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24459 Publications
Investigation into the Formation of Nanoparticles of Tetravalent Neptunium in Slightly Alkaline Aqueous Solution
Husar, R.
Abstract: Considering the worldwide growing discharge of minor actinides and the current need for geological disposal facilities for radioactive waste, this work provides a contribution to the safety case concerning Np transport if it would be released from deep repository sites and moving from alkaline cement conditions (near-field) to more neutral environmental conditions (far-field). The reducing conditions in a nuclear waste repository render neptunium tetravalent, which is assumed to be immobile in aqueous environment due to the low solubility solution of Np(IV). For tetravalent actinide nuclides, the most significant transport should occur via colloidal particles. This work demonstrates the formation of intrinsic neptunium dioxide nanocrystals and amorphous Np(IV) silica colloids under environmentally relevant conditions.

The dissociation of the initial soluble Np(IV) complex (i.e. [Np(IV)(CO3)5]6-) induces the intrinsic formation of nanocrystalline NpO2 in the solution phase. The resulting irregularly shaped nanocrystals with an average size of 4 nm exhibit a face-centered cubic (fcc), fluorite-type structure (space group ). The NCs tend to agglomerate under ambient conditions due to the weakly charged hydrodynamic surface at neutral pH (zetapotential ~0 mV). The formation of micron-sized agglomerates, composed of nanocrystals of 2-5 nm in size, and the subsequent precipitation cause immobilization of the major amount of Np(IV) in the Np carbonate system. Agglomeration of NpO2 nanocrystals in dependence on time was indicated by PCS and UV-vis absorption spectroscopy with the changes of baseline characteristics and absorption maximum at 742 nm.

Hitherto, unknown polynuclear species as intermediate species of NpO2 nanocrystal formation were isolated from solution and observed by HR-TEM. These polynuclear Np species appear as dimers, trimers and hexanuclear compounds in analogy with those reported for other actinides.

Intrinsic formation of NpO2 (fcc) nanocrystals under ambient environmental conditions is prevented by admixing silicic acid: amorphous Np(IV) silica colloids are formed when silicate is present in carbonate solution.

Herein, the initial molar ratio of Si to Np in solution lead to the formation of Np(IV) silica particles of different composition and size where Si content determines the structure and stability of resulting colloids. Implications for different electronic structures of Np(IV) in dependence on Si content in the solid phase are given by the shift of the absorption maximum at 742 nm characteristic for Np(IV) colloids, silica excess of 5 times the magnitude of Si to Np reveal a redshift up to 6 nm in the colloidal UV-vis spectrum. Precipitation of Np(IV) particles in the ternary system results in a different coordination sphere of Np(IV) compared to the binary system, and the incorporation of Si into internal structure of Np(IV) silica colloids in coffinite-like structure is confirmed by EXAFS. TEM confirms different kinds of particle morphologies in dependence on the silica content. Silica-poor systems reveal porous particles in the micron-range which consist of irregular cross-linked hydrolyzed Np(IV) silica compartments with pores <15 nm.

In contrast, long-term stabilized and silica-enriched systems are characterized by isolated particles with an average particle size of 45 nm. Agglomerates of such isolated Np(IV) silica particles appear as consolidated amorphous solids with a densely closed surface and exhibit no internal fractures. The latter mentioned morphology of Np(IV) silica particles might facilitate the migration behavior of Np(IV) in a stabilized colloidal form under environmental conditions. The silica-enriched particles with densely closed surface are long-term stabilized as colloidal dispersion (>1 year) due to repulsion effects caused by significant surface charge. Particles synthesized from Si/Np = 9/1 carry exclusively negative surface charge in nearly the whole pH range from pH 3 to pH 10 with zetapotential = (-) 5 to (-) 30 mV. The zeta potentials of all particle systems containing silica are significantly shifted to more negative values below pH 7 where the isoelectrical point shifts from pH = 8.0 to 2.6 effecting negative charge under ambient conditions which supports electrostatic stabilization of Np(IV) particles. Particle surface charge at the slipping plane, particle size and shape necessarily depend on the initial magnitude of Si content in solution during particle formation. Particular changes of the morphology and internal structure of different Np(IV) silica colloids by aging are indicated by TEM and XPS. The composition and the crystallinity state of the initially formed amorphous phases partially changed into well-ordered nanocrystalline units characterized with fcc structure.

The presence of silicate under conditions expected in a nuclear waste repository significantly influences the solubility of Np(IV) and provoke the stabilization of waterborne Np(IV) up to concentrations of 10-3 M, exceeding Np´s solubility limit by a factor of up 10.000.

Neptunium and silicate significantly interact with each other, and thereby changing their individual hydrolysis and polymerization behavior. Silicate prevents the intrinsic formation of NpO2 NCs in fcc-structure, and at the same time, Np(IV) prevents the polymerization of silicate. Both processes result in the formation of Np(IV) silica colloids which possibly influence the migration behavior and fate of Np in the waste repositories and surrounding environments. For tetravalent actinides in general, the most significant transport in the environment would occur by colloidal particles. Therefore, Np(IV) silica colloids could have a significant implication in the migration of Np, the important minor actinide in the waste repositories, via colloidal transport.

Keywords: Actinides, neptunium, nanoparticles, nanocrystals, environmental chemistry
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Dr. Thorsten Stumpf
    113 Seiten


Registration No. 22375

High-temperature photon-noise-limited performance terahertz quantum-well photodetectors
Jia, J. Y.; Wang, T. M.; Zhang, Y. H.; Shen, W. Z.; Schneider, H.
Abstract: In this paper, we propose using a terahertz quantumwell photodetector (THz QWP) in combination with a terahertz source to realize a detection system with photon-noise limited performance (PLIP) at high temperatures. Systematical investigations on the high-temperature performances of THz QWPs, including required signal power density for PLIP, detectivity, and the signal-to-noise ratio, have been carried out by elaborating their dark current mechanism and photocurrent response both experimentally and theoretically. We also present the optimal doping concentration of THz QWPs designed for different peak wavelengths and the resulting optimum performance regarding the above three key parameters. Numerical results show that optimal designed QWP with peak response frequency of 5.5 THz is expected to achieve PLIP at 77 K at signal power density at 819 W/cm and above. This work gives a precise description of PLIP performance of THz QWPs and will open ways for new applications for high-temperature detection in the THz regime.
Keywords: High temperature, detectivity, photon-noise limited, quantum-well photodetector (QWP), Terahertz (THz) Registration No. 22365

Bispecific antibody releasing-mesenchymal stromal cell machinery for retargeting T cells towards acute myeloid leukemia blasts
Aliperta, R.; Cartellieri, M.; Feldmann, A.; Arndt, C.; Koristka, S.; Michalk, I.; von Bonin, M.; Ehninger, A.; Bachmann, J.; Ehninger, G.; Bornhäuser, M.; Bachmann, M. P.
Abstract: Bispecific antibodies (bsAbs) engaging T cells are emerging as a promising immunotherapeutic tool for the treatment of hematologic malignancies. Because their low molecular mass, bsAbs have short half-lives. To achieve clinical responses, they have to be infused into patients continously, for a long period of time. As a valid alternative we examined the use of mesenchymal stromal cells (MSCs) as autonomous cellular machines for the constant production of a recently described, fully humanized anti-CD33-anti-CD3 bsAb, which is capable of redirecting human T cells against CD33-expressing leukemic cells. The immortalized human MSC line SCP-1 was genetically modified into expressing bsAb at sufficient amounts to redirect T cells efficiently against CD33 presenting target cells, both in vitro and in an immunodeficient mouse model. Moreover, T cells of patients suffering from acute myeloid leukemia (AML) in blast crisis eliminated autologous leukemic cells in the presence of the bsAb secreting MSCs over time. The immune response against AML cells could be enhanced further by providing T cells an additional co-stimulus via the
CD137-CD137 ligand axis through CD137L expression on MSCs. This study demonstrates that MSCs have the potential to be used as cellular production machines for bsAb-based tumor immunotherapy in the future.
Registration No. 22361

Surface Modificationwith heavy Mon- and Polyatomic Ions
Bischoff, L.; Böttger, R.; Heinig, K.-H.
Abstract: Self-organization of nanopatterns on solid surfaces by ion irradiation is a well-established technique to create regular and ordered structures like ripples or dots. Characteristics of patterns can be controlled selecting different ion species as well as by varying their energy, fluence, incidence angle or the sample temperature during irradiation. To date, mostly monatomic ions with masses between 40 (Ar) and 131 amu (Xe) were used for self-organized nanopatterning or contrary for surface smoothing. A comprehensive review is given.Here, self-organization of periodic patterns by bombardment with polyatomic/cluster ion species with masses of up to ~835 amu is studied – a regime not explored so far. Each impact of a very heavy polyatomic projectile deposits within femtoseconds an extremely high energy density into a local, near-surface volume. The achieved energy density exceeds that of irradiation with monatomic ions of medium mass considerably, it is of the order of femtosecond laser irradiation or swift heavy ion bombardment. Therefore, compared to former ion-induced pattern formation, different pattern based on different mechanisms can be expected.A new quality of pattern on Ge surfaces are obtained by Bi2, Bi3, Bi4 and Au2, Au3 ion irradiation. Polyatomic ions are provided by liquid metal (alloy) ion sources (LM(A)IS) in a mass-separating 30 kV focused ion beam (FIB) system. Results are compared to monatomic Bi and Au ion irradiation using otherwise equivalent irradiation parameters. For this, SEM and AFM were applied to investigate the pattern formation in dependence on ion species, energy per projectile atom, fluence, incidence angle and target temperature. Finally, a consistent, qualitative model for the surface evolution relating on energy density deposition sufficient for localized, transient nano melt pool formation is discussed.
Keywords: Self-organization, ripples, dots, mon- and polyatomic ions, FIB
  • Invited lecture (Conferences)
    The 22nd International Conference on Ion-Surface Interactions, ISI - 2015, 20.-24.08.2015, Moscow, Russia
Registration No. 22360

Erbium-ion implantation into various crystallographic cuts of Al2O3
Nekvindova, P.; Mackova, A.; Malinsky, P.; Cajzl, J.; Svecova, B.; Oswald, J.; Wilhelm, R. A.
Abstract: This paper reports on the importance of crystallographic cuts with a different orientation on the luminescent properties and structural changes of Al2O3 implanted with Er+ ions at 190 keV and with a fluence of 1.0 × 1016 cm−2. Post-implantation annealing at 1000 °C in oxygen atmosphere was also done. The chemical compositions and erbium concentration-depth profiles of implanted layers were studied by Rutherford Backscattering Spectrometry (RBS) and compared to SRIM simulations. The same value of the maximum erbium concentration (up to 2 at.%) was observed at a depth of about 40 nm for all crystallographic cuts. The structural properties of the prepared layers were characterised by RBS/channelling. The relative amount of disordered atoms of 70–80% was observed in the prepared implanted layers and discussed for various cuts. It has been found that erbium is positioned randomly in the Al2O3 crystalline matrix, and no preferential positions appeared even after the annealing procedure. Erbium luminescence properties were measured in the wavelength range of 1440–1650 nm for all samples. As-implanted Al2O3 samples had a significant luminescence band at 1530 nm. The best luminescence was repeatedly observed in the 〈0 0 0 1〉 cut of Al2O3. The annealing procedure significantly improved the luminescent properties.
Keywords: Sapphire; Erbium; Ion implantation; Luminescence Registration No. 22355

Magnetoelectricity of the spin-ice compound Ho2Ti2O7
Herrmannsdörfer, T.; Schönemann, R.; Green, E.; Opherden, L.; Skrotzki, R.; Wang, Z.; Kaneko, H.; Suzuki, H.; Wosnitza, J.
  • Lecture (Conference)
    ICM2015 - 20th International Conference on Magnetism, 05.-10.07.2015, Barcelona, Espana
Registration No. 22354

Synthese, 18F-Markierung und radiopharmakologische Charakterisierung eines 30mer-Peptids als potentieller Radiotracer für die molekulare Bildgebung von Claudin-4 mittels PET
Bader, M.; Kuchar, M.; Wodtke, R.; Lenk, J.; Bergmann, R.; Pufe, J.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.; Löser, R.
Abstract: Der Zelloberflächenrezeptor Claudin-4 (Cld-4) wird in verschiedenen Tumoren überexprimiert und stellt daher ein potentielles Target sowohl für die Diagnose als auch die Therapie von Tumoren epithelialen Ursprungs dar. Dies lässt die Entwicklung von Sonden, die das in vivo-Imaging dieses Proteins ermöglichen, attraktiv erscheinen. Im Rahmen dieser Arbeit sollte untersucht werden, inwiefern sich das C-terminale Fragment der C-terminalen Domäne des Clostridium perfringens-Enterotoxins cCPE(290-319) für die PET-Bildgebung von Cld-4 eignet. Dieses Fragment besteht aus 30 Aminsäuren und weist die Sequenz SLDAGQYVLVMKANSSYSGNYPYSILFQKF auf, was den Positionen 290-319 im cCPE entspricht.
Die Synthese des cCPE(290-319) und davon abgeleiteter Analoga, insbesondere N-terminal fluorbenzoylierter und FITC-konjugierter Derivate sowie Varianten, in denen kritische Aminosäuren (Tyr 306 und Leu 315) ausgetauscht wurden, sollte durch Festphasenpeptidsynthese erfolgen. Unter verschiedenen erprobten Strategien erwies sich die sequentielle Festphasenpeptidsynthese unter Einsatz von drei Pseudoprolin-Dipeptiden am effizientesten, um cCPE(290-319) und dessen Derivate zugänglich zu machen. Die Affinität der erhaltenen Peptide zu einem artifiziellen Proteinkonstrukt bestehend aus beiden extrazellulären Domänen des Cld-4 wurde mit Hilfe der Oberflächen-Plasmonenresonanz (SPR) untersucht, wodurch ein Kd-Wert von 1.4 µM für das N-terminal 4-fluorbenzoylierte cCPE(290-319) ermittelt wurde. Die Markierung von CPE(290-319) mit Fluor-18 erfolgte an fester Phase mit Hilfe von N-Succinimidyl-4-[18F]fluorbenzoat ([18F]SFB) und 4-[18F]Fluorobenzoylchlorid. Dabei wurden die besten Resultate erzielt, wenn harzgebundenes cCPE(290-319) mit N-terminalem 6-Aminohexansäure-Spacer mit [18F]SFB zur Reaktion gebracht wurde. Die Inkubation des auf diese Weise erhaltenen Radiotracers mit Zellüberstand und Blutplasma ließ keine Anzeichen von Instabilität in diesen physiologischen Medien erkennen. Die Zellbindung von 18F-markiertem cCPE(290-319) wurde mit den Tumorzelllinien HT29, A375 und A431 untersucht. Dabei konnte die zeitabhängige Bindung des radiomarkierten Peptids an Cld-4-positive A375- und A431-Zellen beobachtet werden, die stärker war als im Fall der Cld-4-negativen HT29-Zellen. Dieses Ergebnis wird gestützt durch konfokale Fluoreszenzmikroskopie mit FITC-konjugiertem cCPE(290-319) an A431-Zellen. Das in vivo-Verhalten von 18F-markiertem cCPE(290-319) wurde durch dynamisches PET-Imaging und Radiometabolit-Analysen in NMRI nu/nu-Mäusen bzw. Wistar-Ratten evaluiert. Dabei hat sich gezeigt, dass 18F-markiertes cCPE(290-319) schnell metabolisiert wird und einer deutlichen Aufnahme in die Leber unterliegt.
  • Poster
    GDCh-Wissenschaftsforum 2015, 30.08.-02.09.2015, Dresden, Deutschland
Registration No. 22351

Targeting of tissue transglutaminase for functional tumour imaging: Studies on novel assay methods and inhibitors for this enzyme
Wodtke, R.; Hauser, C.; Jäckel, E.; Ruiz-Gómez, G.; Wong, A.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.
Abstract: An increased activity of tissue transglutaminase (TGase 2) in tumours correlates with enhanced invasive potential as well as resistance to chemo- and radiotherapy. Therefore, this enzyme represents an interesting target for the development of PET tracers for functional in vivo imaging of tumours.
One important prerequisite for the identification and characterisation of TGase 2-binding compounds are reliable assay methods to measure the enzymatic activity. For this, a continuous fluorimetric activity assay was established, which allows the detection of the TGase 2-activity through the measurement of an increase in fluorescence. In this context, six novel water-soluble fluorogenic acyl donors containing either 7-hydroxycoumarin or 7-hydroxy-4-methylcoumarin (HMC) as fluorogenic leaving groups were developed and extensively characterised concerning their enzymatic hydrolysis and aminolysis. Within these substrates, the dipeptide Z-Glu(HMC)-Gly-OH exhibits not only the most favourable substrate properties of all compounds in this study but also within the peptidic acyl donors described for TGase 2 so far. In addition to that, a fluorescence anisotropy-based assay method was established where the TGase 2-mediated incorporation of either fluorescein- or rhodamine-conjugated cadaverine into N,N-dimethylcasein is quantified.
For the development of PET tracers for molecular imaging of TGase 2, different approaches are pursued. One of those exploits the use of irreversible inhibitors for this enzyme. Among the TGase 2 inhibitors described in the literature, the recently reported Nα-acyl-Nε-acryloyl-lysine-4-pyridylpiperazides seem to be most suitable for radiotracer development as these compounds exhibit strong inhibitory potential and selectivity towards TGase 2 as well as favourable pharmacokinetic properties. Hence, derivatives based on this class of compounds that allow the labelling with radionuclides such as fluorine-18 and iodine-124 were prepared and their inhibitory potential towards TGase 2 was evaluated by the two independent assay methods outlined above. The kinetic characterisation of the compounds revealed interesting structure-activity relationships. Particularly, the introduction of iodine into the C-terminal pyridyl moiety resulted in a significantly increased inhibitory potential towards TGase 2 compared to the lead structure. This was further illustrated by investigations on covalent docking of the lysine-derived inhibitors within the catalytic centre of TGase 2 which simultaneously will open strategies for the design of even more potent inhibitors.
  • Lecture (Conference)
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich
Registration No. 22350

III-V nanocrystals in Silicon via Liquid Phase Epitaxy: Microstructure and related properties
Wutzler, R.; Rebohle, L.; Prucnal, S.; Böttger, R.; Hübner, R.; Grenzer, J.; Helm, M.; Skorupa, W.
Abstract: The integration of III-V compound semiconductors into existing semiconductor technology is a milestone in future development of micro- and opto-electronics. However, one of the main problems is the presence of defects both inside the III-V semiconductor and at its interfaces. In the present case, III-V compound semiconductor nanocrystals (NCs) were fabricated in Si based systems. For NC formation ion implantation and short-time flash lamp annealing (FLA) were used. After the implanted Si is molten by FLA, the NCs grow via liquid phase epitaxy (LPE) in a millisecond regime. Several binary and ternary III-V compounds have been produced using this approach. While binary compounds are fabricated stoichiometrically, ternary compounds can be achieved with varying compositions. Raman spectroscopy measurements confirmed the formation of III-V NCs within the particular, recrystallized matrices and Si doping. Microstructural properties were investigated by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM) and X-ray diffraction analysis. SEM and TEM images show crystalline, strained III-V nanocrystals in recrystallized Si layers.
Keywords: ion implantation, flash lamp annealing, III-V integration, silicon, liquid phase epitaxy
  • Poster
    28th International Conference on Defects in Semiconductors (ICDS), 27.-31.07.2015, Espoo, Finland
Registration No. 22349

Experimental investigations on the influence of adhesive oxides on the metal-ceramic bond
Enghardt, S.; Richter, G.; Richter, E.; Reitemeier, B.; Walter, M. H.
Abstract: The objective of this study was to test the influence of selected base metals, which act as oxide formers, on the metal-ceramic bond of dental veneer systems. Using ion implantation techniques, ions of Al, In and Cu were introduced into near-surface layers of a noble metal alloy containing no base metals. A noble metal alloy with base metals added for oxide formation was used as a reference. Both alloys were coated with a low-temperature fusing dental ceramic. Specimens without ion implantation or with Al2O3air abrasion were used as controls. The test procedures comprised the Schwickerath shear bond strength test (ISO 9693-1), profile height (surface roughness) measurements (ISO 4287; ISO 4288; ISO 25178), scanning electron microscopy (SEM) imaging, auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX). Ion implantation resulted in no increase in bond strength. The highest shear bond strengths were achieved after oxidation in air and air abrasion with Al2O3 (41.5 MPa and 47.8 MPa respectively). There was a positive correlation between shear bond strength and profile height. After air abrasion, a pronounced structuring of the surface occurred compared to ion implantation. The established concentration shifts in alloy and ceramic could be reproduced. However, their positive effects on shear bond strength were not confirmed. The mechanical bond appears to be of greater importance for metal-ceramic bonding.
Keywords: Alloy; Chemical bond; Ion implantation; Mechanical bond; Metal-ceramic bond; Shear bond strength


Registration No. 22348

Linear magnetoresistance in mosaic-like bilayer graphene
Kisslinger, F.; Ott, C.; Heide, C.; Kampert, E.; Butz, B.; Spiecker, E.; Shallcross, S.; Weber, H. B.
Abstract: The magnetoresistance of conductors usually has a quadratic dependence on magnetic field, however, examples exist of non-saturating linear behaviour in diverse materials. Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure. Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations. We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors. Registration No. 22346

Solid-phase synthesis of selectively monofluorobenzoylated polyamines for targeting of transglutaminases and polyamine transporters in tumours
Wodtke, R.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.
Abstract: Transglutaminases and polyamine transporters are promising targets for functional imaging of tumours. Therefore, our aim is to synthesise polyamine-based radiotracers that allow the in vivo imaging of the aforementioned targets by positron emission tomography (PET). Labelling with the radionuclide fluorine-18 can be accomplished via attaching a [18F]fluorobenzoyl group with the prosthetic labelling reagent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). To access the required non- radioactive analogues, a solid-phase synthesis was developed that enables selective fluorobenzoylation at distinct amino groups of various polyamines (e.g. cadaverine, spermidine, spermine) on the basis of a recently described synthetic concept for the selective functionalisation of polyamines. The established route can be directly applied to synthesise the 18F-labelled analogues.
The mono-fluorobenzoylated polyamines were obtained by solidphase synthesis of the corresponding oxopolyamines and subsequent reduction of the amide bond with BH3-THF. By applying Dde and Boc as orthogonal protecting groups and taking advantage of the selective reaction of 2-acetyldimedone with primary amino groups in the presence of secondary amines, the selective fluorobenzoylation (FBz) of different amino groups becomes possible.
Additionally, the selective mono-fluorobenzylation (FBn) of selected diamines by reaction with 4-fluorobenzaldehyde and subsequent reduction of the resulting imine using sodium triacetoxyborohydride was performed. Based on the established methodology, the following compounds among others were obtained in good yields: N-FBzcadaverine, N-FBn-cadaverine, N1-FBz- spermidine, N4-FBz-spermidine, N8-FBz-spermidine and N1-FBz-spermine. Furthermore, the naturally occurring diamine cadaverine was conjugated to different reporter groups such as biotin. The identity of the compounds was confirmed by NMR spectroscopy and mass spectrometry. The kinetic parameters towards transglutaminase 2-catalysed acyl transfer were determined for selected compounds with an in-house fluorimetric assay using the fluorogenic acyl donor Cbz–Glu(HMC)–Gly–OH.
  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1630
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich
Registration No. 22345

Synthesis, 18F-labeling and radiopharmacological characterization of a 30mer peptide as potential radiotracer for PET imaging of claudin-4
Kuchar, M.; Bader, M.; Wodtke, R.; Lenk, J.; Pufe, J.; Bergmann, R.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.; Löser, R.
Abstract: The cell surface receptor claudin-4 (Cld-4) represents a single-chain protein containing four transmembrane domains and constitutes cell–cell contacts of the tight-junction type by engaging in homophilic interactions. Cld-4 is upregulated in various tumors and represents a promising target for both diagnosis and treatment of solid tumors of epithelial origin. Therefore, the development of agents that allow imaging of Cld-4 in vivo such as 18F-labeled compounds for positron emission tomography (PET) appears to be attractive. A suitable ligand to target Cld-4 in vivo seems to be the C-terminal peptidic fragment of the C-terminal domain of the Clostridium perfringens enterotoxin cCPE(290-319). This fragment is of 30 amino acids in length and has the sequence SLDAGQYVLVMKANSSYSGNYPYSILFQKF corresponding to positions 290-319 of cCPE.
The synthesis of cCPE(290–319) and analogues derived thereof, such as N-terminally modified derivatives (fluorobenzoylated and FITC-conjugated) and variants in which critical amino acids (Tyr 306 and Leu 315) have been replaced, was envisaged to be accomplished by solid-phase peptide synthesis (SPPS). Among several approaches, sequential SPPS using three pseudoproline-dipeptide building blocks revealed to be the most efficient one to afford cCPE(290–319) and its derivatives. The affinity of the furnished peptides to a soluble protein construct that contains both extracellular loops of Cld-4 was studied by surface plasmon resonance (SPR), which allowed determining a Kd value of 1.4 lM for the N-terminally fluorobenzoylated cCPE(290-319). Labeling of cCPE(290–319) with fluorine-18 was achieved on solid phase using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) and 4-[18F]fluorobenzoyl chloride as 18F-acylating agents. Most advantageous results were obtained when [18F]SFB was reacted with resin-bound cCPE(290–319) containing an N-terminal 6-aminohexanoic spacer. Stability assays in cell supernatants and plasma indicated no degradation of the resulting radiotracer in these physiological media. Cell binding of 18F-labeled cCPE(290–319) was investigated using the HT29, A375 and A431 tumor cell lines. Timedependent binding of the radiolabeled peptide to the Cld-4-positive A375 and A431 cells was observed, which was stronger than for the Cld-4-negative HT29 cell line. These findings are in accordance with results of confocal microscopy studies using FITC-conjugated cCPE(290–319) and A431 cells. The in vivo behavior of 18F-labeled cCPE(290–319) was studied in NMRI nu/nu mice and Wistar rats by dynamic PET imaging and radiometabolite analyses, respectively. These investigations have shown that 18F-labeled cCPE(290–319) is subject to substantial liver uptake and rapid metabolic degradation in vivo.
In conclusion, the synthesis and 18F-labeling of cCPE(290-319) were successfully established. Its binding to Cld-4 in vitro and in cellulo has been demonstrated. Initial radiopharmacological studies suggest the limited suitability of this peptide in its current non-stabilized form to target Cld-4 in vivo.
  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1629-1630
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich
Registration No. 22344

A new fluorescence anisotropy-based assay for activity determination of tissue transglutaminase
Hauser, C.; Wodtke, R.; Löser, R.; Pietsch, M.
Abstract: Considerable evidence for the implication of tissue transglutaminase (TGase 2) in a variety of pathological processes, such as neurodegenerative diseases, disorders related to autoimmunity and inflammation as well as tumor progression, has been revealed over the recent years. This renders TGase 2 attractive for developing agents which allow the enzyme’s targeting for both therapeutic and imaging purposes. The development of such molecules requires the establishment of reliable methods to assess the interaction with TGase 2, which can be done most conveniently in continuous kinetic assays.
Several assays have been published over the last decades to determine TGase 2 activity, with only very few using the method of fluorescence anisotropy. Measurement of fluorescence anisotropy offers a better signal to noise ratio than other techniques, such as those based solely on fluorescence emission and does not need washing or separation of unbound fluorescent substance.
Here, we report a fluorescence anisotropy-based approach for the determination of TGase 2’s transamidase activity, established and validated by using fluorescein- and rhodamine B-labeled cadaverines as acyl acceptor substrates. The synthesis of the cadaverine derivatives has been accomplished in a solid-phase approach. To allow efficient conjugation of the rhodamine B moiety, different linkers providing secondary amine functions have been introduced between the cadaverine and xanthenyl entities.
The increase in fluorescence anisotropy resulting from covalent binding of the relatively small cadaverine derivatives to the much larger acyl donor substrate N,N-dimethylated casein was followed over time and enzyme activities were derived thereof. The assay was found to be highly reproducible and shows no background signal in the absence of the enzyme for all synthesized cadaverine derivatives. After characterization of the enzyme–substrate interaction by determination of the Michaelis constants, Km, and the maximum velocities of substrate conversion, Vmax, the assay was validated for screening of non-covalent and covalent inhibitors by using the literature-known substances GTP and iodoacetamide, respectively, as well as a recently reported L-lysine acrylamide derivative.
  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1629
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich
Registration No. 22343

18F-Labeled 1,4-Dioxa-8-azaspiro[4.5]decane Derivative: Synthesis and Biological Evaluation of a σ1 Receptor Radioligand with Low Lipophilicity as Potent Tumor Imaging Agent
Xie, F.; Bergmann, R.; Kniess, T.; Deuther-Conrad, W.; Mamat, C.; Neuber, C.; Liu, B.; Steinbach, J.; Brust, P.; Pietzsch, J.; Jia, H.
Abstract: We report the syntheses and evaluation of series of novel piperidine compounds with low lipophilicity as σ1 receptor ligands. 8-(4-(2-Fluoroethoxy)benzyl)-1,4-dioxa-8-azaspiro[4.5]decane (5a) possessed high affinity (Ki = 5.4 ± 0.4 nM) for σ1 receptors and selectivity for σ2 receptors (30-fold) and the vesicular acetylcholine transporter (1404-fold). [18F]5a was prepared using a one-pot, two-step labeling procedure in an automated synthesis module, with a radiochemical purity of >95%, and a specific activity of 25−45 GBq/μmol. Cellular association, biodistribution, and autoradiography with blocking experiments indicated specific binding of [18F]5a to σ1 receptors in vitro and in vivo. Small animal positron emission tomography (PET) imaging using mouse tumor xenograft models demonstrated a high accumulation in human carcinoma and melanoma. Treatment with haloperidol significantly reduced the accumulation of the radiotracer in tumors. These findings suggest that radiotracer with suitable lipophilicity and appropriate affinity for σ1 receptors could be used for tumor imaging.
Keywords: 8 [4 (2 fluoroethoxy)benzyl) 1,4 dioxa 8 azaspiro[4.5]decane f 18; fluorine 18; haloperidol; piperidine derivative; radioligand; radiopharmaceutical agent; sigma 1 opiate receptor; sigma 2 opiate receptor; unclassified drug; vesicular acetylcholine transporter Registration No. 22342

Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce2RuZn4
Hartwig, S.; Prokes, K.; Hansen, T.; Ritter, C.; Gerke, B.; Pöttgen, R.; Mydosh, J. A.; Förster, T.
Abstract: Neutron powder diffraction experiments were performed on the intermediate-valence Ce2RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites ismagnetically active. Ce2RuZn4 orders antiferromagnetically at TN = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector qm = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) μB. Registration No. 22341

Atomic scale interface design and characterisation
Bittencourt, C.; Ewels, C.; Krasheninnikov, A. V.
Abstract: There is no abstract
Keywords: nanotechnology


Registration No. 22339

Solubility of boron, carbon, and nitrogen in transition metals: getting insight into trends from first-principles calculations
Hu, X.; Björkman, T.; Lipsanen, H.; Sun, L.; Krasheninnikov, A. V.
Abstract: Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using first-principles calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the d- shell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials.
Keywords: graphene, solubility, interstitials Registration No. 22337

Broadband THz detection from 0.1 to 22 THz with large area field-effect transistors
Regensburger, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Preu, S.
Abstract: We report on ultrafast detection of radiation between 100 GHz and 22 THz by field-effect transistors in a large area configuration. With the exception of the Reststrahlenband of GaAs, the spectral coverage of the GaAs-based detectors is more than two orders of magnitude, covering the entire THz range (100 GHz - 10 THz). The temporal resolution of the robust devices is yet limited by the 30GHz oscilloscope used for read out. The responsivity roll-off towards higher frequencies is weaker than expected from an RC-roll-off model. Terahertz pulses with peak powers of up to 65 kW have been recorded without damaging the devices.
Keywords: terahertz detetector, field-effect transistor, braodband and fast THz detection


Registration No. 22334

Targeting lysyl oxidase for molecular imaging in breast cancer
Wuest, M.; Kuchar, M.; Sharma, S. K.; Richter, S.; Hamann, I.; Wang, M.; Vos, L.; Mackey, John R.; Wuest, F.; Löser, R.
Abstract: Introduction: Lysyl oxidase (LOX; ExPASy ENZYME entry: EC and members of the LOX-like family, LOXL1–LOXL4, are copper-dependent enzymes that can modify proteins of the extracellular matrix. Expression of LOX is elevated in many human cancers, including breast cancer. LOX expression correlates with the level of tissue hypoxia, and it is known to play a critical role in breast cancer metastasis. The goal of the present study was to target LOX with (1) molecular probe fluorescent labeling to visualize LOX in vitro and (2) a radiolabeled peptide to target LOX in vivo in three different preclinical models of breast cancer.
Methods: Gene expression of all five members of the LOX family was analyzed at the transcript level via microarray analysis using tissue biopsy samples from 176 patients with breast cancer. An oligopeptide sequence (GGGDPKGGGGG) was selected as a substrate-based, LOX-targeting structure. The peptide was labeled with fluorescein isothiocyanate (FITC) for confocal microscopy experiments with the murine breast cancer cell line EMT-6. In vivo molecular imaging experiments were performed using a C-terminal amidated peptide, GGGDPKGGGGG, labeled with a short-lived positron emitter, fluorine-18 (18F), for positron emission tomography (PET) in three different breast cancer models: EMT6, MCF-7 and MDA-MB-231. The PET experiments were carried out in the presence or absence of β-aminopropionitrile (BAPN), an irreversible inhibitor of LOX.
Results: Immunostaining experiments using a LOX-specific antibody on EMT-6 cells cultured under hypoxic conditions confirmed the elevation of LOX expression in these cells. An FITC-labeled oligopeptide, FITC-Ava- GGGDPKGGGGG-NH2, was found to be localized in different cellular compartments under these conditions. After injection of [18F]fluorobenzoate-GGGDPKGGGGG-NH2, radioactivity uptake was visible in all three breast cancer models in vivo. Tumor uptake was reduced by predosing the animals with 2 mg of BAPN 4 h or 24 h before injection of the radiotracer.
Conclusions: The present data support further investigation into the development of LOX-binding radiolabeled peptides as molecular probes for molecular imaging of LOX expression in cancer.


Registration No. 22331

Ultrasound Doppler flow measurements in a liquid metal column under the influence of a strong axial electric current
Starace, M.; Weber, N.; Seilmayer, M.; Kasprzyk, C.; Weier, T.; Stefani, F.; Eckert, S.
Abstract: Magnetohydrodynamic instabilities can constitute a serious hazard to the functionality of liquid metal batteries. Here we consider the Tayler instability, which appears when the electric current, passing through a conducting fluid, reaches a critical value. The experiment discussed in this article involves a column of a eutectic GaInSn alloy, along whose axis an electric current passes. Ultrasound transducers encased in a copper electrode bounding the top of the column were used to obtain the vertical component of fluid flow, once a noise suppression system had been devised. The data thus retrieved will be discussed here.
  • Magnetohydrodynamics 51(2015)2, 249-256
Registration No. 22330

Ion acceleration enhanced by target ablation
Zhao, S.; Lin, C.; Wang, H. Y.; Lu, H.; Tu He, X.; Chen, J.; Cowan, T. E.; Q. Yan, X.
Abstract: Laser proton acceleration can be enhanced by using target ablation, due to the energetic electrons generated in the ablation preplasma. When the ablation pulse matches main pulse, the enhancement gets optimized because the electrons' energy density is highest. A scaling law between the ablation pulse and main pulse is confirmed by the simulation, showing that for given CPA pulse and target, proton energy improvement can be achieved several times by adjusting the target ablation. Registration No. 22329

Caustic structures in the spectrum of x-ray Compton scattering off electrons driven by a short intense laser pulse
Seipt, D.; Surzhykov, A.; Fritzsche, S.; Kämpfer, B.
Abstract: We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. In particular, we observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element. Registration No. 22328

Post-test calculations of UPTF experiments with ANSYS CFX
Höhne, T.
Abstract: The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors because a number of important phenomena such as pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.
The nuclear industry now also recognizes that CFD codes have reached the desired level of maturity (at least for single-phase applications) for them to be used as part of the Nuclear Power Plant (NPP) design process, and it is the objective the research and development teams to assess the current capabilities of such codes in this regard, and contribute to the technology advance in respect to their verification and validation. CFD is already well-established in addressing certain safety issues in NPPs, as reported and discussed at various international workshops. The development, verification and validation of CFD codes in respect to NPP design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. In parallel, it remains an overriding necessity to benchmark the performance of the CFD codes, and for this experimental databases need to be established, first for separate-effect tests but especially for full-size integral tests.
In order to validate the CFD Code ANSYS CFX for reactor safety relevant flow phenomena it is essential to use the UPTF experiments, since they are full scale tests. All other separate effect test rigs and test facilities like ROCOM (Höhne, 2000) are scaled. Scaling parameters of flow conditions are one of the still open topics for the use of CFD codes in nuclear reactor safety. Three UPTF tests were selected and post-test calculation were performed. The major focus was analyzing the qualitative flow behavior.

Keywords: UPTF, CFX, LOCA, PTS
  • Other report
    Dresden: HZDR, 2015
    25 Seiten
Registration No. 22324

Terahertz spectroscopy of 0D and 2D semiconductors with a free-electron laser
Schneider, H.
Abstract: This talk reviews recent experimental studies carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices.
Keywords: free-electron laser, terahertz spectroscopy
  • Lecture (others)
    Seminar, Xi'an University of Technology, 04.05.2015, Xi'an, China
  • Lecture (others)
    Seminar, CAEP, 07.05.2015, Mianyang, China
Registration No. 22321

In Situ Tuning the Conductance of Single Molecular Diarylethene Switches
Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Huhn, T.; Scheer, E.; Kerbusch, J.; Gemming, S.; Erbe, A.
Abstract: A major goal of molecular electronics is the development and implementation of molecular electronic devices such as single molecular switches. In this work we present a detailed study of single diarylethene molecules that were in situ switched from their non-conductive to conductive state in the presence of gold nanoelectrodes via controlled light irradiation. The molecules were dissolved in two different solvents and measured with two different side-groups. Histograms of conductance traces were taken and complemented by extracting the relative position of the current carrying molecular level and its level broadening from current-voltage characteristics by means of the single level transport model. The obtained results show a clear light-induced ring forming isomerization, which is almost independent of the side-groups, while electron withdrawing side groups lead to a reduction of conductance, a decrease of the level broadening and an increased difference between the molecular level and the Fermi energy of the metals. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by the electron-withdrawing substituents.
  • Poster
    Annual Workshop IHRS NanoNet 2014, 29.-30.09.2014, Lohmen/Bastei, Deutschland
  • Poster
    DCCMS Annual Workshop and General Assembly 2014, 20.10.2014, Dresden, Deutschland
Registration No. 22316

Spin-Torque Devices Based on MgO-Based Magnetic Tunnel Junctions
Deac, A. M.
Abstract: Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).

Keywords: magnetism, magnetic tunnel junctions, spin-transfer torque
  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures Gordon Research Conference Nanoscale Spintronics with Magnons, Phonons, and Photons, 26.-31.07.2015, The Hong Kong University of Science and Technology, China
Registration No. 22314

International research environment and career development
Deac, A. M.
Abstract: This talk provides mentoring for students seeking an international career.
Keywords: carrer development
  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures (GRS) Gordon Research Seminar Interplay of Spin, Charge and Lattice Dynamics, 25.-26.07.2015, The Hong Kong University of Science and Technology, China
Registration No. 22313

Zero-field precession and suppression of the output power due to the biasdependence of the TMR in MgO-based spin-torque oscillators Alina Maria Deac
Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Deac, J. Fassbender A. M.
Abstract: Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless
communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).

Keywords: magnetism, spin-transfer torque, magnetic tunnel junction
  • Invited lecture (Conferences)
    20th International Conference on Magnetism, 06.-10.07.2015, Barcelona, Spain
Registration No. 22312

Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium
Radek, M.; Bracht, H.; Mccallum, J. C.; Johnson, B. C.; Posselt, M.; Liedke, B.
Abstract: The atomic mixing of matrix atoms during solid-phase-epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures grown by molecular beam epitaxy on natural Ge wafers. The entire isotope structure and parts of the natural Ge wafer were preamorphized by Ge implantation. Recrystallization of the amorphous Ge layer is performed at temperatures between 350 ˚C and 450 ˚C. The position of the amorphous/crystalline (a/c) interface was monitored during SPE regrowth using a time-resolved-reflectivity (TRR) system. The SPE process was stopped before the a/c interface reached the surface, i.e, before the recrystallization of the amorphous layer was completed. Secondary-ion-mass-spectrometry (SIMS) was applied to determine the self-atom distribution within the amorphous and recrystallized part of each sample. An upper limit of 0.5 nm is determined for the displacement length of the matrix atoms. This small displacement length is consistent with theoretical models and atomistic simulations of SPE predicting that bond-switching with nearest-neighbours across the a/c interface controls the SPE regrowth.
Keywords: Germanium, Solid-phase epitaxial recrystallization, atomic transport, isotope multilayers
  • Poster
    28th International Conference on Defects in Semiconductors (ICDS 2015), 27.-31.07.2015, Espoo, Finland
Registration No. 22311

Dilute ferromagnetic InMnP
Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: We have synthesized a new magnetic semiconductor,InMnP, by Mn ion implantation and pulsed laser annealing [1, 2]. Clear ferromagnetic hysteresis loops and a perpendicular magnetic anisotropy are observed up to a Curie temperature of 42 K. Large values of negative magnetoresistance and magnetic circular dichroism as well as anomalous Hall effect are further evidences of a ferromagnetic order in InMnP. An effort is made to understand the transport mechanism in InMnP using the theoretical models. We find that the valence band of InP does not merge with the impurity band of the heavily doped InMnP (8 %). Our results suggest that impurity band conduction is a characteristic of Mn‐doped InP and GaP which have deep Mn‐ cceptor levels. [1] M. Khalid, et al., Phys. Rev. B 89, 121301(R) (2014) [2] M. Khalid, et al., J. Appl. Phys. 117, 043906 (2015).
  • Poster
    20th International Conference on Mangetism, 05.-10.07.2015, Barcelona, Spain
Registration No. 22309

Mid-infrared ridge waveguide in MgO:LiNbO3 crystal produced by combination of swift O5+ ion irradiation and precise diamond blade dicing
Cheng, Y.; Lv, J.; Akhmadaliev, Sh.; Zhou, S.; Kong, Y.; Chen, F.
Abstract: We report on the fabrication of ridge waveguide operating at mid-infrared wavelength in MgO:LiNbO3 crystal by using O5+ ion irradiation and precise diamond blade dicing. The waveguide shows good guiding properties at the wavelength of 4 μm along the TM polarization. Thermal annealing has been implemented to improve the waveguiding performances. The propagation loss of the ridge waveguide has been reduced to be 1.0 dB/cm at 4 μm after annealing at 310 °C. The micro-Raman spectra indicate that the microstructure of the MgO:LiNbO3 crystal has no significant change along the ion track after swift O5+ ion irradiation.
Keywords: Optical waveguide; MgO:LiNbO3 crystal; Ion irradiation; Diamond blade dicing; Mid-infrared waveguides Registration No. 22308

Ferromagnetism induced by vacancy clusters in Silicon
Liu, Y.; Zhang, X. H.; Yuan, Q.; Han, J. C.; Zhou, S. Q.; Song, B.
Abstract: Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Though it is weak, it can be stable above room temperature. Till now it has been confirmed at least in oxides [1, 2] and carbon based materials [3, 4]. Interestingly, the relation between magnetism and defects in Silicon was demonstrated decades ago [5]. Since then, some progresses were made [6-9] and push forward the research of magnetic Mn doped Si a lot but it is drawn little attention itself. Here, with the latest growth purifying technique and sensitive measurements, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si.
Keywords: defect-induced ferromagnetism, silicon, neutron irradiation, semiconductors
  • Poster
    28th International Conference on Defects in Semiconductors, 27.-31.07.2015, Espoo, Finland
Registration No. 22306

Strong Auger scattering in Landau-quantized graphene evidenced by circularly polarized pump-probe spectroscopy
Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.
Abstract: While the carrier dynamics in graphene in absence of magnetic fields is well researched in a large spectral range ranging from UV to THz, the dynamics in Landau quantized graphene is almost unexplored. We investigate the carrier dynamics within the system of Landau levels (LLs) of index n = -1, n = 0 and n = 1 by pump-probe experiments complemented by microscopic modelling. Using circularly polarized terahertz radiation (at 18 THz) allows one to selectively excite the two energetically degenerate transitions LL-1 → LL0 and LL0 → LL1, respectively (at B  4 T). While three of the four possible configurations give intuitive results (bleaching, when pumping and probing with the same polarization, induced absorption with opposite polarizations), surprisingly, one configuration counterintuitively leads to bleaching while pumping and probing with opposite polarizations (Fig. 1 lower panel). This implies that even though LL0 is being optically pumped, its population decreases [1] ! Calculations show that LL0 is actually depleted by strong Auger scattering. Note that the two configurations shown in the Figure are distinguishable only because of the slight (n-type) doping of the graphene sample.
We discuss the role of carrier-carrier and carrier-phonon scattering in Landau quantized graphene and provide an outlook on the application potential of this system for tunable THz lasers.

Keywords: Graphene, Landau levels, carrier relaxation, pump-probe, free electron laser
  • Lecture (Conference)
    Electronic Properties Of Two-Dimensional Electron Systems (EP2DS-21), 26.-31.07.2015, Sendai, Japan
Registration No. 22305

Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel
Duan, K. J.; Zhang, L.; Yuan, X. Z.; Han, S. S.; Liu, Y.; Huang, Q. S.
Abstract: An induction levitation melting (ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel (UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.
Keywords: ultra-low carbon steel; magnetic field; sulfide precipitation; induction levitation; titanium Registration No. 22304

In-situ observation of 3D particle assembly
Josten, E.; Wetterskog, E.; Glavic, A.; Boesecke, P.; Rücker, U.; Bergström, L.; Brückel, T.
Abstract: The self-assembly of magnetic nanoparticles has a high potential for future applications [1], as it allows mass production processes of very small structures without the use of expensive equipment. The process itself is complex, including several interactions between nanoparticles, solvent, and substrate. A deeper understanding is the key for a better control of the self-organization process.

The present work adds a novel quantitative contribution to the study of the kinetics in 3D long range ordered nanoparticle superstructures. These superstructures have been investigated in-situ during the self-assembly using an optimized GISAXS setup to explore the dynamic growthmodes during deposition. The nanoparticles investigated are well-characterized γ-Fe2O3 nanospheres [2,3], which have been deposited on a substrate to form an ensemble of highly ordered superstructures (mesocrystals) [4].

The time-dependent GISAXS study of the self-assembly process, carried out at the ID01 beamline at ESRF, resulted in an understanding of how the structures evolve with time and how the evaporation can be controlled by external parameters. The in-situ cell (fig.1), which was developed to monitor the structure as well as the height and shape of the droplet, was employed for additional control of the process parameters and the possibility of an accurate identification of key physical parameters governing the process. The time evolution of the ordering process was analyzed by fitting position and width of multiple peaks for all recorded GISAXS patterns (for example fig.2). New insights into the drying and self-assembly process of an ensemble of 3D highly ordered superstructures were obtained and evaporation time-dependent stages of the mesocrystal growth and their spatial positions were identified [5].

Keywords: magnetic nanoparticles, in-situ GISAXS, self-assembly, X-ray scattering, mesocrystals
  • Lecture (Conference)
    GISAS2015, 08.-11.09.2015, Nice, Frankreich
Registration No. 22302

Stability of MR brain-perfusion measurement using arterial spin labeling
Petr, J.; Hofheinz, F.; Platzek, I.; Schramm, G.; van den Hoff, J.
Abstract: Arterial spin labeling (ASL) is an MR technique for assessment of cerebral blood flow (CBF) that does not require use of contrast agents which makes it a less invasive alternative to the 15O-H2O-PET measurement. The repeatability of ASL has been studied extensively but mainly in young healthy volunteers. We have tested repeatability of ASL under realistic clinical conditions in elderly brain tumor patients acquired with a Philips Ingenuity TF PET/MR in the context of an ongoing 11C-Methionine PET/MR study. Twenty three patients (age 54.8±13.0 y) were scanned on two or more session. The patients underwent 6 weeks of concurrent radiochemotherapy with Temozolomide between the first session and second measurement. The mean relative difference of gray matter CBF was 18.6% between the first two session and 13.0% for the second session and further on. The mean gray matter CBF was 46.6±7.2 mL/min/100 g on the first sessions and there was a significant decrease of 9.8% between first and second session (p=0.027). In summary, the ASL presents measurement of CBF with reasonable repeatability also in elderly patients under clinical conditions when it is not possible to control for all sources of variation. Significant decrease of CBF in healthy tissue was observed after the radiochemotherapy. Prospectively, the ASL data together with the also acquired 11C-Methionine PET will be evaluated regarding their separate and combined ability to predict patient outcome and effectiveness of the performed radiochemotherapy.
  • Lecture (Conference)
    PSMR 2015: 4th Conference on PET/MR and SPECT/MR, 17.-21.05.2015, La Biodola, Isola d’Elba, Italy
  • Abstract in refereed journal
    EJNMMI Physics 2(2015)Suppl. 1, A67
    DOI-Link: http://dx.doi.org/10.1186/2197-7364-2-S1-A67


Registration No. 22300

Measuring the Influence of Vessel Geomery on PCASL Labeling Efficiency
Petr, J.; Schramm, G.; van den Hoff, J.
Abstract: TARGET AUDIENCE: Clinicians and researcher interested in efficient planning of the pseudo-continuous arterial spin labeling (ASL).
PURPOSE: The labeling efficiency of pseudo-continuous ASL1 (pCASL) and its inter- and intra-subject reproducibility is a crucial point for reliable cerebral-blood-flow (CBF) measurements with ASL. Potential causes of varying labelling efficiency are, for example, B0 field inhomogeneity2, blood velocity3, or labeling-plane positioning3. The common recommendation is to position the labeling plane on a straight part of the vessel and perpendicular to them6. However, it is not always possible to avoid tortuous parts of the vessels if angiography is not available. Here, we study the effect of vessel geometry on the labeling efficiency both trough simulations and experiments.
METHODS: Simulations: Labeling efficiency was calculated for three cases of vessels geometry using numerical simulations as described by Wu4. Blood velocities between 1 and 40 cm/s were investigated and laminar flow was assumed. First, efficiency was calculated for a plane perpendicular to a straight vessel and angulated at 12.5°, 22.5°, or 45°. Second, a simple bend of the vessel was assumed with a length of the horizontal section of 0, 5, or 10 mm and the labeling plane positioned on the center of it and 2, 6, or 12 mm below (see Fig. 1a). Third, the bend was rotated 0°, 12.5°, 22.5°, or 45° so that the labeling plane intersected the vessel three times (Fig. 1b). Acquisitions: Five healthy young volunteers (age 31.8±3.9 y) were scanned at 3T using an eight-channel head-coil. A 3D TFE T1-weighted sequence and five pCASL sequences (pCASL1-pCASL5) with different position of the labeling plane were acquired. The T1-weighted sequence had voxel size 1×1×1 mm3. The common parameters of the pCASL sequence were: TR/TE = 3765/11 ms, FOV = 220×220 mm2,
pixel size = 2.75×2.75×6 mm3, 17 slices (0.6 mm gap), flip angle = 90°, 20 averages, background suppression with 2 pulses, 2D multi-slice EPI readout, labeling with a Hanning RF-pulse with duration 0.5 ms, tip angle 18°, and inter-pulse pause 0.5 ms, labeling time/post-labeling delay 1525/1650 ms. A reference image was acquired 5000 ms after saturation. For pCASL1, the labeling plane was set parallel with the imaged slices and the gap
was set in a way that the labeling plane intersected vertebral arteries (VA) at the level of siphon. The labeling plane was placed as parallel to the horizontal section of the VAs as possible (Fig. 1c). For pCASL2,3, the labeling plane was positioned 6 and 12 mm lower, respectively, than in pCASL1 (Fig. 1c). In pCASL4, 5 the labeling plane was positioned as in pCASL3 and rotated in the sagittal plane -30° and 30° with the center of rotation in the internal
carotid arteries (ICA), see Fig. 1c.
Preprocessing: The dynamics of all sequences were aligned with the first dynamics of pCASL1, thus coregistering the sequences and compensating for motion within each sequence. The T1-weighted image was aligned to the mean control image and segmented to obtain partial volume fractions for gray matter (GM). CBF was quantified according to the ASL white-paper6. Mean CBF (GM > 70%) in the vascular territories corresponding to the anterior cerebral artery (ACA), posterior cerebral artery (PCA), middle cerebral artery (MCA), and vertebral artery (VA) were computed for each sequence and subject. For pCASL1,2,4,5, the relative difference of the
mean CBF for each region was calculated relative to pCASL3 which was considered optimal as it contained no twists or angulations.
RESULTS: According to the numerical simulations, the decrease in labeling efficiency due to plane angulation is under 5% for most blood velocities and angle up to 30°, but it can go up to 10% for 45° angulation (Fig. 2c). For a bend in the vessel (Fig. 1a) of length 10 mm, the labeling efficiency can be decreased 20-25% (Fig. 2b). With increasing distance of the labeling plane, the decrease is only about 10% at 2mm (Fig. 2a), under 3% at 6mm and under 1% at 12 mm distance. For multiple intersections (Fig. 1b), the labeling efficiency decreased 25-30% regardless of the examined angle. The mean relative difference from sequence pCASL3 for different vascular territories is displayed in Tab. 2.
DISCUSSION: The experiments confirmed that labeling plane shift (pCASL1,2 in Tab. 1) or angulation up to 30° on ICA (pCASL4,5) produced less than 4% change of CBF in the ACA and MCA regions. Positioning the labeling plane on a section of VA parallel with it (pCASL1) caused 5.0% and 14.7% CBF decrease in PCA and VA regions respectively, although only in VA the change was significant. By increasing the distance from the bend (pCASL2), the CBF decrease became lower and not significant. Significant decrease of CBF of 8.4% and 16.9% in both PCA and VA regions, respectively, was achieved by positioning the labeling plane in a way to intersect VA at siphon multiple times. More significant decrease was expected from the simulations. The reason can be, that the actual vessel geometry was different from the worst modeled case. More measurements need to be done to find out why the decrease was lower in PCA than in VA. There are several limitations in this study. The magnetization transfer effects on the label were not taken into account5. Laminar flow profile was assumed, however the vessel thickness with regards to gradient fields was neglected for simplicity. By angulating the labeling plane, it is possible that it can intersect the imaged volume and thus directly or by magnetization transfer effects lower the measured perfusion signal. To minimize influence of this, the pixels where minimal-maximal intensity difference for all sequences was more than 10% were excluded from the analysis.
CONCLUSION: Reasonable angulation of the labeling plane causes only insignificant changes in labeling efficiency and measured CBF. On the other hand, twist and loops of the vessels as well as multiple crossing of the vessels by a labeling plane can cause significant changes of up to 25% and possibly even more, although this has been experimentally demonstrated only in VA region and not in PCA region.
1. W Dai, et al. Magn Reson Med, 2008;60(6):1488–97.
2. H Jahanian, et al. NMR in Biomedicine, 2011;24(10):1202–9.
3. S Aslan, et al. Magn Reson Med, 2010;63(3):765–71.
4. WC Wu, et al. Magn Reson Med, 2007;58(5):1020–7.
5. L Hernandez-Garcia, et al. NMR in Biomedicine, 2007;20(8):733–42.
6. Alsop, et al. Magn Reson Med, 2014; DOI: 10.1002/mrm.25197.
  • Poster
    23rd Annual Meeting of the International Society for Magnetic Resoonance in Medicine (ISMRM), 30.05.-05.06.2015, Toronto, Canada
  • Contribution to proceedings
    23rd Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM), 30.05.-05.06.2015, Toronto, Canada
    ISMRM '15: Proceedings of the 23rd Scientific Meeting and Exhibition of International Society for Magnetic Resonance in Medicine, 2952
Registration No. 22299

An implementation of dead-time corrections in microbeam measurements on a pixel by pixel basis
Munnik, F.
Abstract: In microbeam measurements on inhomogeneous samples large variations in count-rate can occur. These variations result in variations in dead-time that have to be used to correct elemental distribution maps. However, the dead-time is usually not available on a pixel by pixel basis. In this work, a simple model is proposed to calculate the dead-time for each pixel. Measurements to determine the dead-time per event, needed in the model, are presented and the dead-time corrections are presented for real samples.
  • Poster
    Workshops für Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Deutschland
Registration No. 22298

Ionenstrahlanalyseverfahren in der Materialforschung
Schmidt, B.; Wetzig, K.
Abstract: Der Schwerpunkt der Materialanalyse mittels Ionenstrahlen ist die Bestimmung der Zusammensetzung und Struktur von oberflächennahen Festkörperschichten im Tiefenbereich von wenigen nm bis zu einigen µm. Charakteristisch für die verschiedenen Ionenstrahlanalysetechniken sind die Verwendung geeigneter Ionenstrahlen (z.B. Ionenart, Ionenenergie und -strom, Strahlfokus usw.), die Art der Ionen-Festkörper-Wechselwirkung (und deren Wirkungsquerschnitt), die entstehende Strahlungsart (z.B. gesputterte Sekundärionen, gestreute Ionen sowie Ionen-induzierte Photonen- und Elektronenemission). Die Vielzahl der Ionenstrahl-analyseverfahren kann bezüglich der verwendeten Ionenenergien in drei Gruppen eingeteilt werden [1]: 1) niedrige Ionenenergien von einigen keV, 2) mittlere Ionenenergien im Bereich 30-300 keV, und 3) hohe Ionenenergien im Bereich ~0,5-100 MeV. Schwere Ionen (Mi > Moxygen) für eine hinreichende Sputterausbeute an Targetatomen sind notwendig im weit verbreiteten Verfahren der Sekundärionen-Massen-Spektrometrie (SIMS). Leichte Ionen (M < 10, meistens H+, He+) werden in einem breiten Energiebereich für verschiedene Ionenstreuverfahren (LEIS, MEIS, RBS) sowie verschiedene Verfahren der Ionen-induzierten Photonenemission (PIXE, PIGE) eingesetzt. Dagegen werden schwerere, hochenergetische Ionen (z.B. N, O, Cl usw.) hauptsächlich für NRA und ERDA verwendet.
Im Vortrag werden die verschiedenen Ionenstrahlanalyseverfahren mit ihren charakteristischen Analyseparametern und Einsatzgebieten kurz vorgestellt und miteinander verglichen. Dabei wird besonders auf die hochauflösende Tiefen-profilierung für Dotierungsprofile in Halbleitern und die Elementanalyse von Dünnschichtsystemen eingegangen. Hierfür sind besonders die modernen Mikroelektronik- und Dünnschichttechnologien mit Forderungen nach immer dünneren Schichtsystemen und somit nach steigender Tiefenauflösung sowie kleineren Nachweisgrenzen die treibende Kraft. Weiterhin werden ausgewählte Beispiele für den Einsatz von Ionenstrahlanalyseverfahren in anderen Gebieten der Materialwissenschaften, z.B. in der Kunst und Archäometrie sowie in der Medizin diskutiert.
  • Invited lecture (Conferences)
    18. Tagung Festkörperanalytik, 06.07.2015, Wien, Österreich
Registration No. 22297

Probing defect driven tunable spontaneous magnetization in paramagnetic Zn0.95Co0.05O epitaxial films by X-ray absorption investigations
Satyarthi, P.; Ghosh, S.; Wang, Y.; Zhou, S.; Kumar, P.; Kanjilal, D.; Olivi, L.; Bürger, D.; Skorupa, I.; Schmidt, H.; Srivastava, P.
Abstract: In order to address existing unresolved issues related to intrinsic and extrinsic origins of ferromagnetism in Zn1−xCoxO based diluted magnetic semiconductors for varying x, the present work aims to investigate the tunable ferromagnetism triggered in paramagnetic Zn0.95Co0.05O films using 500 KeV inert xenon ion irradiation of different fluences. The origin of ferromagnetism in post irradiated Zn0.95Co0.05O films is understood from different densities of bound magnetic polarons (BMPs) formation through correlated spins of tetrahedrally substituted Co2+ ions and anionic vacancies. The alteration in crystallographic positions of Zn, Co cations, and O anions in the tetrahedral environment as analyzed from Zn and Co K-edgeX-ray absorption and O 1s photoemission is a crucial factor for the stabilization of different density of BMPs. Magnetic field and temperature dependence of X-ray magnetic circular dichroism at the Co L2,3 edge provide experimental evidence of purely paramagnetic contribution from well localized Co2+ ions of Co sublattice for paramagnetic Zn0.95Co0.05O film. The paramagnetic Co2+ ions of Co sublattice persist in irradiated films, which reveal BMPs formation as the origin of ferromagnetism.
Keywords: Diluted magnetic semiconductors; X-ray absorption; Spintronics Registration No. 22296

Two-photon quantum well infrared photodetectors below 6 THz
Franke, C.; Walther, M.; Helm, M.; Schneider, H.
Abstract: Two-photon quantum well infrared photodetectors (QWIPs) are nonlinear detectors for the mid-infrared and terahertz regimes optimized for resonant two-photon absorption. Here we present first results on two-photon QWIP samples based on the GaAs/AlGaAs material system with intersubband energies between 25 and 12 meV (6 to 3 THz) confirmed by photocurrent spectra. The dark current showed large discontinuities, presumably caused by impact ionization. We performed interferometric autocorrelation experiments at the free-electron laser FELBE and observed nonlinear interferograms for all samples.
Keywords: quantum well infrared photodetector; QWIP; interferometric autocorrelation; nonlinear optics; two-photon absorption Registration No. 22289

Innovative once-through thorium fuel cycle for the PTVM LWR concept
Rachamin, R.; Fridman, E.; Galperin, A.
Abstract: An advanced once-through thorium fuel cycle for the novel reactor concept, termed the pressure tube light water reactor with variable moderator control (PTVM LWR), is proposed. The main innovation of the concept is described. The PTVM LWR makes use of a seed-blanket geometry, whereby the core is divided into separated regions of thorium fuel channel assemblies (blanket) and low-enriched uranium fuel channel assemblies (seed). A scheme based on two separate fuel flow routes (i.e., seed route and blanket route) is proposed. Neutronic analysis indicates that the novel scheme has the potential to utilize both seed and blanket in an efficient manner.
Keywords: pressure tube reactor, “breed & burn”, moderator variation, seed-blanket geometry, once-through thorium fuel cycle
  • Contribution to proceedings
    Thorium Energy Conference 2015 (ThEC15), 12.-15.10.2015, Mumbai, India
Registration No. 22288

Nanoporous Ge surface decomposition under ion bombardment: towards settling the dispute about driving forces
Böttger, R.; Liedke, B.; Liedke, M. O.; Heinig, K.-H.; Bischoff, L.
Abstract: First detailed studies of the nanoporous decomposition of Ge under ion irradiation date back more than 30 years. Irradiated Ge alters its (near-)surface morphology into a nanostructure, which remains stable after irradiation even under thermal treatment up to several hundred degrees Celsius. In recent years, this peculiar transformation of Ge has been studied extensively. However, a conclusive assessment of the driving force for the nanoporous Ge decomposition has not been reached yet.

We show that hole patterns and sponge-like layers of irradiated Ge surfaces originate from the same driving force, namely the kinetics of irradiation-induced defects in amorphous Ge layers. Ge hole patterns reported earlier for irradiation with low ion energies around 5 keV were reproduced for low energy Bi+ but also for Ge+ self-irradiation, which proves that the dominating driving force for morphology evolution cannot originate from the implanted impurities. At higher ion energies up to 100 keV the well-known formation of sponge-like Ge surface layers after heavy ion irradiation was found for Bi+ irradiation and Ge+ self-irradiation, too. The transition from smooth surfaces via hole patterns to sponge-like morphologies with increasing ion energy has been studied in detail. A model based on the kinetics of ion beam-induced defects was developed and implemented in 3D kinetic Monte Carlo simulations, which reproduce the transition from hole patterns to sponge-like layers with increasing ion energy. Finally, the proposed defect kinetics driven mechanism is undergird by a systematic positron annihilation spectroscopy investigation.
The authors acknowledge financial funding by the German Research Foundation via the Research Unit 845 “Selforganized nanostructures induced by low-energy ion beam erosion.”

Keywords: porous germanium, ion irradiation, defect kinetic, kinetic Monte-Carlo
  • Lecture (Conference)
    Workshop Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Deutschland
  • Lecture (Conference)
    8th International Workshop on Nanoscale Pattern Formation at Surfaces, 12.-16.07.2015, Krakow, Poland
Registration No. 22283

Distribution of Sb minerals in the Cu and Zn flotation of Rockliden massive sulphide ore in north-central Sweden
Minz, F. E.; Bolin, N.-J.; Lamberg, P.; Bachmann, K.; Gutzmer, J.; Wanhainen, C.
Abstract: The Rockliden massive sulphide Zn-Cu deposit contains minor amounts of Sb minerals. The Sb mineralogy is complex in terms of composition, micro textures and mineral associations. The main Sb minerals comprise tetrahedrite, bournonite, gudmundite and Sb-Pb sulphides such as meneghinite. The presence of these minerals is especially critical to the quality of the Cu-Pb concentrate. To study how they are distributed in a simplified flotation circuit and what controls their process behaviour Sb-rich drill core samples were selected from the Rockliden deposit and a standard laboratory flotation test was run on the composite samples. Scanning electron microscope-based automated mineralogy was used to measure the Sb mineralogy of the test products, and the particle tracking technique was applied to mass balance the different liberation classes to finally trace the distribution of liberated and locked Sb minerals. The mineralogical factors controlling the distribution of Sb minerals are mineral grain size, the degree of liberation, and associated minerals. Similarities in the distribution of specific particle types from the tested composites point towards systematics in the behaviour of particles and predictability of their distribution which is suggested to be used in a geometallurgical model of the deposit.
Keywords: Sulphide ores, Antimony, Liberation analysis, Particle tracking, Froth flotation Registration No. 22279

Pulsed high-field magnets – An efficient way of shaping laser accelerated proton beams for application
Kroll, F.; Bagnoud, V.; Blažević, A.; Brabetz, C.; Busold, S.; Deppert, O.; Jahn, D.; Karsch, L.; Kraft, S.; Masood, U.; Roth, M.; Schumacher, D.; Schramm, U.
Abstract: Compact laser-driven proton accelerators are a potential alternative to complex, expensive conventional accelerators, enabeling unique beam properties, like ultra-high pulse dose. Nevertheless, they still require substantial development in reliable beam generation and transport.

We present experimental studies on capture, shape and transport of laser and conventionally accelerated protons via pulsed high-field magnets. These magnets, common research tools in the fields of solid state physics, have been adapted to meet the demands of laser acceleration experiments.Our work distinctively shows that pulsed magnet technology makes laser acceleration more suitable for application and can facilitate compact and efficient accelerators, e.g. for material research as well as medical and biological purposes.
  • Lecture (Conference)
    DPG-Frühjahrstagung, Wuppertal, 2015, 09.-13.03.2015, Wuppertal, Deutschland
Registration No. 22274

A laser-driven ion beamline for generating well-defined ultra-short ion bunches at highest intensities
Kroll, F.; Busold, S.; Schumacher, D.; Brabetz, C.; Jahn, D.; Deppert, O.; Kraft, S.; Schramm, U.; Cowan, T. E.; Blažević, A.; Bagnoud, V.; Roth, M.
Abstract: The LIGHT collaboration [1] has installed a laser-driven ion beamline at GSI Helmholtz Center for Heavy Ion Research. For the first time it is now possible to study the feasibility and potential of shaping laser-driven ion beams for future applications. We report on the temporal recompression of a laser-accelerated ion bunch.
In the presented experiment (c.f. Fig. 1), a dedicated arm of the high-power laser PHELIX was used to drive a TNSA proton source using gold and titanium foils. The 650 fs short, 20 J laser pulse produces the typical exponentially decaying energy spectrum with about 10^10 particles at an energy of 10±0.5 MeV and energy cut-off at 28.4 MeV. The protons are captured by a pulsed high-field solenoid, energy selected and modulated in a conventional radiofrequency cavity and transported along a drift line to the end station by means of permanent magnetic quadrupoles. However, the long drift between the laser target and the cavity introduces a temporal spread-out of the polychromatic beam.
Most recently, we accomplished a recompression of the ion bunch by a well-chosen acceleration voltage of the rf cavity achieving phase-focusing in the following 3.5 meter long drift behind the cavity. At the end station we measured a central energy of 7.8 MeV; up to 5×10^8 protons could be temporally compressed to a bunch with duration of 462±40 ps (FWHM). The bunches show a moderate energy spread between 10 % and 15 % and are available at 6 m distance to the source, thus well separated from the harsh laser-acceleration environment. Such well-defined sub-nanosecond intense ion bunches are ideal for the generation and study of warm dense matter and can probe transient phenomena with unprecedented time resolution.
Fig. 1. LIGHT beamline experiment setup: a) TNSA proton source driven by the PHELIX laser and captured by the high-field solenoid b). The transported particles are rotated in longitudinal phase space by the cavity c). The permanent magnetic quadrupole doublets d), e) and optionally f) transport the beam towards the end station g) where the beam was diagnosed.
[1] S. Busold et al., Nucl. Instr. Meth. Phys. Res. A 740, 94 (2014).
  • Lecture (Conference)
    Laser Plasma Acceleration Workshop 2015, 10.-15.05.2015, Deshaies, Guadeloupe, Frankreich
Registration No. 22273

Towards highest peak intensities for ultra-short MeV-range ion bunches
Busold, S.; Schumacher, D.; Brabetz, C.; Jahn, D.; Kroll, F.; Deppert, O.; Schramm, U.; Cowan, T. E.; Blažević, A.; Bagnoud, V.; Roth, M.
Abstract: A laser-driven, multi-MeV-range ion beamline has been installed at the GSI Helmholtz center for heavy ion research. The high-power laser PHELIX drives the very short (picosecond) ion acceleration on μm scale, with energies ranging up to 28.4MeV for protons in a continuous spectrum. The necessary beam shaping behind the source is accomplished by applying magnetic ion lenses like solenoids and quadrupoles and a radiofrequency cavity. Based on the unique beam properties from the laser-driven source, high-current single bunches could be produced and characterized in a recent experiment: At a central energy of 7.8MeV, up to 5×10^8 protons could be re-focused in time to a FWHM bunch length of τ=(462±40) ps via phase focusing. The bunches show a moderate energy spread between 10% and 15% (ΔE/E0 at FWHM) and are available at 6m distance to the source und thus separated from the harsh laser-matter interaction environment. These successful experiments represent the basis for developing novel laser-driven ion beamlines and accessing highest peak intensities for ultra-short MeV-range ion bunches.


Registration No. 22272

Flash-Lamp-Enhanced Atomic Layer Deposition of Thin Films
Henke, T.; Knaut, M.; Hossbach, C.; Geidel, M.; Rebohle, L.; Albert, M.; Skorupa, W.; Bartha, J.
Abstract: Within this work flash lamp annealing (FLA) is utilized to thermally enhance the film growth in atomic layer deposition (ALD). First, the basic principles of flash-lamp-enhanced ALD (FEALD) are presented in detail, the technology is reviewed and classified. Thereafter, results of our studies on the FEALD of aluminum-and ruthenium-based thin films are presented. These depositions were realized by periodically flashing on a substrate during the precursor exposure. It is shown that the film growth is induced by the flash heating and that the processes exhibit typical ALD characteristics. The obtained relations between flash parameters and film growth parameters are discussed with the main focus on the impact of the FLA-caused temperature profile on the film growth.
Besides, this work addresses technical challenges for the practical realization of this method and demonstrates the potential of this technology to extend the capabilities of thermal ALD.

Keywords: flash lamp annealing, atomic layer deposition, thin film Registration No. 22270

European activities on crosscutting thermal-hydraulic phenomena for innovative nuclear systems
Cheng, X.; Batta, A.; Bandini, G.; Roelofs, F.; van Tichelen, K.; Gerschenfeld, A.; Prasser, M.; Papukchiev, A.; Hampel, U.; Ma, W. M.
Abstract: Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. In Europe, a consortium is established consisting of 24 institutions of universities, research centers and nuclear industries with the main objectives to identify and to perform research activities on important crosscutting thermal-hydraulic issues encountered in various innovative nuclear systems. For this purpose the large-scale integrated research project THINS (Thermal-Hydraulics of Innovative Nuclear Systems) is launched in the 7th Framework Programme FP7 of European Union. The main topics considered in the THINS project are (a) advanced reactor core thermal-hydraulics, (b) single phase mixed convection, (c) single phase turbulence, (d) multiphase flow, and (e) numerical code coupling and qualification. The main objectives of the project are:
Generation of a data base for the development and validation of new models and codes describing the selected crosscutting thermal-hydraulic phenomena.
Development of new physical models and modeling approaches for more accurate description of the crosscutting thermal-hydraulic phenomena.
Improvement of the numerical engineering tools for the design analysis of the innovative nuclear systems.
This paper describes the technical tasks and methodologies applied to achieve the objectives. Main results achieved so far are summarized.
Registration No. 22269

Hyperspectral remote sensing for mineral mapping of structural related mineralizations around Mount Isa, Queensland, Australia
Jakob, S.; Salati, S.; Gloaguen, R.
Abstract: Alone or combined with other remote sensing data, hyperspectral mineral mapping can be used to investigate mineralizations and deposits via alteration minerals. Their kind, abundance and spatial distribution can deliver important statements about the occurrence and formation of mineralizations and their relation to structural features. The high spectral and spatial resolution of HyMap data exceeds multispectral data distinctly and makes the recognition of even smaller geological structures possible. The spectral unmixing of single endmembers can be used for the accurate mapping of specific materials or minerals.The support of hyperspectral imaging by spectral data gathered in the field and the analysis of the composition of rock samples can help to determine endmembers and to identify absorption features.
This study demonstrates the possibilities and limitations of remote sensing, especially hyperspectral data, for mineral mapping purposes, using the example of the Mount Isa Inlier. This geological area is situated in Northern Queensland, Australia, and is known for its considerable ore deposits and consequent mining of predominantly copper, zinc, lead, silver and gold. Beside hyperspectral HyMap data, multispectral Landsat 8 and SRTM digital elevation data were analyzed. A three-week field study in 2014 supported the investigations.
After preprocessing and vegetation masking the data were analyzed using Spectral Feature Fitting (SFF) and Mixture Tuned Matched Filtering (MTMF) for alteration mineral mapping. The outcomes were combined with results from decorrelation stretch, band ratioing, topographic indices and automated lineament analysis. Additional information was provided by field spectrometer measurements and the XRF and XRD analysis of rock samples.
Throughout the study, mineral mapping using remote sensing data, especially hyperspectral data, turned out to deliver high qualitative results when it is supported by additional information. In situ investigation of the observed mineralizations for validation is important and can deliver such data, for instance by the investigation of rock samples or spectral measurements. Since mineralizations and alterations are often related to structures, their analysis and consideration can provide crucial hints.
The most significant result throughout the study was the determination of a new site of gossanous, silicified ridges south of the Mount Isa mining complex. Their occurrence was validated through fieldwork observations including rock sampling and spectral measurements. The gathered information additionally supported the accurate mapping of those ridges using HyMap data, which confirmed the connection between the north-south trending ridges and the Mount Isa mine deposits. The observed ridges coincide compositionally and spectrally with the outcrops of mineralized parts of the Urquhart Shale, which form the mined Pb-Zn-Ag deposits and are probably related to structures. In samples of the new site, amounts of Pb, Zn, Ag and other metals could be detected. Contrary to the mineralized outcrops of the Urquhart Shale deposits, those ridges occur outside of the common host rock and are not mentioned as mineralizations in any available map or publication.
  • Poster
    EGU General Assembly 2015, 14.04.2015, Wien, Österreich
Registration No. 22268

Formation of Ge-0 and GeOx nanoclusters in Ge+-implanted SiO2/Sithin-film heterostructures under rapid thermal annealing
Zatsepin, A. F.; Zatsepin, D. A.; Zhidkov, I. S.; Kurmaev, E. Z.; Fitting, H. J.; Schmidt, B.; Mikhailovich, A. P.; Lawniczak-Jablonska, K.
Abstract: The results of X-ray photoelectron spectra (XPS valence band and core levels) measurements for Ge+ implanted SiO2/Si heterostructures are presented. These heterostructures have a 30 nm thick Ge+ ion implanted amorphous SiO2 layer on p-type Si. The chemical-state transformation of the host-matrix composition after Ge+ ion implantation and rapid thermal annealing (RTA) are discussed. The XPS-analysis performed allows to conclude the formation of Ge-o and GeOx clusters within the samples under study. It was established, that the annealing time strongly affects the degree of oxidation states of Ge-atoms

Simulating Multi-Scale Physics in Solid Target Laser-Ion Acceleration
Huebl, A.; Kluge, T.; Hilz, P.; Bussmann, M.
Abstract: Laser-ion acceleration from solid targets with ultra-intense laser pulses on the fs time scale is a central research topic for next generation particle accelerators. Accompanying processes are highly non-linear and require precise knowledge about the influence of both ab-initio electro-magnetic and atomic evolution of the plasma.

Consequently, modeling the acceleration process with simulations does not only require kinetic models with very high resolution (from the order of the inverse plasma frequency to the ns acceleration process) but also self-consistent models for non-equilibrium plasma and ionization processes.

We present large scale, 3D3V simulations with the fully-relativistic particle-in-cell code PIConGPU on the ORNL Titan cluster of mass-limited droplet targets related to recent experiments levitating these in Paul-traps.
In comparison with large 2D surveys the dependence of plasma instabilities and resulting ion energies under the variation of target material and laser properties is shown.

Keywords: laser particle acceleration, ion acceleration, mass limited targets, HPC, GPU, simulation, PIConGPU
  • Lecture (Conference)
    42nd EPS Conference on Plasma Physics 2015, 22.-26.06.2015, Lisbon, Portugal
Registration No. 22265

Annual Report 2014 - Institute of Ion Beam Physics and Materials Research
Fassbender, J.; Heera, V.; Helm, M.; Zahn, P. (Editors)
Abstract: This past year 2014 was the year when we finally completely arrived as a “full member” in the Helmholtz Association. This is related to the successfully passed research evaluation in the framework of the Program Oriented Funding (POF), which will give us a stable and predictable funding for the next five years (2015 – 2019). This is particularly true for our large-scale user facilities, like the Ion Beam Center (IBC) and the electron accelerator ELBE with the free-electron laser. Most of our activities are assigned to the program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”.

Our research and facilities were well appreciated by the evaluation committee, who made the following judgement about the Ion Beam Center:
“The Ion Beam Centre (IBC) of HZDR is an internationally leading ion-beam facility (with ion energies ranging from several eV to several tens of MeV). At both the national and international level it is one of the key players and is unique in its kind. The synergy between forefront research and user service has been leading to a very good publication output for both in-house research and user research. …
The very broad range of beam energies, the versatility of techniques and applications – both for ion beam modification of materials and for ion-beam analysis – makes the IBC unique in its kind. …
The strength of IBC is that its activities are based on a combination of forefront research and user service, which mutually interact in synergy and strengthen one another. In turn, this synergy has been leading to a very good publication output for both in-house research and user research.”
In order to make our Annual Report a bit more compact, we have decided to include only four full journal papers this year. This was also triggered by the fact that our publication activities have turned out be become more diverse, in more diverse journals than in the past, and often through longer papers, which would be too long to reprint them here. However, apart from the constantly quantitatively high publication output, we succeeded to publish in excellent journals such as Nature Physics, Nano Letters and Physical Review Letters, in fields as diverse as ion beam physics, magnetism and terahertz spectroscopy.
Two of our scientists, Dr. Artur Erbe and Dr. Alexej Pashkin obtained their Habilitation in 2014, both at University of Konstanz. For the first time, we are hosting an Emmy Noether Young Investigator Group funded by the Deutsche Forschungsgemeinschaft (DFG); the group works on the hot topic of magnonics and is headed by Dr. Helmut Schultheiß.
Finally we would like to cordially thank all partners, friends, and organizations who supported our progress in 2014. Special thanks are due to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Minister of Education and Research of the Federal Government of Germany. Numerous partners from universities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank again all IIM staff for their efforts and excellent contributions in 2014.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-060 2015


Registration No. 22263

Building a New Assessment Tool for Potential Rare Earth Underground Mining Projects
Barakos, G.; Mischo, H.
Abstract: Once an ore body has been probed and outlined and initial resource indications deserve further attention, the evaluation stage has to begin to determine the potential exploitation. This analysis is a sophisticated process, let alone when it comes to underground mining projects and especially on rare earth deposits that are governed by notable boundary conditions. However, the significant numbers of the parameters to be considered and their complexity, as well as the solvency of the outcomes, often result in questioning the suitability of common evaluation methods. This has created a necessity for a new evaluation procedure that focuses on potential rare earth underground mining projects. This paper describes the construction development of an assessment tool that considers not only the mining method selection process but identifies social, economic and environmental impact factors and Rare Earth Element industry-specific criteria as well. Based on the philosophy of previous linguistic and numerical approaches, this combined tool is based on a step-by-step numerical analytical hierarchical process with weighted criteria. The purpose of building this tool is to adjust to the specifications of rare earth underground mining projects and to contribute into having accurate and secure con-clusions for if and when investment decisions should be made and minimize the potential risks regarding the viability of any mining project.
Keywords: rare earths, underground mining method selection, viability, assessment tool
  • Contribution to proceedings
    7th Sustainable Development In Minerals Industry Conference (SDIMI 2015), 12.-15.07.2015, Vancouver, Canada
    Proceedings of SDIMI 2015, Vancouver: University of British Columbia
Registration No. 22260

Setting the REE industry-specific criteria and their significant role in the viability of rare earth underground mining projects
Barakos, G.; Mischo, H.
Abstract: To evaluate the feasibility of a future underground mining operation is a complex problem in itself, with several different parameters to be accounted for and evaluated to secure investment decisions over the viability of any potential underground mining project. This procedure gets even more complicated when it comes to exploiting rare earth deposits. Various concerns are expressed regarding the environmental impacts that an underground mining operation may cause due to the radioactivity of the rare earth elements during mining and in waste treatment. Furthermore, the fragile market and the diversified supply and demand of the different rare earth elements can significantly affect the viability of such a venture, among other factors. This paper deals with the definition and classification of the specific criteria that govern the REE mining industry. Moreover, a thorough investigation is made of how these criteria can determine not only the selection of the underground mining method to be applied, but also of the impact that they may have to the overall feasibility of any given potential project.
Keywords: rare earth elements, underground mining, sustainability, environmental impacts, balance problem
  • Contribution to proceedings
    26th Annual Meeting & Conference of the Society of Mining Professors, 21.-26.06.2015, Freiberg, Deutschland
    Proceedings of the 26th Annual Meeting & Conference of the Society of Mining Professors, Backnang, Stuttgart: WIRmachenDRUCK, 978-3-86012-505-2
Registration No. 22259

Broken vertex symmetry and finite zero-point entropy in the artificial square ice ground state
Gliga, S.; Kákay, A.; Heyderman, L. J.; Hertel, R.; Heinonen, O. G.
Abstract: We study degeneracy and entropy in the ground state of artificial square ice. In theoretical models, individual nanomagnets are typically treated as single spins with only two degrees of freedom, leading to a twofold degenerate ground state with intensive entropy and thus no zero-point entropy. Here, we show that the internal degrees of freedom of the nanostructures can result, through edge bending of the magnetization and breaking of local magnetic symmetry at the vertices, in a transition to a highly degenerate ground state with finite zero-point entropy, similar to that of the pyrochlore spin ices. We find that these additional degrees of freedom have observable consequences in the resonant spectrum of the lattice, and predict the occurrence of edge “melting” above a critical temperature at which the magnetic symmetry is restored.
Keywords: zero-point entropy, artificial spin-ice Registration No. 22258

Simulation studies for the in-vivo dose verification of particle therapy
Rohling, H.
Abstract: An increasing number of cancer patients is treated with proton beams or other light ion beams which allow to deliver dose precisely to the tumor. However, the depth dose distribution of these particles, which enables this precision, is sensitive to deviations from the treatment plan, as e.g. anatomical changes. Thus, to assure the quality of the treatment, a non-invasive in-vivo dose verification is highly desired. This monitoring of particle therapy relies on the detection of secondary radiation which is produced by interactions between the beam particles and the nuclei of the patient’s tissue.
Up to now, the only clinically applied method for in-vivo dosimetry is Positron Emission Tomography which makes use of the beta+-activity produced during the irradiation (PT-PET). Since from a PT-PET measurement the applied dose cannot be directly deduced, the simulated distribution of beta+-emitting nuclei is used as a basis for the analysis of the measured PT-PET data. Therefore, the reliable modeling of the production rates and the spatial distribution of the beta+-emitters is required. PT-PET applied during instead of after the treatment is referred to as in-beam PET. A challenge concerning in-beam PET is the design of the PET camera, because a standard full-ring scanner is not feasible. For instance, a double-head PET camera is applicable, but low count rates and the limited solid angle coverage can compromise the image quality. For this reason, a detector system which provides a time resolution allowing the incorporation of time-of-flight information (TOF) into the iterative reconstruction algorithm is desired to improve the quality of the reconstructed images.
Secondly, Prompt Gamma Imaging (PGI), a technique based on the detection of prompt gamma-rays, is currently pursued. Concerning the emissions of prompt gamma-rays during particle irradiation, experimental data is not sufficiently available, making simulations necessary. Compton cameras are based on the detection of incoherently scattered photons and are investigated with respect to PGI. Monte Carlo simulations serve for the optimization of the camera design and the evaluation of criteria for the selection of measured events.
Thus, for in-beam PET and PGI dedicated detection systems and, moreover, profound knowledge about the corresponding radiation fields are required. Using various simulation codes, this thesis contributes to the modelling of the beta+-emitters and photons produced during particle irradiation, as well as to the evaluation and optimization of hardware for both techniques.
Concerning the modeling of the production of the relevant beta+-emitters, the abilities of the Monte Carlo simulation code PHITS and of the deterministic, one-dimensional code HIBRAC were assessed. The Monte Carlo tool GEANT4 was applied for an additional comparison. For irradiations with protons, helium, lithium, and carbon, the depth-dependent yields of the simulated beta+-emitters were compared to experimental data. In general, PHITS underestimated the yields of the considered beta+-emitters in contrast to GEANT4 which provided acceptable values. HIBRAC was substantially extended to enable the modeling of the depth-dependent yields of specific nuclides. For proton beams and carbon ion beams HIBRAC can compete with GEANT4 for this application. Since HIBRAC is fast, compact, and easy to modify, it could be a basis for the simulations of the beta+-emitters in clinical application. PHITS was also applied to the modeling of prompt gamma-rays during proton irradiation following an experimental setup. From this study, it can be concluded that PHITS could be an alternative to GEANT4 in this context.
Another aim was the optimization of Compton camera prototypes. GEANT4 simulations were carried out with the focus on detection probabilities and the rate of valid events. Based on the results, the feasibility of a Compton camera setup consisting of a CZT detector and an LSO or BGO detector was confirmed. Several recommendations concerning the design and arrangement of the Compton camera prototype were derived. Furthermore, several promising event selection strategies were evaluated. The GEANT4 simulations were validated by comparing simulated to measured energy depositions in the detector layers. This comparison also led to the reconsideration of the efficiency of the prototype. A further study evaluated if electron-positron pairs resulting from pair productions could be detected with the existing prototype in addition to Compton events. Regarding the efficiency and the achievable angular resolution, the successful application of the considered prototype as pair production camera to the monitoring of particle therapy is questionable.
Finally, the application of a PET camera consisting of Resistive Plate Chambers (RPCs) providing a good time resolution to in-beam PET was discussed. A scintillator-based PET camera based on a commercially available scanner was used as reference. This evaluation included simulations of the detector response, the image reconstructions using various procedures, and the analysis of image quality. Realistic activity distributions based on real treatment plans for carbon ion therapy were used. The low efficiency of the RPC-based PET camera led to images of poor quality. Neither visually nor with the semi-automatic tool YaPET a reliable detectability of range deviations was possible. The incorporation of TOF into the iterative reconstruction algorithm was especially advantageous for the considered RPC-based PET camera in terms of convergence and artifacts.
The application of the real-time capable back projection method Direct TOF for the RPCbased PET camera resulted in an image quality comparable to the one achieved with the iterative algorihms. In total, this study does not indicate the further investigation of RPC-based PET cameras with similar efficiency for in-beam PET application.
To sum up, simulation studies were performed aimed at the progress of in-vivo dosimetry. Regarding the modeling of the beta+-emitter production and prompt gamma-ray emissions, different simulation codes were evaluated. HIBRAC could be a basis for clinical PT-PET simulations, however, a detailed validation of the underlying cross section models is required. Several recommendations for the optimization of a Compton Camera prototype resulted from systematic variations of the setup. Nevertheless, the definite evaluation of the feasibility of a Compton camera for PGI can only be performed by further experiments. For PT-PET, the efficiency of the detector system is the crucial factor. Due to the obtained results for the considered RPC-based PET camera, the focus should be kept to scintillator-based PET cameras for this purpose.

Keywords: Monte-Carlo Simulation, Partikeltherapie, in-vivo Reichweitenkontrolle, GEANT4, PHITS, Prompt Gamma Imaging, Compton-Kamera, Positronen-Emissions-Tomographie, Paarbildungskamera, Monte Carlo simulation, particle therapy, in-vivo range verification, GEANT4, PHITS, Prompt Gamma Imaging, Compton camera, positron emission tomography
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-062 2015
    ISSN: 2191-8716


Registration No. 22256

Surface modification with focused polyatomic ion beams
Bischoff, L.; Böttger, R.; Pilz, W.; Heinig, K.-H.
Abstract: In the last decades Focused Ion Beams (FIB) have evolved from a sophisticated idea to a distinguished standard technique for sample preparation for SEM and TEM, prototyping in research and development and analytics in fields like microelectronics or nanotechnology. Most of FIB systems work with Ga beams, but liquid metal ion sources (LMIS) provide a much broader spectrum of other ion species using different source materials and an ion optical column equipped with an ExB mass separator [1]. From the source tip, beside single and double charged monatomic ions also dimers, trimers and heavier projectiles are extracted, which play an increasing role due to their special properties, like shallow penetration depth, enhanced sputtering efficiency and the huge energy deposition due to the simultaneous impact of several atoms in the same point of the sample surface.
Beside others heavy elements or alloys, those containing Au but in particular Bi are very suitable for the emission of polyatomic ions. Such projectiles with masses up to about 1000 amu have an energy spread in the range of EFWHM = 30 … 150 eV, which restrict the final FIB resolution (spot size) due to chromatic aberration to 10 … 100 nm. This is a result of the complex appearance of polyatomic species in the area around the emission point.
One of the main application fields at present is SIMS, which increasingly works with polyatomic Bi beams for defined surface erosion of inorganic as well as organic specimens. Another exciting field of application is the surface modification in terms of surface patterning by heavy dimer and trimer ions (e.g. Aunm+, Binm+). Due to the enormous, surface-near energy density deposition of cluster ions a self-organization process of hexagonally ordered dot arrays on Ge and Si based on transient melt pool formation can be triggered (Fig. 1) [2].
The authors would like to thank S. Facsko and B. Schmidt from HZDR for fruitful contributions to this work.

[1] L. Bischoff, Nucl. Instr. Meth. B 2008, 266, 1846.
[2] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, B. Schmidt, J. Vac. Sci. Technol. B 2012, 30, 06FF12.

Keywords: Surface modification, ion, cluster, FIB, sputtering
  • Lecture (Conference)
    Workshop Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Germany
Registration No. 22255

Polyatomic Focused Ion Beams – Origin and Applications
Bischoff, L.
Abstract: In the last four decades Focused Ion Beams (FIB) have evolved from a sophisticated idea to a distinguished standard technique for sample preparation for SEM and TEM, prototyping in research and development and analytics in fields like microelectronics or nanotechnology. Most of the FIB systems works with Ga beams, but liquid metal ion sources (LMIS) provide a much broader spectrum of other ion species using different source materials and an ion optical column equipped with an ExB mass separator [1]. From the source tip beside single and double charged monatomic ions also dimers, trimers and heavier projectiles are extracted, which play an increasing role due to their special properties, like slight penetration depth, enhanced sputtering efficiency and the huge energy deposition due to the simultaneous impact of several atoms in the same point of the surface.
Beside others heavy elements or alloys, those containing Au but in particular Bi are very appropriate for the emission of polyatomic ions. Such projectiles with masses up to about 1000 amu have an energy spread in the range of ΔEFWHM = 30 … 150 eV, which restrict the final FIB resolution (spot size) due to chromatic aberration to 10 to 100 nm. This is a result of the complex appearance of polyatomic species in the area around the emission point.
One of the main application fields at present is SIMS, which increasingly works with polyatomic Bi beams for defined surface erosion on inorganic as well as organic specimen [2]. A second exciting field of application is the surface modification in terms of surface patterning by heavy dimer and trimer ions (e.g. Aunm+, Binm+). Due to the enormous energy transfer by the cluster ions to the surface a self-organization process of hexagonal ordered dot arrays on Ge and Si could be found surprisingly for pure elemental targets at normal incidence, described by the formation of tiny melt pools [3] shown in the figure.

[1] L. Bischoff, Nucl. Instr. Meth. B 266 (2008) 1846.
[2] F. Kollmer, Appl. Surf. Sci. 231-232 (2004) 153.
[3] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, JVST B 30 (2012) 06FF12.

Keywords: FIB, Cluster ions, LMIS, self-assembly
  • Lecture (Conference)
    10. Dreiländer-FIB-Workshop, 29.-30.06.2015, Halle, Germany
Registration No. 22254

Spin-transfer effects in MgO-based tunnel junctions with an out-of-plane free layer and in-plane polarizer
Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Fassbender, J.; Deac, A. M.
Abstract: Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane (IP) magnetized polarizer (also acting as read-out layer) and out-of-plane (OOP) magnetized free layer allow for the full parallel (P)-to-antiparallel (AP) resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based MTJs under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices, including the spin-torque angular dependence.
Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based MTJs with an IP polarizer and an OOP free layer. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation for a nano-pillar MTJ with circular cross-section, under a constant perpendicular applied current and field. To sustain steady-state precession, the energy supplied by the in-plane spin-torque term and energy dissipated through damping must compensate over a full precession period.
In an MgO-MTJ, the magnitude of the STT is determined by the voltage across the barrier [6]. As the magnetization of the free layer precesses around the put-of-plane direction, the angle between the magnetic moments of the two layers changes and through the magnetoresistance effect the voltage changes if the experiment is conducted at constant applied current [7,8]. This cosine-like angular dependence of the MTJ resistance effectively introduces a spin-torque angle dependence asymmetry. In addition, for a given angle, the resistance exhibits a specific bias dependence, with the resistance of the AP state decreasing approximately linearly with increasing bias, while remaining mostly constant in the P configuration. In this work, we demonstrate that the spin-torque angular asymmetry exhibited in such systems is sufficient to sustain STT-driven dynamics.
Fig. 1 shows dynamic and static phase diagrams of the STNO obtained when neglecting (Fig. 1(a) and 1(c)) and taking into account (Fig. 1(b) and 1(d)) the bias dependence of the AP state resistance. In both cases, stable dynamics occur only for positive currents (colored area), defined as electrons flowing from the free to the reference layer. In MTJs exhibiting no bias dependence of the resistance (dRAP/dV = 0 Ω/V), the onset current for steady-state dynamics (solid lines) scales linearly with the applied current. High output powers can be obtained for relatively low values of applied currents and fields for realistic MTJ parameters, which is beneficial from the point of view of applications. Introducing an experimentally realistic value of dRAP/dV affects mostly the steady-state dynamics, while most of the trends observed for static states are maintained (Fig. 1(b) and 1(d)). Indeed, in this case current-driven precession is only excited for fields lower than the effective anisotropy of the free layer (but still only for positive currents). Moreover, while the symmetry versus field sign is conserved, the onset current no longer increases linearly with the field, but rather exhibits a parabolic-like dependence.

Keywords: spin-torque nano-oscillators (STNOs), magnetic tunnel junctions (MTJs)
  • Poster
    International Colloquium on Magnetic Films and Surfaces (ICMFS 2015), 12.-17.07.2015, Cracow, Poland
Registration No. 22252

Ion microprobe PIXE and PIGE analysis of standards’ trace elements for electron microprobe calibration.
Le Bras, L.; Munnik, F.; Renno, A. D.
Abstract: The purpose of this study is, with the recorded data, to be able to calibrate microanalytical methods, in particular electron microprobe with high precision chemical data standards. Analysis on selected standards by ion microprobe Particle-Induced-X-ray-Emission (PIXE) and Particle-Induced-Gamma-ray-Emission (PIGE) are used to detect and quantify the trace and light elements present in these samples. The presence of those elements makes a specific calibration of the machines necessary.
Electron- and X-ray measurements need good standards for a good quantification of the elements of interest. Actually, certified reference materials for microanalytical methods are very rare. In addition they are mainly glass samples. Utilisation of chosen minerals fixed in a matrix instead of glasses for calibration makes possible the application of the matrix-matched principle and the detection and quantification of trace elements in natural minerals for a resource technology application.
The widespread utilisation of Smithsonian Microbeam Standards makes this study relevant. That is why a 10 sample selection has been made in this collection. The samples’ theoretical compositions in major and trace elements are very important for the achievement of the analysis. In addition to the given element concentrations [1], a bibliographic study has also been performed for each standard in order to find possible trace elements which could be detected.
The standards received from the Smithsonian Institute are composed of crushed particles (500 µm diameter). The sample preparation is also essential. It consists in the fixation of three particles with epoxy resin into a 3 mm diameter messing cylinder.
The analyses are performed with an incident proton beam of 3.5 MeV in order to acquire simultaneously X- and Gamma-ray spectra. The data analysis is performed with GeoPIXE in order to add qualitative and quantitative data about trace elements to the given composition of the major elements. Preliminary results on apatite (NMNH 104021) are in agreement with the literature and show the presence of vanadium, arsenic, strontium, yttrium and light Rare Earth Elements such as lanthanum, cerium and neodymium. These trace elements are important for mineral resources analysis. Elemental mapping is also achieved in order to check the homogeneity of the samples’ particles.

Acknowledgements: Special thanks to Andreas Bartzsch, from the sample’s preparation laboratory of the Helmholtz Institute Freiberg, Germany, for his expertise.

[1] E. Jarosewich, J. A. Nelen, J. A. Norberg, Geostandards Newsletter 4 1980, p. 43-47

Keywords: Mineral standards, PIXE, PIGE, calibration, electron microprobe
  • Lecture (Conference)
    Workshop für Ionenstrahlen und Nanostrukturen, 22.-24.07.2015, Heidelberg, Germany
Registration No. 22249

A comprehensive study on iodine uptake by selected LDH phases via coprecipitation, anionic exchange and reconstruction
Iglesias, L.; Walther, C.; Medina, F.; Holzer, A.; Neumann, A.; Lozano-Rodriguez, M. Janeth; Alvarez, Mayra G.; Torapava, N.
Abstract: We explored the use of selected layered double hydroxides (LDHs) of different compositions and obtained by means of different routes (i.e., coprecipitation, anionic exchange and reconstruction) as iodine/iodate adsorbents. The influence of speciation (iodide vs. iodate) on iodine uptake was rather strong, resulting in much lower iodide incorporation. The Fourier transform of iodine K X-ray absorption edge data (EXAFS) of all iodate-LDHs showed a single I–O scattering path of 1.8 A ° . Thermal stability and leaching experiments showed that the incorporated iodate and iodide were rather loosely bound in the interlayer space and were easily released under heating to 180 C and leaching with Milli-Q water and brine solution.
Keywords: Iodine, Layered double hydroxide, Immobilization, Nuclear waste, Aqueous systems Registration No. 22248

Coffinite, USiO4, Is Abundant in Nature: So Why Is It So Difficult To Synthesize?
Mesbah, A.; Szenknect, S.; Clavier, N.; Lozano-Rodriguez, J.; Poinssot, C.; Den Auwer, C.; Ewing, R. C.; Dacheux, N.
Abstract: Coffinite, USIO4, is the second most abundant U4+ mineral on Earth, and its formation by the alteration of the UO2 in spent nuclear fuel in a geologic repository may control the release of radionuclides to the environment. Despite its abundance in nature, the synthesis and characterization of coffinite have eluded researchers for decades. On the basis of the recent synthesis of USiO4, we can now define the experimental conditions under which coffinite is most efficiently formed. Optimal formation conditions are defined for four parameters: pH, T, heating time and U/Si molar ratio. The adjustment pf pH between 10 and 12 leads probably to the formation of a uranium (IV) hydroxo-silicate complex that acts as a precursor of uranium (IV) silicate colloids and then of coffinite. Moreover, in this pH range, the largest yield of coffinite formation (as compared with those of the two competing byproduct phases, nanometer-scale UO2 and amorphous SiO2) is obtained for 250 C, 7 days and 100% excess silica.
Keywords: coffinite, PXRD, EXAFS, XANES, Raman spectra Registration No. 22247

Relationship Between Kolmogorov Entropy and Characteristic Mixing Length in Narrow Bubble Columns Operated in the Transition Flow Regime
Nedeltchev, S.; Schubert, M.; Donath, Th.; Rabha, S.; Hampel, U.
Abstract: The mixing performance of bubble column reactors depends strongly on the prevailing flow regime. Kawase and Tokunaga (Can. J. Chem. Eng. 69, 1228-1231, 1991) introduced the characteristic mixing length L as an important mixing parameter. In the homogeneous regime the liquid mixing is at the scale of the bubble diameter, whereas in the heterogeneous regime it is at the scale of the column diameter. Our research is aimed at determining the scale of liquid mixing in the transition flow regime by using some advanced methods.
The Kolmogorov entropies (KE) were extracted from gas holdup time series measured (at 2000 Hz) by a new type of wire mesh sensor. It was found that in a relatively narrow bubble column (0.15 m in ID, clear liquid height = 2 m) operated with an air-water system in the transition flow regime the KE values could be correlated to L. The KE in the transition flow regime decreases monotonously and can be correlated to the superficial gas velocity (KE=1.5Ug^-0.38). The same exponent (-0.38) for UG was reported by Kawase and Tokunaga (1991) in their correlation for prediction of L. Therefore, the KE and L values (in a narrow bubble column) are correlated as follows: KE=222.222L.
A new parameter called maximum number of visits per region Nv-max was also introduced and in the same way was related to L in the transition flow regime.

Keywords: Narrow bubble column, Transition flow regime, Kolmogorov entropy, Mixing length, New statistical parameter
  • Lecture (Conference)
    Jahrestreffen der Fachgruppen Mehrphasenströmungen und Wärme- und Stoffübertragung, 24.-26.03.2014, Fulda, Deutschland
Registration No. 22244

18F-FDG PET/MRI for therapy response assessment in sarcoma: Comparison of PET and MR imaging results
Schuler, M. Kajo; Platzek, I.; Beuthien-Baumann, B.; Fenchel, M.; Ehninger, G. E.; van den Hoff, J.
Abstract: Background: 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) has proven to be of substantial benefit in imaging of sarcoma patients. We therefore investigated the feasibility and benefit of combined PET/magnetic resonance imaging (MRI). Methods: Twelve patients with sarcoma who underwent FDG PET/MRI for staging and response assessment after chemotherapy were included. Results: Based on contrast-enhanced MRI and application of Choi criteria, therapy response was classified as stable disease in 6/12 patients (50%) and as partial remission in 6/12 patients (50%). Conclusion: In sarcoma patients, response assessment using Choi criteria based on contrast-enhanced MRI in comparison to FDG PET imaging only demonstrates slight correlation.
Keywords: Cancer imaging; Choi criteria; FDG PET/MRI; Sarcoma Registration No. 22243

New Methods for Flow Regime Identification in Bubble Columns and Fluidized Beds
Nedeltchev, S.
Abstract: New methods for flow regime identification were developed and applied to photon count time series measured in a bubble column (0.162 m in ID) and fluidized bed (0.438 m in ID). The signals in the bubble column (operated with an air-therminol system) were measured by means of Computed Tomography (CT), whereas the data in the fluidized bed (operated with an air-polyethylene system) were recorded by means of Nuclear Gauge Densitometry (NGD). The hidden information in the time series was extracted by means of two new parameters: entropy (bit/s) and information entropy (bit). Both of them were calculated on the basis of multiple reconstructions of the time series. In the case of the bubble column, the well-pronounced local minima were used for identification of three transition velocities (0.04, 0.08 and 0.13 m/s). They distinguished the boundaries of the bubbly flow, transition and churn-turbulent flow regimes. In the case of the fluidized bed, the minimum fluidization velocity (0.086 m/s) and minimum bubbling velocity (0.12 m/s) were also identified on the basis of the well-pronounced local minima in the profiles of the new parameters. They distinguished the boundaries of both the transition and bubbling fluidization regimes.
Keywords: Flow regime identification, Bubble column, Fluidized bed, Transition velocities, Entropy, Information entropy Registration No. 22241

Terahertz emission based on large-area photoconductive emitters illuminated via beam interference
Krauß, N.; Haas, M.; Niemeyer, L.; Winnerl, S.; Helm, M.; Dekorsy, T.
Abstract: The use of beam interference in combination with large-area photoconductive emitters for the generation of pulsed terahertz radiation is presented. An interference pattern with a periode twice that of the terahertz emitter is generated with a transmission phase grating, placed directly in front of the photoconductive emitter. This way, efficient terahertz generation is achieved with a single metallization layer and a single lithography step in the fabrication technology of the THz emitter.
Keywords: THz photoconductive emitter, large-area THz emitter Registration No. 22240

Efficient Auger scattering in Landau-quantized graphene
Wendler, F. H. Funk; Mittendorff, M.; Winnerl, S.; Helm, M.; Knorr, A.; Malic, E.
Abstract: We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene.
Keywords: Graphene, ultrafast spectroscopy, Landau quantization, Auger scattering
  • Lecture (Conference)
    Photonics West Conference, 07.-12.02.2015, San Francisco, USA
  • Contribution to proceedings
    Photonics West Conference, 07.-12.02.2015, San Francisco, USA
    Proceedings of SPIE, 936105
    DOI-Link: http://dx.doi.org/10.1117/12.2075458
Registration No. 22238

Theoretical Prediction of Mass Transfer Coefficients in Two-Phase and Slurry Bubble Columns
Nedeltchev, S.
Abstract: Two-phase and slurry bubble columns are characterized with high volumetric mass transfer coefficients kLa at low energy input. The design, modelling, optimization and scale-up of these reactors require precise knowledge of the mass transfer parameters. The mass transfer coefficients determine the efficiency and dimensions of (slurry) bubble columns. Nedeltchev et al. (2007) developed a correlation for prediction of mass transfer coefficients in gas-liquid bubble columns operated in the homogeneous flow regime. It was based on experimental gas holdups. On the other hand, Nedeltchev and Schumpe (2008) developed a correlation for prediction of gas holdups in gas-liquid bubble columns operated in the homogeneous regime. In this work, the theoretically calculated gas holdups were substituted in the mass transfer model (in the correlation for the interfacial area) of Nedeltchev et al. (2007) and the mass transfer coefficients were recalculated by means of a purely theoretical approach. The same gases and liquids (18 pure organic liquids, 14 adjusted liquid mixtures and tap water) were used and 263 kLa values (only in the homogeneous regime) were successfully predicted at ambient and high pressures (up to 1 MPa).
The same approach was tested in a slurry bubble column. Nedeltchev et al. (2014) predicted successfully the experimental mass transfer coefficients in a slurry bubble column based on bubble sizes which depended on the experimental gas holdups. On the other hand, Nedeltchev (2014) established a new approach for predicting the gas holdups in a slurry bubble column. When these theoretical gas holdups were substituted in the mass transfer model (in the correlations for prediction of bubble size and interfacial area), a purely theoretical kLa values in a slurry bubble column were obtained. The predictions were good not only in the homogeneous regime but also in the heterogeneous regime. The theoretical approach was applicable up to relatively high (18 %) solids concentrations. Six different liquid-solid systems were used and 66 kLa values were successfully predicted. In both mass transfer models, correction factors (a function of Eӧtvӧs numbers) were introduced due to the non-spherical (ellipsoidal) shape of the bubbles.

Keywords: Mass transfer coefficients, Penetration theory, New contact time, Gas-liquid bubble columns, Slurry bubble columns
  • Lecture (Conference)
    12th International Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York, USA
Registration No. 22237

Hydrothermal Alteration of Trachyte Satellite Intrusions in the Cripple Creek District
Rahfeld, A.; Kelly, N.; Monecke, T.
Abstract: The Cripple Creek deposit located in southwestern Colorado represents one of the largest epithermal gold deposits hosted by alkaline volcanic rocks. A petrographic study of the mostly barren satellite intrusions surrounding the deposit was undertaken to investigate and identify regional alteration patterns. Transmitted light, optical cathodoluminescence, and scanning electron microscopy, integrated with whole-rock geochemical data, revealed a complex history of fluid-rock interaction.
Early albitization of trachyte is preserved within weakly potassic-altered rocks. In more intensely altered rocks, potassium feldspar pervasively replaced the sanidine-dominated groundmass. Late alteration of the trachyte involved the formation of white mica and later kaolinite. The mineralogical changes imply a change in the physiochemical conditions of alteration from early sodic to later potassic alteration, followed by alteration caused at progressively decreasing temperatures and increasing acidity.
Tephrite intrusions within the trachyte satellite bodies have not been influenced by these styles of alteration. The tephrite has been altered to Fe-hydroxide minerals and biotite, most likely caused by influx of Fe-rich fluids. Within the mineralized trachyte of the main diatreme, Au-Te mineralization is at least locally associated with this style of Fe-rich alteration.

Keywords: Alkaline rocks, epithermal deposits, Cripple Creek, hydrothermal Alteration
  • Poster
    13th SGA Biennial Meeting (SGA2015), 24.-27.08.2015, Nancy, Frankreich
  • Contribution to proceedings
    13th SGA Biennial Meeting (SGA2015), 24.-27.08.2015, Nancy, Frankreich
    Mineral resources in a sustainable world. 13th SGA Biennial Meeting (SGA2015)
Registration No. 22236

Geochemical and Mineralogical Analysis of Kupferschiefer
Rahfeld, A.; Möckel, R.; Gutzmer, J.
Abstract: Kupferschiefer, i.e. very fine-grained and disseminated polymetallic Cu-Ag ores of the extensive stratabound deposits of the Central European Copperbelt is well known for its mineralogical complexity and the challenges surrounding its characterization. It is marked by a combination of high metal sulfide contents (up to 25 wt%) and organic matter (up to 30 wt%) within a matrix predominantly composed of fine-grained clay and carbonate minerals. Conventional analytical procedures often yield unreliable results of this very complex raw material. Regardless, recent research into the hydrometallurgical and microbiological beneficiation of Kupferschiefer has raised the demand for supplying reliable quantitative data of the mineralogy and the geochemistry for both the raw material and process samples. A research project was thus initiative to establish a robust analytical procedure to quantify both mineralogical as well as geochemical attributes of Kupferschiefer-type ores. A combination of analytical techniques is employed for this purpose, including quantitative X-ray diffraction (QXRD), image analysis based on scanning electron microscopy/mineral liberation analysis (MLA), XRF, ICP-AES, and INAA. Method development was based on selected Kupferschiefer samples obtained from Sangerhausen (Germany) and Polkowice-Sieroszowice (Poland) deposits.

QXRD by Rietveld refinement is particularly well-suited to determine the modal mineralogy of fine-grained samples. Five types of layer silicates were identified in Kupferschiefer samples. These are being characterized in detail in order to build crystal structure files needed to enable a full quantification of the minerals present. The necessary characterization of this set of layer silicates has been inhibited by the presence of organic matter, requiring chemical pre-treatment of the raw material that is specifically developed for this purpose.
SEM-based mineral liberation analysis (MLA) on grain mounts of crushed aliquots of the powder samples used for QXRD is used to verify mineral identification and to determine the amounts, liberation, and types of sulphide minerals contained in the samples. This technique is not suited to determine the abundance of the silicate minerals due to their fine-grained and intimately intergrown texture. Further obstacles, such as misidentification of disordered carbonate minerals by XRD or copper sulfides by MLA, are encountered often and can only be recognized and minimized by verifying results using multiple analytical methods. Independent observations from microscopy or bulk geochemistry by fusion XRF are useful in ensuring a high data quality and to test for consistency.
Whole rock trace element data are acquired using INAA, XRF, and ICP-OES. While INAA can guarantee a full analysis without requiring a problematic digestion treatment, the procedure itself is not available for routine measurements. XRF analysis of pressed pellets has been inhibited by the variable content of organic material and matrix effects caused by high sulfide concentrations. ICP-AES/MS analysis is considered to be the most appropriate technique in this case. Different combinations of hydrogen peroxide, nitric acid, and perchloric acid digestion techniques are tested to identify an optimal procedure for the acid digestion of the diverse sulfide compounds as well as the organic matter contained in Kupferschiefer.

Keywords: Kupferschiefer, Analysis, XRD, MLA, XRF, TXRF, ICP-OES, INAA
  • Poster
    The 9th International Conference on the Analysis of Geological and Environmental Materials - Geoanalysis 2015, 10.-13.08.2015, Leoben, Östereich
Registration No. 22235

Extremely large magnetoresistance and ultrahigh mobility in the topologicalWeyl semimetal candidate NbP
Shekhar, C.; Nayak, A. K.; Sun, Y.; Schmidt, M.; Nicklas, M.; Leermakers, I.; Zeitler, U.; Skourski, Y.; Wosnitza, J.; Liu, Z.; Chen, Y.; Schnelle, W.; Borrmann, H.; Grin, Y.; Felser, C.; Yan, B.
Abstract: Recent experiments have revealed spectacular transport properties in semimetals, such as the large, non-saturating magnetoresistance exhibited by WTe2. Topological semimetals with massless relativistic electrons have also been predicted as three-dimensional analogues of graphene. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states, distinct from those of topological insulators. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temperature) in a magnetic field of up to 9 T, without any signs of saturation, and an ultrahigh carrier mobility of 5x106 cm2 V-1 s-1 that is accompanied by strong Shubnikov–de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topological and conventional electronic phases, with intriguing physical properties resulting from their interplay. Registration No. 22233

Controllable Broadband Absorption in the Mixed Phase of Metamagnets
Pregelj, M.; Zaharko, O.; Zorko, A.; Gomilsek, M.; Sendetskyi, O.; Günther, A.; Ozerov, M.; Zvyagin, S. A.; Luetkens, H.; Baines, C.; Tsurkan, V.; Loidl, A.
Abstract: Materials with broad absorption bands are highly desirable for electromagnetic filtering and processing applications, especially if the absorption can be externally controlled. Here, a new class of broadband-absorption materials is introduced. Namely, layered metamagnets exhibit an electromagnetic excitation continuum in the magnetic-field-induced mixed ferro-and anti-ferromagnetic phase. Employing a series of complementary experimental techniques involving neutron scattering, muon spin relaxation, specific heat, ac and dc magnetization measurements, and electron magnetic resonance, a detailed magnetic phase diagram of Cu3Bi(SeO3)2O2Br is determined and it is found that the excitations in the mixed phase extend over at least ten decades of frequency. The results, which reveal a new dynamical aspect of the mixed phase in metamagnets, open up a novel approach to controllable microwave filtering. Registration No. 22232

Depth Resolved Structural and Compositional Characterization of Ion-Implanted Polystyrene that Enables Direct Covalent Immobilization of Biomolecules
Bilek, M. M. M.; Kondyurin, A.; Dekker, S. A.; Steel, B. C.; Wilhelm, R. A.; Heller, R.; Mckenzie, D. R.; Weiss, A. S.; James, M.; Möller, W.
Abstract: A polystyrene film spun onto polished silicon substrates was implanted with argon ions using plasma immersion ion implantation (PIII) in order to activate its surface for single step immobilization of biological molecules. The film was subsequently investigated by X-ray and neutron reflectometry, ultraviolet (UV)-visible (VIS) and Fourier transform infrared (FTIR) ellipsometry, FTIR and Raman spectroscopy, as well as nuclear reaction analysis to determine the structural and compositional transformations associated with the surface activation. The ion irradiation resulted in a significant densification of the carbon structure, which was accompanied by hydrogen loss. The density and hydrogen profiles in the modified surface layers were found to agree with the expected depths of ion implantation as calculated by the Stopping and Range of Ions in Matter (SRIM) software. The data demonstrate that the reduction in film thickness is due to ion-induced densification rather than the removal of material by etching. Characterization by FTIR, atomic force microscopy (AFM), ellipsometry and X-ray reflectometry shows that polystyrene films modified in this way immobilize dense layers of protein (tropoelastin) directly from solution. A substantial fraction of the immobilized protein layer remains after rigorous washing with sodium dodecyl sulfate solution, indicating that its immobilization is by covalent bonding.
Keywords: Plasma immersion ion implantation, polystyrene, protein immobilization, nuclear reaction analysis, X-ray reflectometry, neutron reflectometry, spectroscopic ellipsometry, Raman and FTIR spectroscopy Registration No. 22230

Response of GaN to energetic ion irradiation: conditions for ion track formation
Karlušić, M.; Kozubek, R.; Lebius, H.; Ban-D’Etat, B.; Wilhelm, R. A.; Buljan, M.; Siketić, Z.; Scholz, F.; Meisch, T.; Jakšić, M.; Bernstorff, S.; Schleberger, M.; Šantić, B.
Abstract: We investigated the response of wurzite GaN thin films to energetic ion irradiation. Both swift heavy ions (92 MeV Xe23+, 23 MeV I6+) and highly charged ions (100 keV Xe40+) were used. After irradiation, the samples were investigated using atomic force microscopy, grazing incidence small angle x-ray scattering, Rutherford backscattering spectroscopy in channelling orientation and time of flight elastic recoil detection analysis. Only grazing incidence swift heavy ion irradiation induced changes on the surface of the GaN, when the appearance of nanoholes is accompanied by a notable loss of nitrogen. The results are discussed in the framework of the thermal spike model.
Keywords: GaN, swift heavy ion, highly charged ion, ion track, thermal spike Registration No. 22226

Formation of shallow boron emitters in crystalline silicon using flash lamp annealing: Role of excess silicon interstitials
Riise, H. N.; Schumann, T.; Azarov, A.; Hübner, R.; Skorupa, W.; Svensson, B. G.; Monakhov, E.
Abstract: Shallow, Boron (B)-doped p+ emitters have been realized using spin-on deposition and Flash Lamp Annealing (FLA) to diffuse B into monocrystalline float zone Silicon (Si). The emitters extend between 50 and 140 nm in depth below the surface, have peak concentrations between 9x1019 cm-3 and 3x1020 cm-3, and exhibit sheet resistances between 70 and 3000 Ohm/Square. An exceptionally large increase in B diffusion occurs for FLA energy densities exceeding approximately 93 J/cm2 irrespective of 10 or 20 ms pulse duration. The effect is attributed to enhanced diffusion of B caused by Si interstitial injection following a thermally activated reaction between the spin-on diffusant film and the silicon wafer. Registration No. 22225

Mass of GaAsN in Pulsed Magnetic Fields up to 60 T with Free-Electron Laser IR Radiation
Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Helm, M.
Abstract: We use the unique combination of the widely tunable (4 μm – 250 μm) Free-Electron laser (FEL) FELBE and pulsed magnetic fields up to 60T of the High Magnetic Field Laboratory HLD to perform spectroscopic investigations on the dilute nitride system GaAsN. We carry out systematic cyclotron resonance (CR) spectroscopy and analyze the dependence of the electron effective mass on the nitrogen content. The red triangles in Figure 1 illustrate our findings for the illumination wavelength 46 μm at 100 K. We observe a slight increase of the effective mass with nitrogen content, which is in very good agreement with the Band Anti-Crossing (BAC) model [1], the empirical Tight Binding (TB) calculations [2] and the Two band BAC model [3], which are represented in Figure 1 by dashed, dotted and dash-dotted black lines, respectively. We compare our results with magneto-photoluminescence (PL) investigations performed by Alberi et al. [4] and Masia et al. [5], which are presented with blue circles and stars respectively. Magneto-PL investigations reveal a very fast increase of the effective mass with nitrogen content, well above the mentioned models [1-3], but consistent with the modified k·p calculations by Lindsay and O’Reilly [6]. Our magneto-PL study (not shown) exhibits a very similar behavior as shown by Alberi et al. and Masia et al., which allows us to exclude the different samples as a source for the deviation.
It is well known that nitrogen tends to form pairs and clusters during the growth, which is only considered in the modified k·p calculations [4]. Magneto-PL is a method which is very sensitive to localization of the neighboring atoms and thus to clusters. For this reason the magneto-PL results are consistent with [4], but cannot be described by [1-3], which do not take clusters into account. On the other hand, CR spectroscopy is only sensitive to delocalized states and this is why our results are in such good agreement with [1-3].

[1] J. Wu et al. Phys. Rev. B 64, 085320 (2000).
[2] N. Shtinkov et al. Phys. Rev. B 67, 081202(R) (2003).
[3] Tomic et al. Phys. Rev. B 69, 245305 (2004).
[4] Alberi et al. Phys. Rev. Lett. 110, 156405 (2013).
[5] Masia et al. Phys. Rev. B 73, 073201, (2006).
[6] A. Lindsay and E. P. O’Reilly Phys. Rev. Lett. 93, 196402 (2004).

Keywords: GaAsN, effective mass, cyclotron resonance spectroscopy, THz spectroscopy in pulsed magnetic fields
  • Lecture (Conference)
    RHMF 2015; International Conference on Research in High Magnetic Fields 2015, 01.-04.07.2015, Grenoble, France
Registration No. 22221

Constraining big bang lithium production with recent solar neutrino data
Takács, M. P.; Bemmerer, D.; Szücs, T.; Zuber, K.
Abstract: The 3He(α, γ)7Be reaction affects not only the production of 7Li in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He(α,γ)7Be provide precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However, there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavour oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He(α,γ)7Be astrophysical S-factor at the solar Gamow peak, Sν (23+6 keV) 34 −5 = 0.548±0.054 keVb. This new data point is then included in a re-evaluation of the 3He(α,γ)7Be S-factor at Big Bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The re-evaluated S-factor curve is then used to re-determine the 3He(α,γ)7Be thermonuclear reaction rate at Big Bang energies. The predicted primordial lithium abundance is 7Li/H = 5.0 ×10−10, far higher than the Spite plateau.
Keywords: solar neutrinos, S34, Big Bang, Standard Solar Model Registration No. 22220

Cyclotron Resonance Spectroscopy of GaAsN in Pulsed Magnetic Fields up to 60 T with Free-Electron Laser IR Radiation
Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Pettinari, G.; Helm, M.
Abstract: The unique combination of the high magnetic field laboratory Dresden (HLD) and the free-electron laser facility FELBE allow us to perform cyclotron resonance spectroscopy experiments with tunable, intense, coherent infrared radiation of high brilliance in the range of 4 - 250 µm in pulsed magnetic fields up to 60 T. The material system of interest is the dilute nitride GaAsN, a promising candidate for electro-optical applications, because of its band gap tunability. The incorporation of a few percent of nitrogen into GaAs enables the gradual decrease of the band gap, which is proportional to the nitrogen content. The description of the band structure and in particular of the effective mass are still challenging despite the number of experimental works (e.g. [1, 2]) that have been performed on this system. In order to contribute to a clarification of this problem, we apply different investigation methods on one sample series of GaAsN with different nitrogen contents (0%; 0.1%; 0.2%).
Probably the most direct and reliable method for the investigation of the effective mass is cyclotron resonance spectroscopy, which has never been applied to bulk GaAsN layers before, according to our best knowledge. Figure 1 illustrates our CR spectroscopy investigation of three samples with different nitrogen contents illuminated with the FEL at wavelengths of 30 µm and 70 µm. These wavelengths have been chosen intentionally to investigate the effective mass behavior below and above the Reststrahlenband of GaAs. We discuss the significance of these CR studies, which were conducted using a range of temperatures, illumination wavelengths and n-type doping of the GaAsN layers. Using a simple Drude-like absorption model we deduce the electron CR mass, the electron mobility, the density of free carriers and the electron relaxation time.

[1] F. Masia et al., Phys. Rev. B 73, 07320 (2006).
[2] K. Alberi et al., Phys. Rev. Lett. 110, 156405 (2013).

Keywords: GaAsN, effective mass, cyclotron resonance spectroscopy, THz spectroscopy in pulsed magnetic fields
  • Lecture (Conference)
    EDiSON'19 19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures, 29.06.-02.07.2015, Salamanca, España
Registration No. 22219

THz free-electron laser investigation of GaAsN in pulsed magnetic fields up to 60 T
Eßer, F.; Schneider, H.; Winnerl, S.; Drachenko, O.; Patanè, A.; Helm, M.
Abstract: We use the unique combination of the free-electron laser FELBE and the High Magnetic Field Laboratory Dresden to perform cyclotron resonance (CR) spectroscopy on the dilute nitride alloy GaAsN. FELBE is a tunable (4 – 250 µm) laser source of high brilliance, which can be used in pulsed magnetic fields up to 60 T. Our CR studies enable us to measure fundamental electronic properties of GaAsN, a very interesting candidate for optoelectronic applications because of the tunability of its band gap energy in the range of 1.4 eV – 0.9 eV by the incorporation of a small concentration of N-atoms (~ 1%). Figure 1 illustrates a typical CR spectrum and our values of the CR electron mass at 100 K and 6.5 THz. We observe a slight increase of the electron CR mass with nitrogen content. This dependence is in very good agreement with that described by the band anticrossing (BAC) model [1] and the empirical tight binding (TB) calculations [2], which are represented in Figure 1 by dashed and dotted black lines, respectively. The comparison with magneto-photoluminescence (PL) investigations performed by Alberi et al. [3] and Masia et al. [4] reveal instead a steep increase of the electron effective mass with nitrogen content, which is consistent with a modified k·p calculation by Lindsay and O’Reilly [5]. This model assumes that nitrogen can form pairs and clusters, not considered in [1,2]. Since PL is very sensitive to carrier localization effects, the results in [3,4] can be well described by [5]. In contrast, CR spectroscopy is only sensitive to delocalized states, which explains the good agreement of the present results with [1,2].

[1] J. Wu et al. Phys. Rev. B 64, 085320 (2000).
[2] N. Shtinkov et al. Phys. Rev. B 67, 081202(R) (2003).
[3] Alberi et al. Phys. Rev. Lett. 110, 156405 (2013).
[4] Masia et al. Phys. Rev. B 73, 073201, (2006).
[5] A. Lindsay and E. P. O’Reilly Phys. Rev. Lett. 93, 196402 (2004).

Keywords: GaAsN, effective mass, cyclotron resonance spectroscopy, THz spectroscopy in pulsed magnetic fields
  • Poster
    German THz Conference 2015, 08.-10.06.2015, Dresden, Deutschland
Registration No. 22218

Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias
Nayak, A. K.; Nicklas, M.; Chadov, S.; Khuntia, P.; Shekhar, C.; Kalache, A.; Baenitz, M.; Skourski, Y.; Guduru, V. K.; Puri, A.; Zeitler, U.; Coey, J. M. D.; Felser, C.
Abstract: Rational material design can accelerate the discovery of materials with improved functionalities. This approach can be implemented in Heusler compounds with tunable magnetic sublattices to demonstrate unprecedented magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn–Pt–Ga, a giant exchange bias (EB) of more than 3 T and a large coercivity are established.
The large exchange anisotropy originates from the Exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. Our design approach is also demonstrated on a second material with a magnetic transition above room temperature, Mn–Fe–Ga, exemplifying the universality of the concept and the feasibility of room-temperature applications. These findings may lead to the development of magneto-electronic devices and rareearth-free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.
Registration No. 22216

Ga, Ge, In and other trace elements in sphalerite from different geological deposit types, with reference to mineralisation events at Freiberg.
Frenzel, M.
Abstract: Sphalerite (ZnS) is an important source of a number of high-tech metals. However, while a large amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last decades, our understanding of the geological controls on their enrichment or depletion remains limited. No comprehensive meta-analysis of this data has ever been conducted. This talk presents the results of such a meta-analysis, based on an extensive collection of data from the scientific literature. Nine elements (Ag, Cd, Co, Cu, Fe, Ga, Ge, In and Mn) were considered. For five of these elements (Fe, Ga, Ge, In, Mn) significant differences were found between different geological types of deposits. The regularity of these differences suggests the operation of a single underlying control parameter – possibly formation temperature – with obvious implications for the identification of future sources of these elements.
  • Lecture (others)
    BHMZ Seminar, 06.05.2015, Freiberg, Deutschland
Registration No. 22214

Lattice location of deep level impurities in hyperdoped Si by ion implantation and short-time annealing
Liu, F.; Prucnal, S.; Gao, K.; Heller, R.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell. However, deep level impurities have relatively low solid solubility limit in Si. We prepared deep level impurities doped silicon to above the Mott insulator concentration by ion implantation followed by sub-second annealing. The degree of crystalline lattice recovery in implanted layers and the lattice location of impurities in Si were analyzed by Rutherford backscattering spectrometry/Channeling. Our results show that S and Se atoms are occupying substitutional lattice sites in Si [1], while Ti impurities have no ordered lattice occupation [2].

[1] S. Zhou, F. Liu, S. Prucnal, K. Gao, M. Khalid, W. Skorupa and M. Helm, Scientific Report 5, 8329 (2015).
[2] F. Liu, et al., in preparation (2015).

Keywords: Ion implantation, deep level impurities
  • Poster
    Jaszowiec 2015, 20.-25.06.2015, Wisła, Poland
Registration No. 22206

Lattice location of deep level impurities in hyperdoped Si by ion implantation and short-time annealing
Liu, F.; Prucnal, S.; Gao, K.; Heller, R.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell. However, deep level impurities have relatively low solid solubility limit in Si. We prepared deep level impurities doped silicon to above the Mott insulator concentration by ion implantation followed by sub-second annealing. The degree of crystalline lattice recovery in implanted layers and the lattice location of impurities in Si were analyzed by Rutherford backscattering spectrometry/Channeling. Our results show that S and Se atoms are occupying substitutional lattice sites in Si [1], while Ti impurities have no ordered lattice occupation [2].

[1] S. Zhou, F. Liu, S. Prucnal, K. Gao, M. Khalid, W. Skorupa and M. Helm, Scientific Report 5, 8329 (2015).
[2] F. Liu, et al., in preparation (2015).

Keywords: Ion implantation, deep level impurities
  • Poster
    IBA 2015 - 22nd International Conference on Ion Beam Analysis, 14.-19.06.2015, Opatija, Croatia
Registration No. 22205

High temperature stable transparent conductive oxides for solar thermal applications
Lungwitz, F.; Schumann, E.; Guillen, E.; Escobar, R.; Krause, M.; Gemming, S.
Abstract: In solar thermal energy conversion systems, receivers containing the heat transfer fluid are coated by a solar selective coating which must exhibit high absorption in the solar region and low thermal emittance. Additionally, the coating materials have to be structurally, optically, and mechanically stable at high temperatures. Nowadays, temperatures of up to 450 °C and up to 550°C are reached using parabolic trough arrays and solar tower absorbers, respectively, whereas temperatures up to 800 °C could be reached if the receiver materials were stable enough. Solar selective coatings can be formed by a transparent conductive oxide (TCOs) film deposited on a black body absorber to have both, high absorption in the ultraviolet, visible and near infrared spectral range (300 nm – 2500 nm) as well as high reflectivity in the infrared (> 2500 nm). The former is to absorb as much sunlight as possible, the latter for preventing thermal radiation losses from the system to the environment. In this work Ta:TiO2 and Ta:SnO2 TCOs thin films are reactively magnetron sputtered from tantalum doped metallic targets. The oxygen flow during deposition is precisely controlled by a plasma emission unit which is crucial to obtain optimal electrical and therefore also optical properties by maintaining high sputtering rates. While the as-deposited films are amorphous and non-conductive, they are crystallized and therefore electrically activated upon a subsequent thermal treatment at 425 °C for 1 hour. The correlation between structural, optical, and electrical properties is shown by Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction (XRD), Raman Spectroscopy, Spectroscopic Ellipsometry (SE) (both at room- and high- temperatures), UV-VIS spectrometry, and Hall Effect measurements. Preliminary tests show that optical constants of Ta:TiO2 films are maintained after annealing at 700ºC.
Keywords: TCO, transparent conductive oxide, solar thermal, magnetron sputtering, TiO2, Cluster Tool, solar selectivity, high temperature
  • Lecture (Conference)
    ICMAT 2015 & IUMRS - ICA 2015, 28.06.-03.07.2015, Singapore, Singapore
Registration No. 22203

Optical and electrical characterization of TiO2- based transparent conductive oxides
Lungwitz, F.; Schumann, E.; Wenisch, R.; Neubert, M.; Guillen, E.; Escobar, R.; Krause, M.; Gemming, S.
Abstract: Transparent conductive oxides (TCOs) are already widely used in the optoelectronic industry e.g. as electrodes for liquid crystal displays (LCDs), organic light emitting diodes (OLEDs), or thin film solar cells. Less attention has been devoted to their optical properties and thermal stability until now.
In this work, Tantalum doped TiO2 and SnO2 TCO films are investigated with respect to their structural, optical, and electrical properties at temperatures from RT to 700°C. The films are prepared at room temperature by direct current reactive magnetron sputtering from metallic as well as ceramic targets and subsequently isothermally annealed at temperatures of 425°C. For compositional and structural analysis x-ray diffraction (XRD), Raman spectroscopy, and Rutherford backscattering spectroscopy (RBS) are used. The optical properties are determined by spectroscopic ellipsometry, spectral photometry, and subsequent modelling. Hall effect measurements are used to determine the electrical properties of the TCO films.
The as-deposited layers are amorphous and isolating. By thermal annealing they are activated and become conductive.

Keywords: TCO, transparent conductive oxide, solar-thermal, thin film, high temperature, magnetron sputtering, energy materials, Cluster Tool
  • Poster
    Frühjahrstagung der DPG, 19.03.2015, Berlin, Deutschland
Registration No. 22202

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Trin-butyl phosphate
Gaillard, C.; Boltoeva, M.; Billard, I.; Georg, S.; Mazan, V.; Ouadi, A.; Ternova, D.; Hennig, C.
Abstract: We present new results on the liquid–liquid extraction of uranium (VI) from a nitric acid aqueous phase into a tri-n-butyl phosphate/1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (TBP/[C4mim][Tf2N]) phase. The individual solubilities of the ionic-liquid ions in the upper part of the biphasic system are measured over the whole acidic range and as a function of the TBP concentration. New insights into the extraction mechanism are obtained through the in situ characterization of the extracted uranyl complexes by coupling UV/Vis and extended X-ray absorption fine structure (EXAFS) spectroscopy. We propose a chemical model to explain uranium (VI) extraction that describes the data through a fit of the uranyl distribution ratio DU. In this model, at low acid concentrations uranium (VI) is extracted as the cationic complex [UO2(TBP)2]2+, by an exchange with one proton and one C4mim+. At high acid concentrations, the extraction proceeds through a cationic exchange between [UO2(NO3)(HNO3)(TBP)2]+ and one C4mim+. As a consequence of this mechanism, the variation of DU as a function of TBP concentration depends on the C4mim+ concentration in the aqueous phase. This explains why noninteger values are often derived by analysis of DU versus [TBP] plots to determine the number of TBP molecules involved in the extraction of uranyl in an ionic-liquid phase.
Keywords: Uranium(VI), aqueous solution, tri-n-butyl phosphate, UV/Vis, EXAFS Registration No. 22200

Contactless magnetic excitation of acoustic cavitation in liquid metals
Grants, I.; Gerbeth, G.; Bojarevics, A.
Abstract: A steady axial magnetic field is applied to a liquid metal zone heated by induction currents. The resulting alternating Lorentz force causes pressure oscillations that being strong enough lead to cavitation in the molten metal. Amplitude of the pressure oscillations is proportional to the product of the induced currents and the steady axial magnetic field induction. We follow an approach where the acoustic pressure is maximized by the induction currents. The onset of cavitation is identified by the occurrence of sub-harmonics of the drive frequency in sound recorded at the surface of the experimental cell. It is demonstrated that cavitation in a liquid metal may be excited by a superimposed axial magnetic field of a moderate 0.5 T induction.

Macro segregation formation mechanism of the primary silicon phase in directionally solidified Al-Si hypereutectic alloys under the impact of electric currents
Zhang, Y.; Miao, X.; Shen, Z.; Han, Q.; Song, C.; Zhai, Q.
Abstract: Understanding the macro segregation formed by applying electric currents is of high commercial importance. This paper investigates how electric currents control the solute distribution in the directionally solidified Al-20.5wt%Si hypereutectic alloy. Experimental results show that a severe macro segregation of the primary silicon phase occurs at the initial solidification stage of the samples. This is accompanied by two interface transitions in the mushy zone: quasi planar → upwards V-shaped → quasi planar. The corresponding numerical simulations present a vortex ring flow pattern as a consequence of the electric current distortion in the mushy zone. The peculiar macro segregation phenomenon can be fully explained by considering the effect of the forced flow on the solute distribution. At the initial growth of the samples, the forced flow generates a rigorous solute exchange between the mushy zone and the bulk melt and encourages the primary silicon to continuously precipitate and segregate. As the solute content in the bulk melt gradually approaches the eutectic point, the precipitation of primary silicon is profoundly reduced. Eventually, a significant segregation of the primary silicon phase is observed in the initial directional growth. The present study not only presents a new approach to control the solute distribution by applying an electric current through a generated forced flow, it also facilitates the understanding of the underlying grain refinement mechanism and the growth of crystals in the solute that are controlled by the electric currents.
Keywords: Al-Si alloys; directional solidification; external electric field; macro segregation; melt convection Registration No. 22197

Regenerative amplification in Yb3+-doped fused silica
Röser, F.; Loeser, M.; Siebold, M.; Albach, D.; Grimm, S.; Langner, A.; Schötz, G.; Schramm, U.
Abstract: We report to our knowledge the first short pulse generation experiment
in bulk volume Yb-doped fused silica utilizing a Q-switched cavity.
  • Contribution to proceedings
    CLEO/Europe-EQEC Conference 2015, 21.-25.06.2015, München, Deutschland
  • Poster
    CLEO/Europe-EQEC Conference 2015, 21.-25.06.2015, München, Deutschland
Registration No. 22195

Code intercomparison and benchmark for muon fluence and absorbed dose induced by an 18-GeV electron beam after massive iron shielding
Fasso, A.; Ferrari, A.; Ferrari, A.; Mokhov, N. V.; Mueller, S. E.; Nelson, W. R.; Roesler, S.; Sanami, T.; Striganov, S. I.; Versaci, R.
Abstract: In 1974, Nelson, Kase, and Svenson published an experimental investigation on muon shielding using the SLAC high energy LINAC. They measured muon fluence and absorbed dose induced by a 18 GeV electron beam hitting a copper/water beam dump and attenuated in a thick steel shielding. In their paper, they compared the results with the theoretical mode ls available at the time. In order to compare their experimental results with present model calculations, we use the modern transport Monte Carlo codes MARS15, FLUKA2011 and GEANT4 to model the experimental setup and run simulations. The results will then be compared between the codes, and with the SLAC data.
  • Contribution to proceedings
    Shielding Aspects of Accelerators, Target and Irradiation Facilities – SATIF 12, 28.-30.04.2014, Batavia (Illinois), USA
    Workshop Proceedings, Online: OECD Nuclear Energy Agency, 240-247


Registration No. 22194

Fermi surface of SrCo2P2: A strongly enhanced Pauli paramagnet
Götze, K.; Klotz, J.; Bergmann, C.; Geibel, C.; Kraft, I.; Lorenz, V.; Rosner, H.; Sheikin, I.; Mccollam, A.; Bruin, J.; Wosnitza, J.
Abstract: es hat kein Abstract vorgelegen
  • Poster
    RHMF 2015, 11th International Conference on Research in High Magnetic Fields, 02.-04.07.2015, Grenoble, France
Registration No. 22193

NMR of the Shastry-Sutherland lattice SrCu2(BO3)2
Stern, R.; Kohlrautz, J.; Haase, J.; Kühne, H.; Green, E.; Zhang, Z.; Wosnitza, J.
Abstract: SrCu2(BO3)2 is a prominent realization of the Shastry-Sutherland lattice model [1]. In this quasi-two-dimensional compound, Cu2+ ions form orthogonal spin-singlet dimers with strong geometrical frustration of the next-nearest and nearest neighbor exchange interactions. SrCu2(BO3)2 has been studied extensively using a variety of techniques, such as nuclear magnetic resonance (NMR) spectroscopy, or recent magnetization measurements up to 118 T. These experiments reveal a complex sequence of magnetization plateaus with differing commensurate magnetic superstructure, stemming from a stripe type order of triplet states [2-4]. Due to its highly sensitive local probe character, NMR can provide deep insight into the spin-coupling mechanisms and excitations at highest magnetic fields. We present 11B NMR spectra measured in pulsed magnetic fields up to 56 T, and compare those with prior results obtained in highest static magnetic fields. Herewith, we prove the feasibility and efficacy of this new technique, yielding the capability for extended studies at highest magnetic fields up to the 100 T regime that determine the spin structure in the 1/3 magnetization plateau and beyond.
  • Poster
    RHMF 2015 - 11th International Conference on Research in High Magnetic Fields, 02.-04.07.2015, Grenoble, France
Registration No. 22192

III-V:Mn Ferromagnetic semiconductors prepared by ion implantation
Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.
Abstract: Ferromagnetic semiconductors (FSs) have been under intensive investigation during the last decade. Until now, the prototype ferromagnetic semiconductor GaMnAs has revealed a variety of unique features induced by the combination of its magnetic and semiconducting properties. As a non-equilibrium process, ion implantation can overcome the difficulty that the Mn concentration in ferromagnetic III-V (FS) is far beyond the solid solubility of Mn in III-V compounds. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing within nanoseconds regime allows the epitaxial growth from a liquid phase. The approach combining ion implantation and pulsed laser melting allows us to prepare ferromagnetic semiconductors covering the full spectrum of III-V compound semiconductors.
We have successfully synthesized ferromagnetic Mn doped III-V from InAs and GaAs to InP and GaP with different bandgaps. The results of magnetization, magnetic anisotropy, resistivity, anomalous Hall effect, magnetoresistance and x-ray magnetic circular dichroism obtained from the synthesized samples confirm the intrinsic origin and the carrier-mediated nature of the ferromagnetism. Moreover, in different III-V hosts we observe distinct differences regarding the magnetic anisotropy and conduction mechanism which are related with the intrinsic parameters such as the lattice mismatch, energy gap and the acceptor level of Mn. These results could allow a panorama-like understanding of III-V:Mn based ferromagnetic semiconductors.
  • Poster
    Jaszowiec 2015, 20.06.2015, Wisla, Poland
Registration No. 22190

Hydrodynamic and mass transfer properties of a bubble column with vertically inserted tube bundles
Šimić, N.; Breiler, K.; Schubert, M.
Abstract: The objective of this study is to examine the influence of different vertical tube bundle designs on the bubble dynamics and on the mass transfer rates in a bubble column. The studies in the open literature examining the performance of bubble columns with vertically inserted tube bundles have focused primarily on the coverage of the cross-sectional area of the bubble column by the tube bundle (CSA). The most frequently used coverages are the 5% and the 25% (± 3%) which mimic the heat exchangers utilized in the processes of methanol and Fischer-Tropsch syntheses. Other than that, the designs of tube bundles seem to be arbitrarily chosen and feature a number of different configurations of layouts, tube diameters and tube lengths. From the current state of research, it is thus rather difficult to draw conclusions on the optimal design of a heat exchanger suitable for use in bubble columns (Youssef et al., 2013). Intuitively, it can be concluded that the most important design features of tube bundles affecting the flow are the distance between the tubes and the unit cell area enclosed by the tubes in their respective arrangements. Accordingly, the study aims on a systematic analysis on the effect of these geometric parameters.
Keywords: bubble column, internals, heat exchanger, tube bundle, hydrodynamics, gas holdup, bubble size distribution, mass transfer, X-ray tomography
  • Poster
    12th International Conference on Gas-Liquid & Gas-Liquid-Solid Reactor Engineering (GLS12), 28.06.-01.07.2015, New York City, USA
Registration No. 22189

High Curie temperature and perpendicular magnetic anisotropy in homoepitaxial InMnAs films
Yuan, Y.; Wang, Y.; Gao, K.; Khalid, M.; Wu, C.; Zhang, W.; Munnik, F.; Weschke, E.; Baehtz, C.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: We have prepared the dilute magnetic semiconductor (DMS) InMnAs with different Mn concentrations by ion implantation and pulsed laser melting. The Curie temperature of the In1−xMnxAs epilayer depends on the Mn concentration x, reaching 82K for x = 0.105. The substitution of Mn ions at the indium sites induces a compressive strain perpendicular to the InMnAs layer and a tensile strain along the in-plane direction. This gives rise to a large perpendicular magnetic anisotropy, which is often needed for the demonstration of the electrical control of magnetization and for spin-transfer-torque induced magnetization reversal
Keywords: dilute magnetic semiconductors, InMnAs, ion implantation, pulsed laser melting, perpendicular magnetic anisotropy Registration No. 22182

P1402-Kontrolle einer therapeutischen Bestrahlung durch eine Bestrahlungseinrichtung mit einem mikrogepulsten Teilchenstrahl
Enghardt, W.; Fiedler, F.; Helmbrecht, S.
Abstract: Die Erfindung betrifft Verfahren und Einrichtungen zur Kontrolle einer therapeutischen Bestrahlung durch eine Bestrahlungseinrichtung mit einem mikrogepulsten Teilchenstrahl mittels eines Positronen-Emissions-Tomografen. Diese zeichnen sich insbesondere dadurch aus, dass eine therapeutische Bestrahlung durch eine Bestrahlungseinrichtung mit einem mikrogepulsten Teilchenstrahl mittels eines Positronen-Emissions-Tomografen während der Bestrahlung kontrollierbar ist. Dazu werden wahre Koinzidenzen mittels – des durch die erlaubte Zeitdifferenz des Auftreffens zweier Photonen in verschiedenen Detektoren des Tomografen bestimmten Koinzidenzzeitfensters und – der Differenz zwischen prompten Fenster und verzögerten Fenster ohne wahre Koinzidenzen ermittelt. Dabei sind sowohl das Koinzidenzzeitfenster als auch die Zeitdifferenz zwischen prompten und verzögerten Fenster ein ganzzahliges Vielfaches der durch die Frequenz der beschleunigenden Wechselspannung des Hochfrequenzbeschleunigers gegebenen Zeitdauer einer Mikropulsperiode des Teilchenstrahls. Die Mikropulsperiode ist durch den Mikropuls und die Pause zwischen Mikropulsen definiert. Diese Zeitdauer ist durch die Frequenz der die Teilchen des Teilchenstrahls beschleunigenden Wechselspannung gegeben und damit zu wählen.
  • Patent
    DE102014202828.0 - Erteilung 15.04.2015; Nachanmeldung: WO
  • Patent
Registration No. 22178

Biomimetic Magnetic Silk Scaffolds
Samal, S. K.; Dash, M.; Shelyakova, T.; Declercq, H. A.; Uhlarz, M.; Banobre-Lopez, M.; Dubruel, P.; Cornelissen, M.; Herrmannsdörfer, T.; Rivas, J.; Padeletti, G.; de Smedt, S.; Braeckmans, K.; Kaplan, D. L.; Dediu, V. A.
Abstract: Magnetic silk fibroin protein (SFP) scaffolds integrating magnetic materials and featuring magnetic gradients were prepared for potential utility in magnetic-field assisted tissue engineering. Magnetic nanoparticles (MNPs) were introduced into SFP scaffolds via dip-coating methods, resulting in magnetic SFP scaffolds with different strengths of magnetization. Magnetic SFP scaffolds showed excellent hyperthermia properties achieving temperature increases up to 8 °C in about 100 s. The scaffolds were not toxic to osteogenic cells and improved cell adhesion and proliferation. These findings suggest that tailored magnetized silk-based biomaterials can be engineered with interesting features for biomaterials and tissue-engineering applications. Registration No. 22176

Capture Gamma-Ray Spectroscopy and Related Topics, Proceedings of the Fifteenth International Symposium
Schwengner, R.; Zuber, K. (Editors)
Abstract: The Fifteenth International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15) was organized by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Technische Universität (TU) Dresden and held at TU Dresden from August 25 to August 29, 2014.
CGS15 was the fifteenth symposium in a series that started in 1969.
This conference continued the general themes of earlier meetings with special emphasis on gamma-ray spectroscopy used in neutron capture and also in a wider context in nuclear structure, nuclear reactions, nuclear astrophysics, statistical properties of nuclei, nuclear probes for fundamental physics, nuclear data, novel techniques and applications.
These proceedings include a collection of articles from all these topics.

Keywords: Gamma-ray spectroscopy
  • Book (Editorship)
    France: EDP Sciences, 2015
    ISBN: 978-2-7598-1794-8


Registration No. 22175
Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199]