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41397 Publications

Full-field PIXE imaging: Multi-frame super-resolution to overcome optics pattern and imaging-based resolution limitations

Buchriegler, J.; Klingner, N.; Munnik, F.; Nowak, S. H.; von Borany, J.; Ziegenrücker, R.

The combination of a pnCCD-based detector (264 x 264 pixels) with a polycapillary X-ray optics was installed and examined at HZDR [1]. The set-up is intended for PIXE imaging with protons (2-4 MeV) to survey large, flat/polished geological samples with respect to their (trace) elemental composition. In the standard configuration a 1:1 polycapillary X-ray optics (78 mm length, 20 µm capillary diameter) is used to guide the emitted photons towards the pnCCD-chip divided into nearly 70000 pixels. Their dimensions of 48 x 48 µm² cause a native lateral resolution of about 100 µm. By applying dedicated sub-pixel algorithms to recalculate the footprint of the photon’s electron cloud in the chip [2], this limitation can be bypassed and the lateral resolution is then mainly determined by the capillary’s diameter.
Nevertheless, all images gathered with this kind of set-up from a single measurement are superimposed by the optics pattern. The optics’ capillaries are grouped in hexagonal bundles during the fabrication process and these bundles are grouped together again. This process results in a reduced transparency in the regions where the bundles are joint making the hexagonal pattern visible. This influence can be (largely) removed by combining several short measurements with slightly shifted positions. The optics pattern is averaged out and in addition the lateral information (shift-lengths) can be used to further improve the resolution limit beyond the pixels’/capillaries’ dimensions. The total measurement time can be kept almost similar by dividing the single measurement time by the number of “shots” without losing statistics/sensitivity.
Results from descriptive image-sets of first test-measurements will be shown to demonstrate the potential of this technique for full-field PIXE imaging.

[1] D. Hanf et al., NIM B, Vol. 377, pp. 17-24 (2016).
[2] S.H. Nowak et al., X-ray Spec., Vol. 44 (3), pp. 135-140 (2015).

Keywords: full-field imaging; capillary optics; super resolution

Related publications

  • Lecture (Conference)
    15th International Conference on Particle Induced X-ray Emission, 02.-07.04.2017, Split, Croatia

Permalink: https://www.hzdr.de/publications/Publ-24934
Publ.-Id: 24934


Unravelling the structure of the ocean-continent transition from high resolution, photo-based 3D reconstructions of onshore dyke complexes

Kirsch, M.; Kaiser, A.; Eltner, A.

The temporal and spatial partitioning of strain between faulting and magmatism during continental breakup has important implications for the development of the crust- and upper mantle structure at rifted margins, but remains poorly understood. Late Neoproterozoic basaltic dyke complexes emplaced into continental basement and sedimentary cover units in the northern Scandinavian Caledonides represent an onshore-analogue of an ocean-continent transition. The dykes and their host-rocks are largely unaffected by Caledonian deformation and metamorphism, and are excellently exposed in three dimensions owing to a combination of glacial dissection and glacial retreat. Many of these outcrops of potentially high scientific value remain unmapped, mainly because they occur along steep, up to 300 m high ridges of glacier cirques in rugged mountain terrain that is largely inaccessible for traditional field mapping. Combined terrestrial and UAV-based Structure-from-Motion (SfM) photogrammetry provides an accurate and quick method of obtaining high resolution 3D information of such outcrops with minimal logistical effort. SfM-derived point clouds can be processed to identify structural discontinuities, such as faults and lithological contacts, and extract parameters such as strike, dip, thickness, density, and relative sequence of emplacement of the dykes. Based this information, the history of progressive intrusion and tilting can be reconstructed, and the amount of tectonic extension vs. magmatic dilation estimated. To demonstrate the effectiveness of this approach, we present a case study from a quarry in Lusatia, Germany. Here, like in northern Scandinavia, several generations of cross-cutting basalt dikes are exposed along a vertical, rocky cliff, but with the benefit of easy accessibility, permitting direct observation and verification of the digital data with field measurements. To improve accuracy, and to allow the extraction of oriented and scaled data as well as draping of independently acquired spectral data, ground control points are established in the scene using total station surveying. Multi-and hyperspectral data will potentially be used as complementary information to accurately distinguish composite dikes lacking intervening screens of host-rock.

Keywords: Structure-from-motion photogrammetry; structural geology; rifting

  • Poster
    2nd Virtual Geoscience Conference, 21.-23.09.2016, Bergen, Norway

Permalink: https://www.hzdr.de/publications/Publ-24933
Publ.-Id: 24933


Differential sorption behavior of U(VI) and Pu(VI) dependent on their redox chemistry

Hellebrandt, S.; Knope, K. E.; Lee, S. S.; Lussier, A. J.; Stubbs, J. E.; Eng, P. J.; Soderholm, L.; Fenter, P.; Schmidt, M.

In a recent paper (Schmidt et al. 2013) our group suggested the surface-catalyzed formation of Pu(IV)-oxo-nanoparticles due to an enhanced concentration of Pu(III) at the surface of muscovite mica in equilibrium with a small amount of Pu(IV). The study took three possible pathways for the reaction into account: (1) Pu(III) adsorbs on the muscovite surface, where the oxidation to Pu(IV) takes place. (2) The oxidation of Pu(III) to Pu(IV) happens in solution, whereupon Pu(IV) adsorbs on the surface. In both cases (1) and (2) the increased Pu(IV) concentration leads to oligomerization and afterwards the formation of Pu(IV)-oxo-nanoparticles. Another pathway (3) is the formation of Pu(IV)-oxo-nanoparticles in solution which subsequently adsorb at the mica surface. This pathway was considered less likely, due to a clear enhancement of the reaction in the presence of the interface, which cannot be explained by this process. Motivation of the current study was to test the viability of these mechanisms, but also to investigate the interfacial reactivity of Pu’s various oxidation states.
The mobility of radionuclides in the environment and thus their hazard potential will be controlled by their reactivity at the water/mineral interface. Thus, it is necessary to understand how Pu behave in contact with mineral surfaces on a molecular level, to make reliable long-term predictions about the safety of a nuclear waste repository. In order to understand these processes analytical methods shall ideally be both surface specific and sensitive. X-ray reflectivity techniques, particularly resonant anomalous X-ray reflectivity (RAXR) and crystal truncation rod (CTR) measurements have proven to be a successful combination to investigate geochemical interfacial regimes (Fenter 2002). Plutonium is one of the most important radionuclides in term of nuclear waste disposal due to its long half-life period and high radiotoxicity. That’s why it has been subject of different studies over the last decades. While these studies could show an enhancement of the mobility of plutonium in the presence of colloidal matter (Kersting et al., 1999 and Novikov et al., 2006), the formation of Pu(IV)-nanoparticles is still content of ongoing research (e.g. Kersting 2013, Walther & Deneke 2013).
In the current study a comparison of the interaction of UO2 2+ and PuO2 2+ ([Pu] = 0.1 mmol L-1, [U] = 1 mM mmol L-1, I(NaCl) = 0.1 mol L-1, pH 3.2 ± 0.2) with muscovite mica and the effect of the actinides’ different redox properties were investigated using a combination of surface X ray diffraction, alpha spectrometry and grazing-incidence X-ray adsorption near-edge structure (GI-XANES) spectroscopy. RAXR data of a Pu(VI) solution in contact with muscovite show a broad Pu distribution, which cannot be explained by simple ionic adsorption of PuO2 2+, indicating the formation of Pu(IV)-oxo-nanoparticles. Alpha spectrometry confirms these findings; the occupancy was determined to be ~ 8.3 Pu/AUC (where AUC = 46.72 Å2 is the unit cell area). This means the mechanism of the redox partner independent formation of Pu(IV)-nanoparticles previously observed for Pu(III) can be confirmed for Pu(VI) as well.
UO2 2+ shows clearly different performance. No RAXR signal was observable, indicating no adsorption of UO2 2+. The persistence of the hexavalent oxidation state of U was confirmed by GI-XANES spectroscopy. Furthermore, Alpha spectrometry and GI-XANES spectroscopy showed very weak signals or no signal at all, in agreement with the RAXR findings. Assuming that the sorption behavior of UO2 2+ and PuO2 2+ is equivalent excluding their redox chemistry, no Pu(VI) should be present at the surface. Therefore, the previously proposed mechanism (1) cannot contribute significantly to the observed formation of Pu(IV)-oxo-nanoparticles from Pu(VI) solution. To distinguish mechanisms (2) and (3) UV/Vis spectroscopy was performed similar to our previous study. No Pu(IV) was detectable, even if measured over a longer periode of time than available for the X-ray reflectivity experiment. Hence mechanism (3) also appears to be implausible. Apparently, the observed formation of Pu(IV)-nanoparticles follows mechanism (2). Because of the redox properties of Pu, an equilibrium of Pu(IV), Pu(V) and Pu(VI) will be present in solution. Thus available Pu(IV) will adsorb on the muscovite (001) basal plane. The tetravalent oxidation state of interfacial Pu was confirmed by GI XANES spectroscopy. Since a threshold is reached polymerization occurs as a consequence of hydrolysis, through an olation (Knope et al., 2015) or oxolation (Knope & Soderholm, 2013) mechanism.

Keywords: Plutonium; Pu; Uranium; U; Redox; Sorption; Muscovite; Nanoparticles

  • Lecture (Conference)
    Plutonium Futures - The Science 2016, 18.-22.09.2016, Baden-Baden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24932
Publ.-Id: 24932


Self-Organized Compound Semiconductor Patterning by Polyatomic Ion Irradiation

Bischoff, L.; Böttger, R.; Pilz, W.; Facsko, S.; Heinig, K.-H.

Irradiation of solids by heavy polyatomic ions (e.g Au2, Bi3) can cause localized melting at the ion impact point due to the enhanced energy density in the collision cascade of a polyatomic ion impact [1]. Former studies demonstrated the formation of high aspect ratio, hexagonal dot patterns on Ge, Si and GaAs after high fluence, normal incidence irradiation choosing a suited combination of energy density deposition (i.e. poly- or monatomic ions) and substrate temperature, which facilitated transient melting of the ion collision cascade volume [2-5].
This study underscores the universality of this ion impact-melting-induced, self-organized pattern formation mechanism probing the compound semiconductors InSb and GaSb under polyatomic Au ion irradiation with various irradiation conditions.
Calculations of the needed melting energies per atom (Emelt) for different materials show, that among others InSb and GaSb are preferring candidates for a successful surface patterning by mon- and polyatomic heavy ions.
HRSEM, AFM and EDX analysis of irradiated surfaces reveal that for compound semiconductors, additional superstructures are evolving on top of the regular semiconductor dot patterns, indicating superposition of a second dominant driving force for pattern self-organization.
[1] C. Anders et al., Phys. Rev. B 87 (2013) 245434.
[2] L. Bischoff et al., Nucl. Instr. Meth. Phys. Res. B 272 (2012) 198.
[3] R. Böttger et al., J. Vac. Sci Technol. B 30 (2012) 06FF12.
[4] R. Böttger et al., Phys. Stat. Sol. RRL 7 (2013) 501.
[5] L. Bischoff et al., Appl. Surf. Sci. 310 (2014) 154.

Keywords: Surface pattern; polyatomic ions; temperature; angle of incidence

Related publications

  • Lecture (Conference)
    Workshop für Ionenstrahlen und Nanostrukturen, 12.-15.02.2017, Göttingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24931
Publ.-Id: 24931


Time of Flight Spectrometry in the HIM

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

Time of Flight Spectrometry in the HIM
N. Klingner1,2*, R. Heller1, G. Hlawacek1, J. von Borany1 and S. Facsko1
1 Ion Beam Center (IBC), Institute for Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstraße 400, 01328 Dresden, Germany
2 Technical University Dresden, School of Science, Helmholtzstraße 10, 01069 Dresden, Germany
*n.klingner@hzdr.de
Helium Ion Microscopy (HIM) is well known for its high-resolution imaging and nano fabrication capabilities. However, in terms of analytic capabilities it lacks behind comparable techniques such scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Although several primary and secondary particles are available, to date none of them has been exploited in a practical way to obtain analytic information.
Here, we present the first successful attempt to use time of flight backscattering spectrometry (TOF-BS) and secondary ion mass spectrometry (TOF-SIMS) in the HIM for materials characterization [1]. The successful use of sputtered particles for analytic purposes has also been demonstrated by adding a sophisticated SIMS spectrometer to the HIM [2].
For the TOF measurements the start pulse is generated by chopping the primary beam of the ion microscope using the build-in blanker and a custom made electronics that allows pulse length of 10 ns to 250 ns. The stop signal is given by the arrival of the backscattered particles at the counting micro channel plate. The setup provides high lateral resolution and a good time resolution. Moreover it is minimal invasive to the microscope and therefore the high-resolution capabilities of the device are not derogated when the TOF setup is not in use.
TOF-BS spectra of thin HfO2 films on Si are presented in fig. 1. The time resolution is limited by the physical length of the microscope blanker to approximately 17 ns or 5.4%. This value can be decreased to 2.7% by using a longer flight path. Thanks to a home built scan electronic to control the beam, TOF data can be recorded also in imaging mode. This allows an efficient post acquisition analysis by applying energy filters to extract the elemental distribution. A lateral resolution of 54 nm has been achieved so far. Although this is significantly worse than the native resolution of the tool, this value is close to the physical limit and can be overcome by using correlative approaches in connection with the high resolution SE data available in the HIM.
Modifying the sample holder slightly one can also perform TOF-SIMS. The sputtered particles are accelerated towards the stop detector of the TOF setup by means of a high voltage applied to the sample and a grounded grid. TOF-SIMS spectra obtained from different samples are presented in fig. 2. TOF-BS and TOF-SIMS performed in-situ complement each other and therefore deliver a maximum of compositional information on the sample.

References
[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J. A. Notte, J. Huang, S. Facsko: “Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry”, Ultramicroscopy 162 (2016), 91-97. DOI:10.1016/j.ultramic.2015.12.005
[2] T. Wirtz, P. Philipp, J.-N. Audinot, D. Dowsett, S. Eswara. “High-resolution high- sensitivity elemental imaging by secondary ion mass spectrometry: from traditional 2D and 3D imaging to correlative microscopy”, Nanotechnology 26 (2015), 434001. DOI:10.1088/0957-4484/26/43/434001

Related publications

  • Lecture (Conference)
    The 1st International Conference on Helium Ion Microscopy and Emerging Focused Ion Beam Technologies, 06.10.2016, Luxembourg City, Luxembourg
  • Poster
    Joint ICTP-IAEA Advanced Workshop on High Sensitivity 2D & 3D Characterisation and Imaging with Ion Beams, 28.09.2016, Trieste, Italien

Permalink: https://www.hzdr.de/publications/Publ-24930
Publ.-Id: 24930


Structural, Optical and Electrical Characteristics of Low Temperature Grown BaSrTiOx Thin Films

Bayrak, T.; Goldenberg, E.; Biyikli, N.

Among several perovskite oxides BaSrTiOx (BST) thin films have attracted a great interest for their potentials in oxide-based electronics. However, their reliability and efficiency depend strongly on the precise knowledge of microstructure, as well as optical and electrical constants. In the present work, BST films were deposited using radio frequency magnetron sputtering technique on UV fused silica and Si substrates at room temperature. The dependences of film microstructure, surface morphology, absorption edge, refractive index, and dielectric constants on deposition pressure, partial oxygen flow and the post-deposition annealing were examined by grazing-incidence X-ray diffraction, scanning electron microscopy, spectrophotometry, ellipsometry, as well as photoluminescence, capacitance-voltage and current-voltage measurements. Well-adhered, uniform and amorphous films were prepared at room temperature. For all as-deposited films, the average optical transmission was ~85% in the visible and near infrared spectrum. The refractive indices of BST films were in the range of 1.90 to 2.07 (λ = 550 nm) as a function of deposition conditions. Post-deposition annealing at 800 oC for 1 hr produced polycrystalline films, increased refractive indices and dielectric constants but considerably lowered film optical transmission. Frequency dependent dielectric constants were found to be 46-72, and the observed leakage current was very small ~1A. Initial results revealed that low-temperature-grown BST thin films have promising properties for device applications.

Related publications

  • Poster
    IHRS NanoNET International Workshop, 30.08.-02.09.2016, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-24929
Publ.-Id: 24929


Coulomb breakup of neutron-rich 29,30Na isotopes near the island of inversion

Rahaman, A.; Datta, U.; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Caesar, C.; Carlson, B. V.; Catford, W. N.; Chakraborty, S.; Chartier, M.; Cortina-Gil, D.; de Angelis, G.; Diaz-Fernandez, P.; Emling, H.; Ershova, O.; Fraile, L. M.; Geissel, H.; Gonzalez-Diaz, D.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kröll, T.; Krücken, R.; Kurcewicz, J.; Langer, C.; Le Bleis, T.; Leifels, Y.; Marganiec, J.; Münzenberg, G.; Najafi, M. A.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Plag, R.; Reifarth, R.; Ricciardi, V.; Rigollet, C.; Rossi, D.; Scheidenberger, C.; Scheit, H.; Simon, H.; Taylor, J. T.; Togano, Y.; Typel, S.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Winfield, M.; Yakorev, D.; Zoric, M.; Weigand, J. S.

First results are reported on the ground state configurations of the neutron-rich 29,30Na isotopes, obtained via Coulomb dissociation (CD) measurements.
The invariant mass spectra of these nuclei have been obtained through measurement of the four-momenta of all decay products after Coulomb excitation of those nuclei on a 208Pb target at energies of 400-430 MeV/nucleon using the FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated inclusive Coulomb-dissociation cross-sections (CD) of 89 (7) mb and 167 (13) mb for one neutron removal from 29Na and 30Na, respectively, have been extracted up to an excitation energy of 10 MeV. The major part of one neutron removal, CD cross-sections of those nuclei populate the core, in its’ ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of 29Na(3/2+) and 30Na(2+) is the d-orbital with a small contribution from the s-orbital, which are coupled with the ground state of the core. One of the major components of the ground state configurations of these nuclei are 28Nags(1+) ⊗ νs,d and 29Nags(3/2+) ⊗ νs,d,respectively. The ground state spin and parity of these nuclei obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the s and d orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with shell model calculation using the MCSM suggests a lower limit of around 4.3 MeV of the sd − pf shell gap in 30Na.

Keywords: Coulomb-dissociation 29Na 30Na breakup spin parity

Permalink: https://www.hzdr.de/publications/Publ-24927
Publ.-Id: 24927


In-situ synchrotron studies of dendritic growth in solidifying Ga – In alloys

Grenzer, J.; Shevchenko, N.; Roshchupkina, O.; Baehtz, C.; Hoppe, D.; Cantelli, V.; Rack, A.

X-ray absorption contrast techniques are an important diagnostic tool to investigate solidification processes in metallic alloys. This work is devoted to an in situ visualization of the dendritic growth during the bottom-up solidification of a Ga-25wt%In alloy under natural convection. The coupling of X-ray imaging with X-ray diffraction techniques provides additionally information of the crystallographic orientation of the growing dendrites.
A main advantage of X-ray radiography is the possibility to study simultaneously solidification phenomena on different length scales delivering information on both: the dendrite structure and the flow patterns especially in the vicinity of solidification front. Melt flow, mainly the convective transport of the solute, induces various effects on the dendrite and grain morphology [5]. All these phenomena depend sensitively on the local conditions like the dendrite arm spacing and orientation, the detachment of side branches, the local direction and intensity of the flow it self [3-5]. A more detailed analysis of these particular processes requires a much better spatial resolution. Using synchrotron radiation the spatial resolution of the radiography experiment was improved by more than a factor of 10 reaching a value of below 1µm. Moreover, using synchrotron radiation, the time to record a tomogram was considerably reduced making it possible to visualize a stable dendrite structure in a melt flow.
An other not sufficiently investigated phenomenon is the orientation selection in dendrite evolution. It was demonstrated that the primary dendrite growth directions can vary continuously between different crystallographic directions as a function of the composition–dependent anisotropy parameters [6]. Therefore a challenging part of this experiment was the combination of two in situ techniques: X-ray radiography and synchrotron X-ray diffraction. X-ray diffraction measurements can help to reconstruct crystallographic orientations of growing dendrites.
The first radiography / diffraction experiments with solidifying Ga-25wt%In alloy were performed at BM20 and ID19 at a spatial resolution of < 0.5 µm. The radiography/ diffraction experiments performed at the beamline BM20 were carried out at an energy of 28.5keV, where as at ID 19 the radiography and tomographic experiments were performed at energies at about 65keV using a filtered undulator spectrum without any additional monochromator.
An existing solidification setup and the solidification cell were improved for synchrotron experiments guaranteeing a stable(~0.1°C) temperature gradient to control the convection inside the cell. The nominal composition of the Ga–25wt%In alloy was prepared from 99.99% Ga and 99.99% In. The alloy was melted and filled into the Plexiglas hele-shaw cell with an area of ~230 x 230 mm2 and inner cell thickness of 150μm. The tomography experiment was carried out using a capillary with an inner diameter of 400µm cell.

Keywords: In-Ga alloy solidification crystal growth

Related publications

  • Poster
    XTOP 2016 – 13th Biennial Conference on High-Resolution X-Ray Diffraction and Imaging, 04.-08.09.2016, Brno, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-24926
Publ.-Id: 24926


Structural changes across the metal-insulator transition in thin epitaxial VO2 films

Grenzer, J.; Facsko, S.; Ou, X.; Ji, Y.

Vanadium dioxide (VO2) got much interest in the recent years not only from the fundamental point of view as a correlated electron system but as well as due to its intriguing electrical and optical properties, like the metal-insulator transition (MIT) close to room temperature. This makes VO2 favourable for optoelectronic, switching or even memory devices. The main challenge for device applications is the epitaxial growth of VO2 on suitable substrates. Sapphire seems to be one of the promising substrate candidates for the growth of high quality epitaxial VO2 phases.
Referring to literature, the MIT is directly connected with a change in the crystal structure, namely the transition from the low temperature monoclinic phase (P21/c) to the high temperature tetragonal (rutile) phase (P42/mnm). However, this symmetry change at the transition temperature should be strongly influenced by the epitaxy itself. Comparing our structural investigations and electrical measurements the results indicate that the MIT as observed by the resistance measurement in epitaxial VO2 thin films seems to be not necessary accompanied by a complete monoclinic to rutile phase transformation. A slight lattice distortion causing a possible change in the atomic positions without breaking the existing the epitaxial relationship appears to be sufficient.

Keywords: in-situ X-ray diffraction

  • Poster
    XTOP 2016 – 13th Biennial Conference on High-Resolution X-Ray Diffraction and Imaging, 04.-08.09.2016, Brno, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-24924
Publ.-Id: 24924


Tidally synchronized Tayler-Spruit dynamos

Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.

The dynamo loop in Tayler-Spruit models for the generation of stellar magnetic fields can only be closed if the kink-type Tayler instability (TI) goes along with some alpha effect. While for large magnetic Prandtl numbers (Pm) some finite alpha can easily result from spontaneous symmetry breaking, low Pm systems show typically a vanishing or an oscillatory alpha effect. If the TI, with its typical m=1 azimuthal dependence, is exposed to an m=2 tidal forcing, we observe a sharp resonance if the tidal frequency equals the frequency of theintrinsic alpha oscillation. In the framework of a very simple alpha-Omega dynamo model we further show that this resonance can lead to synchronization of the dynamo. We also discuss the hypothetical possibility that this mechanism could link the 11.07 year periodicity of the tidally dominant Venus-Earth-Jupiter system with the Hale cycle of the solar magnetic field.

  • Lecture (Conference)
    17th MHD Days, 30.11.-02.12.2016, Göttingen, Germany

Permalink: https://www.hzdr.de/publications/Publ-24923
Publ.-Id: 24923


Liquid metal experiments on dynamo action and magnetically triggered flow instabilities

Stefani, F.

The magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. However, magnetic fields also play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects, i.e. hydromagnetic dynamo action and magnetically triggered flow instabilities, had been the subject of purely theoretical investigations. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability (MRI) was observed in the PROMISE experiment in Dresden-Rossendorf. More recently, the azimuthal MRI was found at the same facility. First evidence of the current-driven Tayler instability in a liquid metal was obtained, too. The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities. New results from the enhanced PROMISE facility with a strongly symmetrized azimuthal magnetic fields are presented. An outlook on future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project, is also given.

  • Invited lecture (Conferences)
    European GDR Meeting 2016, 27.06.-01.07.2016, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-24922
Publ.-Id: 24922


The Tayler instability at low magnetic Prandtl numbers: Chiral symmetry breaking and synchronizable helicity oscillations

Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.

The current-driven, kink-type Tayler instability (TI) is a key ingredient of the Tayler-Spruit dynamo model for the generation of stellar magnetic fields, but is also discussed as a mechanism that might limit the up-scaling of liquid metal batteries. Here, we focus on the chiral symmetry breaking and the related alpha-effect that would be needed to close the dynamo loop in the Tayler-Spruit model. For low magnetic Prandtl number, we observe intrinsic oscillations of the alpha-effect. These oscillations serve then as the basis for a synchronized Tayler-Spruit dynamo model, which could possibly link the periodic tidal forces of planets with the oscillation periods of stellar dynamos.

  • Contribution to proceedings
    10th PAMIR International Conference - Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
    Proceedings of the 10th PAMIR International Conference - Fundamental and Applied MHD, 978-88-90551-93-2, 686-690
  • Open Access Logo Magnetohydrodynamics 53(2017)1, 169-178

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Permalink: https://www.hzdr.de/publications/Publ-24921
Publ.-Id: 24921


Flüssigmetallbatterien als stationäre Speicher - Strömungsmechanische Aspekte

Weier, T.; Barry, L.; Galindo, V.; Gerbeth, G.; Landgraf, S.; Seilmayer, M.; Starace, M.; Stefani, F.; Weber, N.

Flüssigmetallbatterien, d.h. elektrochemische Hochtemperaturbatterien mit vollständig flüssigem Inventar, werden derzeit als preiswerte Regelenergiespeicher diskutiert. Das ursprünglich auf kleinere Zellen als Bestandteil thermisch regenerierbarer Systeme gerichtete Konzept soll auf Zellen mit Grundflächen im Quadratmeterbereich übertragen werden.

Eine elektrochemische Zelle mit vollständig flüssigem Inventar hat eine Reihe von Vorteilen: bei gut abgestimmten Dichten von Elektrolyt und aktiven Materialien ist die Batterie selbstassemblierend, eine stabile Dichteschichtung bildet sich aus. Die strukturlosen (flüssigen) Elektroden sind für Alterungserscheinungen unanfällig, versprechen somit gute Zyklierbarkeit, die Kinetik an den flüssig-flüssig Phasengrenzen und die Diffusionsprozesse sind vergleichsweise schnell, was hohe Stromdichten ermöglicht. Als aktive Materialien können breit und ökonomisch verfügbare Ausgangsstoffe eingesetzt werden. Die Ausnutzung positiver Skaleneffekte ist ein wichtiges Mittel zur Kostensenkung und die einfache Skalierbarkeit eine der grundlegenden Annahmen bei der Entwicklung von Flüssigmetallbatterien.

Hohe Stromdichten und große Phasengrenzflächen resultieren jedoch in erheblichen Zellströmen. Diese generieren Magnetfelder und mithin beträchtliche elektromagnetische Kräfte. Das flüssige Inventar der Zelle kann auf diese elektromagnetischen Einwirkungen mit Instabilitäten und elektromagnetisch getriebener Konvektion reagieren. Die Konsequenzen solcher Strömungen und Maßnahmen zu ihrer Begrenzung werden diskutiert und realisierte Flüssigmetallbatterien vorgestellt.

Keywords: Flüssigmetallbatterie; Tayler Instabilität; Elektro-Wirbel-Strömung

  • Invited lecture (Conferences)
    Materialforum Rhein-Main, 22.02.2016, Gelnhausen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24920
Publ.-Id: 24920


Visual observations and charge/discharge behavior of liquid metal cells

Weier, T.; Landgraf, S.; Starace, M.; Stefani, F.; Weber, N.

Liquid metal batteries (LMBs) consist of a stable density stratification of a molten alkaline metal on the top, a liquid heavy metal on the bottom and a fused salt mixture sandwiched in between. Initially developed as part of energy conversion systems, today they are considered an inexpensive means for stationary large-scale storage of electrical energy. A special feature of LMBs is their very high current density enabled by the fast kinetics at liquid-liquid interfaces and the rapid mass transfer processes in fluids. Scale-up on the cell level will therefore result in large total currents per cell that might however trigger electromagnetic instabilities and/or generate electro-vortex flows.
To allow for an experimental verification of the numerical predictions, a number of low temperature liquid metal cells were tested in order to optimize operating conditions and material combinations. The final aim is the construction of a larger cell able to generate a considerable current.
Na and Li were tested as negative electrode materials versus a positive electrode made of Bi in both cases. Na has a relatively high solubility in its salts and forms a dark metal fog in the electrolyte. While this enables the visualization of an intense flow in the electrolyte, it also leads to an unwanted electronic conduction and accompanying capacity fading. Li solubility in its salts is much weaker and no metal fog formation was observed. Cycling behavior in the tethered drop cell is considerably more stable for Li than for Na. Estimated current densities based on the immersed surface of the drop exceed 2 A/cm2 by far, both for Na and Li. Electrolytes are varied as well since for the metal combinations mentioned above the melting point of the salt mixture determines the cell operating temperature.

Keywords: liquid metal battery; electrochemical energy storage

  • Poster
    67th Annual Meeting of the International Society of Electrochemistry, 21.-26.08.2016, Den Haag, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-24919
Publ.-Id: 24919


The Need for Accurate Geometric and Radiometric Corrections of Drone-Borne Hyperspectral Data for Mineral Exploration: MEPHySTo—A Toolbox for Pre-Processing Drone-Borne Hyperspectral Data

Jakob, S.; Zimmermann, R.; Gloaguen, R.

Drone-borne hyperspectral imaging is a new and promising technique for fast and precise acquisition, as well as delivery of high-resolution hyperspectral data to a large variety of end-users. Drones can overcome the scale gap between field and air-borne remote sensing, thus providing high-resolution and multi-temporal data. They are easy to use, flexible and deliver data within cm-scale resolution. So far, however, drone-borne imagery has prominently and successfully been almost solely used in precision agriculture and photogrammetry. Drone technology currently mainly relies on structure-from-motion photogrammetry, aerial photography and agricultural monitoring. Recently, a few hyperspectral sensors became available for drones, but complex geometric and radiometric effects complicate their use for geology-related studies. Using two examples, we first show that precise corrections are required for any geological mapping. We then present a processing toolbox for frame-based hyperspectral imaging systems adapted for the complex correction of drone-borne hyperspectral imagery. The toolbox performs sensor- and platform-specific geometric distortion corrections. Furthermore, a topographic correction step is implemented to correct for rough terrain surfaces. We recommend the c-factor-algorithm for geological applications. To our knowledge, we demonstrate for the first time the applicability of the corrected dataset for lithological mapping and mineral exploration.

Keywords: UAV; UAS; drone; hyperspectral; exploration; processing; structure-from-motion; point matching; Minas de Riotinto

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Permalink: https://www.hzdr.de/publications/Publ-24918
Publ.-Id: 24918


Nonmodal analysis of helical and azimuthal magnetorotational instabilities

Mamatsashvili, G.; Stefani, F.

The helical and the azimuthal magnetorotational instabilities operate in rotating magnetized flows with relatively steep negative or extremely steep positive shear. The corresponding lower and upper Liu limits of the shear, which determine the threshold of modal growth of these instabilities, are continuously connected when some axial electrical current is allowed to pass through the rotating fluid. We investigate the nonmodal dynamics of these instabilities arising from the nonnormality of shear flow in the local approximation, generalizing the results of the modal approach. It is demonstrated that moderate transient/nonmodal amplification of both types of magnetorotational instability occurs within the Liu limits, where the system is stable according to modal analysis. We show that for the helical magnetorotational instability this magnetohydrodynamic behavior is closely connected with the nonmodal growth of the underlying purely hydrodynamic problem.

Keywords: Transient/nonmodal growth; nonormality; magnetorotational instability; liquid metals; astrophysical disks

  • Contribution to proceedings
    10th PAMIR International conference fundamental and applied MHD, 20.-24.06.2016, Cagliari, Italy
  • Open Access Logo Magnetohydrodynamics 53(2017), 107-117

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Permalink: https://www.hzdr.de/publications/Publ-24917
Publ.-Id: 24917


Dynamics of homogeneous shear turbulence: a key role of the nonlinear transverse cascade in the bypass concept

Mamatsashvili, G.; Khujadze, G.; Chagelishvili, G.; Dong, S.; Jiménez, J.; Foysi, H.

To understand the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain with subsequent analysis of the dynamical processes in spectral or Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of Fourier harmonics of perturbations due to the shear flow non-normality. This non-normality-induced growth, also known as nonmodal growth, is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space is the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade. This course of events reliably exemplifies a well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance: Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) varies, but always remains quite large (equal to 36, 86, and 209) in the considered here three aspect ratios. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models.

Keywords: Transient growth; turbulence; bypass concept

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Permalink: https://www.hzdr.de/publications/Publ-24916
Publ.-Id: 24916


RLumShiny - A graphical user interface for the R Package ’Luminescence’

Burow, C.; Kreutzer, S.; Dietze, M.; Fuchs, M.; Fischer, M.; Schmidt, C.; Brückner, H.

Since the release of the R package ’Luminescence’ in 2012 the functionality of the package has been greatly enhanced by implementing further functions for measurement data processing, statistical analysis and graphical output. Along with the accompanying increase in complexity of the package, working with the command-line interface of R can be tedious, especially for users without previous experience in programming languages. Here, we present a collection of interactive web applications that provide a user-friendly graphical user interface for the ’Luminescence’ package. These applications can be accessed over the internet or used on a local computer using the R package ’RLumShiny’. A short installation and usage guide is accompanied by the presentation of two exemplary applications.

Keywords: R; Software; GUI; Luminescence dating; Abanico Plot; Cosmic Dose Rate

  • Open Access Logo Ancient TL 34(2016)2, 22-32

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Permalink: https://www.hzdr.de/publications/Publ-24915
Publ.-Id: 24915


Collision cascades enhanced hydrogen redistribution in cobalt implanted hydrogenated diamond-like carbon films

Gupta, P.; Becker, H.-W.; Williams, G. V. M.; Hübner, R.; Heinig, K.-H.; Markwitz, A.

Hydrogenated diamond-like carbon films produced by C3H6 deposition at 5 kV and implanted at room temperature with 30 keV Co atoms to 12 at.% show not only a bimodal distribution of Co atoms but also a massive redistribution of hydrogen in the films. Resonant nuclear reaction analysis was used to measure the hydrogen depth profiles (15N-method). Depletion of hydrogen near the surface was measured to be as low as 7 at.% followed by hydrogen accumulation from 27 to 35 at.%. A model is proposed considering the thermal energy deposited by collision cascade for thermal insulators. In this model, sufficient energy is provided for dissociated hydrogen to diffuse out of the sample from the surface and diffuse into the sample towards the interface which is however limited by the range of the incoming Co ions. At a hydrogen concentration of ∼35 at.%, the concentration gradient of the mobile unbounded hydrogen atoms is neutralised effectively stopping diffusion towards the interface. The results point towards new routes of controlling the composition and distribution of elements at the nanoscale within a base matrix without using any heat treatment methods. Exploring these opportunities can lead to a new horizon of materials and device engineering needed for enabling advanced technologies and applications.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24913
Publ.-Id: 24913


Compositional Calibration

van den Boogaart, K. G.; Tolosana-Delgado, R.; Renno, A. D.

An emerging field in the statistics of (geo)chemical data is compositional data analysis. In this field the ratio of concentrations between elements is seen as the essential information, while the absolute concentration is considered irrelevant. E.g. for physical age determination the ratio of concentration of various nuclides is very important, while the absolute concentrations change subject to dilution and depletion processes. In many applications chemical data is rescaled to 100%, or transformed with a log ratio transformation. In both cases the information about the absolute concentration is lost.

The aim of the contribution is to initiate a discussion on how the compositional approach might modify the tasks and methods of metrology. Asking a sligthly different question might lead to different answers. We will consider the calibration of an LA-ICP-MS (laser ablation inductive coupled plasma mass spectrometer), which measures multiple, but not all elements (quasi) simultaneously.

If log ratios are considered the relevant quantity, we should be able to measure them unbiasedly and provide a precision assessment of their measurement. We show that both aspects are problematic, when the log ratio is applied to measurements independently calibrated with respect to absolute standards. The same individual absolute errors can correspond to very different relative errors due to inherent correlation between the counts.

A supplementary concept for a traceable calibration of relative concentrations is introduced and discussed. In the example we use a method based on multivariate Poisson regression for a compositional calibration of LA-ICP-MS measurements. A compositionally calibrated measurement does not carry absolute information, but only relative information about a subset of elements. The concept of a compositional error compatible with the variance concepts in compositional data analysis is introduced. This error can not be computed from classical absolute calibration information of single elements and provides essential information for compositional methods.

In the case of the LA-ICP-MS the absolute amount of material turned into plasma is strongly matrix dependent, while the counting ratios for different elements are much less so. In such cases a relative calibration can guarantee better compositional precision and allows the useage of much loosely matrix-matched standards in a well-defined range of matrix compositions.

  • Lecture (Conference)
    MATHMET 2016 - International Workshop on Mathematics and Statistics for Metrology, 07.-09.11.2016, Berlin, Germany
  • Lecture (Conference)
    Geoanalysis 2022, 06.-12.08.2022, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24912
Publ.-Id: 24912


Filtering lack of microhomogeneity in reference materials for microanalytical methods

van den Boogaart, K. G.; Renno, A. D.; Tolosana-Delgado, R.

Homogeneity is a relative property of a sample in relation to the measurement (analytical method), the analyte, and the intended purpose, like the usage as a reference material (RM). The verification of homogeneity is essential to define a RM as fit for purpose. In this context, there have been recent efforts to check the possible superiority of synthetic RMs over natural ones. The assessment of homogeneity is an integral part of these synthesis tests and of the following certification for use as RM. With regard to their spatial variability, five types of microheterogeneity of RMs can be found in the literature, depending on which is the source of heterogeneity that it presents: random, systematic, periodic, nugget and island.

This contribution presents a first attempt towards such tests of microhomogeneity for discussion. In a first step, we define a stochastic random function model that will describe each of the types of microheterogeneity mentioned before. Then, in a quite natural manner a particular sampling strategy for each of them is derived in the second step, with the goal to filter out the undesired source of variability. In the third step, we derive a strategy of characterization of the material, namely a strategy of estimation of the heterogeneity properties of the RM that should be used to certify the reference nature of the material. These the adequacy of these strategies is shown in this contribution by using simulations of the several heterogeneity structures and of the proposed sampling and characterization strategies.

For instance, for the case of a random heterogeneity we may assume that the concentration of the target element is described by a random function (RF). If the covariance function of this RF would be known, the sampling strategy would be to repeat measurements on random positions of a very fine regular grid in such a way that the variance of their average decreases as fast as possible, using as many locations as necessary to ensure that it falls below the method specifications. Finally, the way to characterise the RM would require calibrating the concentration of the target element on a coarser grid, on as many locations as necessary to appropriately set the covariance function, using classical concepts and models of Geostatistics. Similar strategies can be derived for the rest of the heterogeneity structures, like robust methods for nugget heterogeneity or geostatistical concepts related to intrinsic functions of order k for systematic heterogeneity

  • Lecture (Conference)
    MATHMET 2016 - International Workshop on Mathematics and Statistics for Metrology, 07.-09.11.2016, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24911
Publ.-Id: 24911


Resource Model Updating by Compositional Sequential Ensemble Filtering

Prior-Arce, A.; Tolosana-Delgado, R.; Verlaan, M.; Bendorf, J.

In mining engineering, resource and grade control models aim to characterize the spatial distribution generating by geostatistics methods of ore tonnage and grade in an deposit. A continuously self-updating resource model concept has recently been developed by Wambeke and others (2016) and aims to improve the raw material quality control and process efficiency of any type of mining operation. The proposed concept integrates sensor data measured with different support along the production line into the resource or grade control model and provides continuously locally more accurate estimates. Applications in underground mines include the identification of different components of the mineralogy and geochemistry.

This study aims to develop an efficient updating framework based on a sequential ensemble filtering on a compositional environment (Tolosana-Delgado (2013)). The importance of respecting as well physical conservation principles has long been recognized. During the data assimilation procedure, the mass of each component should be preserved within each ensemble member through the procedure used to update the model. Different approaches to constraining ensemble based Kalman Filters have been presented as solutions of a set of regularized least squares optimization problems. Some of these have been formulated by imposing non-negativity constrains or by using transform methods such as anamorphosis, at the price of violating mass preservation.

Compositional approaches supersede this problem by dealing with the positivity condition and the mass preservation implicitly through assimilating log-ratios instead of the original components. After a detailed literature review, a compositional sequential ensemble filter approach adapted to specific application in mining is presented. Method validation results are presented for a 2D case study in a fully controllable environment. After validation, a sensitivity analysis investigates the effects of different parameters and derived practical implementation aspects for an effective application.

This research is part of the European Union funded "Real Time Mining" project, which aims at developing a new framework to reduce uncertainties during the block extraction process. New sensor based technology will provide georeferenced information about mineralogy and grades by taking images of the mine face, during block extraction from the muckpile, or via sensors installed on the conveyor belt about the mean composition of the ores. Based on a discrete time event simulation, the project will test the capabilities of incorporating sensor imaging information as pointwise data and of mean compositions as block data.

  • Lecture (Conference)
    CoDaWork 2017, The 7th International Workshop on Compositional Data Analysis, 06.-09.06.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24910
Publ.-Id: 24910


Applications of the atomic force microscope in flotation research

Babel, B.; Rudolph, M.

This abstract gives an overview of the applications of the Atomic Force Microscope (AFM) in flotation research. The AFM, which has a broad application in different disciplines, is a versatile tool to measure surface properties and particle-particle interactions. In the field of mineral processing the AFM can be utilized to gather information of mineral surfaces such as the surface roughness or particle-particle interactions related to separation processes like magnetic separation, triboelectric separation and flotation. In the context of flotation it is possible to measure the hydrophobic interaction between a colloidal probe (CP-AFM) and the mineral surface. One drawback of this technique is the missing link between the hydrophobicity and the chemical composition of the mineral surface, respectively the adsorbed layers. This limitation can be exceeded by the combined utilization of the AFM and Raman Spectroscopy named Tip-Enhanced Raman Spectroscopy (TERS). This surface sensitive technique enables the chemical analysis of thin films with nanometer resolution by the utilization of a plasmonic effect that occurs at the surfaces of noble metal nanoparticles. The aim is the detection of adsorbed flotation reagents on mineral surfaces. The combination of TERS and CP-AFM measurements enables the investigation of the adsorption of flotation reagents on mineral surfaces and their effect on hydrophobicity.

As outlined the application of the AFM in mineral processing can give a deeper understanding of occurring micro processes and thereby a better physical and chemical description of macro processes. Especially TERS offers a better understanding of the adsorption of flotation reagents.

The paper presents fundamental investigations of CP-AFM and TERS on actual mineral specimens (quartz, cassiterite, apatite, calcite, scheelite) which are prepared to achieve a surface roughness of less than 10 nm. The impact of collector and depressant adsorption on the measurement, i.e. hydrophobic interactions with CP-AFM and vibrational spectroscopy with TERS is shown.

Keywords: atomic force microscope; tip-enhanced Raman spectroscopy; flotation

  • Poster
    XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec city, Canada

Permalink: https://www.hzdr.de/publications/Publ-24909
Publ.-Id: 24909


Analysis of temporal changes of a mining site affected by AMD. UAV based hyperspectral monitoring of the Litov tailing (Sokolov, CZ)

Jackisch, R.; Jakob, S.; Zimmermann, R.; Gloaguen, R.

In this study we test and validate hyperspectral mineral mapping for acid mine drainage (AMD) detection using Unmanned Aerial Systems (UAS). The investigated area is a re-cultivated tailing and part of the Sokolov coal mine district in the Czech Republic. The dumped mining waste material bears pyrite and the consecutive weathering products. Mainly iron hydroxides and oxides affect the natural pH values of the Earth’s surface. While previous research done in this area relies on satellite and air-borne data, our approach focuses on lightweight drone systems providing ground readiness within hours. During April to September 2016, several field and flight campaigns were conducted. For validation, the waste heap was probed in-situ for pH, X-ray florescence (XRF), reflectance spectrometry and surveyed by GPS. Collected samples were measured for pH, X-ray diffraction (XRD) and XRF in laboratory conditions. A new in-house developed toolbox allowing the processing as well as the correction of topography and illumination effects, is applied on the UAS data. High-resolution point clouds and digital elevation models are build from UAS-borne data with Structure-from-Motion photogrammetric techniques. Changes of the canopy, topographic profiles and erosion values are derived from the 3D models. The classification of hyperspectral (HS) data detected the proposed minerals jarosite and goethite, which are associated with the acidic environmental conditions (mean pH = 2.9). The specific iron absorption bands are visible in the UAS-HS data, and can be confirmed with ground-truth spectroscopy. Evaluation of geochemical data shows a negative correlation for pH with sulfur content, which is in accordance with previous studies on AMD conditions. Interpolations of in-situ pH data support the UAS-based results. The evaluation of the applied methods highlights the UAS approach as a fast, non-invasive, inexpensive technique for multi-temporal monitoring.

Keywords: Hyperspectral; AMD; remote sensing; UAS; pH mapping; Absorption feature

  • Lecture (Conference)
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-24908
Publ.-Id: 24908


Drone-borne hyperspectral remote sensing of REE deposits in Namibia

Booysen, R.; Gloaguen, R.; Zimmermann, R.; Jakob, S.

Traditional exploration techniques are mainly based on extensive field work supported by geophysical surveying. These techniques can be restricted by field accessibility, financial status, area size and climate. Therefore, we suggest to increase the use of multi-scale hyperspectral remote sensing in order to decrease conventional restrictions in the exploration of minerals through the use of Unmanned Aerial Systems (UAS). We further argue that the addition of drone based hyperspectral data can vastly improve the accuracy of field mapping in future mineral exploration. Drone-borne measurements can supplement and direct geological observation immediately in the field and therefore allow better integration with in-situ ground investigations. In particular, in inaccessible and remote areas with little infra-structure, such systems are beneficial because it allows a systematic, dense and completely non-invasive surveying, which is often not possible using ground- based techniques. We use a hyperspectral camera attached to a hexacopter to acquire data from the visible (VIS) to the near-infrared (NIR) range of the electromagnetic spectrum. The hyperspectral data is then corrected of radiometric and geometric distortions using a new python-based in-house toolbox. In addition, high-resolution Digital Surface Models (DSM) and Orthomosaics are generated from drone data using Structure- from-Motion photogrammetry. The corrected data provide information on the spectral signatures of outcropping lithologies to the field geologists and the exploration teams. This is achieved by using end-member modelling and classification techniques such as non- linear machine learning algorithms, e.g., Neural Networks and tree based methods. The validation of the hyperspectral data is performed via field spectroscopy and portable XRF. The proposed method is currently tested on carbonatite-hosted REE occurrences in several locations in Namibia. These locations are characterised by difficult terrains and remote environments, that would impede or restrict traditional field surveys. Preliminary results indicate that UAS-based surveying has a very high potential in fundamentally lowering the acquisition costs and increasing the information potential of data captured in the field.

  • Lecture (Conference)
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-24907
Publ.-Id: 24907


Integrated drone-borne and ground-based hyperspectral imaging for exploration targeting

Herrmann, E.; Zimmermann, R.; Gloaguen, R.

The Iberian Pyrite Belt (IPB) in Southwest Spain and South Portugal is best known for its numerous massive sulphide deposits. With their 4000 years history of mining, the mines of Rio Tinto are of important economic importance in the IPB. Orebodies and related alteration zones were mined for copper, gold, silver and many other pre- cious metals. We selected this site as a case study for the exploration of massive sulphide deposits due to its excellent data basis, economic importance and excellent outcrops. Ground-based and drone-borne hyperspectral data were acquired during 3 field campaigns in 2017 and 2017. Drone-borne hyperspectral images are acquired by a RIKOLA Hyperspectral Imager in the wavelength range from 500 to 900 nm. Not only spectral information can be gathered that way, overlapping images can also be used to calculate 3D surface models using Structure-from-Motion photogrammetry. Resulting point cloud can be basis for 3D data integration and correlation of spatial orientation of surfaces to spectral characteristics. Ground-based data are acquired with a Specim AisaFenix hyperspectral camera with a wavelength range from 400 to 2500 nm.
A complex geological history lead to the appearance of numerous regional geochem- ical and structural characteristics correlated to the orebodies that comprise different types of syn- and post-mineralisation alteration zones. These features are hardly re- cognisable using classical geological fieldwork techniques. Until now, time consum- ing and expensive geological interpretations rely almost exclusively on geochemical data. Instead, we argue that by using in hyperspectral data, those alteration zones can easily be determined, due to characteristic features in the VNIR and SWIR range. This provides a powerful tool for a fast, low-cost and spatially precise altera- tion mapping to guide the exploration process. The result of this data integration is comparable to an early stage geological surface model. It can provide a very precise tool for exploration and mining at all stages.
We chose the Corta Atalaya in Riotinto/Spain, one of the most profitable mines in the Spanish part of the Iberian pyrite belt, to demonstrate this approach of modern, re- mote sensing based geological exploration methods. Methods include traditional al- gorithms like Spectral Feature Fitting and Mapping absorption wavelength, but also non-linear unsupervised classification algorithms. Different kind of alteration zones are discriminated and interpreted in terms of their spectral-spatial distribution.

  • Poster
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-24906
Publ.-Id: 24906


Hyperspectral imaging for structural geology: An example for more interdisciplinary data analysis in mineral exploration

Zimmermann, R.; Herrmann, E.; Rosa, D.; Kirsch, M.; Gloaguen, R.

Since the applications of hyperspectral imaging found their way into geological investigations, mineral mapping has reached a completely new level of spatial and spectral resolution. Thanks to increasing technological developments in hyperspectral imaging, system resolutions steadily became better at lower prices. Although these methods are already frequently applied in the field of economic geology and petrology, so far, these techniques have rarely been used for structural mapping and interpretation. The actual tool of choice, photogeology, makes just the use of true-color RGB images. However, detailed mineral and lithological maps from hyperspectral imaging can bring a new dimension. Hyperspectral imaging can highlight small mineralogical differences in rocks that cannot be picked-up in traditional RGB images and thus allow lithological contacts to be easily identified. Potential applications include, e.g., mapping dykes of different spectral signatures and their genetic relations or folds in (inaccessible) homogeneous rocks like marbles or quartzites. Furthermore, different types of alteration, associated with structural information can allow the detection of pathways for mineralising fluids and their structural control, one of the most important application of applied structural geology in mineral exploration. Potential methods include mapping absorption wavelength, spectral unmixing and non-linear classifications. All hyperspectral results are integrated into 3D point-clouds for interpretation. We exemplify the interdisciplinary analysis of hyperspectral data, independent of scale and source and their use for structural geology.
In the first case the barely accessible, 1000 m high marble cliffs of Maarmorilik/Greenland were scanned with a ground-based hyperspectral imaging (HSI) system. In certain structural positions a Pb-/Zn-mineralisation is hosted. A preliminary analysis with focus on carbonate mineralogy using absorption wavelengths identified fold structures of calcite-rich and dolomite-rich marbles, which are not visible in standard RGB images. Furthermore, some marble horizons are rich in evaporite minerals (e.g., anhydrite). The distribution of those horizons is mapped using spectral unmixing techniques and can be used to elucidate the structural relationship between deformation, mineralising fluids and ore emplacement.
At the inaccessible mine-pit of Peña de Hierro/Spain hyperspectral imaging is used to enhance the understanding of ore emplacement in relation with faults. Various mineral mapping methods, e.g., Spectral Feature Fitting, and non-linear unsupervised clustering, e.g., Self-Organising Maps, are applied. Faults and folds can easily recognised in RGB images here. However, in hyperspectral data we observe a degradation of hydrothermal activity around faults and orebodies that lead to a better understanding of the interaction between faulting and ore emplacement. Small scale structures in overlying meta- sedimentary rocks are highlighted in hyperspectral images too. They give indication of post-mineralisation deformation and, thus, pathways for secondary alteration and ore replacement.

  • Poster
    10th EARSeL SIG Imaging Spectroscopy Workshop, 19.-21.04.2017, Zürich, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-24905
Publ.-Id: 24905


Modeling patterns of anatomical deformations in prostate patients undergoing radiation therapy with an endorectal balloon

Brion, E.; Richter, C.; Macq, B.; Stützer, K.; Exner, F.; Troost, E.; Hölscher, T.; Bondar, L.

External beam radiation therapy (EBRT) treats cancer by delivering daily fractions of radiation to a target volume. For prostate cancer, the target undergoes day-to-day variations in position, volume, and shape. For stereotactic photon and for proton EBRT, endorectal balloons (ERBs) can be used to limit variations. To date, patterns of non-rigid variations for patients with ERB have not been modeled. We extracted and modeled the patient-specific patterns of variations, using regularly acquired CT-images, non-rigid point cloud registration, and principal component analysis (PCA). For each patient, a non-rigid point-set registration method, called Coherent Point Drift, (CPD) was used to automatically generate landmark correspondences between all target shapes. To ensure accurate registrations, we tested and validated CPD by identifying parameter values leading to the smallest registration errors (surface matching error 0.13+-0.09 mm). PCA demonstrated that 88+-3.2% of the target motion could be explained using only 4 principal modes. The most dominant component of target motion is a squeezing and stretching in the anterior-posterior and superior-inferior directions. A PCA model of daily landmark displacements, generated using 6 to 10 CT-scans, could explain well the target motion for the CT-scans not included in the model (modeling error decreased from 1.83+-0.8 mm for 6 CT-scans to 1.6+-0.7 mm for 10 CT-scans). PCA modeling error was smaller than the naive approximation by the mean shape (approximation error 2.66+-0.59 mm). Future work will investigate the use of the PCA-model to improve the accuracy of EBRT techniques that are highly susceptible to anatomical variations such as, proton therapy.

Keywords: External beam radiation therapy; nonrigid registration; principal component analysis; mathematical modeling; motion management in radiotherapy; prostate cancer

  • Contribution to proceedings
    SPIE Medical Imaging 2017, 11.-16.02.2017, Orlando, USA
    Proc. SPIE 10135, Medical Imaging 2017: Image-Guided Procedures, Robotic Interventions, and Modeling: SPIE digital library, 1013506-1-1013506-9
    DOI: 10.1117/12.2251933
    Cited 1 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-24904
Publ.-Id: 24904


Understanding actinide reactivity at the water-mineral interface

Stumpf, T.

The behaviour of radionuclides in the environment is determined by interfacial reactions such as adsorption, ion exchange and incorporation processes. In literature such processes are often described by operational solid-liquid distribution ratios (Rd values). Distribution ratios are defined as the ratio of the quantity of a radionuclide sorbed per solid mass and the equilibrium concentration of the radionuclide. They are macroscopic parameters which are strictly valid only for the mineral and solute combination in the experimental system. For reliable and trustworthy long-term predictions of radionuclide transport behaviour, interaction mechanisms and processes occurring at the solid-water interface, they need to be understood at the molecular level. This can only be achieved by the application of spectroscopic methods.
In the talk a multi-spectroscopic approach will be presented. We used a combination of microscopy, laser and X-ray based techniques to gain process understanding on a molecular level of the interaction of actinides with mineral surfaces. The derived data are used to improve surface complexation modelling. Therefore, the advanced spectroscopic techniques used in Dresden-Rossendorf are an important contribution to the long-term performance assessment of a nuclear waste disposal.

Keywords: radionuclides; nuclear waste disposal

  • Invited lecture (Conferences)
    les Journées Nationales de Radiochimie et de Chimie Nucléaire (JNR) 2016, 08.-09.09.2016, Nice, Frankreich
  • Lecture (Conference)
    Frontiers in Environmental Radioactivity 2016, 06.-07.01.2016, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-24902
Publ.-Id: 24902


Electron effective mass enhancement in Ga(AsBi) alloys probed by cyclotron resonance spectroscopy

Pettinari, G.; Drachenko, O.; Lewis, R. B.; Tiedje, T.

The effect of Bi incorporation on the conduction band structure of Ga(AsBi) alloys is revealed by a direct estimation of the electron effective mass via cyclotron resonance absorption spectroscopy at THz frequencies in pulsed magnetic fields up to 65 T. A strong enhancement in the electron effective mass with increasing Bi content is reported, with a value of mass ∼40% higher than that in GaAs for ∼1.7% of Bi. This experimental evidence unambiguously indicates a Bi-induced perturbation of the host conduction band states and calls for a deep revision of the theoretical models describing dilute bismides currently proposed in the literature, the majority of which neglect or exclude that the incorporation of a small percentage of Bi may affect the conduction band states of the host material.

Permalink: https://www.hzdr.de/publications/Publ-24901
Publ.-Id: 24901


Organic synthesis, radiofluorination and in vitro evaluation of two novel fluorenones targeting the alpha 7 nicotinic acetylcholine receptor (α7 nAChR)

Scheunemann, M.; Teodoro, R.; Wenzel, B.; Deuther-Conrad, W.; Steinbach, J.; Brust, P.

Objectives: Derivatives of the antiviral drug tilorone have recently been discovered as novel α7 nAChR ligands. Based on a tricyclic heteroaromatic unit linked to one or two conformationally rigidified cyclic amines, highly affine compounds were obtained [1]. [18F]DBT10 [2] and [18F]ASEM [3] (Fig.) were developed as promising α7 nAChR PET tracers. This study investigates bioisosteric sulfur-free analogues of DBT10 and its ortho-isomer obtained by replacement of the functional group SO2 by CO.
Methods: The p-fluoro and o-fluoro derivatives 1 and 2 and the corresponding nitro precursors were prepared in three and five steps from the appropriate nitro-fluoren-9-ones. Affinities towards human α7, α4β2, and α3β4 nAChRs were determined. Radiosynthesis of [18F]1 and [18F]2 via nucleophilic aromatic radiofluorination was optimised and finally performed using an automated module. In vitro autoradiography of [18F]1 on pig brain slices was performed.
Results: The fluorenones 1 and 2 were prepared in 25% yield. Both bind with high affinity and selectivity towards nAChRs (1: Ki = 1.18 nM, 1500 nM, and 46.0 nM; 2: Ki = 1.12 nM, 1796 nM, and 33.2 nM for α7, α4β2, and α3β4 nAChR, respectively). Highest labeling efficiencies (≈ 80%) were obtained in DMF under microwave assisted heating, yielding [18F]1 and [18F]2 with radiochemical purities of ≥ 97% and molar activities of 30 ± 6 GBq/μmol and 44 ± 3 GBq/μmol, respectively. Binding of [18F]1 on pig brain slices was markedly reduced by α7 nAChR-specific ligands.
Conclusions: New highly affine α7 nAChR ligands were synthesized based on the tilorone scaffold by replacement of the SO2 by a CO group. The high nitro-to-[18F]fluoro conversion obtained for the fluorenones suggests a comparable electron withdrawing effect of the two functionalities. Further studies will investigate the potential of [18F]1 and [18F]2 as PET imaging agents.
References [1] M. R. Schrimpf, K. B. Sippy, C. A. Briggs, et al. Bioorg. Med. Chem. Lett. 2012, 22, 1633-1638. [2] R. Teodoro, M. Scheunemann, W. Deuther-Conrad, et al. Molecules 2015, 20, 18387-18421. [3] A. G. Horti, Y. Gao, H. Kuwabara, et al. J. Nucl. Med. 2014, 55, 672-677.

Keywords: α7 nAChR ligands; fluorenones; radiofluorination

  • Poster
    22nd International Symposium On Radiopharmaceutical Sciences (ISRS 2017), 14.-19.05.2017, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)1, 585
    DOI: 10.1002/jlcr.3508
    ISSN: 1099-1344
    Cited 3 times in Scopus

Permalink: https://www.hzdr.de/publications/Publ-24900
Publ.-Id: 24900


Emission spectroscopy for the identification of rare earth elements using laser-induced photoluminescence

Fuchs, M. C.; Gloaguen, R.; Beyer, J.; Jakob, S.; Heitmann, J.

We present rare earth element (REE) emission spectra stimulated by lasers with wavelength of 325 nm, 442 nm and 532 nm. Measured spectra represent REE standards in phosphates and fluorides, one set embedded in epoxy resin and one set in form of free-standing single grains. The comparison of emission features from the different specimen allows to evaluate, which emission peaks are robust and unequivocal for REE identification. Results showed that photoluminescence spectroscopy allows successful identification of characteristic emission peaks for Dy3+, Er3+, Eu3+, Gd3+, Nd3+, Sc3+, Sm3+, Tb3+, and Yb3+, when using laser stimulation at 325 nm. However, strong matrix emissions such as from epoxy resin may mask weaker luminescence emissions. In such cases, the adequate choice of longer stimulation wavelength is crucial to suppress the strong matrix emission without loosing the REE luminescence. Using laser stimulation at 442 nm and 532 nm shows promising results, but the optimal laser wavelength seems to be REE-specific and consequently, requires comprehensive analyses.

Keywords: emission spectroscopy; photoluminescence; rare earth elements; exploration; raw materials

  • Lecture (Conference)
    WHISPERS - 8th workshop on hyperspectral image and signal processing, 21.-24.08.2016, Los Angeles, USA

Permalink: https://www.hzdr.de/publications/Publ-24898
Publ.-Id: 24898


Preclinical Applications of Brain PET/MRI

Deuther-Conrad, W.

The two imaging techniques positron emission tomography (PET) and magnetic resonance imaging (MRI) enable advanced in vivo imaging in different fields of biomedical research. The combination of these two imaging modalities into a single device merges functional and morphologic information. High-resolution MRI of morphology with good soft-tissue contrast and spectroscopic detection of endogenous metabolite distributions is completed by means of high-sensitive PET by functional parameters such as glucose metabolism, amino acid transport, proliferation, receptor density, or drug concentration.
In preclinical research, the acquisition of PET and MR images of the same animal has been realized using different strategies in recent years. While initially most studies have been performed on separate devices with subsequent co-registration of the images, new and more integrated systems are available. Accordingly, fused images are obtained by the use of (i) separate instruments, (ii) in-line/sequential PET/MRI, or (iii) fully integrated PET/MRI scanners. Preclinical PET/MRI benefits in particular brain imaging in various small-animal models of diseases, including genetically-engineered animals. By providing a powerful tool for identification as well as functional characterization of new drug targets or disease biomarkers, the obtained information supports e.g. the development and follow-up of the efficacy of accordingly targeting drugs significantly.
Our research group at the Helmholtz-Zentrum Dresden-Rossendorf has been focused on the development of radiopharmaceuticals for brain PET imaging for almost two decades. Four newly developed radioligands for imaging of depression and dementia have been translated into human application within the last eight years. Related to the programme-oriented research within the Helmholtz Association the main emphasis of the group has recently moved into cancer research trying to visualize and characterize molecular switches which are involved in brain tumor development and progression by means of preclinical PET/MRI.

  • Invited lecture (Conferences)
    BRAIN & BRAIN PET 2017, 01.-04.04.2017, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24897
Publ.-Id: 24897


3D Mapping of electric potentials and magnetic fields at the nanoscale using Electron Holographic Tomography

Wolf, D.; Lubk, A.; Lichte, H.

Off-axis electron holography (EH) is a TEM technique that records the phase information of an electron wave transmitted through a thin specimen in an electron hologram. By reconstructing this phase information, it enables electrostatic and magnetic potentials to be mapped quantitatively with high spatial resolution and, when combined with tomography to electron holographic tomography (EHT), in three dimensions (3D) [1,2]. Tomograms obtained by EHT provide the 3D mean inner potential (MIP) distribution of nanoscale materials from which the 3D morphology and the chemical composition can be inferred [3]. Moreover, functional potentials, e.g., introduced by doping of impurities in semiconductors, have been successfully revealed in 3D [4]. Recently, we succeeded in the 3D reconstruction of the axial component of the B-field prevailing in magnetic nanowires [5,6].

EHT as applied on magnetic samples proceeds as follows (see Fig. 1): (1) an electron hologram tilt series (ideally covering a range of 360°) is acquired, (2) the phase image tilt series is reconstructed from the holograms, (3) electric and magnetic phase shifts are separated by computing half of the sum/difference between opposite (180° tilted) projections, and (4) both the electric potential and the B-field component parallel to the tilt axis are reconstructed with tomographic techniques. Here, we report EHT studies achieved by means of tomography-dedicated TEM sample holders, in combination with advanced in-house developed software packages for acquisition, alignment and tomographic reconstruction.

Fig. 2 shows the 3D electric potential reconstruction of a GaAs/AlGaAs core-multishell nanowire (NW) grown by metalorganic vapour phase epitaxy (MOVPE) using an Au nanoparticle (NP) as catalyst. Such NWs may serve as novel coherent nanoscale light sources (lasers), because they provide an effective gain medium, low-loss optical waveguiding, and strong optical confinement for axially guided optical modes. The difference in the MIP allows discriminating between GaAs and AlGaAs within the NW. Longitudinal (Fig. 2b) and cross-sectional (Fig. 2e) 2D slices averaged over a well-defined thickness reveal not only the GaAs core and the AlGaAs shell, but also a 5nm thin GaAs shell within the AlGaAs, which acts as a quantum well.

Fig. 3 comprises two recent EHT studies revealing the B-field within a Co nanowire (NW) [5] and a Co2FeGa Heusler alloy NW [6] both with spatial resolution higher than 10 nm. The reconstructions of the dominant axial component of the magnetic induction exhibit a small inversion domain at the apex of the Co NW, whereas at the Co2FeGa NW, a magnetic dead layer of 10 nm width could be revealed.

The powerful approach presented here is widely applicable to a broad range of 3D electric and magnetic nanostructures and may trigger the progress of novel nanodevices.

[1] P A Midgley and R E Dunin-Borkowski, Nat. Mater. 8 (2009) p. 271.

[2] D Wolf, A Lubk, F Röder and H Lichte, Curr. Opin. Solid State and Mater. Sci. 17 (2013) p. 126.

[3] A Lubk, D Wolf, P Prete, N Lovergine, T Niermann, S Sturm and H Lichte, Phys. Rev. B 90 (2014) p. 125404.

[4] D Wolf, A Lubk, A Lenk, S Sturm and H Lichte, Appl. Phys. Lett. 103 (2013) p. 264104.

[5] D Wolf et al., Chem. Mater. 27 (2015) p. 6771.

[6] P Simon, D Wolf, C Wang, A A Levin, A Lubk, S Sturm, H Lichte, G H Fecher and C Felser, Nano letters 16 (2016) p. 114.

[7] We thank N Lovergine of University of Salento, Lecce for provision of the GaAs/AlGaAs core-multishell nanowire samples.

[8] This work was supported by the European Union under the Seventh Framework Program under a contract for an Integrated Infrastructure Initiative Reference 312483-ESTEEM2.

Keywords: 3D reconstruction; magnetic induction; mean inner potential; nanowires

  • Invited lecture (Conferences)
    The 16th European Microscopy Congress, Lyon, France, 28.08.-02.09.2016, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-24896
Publ.-Id: 24896


Optimization of the Aeration System in Municipal Wastewater Treatment Plant

Mohseni, E.; Herrmann-Heber, R.; Reinecke, S.; Hampel, U.

In Germany wastewater is treated in 10000 plants which use 4.400 GWh of energy per year. From this big figure, up to 70% is consumed in the biological treatment and the portion of only aeration of waste water in activated sludge tank is about 50% of the whole figure. Aeration is the essential part of the process since the microorganisms need to be provided by sufficient amount of oxygen to degrade ammonia. Aerators with flexible membranes located at the bottom of the aeration tank are currently state of the art for this process. However the process suffers from some limitations such as high pressure drop, insufficient mixing and underutilization of oxygen. These are mainly due to scarce knowledge about gas dispersion inside the tank.
Initial bubble size in gas dispersion is of a great importance since it determines the ascent and coalescence rate, macro mixing by turbulence, and oxygen transfer from the bubble to the fluid phase. The initial bubble size is drastically influenced by the type of aerator which is being used in the tank. The typical bubble size generated by flexible membrane aerators has been determined to be between 2-4 mm by Hasanen et al. (Hasanen, 2006). However, this is considerably higher than the optimal bubble size calculated by Motarjemi and Jameson (Motarjemi, 1978) who reported the range of 0.7-1.0 mm for the optimal value for the 95% oxygen transfer to water in 3-6 m tank depth.
A novel approach uses solid perforated stainless steel aerators with fine pores in micro scale for gas dispersion. In this work bubble formation of stainless steel aerators has been experimentally investigated with a high resolution optical measurement technique by means of videometry and the results are compared with membrane aerators. Preliminary results of the stainless steel membrane sparger showed a significant reduction in the bubble size up to 47 % and consequently an increase in bubble residence time in comparison with flexible membranes.
A comprehensive set of experiments have been conducted in which the bubble formation with respect to pore size, pore density, plate thickness, flow rate, membrane surface roughness, and bubble generation frequency have been investigated. Thanks to the state of the art manufacturing technique, very fine pores starting at 30 µm up to 200 µm have been processed which resulted in formation of bubbles in the range down to 1.4 mm diameter.
Current poster, presents the motivation of the project and the purposed approaches toward a solution and the initial results of the preliminary experiments done by means of videometry technique.

Keywords: Bubble Generation; Activated Sludge; Aeration; Biological Wastewater Treatment; Multiphase Flow

  • Poster
    11th HZDR PhD Seminar, 17.-19.10.2016, Oberwiesenthal, Germany

Permalink: https://www.hzdr.de/publications/Publ-24895
Publ.-Id: 24895


Development of concepts for high quality image reconstruction based on adaptive grid sizes

Pfahl, A.; Wagner, M.; Bieberle, A.; Buzug, T. M.

In this work an alternative data processing concept is investigated for the correct reconstruction of slice images acquired by an ultrafast electron beam X-ray tomography scanner mainly used for analyzing multiphase flows. Currently, image reconstruction is performed on regular pixel grids by filtered back projection to achieve rapid data processing performances but leading to non-optimal image qualities. To accomplish an improved image quality the usage of irregular reconstruction grids and iterative reconstruction methods is analyzed considering the geometric arrangement and, thus, the real spatial resolution of the ultrafast CT scanner. Finally, a two-stage reconstruction approach is proposed reducing the required amount of computer memory as well as the computational time and inserting prior knowledge about the object of interest. First simulations of different irregular grids provide a promising basis for further successful implementation of the proposed two-stage reconstruction concept.

Keywords: computed tomography; irregular grids

  • Contribution to proceedings
    Studierendentagung Lübeck, 07.-09.03.2017, Lübeck, Deutschland
    Student Conference Proceedings 2017
  • Poster
    Studierendentagung Lübeck, 07.-09.03.2017, Lübeck, Deutschland
  • Lecture (Conference)
    Studierendentagung Lübeck, 07.-09.03.2017, Lübeck, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24894
Publ.-Id: 24894


Experimentelle Untersuchung zur Hydrodynamik der Partialoxidation von Isobutan in einem Mikroreaktor

Reichelt, C.

Die hydrodynamischen Eigenschaften eines zweiphasigen Gemisches aus Isobutan und Stickstoff wurden in einem Mikroreaktor experimentell untersucht. Dazu wurden eine Hochgeschwindigkeitskamera und eine spezielle Bildanalysesoftware verwendet, mit der Isobutan Gas Strömungen in einer Glaskapillare analysiert und ausgewertet werden konnten. Anhand der erhaltenen Ergebnisse konnten Rückschlüsse auf die Bedingungen der Isobutanoxidation in jenem Reaktor gezogen werden. Ziel war es, den Einfluss der betrachteten Parameter (Eduktströme und Betriebsdruck) auf die Zwei-Phasen-Strömung zu analysieren und zu verstehen. Spezielle Strömungsregime können dabei entscheidende Auswirkungen auf den Stofftransport und somit auf reaktionstechnische Kenngrößen wie Umsatz, Selektivität oder Ausbeute haben. Regelmäßige Taylor-Strömungen zeichnen sich in Mikrokanälen durch besonders gute Stoff- und Wärmetransporteigenschaften aus. Aus diesem Grund wurden die Parameter so gewählt, dass sich dieses Strömungsregime ausbildet. Durch diese Arbeit konnten die Strömungsregime der meisten der bisher durchgeführten Oxidationsexperimente als unregelmäßige Taylor-Strömungen charakterisiert werden. Darüber hinaus konnten die Einflüsse der jeweiligen Versuchsbedingungen auf die charakteristischen Kennzahlen der Taylor-Strömung ermittelt werden. Die Arbeit bietet aufgrund ihrer Ergebnisse eine wichtige Grundlage für die Durchführung der partiellen Oxidation von Isobutan im Mikroreaktor.

Keywords: Isobutan; Zweiphasenprozess; Taylor Flow; Charakteristik

  • Study thesis
    Hochschule für Technik und Wirtschaft Dresden, 2016
    Mentor: Thomas WIllms
    34 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24893
Publ.-Id: 24893


In-situ spectroscopic identification of actinide(V/VI) sorption complexes at the mineral oxide water interface

Müller, K.

For the long-term safety assessment of nuclear waste repositories, neptunium and uranium are two of the most environmentally relevant components of nuclear waste to be considered. Hence, great attention is attracted to their geochemistry and migration behavior. Among the various geochemical processes, the migration of radioactive contaminants in the environment is strongly affected by molecular reactions in aqueous solution and at the solid-water interface, e.g. complexation with organic/inorganic ligands, sorption onto mineral phases, surface precipitation, and colloid formation. A detailed description of these interactions on a molecular level is required for a reliable modeling of the contaminants dissemination in the environment.
In the past decade, vibrational spectroscopy has been developed to a powerful tool for the study of dissolved complexes of heavy metal ions with a variety of inorganic and organic ligands and surface complexes on solid phases. In particular, a combined approach of in situ vibrational, time-resolved laser fluorescence and X-ray absorption spectroscopy potentially provides comprehensive molecular information. A survey of very recent spectroscopic results obtained from geochemical reactions of radionuclides, namely Np(V) and U(VI), is given.

Keywords: actinides; vibrational spectroscopy

Related publications

  • Lecture (others)
    Institutskolloquium, 29.11.2016, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-24892
Publ.-Id: 24892


Ferromagnetic resonance study of equiatomic FeRh thin films

Semisalova, A.; Stienen, S.; Barton, C. W.; Boettger, R.; Bali, R.; Thomson, T.; Farle, M.; Fassbender, J.; Potzger, K.; Lindner, J.

Chemically ordered FeRh alloy with nearly equiatomic composition is antiferromagnetic at room temperature and exhibits a first-order phase transition to the ferromagnetic (FM) state at 370 K. Here, we present the study of FM resonance (FMR) in non-capped and Pt-capped magnetron sputtered 40 nm FeRh films on a MgO(100) substrate and analyse the influence of ion irradiation and chemical disordering on their magnetic properties. The temperature dependent FMR study between 200-500 K allowed us to observe the hysteretic temperature behavior, accompanied by a clear transformation of the FMR line, and explore the complex magnetic structure of films. We distinguished and characterized the contribution of anomalous FM interfacial layers induced by atomic intermixing and lattice strain. Finally, we have revealed the formation of a magnetic phase with an out-of-plane easy axis of magnetization caused by low-fluence irradiation with Ne+ ions.

Related publications

  • Lecture (Conference)
    80th Annual Conference of the DPG and DPG Spring Meeting, 06.-11.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24891
Publ.-Id: 24891


Ferromagnetic resonance in Ferh thin films near the antiferromagnetic-ferromagnetic phase transition

Semisalova, A.; Stienen, S.; Barton, C. W.; Boettger, R.; Bali, R.; Thomson, T.; Farle, M.; Fassbender, J.; Potzger, K.; Lindner, J.

High-temperature FMR on FeRh thin films

Keywords: FeRh; phase transition; ferromagnetic resonance; ion irradiation

Related publications

  • Lecture (Conference)
    Euro-Asian Symposium “Trends in Magnetism” (EASTMAG-2016), 15.-19.08.2016, Krasnoyarsk, Russia
  • Invited lecture (Conferences)
    AMP 2017, Interdisciplinary workshop “Acousto-magneto-plasmonics meets quantum optics”, 28.-30.06.2017, Versailles, France
  • Invited lecture (Conferences)
    International School-Conference Spinus 2018, 01.-06.04.2018, Saint Petersburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-24890
Publ.-Id: 24890


Observation of Negative Magnetic Hysteresis Loop in ZnO Thin Films

Haseman, M.; Winarksi, D.; Saadatkia, P.; Hernandez, A.; Kusz, M.; Anwand, W.; Wagner, A.; Thapa, S.; Colosimo, A. M.; Selim, F. A.

We report on the observation of an unusual negative magnetic hysteresis loop in ZnO thin film co-doped with cobalt and aluminum (Co-Al:ZnO), while other transition-metal doped ZnO films such as Cu-doped ZnO and Mn-doped ZnO, exhibit normal hysteresis loops. The unusual magnetic behavior is ascribed to the presence of double magnetic layers with different magnetic moments due to the change of structural defects across the film layers. Positron annihilation measurements confirmed the presence of unique microstructural changes in the Co-Al:ZnO film. This study shows that defects in diluted magnetic semiconductors may induce not only ferromagnetism but also novel magnetic behaviors.

Keywords: magnetism ZnO hysteresis

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24889
Publ.-Id: 24889


Colloidal particle at a fluidic interface: a direct numerical simulation

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

Froth flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The “Smooth Profile Method”, a numerical method originally developed at the University of Kyoto for the direct numerical simulation of colloidal particles in monophasic fluids, was here combined with a newly-defined binary fluid model. The change in the trajectory as the particle approaches the fluid–fluid interface, the collision process, and the sliding down the bubble surface were all reproduced and compared remarkably well with on-site microscale experiments.

  • Lecture (Conference)
    NetFlot: Network of Infrastructure (NOI) - Modelling the Flotation Process, 19.-21.10.2016, Krakau, Gliwice, Polkowice, and Wroclaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-24888
Publ.-Id: 24888


Beschleunigermassenspektrometrie in Dresden

Rugel, G.; Scharf, A.; Ziegenrücker, R.; Merchel, S.

Beschleunigermassenspektrometrie (AMS, accelerator mass spectrometry) ist eine höchstsensitive Methode um langlebige Radionuklide mit einer Halbwertszeit von einigen Jahren und länger zu messen. Seit Herbst 2011 werden an der AMS-Anlage DREAMS (DREsden AMS, siehe Abbildung), routinemäßig Radionuklide gemessen. Aus der zu analysierenden – bereits chemisch aufbereiteten – Probe werden in einer Cäsium-Sputterionenquelle negative Ionen (Moleküle oder Atome) extrahiert. Diese einfach negativ geladenen Ionen werden in einem Niederenergie-Massenspektrometer nach Energie und Impuls analysiert und gelangen nachfolgend in den Tandembeschleuniger, wo sie durch eine positive Hochspannung (bis zu 6 MV) beschleunigt werden. Beim Durchgang durch ein Argon-Stripper-Gas werden Elektronen abgestreift, dadurch Moleküle zerstört, und die nun positiven Ionen ein zweites Mal beschleunigt. Im Hochenergie-Massenspektrometer werden die Radionuklide dann mit einem geeigneten Detektionssystem (u. a. einer Ionisationskammer) identifiziert. Mit diesem Aufbau lassen sich Isobare sehr effizient, sowie molekularer Untergrund vollständig unterdrücken.
Momentan werden an DREAMS Routinemessungen der Nuklide 10Be, 26Al, 36Cl, 41Ca und 129I – meist in Kooperation mit externen Partnern - durchgeführt [1,2]. Die Nachweisgrenze liegt im Bereich von 10-15 – 10-16 Radionuklid zu stabilem Nuklid.
Um DREAMS weiterzuentwickeln wurde erfolgreich eine Ionenquelle für volatile Ionen - wie Chlor und Iod - entwickelt, die ein geringes Übersprechen (kurz- sowie langfristig) zeigt [3]. Eine Ionenquelle, die effizienter die wertvollen Proben ionisieren soll und damit neue Forschungsbereiche ermöglichen wird, ist gerade in Entwicklung [4].

Ref.: [1] S. Akhmadaliev et al., NIMB 294 (2013) 5. [2] G. Rugel et al., NIMB 370 (2016) 94. [3] S. Pavetich et al., NIMB 329 (2014) 22.
[4] BMBF-Verbundprojektforschung 05K16MG1 (H. Hofsäß, U Göttingen) & 05K16KTB (J. Feige, TU Berlin).

Keywords: AMS; accelerator mass spectrometry

Related publications

  • Lecture (Conference)
    Ionentreffen, 13.-15.02.2017, Göttingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24887
Publ.-Id: 24887


Upgrade of the nuclear microprobe at the Ion Beam Center at HZDR

Munnik, F.; Hanf., D.; Heller, R.

The nuclear microprobe that was installed in 1994 at the Ion Beam Center of the Helmholtz-Zentrum Dresden-Rossendorf [1], has been in operation up to 2014 with only minor changes. After 20 years it became necessary to make an upgrade to replace old components and bring the setup up to current standards of technology and good working practice.
The major drawback of the old system was the optical microscope, especially the poor resolution and low contrast and brightness. However, a good optical image is essential to localise the areas of interest on, for example, large geological samples. Since the focused beam of MeV ions and the corresponding detectors is the principal investigative tool, any other equipment such as an optical microscope has to be designed around this device. A new microscope has been installed for which the first light-collecting lens is mounted directly into the chamber at only a few centimetres from the sample. The light is then guided over large mirrors and focussed on a CCD camera outside the sample chamber. The illuminating light is fed in through the lenses instead of using an external light source as in the old system. In addition, there is also a light source opposite to the microscope, allowing transmission illumination including through a polarising filter making polarised imaging possible.
Other improvements concern the control of the scanning system as well as the control and monitoring of all relevant experimental parameters. The control of the scan magnets is done by custom-designed hardware to guarantee real-time execution of the scanning without the need for a computer running a real-time operating system. Controlling and monitoring of the experiment are implemented to facilitate easy and secure operation of the microprobe by the user with special emphasis on operation by un-experienced users, since the device is part of the user facility IBC. All standard IBA techniques like PIXE, PIGE, RBS, NRA, ERDA and STIM are available and, in addition, a Channeltron detector has been installed to detect secondary electrons that allow quick imaging of the measurement area.
Technical details and first test measurements with the new system are presented.

[1] F. Herrmann, D. Grambole, Nucl. Instr. Meth. B 104 (1995) 26.

Related publications

  • Poster
    Ionentreffen (Teil der Serie Workshop Ionenstrahlphysik), 13.-15.02.2017, Göttingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24886
Publ.-Id: 24886


GMR films with crossed anisotropies for perpendicular field measurements

Ganss, F.; Raberg, W.; Luber, S.; Arekapudi, S. S. P. K.; Hellwig, O.; Albrecht, M.

As 3-dimensional field sensors require one part being susceptible to perpendicular fields, thin film GMR stacks with a linear and reversible response to such fields are of interest for the development of monolithic sensor devices. Stacks with such a behavior can be achieved by combining a pinning layer with perpendicular easy axis and a free layer with perpendicular hard axis. Furthermore, the stray field of the pinning layer can be minimized and its coercivity enhanced if a ferrimagnet (or antiferromagnet) is used. For the present study, TbxCo100−x alloys have been chosen as the pinning layer material and Ni81Fe19 for the free layer. The single layers have been characterized by SQUID-VSM measurements, the complete layer stack by magneto-resistance measurements. Initial films confirm the expected behavior and exhibit a change in resistivity of 5% in a field range of 10 kOe. Further films will be optimized regarding their magnetic and electric properties. They shall be micro-structured then and equipped with bottom contacts through the substrate.

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24885
Publ.-Id: 24885


Magnetic properties of nanostructured Tb-Fe alloy thin films

Arekapudi, S. S. P. K.; Hellwig, O.; Albrecht, M.

Nanostructured ferrimagnetic Tb-Fe alloy thin films were prepared on pre-patterned substrates as underlying template, consisting of nanodot arrays with a dot diameter of 30 nm and a period of 60 nm. Two distinct magnetic configuration are possible, one where the magnetic material on the nanodot and in the trenches is decoupled from each other for film thicknesses below the nanodot height, and the other where full exchange coupling between magnetic material on the dots and in the trenches is effective for magnetic films thicker than the nanodot height. Regardless, of the magnetic configuration the reversal of the magnetic material on top of the nanodots is found to be nucleation dominated, while the magnetic material in the trenches reverses via domain wall propagation, as confirmed by in-field magnetic force microscopy. The distinct behavior in this system is attributed to the reduced exchange stiffness followed by relatively narrow domain walls (approx. 3-4 nm) present in these rare earth - transition metal alloys. A systematic study of magnetic properties on nanostructured Tb-Fe alloy films as a function of composition and film thickness will be presented.

  • Lecture (Conference)
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 19.-24.03.2017, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24884
Publ.-Id: 24884


A Comparative Study on Electrical Characteristics of Crystalline AlN Thin Films Deposited by ICP and HCPA-Sourced Atomic Layer Deposition

Altuntas, H.; Bayrak, T.

In this work, we aimed to investigate the effects of two different plasma sources on the electrical properties of low-temperature plasma-assisted atomic layer deposited (PA-ALD) AlN thin films. To compare the electrical properties, 50 nm thick AlN films were grown on p-type Si substrates at 200 °C by using an inductively coupled RF-plasma (ICP) and a stainless steel hollow cathode plasma-assisted (HCPA) ALD systems. Al/AlN/p-Si metal-insulatorsemiconductor (MIS) capacitor devices were fabricated and capacitance versus voltage (C-V) and current-voltage (I-V) measurements performed to assess the basic important electrical parameters such as dielectric constant, effective charge density, flat-band voltage, breakdown field, and threshold voltage. In addition, structural properties of the films were presented and compared. The results show that although HCPA-ALD deposited AlN thin films has structurally better and has a lower effective charge density (Neff) value than ICP-ALD deposited AlN films, those films have large leakage current, low dielectric constant, and low breakdown field. This situation was attributed to the involvement of Si atoms into the AlN layers during the HCPA-ALD processing leads to additional current path at AlN/Si interface and might impair the electrical properties.

Keywords: aluminum nitride; effective charge density; atomic layer deposition (ALD); hollow-cathode plasma; inductively coupled RF-plasma; dielectric

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Publ.-Id: 24883


Magnetic Reversal and Microstructure Phases in Antiferromagnetically Coupled Multilayer Systems with Perpendicular Anisotropy

Hellwig, O.

Strong perpendicular anisotropy systems consisting of Co/Pt or Co/Pd multilayer stacks that are antiferromagnetically coupled via thin Ru or Ir layers have been used as model systems to study the competition between interlayer exchange, perpendicular anisotropy and long-range dipolar interactions [1,2]. The typical layer structure for such systems is illustrated in Fig.1 for a [(Co/Pt)Co/Ru] multilayer system.
Magnetometry and Magnetic Force Microscopy (MFM) studies of such systems reveal complex magnetic phases with a mix of tilted versus non-tilted and antiferromagnetic (AF) versus ferromagnetic (FM) phases depending on the dominance of the various energy contributions. For thin Co/Pt multilayer blocks AF-exchange is dominating and the magnetic structure remains laterally uniform at any stage of the reversal process and is for even number of AF-coupled blocks characterized by bulk and surface spin-flop transitions as shown on the left in Fig. 2. For thicker Co/Pt multilayer blocks the perpendicular anisotropy term takes the lead and prevents any tilting of the spins away from the easy axis normal to the film plane. In this case the reversal into the AF-coupled remanent state occurs via FM/AFM domain formation as shown in the middle part of Fig. 2. For even thicker Co/Pt multilayer blocks the AF-exchange is also overcome by the demagnetization energy and the uniform AF remanent state is replaced by a laterally heterogeneous FM stripe domain state, as illustrated in Fig. 2 on the right.
Ion beam irradiation may be able to control the rich variety of phases in this system on a nanoscopic length scale, thus allowing for a lateral co-existance of all these phases within one and the same sample. This could allow fabricating an infrastructure for controlled spin-wave propagation, such as motivated by recent studies for domain walls and perpendicular anisotropy systems [3,4]. Examples of such initial studies will be discussed.

  • Lecture (Conference)
    Intermag 2017, 24.-28.04.2017, Dublin, Ireland

Permalink: https://www.hzdr.de/publications/Publ-24882
Publ.-Id: 24882


Far-Infrared Nonlinear Optics in Multilayer Epitaxial Graphene

Suess, R. J.; Winnerl, S.; Schneider, H.; Helm, M.; Berger, C.; de Heer, W. A.; Murphy, T. E.; Mittendorff, M.

We report terahertz pump-probe experiments on multilayer graphene that measure both reflected and transmitted radiation. The data reveal complex reflection and transmission dynamics which calculations attribute to a transition from interband to intraband processes.

Keywords: graphene; pump-probe spectroscopy; refelection; transmission

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  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-10.06.2016, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-24881
Publ.-Id: 24881


Nonlinear Plasmonic THz Absorption in Graphene Ribbons

Mittendorff, M.; Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.

We investigate the nonlinear plasmonic absorption in graphene ribbons by THz pump-probe spectroscopy. The optical nonlinearity is increased by more than one order of magnitude, which is in excellent agreement with theoretical calculations.

Keywords: graphene ribbons; plasmonics; nonlinear optics

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  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-10.06.2016, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-24880
Publ.-Id: 24880


Three-dimensional Induction Mapping of Magnetic Nanoscale Materials by Electron Holographic Tomography

Wolf, D.; Lubk, A.; Lichte, H.

Off-axis electron holography (EH) is a powerful TEM technique that provides access to the 2D projections of both the electric potential, i.e., mainly the mean inner potential (MIP) contribution, and the components of the magnetic induction (B-field) that lie perpendicular to the electron beam path.
Currently, 2D magnetic induction maps may be obtained with a spatial resolution of a few nanometer [1,2] and a sensitivity of a few millitesla [2]. Frequently, however, nanomagnetic applications, such as spin valves or magnetic nanowires require a characterization of the 3D magnetic induction distribution.
In the following, we therefore elaborate on how electron holography is combined with electron tomography to electron holographic tomography (EHT) [1,3] in order to retrieve the 3D distribution of the magnetic induction.
As shown in Fig. 1, the tomographic reconstruction of one B-field component starts with acquiring a tilt series of electron holograms that is subsequently reconstructed to obtain a tilt series of phase images. In order to collect data for the crucial separation of electric and magnetic phase shifts, either a tilt series over 360° (Fig. 1), or two tilt series, one before and one after reversing the direction of magnetization in the specimen (e.g., using the TEM objective lens or flipping the sample up-side down in the holder), have to be acquired. Before separation of electric/magnetic phase shifts by computing half of the sum/difference of corresponding image pairs, relative displacements, rotations, and direction dependent magnification changes between the two phase images are corrected. Also, the alignment of the whole tilt series, i.e., an accurate tilt axis determination and subpixel displacements correction, is of crucial importance. Finally, from the aligned tilt series, tomograms of both the electric potential and the B-field component parallel to the tilt axis are reconstructed with tomographic reconstruction algorithms.
Fig. 2 shows two recent EHT studies revealing the B-field within a Co nanowire (NW) [4] and a Co2FeGa Heusler alloy NW [5] both with spatial resolution higher than 10 nm. The reconstructions of the dominant axial component of the magnetic induction exhibit two interesting features for each case: At the Co NW, a small inversion domain at the apex was observed, whereas at the Co2FeGa NW, a magnetic dead layer of 10 nm width was found. These results were achieved by means of dedicated TEM sample holders for acquisition, in combination with advanced in-house developed software packages for acquisition, alignment and tomographic reconstruction. The powerful approach presented here is widely applicable to a broad range of 3D magnetic nanostructures and may trigger the progress of novel spintronic nonplanar nanodevices. In a next step the reconstruction of all B-field components is envisaged.
References:
[1] P A Midgley and R E Dunin-Borkowski, Nat. Mater. 8 (2009) p. 271.
[2] M Körner, F Röder, K Lenz, M Fritzsche, J Lindner, H Lichte and J Fassbender, Small 10 (2014) p. 5161.
[3] D Wolf, A Lubk, F Röder and H Lichte, Current Opinion in Solid State and Materials Science 17(2013) p. 126.
[4] D Wolf et al., Chem. Mater. 27 (2015) p. 6771.

Keywords: magnetic induction; 3D reconstruction; nanostructure; electron holography; electron tomography

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Publ.-Id: 24879


Unusual Coulomb scattering processes in graphene

Winnerl, S.

Graphene, the two-dimensional allotrope of carbon, is characterized by a gapless linear band structure. This unique band structure is directly related to some unusual phenomena regarding the ultrafast Coulomb dynamics in the material. The understanding of this dynamics is of vital interest, both from a fundamental as well as from an application oriented point of view. The elastic Coulomb scattering is the main mechanism for thermalization of a non-equilibrium carrier distribution.
We investigate the carrier dynamics in a regime, where scattering via optical phonons is strongly suppressed. To this end, time resolved spectroscopy was performed with radiation of photon energies around 75 meV, which is smaller than the optical phonon energy (~200 meV). In polarization resolved experiments using co- and cross-polarized linearly polarized pump and probe beams, respectively, the Coulomb scattering dynamics is investigated. We find a two-fold nature of this process, namely very fast (fs timescale) collinear Coulomb scattering but surprisingly slow (ps-timescale) non-collinear scattering [1].
In the presence of a magnetic field, the linear band structure of graphene splits up into a series of non-equidistant Landau levels. Studying the transitions between the lowest Landau levels in pump-probe and four-wave mixing experiments, we find evidence for strong Auger scattering [2, 3].

[1] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).

[2] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Phys. 11, 75 (2015).

[3] J. C. König-Otto, Y. Wang, A. Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl (submitted).

Keywords: graphene; carrier dynamics; Coulomb scattering; Auger scattering; ultrafast spectroscopy

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  • Lecture (others)
    MML Workshop at DESY 2016, 14.-16.12.2016, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24878
Publ.-Id: 24878


Plasmonic superlens based on doped GaAs

Winnerl, S.; Fehrenbacher, M.; Kuschewski, F.; von Ribbeck, H.-G.; Döring, J.; Kehr, S.; Eng, L. M.; Schneider, H.; Helm, M.

Infrared and THz free-electron lasers are interesting sources for near-field investigations as they are tunable in a range where suitable tabletop sources exist only at particular frequencies. The free-electron laser FELBE at Dresden covers the frequency range from 1.3–75 THz with narrowband (~ 1 % spectral width) radiation. We briefly show for the low-frequency region of FELBE (1.3–75 THz) that scattering near-field microscopy can be performed with a constant spatial resolution of 50 nm, which is determined by the diameter of the scattering tip. For the longest wavelength, this corresponds to /4600 [1]. Mainly, we present results on a superlens, which consists of a doped GaAs layer sandwiched between two intrinsic GaAs layers. Superlensing is expected when the condition 〖Re(ε〗_GaAs^doped)=〖-Re(ε〗_GaAs^intrinsic) is met in the spectral vicinity of the plasmonic resonance. Here, the Drude response in the doped layer induces resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around 15 THz (see Fig. 1) [2]. The resonance frequency is adjustable by changing the doping concentration. Compared to superlenses based on phononic resonances the plasmonic superlance features a somewhat broader range of the resonant response. Such a tunable superlense consisting of a single semiconductor material is
a versatile device to enhance signal and spatial resolution in near-field imaging of buried structures.

Keywords: near-field microscopy; superlens; plasmonics; free-electron laser

Related publications

  • Invited lecture (Conferences)
    Samller and Faster: Infrared and Terahertz Spectral-Imaging at the Nanoscale with Synchrotron and Free Electron Laser Sources (SAFE), 01.-02.12.2016, Trieste, Italy

Permalink: https://www.hzdr.de/publications/Publ-24877
Publ.-Id: 24877


Carrier dynamics in Graphene

Winnerl, S.

We review our results ion the carrier dynamics in graphene and present an applacitation example, namely a high-speed ultra-broadband detector.

Keywords: graphene; carrier dynamics; detector

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  • Lecture (others)
    4. Workshop of SPP 1459 "Graphene", 25.-29.09.2016, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-24876
Publ.-Id: 24876


Population and polarization dynamics in Landau-quantized graphene - evidence for strong Auger scattering

Winnerl, S.; Mittendorff, M.; König-Otto, J. C.; Wendler, F.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.

The linear band structure of graphene results in a non-equidistant spectrum of Landau levels (LLs). While transport phenomena have been widely explored after the discovery of graphene in 2004, the ultrafast optical properties of Landau-quantized graphene have been investigated only recently. Predictions of very strong nonlinearities [1], carrier multiplication [2] and Landau-level gain [3] make the system very interesting both from a fundamental and an application-oriented point of view.
Here we present experiments complemented by microscopic theory on the population and polarization dynamics in the subsystem of Landau levels -1, 0 and 1. To this end, multilayer epitaxial graphene in a magnetic field of ~4 T is excited resonantly by ps-pulses of mid-infrared radiation (photon energy 75 meV). Applying circularly polarized radiation allows one to pump and probe the energetically degenerate LL-1 → LL0 and LL0 → LL1 transitions selectively. In pump-probe experiments using all four combinations of pumping and probing with right and left circularly polarized radiation, a surprising change in sign of the measured signal (i.e. induced transmission instead of induced absorption) is observed in one of these configurations. Our analysis shows that this can be associated with a depletion of the LL0 level, even though this level is optically pumped at the same time. Very efficient Auger scattering is responsible for this depletion [4].
Furthermore, we show a very recent study of the polarization dynamics in Landau quantized graphene by means of degenerate four-wave mixing (FWM) spectroscopy. It is carried out on the same subsystem of Landau levels and utilizes similar values of magnetic field and photon energy as in the pump-probe experiments. However, the two incoming beams are linearly polarized in the FWM experiment. A rapid dephasing of the microscopic polarization on a timescale shorter than the pulse duration (4 ps) is observed and attributed to Auger scattering. The FWM signals show the expected dependences on the power of two incoming beams and on the magnetic field.
The results, both for the population as well as the polarization dynamics, depend crucially on the doping level of the sample. The graphene used in the experiments is almost intrinsic, corresponding to a full LL-1 and empty LL1. The occupation of LL0 of about 0.64 is slightly larger than the half-filling corresponding to intrinsic graphene. We will evaluate the implications of this symmetry breaking on Auger scattering and on the FWM signals. Finally, the implications of our results on the feasibility of a graphene based Landau-level laser, which is tunable by the magnetic field, will be discussed.
The sample was grown by C. Berger and W.A. de Heer. We acknowledge valuable discussions with M. Orlita, M. Potemski, Y. Wang, and A. Belyanin. We are grateful to P. Michel and the FELBE team for their dedicated support.
References
[1] X. Yao and A. Belyanin, Phys. Rev. Lett. 108, 255503 (2012).
[2] F. Wendler, A. Knorr, and E. Malic, Nature Commun. 5, 3703 (2014).
[3] F. Wendler and E. Malic, Sci. Rep. 5, 12646 (2015).
[4] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C.

Keywords: Carrier; dynamics; graphene; Landau quantization; Auger scattering; polarization dynamics; four-wave mixing

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  • Invited lecture (Conferences)
    22nd International Conference on High Magnetic Fields in Semiconductor Physics (HMF-22), 24.-29.07.2016, Sapporo, Japan

Permalink: https://www.hzdr.de/publications/Publ-24875
Publ.-Id: 24875


Zero-Offset Hall: A new concept for Antiferromagnetic Spintronics

Kosub, T.; Kopte, M.; Radu, F.; Schmidt, O. G.; Makarov, D.

Antiferromagnets have the potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order. The tiny uncompensated magnetic moment of the locally uncompensated antiferromagnetic lattice determines not only the physics of the materials, e.g. topology of antiferromagnetic domain walls [1], but also their application potential for novel magnetoelectric random access memory (MERAM) devices [2] or
antiferromagnetic analogues to racetrack devices. The rich physics of thin film antiferromagnets can be harnessed for prospective spintronic devices given that all-electric assessment of the tiny uncompensated magnetic moment is achieved.

We put forth a new method providing all-electric access to the field-invariant magnetization of antiferromagnetic thin films [3]. This technique – zero-offset Hall – is based on the combination of Anomalous Hall effect magnetometry with dynamic spinning-current offset compensation. We show that this technique opens the scope for magnetic phenomena that can go amiss in conventional Hall measurements with stationary current direction. The adoption of this technique will therefore substantially improve the reach of lab-based transport investigations in the thriving field of antiferromagnetic spintronics and
lead to new application concepts.

On the examples or metallic IrMn and insulating Cr 2 O 3 antiferromagnetic thin films, we demonstrate, that zero-offset Hall can probe thin film magnetism at unprecedented sensitivity, which allows us to reveal previously unknown peculiarities of the physical behavior. The access to insulating magnetic films is enabled by the magnetic proximity effect of certain conductors such as Pt.

The method is not exclusive to anomalous Hall measurements. Instead, all phenomena that alter the transversal resistance, such as the topological Hall effect and the quantum Hall effects, can be studied in greatly improved detail. At the same time, the measurements are technically easy and can be realized in most laboratories making it fast to adopt. Therefore, we believe that zero-offset Hall is of strong relevance for the community of topological and spin phenomena in nanostructures.

[1] M. Bode et al., Nature Materials 5, 477 (2006)
[2] X. He et al., Nature Materials 9, 579 (2010)
[3] T. Kosub et al., Phys. Rev. Lett. 115, 097201 (2015)

Keywords: Zero-Offset Hall; Antiferromagnetic Spintronics

  • Lecture (Conference)
    TOPSPIN 2, 18.-20.05.2016, Groningen, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-24874
Publ.-Id: 24874


Long-lived Anisotropy of Photoexcited Graphene Electrons

Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.

In polarization resolved pump-probe experiments complemented by microscopic modeling we show that an anisotropic carrier distribution persists on ps timescales. In particular, we evaluate the role of non-collinear Coulomb scattering.

Keywords: Carrier dynamics; graphene; ultrafast spectroscopy; Coulomb scattering

Related publications

  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-11.06.2016, San Jose, USA

Permalink: https://www.hzdr.de/publications/Publ-24873
Publ.-Id: 24873


All-electric measurement of the field-invariant magnetization of antiferromagnets

Kosub, T.; Kopte, M.; Schmidt, O. G.; Makarov, D.

Antiferromagnetic materials combine magnetic properties in peculiar combination that is not found in their ferromagnetic counterparts. They are more robust against magnetic disturbances and show great promises in e.g. magnetoelectric applications [1,2]. Despite these fascinating fundamental properties, both the understanding of antiferromagnets and their commercial establishment have progressed slower than for ferromagnets. The tiny uncompensated magnetic moment of the locally uncompensated antiferromagnetic lattice is often the linking element to intrinsic processes that experimenters can exploit or devices can rely on.
One of the most sensitive techniques for thin film magnetometry, the anomalous Hall effect (AHE) [3], is routinely employed to study magnetization eversal in ferromagnets [4] by monitoring the magnetization-proportional anomalous Hall resistance.
However, this typically suffers from a sizable parasitic signal offset due to imperfect device geometry. But, the offset also contains real AHE signals generated by field-invariant magnetization components which are inaccessible in conventional Hall measurements.
We demonstrate, that AHE magnetometry using the spinning-current technique can measure such field-invariant magnetization on an absolute scale by dynamically compensating the parasitic resistance contribution (Fig.) [5]. Thus, we acquire previously unattainable figures about antiferromagnetic materials and refine existing measurements due to the great precision and time-efficiency of AHE magnetometry.
We establish that this technique is suitable to probe a wide range of materials by applying it to polycrystalline IrMn thin films as well insulating Cr 2 O 3 films. Moreover, our all-electric measurements also prove that it is feasible to entirely omit ferromagnets in antiferromagnet-based applications. Doing so paves the way to all-antiferromagnet spintronics with improved performance or improved reliability [6].

[1] X. He, Y. Wang, N. Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben, and C. Binek, Nature Materials 9, 579 (2010).
[2] J. Heron, J. Bosse, Q. He, Y. Gao, M. Trassin, L. Ye, J. Clarkson, C. Wang, J. Liu, S. Salahuddin, and others, Nature 516, 370 (2014).
[3] N. Nagaosa, J. Sinova, S. Onoda, A. MacDonald, and N. Ong, Rev. Mod. Phys. 82, 1539 (2010).
[4] D. Bhowmik, L. You, and S. Salahuddin, Nature Nanotechnology 9, 59 (2014).
[5] T. Kosub, M. Kopte, F. Radu, O. G. Schmidt, and D. Makarov, Phys. Rev. Lett. 1, 1 (2015).
[6] T. Kosub, O. G. Schmidt, and M. Denys, Patent Applied For (n.d.).

Keywords: Zero-Offset-Hall; antiferromagnetic spintronics

  • Lecture (Conference)
    Joint MMM/Intermag San Diego, 11.-15.01.2016, San Diego, USA
  • Lecture (Conference)
    DPG Regensburg, 14.-18.03.2016, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24872
Publ.-Id: 24872


Analytical Electron Microscopy Study to Resolve the Phase Morphology of Organic Solar Cell Blends

Sedighi, M.; Löffler, M.; Röder, F.; Zschech, E.

To increase the efficiency of bulk heterojunctions for organic photovoltaic devices, the complicated photon-to-electron conversion process has to be understood in detail. To this aim, one challenge is to resolve the correlation between processing parameters of organic solar cells (OSC), the resulting nanoscale morphology of the absorber layer, and efficiency of the completed device. Here, we present the effect of substrate heating on the morphology of the OSC where the active layer is a blend of two small molecules; ZnPc (ZnC32H18N8) as donor and C60 as acceptor.

Obtaining insights into the morphology of the active layer requires the spatial resolution and a contrast mechanism to discriminate two phases with similar average atomic number. To tackle this challenge, we combine electron microscopy imaging with different analytical techniques; energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) in TEM, as well as Energy selective Backscattered (EsB) imaging in SEM.

We imaged different phases of the donor and acceptor, forming ordered and non-ordered regions, depending on the way the heterojunction is fabricated. To this aim, we fabricated samples at substrate temperatures of 110°C and 150°C, each in two different configurations:

1) Focused ion beam prepared ultrathin lamella of a complete solar cell stack with glass substrate, Indium tine oxide (ITO) electrode, ZnPc:C60 blend of the active layer between electron and hole transport layers and aluminum top electrode.
2) Plane view sample as ZnPc:C60 blend deposited on a TEM grid coated with ITO layer.

It was shown that at a substrate temperature of 110°C, the solar cell device has high efficiency [1]., so we consider this as the optimum substrate temperature.

Since identification of the composition of each phase in the plane view sample is more straight forward, we use the plane view sample to attribute each structure to one component of the blend. SEM images recorded by using secondary electron detector show that, the high temperature sample consists of rod-like features and cube-shaped material in between the rods. By combination of analytical microscopy techniques, we can attribute the rod-like structures to ZnPc.

An energy-selective backscatter (EsB) electron detector in a SEM is used to obtain backscattered contrast of the plane view sample. Due to the atomic number difference between the donor phase and the acceptor phase, (the average atomic number of 8.6 for ZnPc and 6 for the C60) sufficient contrast can be achieved [2].

A clear confirmation for the attribution of the ZnPc phase to the rod-like features and the attribution of C60 to the granular structure in between can be drawn from the investigation of the sample in SEM using EDX and with even higher precision in TEM using an improved EDX system. The chemical mapping of zinc and carbon, proves the correct phase assignment, in both plane view and ultrathin samples, prepared at high temperature. For the sample produced at optimum temperature, a much smaller roughness was observed because of the absence of large ordered regions. Even in the plane view sample, the imaging contrast is low due to less separated phases and smaller domains.

To conclude, we clearly resolved the phase morphology of the interpenetrating network of ZnPc:C60 blends for high and optimum temperature samples in plane view and furthermore we were even able to reveal the morphology from TEM images of cross-section lamellas of the real solar cell stacks.

Since the ideal active layer should have domain sizes at the range of the exciton diffusion length (10-20nm), the sample produced at high temperature does not show the desired microstructure. Due to the domain sizes of ~100 nm there is no closed path for exciton dissociation. In addition to that, the sample shows a quite high roughness.

Acknowledgement:

Authors thank A. G. Cid for SEM images. This work was supported by the German Science Council Center of Advancing Electronics Dresden (cfaed). TEM-EDX results were achieved by funding (support code 03SF0451) through the Helmholtz Energy Materials Characterization Platform (HEMCP) initiated by the Helmholtz Association and the German Federal Ministry of Education and Research (BMBF).

References:

[1] S. Pfuetzner, C. Mickel, J. Jankowski, M. Hein, J. Meiss, C. Schuenemann, C. Elschner, A.A. Levin, B. Rellinghaus, K. Leo and M. Riede, “The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells” Org. Electron., 12 (2010), pp. 435–441
[2] A. G. Cid, M. Sedighi, M. Löffler, W. F. van Dorp and E. Zschech, “Energy-Filtered Backscattered Imaging Using Low-Voltage Scanning Electron Microscopy: Characterizing Blends of C60:ZnPc for Organic Solar Cells”. (DOI: 10.1002/adem.201600063)

  • Poster
    EMRS Fall Meeting 2016, 19.-22.09.2016, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-24871
Publ.-Id: 24871


Surprising Coulomb-scattering effects in graphene revealed by polarization-resolved THz spectroscopy

Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Helm, M.; Winzer, T.; Wendler, F.; Malic, E.; Knorr, A.

We present experiments complemented by microscopic theory that highlight surprising Coulomb scattering effects. In particular, we find that non-collinear Coulomb scattering is compa-rably slow, namely on a scale of few ps. For the case of Landau-quantized graphene we find evidence for strong Auger scattering that can deplete a Landau level that is optically pumped at the same time. Both Coulomb effects are relevant for graphene based THz devices.

Keywords: graphene; carrier dynamcis; Coulomb scattering; Auger scattering; Landau quantization

Related publications

  • Invited lecture (Conferences)
    5th EOS Topical Meeting on Terahertz Science & Technology, 08.-11.05.2016, Pecs, Hungary

Permalink: https://www.hzdr.de/publications/Publ-24870
Publ.-Id: 24870


Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: high-speed detector; broadband detector; graphene

Related publications

  • Lecture (Conference)
    7th internationale Workshop Terahertz Technology and Applications, 15.-16.03.2016, Kaiserslautern, Germany

Permalink: https://www.hzdr.de/publications/Publ-24869
Publ.-Id: 24869


Radio-U(H)PLC - the search on the optimal flow cell for the gamma-detector

Kniess, T.; Meister, S.; Fischer, S.; Steinbach, J.

kein Abstract verfügbar

  • Poster
    18th European Symposium on Radiopharmacy and Radiopharmaceuticals, 07.-10.04.2016, Salzburg, Österreich

Permalink: https://www.hzdr.de/publications/Publ-24868
Publ.-Id: 24868


HgCdTe-based heterostructures for Terahertz photonics

Ruffenach, S.; Kadykov, A.; Rumyantsev, V. V.; Torres, J.; Coquillat, D.; But, D.; Krishtopenko, S. S.; Consejo, C.; Knap, W.; Winnerl, S.; Helm, M.; Fadeev, M. A.; Mikhailov, N. N.; Dvoretskii, S. A.; Gavrilenko, V. I.; Morozov, S. V.; Teppe, F.

Due to their specific physical properties, HgCdTe-based heterostructures are expected to play an important role in terahertz photonic systems. Here, focusing on gated devices presenting inverted band ordering, we evidence an enhancement of the terahertz photoconductive response close to the charge neutrality point and at the magnetic field driven topological phase transition. We also show the ability of these heterostructures to be used as terahertz imagers. Regarding terahertz emitters, we present results on stimulated emission of HgCdTe heterostructures in their conventional semiconductor state above 30THz, discussing the physical mechanisms involved and promising routes towards the 5–15 THz frequency domain.

Keywords: narrow-gap semiconductors; HgCdTe (MCT); THz detectors; THz sources

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Permalink: https://www.hzdr.de/publications/Publ-24867
Publ.-Id: 24867


A fluorine-18 radiolabelled celecoxib-based PET probe for Cyclooxygenase-2 monitoring - COX-2 affinity, radiosynthesis and in vitro studies

Kniess, T.; Bechmann, N.; Steinbach, J.; Pietzsch, J.

kein Abstract verfügbar

  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 43(2016)S1, EP844
  • Poster
    Annual Congress of the European Association of Nuclear Medicine, EANM, 15.-19.10.2016, Barcelona, Spanien

Permalink: https://www.hzdr.de/publications/Publ-24866
Publ.-Id: 24866


Dynamics of non-equilibrium charge carriers in p-germanium doped by gallium

Deßmann, N.; Pavlov, S. G.; Tsyplenkov, V. V.; Orlova, E. E.; Pohl, A.; Shastin, V. N.; Zhukavin, R. K.; Winnerl, S.; Mittendorff, M.; Klopf, J. M.; Abrosimov, N. V.; Schneider, H.; Hübers, H.-W.

The low-temperature relaxation processes of non-equilibrium holes into gallium centers in moderately doped p-germanium (NA ≈ 2×10^15 cm-3) has been investigated by a degenerate pump-probe experiment using the free electron laser FELBE. The capture time decreases with increasing average photon flux density of the excitation pulse from about 10.9 ns (at ~1.2×10^24 cm-2 s-1) to ~1.2 ns (~2×10^26 cm-2 s-1). Relaxation inside the valence band is almost independent on pump light intensity and its characteristic time is about 200 ps. In Addition, the intracenter relaxation times of the lowest excited Ga states were measured. The lifetimes scale with the phonon density of states controlling a bound hole – acoustic phonon interaction. The lifetime of the lowest excited state, 1Γ_8^-, was measured to be ~275 ps; while the lifetimes of the higher excited states, 2Γ_8^-and 3Γ_8^-, were found to be ~157 ps and 162 ps, respectively.

Keywords: extrinsic semiconducturs; impurity transitions; carrier dynamics

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Permalink: https://www.hzdr.de/publications/Publ-24865
Publ.-Id: 24865


Improving the quantification accuracy of a PET/CT-scanner with pixelated large area detector

Nemer, U.; Maus, J.; Schramm, G.; Meyer, P. T.; Hennig, J.; Mix, M.

One of the main benefits of PET/CT imaging is its ability for absolute quantification. Calibration according to the manufacturer‘s procedure specifies an accuracy of about 10%, whereas especially in dynamic clinical studies a higher quantification accuracy is desired. Therefore a more accurate calibration is needed. At the Gemini TF, a scanner with pixelated large-area LYSO detectors, there are differences in the measurement set-up between calibration and clinical acquisition. This study intends to evaluate the influence of those differences on the calibration with the aim to increase the accuracy of quantification. The major difference herein is the acquisition format, as calibration is performed in histogram-mode (HM-Cal) and clinical acquisition in list-mode format. Using the list-mode format for the calibration (LM-Cal), increases the activity recovery coefficient for the histogram-based acquisition from 0.93±0.08 up to 1.00±0.03. This is however only valid for the calibration set-up but not for clinical situations. Considering more realistic situations like lesions outside the centre of the field of view (FOV) or additional random events coming from highly accumulating regions outside the FOV (like bladder or brain), a different calibration can be found (ALL-Cal). In the evaluation of clinical oncological datasets with low count rates, a significant improvement of the reconstructed mean activity concentration in the bladder (compared to measured urine samples) up to 4% (LM-Cal) was achieved. For very high count rates the normalization of the scanner has to be adapted to improve the quantification accuracy as well.

Keywords: Calibration; Image reconstruction; Phantoms; Table lookup; Positron emission tomography; Bladder; Detectors

  • Contribution to proceedings
    2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 31.10.-07.11.2015, San Diego, USA
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015 IEEE, USA: IEEE, 978-1-4673-9862-6
    DOI: 10.1109/NSSMIC.2015.7582097

Permalink: https://www.hzdr.de/publications/Publ-24864
Publ.-Id: 24864


Unconventional double-bended saturation of optical transmission in graphene due to many-particle interactions

Winzer, T.; Mittendorff, M.; Winnerl, S.; Mittenzwey, H.; Jago, R.; Helm, M.; Malic, E.; Knorr, A.

We present a joint theory-experiment study on the transmission/absorption saturation after ultrafast pulse excitation in graphene. We reveal an unconventional double-bended saturation behavior: Both bendings separately follow the standard saturation model exhibiting two saturation fluences, however, the corresponding fluences differ by three orders of magnitude and have different physical origin. Our results reveal that this new and unexpected behavior can be ascribed to an interplay between fluence- and time-dependent many-particle scattering processes and phase-space filling effects.

Keywords: graphene; nonlinear optics; saturation; carrier dynamics

Permalink: https://www.hzdr.de/publications/Publ-24863
Publ.-Id: 24863


Radiosynthesis of O-3-(2-[18F]fluoroethyl)-L-DOPA ([18F]OFED) – a new fluorine-18 labeled phenylalanine derivative.

Kniess, T.; Schröder, S.; Hoepping, A.; Zessin, J.; Fuechtner, F.; Bergmann, R.; Steinbach, J.

kein Abstract verfügbar

  • Abstract in refereed journal
    Journal of Nuclear Medicine 57(2016)S2, 1039
  • Poster
    Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging, SNMMI, 11.-15.06.2016, San Diego, USA

Permalink: https://www.hzdr.de/publications/Publ-24862
Publ.-Id: 24862


Symmetry-Breaking Supercollisions in Landau-Quantized Graphene

Wendler, F.; Mittendorff, M.; König-Otto, J. C.; Brem, S.; Berger, C.; de Heer, W. A.; Böttger, R.; Schneider, H.; Helm, M.; Winnerl, S.; Malic, E.

Recent pump-probe experiments performed on graphene in a perpendicular magnetic field have revealed carrier relaxation times ranging from picoseconds to nanoseconds depending on the quality of the sample. To explain this surprising behavior, we propose a novel symmetry-breaking defect-assisted relaxation channel. This enables scattering of electrons with single out-of-plane phonons, which drastically accelerate the carrier scattering time in low-quality samples. The gained insights provide a strategy for tuning the carrier relaxation time in graphene and related materials by orders of magnitude.

Keywords: Carrier dynamics; graphene; Landau quantization; supercollisions

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Permalink: https://www.hzdr.de/publications/Publ-24861
Publ.-Id: 24861


Automatisierte Radiosynthese von O-2[18F]Fluorethyl-L-DOPA ([18F]OFED) – eine neue 18F-markierte Aminosäure für die Tumor-Diagnostik

Kniess, T.; Schröder, S.; Hoepping, A.; Füchtner, F.; Zessin, J.; Bergmann, R.; Steinbach, J.

kein Abstract vorhanden

  • Poster
    Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin 2016, 20.-23.04.2016, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Nuklearmedizin 55(2016)2, P51

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Permalink: https://www.hzdr.de/publications/Publ-24860
Publ.-Id: 24860


Ultrafast processes in graphene: from fundamental manybody interactions to device applications

Winnerl, S.; Mittendorff, M.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winzer, T.; Knorr, A.; Malic, E.

A joint experiment-theory investigation of the carrier dynamics in graphene, in particular in the energetic vicinity of the Dirac point, is reviewed. Radiation of low photon energy is employed in order to match the intrinsic energy scales of the material, i.e. the optical phonon frequency (~200 meV) and the Fermi energy (10-20 meV), respectively. Significant slower carrier cooling is predicted and observed for photon energies below the optical phonon frequency. Furthermore, a strongly anisotropic distribution of electrons in k-space upon excitation with linearly polarized radiation is discussed. Depending on photon energy, the anisotropic distribution decays either rapidly via optical phonon emission, or slowly via non-collinear Coulomb scattering. Finally, a room temperature operated ultra-broadband hot-electron bolometer is demonstrated. It covers the spectral range from the THz to visible region with a single detector element featuring a response time of 40 ps.

Keywords: graphene; carrier dynamics; detectors

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Permalink: https://www.hzdr.de/publications/Publ-24859
Publ.-Id: 24859


Eddy current flowrate and local ultrasonic velocity measurements in liquid sodium

Krauter, N.; Franke, S.; Gerbeth, G.; Eckert, S.; Stefani, F.; Gastaldi, O.; Girard, M.

For the safe operation of sodium cooling systems a monitoring of the flow field is often desirable. We report first on the development of a new eddy current flowmeter (ECFM) and related tests in sodium. The objective of this sensor is its positioning above the fuel subassemblies and the detection of possible blockages of the sodium flow through the multitude of subassemblies. The sensor consists of a number of coils a part of which is fed by an excitation AC current. The assembly of coils is placed in a thimble and the measured flowrate is proportional to the integral flow around this thimble. In the second part we report on local ultrasonic velocity measurements. Here, the objective is to study the flow field resulting from a large electromagnetic pump installed at the PEMDYN facility of CEA. Both measuring techniques were tested at the sodium facility NATAN of HZDR.

Keywords: Eddy Current Flow Meter; Ultrasound Doppler Method; Liquid metal flow

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 26.-29.06.2017, Yekaterinburg, Russland
  • Lecture (Conference)
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 28.06.2017, Yekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-24858
Publ.-Id: 24858


Design, synthesis, radiosynthesis, and biological evaluation of radiofluorinated quinoline derivatives for PET imaging of PDE5A in brain

Liu, J.; Wenzel, B.; Dukic-Stefanovic, S.; Teodoro, R.; Ludwig, F.-A.; Deuther-Conrad, W.; Schröder, S.; Chezal, J.-M.; Moreau, E.; Brust, P.; Maisonial-Besset, A.

kein Abstract vorhanden

  • Poster
    EFMC – International Symposium on Medicinal Chemistry 2016, 28.08.2016, Manchester, UK

Permalink: https://www.hzdr.de/publications/Publ-24857
Publ.-Id: 24857


The IAEA Coordinated Research Project on Sodium Properties and Safe Operation of Experimental Facilities in Support of the Development and Deployment of Sodium-cooled Fast Reactors (NAPRO)

Azpitarte, O.; Japas, M.; Chocrón, M.; Vázquez, E.; Villanueva, A.; Long, B.; Xu, C.; Xie, C.; Latgé, C.; Gerschenfeld, A.; Anderhuber, M.; Chacon, L.; Matteo, L.; Cavaro, M.; Féron, D.; Trabuc, P.; Bubelis, E.; Perez-Martin, S.; Stieglitz, R.; Eckert, S.; Krauter, N.; Selvaraj, P.; Raghvachary, S.; Athmalingam, S.; Chellapandi, P.; Ohira, H.; Lee, J.; Park, S.; Lee, Y.; Hong, J.; Jayaraju, S.; Roelofs, F.; Marinenko, E.; Zagorulko, Y.; Passerini, S.; Gerardi, C.; Grandy, C.; Monti, S.; Kriventsev, V.

The International Atomic Energy Agency (IAEA) recently established a Coordinated Research Project (CRP) on “Sodium Properties and Safe Operation of Experimental Facilities in Support of the Development and Deployment of Sodium-cooled Fast Reactors - NAPRO”, to be carried out in the period 2013 – 2017. Eleven institutions from ten Member States participate in this CRP. The complete scope of this CRP is covered by three work packages. A specific work package (WP1), under the coordination of ANL (USA), is focused on the compilation and expert assessment of data sets of Na physical and chemical properties, as well as correlations for pressure drops and heat transfer in Na facilities. A second work package (WP2), under the coordination of IPPE (Russian Federation), addresses the compilation, evaluation and development of best practices and guidelines for the design, operation and maintenance of Na facilities. Finally, Work Package 3 (WP3), coordinated by CEA (France), concentrates on the compilation and development of guidelines and rules for the safe operation of Na facilities, including the prevention, detection and mitigation of Na leaks and fires. Finally, this work presents some examples of the principal results obtained so far by WP 1.

Keywords: sodium properties; sodium facilities design; sodium safety

  • Contribution to proceedings
    International Conference on Fast Reactors and Related Fuel Cycles: Next Generation Nuclear Systems for Sustainable Development (FR17), 26.-29.06.2017, Yekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-24856
Publ.-Id: 24856


Local etching of a SiOx layer on Si(111) by Ga droplets and its influence on GaAs nanowire growth

Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.

GaAs nanowires (NWs) can be grown epitaxially on Si(111) substrates in the vapour-liquid-solid mode. Typically, Au is used as catalyst, but affects the NW and substrate properties due to contamination. Thus, the self-catalyzed mode appears to be advantageous. The NW growth is initialized by the formation of Ga droplets on the substrate surface, which is normally covered by a thin SiOx layer. The yield of vertical NWs depends on the thickness and the nature of the SiOx, pointing out the complex interaction of the liquid Ga with the SiOx. This work investigates the local etching of a native SiOx on Si(111) by liquid Ga droplets, a mechanism, which is thought to precede the NW nucleation. The droplet formation, the etching process, and their effect on the NW growth were studied as a function of the substrate temperature and the etching time using molecular beam epitaxy. In contrast to previous studies, the oxide etching is distinguished from the subsequent NW nucleation by inserting a thermal annealing step, during which the Ga droplets are evaporated completely from the surface. Finally, the yield of vertical NWs and the NW number density can be controlled just by choosing the appropriate conditions for the oxide etching, independent of those used for the subsequent NW growth.

Related publications

  • Poster
    DPG Spring Meeting, 06.03.2016, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-24855
Publ.-Id: 24855


Erstellung einer Benutzeroberfläche in LabVIEW zur Steuerung der Mikroreaktoranlage zur Partialoxidation von Isobutan in flüssiger Phase.

Lu, X.

Im Rahmen des Belegs wurde eine graphische Oberfläche unter Labview entwickelt, die zur Durchführung von Steuerungs-, Regelungs- und Messaufgaben für einen im Rahmen des Projektes Helmholtz-Energieallianz entworfenen und aufgebauten Reaktor benötigt wurde.

Keywords: Labview; GUI; MSR software; Mikroreaktor

  • Study thesis
    TU-Dresden, 2014
    Mentor: Thomas Willms
    31 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24854
Publ.-Id: 24854


The effect of deposition processing on structural and luminescent properties of a-SiOC: H thin films fabricated by RF-magnetron sputtering

Vasin, A. V.; Rusavsky, A. V.; Kysil, D. V.; Prucnal, S.; Piryatinsky, Y.; Starik, S. P.; Nasieka, I.; Strelchuk, V. V.; Lysenko, V. S.; Nazarov, A. N.

Amorphous silicon oxicarbide thin films (a-SiOC(:H)) were deposited by RF-magnetron sputtering using Si or SiC target in Ar/CH4/O2 flow. Interatomic bonding and light emission properties were analyzed by FTIR in transmission and attenuation total reflection (ATR) mode, Raman scattering and photoluminescence spectroscopy. Comparison of the results obtained by FTIR and ATR allows us to suggest that structural properties of the near-surface region and the bulk of the films are significantly different. The surface layer contains a significant fraction of polymer-like SiOC structural components in the form of Si-O-Si/Si-O-C chains and cages, while bulk of the film is represented by inorganic amorphous SiOx network with amorphous carbon precipitates. Samples with the high fraction of carbon precipitates exhibit white luminescence at room temperature. The origin of strong photoluminescence is discussed.

Keywords: Amorphous silicon oxicarbide thin films; ATR; FTIR; Photoluminescence

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Permalink: https://www.hzdr.de/publications/Publ-24853
Publ.-Id: 24853


Untersuchungen zur Partialoxidation von Isobutan in einem Mikroreaktor unter überkritischen Bedingungen.

Huiras, J.

Die partielle Oxidation von Isobutan durch Sauerstoff in einem Mikroreaktor wurde im überkritischem Zustand zwischen 135 °C und 145 °C unter Verwendung von di-t-butyl peroxide (DTBP) als Initiator untersucht. Dabei wurden das Verhältnis zwischen Isobutan und Sauerstoff, die Verweilzeit, der Druck, die Initiatorkonzentration und die Temperatur variiert. Ziel war es, die Effizienz des Prozesses durch eine Erhöhung der Selektivität des Produkts t-Butyl hydroperoxide (TBHP) und des Umsatzes zu verbessern. Es war insbesondere zu überprüfen, ob sich der Prozess unter diesen Bedingungen durch die Aufhebung von Stofftransportwiderständen gegenüber dem Zweiphasenprozess bei niedrigeren Temperaturen optimieren lässt. Die Reaktionsprodukte TBHP, Azeton, t-butanol und DTBP wurden mittels GC\MS analysiert. Im Rahmen der Arbeit gelang es die höchsten bisher mit einem Mikroreaktor erzielten Umsätze für die Isobutanoxidation zu erzielen. Jedoch gingen die Umsätze nicht wesentlich über die Umsätze hinaus, die aufgrund des zu erwartenden Temperatureffekts bei der Nutzung von überkritischen Bedingungen zu erwarten waren. Auch war die Umsatzerhöhung nur auf Kosten der Selektivität des TBHP zu erzielen. Die Arbeit bietet jedoch aufgrund Ihrer Ergebnisse eine wichtige Grundlage für weitere Untersuchungen.

Keywords: Isobutanoxidation; überkritischer Prozess; Effizienzoptimierung; t-Butylhydroperoxid; Mikroreaktor

  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    63 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24852
Publ.-Id: 24852


Time-Resolved Studies of the Light-Induced Insulator-Metal Transition in NbO2 and VO2 Thin Films

Beebe, M.; Klopf, J. M.; Wang, Y.; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Lukaszew, R. A.

While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.

Keywords: (240.0310) Thin films; (310.6860) Thin films; (310.6845) Thin film devices and applications; (320.7100) Ultrafast measurements; (320.7130) Ultrafast processes in condensed matter; optical properties

Permalink: https://www.hzdr.de/publications/Publ-24851
Publ.-Id: 24851


The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates

Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.

We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.

Keywords: Nanowire; Ga droplets; oxide etching; nanoholes; GaAs; Si substrate

Related publications

  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy, 04.09.2016, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-24850
Publ.-Id: 24850


Optimierung und Validierung der GC/MS-Methode zur Bestimmung der Reaktionsprodukte der Partialoxidation von Isobutan mit Sauerstoff im Mikroreaktor.

Liu, W.

Die partielle Oxidation von Isobutan, t-Butyl Hydroperoxid (TBHP) wurde zum ersten Mal als ein Zwei-Phasen-Prozess in einer Kapillare als Mikro Reaktor durchgeführt und analytisch untersucht. Um detaillierte Informationen über Produkte, Ausbeute, Selektivität und Reaktion Wege zu erhalten, mussten die Produkte mittels GC-MS analysiert werden. Zur Trennung der flüssigen Produkte wurde eine GC-MS Methode erstellt, optimiert und validiert, die eine Rxi-5ms-Säule und einen PTV-Injek-tors verwendet. Im Rahmen der Validierung wurden der Konzentrationsfehler wie auch der Mess¬fehler des MS-Signals aus sämtlichen Kalibrierschritten ermittelt sowie die entsprechenden analytischen Normen (z. B. DIN 38402) für die Kalibrierung berücksichtigt. Außerdem wurden statistische Tests auf Trends (nach Neumann), Ausreißer (nach Dixon), Normalverteilung (nach David) etc. durchgeführt. Die flüssigen Produkte wurden mittels MS identifiziert: Als Hauptprodukte traten TBHP, di-t-Butyl-Peroxid (DTBP), t-Butanol (TBA) und Propanone auf. Für die Zielprodukte TBHP und DTBP wurden Korrelationkoeffiuienten von r2 > 0,999, für TBA und Azeton r2 > 0,995 erzielt. Daneben traten Nebenprodukte wie z. B. Methanal, Methanol, Isopropanol, Isobutanol und Isobutanal auf, von denn alle bis auf Methanol und Methanal ebenfalls kalibriert wurden.

Keywords: TBHP; DTBP; Vslidierung; isobutanoxidation

  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas Willms
    68 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24849
Publ.-Id: 24849


“Reverse Epitaxy” on semiconductor surfaces by low energy ion irradiation

Engler, M.; Ou, X.; Facsko, S.

Ion beam irradiation can produce different patterns on semiconductor surface. While the surface is amorphized at low temperatures, the surface remains crystalline above the dynamic recrystallization temperature. Reverse Epitaxy leads to pattern formation, which is driven by diffusion of vacancies and adatoms on the surface, above this temperature. The mechanisms of Reverse Epitaxy epitaxy are quite similar to mound formation in homoepitaxial growth. The surface is destabilized in both cases by an effective uphill diffusion current driven by Ehrlich-Schwoebel barriers. The patterns formed depend of step formation energies, diffusion on terraces, and Ehrlich-Schwoebel barriers, which all are anisotropic. Their anisotropy is determined by the surface symmetry. By changing the surface symmetry the resulting patterns are be changed.

Related publications

  • Invited lecture (Conferences)
    XI-th International Conference on Ion Implantation and other Applications of Ions and Electrons - ION 2016, 13.06.2016, Kazimierz Dolny, Polska

Permalink: https://www.hzdr.de/publications/Publ-24848
Publ.-Id: 24848


Compositional Non-parametric Tests

van den Boogaart, K. G.; Tolosana-Delgado, R.

Current compositional methods typically rely on some sort of normality hypothesis for testing. Typical well-known non-parametric tests rely on ranks transforms, which are undefined for multivariate problems. The aim of this contribution is thus to investigate the possibilities for truly multivariate non-parametric tests of location and distribution for compositonal data. The challenge is the to ensure subcompositional coherence, which would bring the possibility to attribute deviations to certain subcompositions.

For the case of tests for a known compositional mean, we propose a bootstrap method, measuring how extreme this mean is with respect to a bootstrap sample of the empirical compositional mean. The extremity is checked in each of the pairwise log-ratios. This ensures a subcompositional coherence in the sense that a rejected hypothesis will always be rejected in at least one subcomposition.

For the case of a two sample test comparing two populations, the same principle can be extended. The mean difference is compared with bootstrap samples of mean differences. The same subcompositional coherence applies.

For multiple samples we can extend the idea of ANOVA of measuring the variability of the group means. The variability is measured in terms of the variation matrix. For each entry of the variatin matrix we quantify its quantile in the bootstrap population. We take then the maximum of the quantiles and bootstrap this maximum. In this way we again get a subcompositionally test for equal mean in all samples. Weighted modifications might improve power of the test in case of unequal sample sizes.

  • Lecture (Conference)
    CoDaWork 2017, 06.-9.6.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24847
Publ.-Id: 24847


Compositional Non-parametric Regression

Tolosana-Delgado, R.; van den Boogaart, K. G.

Compositional regression is concerned with modelling the dependence of a composition on one or more covariables, or vice versa. State of the art methods typically rely on the assumptions of linearity of the dependence and for tests on the additive logistic normal distribution of the errors. Several different solutions for non-linear regression and tests without normality assumption are available for non-compositional data. Based on them, this contribution derives non-parametric regression models and methods valid for compositional data.

With respect to the non-linear dependence, some sort of regularisation assumption is always required. Different classical approaches can be adapted for compositonal data. LOESS smoothing on pairwise log-ratios or logratio transforms would correspond to some sort of smooth (compositional) derivatives. Regression splines and smoothing splines are already defined in a multivariate way and allow to control the degree of continuity and smoothness by explicit parameters. Piecewise regression needs to be applied to log-ratio transforms and allows to model non-continuous dependence. Geostatistical interpolation or, equivalently, reproducing kernel splines, allow a precise control over the level of continuity and complexity through the variogram.

All methods mentioned admit a multivariate extension which, by virtue of the principle of working in coordinates, automatically give rise to compositional versions of those methods. Moreover, all are either affine equivariant, or else very slight restrictions of them are. Thus, the associated compositional versions deliver results which are: invariant with respect to the choice of basis, scaling invariant, and subcompositionally coherent (in the case of regression with compositional response).

With regard to testing, there are some philosophical difficulties in a classical ``zero slope hypothesis''. A strict test for dependence could be very misleading when used for model selection in a non-parametric setting. As an alternative we propose to check, whether the prediction by the non-parametric model outperforms the prediction by parametric (constant) one. We propose to compare the jacknifed residuals of the two models. This construction allows to construct all meaningful tests of compositional dependence, namely: global lack of dependence, lack of dependence within a subcomposition, as well as restricted dependence within a subcomposition.

  • Lecture (Conference)
    CoDaWork 2017, 06.-09.06.2017, Abbadia San Salvatore, Italia

Permalink: https://www.hzdr.de/publications/Publ-24846
Publ.-Id: 24846


Fluid dynamics in novel sandwich packings for absorption and distillation

Sohr, J.; Schubert, M.; Hampel, U.

Poster zum EMR-Meeting am 21.09.2016 am HZDR

  • Poster
    EMR-Meeting, 21.09.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24845
Publ.-Id: 24845


X-Ray Photoelectron Study of Ion Implanted Tetrahedral Carbon

Berova, M.; Sandulov, M.; Tsvetkova, T.; Avramova, I.; Boettger, I.; Bischoff, L.

Samples of thin film (d~40nm) tetrahedral amorphous carbon (ta-C), deposited by filtered cathodic vacuum arc (FCVA), have been implanted with N+ and Ga+ at ion energy E = 20 keV and ion fluences D = 3.1014÷3.1015 cm-2. This results in optical properties modification, best manifested by a significant shift of the optical absorption edge to lower photon energies, which is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by X-ray photo-electron spectroscopy (XPS) measurements. The nonimplanted films show the expected variety of carbon-carbon chemical bonds: three- and fourfold coordinated carbon, while the X-ray results show that ion implantation leads to the introduction of additional disorder in the films. The X-ray photoelectron spectra of the implanted films show that, in addition to the already mentioned changes, the ion bombardment results in an increase of the threefold coordinated as compared to the fourfold coordinated carbon bonds, i.e. increased graphitization of the carbon content in the films. These structural modifications, due to the ion implantation, are the reasons for the observed changes in the optical properties of the films, which could be made use of in the area of high-density optical data storage using focused Ga+ ion beams.

Keywords: tetrahedral amorphous carbon; focused ion beams; optical data storage

Related publications

Permalink: https://www.hzdr.de/publications/Publ-24844
Publ.-Id: 24844


Metalle schürfen aus Elektronikschrott

Ell, R.; Scharf, C.; (Editors)

Metallurgen entwickeln neue Strategien, um Rohstoffe aus alten Handys zurückzugewinnen.

  • VDI-Nachrichten 44(2016), 23-23

Permalink: https://www.hzdr.de/publications/Publ-24843
Publ.-Id: 24843


Kritische Rohstoffe aus zweiter Hand

Scharf, C.

Seit drei Jahren lehre und forsche ich als Professorin für Metallurgie und Recycling der Hochtechnologiemetalle in Freiberg. Mein Team und ich setzen uns für einen nachhaltigen Umgang mit kritischen Metallen und anderen Industriemineralen ein. Wir erforschen neue Verfahren, um beispielsweise Produktionsabfälle zu reduzieren und die Wiederverwertung von Rohstoffen aus Altgeräten zu verbessern. Schlacken, Schlämme, Stäube, Späne oder Abwässer — in der Mineralrohstoff und Metallindustrie gibt es, technisch bedingt, viele Rückstände und damit auch eine große Menge bisher nicht genutzter Wertstoffe. Gemeinsam mit den wiederverwertbaren Stoffen, die in alten Elektrogeräten und sonstigen ausgedienten Produkten stecken, gelten sie inzwischen
als wichtiger Hebel für das Erreichen einer maximalen Ressourceneffizienz in der Kreislaufwirtschaft. Um solche „Rohstoffe aus zweiter Hand“, auch sekundäre Ressourcen genannt, dreht sich die Arbeit meines Forscherteams.

  • Contribution to external collection
    Prof. Roewer: ACAMONTA - Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg, Marienberg: Erzdruck GmbH, 2016, ISSN 2193-309X, 27-28

Permalink: https://www.hzdr.de/publications/Publ-24842
Publ.-Id: 24842


Synthese neuer Imidazol-Derivate für die Entwicklung eines 18F-PET-Radioliganden zur Bildgebung des Cannabinoid Rezeptors 2 im Gehirn

Hausmann, K.

Es ist kein Abstract vorhanden.

  • Master thesis
    Universität Leipzig, 2016
    Mentor: Dr. R.-P. Moldovan
    71 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24841
Publ.-Id: 24841


Entwicklung eines 18F-markierten Radioliganden zur Bildgebung der Phosphodiesterase 10A im Gehirn durch Positronen-Emissions-Tomographie

Wagner, S.

Es ist kein Abstract vorhanden.

  • Doctoral thesis
    Universität Leipzig, 2016
    Mentor: Dr. Matthias Scheunemann
    166 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24840
Publ.-Id: 24840


Preliminary Studies on the Partial Oxidation of Isobutane with Oxygen in Multiphase Flows.

Lu, X.

Oxidation of hydrocarbon is an industrially important reaction. Many valuable chemicals are synthesized by the oxidation of relatively cheap raw materials derived from petroleum. The oxidation of isobutane is one of the most important oxidation oxidation processes. For example, isobutane oxidation can be conducted as the preoxidation in oxirane process to produce propylene oxide and tert.-butanol, in which propylene oxide and TBA are important industrial raw materials and widely used in the syntheses of pharmaceuticals, agrochemicals and other fine chemicals (Qi et al., 2014).
In more recent times, there is more and more interest of researchers in the application of microreactors in chemical engineering because of the opportunities of microreactors in chemical process development and intensification, such as excellent heat and mass transfer (Kashid et al., 2014). In this thesis, the oxidation of isobutane in two-phase flow is investigated in a microreactor (100 m long, 1mm ID). The experiments were carried out under different conditions. The start-up behavior of the oxidation of isobutane has been investigated and discussed. In addition, the effect of temperature, pressure, residence time, oxygen-isobutene ratio, the nitrogen dilution and initiator concentration on the performance of isobutane has also been preliminary investigated and discussed. Furthermore, the rate constant of isobutene oxidation has been calculated for 130 °C.

Keywords: microreactor; isobutane oxidation; two phase flow

  • Diploma thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    89 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24839
Publ.-Id: 24839


Partikelentstehung und -transport im Reaktorwasser von DWR nach Kühlmittelverluststörfällen (KMV) - Untersuchungen im Labormaßstab

Harm, U.; Kryk, H.; Hampel, U.; Seliger, A.; Renger, S.; Kästner, W.

Im Rahmen der nuklearen Sicherheitsforschung des Bundesministeriums für Wirtschaft und Energie (BMWi) erfolgten an der Hochschule Zittau/Görlitz (HSZG) in Kooperation mit der Technischen Universität Dresden (TUD) und dem Helmholtz-Zentrum Dresden-Rossendorf (HZDR) experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen im Kühlmittel und deren Auswirkungen auf thermo-fluiddynamische Prozesse im Reaktorkern, welche während des Sumpfumwälzbetriebes als Langzeitnachkühlung nach Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren (DWR) auftreten können. Durch Korrosionsprozesse an feuerverzinkten Installationen im Sicherheitsbehälter (SHB) von DWR wird Zink in ionischer Form im borierten Kühlwasser gelöst. Die freigesetzten Zink-Ionen werden aus dem Reservoir des Nachkühlmittels im SHB über die Not- und Nachkühlsysteme bis in den Reaktorkern gefördert. Im Reaktor wird das eingespeiste Kühlmittel (KM) aufgeheizt.
Im Fokus generischer Experimente standen Untersuchungen zum Verhalten derart zusam-mengesetzter Fluide unter Berücksichtigung von Temperaturunterschieden zwischen dem Kühlmittelreservoir im SHB und dem Reaktorwasser an den Brennstäben im Reaktorkern. Diese generischen Untersuchungen erfolgten an elektrisch beheizten Stabkonfigurationen, welche die durch Nachzerfallsleistung beheizten Brennstäbe im Kern von DWR nachbildeten. Bei der Aufheizung des zinkhaltigen KM innerhalb solcher Konfigurationen wurden Trübungen durch Kolloidbildung beobachtet, gefolgt von Ausscheidungen partikelförmiger, fester Korrosionsprodukte in Form von Zinkboraten. Diese erschienen in Abhängigkeit von der umgebenden KM- bzw. Staboberflächentemperatur als leicht mobilisierbare, flockenartige Dispersphase oder wiesen schichtenbildenden Charakter auf.
Die temperaturabhängigen Umwandlungen von gelösten Zink-Ionen in feststoffartige Zinkborate bewirkten sowohl Ablagerungen an den Heizstäben als auch an den Abstandshaltern (AH) und führten zu erhöhtem Differenzdruckaufbau über die AH sowie Strömungsumverteilungen in der Stabkonfiguration. In Folge dieser Ablagerungen wurden Änderungen des Wärmetransports vom beheizten Stab ans Fluid nachgewiesen, die eine Aufheizung der Heizstäbe bewirkten und damit sicherheitsrelevanten Charakter hinsichtlich der Nachwärmeabfuhr tragen. Aktuell wird dieses generisch ermittelte Verhalten des Reaktorwassers hinsichtlich der Übertragbarkeit auf sicherheitsrelevante Fragestellungen realer DWR mit Bezug auf anzunehmende Leckgrößen und Nachkühlbedingungen und den daraus resultierenden thermohydraulischen Randbedingungen im Sicherheitsbehälter und im Reaktorkern untersucht. Hierfür werden durch Störfallanalysen die Zustände und Bedingungen abgrenzend ermittelt, bei denen eine Gefährdung der Kernkühlung aus Sicht vorhandener Erkenntnisse zu den physiko-chemischen Effekten eintreten könnte. Wesentliche Untersuchungsschwerpunkte bilden die im SHB von DWR auftretenden chemischen und thermodynamischen Einflüsse auf die Zinkfreisetzung und das Ausfällungs- und Ablagerungsverhalten der Korrosionsprodukte an Heißstellen im Reaktorkern.
Die Untersuchungsergebnisse finden u. a. für die Parametrierung von Simulationscodes sowie in alternativen Modellansätzen Verwendung und dienen der sicherheitstechnischen Einschätzung des DWR-Reaktorverhaltens für verschiedene KMV-Störfallszenarien. Die quantitative Analyse der experimentellen Daten zum zeitlichen Ablauf des Quelle-Senke-Mechanismus der Zinkkorrosion und der Umwandlung des gelösten Zinks in feste Produkte unter realen Störfallbedingungen stellt auf Grund der Komplexität und der gegebenen Rückwirkungen eine Herausforderung dar.
Die Vorhaben werden mit Mitteln des Bundesministeriums für Wirtschaft und Energie (BMWi) unter den Förderkennzeichen 150 1491 und 150 1496 gefördert und fachlich von einer Monitoring Group begleitet, welche sich aus Repräsentanten der Forschungsbetreuung des Projektträgers, Gutachtern, Herstellern und Anlagenbetreibern zusammensetzt.

Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments

  • Contribution to proceedings
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2016, Zittau, Deutschland
    Proceedings des Zittauer Kraftwerkschemischen Kolloquiums
  • Lecture (Conference)
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 23.09.2016, Zittau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24838
Publ.-Id: 24838


Helmholtz-Zentrum Dresden-Rossendorf Helmholtz Institute Freiberg for Resource Technology Introduction CHROMIC

Scharf, C.; Kelly, N.; Helbig, T.

Helmholtz-Zentrum Dresden-Rossendorf
Helmholtz Institute Freiberg for Resource Technology
Introduction
CHROMIC
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.

  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24837
Publ.-Id: 24837


CHROMIC WP4 Presentation

Scharf, C.; Kelly, N.; Helbig, T.

CHROMIC
WP4 Presentation
Prof. Dr.-Ing. Christiane Scharf (HZDR, HIF)
This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No 730471
This presentation reflects only the author’s views and neither Agency nor the Commission are responsible for any use that may be made of the information contained therein.

  • Invited lecture (Conferences)
    CHROMIC, Kick-Off-Meeting, 07.-08.12.2016, Mol, Belgien

Permalink: https://www.hzdr.de/publications/Publ-24836
Publ.-Id: 24836


Koordinierungsgespräch HIF – Technikum

Scharf, C.

Koordinierungsgespräch
HIF – Technikum
Christiane Scharf
29.4.2016, Helmholtz-Zentrum Dresden-Rossendorf

  • Lecture (others)
    Koordinierungsgespräch, SMWK, SAB, SIB, HZDR, 29.04.2016, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24835
Publ.-Id: 24835


„Der Weg ist für jeden hürdenreich“ Neue Veranstaltungsreihe beleuchtet Karrierewege für Frauen in der Wissenschaft

Scharf, C.

Obwohl sich die Anzahl weiblicher und männlicher Hochschulabsolventen in etwa die Waage hält, sind auf den akademischen Führungspositionen nur selten Frauen zu finden. Über die Gründe wird viel diskutiert. Unter anderem würden den jungen Forscherinnen geeignete Vorbilder fehlen. Die HZDR-Zentralabteilung Verwaltung hat eine Veranstaltungsreihe aufgesetzt, in der Professorinnen des Zentrums ihren Weg in der Wissenschaft vorstellen. Den Anfang machte im März Prof. Christiane Scharf. Sie hält seit Oktober 2013 die Professur für Metallurgie und Recycling von Hochtechnologiemetallen an der TU Bergakademie Freiberg. Außerdem leitet sie die Abteilung Metallurgie und Recycling am Helmholtz-Institut Freiberg für Ressourcentechnologie. insider hat sich mit ihr über die Situation für Frauen in der Wissenschaft unterhalten.

insider: Frau Scharf, Sie sind ein seltener Fall. Nur ein Fünftel aller deutschen Professuren ist weiblich besetzt. Wie kommt das?
Christiane Scharf: Ich persönlich denke, dass das deutsche Familien- und vor allem Frauenbild hier immer noch eine sehr starke Rolle spielt. Der Einfluss des direkten familiären Umfeldes hat enorme Auswirkungen auf die Karriere. Kommt aus dieser Richtung zusätzlicher Widerstand, was wohl leider nicht selten der Fall ist, wird es sehr schwierig, die ohnehin hohen Hürden zu meistern. Wenn man allerdings den Rückhalt spürt, wird Vieles wesentlich leichter. Häufig genügen dafür schon ein oder zwei Personen, auf die man sich verlassen kann.

Gerade bei Frauen kommt es relativ häufig vor, dass sie einen Ruf nicht annehmen. Könnte das in diesen Fällen auch eine Rolle spielen?
Absolut. Industrie und Wissenschaft haben mittlerweile zum großen Teil begriffen, dass viele Frauen alle Qualifikationen mitbringen und neue Ideen beisteuern können. Eine Führungsposition bringt jedoch automatisch neue Pflichten und einen höheren Grad an Verantwortung mit sich. Ob man sich selbst zutraut, dies zu erfüllen, hängt wiederum stark vom persönlichen Umfeld ab. Dabei sollten auch gesellschaftliche Vorstellungen – ich nenne hier zum Beispiel den Begriff der Rabenmutter, selbst wenn das altertümlich klingen mag – nicht unterschätzt werden.

An welcher Stelle könnte man ansetzen, um das zu ändern?
Zu meiner Schulzeit wurde noch stark das Bild vermittelt, dass Frauen in technischen und naturwissenschaftlichen Berufen nichts verloren hätten. Glücklicherweise ändert sich das seit etwa fünfzehn Jahren. Gesellschaftlich hat sich schon viel getan. Am Ende ist es natürlich trotzdem eine Persönlichkeitsfrage: Wie gehe ich zum Beispiel mit Niederlagen um? Nach meinem Chemieingenieursstudium habe ich mehr als 100 Absagen erhalten.

Und wie gingen Sie damit um?
Ich habe als chemische Fachkraft bei einem Privatunternehmen angefangen. Diese Erfahrungen aus der Industrie haben mir später sehr weitergeholfen. In den meisten Fällen ist die größte Hürde, erst einmal in das gewünschte Feld hineinzukommen. Sobald man auf einer sachlichen Ebene diskutiert, sind die Vorurteile sehr schnell entkräftet.

Könnte das auch eine Lösung für ein zurückhaltendes Umfeld sein?
Aus meiner persönlichen Erfahrung würde ich sagen ja. Mit zunehmendem Erfolg wird auch das kritische Umfeld immer ruhiger. Jungen Forscherinnen, und natürlich auch jungen Forschern, kann ich deswegen nur den Mut zusprechen, in sich selbst zu vertrauen, auch wenn die Herausforderungen hoch erscheinen. Man sollte sich immer selbst klar machen, welche Chancen dieser Weg mit sich bringt.

Was war dabei Ihr Erfolgsrezept?
Ich würde sagen, eine Strategie der kleinen Schritte. Wenn ich mir schon beim Abitur denke, in 20 Jahren musst du auf dieser Position sitzen, dann ist das eine riesige Hürde. Es kann dann schnell passieren, dass man bei den ersten Niederlagen, die mit großer Wahrscheinlichkeit kommen werden, zu verzweifeln beginnt. Es geht eher darum, immer am Ball zu bleiben. Der rote Faden muss erkennbar bleiben, ohne krampfhaft auf ein einziges Ziel hinzuarbeiten. Jeder erfolgreiche Schritt, auch wenn er klein sein mag, bringt dann neue positive Energie.
Das Interview führte Simon Schmitt.

  • Communication & Media Relations
    Interview 11.03.2016
    1 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24834
Publ.-Id: 24834


Frauen in der Wissenschaft - Karrierewege

Scharf, C.

Frauen in der Wissenschaft - Karrierewege
Christiane Scharf
Helmholtz-Zentrum Dresden-Rossendorf, 4.3.2016

  • Lecture (others)
    Einladung HZDR-Veranstaltung, Gleichstellungsbüro, 10.03.2016, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24833
Publ.-Id: 24833


KIC – Network of Infrastructure for Metal-based Lightweight Materials Metallurgy and Recycling Department

Scharf, C.; Balinski, A.

KIC – Network of Infrastructure for Metal-based Lightweight Materials
Metallurgy and Recycling Department
Christiane Scharf
Freiberg, 29th November 2016

  • Invited lecture (Conferences)
    KIC – Network of Infrastructure for Metal-based Lightweight Materials Kick-Off-Meeting, 29.11.2016, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24832
Publ.-Id: 24832


High Magnetic Moment in Ferrimagnetic NiCo2O4 films via He Ion Irradiation

Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Gemming, S.; Helm, M.; Chu, Y.-H.; Zhou, S.

The spinel NiCo2O4 (NCO) exhibits unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order, which makes it an attractive material for spintronic applications.1 The NCO thin-films electrical and magnetic properties can be manipulated from high temperature ferrimagnetic and metallic to low temperature ferromagnetic and insulating by changing the growth temperature.2 The high quality epitaxial NCO films were grown on MgAl2O4 (100) substrate at ~ 400°C exhibits metallic behavior accompanied by ferrimagnetic order with moment ~ 2 μB/fu.1,2 Here, we report the impact of He-ion irradiation with fluence ranging from 5×1015/cm2 – 3×1016/cm2 on these metallic NCO films. The use of He-ion irradiation results in the coherent control of out-of-plane lattice parameter of these films without changing its in-plane lattice parameter (Figure 1). The comprehensive study of magnetization data reveals the magnetic moment increases drastically to ~ 4 μB/fu (Figure 1). The X-ray absorption spectroscopic study also suggests the possible charge redistribution within the octahedral sites of the NCO films which corroborates well with the increase in the magnetic moment.

Related publications

  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Germany

Permalink: https://www.hzdr.de/publications/Publ-24831
Publ.-Id: 24831


SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch Calixarene

Scharf, C.; Balinski, A.

Ausgangssituation und Zielsetzung
Die Gewinnung von Seltenen Erden (SE) ist aufgrund ihrer Eigenschaften sehr komplex, aufwendig und dadurch kostspielig. Die größten Herausforderungen liegen in der Separation der einzelnen SE-Elemente sowie in der notwendigen Abtrennung von Uran und Thorium. Ziel des Projektes SE-FLECX ist die Entwicklung neuer Extraktionsmittel zur effizienten Trennung der Actinoide (Typ A) und der SE-Elemente (Typ B) und die Auslegung ihres Herstellungsprozesses im industriellen Maßstab.

  • Poster
    r4-Konferenz, Statusveranstaltung, 20.-21.10.2016, Hannover, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24830
Publ.-Id: 24830


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