Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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29177 Publications
Annealing effect on ferromagnetic properties, hole concentration and electronic band structure of GaMnAs epitaxial layers
Zhu, J. J.; Li, L.; Chen, L.; Prucnal, S.; Grenzer, J.; Zhao, J. H.; Helm, M.; Zhou, S. Q.
In this paper, we analyze the correlation of the magnetism and the carrier concentration with the shift of the spectroscopic critical points for low compensated GaMnAs samples with a high Curie temperature of around 150 K. The GaMnAs layers were grown by low-temperature molecular beam epitaxy. The low-temperature annealing leads to a reduction of Mn interstitials from 0.8 to 0.4% and an enhancement in the hole concentration. The saturation magnetization is 51 emu/cm and the Curie temperature is 150 K after post-growth annealing, while those of as-grown layers are 37 emu/cm and 80 K. The resistivity dropped significantly after the post-growth annealing, due to the fact that the number of Mn, which act as double donors and compensate holes, was significantly reduced by the low-temperature and long-time annealing. The electronic band structure is investigated by spectroscopic ellipsometry. The transition energies of critical points show redshift after post-growth annealing due to the annealing-induced enhancement of the hole concentration. Our results support the valence band picture (the Zener model) in ferromagnetic GaMnAs.
Keywords: GaMnAs, DMS, doping, magnetic properties

Registration No. 26831 - Permalink


Low energy dynamics in charge ordered R0.5Sr0.5MnO3 (R = Nd and Pr) manganite thin films
Rana, R.; Schmidt, J.; Grenzer, J.; Schneider, H.; Helm, M.; Pashkin, A.
Transition metal oxides represent an exotic class of correlated systems in which a complex interplay between the spin, charge, orbital and lattice degrees of freedom may result in colossal magnetoresistance, superconductivity; charge ordered (CO) phases, etc. The half-doped Pr0.5Sr0.5MnO3 manganite represents a unique stripe type CO-orbital order that induces transport and magnetic anisotropy whereas the CO in Nd0.5Sr0.5MnO3 is charge-exchange (CE)-type which is isotropic in nature.

We have systematically explored ~ 200nm epitaxial manganite thin films grown on (100), (110), and (111) oriented (LaAlO3)0.3(Sr2TaAlO6)0.7 substrates by pulsed laser deposition technique. Our Terahertz (THz) time-domain spectroscopic data reveal charge density wave (CDW) resonance centered around 5-6 meV for (110) oriented films and Drude-like conductivity for (100) and (111) oriented films. The CDW resonance in the optical conductivity spectra can be tuned from 4 meV to 6 meV for (110) oriented films and depends on the amount of ferromagnetic phase fraction in the CO matrix and corroborates well with the magnetization measurements. The nonlinear conductivity related to the sliding of the pinned CDW character makes the studied systems promising candidates for ultrafast coherent control of charge transport by resonant THz pumping.
Keywords: Manganites; charge order; terahertz
  • Poster
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Registration No. 26817 - Permalink


Junctionless Nanowire Transistors: Promising Devices for Biosensor Applications
Georgiev, Y. M.ORC
Junctionless nanowire transistors (JNTs) are gated resistors where the source, channel and drain have the same type of doping without any dopant concentration gradient. The JNT is the simplest transistor structure possible and probably the most scalable of all field effect transistor (FET) structures. It is easier to fabricate than standard metal-oxide-semiconductor FETs (MOSFETs) and has also a number of performance advantages over them. , , Two of the advantages are especially important for the JNT application as sensors:

1. The current flow in JNTs is not controlled by a reverse biased p-n junction as in standard MOSFETs but entirely by the gate potential. Therefore, they are more sensitive to any change in the electrostatic potential on the channel surface acting as a gate potential.

2. JNTs demonstrate bulk conductance near the centre of the channel, in contrast to the conductance in a thin surface inversion or accumulation layer near the gate in the inversion mode or accumulation mode MOSFETs, which leads to higher drive currents. Moreover, this fact makes the conduction in JNTs less affected by the noise-inducing parasitic surface states than in the case of conventional MOSFETs, which is very important for achieving high signal-to-noise ratio and low detection limit.

In the presentation, these advantages will be discussed in detail followed by results of implementation of silicon (Si) JNTs as chemical and biological sensors. A series of experiments for sensing the ionic strength and the pH value of buffer solutions have proven the excellent sensitivity of these sensors. , Moreover, sensing of the protein streptavidin at a concentration as low as 580 zM has been observed, which is by far the lowest concentration of this protein ever detected and corresponds to detection in the range of only few molecules.

The high sensitivity of JNT sensors, combined with their very simple structure and relaxed fabrication process, makes them promising candidates for cheap mass production by the conventional microelectronic technology. This can enable their numerous applications in various fields where fast, low-cost, label-free, low-volume and real-time detection of chemical and biological species at low detection levels is required.


REFERENCES:

1. J.P. Colinge, C.-W. Lee, A. Afzalian, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, B. O'Neill, A. Blake, M. White, A.-M. Kelleher, B. McCarthy, R. Murphy. Nanowire transistors without junctions. Nature Nanotech. 5, 225 (2010).
2. J. P. Colinge, C. W. Lee, N. D. Akhavan, R. Yan, I. Ferain, P. Razavi, A. Kranti, R. Yu. Junctionless Transistors: Physics and Properties, in Semiconductor-On-Insulator Materials for Nanoelectronics Applications. (Eds: A. Nazarov, J. P. Colinge, F. Balestra, J.-P. Raskin, F. Gamiz, V. S. Lysenko), Springer-Verlag Berlin, Heidelberg, Germany, pp.187-200, Ch. 10 (2011).
3. J. P. Colinge, A. Kranti, R. Yan, C. W. Lee, I. Ferain, R. Yu, N. D. Akhavan, P. Razavi. Junctionless Nanowire Transistor (JNT): Properties and design guidelines. Solid State Electron. 65-66, 33 (2011).
4. Y.M. Georgiev, N. Petkov, B. McCarthy, R. Yu, V. Djara, D. O'Connell, O. Lotty, A. M. Nightingale, N. Thamsumet, J. C. deMello, A. Blake, S. Das, J. D. Holmes. Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices. Microelectron. Eng. 118, 47 (2014).
5. Y. M. Georgiev, R. Yu, N. Petkov, O. Lotty, A. M. Nightingale, J. C. deMello, R. Duffy, J. D. Holmes. Silicon and Germanium Junctionless Nanowire Transistors for Sensing and Digital Electronics Applications, In "Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting", (Eds: A. Nazarov, F. Balestra, V. Kilchytska, D. Flandre), Springer International Publishing AG, Cham, Switzerland, pp. 367-388, Ch. 17 (2014).
  • Lecture (Conference)
    NanoBioSensors Conference, 04.-05.09.2017, Dresden, Germany

Registration No. 26809 - Permalink


High Resolution Nanofabrication
Georgiev, Y. M.ORC
Nanofabrication aims at creating structures and devices having minimum dimensions below 100 nm. This is possible to achieve in two main ways: bottom-up and top-down. In the former, the structures and devices are created from small to large in an additive fashion, which relies to a great extent on self-organisation processes. In the latter, the fabrication goes from large to small where nano-structures and devices are carved from a larger piece of material in a subtractive fashion. The top-down approach is much more mature than the bottom-up one and is based on two long-established processes: (i) nanolithography, where a stencil with the required pattern is created in a sacrificial layer called “resist”, deposited on the main working material (substrate), and (ii) pattern transfer through the resist stencil into the base material.
In this paper we will present results on high-resolution nanofabrication of structures and devices with critical dimensions (CD) below 10 nm on silicon (Si), silicon-on-insulator (SOI), germanium (Ge) and germanium-on-insulator (GeOI) substrates. The fabrication was mainly within the frames of the top-down approach and was based on electron beam lithography (EBL) with positive or negative resists followed by a pattern transfer with both additive (metal deposition and lift-off) and subtractive (dry etching) methods.[1-4] Moreover, high-end results on combination of bottom-up and top-down approaches will also be presented such as (i) contacting of bottom-up grown and randomly distributed nanostructures for their integration into functional devices [5] as well as (ii) pattern density multiplication by directed self assembly (DSA) of block-copolymers (BCP).[6,7] We believe that these results are showing some of the promising trends for future development of high-resolution nanofabrication.
References:
[1] Küpper, D., Küpper, D., Wahlbrink, T., Bolten, J., Lemme, M. C., Georgiev, Y. M., & Kurz, H. (2006). Megasonic-assisted development of nanostructures. Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 24(4), 1827.
[2] Georgiev, Y. M., Petkov, N., McCarthy, B., Yu, R., Djara, V., O’Connell, D., … Holmes, J. D. (2014). Fully CMOS-compatible top-down fabrication of sub-50nm silicon nanowire sensing devices. Microelectronic Engineering, 118, 47-53.
[3] Gangnaik, A., Georgiev, Y. M., McCarthy, B., Petkov, N., Djara, V., & Holmes, J. D. (2014). Characterisation of a novel electron beam lithography resist, SML and its comparison to PMMA and ZEP resists. Microelectronic Engineering, 123, 126-130.
[4] Gangnaik, A. S., Georgiev, Y. M., Collins, G., & Holmes, J. D. (2016). Novel germanium surface modification for sub-10 nm patterning with electron beam lithography and hydrogen silsesquioxane resist. Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 34(4), 041603.
[5] Teschome, B., Facsko, S., Schönherr, T., Kerbusch, J., Keller, A., & Erbe, A. (2016). Temperature-Dependent Charge Transport through Individually Contacted DNA Origami-Based Au Nanowires. Langmuir, 32(40), 10159-10165.
[6] Cummins, C., Gangnaik, A., Kelly, R. A., Borah, D., O'Connell, J., Petkov, N., … Morris, M. A. (2015). Aligned silicon nanofins via the directed self-assembly of PS-b-P4VP block copolymer and metal oxide enhanced pattern transfer. Nanoscale, 7(15), 6712-6721.
[7] Cummins, C., Gangnaik, A., Kelly, R. A., Hydes, A. J., O’Connell, J., Petkov, N., … Morris, M. A. (2015). Parallel Arrays of Sub-10 nm Aligned Germanium Nanofins from an In Situ Metal Oxide Hardmask using Directed Self-Assembly of Block Copolymers. Chemistry of Materials, 27(17), 6091-6096.
  • Invited lecture (Conferences)
    5th International workshop “Nano-Fabrication, Devices & Metrology”, 19.-20.06.2017, Eindhoven, The Netherlands

Registration No. 26808 - Permalink


Dopant Induced Single Electron Tunneling within the Sub-bands of Single Silicon NW Tri-gate Junctionless n-MOSFET
Uddin, W.; Georgiev, Y. M.ORC; Maity, S.; Das, S.
We report 1D electron transport of silicon functionless tri-gate n-type transistor at 4.2 K. The step like curve observed in the current voltage characteristic suggests 1D transport. Besides the current steps for 1D transport, we found multiple spikes within individual steps, which we relate to inter-band single electron tunnelling, mediated by the charged dopants available in the channel region. Clear Coulomb diamonds were observed in the stability diagram of the device. It is shown that a uniformly doped silicon nanowire can provide us the window for the single electron tunnelling. Back-gate versus front-gate color plot, where current is in a color scale, shows a crossover of the increased conduction region. This is a clear indication of the dopant–dopant interaction. It has been shown that back-gate biasing can be used to tune the coupling strength between the dopants.
Keywords: functionless transistor, 1D transport, single electron tunnelling, Coulomb blocked, dopant–dopant interaction

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Registration No. 26807 - Permalink


Doping top-down e-beam fabricated germanium nanowires using molecular monolayers
Long, B.; Alessio Verni, G.; O’Connell, J.; Shayesteh, M.; Gangnaik, A.; Georgiev, Y. M.ORC; Carolan, P.; O’Connell, D.; Kuhn, K. J.; Clendenning, S. B.; Nagle, R.; Duffy, R.; Holmes, J. D.
This paper describes molecular layer doping of Ge nanowires. Molecules containing dopant atoms are chemically bound to a germanium surface. Subsequent annealing enables the dopant atoms from the surface bound molecules to diffuse into the underlying substrate. Electrical and material characterisation was carried out, including an assessment of the Ge surface, carrier concentrations and crystal quality. Significantly, the intrinsic resistance of Ge nanowires with widths down to 30 nm, doped using MLD, was found to decrease by several orders of magnitude.
Keywords: Molecular layer doping, Nanowires, Semiconductors, Germanium, Conformal, Non-destructive

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Registration No. 26806 - Permalink


Magnetotransport in Half-Metallic Manganese Ruthenium Gallium
Fowley, C.; Rode, K.; Borisov, K.; Atcheson, G.; Lau, Y.-C.; Thiyagarajah, N.; Coey, M.; Stamenov, P.; Gallardo, R.; Kampert, E.; Wang, Z.; Lindner, J.; Deac, A. M.
The recently discovered fully-compensated half-metal, manganese ruthenium gallium (MRG), is a very promising material for spintronics. It possesses tunable magnetic moment, high magnetic anisotropy field and high spin polarisation. Here, we use the extraordinary Hall effect and longitudinal magnetoresistance to characterise the properties of MRG. Experiments are carried out in pulsed magnetic fields up to 60 T at the Dresden High Magnetic Field Laboratory (HLD). The spin-flop transition, as well as a large spontaneous Hall angle are observed. The spontaneous Hall angle is over 2% and is seen to be independent of temperature. The magneto-transport in MRG is shown to be dominated by one sublattice only, even at the magnetic compensation temperature (i.e. when the total magnetic moment is zero). MRG behaves magnetically an antiferromagnet and electrically as a normal ferromagnet with a sizeable spin-polarisation.
Keywords: anomalous Hall effect, half-metals, Heusler alloys, ferrimagnetism, high magnetic fields
  • Lecture (Conference)
    81. DPG-Frühjahrstagung, 19.-24.03.2017, Dresden, Germany
  • Lecture (Conference)
    Intermag 2017, 24.-28.04.2017, Dublin (Baile Átha Cliath), Ireland (Éire)

Registration No. 26804 - Permalink


Incorporation of Europium(III) into Scheelite-Related Host Matrices ABO4 (A = Ca2+, Sr2+, Ba2+; B = W6+, Mo6+): Role of A- and B- Sites on the Dopant Site-Distribution and Photoluminescence
Xiao, B.; Schmidt, M.
Calcium orthotungstates and -molybdates are naturally occurring minerals that have been studied extensively. The minerals are named scheelite (CaWO4) and powellite (CaMoO4), respectively. Scheelite is the most important economic W mineral. Powellite is actively studied in the nuclear waste management field. Powellite is one of the primary Mo crystalline phases expected to form in high-level nuclear waste (HLW) borosilicate glasses during waste processing.
Both scheelite and powellite have a large number of synthetic derivatives that are based on a general formula ABO4 (A = Ca2+, Sr2+, Ba2+; B = W6+, Mo6+). Recently, much of the interest in study of scheelite-type materials arises from their exceptional compositional variability. In the context of nuclear waste disposal, this compositional variability offers a potential pathway for the effective retention of highly radiotoxic actinides like Pu and Am in a powellite secondary phase. However, the thermodynamic stability of these solid solutions will depend on their structural deviation from the stoichiometric phases.
Investigations have shown that the presence of excess positive charge in scheelite-typed ABO4 materials upon incorporation of each trivalent ion is compensated via coupled substitution with a monovalent alkali cation. Single-crystal X-ray measurements demonstrate that the crystal structure of the resulting solid solutions is disordered, that is, the trivalent dopant and monovalent charge-compensating cation statistically occupy the same divalent A2+ site in ABO4 structure. However, the structural details behind such disordered substitution, such as specific ionic environment around dopants, number of non-equivalent doping species as well as spatial accommodation of doping centers, are difficult parameters to characterize from the crystallographic data, especially when the dopant is present at trace concentration levels.
Polarization-dependent site-selective time resolved laser-induced fluorescence spectroscopy (p-TRLFS) is unique in its capability to characterize the local environment of a fluorescent probe, here Eu3+, in a multi-species system with point-group accuracy at trace concentration levels. This work aims to clarify the impact of site effect on the local symmetry distortion from the bulk crystallographic site symmetry in scheelite-type ABO4 single crystals. This will improve our understanding of the formation of solid solutions on the molecular scale.
Keywords: TRLFS
  • Lecture (Conference)
    GeoBremen, 24.-29.09.2017, Bremen, Germany

Registration No. 26801 - Permalink


GaAs-based core/shell nanowires with extremely large lattice mismatch grown on Si substrates
Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Grenzer, J.; Ghorbani Asl, M.; Krasheninnikov, A.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.
The geometry and high surface-to-volume ratio of nanowires offer unique possibilities for strain engineering in epitaxial semiconductor heterostructures with large lattice mismatch. In addition, the possibility to grow nanowires of high crystal quality epitaxially on Si substrates adds to their technological significance. In this work, we have investigated the growth of free-standing GaAs/InxGa1-xAs and GaAs/InxAl1-xAs core/shell nanowires on Si(111) substrates by molecular beam epitaxy, the accommodation of the lattice mismatch therein, and its effect on the nanowire properties.
Very thin GaAs core nanowires (20-25 nm in diameter) were grown in the self-catalyzed mode with a sufficiently low number density (to avoid beam shadowing effects) on SiOx/Si(111) substrates, after an in situ treatment of the latter with Ga droplets. This resulted in zinc blende nanowires with their axis along the [111] crystallographic direction and six {1-10} sidewalls. Subsequently, conformal overgrowth of the InxGa1-xAs or InxAl1-xAs shell was obtained only under kinetically limited growth conditions that suppressed mismatch-induced bending phenomena.
The strain in the core and the shell was studied systematically as a function of the shell composition and thickness. To that end, we used Raman scattering spectroscopy, transmission electron microscopy and synchrotron X-ray diffraction, and compared the results with theoretical predictions based on continuum elasticity and density functional theories. Our results demonstrate that highly mismatched core/shell nanowires with defect-free interface can be obtained beyond what is possible in thin film heterostructures.
More interestingly, nanowires with strain-free shell and fully strained core can be grown under certain conditions. The large strain in the GaAs core is expected to have a strong effect on its fundamental properties. Here, we demonstrate a large shrinkage of the band gap, which can be as high as 35 % depending on the composition of the shell.
  • Lecture (Conference)
    Austrian MBE Workshop 2017, 28.-29.09.2017, Wien, Austria

Registration No. 26799 - Permalink


Compositional and strain analysis of In(Ga)N/GaN short period superlattices
Dimitrakopulos, G. P.; Vasileiadis, I. G.; Bazioti, C.; Smalc-Koziorowska, J.; Kret, S.; Dimakis, E.ORC; Florini, N.; Kehagias, T.; Suski, T.; Karakostas, T.; Moustakas, T. D.; Komninou, P.
Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising twodimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry, and strain. The high angle annular dark field Z-contrast observations were quantified for such layers, regarding the indium content of the QWs, and were correlated to their strain state using peak finding and geometrical phase analysis. Image simulations taking into thorough account the experimental imaging conditions were employed in order to associate the observed Z-contrast to the indium content. Energetically relaxed supercells calculated with a Tersoff empirical interatomic potential were used as the input for such simulations. We found a deviation from the tetragonal distortion prescribed by continuum elasticity for thin films, i.e., the strain in the relaxed cells was lower than expected for the case of 1 ML QWs. In all samples, the QW thickness and strain were confined in up to 2 ML with possible indium enrichment of the immediately abutting MLs. The average composition of the QWs was quantified in the form of alloy content.

Registration No. 26796 - Permalink


How indium nitride senses water
Jovic, V.; Moser, S.; Ulstrup, S.; Goodacre, D.; Dimakis, E.ORC; Koch, R.; Katsoukis, G.; Moreschini, L.; Mo, S.-K.; Jozwiak, C.; Bostwick, A.; Rotenberg, E.; Moustakas, T. D.; Smith, K. E.
The unique electronic band structure of indium nitride InN, part of the industrially significant III−N class of semiconductors, offers charge transport properties with great application potential due to its robust n-type conductivity. Here, we explore the water sensing mechanism of InN thin films. Using angle-resolved photoemission spectroscopy, core level spectroscopy, and theory, we derive the charge carrier density and electrical potential of a two-dimensional electron gas, 2DEG, at the InN surface and monitor its electronic properties upon in situ modulation of adsorbed water. An electric dipole layer formed by water molecules raises the surface potential and accumulates charge in the 2DEG, enhancing surface conductivity. Our intuitive model provides a novel route toward understanding the water sensing mechanism in InN and, more generally, for understanding sensing material systems beyond InN.
Keywords: Sensor, two-dimensional electron gas (2DEG), ARPES, surface electronic potential, quantum well

Registration No. 26792 - Permalink


Investigating the structure of crosslinked polymer brushes (brush-gels) by means of Positron Annihilation Spectroscopy
Dehghani, E. S.; Aghion, S.; Anwand, W.; Consolati, G.; Ferragut, R.; Panzarasa, G.
Polymer brushes can be useful as small-scale reactors for the controlled synthesis of nanoparticles, an approach which is gaining increasing interest. In this context, chemical crosslinking of polymer brushes could be considered as a viable approach to control the size and size distribution of the formed nanoparticles. Here we describe the application of Positron Annihilation Spectroscopy (PAS) for the characterization of crosslinked polymer brushes (brush-gels). Poly(hydroxyethyl methacrylate) (PHEMA) brushes were obtained on silicon substrates by means of a surface-initiated atom transfer radical polymerization (SI-ATRP). Crosslinking was achieved during the polymerization by adding different amounts of diethyleneglycol dimethacrylate (DEGDMA) as a difunctional monomer. The resulting brushes, both un- and crosslinked, were then post-modified with carboxylic acid groups, allowing the in situ synthesis of silver nanoparticles after ion exchange with silver nitrate and reduction with sodium borohydride. The detailed characterization of such systems is notoriously challenging and PAS proved to be an effective, non-invasive technique to acquire insight on the structure of the brushes and of their nanoparticle composites.
Keywords: Polymer brushes nanoparticles Positron Annihilation Spectroscopy

Registration No. 26788 - Permalink


Comparison of tumour hypoxia measured by FMISO-PET and gene signatures for patients with HNSCC
Löck, S.; Linge, A.; Seidlitz, A.; Bandurska-Luque, A.; Großer, M.; Baretton, G. B.; Zöphel, K.; Zips, D.; Troost, E. G. C.; Krause, M.; Baumann, M.
Purpose: Tumour hypoxia is well known to increase radio-resistance of tumours. In a recent prospective biomarker imaging trial, hypoxia has been measured by [18F]fluoromisonidazole positron emission tomography (FMISO-PET) scans [1,2]. Here, we compared hypoxia imaging with the expression of hypoxia-associated gene signatures for patients with locally advanced head and neck squamous cell carcinoma (HNSCC) treated by primary radiochemotherapy (RCHT).

Material and methods: FMISO-PET imaging and gene expression analyses were performed on the cohort of 50 HNSCC patients [1,2]. For this study, the FMISO-PET parameters tumour-to-background ratio (TBPpeak) and hypoxic tumour volume (HV1.6) analysed before RCHT were considered. Expressions of 15-, 26- and 30-gene hypoxia-associated signatures [3-5] were analysed from formalin-fixed paraffin-embedded (FFPE) tumour biopsies obtained before RCHT using the GeneChip® Human Transcriptome Array 2.0 (Affymetrix) and nanoString analysis. Gene expressions were compared between the two methods using the Pearson correlation coefficient. Linear regression was applied to relate TBRpeak and HV1.6 to the mean expression of the gene signatures, including the interaction with tumour volume which was assessed on the planning CT by an experienced radiation oncologist. The association of FMISO-PET parameters and gene expressions to loco-regional control (LRC) and progression-free survival (PFS) was assessed by Cox regression.

Results: The mean expressions of all hypoxia-associated gene signatures were highly correlated between Affymetrix and nanoString analyses (R>0.5). While TBRpeak and HV1.6 were weakly correlated with the expression of hypoxia-associated genes alone, significant correlations were observed if the interaction term of gene expression and tumour volume was included (R>0.5). Both FMISO-PET parameters were significantly correlated with LRC and PFS (p<0.01), while the combination of hypoxia-associated gene expressions and their interaction with tumour volume showed a significant but weaker correlation for the 30-gene signature to LRC and for the 15- and 30-gene signature to PFS (p<0.05). The figure shows patient stratifications using HV1.6 (p=0.02), the 30-gene signature (p=0.07) and their combination (p<0.01).

Conclusion: Hypoxia imaging correlates to the expression of hypoxia-associated genes if the interaction of gene expression and tumour volume is included. Interestingly, both methods may complement each other, which may be of advantage for identifying patients who are at high risk of treatment failure and may benefit from dose escalation. While FMISO-PET directly measures hypoxia, the gene signatures are also associated with other radiobiologic phenomena such stemness of cancer cells.
  • Lecture (Conference)
    ESTRO 36, 05.-09.05.2017, Wien, Österreich

Registration No. 26784 - Permalink


Development of short-pulsed, high-field electromagnets for laser-based proton therapy
Schürer, M.; Herrmannsdörfer, T.; Karsch, L.; Kroll, F.; Masood, U.; Sobiella, M.; Pawelke, J.
The new particle acceleration by high intensity laser promises more compact and economic accelerators for cancer treatment. However, the resulting particle beam is pulsed with an ultra-short pulse-duration (~ ps) and has a large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of laser-driven proton beams is investigated including the development of a laser accelerator and suitable beam transport. The designed magnets are intended for a compact beam transport system (gantry) which efficiently transports proton pulses (≤ 220 MeV) from generation to treatment site. For this purpose the initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and focussed by quadrupole magnets, while the energy window is selected by adjustable lead apertures. The implementation as short-pulsed (~ 1 ms) electromagnets allows to generate very high magnetic field strengths (up to 20 T) for short times, which enables the compact construction of both individual magnets and the whole gantry system. The pulse frequency of the magnets can be synchronized with that of the laser accelerator. The high field strengths demand high peak currents (up to 20 kA) and the resultant heating is dissipated by a cooling integrated into the magnets. The in-house developed pulsed magnets will enable a proton gantry 2-3 times smaller than those used in current clinical installations. Pulsed solenoids have been completely engineered and tested, and are routinely applied at laser particle accelerators. Two prototypes of a pulsed dipole and a first pulsed quadrupole were designed and manufactured, and their experimental characterization at the University Proton Therapy Dresden is in progress.
Pulsed electromagnets are crucial components of a compact gantry and after their extensive individual testing they will be combined step-by-step and used at the laser proton accelerator.
  • Poster
    Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland
    DOI: 10.1515/bmt-2017-5078

Registration No. 26783 - Permalink


Saturation correction in pulsed fields of high dose-per-pulse
Gotz, M.; Karsch, L.; Pawelke, J.
Current developments in accelerator technology and beam application have the potential to bring pulsed radiation sources with very high dose-per-pulse into clinical application. In particular, laser-based particle accelerators and pencil beam scanning using synchro-cyclotrons provide intensely pulsed beams. Current methods to determine the saturation correction factor (ks) in ionization chambers are not intended for use at such high dose-per-pulse, possibly leading to an inaccurate dosimetry. We present a method based on the numerical approximation of the ionization, charge reaction and transport processes in an ionization chamber, which is able to overcome the limitations of current procedures used to calculate ks . This numerical work is supported by experimental data of a plane-parallel advanced Markus ionization chamber irradiated with a pulsed electron beam of a dose-per-pulse up to 600 mGy. At a low collection voltage of 100 V a satisfactory description of the saturation correction dependency on dose-per-pulse can be achieved using existing models and tuning their parameter values. However, at the reference voltage of 300 V this is not possible and the newly presented method shows marked improvements. Chief among the additional effects considered in the presented numerical method is the shielding of the electric field by the liberated charges, which alters the dose-per-pulse dependency of ks in a way that can not be replicated by existing approaches.
  • Poster
    Jahrestagung der BIOMEDIZINISCHEN TECHNIK und Dreiländertagung der MEDIZINISCHEN PHYSIK, 10.-13.09.2017, Dresden, Deutschland
    DOI: 10.1515/bmt-2017-5029

Registration No. 26779 - Permalink


Shielding and activation calculations around the reactor core for the MYRRHA ADS design
Ferrari, A.; Mueller, S.; Konheiser, J.; Castelliti, D.; Sarotto, M.; Stankovskiy, A.
In the frame of the FP7 European project MAXSIMA, an extensive simulation study has been done to assess the main shielding problems in view of the construction of the MYRRHA accelerator-driven system at SCK·CEN in Mol (Belgium). An innovative method based on the combined use of the two state-of-the-art Monte Carlo codes MCNPX and FLUKA has been used, with the goal to characterize complex, realistic neutron fields around the core barrel, to be used as source terms in detailed analyses of the radiation fields due to the system in operation, and of the coupled residual radiation. The main results of the shielding analysis are presented, as well as the construction of an activation database of all the key structural materials. The results evidenced a powerful way to analyse the shielding and activation problems, with direct and clear implications on the design solutions.
Keywords: Shielding, ADS systems, Monte Carlo, FLUKA, MCNPX
  • Open Access LogoContribution to proceedings
    ICRS-13 & RPSD-2016, 13th International Conference on Radiation Shielding & 19th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society - 2016, 03.-06.10.2016, Paris, France
    Shielding and activation calculations around the reactor core for the MYRRHA ADS design: EPJ Web Conf., 153 (2017) 05001
    DOI: 10.1051/epjconf/201715305001
  • Lecture (Conference)
    ICRS-13 & RPSD-2016, 13th International Conference on Radiation Shielding & 19th Topical Meeting of the Radiation Protection and Shielding Division of the American Nuclear Society - 2016, 03.-06.10.2016, Paris, France

Registration No. 26773 - Permalink


Magnetic e-skins enabled somatic and touchless interactive devices
Jin, G.; Xu, W.; Gilbert Santiago, C. B.; Changan, W.; Shengqiang, Z.; Jürgen, F.; Denys, M.
Humans skin provide perceptions of the temperature of objects, strain and pressure on skin, friction for holding objects, which help humans interact very precisely with unstructured surroundings [1]. Electronic skins [2-4] allow for the realization of similar sensing functions and also having the possibility of integrating other sensing functions beyond humans, for example, touchless feeling. Very recently we demonstrated magnetosensitive e-skins, which is an important step towards the realization of artificial magnetoception for humans [5,6].
Here, we present a magnetic e-skin that not only has the ability to detect the position and movement of magnetic objects in a touchless mode but also is sensitive to mechanical forces. The magnetic skin is a stack of a magnetoresistive (MR) sensor layer and a surface-pyramid-structured magnetic foil. The MR sensor of the magnetic skin is sensitive to the surrounding magnetic field change. When the surface of the target object is fixed with a magnet, the magnetic e-skin will have the ability to detect the distance change between itself and the target object in a touchless mold. Furthermore, when a pressure is applied on the surface of the magnetic e-skin, the induced distance change between the MR sensor and the magnetic foil will also result in the resistance change of the MR sensor. As a result, this magnetic e-skin also has the ability to detect the pressure change applied on its surface in a touch mold (somatic interaction). This multi-functional magnetic e-skin will hold a great promise for the realization of advanced humanoid robots, biomedical prostheses, and surgical electronic gloves.

1. A. Zimmerman, et al. Science 346, 950 (2014).
2. T. Someya, et al. Proc. Natl. Acad. Sci. U.S.A. 101, 9966 (2004).
3. Z. Ma, et al. Science 333, 830 (2011).
4. Z. Bao, et al. Adv. Mater. 25, 5997 (2013).
5. M. Melzer, et al, Nat. Commun. 6, 6080 (2015).
6. D. Makarov, et al., Appl. Phys. Rev. 3, 011101 (2016).
Keywords: e-skin, pressure sensor, flexible, magnetic sensor, multi-functional
  • Lecture (Conference)
    2017 MRS Fall Meeting, 26.11.-01.12.2017, Boston, America

Registration No. 26768 - Permalink


Mesoscale Dzyaloshinskii-Moriya interaction in curvilinear geometries: one-dimensional and two-dimensional cases
Volkov, O.; Kravchuk, V.; Sheka, D.; Makarov, D.;  Fassbender, J.; Gaididei, Y.; Roessler, U.; van den Brink, J.; Fuchs, H.; Fangohr, H.
A broken chiral symmetry in a magnetic system manifests itself as the appearance of either periodical (e.g. helical or cycloid modulations [1]) or localized magnetization structures (e.g. chiral domain walls and skyrmions [2]). The origin of these magnetic textures is spin-orbit Dzyaloshinskii-Moriya interaction (DMI), which is observed in bulk magnetic crystals with low symmetry [3-4] or at interfaces between a ferromagnet and a nonmagnetic material with strong spin-orbit coupling [5]. This DMI is intrinsic to the crystal or layer stack. Recently, it was reported that geometrically-broken symmetry in curvilinear magnetic systems leads to the appearance of curvature-driven DMI-like chiral contribution in the energy functional [6]. This chiral term is determined by the sample geometry, e.g local curvature and torsion, and is therefore extrinsic to the crystal or layer stack. It reveals itself in the domain wall pinning at a localized wire bend and is responsible for the existence of magnetochiral effects in curvilinear magnetic
systems, e.g. in ferromagnetic Möbius rings, nanorings and helix wires [7].
The intrinsic and extrinsic DMI act at different length scales and, hence, their combination can be referred to as a mesoscale DMI. The symmetry and strength of this term are determined by the geometrical and material properties of the three-dimensional (3D) object. Although, intrinsic and extrinsic terms separately are broadly investigated, their synergistic impact is not known yet. Here, we study the properties of the mesoscale DMI in a 1D curvilinear wire and in 2D curvilinear shells. We derive the general expressions for the mesoscale DMI term and analyze the magnetization states which arise in a helix wire and in a thin spherical shell with intrinsic DMI.
[1] I. E. Dzyaloshinskii, Sov. Phys. JETP, vol. 19, pp. 964–971 (1964).
[2] N. Nagaosa and Y. Tokura, Nature Nanotechnology, vol. 8, pp. 899–911 (2013).
[3] I. E. Dzialoshinskii, Sov. Phys. JETP, vol. 5, pp. 1259–1272 (1957).
[4] T. Moriya, Phys. Rev. Lett., vol. 4, pp. 228–230 (1960).
[5] A. Fert, Materials Science Forum, vol. 59-60, pp. 439–480 (1990).
[6] Y. Gaididei, V. P. Kravchuk, and D. D. Sheka, Phys. Rev. Lett., vol. 112, p. 257203 (2014).
[7] R. Streubel, P. Fischer, F. Kronast, V. P. Kravchuk, D. D. Sheka, Y. Gaididei, O. G. Schmidt, and D. Makarov, Journal of Physics D: Applied Physics, vol. 49, p. 363001 (2016)
Keywords: Dzyaloshinskii-Moriya interaction, curved geometry, helical wire, magnetochirality, mesoscale, skyrmion
  • Lecture (Conference)
    TOP-SPIN 3: Spin and Topological Phenomena in Nanostructures - Towards Topological Materials Science, 25.-28.04.2017, Dresden, Germany

Registration No. 26765 - Permalink


Mesoscale Dzyaloshinskii-Moriya interaction: one-dimensional and two-dimensional cases
Volkov, O.; Kravchuk, V.; Sheka, D.; Makarov, D.; Fassbender, J.; Gaididei, Y.; Roessler, U.; van den Brink, J.; Fuchs, H.; Fangohr, H.; Kosub, T.
A broken chiral symmetry in a magnetic system manifests itself as the appearance of either periodical (e.g. helical or cycloid modulations [1-3]) or localized magnetization structures (e.g. chiral domain walls and skyrmions [3-6]). The origin of these magnetic textures is spin-orbit Dzyaloshinskii-Moriya interaction (DMI), which is observed in bulk magnetic crystals with low symmetry [7-8] or at interfaces between a ferromagnet and a nonmagnetic material with strong spin-orbit coupling [9]. This DMI is intrinsic to the crystal or layer stack. Recently, it was reported that geometrically-broken symmetry in curvilinear magnetic systems leads to the appearance of curvature-driven DMI-like chiral contribution in the energy functional [10-14]. This chiral term is determined by the sample geometry, e.g local curvature and torsion, and is therefore extrinsic to the crystal or layer stack. It reveals itself in the domain wall pinning at a localized wire bend [15] and is responsible for the existence of magnetochiral effects in curvilinear magnetic systems, e.g. in ferromagnetic Möbius rings [16], nanorings [11] and helix wires [12, 13, 17].
The intrinsic and extrinsic DMI act at different length scales and, hence, their combination can be reffered to as a mesoscale DMI. The symmetry and strength of this term are determined by the geometrical and material properties of a three-dimensional (3D) object. Although, intrinsic and extrinsic terms separately are broadly investigated, their synergistic impact is not known yet. Here, we study the properties of the mesoscale DMI in a 1D curvilinear wire and in 2D curvilinear shells. We derive the general expressions for the mesoscale DMI term and analyse the magnetization states which arise in a helix wire and in a thin spherical shell with intrinsic DMI.
The clear cut comparison a helix wire with a straight wire with homogeneous tangential intrinsic DMI reveals: (i) The magnetic states of a curved wire is governed by a single vector of magnetochirality — a vector of the mesoscale DMI — originating from the vector sum of the intrinsic and extrinsic DMI vectors; (ii) The symmetry and period of the chiral structures are determined by the strength and direction of the vector of the mesoscale DMI, which depends on both material and geometrical parameters of a curvilinear wire (Figure, panel a); (iii) Similarly to the case of the straight wire [18] both types of phase transitions (of the first and the second order) are found in the helix. The appearance of
each state can be determined by measuring of the average values of the magnetization components and/or by establishing space Fourier spectra of the coordinate-dependent magnetic signals from the helices.
In the case of 2D curvilinear magnetic shells, it’s shown the existence of a skyrmion solution on a thin magnetic spherical shell even without any additional intrinsic DMI [19]. Such skyrmions can be stabilized by curvature effects only, namely by the curvature-induced, extrinsic DMI (Figure, panel b). In addition to the striking difference to the case of a planar skyrmion, magnetic skyrmions on a spherical shell are topologically trivial. This is due to a shift of the topological index of the magnetization field caused by topology of the surface itself. As a result, a skyrmion on a spherical shell can be induced by a uniform external magnetic field. Further, the curvature stabilized skyrmions are very small, with a lateral extension of several nm only (Figure, panel b). The size of the skyrmion core can be tailored e.g. by an additional intrinsic DMI (Figure, panel c). One can note here, that the curvature stabilized skyrmions are always of Neel type (at least, for a surface of rotation). Due to their small sizes and ease in manipulating using homogeneous magnetic fields, we envision those topological objects to be relevant for the realization of on-demand tunable topological logic. Indeed, topological Hall effect can be digitally switched on or off by exposing a sample withferromagnetic spherical shells submerged by a nonmagnetic conductor.
References:
[1] I. E. Dzyaloshinskii, “Theory of helicoidal structures in antiferromagnets. i. nonmetals,” Sov. Phys. JETP, vol. 19, pp. 964–971 (1964).
[2] A. Bogdanov, U. Rössler, and C. Pfleiderer, “Modulated and localized structures in cubic helimagnets,” Physica B: Condensed Matter, vol. 359-361, pp. 1162–1164 (2005).
[3] S. Rohart and A. Thiaville, “Skyrmion confinement in ultrathin film nanostructures in the presence of dzyaloshinskii-moriya interaction,” Physical Review B, vol. 88, p. 184422 (2013).
[4] A. Thiaville, S. Rohart, É. Jué, V. Cros, and A. Fert, “Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films,” EPL (Europhysics Letters), vol. 100, p. 57002 (2012).
[5] A. Bogdanov and A. Hubert, “The stability of vortex-like structures in uniaxial ferromagnets,” Journal of Magnetism and Magnetic Materials, vol. 195, pp. 182–192 (1999).
[6] N. Nagaosa and Y. Tokura, “Topological properties and dynamics of magnetic skyrmions,” Nature Nanotechnology, vol. 8, pp. 899–911 (2013).
[7] I. E. Dzialoshinskii, “Thermodynamic theory of “weak” ferromagnetism in antiferromagnetic substances,” Sov. Phys. JETP, vol. 5, pp. 1259–1272 (1957).
[8] T. Moriya, “New mechanism of anisotropic superexchange interaction,” Phys. Rev. Lett., vol. 4, pp. 228–230 (1960).
[9] A. Fert, “Magnetic and transport properties of metallic multilayers,” Materials Science Forum, vol. 59-60, pp. 439–480 (1990).
[10] Y. Gaididei, V. P. Kravchuk, and D. D. Sheka, “Curvature effects in thin magnetic shells,” Phys. Rev. Lett., vol. 112, p. 257203 (2014).
[11] D. D. Sheka, V. P. Kravchuk, and Y. Gaididei, “Curvature effects in statics and dynamics of low dimensional magnets,” Journal of Physics A: Mathematical and Theoretical, vol. 48, p. 125202 (2015).
[12] D. D. Sheka, V. P. Kravchuk, K. V. Yershov, and Y. Gaididei, “Torsion-induced effects in magnetic nanowires,” Phys. Rev. B, vol. 92, p. 054417 (2015).
[13] O. V. Pylypovskyi, D. D. Sheka, V. P. Kravchuk, K. V. Yershov, D. Makarov, and Y. Gaididei, “Rashba torque driven domain wall motion in magnetic helices,” Scientific Reports, vol. 6, p. 23316 (2016).
[14] R. Streubel, P. Fischer, F. Kronast, V. P. Kravchuk, D. D. Sheka, Y. Gaididei, O. G. Schmidt, and D. Makarov, “Magnetism in curved geometries (topical review),” Journal of Physics D: Applied Physics, vol. 49, p. 363001 (2016).
[15] K. V. Yershov, V. P. Kravchuk, D. D. Sheka, and Y. Gaididei, “Curvature-induced domain wall pinning,” Phys. Rev. B, vol. 92, p. 104412 (2015).
[16] O. V. Pylypovskyi, V. P. Kravchuk, D. D. Sheka, D. Makarov, O. G. Schmidt, and Y. Gaididei, “Coupling of chiralities in spin and physical spaces: The Möbius ring as a case study,” Phys. Rev. Lett., vol. 114, p. 197204 (2015).
[17] K. V. Yershov, V. P. Kravchuk, D. D. Sheka, and Y. Gaididei, “Curvature and torsion effects in spin-current driven domain wall motion,” Phys. Rev. B, vol. 93, p. 094418 (2016).
[18] M. Heide, G. Bihlmayer, and S. Blügel, “Non-planar dzyaloshinskii spirals and magnetic domain walls in noncentrosymmetric systems with orthorhombic anisotropy,” Journal of Nanoscience and Nanotechnology, vol. 11,
pp. 3005–3015 (2011).
[19] V. P. Kravchuk, U. K. Rößler, O. M. Volkov, D. D. Sheka, J. van den Brink, D. Makarov, H. Fuchs, H. Fangohr, and Y. Gaididei, “Topologically stable magnetization states on a spherical shell: Curvature-stabilized skyrmions,” Phys. Rev. B, vol. 94, p. 144402 (2016).
Keywords: Dzyaloshinskii-Moriya interaction, curved geometry, helical wire, magnetochirality, mesoscale, skyrmion
  • Poster
    2017 IEEE International Magnetics Conference, 24.-28.04.2017, Dublin, Ireland

Registration No. 26764 - Permalink


An attempt to enrich holmium ions in a flow system by inhomogeneous magnetic fields.
Kolczyk, K.; Wojnicki, M.; Zabinski, P.; Yang, X.; Mutschke, G.
Recent experimental results regarding an attempt to enrich holmium ions in a flow system by inhomogeneous magnetic fields
are presented.
Keywords: magnetic field, magnetic separation
  • Invited lecture (Conferences)
    International Workshop ECMAG - Magnetic Field Effects on Aqueous Solutions, 20.-21.04.2017, Dresden, Deutschland

Registration No. 26763 - Permalink


Magnetic e-skins enabled somatic and touch-less interactive devices
Jin, G.; Xu, W.; Gilbert Santiago, C. B.; Jürgen, F.; Denys, M.
Humans skin provide perceptions of the temperature of objects, strain and pressure on skin, friction for holding objects, which help humans interact with unstructured surroundings very precisely. Electronic skins [1,2] allow for the realization of similar sensing functions and also having the possibility of integrating other sensing functions beyond humans. Very recently we demonstrated magnetosensitive e-skins, which is an important step towards the realization of artificial magnetoception for humans [3,4].
Here, we present a magnetic e-skin that not only is sensitive to mechanical forces and deformation, but also has the ability to detect the position and movement of magnetic objects in a touch-less manner. The magnetic skin is a stack of a wrinkled magnetic sensor layer and a pyramid-structured magnetic foil. The GMR sensor enables the sensing of the movement of the remote magnetic objects (touch-less interaction). Furthermore, the distance change between the sensor and the magnetic foil make the magnetic skin sensitive to pressure, stretch and flexion (somatic interaction). This magnetic e-skin will hold great promise for the realization of humanoid robots, biomedical prostheses, and surgical electronic gloves.

1. Z. Ma et al. Science 333, 830 (2011).
2. Z. Bao et al. Adv. Mater. 25, 5997 (2013).
3. M. Melzer et al, Nat. Commun. 6, 6080 (2015).
4. D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
Keywords: e-skin, pressure sensor, magnetoresistance, artificial skin, GMR sensor
  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Registration No. 26762 - Permalink


Mesoscale Dzyaloshinskii-Moriya interaction
Volkov, O.; Sheka, D.; Makarov, D.; Fassbender, J.; Kravchuk, V.; Gaididei, Y.
A broken chiral symmetry in a magnetic system leads to the appearance of both periodical and localized magnetization structures. Intrinsic to the crystal spin-orbit driven Dzyaloshinskii-Moriya interaction (DMI) is the origin of all those magnetic textures [1]. Recently, we reported [2,3] that geometrically broken symmetry in curvilinear magnetic systems also leads to the appearance of shape-induced effective DMI.
The combined intrinsic and shape-induced DMI can be reffered to as a mesoscale DMI, whose symmetry and strength depend on the geometrical and material parameters. The mesoscale DMI determines chiral properties of 3D curved systems. We derive the general expression for the mesoscopic DMI terms and determined the conditions for periodical magnetisation structures to appear in one-dimensional ferromagnetic helix wires.
[1] A. Soumyanarayanan et. al., Nature 539, 509-517 (2016).
[2] Y. Gaididei et. al, Phys. Rev. Lett. 112, 257203 (2014).
[3] D. D. Sheka et. al., J. Phys. A: Math. Theor. 48, 125202 (2015).
Keywords: Dzyaloshinskii-Moriya interaction, curved geometry, helical wire, magnetochirality, mesoscale
  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Registration No. 26760 - Permalink


Mesoscale Dzyaloshinskii-Moriya interaction in curved geometry
Volkov, O.; Sheka, D.; Kravchuk, V.; Makarov, D.; Fassbender, J.; Gaididei, Y.
A broken chiral symmetry in magnetic systems manifests itself at the appearance of either periodical (e.g. helical or cycloid modulations) or localized magnetization structures (e.g. chiral domain walls and skyrmions) [1,2]. The origin of these magnetic textures is spin-orbit driven Dzyaloshinskii-Moriya interaction (DMI), which is intrinsic to the crystal or layer stack. Recently, it was reported that geometrically broken symmetry in curvilinear systems leads to the appearance of exchange-driven DMI-like chiral term in energy functional [3,4]. This term is determined by the sample geometry (it is linear with respect to curvature and torsion) and is therefore extrinsic to the crystal or layer stack. The magnetic properties of curvilinear magnets with intrinsic DMI will be necessarily determined by the interplay between two types of chiral interactions. Hence, the resulting chiral term in such type of objects is referred to as a vector of mesoscale DMI, which is the vector sum of the intrinsic and extrinsic DMI vectors. The symmetry and strength of this term are determined by the geometrical and material properties of the curvilinear magnet. Here we study the properties of the mesoscale DMI using a one-dimensional helical wire as a case of study. The clear cut comparison with the straight wire with intrinsic DMI reveals: (i) a single vector of magnetochirality, which is referred to as vector of the mesoscale DMI, originates from the vector sum of the intrinsic and extrinsic DMI vectors; (ii) a symmetry and period of the chiral modulated structures are determined by the strength and direction of the mesoscale DMI vector; (iii) a phase transition between homogeneous and chiral modulated states in the case of mesoscale DMI is a complex second-order phase transition with the intermediate conical state.

References

[1] U. K. Rößler, A. N. Bogdanov, C. Pfleiderer, Nature 442, 797801 (2006)
[2] N. Nagaosa, Y. Tokura, Nature Nanotechnology 8, 899-911 (2013)
[3] Y. Gaididei, V. P. Kravchuk, D. D. Sheka, Phys. Rev. Lett. 112, 257203 (2014)
[4] O. V. Pylypovskyi, V. P. Kravchuk, D. D. Sheka, D. Makarov, O. G. Schmidt, Y. Gaididei, Phys. Rev. Lett. 114, 197204 (2015)
Keywords: Dzyaloshinskii-Moriya interaction, curved geometry, helical wire, magnetochirality, mesoscale
  • Poster
    633. Wilhelm und Else Heraeus-Seminar, Spin Orbit Dynamics, 04.-06.01.2017, Physikzentrum Bad Honnef, Germany

Registration No. 26757 - Permalink


Simplified expression and production of small metal binding peptides for biosorptive materials
Braun, R.ORC; Schönberger, N.; Jain, R.ORC; Matys, S.ORC; Lederer, F.; Pollmann, K.
Phage display for discovery of specific binding peptides is nowadays widely used in the pharmaceutical industry and in many biotechnological applications. Using state-of-the-art cloning techniques we developed an easy-to-use cloning and expression system, allowing the fast production of identified peptides while avoiding proteolysis.
Keywords: protein expression, metal binding, peptide, biosorption, phage display, molecular genetics, gibson assembly, metal interaction, biomaterials
  • Poster
    HZDR Doktorandenseminar 2017, 16.-18.10.2017, Seiffen, Deutschland

Registration No. 26755 - Permalink


Analysis of the defect clusters in the congruent lithium tantalate
Vyalikh, A.; Zschornak, M.; Köhler, T.; Nentwich, M.; Weigel, T.; Hanzig, J.; Zaripov, R.; Vavilova, E.; Gemming, S.; Brendler, E.; Meyer, D. C.
A wide range of technological applications of lithium tantalate LiTaO3 (LT) is closely related to the defect chemistry. Several cation substitution defect models have been considered in literature since decades. Here we report a combinational approach based on DFT calculations of electric field gradients (EFG) and solid-state NMR in order to reveal the defect structure in congruent lithium tantalate. Using this approach, we were able to identify the cation substitution structure attributed to the Empty site defect model in one of two congruent LT crystals studied in our work. This observation is supported by the calculation of the energy for defect formation as well as by evaluation of the defect models based on the structural refinements and chemical reasonability reported in literature. After thermal treatment, hydrogen out diffusion and homogenation of other defects in lithium tantalate have been observed by electron spin resonance (ESR), NMR and FTIR spectroscopies. Identification of the defect structure in the second LT sample seems to be more challenging, as the extrinsic defects for balancing other impurities and/or an inhomogeneous defect distribution have to be taken into account. We have found that, although grown by the same method; the two congruent LT samples provided by two manufacturers show rather different defect structures, which is manifested not only in the distribution of EFGs at 7Li, but also in the FTIR and ESR spectra and in the 7Li spin-lattice relaxation behaviour. This observation has to be taken into account when attempting to favour one specific defect model within the scientific community and when studying the physical – particularly, magneto-optical – phenomena in the systems where lithium tantalate is used as a substrate.
Keywords: Lithium tantalate, defect models, cation substitution, DFT, solid-state 7Li NMR, spin-lattice relaxation, ESR , ferroic

Registration No. 26747 - Permalink


A comparative biocompatibility study of graded TiC/a-C coatings prepared by dcMS and chopped-HiPIMS
Meško, M.; Gotzmann, G.; Bohovičová, J.; Zacková, P.; Čaplovič, Ľ.; Munnik, F.; Čaplovičová, M.; Vančo, Ľ.; Skákalová, V.; Krause, M.
Differences in the structural and biocompatibility properties of graded TiC/a-C coatings prepared by direct current magnetron sputtering (dcMS) and chopped -high power impulse magnetron sputtering (c-HiPIMS) were studied. The higher ID/IG ratio in c-HiPIMS a-C films is due to the clustering of the sp2 phase as indicated by Raman spectroscopy. C-HiPIMS a-C films are more hydrophobic with contact angle difference of about 9 % in comparison to the dcMS films at average power of 250W. The metabolic activity of human fibroblast cells cultivated on the samples grown by c-HiPIMS is of about 20 % higher than that of the samples deposited by dcMS. The increased metabolic activity is due to a confluent cell layer on these surfaces. The investigation of the cell morphology revealed no negative influence on biocompatibility for both deposition methods.
  • Contribution to proceedings
    The Fourteenth International Symposium on Sputtering and Plasma Processes (ISSP 2017), 05.-07.07.2017, Kanazawa, Japan, ISSN 2187-7637, 256-259
  • Poster
    The Fourteenth International Symposium on Sputtering and Plasma Processes (ISSP 2017), 05.-07.07.2017, Kanazawa, Japan

Registration No. 26745 - Permalink


Chancen und Grenzen der Circular Economy: Wie recycelbar sind Mobiltelefone?
Reuter, M. A.; Weigl, A.
Um Ressourcen verantwortungsvoll und effizient zu nutzen, ist eine fortschrittliche Circular Economy (CE ─ Kreislaufwirtschaft), in der Recycling ein Kernelement ist, der vielversprechendste Ansatz. Auf der politischen Agenda Europas ist die CE ganz oben angekommen. Circular Economy und Recycling sollten, so fordert zum Beispiel der französische Premierminister, Emmanuel Macron, eine wichtige Säule bei der Rohstoffsicherung für die heimische Industrie bilden (1). Auch verhandeln derzeit die EU-Mitgliedstaaten über ein europäisches Kreislaufwirtschaftspaket (2).
Wieviel Recycling ist aber angesichts von immer komplexeren elektronischen Geräten und anderen Hochtechnologieanwendungen derzeit überhaupt möglich? Eine aktuelle Recyclingstudie zeigt am Beispiel eines Mobiltelefons die Chancen und Grenzen der Circular Economy auf.
Keywords: Circular Economy, Kreislaufwirtschaft, CE, Recycling, Recyclingstudie, Mobiltelefon, Rohstoffe, Recycelbarkeit, Metallurgie
  • ACAMONTA - Zeitschrift für Freunde und Förderer der TU Bergakademie Freiberg 24(2017), 65-68

Registration No. 26740 - Permalink


Central receiver coatings for high-temperature concentrated solar power studied by in situ RBS, Raman spectroscopy and spectroscopic ellipsometry
Lungwitz, F.; Heras, I.; Janke, D.; Wenisch, R.; Schumann, E.; Guillén Rodriguez, E.; Escobar Galindo, R.; Gemming, S.; Krause, M.
The development of solar-selective CSP receiver coatings with high-temperature and environmental stability requires new concepts of design and in operando monitoring. Solar receiver tubes are a key component of solar thermal power plants. The increase of their operation temperature from today’s maximum of 550°C to about 800°C could increase the CSP efficiency by approximately 15 to 20% and improve the competiveness of this technology compared to other ones of carbon-free electricity generation. Potential alternatives to fast degrading state-of-the-art pigment paint receiver tube coatings are based on refractive metal carbides, nitrides, and oxides because of their high thermal stability and oxidation resistance.
New types of solar-selective coatings were studied in situ at temperatures of up to 830°C by Rutherford backscattering spectrometry, Raman spectroscopy, and spectroscopic ellipsometry within a cluster tool. High-temperature stability in high-vacuum is demonstrated for carbon-metal- and oxynitride-absorber-based multilayers as well as for a solar-selective transmitter based on a transparent conductive oxide.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.
Keywords: Solar selective coatings, Oxynitrides, Thermosolar energy, Optical simulation, in situ analysis
  • Poster
    X Iberian Vacuum Conference, RIVA, 04.-06.10.2017, Bilbao, Espana

Registration No. 26738 - Permalink


An update on possibilities of metals recovery from Polish copperores by biotechnology. Project Ecometals
Szubert, A.; Guezennec, A.-G.; Bodénan, F.; Dirlich, S.; Pawłowska, A.; Grotowski, A.; Sadowski, Z.; Witecki, K.
The possibilities of metals recovery from copper ores with the biotechnological methods are widely known. The methods consist in bioleaching of copper ores, copper concentrates and byproducts of their production, as well as metals recovery from leaching solutions. Biohydrometallurgical methods were tested for years to be applied at KGHM Polska Miedź S.A., in order to improve efficiency of copper production. Several different research units worked on the topic, and the most significant and wide range initiatives in this area are mentioned in this article. One of the initiatives is an ongoing German and French Ecometals project. KGHM Polska Miedź S.A. and KGHM Cuprum Ltd. Research and Development Centre are this project Partners. In the frame of the project different metals bearing materials (ores, concentrates and tailings) are tested. Among them three lithological types of the copper ore from Rudna mine and the copper concentrate from Lubin concentrator are used for studies. The article gives a general overview of these activities, with the main focus on results of bioleaching studies of selected materials, conducted by KGHM Cuprum. In these studies sandstone and shale, as well as so called “shale concentrate” (containing 39% of the shale) were used for experiments, and possibilities of their bioleaching were evaluated.
Keywords: Biohydrometallurgie; biohydrometallurgy; Biolaugung; bioleaching, Kupfer; copper
  • Open Access LogoContribution to proceedings
    Mineral Engineering Conference MEC2017, 20.-23.09.2017, Wisła, Polska
    E3S Web of Conferences 18 , 01015
    DOI: 10.1051/e3sconf/201712301015

Registration No. 26736 - Permalink


Bewertung - zwischen Vollständigkeit und Praxisnähe
Dirlich, S.
Der Buchbeitrag beschäftigt sich mit der Bewertung von Handlungsoptionen in verschiedenen Themenfelder der Siedlungsentwicklung, die in einem Projekt im BMBF-Förderprogramm "Nachhaltiges Landmanagement" entwickelt wurde. Eine Bewertung der vorgeschlagenen Handlungsoptionen ist erforderlich, um deren Wirkungen aus Sicht der Ressourceneffizienz und Emissionsarmut einzuschätzen und miteinander zu vergleichen. Aufgrund der Bandbreite der Themenfelder von der Abfallwirtschaft bis hin zur Siedlungsentwicklung und der transdisziplinären Herangehensweise ist ein projektspezifischer angepasster Ansatz nötig, der sowohl den Erfordenissen der Wissenschaft nach Vollständigkeit und Vergleichbarkeit gerecht wird, als auch den Anforderungen der beteiligten Akteure entspricht.
Keywords: nachhaltiges Landmanagement; sustainable land management; Bewertung; assessment; Siedlungsentwicklung; settlement development;
  • Open Access LogoBook chapter
    Schiller, Georg: Wege zur Umsetzung von Ressourceneffizienzstrategien in der Siedlungs- und Infrastrukturplanung IÖR Schriften Band 74, Berlin: RHOMBOS-Verlag, 2017, 978-3-944101-74-3

Registration No. 26735 - Permalink


Relativistic Effects in Laser Plasmas -Plasma Birefringence and Generation of Mega-Tesla Magnetic Field-
Arefiev, A.; Stark, D. J.; Toncian, T.; Murakami, M.
と呼ばれる物理現象は,高強度レーザーとプラズマとの相互作用に対する近年の当該領 域の研究の中でもパラダイムシフトとも言うべき極めて興味深いものである.超高強度レーザーの照射によりプ ラズマ中の電子温度が急速に相対論領域(!500 keV)にまで上昇すると,たとえ非相対論領域においてレーザー が完全反射されるほどの高密度のプラズマでも,レーザー光はプラズマの奥深く浸透することが可能となり,こ の特性は「相対論的透明性」と呼ばれる.本章では,相対論的透明性が顕著に見られる2つの集団現象にスポッ トを当てることにより,レーザーと物質との相互作用において同特性が演じる重要な役割を俯瞰する.第一の現 象は,相対論領域におけるプラズマ中で見られる複屈折である.この相対論的複屈折では超高強度レーザー照射 によってプラズマが非等方性を持ち,結果としてその光学特性がレーザーの偏光に強く依存する.第二の現象は, 高密度プラズマと超高強度レーザーとの(極小幅を持つ境界面ではなく奥行きを持った有限空間に分布する)体 積的相互作用により誘起される超高強度の準静磁場の生成である.このような相対論的高エネルギー密度領域で は MeV オーダーの
Keywords: relativistic transparency, laser-matter interaction, megatesta magnetic field, plasma birefringence
  • Open Access LogoJournal of Plasma and Fusion Research 93(2017)11, 535-544

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Registration No. 26734 - Permalink


Integration of mineralogical and hyperspectral data for drill-core characterization
Tusa, L.; Andreani, L.; Contreras, C. I.; Ivascanu, P.; Gloaguen, R.; Gutzmer, J.
Mineral exploration and resource definition require extensive drilling campaigns that are generally done with tight deadlines and often rely only on visual qualitative evaluation of the rock characteristics (core logging) and limited chemical analyses. The aim of these campaigns is to understand the genesis and zonality of mineral deposits. The ore, in many cases, is closely related to the distribution of hydrothermal alterations and their associated structures. Therefore, the host characteristics are analysed in order to build a distribution model of the mineralization. However, traditional techniques such as core logging can present limitations in the identification of often subtle and therefore similar mineral assemblages and the acquired data are only qualitative. Additionally, the identification and quantification of other textural and structural features, such as veins, is slow, laborious and frequently limited by the subjectivity of the observer.
Our aim is to develop new methods which respond to the need for rapid, automated and precise extraction of mineralogical, textural and structural information from cores. We propose to process hyperspectral VNIR/SWIR data from core scanners, using innovative image segmentation and classification techniques in order to quickly extract precise numerical parameters of both mineralogical and structural information. We use scanning electron microscopy (SEM)-based analyses on selected samples to train the classifier and validate the results. SEM shows great potential in the identification of the main alteration assemblages as well as of the main hydrothermal events they are associated with. Even though it requires extensive sample preparation and the measurements are time consuming, by analysing representative samples for different alteration types, SEM-based analyses provide control information for the interpretation and classification of hyperspectral data. Hyperspectral data allow the identification of the main alteration phases and the distribution of specific mineral assemblages as each vein type displays a specific signature in the VNIR-SWIR region of the electromagnetic spectrum. Image segmentation techniques allow us to extract veins and additional parameters such as orientations and densities. The interest of this approach is that it (1) allows the combined analysis of compositional and structural features, (2) provides a very rapid and validated mapping of the cores that is based on (3) the upscaling of SEM data.
The proposed methodology has been tested on selected core samples from the Bolcana copper-gold porphyry system (Romania). This site is located in the Golden Quadrilateral (Apuseni Mountains) where extensive drilling has been performed by Eldorado Gold using state of art methodology that includes thorough chemical analyses, detailed logging and spectral characterization of assay pulps. The mineralization in Bolcana is hosted in Neogene subvolcanic dioritic intrusions and associated magmatic-hydrothermal breccias that intruded in a shallow volcanic environment. The system is characterized by complex transitions on lithological and alteration assemblages. The porphyry mineralization is also overprinted by later epithermal events that lead to different alteration patterns than those usually encountered in porphyry systems.
The analyses of the cores collected from the Bolcana site have shown a preferential association of specific alteration assemblages with different vein generations such as white mica dominant assemblages for late stage pyrite veins, a chlorite-epidote dominant assemblage on early chalcopyrite veins and low intensity white mica dominant assemblage associated with early quartz veins. At core scale a preferential orientation of these veins was additionally observed.
The integration of this new approach with traditional logging methods performed by site geologists as well as with structural data (Reflex IQ-logger) provided by Eldorado Gold gives us an insight on the spatial and directional distribution of the main vein types and their characteristic alteration assemblages in the Bolcana site. The integration of such new methodologies in the exploration campaign allows for better and faster exploration targeting based on key mineral assemblages and structural features, as well as a more comprehensive preliminary ore evaluation and resource modelling. This would be achieved by the implementation of on-site drill-core scanning.
  • Poster
    Applied Geological Remote Sensing, 12.-15.12.2017, Lisbon, Portugal

Registration No. 26731 - Permalink


Distribution of lead- and zinc-bearing minerals in the gossan of the Gamsberg Zn deposit, South Africa
Tusa, L.; Moeckel, R.; Gutzmer, J.
The giant Gamsberg massive sulphide deposit is currently being developed by Vedanta Resources. During mine development, the massive gossan zone is stripped in order to expose the sulphide orebody. During a field visit In September 2016, a suite of samples was collected from the gossan in the developing open pit. Three lithologically distinct zones were recognized. The topmost zone is a goethitic hard cap that is also well exposed at the present-day land surface (Rozendaal, 1986). The goethitic hard cap grades down into an iron oxide-poor zone that comprises of very friable siliceous material. The latter is cross-cut by fractures filled by hematite. The third zone of the gossan is marked by an abundance of fine-grained earthy hematite intergrown with semi-friable silica. Vugs are commonly lined by chalcedony. A detailed study revealed the presence of a complex suite of secondary lead and zinc minerals. Zinc is most abundant in the goethite cap – apparently related to the occurrence iron-rich smectite group minerals. Minor amounts of Pb-rich minerals, such as anglesite and members of the corkite-beaudantite were also identified. Most abundant, however, is lead below the goethitic cap where anglesite and members of the mimetite- pyromorphite and corkite-beaudantite series are very common. The lowermost gossan zone consists of mainly fine grained silica and hematite. Lead- and zinc-bearing minerals are conspicuously absent. The results obtained are consistent with observations by Rozendaal (1986) – and the apparent enrichment of lead-bearing secondary minerals in the gossan - relative to scarce nature of galena in the sulphide orebody. This apparent enrichment is attributed to the greater mobility of zinc – relative to lead - in the supergene environment.
  • Poster
    Geology of Ore Deposits, 08.-11.03.2017, Hannover, Germany

Registration No. 26730 - Permalink


3D Si-SiO2 nano-networks formed by diode laser-induced liquid- and solid-state decomposition of SiOx
Schumann, E.; Hübner, R.; Carcelen, V.; Grenzer, J.; Heinig, K.-H.; Gemming, S.; Krause, M.
Thin films of nano-structured crystalline silicon (nc-Si) are potential absorber and supporting layers for next-generation Si solar cells. As one candidate, Si-SiO2 nanocomposites with percolated nc-Si have been fabricated by rapid thermal annealing (RTA) of sputter-deposited SiOx films (x≈1). A percolated silicon network has been formed by solid state phase separation into nc-Si and SiO2 [1, 2].
In the present study, SiO0.6 layers of ~500nm thickness are grown on quartz by ion beam sputter (IBS) as well as by reactive magnetron sputter (RMS) deposition. Formation of percolated Si-SiO2 nanocomposites is achieved by two different modes of thermal treatment: (i) Furnace annealing at 950°C and (ii) scanning laser processing. In case (ii), a diode laser with dwell times in the ms range, power densities of ~30 kW/cm², a wavelength of λ= 808nm and a line focus of 100µm x 11mm is applied. This process is ~106 times faster than isothermal treatment and ~103 times faster than RTA. Another advantage of this method is the usability of temperature sensitive substrates and maintaining homogeneous processing.
Rutherford backscattering spectra of as-deposited and processed SiO0.6 reveals a compositional change in thin surface and interface layers, but no significant change in the bulk composition. Raman spectroscopy and X-ray diffraction show that the crystallinity of the nc-Si is higher for the laser-treated sample.
High resolution- and energy-filtered transmission electron microscopy (HTEM, EFTEM) show additionally, that in both cases the as-deposited SiO0.6 is transformed into a percolated nanocomposite consisting of amorphous SiO2 and nc-Si.
In more detail, laser processing of IBS-deposited layers leads to isotropic morphologies self-similar to furnace-annealed samples, but scaled up by a factor of ~5. This is explained by a phase separation in the liquid state and the solid state, respectively, which cause diffusion coefficients differing by several orders of magnitude.
During the deposition by RMS, phase separated filament-like morphologies form. Here, furnace annealing leads to enhanced phase separation accompanied by crystallization. In contrast laser processing erases the as-deposited filaments and produces isotropic morphologies similar to IBS-deposited and laser-processed samples

[1] Friedrich, D. et al. Sponge-like Si-SiO2 nanocomposite - Morphology studies of spinodally decomposed silicon-rich oxide. Appl. Phys. Lett. 103, 131911 (2013).
[2] Ilday, S. et al. Multiscale Self-Assembly of Silicon Quantum Dots into an Anisotropic Three-Dimensional Random Network. Nano Lett. 16, 1942–1948 (2016).
  • Lecture (Conference)
    2017 MRS Spring Meeting & Exhibit, 17.-21.04.2017, Phoenix, USA

Registration No. 26728 - Permalink


Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-y(OxN1-x). Part 1: Advanced microstructural characterisation and optical simulation
Heras, I.; Guillén, E.; Lungwitz, F.; Rincón-Llorente, G.; Munnik, F.; Schumann, E.; Azkona, I.; Krause, M.; Escobar-Galindo, R.
Aluminium titanium oxynitrides were studied as candidate materials for high temperature absorbers in solar selective coatings due to their excellent stability and their tuneable optical behaviour. A set of individual AlyTi1-y(OxN1-x) layers with different oxygen content was prepared by cathodic vacuum arc (CVA) deposition. The composition, morphology, phase structure and microstructure of the films were characterized by elastic recoil detection (ERD), scanning and transmission electron microscopy and X-ray diffraction. An fcc phase structure is found in a broad compositional range of AlyTi1-y(OxN1-x). Simultaneously, sample microstructure and morphology undergo systematic changes from a columnar growth to the development of a heterogeneous structure with spherical nanoparticle inclusions when the oxygen concentration is increased. The optical properties were determined by spectroscopic ellipsometry and UV–Vis–NIR and FTIR spectrophotometry. A comprehensive analysis of the film properties allowed an accurate modelling of the optical constants of the AlyTi1-y(OxN1-x) in the whole wavelength range of solar interest (from 190 nm to 25 µm). It points to a transition from metallic to dielectric behaviour with increasing oxygen content. Consequently, it is demonstrated that the optical properties of these AlyTi1-y(OxN1-x) deposited films can be controlled in a wide range from metallic to dielectric character by adjusting the oxygen concentration, opening a huge range of possibilities for the design of solar selective coatings (SSC) based on this material. Complete SSC, including a TiN layer as IR reflector, were designed by applying optical simulations, obtaining excellent optical selective properties of α=94.0% and εRT = 4.8%.
Keywords: Solar selective coatings, Oxynitrides, Thermosolar energy, Optical simulation

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  • Secondary publication expected from 22.12.2018

Registration No. 26727 - Permalink


Phase Transitions in C:Ni Nanocomposite Templates during Diameter-Selective CVD Synthesis of SWCNTs
Krause, M.; Melkhanova, S.; Hübner, R.; Haluska, M.; Gemming, S.
Phase transitions in carbon: nickel nanocomposite templates during diameter-selective CVD synthesis of SWCNTs were studied. While almost conserving their pre-defined diameter distribution, as-deposited Ni3C nanoparticles transform into fcc-NiO during activation in low-pressure air atmosphere, and are reduced to a mixture of fcc-Ni and Ni3C under nanotube growth conditions. The first phase transition leads to a substitutional replacement of the protective carbon matrix by a protective oxide layer. The second one reflects competing reduction processes of NiO. A mechanism for the complementary roles of carbon matrix and Ni species in the three-step CVD synthesis is proposed that includes nanoparticle immobilization, carbon delivery and catalysis of nanotube growth.
Keywords: nanocomposites, single-walled carbon nanotubes, catalysis, transmission electron microscopy, Raman spectroscopy

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  • Secondary publication expected from 16.11.2018

Registration No. 26726 - Permalink


On the synchronizability of Tayler–Spruit and Babcock–Leighton type dynamos
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.
The solar cycle appears to be remarkably synchronized with the gravitational torques exerted by the tidally dominant planets Venus, Earth and Jupiter. Recently, a possible synchronization mechanism was proposed that relies on the intrinsic helicity oscillation of the current-driven Tayler instability which can be stoked by tidal-like perturbations with a period of 11.07 years. Inserted into a simple alpha-Omega dynamo model these resonantly excited helicity oscillations led to a 22.14 years dynamo cycle. Here, we assess various alternative mechanisms of synchronization. Specifically we study a simple time-delay model of Babcock–Leighton type dynamos and ask whether periodic changes of either the minimal amplitude for rising toroidal flux tubes or the Omega effect could eventually lead to synchronization. In contrast to the easy and robust synchronizability of Tayler–Spruit dynamo models, our answer for those Babcock–Leighton type models is less propitious.

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  • Secondary publication expected from 10.01.2019

Registration No. 26725 - Permalink


Metallurgie und Recycling im HIF - Gegenwart und Zukunft
Kelly, N.; Scharf, C.
  • Lecture (others)
    Topictreffen „Ressourcentechnologie“, 03.-04.07.2017, Freiberg, Deutschland

Registration No. 26724 - Permalink


FWGM - Division METALLURGY & RECYCLING - Helmholtz Institute Freiberg for Resource Technology
Kelly, N.; Scharf, C.
  • Lecture (others)
    Meeting VITO - FWGM, 26.-27.01.2017, Freiberg, Deutschland

Registration No. 26723 - Permalink


FWGM - Division METALLURGY & RECYCLING - Helmholtz Institute Freiberg for Resource Technology
Kelly, N.; Scharf, C.
  • Lecture (others)
    Meeting IWKS - FWGM, 13.02.2017, Freiberg, Deutschland

Registration No. 26722 - Permalink


Current Projects and Objectives at Helmholtz Institute Freiberg – Department of Metallurgy and Recycling
Kelly, N.; Scharf, C.
Current Projects and Objectives at Helmholtz Institute Freiberg – Department of Metallurgy and Recycling
  • Poster
    International Workshop ECMAG - Magnetic Field Effects on Aqueous Solutions, 20.-21.04.2017, Dresden-Rossendorf, Deutschland

Registration No. 26721 - Permalink


Screening the potential of Halophilic bacteria for Pyrite bio depression
Luque Consuegra, G.; Kutschke, S.; Rudolph, M.; Pollmann, K.
The separation of minerals has been a pressing issue in the last decades. One of the most common techniques to separate useful minerals from gangue minerals is Froth Flotation. Flotation is a relatively cheap and efficient process but the use of harmful chemicals and continuous decrease in ore quality due to the scarcity of high grade ores has motivated researchers to find alternative solutions to the standard flotation reagent scheme in order to make the process more efficient and environmentally friendly. Bioflotation has the potential of making the beneficiation of minerals more efficient and environmentally friendlier. Different bacteria and bacterial products have demonstrated to have prospective applications in bio flotation of different minerals (Behera and Mulaba-Bafubiandi, 2016). Halophilic bacteria are adapted to high salinity environments and other extreme conditions. Halophilic bacteria produce Extracellular Polymeric Substances (EPS) that aid them in the formation of biofilms and resist abrupt changes in salinity, pH, temperature and pressure. These EPS could have potential applications in flotation operations performed in sea water, such as the Copper-Molybdenum flotation operations in Chile. To date, there are no reports of halophilic bacteria been used in bio flotation experiments.
Halomonas boliviensis, Marinobacter spp, Halobacillus sp, Marinococcus sp and Halomonas eurihalina were studied to examine their potential as pyrite bio depressants, a gangue mineral common in Cu-Mo flotation. Micro flotation experiments using Hallimond tubes as well as flocculation, adsorption and Zeta potential experiments were performed in order to report the potential of these bacteria in the flotation process. In this study we will show the first results of using halophilic bacteria as Pyrite bio depressants, as well as an initial characterisation of the Extracellular Polymeric Substances excreted by these bacteria that could have an influence on the adsorption and mechanism by which these bacteria alter the surface of Pyrite.
Keywords: Biodepression, Halophilic bacteria, Pyrite
  • Poster
    Tagung 2017 Aufbereitung und Recycling, 08.-09.11.2017, Freiberg, Deutschland

Registration No. 26720 - Permalink


Optimization of an SRF Gun for High Bunch Charge Applications at ELBE
Lu, P.
As a cutting-edge type of photoinjectors, SRF gun is expected to provide a CW electron beam with high bunch charge and low emittance, which is highly demanded by the development of future FELs, ERLs and 4th/5th generation light sources. However, existing researches have not explored the full potential of SRF gun predicted by theory.
Keywords: photo injector, superconducting RF, SRF gun, ELBE facility, electron beam transport, simulation
  • Doctoral thesis
    TU Dresden, 2017
    Mentor: Dr. Jochen Teichert
    134 Seiten

Registration No. 26717 - Permalink


Operation of the SRF Gun with Mg Photocathodes for Production of Neutrons and THz Radiation at ELBE
Teichert, J.
Status Report on Superconducting Rf Photoinjector application at ELBE
Keywords: SRF gun, photo injector, ELBE
  • Lecture (Conference)
    PITZ Collaboration Meeting, 05.-06.12.2017, Zeuthen, Germany

Registration No. 26716 - Permalink


The Superconducting RF Photoinjector and its Present and Future Use at the ELBE Accelerator
Teichert, J.
The Superconducting RF Photoinjector and its Present and Future Use at the ELBE Accelerator
Keywords: SRF Gun, ELBE facility, superconducting RF, photocathodes, Nb resonator
  • Lecture (others)
    Seminar talk, 06.-10.11.2017, Chengdu, P.R. China

Registration No. 26715 - Permalink


Operational Aspects of Photocathodes for SRF Guns
Teichert, J.; Xiang, R.
The talk reports on operational aspects and experiences of photocathodes for the superconducting Rf photo injector at the ELBE accelerator
Keywords: photocathode, SRF gun, photo injector, cathode handling
  • Invited lecture (Conferences)
    EWPAA workshop, 20.-22.09.2017, Berlin, Germany

Registration No. 26714 - Permalink


Using the Mineral Liberation Analyzer for mineralogical studies of a carbonaceous apatite ore
Hoang, D. H.ORC; Leißner, T.ORC; Haser, S.; Rudolph, M.ORC; Peuker, U. A.ORC
Liberation analysis on grinding products is a very important subject for application in respect of both mineralogical characteristics and beneficiation process relevant parameters. The Mineral Liberation Analyzer (MLA) combines a large specimen chamber automated Scanning Electron Microscope (SEM), multiple Energy Dispersive X-ray detectors (EDX) with automated quantitative mineralogy software. SEM-based automated mineralogy tools are essential in measuring parameters, such as modal mineralogy, mineral locking, mineral association, theoretical grade - recovery and mineral liberation.
Such quantitative information is fundamental to investigate and evaluate the mineral processing of ores. In this study carbonaceous apatite ore samples from Lao Cai deposit (Vietnam) was used. The petrographic, mineralogical and mineral liberation observations showed that the ore sample is quite
complex, containing carbonate impurities (dolomite and calcite) and having very fine intergrown texture. The separation of carbonate from apatite has been recognized as one of the most difficult subjects in mineral processing due to the similarities in their physiochemical properties.
Keywords: Mineral Liberation Analyzer; automated mineralogy; carbonaceous apatite; flotation.
  • Contribution to proceedings
    International Conferences on Earth Sciences and Sustainable Geo-Resources Development, 12.-15.11.2016, Hanoi, Vietnam
    Proceedings of the ESASGD 2016, Hanoi, Vietnam: Transport Publishing House, 978-604-76-1171-3, 42-51

Registration No. 26713 - Permalink


Diagnostics of ELBE SRF Gun - Status and Future Design
Lu, P. N.; Arnold, A.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.
Report on the Diagnostics for Beam Characterization of the ELBE SRF-Gun
Keywords: SRF gun, photo injector, transverse emittance, beam charactetization
  • Poster
    IBIC 2017 - International Beam Instrumentation Conference, 20.-24.08.2017, Grand Rapids, USA

Registration No. 26712 - Permalink


Optimization of ELBE SRF Gun II for high-bunch-charge applications
Lu, P.; Arnold, A.; Vennekate, H.; Murcek, P.; Teichert, J.; Xiang, R.
Report on the beam transport simulation of the ELBE accelerator for injection with the SRF gun for THz, neutron and CBS applications.
Keywords: SRF gun, electron source, superconducting acceleerator
  • Poster
    The 3rd annual meeting of Matter and Technologies, 31.01.-02.02.2017, Darmstadt, Germany

Registration No. 26711 - Permalink


Metal and Semiconductor Photocathodes in the HZDR SRF Gun
Teichert, J.; Arnold, A.; Lu, P.; Murcek, P.; Vennekate, H.; Xiang, R.
The superconducting RF photoelectron gun at the ELBE accelerator facility is a high-repetition rate electron injector for CW operation and can provide high average current and high brightness electron beams. During commissioning and operating time different types of photocathodes, metallic (Cu, Mg) and semiconductors (Cs2Te), have been used. We present the preparation processes, properties as well as performance and operational experience of the cathodes in the SRF gun. Furthermore, specific issues like cathode cooling, multipacting, and dark current will be discussed.
Keywords: SRF gun, electron source, photocathode, Mg, Cu, Cs2Te
  • Invited lecture (Conferences)
    ERL 17 - The 59th ICFA Advanced Beam Dynamics Workshop on Energy recovery Linacs, 18.-23.06.2017, Geneva, Switzerland

Registration No. 26710 - Permalink


RF Performance and Beam Parameter Measurement of the 2nd 3.5 cell SRF Gun for ELBE
Arnold, A.; Freitag, M.; Lu, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.; Ciovati, G.; Turlington, L.
In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In our contribution we will report on the commissioning of the SRF gun by presenting a full set of RF performance results as well as detailed beam parameter measurements up to a bunch charge of 300 pC. Additionally, we will present the results of the first two user experiments (neutron and THz generation) that demonstrated the reliability of this gun concept.
Keywords: SRF gun, electron source, superconducting accelerator, ELBE, beam parameter
  • Poster
    ERL 17 The 59th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 18.-23.06.2017, Geneva, Switzerland

Registration No. 26709 - Permalink


Application status of SRF gun II as the injector for the ELBE radiation center
Xiang, R.; Arnold, A.; Lehnert, U.; Lu, P.; Michel, P.; Murcek, P.; Teichert, J.; Vennekate, H.
An improved SRF gun (ELBE SRF Gun II) has been installed at the ELBE radiation center as an additional electron source since 2014. This new gun is able to produce up to 300 pC bunch charges in CW mode. This poster summarizes the latest results of user application with SRF Gun II
Keywords: SRF Gun, photo injector, ELBE, CW mode
  • Poster
    IPAC 2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark

Registration No. 26708 - Permalink


Beam Transport Optimization for Applying an SRF Gun at the ELBE Center
Lu, P. N.; Arnold, A.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.
An SRF gun at the ELBE center has been operated with a magnesium cathode. Electron beams were produced with a maximum bunch charge of 200 pC and an emittance of 7.7 μm. Simulations have been conducted with ASTRA and Elegant for applying the SRF gun to ELBE user experiments, including neutron beam generation, positron beam generation, THz radiation and Compton backscattering experiment. Beam transport has been optimized to solve the best beam performance for these user stations at the bunch charge of 200 pC. Simulation results indicate that the SRF gun is potential to benefit the high bunch charge applications at ELBE.
Keywords: SRF gun, photo injector, electron source, ELBE, simulation, electron accelerator
  • Poster
    IPAC 2017- 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark
  • Open Access LogoContribution to proceedings
    IPAC 2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark
    Proceedings of the 8th International Particle Accelerator Conference, G: JACoW

Registration No. 26707 - Permalink


In situ RBS and Raman spectroscopy study of nickel-catalyzed amorphous carbon graphitization
Janke, D.; Hulman, M.; Wenisch, R.; Munnik, F.; Gemming, S.; Rafaja, D.; Krause, M.
Session: Thin films type of contribution: Poster
Metal-induced crystallization with and without layer exchange (MIC w/o LE) is a method to decrease the crystallization temperature of amorphous group 14 elements (G14E) by up to several hundred degrees. In situ experiments are expected to provide new insights into thin film evolution and elementary process steps of MIC w/o LE and to improve existing models of this type of phase transformation. While MIC w/o LE has been widely studied for Si and Ge in contact with catalytic metals, there exist only a few studies for the crystallization of amorphous carbon. Therefore, in this contribution in situ Rutherford backscattering spectrometry (RBS), Raman spectroscopy and spectroscopic ellipsometry studies were performed during annealing of amorphous carbon/nickel (a-C/Ni) layer stacks at temperatures up to 750°C.
Due to its small lattice mismatch with the basal plane of graphite and high diffusivity of C atoms, Ni is a suitable catalyst for the growth of graphene and crystalline graphitic nanostructures. During the annealing of an a-C/Ni layer stack covalent bonds between the carbon atoms at the catalyst interface are weakened. Liberated carbon atoms can move along the interface and diffuse along the grain boundaries into the Ni layer towards the catalyst surface, where nucleation and grain growth of graphitic crystallites occur. Our in situ studies showed a change in the stacking sequence between C and Ni layers under defined experimental conditions. According to in situ Raman measurements, this mechanism occurs independent of the stacking sequence, while the velocity of the LE differs significantly. As observed in time and temperature resolved Raman spectra, the position of the G peak and the I(D)/I(G) ratio changed according to the Three-Stage-Model by Ferrari and Robertson, confirming the transformation of amorphous carbon to nc-graphite. With the in situ RBS measurements more insight into LE was given. Here peak positions of C and Ni were shifted, indicating a change of the energy of the scattered ions for both layers respectively and proving the combination of the observed graphitization process with LE during annealing. The thickness of the synthesized crystalline graphitic layer is controlled by the finite carbon source – the deposited a-C film, which is a decisive advantage of this process compared to CVD. It is demonstrated that the structure and the crystallite size of the metallic catalyst layer has a strong influence on the crystallite size and the quality of the graphitic film.
LE is potentially interesting for industrial applications, as it allows the formation of polycrystalline thin films of G14E at much lower temperatures - than during thermal annealing without the metallic catalyst. Depending on the initial stacking sequence, the crystalline graphitic film can be deposited on a suitable device-ready substrate or transferred to another substrate after the dissolution of the transition metal catalyst.
  • Poster
    Iberian Vacuum Conference, RIVA-X, 04.-05.10.2017, Bilbao, Spanien

Registration No. 26702 - Permalink


Development in the application of contactless inductive flow tomography
Ratajczak, M.ORC; Wondrak, T.ORC; Timmel, K.; Stefani, F.; Eckert, S.
The contactless inductive flow tomography (CIFT) allows for reconstructing the mean flow structure of liquid metals by measuring the flow induced perturbations of one or more applied magnetic fields. These measurements are utilized to infer the flow field by solving a linear inverse problem using an appropriate regularization technique. We will give an overview of the application of CIFT to three models of continuous casting available at the Helmholtz-Zentrum Dresden – Rossendorf. These include a 1:8 and a 1:2 model of a slab casting mould as well as a 1:3 model of a cylindrical mould.
Keywords: Slab casting, round billet casting, flow measurement, contactless inductive flow tomography, electromagnetic brake
  • Lecture (Conference)
    9th ECCC European Continuous Casting Conference – ECCC 2017, 29.06.2017, Wien, Österreich
  • Contribution to proceedings
    9th ECCC European Continuous Casting Conference – ECCC 2017, 29.06.2017, Wien, Österreich

Registration No. 26701 - Permalink


Computation of the forward problem of the contactless inductive flow tomography
Jacobs, R. T.; Wondrak, T.; Stefani, F.
The Contactless Inductive Flow Tomography is a procedure that enables the reconstruction of the global three-dimensional flow structure of an electrically conducting fluid by measuring the flow induced magnetic flux density outside the melt and by subsequently solving the associated linear inverse problem. The accurate computation of the forward problem which is essential for the inversion represents the focal point of this investigation. The tomography procedure is described by a system of coupled integral equations where the integrals contain a singularity when a source point coincides with a field point. The contribution of a singular point to the value of the surface and volume integrals in the system is considered in detail. A significant improvement of the accuracy is achieved by applying higher order elements and by attributing special attention to the singularities inherent in the integral equations. The treatment of the singularities described in this investigation is similar to the procedure applied in the boundary element method. It represents a novelty in the Contactless Inductive Flow Tomography.
Keywords: contactless inductive flow tomography, magnetohydrodynamics, integral equations, inverse problems
  • Lecture (Conference)
    International Symposium on Theoretical Electrical Engineering (ISTET), 16.-19.07.2017, Ilmenau, Deutschland

Registration No. 26700 - Permalink


Numerical and experimental study of the effect of the induced electric potential in Lorentz force velocimetry
Hernández, D.; Böck, T.; Karcher, C.; Wondrak, T.
Lorentz force velocimetry (LFV) is a contactless velocity measurement technique for electrically conducting fluids. When a liquid metal or a molten glass flows through an externally applied magnetic field, eddy currents and a flow-braking force are generated inside the liquid. This force is proportional to the velocity or flow rate of the fluid and, due to Newton's third law, a force of the same magnitude but in opposite direction acts on the source of the applied magnetic field which in our case are permanent magnets. According to Ohm's law for moving conductors at low magnetic Reynolds numbers, an electric potential is induced which ensures charge conservation. In this paper, we analyze the contribution of the induced electric potential to the total Lorentz force by considering two different scenarios: conducting walls of finite thickness and aspect ratio variation of the cross-section of the flow. In both the cases, the force component generated by the electric potential is always in the opposite direction to the total Lorentz force. This force component is sensitive to the electric boundary conditions of the flow of which insulating and perfectly conducting walls are the two limiting cases. In the latter case, the overall electric resistance of the system is minimized, resulting in a considerable increase in the measured Lorentz force. Additionally, this force originating from the electric potential also decays when the aspect ratio of the cross-section of the flow is changed. Hence, the sensitivity of the measurement technique is enhanced by either increasing wall conductivity or optimizing the aspect ratio of the cross-section of the flow.
Keywords: flow measurement, conducting walls, liquid metals, Lorentz force, magnetohydrodynamics

Registration No. 26695 - Permalink


UHV Photocathode Plug Transfer Chain for the BERLinPro SRF-Photoinjector
Kühn, J.; Borninkhof, J.; Bürger, M.; Frahm, A.; Jankowiak, A.; Kamps, T.; Schmeißer, M. A. H.; Schuster, M.; Murcek, P.; Teichert, J.; Xiang, R.
A dedicated particle free UHV photocathode plug transfer chain from the preparation system to the SRF-Photoinjector was set up and commissioned at HZB for the bERLinPro project. The plug handling system was designed in collaboration with the ELBE team at HZDR, where the same transfer chain is in commissioning phase. In the future the exchange of photocathodes between the laboratories offers the possibility to test different types of photocathodes in different SRF-photoinjectors.
Keywords: photocathode SRF-photoinjector, electron source, plug transfer
  • Poster
    IPAC 2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark
  • Open Access LogoContribution to proceedings
    IPAC 2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark
    Proceedings of the 8th International Particle Accelerator Conference, Genf: JACoW

Registration No. 26694 - Permalink


Improvement of the Photoemission Efficiency of Magnesium Photocathodes
Xiang, R.; Arnold, A.; Lu, P. N.; Michel, P.; Murcek, P.; Teichert, J.; Vennekate, H.; Patra, P.
To improve the quality of photocathodes is one of the critical issues in enhancing the stability and reliability of photo-injector systems. Presently the primary choice is to use metallic photocathodes for the ELBE SRF Gun II to reduce the risk of contamination of the superconducting cavity. Magnesium has a low work function (3.6 eV) and shows high quantum efficiency (QE) up to 0.3 % after laser cleaning. The SRF Gun II with an Mg photocathode has successfully provided electron beam for ELBE users. However, the present cleaning process with a high intensity laser (activation) is time consuming and generates unwanted surface roughness. This paper presents the investigation of alternative surface cleaning procedures, such as thermal treatment. The QE and topography of Mg samples after treatment are reported.
Keywords: photocathode, photo-injector, electron source, magnesium, quantum efficiency
  • Poster
    IPAC 2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark
  • Open Access LogoContribution to proceedings
    IPAC 2017 - 8th International Particle Accelerator Conference, 14.-19.05.2017, Copenhagen, Denmark
    Proceedings of the 8th International Particle Accelerator Conference, Genf: JACoW

Registration No. 26693 - Permalink


Synchrotron X-ray diffraction on ensemble and individual GaAs/InxGa1-xAs core/shell nanowires at beamline P08 – PETRA III (DESY)
Bussone, G.; Grifone, R.; Balaghi, L.; Dimakis, E.
Chemical composition, strain, structural polytypism and stacking faults in semiconductor nanostructures can be described quantitatively by high-resolution X-ray diffraction. It is a non-destructive technique that is suitable for the characterization of epitaxial nanostructures on their original substrates. The extracted information can be a valuable contribution to the understanding of the growth and strain relaxation mechanisms, which in turn are essential elements for tailoring the electronic properties in functional devices. Beamline P08 at PETRA III, Hamburg, offers a well-functioning high-resolution X-ray diffraction setup for the characterization of nanowire ensembles. Moreover, a newly developed configuration with a nano-focused beam is operational and can be used for the investigation of individual nanostructures.
The strengths of our setup have been tested in the characterization of GaAs/InxGa1-xAs core/shell nanowires. The nanowires were grown vertically on Si(111) substrates by molecular beam epitaxy (at HZDR). A set of samples with different shell thicknesses (5-80 nm) but the same In concentration (x≈0.20) and the same core diameter (25 nm) has been characterized. The measured in-plane and out-of-plane lattice constants as a function of the shell thickness suggest that the shell grew coherently around the core even for the thickest shell, the thickness of which is well beyond the critical value for planar In0.2Ga0.8As layers on GaAs. Furthermore, the tensile strain of the core due to the lattice mismatch with the shell increases with increasing the shell thickness up to 40nm, whereas the corresponding compressive strain of the shell decreases gradually to zero. All aforementioned results demonstrate the unique possibilities for strain engineering in core/shell nanowires.
Keywords: high-resolution X-ray diffraction, core/shell nanowires, structural characterization
  • Poster
    Nanowire Week 2017, 29.05.-02.06.2017, Lund, Sweden

Registration No. 26692 - Permalink


Low-temperature intracenter relaxation times of shallow donors in germanium
Zhukavin, R. K.; Kovalevskii, K. A.; Sergeev, S. M.; Choporova, Y. Y.; Gerasimov, V. V.; Tsyplenkov, V. V.; Knyazev, B. A.; Abrosimov, N. V.; Pavlov, S. G.; Shastin, V. N.; Schneider, H.; Deßmann, N.; Shevchenko, O. A.; Vinokurov, N. A.; Kulipanov, G. N.; Hübers, H.-W.
The relaxation times of localized states of antimony donors in unstrained and strained germanium uniaxially compressed along the [111] crystallographic direction are measured at cryogenic temperatures. The measurements are carried out in a single-wavelength pump–probe setup using radiation from the Novosibirsk free electron laser (NovoFEL). The relaxation times in unstrained crystals depend on the temperature and excitation photon energy. Measurements in strained crystals are carried out under stress bar, in which case the ground-state wavefunction is formed by states belonging to a single valley in the germanium conduction band. It is shown that the application of uniaxial strain leads to an increase in the relaxation time, which is explained by a decrease in the number of relaxation channels.
Keywords: free-electron laser, shallow impurities, germanium, terahertz pump-probe

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Registration No. 26689 - Permalink


FLUKA simulations of neutron transport in the Dresden Felsenkeller
Grieger, M.; Bemmerer, D.; Müller, S. E.; Szücs, T.; Zuber, K.
A new underground ion accelerator with 5 MV acceleration potential is currently being readied for installation in the Dresden Felsenkeller. The Felsenkeller site consists of altogether nine mutually connected tunnels. It is shielded from cosmic radiation by a 45 m thick rock overburden, enabling uniquely sensitive experiments. In order to exclude any possible effect by the new accelerator in tunnel VIII on the existing low-background gamma-counting facility in tunnel IV, Monte Carlo simulations of neutron transport are being performed. A realistic neutron source field is developed, and the resulting additional neutron flux at the gamma-counting facility is modeled by FLUKA simulations. – Supported by NAVI (HGF VH-VI-417).
  • Lecture (Conference)
    DPG Frühjahrstagung, 23.-27.03.2015, Heidelberg, Deutschland

Registration No. 26685 - Permalink


Strahlenschutzrechnungen für den Untertage-Ionenbeschleuniger am Standort Felsenkeller
Grieger, M.
Geringe natürliche Hintergrundstrahlung ist für die Untersuchung von Brennprozessen in Sternen von hoher Bedeutung. Für mehrere Szenarien wurden detaillierte FLUKA durchgeführt um die zusätzliche Strahlungserzeugung durch den neuen 5 MV Pelletron Beschleuniger zu studieren - mit dem Ziel die benötigte Abschirmung zu optimieren.
  • Poster
    Lange Nacht der Wissenschaften Dresden, 16.06.2017, Dresden, Deutschland

Registration No. 26684 - Permalink


Flue dust from the copper converter process - Recovery of Cu and In by solvent extraction
Rädecker, P.; Scharf, C.; Zürner, P.; Frisch, G.; Pieplow, G.; Lindner, D.; Koch, J.
Flue dusts from copper metallurgy are resources for base metals such as copper, zinc, tin or lead. However, there is also a potential for the recovery of strategic elements like indium. At the moment flue dusts are recirculated within the copper process, but residues are available from historic produc-tion processes.
Hydrometallurgical processes seem to be a promising method to recover the base and strategic met-als from these fine-grained flue dusts. In preparation for further processing, the secondary material was characterized by mineral liberation analysis (MLA) and electron probe micro analysis (EPMA). An iron- and zinc-rich spinel phase (Zn,Fe,Mn)(Fe,Mn)2O4 was detected as the main phase (76 wt.-%) in the flue dust. The chemical composition of the flue dust was analysed by X-ray fluo-rescence spectroscopy (XRF spectroscopy). Leaching by sulfuric acid leads to precipitation of lead sulphate and calcium sulphate, which remain in the residue. The level of some impurities in the solu-tion can be controlled.
This work focuses on the selective recovery of copper and indium by solvent extraction from the leaching solution. Preliminary synthetic solutions of copper, iron(III), zinc, indium and mixtures of them were used for the investigations. The influence of pH value, concentration of acidic extract-ants, extraction time, and phase ratio on the extraction of copper, iron(III), zinc, and indium were studied. The results of the selective extraction of copper in the presence of iron(III) will be present-ed.
  • Lecture (Conference)
    European Metallurgical Conference EMC 2017, 25.-28.06.2017, Leipzig, Deustchland

Registration No. 26682 - Permalink


The Natural Neutron Background Underground: Measurement Using Moderated ³He Counters in Felsenkeller
Grieger, M.
A FLUKA simulation has been made to analyse the propagation of neutrons from the future Felsenkeller accelerator throughout the tunnel system of Felsenkeller. A neutron flux measurement with detectors loaned by the BELEN-collaboration has been performed to put the accelerator induced neutron flux into perspective with the natural neutron background. To deduce the neutron flux from the counting rates, FLUKA has been used to simulate the detector responses. The three measured locations in the existing γ-measurement facility in tunnel IV show different traits in their neutron spectra. Their cause has been analysed and the results had an impact on the construction planning of the new Felsenkeller laboratory in tunnels VIII and IX.
  • Poster
    Felsenkeller Workshop, 26.-28.06.2017, Dresden, Deutschland
  • Poster
    NDRA 2016, 29.06.-02.07.2016, Riva del Garda, Italia
  • Lecture (Conference)
    DPG Frühjahrstagung, 14.-18.03.2016, Darmstadt, Deutschland
  • Master thesis
    TU Dresden, 2016
    Mentor: PD Dr. Daniel Bemmerer

Registration No. 26681 - Permalink


FLUKA Radiation Safety Calculations for the Underground Accelerator Laboratory Felsenkeller/Dresden
Grieger, M.; Bemmerer, D.
The study of stable stellar burning reactions in nuclear astrophysics requires the use of ion accelerators in a low-background setting underground. Currently, there is only one such laboratory, the LUNA 0.4 MV accelerator deep underground in Gran Sasso/Italy. Several higher-energy underground accelerators are under development worldwide, including a 5 MV Pelletron to be placed in the Felsenkeller underground laboratory in Dresden/Germany. The shielding requirements for underground accelerators, where the paramount concern is the background in neighbouring rare-event searches is reviewed. Detailed FLUKA simulations have been carried out to study several different operating scenarios of the new 5 MV Felsenkeller accelerator, with a focus on the side effects on an existing γ-counting facility in the same tunnel system. The results of the simulations and practical implications will be discussed.
  • Poster
    Felsenkeller Workshop, 26.-28.06.2017, Dresden, Deutschland

Registration No. 26678 - Permalink


FLUKA shielding calculations for the underground accelerator laboratory Felsenkeller/Dresden
Grieger, M.
The study of stable stellar burning reactions in nuclear astrophysics requires the use of ion accelerators in a low-background setting underground. Currently, there is only one such laboratory, the LUNA 0.4 MV accelerator deep underground in Gran Sasso/Italy. Several higher-energy underground accelerators are under development worldwide, including a 5 MV Pelletron to be placed in the Felsenkeller underground laboratory in Dresden/Germany. The shielding requirements for underground accelerators, where the paramount concern is the background in neighbouring rare-event searches is reviewed. Detailed FLUKA simulations have been carried out to study several different operating scenarios of the new 5 MV Felsenkeller accelerator, with a focus on the side effects on an existing γ-counting facility in the same tunnel system. The results of the simulations and practical implications will be discussed.
  • Poster
    SATIF-13, 10.-12.10.2016, Dresden, Deutschland

Registration No. 26677 - Permalink


XPS spectra, electronic structure, and magnetic properties of RFe5Al7 intermetallics
Finkelstein, L. D.; Efremov, A. V.; Korotin, M. A.; Andreev, A. V.; Gorbunov, D. I.; Mushnikov, N. V.; Zhidkov, I. S.; Kikharenko, A. I.; Cholakh, S. O.; Kurmaev, E. Z.
The results of X-ray photoelectron spectroscopy measurements (core levels and valence bands) of RFe5Al7 (R = Lu, Tm, Er, Ho, Dy, Tb, Gd) single crystals are presented in comparison with the results of bulk magnetization studies and electronic structure calculations. It is shown that the increase of the Curie temperature in RFe5Al7 from Tm to Gd is associated with an increase of the indirect R 4f - Fe 3d exchange interaction at the expense of the multiplicity 2S + 1 (statistical weight) in the ground state 2S + 1LJ of R3+ ions. The nonmonotonic behavior of the ferrimagnetic compensation temperature, Tcomp, as well as the values of the spontaneous magnetic moment, Ms, and formation energy, Eform, of the 4fn levels in R metals in a series from ErFe5Al7 to GdFe5Al7 are explained by the difference in the quantum numbers L, J and S of the ground state of R3+ ions, leading to a maximum value of Tcomp, Ms and Eform for the Dycontaining compound. The electronic structure of Gd/LuFe5Alsub>7 is calculated using the GGA+U approach, on the basis of which the physical mechanism and relative strength of the interatomic R-Fe and Al-Fe interactions are considered, and also the difference in the magnetic moments of iron atoms in different structural positions is explained.

Registration No. 26676 - Permalink


Process Simulation of Si Dot Fabrication for SETs by Ion Beam Mixing and Phase Separation in Nanopillars
Prüfer, T.; Heinig, K. H.; Möller, W.; Xu, X.; Hlawacek, G.; Facsko, S.; Hübner, R.; Wolf, D.; Bischoff, L.; von Borany, J.
The single electron transistor (SET) is considered a promising candidate to continue the revolution of information technology due to its very low energy consumption (~100 times less then common FET). The big challenge is the manufacturability of SETs working at room temperature (RT). This requires the fabrication of much smaller structures (<5nm) than present-day and even future (multi-E-beam or EUV) lithography can provide.

Here we propose an ion-beam-assisted, CMOS compatible fabrication process of SETs. To realize the controlled tunneling of single electrons we propose a nanopillar of a Si/SiO2/Si stack with a single Si quantum dot embedded in SiO2 and connected by tunnel junctions to Si electrodes, which makes the drain and source. For RT operation the quantum dot has to be smaller than 5nm and requires tunnel distances lower than 2nm. The size of this pillar needs to be in the range of 10-20nm.

In this presentation we show the simulation of a CMOS compatible process to fabricate this quantum dot by using ion beam mixing and self-assembly. Earlier projects proved already the reliability of dot formations using ion beam mixing technologies. Starting with a layerstack of Si/SiO2/Si, the ion beam irradiation by high energy Si+ ions causes mixing of the two Si/SiO2 interfaces what transforms the SiO2 layer into metastable SiOx (Figure 1). During subsequent heat treatment the mixed region of SiOx (<10nm2) separates into Si and SiO2, what leads to the formation of one single Si nanodot in the SiO2 layer (Figure 2). The irradiation simulations are done by TRIDYN and TRI3DYN program codes and the annealing by a self-developed Kinetic Monte Carlo program. We will present, how this process can be controlled using the ion beam irradiation values, geometrical sizes and the heat treatment parameters, so that it is yielding suitable conditions for application in hybrid SET-CMOS devices operating at RT.

This part of the work is being funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).
Keywords: SET, CMOS, Phase Separation, Ion Beam Mixing
  • Lecture (Conference)
    Electron, Ion, and Photon Beam Technology and Nanofabrication, 30.05.-02.06.2017, Orlando, USA

Registration No. 26675 - Permalink


Determining antiferromagnetic domain patterns electrically
Kosub, T.; Hübner, R.; Appel, P.; Shields, B.; Maletinsky, P.; Kopte, M.; Schmidt, O. G.; Faßbender, J.; Makarov, D.
Extrinsic effects on Cr2O3 thin films are shown. Also a statistical method to evaluate AF domain pattern in an electric way is demonstrated.
  • Poster
    AF Spintronics Workshop, 25.10.2017, Grenoble, France

Registration No. 26672 - Permalink


Purely Antiferromagnetic Magnetoelectric RAM
Kosub, T.; Kopte, M.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Fassbender, J.; Schmidt, O. G.; Makarov, D.
MERAM based on Cr2O3/Pt is presented
  • Lecture (Conference)
    DPG-Frühjahrstagung, 19.03.2017, Dresden, Germany

Registration No. 26671 - Permalink


Purely Antiferromagnetic MERAM
Kosub, T.; Kopte, M.; Appel, P.; Shields, B.; Maletinsky, P.; Hübner, R.; Schmidt, O. G.; Faßbender, J.; Makarov, D.
Magnetoelectric and purely antiferromagnetic RAM is shown based on Cr2O3/Pt
  • Lecture (Conference)
    IEEE Dublin, 24.04.2017, Dublin, Ireland

Registration No. 26669 - Permalink


Unconventional spin dynamics in the honeycomb-lattice material α-RuCl3: High-field electron spin resonance studies
Ponomaryov, A. N.; Schulze, E.; Wosnitza, J.; Lampen-Kelley, P.; Banerjee, A.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Kolezhuk, A. K.; Zvyagin, S. A.
We present high-field electron spin resonance (ESR) studies of the honeycomb-lattice material α-RuCl3, a prime candidate to exhibit Kitaev physics. Two modes of antiferromagnetic resonance were detected in the zigzag ordered phase, with magnetic field applied in the ab plane. A very rich excitation spectrum was observed in the field-induced quantum paramagnetic phase. The obtained data are compared with the results of recent numerical calculations, strongly suggesting a very unconventional multiparticle character of the spin dynamics in α-RuCl3. The frequency-field diagram of the lowest-energy ESR mode is found consistent with the behavior of the field-induced energy gap, revealed by thermodynamic measurements.

Registration No. 26668 - Permalink


Optimized Synthesis of the Bismuth Subiodides BimI4 (m = 4, 14, 16, 18) and the Electronic Properties of Bi14I4 and Bi18I4
Weiz, A.; Le Anh, M.; Kaiser, M.; Rasche, B.; Herrmannsdörfer, T.; Doert, T.; Ruck, M.
We optimized the syntheses of α- and β-Bi4I4 and transferred the method to the very bismuth-rich iodides Bi14I4, Bi16I4, and Bi18I. Phase-pure, microcrystalline powders of BimI4 (m = 4, 14, 18) can now by synthesized on a multigram scale. Conditions for the growth of single crystals of Bi16I4 and Bi18I4 were determined. The redetermination of the crystal structure of Bi16I4 hints at a stacking disorder or the presence of 1͚[BimI4] ribbons with m = 14 and 18 among the dominant type along with m = 16. The electronic band structures for m = 14, 16, and 18 were calculated including spin-orbit coupling. They vary markedly with m and show numerous bands crossing the Fermi level, predicting a 3D-metallic behavior. Measurements of the electrical resistivity of a polycrystalline sample of Bi14I4 as well as polycrystalline and single-crystalline samples of Bi18I4 confirmed their metallic nature over the temperature range 300 K to 2 K. For BiI4, a positive and strictly linear magnetoresistance at 2 K in static magnetic fields up to 14 T was observed, which could indicate a topologically nontrivial electronic state.

Registration No. 26667 - Permalink


Transglutaminase 2 as a target for functional tumour imaging: From substrates to inhibitors to radiotracers
Löser, R.
The talk is covering the efforts of our group in the development of inhibitor-based radiotracers for the imaging of tumour-associated transglutaminase 2. After introducing the biological function of transglutaminase 2, the development of substrates for fluorimetric activity assays will be lined out. Major emphasis will be put on the synthesis, kinetic characterisation and in vitro pharmacokinetic profiling of acrylamide-based irreversible inhibitors. Finally, labelling of these compounds with fluorine-18 and initial results towards their radiopharmacological evaluation will be discussed.
  • Lecture (others)
    Pharmazeutisches Kolloquium, 03.11.2017, Bonn, Deutschland

Registration No. 26665 - Permalink


Metallic Photocathodes for Superconducting RF Photo Guns
Teichert, J.; Xiang, R.
Report on results and status of photocathode development and measurement in the EC project EuCARD2.
Keywords: photocathode, quantum efficiency, magnesium, lead, niobium
  • Lecture (Conference)
    EuCARD2 WP11 Annual Meeting, 14.-15.03.2017, Warsaw/Swierk, Poland

Registration No. 26664 - Permalink


MoS₂ quantum dots as an efficient catalyst material for oxygen evolution reaction
Mohanty, B.; Ghorbani-Asl, M.ORC; Kretschmer, S.ORC; Ghosh, A.; U. Guha, P.; Panda, S. K.; Jena, B.; Krasheninnikov, A. V.ORC; Jena, B. K.
The development of an active, earth-abundant and inexpensive catalyst for oxygen evolution reaction (OER) is highly desirable but remains a great challenge. Here, by combining experiments and first-principles calculations, we demonstrate that MoS₂ quantum dots (MSQDs) are an efficient material for OER. We use a simple route for the synthesis of MSQDs from a single precursor in aqueous medium avoiding the formation of unwanted carbon quantum dots (CQDs). The as-synthesized MSQDs exhibit higher OER activity with the lower Tafel slope as compared to that for the state-of-the-art catalyst IrO₂/C. The potential cycling of the MSQDs activates the surface and improves the OER catalytic properties. The density functional theory calculations reveal that MSQD vertices are reactive and the vacancies at the edges also promote the reaction, which indicates that the small flakes with defects at the edges are efficient for OER. The presence of CQDs affects the adsorption of reaction intermediates and dramatically suppresses the OER performance of the MSQDs. Our theoretical and experimental findings provide important insights into the synthesis process of MSQDs and their catalytic properties and suggest promising routes to tailoring the performance of the catalysts for OER applications.
Keywords: MoS₂, Quantum Dots, Electrocatalysis, Oxygen Evolution Reaction, First-Principles Calculations, Defects

Registration No. 26662 - Permalink


Si amorphization by focused ion beam milling: Point defect model with dynamic BCA simulation and experimental validation
Huang, J.; Loeffler, M.; Muehle, U.; Moeller, W.; Mulders, J. J. L.; Kwakman, L. F. T.; van Dorp, W. F.; Zschech, E.
A Ga focused ion beam (FIB) is often used in transmission electron microscopy (TEM) analysis sample preparation. In case of a crystalline Si sample, an amorphous near-surface layer is formed by the FIB process. In order to optimize the FIB recipe by minimizing the amorphization, it is important to predict the amorphous layer thickness from simulation. Molecular Dynamics (MD) simulation has been used to describe the amorphization, however, it is limited by computational power for a realistic FIB process simulation. On the other hand, Binary Collision Approximation (BCA) simulation is able and has been used to simulate ion-solid interaction process at a realistic scale. In this study, a Point Defect Density approach is introduced to a dynamic BCA simulation, considering dynamic ion-solid interactions. We used this method to predict the c-Si amorphization caused by FIB milling on Si. To validate the method, dedicated TEM studies are performed. It shows that the amorphous layer thickness predicted by the numerical simulation is consistent with the experimental data. In summary, the thickness of the near-surface Si amorphization layer caused by FIB milling can be well predicted using the Point Defect Density approach within the dynamic BCA model.
Keywords: Amorphization, Beam plasma interactions, Computational chemistry, Defect density, Focused ion beams,High resolution transmission electron microscopy, Ion beams, IonsMilling (machining), Molecular dynamics, Point defects, Silicon, Surface defects, Transmission electron microscopy

Registration No. 26661 - Permalink


Addendum: Ion beam irradiation of nanostructures: sputtering, dopant incorporation, and dynamic annealing
Holland-Moritz, H.; Johannes, A.; Möller, W.; Ronning, C.
A previously published formalism to derive nanosphere sputtering yields is corrected and refined.
Keywords: Ion Irradiation, Nanostructures, Sputtering

Registration No. 26660 - Permalink


Strain distribution in GaAs/InxGa1-xAs core/shell nanowires grown by molecular beam epitaxy on Si(111) substrates
Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Hlawacek, G.; Grenzer, J.; Schneider, H.; Helm, M.; Dimakis, E.
Strain distribution in GaAs/InxGa1-xAs core/shell nanowires grown by molecular beam epitaxy on Si(111) substrates
  • Lecture (Conference)
    Workshop on Surface and Interface Diffraction in Condensed Matter Physics and Chemistry (CMPC), 09.-10.03.2017, DESY, Hamburg, Germany

Registration No. 26656 - Permalink


Strain distribution in highly mismatched GaAs/(In,Ga)As core/shell nanowires
Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Ghorbani, M.; Krasheninnikov, A.; Hlawacek, G.; Grenzer, J.; Schneider, H.; Helm, M.; Dimakis, E.
The core/shell nanowire (NW) geometry is suitable for the pseudomorphic growth of highly mismatched semiconductor heterostructures, where the shell thickness can exceed significantly the critical thickness in equivalent planar heterostructures. We have investigated the accommodation of misfit strain in self-catalyzed GaAs/(In,Ga)As core/shell NWs grown on Si (111) substrates by molecular beam epitaxy. The NWs have their axis along the [111] crystallographic direction, six {11 ̅0} sidewalls, and their crystal structure is predominantly zinc blende. For strain analysis, we used Raman scattering spectroscopy, transmission electron microscopy, X-ray diffraction and photoluminescence spectroscopy. Within a certain range of core/shell dimensions and shell composition, our findings reveal that the elastic energy in NWs without misfit dislocations can be confined exclusively inside the core, allowing for the shell to be strain-free. The experimental results are also compared with theoretical simulations of the strain (continuum elasticity theory) and phonon energy (density functional theory).
  • Lecture (Conference)
    DPG Spring Meeting 2017, 19.-24.03.2017, Dresden, Germany

Registration No. 26655 - Permalink


Nanoscale surface patterning by non-equilibrium self-assembly of ion-induced vacancies and ad-atoms
Facsko, S.; Ou, X.; Engler, M.; Erb, D.; Skeren, T.; Bradley, R. M.
Various self-organized nanoscale surface patterns can be produced by low- and medium-energy ion beam irradiation [1], depending on the irradiation conditions. Hexagonally ordered dot or pit patterns, checkerboard patterns, as well as periodic ripple patterns oriented perpendicular or parallel to the ion beam direction are formed spontaneously during the continuous surface erosion by ion sputtering. On amorphous surfaces, the formation of these patterns results from an interplay of different roughening mechanisms, e.g. curvature dependent sputtering, ballistic mass redistribution, or altered surface stoichiometry on binary materials, and smoothing mechanisms, e.g. surface diffusion or surface viscous flow.

An additional surface instability arises above the recrystallization temperature of the material. In this case, ion induced bulk defects are dynamically annealed and amorphization is prevented. The diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is now affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. Vacancies and ad-atoms are trapped on terraces and can nucleate to form new extended pits or terraces, respectively [2].

For the mathematical description of the pattern formation and evolution in the reverse epitaxy regime, a continuum equation can be used which combines the ballistic effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By comparison with experimental studies of pattern formation on Ge and GaAs surfaces at different angles and temperatures, we will show that the pattern evolution is determined by the surface instability due to the ES barrier, surface diffusion, and ballistic effects of ion irradiation.

[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, and S. Facsko, Nanoscale 7, 18928 (2015).
Keywords: ion beam irradiation, surface patterning, reverse epitaxy
  • Invited lecture (Conferences)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

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Ion-induced patterning of Ge surfaces above the recrystallization temperature
Facsko, S.; Ou, X.; Engler, M.; Erb, D.; Skeren, T.; Bradley, R. M.
Low- and medium-energy ion beam irradiation can lead to various self-organized nanoscale surface patterns depending on the irradiation conditions [1]. If the sample temperature is below the material recrystallization temperature, the ion bombardment results in amorphization of the surface. On such amorphous surfaces, the formation of nanoscale patterns is driven by the interplay of different ion beam induced roughening and smoothing mechanisms: curvature dependent sputtering, ballistic mass redistribution or altered surface stoichiometry (on binary materials) are roughening the surface, while surface diffusion or surface viscous flow are smoothing it.

An additional surface instability arises above the recrystallization temperature of the material, when the surface remains crystalline during ion irradiation. In this case, the diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. Vacancies and ad-atoms are thereby trapped on terraces and nucleate to form new extended pits or islands, respectively [2]. In molecular beam epitaxy mounds with different facets are formed due to the ES barrier. In ion-induced reverse epitaxy the additionally diffusing vacancies lead to different morphologies, like inverse pyramid and checkerboard patterns.

However, on Ge (001) surfaces irradiated at incidence angles greater than 50° mound patterns are formed and for angles greater than 75° the pattern turns into ripples. This transition from checkerboard over mound to ripple patterns in the reverse epitaxy regime can be described by a continuum equation which combines the ballistic effects of ion irradiation and the effective diffusion currents due to the ES barrier on the crystalline surface.

[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).
Keywords: ion beam irradiation, surface patterning, reverse epitaxy
  • Lecture (Conference)
    Nanopatterning 2017, 26.-28.06.2017, Helsinki, Finland

Registration No. 26652 - Permalink


Extremely lattice mismatched GaAs/InxGa1-xAs core/shell nanowires: coherent growth and strain distribution
Balaghi, L.; Hübner, R.; Bussone, G.; Grifone, R.; Grenzer, J.; Ghorbani Asl, M.; Krasheninnikov, A.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.
Compound semiconductors are versatile materials due to the possibility to tailor their (opto)electronic properties by selecting their composition appropriately. When grown heteroepitaxially, though, this possibility is constrained by the lattice mismatch with the substrate. InxGa1-xAs is a good example because it can have, depending on x, a suitable direct optical band gap for optoelectronic applications in the infrared (e.g. telecommunication wavelengths) or high electron mobility for high-speed transistors. However, the practical choices of x are limited by the available substrates, typically GaAs for low x or InP for x≈0.53.
Nanowires are a promising alternative for the realization of epitaxial heterostructures with high lattice mismatch due to their unique geometry and high surface-to-volume ratio. In addition, the possibility of monolithic integration in Si-CMOS platforms adds to their technological significance. In this work, we have investigated the growth of free-standing GaAs/InxGa1-xAs core/shell nanowires on Si(111) substrates by molecular beam epitaxy and the accommodation of lattice mismatch therein. Specifically, we have concentrated on highly lattice mismatched heterostructures (x=0.20-0.80) and very thin cores (diameter < 25 nm).
Self-catalyzed growth of very thin GaAs core nanowires with a sufficiently low number density (to avoid beam shadowing during the shell growth) was possible on native-oxide/Si(111) substrates, after an in situ treatment of the latter with Ga droplets. This resulted in zinc blende nanowires with their axis along the [111] crystallographic direction and six {1-10} sidewalls. Subsequently, conformal overgrowth of the InxGa1-xAs shell was obtained only under kinetically limited growth conditions that suppressed mismatch-induced bending phenomena. The strain in the core and the shell was studied systematically as a function of the shell composition and thickness. To that end, we used Raman scattering spectroscopy, transmission electron microscopy and (synchrotron/lab source) X-ray diffraction, and compared the results with theoretical predictions based on continuum elasticity and density functional theories. All findings point to the existence of anisotropic tensile strain in the core that increases (as quantified by Raman measurements) with increasing the shell thickness, whereas the corresponding compressive strain in the shell decreases to zero. Our work demonstrates the opportunity to grow not only relaxed InxGa1-xAs shells with high structural quality (as adopted from the GaAs core) in a wide, if not the whole, compositional range, but also highly strained (tensile) GaAs cores with (opto)electronic properties that remain to be explored.
Keywords: core/shell nanowire, strained core, relaxed shell
  • Poster
    Nanowire Week 2017, 29.05.-02.06.2017, Lund, Sweden

Registration No. 26650 - Permalink


Nanoscale surface patterning of crystalline semiconductor surfaces by broad ion beam irradiation
Facsko, S.; Ou, X.; Engler, M.; Erb, D.; Skeren, T.; Bradley, R. M.
arious self-organized nanoscale surface patterns can be produced by low- and medium-energy ion beam irradiation [1], depending on the irradiation conditions. Hexagonally ordered dot or pit patterns, checkerboard patterns, as well as periodic ripple patterns oriented perpendicular or parallel to the ion beam direction are formed spontaneously during the continuous surface erosion by ion sputtering. On amorphous surfaces, the formation of these patterns results from an interplay of different roughening mechanisms, e.g. curvature dependent sputtering, ballistic mass redistribution, or altered surface stoichiometry on binary materials, and smoothing mechanisms, e.g. surface diffusion or surface viscous flow.
An additional surface instability arises above the recrystallization temperature of the material. In this case, ion induced bulk defects are dynamically annealed and amorphization is prevented. The diffusion of ion-induced vacancies and ad-atoms on the crystalline surface is now affected by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier to cross terrace steps. Vacancies and ad-atoms are trapped on terraces and can nucleate to form new extended pits or terraces, respectively [2].
For the description of the pattern formation and evolution in the reverse epitaxy regime, a continuum equation can be used which combines the ballistic effects of ion irradiation and effective diffusion currents due to the ES barrier on the crystalline surface. By comparison with experimental studies of pattern formation on Ge and GaAs surfaces at different angles and temperatures, we will show that the pattern evolution is determined by the combined action of surface instability due to the ES barrier, surface diffusion, and ballistic effects of ion irradiation.
[1] A. Keller and S. Facsko, Materials 3, 4811 (2010).
[2] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, and S. Facsko, Nanoscale 7, 18928 (2015).
Keywords: ion irradiation, surface patterning, reverse epitaxy
  • Invited lecture (Conferences)
    MRS Fall Meeting, 26.11.-1.12.2017, Boston, USA

Registration No. 26648 - Permalink


Positronium probing of pores in zirconia nanopowders
Prochazka, I.; Cizek, J.; Lukac, F.; Melikhova, O.; Hruska, P.; Anwand, W.; Liedke, M. O.; Konstantinova, T. E.; Danilenko, I. A.
Zirconium di-oxide (ZrO2 , zirconia) receives nowadays a big attention because of a variety of advantageous properties which make zirconia-based materials useful in numerous fields of practice, in particular, in ceramic industry and other high-temperature applications. To make high-temperature phases of zirconia stabilised down to room temperature, doping of the host lattice by proper metal cations has to be usually performed. Nanopowders are currently focused on as starting substances for manufacturing ZrO2-based ceramics by sintering, because well-homogenised materials of a low porosity can be produced more easily. Nanometer-sized defects associated to grain boundaries (GBs) become then to play an enhanced role in nanopowders due to enlarged volume fraction of GBs. Positrons and positronium (Ps) atoms can serve as efficient probes of different structures encountered in particular stages of manufacturing ZrO2-based functional materials. In the present contribution, conventional positron and Ps lifetime measurements were carried out on a variety of zirconia-based nanopowders and ceramics obtained by sintering these nanopowders. Nanopowders studied were doped with various metal cations (Y3+, Cr3+, Ce4+, Mg2+) and differed also in thermal treatment prior sintering. Lifetime experiments were conducted in air or in vacuum and combined with Doppler broadening measurements using slow-positron beam and supplemented with X-ray diffraction (XRD) and mass-density (MD) measurements. In Figure, variability of the lifetime spectra observed is illustrated. In a range of lifetimes from a few ns to ≈ 70 ns, up to three individual lifetime components could be identified, see Figure, (a) and (b). Such observations unambiguously testified Ps formation with subsequent ortho-Ps annihilation. On the other hand, an absence of the ortho-Ps components was found in certain nanopowders giving thus an evidence of a strong Ps inhibition, see Figure, (c). Pore sizes were estimated using current models of correlation between observed ortho-Ps lifetime and pore size. Origins of pores will be discussed on the basis of the ortho-Ps data in combination with the results of slowpositron beam, XRD and MD measurements.
Keywords: zirconia nanopowders, Positronium, grain boundaries, PAS, PALS
  • Poster
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

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Positronium formation in nanostructured metals
Čížek, J.; Melikhova, O.; Hruška, P.; Vlček, M.; Anwand, W.; Liedke, M. O.; Novotný, M.; Bulíř, J.; Cheng, Y.
Nanostructured metals containing nano- and micro-cavities can be prepared by various methods. Morphology of cavities can be controlled by varying the parameters of preparation. This enables fabrication of nanostructured metals with properties tailored for particular applications, e.g. nanostructured metals containing fractal-like cavities with a wide size distribution are used as omnidirectional absorbers of light from the visible into the infrared spectral region. Positronium (Ps) is a non-destructive probe of nanoscopic cavities capable of precise determination of their size distribution. In conventional metals Ps does not form since any bound state of positron and electron is quickly destroyed by the screening of conduction electrons. However, a thermalized positron escaping from a metal through inner surface into a cavity may form Ps by picking an electron on the surface. This process was examined in the present work on nanostructured metals prepared three various methods: (i) thin films of black metals (Au and Al) evaporated in N2 atmosphere; (ii) nano-porous bulk Pd prepared by electrochemical etching of PdCo alloy; (iii) nanostructured Gd prepared by selective evaporation of Mg from MgGd alloy. Our investigations confirmed that Ps was formed in nanostructured metals. The the size distribution of nano-pores in the samples has been determined. The mechanism of Ps formation in these samples is discussed in the paper.
Keywords: Positronium, Nanostructured metals, pores, black Au, Al, Pd, Gd
  • Lecture (Conference)
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

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Nanomembranes Modified by Highly Charged Ions
Facsko, S.; Wilhelm, R. A.; Gruber., E.; Heller, R.; Gölzhäuser, A.; Beyer, A.; Turchanin, A.; Aumayr, F.
Smart membranes play a key role in different sensor applications, e.g. for drug and explosive detection. By tailoring the structure and properties of these membranes physical-chemical functionality can be added to the sensor. One way of modifying membranes is by particle irradiation with electrons or ions. Specifically, highly charged ions (HCI) carry a large amount of potential energy (the stored ionization energy) which is released when interacting with the membrane creating nanopores by a single HCI impact. In order to be able to control the ion induced modification, e.g. defining the pore size, the energy deposition in the membranes has to be determined.
For the interaction of HCI with thin membranes this is particularly interesting because the HCIs are still in a pre-equilibrium interaction regime for thicknesses below a few nm. Within 1 nm thick carbon nano membranes (CNMs) for instance, holes are produced by the passage of highly charged Xeq+ ions only above a threshold in the potential energy of the HCI which depends on the kinetic energy [1]. In order to study the stopping force of the HCIs in the membrane we examined the charge state and the energy loss of the Xeq+ ions after their passage through the CNM. Surprisingly, two distinct exit charge distributions were observed [2]. While some of the ions pass the membrane with almost no charge loss, other ions lose most of their charge. Apparently, the observed charge distribution reflects two different impact parameter regimes. The different impact parameter regimes are also connected to different energy losses: ions with large impact parameters are not stopped, whereas ions in close collisions exhibit high stopping force which is strongly dependent on the incident charge state.
[1] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, A. Beyer, A. Turchanin, N. Klingner, R. Hübner, M. Stöger-Pollach, H. Vieker, G. Hlawacek, A. Gölzhäuser, S. Facsko, and F. Aumayr, 2D Mater. 2, 1 (2015).
[2] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).
Keywords: highly charged ions, nanomembranes
  • Invited lecture (Conferences)
    Towards Reality in Nanoscale Materials IX, 13.-16.02.2017, Levi, Finland

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Porosimetry of ultra-low K materials and transformed porous glass-thin layers by Monenergetic Positron Source at ELBE facility
Attallah, A. G.; Koehler, N.; Dornberg, G.; Butterling, M.; Liedke, M. O.; Wagner, A.; Schulz, S. E.; Badawi, E.; Enke, D.; Krause-Rehberg, R.
The pore size of spin-on coated ultra-low K (ULK) materials cured at 4500C for different times was studied by the pulsed slow positron beam (MePS) at ELBE/HZDR. To investigate the pore formation in cured porous spin-on dielectrics, the pore size as a function of positron implantation energy was obtained for samples with different curing times. Such a study is performed to understand the dielectric damage behaviour of ULK dielectrics for the integration in Back-End of Line (BEOL). MePS results revealed that the films contain open and closed pores with ~ 3 nm in diameter which was confirmed by capping the samples. The highest pore concentration is located beneath the surface in the 0.2 - 0.5 m range (We plan to carry out ellipsometric porosimetry and FTIR during this summer). Pseudomorphic transformation of porous glass-thin layers, with pores of 40 - 50 nm diameter and a relatively small surface area, to MCM-41 with ~4 nm pores, with a higher surface area, was studied by MePS. The small pore size of MCM-41 was successfully detected with an intensity growth with transformation degree but the large pores were not detected at all. To understand the disability of detecting the large pores by positron annihilation lifetime, we plan to perform SEM measurements in the same depth as that of the implanted positrons (0.005-2.4 m).
Additionally, the increase in the intensity of positronium lifetime, which correlates the small pores, as a function of positron implantation energy could reflect inner pore isolation or poor interconnectivity.
Keywords: ultra-low K materials, Porosimetry, MePS, ELBE, Positronium
  • Lecture (Conference)
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

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In-situ investigations of the curing process in ultra low-k materials
Liedke, M. O.; Koehler, N.; Butterling, M.; Attallah, A. G.; Krause-Rehberg, R.; Hirschmann, E.; Schulz, S. E.; Wagner, A.
Porous spin-on glasses belong to ultra low-k (ULK) dielectrics and are promising candidates for integration in the semiconductor device fabrication technology. Their microstructure consists usually of interconnected pore networks distributed across the film rather than separated voids. The pore size and distribution are controllable to a large extent, however, the pore formation process itself is still not well understood. A dielectric damage during integration and material degradation of films with large porosity are still problematic issues. The first results on in-situ investigations of the pore formation during a curing process – a porogen removal by vacuum annealing will be presented. The main motivation is to obtain the insight into early stages of the pore formation and up to its full development. The in-situ annealing and Doppler Broadening – Positron Annihilation Spectroscopy (DB-PAS) measurements have been done on our Apparatus for In-situ Defect Analysis (AIDA) system [1], which is the end-station of the slow positrons beamline at HZDR. The comparison between preliminary ex-situ studies by means of DB-PAS [see Fig. 1], Positron Annihilation Lifetime Spectroscopy (PALS), and Fourier Transform Infrared Spectroscopy (FTIS) will be given.
In Fig. 1(a) it is shown that o-Ps emission increases with t, thus can be a probe of films porosity as long as they are capped. The curing time of 5-30min. is sufficient to fully develop the pore network [Fig. 1(b)]. Porosity development and distribution will be discussed for annealing temperatures in the 100-400°C range and varied annealing time.
[1] M.O. Liedke et al., Journal of Applied Physics 117, 163908 (2015).
Keywords: low-k materials, curing process, Porous spin-on glasses, PAS, AIDA, Positron Annihilation Spectroscopy,
  • Lecture (Conference)
    12th International Workshop on Positron and Positronium Chemistry, 28.08.-01.09.2017, Lublin, Poland

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Ion Beam-Enabled CMOS-Compatible Manufacturing of SETs Operating at Room Temperature
Facsko, S.; Heinig, K. H.; Stegemann, K. H.; Pruefer, T.; Xu, X.; Hlawacek, G.; Huebner, R.; Wolf, D.; Bischoff, L.; Moeller, W.; von Borany, J.
Electronics has been dominated by silicon since half a century. Si will dominate electronics another decade, however its functionality might change from classical field-controlled currents through channels (the Field Effect Transistor FET) to quantum mechanical effects like field-controlled hopping of single electrons from a source to a drain via a quantum dot (the Single Electron Transistor SET). Due to single electron hopping, the SET is the champion of low-power consumption. This is very attractive for the expanding Internet of Things (IoT): more and more devices need batteries and plugs. Therefore, together with improved batteries, advanced computation and communication must be delivered at extremely low-power consumption. At very low temperatures, the perfect functionality of SETs has been proven for tiny metal dots [1] and larger Si islands [2]. However, large-scale use of SETs requires Room Temperature (RT) operation, which can be achieved with tiny Si dots (<4 nm) in SiO2, exactly located between source and drain with distances of ~1…2 nm allowing quantum mechanical tunneling. Manufacturability of such nanostructures is the roadblock for large-scale use of SETs. Lithography cannot deliver the feature sizes of 1…3 nm required for RT operation. Therefore, there are currently intense studies to fulfill these requirements by self-organization processes. Convincing proof of concepts have been reported [see, e.g., 3] on room temperature operation of silicon based SETs. However, the self-organization processes developed so far are not reliable enough for large-scale integration.
The ion beam technique is a well-established technology in microelectronics used for doping and amorphization of semiconductors and even for ion beam synthesis of buried layers. The parameters of ion beam processing like ion flux, fluence and energy as well as the temperature and time of the subsequent thermal treatment are very well controllable. Therefore we searched for a self-organization process based on ion irradiation which overcomes the bottleneck of manufacturability of SETs working at room temperature.
Thus, in the framework of an international project funded by the European Commission [4], we develop an ion-assisted, CMOS-compatible process [4] which will provide both (i) self-assembly of a single Si dot and (ii) its self-alignment with source and drain.
Based on our knowledge of ion implantation [5,6] and irradiation [7] induced phase separation and Ostwald ripening processes as well as ion-assisted fabrication of non-volatile nanocluster memories [8], we concluded by computer simulations that phase separation of tiny, metastable SiOx volumes (<103 nm3) will transiently lead to a single Si nanodot in SiO2 (see Fig.2).
The tiny, metastable SiOx volume is formed by ion beam mixing of a bulk Si/SiO2/a-Si layer stack. In order to get the very small SiOx volume necessary for single dot formation, two approaches are used: (i) point-like Ne+ irradiation for fundamental studies, and (ii) broad beam Si+ irradiation of nanopillars for the device fabrication (see Fig. 3).
For both approaches, the predictive computer simulations use for the dynamical 3D ion beam mixing the recently developed program TRI3DYN [9]. TRI3DYN provides the initial conditions for phase separation and coarsening processes simulated (see, e.g. Fig. 2) with the 3D kinetic Monte Carlo program 3DkMC [6].
First results of our studies with the Helium Ion Microscope are shown in Figs. 4 and 5. The ion beam mixing of the SiO2 layer as imaged by EFTEM agrees nicely with that predicted by TRI3DYN simulations. Using this mixing profile as input for 3DkMC simulations, a single Si nanocluster is formed (Fig. 4). Although it appears to be extremely difficult to image a single Si nanodot of 2…3 nm diameter embedded in SiO2 in a ~50 nm thick TEM lamella, Fig 5 proves that after annealing such a single cluster can be formed. The next activities will be focused on the single Si nanodot fabrication in Si nanopillars and the optimization of this process for RT-SET fabrication.

This work has been funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No 688072.

1. K. Maeda et al., ACS Nano (2012) 2798.
2. S. Ihara et al., Appl. Phys. Lett. 107 (2015) 13102. SET in SOI
3. V. Deshpande et al., Proc. of the IEDM12-Conf. (2012) 195.
4. Research Project IONS4SET funded by the European Commission
5. M. Strobel et al., NIM B147 (1999) 343.
6. M. Strobel, K.-H. Heinig, W. Möller, Phys. Rev. B64 (2001) 245422.
7. K.H. Heinig, T. Müller, B. Schmidt, M. Strobel, W. Möller, Appl. Phys. A77 (2003) 17.
8. T. Mueller et al., Appl .Phys. Lett. 81 (2002) 3049; ibid 85 (2004) 2373.
9. W. Möller, NIM B322 (2014) 23.
Keywords: ion irradiation, self-assembly, Si nanocrystals, single electron transistor
  • Invited lecture (Conferences)
    Ion-Surface Interactions 2017, 21.-25.08.2017, Moskow, Russia

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Hydrogen-induced defects in Ti and their thermal stability
Melikhova, O.; Čížek, J.; Hruška, P.; Lukac, F.; Knapp, J.; Havela, L.; Mašková, S.; Anwand, W.; Liedke, M. O.
Titanium readily absorbs hydrogen and undergoes phase transition into the hydride phase (TiH2). In the hydride phase Ti is able to absorb the hydrogen concentration as high as 1.4 wt.%. These properties make Ti and Ti-based alloys attractive for hydrogen storage applications. Hydrogen absorption in titanium matrix may introduce open volume defects since the volume of TiH2 phase exceeds that of titanium matrix. Absorbed hydrogen may segregate at these defects forming defect-hydrogen complexes.
In the present work positron annihilation spectroscopy was employed for characterization of hydrogen-induced defects in titanium. Defects created by hydrogen loading from the gas phase were compared with those introduced by electrochemical hydrogen charging. In general hydrogen loading introduces a high density of dislocations and vacancy clusters created by agglomeration of hydrogen-induced vacancies. The mean size of vacancy clusters depends on the hydrogen absorption temperature.
Thermal stability of hydrogen absorbed in titanium and recovery of hydrogen-induced defects were studied by positron lifetime spectroscopy combined with in-situ X-ray diffraction and thermal desorption spectroscopy. Fig. 1 shows the temperature dependence of positron lifetimes and relative intensities of individual components for hydrogen gas loaded titanium. The decomposition of TiH2 phase is accompanied with introduction of additional vacancies agglomerating into vacancy clusters. Further annealing of the sample above 500 °C leads to recovery of dislocations.
Keywords: Ti, hydrogen, hydride phase, open volume defects, positron annihilation spectroscopy, positron lifetime
  • Poster
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

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Defects in high entropy alloy HfNbTaTiZr prepared by spark plasma sintering
Lukac, F.; Dudr, M.; Cinert, J.; Vilemova, M.; Cizek, J.; Harcuba, P.; Vlasak, T.; Zyka, J.; Malek, J.; Liedke, M. O.
High entropy alloys exhibit various combinations of interesting physical properties due to the formation of solid solution stabilized by high configurational entropy. High entropy alloy HfNbTaTiZr exhibits single phase solid solution with BCC structure when prepared by arc melting [1]. Grain refinement achieved in cold rolled samples after recrystallization remarkably enhanced ductility of this alloy [2]. Mechanical alloying by milling and subsequent sintering is a frequent production way of preparing fine grained alloys from chemical elements with high melting temperature. In addition, spark plasma sintering (SPS) method with applied pressure serves as a unique tool of powder metallurgy thanks to fast heating rates and low time of exposition to elevated temperatures. Therefore, the deformation energy introduced during mechanical alloying may be effectively consumed during short sintering process and presents the additional parameter for grain refinement. The present work presents characterization of HfNbTaTiZr alloy prepared by SPS.
Microstructure of samples prepared by SPS was compared with as cast ingots. The samples were characterized by X-ray diffraction and scanning electron microscopy. Positron annihilation spectroscopy was employed for characterization of defects introduced by SPS and their thermal stability.
[1] O.N. Senkov, J.M. Scott, S.V. Senkova. D.B. Miracle, C.F. Woodward: Journal of Alloys and Compounds 509, 6043-6048 (2011).
[2] O.N. Senkov, S.L. Semiatin; Journal of Alloys and Compounds 649, 1110-1123 (2015).
Keywords: High entropy alloys, HfNbTaTiZr, spark plasma sintering, Positron annihilation spectroscopy, X-ray diffraction, scanning electron microscopy
  • Poster
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Registration No. 26640 - Permalink


Slow positron beam spectroscopy study of PMMA nanocomposite films with ion-synthesized silver nanoparticles
Kavetskyy, T. S.; Iida, K.; Nagashima, Y.; Elsayed, M.; Liedke, M. O.; Srinivasan, N.; Wagner, A.; Krause-Rehberg, R.; Šauša, O.; Telbiz, G.; Stepanov, A. L.
Understanding how the size, shape, and the aggregation state of the silver nanoparticles (NPs) are changed after integration into a target matrix is critical to enhance their performance, including molecular diagnostics, photonic and biomedical devices, which take advantage of the novel optical properties of these nanomaterials. In particular, the nanocomposites containing noble metal NPs dispersed in the polymer matrix by high-dose (> 1016 ions/cm2) implantation at low-energy ions (< 100 keV) can be used for the construction of plasmonic waveguides [1] and diffraction gratings [2]. Typically, form and size of Ag NPs in optically transparent matrices are connected with an appearance in visible absorption spectra of composite a surface plasmon resonance band. However, synthesis of Ag NPs by ion implantation in transparent polymer matrix such as polymethylmethacrylate (PMMA) has been found [1] to be quite difficult and unusual.
This problem can be solved with a powerful technique for the characterization of thin films – positron annihilation spectroscopy (PAS) using a variable-energy positron beam (VEPAS), – allowing depth-profiles from tens of nanometers up to several micrometers. This technique has been emerged as a key experimental tool for the understanding high-dose 40 keV boron-ion-implanted polymethylmethacrylate (B:PMMA) [3] with carbon nanostructures and Ag NPs loaded polymer brushes [4]. Also, the first attempt to find difference between the effects of carbonization and formation of Ag NPs in high-dose B:PMMA and Ag:PMMA nanocomposites has been done in the work [5] by using the Doppler broadening slow positron beam spectroscopy (DB-SPBS).
In the present work, the DB-SPBS technique was applied to characterize further the 30 keV Ag:PMMA nanocomposites fabricated by low-energy high-dose Ag-ion implantation. The results of depth profile of the S(Ep) parameter in the near-surface region of irradiated polymer were used to clarify indirectly a formation of Ag NPs in PMMA in dependence on ion dose. By comparative analysis with the S(Ep) parameter trend in polymer brushes with loaded Ag NPs [4], it is found that the density or mass of Ag NPs (‘Ag filling’) in Ag:PMMA increases as ion dose grows. The results obtained are discussed in terms of the positronium formation fraction in the irradiated part of polymer matrix and the model of carbon-shell Ag-core nanoparticles.
[1] A.L. Stepanov, Tech. Phys. 49, 143 (2004).
[2] M.F. Galyautdinov et al., Tech. Phys. Lett. 42, 182 (2016).
[3] T. Kavetskyy et al., J. Phys. Chem. B 118, 4194 (2014).
[4] G. Panzarasa et al., Nanotechnology 27, 02LT03 (2016).
[5] T. Kavetskyy et al., J. Phys.: Conf. Ser. 791, 012028 (2017).
Keywords: positron annihilation spectroscopy (PAS), variable-energy positron beam (VEPAS), PMMA nanocomposite films, Ag
  • Lecture (Conference)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Registration No. 26639 - Permalink


Defects and porosity in zirconia-based nanomaterials: a study by slow-positron beam technique
Prochazka, I.; Cizek, J.; Melikhova, O.; Lukac, F.; Hruska, P.; Anwand, W.; Liedke, M. O.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.
A variety of advantageous thermal, electrical and mechanical properties of zirconium di-oxide (ZrO2, zirconia) make zirconia-based materials widely used in many industrial areas, in particular, in ceramic industry and other high-temperature applications. Doping of the ZrO2 host lattice by proper metal cations is a prerequisite of stabilisation of the high- temperature cubic and tetragonal phases down to room temperature as well as improvement of other functional properties. The use of nanopowders as initial substances in manufacturing ZrO2-based nanoceramics by sintering leads to well-homogenised materials of a low porosity. Due to an appreciable volume fraction of grain boundaries (GBs), pores and nanometer-sized open-volume defects associated to GBs become significant in nanopowders. Obviously, positron as well as positronium (Ps) atom becomes efficient
probes of microstructure evolution during production of ZrO2-based functional nanomaterials by sintering.
In the present contribution, investigation of several zirconia-based nanopowders as well as ceramics, obtained by sintering these nanopowders, will be reported. Nanopowders under study were doped with metal cations of various valency (Mg2+, Y3+, Cr3+, Ce4+) and differed also in thermal treatment. Doppler broadening (DB) measurements using slow-positron beam were conducted in the positron energy E ranging from 0.03 eV to 35 keV and the ordinary S and W shape parameters as well as the relative 3γ fractions were evaluated as functions of E. In Figure, an example of measured S(E) curves is given illustrating the sintering induced disappearance of open volume defects and para-Ps formation as well as grain growth could be observed. The VEPFIT models were fitted to the measured S(E), W(E) curves. The DB experiments were supplemented with the conventional positron lifetime, X-ray diffraction (XRD) and mass-density (MD) measurements. Nature and depth distributions of open-volume defects will be discussed on the basis of the slowpositron beam results correlated with the data on positron lifetimes, XRD and MD.
Keywords: positron annihilation spectroscopy, zirconia, nanomaterials, nanopowders
  • Lecture (Conference)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Registration No. 26638 - Permalink


Slow positron annihilation studies of Pd-Mg multilayers
Hruška, P.; Čížek, J.; Bulíř, J.; Lukáč, F.; Anwand, W.; Liedke, M. O.; Fekete, L.; Melikhova, O.; Lančok, J.
Palladium is well known for its excellent hydrogen absorption kinetics. The gravimetric hydrogen absorption capacity of Pd is however only 0.93 wt. %. Magnesium exhibits a high hydrogen absorption capacity up to 7.6 wt. %, however the hydrogen absorption kinetics is slow. The aim of this work was to create thin Pd-Mg multilayered films combining positive hydrogen absorption properties of both elements. Pd-Mg multilayers were deposited by RF magnetron sputtering on fused silica substrates coated with 100 nm thick Pd wetting layer. The multilayers consist of alternating Pd and Mg layers (3, 12 and 60) of the same thickness. Three types of Pd-Mg multilayers were compared: (i) as deposited samples, (ii) hydrogen gas loaded samples at room temperature and H2 pressure of 4000 Pa for 2 h, (iii) samples annealed up to 450°C under Ar atmosphere. Defect structure of Pd-Mg multilayers was characterized using variable energy positron annihilation spectroscopy. Doppler broadening of the annihilation photopeak was analyzed using the S and W line-shape parameters and the measured S(E) curves were fitted using the VEPFIT code. The development of the structure during the annealing of the films was monitored by in-situ X-ray diffraction. Atomic force microscopy was employed for the study of the surface morphology. All films were characterized by nanocrystalline structure with a high density of grain boundaries with open-volume defects capable of positron trapping. The density of grain boundaries is determined by the mean grain size which increases with increasing thickness of a single phase layer. Hydrogen loading led to buckling of the film and introduced additional defects into the film. Annealing of the multilayers leads to diffusion of Mg atoms into the Pd layers and precipitates of Mg-Pd phase are formed.
Keywords: PAS, slow positron beam, positron annihilation spectroscopy, Pd, Mg, multilayers
  • Lecture (Conference)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Registration No. 26637 - Permalink


Magnetic phase transitions in ns-laser irradiated FeAl systems: the role of open volume defects
Liedke, M. O.; Bali, R.; Hübner, R.; Gradauskaite, E.; Ehrler, J.; Wang, M.; Potzger, K.; Zhou, S.; Wagner, A.
Fe60Al40 alloys exhibit disorder dependent magnetic phase transitions (MPT), e.g., a ferromagnetic disordered A2-phase turns into a paramagnetic ordered B2-phase [1]. The ordered B2-phase, formed due to annealing up to 500°C in vacuum can be reversed to the disordered A2-phase via ion-irradiation [2]. It has been shown that the physical origin of MPT is related to the so-called anti-site disorder (ASD), i.e., variations in the number of Fe-Fe nearest neighbors due to disordering of the system [3]. However, variations of the lattice parameter, secondary phases, and changes in the concentration and size of open volume defects may play an important role as well. Here, an excimer UV ns-laser has been utilized to induced defects and examine the role of ASD and defects onto magnetic properties of Fe60Al40. Samples of 40 nm thick Fe60Al40 films with different initial order levels were exposed to a range of laser fluences: (i) Ne+ irradiated fully-disordered (A2- Fe60Al40), and (ii) vacuum annealed ordered alloys (B2- Fe60Al40) and (iii) as-grown semi-disordered (A2/B2- Fe60Al40). It is seen that for laser pulses of fluences below 100 mJ·cm^-2 cause subtle changes to the magnetization depending on the Fe60Al40 initial state, whereas for fluences above 150 mJ·cm-2, strong increase in ferromagnetism is observed for all Fe60Al40 initial states. The laser irradiated samples were probed with the Positron Annihilation Spectroscopy (PAS) to analyze for the existence of vacancies and/or phase separation. Although the low fluence region shows nearly no variation in vacancy defect concentration, a slight increase in the number of Al atoms around defect sites is found. For the high fluence regime, it is seen that a large variation in vacancy defects occurs, followed by pronounced phase separation. Structural analysis of the phase separated films shows strong migration of Al atoms leaving behind Fe-enriched regions, consistent with the PAS spectra.
[1] M. O. Liedke et al., J. Appl. Phys. 117, 163908 (2015)
[2] J. Fassbender, et. al., Phys. Rev. B 77, 174430 (2008)
[3] R. Bali, et al., Nano Lett. 14, 435 (2014)
Keywords: positron, positron annihilation spectroscopy, MOKE, ns-laser, magnetic phase transition, order, disorder
  • Invited lecture (Conferences)
    The International Workshop on Positron Studies and Defects 2017 (PSD-17), 03.-08.09.2017, Dresden, Deutschland

Registration No. 26636 - Permalink


Reversible Tuning of Ferromagnetism and Resistive Switching in ZnO/Cu Thin Films
Younas, M.ORC; Xu, C.; Arshad, M.; Ho, L.; Zhou, S.; Azad, F.; Akhtar, M.; Su, S.; Azeem, W.; Ling, F.
Systematic magnetic, electronic, and electrical studies on the Cu0.04Zn0.96O/Ga0.01Zn0.99O cell structure grown on (001) sapphire by the pulsed laser deposition technique show that the Cu multivalent (CuM+) ions modulate magnetic and resistive states of the cells. The magnetic moment is found to be reduced by ∼30% during the high resistance state (HRS) to low resistance state (LRS) switching. X-ray photoelectron spectroscopy results reveals an increase of the Cu+/Cu2+ oxidation state ratio (which has been determined by the relative positions of the Fermi level and the Cu acceptor level) during the HRS to LRS transition. This decreases the effective spin-polarized Cu2+−Vö−Cu+ channels and thus the magnetic moment. A conduction mechanism involving the formation of conductive filaments from the coupling of the CuM+ ions and Vö has been suggested.

Registration No. 26635 - Permalink


Towards Substitutionally-Inert Ru(II) Complexes as Photoactivatable Anticancer Agents
Joshi, T.; Pierroz, V.; Ferrari, S.; Spiccia, L.; Gasser, G.
The severe side effects encountered with platinum-based anticancer agents has driven the pursuit of new metal-based chemotherapeutics. The best examples of these are ruthenium compounds which have shown a promising potential to circumvent these side effects on account of their broad antiproliferative profile and novel mechanistic of action against cancer cells. Our work aims at the development of substitutionally inert Ru(II)-tris(diimine) complexes as new anticancer agents. Here we present the anticancer action and cytotoxicity mechanism of a [Ru(dppz)2(CppH)](PF6)2 (1) (CppH = 2-(2′-pyridyl)pyrimidine-4-carboxylic acid; dppz = dipyrido[3,2-a:2′,3′-c]phenazine), a substitutionally-inert polypyridyl Ru(II) complex. Complex 1 induces inhibitory effects comparable to that of cisplatin, targets mitochondria and impairing the mitochondrial membrane potential eventually leads to cell death by apoptosis [1]. Structure-activity correlation studies identify the key functional role of the carboxylate group on the CppH ligand and of the bis(dppz) framework in the cytotoxic activity of 1, with any lipophilicity, charge, and size-based structural and functional modifications resulting in its decreased activity [2]. Complementing these findings, we recently illustrated the first example of a substitutionally-inert metal complex-based prodrug candidate which can efficiently respond to activation by UV-A light (2.58 J cm-2) to display cytotoxicity "on demand" against cervical (HeLa) and bone cancer (U2OS) cells [3]. The reported findings represent a major advancement towards achieving a site-directed spatially and temporally controlled anti-cancer activity from such metallo cytotoxics.

References
[1] V. Pierroz, T. Joshi, A. Leonidova, C. Mari, J. Schur, I. Ott, L. Spiccia, S. Ferrari, G. Gasser J. Am. Chem. Soc. 134 (2012) 20376−20387.
[2] T. Joshi, V. Pierroz, S. Ferrari, G. Gasser ChemMedChem 9 (2014) 1419–1427.
[3] T. Joshi, V. Pierroz, C. Mari, L. Gemperle, S. Ferrari, G. Gasser Angew. Chem. Int. Ed. 53 (2014) 2960–2963.
  • Invited lecture (Conferences)
    II International Caparica Congress on Translational Chemistry, 04.-07.12.2017, Caparica, Lisbon, Portugal

Registration No. 26633 - Permalink


Der Beitrag geowissenschaftlicher Forschung zur Erkundung von mineralischen Rohstoffen in Deutschland
Gutzmer, J.; Markl, G.
Invited keynote presentation for the 3rd BGR-Rohstoffkonferenz in Hannover.
  • Lecture (others)
    3. BGR-Rohstoffkonferenz, 29.-30.11.2017, Hannover, Deutschland

Registration No. 26627 - Permalink


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