Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34133 Publications

Euler-Euler Modeling of Mass-Transfer in Bubbly Flows

Rzehak, R.; Krepper, E.

CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. Concerning the fluid dynamics of bubbly flows a certain degree of predictive capability has been reached recently. However, concerning mass transfer only few studies have been performed to date.
The present contribution gives an overview over the available results on closure relations for physical absorption/desorption, i.e. mass transfer without chemical reactions. Unsolved issues are highlighted, in particular on which parameters a suitable correlation for the mass transfer coefficient should be based.
In addition, a preliminary study on model validation is presented which makes use of experimentally determined mass transfer coefficients. The need for and requirements on suitable data for this purpose are emphasized.

Keywords: mass-transfer; dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; CFD simulation; model validation

  • Lecture (Conference)
    14th Workshop on Two-Phase Flow Predictions, 07.-10.09.2015, Halle, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22637
Publ.-Id: 22637


Charge-state-dependent energy loss of slow ions. II. Statistical atom model

Wilhelm, R.; Möller, W.

A model for charge-dependent energy loss of slow ions is developed based on the Thomas-Fermi statistical model of atoms. Using a modified electrostatic potential which takes the ionic charge into account, nuclear and electronic energy transfers are calculated, the latter by an extension of the Firsov model. To evaluate the importance of multiple collisions even in nanometer-thick target materials we use the charge-state-dependent potentials in a Monte Carlo simulation in the binary collision approximation and compare the results to experiment. The Monte Carlo results reproduce the incident charge-state dependence of measured data well [see R. A. Wilhelm et al., Phys. Rev. A 93, 052708 (2016)], even though the experimentally observed charge exchange dependence is not included in the model.

Keywords: low energy ions; ion charge state; stopping power; energy loss; highly charged ion; charge exchange

Permalink: https://www.hzdr.de/publications/Publ-22636
Publ.-Id: 22636


Charge-state-dependent energy loss of slow ions. I. Experimental results on the transmission of highly charged ions

Wilhelm, R.; Gruber, E.; Smejkal, V.; Facsko, S.; Aumayr, F.

We report on energy loss measurements of slow (v≪v0), highly charged (Q>10) ions upon transmission through a 1-nm-thick carbon nanomembrane. We emphasize here the scaling of the energy loss with the velocity and charge exchange or loss. We show that a weak linear velocity dependence exists, whereas charge exchange dominates the kinetic energy loss, especially in the case of a large charge capture. A universal scaling of the energy loss with the charge exchange and velocity is found and discussed in this paper. A model for charge-state-dependent energy loss for slow ions is presented in paper II in this series [R. A. Wilhelm and W. Möller, Phys. Rev. A 93, 052709 (2016)].

Keywords: low energy ions; ion charge state; stopping power; energy loss; highly charged ion; charge exchange

Permalink: https://www.hzdr.de/publications/Publ-22635
Publ.-Id: 22635


Unified modeling of bubbly flows in pipes, bubble columns, and airlift columns

Rzehak, R.; Ziegenhein, T.; Kriebitzsch, S.; Krepper, E.; Lucas, D.

The purpose of computer-aided process engineering (CAPE) is to assist the development and operation of complex processes involving chemical or physical change. Computational fluid dynamics (CFD) simulations are a means to study in detail unit operations, such as mixing, reaction, separation or combinations thereof, performed in a specific type of equipment. In particular scale-up studies and the evaluation of concepts for process intensification in an early design phase promise high benefits in terms of identifying energy- and resource-efficient solutions that are expensive to assess by conventional semi-empirical methods.
CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models describing the physics on the scale of individual bubbles or groups thereof. A large number of works exists, in each of which largely a different set of closure relations is compared to a different set of experimental data. For the limited range of conditions to which each model variant is applied, reasonable agreement with the data is mostly obtained, but due to a lack of comparability between the individual works no complete, reliable, and robust formulation has emerged so far. Moreover, the models usually contain a number of empirical parameters that have been adjusted to match the particular data that were used in the comparison. Predictive simulation, however, requires a model that works without any adjustments within the targeted domain of applicability.
As a step towards this goal, an attempt has been made to collect the best available description for all aspects known to be relevant for adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases. Apart from interest in its own right, results obtained for this restricted problem also provide a good starting point for the investigation of more complex situations including heat and mass transport and possibly phase change or chemical reactions.
Aspects requiring closure for the case under consideration are: (i) the exchange of momentum between liquid and gas phases, (ii) the effects of the dispersed bubbles on the turbulence of the liquid carrier phase, and (iii) processes of bubble coalescence and breakup that determine the distribution of bubble sizes. All of these aspects are coupled and therefore in principle have to be considered as a whole.
At the same time it is highly desirable to separately validate the individual sub-models of this complex coupled problem. To this end we use a step-by-step procedure where we first consider situations where a fixed distribution of bubble sizes may be imposed. In this way the sub-models for bubble forces (i) and bubble-induced turbulence (ii) can be validated independently of bubble coalescence and breakup processes (iii). The latter will be added later on in a second step building on the already established sub-models for the former.
In the present contribution the baseline model referred to above is applied to several different configurations commonly encountered in chemical engineering applications, namely bubbly flows in pipes, bubble columns, and airlift columns. Since in all of these systems the small scales are governed by the same physics it is expected that they can be treated in a unified manner using the same set of closure relations. By comparison of simulation results to experimental data taken from the literature this is shown to be the case within a certain accuracy and the model is validated for all of these configurations.
In this way a starting point for the prediction of flow phenomena is obtained. Expanding the range of applicability as well as the achieved accuracy is a continuously ongoing development effort. From the observed level of agreement between simulation and experiment issues requiring further investigation can be identified. This includes both the need for further model development and the need for CFD-grade experimental investigations.

Keywords: Dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; closure relations; CFD simulation; model validation; pipe flow; bubble column; airlift column

  • Lecture (Conference)
    12th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering, 28.06.-01.07.2015, New York, USA
  • Open Access Logo Chemical Engineering Science 157(2017), 147-158
    DOI: 10.1016/j.ces.2016.04.056

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-22634
Publ.-Id: 22634


Baseline Model for Simulation of Bubbly Flows

Rzehak, R.; Ziegenhein, T.; Krepper, E.; Lucas, D.

CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. A large body of work using different closure relations of varying degree of sophistication exists, but no complete, reliable, and robust formulation has been achieved so far.
The closure relations describe phenomena on the small spatial scale of individual bubbles. Hence, for all systems where this small scale behavior is governed by the same physics, the same set of closure relations should be applicable. Therefore it is expected that many systems differing on larger scales can be treated in a unified manner. To show this feasibility we presently consider adiabatic bubbly flows where only momentum is exchanged between liquid and gas phases.
The best available descriptions for the forces acting on the bubbles and the bubble-induced turbulence, which are the relevant aspects requiring closure under these circumstances, have been collected into a baseline model. By keeping all correlations and all parameter values fixed, the applicability of this model to a variety of situations is demonstrated. Future improvements of the model should work for the entire domain of applications.
The model has previously been validated against data for steady flows in pipes and bubble columns. Here, further comparison is made for an airlift column and plume oscillations in bubble columns. A crucial parameter in the model is the bubble size for which reliable measurements are often not available. In this case parametric variations are investigated. From the observed level of agreement between simulation and experiment, issues requiring further investigation will be identified.

  • Lecture (Conference)
    ProcessNet Fachgruppertreffen CFD, 19.-20.03.2015, Lüneburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22633
Publ.-Id: 22633


Simple scaling equations for electron spectra, currents and bulk heating in ultra-intense short-pulse laser-solid interaction

Kluge, T.; Bussmann, M.; Cowan, T. E.; Schramm, U.

Intense and energetic electron currents can be generated by ultra-intense lasers interacting with solid density targets.
Especially for ultra-short laser pulses their temporal evolution needs to be taken into account for many non-linear processes as instantaneous currents may differ significantly from the average.
Hence, a dynamic model including the temporal variation of the electron currents which goes beyond a simple bunching with twice the laser frequency but otherwise constant current is needed.
Here we present a new time-dependent model to describe the laser generated currents and obtain simple expressions for the temporal evolution and resulting corrections of averages.
To exemplify the model and its predictive capabilities we show the impact of temporal evolution, spectral distribution and spatial modulations on Ohmic heating of the bulk target material.

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Permalink: https://www.hzdr.de/publications/Publ-22632
Publ.-Id: 22632


Characterisation of irradiation-induced defects in ZnO single crystals

Prochazka, I.; Cizek, J.; Lukac, F.; Melikhova, O.; Valenta, J.; Havranek, V.; Anwand, W.; Skuratov, V. A.; Strukova, T. S.

Positron annihilation spectroscopy (PAS) combined with optical methods was employed for characterisation of defects in the hydrothermally grown ZnO single crystals irradiated by 167 MeV Xe26+ ions to fluences ranged from 3×10^12 to 1×10^14 cm−2. The positron lifetime (LT), Doppler broadening as well as slow-positron implantation spectroscopy (SPIS) techniques were involved. The ab-initio theoretical calculations were utilised for interpretation of LT results. The optical transmission and photoluminescence measurements were conducted, too. The virgin ZnO crystal exhibited a single component LT spectrum with a lifetime of 182 ps which is attributed to saturated positron trapping in Zn vacancies associated with hydrogen atoms unintentionally introduced into the crystal during the crystal growth. The Xe ion irradiated ZnO crystals have shown an additional component with a longer lifetime of ≈ 360 ps which comes from irradiation-induced larger defects equivalent in size to clusters of ≈ 10 to 12 vacancies. The concentrations of these clusters were estimated on the basis of combined LT and SPIS data. The PAS data were correlated with irradiation induced changes seen in the optical spectroscopy experiments.

Keywords: ZnO; Xe irradiation; defects; positron annihilation

Permalink: https://www.hzdr.de/publications/Publ-22631
Publ.-Id: 22631


Electron beam final focus system for Thomson scattering at ELBE

Krämer, J. M.; Budde, M.; Bødker, F.; Irman, A.; Jochmann, A.; Kristensen, J. P.; Lehnert, U.; Michel, P.; Schramm, U.

The design of an electron beam final focus system (FFS) aiming for high-flux laser-Thomson backscattering X-ray sources at ELBE is presented. A telescope system consisting of four permanent magnet based quadrupoles was found to have significantly less chromatic aberrations than a quadrupole doublet or triplet as commonly used. Focusing properties like the position of the focal plane and the spot size are retained for electron beam energies between 20 and 30 MeV by adjusting the position of the quadrupoles individually on a motorized stage. The desired ultra-short electron bunches require an increased relative energy spread up to a few percent and, thus, second order chromatic effects must be taken into account. We also present the design and test results of the permanent magnet quadrupoles. Adjustable shunts allow for correction of the field strength and compensation of deviations in the permanent magnet material.
For a beam emittance of 13 mm mrad, we predict focal spot sizes of about 40 μm (rms) and divergences of about 10 mrad using the FFS.

Keywords: PMQ; Final focus system; Chromatic aberration; Thomson scattering; ICS

Permalink: https://www.hzdr.de/publications/Publ-22630
Publ.-Id: 22630


Investigation of nanocrystalline Gd films loaded with hydrogen

Hruska, P.; Cizek, J.; Dobron, P.; Anwand, W.; Mücklich, A.; Gemma, R.; Wagner, S.; Uchida, H.; Pundt, A.

The present work reports on microstructure studies of hydrogen-loaded nanocrystalline Gd films prepared by cold cathode beam sputtering on sapphire (1 1 -2 0) substrates. The Gd films were electrochemically step-by-step charged with hydrogen and the structural development with increasing concentration of absorbed hydrogen was studied by transmission electron microscopy and in-situ X-ray diffraction using synchrotron radiation. The relaxation of hydrogen-induced stresses was examined by acoustic emission measurements. In the low concentration range absorbed hydrogen occupies preferentially vacancy-like defects at GBs typical for nanocrystalline films. With increasing hydrogen concentration hydrogen starts to occupy interstitial sites. At the solid solution limit the grains gradually transform into the beta-phase (GdH2). Finally at high hydrogen concentrations xH > 2:0 H/Gd, the film structure becomes almost completely amorphous. Contrary to bulk Gd specimens, the formation of the gamma-phase (GdH3) was not observed in this work.

Keywords: Gadolinium; hydrogen; defects; thin films

Permalink: https://www.hzdr.de/publications/Publ-22629
Publ.-Id: 22629


Defect studies of H+ implanted niobium

Prochazka, I.; Cizek, J.; Havranek, V.; Anwand, W.

Defects in Nb specimens implanted with H+ ions were investigated using three complementary techniques of positron annihilation spectroscopy: (i) the positron lifetime (LT) measurements employed for identification of defects in implanted specimens, (ii) the coincidence Doppler broadening (CDB) technique used for investigation of chemical surroundings of defects, and (iii) the variable energy positron annihilation spectroscopy (VEPAS) served for defects depth profiling studies. The virgin Nb sample exhibits a single component spectrum with lifetime of 128 ps which testifies that the sample can be considered as a defect-free material. The sample implanted with H+ ions exhibits two additional positron components with lifetimes of 182 and 204 ps. These components were attributed to the implantation-induced vacancies surrounded by two and one hydrogen atom, respectively. The presence of hydrogen attached to vacancies was confirmed also by CDB investigations.

Keywords: niobium; hydrogen; defects; positron annihilation

Permalink: https://www.hzdr.de/publications/Publ-22628
Publ.-Id: 22628


Tomographic characterisation of gas-jet targets for laser wakefield acceleration

Couperus, J. P.; Köhler, A.; Wolterink, T. A. W.; Jochmann, A.; Zarini, O.; Bastiaens, H. M. J.; Boller, K. J.; Irman, A.; Schramm, U.

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. The acceleration medium is provided by a target that creates a local well-defined gas-density profile inside a vacuum vessel. Target development and analysis of the resulting gas-density profiles is an important aspect in the further development of LWFA.
Gas-jet targets are widely used in regimes where relatively high electron densities over short interaction lengths are required (up to several millimetres interaction length, plasma densities down to ~1018 cm-3).
In this paper we report a precise characterisation of such gas-jet targets by a laser interferometry technique. We show that phase shifts down to 4 mrad can be resolved. Tomographic phase reconstruction enables detection of non-axisymmetrical gas-density profiles which indicates defects in cylindrical nozzles, analysis of slit-nozzles and nozzles with an induced shock-wave density step. In a direct comparison between argon and helium jets we show that it cannot automatically be assumed, as is often done, that a nozzle measured with argon will provide the same gas density with helium.

Keywords: Laser wakefield acceleration; LWFA; gas-jet analysis; interferometry; tomography

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Permalink: https://www.hzdr.de/publications/Publ-22627
Publ.-Id: 22627


P1304 - Komplementärer Widerstandsschalter, dessen Herstellung und Verwendung

Schmidt, H.; You, T.; Du, N.; Bürger, D.; Skorupa, I.

Die Erfindung beschreibt die Herstellung eines komplementären Widerstandsschalters mit zwei Terminals T1 und T2, in welchen jede Boolesche Grundfunktion nichtflüchtig durch Anlegen einer Schreibspannung im Zweischritt-Verfahren geschrieben werden kann. Der Zustand des komplementären Widerstandsschalters kann durch Anlegen einer konstanten, von den Eingangsparametern der Booleschen Funktion abhängigen, niedrigen positiven oder negativen Lesespannung ("Level Read") ausgelesen werden. Weiterhin wird die Integration des komplementären Widerstandsschalters an den Kreuzungspunkten einer Gitterstruktur (Array) als Logiktor in einem Logikschaltkreis zur Realisierung nichtflüchtiger Boolescher Funktionen oder als analoger Block mit Logiktor zur Realisierung von Filtern und Verstärkern beschrieben.

  • Patent
    DE102013200615 - Offenlegung 17.04.2014, Nachanmeldungen: WO als P1401

Permalink: https://www.hzdr.de/publications/Publ-22626
Publ.-Id: 22626


P1401 - Komplementärer Widerstandsschalter, kontaktierte polykristalline piezo- oder ferroelektrische Dünnschicht, Verfahren zum Verschlüsseln einer Bitfolge

Bürger, D.; Du, N.; Kolitsch, A.; Manjunath, N.; Ou, X.; Schmidt, H.; Shuai, Y.; Skorupa, I.; You, T.

Gemäß verschiedenen Ausführungsformen kann ein komplementärer Widerstandsschalter aufweisen: zwei äußere Kontakte (T1, T2 ), zwischen denen zwei piezo- oder ferroelektrische Schichten (11a und 11b) liegen, die durch einen inneren gemeinsamen Kontakt voneinander getrennt sind, dadurch gekennzeichnet, dass mindestens ein Bereich der piezo- oder ferroelektrischen Schicht (11a und 11b) mindestens einmal derart modifiziert ist, dass in der piezo- oder ferroelektrischen Schicht (11a und 11b) jeweils zwischen dem inneren Kontakt und dem zugehörigen äußeren Kontakt ein Bereich (11') der Dicke (d ') entsteht, weicher mindestens zusätzlich in einem Bereich (11") der Dicke (d") modifiziert sein kann, wobei a) die äußeren Kontakte Oberflächenkontakte (Sa) und (Sb) und der innere Kontakt ein gemeinsamer zugehöriger Gegenkontakt (O) oder die äußeren Kontakte Gegenkontakte (Oa) und (Ob) und der innere Kontakt ein gemeinsamer zugehöriger Oberflächenkontakt (S) sind, b) die Oberflächenkontakte (S), (Sa) und (Sb) gleichrichtend und die Gegenkontakte (O) bzw. (Oa) und (Ob) nicht-gleichrichtend sind, c) sich die modifizierten Bereiche in der piezo- oder ferroelektrischen Schicht (11a und 11b) an den Oberflächenkontakten (S) bzw. (Sa) und (Sb) ausbilden, d) die piezo- oder ferroelektrische Schichten (11, 11', 11") verschiedene verspannungsabhängige strukturelle Phasen mit unterschiedlicher Bandlücke und/oder unterschiedlicher Polarisationsladung aufweisen, und e) die elektrische Leitfähigkeit der piezo- oder ferroelektrischen Schichten (11, 11', 11") unterschiedlich ist.

  • Patent
    WO2014111481 - Offenlegung 24.07.2014, Nachanmeldungen: EP, US

Permalink: https://www.hzdr.de/publications/Publ-22624
Publ.-Id: 22624


Targetry for Laser Wakefield Acceleration

Couperus, J. P.; Irman, A.; Jochmann, A.; Köhler, A.; Messmer, M.; Zarini, O.; Schramm, U.

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. Target development and analysis is an important aspect in the further development of LWFA.
For short interaction length, high density LWFA schemes (up to several millimetres interaction length, plasma densities down to ~1018 cm3) gas-jet targets are used. These targets are analysed by a laser interferometry setup which can resolve phase shifts down to 4 mrad. Tomographic reconstruction enables detection of non-axisymmetrical defects in cylindrical nozzles and analysis of slit-nozzles and nozzles with an induced shock-wave density step.
For lower density and longer interaction length LWFA schemes, high laser intensity must be maintained over distances much longer than the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterised using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulsed Ti:Sa laser are shown. The results show a broad, easy to realise parameter window for pressure and time in which a laser intensity transmission of above 75% is achieved.

Keywords: Laser wakefield acceleration; LWFA; gas-jet analysis; interferometry; tomography

  • Lecture (Conference)
    Laser Applications at Accelerators, 26.03.2015, Palmanova, Spain

Permalink: https://www.hzdr.de/publications/Publ-22623
Publ.-Id: 22623


Development and characterisation of gas-jet and discharge capillary targets for LWFA

Couperus, J. P.; Irman, A.; Jochmann, A.; Köhler, A.; Messmer, M.; Zarini, O.; Schramm, U.

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. Target development and analysis is an important aspect in the further development of LWFA.
For short interaction length, high density LWFA schemes (up to several millimetres interaction length, plasma densities down to ~1018 cm3) gas-jet targets are used. These targets are analysed by a laser interferometry setup which can resolve phase shifts down to 4 mrad. Tomographic reconstruction enables detection of non-axisymmetrical defects in cylindrical nozzles and analysis of slit-nozzles and nozzles with an induced shock-wave density step.
For lower density and longer interaction length LWFA schemes, high laser intensity must be maintained over distances much longer than the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterised using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulsed Ti:Sa laser are shown. The results show a broad, easy to realise parameter window for pressure and time in which a laser intensity transmission of above 75% is achieved.

Keywords: Laser wakefield acceleration; LWFA; gas-jet analysis; interferometry; tomography

  • Poster
    Laser Plasma Acceleration Workshop 2015, 10.-15.05.2015, Guadeloupe, France

Permalink: https://www.hzdr.de/publications/Publ-22622
Publ.-Id: 22622


European Ion Beam Infrastructures for Materials and Transdisciplinary Research

Fassbender, J.

Ion beam techniques have emerged as key enabling technologies across the international research landscape, vital to innovation in functional materials for special applications, and fields as diverse as cancer treatment, nanomaterials, renewable energy, advanced electronics, and the preservation of cultural heritage. Europe maintains one of the largest groupings of ion beam facilities in the world, and through strategic EU and national support, is poised to become a global leader in ion beam innovation.
Within the HZDR-coordinated EU-FP7 program SPIRIT the leading European ion beam centers have established common standards, best practices and a single point of access for European users to these facilities in the area of materials research which led to an increasing user interest. Now these best practices have to be transferred.
On the one hand to ion beam centers, which could not participate in the previous project, in order to broaden the accessibility of ion beam technology. One current example is the technology transfer of HZDR to the newly established ion beam center SLOVAKION in Trnava in Slovakia in the framework of an EU teaming activity. On the other hand ultra-sensitive technologies like accelerator mass spectrometry, which have not been in the focus of the past integrating activities mainly devoted to materials research, have to be structured at the European level in a similar way in order to significantly widen the potential user community to transdisciplinary research, i.e. in the areas of climate change, efficient and safe use of energy and resources, and healthcare. Last but not least, the industrial use of ion beam technology has to be further promoted. In contrast to rather small industrial use of synchrotron and neutron facilities, the leading ion beam centers in Europe deliver typically around 20% of their beam time to industrial users. However, past experience has shown that industrial use of ion beam technology is predominantly on a national scale basis. Hence, it becomes even more important to foster ion beam technology in European countries that have not yet developed their capabilities to full extent.

Keywords: IBC; SPIRIT; EU

  • Invited lecture (Conferences)
    INARIE - Integrating Access to Pan-European Research Infrastructures in Central and Eastern Europe, 30.11.-02.12.2015, Debrecen, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-22621
Publ.-Id: 22621


Laser Microstructured Metal Thin Films as Promising Alternative for Indium Based Transparent Electrodes

Eckhardt, S.; Siebold, M.; Lasagni, A. F.

In the search of alternative materials for substituting indium tin-oxide, thin films of copper and aluminum (5 to 40 nm) were structured using direct laser interference patterning with nanosecond and picosecond pulse lasers to improve their optical properties. Using this method, periodic patterns consisting on micro-scaled holes were produced. It was found that the optical transmittance of the structured layers could be increased between 25 to 125% while the electrical resistance was marginally influenced. In addition, improvements in the diffuse transmittance are demonstrated for the processed materials. The laser treatment could enhance the diffuse to total transmission ratio (HAZE) by values ranging from 30 to 82%. The results also show that both of the studied metals succeed to match the frame of properties that is set by typical applications requiring indium thin oxide (ITO) films. For both ns- and ps-based structuring processes, numerical simulations are performed to investigate the ablation mechanisms of the thin films.

Keywords: Laser materials processing; Photovoltaic; Thin films

Permalink: https://www.hzdr.de/publications/Publ-22620
Publ.-Id: 22620


Application of a Yield Approach for the Prediction of Positron Emitter Distributions Produced During Therapeutic Carbon-Ion Beam Irradiation

Helmbrecht, S.; Priegnitz, M.; Enghardt, W.; Rohling, H.; Fiedler, F.

Positron-Emission-Tomography is a clinically implemented method for in vivo verification of treatment delivery in ion beam therapy. The dose distribution is the relevant measure but PET captures a β+-activity distribution, that is created as a side product during the irradiation.
Therefore, a prediction of the activity distribution is required. We present a simulation code that makes use of measured yields of β+ emitters to perform this task. The yields are available in three reference materials. A conversion from X-ray grey values to a combination of these materials has been set up. The lateral properties of the ion beam are described by means of a formulation of Moliere's scattering theory in thick targets.
A model of the annihilation point density around an emitting nuclide has been implemented in the software to describe the movement of the positrons.
Simulations of phantom experiments as well as of a real patient case were performed. The results are comparable or superior to the results obtained from an established condensed history Monte Carlo code.
We conclude that measured yields can be used as raw data for the calculation of ion beam induced β+-activity distribution instead of nuclear cross sections.

Keywords: PET; simulation; in-beam positron emission tomography; ion beam tumor therapy; hadron therapy; positron emitter distribution; prediction method

Permalink: https://www.hzdr.de/publications/Publ-22619
Publ.-Id: 22619


Complex formation of tetravalent actindies with small carboxylate ligands

Hennig, C.; Ikeda-Ohno, A.; Takao, S.; Takao, K.; Kraus, W.; Scheinost, A. C.

Tetravalent actinides form strong complexes with the carboxylic acids. Although there is a number of thermodynamic data reported [1-2] there is no information available on the complex structure in aqueous solution.
We used EXAFS spectroscopy to estimate the complex structure of Th4+, U4+, Np4+ and Ce4+ with different carboxylates (RCOO–; R = H, CH3, C2H2NH2) in aqueous solution [3-6]. The structural information from EXAFS data is limited to radial pair distribution functions. To overcome this limitation we forced single crystals to precipitate in different stability ranges of the solution species. Whether or not a species is preserved in a crystal structure was subsequently investigated by EXAFS spectroscopy. The crystal structure, revealed
by single-crystal diffraction, and combined with EXAFS spectroscopy on liquid and solid samples, provides precise information of coordination and structure of the related solution species. These studies show that in all of the investigated aqueous systems hexanuclear complexes [M6O4(OH)4(RCOO)12] appear, which become predominant with increasing ligand concentration as well as increasing pH, and dominate finally the species distribution.
An example is shown in Figure 1. EXAFS spectra were recorded on samples in aqueous solution with 0.05 M Th(IV), 1 M glycine and pH values ranging from 0.5 to 3.2. The spectrum at pH 0.5 shows a single peak representing mononuclear complexes of Th(OH)n (4n)+ with n  2. With increasing pH, the first peak in the Fourier transform becomes more asymmetric and finally splits. A second peak appears at R+ = 3.75 Å, and its intensity rises with increasing pH. This latter feature represents a Th-Th scattering interaction. The data fit indicate the appearance of a hexanuclear complex. This complex is stable until pH 3.2. At higher pH values precipitates a crystalline material. The EXAFS spectrum of this precipitate is identical with that of the solution at pH 3.2, indicating that the structure of the solution species remains preserved in the crystal structure.
Crystals from the precipitate were used for structure analysis by X-ray diffraction. A drawing of the crystal structure is shown in Figure 2, which is in turn representative for the coordination of the predominating solution species at pH 3.2.
The appearance of hexanuclear complexes in aqueous solution corresponds with both, the onset of the metal hydrolysis at the one hand, and the deprotonation of the carboxylic function at the other hand. This results in a competing reaction between hydrolysis and ligation. The hydrolysis results in a polymerization via oxo and hydroxo bonds, whereas the carboxylic function of the ligand results in the formation of 12 terminating chelate rings providing charge neutrality of the hexanuclear core and preventing further polymerization. Most of the thermodynamic data of actinide(IV) carboxylates are estimated assuming mononuclear solution species.
Our studies indicate that future work on tetravalent actinide carboxylates in aqueous solution need consideration of hexanuclear species.
[1] G.M. Sergeev, Radiokhimija 22, 536 (1980).
[2] A. Bismondo, L. Rizzo, G. Tomat, Inorg. Chim. Acta 74, 21 (1983).
[3] S. Takao, K. Takao, W. Kraus, F. Emmerling, A.C. Scheinost, G. Bernhard, C. Hennig, Eur. J. Inorg. Chem. 4771 (2009).
[4] K. Takao, S. Takao, A.C. Scheinost, G. Bernhard, C. Hennig, Inorg. Chem. 51, 1336 (2012).
[5] C. Hennig, S. Takao, K. Takao, S. Weiss, W. Kraus, F. Emmerling, A.C. Scheinost, Dalton Trans. 41, 12818 (2012).
[6] C. Hennig, A. Ikeda-Ohno, W. Kraus, S. Weiss, P. Pattison, H. Emerich, P.M. Abdala, A.C. Scheinost, Inorg. Chem. 52, 11734 (2013).

Keywords: actinides; xafs; thorium; uranium; neptunium; cerium

  • Lecture (Conference)
    Migration 2015: 15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-22618
Publ.-Id: 22618


Artifical neural networks - another view on actinide chemistry

Rossberg, A.; Scheinost, A. C.

Driven by the enormous increase of computing power in the last few years, several theoretical models for biological neural networks have been developed and new modelling concepts are coming up. Close to their biological counterpart, artificial neural networks (ANNs) have been developed, which can be trained by presenting input data along with the desired output [1]. ANNs are used for example to recognize hand-written text, human faces, natural speech or personal interests, all features now commonly used by web-based social networks like Facebook or by search engines like Google. Another step forward was the development of spiking neural networks, a third generation ANN, which counts at the moment as the closest approximation of biological neural networks [2] and is strongly discussed in the community [3]. In general, ANNs can be considered as a method to infer functional relationships between a cause and the resulting effect. Note that these functional relationships are not inferred from mathematical models; first, the mathematical treatment would be too complex, and second, the required mathematical simplifications by using justified assumptions and constraints would most probably lead to a poor description of the problem. Therefore ANNs are seen as a more efficient and more accurate method to describe complex functional relationships. Here we demonstrate using two examples, that selforganizing maps (SOM) [4,5], a special kind of ANN, are well suited for analysing the complex chemistry of actinides.
The first example shows the relationships between the structure of aliphatic ((di-)hydroxy-)carboxylic acids and their complexation mode towards uranyl (UVI). For this, U LIII-edge EXAFS spectra from 13 aliphatic carboxylic acids (acetic, succinic, tartaric, lactic, 3-hydroxybutyric, citric, formic, malic, maleic, malonic, oxalic, propionic, and tricarballylic acid) at a range of pH, uranium and ligand concentrations were measured, resulting in 60 EXAFS spectra [6]. Based on the known structures of the ligands, SOM was used to determine the dependencies between the structure of the UVI carboxylate complexes and the structure of the interacting ligands, and to derive a predictive classification of the former. SOM revealed, for instance, that acids with an OH-group in α-position cause the formation of monomeric chelates and dimeric and trimeric UVI complexes, while an OH-group in β-position leads only to monomers, where uranyl is bidentately coordinated to the carboxylic group. In the second example, we apply SOM to the U LIII-edge EXAFS spectra of UVI sorption complexes with Al(hydr)oxides in order to determine the dependency of the structure of the formed sorption complexes on relevant physicochemical parameters like pH, pCO2, surface area, and surface loading. SOM here clearly reveals, for example, that polynuclear sorption complexes become predominant the higher the pH and the surface loading, while at low pH mononuclear complexes are present either as binary complexes or – in the presence of carbonate - as ternary complexes.
A properly trained SOM can also be used for the prediction of the spectra and the fractions of the complexes for a given ligand and a set of physicochemical parameters, hence SOM can replace thermodynamic speciation calculations, in case complex formation constants are not available. In turn, for a given spectrum, the corresponding physicochemical parameter can be predicted. SOM is not only restricted to EXAFS, but can use input from any other spectroscopy like NMR, UV-vis, infrared and Raman, or from diffraction/scattering patterns -together with chemical information- in order to derive a reliable multiscale speciation of actinides.

Keywords: Neuronal networks; artifical intelligence

  • Poster
    Migration 2015: 15th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 13.-18.09.2015, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-22617
Publ.-Id: 22617


Nuclear methods for real-time range verification in proton therapy based on prompt gamma-ray imaging

Hueso-González, F.

Accelerated protons are excellent candidates for treating several types of tumours. Such charged particles stop at a defined depth, where their ionisation density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimises the damage to normal tissue compared to photon therapy. Nonetheless, inherent range uncertainties cast doubts on the irradiation of tumours close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of proton over photon therapy and limits its ultimate aspirations. Prompt gamma rays, a by-product of the irradiation that is correlated to the dose deposition, are reliable signatures for the detection of range deviations and even for three-dimensional in vivo dosimetry. In this work, two methods for Prompt Gamma-ray Imaging (PGI) are investigated: the Compton camera (Cc) and the Prompt Gamma-ray Timing (PGT). Their applicability in a clinical scenario is discussed and compared. The first method aspires to reconstruct the prompt gamma ray emission density map based on an iterative imaging algorithm and multiple position sensitive gamma ray detectors. These are arranged in scatterer and absorber plane. The second method has been recently proposed as an alternative to collimated PGI systems and relies on timing spectroscopy with a single monolithic detector. The detection times of prompt gamma rays encode essential information about the depth-dose profile as a consequence of the measurable transit time of ions through matter. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and OncoRay, detector components are characterised in realistic radiation environments as a step towards a clinical Cc. Conventional block detectors deployed in commercial Positron Emission Tomography (PET) scanners, made of Cerium-doped lutetium oxyorthosilicate - Lu2SiO5:Ce (LSO) or Bismuth Germanium Oxide - Bi4Ge3O12 (BGO) scintillators, are suitable candidates for the absorber of a Cc due to their high density and absorption efficiency with respect to the prompt gamma ray energy range (several MeV). LSO and BGO block detectors are compared experimentally in clinically relevant radiation fields in terms of energy, spatial and time resolution. On a different note, two BGO block detectors (from PET scanners), arranged as the BGO block Compton camera (BbCc), are deployed for simple imaging tests with high energy prompt gamma rays produced in homogeneous Plexiglas targets by a proton pencil beam. The rationale is to maximise the detection efficiency in the scatterer plane despite a moderate energy resolution. Target shifts, increase of the target thickness and beam energy variation experiments are conducted. Concerning the PGT concept, in a collaboration among OncoRay, HZDR and IBA, the first test at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with several detectors and heterogeneous phantoms is performed. The sensitivity of the method to range shifts is investigated, the robustness against background and stability of the beam bunch time profile is explored, and the bunch time spread is characterised for different proton energies. With respect to the material choice for the absorber of the Cc, the BGO scintillator closes the gap with respect to the brighter LSO. The reason behind is the high energies of prompt gamma rays compared to the PET scenario, which increase significantly the energy, spatial and time resolution of BGO. Regarding the BbCc, shifts of a point-like radioactive source are correctly detected, line sources are reconstructed, and one centimetre proton range deviations are identified based on the evident changes of the back projection images. Concerning the PGT experiments, for clinically relevant doses, range differences of five millimetres in defined heterogeneous targets are identified by numerical comparison of the spectrum shape. For higher statistics, range shifts down to two millimetres are detectable. Experimental data are well reproduced by analytical modelling. The Cc and the PGT are ambitious approaches for range verification in proton therapy based on PGI. Intensive detector characterisation and tests in clinical facilities are mandatory for developing robust prototypes, since the energy range of prompt gamma rays spans over the MeV region, not used traditionally in medical applications. Regarding the material choice for the Cc: notwithstanding the overall superiority of LSO, BGO catches up in the field of PGI. It can be considered as a competitive alternative to LSO for the absorber plane due to its lower price, higher photoabsorption efficiency, and the lack of intrinsic radioactivity. The results concerning the BbCc, obtained with relatively simple means, highlight the potential application of Compton cameras for high energy prompt gamma ray imaging. Nevertheless, technical constraints like the low statistics collected per pencil beam spot (if clinical currents are used) question their applicability as a real-time and in vivo range verification method in proton therapy. The PGT is an alternative approach, which may have faster translation into clinical practice due to its lower price and higher efficiency. A proton bunch monitor, higher detector throughput and quantitative range retrieval are the upcoming steps towards a clinically applicable prototype, that may detect significant range deviations for the strongest beam spots. The experimental results emphasise the prospects of this straightforward verification method at a clinical pencil beam and settle this novel approach as a promising alternative in the field of in vivo dosimetry.

Keywords: proton therapy; range verification; in vivo dosimetry; prompt gamma ray imaging; Compton camera; block detector; scintillation; prompt gamma ray timing

  • Doctoral thesis
    TU Dresden, 2016
    Mentor: Prof. Dr. Wolfgang Enghardt
    141 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-22616
Publ.-Id: 22616


Prompt Gamma Imaging of a Pencil Beam with a High Efficiency Compton Camera at a Clinical Proton Therapy Facility

Hueso-González, F.; Petzoldt, J.; Römer, K. E.; Schöne, S.; Fiedler, F.; Golnik, C.; Kormoll, T.; Pausch, G.; Enghardt, W.

Protons are excellent particles for tumour treatment due to the increased ionization density close to their stopping point. In practice, the uncertainty on the particle range compromises the achievable accuracy. Compton cameras imaging prompt gamma rays, a by-product of the irradiation, have been proposed for indirect range verification years since. At Universitäts Protonen Therapie Dresden, two BGO block detectors (from PET scanners) arranged as Compton camera are deployed for imaging tests with high energy prompt gamma rays produced in PMMA by a proton pencil beam. Target shifts, thickness increase and beam energy variation experiments are conducted. Each measurement lasts about 15 minutes at a low proton beam current. The effect of one centimetre proton range deviations on the backprojected images is analysed. In conclusion, the experimental results highlight the potential application of Compton cameras for high energy prompt gamma ray imaging of pencil beams, as a real-time and in vivo range verification method in proton therapy.

Keywords: proton therapy; prompt gamma ray imaging; range verification; Compton camera; BGO block detector

  • Lecture (Conference)
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference, 31.10.-07.11.2015, San Diego, USA
  • Contribution to proceedings
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference, 31.10.-07.11.2015, San Diego, USA
    DOI: 10.1109/NSSMIC.2015.7582136
  • Poster
    NCRO-Retreat, 14.-16.04.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22615
Publ.-Id: 22615


Bioleaching of covellite - A model system for Kupferschiefer

Barthen, R.; Karimzadeh, L.; Gründig, M.; Grenzer, J.; Scholz, A.; Bischoff, L.; Franke, K.; Lippmann-Pipke, J.

Copper is an important base metal with manifold applications. Rising global demand makes low grade copper deposits increasingly attractive. Kupferschiefer represents Europe´s largest copper deposit. However, economic copper extraction from this calciferous, carbon rich ore with finely dispersed copper minerals is difficult. We aim for a deeper understanding of processes of copper (bio-)leaching at neutral pH. We employ synthetic covellite, microbial strains from Johanngeorgenstadt (Germany), model ligands, and geochemical modelling for elucidation of relevant parameters. We differentiate mineral dissolution, complexation, adsorption, and advection.

Keywords: Bioleaching; synthetic covellite; Kupferschiefer; glutamic acid; complexation

  • Poster
    10. PhD-seminar in Altenberg, 02.-04.11.2015, Altenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22614
Publ.-Id: 22614


Joint compositional calibration: a geochronological example

Tolosana-Delgado, R.; van den Boogaart, K. G.; Fiserova, E.; Hron, K.; Dunkl, I.

This contribution explores several issues arising in the measurement of a (geo)chemical composition, specially in the case that the quantities of interest are linear functions of (log)-ratios. This is the case of multi-isotopic geochronological analyses, where an age of a geological material is inferred as a function of several logratios in the isotopic system (Hg202, Pb204, Pb206, Pb207, Pb208, Th232, U235, U238), by using several ratios (e.g., Pb208/Pb206, Pb206/Pb204, Hg202/Pb204, U238/U235), quantities that are scaling invariant and subcompositionally coherent, but which in general cannot be estimated without taking into account additive noise effects incompatible with a purely compositional approach. The proposed ways to a solution heavily build upon the multi- Poisson distribution, higlighting the counting nature of the readings delivered by these measuring machines.

  • Open Access Logo Contribution to proceedings
    6th International Workshop on Compositional Data Analysis, 01.-05.06.2015, L'Escala, Girona, Espana
    Proceedings of the 6th International Workshop on Compositional Data Analysis, 978-84-8458-451-3, 241-257

Permalink: https://www.hzdr.de/publications/Publ-22613
Publ.-Id: 22613


Biplots for Compositional Regression

Graffelman, J.; Tolosana-Delgado, R.

In the statistical modeling of compositions, the latter can appear as response or explanatory variables, or even in both roles simultaneously. Such modeling is of multivariate nature because compositions consists of vectors of D elements, with potentially large D. Prior to fitting a model, the compositions are typically first transformed by a log-ratio transformation. The transformed compositions remain, however, of multivariate nature. Several techniques from the field of multivariate analysis can be used to analyze the data of which we mention multivariate regression, canonical correlation analysis and redundancy analysis. In multivariate regression the interpretation of the results is complicated by the large number of regression coefficients obtained, and collected in the matrix of regression coefficients B[p,q] with p explanatory and q response variables. Van den Boogaart and Tolosana-Delgado (2013) applied the singular value decomposition of the matrix of regression coefficients in order to find rank two approximations to B so that biplots can be constructed that summarize the relationships between the variables. However, the regression coefficients depend on the scale of the explanatory variables and their variances can be of very different order of magnitude. It is thus more natural to \standardize" the regression coefficient with a Mahanalobis-like transformation prior to biplot construction. Such an approach amounts to a redundancy analysis (also known as reduced-rank regression) of the data, and biplots for this method are discussed in detail by Ter Braak & Looman (1994). In this contribution we develop and apply redundancy analysis in a compositional context, discussing its biplots with empirical geological data and its compositional geometric interpretation.

Keywords: Redundancy analysis; Multivariate regression; Biplot; Conditional biplot; centred log-ratio (clr) transformation

  • Open Access Logo Contribution to proceedings
    6th International Workshop on Compositional Data Analysis, 01.-05.06.2015, L'Escala, Girona, Espana
    Proceedings of the 6th International Workshop on Compositional Data Analysis, 978-84-8458-451-3, 141-147

Permalink: https://www.hzdr.de/publications/Publ-22612
Publ.-Id: 22612


Linear models for the conditional distribution

van den Boogaart, K. G.; Lehmann, M.; Tolosana Delgado, R.

Our aim is to introduce a regression model for the conditional probablity distributions, of observable random variables as a function of regressors. The approach linear models in Bayes spaces. Bayes spaces are a generalisation of the Aitchison Simplex, which can be seen as the space of all distributions with support 1,...,n to probablity distributions on arbitrary measure spaces. Compositional linear models on the Aitchison simplex turn out to be equivalent to multivariate logistic regression if written in alr representation. Then, likelihood theory for generalized linear models is used to estimate the regression coefficients based on observed realisation of the random variable instead of observed compositions as in compositional regression. This idea is generalized towards Bayes spaces, generating a technique allowing to define and estimate models for the conditional distribution of an observed quantity as a Bayes-space-linear function of regressors.

Keywords: Multinomial Logistic Regression; Bayes Spaces; Compositional Regression

  • Open Access Logo Contribution to proceedings
    6th International Workshop on Compositional Data Analysis, 01.-05.06.2015, L'Escala, Girona, Espana
    Proceedings of the 6th International Workshop on Compositional Data Analysis, 978-84-8458-451-3, 45-53

Permalink: https://www.hzdr.de/publications/Publ-22611
Publ.-Id: 22611


Baseline Model for Bubbly Flows in OpenFoam: Current Implementation and Future Needs

Kriebitzsch, S.; Rzehak, R.

Many technical processes in industries such as chemical or energy but also numerous natural phenomena involve multiphase flow. Due to the complex physics and the broad range of relevant length scales involved, it is a formidable task to achieve a better understanding of such flows. A detailed insight into the local flow field can be obtained from multiphase computational fluid dynamics, which therefore is a potentially valuable optimization and design tool. Such simulations are feasible within the framework the so-called multi-fluid modelling, in which the different phases are described as interpenetrating continua. Within this framework closure models are necessary to describe the interaction of the phases and a large body of work using different closure relations of varying degree of sophistication exists, but no complete, reliable, and robust formulation has been achieved so far. Accurate and trustworthy predictions with multiphase CFD are only possible if a fixed set of closures is available that has been validated for a wide range of flow conditions and can therefore reliably be used also for unknown flow problems.
In this work a set of closure relations has been implemented into OpenFOAM, which represents the best available knowledge and is applicable for monodisperse turbulent adiabatic bubbly flow. Specifically we select closures for the exchange of momentum, i.e. drag and non-drag forces, and the effect of the disperse phase on the carrier-phase turbulence, the so-called bubble-induced turbulence. This set of closure models may serve as a baseline for further improvements and extensions to more general situations.
Experimental data for bubbly air-water flows, available from literature and from in-house experiments, are used to validate the model. Overall all three experimental data sets are reasonably well reproduced by the simulation results, in particular in the bulk of the flow. Larger discrepancies show up especially in the near-wall region and for the turbulent quantities. Also for bubble sizes around 4.5 to 5 mm, the reproduction of the experimental data with a monodisperse model becomes challenging. From the validation cases the following needs for further developments are identified:
• improved modelling of the near-wall region
• refined description of the bubble-induced turbulence
• modelling of the bubble-size distribution coupled with multiple momentum equations for the disperse phase.
The authors acknowledge the Helmholtz Association for support of the research within the frame of the Helmholtz Energy Alliance 'Energy Efficient Chemical Multiphase Processes'.

Keywords: OpenFOAM; Bubbly Flow; Modelling; CFD

  • Lecture (Conference)
    The 3rd OpenFOAM User Conference 2015, 19.-20.10.2015, Stuttgart, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22610
Publ.-Id: 22610


PET imaging evaluation of [18F]DBT-10, a novel radioligand specific to α7 nicotinic acetylcholine receptors, in nonhuman primates

Hillmer, A. T.; Zheng, M.-Q.; Li, S.; Scheunemann, M.; Lin, S.-F.; Holden, D.; Labaree, D.; Ropchan, J.; Teodoro, R.; Deuther-Conrad, W.; Carson, R. E.; Brust, P.; Huang, Y.

Purpose Positron emission tomography (PET) radioligands specific to α7 nicotinic acetylcholine receptors (nAChRs) afford in vivo imaging of this receptor for neuropathologies such as Alzheimer’s disease, schizophrenia, and substance abuse. This work aims to characterize the kinetic properties of an α7 -nAChR-spe c i f i c radioligand, 7-( 1 ,4-diazabicyclo[3.2.2]nonan-4-yl)-2-[18F]-fluorodibenzo[b,d]thiophene 5,5-dioxide ([18F]DBT-10), in nonhuman primates.
Methods [18F]DBT-10 was produced via nucleophilic substitution of the nitro-precursor. Four Macaca mulatta subjects were imaged with [18F]DBT-10 PET, with measurement of [18F]DBT-10 parent concentrations and metabolism in arterial plasma. Baseline PET scans were acquired for all subjects.
Following one scan, ex vivo analysis of brain tissue was performed to inspect for radiolabeled metabolites in brain. Three blocking scans with 0.69 and 1.24 mg/kg of the α7-nAChRspecific ligand ASEM were also acquired to assess dosedependent blockade of [18F]DBT-10 binding. Kinetic analysis of PET data was performed using the metabolite-corrected input function to calculate the parent fraction corrected total distribution volume (VT/fP).
Results [18F]DBT-10 was produced within 90 min at high specific activities of 428±436 GBq/μmol at end of synthesis.
Metabolism of [18F]DBT-10 varied across subjects, stabilizing by 120 min post-injection at parent fractions of 15–55 %. Uptake of [18F]DBT-10 in brain occurred rapidly, reaching peak standardized uptake values (SUVs) of 2.9–3.7 within 30 min. The plasma-free fraction was 18.8±3.4 %. No evidence for radiolabeled [18F]DBT-10 metabolites was found in ex vivo brain tissue samples. Kinetic analysis of PET data was best described by the two-tissue compartment model. Estimated VT/fP values were 193–376 ml/cm3 across regions, with regional rank order of thalamus>frontal cortex>striatum>hippocampus>occipital cortex>cerebellum>pons. Dosedependent blockade of [18F]DBT-10 binding by structural analog ASEMwas observed throughout the brain, and occupancy plots yielded a VND/fP estimate of 20±16 ml/cm3.
Conclusion These results demonstrate suitable kinetic properties of [18F]DBT-10 for in vivo quantification of α7-nAChR binding in nonhuman primates.

Keywords: Nicotine; Nicotinic acetylcholine receptor; Alpha 7; PET

Permalink: https://www.hzdr.de/publications/Publ-22608
Publ.-Id: 22608


Effects of ionic strength and fulvic acid on the adsorption of Tb3+ and Eu3+ onto clay

Poetsch, M.; Lippold, H.

High salinity and natural organic matter are both known to facilitate migration of toxic or radioactive metals in geochemical systems, but little is known on their combined effect.
We investigated complexation of Tb3+ and Eu3+ (as analogues for trivalent actinides) with fulvic acid and their adsorption onto clay in the presence of NaCl, CaCl2 and MgCl2 at ionic strengths up to saturation. 160Tb, 152Eu and 14C were employed as radiotracers, allowing invesitigations at very low concentrations according to probable conditions in far-field scenarios of nuclear waste repositories.
A composite approach (linear additive model) was tested for suitability in the prediction of Kd values for solid-liquid distribution of Tb(III) and Eu(III) in the ternary system of metal ion, clay and fulvic acid based on the constituent binary subsystems. The model was found suitable in reproducing the influence of fulvic acid as a function of ionic strength for bivalent electrolyte cations. In this analysis, it could be shown that high ionic strength does not further enhance the mobilizing potential of humic matter.

Keywords: fulvic acid; metal binding; linear additive model; adsorption; ionic strength

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Permalink: https://www.hzdr.de/publications/Publ-22605
Publ.-Id: 22605


Characterization of scintillator crystals for usage as prompt gamma monitors in particle therapy

Roemer, K.; Pausch, G.; Bemmerer, D.; Berthel, M.; Dreyer, A.; Golnik, C.; Hueso-González, F.; Kormoll, T.; Petzoldt, J.; Rohling, H.; Thirolf, P.; Wagner, A.; Wagner, L.; Weinberger, D.; Fiedler, F.

Particle therapy in oncology is advantageous compared to classical radiotherapy due to its well-defined penetration depth. In the so-called Bragg peak, the highest dose is deposited; the tissue behind the cancerous area is not exposed. Different factors influence the range of the particle and thus the target area, e.g. organ motion, mispositioning of the patient or anatomical changes. In order to avoid over-exposure of healthy tissue and under-dosage of cancerous regions, the penetration depth of the particle has to be monitored, preferably already during the ongoing therapy session. The verification of the ion range can be performed using prompt gamma emissions, which are produced by interactions between projectile and tissue, and originate from the same location and time of the nuclear reaction. The prompt gamma emission profile and the clinically relevant penetration depth are correlated. Various imaging concepts based on the detection of prompt gamma rays are currently discussed: collimated systems with counting detectors, Compton cameras with (at least) two detector planes, or the prompt gamma timing method, utilizing the particle time-of-flight within the body. For each concept, the detection system must meet special requirements regarding energy, time, and spatial resolution. Nonetheless, the prerequisites remain the same: the gamma energy region (2 to 10 MeV), high counting rates and the stability in strong background radiation fields. The aim of this work is the comparison of different scintillation crystals regarding energy and time resolution for optimized prompt gamma detection.

Keywords: Instrumentation for hadron therapy; Scintillators, scintillation and light emission processes (solid, gas and liquid scintillators)

Permalink: https://www.hzdr.de/publications/Publ-22604
Publ.-Id: 22604


On the hydrodynamics of airlift reactors, Part I: Experiments

Ziegenhein, T.; Zalucky, J.; Rzehak, R.; Lucas, D.

It is more and more possible to design bubbly flow reactors with methods of the computational fluid dynamics (CFD). However, measurements that can be used for model validation are often missing, especially for complex setups like airlift reactors. Such measurements include locally resolved information about the dispersed and continuous phase, particularly the flow field and interface structure. In the present work Reynolds stresses, liquid velocity and gas void fraction profiles as well as bubble size distributions are provided at several positions in the riser and the downcomer in a rectangular airlift reactor for this purpose. In addition, the hydrodynamics inside this airlift reactor are in detail described by the measured values.

Keywords: dispersed gas-liquid multiphase flow; airlift reactor; model validation; particle tracking velocimetry; turbulence; videography; bubble size distribution

Permalink: https://www.hzdr.de/publications/Publ-22603
Publ.-Id: 22603


Particle tracking using micro bubbles in bubbly flows

Ziegenhein, T.; Garcon, M.; Lucas, D.

Micro bubbles do not contaminate multiphase flows like conventional tracer particles so that the velocity in such can be determined completely non-intrusive by tracking them. Micro bubbles, however, are often larger as conventional tracer particles and have a significantly different density than the surrounding fluid. The ability of micro bubbles to follow the flow is investigated in this work. For this purpose, the particle tracking velocimetry results that are obtained with naturally occurring micro bubbles are compared to particle image velocimetry measurements using PMMA tracer particles. In combination with the used volume illumination, a simple, robust and reliable measuring technique is presented, which is deployable for complex problems from biological to oceanic engineering.
Averaged liquid velocities as well as basic turbulence parameters are determined in a rectangular bubble column for different gas volume flow rates. High flow rats are good manageable due to the volume illumination whereas the PIV measurements using a light sheet are approaching their limits. The general sampling bias in multiphase flows found recently for PIV measurements is also present for particle tracking methods; a hold processor that waits a time depending on the distribution of the particle information over the measuring area gives reasonable results.

Keywords: Velocity measurement; sampling bias; multiphase flow; particle tracking velocimetry; particle image velocimetry; bubble tracking velocimetry; volume illumination

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Permalink: https://www.hzdr.de/publications/Publ-22602
Publ.-Id: 22602


Towards a unified approach for modelling uniform and non‐uniform bubbly flows

Ziegenhein, T.; Rzehak, R.; Ma, T.; Lucas, D.

An important ingredient of closure relations for the Euler-Euler two-fluid model is the description of turbulent fluctuations. Models proposed in the literature disagree concerning the treatment of such on all scales. The large scale fluctuation structures as well as the bubble induced turbulence might be neglected or resolved and/or modeled respectively in different ways. Each treatment has been demonstrated to work for a certain application but a unifying perspective is lacking so far.
To this end a set of closure relations for the fluid dynamics of bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions. This model comprises a set of bubble forces as well as a turbulence model including turbulence modification due to the bubbles and has been successfully validated for bubbly flows in pipes and bubble columns. Here it is applied to two sets of data representing non-uniform and uniform flows in bubble columns which are dominated by large scale fluctuations and bubble induced turbulence respectively.

Keywords: dispersed gas-liquid multiphase flow; Euler-Euler two-fluid model; CFD simulation; bubble column; bubble-induced turbulence

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Permalink: https://www.hzdr.de/publications/Publ-22601
Publ.-Id: 22601


Visualising the molecular alteration of the calcite (104) – water interface by sodium nitrate

Hofmann, S.; Voitchovsky, K.; Spijker, P.; Schmidt, M.; Stumpf, T.

The reactivity of calcite, one of the most abundant minerals in the earth’s crust, is determined by the molecular details of its interface with the contacting solution. Recently, it has been found that trace concentrations of NaNO3 severely affect calcite’s (104) surface and its reactivity. Here we combine molecular dynamics (MD) simulations, X-ray reflectivity (XR) and in situ atomic force microscopy (AFM) to probe the calcite (104)-water interface in the presence of NaNO3. Simulations reveal density profiles of different ions near calcite’s surface, with NO3- able to reach closer to the surface than CO32- and in higher concentrations. Reflectivity measurements show a structural destabilisation of the (104) surfaces’ topmost atomic layers in NaNO3 bearing solution, with distorted rotation angles of the carbonate groups and substantial displacement of the lattice ions. Nanoscale AFM results confirm the alteration of crystallographic characteristics and the ability of dissolved NaNO3 to alter the structure of interfacial water was observed by AFM force spectroscopy. Our experiments and simulations consistently evidence a dramatic deterioration of the crystals’ surface, with potentially important implications for geological and industrial processes.

Keywords: Calcite; lanthanides; surface; AFM; Molecular dynamics; Surface X-ray Diffraction; nitrate

Permalink: https://www.hzdr.de/publications/Publ-22599
Publ.-Id: 22599


Defect-induced magnetism in SiC: The new opportunity in spintronics

Liu, Y.

The charge and spin are two intrinsic properties of electron. Electronic devices mainly utilize the charge of electrons, while mass storage devices are based on the spin of electrons. Diluted magnetic semiconductors provide the opportunity to use the charge and spin of electrons simultaneously, which may bring revolutionary changes in the information technology. Progresses have been achieved in the preparation of magnetic wide band-gap semiconductors with Curie temperatures at around room temperature by dopings. However, limited solubility of transition metals often leads to the precipitation of second phases, thwarting the attempts to get the unambiguous experimental results. Recently, there has been increasing evidence that traditional magnetic elements are not the sole source in inducing intrinsic magnetism. The effect of defects on magnetism formation is gradually being realized.
Our work has been focusing on the origin of magnetism in SiC for many years. Early research demonstrated that Mn is not the only source to determine the magnetic ordering in Mn doped SiC. Subsequently, ferromagnetism was induced in SiC by non-TM element Al dopings. Based on the results mentioned above, we carefully investigated the magnetism of neutron irradiated / noble gas ion implanted SiC single crystals in a series of work. The results unambiguously verified that defects can induce magnetism. The intentionally created defects dominated by divacancies (VSiVC) are responsible for the observed magnetism. The long-range ferromagnetic coupling can be attributed to the p electrons of the nearest-neighbor carbon atoms around VSiVC. Besides, the concentration of VSiVC has an optimal value and excess defects will depress the magnetism.

Keywords: Defect-induced magnetism; semiconductor; spintronics; SiC

  • Lecture (others)
    Seminar in the State University of New York at Buffalo, 13.10.2015, Buffalo, United States of America
  • Lecture (others)
    Seminar in Shanghai Institute of Ceramics, Chinese Academy of Sciences, 25.01.2016, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-22598
Publ.-Id: 22598


LIM-only protein FHL2 critically determines survival and radioresistance of pancreatic cancer cells.

Zienert, E.; Eke, I.; Aust, D.; Cordes, N.

Numerous factors determine the current poor prognosis of pancreatic ductal adenocarcinoma (PDAC). One of the greatest challenges to overcome is treatment resistance. Among a large repertoire of intrinsic resistance mechanisms, integrin-mediated cell adhesion to extracellular matrix (ECM) has been identified to be fundamental. Coalesced in focal adhesion complexes, integrins, receptor tyrosine kinases, protein kinases and adapter proteins mediate prosurvival signaling. Four and a half LIM domains protein 2 (FHL2) is one of these adapter proteins, which operates through protein-protein interactions and shows tumor-specific expression. Based on this, we investigated FHL2 expression in PDAC specimens and three-dimensionally grown cell lines and how FHL2 mechanistically contributes to cell survival, cell cycling and radiation resistance. PDAC exhibited a significantly increased and heterogeneous FHL2 expression. Upon FHL2 depletion, pancreatic cancer cell lines showed significantly decreased cell survival, proliferation and radioresistance as well as enhanced apoptosis and MEK/ERK signaling and cyclin D1, E, A and B1 expression were strongly induced. Targeting of FHL2 and MEK1 was similarly effective than FHL2 depletion alone, suggesting MEK1 as a downstream signaling mediator of FHL2. Taken together, our results provide evidence for the importance of the focal adhesion protein FHL2 in pancreatic cancer cell survival, proliferation and radiosensitivity.

Permalink: https://www.hzdr.de/publications/Publ-22596
Publ.-Id: 22596


DNA Damage Response Assessments in Human Tumor Samples Provide Functional Biomarkers of Radiosensitivity.

Willers, H.; Gheorghiu, L.; Liu, Q.; Efstathiou, J. A.; Wirth, L. J.; Krause, M.; von Neubeck, C.

Predictive biomarkers are urgently needed for individualization of radiation therapy and treatment with radiosensitizing anticancer agents. Genomic profiling of human cancers provides us with unprecedented insight into the mutational landscape of genes directly or indirectly involved in the response to radiation-induced DNA damage. However, to what extent this wealth of structural information about the cancer genome produces biomarkers of sensitivity to radiation remains to be seen. Investigators are increasingly studying the subnuclear accumulation (ie, foci) of proteins in the DNA damage response (DDR), such as gamma-H2AX, 53BP1, or RAD51, as a surrogate of treatment sensitivity. Recent findings from preclinical studies have demonstrated the predictive potential of DDR foci by correlating foci with clinically relevant end points such as tumor control probability. Therefore, preclinical investigations of DDR foci responses are increasingly moving into cells and tissues from patients, which is the major focus of this review. The advantage of using DDR foci as functional biomarkers is that they can detect alterations in DNA repair due to various mechanisms. Moreover, they provide a global measurement of DDR network function without needing to know the identities of all the components, many of which remain unknown. Foci assays are thus expected to yield functional insight that may complement or supersede genomic information, thereby giving radiation oncologists unique opportunities to individualize cancer treatments in the near future.

Permalink: https://www.hzdr.de/publications/Publ-22595
Publ.-Id: 22595


Implementation of a software for REmote COMparison of PARticlE and photon treatment plans: ReCompare.

Löck, S.; Roth, K.; Skripcak, T.; Worbs, M.; Helmbrecht, S.; Jakobi, A.; Just, U.; Krause, M.; Baumann, M.; Enghardt, W.; Lühr, A.

PURPOSE:

To guarantee equal access to optimal radiotherapy, a concept of patient assignment to photon or particle radiotherapy using remote treatment plan exchange and comparison - ReCompare - was proposed. We demonstrate the implementation of this concept and present its clinical applicability.
MATERIALS AND METHODS:

The ReCompare concept was implemented using a client-server based software solution. A clinical workflow for the remote treatment plan exchange and comparison was defined. The steps required by the user and performed by the software for a complete plan transfer were described and an additional module for dose-response modeling was added.
RESULTS:

The ReCompare software was successfully tested in cooperation with three external partner clinics and worked meeting all required specifications. It was compatible with several standard treatment planning systems, ensured patient data protection, and integrated in the clinical workflow.
CONCLUSION:

The ReCompare software can be applied to support non-particle radiotherapy institutions with the patient-specific treatment decision on the optimal irradiation modality by remote treatment plan exchange and comparison.

Keywords: Bestrahlungsplanvergleich; Entscheidungsunterstützung; Partikeltherapie; Patientenauswahl; Radiotherapy; Strahlentherapie; decision support; particle therapy; patient selection; treatment plan comparison

Permalink: https://www.hzdr.de/publications/Publ-22594
Publ.-Id: 22594


Exploring the joint compositional variability of major components and trace elements in the TELLUS soil geochemistry campaign (Northern Ireland)

Tolosana-Delgado, R.; Mckinley, J.

Geochemical datasets are growing in both their number of samples and components, including elements which typical values cover the ranges of magnitude from % to ppm or even ppb. Moreover, the sources of variability increase as well. It is becoming thus increasingly necessary to have appropriate tools to explore this geochemical variability. An example of such framework is provided by any modern regional geochemistry campaign, typically having thousands of samples analysed for several tens of elements covering diverse geological units in non-homogeneous climate-landscape environments. Using the TELLUS soil geochemical survey of Northern Ireland, this paper primarily aims to present one such exploratory case study.

The typical tools to use in this context are all based on principal component analysis (PCA) and variants. Several different alternatives are considered: raw data, standardized data and log-ratio transformed data; classical PCA vs robust PCA; only major components vs. a mixture of major and trace elements. Using the 12 resulting analyses, insights into the nature of the dominant factors of geochemical variability are extracted, and the advantages of a log-ratio approach highlighted.

From a methodological point of view, we show: (i) that raw data should seldom be considered; (ii) standardised data do not show any difference relevant between robust and classical PCA; and (iii) that standardised data and log-ratio data deliver a roughly similar picture, but (iv) logratio data offer much more insights, especially when comparing robust and classical PCA using all variables available.

From the perspective of the case study presented, we conclude that the first two sources of soil geochemical variation are related to the background geology and the presence/absence of blanket peat (a major feature of the landscape of Northern Ireland). Which of the two factors is the dominant one depends on whether robust or classical PCA was used. Besides this (rather expected) result, the analysis showed in addition striking positive correlations between the logratios Se/LOI, MnO/CaO and I/Br; between Br/Ni, Cl/Cr, Sb/TiO2 and Cd/MnO; or between Cs/I, Rb/Zn and Cr/Ni. Also null correlations are detected between the ratios of the second and third groups. Taking into account information on the major lithologies present in Northern Ireland, the third group of ratios appears to describe lithological changes, while the second group of ratios is strongly related. to peat building processes, which not only enrich in LOI (as expected) but in Br, Cl, Cd and Sb as well.

Permalink: https://www.hzdr.de/publications/Publ-22593
Publ.-Id: 22593


Lorentz TEM Imaging of Stripe Structures Embedded in a Soft Magnetic Matrix

Basith, M.; McVitie, S.; Strache, T.; Fritzsche, M.; Mücklich, A.; Fassbender, J.; McCord, J.

Néel walls in soft magnetic NiFe/NiFeGa hybrid stripe structures surrounded by a NiFe film are investigated by high-resolution Lorentz transmission-electron-microscopic imaging. An antiparallel orientation of magnetization in 1000-nm-wide neighboring unirradiated-irradiated stripes is observed by forming high-angle domain walls during magnetization reversal. Upon downscaling the stripe structure size from 1000 to 200 nm, a transition from a discrete domain pattern to an effective magnetic medium is observed for external magnetic-field reversal. This transition is associated with the vanishing ability of hosting high-angle domain walls between adjacent stripes.

Keywords: magnetism; domains; imaging; ion irradiation

Permalink: https://www.hzdr.de/publications/Publ-22592
Publ.-Id: 22592


Study of solar wind ions implantation effects in optical coatings in view of Solar Orbiter space mission operation

Bacco, D.; Corso, A. J.; Zuppella, P.; Böttger, R.; Gerlin, F.; Napolitani, E.; Tessarolo, E.; Nardello, M.; Pelizzo, M. G.

Low energy ions coming from the quite solar wind are considered among the causes of potential damage of the optical instrumentation and components on board of ESA Solar Orbiter. Predictions of space radiation parameters are available for instruments on board of such mission. Accelerators are commonly used to reproduce the particle irradiation on a spacecraft during its lifetime at the ground level. By selecting energies and equivalent doses it is possible to replicate the damage induced on space components. Implantation of Helium ions has been carried out on different single layer thin films at LEI facility at Forschungszentrum Dresden-Rossendorf varying the total dose. Profile of the implanted samples has been experimentally recovered by SIMS measurements. The change in reflectance performances of such coatings has been experimentally evaluated and modelled. The outcomes have been used to verify the potential impact on the METIS instrument and to drive the optimization of the M0 mirror coating..

Keywords: Ions; Optical coatings; Equipment and services; Helium; Mirrors; Particles; Radiation; Reflectivity; Thin films; Coating

Permalink: https://www.hzdr.de/publications/Publ-22590
Publ.-Id: 22590


Ferromagnetism induced by vacancy clusters in Silicon

Liu, Y.; Zhang, X. H.; Yuan, Q.; Han, J. C.; Zhou, S. Q.; Song, B.

Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Though it is weak, it can be stable above room temperature. Till now it has been confirmed at least in oxides [1, 2] and carbon based materials [3, 4]. Interestingly, the relation between magnetism and defects in Silicon was demonstrated decades ago [5]. Since then, some progresses were made [6-9] and push forward the research of magnetic Mn doped Si a lot but it is drawn little attention itself. Here, with the latest growth purifying technique and sensitive measurements, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors

  • Poster
    ALS User Meeting, 05.-07.10.2015, Berkeley, United States of America

Permalink: https://www.hzdr.de/publications/Publ-22589
Publ.-Id: 22589


Discrepancy between fluvial incision and denudation rates at the western Pamir margin

Fuchs, M.; Gloaguen, R.; Pohl, E.; Merchel, S.; Andermann, C.; Krbetschek, M.; Rugel, G.

Surface process rates provide keys to unravel controls of tectonics and climate on mountain evolution. In the Pamir, significant discrepancies exist between fluvial incision and denudation rates. Optically stimulated luminescence (OSL)-based fluvial incision outpaces cosmogenic nuclide (Be-10)-based denudation by up to 10 times at the western Pamir margin.
Differences in averaging times of determined rates cannot explain the contrast. The millennial denudation rates are highest (1.0 – 1.5 mm/yr) where long-term (104years) fluvial incision is moderate (2 – 5 mm/yr). In contrast, denudation is lower (~0.8 mm/yr) where incision is highest (7 – 10 mm/yr).

Process rates across the Pamir reveal differing control factors. The longitudinal profile and valley profiles of the Panj highlight links between fluvial incision and tectonic structures. Convex river reaches across the Pamir domes correspond to intense incision, whereas graded river segments coincide with southern dome boundaries. The indicated river captures induce intense incision and base level lowering for basins at the Pamir margins. Both, rapid incision and base level changes, maintain the steep slopes (0.75 quartiles) that are the predominant driver (R2 of ~0.8) for high denudation rates at the Pamir margins (0.5 – 1.5 mm/yr). However, highest denudation and lowest discrepancy to fluvial incision (~2 - 3 times) coincides with the areas receiving the highest annual precipitation. Multiple linear regression of denudation rates with the 0.75 quartiles of basin slopes and precipitation shows an R2 of 0.93. We propose that river captures are responsible for driving the intense incision along the Panj and consequently, provide the conditions for hillslope adjustment that contributes to the high denudation at the Pamir margins. Winter precipitation, and related concentrated discharge during the melting season, may act as limiting factor to hillslope adjustment and consequently, to denudation processes.

Keywords: accelerator mass spectrometry

  • Poster
    AGU Fall Meeting, 14.-18.12.2015, San Francisco, USA

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-22588
Publ.-Id: 22588


Tailoring dynamic magnetic characteristics of Fe60Al40 films through ion irradiation

Tahir, N.; Bali, R.; Gieniusz, R.; Mamica, S.; Gollwitzer, J.; Schneider, T.; Lenz, K.; Potzger, K.; Lindner, J.; Krawczyk, M.; Fassbender, J.; Maziewski, A.

Magnetization dynamics in Fe60Al40 thin films possessing depth-varying saturation magnetization (Ms) has been studied experimentally and theoretically. Variation in Ms was achieved by irradiation of 40 nm thick, chemically ordered (B2) Fe60Al40 films with Ne+ ions with energies between 0 – 30 keV. The initial B2 phase is paramagnetic and as the penetrating ions cause chemical disordering, the ion-affected region transforms to the ferromagnetic A2 phase. The effective ferromagnetic thickness and the depth of the A2/B2 phase boundary depend on the ion-energy (E); the effective thicknesses are 8.5 and 40 nm respectively for E = 2.5 and 30 keV. Thermally excited spin-waves in films with varying effective ferromagnetic thicknesses were analyzed by employing Brillouin light scattering and vector network analyzer ferromagnetic resonance spectroscopy. The analytical calculations are in good agreement with the experimental values, and show that the observed spin-wave modes are directly related to the effective ferromagnetic thickness; films irradiated with E < 5 keV only show the Damon-Eshbach mode, whereas for 15 < E < 20 keV an additional lower frequency standing spin-wave mode is observed. In films irradiated with E > 20 keV the Damon- Eshbach mode is observed to lie between two standing spin-wave modes. Furthermore, the A2/B2 phase boundary can be shown to act as an asymmetric pinning site. Controlling the depth of the phase boundary by varying the ion-energy can be a path to manipulate spin-wave propagation in materials displaying the phenomenon of disorder induced ferromagnetism.

Permalink: https://www.hzdr.de/publications/Publ-22587
Publ.-Id: 22587


Evolution of magnetic domain structure formed by ion-irradiation of B2-Fe0.6Al0.4

Tahir, N.; Gieniusz, R.; Maziewski, A.; Bali, R.; Potzger, K.; Lindner, J.; Fassbender, J.

Magnetic domains and magnetization reversal in 40 nm thick films of Fe0.6Al0.4, have been studied by longitudinal magneto-optical Kerr effect. By varying the Ne+ ion-energy E between 2 and 30 keV (keeping a constant fluence), we varied the depth-penetration of the ions, and thereby influenced the homogeneity of the induced saturation magnetization Ms. The dependence of coercivity on ion energy shows maximum for 5 keV Ne+. Considerable differences in the magnetic domain formation and magnetization reversal processes were observed: at low E (≤ 5keV), the reversal process is dominated by domain nucleation mechanism (high density of domain nucleation sites), consistent with the occurrence of an inhomogeneous Ms. Films irradiated with E > 5keV ions exhibit significantly low domain nucleation density, and the reversal is dominated by domain propagation mechanism, suggesting homogeneity in induced Ms. These results demonstrate the tunability of magnetization reversal behavior in materials possessing disorder induced magnetic phase transitions.

Permalink: https://www.hzdr.de/publications/Publ-22586
Publ.-Id: 22586


Prompt gamma imaging of passively shaped proton fields with a knife-edge slit camera

Priegnitz, M.; Barczyk, S.; Keitz, I.; Mein, S.; Vander Stappen, F.; Janssens, G.; Hotoiu, L.; Smeets, J.; Fiedler, F.; Prieels, D.; Enghardt, W.; Pausch, G.; Richter, C.

Range verification in proton therapy is highly desirable to fully exploit the advantageous properties of proton beams for tumor therapy. In this context, prompt gamma imaging (PGI) is of growing interest and different technical concepts for realization are currently under investigation. The feasibility of range shift detection with a slit camera has previously been shown for different targets irradiated with protons in pencil beam scanning mode. In preparation of the clinical application of the slit camera within a patient study, we report on the first application of the slit camera to passively shaped proton beams.

Keywords: prompt gamma imaging; slit camera; proton range verification

  • Poster
    ICTR-PHE 2016, International Conference on Translational Research in Radio-Oncology | Physics for Health in Europe, 15.-19.02.2016, Geneva, Switzerland
  • Poster
    2. Heidelberg Symposium on Novel Techniques in Ion Beam Radiotherapy, 09.-11.03.2016, Heidelberg, Deutschland
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)Suppl. 1, S86-S87
    DOI: 10.1016/S0167-8140(16)30177-3

Permalink: https://www.hzdr.de/publications/Publ-22585
Publ.-Id: 22585


LiPON Thin Films with High Nitrogen Content for Application in Lithium Batteries and Electrochromic Devices Prepared by RF Magnetron Sputtering

Su, Y.; Falgenhauer, J.; Polity, A.; Leichtweiß, T.; Kronenberger, A.; Obel, J.; Zhou, S.; Schlettwein, D.; Janek, J.; Meyer, B. K.

Transparent amorphous lithium phosphorus oxynitride (LiPON) thin films with different thickness have been prepared by RF magnetron sputtering at a growth rate of 14 nm/min. The mean ionic conductivity of as-deposited LiPON films determined by impedance spectroscopy was 4.9 μS/cm at 22 °C with the activation energy of 0.55 eV. The electronic partial conductivity was measured to be 1.6 × 10− 6 μS/cm by recording the current–time curves at a constant voltage. The optical transmission of LiPON films were measured by UV–Vis/IR spectroscopy. The prepared LiPON films on silica glass substrate showed transmission higher than 80% in the visible light range. The complex refractive index and bandgap (~ 2.94 eV) were estimated by fitting the transmission data with the Tauc–Lorentz dielectric function model. The local structure of the film was investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Both methods confirmed the incorporation of nitrogen in the matrix. Nitrogen is present in two different chemical environments, corresponding to P − N < PP and Psingle bondNdouble bond; length as m-dashP. Inductively coupled plasma-optical emission spectrometry (ICP-OES) and Rutherford backscattering spectrometry (RBS) measurements showed that the composition of the LiPON film was Li3.13PO1.69N1.39. The high nitrogen content and low oxygen content appears to be responsible for the specific electrical and optical properties of the LiPON films.

Keywords: LiPON; Lithium solid electrolyte; Solid state battery; Electrochromic device

Permalink: https://www.hzdr.de/publications/Publ-22584
Publ.-Id: 22584


Interaction of Selected Actinides and Lanthanides with Degradation Products of Organic Low and Intermediate Level Waste

Brinkmann, H.; Moll, H.; Arnold, T.; Stumpf, T.

Organic compounds present in LILW in a deep geological disposal are exposed to different conditions affecting their structure and chemical properties. Ionizing radiation, high pH, and microbial activity may lead to the generation of small water soluble organic compounds. These degradation products can probably enhance the mobility of radionuclides due to complex formation. Therefore the interaction of selected degradation products with certain actinides/lanthanides has to be investigated. This is necessary to predict the safety and long term evolution of a nuclear waste repository. This poster presents the objectives of the doctoral thesis and first results.

Keywords: actinides; lanthanides; organic radioactive waste; degradation; complexation

  • Poster
    10th HZDR PhD-Seminar, 02.-04.11.2015, Altenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22583
Publ.-Id: 22583


Direct Depth- and Lateral- Imaging of Nanoscale Magnets Generated by Ion Impact

Röder, F.; Hlawacek, G.; Wintz, S.; Hübner, R.; Bischoff, L.; Lichte, H.; Potzger, K.; Lindner, J.; Fassbender, J.; Bali, R.

Nanomagnets form the building blocks for a variety of spin-transport, spin-wave and data storage devices. In this work we generated nanoscale magnets by exploiting the phenomenon of disorder-induced ferromagnetism; disorder was induced locally on a chemically ordered, initially non-ferromagnetic, Fe60Al40 precursor film using a ∼ 2 nm diameter beam of Ne+ ions at 25 keV. The beam of energetic ions randomized the atomic arrangement locally, leading to the formation of ferromagnetism in the ion-affected regime. The interaction of a penetrating ion with host atoms is known to be spatially inhomogeneous, raising questions on the magnetic homogeneity of nanostructures caused by ion-induced collision cascades. Direct holographic observations of the flux-lines emergent from the disorder-induced magnetic nanostructures were made in order to measure the depth- and lateral- magnetization variation at ferromagnetic/non-ferromagnetic interfaces. Our results suggest that high-resolution nanomagnets of practically any desired 2-dimensional geometry can be directly written onto selected alloy thin films using a nanofocussed ion-beam stylus, thus enabling the rapid prototyping of novel magnetization configurations and testing for their magneto-coupling and spin-wave phenomena.

Keywords: phase transitions; chemical disorder; electron holography; magnetic imaging; nanomagnets

Permalink: https://www.hzdr.de/publications/Publ-22582
Publ.-Id: 22582


Spin wave eigenmodes in transversely magnetized thin film ferromagnetic wires

Duan, Z.; Krivorotov, I.; Arias, R.; Reckers, N.; Stienen, S.; Lindner, J.

We report experimental and theoretical studies of spin wave eigenmodes in transversely magnetized thin film Permalloy wires. Using broadband ferromagnetic resonance technique, we measure the spectrum of spin wave eigenmodes in individual wires as a function of magnetic field and wire width. Comparison of the experimental data to our analytical model and micromagnetic simulations shows that the intrinsic dipolar edge pinning of spin waves is negligible in transversely magnetized wires. Our data also quantify the degree of extrinsic edge pinning in Permalloy wires. This work establishes the boundary conditions for dynamic magnetization in transversely magnetized thin film wires for the range of wire widths and thicknesses studied, and provides a quantitative description of the spin wave eigenmode frequencies and spatial profiles in this system as a function of the wire width.

Permalink: https://www.hzdr.de/publications/Publ-22581
Publ.-Id: 22581


Correction of quantification errors in pelvic and spinal lesions caused by ignoring higher photon attenuation of bone in [18F]NaF PET/MR

Schramm, G.; Maus, J.; Hofheinz, F.; Petr, J.; Lougovski, A.; Beuthien-Baumann, B.; Oehme, L.; Platzek, I.; van den Hoff, J.

Purpose:
MR-based attenuation correction (MRAC) in routine clinical whole-body positron emission tomography and magnetic resonance imaging (PET/MRI) is based on tissue type segmentation. Due to lack of MR signal in cortical bone and the varying signal of spongeous bone, standard whole-body segmentation-based MRAC ignores the higher attenuation of bone compared to the one of soft tissue (MRACnobone). The authors aim to quantify and reduce the bias introduced by MRACnobone in the standard uptake value (SUV) of spinal and pelvic lesions in 20 PET/MRI examinations with [18F]NaF.
Methods:
The authors reconstructed 20 PET/MR [18F]NaF patient data sets acquired with a Philips Ingenuity TF PET/MRI. The PET raw data were reconstructed with two different attenuation images. First, the authors used the vendor-provided MRAC algorithm that ignores the higher attenuation of bone to reconstruct PETnobone. Second, the authors used a threshold-based algorithm developed in their group to automatically segment bone structures in the [18F]NaF PET images. Subsequently, an attenuation coefficient of 0.11 cm−1 was assigned to the segmented bone regions in the MRI-based attenuation image (MRACbone) which was used to reconstruct PETbone. The automatic bone segmentation algorithm was validated in six PET/CT [18F]NaF examinations. Relative SUVmean and SUVmax differences between PETbone and PETnobone of 8 pelvic and 41 spinal lesions, and of other regions such as lung, liver, and bladder, were calculated. By varying the assigned bone attenuation coefficient from 0.11 to 0.13 cm−1, the authors investigated its influence on the reconstructed SUVs of the lesions.
Results:
The comparison of [18F]NaF-based and CT-based bone segmentation in the six PET/CT patients showed a Dice similarity of 0.7 with a true positive rate of 0.72 and a false discovery rate of 0.33. The [18F]NaF-based bone segmentation worked well in the pelvis and spine. However, it showed artifacts in the skull and in the extremities. The analysis of the 20 [18F]NaF PET/MRI examinations revealed relative SUVmax differences between PETnobone and PETbone of (−8.8% ± 2.7%, p = 0.01) and (−8.1% ± 1.9%, p = 2.4×10−8) in pelvic and spinal lesions, respectively. A maximum SUVmax underestimation of −13.7% was found in lesion in the third cervical spine. The averaged SUVmean differences in volumes of interests in lung, liver, and bladder were below 3%. The average SUVmax differences in pelvic and spinal lesions increased from −9% to −18% and −8% to −17%, respectively, when increasing the assigned bone attenuation coefficient from 0.11 to 0.13 cm−1.
Conclusions:
The developed automatic [18F]NaF PET-based bone segmentation allows to include higher bone attenuation in whole-body MRAC and thus improves quantification accuracy for pelvic and spinal lesions in [18F]NaF PET/MRI examinations. In nonbone structures (e.g., lung, liver, and bladder), MRACnobone yields clinically acceptable accuracy.

Keywords: PET/MRI; attenuation correction; quantification

Permalink: https://www.hzdr.de/publications/Publ-22580
Publ.-Id: 22580


Sensitivity analysis and implications for surface processes from a hydrological modelling approach in the Gunt catchment, high Pamir Mountains

Pohl, E.; Knoche, M.; Gloaguen, R.; Andermann, C.; Krause, P.

A clear understanding of the hydrology is required to capture surface processes and potential inherent hazards in orogens. Complex climatic interactions control hydrological processes in high mountains that in their turn regulate the erosive forces shaping the relief. To unravel the hydrological cycle of a glaciated watershed (Gunt River) considered representative of the Pamir Mountains' hydrologic regime, we developed a remote-sensing-based approach. At the boundary between two distinct climatic zones dominated by the Westerlies and Indian summer monsoon, the Pamir Mountains are poorly instrumented and only a few in situ meteorological and hydrological data are available. We adapted a suitable conceptual distributed hydrological model (J2000g). Interpolations of the few available in situ data are inadequate due to strong, relief-induced, spatial heterogeneities. Instead of these we use raster data, preferably from remote sensing sources depending on availability and validation. We evaluate remote-sensing-based precipitation and temperature products. MODIS MOD11 surface temperatures show good agreement with in situ data, perform better than other products, and represent a good proxy for air temperatures. For precipitation we tested remote sensing products as well as the HAR10 climate model data and the interpolation-based APHRODITE data set. All products show substantial differences both in intensity and seasonal distribution with in situ data. Despite low resolutions, the data sets are able to sustain high model efficiencies (NSE ≥ 0.85). In contrast to neighbouring regions in the Himalayas or the Hindu Kush, discharge is dominantly the product of snow and glacier melt, and thus temperature is the essential controlling factor. Eighty percent of annual precipitation is provided as snow in winter and spring contrasting peak discharges during summer. Hence, precipitation and discharge are negatively correlated and display complex hysteresis effects that allow for the effect of interannual climatic variability on river flow to be inferred. We infer the existence of two subsurface reservoirs. The groundwater reservoir (providing 40 % of annual discharge) recharges in spring and summer and releases slowly during autumn and winter, when it provides the only source for river discharge. A not fully constrained shallow reservoir with very rapid retention times buffers meltwaters during spring and summer. The negative glacier mass balance (-0.6 m w.e. yr-1) indicates glacier retreat, which will ultimately affect the currently 30 % contribution of glacier melt to annual stream flow. The spatiotemporal dependence of water release from snow and ice during the annual cycle likewise implies spatiotemporally restricted surface processes, which are essentially confined to glaciated catchments in late summer, when glacier runoff is the only source of surface runoff. Only this precise constraint of the hydrologic cycle in this complex region allows for unravelling of the surface processes and natural hazards such as floods and landslides as well as water availability in the downstream areas. The proposed conceptual model has a tremendous importance for the understanding of the denudation processes in the region. In the Pamirs, large releases of running water that control erosion intensity are primarily controlled by temperature and the availability of snow and glaciers, thus making the region particularly sensitive to climatic variations.
________________________________________

Keywords: hydrological modelling; sensitivity Analysis; Pamir Mountains

Permalink: https://www.hzdr.de/publications/Publ-22579
Publ.-Id: 22579


Clinical applicability of the Compton camera for Prompt y-ray Imaging during proton therapy

Rohling, H.; Priegnitz, M.; Schöne, S.; Schumann, A.; Enghardt, W.; Golnik, C.; Hueso-Gonzalez, F.; Kormoll, T.; Pausch, G.; Petzoldt, J.; Römer, K.; Fiedler, F.

(1) Purpose
In order to guarantee the best outcome of a therapeutic irradiation with protons and other light ions a non-invasive in-vivo range verification is desired. One approach in this field is Prompt y-ray Imaging (PGI). A possible detection system for the prompt y-rays is the Compton camera. Several groups have been working on the construction of Compton camera prototypes (Kormoll et al., 2011; Llosá et al., 2013; Thirolf et al., 2014; Hueso-González et al., 2014). Up to now, Compton cameras have not been used in clinical practice for the monitoring of particle therapy. Therefore, by means of Geant4 simulations, we performed an end-to-end test to evaluate the clinical applicability of a Compton camera detection system and to determine the requirements regarding hardware and image reconstruction.
(2) Materials/methods
First, a treatment plan for a therapeutic proton irradiation for the head-neck region was prepared using XiO (Electa AB, Sweden). Based on this treatment plan, the y-ray emissions from the patient's tissue were simulated with Geant4. As a next step, the detector response was modelled, also with Geant4, for two large Compton cameras arranged around the patient in an angle of 90 degrees. Large-area detectors were already recommended (McCleskey et al., 2015). Each camera was built up from a scatter layer (CdZnTe) of dimension 10 × 10 × 0.5 cm3 and an absorber layer (LuSiO) of size 20 × 20 × 2 cm3. In practice, these cameras would be replaced by several smaller camera modules. For the simulation of the detector response a total number of previously simulated y-ray emissions were used as input corresponding to an applied dose of 1 Gy, i.e. a common dose of one field of one treatment session. After extracting the resulting coincident events, the image was reconstructed using a 3D MLEM algorithm (Schoene et al., 2015). The impact of the number of events as well as background on the image quality was also studied.
(3) Results
Figure 1 shows the images for the planned dose, the distribution of the y-ray emissions and the reconstructed image obtained with 128 iterations of the MLEM algorithm. For the considered number of events and the chosen voxels of 5 mm3 the runtime of the reconstruction was about two days on a cluster.

(4) Conclusions
For the considered large camera system and the realistic patient scenario with a dose of 1 Gy adequate images are obtained, which certainly could be applied to detect range deviations in the range of centimeters. Thus, this study demonstrates in principle the clinical applicability. The reconstruction algorithm still has potential for improvements with respect to performance. Furthermore, in practice, the costs of this complex detection system could lead to the preference of simpler methods of PGI.

Keywords: Compton camera; Geant4 simulations; image reconstruction

  • Poster
    ICTR-PHE 2016 - International Conference on Translational Research in Radio-Oncology | Physics for Health in Europe, 15.-19.02.2016, Geneve, Schweiz
  • Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)S1, S90-S91
    DOI: 10.1016/S0167-8140(16)30185-2

Permalink: https://www.hzdr.de/publications/Publ-22577
Publ.-Id: 22577


Characterization of defects in thick semiconducting amorphous YMnO3

Bogusz, A.; Anwand, W.; Blaschke, D.; Scholz, A.; Cornelius, S.; Bürger, D.; Skorupa, I.; Schmidt, O. G.; Schmidt, H.

In recent years amorphous semiconducting oxides have gained a lot of attention both from science and industry [1]. The rapid development in this field can be illustrated with the example of amorphous oxide semiconductor thin film transistors. Although invented only approximately one decade ago, they are already commercialized for active-matrix liquid crystal display backplane applications. Comparing to single-crystalline and polycrystalline materials, processing of amorphous oxides benefits from the easiness of production on the large, both plastic and glass areas (e.g. for solar cells) at low temperatures. In addition, thanks to amorphous nature, the problem of scattering (e.g. of light or carriers) and trapping at the defects of crystal structure and/or grain boundaries is avoided. “Amorphous”, however, does not mean “defect free” and as in the case of crystals, defects significantly influence the electronic, vibrational, optical and transport properties of the material. In this work, we present an attempt to identify and characterize defects in amorphous YMnO3, a well-known multiferroic when in crystalline form [2], deposited on sapphire by multiple techniques. We use X-ray diffractometry, Rutherford backscattering spectroscopy, scanning electron and atomic force microscopy to define composition, structural and surface properties of the oxides. Optical properties in the range between 210 and 1000 nm are measured and modelled by variable angle spectroscopic ellipsometry. Open volume defects are probed by positron annihilation spectroscopy (PAS). Comparison of results obtained on as-grown films and films annealed at T= 400°C for 5 and 10 hours in air allows for qualitative description of defects formed in YMnO3. According to the results of PAS presented in Figure 1, we consider following scenarios: (1) two types of negatively charged, vacancy-type defects are formed during the growth of which one was annealed out and (2) one type of negatively charged, vacancy-type defect is formed during the growth which agglomerates to bigger and stable form during annealing. Our research enables qualitative description of the defects in the amorphous semiconducting films. Obtained results might be used for (1) further optimization of film processing in order to reduce amount of defects, or for (2) defect engineering in order to prepare a film with tuned properties.
[1] T. Kamiya, H. Hosono, NPG Asia Mater. 2 (2010) 15-22
[2] B. B. Van Aken, T. T. M. Palstra, A. Filippetti, N. A. Spaldin, Nat. Mater. 3 (2004) 164-170

  • Lecture (Conference)
    The 16th conference on defects-recognition, imaging and physics in semiconductors, 06.-10.09.2015, Suzhou, China

Permalink: https://www.hzdr.de/publications/Publ-22576
Publ.-Id: 22576


Comparison of Consolidation Routes for Mo-Si-B Materials Prepared by Using Nitride Containing Powders

Wiltner, A.; Klöden, B.; Hilger, I.; Weißgärber, T.; Kieback, B.

Pressureless sintering is a well-established powder metallurgical route for processing and consolidation of mixed materials. Especially materials exhibiting a high melting point could be densified without tool abrasion by this sintering technique. As the sintering temperatures are often higher compared to pressure-assisted techniques care must be taken by means of grain growth. In our studies we used a ternary compound mixture to obtain Mo-based alloys. Consolidation applying pressure-assisted methods (hot pressing, spark plasma sintering) and pressureless sintering were used, respectively. The densities reached and the microstructures obtained were compared. These Mo-Si-B alloys were processed using a nitride-powder-based route offering lower impurity contents due to short processing times by avoiding time consuming mixing / milling steps. The sintering conditions depending on the powder particle size as well as the sample shape will be presented in detail. The composition investigated in this article offered a continuous α-Mo matrix with intermetallic islands consisting of Mo3Si and Mo5SiB2 (T2) phases. The combination of a ductile α-Mo matrix and intermetallic phases embedded within offered an enhanced mechanical behavior at room temperature compared to MoSi2 or other intermetallic alloys. Moreover, the intermetallic compounds as well as Mo are candidates for high-temperature applications. As the high-temperature behavior could be strongly influenced by the respective microstructure we present here the processing and the microstructure obtained.

Keywords: Grain growth; High temperature applications; Hot pressing; Intermetallics; Metallurgy; Microstructure; Nitrides; Particle size; Silicon; Silicon alloys; Sintering; Spark plasma sintering; Ternary alloys; High temperature behavior; Intermetallic alloys; Intermetallic phasis; Mechanical behavior; Powder metallurgical; Pressure-less sintering; Sintering condition; Sintering temperatures

Permalink: https://www.hzdr.de/publications/Publ-22575
Publ.-Id: 22575


Solarenergie und Photovoltaik - Nanostrukturen für mehr Leistungsfähigkeit

Schumann, E.

Der Vortrag führt in die verschiedenen Methoden zur Stromerzeugung aus Sonnenlicht ein. Nach einer Motivation über die Rahmenbedingungen werden die verschiedenen Konzepte und Funktionsweisen der Solarthermie und der Photovoltaik vorgestellt. In einer engen Partnerschaft mit industriellen Partnern arbeitet die Gruppe Nanokompositmaterialien des Instituts für Ionenstrahlphysik und Materialforschung an neuartigen Nanostrukturen. Diese können in unterschiedlichsten Komponenten von solarthermischen Kraftwerken und Solarzellen, ähnlich der von Dünnschichtsilizium, zur Anwendung kommen.

  • Invited lecture (Conferences)
    Lehrerfortbildung 2015, 13.02.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22574
Publ.-Id: 22574


Spectroscopic Ellipsometry - short course

Schumann, E.; Lungwitz, F.

A short introduction into spectroscopic ellipsometry. Covering topics starting with the nature and description of polarized light. The optical constants and dielectric function is introduced and the interaction from light with bulk matter and multiple thin films is discussed. The first part concludes with the explanation of what an ellipsometer measures.
The second half of the course comprises basic analysis procedures, model building with oscillator models, fitting and walk through steps of some examples.

  • Lecture (others)
    Workshop, 15.10.2015, Sevilla, Espana

Permalink: https://www.hzdr.de/publications/Publ-22573
Publ.-Id: 22573


Investigation of mass transfer in milli-channels using high-resolution microfocus X-ray imaging

Haghnegahdar, M.; Boden, S.; Hampel, U.

In this work, the absorption rate of a single Taylor bubble of carbon dioxide in water was investigated within vertical capillaries using high resolution X-ray imaging. The liquid side mass transfer coefficient was calculated from the changes in the size of the bubble at constant pressure obtained from the high-resolution X-ray images by image processing. The bubbles were continuously monitored by holding the bubble stationary in a downward flow of liquid. The processed images, which give the volume of the bubble with high accuracy as a function of time, were processed to evaluate the liquid side mass transfer coefficient between bubble and liquid using the mass conservation equation.
The experiments covered a large range of initial Taylor bubble length varying from 5 to 22 mm. The results show that the measured Sherwood numbers depend strongly on the bubble length and also equivalent diameter, which is the same trend as in previously reported results for larger pipe sizes. However the values of measured Sherwood numbers could not be predicted by available correlations. As a result a new mass transfer coefficient in the form of Sherwood number and as a function of Peclet number as well as the ratio of bubble equivalent diameter to capillary diameter (deq/D) is presented. The proposed correlation is applicable for a large range of the ratio deq/D that varies from 0.8 to 1.6. The average relative error between measured Sherwood number and the one calculated with the new correlation is less than 9.6%.

Keywords: mass transfer; Taylor bubble; carbon dioxide; X-ray imaging; milli-channels

Permalink: https://www.hzdr.de/publications/Publ-22572
Publ.-Id: 22572


Leitwertkontrolle einzelner elektrisch kontaktierter Moleküle

Sendler, T.

Die molekulare Elektronik setzt sich zum Ziel, passive und aktive Bausteine in integrierten Schaltkreisen auf molekularer Ebene zu realisieren. Dabei ist entscheidend, dass sich der elektrische Leitwert der molekularen Bauelemente hinreichend regulieren lässt. Um zu belegen, dass dies möglich ist, wird in dieser Dissertation die gezielte Leitwertkontrolle einzelner über Nanoelektroden kontaktierter Moleküle nachgewiesen. Die erzielten Ergebnisse ergänzen dabei nahtlos aktuellste Studien.
Zum einen werden kontaktierte molekulare Schalter durch Bestrahlung mit Licht einer bestimmten Wellenlänge in-situ von einem nicht-leitenden in einen leitenden Zustand geschaltet, wobei der Einfluss unterschiedlicher Seitengruppen für eine zusätzliche Modifikation des Leitwerts sorgt. Ausschlaggebend ist hierbei die elektronische Anbindung des Moleküls an die Elektroden. Zum anderen werden Molekül-Metall-Komplexe durch die Einbindung eines Übergangsmetallions von einem isolierenden in einen leitenden Zustand versetzt. In diesem Fall lässt sich der leitende Zustand durch die Wahl des Ions innerhalb einer Größenordnung variieren, was eine völlig neue Möglichkeit der Leitwertkontrolle in molekularen Bausteinen darstellt. Das Ion bestimmt dabei sowohl die mechanische Stabilität als auch die elektronische Struktur des Moleküls.
Für die Kontaktierung einzelner Moleküle kommt die Technik des mechanisch kontrollierten Bruchkontakts zum Einsatz. So lassen sich feine Goldnanoelektroden herstellen, an die Moleküle anbinden. Um eine präzise Analyse durchzuführen, werden über zwei unabhängige Messstrategien Informationen über das elektrische Transportverhalten sowie über die elektronische Struktur der Moleküle erworben.
In dieser Arbeit sind echte Neuentwicklungen auf dem Gebiet der molekularen Elektronik gelungen, die einen wesentlichen Beitrag für die Umsetzung integrierter molekularer Schaltkreise leisten.

  • Doctoral thesis
    TU Dresden, 2015
    129 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22570
Publ.-Id: 22570


Induced Conductance in Single-Molecule Junctions

Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, J. W.; Mortensen, M.; Gothelf, K.; Helm, M.; Gemming, S.; Kerbusch, J.; Scheer, E.; Huhn, T.; Erbe, A.

The goal of molecular electronics is the realization of integrated molecular circuits. For this purpose reliable contacts to single molecules have to be built and the characteristics of those junctions need to be investigated. We have demonstrated that the mechanically controllable break junction (MCBJ) technique is a suitable tool to study the electrical transport through molecular junctions and to analyze the electronic structure of the molecules. Furthermore, based on the use of complex molecules, we are able to control the conductance of single molecular junctions. On the one hand, molecular switches are transformed in-situ from a non-conductive “off”- to a conductive ”on”-state via light-irradiation of a well-defined wavelength. On the other hand molecule-metal complexes are turned from an isolating to a conductive state by introducing metal centers into the molecular structures. The findings provide a significant contribution to the development of functional molecular junctions.

  • Poster
    Annual Workshop IHRS NanoNet 2015, 30.09.-02.10.2015, Lohmen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22569
Publ.-Id: 22569


Zellbasierte Sensor- und Aktormaterialien für strategisch relevante Metalle

Vogel, M.; Matys, S.; Raff, J.

Unter dem Leitmotiv „Lebende Zellen auf Oberflächen – hochempfindlich, trotzdem stabil“ soll die BioSAM-Technologieplattform für eine breite wirtschaftliche Nutzung von zellbasierten Sensor-Aktor-Systemen in den Bereichen Bioverfahrenstechnik, Wasser- und Umwelttechnologie sowie Klimatechnik erschlossen werden. Im Rahmen des Teilprojektes BioNEWS geht es um Langzeitstabile Zellen zum Aufbau und zur Regenerierung von Sensor- und Aktorsystemen für den Nachweis und die Bindung strategisch relevanter Metalle (insbesondere Seltene Erden). Hier werden die Detektions- und Sorptionskonzepte sowie erste Ergebnisse zu den entsprechnden zellbasierten Sensor- und Aktormaterialien vorgestellt.

Keywords: Sensor; Aktor; Seltene Erden; S-Layer; Zellen

  • Poster
    "Wachstumskern BioSAM - Themenworkshop" - Biologische Sensor-Aktor-Systeme auf der Basis von funktionalisierten Mikroorganismen (BioSAM), 04.11.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22568
Publ.-Id: 22568


Single-Layer ReS2: Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy

Lin, Y.-C.; Komsa, H.-P.; Yeh, C.-H.; Björkman, T.; Liang, Z.-Y.; Ho, C.-H.; Huang, Y.-S.; Chiu, P.-W.; Krasheninnikov, A. V.; Suenaga, K.

Rhenium disulfide (ReS2) and diselenide (ReSe2), the group 7 transition metal dichalcogenides (TMDs), are known to have a layered atomic structure showing an in-plane motif of diamond-shaped-chains (DS-chains) arranged in parallel. Using a combination of transmission electron microscopy and transport measurements, we demonstrate here the direct correlation of electron transport anisotropy in single-layered ReS2 with the atomic orientation of the DS-chains, as also supported by our density functional theory calculations. We further show that the direction of conducting channels in ReS2 and ReSe2 can be controlled by electron beam irradiation at elevated temperatures and follows the strain induced to the sample. Furthermore, high chalcogen deficiency can induce a structural transformation to a nonstoichiometric phase, which is again strongly direction-dependent. This tunable in-plane transport behavior opens up great avenues for creating nanoelectronic circuits in 2D materials.

Keywords: transition metal dichalcogenides; 2D materials; defects

Permalink: https://www.hzdr.de/publications/Publ-22567
Publ.-Id: 22567


Xe irradiation of graphene on Ir(111): From trapping to blistering

Herbig, C.; Åhlgren, E. H.; Schröder, U. A.; Martínez-Galera, A. J.; Arman, M. A.; Kotakoski, J.; Knudsen, J.; Krasheninnikov, A. V.; Michely, T.

Using x-ray photoelectron spectroscopy, thermal desorption spectroscopy, and scanning tunneling microscopy, we show that upon keV Xe+ irradiation of graphene on Ir(111), Xe atoms are trapped under the graphene. Upon annealing, aggregation of Xe leads to graphene bulges and blisters. The efficient trapping is an unexpected and remarkable phenomenon given the absence of chemical binding of Xe to Ir and to graphene, the weak interaction of a perfect graphene layer with Ir(111), as well as the substantial damage to graphene due to irradiation. By combining molecular dynamics simulations and density functional theory calculations with our experiments, we uncover the mechanism of trapping. We describe ways to avoid blister formation during graphene growth, and also demonstrate how ion implantation can be used to intentionally create blisters without introducing damage to the graphene layer. Our approach may provide a pathway to synthesize new materials at a substrate—2D material interface or to enable confined reactions at high pressures and temperatures.

Keywords: Graphene; irradiation; defects

Permalink: https://www.hzdr.de/publications/Publ-22566
Publ.-Id: 22566


Anwendungen der Röntgenfarbkamera SLcam® in der Geologie und Resourcentechnologie

Scharf, O.; Arkadiev, V.; Buchriegler, J.; Dressler, S.; Kühn, A.; Renno, A.; Ziegenrücker, R.

Die Messung von mikro-Röntgenfluoreszenzspektren über einer Fläche, ein Vollfeld Röntgenfluoreszenzdatensatz, ermöglicht die Verteilung von Elementen und deren Konzentrationen in einer Probe zu bestimmen. Diese Informationen sind wichtig für die Analyse von Gesteinsproben und die (Rück-)Gewinnung von Wertstoffen, da sich der Aufschluss und die Aufbereitung neben der chemischen Zusammensetzung auch nach den umgebenden Stoffen und der Größen- und Formverteilung richten. Diese Daten werden vor allem durch die Mineral Liberation Analyse am Rasterelektronenmikroskop gewonnen und durch gezielte Messungen an ausgewählten Punkten verfeinert.
In jüngster Zeit wurden zwei Forschungsprojekte gestartet, die den Vollfeld Röntgenfluoreszenzdatensatz mit Hilfe der Röntgenfarbkamera gewinnen. Im Helmholtz-Zentrum Dresden-Rossendorf wurde die High-Speed PIXE Anlage in Betrieb genommen, die einen Vollfeld Röntgenfluoreszenzdatensatz über eine 1,44 cm2 große Fläche mit Hilfe der protoneninduzierten Röntgenfluoreszenz aufnimmt. In der gleichen Geometrie wurde ein Auftischgerät entwickelt (MEGA), das zur Anregung eine 1.2 kW Röntgenröhre nutzt. Zusätzlich wurde ein Polarisationsmikroskop integriert. Beide Geräte arbeiten im Vakuum und können mit unterschiedlichen Optiken verwendet werden.
Die Projekte werden vorgestellt und erste Ergebnisse werden präsentiert.

Projekt Mega:
MEGA - Methodische und gerätetechnische F&E für die schnelle Vorort-Analyse der feinkörnigen und inhomogenen Verteilung von Hochtechnologiemetallen in Lagerstätten

Projekt HS-Pixe:
This work has been supported by Marie Curie Actions - Initial Training Networks (ITN) as an Integrating Activity Supporting Postgraduate Research with Internships in Industry and Training Excellence (SPRITE) under EC contract no. 317169.

Keywords: SLcam; X-ray; PIXE; XRF

  • Poster
    PRORA 2015 - Prozessnahe Röntgenanalytik, 12.-13.11.2015, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22565
Publ.-Id: 22565


My Interpretation of DREsden AMS – Status, Developments, Ideas

Rugel, G.

DREAMS, the DREsden AMS-facility at the Helmholtz-Zentrum Dresden-Rossendorf is performing routine accelerator mass spectrometry of 10Be, 26Al, 36Cl, 41Ca, and 129I for a wide range of applications [1]. I will give an overview of the facility with its 6 MV HVEE tandetron and also its performance the last four years. Recent technical developments such as a low-memory ion source for 36Cl and 129I will be shown. Some of the applications will be highlighted. I will also briefly report the status of the Super-SIMS project, which will connect a CAMECA SIMS (SIMS = Secondary Ion Mass Spectrometry) to the tandem accelerator aiming for lower detection limits for analysing geological samples within our focus of resource technology. Ref.: [1] www.dresden-ams.de

  • Lecture (others)
    Vera-Seminar, 15.10.2015, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-22564
Publ.-Id: 22564


Strengths of the resonances at 436, 479, 639, 661, and 1279 keV in the 22Ne(p,γ)23Na reaction

Depalo, R.; Cavanna, F.; Ferraro, F.; Slemer, A.; Al-Abdullah, T.; Akhmadaliev, S.; Anders, M.; Bemmerer, D.; Elekes, Z.; Mattei, G.; Reinicke, S.; Schmidt, K.; Scian, C.; Wagner, L.

The 22Ne(p,γ)23Na reaction is included in the neon-sodium cycle of hydrogen burning. A number of narrow resonances in the Gamow window dominates the thermonuclear reaction rate. Several resonance strengths are only poorly known. As a result, the 22Ne(p,γ)23Na thermonuclear reaction rate is the most uncertain rate of the cycle. Here, a new experimental study of the strengths of the resonances at 436, 479, 639, 661, and 1279 keV proton beam energy is reported. The data have been obtained using a tantalum target implanted with 22Ne. The strengths ωγ of the resonances at 436, 639, and 661 keV have been determined with a relative approach, using the 479 and 1279 keV resonances for normalization. Subsequently, the ratio of resonance strengths of the 479 and 1279 keV resonances was determined, improving the precision of these two standards. The new data are consistent with, but more precise than, the literature with the exception of the resonance at 661 keV, which is found to be less intense by one order of magnitude. In addition, improved branching ratios have been determined for the gamma decay of the resonances at 436, 479, and 639 keV.

Keywords: Nuclear Astrophysics; Radiative Capture; Underground Nuclear Astrophysics; Nova nucleosynthesis; Explosive hydrogen burning

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-22563
Publ.-Id: 22563


Diffusive magnetohydrodynamic instabilities beyond the Chandrasekhar theorem

Rüdiger, G.; Schultz, M.; Stefani, F.; Mond, M.

We consider the stability of axially unbounded cylindrical flows that contain a toroidal magnetic background field with the same radial profile as their azimuthal velocity. For ideal fluids, Chandrasekhar had shown the stability of this configuration if the Alfven velocity of the field equals the velocity of the background flow, i.e., if the magnetic Mach number Mm = 1. We demonstrate that magnetized Taylor–Couette flows with such profiles become unstable against non-axisymmetric perturbations if at least one of the diffusivities is finite. We also find that for small magnetic Prandtl numbers Pm the lines of marginal instability scale with the Reynolds number and the Hartmann number. In the limit Pm -> 0 the lines of marginal instability completely lie below the line for Mm = 1 and for Pm -> infinity they completely lie above this line. For any finite value of Pm, however, the lines of marginal instability cross the line Mm = 1, which separates slow from fast rotation. The minimum values of the field strength and the rotation rate that are needed for the instability (slightly) grow if the rotation law becomes flat. In this case, the electric current of the background field becomes so strong that the current-driven Tayler instability (which also exists without rotation) appears in the bifurcation map at low Hartmann numbers.

Permalink: https://www.hzdr.de/publications/Publ-22562
Publ.-Id: 22562


Transient eddy current flow metering

Forbriger, J.; Stefani, F.

Measuring local velocities or entire flow rates in liquid metals or semiconductor melts is a notorious problem in many industrial applications, including metal casting and silicon crystal growth. We present a new variant of an old technique which relies on the continuous tracking of a flow-advected transient eddy current that is induced by a pulsed external magnetic field. This calibration-free method is validated by applying it to the velocity of a spinning disk made of aluminum. First tests at a rig with a flow of liquid GaInSn are also presented.

Permalink: https://www.hzdr.de/publications/Publ-22561
Publ.-Id: 22561


Collinear order in the frustrated three-dimensional spin-1/2 antiferromagnet Li2CuW2O8

Ranjith, K. M.; Nath, R.; Skoulatos, M.; Keller, L.; Kasinathan, D.; Skourski, Y.; Tsirlin, A. A.

Magnetic frustration in three dimensions (3D) manifests itself in the spin-1/2 insulator Li2CuW2O8. Density-functional band-structure calculations reveal a peculiar spin lattice built of triangular planes with frustrated interplane couplings. The saturation field of 29 T contrasts with the susceptibility maximum at 8.5 K and a relatively low Néel temperature TN similar or equal to 3.9 K. Magnetic order below TN is collinear with the propagation vector (0, 1/2,0) and an ordered moment of 0.65(4) µB according to neutron diffraction data. This reduced ordered moment together with the low maximum of the magnetic specific heat (Cmax/R similar or equal to 0.35) pinpoint strong magnetic frustration in 3D. Collinear magnetic order suggests that quantum fluctuations play a crucial role in this system, where a noncollinear spiral state would be stabilized classically.

Permalink: https://www.hzdr.de/publications/Publ-22560
Publ.-Id: 22560


High-field magnetization study of a HoFe6Al6 single crystal

Gorbunov, D. I.; Andreev, A. V.; Skourski, Y.; Tereshina, E. A.

Magnetization measurements have been performed in static (up to 14 T) and pulsed (up to 60 T) magnetic fields on a HoFe6Al6 single crystal with a tetragonal crystal structure of ThMn type. HoFe6Al6 is a ferrimagnet with exact compensation of the Ho and Fe sublattices at low temperatures, the spontaneous magnetic moment is Ms = 0 at 4.2 K. At elevated temperatures, Ms passes through a wide maximum (4.2 µB at 200 K) and vanishes at the Curie temperature, TC = 315 K. The compound displays a high magnetic anisotropy of the easy-plane type, a noticeable anisotropy exists also within the easy plane with the [110] axis as the easy magnetization direction. HoFe6Al6 exhibits two field-induced magnetic phase transitions along the easy [110] axis and two more along the [100] axis, the hard direction in the basal plane. The critical fields of the lower-and higher-field transitions display qualitatively different temperature dependencies. A T-H magnetic phase diagram has been constructed for the [100] and [110] directions. The Ho-Fe inter-sublattice exchange constant has been determined to be nHoFe = 3.8 T/µB.

Permalink: https://www.hzdr.de/publications/Publ-22559
Publ.-Id: 22559


MLA-based partition curves for magnetic separation

Leißner, T.; Bachmann, K.; Gutzmer, J.; Peuker, U. A.

Mineral liberation analysis (MLA) allows access to detailed information on the composition of a sample as well as of single particles visible on the cross-sectioned surface of a grain mount. This information can be used to evaluate processing related to the liberation distribution of valuables or to the distribution of a feature used for separation of valuables from barren particles. When separation processes are studied, the separation feature has to be added to the particle population data. In case of density separation (particle size and particle density) this is already been done by MLA software. For magnetic separation the MLA data has to be combined with mineral susceptibilities using additional software.
This article describes the calculation of partition curves for magnetic separation based on the liberation analysis of the feed and the products. Magnetic susceptibility data from measurements of pure minerals and from literature are is and combined with the particle composition data from the liberation analysis. Using sieved fractions in the magnetic separation experiments the evolution of cut susceptibility and separation efficiency with particle size is studied. The effects of a stereological correction and of the width of susceptibility classes as well as of the mineral susceptibilities used in calculation are discussed.

Keywords: partition curves; magnetic separation; mineral liberation analysis

Permalink: https://www.hzdr.de/publications/Publ-22558
Publ.-Id: 22558


Spectroscopic screening for the speciation of europium and curium in the gastrointestinal tract

Wilke, C.; Barkleit, A.; Stumpf, T.

Lanthanide and actinide elements are exogenous metals, which have no essential role in normal biochemistry. Through different processes these heavy metals could be potentially released into the environment where they could be further incorporated into the food chain. Because of their potential chemical- and radiotoxicity, it is important to understand their chemical and biological behavior in the human body. This study focuses particularly on the biochemical behavior of Ln(III) and An(III) in the human gastrointestinal tract. To this end, a spectroscopic screening was performed for Eu(III), as a representative of Ln(III) and An(III), by time-resolved laser-induced fluorescence spectroscopy (TRLFS) to identify their possible binding partners in the human gastrointestinal system simulated by using an in vitro digestion model.

Keywords: body fluids; digestive system; lanthanides; actinides; europium; curium; TRLFS

  • Lecture (Conference)
    RANC-International Conference on Radioanalytical and Nuclear Chemistry, 10.-15.04.2016, Budapest, Ungarn

Permalink: https://www.hzdr.de/publications/Publ-22557
Publ.-Id: 22557


Using quasi-DNS to investigate the deposition of elongated aerosol particles in a wavy channel flow

Lecrivain, G.; Rayan, R.; Hurtado, A.; Hampel, U.

In gas-cooled high temperature reactors, the diffusion of the fission products into the graphite matrix causes a radioactive contamination of the carbonaceous dust. The contaminated graphite aerosol particles often exhibit large aspect ratios and deposit in complex geometries, which hinders a detailed experimental investigation. The use of quasi Direct Numerical Simulation (quasi-DNS) to simulate the turbulent flow in nuclear reactors has seen an increased interest over the last few years. The capabilities of a quasi-DNS to simulate the transport and the deposition of elongated particles in an wavy channel flow are presently tested. It is shown that quasi-DNS effectively predicts deposition and that, unlike the deposition in a plane channel flow, the particle aspect ratio has no significant effect on the overall deposition rate in a wavy channel. It is suggested that in numerical studies of particle deposition on a significantly roughened channel, the particle can be assumed to be spherical without affecting the results of the deposition study.

Keywords: Graphite dust deposition; high temperature reactor; quasi-DNS; deposition of elongated particles; wavy channel flow

Permalink: https://www.hzdr.de/publications/Publ-22556
Publ.-Id: 22556


Gravitational settling of glass fibers on an air bubble

Lecrivain, G.; Petrucci, G.; Hampel, U.; Yamamoto, R.

Froth flotation is a separation process in which air bubbles are introduced in a water tank to separate the valuable commodities from the valueless material. Based on their relative affinity to water the valuable particles attach to the bubble surface and are carried to the top of the flotation tank to form the froth layer. The resulting froth layer is eventually collected to produce the concentrate. Froth flotation has been used for more than a century in mining operations to separate valuable materials such as rare earth metals from excavated ores. More recently, froth flotation has been employed for the treatment of contaminated water. In the present study, the effect of the particle elongation on the attachment mechanism is investigated in great detail. Using an in-house optical micro-bubble sensor the attachment of micron glass fibres on the surface of a stationary air bubble immersed in stagnant water is investigated. The attachment mechanism is here defined as three successive events: the approach of the particle near the bubble upstream pole, the collision of the solid particle with the gas-liquid interface and the particle sliding on the gas bubble surface. The translational particle velocities together with the particle orientation during entire attachment process are measured and compared with a theoretical model. For the first time the existence of two types of attachment is shown. Upon collision near the upstream pole of the gas bubble the major axis of the fibre aligns with the local bubble surface. If collision occurs at least 30° further downstream the contact is likely to take a punctual form, i.e. the head of the fibre is in contact with the gas-liquid interface.

Keywords: Froth flotation; particle attachment; gas bubble; micro-bubble sensor

  • Contribution to proceedings
    ASME-JSME-KSME Joint Fluids Engineering Conference, 26.-31.07.2015, Seoul, South Korea
    Proceedings of the ASME-JSME-KSME Joint Fluids Engineering Conference
    DOI: 10.1115/AJKFluids2015-16458

Permalink: https://www.hzdr.de/publications/Publ-22555
Publ.-Id: 22555


Universal ultrafast detector for short optical pulses based on graphene

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.

Graphene has unique optical and electronic properties that make it attractive as an active material for broadband ultrafast detection. We present here a graphene-based detector that shows 40-picosecond electrical rise time over a spectral range that spans nearly three orders of magnitude, from the visible to the far-infrared. The detector employs a large area graphene active region with interdigitated electrodes that are connected to a log-periodic antenna to improve the long-wavelength collection efficiency, and a silicon carbide substrate that is transparent throughout the visible regime. The detector exhibits a noise-equivalent power of approximately 100 μW·Hz–½ and is characterized at wavelengths from 780 nm to 500 μm.

Keywords: detector; broadband detector; fast detector; graphene

Permalink: https://www.hzdr.de/publications/Publ-22554
Publ.-Id: 22554


THz Autocorrelators for ps Pulse Characterization Based on Schottky Diodes and Rectifying Field-Effect Transistors

Preu, S.; Mittendorff, M.; Winnerl, S.; Cojocari, O.; Penirschke, A.

When operating Schottky diodes andr ectifying field-effect transistors in the saturation regime, where they show a sub-
linear response to incident THz power, they can be used as fast autorcorrelators yielding information on the pulse envelope. We report on autocorrelation measurements at 3.41 THz of high-power THz pulses for determination of the pulse duration and pulse structure. By fringe resolved measurements, the THz frequency of the pulse is also obtained. We develop a theoretical model for the rectification process and compare the performance of anantenna-coupled Schottky diode to a large-area field-effecttransistorrectifier. While the Schottky diode saturates earlier and can therefore be used for autocorrelation measurements at lower input power, antenna-less large-area field-effect transistors can be used for highest power levels - even at free electron lasers - and turn out to be very robust.

Keywords: autocorrelator; detector; Schottky diode; field-effect transistor

Permalink: https://www.hzdr.de/publications/Publ-22553
Publ.-Id: 22553


Schlussbericht: Apparatus for in-situ defect Analysis (AIDA)

Fassbender, J.; Potzger, K.; Wagner, A.

Ziel des Antrages ist die Entwicklung eines Systems (Apparatus for in-situ defect analysis, AIDA) zur Untersuchung und zur experimentellen Simulation der Defektentstehung in neuartigen, für die Energiewende relevanten Materialien. Das Besondere am AIDA-System ist, dass diese Untersuchungen/Simulationen im oberflächennahen Bereich bereits auf der atomaren Skala, d.h. in einem frühen Stadium der Defektentstehung erfolgen, sowie in-situ („live“-Messungen) und somit ein grundlegendes Verständnis der Defektentstehung erlauben.

Keywords: Materialien für die Energiewende; Defekte; Positronenannihilationsspektroskopie; Ionenstrahlanalytik

  • Other report
    Dresden: Eigenverlag, 2015

Permalink: https://www.hzdr.de/publications/Publ-22552
Publ.-Id: 22552


Investigation of the release of zinc in the reactor sump and the behavior of dissolved zinc at hotspots in the reactor core after a loss of coolant accident

Renger, S.; Alt, S.; Kästner, W.; Seeliger, A.; Kryk, H.

Generic experimental and methodical investigations were carried out aiming at the systematical elucidation of physico-chemical mechanisms and their influence on thermo-hydraulic processes, which can occur during the sump circulation operation after loss-of-coolant accidents in PWR. In such cases, boric acid containing coolant with dissolved zinc, which is formed by corrosion of zinc-coated containment internals, may reach core regions with higher temperature (hot-spots).
The experimental studies done at semi-technical scale were focused on the influence of such zinc containing coolants on thermo-hydraulics at heating configurations similar to those inside the core of PWR. The impact of physico-chemical mechanisms on thermo-fluid-dynamical behavior of the coolant inside a 3×3 heating rod configuration with spacer segments was determined. As an initial condition, boric coolant with dissolved zinc was used at a fluid temperature in the range of 45...50°C.
During the heating of zinc-containing coolant, an increasing turbidity of the fluid caused by formed colloids was observed first, followed by the formation of several solid corrosion products consisting of zinc borates. In dependence of the temperatures of fluid and heatable surfaces, the solids showed a different behavior concerning their mobilization potential, density and ability to layer formation. Deposits occurred at the rod surfaces as well as at the spacer segments. They effected a hindered heat transfer from the rod surfaces to the fluid, an increasing head loss at the spacers and some changes of the flow distribution. In addition, quantifications of the formed solid corrosion products including a characterization of the released particles were done. Subsequently, investigations were expanded considering original zinc sources (zinc-coated gratings) and a 16×16 fuel rod dummy with a centered 8×8 heating rod configuration.
Summing up, achieved experimental results allow conclusions about the solubility behavior of zinc corrosion products in boric coolant as well as about the formation of solids and the effects thereof. Beside processes of deposit layer formation and particle release, effects like outgassing of air dissolved in the coolant and local subcooled boiling phenomena were observed, which can contribute to the remobilization of formed solids and may strengthen the mentioned mechanisms.

Keywords: reactor safety research; loss of coolant accident; particle formation; corrosion; zinc release; zinc borate; experiment

  • Lecture (Conference)
    NURETH-16, 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    NURETH-16, 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, 30.08.-04.09.2015, Chicago, USA
    Proceedings of NURETH-16

Permalink: https://www.hzdr.de/publications/Publ-22551
Publ.-Id: 22551


Kerntechnische Ausbildung und Forschung in Deutschland – Quo vadis?

Hampel, U.

Der Vortrag widmet sich der Fragestellung, mit welchen Themen und in welcher Tiefe und Breite kerntechnische Ausbildung und Forschung derzeit in Deutschland stattfindet und wie die aktuellen Entwicklungsprognosen dazu sind. Im Zentrum stehen die Fragen: Welche Kompetenzen braucht Deutschland in Zukunft im Bereich nukleare Sicherheit, wie ist die kerntechnische Ausbildung an den Universitäten und Helmholtz-Einrichtungen zu sehen und welche Rolle spielt der Kompetenzverbund Kerntechnik?

Keywords: Kompetenzerhalt Kerntechnik

  • Invited lecture (Conferences)
    Kompetenznetzwerk Forschung und Lehre „Perspektive Kerntechnik“, 07.-08.09.2015, Mannheim, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22550
Publ.-Id: 22550


Melting behavior of americium-doped uranium dioxide

Prieur, D.; Lebreton, F.; Caisso, M.; Martin, P.; Scheinost, A. C.; Somers, J.; Delahaye, T.; Manara, D.

Uranium-americium mixed oxides are considered as potential blankets for americium transmutation in fast neutron reactors. Their thermophysical properties and notably their melting behavior have not been properly assessed although required in order to evaluate the safety of these compounds under irradiation. In this study, we measured via laser heating the melting points under inert atmosphere (Ar) of U1 xAmxO2±δ samples with Am/(U+Am) contents equal to 10, 15 and 20 mol.%. The experimental atmosphere was chosen in order to maintain, as much as possible throughout the heating/cooling cycles, the oxygen-to-metal ratio, initially set very close to 2.00. Structural characterizations of the samples carried out before and after melting confirm that this goal was satisfactorily attained. The obtained melting/solidification temperatures, measured here for the first time, indicate that under the current experimental conditions and as far as the investigated AmO2 contents, the solidus line of the UO2-AmO2 system follows with very good approximation the ideal solution behavior. Accordingly, the observed liquidus formation temperature decreases from 3130 ± 20 K for pure UO2 to 3051 ± 30 K for U0.8Am0.2O2±δ.

Keywords: uranium; americium; XAFS; transmutation

Permalink: https://www.hzdr.de/publications/Publ-22549
Publ.-Id: 22549


Entstehung und Vermeidung von Gasmitriss bei Notkühlung – numerische und experimentelle Analysen

Schäfer, T.

Kreiselpumpen kommen im Kraftwerksbereich in vielfältiger Weise zum Einsatz. Sie werden unter anderem als Speisepumpen oder als Umwälzpumpen in Kühlkreisläufen genutzt. Neben hoher Effizienz bei geringem Energieverbrauch bieten sie ein Reihe weiterer Vorteile, wie zum Beispiel ruhiger und kontinuierlicher Förderstrom und hohe Haltbarkeit und Beständigkeit. Erfolgt der Einsatz auch in sicherheitsrelevanten Bereichen, wie z.B. in der Reaktornotkühlung von Kernkraftwerken, muss unbedingt ein störungsfreier und zuverlässiger Betrieb gewährleistet werden. Dies kann nicht mehr sichergestellt werden, wenn es bei der Förderung des Notkühlmittels zu einem Gaseintrag durch Hohlwirbelbildung im Kühlmittelreservoir kommt.
Die vorgestellte Arbeit erläutert zunächst das Problem des Gasmitrisses durch Hohlwirbelbildung. Anschließend werden experimentelle Untersuchungen von Hohlwirbeln und Einlaufgeometrien beschrieben und Maßnahmen zur Vermeidung von Hohlwirbeln vorgeschlagen. Es werden Möglichkeiten der numerische Modellierung von Hohlwirbeln beschrieben und mit den experiementellen Untersuchungen verglichen. Weiterhin werden ausgewählte Tests an nuklearen Armaturen erläutert. Darüber hinaus werden die Auswirkungen des Gaseintrages in sicherheitsrelevante Systemkomponenten, wie Kreiselpumpen und Armaturen mittels tomographischen Untersuchungen aufgeschlossen und analysiert und es werden vorbeugende Maßnahmen vorgeschlagen. Auf den gewonnenen Ergebnissen basierend, können Betriebshinweise für Anlagenbetreiber optimiert werden. Darüber hinaus können verbesserte Design- und Auslegungsempfehlungen für sicherheitsrelevante Systemkomponenten erarbeitet und validiert werden.

Keywords: Notkühlung; Hohlwirbelbildung; Gaseintrag; Kreiselpumpe; Armaturen; Experimente; numerische Modellierung; Computertomographie; emergency cooling; hollow vortex formation; gas entrainment; centrifugal pump; valves; experiments; numeric modelling; computed tomography

  • Invited lecture (Conferences)
    47. Kraftwerkstechnisches Kolloquium, 13.-14.10.2015, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22548
Publ.-Id: 22548


Synthesis and Structural/Physical Properties of U3Fe2Ge7: A Single-Crystal Study

Henriques, M. S.; Gorbunov, D. I.; Waerenborgh, J. C.; Pasturel, M.; Andreev, A. V.; Dusek, M.; Skourski, Y.; Havela, L.; Goncalves, A. P.

A single crystal of U3Fe2Ge7 was synthesized by the tin-flux method, and its structural and electronic properties were studied. The compound crystallizes in the orthorhombic crystal structure of La3Co2Sn7 type with two Wyckoff sites for the U atoms. U3Fe2Ge7 displays a ferromagnetic order below TC = 62 K. Magnetization measurements in static (up to 14 T) and pulsed (up to 60 T) magnetic fields revealed a strong two-ion uniaxial magnetic anisotropy. The easy magnetization direction is along the c axis and the spontaneous magnetic moment is 3.3 μB per formula unit at 2 K. The moment per Fe atom is 0.2 μB, as follows from Mössbauer spectroscopy. The magnetic moments are oriented perpendicular to the shortest inter-uranium distances that occur within the zigzag chains in the ab plane, contrary to other U-based isostructural compounds. The magnetization along the a axis reveals a first-order magnetization process that allows for a quantitative description of the magnetic anisotropy in spite of its enormous energetic strength. The strong anisotropy is reflected in the specific heat and electrical resistivity that are affected by a gap in magnon spectrum.

Permalink: https://www.hzdr.de/publications/Publ-22547
Publ.-Id: 22547


Giant low field magnetocaloric effect and field-induced metamagnetic transition in TmZn

Li, L.; Yuan, Y.; Zhang, Y.; Namiki, T.; Nishimura, K.; Pöttgen, R.; Zhou, S.

The magnetic properties and the magnetocaloric effect (MCE) in TmZn have been studied by magnetization and heat capacity measurements. The TmZn compound exhibits a ferromagnetic state below a Curie temperature of TC=8.4K and processes a field-induced metamagnetic phase transition around and above TC. A giant reversible MCE was observed in TmZn. For a field change of 0-5T, the maximum values of magnetic entropy change (-ΔSMmax) and adiabatic temperature change (ΔTadmax) are 26.9J/kg K and 8.6K, the corresponding values of relative cooling power and refrigerant capacity are 269 and 214J/kg, respectively. Particularly, the values of -ΔSMmax reach 11.8 and 19.6J/kg K for a low field change of 0-1 and 0-2T, respectively. The present results indicate that TmZn could be a promising candidate for low temperature and low field magnetic refrigeration.

Permalink: https://www.hzdr.de/publications/Publ-22546
Publ.-Id: 22546


Detection of mixed-range proton pencil beams with a prompt gamma slit camera

Priegnitz, M.; Helmbrecht, S.; Janssens, G.; Perali, I.; Smeets, J.; Vander Stappen, F.; Sterpin, E.; Fiedler, F.

With increasing availability of proton and particle therapy centers for tumor treatment, the need for in-vivo range verification methods comes more into the focus. Imaging of prompt gamma rays emitted during the treatment is one of the possibilities currently under investigation. A knife-edge shaped slit camera was recently proposed for this task and measurements proved the feasibility of range deviation detection in homogeneous and inhomogeneous targets. In the present paper, we concentrate on laterally inhomogeneous materials, which lead to range mixing situations when crossed by one pencil beam: different sections of the beam have different ranges.
We chose exemplative cases from clinical irradiation and assembled idealized tissue equivalent targets. One-dimensional emission profiles were obtained by measuring the prompt gamma emission with the slit camera. It could be shown that the resulting range deviations can be detected by evaluation of the measured data with a previously developed range deviation detection algorithm. The retrieved value, however, strongly depends on the target composition, and is not necessarily in direct relation to the ranges of both parts of the beam. By combining the range deviation detection with an analysis of the slope of the distal edge of the measured prompt gamma profile, the origin of the detected range deviation, i.e.\ the mixed range of the beam, is also identified. It could be demonstrated that range mixed prompt gamma profiles exhibit less steep distal slopes than profiles from beams traversing laterally homogeneous material. For future application of the slit camera to patient irradiation with double scattered proton beams, situations similar to the range mixing cases are present and results could possibly apply.

Permalink: https://www.hzdr.de/publications/Publ-22545
Publ.-Id: 22545


A novel thermoregulatory role for PDE10A in mouse and human adipocytes

Hankir, M.; Kranz, M.; Gnad, T.; Wagner, S.; Deuther-Conrad, W.; Bronisch, F.; Steinhoff, K.; Luthardt, J.; Klöting, N.; Hesse, S.; Seibyl, J.; Blüher, M.; Sabri, O.; Pfeifer, A.; Brust, P.; Fenske, W.

Phosphodiesterase type 10A (PDE10A) is highly enriched in striatum and a novel drug target for several psychiatric and neurodegenerative diseases. PDE10A has additionally been implicated in the regulation of energy homeostasis, but the mechanisms remain unclear. Here, we showed marked levels of PDE10A in interscapular brown adipose tissue (BAT) of mice by utilizing small animal PET/MRI and the novel radioligand [18F]-AQ28A. In addition to BAT, Pde10a mRNA is also expressed in perigonadal visceral white adipose tissue (VAT). Pharmacological targeting of PDE10A with the selective inhibitor MP-10 increased [18F]-FDG uptake by BAT and enhanced thermogenesis in vivo. Moreover, acute MP-10 treatment of mouse brown adipocytes stimulated lipolysis and chronic treatment induced browning of primary human white adipocytes. Functional studies on diet induced obese mice further demonstrated that MP-10 produces weight loss independent of changes in food intake associated with increased energy expenditure and browning of VAT. Finally, human PET imaging with the radioligand [18F]-MNI-659 revealed marked levels of PDE10A in the supraclavicular region where brown/beige adipocytes are clustered in adults. Collectively, our findings highlight a novel thermoregulatory role for PDE10A in mouse and human adipocytes and promote PDE10A inhibitors as promising candidates for the treatment of obesity.

Permalink: https://www.hzdr.de/publications/Publ-22544
Publ.-Id: 22544


Synthese von substituierten Benzo[4,5]thienopyridinen für die Entwicklung von α7-nAChR-Liganden für die Positronen-Emissions-Tomographie (PET)

Paternoga, E.

Es ist kein Abstract vorhanden.

  • Bachelor thesis
    Universität Leipzig, Fakultät für Chemie und Mineralogie, 2015
    Mentor: Prof. Dr. Dr. Athanassios Giannis, Prof. Dr. Peter Brust
    44 Seiten

Permalink: https://www.hzdr.de/publications/Publ-22543
Publ.-Id: 22543


A hybrid electron cyclotron resonance metal ion source with integrated sputter magnetron for the production of an intense Al+ ion beam

Weichsel, T.; Hartung, U.; Kopte, T.; Zschornack, G.; Kreller, M.; Philipp, A.

A metal ion source prototype has been developed: a combination of magnetron sputter technology with 2.45 GHz electron cyclotron resonance (ECR) ion source technology—a so called magnetron ECR ion source (MECRIS). An integrated ring-shaped sputter magnetron with an Al target is acting as a powerful metal atom supply in order to produce an intense current of singly charged metal ions. Preliminary experiments show that an Al+ ion current with a density of 167 μA/cm2 is extracted from the source at an acceleration voltage of 27 kV. Spatially resolved double Langmuir probe measurements and optical emission spectroscopy were used to study the plasma states of the ion source: sputter magnetron, ECR, and MECRIS plasma. Electron density and temperature as well as Al atom density were determined as a function of microwave and sputter magnetron power. The effect of ECR heating is strongly pronounced in the center of the source. There the electron density is increased by one order of magnitude from 6 × 109 cm−3 to 6 × 1010 cm−3 and the electron temperature is enhanced from about 5 eV to 12 eV, when the ECR plasma is ignited to the magnetron plasma. Operating the magnetron at constant power, it was observed that its discharge current is raised from 1.8 A to 4.8 A, when the ECR discharge was superimposed with a microwave power of 2 kW. At the same time, the discharge voltage decreased from about 560 V to 210 V, clearly indicating a higher plasma density of the MECRIS mode. The optical emission spectrum of the MECRIS plasma is dominated by lines of excited Al atoms and shows a significant contribution of lines arising from singly ionized Al. Plasma emission photography with a CCD camera was used to prove probe measurements and to identify separated plasma emission zones originating from the ECR and magnetron discharge.

Permalink: https://www.hzdr.de/publications/Publ-22542
Publ.-Id: 22542


Gallium-Recycling aus Prozessabwässern mit Dialyseverfahren

Reinhold, T.; Zeidler, O.

Der Vortrag zeigt die Entwicklung eines Recycling-Projektes für Gallium vom Labor- bis in den Pilotmaßstab und zeigt technologische, sowie ökonomische Aspekte. Das erfolgreiche Projekt der Freiberger Compound Materials GmbH mit den Forschungseinrichtungen TU Bergakademie Freiberg und Helmholtz-Institut Freiberg wurde 2014 mit dem Deutschen Rohstoff-Effizienzpreis ausgezeichnet.

  • Invited lecture (Conferences)
    Vortragsreihe Materialeffizienz - ein Gewinn für Unternehmen, 13.04.2015, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22541
Publ.-Id: 22541


Chiral symmetry aspects in the open charm sector

Buchheim, T.; Hilger, T.; Kämpfer, B.

QCD sum rules serve as tools to investigate changing hadronic properties in a hot and/or dense nuclear medium. The role of chiral symmetry breaking and restoration effects in a medium can be addressed also in the heavy-light meson sector. Thus, we consider Weinberg sum rules which refer to chiral partner mesons composed of a light and a heavy quark.

Permalink: https://www.hzdr.de/publications/Publ-22540
Publ.-Id: 22540


Non-equilibrium thermal processing towards p-n junction formation in TCOs

Prucnal, S.; Wu, J.; Gago, R.; Gao, K.; Liu, F.; Zhou, S.; Cai, H.; Zahn, D. R. T.; Gordan, O. D.; Skorupa, W.

Wide band gap semiconductors (> 3.0 eV) like ZnO and TiO2 are widely investigated in the field of optoelectronics for ultraviolet lasers, heterojunction solar cells, thin film transistors and light emitting diodes. Nowadays, the transparent conductive oxides (TCO) like Al- or F-doped ZnO (AZO or FZO) are basic materials for the front contact in thin-film photovoltaics. A highly doped n-type ZnO thin layer is an attractive candidate to replace the much more expensive indium-tin-oxide layer in the microelectronics industry. The optoelectronic properties of TCOs are determined by the type of doping and carrier concentration. The n-type conductivity of ZnO is easily achieved by substitution of Zn by group III elements (Al, Ga, In), or by doping with halogen elements (F, Cl or I) substituting oxygen in the lattice site. In the case of TiO2 the n-type material can be achieved by doping with Nb, Ta or F ions while p-type TiO2 can be realized by e.g. Cr doping. Here, we will present the utilization of highly non-equilibrium thermal processing of TCO/Si heterojunctions using millisecond (ms) range flash lamp annealing (FLA) techniques for the structural modification and dopant activation to form highly doped p- and n-type TCOs films on silicon substrate. The n- and p-type doping in ZnO was made by incorporation of Al and F or N and P into ZnO, respectively. While the conductivity of TiO2 films was controlled by efficient incorporation of Ta and Cr into the lattice side of titania. It will be presented that via millisecond range FLA treatment not only the optoelectronic properties but also the crystallographic orientation and phase formation of TCOs can be modified. The optical properties of fabricated TCOs were investigated using temperature dependent photoluminescence, Raman and transmission spectroscopy. X-Ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM) were utilized to study the microstructural properties while the electrical properties of the TCO layers and heterojunctions were measured using Hall Effect and current-voltage characterization, respectively. Moreover, it is shown that the annealing atmosphere, even during ms range annealing, can efficiently passivates the surface state and bulk defects in the TCOs significantly improving the near band gap emission. - See more at: http://www.european-mrs.com/2015-fall-symposium-g-european-materials-research-society#sthash.tu4VYSCO.dpuf

Keywords: TCOs; FLA; doping; ZnO

  • Lecture (Conference)
    2015 E-MRS Fall Meeting, 15.-18.09.2015, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-22539
Publ.-Id: 22539


Lateral growth of Ge nanowires and GeOI via millisecond range explosive recrystallization: solid vs. liquid case

Prucnal, S.; Pezoldt, J.; Tiagulskyi, S.; Kerbusch, J.; Bischoff, L.; Rebohle, L.; Voelskow, M.; Wutzler, R.; Pyszniak, K.; Skorupa, W.

The incorporation of different functional optoelectronic elements on a single chip enables performance progress, which can overcome the downsizing limit in silicon technology. For example, the use of Ge instead of silicon as a basic material in nanoelectronics would enable faster chips containing smaller transistors. In order to improve the device performance and fully exploit the unique properties of germanium, the germanium on insulator (GeOI) structure using the ultrathin body (UTB) GeOI architecture with an active doping concentration above 6×1019 cm-3 has to be explored. Here we present a new concept for the development, optimisation and fabrication of high-mobility channel materials based on Ge using plasma enhanced chemical vapour deposition of Ge and its recrystallization via millisecond range lateral explosive epitaxy. It is shown that the mechanism of explosive recrystallization (solid vs liquid) can be controlled by Sn co-doping and/or varying the annealing time. An influence of the explosive recrystallization and co-doping of Sn on the dopant activation efficiency and the carrier distribution in the ultra-thin GeOI and Ge NWs after millisecond range flash lamp annealing is discussed. Finally, the nanowire FETs will be presented. - See more at: http://www.european-mrs.com/2015-spring-symposium-z-european-materials-research-society#sthash.fI9UKy1b.dpuf

Keywords: Ge; explosive recrystallization; FLA; GeOI

  • Lecture (Conference)
    2015 E-MRS Spring Meeting, 11.-15.05.2015, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-22538
Publ.-Id: 22538


Optical and electrical properties of ZnO/Si heterostructures after plasma treatment and millisecond annealing

Prucnal, S.; Gao, K.; Zhou, S.; Wu, J.; Cai, H.; Gordan, O. D.; Skorupa, W.

Nowadays, the transparent and conductive ZnO layer is a basic material for the front contact in thin-film photovoltaics. A highly doped n-type ZnO thin layer is an attractive candidate to replace the much more expensive indium-tin-oxide layer in the microelectronic industry. The optoelectronic properties of the ZnO are determined by the type of doping and carrier concentration. The n-type conductivity of ZnO is easily achieved by substitution of Zn by group III elements (Al, Ga, In), or by doping with halogen elements (F, Cl or I) substituting into the oxygen lattice site. Here we will present the utilisation of plasma immersion ion implantation (PIII) and millisecond range flash lamp annealing (FLA) techniques for the formation of highly p- and n-type ZnO films on silicon substrate. Whereas the n-type doping is made by incorporation of F into ZnO, the p-type ZnO films are obtained due to the PIII of N and P. Both p- and n-type dopants are activated using post-implantation millisecond range FLA process. The microstructural and opto-electrical investigations confirm the formation of a high-quality, highly-doped ZnO layer. Moreover the current-voltage characteristics show a heterojunction between ZnO and Si. It is shown that the SF6 plasma treatment efficiently passivates the surface state and bulk defects in the ZnO film significantly improving the near band gap emission from ZnO.

Keywords: ZnO; doping; FLA

  • Lecture (Conference)
    2015 E-MRS Spring Meeting, 11.-15.05.2015, Lille, France

Permalink: https://www.hzdr.de/publications/Publ-22537
Publ.-Id: 22537


Millisecond range liquid phase processing of nanowire structures

Prucnal, S.

A key milestone for the next generation of high-performance microelectronic devices is the monolithic integration of germanium or III-V compound semiconductors with silicon technology. The incorporation of different functional optoelectronic elements on a single chip enables performance progress, which can overcome the downsizing limit in silicon technology. For example, the use of Ge or III-V compound semiconductors instead of silicon as a basic material in nanoelectronic would enable faster chips containing smaller transistors. Conventionally, the integration of III-V semiconductors or Ge with silicon is based on the heteroepitaxial growth of multi-layered structures on silicon or a variety of wafer bonding techniques [1]. Devices based on such structures combine the high carrier mobility and high luminescence efficiency of III-V semiconductors with the advantages of the well-developed silicon technology. On the other hand, the nearly 1D nanostructure of semiconductor nanowires offers a great potential for the future nanoelectronics. Silicon heteronanowires with integrated III-V segments are one of the most promising candidates for nanophotonic devices operating in the single-electron or single-photon regime [2]. Here we present the fundamental research on the physics of Ge micro- and nanostructures and III-V/Si hetero-nanowires to enable the integration of innovative Ge and III-V based devices for the main stream of Si CMOS technology. The proposed concept for the development, optimisation and fabrication of high-mobility channel materials is based on millisecond range explosive epitaxy performed with the flash lamp annealing (FLA) process.

Keywords: FLA; III-V; silicon

  • Invited lecture (Conferences)
    NATO Advanced Workshop “Functional Nanomaterials and Devices for Electronics, Sensors, Energy Harvesting”, 13.-16.04.2015, Lviv, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-22536
Publ.-Id: 22536


Cladding-like waveguide structure in Nd:YAG crystal fabricated by multiple ion irradiation for enhanced waveguide lasing

Shang, Z.; Tan, Y.; Akhmadaliev, S.; Zhou, S.; Chen, F.

We report on a cladding-like waveguide structure in Nd:YAG crystal fabricated by the multiple carbon ion beam irradiation. After the designed multiple irradiation process, the cladding-like waveguide with triple refractive-index layers were constructed in the region near the surface of the crystal. With such a structure, the waveguiding core was compressed and refractive index profile was modified, resulting in a higher light intensity than that of the single ion-beam-irradiated monolayer waveguide. The waveguide lasing at wavelength of 1064 nm was achieved with enhanced performance in the cladding-like structures with both planar and ridge configurations by the optical pump at 810 nm.

Permalink: https://www.hzdr.de/publications/Publ-22535
Publ.-Id: 22535


N and Cr (co-)doping of TiO2 Thin Films Prepared by Reactive Magnetron Sputtering

Gago-Fernandez, R.; Prucnal, S.; Palomares, F. J.; Caretti, I.; Redondo-Cubero, A.; Vinnichenko, M.

The photoactivity of TiO2 has been exploited in many applications ranging from photocatalysis, hydrogen production, pigments or solar cells [1]. However, optical absorption in TiO2 is mostly limited to the ultraviolet region of the solar spectrum (band-gap > 3 eV), triggering strong efforts to achieve visible-light (VISL) response by band-gap narrowing [1]. Non-metal (anion) doping seems to be a promising approach, as shown for the case of nitrogen (N) doped films [2]. However, it is unclear if the effective optical absorption of N-doped TiO2 is based on real band-gap narrowing or the formation of intragap localized states [3]. Recently, it has been argued that narrow-gap TiO2 would require heavy doping, relating VISL absorption to oxygen vacancies and color centers [4]. Another obstacle is the low thermodynamic solubility of dopants at substitutional sites [4]. This situation does not only compromise the effectiveness of band-gap narrowing but also provide recombination centers that are responsible for the loss of photogenerated electron-hole pairs [4]. A recent concept relies on N and Cr co-doping [5] to increase the solubility limit by non-compensated dopants where the opposite charge state of p- and n-type sites substantially enhances the thermodynamic kinetics of dopant pairs. In any case, a critical aspect of cation (co)doping relies in the introduction of large structural distortions in the host TiO2 matrix [4], needing processing or post-processing thermal treatments at moderate temperatures (~500ºC). In this work, we address the production and characterization of TiO2 (co)doped films by magnetron sputtering. We also compare different thermal annealing methods for further dopant activation and enhancement/design of the structural order, with special attention to the influence of as-grown films. The potential of novel rapid thermal processing such as flash-lamp annealing is also explored. The electronic structure of as-grown and modified films is assessed by means of X-ray absorption fine-structure and photoelectron spectroscopy, which permits the analysis of either (nano)crystalline or disordered structures. The optical response is derived from spectroscopic ellipsometry and transmission measurements. Finally, the structural, optical and electronic properties are correlated with the photocatalytic response of the samples. REFS: [1] M.A. Henderson, Surf. Sci. Rep. 66, 185 (2011); [2] R. Asahi et al. Science 293, 269 (2001) ; [3] M. Batzill et al. Phys. Rev. Lett. 96, 026103 (2006); [4] N. Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [5] W. Zhu et al., Phys. Rev. Lett. 103, 226401 (2009)

Keywords: TiO2; nitrogen; band-gap narrowing

  • Lecture (Conference)
    2015 MRS Spring Meeting & Exhibit, 06.-10.04.2015, San Francisco, California, USA

Permalink: https://www.hzdr.de/publications/Publ-22534
Publ.-Id: 22534


Analysis Methods of Magnesium Chips

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

The quality of recycled magnesium from chips depends strongly on their exposure to inorg. and org. impurities that are added during the prodn. processes. Different kinds of magnesium chips from these processes were analyzed by several methods. In addn., the accuracy and effectiveness of the methods are discussed. The results show that the chips belong either to the AZ91, AZ31, AM50​/60, or AJ62 alloy. Some kinds of chips show deviations from the above-​mentioned normations. Different impurities result mainly from transition metals and lime. The water and oil content does not exceed 25​%, and the chip size is not more than 4 mm in the diam. The sieve anal. shows good results for oily and wet chips. The detn. of oil and water shows better results for the application of a Soxhlet compared with the addn. of lime and vacuum distn. The most accurate values for the detn. of water and oil are obtained by drying at 110°C (for water) and washing with acetone (for oil) by hand.

Permalink: https://www.hzdr.de/publications/Publ-22533
Publ.-Id: 22533


Oxyhydroxy silicate colloids: A new type of waterborne actinide(IV) colloids

Zänker, H.; Weiss, S.; Hennig, C.; Brendler, V.; Ikeda-Ohno, A.

At the near-neutral and reducing aquatic conditions expected in undisturbed ore deposits or in closed nuclear waste repositories, the actinides Th, U, Np and Pu are primarily tetravalent. These tetravalent actinides (An(IV)) are sparingly soluble in aquatic systems and, hence, are often assumed to be immobile. However, An(IV) could become mobile if they occur as colloids. This mini-review focuses on a new type of An(IV) colloids, oxyhydroxy silicate colloids. We herein discuss the chemical characteristics of these colloids and the potential implication for their environmental behavior. The binary oxyhydroxy silicate colloids of An(IV) could be potentially more mobile as a waterborne species than the well-known mono-component oxyhydrox-ide colloids.

Keywords: Tetravalent actinides; thorium(IV); uranium(IV); neptunium(IV); silica; colloids; colloid stability; nuclear waste repositories

Permalink: https://www.hzdr.de/publications/Publ-22532
Publ.-Id: 22532


All-optical free electron lasers with Traveling-wave Thomson-scattering -- Realizable with existing machines

Debus, A.; Steiniger, K.; Pausch, R.; Irman, A.; Jochmann, A.; Schramm, U.; Cowan, T.; Bussmann, M.

Optical free-electron lasers (OFEL) based on the Traveling-wave Thomson scattering (TWTS) geometry [*] are realizable using existing petawatt class laser systems and electron beams from either conventional or Laser-wakefield accelerators. Such OFELs operate in the EUV to x-ray range, while at the same time remaining compact with centimeter to sub-meter total length.

Based on results from our analytical 1.5D-theory, as well as numerical investigations, we show using example scenarios that TWTS OFELs can be realized in SASE mode with existing RF sources such as ELBE at HZDR as well as Laser-wakefield accelerated electrons. We detail the necessary equipment for a TWTS OFEL experiment and discuss how current experimental limitations affect the design.

Keywords: Thomson-scattering; X-ray; FEL; PIConGPU; OFEL; optical free-electron laser; EUV; Traveling-wave; TWTS

  • Poster
    37th International Free Electron Laser Conference - FEL2015, 23.-28.08.2015, Daejeon, Südkorea

Permalink: https://www.hzdr.de/publications/Publ-22531
Publ.-Id: 22531


All-optical free-electron lasers with Traveling-wave Thomson-scattering -- Theory and scaling

Debus, A.; Steiniger, K.; Pausch, R.; Irman, A.; Jochmann, A.; Schramm, U.; Cowan, T.; Bussmann, M.

In Traveling-Wave Thomson-Scattering (TWTS) an optical, high-power laser pulse is scattered off a relativistic electron pulse to realize optical ree-electron lasers (OFELs) with a wavelength ranging from ultraviolet to Angstrom [*].

Such TWTS-OFELs optimally exploit the high spectral photon density in high-power laser pulses by spatially stretching the laser pulse and overlapping it with the electrons in a side scattering setup. The introduction of a laser pulse-front tilt provides for interaction lengths appropriate for FEL operation, so that beam electrons witness an undulator field of near-constant strength and wavelength over hundreds to thousands of undulator periods, thus giving enough time for self-amplified spontaneous emission (SASE) to seed the FEL instability and the realization of large laser gains.

In contrast to head-on OFEL schemes, TWTS-OFEL operates at sub-mm to mm effective undulator wavelength. Thus previous show-stoppers to OFELs due to small transverse coherence, large space charge or significant quantum effects are avoided. One of the key advantages of this approach is its scalability to x-ray wavelengths with existing lasers. We present the complete analytical description of the TWTS field and a self-consistent 1.5D theory of TWTS OFELs. We discuss the main scalings of resulting
TWTS OFELs with respect to electron and laser beam properties.

Keywords: Traveling-wave; Thomson scattering; X-ray; EUV; OFEL; FEL; optical free-electron laser

  • Poster
    37th International Free Electron Laser Conference - FEL2015, 23.-28.08.2015, Daejeon, Südkorea

Permalink: https://www.hzdr.de/publications/Publ-22530
Publ.-Id: 22530


Realizing All-Optical Free-Electron Lasers with Traveling-Wave Thomson-Scattering

Debus, A.; Steiniger, K.; Pausch, R.; Bussmann, M.; Irman, A.; Jochmann, A.; Röser, F.; Schramm, U.; Sauerbrey, R.

We show how all-optical free-electron lasers (OFELs) from EUV to the X-ray range can be realized using existing high-power lasers and electron accelerators.

Keywords: Traveling-wave; Thomson scattering; OFEL; FEL; optical free-electron laser; X-ray; EUV

  • Poster
    3rd ARD ST3 Workshop, 15.-17.07.2015, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-22529
Publ.-Id: 22529


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