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29070 Publications
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


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

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


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


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


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, 14.-19.05.2017, Copenhagen, Denmark

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

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

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


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


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


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


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

Registration No. 26654 - Permalink


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


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

Registration No. 26647 - Permalink


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

Registration No. 26646 - Permalink


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

Registration No. 26645 - Permalink


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

Registration No. 26644 - Permalink


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

Registration No. 26643 - Permalink


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

Registration No. 26641 - Permalink


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


Rhenium recovery from diluted solutions by solvent extraction
Helbig, T.; Scharf, C.
A total of 230.000 tons of the so called “Theisenschlamm”, a waste material of the former copper shale processing in the Mansfeld region, was deposited between the years 1978 and 1990. Besides about 20 wt.-% of zinc and minor amounts of lead, copper and tin, this material also contains valuable strategic elements, like rhenium and germanium. Nowadays rhenium is used as an important alloying element in nickel-base superalloys, or in catalysts.
The r4-project “Theisenschlamm” aims at a recovery of the valuable metal content by bioleaching, followed by element specific separation methods. An effective method for the selective separation and concentration of metals is solvent extraction where an organic phase is used to extract the elements of interest from an aqueous phase. But since the metal concentrations in the bioleaching solution are low, the processing is challenging. However, there are multiple parameters allowing an optimization of the solvent extraction process. The findings for a selective enrichment of rhenium from synthetic (bioleaching) solution will be presented in this talk.
  • Lecture (Conference)
    67. Berg- und Hüttenmännischer Tag, 08.-10.06.2016, Freiberg, Deutschland

Registration No. 26623 - Permalink


Recovery of Rhenium from Low Concentrated Bioleaching Solutions by Solvent Extraction
Helbig, T.; Scharf, C.
The r4-project "Theisenschlamm" focuses on the recovery of elements of strategic economic importance (like Rhenium or Molybdenum). The first step within the research approach is bioleaching of the Theisenschlamm, which is a waste material of the former copper shale processing in the Mansfeld region (Germany). As a next process step the project partners investigate different element selective separation methods to recover the valuable elements from the bioleaching solution. An efficient rhenium recovery from synthetic (bioleaching) solutions is achieved using solvent extraction with teriary amines. It could be shown that rhenium can be enriched in the organic phase and that a good selectivity over zinc, copper, cobalt, germanium and iron(III) is obtained.
  • Poster
    "24 Stunden für Ressourceneffizienz", Ressourceneffizienz-Kongress für Nachwuchsforscherinnen und Nachwuchsforscher, 14.-15.02.2017, Pforzheim, Deutschland

Registration No. 26622 - Permalink


Atomistic study of the hardening of ferritic iron by Ni-Cr decorated dislocation loops
Bonny, G.; Bakaev, A.; Terentyev, D.; Zhurkin, E.; Posselt, M.
The exact nature of the radiation defects causing hardening in reactor structural steels consists of several components that are not yet clearly determined. While generally, the hardening is attributed to dislocation loops, voids and secondary phases (radiation-induced precipitates), recent advanced experimental and computational studies point to the importance of solute-rich clusters (SRCs). Depending on the exact composition of the steel, SRCs may contain Mn, Ni and Cu (e.g. in reactor pressure vessel steels) or Ni, Cr, Si, Mn (e.g. in high-chromium steels for generation IV and fusion applications). One of the hypotheses currently implied to explain their formation is the process of radiation-induced diffusion and segregation of these elements to small dislocation loops (heterogeneous nucleation), so that the distinction between SRCs and loops becomes somewhat blurred. In this work, we perform an atomistic study to investigate the enrichment of loops by Ni and Cr solutes and their interaction with an edge dislocation. The dislocation loops decorated with Ni and Cr solutes are obtained by Monte Carlo simulations, while the effect of solute segregation on the loop's strength and interaction mechanism is then addressed by large scale molecular dynamics simulations. The synergy of the Cr-Ni interaction and their competition to occupy positions in the dislocation loop core are specifically clarified.
Keywords: Iron, Ferritic steel, Precipitation, Dislocation, Molecular dynamics
  • Journal of Nuclear Materials 498(2018), 430-437

Registration No. 26621 - Permalink


The Transition from a Thin Film to a Full Magnonic Crystal and the Role of the Demagnetizing Field
Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Lenz, K.; Lindner, J.; Landeros, P.; Fassbender, J.
The transition from a film to a full magnonic crystal is studied by sequentially ion-milling a 40 nm Ni80Fe20 film. The spin-wave resonances of each stage are detected by ferromagnetic resonance for both in-plain field main axes. Theoretical calculations and micromagnetic simulations yield the individual mode profiles, which are analyzed in order to track changes of the mode character. The latter is strongly linked to the evolution of the internal demagnetizing field. It’s role is further studied by electron holography measurements of a hybrid magnonic crystal with 10 nm deep surface modulation. The complex effects of mode coupling, mode localization and anisotropy-like contributions by the internal field are unraveled. Simple transition rules from the 𝑛th film mode to the 𝑚th mode of the full magnonic crystal are formulated.
Keywords: Ferromagnetic resonance, magnonic crystals, demagnetizing fields, thin films, spin waves
  • Poster
    81. Frühjahrstagung der Sektion Kondensierte Materie der DPG, 19.-24.03.2017, Dresden, Deutschland

Registration No. 26619 - Permalink


The Role of the Demagnetizing Fields in the Transition from Thin Films to Magnonic Crystals
Lenz, K.; Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Lindner, J.; Landeros, P.; Fassbender, J.
The transition from a film to a full magnonic crystal is studied by sequentially ion-milling a periodic stripe pattern into a 40 nm thick Ni$_{80}$Fe$_{20}$ film. The spin-wave resonances of each milling stage are detected by ferromagnetic resonance for both in-plain main field axes, i.e. parallel and perpendicular to the stripe pattern. Theoretical calculations and micromagnetic simulations yield the individual mode profiles, which are analyzed in order to track changes of the mode character. The latter is strongly linked to the evolution of the internal demagnetizing field. It’s role is further studied and imaged by electron holography measurements on a hybrid magnonic crystal, which is made with a 10 nm deep surface modulation. The complex effects of mode coupling, mode localization, and anisotropy-like contributions by the internal field are unraveled. Simple transition rules from the $𝑛^_\mathrm{th}$ film mode to the $𝑚\mathrm{th}$ mode of the full magnonic crystal are formulated.
This work has been supported by DFG grant KL2443/5-1.
Keywords: Ferromagnetic resonance, magnonic crystals, demagnetizing fields
  • Poster
    Magnonics 2017, 07.-11.08.2017, Oxford, United Kingdom

Registration No. 26618 - Permalink


Maternal immune activation results in complex microglial transcriptome signature in the adult offspring that is reversed by minocycline treatment
Mattei, D.; Ivanov, A.; Ferrai, C.; Jordan, P.; Guneykaya, D.; Buonfiglioli, A.; Schaafsma, W.; Przanowski, P.; Deuther-Conrad, W.; Brust, P.; Hesse, S.; Patt, M.; Sabri, O.; Ross, T. L.; Eggen, B. J. L.; Bodecke, E. W. G. M.; Kaminska, B.; Beule, D.; Pombo, A.; Kettenmann, H.; Wolf, S. A.
Maternal immune activation (MIA) during pregnancy has been linked to an increased risk of developing psychiatric pathologies in later life. This link may be bridged by a defective microglial phenotype in the offspring induced by MIA, as microglia have key roles in the development and maintenance of neuronal signaling in the central nervous system. The beneficial effects of the immunomodulatory treatment with minocycline on schizophrenic patients are consistent with this hypothesis. Using the MIA mouse model, we found an altered microglial transcriptome and phagocytic function in the adult offspring accompanied by behavioral abnormalities. The changes in microglial phagocytosis on a functional and transcriptional level were similar to those observed in a mouse model of Alzheimer’s disease hinting to a related microglial phenotype in neurodegenerative and psychiatric disorders. Minocycline treatment of adult MIA offspring reverted completely the transcriptional, functional and behavioral deficits, highlighting the potential benefits of therapeutic targeting of microglia in psychiatric disorders.

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Registration No. 26617 - Permalink


Circular Economy
Reuter, M. A.
Prof Markus Reuter, Director at the Helmholtz Institute for Resource Technology in Freiberg in Germany, was awarded the degree Doctor of Engineering (DEng), honoris causa for his outstanding contributions to the science and technology of the production and recycling of metals, as well as to the integration of academic research and practice. His work on recycling, design for recycling, and resource efficiency has contributed towards the creation of processes and tools to develop a sustainable society.
  • Lecture (others)
    Awarding of Degrees, Diplomas and Certificates (including Doctoral Degrees), 04.-08.12.2017, Stellenbosch, Südafrika

Registration No. 26616 - Permalink


Digitizing the Circular Economy
Reuter, M. A.
Metallurgy is a key enabler of a circular economy (CE), its digitization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of metallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT. It is the linkage of the global carrier metallurgical processing system infrastructure that maximizes the recovery of all minor and technology elements in its associated refining metallurgical infrastructure. This course will illustrate some of these concepts with hands-on training.
Keywords: circular economy, recycling
  • Invited lecture (Conferences)
    Digitizing the Circular Economy / Summer school, 17.-20.07.2017, Leuven, Belgien

Registration No. 26615 - Permalink


Attachment of non-spherical particles to the fluidic surface – Experiment and direct numerical simulations
Lecrivain, G.; Eckert, K.; Hampel, U.; Yamamoto, R.; Taniguchi, T.
The attachment of colloidal particles to the fluidic surface of immersed fluid droplets is central to a wide variety of industrial applications, among which stand out the recovery of minerals by gas bubbles, a process known as flotation. The flotation process involves the attachment of hydrophobised colloidal particles to the surface of rising air bubbles, while the commercially valueless hydrophilic material settles down the cell. Experimental and numerical works dealing with the attachment of non-spherical particles to a fluidic interface are here presented. Using an optical microbubble sensor the various microprocesses associated with the colloidal attachment of elongated fibers are first investigated. In a second stage direct numerical simulations are used to predict the dynamics of such particles at a fluidic interface. Unlike spherical particles, it is found that plate-like particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force.
Keywords: Flotation Fundamentals: Physics and Chemistry / bubble-particle interactions
  • Poster
    Flotation '17, 13.-16.11.2017, Cape Town, South Africa

Registration No. 26613 - Permalink


Structure variations within certain rare earth-disilicides
Nentwich, M.; Zschornak, M.; Sonntag, M.; Gumeniuk, R.; Gemming, S.; Leisegang, T.; Meyer, D. C.
The dimorphism of the RSi2 and R2TSi3 compounds is a well known phenomenon (R is an alkaline earth metal, rare earth metal or actinoide, T is a transition metal). They crystallize in structures, which derive from hexagonal AlB2 or tetragonal ThSi2 prototypes. Despite their local similarities, both prototypes do not have a common root in the Bärnighausen diagram, which summarizes the symmetry relations between the high symmetrical basic structures and their lower symmetric variations.
We performed an extensive literature research based on more than 400 structure reports of the RSi2 and R2TSi3 compounds. To gain an overview of the various structure reports within these compounds we summarized composition, lattice parameters a and c, ratios c/a, formula units per unit cell, and structure types in an extensive table. We performed DFT calculations on carefully chosen compounds to evaluate the probability of a successful synthesis. Finally, we discuss peculiarities of symmetry distribution among the RSi2 and R2TSi3 compounds and several correlations related to structural parameters.
We found that the thermal treatment has a massive effect to the formation of superstructures. Furthermore, there are two different kinds of hexagonal R2TSi3 compounds being ionic or metallic, depending on the R element. Additionally, the main influence to the variation of the Si-T bonds is the electronic interplay between R element and Si lattice rather than the R radii.
Keywords: rare earth, silicides, density-functional
  • Lecture (Conference)
    IUCR 2017 - 24th Congress of the International Union of Crystallography, 21.-27.08.2017, Hyderabad, Indien

Registration No. 26612 - Permalink


THz-spectroscopic studies on electron dynamics in a GaAs single quantum well and an InAs single quantum dot
Schneider, H.; Schmidt, J.; Stephan, D.; Bhattacharyya, J.; Winnerl, S.; Dimakis, E.; Helm, M.
Intense, spectrally narrow terahertz fields from the free-electron laser (FEL) facility FELBE in Dresden, Germany, provide interesting opportunities for investigating the carrier dynamics in III-V semiconductor nanostructures. This talk will focus on recent FEL studies on dressing intersubband transitions in a wide GaAs single quantum well using terahertz time-domain spectroscopy, and on exciton dynamics in a single InAs/GaAs quantum dot using time-dependent photoluminescence.
Keywords: terahertz free-electron laser, intersubband, exciton, quantum well, quantum dot
  • Invited lecture (Conferences)
    14-th International Conference on Intersubband Transitions in Quantum Wells (ITQW2017), 10.-15.09.2017, Singapore, Singapore

Registration No. 26611 - Permalink


Luminescence of defects in the structural transformation of layered tin dichalcogenides
Sutter, P.; Komsa, H.-P.; Krasheninnikov, A. V.ORC; Huang, Y.; Sutter, E.
Layered tin sulfide semiconductors are both of fundamental interest and attractive for energy conversion applications. Sn sulfides crystallize in several stable bulk phases with different Sn:S ratios (SnS2, Sn2S3, and SnS), which can transform into phases with a lower sulfur concentration by introduction of sulfur vacancies (VS). How this complex behavior affects the optoelectronic properties remains largely unknown but is of key importance for understanding light-matter interactions in this family of layered materials. Here, we use the capability to induce VS and drive a transformation between few-layer SnS2 and SnS by electron beam irradiation, combined with in-situ cathodolumines- cence spectroscopy and ab-initio calculations to probe the role of defects in the luminescence of these materials. In addition to the characteristic band-edge emission of the endpoint structures, our results show emerging luminescence features accompanying the SnS2 to SnS transformation. Comparison with calculations indicates that the most prominent emission in SnS2 with sulfur vacancies is not due to lumi- nescence from a defect level but involves recombination of excitons bound to neutral VS in SnS2. These findings provide insight into the intrinsic and defect-related optoelectronic properties of Sn chal- cogenide semiconductors.
Keywords: 2D materials, spectroscopy, defects, first-principles calculations

Registration No. 26610 - Permalink


Terahertz dephasing of Landau level transitions in graphene
Schneider, H.; König-Otto, J. C.; Pashkin, A.; Helm, M.; Winnerl, S.; Wang, Y.; Belyanin, A.
Using degenerate four-wave mixing (DFWM), we have investigated the coherent polarization between the lowest Landau levels in graphene under resonant excitation with narrowband THz pulses. A pronounced DFWM signal is observed and its dependence on THz field strength and magnetic field detuning is explored and compared with theoretical expectations.
Keywords: terahertz, graphene, four-wave mixing, coherent polarization, free-electron laser
  • Lecture (Conference)
    The 42nd International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2017), 27.08.-01.09.2017, Cancun, Mexico
  • Contribution to proceedings
    The 42nd International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2017), 27.08.-01.09.2017, Cancun, Mexico
    Proceedings of the IRMMW-THz'2017
    DOI: 10.1109/IRMMW-THz.2017.8066873

Registration No. 26609 - Permalink


The Exchange bias in oxygen-implanted Co/Au thin film heterostructures
Perzanowski, M.; Gregor-Pawłowski, J.; Zarzycki, A.; Böttger, R.; Hübner, R.; Potzger, K.; Marszałek, M.
Magnetic systems exhibiting exchange bias effect are being considered as functional parts of modern data storage devices. A model system for the investigation of this effect is an antiferromagnetic-ferromagnetic CoO/Co interface. In this paper we present the studies of magnetic properties of Co-CoO/Au multilayers where the cobalt oxide was formed by oxygen ion beam implantation. Special emphasis is given to the role of the oxygen concentration profile in the magnetic properties. By properly designed the implantation conditions (ion beam energy and fluence) it is possible to fabricate a system revealing controlled stepwise magnetization reversal process. This underlines the great potential of this approach to tailor the magnetic properties through modification of implantation profiles.

This work was supported by DAAD Service with contract No. PPP-PL 57214850 „Magnetic anisotropies in cobalt heterostructures induced by oxidation”.
Keywords: Ion Implantation Magnetic multilayers
  • Poster
    The European Conference Physics of Magnetism 2017, PM’17, 26.-30.06.2017, Poznan, Polen

Registration No. 26607 - Permalink


Metallurgy key enabler of the Circular Economy
Reuter, M. A.
Metallurgy is a key enabler of a circular economy (CE), its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated.
Keywords: Circular Economy, Circular Economy Engineering, Fairphone, Recycling
  • Lecture (others)
    Workshop, 30.11.2017, Madrid, Spanien

Registration No. 26606 - Permalink


Phase Formation and Selectivity on Cr (co-)Doped TiOU+2082 through Interface Engineering and Post-Deposition Flash Lamp Annealing
Gago, R.; Prucnal, S.; Palomares, J.; Jiménez, I.; Hübner, R.
Many applications of TiO2 partially rely on its good performance as solvent for numerous impurities [1]. In particular, metal (cation) dopants have been used to functionalize or enhance TiO2 as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. One of the most interesting properties of TiO2 relies on its photoactivity, exploited in many applications from catalysis, hydrogen production, pigments or solar cells [2]. However, TiO2 is mostly active in the ultraviolet (UV) region of the solar spectrum (band-gap > 3 eV) and there is a great interest in band-gap narrowing of TiO2 to achieve visible-light (VISL) response [2]. Metal doping do so and increases VISL absorption significantly but, unfortunately, introduces structural distortions in the host matrix that result in carrier recombination centers [5]. Apart from the structural quality, another relevant consideration on the production of doped TiO2 relies on the particular oxide matrix phase (anatase/rutile) [6]. For example, anatase has superior photoactivity than rutile although phase mixtures with high anatase content may present even higher photoactivity [7]. Therefore, special attention should also be devoted to the phase selectivity. Moreover, (heavily) doped TiO2 may display a completely different electronic structure that the pristine oxide material.
The aim of this study is to promote customized phase formation in Cr (co-)doped TiO2 films produced by magnetron co-sputtering. Special attention is paid to the structural arrangements around host and dopant sites from the X-ray absorption near-edge structure. We report the conditions driving to single- or mixed-phase formation with the novelty of exploring film architectures based on interface engineering and/or post-deposition flash-lamp annealing (FLA) [8]. The latter is a non-contact rapid thermal processing extensively used in Microelectronics but yet to be explored in the present context. Hence, FLA can be attractive for many industrial applications dealing with the synthesis of band-gap engineered TiO2-based materials.
REFERENCES:
[1] Sacerdoti et al., J. Solid State Chem. 177, 1781 (2004); [2] Henderson, Surf. Sci. Rep. 66, 185 (2011); [3] Matsumoto et al. Science 291, 854 (2001); [4] Furubayashi et al., Appl. Phys. Lett. 86, 252101 (2005); [5] Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [6] Yang, et al., Phys. Rev. B 76, 195201 (2007); [7] Scanlon et al., Nat. Mater. 12, 798 (2013); [8] D. Reichel et al., Phys. Status Solidi C 9, 2045 (2012)
  • Invited lecture (Conferences)
    2017 MRS Fall Meeting & Exhibit, 26.11.-01.12.2017, Boston, MA, USA

Registration No. 26600 - Permalink


Energy-filtered TEM studies on silicon nanoparticles acting as quantum dots in single electron transistors
Wolf, D.; Xu, X.; Prüfer, T.; Hlawacek, G.; Bischoff, L.; Möller, W.; Engelmann, H.-J.; Facsko, S.; von Borany, J.; Heinig, K.-H.; Hübner, R.
The miniaturization of computing devices and the introduction of the internet of things generate an increasing demand for the development of low-power devices. Single electron transistors (SETs) are ideally suited for this demand, because they are promising very low power dissipation devices. For roomtemperature operation of an SET it is necessary to create a single quantum dot (QD) with a diameter below 5 nm exactly positioned between source and drain at a tunnel distance of only a few nanometers. Within the IONS4SET project [1], we aim to achieve this goal by ion irradiation induced Si-SiO2 mixing and subsequent thermally activated self-assembly of single Si nanocrystals surrounded by a thin SiO2 layer. This process is illustrated in Fig. 1 by means of simulations results.
Here, we present energy-filtered (EF)TEM studies in order to monitor the influence of process parameters, such as stack geometry, ion fluence for irradiation, annealing temperature and annealing time, on the self-assembly of Si QDs. Fig. 2 shows representative EFTEM micrographs of a Si-SiO2-Si layer stack imaged using different electron energy-loss (EEL) windows. The Si plasmon-loss filtered images yield thereby the best signal-to-noise for detection of Si nanodots, because the Si plasmon peak is the most intense peak with a relatively small FWHM of 4 eV in the EEL spectrum.
Moreover, since the obtained (raw) EFTEM images provide only qualitative information about the Si concentration in the oxide layer, they cannot give a clear answer if for example the observed contrast corresponds to one or more Si nanodots (NDs) in projection. Therefore, EFTEM images are quantified further by converting them into so-called thickness over mean free path length (MFPL) t/λSi maps, in which λSi is the MFPL corresponding to the chosen energy range. The experimental t/λSi maps are then compared with simulated t/λSi maps of a single Si ND. Fig. 3 depicts that our approach enables us not only to detect single Si nanodots (Fig. 3c,e) but also to count them if they are arranged in projection direction of the electron beam (Fig. 3d,f). For these experiments, the layer stacks were irradiated with Ne+ ions within an Orion NanoFab (Zeiss). This allows controlled line or point irradiation and ensures Si QD formation within a confined region. In a next step, confined regions will be established by fabricated nanopillars that enhances reproducibility as the volume relevant for the self-assembly of the nanocluster will be better defined.
[1] We thank for financial support within the European Union"s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET).
  • Lecture (Conference)
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland
  • Contribution to proceedings
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland, 12-14

Registration No. 26599 - Permalink


Insights into the 3D electric potential structure of III-V semiconductor core-multishell nanowires through combined STEM and holographic tomography
Wolf, D.; Hübner, R.; Sturm, S.; Lubk, A.
Off-axis electron holographic tomography (EHT) has been successfully applied to reveal the 3D structure of III-V semiconductor core-shell nanowires (NWs) [1,2]. The technique probes the phase shift of an electron wave transmitted through such a NW that is proportional to the NWs projected electrostatic potential. Thus, a tilt series of phase images (projected potentials) can be used as input to compute a 3D tomogram of the electrostatic potential by tomographic reconstruction algorithms. Typically, the recovered 3D potential is dominated by the mean inner potential (MIP), which is related to the materials composition. Consequently, space charge potentials determining for example the electric properties, e.g., at interfaces or pn-junctions in semiconductors [2] may be superimposed by MIP variations caused by compositional changes within the heterostructures.
Here, we show on the example of a GaAs/AlGaAs core-multishell NW, how the space charge potentials can be uncovered from materials contrast (MIP) by determining the latter independently: To this end, high-angle annular dark-field (HAADF) STEM tomography was applied in addition to EHT on the same NW. STEM tomograms provide solely materials contrast that depends exponentially on the atomic number. Fig. 1 compares both methods in terms of the relation between reconstructed signal and projected property, exemplary for three different tomogram regions identified as pure Au, GaAs and AlGaAs: In case of EHT between the reconstructed potential and the MIP, and in case of STEM tomography between the reconstructed intensity and the atomic number. The latter relation enables converting the STEM tomogram in units of (mean) atomic numbers.
Tilt series were acquired from -70° to +71° with 3° tilt steps in holography mode, and from -68° to +68° with 2° tilt steps in STEM mode. Since phase images of axially scattered electrons are used for EHT, it suffers much more from diffraction contrast than STEM tomography (high-angle scattering). Consequently, only 39 projections could be used for tomographic reconstruction in the case of EHT compared to 68 in the case of STEM tomography. For this reason, resolution and contrast in the 3D potential are slightly lower than in the STEM tomogram, which can be seen on the cross-section of the NW in Fig. 2. Nevertheless, the core-shell structure, the ca. (5-10) nm thick GaAs shell acting as quantum well tube (QWT), and unintended Al segregations are clearly resolved in both cases. Last but not least, longitudinal slices (Fig.3) exhibit clear differences of both tomograms that strongly suggest additional local space-charge related potentials to be investigated in greater detail in a next step.
References:
[1] A Lubk, D Wolf, P Prete, N Lovergine, T Niermann, S Sturm and H Lichte, Phys. Rev. B 90 (2014) p. 125404.
[2] D Wolf, A Lubk, P Prete, N Lovergine and H Lichte, J. Phys. D: Appl. Phys. 49 (2016) p. 364004
[3] We thank N Lovergine of University of Salento, Lecce for provision of the samples.
[4] We thank the group of Michael Lehmann at TU Berlin for access to the TEM FEI Titan 80-300 Berlin Holography Special.
[5] DW acknowledges financial support within the European Union"s Horizon 2020 research and innovation program under Grant Agreement No 688072 (Project IONS4SET). AL has received funding from the European Research Council (ERC) under the European Union"s Horizon 2020 research and innovation programme (grant agreement No 715620).
  • Poster
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland
  • Contribution to proceedings
    Microscopy Conference 2017, MC 2017, 21.-25.08.2017, Lausanne, Switzerland, 753-755

Registration No. 26598 - Permalink


Subsurface Engineering of Silicon for 3D Devices
Tokel, O.; Turnali, A.; Makey, G.; Elahi, P.; Ilday, S.; Colakoglu, T.; Yavuz, O.; Hübner, R.; Zolfaghari, M.; Pavlov, I.; Bek, A.; Turan, R.; Ilday, O.
Recently we have demonstrated a new 3D-laser-fabrication method which enabled, for the first time, creating highly-controlled subsurface structural modifications (structural imperfections, or defects) buried deep inside Silicon (Si) wafers [1]. Characterizing the material properties of these subsurface Si structures are very critical towards enabling new optical and micro-mechanical applications inside chips [2,3]. Here, we present optical, chemical and microscopic analysis of these buried structures. Specifically, Transmission Electron Microscopy (TEM) studies, Optical Birefringence Analysis and Selective Chemical Etching analysis of the modifications will be presented. Infrared Transmission Microscopy will be shown to be applicable for subsurface imaging, providing a diagnostic tool without damaging the samples.

Material properties of the disruptions in the crystal lattice are then exploited for fabricating various micro-devices. For instance, oxidation-reduction chemistry on laser-induced modifications enables the creation of highly-controllable, uniform and large-area micropillar arrays for solar cell applications, embedded microfludic channels for chip cooling and thru-Si vias for electrical interconnects in Si. These elements, which are challenging to form with conventional methods, can find use in various MEMS and electronics applications. The optical properties (refractive index change) of the structures are used to fabricate functional components such as lenses and gratings buried in chips. Further, the birefringence effect induced in Si may lead to holograms and other photonic applications, such as creating wave plates and polarizers. These functional optical and MEMS elements created inside Si, may find use in imaging and sensing in the near- and mid-infrared wavelength range, as well as in micro-devices towards micro-surgical tools, micro-motors, and micro-resonators. Thus, these capabilities are leading to a new fabrication approach in Si, which is fully CMOS compatible, rapid and mechanically robust, and builds on the optical,electrical and chemical properties of the modified volumes in Si.

[1] Tokel et. al., arxiv.org/abs/1409.2827
[2] Tokel et. al, Direct Laser Writing of Volume Fresnel Zone Plates in Silicon., CLEO/Europe - EQEC, Munich, Germany, 2015.
[3] Tokel et. al., 3D Functional Elements Deep Inside Silicon with Nonlinear Laser Lithography, APS March Meeting, Baltimore, USA, 2016.
  • Poster
    2017 MRS Spring Meeting & Exhibit, 17.-21.04.2017, Phoenix, AZ, USA

Registration No. 26597 - Permalink


Application of Ion Beams to Fabricate and Modify Properties of Dilute Ferromagnetic Semiconductors
Yuan, Y.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.
Dilute ferromagnetic semiconductors (DFS) have been investigated for more than two decades due to their potentials for spintronics. Mn doped III-V semiconductors have been regarded as the prototype of the type. In this contribution, we will show how ion beams can be utilized in fabricating and modifying DFS. First, ion implantation followed by pulsed laser melting (II-PLM) provides an alternative to low-temperature molecular beam epitaxy (LTMBE) to prepare diverse DFS. The prepared DFSs exhibit pronounced magnetic anisotropy, large X-ray magnetic circular dichroism, anomalous Hall effect and magnetoresistance [1-9]. Going beyond LTMBE, II-PLM is successful to bring two new members, GaMnP and InMnP, into the family of III-Mn-V. Both GaMnP and InMnP show clear signatures of ferromagnetism and an insulating behavior. Second, helium ions can be used to precisely compensate the holes while keeping the Mn concentration constant [10-12].
For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC over a wide temperature range with carrier compensation while the conduction is changed from metallic to insulating. We can tune the uniaxial magnetic easy axis of (Ga,Mn)(As,P) from out-of-plane to in-plane with an isotropic-like intermediate state. These materials synthesized or modified by ion beams provide an alternative avenue to understand how carrier-mediated ferromagnetism is influenced by localization.
  • Lecture (Conference)
    20th International Conference on Surface Modification of Materials by Ion Beams, 09.-14.07.2017, Lisbon, Portugal

Registration No. 26596 - Permalink


Modelling of turbulence modulation in bubbly flows with the aid of DNS
Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.
Modelling of turbulence modulation in bubbly flows with the aid of DNS data
  • Poster
    15th Multiphase Flow Conference and Short Course, 14.-17.11.2017, Dresden, Deuschland

Registration No. 26595 - Permalink


new model for bubble-induced turbulence based on direct numerical simulation data
Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.
Three main issues are addressed in the present study. First, an appropriate time scale is selected with the aid of the energy spectra determined on the basis of the DNS data. Then, links between the unclosed terms in the transport equations of the turbulence quantities and the DNS data for small bubbles are established. Third, a suitably chosen iterative procedure employing the full Reynolds-averaged model provides suitable coefficients for the closure of the terms resulting from BIT while largely removing the influence of others. Here, using DNS data with iterations to obtain term-by-term match (Figure 1b) in the model equations avoids pitfalls of ad hoc models targeting the TKE only. At the same time these results validate the closure, exhibiting very good agreement with the DNS and better performance than the standard closures. Beyond the resulting model itself the study also furnishes a systematic procedure which is of general use. The model is now ready for use and can be employed in practical Euler-Euler simulations.
  • Lecture (Conference)
    The 3rd International Conference on Numerical Methods in Multiphase Flows, 26.-29.06.2017, Tokyo, Japan

Registration No. 26594 - Permalink


DNS-based RANS closure for bubble-induced turbulence
Ma, T.; Santarelli, C.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.
DNS-based RANS closure for bubble-induced turbulence
Keywords: DNS, RANS, bubble-induced turbulence
  • Lecture (Conference)
    ProcessNet Jahrestreffen Dresden, 14.-17.03.2017, Dresden, Deuschland

Registration No. 26593 - Permalink


A contribution to turbulence modelling in bubbly flows
Ma, T.
Modelling turbulence in bubbly flows that arise in the engineering and environment is of great challenges for multiphase Computational Fluid Dynamics. In the present book various turbulence modelling approaches are investigated in bubble columns and bubbly channel flows. The considered approaches contain Scale Resolving Simulations and the traditional Reynolds-averaged Navier-Stokes closure. The focus is set on the representation of the so-called bubble-induced turbulence in the modelling framework. A major chapter addresses a complete route to construct such a model embedded in Euler-Euler approach with the aid of Direct Numerical Simulation data. This procedure is employed to propose an improved model for bubble-induced turbulence.
Keywords: Scale Resolving Simulation, Direct Numerical Simulation data, bubble-induced turbulence
  • Book (Authorship)
    Dresden: TUDpress, 2017

Registration No. 26592 - Permalink


Simulation of Reconfigurable Field-effect Transistors: Impact of the NiSi2-Si Interfaces, Strain, and Crystal Orientation
Fuchs, F.; Schuster, J.; Gemming, S.
Reconfigurable transistors (RFETs) can be switched between electron and hole current by changing the polarity of the gate potential. The device performance of such a transistor is strongly dominated by the contact physics.
In this work, the electron transport across the NiSi2-Si interface is studied using the NEGF formalism and density functional theory. A new model is presented which relates the electron transport through the interface to the transfer characteristic of an RFET. The model is compared to experimental data showing good agreement.
Based on the model, the influence of strain and the choice of the crystal orientation is discussed. It is demonstrated that best symmetry between electron and hole current is achieved for the <110> orientation. Furthermore, this symmetry can be tuned by strain, which is not possible for the <100> and <112> orientations. A discussion of these differences based on band structure analysis will be given, too.
Keywords: Reconfigurable field-effect transistor, silicon, interface
  • Lecture (Conference)
    IHRS NanoNet Annual Workshop 2017, 16.-18.08.2017, Neuklingenberg, Deutschland

Registration No. 26591 - Permalink


Injection locking of constriction based spin Hall nano-oscillators
Hache, T.; Weinhold, T.; Arekapudi, S. S. P. K.; Hellwig, O.; Schultheiss, H.
Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs under the forcing influence of an added alternating current. We show the possibility of injection locking between the applied external signal and the auto-oscillations driven by a direct current. Within the locking range the frequency of the auto-oscillations is forced to the external stimulus. In addition the intensity of the oscillations is increased strongly and the linewidth decreases. Due to the controllability of the auto-oscillations of the magnetization, injection locking can be used to influence the properties of future communication technologies, i.e. based on synchronized constriction based spin Hall nano-oscillators arrays.
Keywords: spin Hall, spin Hall nano-oscillators, auto-oscillations, injection locking, phase locking, Auto-Oszillationen, Spin-Hall Nanooszillatoren
  • Poster
    2017 European School on Magnetism: Condensed Matter Magnetism : bulk meets nano, 09.-20.10.2017, Cargese, France

Registration No. 26590 - Permalink


Möglichkeiten der Kreislaufwirtschaft
Reuter, M. A.
Knapp 780.000 Tonnen Elektro-Altgeräte wurden laut Umweltbundesamt im Jahr 2010 in Deutschland gesammelt. Das entspricht 8,8 Kilogramm pro Einwohner und Jahr. Viele wertvolle Metalle, Legierungen, funktionale Materialien sowie Kunststoffe sind darin enthalten. Wie kann man die Wertstoffe im Sinne einer Kreislaufwirtschaft (Circular Economy) bestmöglich zurückgewinnen, um neue Güter herzustellen? Was leistet Recycling schon heute? Was müsste getan werden, um es weiter zu verbessern? Und wie energetisch sinnvoll ist es überhaupt?
Prof. Markus Reuter, Direktor am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) des HZDR, widmet sich diesen Fragen. Der Metallurge und Recyclingexperte beschäftigt sich mit der Wiederverwertbarkeit von Produkten und erforscht innovative, digitale Systeme und Prozesse für optimales Recycling.
Keywords: Kreislaufwirtschaft
  • Lecture (others)
    Möglichkeiten der Kreislaufwirtschaft / Wintersemester der Seniorenakademie, 06.11.2017, Dresden, Deutschland

Registration No. 26589 - Permalink


Auto-oscillations in double constriction spin Hall nano-oscillators
Hache, T.; Wagner, K.; Arekapudi, S. S. P. K.; Hellwig, O.; Lindner, J.; Schultheiss, H.
Spin-Hall nano-oscillators (SHNOs) are modern auto-oscillation devices. Their simple geometry allows for an optical characterization by Brillouin-Light-Scattering microscopy at room temperature. Here we report on the observation of auto-oscillations in constriction based SHNOs. These are devices where the current density is increased locally due to lateral confinement. Hence, the spin current generated by the spin Hall effect can create well defined hot-spots for auto-oscillations.
We present BLS measurements of auto-oscillations in Co60Fe20B20(5 nm)/Pt(7 nm) based samples with two interacting, neighbouring nanoconstrictions.
The precession amplitude in these samples can be driven far from equilibrium, resulting in clear nonlinear signatures in the spinwave spectra. The spatial distributions of the observed modes and current dependencies are shown.
Keywords: spin Hall, spin Hall nano-oscillators, Spin-Hall Nanooszillatoren, spin current, auto-oscillations, Autooszillationen
  • Poster
    DPG-Frühjahrstagung SKM, 19.-24.03.2017, Dresden, Deutschland

Registration No. 26588 - Permalink


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