affinity for the respective antigen, these proteins have been identified as attractive targeting moieties for molecular imaging and drug delivery. Furthermore, sdAbs are easily engineered into bivalent and bispecific constructs by genetic in-frame joining of two identical or two different sdAbs, respectively. This results in increased antigen binding through avidity effects and in enhanced construct specificity by simultaneous interaction with two different antigens, respectively.
In addition to intrinsic agonistic or antagonistic effects on their target, sdAbs appear to be ideally suited to create novel tailored derivatives equipped with innovative effector functions. The chemical or genetic linkage of sdAbs to accessory effector moieties such as toxins and enzymes results in a new class of target-specific anticancer therapeutics. Thereby, the sdAb guides the effector moiety to the diseased tissue, where it carries out its particular function.
Herein the application of radiolabelled epidermal growth factor receptor (EGFR) specific sdAbs as in vivo molecular imaging tracers as well as their intrinsic antagonistic effects on tumor cells will be described. Furthermore, the construction and characterisation of sdAb-based therapeutics will be exemplified. Thus, this contribution sheds light on the future application of sdAb derivatives in the field of cancer diagnosis and therapy.
  • Lecture (Conference)
    PACHIFICHEM 2015, 15.-20.12.2015, Honolulu, USA
Registration No. 23614 - Permalink

Field-Induced Magnonic Liquid in the 3D Spin-Dimerized Antiferromagnet Sr3Cr2O8
Wang, Z.; Quintero-Castro, D. L.; Zherlitsyn, S.; Yasin, S.; Skourski, Y.; Islam, A. T. M. N.; Lake, B.; Deisenhofer, J.; Loidl, A.
Abstract: We report on ultrasound and magnetization studies in three-dimensional, spin-dimerized Sr3Cr2O8 as a function of temperature and external magnetic field up to 61 T. It is well established [A. A. Aczel et al., Phys. Rev. Lett. 103, 207203 (2009)] that this system exhibits a magnonic-superfluid phase between 30 and 60 T and below 8 K. By mapping ultrasound and magnetization anomalies as a function of magnetic field and temperature we establish that this superfluid phase is embedded in a domelike phase regime of a hightemperature magnonic liquid extending up to 18 K. Compared to thermodynamic results, our study indicates that the magnonic liquid could be characterized by an Ising-like order but has lost the coherence of the transverse components. Registration No. 23607 - Permalink

Measurement of the 92,93,94,100Mo(γ,n) reactions by Coulomb Dissociation
Göbel, K.; Adrich, P.; Altstadt, S.; Alvarez-Pol, H.; Aksouh, F.; Aumann, T.; Babilon, M.; Behr, K.-H.; Benlliure, J.; Berg, T.; Böhmer, M.; Boretzky, K.; Brünle, A.; Beyer, R.; Casarejos, E.; Chartier, M.; Cortina-Gil, D.; Chatillon, A.; Pramanik, U. D.; Deveaux, L.; Elvers, M.; Elze, T. W.; Emling, H.; Erhard, M.; Ershova, O.; Fernandez-Dominguez, B.; Geissel, H.; Górska, M.; Heftrich, T.; Heil, M.; Hellstroem, M.; Ickert, G.; Johansson, H.; Junghans, A. R.; Käppeler, F.; Kiselev, O.; Klimkiewicz, A.; Kratz, J. V.; Kulessa, R.; Kurz, N.; Labiche, M.; Langer, C.; Bleis, T. L.; Lemmon, R.; Lindenberg, K.; Litvinov, Y. A.; Maierbeck, P.; Movsesyan, A.; Müller, S.; Nilsson, T.; Nociforo, C.; Paar, N.; Palit, R.; Paschalis, S.; Plag, R.; Prokopowicz, W.; Reifarth, R.; Rossi, D. M.; Schnorrenberger, L.; Simon, H.; Sonnabend, K.; Sümmerer, K.; Surówka, G.; Vretenar, D.; Wagner, A.; Walter, S.; Waluś, W.; Wamers, F.; Weick, H.; Weig, M.; Winckler, N.; Winkler, M.; Zilges, A.
Abstract: The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100 Mo , of the unstable isotope 93 Mo were measured at the L, /R 3 B setup at GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94 Mo , 96,98 Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93 Mo(γ,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94 Mo(γ,n) reaction is presented. Further analysis will complete the experimental database for the (γ,n) production chain of the p-isotopes of molybdenum.

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Registration No. 23603 - Permalink

Application of solvent extraction to environmental science - Identification of radioactive contaminants in surface water
Ikeda-Ohno, A.
Abstract: Solvent extraction is a very traditional but still a very versatile technique with a variety of applications. This presentation will focus on the application of solvent extraction particularly to the environmental science associated with radioactive contamination.
Keywords: Solvent extraction / separation / surface water / environmental science / speciation / actinides / radionuclides / radioactive contamination
  • Invited lecture (Conferences)
    Interdisciplinary German-Japanese Symposium iJaDe2016 - 2nd German-Japanese Microsymposium "Solvent Extraction: From Fundamentals to Applications", 10.05.2016, Dresden, Germany
Registration No. 23598 - Permalink

U(VI) reduction by anaerobic microorganisms isolated from the flooding water of the former uranium mine Königstein (Saxony)
Gerber, U.; Röder, G.; Krawczyk-Bärsch, E.; Arnold, T.; Scheinost, A. C.
Abstract: The former uranium mine Königstein (Saxony, Germany) is currently in the process of remediation. The underground is flooded in a controlled way, and the flooding water is cleaned up in a dedicated waste water treatment plant. Despite high U concentrations up to 13 mg/L and a low pH of 2.9, these waters contain a high microbial diversity as detected by culture-independent methods. Microorganisms are known to interact with metals and radionuclides in different ways [1]. Anaerobic bacteria which are able to gain energy from the reduction of several metals, are known to change the redox state of metals and radionuclides. For instance, anaerobic sulfate-reducing bacteria (SRB) reduce U(VI) to U(IV) and thus change the migration behavior from the more soluble U(VI) into the less soluble U(IV) [2]. Genomic sequence analysis of the flooding water revealed the presence of such anaerobic SRB. By culture-dependent methods it was possible to isolate anaerobic microorganisms from the flooding water. They were incubated with 10 mM glycerol using the flooding water as background medium. During an incubation time of six weeks the redox potential decreased from 660 mV to 300 mV. After four and six weeks of incubation, the cells were separated from the incubation medium by centrifugation and than analyzed by U-LIII edge EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) measurements. By Iterative Target-Factor Analysis (ITFA) we determined that 100 % of U(VI) was reduced to U(IV). Simultaneously, investigations of the supernatant with UV-vis resulted in the same findings. The results show that naturally occurring anaerobic microorganisms within the flooding water of the former uranium mine Königstein are able to reduce U(VI) to U(IV).

1. Lloyd, J.R.M., L. E. , Interactions of microorganisms with radionuclides. Elsevier Science. 2002.
2. Lovley, D.R., et al., Enzymatic Iron and Uranium Reduction by Sulfate-Reducing Bacteria. Marine Geology, 1993. 113(1-2): p. 41-53.

Keywords: Uranium, Reduction, Sulfate-reducing bacteria, Bioremediation
  • Lecture (others)
    5. Workshop - TransAqua, 06.-07.04.2016, Dresden, Deutschland
Registration No. 23587 - Permalink

Polyglycerol-Based Copper Chelators for the Transport and Release of Copper Ions in Biological Environments
Albrecht, R.; Fehse, S.; Pant, K.; Nowag, S.; Stephan, H.; Haag, R.; Tzschucke, C. C.
Abstract: Here, the synthesis and characterization of three improved nanosystems is presented based on amino functionalized hyperbranched polyglycerol (hPG; M w = 16.8 kDa) as potential copper( II ) chelators. The ligands, N -methyl- N -picolylglycine amide, 2,6-pyridine dicarboxylic acid monoamide, and cyclam tetraacetic acid (TETA) monoamide, are covalently attached to the polymer with amide bonds. In this paper, the Cu( II ) loading capacity, the stability of the Cu( II )- loaded carriers at different pHs, with competing ligands and in human serum, as well as the transport of Cu( II ) in biological systems are investigated. For the fi rst time, a different cytotoxicity of functionalized polymer nanoparticles with and without Cu( II ) is observed. The cyclam-based carrier combines the highest loading capacity (29 Cu ions/nanoparticle), best stability with respect to pH and EDTA (45% remaining Cu after 24 h), lowest cytotoxicity (IC 50 > 100 × 10 −6 M (unloaded), 1500 × 10 −6 M Cu( II ); Cu:carrier 29:1), and the highest stability in human serum. Registration No. 23584 - Permalink

ESR modes in a Strong-Leg Ladder in the Tomonaga-Luttinger Liquid Phase
Zvyagin, S.; Ozerov, M.; Maksymenko, M.; Wosnitza, J.; Honecker, A.; Landee, C. P.; Turnbull, M.; Furuya, S.; Giamarchi, T.
Abstract: es hat kein Abstract vorgelegen
  • Lecture (Conference)
    APS March Meeting 2016, 14.-18.03.2016, Baltimore, USA
Registration No. 23580 - Permalink

Numerical simulation of liquid metal batteries
Weber, N.; Beckstein, P.; Galindo, V.; Herreman, W.; Landgraf, S.; Nore, C.; Stefani, F.; Weier, T.
Abstract: Considering the increasing deployment of renewable energies, large-scale stationary energy storage will be a key-technology for the future. One potentially ideal grid-scale energy storage system is the liquid metal battery (LMB), consisting of a totally liquid interior. The long life time and abundant raw materials of LMBs offer a very cheap way of building batteries.

Building LMBs cheap means to make them large. Strong currents in the order of kA will drive a fluid flow, which may increase the battery's performance, or lead to a short circuit in the worst case.

A numerial model for describing the MHD fluid flow is presented and used to describe the Tayler instability, electro-vortex flow and interface instabilities in LMBs.
  • Lecture (others)
    Vortrag am Departament de Física Aplicada an der Universitat Politècnica de Catalunya, 26.04.2016, Barcelona, Spanien
Registration No. 23578 - Permalink

Open Access-Transformationsinitiative "OA2020"
Reschke, E.
Abstract: Vorstellung der Open Access Transformationsinitiative OA2020
Keywords: Open Access, OA2020, publication fees, author publication charge, White Paper, DEAL
  • Lecture (others)
    Arbeitskreis Spezialbibliotheken Dresden - Frühjahrstreffen,, 20.04.2016, Dresden, Deutschland
Registration No. 23577 - Permalink

Kerndatensatz Forschung
Reschke, E.
Abstract: Vorstellung der Kategorien, die sich auf das Publizieren beziehen.
Keywords: Kerndatensatz, Research, Publications
  • Lecture (others)
    Arbeitskreis Spezialbibliotheken Dresden - Frühjahrstreffen, 20.04.2016, Dresden, Deutschland
Registration No. 23576 - Permalink

Dynamical properties of the sine-Gordon quantum spin magnet Cu-PM at zero and finite temperature
Tiegel, A. C.; Honecker, A.; Pruschke, T.; Ponomaryov, A.; Zvyagin, S. A.; Feyerherm, R.; Manmana, S. R.
Abstract: The material copper pyrimidine dinitrate (Cu-PM) is a quasi-one-dimensional spin system described by the spin-1/2 XXZ Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions. Based on numerical results obtained by the density-matrix renormalization group, exact diagonalization, and accompanying electron spin resonance (ESR) experiments we revisit the spin dynamics of this compound in an applied magnetic field. Our calculations for momentum and frequency-resolved dynamical quantities give direct access to the intensity of the elementary excitations at both zero and finite temperature. This allows us to study the system beyond the low-energy description by the quantum sine-Gordon model. We find a deviation from the Lorentz invariant dispersion for the single-soliton resonance. Furthermore, our calculations only confirm the presence of the strongest boundary bound state previously derived from a boundary sine-Gordon field theory, while composite boundary-bulk excitations have too low intensities to be observable. Upon increasing the temperature, we find a temperature-induced crossover of the soliton and the emergence of new features, such as interbreather transitions. The latter observation is confirmed by our ESR experiments on Cu-PM over a wide range of the applied field. Registration No. 23562 - Permalink

Comparison Between the Magnetic Irreversibility and Zero Resistance of High-Quality Melt-Processed YBaCuO Superconductors
Dias, F. T.; Vieira, V. D. N.; Wolff-Fabris, F.; Kampert, E.; Hneda, M.; Schaf, J.; Farinela, G. F.; Gouvea, C. D.; Rovira, J. J. R.
Abstract: This paper portrays a detailed study of the magnetic irreversibility limit Tirr (H) and of the zero resistance point Tc0 (H) of three different top-seeding melt-textured YBa2Cu3O7−δ superconducting samples, with well-aligned c-axis and doped with a high density of nonsuperconducting Y2Ba1Cu1O5 (Y211) pinning centers. We have performed measurements for applied magnetic fields up to 140 kOe and for the whole set of the different field–current configurations. The magnetization measurements were performed using an MPMS-XL SQUID magnetometer and a vibrating sample magnetometer, both from Quantum Design. The electric transport measurements were made using a physical properties measurement system from Quantum Design. The goal of this exhaustive study is obtaining precise data about magnetic flux mobility along the various directions in the sample for the different field–current configurations, thereby defining the nature and effects, due to the strength and anisotropy of the pinning mechanisms and disclosing the various physical mechanisms dissipating electric transport in these systems below the superconducting transition temperature. We discuss our results in terms of the anisotropic flux pinning by the Y211 grains dispersed into the superconducting matrix. Registration No. 23561 - Permalink

Electron spin resonance in a strong-rung spin-1/2 Heisenberg ladder
Ponomaryov, A. N.; Ozerov, M.; Zviagina, L.; Wosnitza, J.; Povarov, K. Y.; Xiao, F.; Zheludev, A.; Landee, C.; Cizmar, E.; Zvyagin, A. A.; Zvyagin, S. A.
Abstract: Cu(C8H6N2)Cl2, a strong-rung spin-1/2 Heisenberg ladder compound, is probed by means of electron spin resonance (ESR) spectroscopy in the field-induced gapless phase above Hc1. The temperature dependence of the ESR linewidth is analyzed in the quantum field theory framework, suggesting that the anisotropy of magnetic interactions plays a crucial role, determining the peculiar low-temperature ESR linewidth behavior. In particular, it is argued that the uniform Dzyaloshinskii-Moriya interaction (which is allowed on the bonds along the ladder legs) can be the source of this behavior in Cu(C8H6N2)Cl2. Registration No. 23560 - Permalink

Tunnelling magnetoresistance of the half-metallic compensated ferrimagnet Mn2RuxGa
Borisov, K.; Betto, D.; Lau, Y. C.; Fowley, C.; Titova, A.; Thiyagarajah, N.; Atcheson, G.; Lindner, J.; Deac, A. M.; Coey, J. M. D.; Stamenov, P.; Rode, K.
Abstract: Tunnel magnetoresistance ratios of up to 40% are measured between 10K and 300K when the highly spin-polarized compensated ferrimagnet, Mn2RuxGa, is integrated into MgO-based perpendicular magnetic tunnel junctions. Temperature and bias dependences of the tunnel magnetoresistance effect, with a sign change near −0.2 V, reflect the structure of the Mn2RuxGa interface density of states. Despite magnetic moment vanishing at a compensation temperature of 200K for x ≈ 0.8, the tunnel magneto resistance ratio remains non-zero throughout the compensation region, demonstrating that the spin-transport is governed by one of the Mn sub-lattices only. Broad temperature range magnetic field immunity of at least 0.5T is demonstrated in the same sample. The high spin polarization and perpendicular magnetic anisotropy make Mn2RuxGa suitable for applications in both non-volatile magnetic random access memory cells and terahertz spin-transfer oscillators.
Keywords: Tunneling Magnetoresistance, Half-Metal, Mn-based alloys, MRAM, Spin Polarisation, Heusler alloy, Ferrimagnetic, Perpendicular Magnetic Anisotropy Registration No. 23559 - Permalink

The TurbEFA Field Experiment - Measuring the Influence of a Forest Clearing on the Turbulent Wind Field
Queck, R.; Bernhofer, C.; Bienert, A.; Schlegel, F.
Abstract: Abstract Forest ecosystems play an important role in the interaction between the land surface and the atmosphere. Measurements and modelling efforts have revealed significant uncertainties in state-of-the-art flux assessments due to spatial inhomogeneities in the air-flow and land surface. Here, a field experiment is used to describe the turbulent flow across a typical Central European forest clearing. A three-dimensional model of the inhomogeneous forest stand was developed using an innovative approach based on terrestrial laser-scanner technology. The comparison of the wind statistics of two measurement campaigns (5 and 12 months long) showed the spatial and temporal representativeness of the ultrasonic anemometer measurements within the canopy. An improved method for the correction of the vertical velocity enables the distinction between the instrumental offsets and the vertical winds due to the inclination of the instrument. Despite a 13 % fraction of deciduous plants within the otherwise evergreen canopy, the effects of phenological seasons on the velocity profiles were small. The data classified according to the wind speed revealed the intermittent nature of recirculating air in the clearing. Furthermore, the development of sub-canopy wind-speed maxima is explained by considering the velocity moments and the momentum equation (including measurements of the local pressure gradient). Clearings deflect the flow downward and feed the sub-canopy flow, i.e., advective fluxes, according to wind speed and, likely, clearing size, whereas local pressure gradients play an important role in the development of sub-canopy flow. The presented dataset is freely available at the project homepage.
Keywords: Forest inhomogeneity, Metström, Momentum balance, Turbulence measurements, Vegetation model Registration No. 23548 - Permalink

Multimodal Somatostatin Receptor Theranostics Using [64Cu]Cu-/[177Lu]Lu-DOTA-(Tyr3)octreotate and AN-238 in a Mouse Pheochromocytoma Model.
Ullrich, M.; Bergmann, R.; Peitzsch, M.; Zenker, E.; Cartellieri, M.; Bachmann, M.; Ehrhart-Bornstein, M.; Block, N.; Schally, A.; Eisenhofer, G.; Bornstein, S.; Pietzsch, J.; Ziegler, C.
Abstract: Pheochromocytomas and extra-adrenal paragangliomas (PHEO/PGLs) are rare catecholamine-producing chromaffin cell tumors. For metastatic disease, no effective therapy is available. Overexpression of somatostatin type 2 receptors (SSTR2) in PHEO/PGLs promotes interest in applying therapies using somatostatin analogs linked to radionuclides and/or cytotoxic compounds, such as [(177)Lu]Lu-DOTA-(Tyr(3))octreotate (DOTATATE) and AN-238. Systematic evaluation of such therapies for the treatment of PHEO/PGLs requires sophisticated animal models. In this study, the mouse pheochromocytoma (MPC)-mCherry allograft model showed high tumor densities of murine SSTR2 (mSSTR2) and high tumor uptake of [(64)Cu]Cu-DOTATATE. Using tumor sections, we assessed mSSTR2-specific binding of DOTATATE, AN-238, and somatostatin-14. Therapeutic studies showed substantial reduction of tumor growth and tumor-related renal monoamine excretion in tumor-bearing mice after treatment with [(177)Lu]Lu-DOTATATE compared to AN-238 and doxorubicin. Analyses did not show agonist-dependent receptor downregulation after single mSSTR2-targeting therapies. This study demonstrates that the MPC-mCherry model is a uniquely powerful tool for the preclinical evaluation of SSTR2-targeting theranostic applications in vivo. Our findings highlight the therapeutic potential of somatostatin analogs, especially of [(177)Lu]Lu-DOTATATE, for the treatment of metastatic PHEO/PGLs. Repeated treatment cycles, fractionated combinations of SSTR2-targeting radionuclide and cytotoxic therapies, and other adjuvant compounds addressing additional mechanisms may further enhance therapeutic outcome.
Keywords: neuroendocrine tumors, catecholamines, DOTATATE, PET, SPECT, optical in vivo imaging, doxorubicin

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Registration No. 23539 - Permalink

The strange implications of electron-electron scattering in graphene
Helm, M.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Winnerl, S.; Wendler, F.; Winzer, T.; Malic, E.; Knorr, A.
Abstract: Electron-electron scattering in graphene gives rise to some unexpected behavior in the electron dynamics, as observed by pump-probe measurements.
When excited with a near-infrared femtosecond laser pulse, the pump-probe signal depends on the angle between the linear polarization of the pump and the probe pulse, which is due to preferential excitation of electrons perpendicular to the laser electric field. This indicates an anisotropic distribution function in momentum space that is preserved by electron-electron scattering, since it mainly occurs collinearly along the Dirac cone. Only after 150 fs the distribution function is rendered isotropic through optical-phonon scattering. The effect is even more pronounced when exciting at small photon energies (88 meV), below the optical-phonon energy: In this case the anisotropic distribution function survives for as long as 5 ps, when it is finally thermalized by non-collinear Coulomb scattering. These results challenge the common view of ultrafast thermalization by electron-electron scattering.
When a magnetic field is applied to graphene, Landau levels are formed that can be selectively excited by circular-polarized radiation. In a pump-probe experiment, exciting and probing all possible transitions between the n=-1, n=0 and n=+1 Landau levels in slightly n-type graphene, we observe an unexpected sign reversal of the n=0 →1 probe signal when pumping the -1→0 transition. This directly reflects the fact that the n=0 Landau level is depleted by electron-electron Auger-type scattering, even though it is optically pumped at the same time.
Both effects can be quantitatively reproduced by a microscopic calculation based on the graphene Bloch equations, and shed new light on the possibility of infrared and THz devices based on hot carriers in graphene.

Keywords: graphene, pump-probe, free-electron laser, Landau levels
  • Invited lecture (Conferences)
    International Conference on Terahertz Emission, Metamaterials and Nanophotonics (TERAMETANANO 2016), 03.-10.04.2016, Cartagena, Colombia
Registration No. 23533 - Permalink

Prompt γ-ray based proton range verification: From experiments to clinical application
Priegnitz, M.; Nenoff, L.; Barczyk, S.; Golnik, C.; Hotoiu, L.; Keitz, I.; Smeets, J.; Trezza, A.; Vander Stappen, F.; Werner, T.; Fiedler, F.; Prieels, D.; Baumann, M.; Enghardt, W.; Pausch, G.; Richter, C.
Abstract: no abstract available
  • Poster
    National Center for Radiation Oncology 2nd Scientific Retreat, 14.-16.04.2016, Dresden, Deutschland
Registration No. 23531 - Permalink

Beta-Amyloid-PET-Bildgebung des Gehirns - DGN-Handlungsempfehlung
Barthel, H.; Meyer, P. T.; Drzezga, A.; Bartenstein, P.; Boecker, H.; Brust, P.; Buchert, R.; Coenen, H. H.; Fougère, C. L.; Gründer, G.; Grünwald, F.; Krause, B. J.; Kuwert, T.; Schreckenberger, M.; Tatsch, K.; Langen, K. J.; Sabri, O.
Abstract: Seit Kurzem sind mehrere Radiopharmaka für die klinische Positronen-Emissions-Tomographie (PET) von mit der Alzheimer-Krankheit assoziierten zerebralen beta-Amyloid(Aß-Plaques zugelassen. Mit der zunehmenden Verbreitung dieser Methode entsteht der Bedarf für entsprechende Handlungsanweisungen. Diese S1-Leitlinie der Deutschen Gesellschaft für Nuklearmedizin beschreibt die adäquate Vorgehensweise bei der Aß-Plaque-PET-Bildgebung. Maßnahmen zur Patientenvorbereitung, zur Anamnese-Erhebung und zu Vorsichtsmaßnahmen werden ebenso vorgestellt wie die betreffenden Radiopharmaka, Maßnahmen zur PET-Daten-Gewinnung, -Verarbeitung, -Analyse und -Befundung. Damit soll ein Beitrag zur Qualitätssicherung in der Nuklearmedizin in Deutschland geleistet werden.
Keywords: beta-Amyloid, Plaques, Positronen-Emissions-Tomographie, PET, Leitlinie Registration No. 23529 - Permalink

Modellierung und Validierung von Feldionisation in parallelen Particle-in-Cell-Codes
Garten, M.
Abstract: Die Modellierung von Feldionisation in Particle-in-Cell(PIC)-Codes ist eine wichtige Voraussetzung zur Untersuchung der Wechselwirkung hochintensiver, ultrakurzer Laserpulse mit Materie. Es existieren bereits zahlreiche Modelle, die akkurate Vorhersagen im Bereich nicht-relativistischer Intensitäten und oberhalb atomarer Zeitskalen treffen können. Weiterhin existieren auch zahlreiche PIC-Codes, die für den Einsatz auf CPUs konzipiert wurden und Feldionisation berücksichtigen. Das Ziel dieser Arbeit ist die Modellierung von Feldionisation auf neuen, hochparallelen GPU-Architekturen. Diese werden in den letzten Jahren verstärkt für wissenschaftliche Simulationen eingesetzt und bieten einen deutlichen Geschwindigkeitsvorteil gegenüber CPUs. Die Modellierung von Feldionisation auf GPGPUs birgt einige Herausforderungen und es ist das erweiterte Ziel dieser Arbeit, die Implementierung auch zu verifizieren. Dabei wird ein Einblick in die Schwierigkeiten gegeben, die bei der Anwendung existierender Ionisationsmodelle durch Einschränkungen der Modelle selbst, des PIC-Schemas sowie der Plasmadynamik zu beachten sind. In Folge dieser Arbeit wurde PIConGPU, der derzeit schnellste, vollständig relativistische Particle-in-Cell-Code der Welt, um ein allgemeines Werkzeug zur Modellierung von Ionisation erweitert. Dieses ermöglicht die Simulation neuer und spannender physikalischer Anwendungsfälle im Bereich der Laser-Plasmaphysik.
Keywords: Particle-In-Cell, field ionization, GPGPU, PIConGPU, ADK, BSI
  • Master thesis
    HZDR, TU Dresden, 2015
    Mentor: Prof. Dr. Thomas Cowan, Prof. Dr. Ulrich Schramm, Dr. Michael Bussmann
    0097 Seiten
Registration No. 23518 - Permalink

Application of X-ray absorption spectroscopy to actinide research
Scheinost, A. C.
Abstract: An overview will be given on the applications of x-ray absorption spectroscopy to actinide research, including topics in nuclear waste management and development of fourth generation nuclear fuel
Keywords: XAFS Nuclear fuel nuclear waste disposal
  • Invited lecture (Conferences)
    11th School on the Physics and Chemistry of the Actinides, 13.-16.03.2016, Grenoble, France
Registration No. 23514 - Permalink

Distillation Tray Efficiency Modeling: A Forgotten Chapter
Vishwakarma, V.; Schubert, M.; Hampel, U.
Abstract: Cross-flow trays are highly reputed among vapour-liquid contacting devices due to their versatility. They have been into existence for two centuries; still the estimation of their mass transfer efficiency relies mostly on experience. There have been numerous attempts in the past to understand the nature of liquid mixing and flow patterns on trays. However, very few have managed to relate their findings with tray efficiency.
The present work aims at reviewing mathematical models developed for predicting distillation tray efficiency. These models were developed by considering simplified assumptions namely plug flow, uniform vapour composition, constant froth height etc. It is needless to mention the requirement of an improved mathematical model accounting real flow scenarios. This work also attempts to encourage the fraternity of fluid separation technology to revive the efficacy of tray modeling.

Keywords: Distillation Trays, Murphree Tray Efficiency, Eddy Diffusion Model, Residence Time Distribution
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Fluidverfahrenstechnik, 16.-17.03.2016, Garmisch-Partenkirchen, Germany
Registration No. 23512 - Permalink

A gas cell for stopping, storing and polarizing radioactive particles
Sytema, A.; van den Berg, J. E.; Böll, O.; Chernowitz, D.; Dijck, E. A.; Grasdijk, J. O.; Hoekstra, S.; Jungmann, K.; Mathavan, S. C.; Meinema, C.; Mohanty, A.; Müller, S. E.; Nuñez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; Willmann, L.; Wilschut, H. W.
Abstract: A radioactive beam of 20Na is stopped in a gas cell filled with Ne gas. The stopped particles are polarized by optical pumping. The degree of polarization that can be achieved is studied. A maximum polarization of 50% was found. The dynamic processes in the cell are described with a phenomenological model.
Keywords: β decay; Gas catcher; Polarization in buffer gas; Plasma Registration No. 23511 - Permalink

Controlled polar asymmetry of few-cycle and intense mid-infrared pulses
Schmidt, C.; Bühler, J.; Mayer, B.; Pashkin, A.; Leitenstorfer, A.; Seletskiy, D.
Abstract: We demonstrate synthesis of ultrabroadband and phase-locked two-color transients in the multi-terahertz frequency range with amplitudes exceeding 13 MV cm−1. Subcycle polar asymmetry of the electric field is adjusted by changing the relative phase between superposed fundamental and second harmonic components. The resultant broken symmetry of the field profile is directly resolved via electro-optic sampling. Access to such waveforms provides a direct route for control of low-energy degrees of freedom in condensed matter as well as non-perturbative light–matter interactions under highest non-resonant electric bias.
Keywords: polar asymmetry, THz, harmonic synthesis, quantum control, mid-infrared, high field, non-perturbative light–matter interaction Registration No. 23510 - Permalink

Polycrystalline ZnTe thin film on silicon synthesized by pulsed laser deposition and subsequent pulsed laser melting
Xu, M.; Gao, K.; Wu, J.; Cai, H.; Yuan, Y.; Prucnal, S.; Hübner, R.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: ZnTe thin films on Si substrates have been prepared by pulsed laser deposition and subsequent pulsed laser melting (PLM) treatment. The crystallization during PLM is confirmed by Raman scattering, x-ray diffraction and room temperature photoluminescence (PL) measurements. The PL results show a broad peak at 574 nm (2.16 eV), which can be assigned to the transitions from the conduction band to the acceptor level located at 0.145 eV above the valence band induced by zinc-vacancy ionization. Our work provides an applicable approach to low temperature preparation of crystalline ZnTe thin films.
Keywords: ZnTe, Pulsed laser melting

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Registration No. 23505 - Permalink

Crystalline Electric Field and Kondo Effect in SmOs4Sb12
Mombetsu, S.; Yanagisawa, T.; Hidaka, H.; Amitsuka, H.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Ho, P.-C.; Maple, M. B.
Abstract: Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs4Sb12 has the Γ67 quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the Γ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic Response below ≈20 T cannot be explained using the localized 4f-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures. Registration No. 23504 - Permalink

Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis
Hannaske, R.
Abstract: Zwischen 10 und 1000 s nach dem Urknall bildeten sich während der Big Bang Nukleosynthese (BBN) die ersten leichten Elemente aus Protonen und Neutronen. Die primordialen Häufigkeiten dieser Elemente hingen von denWirkungsquerschnitten der beteiligten Kernreaktionen ab. Vergleiche zwischen den Ergebnissen nuklearer Netzwerkrechnungen mit astronomischen Beobachtungen bieten eine einzigartige Möglichkeit, etwas über das Universum zu dieser Zeit zu erfahren.
Da es für die p(n,g)d-Reaktion, die eine Schlüsselreaktion der BBN ist, kaum Messungen im relevanten Energiebereich gibt, beruht deren Reaktionsrate in Netzwerkrechnungen auf theoretischen Berechnungen. Darin fließen auch experimentelle Daten der Nukleon-Nukleon-Streuung, des Einfangquerschnitts für thermische Neutronen sowie (nach Anwendung des Prinzips des detaillierten Gleichgewichts) der d(g,n)p-Reaktion mit ein. Diese Reaktion, die Photodissoziation des Deuterons, ist bei BBN-Energien (Tcm = 20–200 keV) ebenfalls kaum vermessen. Die großen experimentelle Unsicherheiten machen Vergleiche mit den präzisen theoretischen Berechnungen schwierig. In den letzten Jahren wurde die d(g,n)p-Reaktion und insbesondere der M1-Anteil des Wirkungsquerschnitts mit quasi-monoenergetischen g-Strahlen aus Laser-Compton-Streuung oder durch Elektrodesintegration untersucht. Üblicherweise verwendete man für Messungen des d(g,n)p-Wirkungsquerschnitts entweder die auf wenige diskrete Energien beschränkte Strahlung des g-Zerfalls oder Bremsstrahlung, für die aber eine genaue Photonenflussbestimmung sowie der Nachweis von einem der Reaktionsprodukte und dessen Energie nötig ist. Da diese Energie im Bereich der BBN relativ gering ist, gab es bisher noch keine absoluten Messung des d(g,n)p-Wirkungsquerschnitts bei Tcm < 5 MeV mit Bremsstrahlung.
Das Ziel dieser Dissertation ist eine solche Messung mit einer Unsicherheit von 5 % im für die BBN relevanten Energiebereich und darüber hinaus bis Tcm ~ 2,5 MeV unter Verwendung gepulster Bremsstrahlung an der Strahlungsquelle ELBE. Dieser supraleitende Elektronenbeschleuniger befindet sich am Helmholtz-Zentrum Dresden-Rossendorf und stellte einen Elektronenstrahl hoher Intensität bereit. Die kinetische Elektronenenergie von 5 MeV wurde mit einem Browne-Buechner-Spektrometer präzise gemessen. Die Energieverteilung der in einer Niob-Folie erzeugten Bremsstrahlungsphotonen wurde berechnet. Die Photonenflussbestimmung nutzte die Kernresonanzstreuung an 27Al, das sich mit deuteriertem Polyethylen in einem mehrschichtigen Target befand. Die 27Al-Abregungen wurden mit abgeschirmten, hochreinen Germanium-Detektoren nachgewiesen, deren Effektivität mit GEANT4 simuliert und durch Quellmessungen normiert wurde. Die Messung der Energie der Neutronen aus der d(g,n)p-Reaktion erfolgte mittels deren Flugzeit in Plastikszintillatoren, die an zwei Seiten von Photoelektronenvervielfachern mit hoher Verstärkung ausgelesen wurden. Die Nachweiseffektivität dieser Detektoren wurde in einem eigenen Experiment in den Referenz-Neutronenfeldern der PTB Braunschweig kalibriert. Die Nachweisschwelle lag bei etwa 10 keV kinetischer Neutronenenergie.Wegen der guten Zeitauflösung der Neutronendetektoren und des ELBE-Beschleunigers genügte eine Flugstrecke von nur 1 m. Die Energieauflösung betrug im d(g,n)p-Experiment 1–2 %. Leider gingen viele Neutronen bereits durch Streuung in dem großen Target verloren oder sie wurden erst durch Teile des kompakten Experimentaufbaus in die Detektoren gestreut. Beide Effekte wurden mit Hilfe von FLUKA simuliert um einen Korrekturfaktor zu bestimmen, der aber bei niedrigen Energien relativ groß war.
Der d(g,n)p-Wirkungsquerschnitts wurde daher nur im Bereich 0.7 MeV < Tcm < 2.5 MeV bestimmt. Die Ergebnisse stimmen mit anderen Messungen, Daten-Evaluierungen sowie theoretischen Rechnungen überein. Die Gesamtunsicherheit beträgt circa 6.5 % und kommt zu fast gleichen Teilen von den statistischen und systematischen Unsicherheiten. Die statistische Unsicherheit könnte durch eine längere FLUKA Simulation noch von 3–5 % auf 1 % verringert werden. Die systematische Unsicherheit von 4.5 % ist vorrangig auf die Photonenflussbestimmung, die Neutronen-Nachweiseffektivität und die Target-Zusammensetzung zurückzuführen.

Keywords: Big Bang nucleosynthesis, bremsstrahlung, gamma-ray spectroscopy, neutron time-of-flight, nuclear astrophysics, photon scattering, neutron detector, efficiency, FLUKA
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-071 2016

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Registration No. 23501 - Permalink

Single-shot betatron source size measurement from a laser-wakefield accelerator
Köhler, A.; Couperus, J. P.; Zarini, O.; Jochmann, A.; Irman, A.; Schramm, U.
Abstract: Betatron radiation emitted by accelerated electrons in laser-wakefield accelerators can be used as a diagnostic tool to investigate electron dynamics during the acceleration process. We analyse the spectral characteristics of the emitted betatron pattern utilizing a 2D x-ray imaging spectroscopy technique. Together with simultaneously recorded electron spectra and x-ray images, the betatron source size, thus the electron beam radius, can be deduced at every shot.
Keywords: Betatron radiation, Laser wakefield acceleration, x-rays
  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland
Registration No. 23499 - Permalink

Quantum oscillations and the Fermi surface topology of the Weyl semimetal NbP
Klotz, J.; Wu, S.-C.; Shekhar, C.; Sun, Y.; Schmidt, M.; Nicklas, M.; Baenitz, M.; Uhlarz, M.; Wosnitza, J.; Felser, C.; Yan, B.
Abstract: The Weyl semimetal NbP was found to exhibit topological Fermi arcs and exotic magnetotransport properties. Here, we report on magnetic quantum-oscillation measurements on NbP and construct the three-dimensional Fermi surface with the help of band-structure calculations. We reveal a pair of spin-orbit-split electron pockets at the Fermi energy and a similar pair of hole pockets, all of which are strongly anisotropic. The Weyl points that are located in the kz ≈ π/c plane are found to exist 5 meV above the Fermi energy. Therefore, we predict that the chiral anomaly effect can be realized in NbP by electron doping to drive the Fermi energy to the Weyl points. Registration No. 23498 - Permalink

Exotic Ground State and Elastic Softening under Pulsed Magnetic Fields in PrTr2Zn20 (Tr = Rh, Ir)
Ishii, I.; Goto, H.; Kamikawa, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Onimaru, T.; Matsumoto, K. T.; Takabatake, T.; Suzuki, T.
Abstract: To investigate a field-induced level crossing of the ground-state doublet in PrTr2Zn20 (Tr = Rh, Ir), we performed ultrasonic measurements in pulsed magnetic fields applied along the [110] and [001] directions and analyzed the results in the framework of the strain-susceptibility approach. Above 40 T for H ∣∣ [110], we observed an elastic softening of the transverse modulus (C11 − C12)/2 corresponding to the ground-state doublet. In both compounds the softening is followed by a minimum at about 47 T at low temperatures. We predict the presence of a new field-induced phase boundary in PrTr2Zn20 at this field with two possible cases. The magnetic field of the minimum cannot be explained by only the quadrupole interaction. Registration No. 23497 - Permalink

Magnetic phase diagram of the helimagnetic spinel compound ZnCr2Se4 revisited by small-angle neutron scattering
Cameron, A. S.; Tymoshenko, Y. V.; Portnichenko, P. Y.; Gavilano, J.; Tsurkan, V.; Felea, V.; Loidl, A.; Zherlitsyn, S.; Wosnitza, J.; Inosov, D. S.
Abstract: We performed small-angle neutron scattering (SANS) measurements on the helimagnetic spinel compound ZnCr2Se4. The ground state of this material is a multi-domain spin-spiral phase, which undergoes domain selection in a magnetic field and reportedly exhibits a transition to a proposed spin-nematic phase at higher fields. We observed a continuous change in the magnetic structure as a function of field and temperature, as well as a weak discontinuous jump in the spiral pitch across the domain-selection transition upon increasing field. From our SANS results we have established the absence of any long-range magnetic order in the high-field (spin-nematic) phase. We also found that all the observed phase transitions are surprisingly isotropic with respect to the field direction. Registration No. 23496 - Permalink

Performance and Application Status of the Superconducting Photoinjector at ELBE
Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Vennekate, H.; Xiang, R.
Abstract: A new SRF gun has been commissioned at the ELBE linac. The gun has an improved 3.5-cell cavity and a superconducting solenoid is integrated. Beam parameter measurements have been carried out with a Cu photocathode.
Keywords: photoinjector, superconducting cavity, electron source, photocathode
  • Invited lecture (Conferences)
    OSA High-Brightness Sources and Light-Driven Interaction Congress, 20.-22.03.2016, Long Beach, USA
Registration No. 23486 - Permalink

Synthesis and characterization of modified ultrasmall nanoparticles as multimodal imaging agents
Singh, G.; Hunoldt, S.; Licciardello, N.; Stephan, H.; Faramus, A.; De Cola, L.
Abstract: The synthesis of multimodal imaging agents is indeed a growing field and a lot of research is currently being done in this area because of its wide biomedical applications.[1] The idea behind this research is to prepare a single molecule/nanoparticle which is suitable for two or more imaging techniques and thus can act as a multimodal imaging agent, for example, the combination of optical and nuclear imaging modalities may provide complementary information for improving diagnosis as well as the treatment of diseases. These imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability. The high hydrophilicity of the nanoparticles and fast renal clearance of the complex from the body are the major highlights.
Amine terminated ultrasmall Silicon nanoparticles[2] (Si NPs) of size <5 nm were synthesized by hydrothermal method and purified by dialysis. Sulfo-Cyanine 5[3] dye was attached selectively to the amine terminated Si NPs. The single domain antibody is also conjugated with the particles for specific targeting of the cancerous tumors via a molecular handle such as PEG-Maleimide, which facilitates the targeting as well as maintains the hydrophilicity of the particles at the same time. Bispidines[4] are to be used as a copper chelator for radiolabeling the particles by 64Cu and could be used for the in vitro and in vivo studies by Positron emission tomography.
The substituents after coupling with the USNPs are assumed to act as excellent multimodal imaging agent which can be used for the cancer diagnosis and therapy.

References
[1] G. J. Cheon, Y. Chang, J. Yoo, J. Cheon, Angew. Chem. 2008, 120, 6355 –6358.
[2] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S. Lee, Y. He, J. Am. Chem. Soc. 2013, 135, 8350−8356.
[3] K. Viehweger, L. Barbaro, K. P. García, T. Joshi, G. Geipel, J. Steinbach, H. Stephan, L. Spiccia, B. Graham, Bioconjugate Chem. 2014, 25, 1011−1022.
[4] H. Stephan, M. Walther, S. Fähnemann, P. Ceroni, J. Molloy, G. Bergamini, F. Heisig, C. E. Müller, W. Kraus, P. Comba, Chem. Eur. J. 2014, 20, 17011-17018.
  • Poster
    Analytica Conference 2016, 10.-12.05.2016, Munich, Germany
Registration No. 23480 - Permalink

Intrinsic diamagnetism in the Weyl semimetal TaAs
Liu, Y.; Li, Z.; Guo, L.; Chen, X.; Yuan, Y.; Liu, F.; Prucnal, S.; Helm, M.; Zhou, S.
Abstract: We investigate the magnetic properties of TaAs, a prototype Weyl semimetal. TaAs crystals show diamagnetism with magnetic susceptibility of about −7×10−7 emu/(g Oe) at 5 K. A general feature is the appearance of a minimum at around 185 K in magnetization measurements as a function of temperature, which resembles that of graphite. No phase transition is observed in the temperature range between 5 K and 400 K.
Keywords: Diamagnetism; Weyl semimetal; TaAs; Magnetic susceptibility Registration No. 23479 - Permalink

Untersuchung zum Einfluss lokaler Strömungszustände auf das Auftreten der Siedekrise
Geißler, T.; Franz, R.; Hampel, U.
Abstract: Die Effizienz von Verdampfungssystemen hängt maßgeblich von der übertragbaren Wärmestromdichte ab. Eine Leistungssteigerung ist durch das Auftreten der Siedekrise limitiert. Dabei kommt es durch ein abruptes Abfallen des Wärmeübergangskoeffizienten in leistungsbestimmten Systemen zu einem starken Temperaturanstieg der Heizfläche, welcher zu einem Versagen der Strukturelemente führen kann. Sicherheitsmargen sorgen in industriellen Anwendungen für einen ausreichenden Schutz vor diesem kritischen Zustand. Mit einer verlässlichen Vorhersage der Siedekrise können diese Margen allerdings reduziert werden. Durch Experimente mit hochaufgelöster Messung der Wandtemperatur und Bestimmung der Phasenverteilung während des Siedens werden Verdampfungsprozesse besser verstanden und CFD-Modell-Entwicklung unterstützt.
  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Wärme- und Stoffübertragung, 01.-02.03.2016, Kassel, Deutschland
Registration No. 23475 - Permalink

Electron Dynamics in Silicon−Germanium Terahertz Quantum Fountain Structures
Sabbagh, D.; Schmidt, J.; Winnerl, S.; Helm, M.; Di Gaspare, L.; de Seta, M.; Virgilio, M.; Ortolani, M.
Abstract: Asymmetric quantum well systems are excellent candidates to realize semiconductor light emitters at far-infrared wavelengths not covered by other gain media. Group-IV semiconductor heterostructures can be grown on silicon substrates, and their dipole-active intersubband transitions could be used to generate light from devices integrated with silicon electronic circuits. Here, we have realized an optically pumped emitter structure based on a three-level Ge/Si0.18Ge0.82 asymmetric coupled quantum well design. Optical pumping was performed with a tunable free-electron laser emitting at photon energies of 25 and 41 meV, corresponding to the energies of the first two intersubband transitions 0 → 1 and 0 → 2 as measured by Fourier-transform spectroscopy. We have studied with a synchronized terahertz timedomain spectroscopy probe the relaxation dynamics after pumping, and we have interpreted the resulting relaxation times (in the range 60 to 110 ps) in the framework of an out-of-equilibrium model of the intersubband electron−phonon dynamics. The spectral changes in the probe pulse transmitted at pump−probe coincidence were monitored in the range 0.7−2.9 THz for different samples and pump intensity and showed indication of both free carrier absorption increase and bleaching of the 1 → 2 transition. The quantification from data and models of the free carrier losses and of the bleaching efficiency allowed us to predict the conditions for population inversion and to determine a threshold pump power density for lasing around 500 kW/cm2 in our device. The ensemble of our results shows that optical pumping of germanium quantum wells is a promising route toward siliconintegrated far-infrared emitters.
Keywords: silicon photonics, quantum wells, chemical vapor deposition, terahertz spectroscopy, pump−probe spectroscopy, germanium Registration No. 23472 - Permalink

Terahertz Near-Field Investigation of a Plasmonic GaAs Superlens
Fehrenbacher, M.
Abstract: This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration.
For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-070 2016

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Registration No. 23470 - Permalink

Design Study of a Traveling-Wave Thomson-Scattering Experiment for the Realization of Optical Free Electron Lasers
Steiniger, K.; Albach, D.; Debus, A.; Loeser, M.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Bussmann, M.
Abstract: We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric fi eld of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator fi eld. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses.
An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. In the talk we show how diff raction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser fi eld along the electron trajectory. Furthermore we give tolerance limits on alignment errors to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the scheme.

Keywords: traveling-wave, thomson-scattering, FEL, x-ray, pulse-front tilt, out-of-focus
  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland
Registration No. 23469 - Permalink

Design Study for an Optical Free-Electron Laser Realized by Traveling-Wave Thomson-Scattering
Steiniger, K.; Albach, D.; Bussmann, M.; Irman, A.; Jochmann, A.; Loeser, M.; Pausch, R.; Röser, F.; Schramm, U.; Debus, A.
Abstract: We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric field of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator field. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses. An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. The poster shows how diffraction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser field along the electron trajectory. Furthermore we give limits on alignment tolerances to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the design.
Keywords: traveling-wave, Thomson scattering, FEL, x-ray, tilted laser pulse, out-of-focus
  • Lecture (Conference)
    Student Retreat@2. Annual MT Meeting, 07.-08.03.2016, Karlsruhe, Deutschland
  • Poster
    2. Annual MT Meeting, 08.-11.03.2016, Karlsruhe, Deutschland
Registration No. 23468 - Permalink

Free - Surface Modelling in the Ribbon Growth on Substrate (RGS)process
Beckstein, P.; Galindo, V.; Gerbeth, G.
Abstract: The cost efficient, high throughput production of metal- and semiconductor alloys is the foundation of many advanced technologies. With the development of the Ribbon Growth on Substrate (RGS) technology, a new crystallization technique is available that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. In contrast to other crystallization methods, like e.g. melt spinning or even directional solidification, the RGS process allows high volume manufacturing, better crystallization control and a high material yield due to a substrate driven process. To optimize the application of RGS further, insights from modelling the liquid metal flow are very desirable. We have already conducted extensive numerical investigations in order to study the involved AC magnetic fields. For the RGS technology, these magnetic fields play an essential role in realizing inductive heating and an additional magnetic retention effect.
New simulation results demonstrate the effect of the applied AC magnetic fields on the melt flow of liquid silicon. The focus is thereby devoted to the simulation of the melt surface deformation based on a multi-physical modelling approach in OpenFOAM (foam-extend). Our developed numerical tool allows us to model hydrodynamic and magnetodynamic effects and their interaction. Studies of the time-dependent free-surface flow under the influence of magnetic forces are the key for improving the RGS process as main flow structures and possible instabilities strongly depend on the melt shape.

Keywords: RGS process, OpenFOAM extend, Free-Surface Modelling
  • Poster
    1st German Czechoslovak Conference on Crystal Growth, GCCCG-1 / DKT2016, 16.-18.03.2016, Dresden, Germany
Registration No. 23466 - Permalink

Translation of a prompt gamma based proton range verification system to first clinical application
Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Golnik, G.; Bombelli, L.; Enghardt, W.; Fiedler, F.; Fiorini, C.; Hotoiu, L.; Janssens, G.; Keitz, I.; Mein, S.; Perali, I.; Prieels, D.; Smeets, J.; Thiele, J.; Vander Stappen, F.; Werner, T.; Baumann, M.
Abstract: To improve precision of particle therapy, in vivo range verification is highly desirable to reduce range uncertainties and thereby increase the advantage of proton therapy. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically, although proposed 12 years ago. We report on the translational implementation as well as the worldwide first clinical application of prompt gamma imaging (PGI) based range verification. A prototype of a PGI camera was used to measure the prompt gamma depth distribution during proton treatment of a head and neck tumor. Inter-fractional variations of the prompt gamma profile were evaluated and anatomical changes were independently verified.
  • Lecture (Conference)
    ESTRO 35, European society for radiotherapy and oncology, 29.04.-03.05.2016, Turin, Italy
Registration No. 23458 - Permalink

First clinical application of a prompt gamma based in vivo proton range verification using a knife-edge slit camera
Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Bombelli, L.; Fiorini, C.; Hotoiu, L.; Perali, I.; Prieels, D.; Enghardt, W.; Baumann, M.
Abstract: To improve precision of particle therapy, in vivo range verification is highly desirable. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically. Here we report on the worldwide first clinical application of prompt gamma imaging (PGI) based range verification.
  • Lecture (Conference)
    ICTR-PHE 2016, International Conference on Translational Research in Radio-Oncology | Physics for Health in Europe, 15.-19.02.2016, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)Suppl. 1, S89-S90
    DOI-Link: http://dx.doi.org/10.1016/S0167-8140(16)30184-0
    Button zum Volltext
Registration No. 23457 - Permalink

Comparison of SIMS and RBS for depth profiling of silica glasses implanted with metal ions
Lorinčík, J.; Veselá, D.; Vytykáčová, S.; Švecová, B.; Nekvindová, P.; Macková, A.; Mikšová, R.; Malinský, P.; Böttger, R.
Abstract: Ion implantation of metal ions, followed by annealing, can be used for the formation of buried layers of metal nanoparticles in glasses. Thus, photonic structures with nonlinear optical properties can be formed. In this study, three samples of silicaglasses were implanted with Cu+, Ag+, or Au+ ions under the same conditions (energy 330 keV and fluence 1 × 1016 ions/cm2), and compared to three identical silicaglass samples that were subsequently coimplanted with oxygen at the same depth. All the implantedglasses were annealed at 600 °C for 1 h, which leads to the formation of metal nanoparticles. The depth profiles of Cu,Ag, and Au were measured by Rutherford backscattering and by secondary ion mass spectrometry and the results are compared and discussed.
Keywords: Rutherford backscattering, Secondary ion mass spectroscopy, Gold, Silver, Amorphous metals Registration No. 23456 - Permalink

A strategy for the qualification of multi-fluid approaches for nuclear reactor safety
Lucas, D.; Rzehak, R.; Krepper, E.; Ziegenhein, Th.; Liao, Y.; Kriebitzsch, S.; Apanasevich, P.
Abstract: CFD-simulations for two-phase flows applying the multi-fluid approach are not yet qualified to provide reliable predictions for unknown flows. Among others, one important reason is the missing agreement within the community on closure models to be used. Considering specific phenomena or not, using different models and adjustable constants, most papers presenting a model validation end up with a good agreement with experimental data. However a case by case selection of models and constants does not help to improve the predictive capabilities of such models. For this reason the definition of baseline models considering all known phenomena that could be important is proposed. In such baseline models all parameter have to be defined, i.e., there are no tuning parameters by definition. Therefore these baseline models have to be applied to many experiments with different complexity. Shortcomings of the models and our physical understanding of the complex flow phenomena have to be identified by detailed analyses on the deviations between experimental data and simulation results. A modification of the baseline model will only be done if it bases on physical considerations and improves the overall performance of the model. This requires a huge effort, but seems to be the only way to improve the situation. In particular more complete experimental data are required. Joint activities on the development of such baseline models are desirable. The paper illustrates this strategy by a baseline model for polydisperse bubbly flows which is presently developed at HZDR.
Keywords: CFD, two-phase flow, multi-fluid, bubbly flow, validation Registration No. 23455 - Permalink

Terahertz spectroscopy of individual donors in silicon by low-temperature s-SNOM
Lang, D.; Winnerl, S.; Schneider, H.; Li, J.; Clowes, S.; Murdin, B.; Döring, J.; Kehr, S. C.; Eng, L. M.; Helm, M.
Abstract: Isolated atoms or ions, typically confined in traps, are ideal systems for studying fascinating coherent quantum effects such as photon echoes. Likewise, isolated donor impurity atoms in semiconductors like silicon show a hydrogen-like spectrum, shifted to the far infrared due to the small effective mass and high dielectric constant [1]. Excited Rydberg states are of particular interest for quantum information, because they allow one to prepare long-living microscopic polarization states.

In contrast to previous far-field spectroscopic studies which probed ensembles of many impurities, we aim here at studying individual impurity centers. To this end, low-temperature scattering-type scanning near-field optical microscopy (s-SNOM) is employed and a free-electron laser is used as a precisely tunable terahertz source [2]. Our silicon samples contain different donors (P, Bi) with different defect densities, respectively, and are pre-characterized by conventional Fourier transform infrared spectroscopy.

[1] Greenland et al., Nature 465, 1057 (2010).
[2] Döring et al., Appl. Phys. Lett. 105, 053109 (2014).

Keywords: terahertz, silicon, nanoscopy, s-SNOM, spectroscopy, low-temperature, impurities, free-electron laser
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23454 - Permalink

Bipolar resistive switching of p-YMnO3/n-SrTiO3:Nb junctions
Bogusz, A.; Blaschke, D.; Abendroth, B.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.
Abstract: Resistive switching (RS) phenomena of oxides in metal-insulatormetal structures have been widely investigated due to promising applications as a non-volatile memory and in neuromorphic circuits. In our previous works, we have demonstrated unipolar RS of YMnO3-based structures [1]. This work investigates the non-volatile RS switching in Au/YMnO3-/Nb:SrTiO3-/Al structures with (p-YMnO3-)-(n-Nb:SrTiO3-) junctions. The YMnO3- films are deposited by pulsed laser deposition on the (100)-SrTiO3- doped with 0.5 wt.% of Nb substrates and exhibit bipolar RS. Observed RS behavior is assigned to the coupled electronic and ionic processes which depend on the depletion layer extension in the p-n junction. Exploitation of RS in p-n junctions offers additional functionalities of memristive devices, e.g. related to their optical properties.
[1] A. Bogusz et al., AIP Advances 4 (2014), A. Bogusz et al., Adv. Mater. Res. 1101 (2015).
  • Lecture (Conference)
    DPG Spring Meeting, 06.-11.03.2016, Regensburg, Germany
Registration No. 23452 - Permalink

Nonlinear Terahertz Absorption of Graphene Plasmons
Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.
Abstract: Subwavelength graphene structures support localized plasmonic resonances in the terahertz and mid-infrared spectral regimes. The strong field confinement at the resonant frequency is predicted to significantly enhance the light-graphene interaction, which could enable nonlinear optics at low intensity in atomically thin, subwavelength devices. To date, the nonlinear response of graphene plasmons and their energy loss dynamics have not been experimentally studied. We measure and theoretically model the terahertz nonlinear response and energy relaxation dynamics of plasmons in graphene nanoribbons. We employ a terahertz pump − terahertz probe technique at the plasmon frequency and observe a strong saturation of plasmon absorption followed by a 10 ps relaxation time. The observed nonlinearity is enhanced by 2 orders of magnitude compared to unpatterned graphene with no plasmon resonance. We further present a thermal model for the nonlinear plasmonic absorption that supports the experimental results. The model shows that the observed strong linearity is caused by an unexpected red shift of plasmon resonance together with a broadening and weakening of the resonance caused by the transient increase in electron temperature. The model further predicts that even greater resonant enhancement of the nonlinear response can be expected in high-mobility graphene, suggesting that nonlinear graphene plasmonic devices could be promising candidates for nonlinear optical processing.
Keywords: Graphene, plasmons, nonlinear, pump−probe, terahertz Registration No. 23451 - Permalink

Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible
Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.
Keywords: Detector, graphene, fast detctor, broadband detector
  • Lecture (Conference)
    7th international workshop on terahertz technology and applications, 15.-16.03.2016, Kaiserslautern, Deutschland
Registration No. 23447 - Permalink

Graphene-based fast hot-electron bolometer with bandwidth from THz to VIS
Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. S.; Murphy, T. E.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: We present a fast detector (rise time 40 ps) operating at room temperature that is capable to detect radiation from the THz to visible spectral range (demonstrated wavelengths 500 µm – 780 nm) [1]. The detector consists of a CVD-grown graphene flake contacted by a broadband logarithmic periodic antenna. SiC acts as a substrate material that does not interfere with the detection mechanism in the desired frequency range, even within the Reststrahlen band of SiC (6 – 12 µm). The detector is ideal for timing purposes. Near infrared (mid- and far infrared) pulse energies of the order of 10 pJ (1 nJ) are sufficient to obtain good signal-to-noise ratios. We suggest that the bandwidth is limited by the antenna dimensions (typically several mm) on the long wavelength side and by the bandgap of SiC (380 nm) on the short wavelength side.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: detector, graphene, fast detector, broadband detector
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23446 - Permalink

Noncollinear Coulomb scattering in graphene
König-Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial nonequilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88 meV to suppress efficiently the optical phonon scattering. In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process. This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling.
[1] M. Mittendorff et al., Nano Lett. 14, 1504 (2014).

Keywords: graphene, ultrafast dynamics, anisotropy
  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 23445 - Permalink

Unusual Coulomb Effects in Graphene
Winnerl, S.
Abstract: After a brief overview on the ultrafast carrier dynamics in graphene we focus on two Coulomb-mediated effects. The first one is related to the very different scattering times for collinear versus non-collinear scattering. Collinear Coulomb scattering, due to many possibilities to fulfill energy and momentum conservation requirements, is extremely fast (sub-100 fs timescale). Non-collinear scattering, on the other hand, can be surprisingly slow, namely on the scale of a few ps. This observation is in contrast to the common belief that a non-equilibrium carrier distribution in graphene fully thermalizes on a sub-100 fs timescale. We show that polarization resolved pump-probe experiments at low photon energies, i.e. below the optical phonon energy of ~200 meV, allow one to trace the non-collinear Coulomb scattering and to control its efficiency by varying the pump fluence. The second surprising Coulomb effect is the direct observation of strong Auger scattering in Landau quantized graphene. The Auger scattering in this case can efficiently deplete an energy level while that level is optically pumped at the same time. Finally the potential of graphene for photonic and fast optoelectronic devices such as THz sources and detectors will be discussed.
Keywords: graphene, ultrafast dynamics
  • Lecture (others)
    Seminarvortrag im Rahmen des Graduiertenkollegs Electronic Properties of Carbon Based Nanostructures, 22.01.2016, Regensburg, Deutschland
Registration No. 23444 - Permalink

Arguing on entropic and enthalpic first-order phase transitions in strongly interacting matter
Wunderlich, F.; Yaresko, R.; Kämpfer, B.
Corresponding author: Kämpfer, B.
Abstract: The pattern of isentropes in the vicinity of a first-order phase transition is proposed as a key for a sub-classification. While the confinement–deconfinement transition, conjectured to set in beyond a critical end point in the QCD phase diagram, is often related to an entropic transition and the apparently settled gas-liquid transition in nuclear matter is an enthalphic transition, the conceivable local isentropes w.r.t. ”incoming” or ”outgoing” serve as another useful guide for discussing possible implications, both in the presumed hydrodynamical expansion stage of heavy-ion collisions and the core-collapse of supernova explosions. Examples, such as the quark-meson model and two-phase models, are shown to distinguish concisely the different transitions.

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Registration No. 23439 - Permalink

Laser assisted Breit-Wheeler and Schwinger processes
Nousch, T.; Otto, A.; Seipt, D.; Kämpfer, B.; Titov, A. I.; Blaschke, D.; Panferov, A. D.; Smolyansky, S. A.
Abstract: The assistance of an intense optical laser on electron-positron pair production by the Breit-Wheeler and Schwinger processes in XFEL fields is analyzed. The impact of a laser beam on high-energy photon collisions with XFEL photons consists in a phase space redistribution of the pairs emerging in the Breit-Wheeler sub-process. We provide numerical examples of the differential cross section for parameters related to the European XFEL. Analogously, the Schwinger type pair production in pulsed fields with oscillating components referring to a superposition of optical laser and XFEL frequencies is evaluated. The residual phase space distribution of created pairs is sensitive to the pulse shape and may differ signifcantly from transiently achieved mode occupations. Registration No. 23438 - Permalink

Electromagnetic probes of pure glue initial state in nucleus-nucleus collisions at LHC
Vovchenko, V.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stöcker, H.
Abstract: Partonic matter produced at the early stage of ultrarelativistic nucleus-nucleus collisions is assumed
to be composed mainly of gluons, but quarks and antiquarks are produced at later times.
The dynamical evolution of this chemically nonequilibrium system is described by the ideal (2+1)–dimensional hydrodynamics with a time dependent (anti)quark fugacity. The equation of state is taken as a linear interpolation of the lattice data for the pure gluonic matter and the chemically equilibrated quark-gluon plasma. The spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy. The results are obtained assuming different equilibration times, including the case when the complete chemical equilibrium of partons is reached already at the initial stage. It is shown that a suppression of quarks at early times leads to a significant reduction of the invariant mass spectra of dileptons, but a rather modest suppression of the pT -distributions of direct photons. It is demonstrated that a noticeable enhancements of photon and dilepton elliptic flows might be a good signature of the pure glue initial state.
Registration No. 23437 - Permalink

Bonding structure and morphology of chromium oxide films grown by pulsed-DC reactive magnetron sputter deposition
Gago, R.; Vinnichenko, M.; Hübner, R.; Redondo-Cubero, A.
Abstract: Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (f) and for substrate temperatures, Ts, up to 450 ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), scanning (SEM) and transmission (TEM) electron microscopy, X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES). On unheated substrates, by increasing f the growth rate is higher and the O/Cr ratio (x) rises from ~2 up to ~2.5. Inversely, by increasing Ts the atomic incorporation rate drops and x falls to ~1.8 . XRD shows that samples grown on unheated substrates are amorphous and that nanocrystalline Cr2O3 (x = 1.5) is formed by increasing Ts. In amorphous CrOx , XANES reveals the presence of multiple Cr environments that indicate the growth of mixed-valence oxides, with progressive promotion of hexavalent states with f. XANES data also confirms the formation of single-phase nanocrystalline Cr2O3 at elevated Ts. These structural changes also reflect on the optical and morphological properties of the films.
Keywords: oxide materials; vapour deposition; atomic scale structure; NEXAFS/XANES Registration No. 23435 - Permalink

Attachment of hydrophobic particles to the surface of an immersed gas bubble
Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.
Abstract: The transport of colloidal particles at the fluidic interface of a binary fluid is of significant importance to the flotation process. Flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The fine attaching particles have so far been modelled as point particles, thereby neglecting the deformation of the fluidic interface. Here the combination of the smooth profile method with an in-house binary fluid model is suggested to directly simulate the attachment of a single particle to an immersed bubble under various capillary numbers.
Keywords: Froth flotation, Three-phase system, Particle attachment
  • Contribution to proceedings
    81st Annual meeting of the Society of Chemical Engineers Japan, 13.-15.03.2016, Kansai University, Senriyama Campus, Japan
    Proceedings of the 81st Annual meeting of the Society of Chemical Engineers Japan
Registration No. 23434 - Permalink

Proton Beams for Physics Experiments at OncoRay
Helmbrecht, S.; Fiedler, F.; Meyer, M.; Kaever, P.; Kormoll, T.
Abstract: Purpose: At the OncoRay center in Dresden at proton therapy facility is in operation. The first patient was treated in December 2014. The system is driven by an IBA (IBA Proton Therapy, Louvain-la-Neuve, Belgium) Cyclone 230 isochronous cyclotron with a maximum proton energy of 230 MeV. Patients are treated in one room equipped with a 360° rotating gantry. Besides patient treatment a strong focus is on research. A dedicated experimental room is part of the facility. In the current state of expansion this room is equipped with a fixed beam line. Beam energies between 70 and 230 MeV and currents up to about 120 nA at 230 MeV can be provided.
Materials and Methods: An in house developed control system (figure 1) allows for a parallel operation of the treatment and the experimental beamline. Absolute priority for the treatment room is ensured by the control software.
The beam current is controlled by a dedicated hardware directly. Continuous wave beams as well as pulsed beams with repetition rates up to 333 Hz with variable duty cycles are available. The beam is monitored by means of a segmented ionization chamber. The beam can be activated manually, for a defined time or until a certain charge has been reached at the beam exit. A direct continuance after a beam switch to the treatment room is possible.
Results: The proton therapy system itself is operated by an IBA team, that ensures excellent beam stability and availability. Since only one treatment room is present, experiments can be performed conveniently during the day shifts. Requests from the treatment room cause interruptions of 1-2 min duration in intervals of about 20 min.
Conclusions: In summary, the OncoRay center is equipped with an experimental beamline that combines the reliability and beam quality of a commercial clinical proton therapy system with the flexibility of an in house developed control system whose design parameters are governed by the needs of physical and translational research.
  • Poster
    ICTR-PHE 2016 - International Conference on Translational Research in Radio-Oncology - Physics for Health in Europe, 15.05.2016, Genf, Schweiz
  • Radiotherapy and Oncology 118(2016), 60-61
    DOI-Link: http://dx.doi.org/10.1016/S0167-8140(16)30124-4
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Registration No. 23433 - Permalink

Development of antioxidant COX-2 inhibitors as radioprotective agents for radiation therapy – a hypothesis-driven review
Laube, M.; Kniess, T.; Pietzsch, J.
Corresponding author: Laube, M.
Corresponding author: Pietzsch, J.
Abstract: Radiation therapy (RT) evolved to be a primary treatment modality for cancer patients. Unfortunately, the cure or relief of symptoms is still accompanied by radiation-induced side effects with severe acute and late pathophysiological consequences. Inhibitors of cyclooxygenase-2 (COX-2) are potentially useful in this regard because radioprotection of normal tissue and/or radiosensitizing effects on tumor tissue have been described for several compounds of this structurally diverse class. This review aims to substantiate the hypothesis that antioxidant COX-2 inhibitors are promising radioprotectants because of intercepting radiation-induced oxidative stress and inflammation in normal tissue, especially the vascular system. For this, literature reporting on COX inhibitors exerting radioprotective and/or radiosensitizing action as well as on antioxidant COX inhibitors will be reviewed comprehensively with the aim to find cross-points of both and, by that, stimulate further research in the field of radioprotective agents.
Keywords: Coxibs, Cyclooxygenases, Normal tissue, NSAIDS, Oxidative stress, Radiation-induced vascular dysfunction, Radioprotection, Radiosensitization, Reactive oxygen/nitrogen species, Tumor models Registration No. 23428 - Permalink

Modellierung von Tayler-Instabilität und Elektrowirbelströmungen in Flüssigmetallbatterien
Weber, N.
Abstract: Diese Arbeit behandelt numerisch die Fluiddynamik in Flüssigmetallbatterien. Insbesonders die Tayler-Instabilität und Elektrowirbelströmungen werden ausführlich betrachtet. Die Motivation der Untersuchungen besteht zum einen in einer Steigerung von Leistung und Sicherheit und zum anderen in der Senkung von Produktions- und Betriebskosten von Flüssigmetallbatterien.
Es wird ein Lösungsverfahren für zeitabhängige magnetohydrodynamische Strömungen entwickelt und in OpenFOAM implementiert. Die Basisversion des Lösers erlaubt die Analyse einer flüssige Elektrode. Eine Erweiterung dient der Untersuchung des Einflusses von Stromsammler und Zuleitung der Batterie. Simulationen werden vorwiegend für zylindrische, aber auch für quaderförmige Elektrodengeometrien durchgeführt.
Der Hauptteil der Arbeit widmet sich der stromgetriebenen Tayler-Instabilität, die in großen Batterien bei Strömen von einigen Kiloampere auftritt und dort zu einer Strömung in Form von Konvektionszellen führt. Das Auftreten, Wachstum und die Geschwindigkeiten dieser Instabilität werden analysiert und deren Bedeutung für die Batterie diskutiert. Zur Dämpfung bzw. Unterdrückung der Strömung werden eine Reihe von Gegenmaßnahmen vorgestellt und deren praktischer Nutzen bewertet. Der zweite, kürzere Teil der Arbeit befasst sich mit Elektrowirbelströmungen, deren Charakterisierung und ihren Wechselwirkungen mit der Tayler-Instabilität. Die besondere Bedeutung von Elektrowirbelströmungen für die Integrität der Elektrolytschicht sowie ihre Anwendbarkeit für die Verbesserung des Stofftransports in Flüssigmetallbatterien werden hervorgehoben.

Keywords: Tayler Instabilität, Elektrowirbelströmung; Flüssigmetallbatterie
  • Doctoral thesis
    TU Dresden, 2016
Registration No. 23425 - Permalink

Vibrational spectroscopy of Ga+ ion implanted ta-C films
Berova, M.; Sandulov, M.; Tsvetkova, T.; Bischoff, L.; Boettger, R.; Abrashev, M.
Abstract: In the present work, low energy Ga+ ion beam implantation was used for the structural and optical properties modification of tetrahedral amorphous carbon (ta-C) thin films, using gallium (Ga+) as the ion species. Thin film samples (d~40nm) of ta-C, deposited by filtered cathodic vacuum arc (FCVA), have been implanted with Ga+ at ion energy E = 20 keV and ion doses D=3.1014÷3.1015 cm-2. The Ga+ ion beam induced structural modification of the implanted material results in a considerable change of its optical properties, displayed in a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitisation, as well as to accompanying formation of bonds between the implanted ions and the host atoms of the target, as confirmed by infra-red (IR) and Raman measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of for information archiving, in the area of high-density optical data storage, while using focused Ga+ ion beams.
Keywords: ta-C, ion implantation, Raman, FTIR, spectroscopy Registration No. 23423 - Permalink
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