Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
More Moore or More-than-Moore or Nothing more? A nanoView on silicon & germanium...
Skorupa, W.;
It is obvious that we approach the limits of Moore’s law and have to think about moving on, or, move different route, or, may be, move not anymore? Having spent more than 35 years with microelectronics and chip technology the answer to this question is not simple for me… In this talk I will try to discuss some aspects of that kind of “cultural doubting”, but will not miss to present also a review of our recent results regarding advanced processing for silicon and germanium nanostructures based on ion beam processing and/or short time annealing in the millisecond range: a) III-V nanocrystals heteroepitaxially arranged on silicon nanowires (S. Prucnal et al., NanoLett. 11, 2814 (2011)) b) Superconductivity from Ga-rich nanoscale layers at Si/Ge-SiO2 interfaces (J. Fiedler et al., Phys.Rev. B 85, 134530 (2012)) c) Horizontal silicon nanowires on insulator by ion beam erosion (X. Ou et al., AIP Advances 1, 042174 (2011))
Keywords: short time annealing, Moore’s law, ion beam processing
  • Invited lecture (Conferences)
    E-MRS 2012 FALL MEETING, 17.-21.09.2012, Warsaw, Poland

Publ.-Id: 18372 - Permalink


Dot and Ripple Nanopatterns on Ge Surfaces by Normal and Tilted Bombardment with Bi2 and Bi3 Ions
Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.;
The self-organisation of surface pattern on (001)Ge was investigated after bombardment with different heavy bismuth species of monomers Bi+, Bi++ and clusters Bi2+, Bi3+, Bi4+, and Bi3++, obtained from a Bi-liquid metal ion source [1] in a mass separating 30 kV focused ion beam system. The surface patterns, depending on the angle of ion cluster incidence at ion irradiation differ drastically from the well-known porous or sponge-like nanostructures formed on Ge at monomer ion irradiation so far: the surface remains crystalline as proven by Raman measurements, and the dots and ripples heights were in the order of their wavelengths in contrast to monomer irradiation where an porous surface layer was obtained. The structure formation was investigated in the fluence range from1015 to 1017 ions/cm2 as a function of angle of incidence and energy per atom of the different projectile ions. The high mass of the cluster ions leads to a patterning mechanism different from the Bradley-Harper model, which becomes strikingly apparent by the crystalline Ge surface. An identified threshold of this new patterning mode could help to understand the mechanism: The ion-impact-induced deposition of energy per volume (as estimated by SRIM) must exceed a value which coincides with the energy needed for melting. Thus, Bi segregation during melt pool re-solidification and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed. [1] L. Bischoff, W. Pilz, P. Mazarov, and A.D. Wieck, Appl. Phys. A 99 (2010) 145.
Keywords: ion-solid-interaction, heavy polyatomic ions, germanium, surface patters, modeling
  • Poster
    MRS 2011 Spring Meeting, 26.-29.04.2011, San Francisco, USA

Publ.-Id: 18371 - Permalink


Anticorrosion studies for pipe organ-related materials using plasma processing
Skorupa, W.; Cherkouk, C.; Henke, D.; Prucnal, S.; Reuther, H.; Werner, H.; Pfeifer, D.; Eule, A.-C.;
There is no doubt that lead (and its alloys with tin) and brass materials do not really belong to the stuff of primary interest for advanced materials studies. Also, lead gets more and more removed from the technology of soldering in electronics etc., and brass is, at least, a material of doubtful character if treated in vacuum. On the other hand these metals are of primary interest for the construction of pipe organs, and that already for millenia! Corrosion of lead and brass are a serious obstacle in old and even new pipe organs if the microclimate inside of the organ, the church, the concert hall etc. is containing special residuals or impurities leading to the growth of corrosive layers. Finally, even holes can be “drilled” into metal pipes making them voiceless!
For this end we have started to fight with this problem by using nanotechnology to cover metallic sheets of lead and brass with thin layers of anticorrosive material. Plasma immersion ion implantation of nitrogen was used to keep the technology simple and to have certain intermixed interface layers between the surface and the substrate. AES and XPS demonstrated surface layers with a thickness in the range below 50 nm. The exact composition and mechanism is a matter of discussion yet. Laboratory-based corrosion studies were developed and applied to the plasma-treated surfaces. First results were quite promising and showed strong corrosion resistance, especially for lead. Field studies at historical organs in Saxony and Mecklenburg are ongoing.
Keywords: pipe organ, plasma immersion, corrosion protection, lead, brass
  • Lecture (Conference)
    13th International Conference on Plasma Surface Engineering, 10.-14.09.2012, Garmisch-Partenkirchen, Germany

Publ.-Id: 18370 - Permalink


Shaping of Au and Ge Nanoparticles by Irradiation with Swift Heavy Ions
Heinig, K.-H.; Schmidt, B.; Muecklich, A.; Akhmadaliev, C.;
The driving forces of nanomaterials processing by swift heavy ions as identified by our studies are (i) the materials dependent electronic stopping power, (ii) the volume change upon melting as well as (iii) far-from-equilibrium steady-state solubilities and strongly anisotropic diffusion coefficients. Size distributions, shapes and anisotropies of nanoparticles can be tailored by appropriate tuning of these driving forces. The evolution of Au and Ge nanospheres under swift heavy ion irradiation was studied experimentally and by atomistic computer simulations. Au nanospheres of 15 nm di-ameter elongate to rods, whereas Ge nanospheres become flat. Surprisingly, this shaping as well as the quantitative dependence on experimental conditions can be described completely with classical thermodynamics, which will be demonstrated by our atomistic computer simulation studies: For instance, the ratio (rod length)/(initial sphere diameter) increases with the square root of the ion fluence, and the speed of the elongation follows the law of Hagen-Poiseuille. Of special interest is the nanostructure evolution when en-ergy deposition into the nanoparticle suffice melting only for central tracks. This rare event for broad size distributions can be seen, e.g., in Phys.Rev. B78(2008)054102. Us-ing unimodal size distributions and changing the ion direction during irradiation, tailor-ing of very exotic nanoparticle shapes become feasible.
Keywords: ion-solid-interaction, swift heavy ions, nanoparticles, shaping, electron microscopy, modeling, computer simulations
  • Lecture (Conference)
    MRS 2011 Spring Meeting, 26.-29.04.2011, San Francisco, USA

Publ.-Id: 18369 - Permalink


Response of bacteria in pore water of opalinus clay to addition of nitrate and acetate
Selenska-Pobell, S.; Geissler, A.; Moors, H.; Leys, N.;
The in situ BN experiment performed at the international underground rock laboratory Mont Terry in Switzerland estimates the risks of release of nitrate and organic molecules into the opalinus clay due to the weathering of the bitumen containers, foreseen for disposal of long-living radioactive waste. The changes induced by the bitumen degradation products in the opalinus clay have many different bio-geo-chemical aspects which may facilitate migration of radionuclides. For this reason the BN experiment exploits a set of interdisciplinary (chemical, technical, and biological) approaches [1]. Response of bacteria present in the pore water of the interval 2 of the BN experiment to addition of nitrate, nitrite, and acetate is reported here.
Bacterial diversity in three samples collected from interval 2 of the BN experiment was studied by using ribosomal intergenic spacer amplification (RISA), cloning and sequencing of the 16S rRNA-gene of the RISA amplicons as described in [2]. The first sample was collected before the supplementation, the second sample - one day after the addition of 70 mg/L NO3-, 35 mg/L NO2- and 46 mg/L acetate, and the third sample - five days after the treatment.
The chemical analyses of the samples monitored by Bleyen at al. [1] demonstrated that three days after the supplementation the added nitrate was fully reduced to nitrite. Between the third and the fifth days from the beginning of the experiment fast reduction of nitrite occurred. After the fifth day - complete consumption of acetate was monitored and a process of slow nitrite reduction started which finished with complete removal of the latter two weeks after the supplementation.
The RISA molecular analyses performed in this work demonstrated strong shifting in bacterial community of the interval 2 only 24 hours after the addition of nitrate, nitrite and acetate. The strongly predominant in the untreated sample Firmicutes were almost completely overgrown by Alphaproteobacteria and by one particular population of Pseudomonas stutzeri (Gammaproteobacteria). The latter not identified in the non-supplemented samples. As P. stutzeri can use acetate as electron donor for nitrate reduction our results clearly demonstrate that this species is involved in the above reported [1] rapid reduction of nitrate to nitrite during the first 3 days after the treatment. The RISA analyses demonstrated that P. stutzeri was even more predominant in the sample collected five days after the treatment. On the basis of this result we suggested that this species plays also the major role in the fast reduction of nitrite. Our suggestion is in agreement with the published capability of P. stutzeri to perform fast reduction of nitrite to molecular nitrogen with acetate under conditions similar to ours [3]. The role (if any) of the rest of the bacterial community in the fast nitrate and nitrite reduction has to be cleared.
Analyses of additional samples collected between the 5th and the 14th days after the supplementation is needed in order to clear the role of the other members of the bacterial community of interval 2 in the slow nitrite reduction occurring after the 5th day of the treatment when acetate was completely utilized.

REFERENCES
[1] Bleyen et al. (2012) Clays in natural and engineered barriers for radioactive waste confinement. Montpellier, 22-25.10.2012, p.755.
[2] Selenska-Pobell et al (2001) Ant. Van Leeuvenhoek.79., 149-161.
[3] Strohm et al. (2007) Appl. Environ. Microbiol. 73, 1420-1424.
Keywords: Deposition of nuclear waste, bacterial diversity in opalinus clay
  • Lecture (Conference)
    Mont Terri Project: Joint HT-MA-BN-GD-PCC Meeting, 11.-12.02.2013, St- Ursanne, Switzerland

Publ.-Id: 18368 - Permalink


Millisecond annealing and beyond
Skorupa, W.;
This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material based on a highly doped Ga-rich layer at the surface. Moreover we demonstrated that carrier-mediated ferromagnetism can be reached in manganese-implanted and Laser-annealed Ge. Regarding photovoltaic applications, we dealt with two aspects: (i) the thermal processing of so-called dirty silicon demonstrating a distinct improvement of the metal diffusion suppression compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation Whereas all these examples base on solid phase processing the more sophisticated approach of subsecond thermal processing regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (Nano Lett. 11 (2011) 2814).
Keywords: flash lamp annealing
  • Lecture (others)
    Eingeladener Seminarvortrag, 12.10.2012, Oslo, Norway

Publ.-Id: 18367 - Permalink


Si Nanosponge Embedded in Silica - A More Efficient Thin-film PV Cell Semiconductor?
Heinig, K.-H.; Schmidt, B.; Stegemann, K.-H.; Muecklich, A.; Liedke, B.; Friedrich, D.;
Nanostructured thin-film PV materials are expected to become more and more important due to their high competitiveness in cost reduction. Assemblies composed of quantum dots and/or wires have been reported in which quantum confinement is used as a design parameter. However, there are still problems related to the low-cost fabrication of such structures, and, in case of quantum dots embedded in a dielectric matrix, to charge carrier separation. Here, we present Si nanosponge embedded in silica as a new nanostructured active PV cell material which could overcome such problems. The Si nanosponge has typical feature sizes of 2…4 nm. This is much smaller than the ~100nm of electrochemically etched porous Si, which was studied intensively several years ago. Thus, the nanosponge shows a band gap widening by quantum confinement which allows band gap engineering for optimum adjustment to the solar spectrum. Furthermore, the Si sponge/SiO2 matrix interface is electrically passive which lowers losses. And, the Si sponge is electrically percolated, resulting in an efficient charge carrier separation. Si nanosponge is expected to replace easily a-Si in thin-film PV cell production lines. The PECVD equipment will be used to deposit SiOx instead of a-Si. The Si nanosponge is formed by thermally activated spinodal decomposition of SiOx. The large glass panels of thin-film PV cells allow a low thermal budget only, therefore scanned laser processing with ms dwell times has to be used. EFTEM images of Si nanosponge formed by co-sputtering of SiOx followed by rapid thermal processing are in full agreement with atomistic simulations of the spinodal decomposition process. Electrical and optical properties measured so far are in agreement with the expectations. Studies on the morphology of sponges form by very rapid thermal processing are under way.
Keywords: nanocomposite, silicon, silica, embedded sponge, sputter deposition, spinodal phase separation, computer simulations
  • Poster
    MRS 2011 Spring Meeting, 26.-29.04.2011, San Francisco, USA

Publ.-Id: 18366 - Permalink


Self-organization of Nanopatterns under Ion Irradiation: Atomistic 3D Simulations including Collision Cascades and Thermally Activated Kinetics
Heinig, K.-H.; Liedke, B.; Moeller, W.;
The dominating driving force for self-organisation of surface nanopattern during low-energy ion irradiation is still under discussion. Thus, so far continuum models cannot include 3D non-local processes of ion-solid interactions. On the other hand, till now atomistic simulations could not describe pattern dynamics on the spatiotemporal scale of experiments.
Combining collision cascades of ion impacts with continuum equations [1] is one approach to achieve a better understanding of mechanisms, like surface smoothing by an effective ‘downhill’ mass current which are neglected so far [2][3].
Here we present a novel program package, which unifies atomistic 3D simulations of the col-lision cascades with 3D kinetic Monte-Carlo simulations. Atom relocations were calculated with the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of ener-getic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic lattice Monte Carlo program. Effects like ballistic mass drift or dependence of lo-cal morphology on sputtering yield are automatically included by this approach.
The mechanism of ripple formation induced by local surface currents is studied. The quantita-tive description of current vectors for different environmental parameters, and initial surface condition of sinusoidal structure, can be analized in time and space, following the local atomic drift. Different mechanisms can be distinguished. Without ion irradiation the mass current vec-tors parallel to the surface cause always surface smoothing by Mullins-Herring diffusion. Surface defects created by collsion cascades may inverse the surface mass currents, resulting in self-organization of nanopatterns.
Sputtering violates mass conservation of processes mentioned till now. The majority of pub-lished papers assume that sputtering is the dominating driving force for pattern formation. Here it will be shown that ripple patterns perpendicular to oblique ion impacts originate not from the sputtering process but from defect kinetics. Sputtering dominates only formation of ripple pat-terns parallel to the ion beam at grazing incidence.
[1] S. A. Norris and M. P. Brenner and M. J. Aziz J. Phys. Condens. Matter 21 (2009) 224017.
[2] G. Carter and V. Vishnyakov PRB 54 (1996) 17647.
[3] M. Moseler and P. Gumbsch and C. Casiraghi and A. C. Ferrari and J. Robertson Science 309 (2005) 1545.
Keywords: Computer simulations, kinetic Monte Carlo, TRIM, new algorithmen, nanopatterns, self-organization
  • Invited lecture (Conferences)
    MRS 2011 Spring Meeting, 25.-29.04.2011, San Francisco, USA

Publ.-Id: 18365 - Permalink


Nanoclusters and interfaces under ion irradiation: Inverse Ostwald ripening and pattern formation
Heinig, K.-H.;
Ion irradiation of solids can change well-known processes of structure evolution dramatically. For instance, the thermally activated corsening of nanocluster ensembles embedded in a matrix (i.e. Ostwald ripening) can change to inverse Ostwald ripening under ion irradiation if ion-beam-induced atomic displacements dominate the kinetics. Inverse ripening means that the nanocluster sizes no longer coarsens with time, but all nanocluster reach asymtodically the same size. On the other hand, intense ion-beam-induced displacements can result in self-organization of ordered surface pattern. Here, the competion between thermally activated smoothening and the ion-beam-induced roughening are the driving forces for surface patterning.
Keywords: ion-solid-interaction, inverse Ostwald ripening, self-organization, surface pattern, modeling, computer simulations
  • Lecture (others)
    Seminar, 16.12.2011, Kyoto, Japan

Publ.-Id: 18364 - Permalink


Ion Beam Induced Self-Organization and Modification of Nanostructures
Heinig, K.-H.;
This presentation consists of three parts:
(i) The self-organization of regular morphologies on elemental semiconductor surfaces under ion
irradiation will be discussed. At least for low-energy ions the driving force is not sputtering, as it was
claimed in most published papers so far, but ion impact induced mass drift.
(ii) Our progress on shaping of metal and semiconductor nanospheres using swift heavy ions will be
reported. Metal spheres can be shaped into rods and quadruples, whereas germanium nanospheres have been shaped into disks. A quantitative model will be presented.
(iii) Nanowires have been synthesized by FIB implantation. By subsequent thermal treatment, nanocluster chains have been formed by a controlled decay of these wires. Atomistic simulations show that rather complex nanostructures can be fabricated.
Keywords: ion-solid-interaction, surface patterning, self-organization, nanoparticle shaping, nanowire synthesis, modeling, computer simulations
  • Invited lecture (Conferences)
    21st MRS-Japan Academic Symposium, 19.-21.12.2011, Yokohama, Japan

Publ.-Id: 18363 - Permalink


Möglichkeiten und Anwendungen der Laserfluoreszenzmikroskopie bei extrem tiefen Temperaturen
Großmann, K.; Tondera, C.; Mosch, B.; Wimmer, C.; Arnold, T.; Pietzsch, J.;
kein Abstract, geladener Vortrag (Institutsseminar)
  • Lecture (others)
    Institutskolloquium, 15.01.2013, Mainz, Deutschland

Publ.-Id: 18362 - Permalink


Nanoporous Si in Silica – an Efficient Absorber for Thin Film PV Cells ?
Heinig, K.-H.; Schmidt, B.; Stegemann, K.-H.; Mücklich, A.; Liedke, B.; Friedrich, D.;
Nanostructured thin-film PV materials are expected to become more and more important due to their high competitiveness in cost reduction. Assemblies composed of quantum dots and/or wires have been reported in which quantum confinement is used as a design parameter. However, there are still problems related to the low-cost fabrication of such structures, and, in case of quantum dots embedded in a dielectric matrix, to charge carrier separation. Here, we present Si nanosponge embedded in silica as a new nanostructured active PV cell material which could overcome such problems. The Si nanosponge has typical feature sizes of 2…4 nm. This is much smaller than the ~100nm of electrochemically etched porous Si, which was studied intensively several years ago. Thus, the nanosponge shows a band gap widening by quantum confinement which allows band gap engineering for optimum adjustment to the solar spectrum. Furthermore, the Si sponge/SiO2 matrix interface is electrically passive which lowers losses. And, the Si sponge is electrically percolated, resulting in an efficient charge carrier separation. Si nanosponge is expected to replace easily a-Si in thin-film PV cell production lines. The PECVD equipment will be used to deposit SiOx instead of a-Si. The Si nanosponge is formed by thermally activated spinodal decomposition of SiOx. The large glass panels of thin-film PV cells allow a low thermal budget only, therefore scanned laser processing with ms dwell times has to be used. EFTEM images of Si nanosponge formed by co-sputtering of SiOx followed by rapid thermal processing are in full agreement with atomistic simulations of the spinodal decomposition process. Electrical and optical properties measured so far are in agreement with the expectations. Studies on the morphology of sponges form by very rapid thermal processing are under way.
Keywords: nanocomposite, silicon, silica, spinodal phase separation, embedded Si sponge, solar cell
  • Lecture (Conference)
    XX. International Materials Research Congress - IMRC XX, 14.-19.08.2011, Cancun, Mexico

Publ.-Id: 18361 - Permalink


Novel Nanopattern on Ge after Heavy Bi Cluster Bombardment
Heinig, K.-H.; Bischoff, L.; Schmidt, B.;
Ge surfaces have been irradiated with 30 keV Bi+ and 60 keV Bi++ monomers, 30 keV Bi2+ dimers, 60 keV Bi3++ trimers as well as 30 keV Bi4+. The ions are obtained from a Bi-liquid metal ion source in a mass separating 30 kV focused ion beam system. The surface pattern found after dimer and trimer irradiation differ drastically from the well-known porous or sponge-like nanostructures formed on Ge by ion irradiation with monomers: The surface remains crystalline as proven by Raman measurements, and the dots and ripples heights were in the order of their wavelengths. Under monomer irradiation a porous surface layer was obtained. The structure formation was investigated in the fluence range from1015 to 1017 ions/cm2 in dependence on the angle of incidence and the energy per atom of the different projectile ions. The high mass of the cluster ions leads to a patterning mechanism different from the Bradley-Harper mechanism, which becomes strikingly apparent by the crystalline Ge surface. An identified threshold of this new patterning helped to understand the mechanism: The ion-impact-induced deposition of energy per volume (as estimated by SRIM) must exceed a value which coincides with the energy needed for melting. Thus, Bi segregation during melt pool re-solidification and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.
Keywords: ion-solid-interaction, polyatomic ions, germanium, surface patterns, focussed ion beam, modeling, computer simulations
  • Lecture (Conference)
    XX. International Materials Research Congress - IMRC XX, 14.-19.08.2011, Cancun, Mexico

Publ.-Id: 18360 - Permalink


Surface Nanopatterning and Nanocluster Shaping using Ion Beams
Heinig, K.-H.; Schmidt, B.; Bischoff, L.; Röntzsch, L.; Numazawa, S.; Liedke, B.;
Ion irradiation of solids can result in self-organization of very regular surface morphologies and in shaping of particles embedded in a solid matrix. Regular chains of nanoparticles can be formed by the decay of nanowires which were synthesized using focused ion beams. This presentation consists of three parts: (i) The self-organization of pattern on elemental semiconductor surfaces under irradiation with ions of 100 eV to a few tens of keV will be reported. It will be proven by comparisons of atomistic computer simulations with experiments that the driving force for this pattern formation is not sputtering, as it was claimed in most published papers so far, but ion impact induced mass drift. Only a minority of former studies came to the same conclusion (see, e.g. [1, 2]), whereas very recently this understanding is more and more convincingly proven [3,4]. (ii) Our progress of shaping of metal and semiconductor nanospheres embedded in silica using swift heavy ions will be reported. Metal spheres can be shaped into rods and quadruples, whereas germanium nanospheres have been shaped into disks. It will be proven that electronic stopping power melts the nanoparticles, and that the volume change upon melting causes the shaping. (iii) Nanowires have been synthesized by FIB implantation, e.g. CoSi2 wires in silicon. By subsequent thermal treatment, nanocluster chains have been formed by a controlled decay of these wires. Computer experiments will show that rather complex nanostructures can be fabricated by this technique.
[1] G. Carter, V. Vishnyakov PRB 54 (1996) 17647.
[2] M. Moseler et al., Science 309 (2005)
[3] S.A. Norris et al., Nature Comm., 2011, Apr12, DOI: 10.1038/ncomms1280
[4] C.S. Madi et al., PRL 106, 066101 (2011)
Keywords: ion-solid-interaction, surface patterning, nanoparticle deformation, theory, computer simulations
  • Invited lecture (Conferences)
    XX. International Materials Research Congress - IMRC2011, 14.-18.08.2011, Cancun, Mexico

Publ.-Id: 18359 - Permalink


Computer experiments on ion-induced pattern formation vs. continuum equations
Heinig, K.-H.; Liedke, B.; Numazawa, S.; Facsko, S.;
Ripple pattern and hexagonally ordered dot pattern are frequently found after ion irradiation under off-normal incidence and under normal or close to normal ion incidence, respectively [1]. A first consistent analytical model for the evolution of these patterns was given by Bradley and Harper [2]. They showed that a surface curvature dependent ion erosion rate can result in a surface instability, whereas a surface smoothing process by surface-curvature-driven diffusion (Mullins-Herring diffusion) competes with that instability. By this competition regular surface patterns may evolve. Lateron, this simple model was extended to more sophisticated partial differential equations like the Kuramoto-Sivashinsly equation in order to improve the agreement with experimental findings. However, it remains difficult to describe details of the pattern evolution and dynamics by continuum equations.
Here we present atomistic 3D computer simulations on ion irradiation of surfaces which unify both, the collision cascades caused by the incident ions (including sputtering, mass drift, ion beam mixing) and the thermally excited relaxation processes (including surface and bulk diffusion of defects and impurities, phase separation, Mullins-Herring diffusion,…). For that aim, the collision cascade simulations in the BCA approximation are carried out for atom densities on the 3D lattice of the kinetic Monte Carlo (kMC) simulation which contains the full history of defects, surface undulations etc. Each ion impact is followed immediately by some kMC steps. The computer experiments show that, with the exception of grazing incidence, in silicon the Ar+ ion induced patterns are dominated by defect kinetics rather than sputtering. The results are in nice agreement with recent experiments of Madi [3]. Secondly, we show how this computer experiments can be directly related to continuum equations. In the computer all atomic jumps and the time evolution of the surface heights as well as of its slopes, curvatures etc can be registered. Thus, it might be possible to find out which term(s) of the partial differential equations should dominate the pattern formation.
[1] W. L. Chan and E. Chason, Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering, J. Appl. Phys. 101, 121301 (2007).
[2] R. M. Bradley and J. M. E. Harper, Theory of Ripple Topography Induced by Ion-Bombardment, J. Vac. Sci. Technol. A 6, 2390 (1988).
[3] C.S. Madi, H.B. George and M.J. Aziz, Linear stability and instability patterns in ion-sputtered silicon, J. Phys.: Cond. Mat. 21, 224010 (2009).
Keywords: Ion-solid-interaction, surface pattern, self-organisation, theory, computer simulations
  • Invited lecture (Conferences)
    International Conference on Ion-Beam Induced Nanopatterning of Materials (IINM-2011), 06.-10.02.2011, Bhubaneswar, India

Publ.-Id: 18358 - Permalink


Nanostructure Formation and Modification with Ion Beams
Heinig, K.-H.;
This presentation consists of three parts:
(i) The self-organization of regular morphologies on elemental semiconductor surfaces under irradiation with ions will be discussed. It will be proven that at least for low-energy ions the driving force for this pattern formation is not sputtering, as it was claimed in most published papers so far, but ion impact induced mass drift.
(ii) Our progress on shaping of metal and semiconductor nanospheres embedded in silica using swift heavy ions will be reported. Metal spheres can be shaped into rods and quadruples, whereas germanium nanospheres have been shaped into disks. It will be shown that electronic stopping power melts the nanoparticles, and that the volume change upon melting is the driving force for shaping.
(iii) Nanowires have been synthesized by FIB implantation, e.g. CoSi2 wires in silicon. By subsequent thermal treatment, nanocluster chains have been formed by a controlled decay of these wires. Computer experiments will show that rather complex nanostructures can be fabricated by this technique.
Keywords: Nanostructures, Ion-solid-interaction, self-organisation, nanowires, computer experiments
  • Lecture (others)
    Physics Department Seminar, 05.10.2011, Ankara, Turkey

Publ.-Id: 18357 - Permalink


Berechnungen bezüglich des Strahlenschutzes für die Errichtung der Protonentherapieanlage in Dresden
Kunath, D.; Enghardt, W.;
  • Poster
    43. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 26.-29.09.2012, Jena, Deutschland

Publ.-Id: 18356 - Permalink


Uranium(VI) Complexation with Carbonate studied by Cryo-TRLFS and PARAFAC
Steudtner, R.; Drobot, B.; Raff, J.; Scheinost, A.; Brendler, V.;
Cryogenic techniques in laser spectroscopy are currently used in scanning tunneling microscopy (STM) and single molecule spectroscopy. Recently such cryogenic devices have also been adapted to time-resolved laser-induced fluorescence spectroscopy (TRLFS) applied to uranium. We used TRLFS at low temperatures (cryo-TRLFS) to investigate the uranium(VI) complexation with carbonate. The luminescence spectra were analyzed with parallel factor analysis (PARAFAC). The PARAFAC modeling provided the luminescence spectra, decay lifetimes, and relative intensity profiles of four U(VI) species in presence of carbonate. The U(VI) species distribution calculated from the known stability constants of relevant U(VI) hydrolysis and carbonate species,compared well with the pH-depending U(VI) speciation derived from PARAFAC-analyzed TRLFS spectra. In the acidic pH range below pH 4.5 the U(VI) speciation is dominated by the free UO22+ and one UO22+/OH- species. With increasing pH we observed the formation of two different U(VI) carbonate species. Our results suggest that PARAFAC is a promising data analysis tool for TRLFS in the context of speciation studies of fluorescent metal ions.
Keywords: U(VI), Luminescence, Low temperature, Analysis
  • Poster
    ANAKON 2013, 04.-07.03.2013, Essen, Deutschland
  • Poster
    ThUL summer school 2014, 02.-06.06.2014, Karlsruhe, Germany

Publ.-Id: 18355 - Permalink


U(VI) removal kinetics in presence of synthetic magnetite nanoparticles
Huber, F.; Schild, D.; Vitova, T.; Rothe, J.; Kirsch, R.; Schaefer, T.;
The interaction of hexavalent U with a freshly synthesized nanoparticulate magnetite ((FeFe2O4)-Fe-II-O-III) (stochiometric ratio x(Fe(II)/Fe-TOT) = 0.25-0.33), a partly oxidized synthetic nanoparticulate magnetite (x = 0.11-0.27) and maghemite nanoparticles (x = 0-1) under anoxic conditions and exclusion of CO2 as function of pH, contact time and total U concentration (3 x 10(-5) M and 1 x 10(-7) M) has been examined. Short term kinetic batch experiments (contact time of 90 d) for four different pH values have been conducted. Moreover, classical batch pH sorption edges have been prepared for two different uranium concentrations for a contact time of 550 d. Spectroscopic techniques (XPS, XAS) were applied to probe for the presence and amount of reduced U on the magnetite surface. Batch kinetic studies revealed a fast initial U removal from aqueous solution with >90% magnetite associated U after 24 h within the pH range 5-11. Long-term contact time batch experiments (550 d) showed neither a U removal below pH < 3 nor a decrease in the magnetite associated U at pH >= 9. Redox speciation by XPS verifies the presence of reduced U (both U(IV) and U(V) were resolved if the satellite structures were used in the fitting procedure) at the near surface of magnetite up to a contact time of 550 d and a clear correlation of the amount of available Fe(II) on the magnetite surface and the amount of reduced U is observed. XANES investigation supports presence of U(V)/U(VI) uranate and U(IV). Interpretation of the EXAFS for one sample is consistent with incorporation of U into an Fe oxide phase, after long reaction times. Thermodynamic calculations based on the experimentally determined redox potentials corroborate the spectroscopic findings of U oxidation states. Overall, the results reflect the importance of structurally bound Fe(II) as redox partner for uranyl reduction.
Keywords: uranyl magnetite XAS ROBL

Publ.-Id: 18354 - Permalink


The Fulde-Ferrell-Larkin-Ovchinnikov state in BEDT-TTF-based organic superconductors
Wosnitza, J.;
  • Invited lecture (Conferences)
    International Symposium on Materials Science Opened by Molecular Degrees of Freedom (MDF2012), 01.-04.12.2012, Miyazaki, Japan

Publ.-Id: 18353 - Permalink


The Fulde-Ferrell-Larkin-Ovchinnikov state in quasi-two-dimensional organic superconductors
Wosnitza, J.;
  • Lecture (Conference)
    Conference on Materials and Mechanisms of Superconductivity, 29.07.-03.08.2012, Washington DC, USA

Publ.-Id: 18352 - Permalink


Evidence for Fulde-Ferrell-Larkin-Ovchinnikov states in layered organic superconductors
Wosnitza, J.;
  • Invited lecture (Conferences)
    12th Japanese-German Symposium Emergent Phenomena in Novel Quantum Phases of Condensed Matter, 14.-17.07.2012, Izu, Japan

Publ.-Id: 18351 - Permalink


Tracking ore mineral characteristics from mine to concentrate: The fate of electrum at the Cavanacaw gold deposit, Northern Ireland
Birtel, S.; Wunderlich, I.; Gutzmer, J.;
A systematic geometallurgical assessment was carried out to follow changes of mineral composition and microfabric following the ore extracted from two ore blocks at the Cavanacaw Au Mine through the beneficiation process. SEM-based image analysis was used to carry out the investigation on the finely disseminated Au ores. A general assessment quickly reveals that the beneficiation plant suffers only little loss to the tailings. Despite this positive assesment results illustrate that there are some losses that appear to be systemic: Large electrum grains (>16 µm ecd) are abundant in the original uncrushed material only make a minor contribution to the final concentrate. Due to the ductile behaviour of electrum, fracturing of larger electrum grains into smaller grain sizes appears unlikely – it is thus concluded that these particles may be captured in the plant during processing.
Our results reveal that sulphide-rich veins are typically higher in grade than the final concentrate. This results from processing a mixture of high-grade ore and low-grade wall rock. To reduce processing costs it might be considered to introduce an early stage of optical sorting
Keywords: gold, MLA, mineral processing, geometallurgy
  • Open Access LogoContribution to proceedings
    12th SGA Biennial Meeting, 12.-15.08.2013, Uppsala, Sweden
    Mineral deposit Research for a high-tech world Proceedings, Volume 1, Sweden: Elanders Sverige AB, 978-91-7403-207-9, 306-309
  • Lecture (Conference)
    12th SGA Biennial Meeting, 12.08.-15.11.2013, Uppsala, Sweden
  • Lecture (Conference)
    Workshop on Advanced Analysis Techniques in Process Mineralogy, 03.02.2014, Lulea, Sweden

Publ.-Id: 18350 - Permalink


Competing exchange interactions in Co-doped ZnO: Departure from the superexchange picture
D'Ambrosio, S.; Pashchenko, V.; Mignot, J.; Ignatchik, O.; Kuzian, R.; Savoyant, A.; Golacki, Z.; Grasza, K.; Stepanov, A.;
We report the results of a comprehensive study of the exchange interactions in Co-doped ZnO using inelastic neutron scattering, electron paramagnetic resonance, and magnetic property measurements. In particular, we observe an unprecedentedly strong spatial anisotropy of the two nearest-neighbor exchanges, J((1)) = -25.6 +/- 0.3 K and J((2)) = -8.5 +/- 0.4 K, along with the distant-neighbor J values of ferromagnetic sign. We argue that the superexchange mechanism alone cannot account for the obtained data and we suggest that an additional mechanism leading to a strong ferromagnetic spin coupling is responsible for these findings. We also discuss the origin of this ferromagnetic mechanism.

Publ.-Id: 18349 - Permalink


Spin dynamics of S = 1/2 Heisenberg chains with a staggered transverse field: electron spin resonance studies
Zvyagin, S. A.;
This article is a review of the recent achievements in experimental studies of magnetic excitations in the copper pyrimidine dinitrate [PM-Cu(NO3)(2)(H2O)(2)](n) (PM = pyrimidine), an S = 1/2 antiferromagnetic chain material with an alternating g-tensor and the Dzyaloshinskii-Moriya interaction, by means of high-field electron spin resonance (ESR). Due to this alternation, in the 1D critical regime this material exhibits a field-induced gap. The excitation spectrum is formed by solitons and their bound states, breathers, and can be effectively described using the sine-Gordon model. With increasing temperature, the soliton-breather regime can be suppressed, resulting in a substantial evolution of ESR parameters. These changes can be described using a new theoretical concept recently proposed for S = 1/2 AF chains with a staggered transverse field. High magnetic field induces a transition into the spin-polarized state with the excitation spectrum formed by magnons. Nonmonotonous behavior of the field-induced gap is observed in vicinity of the saturation field. Experimental data are compared with results of existing theoretical approaches, revealing excellent agreement with predictions.

Publ.-Id: 18348 - Permalink


Magnetic excitations in the spin-1 anisotropic antiferromagnet NiCl2-4SC(NH2)2
Psaroudaki, C.; Zvyagin, S. A.; Krzystek, J.; Paduan-Filho, A.; Zotos, X.; Papanicolaou, N.;
The spin-1 anisotropic antiferromagnet NiCl2-4SC(NH2)2 exhibits a field-induced quantum phase transition that is formally analogous to Bose-Einstein condensation. Here we present results of systematic high-field electron spin resonance (ESR) experimental and theoretical studies of this compound with a special emphasis on single-ion two-magnon bound states. In order to clarify some remaining discrepancies between theory and experiment, the frequency-field dependence of magnetic excitations in this material is reanalyzed. In particular, a more comprehensive interpretation of the experimental signature of single-ion two-magnon bound states is shown to be fully consistent with theoretical results. We also clarify the structure of the ESR spectrum in the so-called intermediate phase.

Publ.-Id: 18347 - Permalink


Soliton-magnon crossover in spin-1/2 Heisenberg chains
Zvyagin, S.;
Copper pyrimidine dinitrate ([PM-Cu(NO3)2(H2O)2]n, PM = pyrimidine) is a spin-1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interactions, whose spin dynamics can be described using the effective sine-Gordon model. Due to the presense of alternating staggered magnetization, this material exhibits a field-induced spin gap, formed by first breather. Here, we report on electron spin resonance (ESR) studies of this material in magnetic fields up to 64 T. In particular, a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the quantum disordered sine-Gordon (with soliton-breather elementary excitations in the magnetic excitation spectrum) to a spin-polarized state (with excitation spectrum formed by magnons) has been observed. This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG calculations for spin-1/2 Heisenberg chain with a staggered transverse field [1]. Such a behavior appears to be a general feature of the high-field excitation spectrum of quantum spin-1/2 chain systems with alternating g-tensor and/or Dzyaloshonskii-Moriya interactions
  • Invited lecture (Conferences)
    JEMS 2012 - Joint European Magnetic Symposia, 13.09.2012, Parma, Italy

Publ.-Id: 18345 - Permalink


High density plasma instabilities in intense laser irradiation
Kluge, T.; Cowan, T.; Huang, L.; Metzkes, J.; Schramm, U.; Gutt, C.; Schlenvoigt, H.-P.; Bussmann, M.;
High energy electron channel formation in solid targets is discussed on two exemplary PIC simulations. The feasibility of SAXS diagnostics in laser accelerated plasma physics is discussed on the basis of scattering at high density plasma waves.
  • Lecture (Conference)
    33rd International Workshop on Physics of High Energy Density in Matter, 13.-18.01.2013, Hirschegg, Österreich
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18344 - Permalink


Coexistence of ferromagnetism and superconductivity in single-nanostructures
Herrmannsdörfer, T.;
  • Invited lecture (Conferences)
    PNI in-house workshop on "Magnetism and highly correlated electron systems", 11.06.2012, Freising, Deutschland

Publ.-Id: 18343 - Permalink


Electron Spin Resonance in High Magnetic Fields
Zvyagin, S.;
  • Invited lecture (Conferences)
    Dynamics and Transport in Quantum Magnets LOTHERM, Summer School 2012, 05.06.2012, Ljubljana, Slovenia

Publ.-Id: 18340 - Permalink


The Rossendorf Beamline at ESRF: A Pooled Facility of ACTINET-I3
Scheinost, A. C.;
Overview on experimental possibilities and Joint Research Projects performed at The Rossendorf Beamline during ACTINET-I3
Keywords: XAS
  • Invited lecture (Conferences)
    2nd ACTINET-I3 Plenary Meeting, 23.-24.01.2013, Avignon, France

Publ.-Id: 18339 - Permalink


AcXAS: Actinide Reference X-ray Absorption Spectroscopy Database
Scheinost, A. C.; Schmeisser, N.; Banerjee, D.; Rossberg, A.; Denecke, M.; Dardenne, K.; Rothe, J.; Daehn, R.;
Why do we need an Actinide Reference X-Ray Absorption Spectroscopy Database?
The team
The concept
The work status
Keywords: XAS actinides
  • Invited lecture (Conferences)
    2nd ACTINET Plenary Meeting, 23.-24.01.2013, Avignon, France

Publ.-Id: 18338 - Permalink


Nanostructures by mass-separated FIB
Bischoff, L.; Böttger, R.; Philipp, P.; Schmidt, B.;
The introduction of mass-separated systems in the field of focused ion beams significantly increases the area of application in nanotechnology due to the availability of a broad spectrum of ions with the same advantages compared to classical Ga instruments. A short description of the configuration of a mass-separated FIB tool is given as well as the fundamentals of alloy liquid metal ion sources. Examples of application include patterned tailoring of functional surfaces and ion-induced phase transformation in thin layers, in particular the Si nanowire fabrication by FIB implantation and subsequent wet-chemical, anisotropic etching and the FIB lithography of thin ta-C films. Furthermore, the ion beam synthesis of CoSi2 nanostructures by Co-FIB writing and annealing, and the modification of surface morphology by various mono- and polyatomic projectiles in a broad energy- and temperature range in different materials are described and discussed.
Keywords: mass-separated focused ion beam, alloy liquid metal ion source, ExB filter, Si nanowire, ion beam synthesis, CoSi2 nanostructures, ta-C films, self-organized surface morphology, polyatomic ions
  • Book chapter
    Zhiming Wang: “FIB Nanostructures” Springer Series in Materials Science Lecture Notes on Nanoscale Science and Technology, Peking, Berlin: Springer, 2013, 978-3-319-02874-3

Publ.-Id: 18337 - Permalink


Scanning Tunnelling Spectroscopy of FIB-induced Local Phase Changes in Tetrahedral Amorphous-Carbon
Klein, F.; Philipp, P.; Bischoff, L.; Mühl, T.;
Ion irradiation of tetrahedral amorphous-carbon leads to both an ion implantation and a local phase change of the carbon. The latter is equivalent to an increase of the carbon sp2/sp3 bond ratio. It is caused by the deposition of the ion energy and leads to an increased electrical conductivity. We perform spatially resolved scanning tunneling spectroscopy in order to investigate the impact of different ion species (Ga, Si, Ge, Au). A direct contribution of the implanted metal will be carefully considered.
Keywords: tetrahedral amorphous-carbon, ion implantation, spatially resolved STM
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18336 - Permalink


Watching the quantum race of electrons
Schütte, B.; Bauch, S.; Frühling, U.; Wieland, M.; Gensch, M.; Ploenjes, E.; Gaumnitz, T.; Azima, A.; Bonitz, M.; Drescher, M.;
When a photon of sufficient high energy hits an atom it may kick out an electron. Quantum mechanics predicts that the electron behaves like a wave that runs away from the atom. If the photon energy was chosen right then a second electron (Auger electron) may be liberated from the atom, racing behind the first one. We were able to detect how this second electron overtakes the first one within only a few femtoseconds (1 fs = 10-15 seconds) and observe the dynamic exchange of energy between the two electrons when they are passing each other.
Keywords: THz, X-ray, pump probe, femtosecond, super-radiant THz sources
  • Open Access LogoContribution to external collection
    in: DESY - Photon Science 2012: Highlights, Hamburg: DESY, 2013, 48-49

Publ.-Id: 18335 - Permalink


Interaction of energetic ultraheavy ions with surfaces
Bischoff, L.; Böttger, R.; Heinig, K.-H.; Facsko, S.;
Energetic ultraheavy polyatomic ions like Bi3++ and Bi2+ produce very dense collision cascades in surface layers. Compared to monatomic ion impacts, which do not overlap in space and time within the heat relaxation time, the simultaneous impact of a few atoms in the same point can cause very different effects. Here, we report on FIB irradiation with fluences up to 1017 cm−2 using a liquid metal ion source. Using ultraheavy ions, a significantly increased sputter yield of Ge has been found, which can be attributed to thermal processes. Another, more striking feature is the dramatic difference in the surface morphologies caused by monatomic and ultraheavy ion irradiation. For instance, the well-known spongy surface layer forms on Ge upon 20 keV Bi+ irradiation, whereas normal incidence Bi3++ irradiation with the same energy per atom results in hexagonally ordered dot pattern having an aspect ratio of about one. Similar pattern have been found on Si by ultraheavy ion irradiation, but only under substantial substrate heating. And, in hot Ge substrates, normal incidence monatomic Bi+ ions produce no longer Ge sponge but also dot pattern. A crude thermal analysis of the experiments shows that the considered dot pattern formation is associated with a critical energy density deposited by an ion close to the surface. A more comprehensive model on this pattern formation will be presented in a subsequent talk by K.-H. Heinig.
R. Böttger, L. Bischoff, K.-H. Heinig, et al. JVST B30 (2012)06FF12
Keywords: ultraheavy polyatomic ions, bismuth, liquid metal ion source, germanium, sponge, dot pattern
  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18334 - Permalink


Account of the intratrack radiolytic processes for interpretation of the AMOC spectrum of liquid water
Zvezhinskiy, D.; Butterling, M.; Stepanov, S.; Krause-Rehberg, R.; Wagner, A.;
Recent development of the Gamma-induced Positron Spectroscopy (GiPS) setup significantly extends applicability of the Age-Momentum Correlation technique (AMOC) for studies of the bulk samples. It also provides many advantages comparing with conventional positron annihilation experiments in liquids, such as extremely low annihilation fraction in vessel walls, absence of a positron source and e+ annihilations in it. We have developed new approach for processing and interpretation of the AMOC-GiPS data based on the diffusion recombination model of the intratrack radiolytic processes. This approach is verified in case of liquid water, which is considered as a reference medium in the positron and positronium chemistry.
Keywords: Gamma-induced Positron Spectroscopy, Age-Momentum Correlation, Positronium Chemistry
  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, Great Britain
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012057
    DOI: 10.1088/1742-6596/443/1/012057

Publ.-Id: 18333 - Permalink


Optimization of growth parameters of TiO2 thin films using a slow positron beam
Butterling, M.; Anwand, W.; Cornelius, S.; Potzger, K.; Smekhova, A.; Vinnichenko, M.; Wagner, A.;
TiO2 thin films grown on fused silica were investigated using positron Doppler broadening spectroscopy at the slow-positron-beam SPONSOR at the Helmholtz-Zentrum Dresden-Rossendorf.
Effects of changes in different parameters like temperature or oxygen flow during film deposition on positron sensitive parameters have been investigated and first results will be presented.
Keywords: Slow Positron, Doppler Broadening Spectroscopy, Thin Films
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012073
    DOI: 10.1088/1742-6596/443/1/012073
  • Poster
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, Great Britain

Publ.-Id: 18332 - Permalink


Si nanowire networks for 3rd generation solar cells
Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Liedke, B.; Kelling, J.; Friedrich, D.; Hauschild, D.; Stegemann, K.-H.; Bulutay, C.; Keles, U.; Aydinli, A.;
Large-scale self-structuring by spinodal decomposition of metastable SiO is a very promising synthesis process of novel nanostructured Si absorbers for 3rd generation solar cells [1]. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP) and laser annealing. When the volume fraction of Si exceeds ~30% after the phase separation SiOx-->0.5SiO2+(1-0.5x)Si, then Si forms a nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on bit-coded kinetic Monte-Carlo accelerated by Massive Parallel Programming on NVIDIA graphic cards using a CUDA code. There is a considerable Si band gap widening due to quantum confinement in the nanowire network. As the wire diameter coarsens with time of heat treatment like d~t0.33, the band gap of the Si nanosponge can be optimized for solar cell application. Using an atomistic pseudopotential method, the band gaps of sponge have been studied. Finally it will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way by industrial partners.
Keywords: nanocomposite, silicon, silica, sponge, sputter deposition, solar cell, band gap, atomistic simulations
  • Invited lecture (Conferences)
    4th International Conference on Nanostructure Selfassembly (NANOSEA2012), 25.-29.06.2012, Margherita di Pula, Sardinia/Italy

Publ.-Id: 18331 - Permalink


Networks of Si nanowires in SiO2 for solar cells
Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Liedke, B.; Kelling, J.; Friedrich, D.; Hauschild, D.; Stegemann, K.-H.; Keles, U.; Bulutay, C.; Aydinli, A.;
In Si-based thin film solar cells the a-Si:H or nanocrystalline absorber layer can be replaced by a network of Si nanowires (Si nanosponge) embedded in SiO2[1]. The Si nanosponge is formed by spinodal decomposition of metastable SiO layers which have been deposited by different techniques, sputtering, CVD and e-beam evaporation. The spinodal decomposition has been activated by Rapid Thermal Processing and laser annealing. When the volume fraction of Si exceeds ~30% after the phase separation SiOx-->0.5SiO2+(1-0.5x) Si, then Si forms a nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on bit-coded kinetic Monte-Carlo. There is a considerable Si band gap widening due to quantum confinement in the nanowire network. As the wire diameter coarsens with time of heat treatment like d~t0.33, the band gap of the Si nanosponge can be optimized for solar cell application. Using an atomistic pseudopotential method, the band gap of sponges have been studied. Finally it will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way by industrial partners. [1] BMBF-TÜBITAK project “RainbowEnergy”, coordinators K.-H. Heinig and A. Aydinli
Keywords: nanocomposite, silicon, silica, sponge, solar cell, sputter deposition, laser annealing, band gap, atomistic simulations
  • Lecture (Conference)
    E-MRS Spring Meeting 2012, Symp. A, 14.-18.05.2012, Strasbourg, Frankreich

Publ.-Id: 18330 - Permalink


Morphology of Ge surfaces after Bi, Bi2 and Bi3 ion impacts: holes, dots and sponge
Heinig, K.-H.; Böttger, R.; Bischoff, L.; Liedke, B.; Urbassek, H.; Anders, C.;
Outline: (1) Motivation; (2) Patterns after normal Bi_n^+ and Bi_n^++ impacts; (3) Patterns after normal Bi_1^+ and Bi_1^++ impacts; (4) Different regions in the T-E_i phase diagram --> driving forces; (5) MD simulations; (6) kMC simulations; (7) Predictions of damped KS equation; (8) Conclusions
Keywords: polyatomic ions, ion-solid interaction, surface morphology, self-organization
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 10.-11.07.2012, Augsburg, Germany

Publ.-Id: 18329 - Permalink


Surface Patterning of Ge and Si by Heavy Ion and Cluster Impacts: Experiments, Atomistic Simulations and Theory
Heinig, K.-H.; Böttger, R.; Liedke, B.; Bischoff, L.; Anders, C.; Urbassek, H.;
The driving forces for pattern formation on surfaces by ion irradiation have been under discussion for many years. Bradley and Harper published a straightforward derivation of a partial differential equation based on the surface curvature dependent sputtering, which describes some features. Later on, ion impact induced viscous flow and a mass drift in the amorphous surfaces layer caused by the impinging ions where discussed. Only a few years ago it became obvious that on semiconductor surfaces the formation of many of the beautiful patterns are dominated by contaminations with metals. Thus, a discussion started, whether the pattern formation is induced by preferential sputtering of one of the components or by driving forces like phase separation. Additionally, the kinetics of the collision-induced defects in a sub-surfaces layer can produce instabilities resulting in surface pattern. In order to identify the dominating driving forces at least for Ge and Si surface patterning by heavy ion (Bi) and cluster (Bi3) impacts of a few to a few tens of keV, experimental Focussed Ion Beam (FIB) and broad-beam studies were combined with computer experiments (MD and kinetic Monte Carlo simulations) and theoretical studies, e.g. of the damped Kuramoto-Sivashinsky equation. A detailed comparison between experiments, simulations and PDE solutions of the surfaces evolution of specificmorphologies is a powerful approach for a deeper understanding of this kind of self-organization of structures. In this abstract for each approach, experiment, simulation and theory, an example is presented. Experiments cover a wide range of ion energies and fluences. The atomistic simulations study the influence of the ion collision cascades on the pattern formation via defect kinetics. And finally, relations of this defect kinetics to parameters of the damped Kuramoto-Sivashinsky equation are studied.
Keywords: ion-solid interaction, self-organization, surface pattern, theory, kinetic Monte Carlo simulation
  • Lecture (Conference)
    19th International Workshop on Inelastic Ion-Surface Collisions (IISC-19), 16.-21.09.2012, Frauenchiemsee, Germany

Publ.-Id: 18328 - Permalink


Near-surface depth profiling of solids by mono-energetic positrons
Ganguly, B. N.; Brauer, G.; (Editors)
This work reflects the wide and fascinating range of fields to which positrons have made important contributions. This covers, in particular, the development of low-energy (eV-keV) beams of essentially mono-energetic positrons, in the late 1960s, which opened the door to an even wider range of fundamental and technological studies: from surface physics to polymer films. The volume offers some background knowledge on the extent to which positrons have influenced and contributed to work in numerous fields.
Keywords: mono-energetic positrons, near-surface depth profiling, advances in techniques
  • Book (Authorship)
    Durnten-Zurich: Trans Tech Publications Ltd, 2012
    296 Seiten

Publ.-Id: 18327 - Permalink


Cerebral blood flow quantification in the rat: a direct comparison of arterial spin labeling MRI with radioactive microsphere PET
Bos, A.; Bergmann, R.; Strobel, K.; Hofheinz, F.; Steinbach, J.; van den Hoff, J.;
Background
Arterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognised as a valuable method for non-invasive assessment of cerebral blood flow but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals. We have conducted the present study with the aim of comparing ASL flow-sensitive alternating inversion recovery (FAIR)-derived unidirectional water uptake (K1) and 68Ga=64Cu microsphere (MS)-derived blood flow (f ) in the rat brain.
Methods
In 15 animals, K1 and f were determined successively in dedicated small animal positron emission tomography and MR scanners. The Renkin-Crone model modified by a scaling factor was used for the quantification of f and K1.
Results
Below about 1 mL/min/mL, we obtain an approximately linear relationship between f and K1. At higher flow values, the limited permeability of water at the blood brain barrier becomes apparent. Within the accessed dynamic flow range (0.2 to 1.9 mL/min/mL), the data are adequately described by the Renkin-Crone model yielding a permeability surface area product of .1.53 ± 0.46/ mL/min/mL.
Conclusion
The ASL-FAIR technique is suitable for absolute blood flow quantification in the rat brain when using a one-compartment model including a suitable extraction correction for data evaluation.

Trial registration
24-9168.21-4/2004-1 (registered in Freistadt Sachsen, Landesdirektion Dresden)
Keywords: Arterial spin labeling; Cerebral blood flow; Positron emission tomography; Kinetic modeling; Blood brain barrier.

Publ.-Id: 18326 - Permalink


Velocity Measurement Using ROFEX Ultrafast Dual Plane X-ray CT Imaging
Barthel, F.; Hoppe, D.; Hampel, U.;
Ultrafast electron beam X-ray computed tomography was developed at HZDR as a powerful imaging tool to observe two phase flows in several industrial applications, such as pipe flow that cannot be accessed by optical techniques. The ROssendorf Fast Electron beam X-ray Tomograph (ROFEX) combines advantages of non-invasive conventional CT systems, with a very high temporal and spatial resolution. This CT system is specially designed for investigations at a vertical test section at TOPFLOW (Transient two phase flow test facility) at HZDR. As a step forward recently ultrafast dual plane X-ray CT imaging was implemented, using new fast double ring X-ray detector electronics and a dual source path target in the ROFEX scanner. For the first time measurements of velocities in gas/water and steam/water flow are possible without any influence to the flow itself. The system provides pairs of slice images with an axial distance of 11mm at frame rates of up to 8000 kHz in time multiplex mode on both CT imaging planes. Thus one can assess the velocity of the interfacial area in the flow using cross correlation algorithm in two corresponding slice images. Beside parameters like phase fraction distribution, bubble sizes and interfacial areas, measurement of gas fraction velocity is possible for the first time non-invasively. From these data one can estimate slip between gas and liquid phase and calculate volumetric gas fraction. Furthermore CFD (Computational Fluid Dynamics) models can be enhanced providing parameters for calculations of bubble forces such as drag force or lift force, which influence shape and flow of bubbles. In chemical engineering applications like catalytic packaging or monolith ceramics it is possible to assess the residence time as well.
Keywords: velocity measurements, electron beam X-ray CT, dual plane CT
  • Lecture (Conference)
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa
  • Contribution to proceedings
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa
    Proceedings of 6th International Symposium on Process Tomography

Publ.-Id: 18325 - Permalink


Si Nanocrystal Networks by Si/SiO2 Phase Separation in SiOx Thin Films for Third Generation Solar Cells
Gündoğdu, S.; Özen, E. S.; İlday, S.; Heinig, K.-H.; Turan, R.; Aydinli, A.;
Si/SiO2 phase separation in Silicon rich oxides is a very promising synthesis process of novel nanocrystaline Si (nc-Si) structures for 3rd generation thin-film solar cells. The incorporation of larger band gap nanocrystaline silicon into the solar cell structure can be utilized to improve the single band gap silicon solar cells efficiency by allowing a better use of the solar spectrum. We present cw laser annealing of Si-rich oxide thin films with varying Si content to obtain nc-Si embedded in silica. Silicon nanocrystals in the form of a nanocrystaline network (sponge-like) are particularly interesting for their percolated structure. Calculations show that considerable Si band gap widening due to quantum confinement in the nanocrystals network is expected. Beside this wide band gap, sponge-like Si has another potential advantage of suppressing the carrier recombination loss mechanism by electrically percolated nanostructures. SiOx thin films with x<2 were obtained by plasma enhanced chemical vapour deposition (PECVD). Hydrogen or nitrogen diluted silane (SiH4) gas was used as the Si source and two different precursor gasses, N2O and CO2, were used for oxygen incorporation. Fine tuning the Si excess in SiOx and optimizing the annealing conditions is pursued to control the inter-nanocrystal distance to generate a network of Si nanocrystals. The network formation depends critically on the precise control of composition during deposition. In the case of SiOx films, it is expected that the network is formed upon phase separation when the stoichiometry parameter of the initial SiOx film is x ~ 1 [1]. Nevertheless, in the case of PECVD grown Si-rich oxides, different elements such as nitrogen, carbon and especially hydrogen can be present in the films. A detailed elemental study has been performed to determine the precise composition of the films using ion beam techniques as elastic recoil detection analysis (ERDA) and Rutherford back scattering (RBS), as well as X-Ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ellipsometry. The presence of hydrogen in PECVD grown samples makes ERDA an essential technique for compositional analysis although it is an expensive and hard to reach method. We have compared the ERDA data of different sets of samples with XPS, FTIR and ellipsometry analysis within the scope of listing a number of correlations between them and, further to be able to obtain the compositional information with these more accessible techniques. After the characterisation of the as-grown samples, the role of the composition in phase separation, as well as the laser irradiation parameters have been investigated and hydrogen has been identified as a key parameter for the Si/SiO2 phase separation. This research is supported by BMBF-TÜBITAK project "RainbowEnergy". [1] T. Muller et al, Applied Physics Letters, 85, 2373 (2004).
Keywords: Phase separation, SiOx, nuclear analysis, layer deposition
  • Lecture (Conference)
    Solar Electricity Conference & Exhibition (SOLARTR-2), 07.-09.11.2012, Antalya, Turkey

Publ.-Id: 18324 - Permalink


The recovery procedure of pin-by-pin fields of power distribution in the core of VVER type reactor for the program BIPR-8. Verification calculations
Gordienko, P.; Kotsarev, A.; Lisorkin, M.; Kozmenkov, Y.; Kliem, S.;
Reconstruction of power distribution gives a means to check the compliance with design limits in steady-state calculations and to take account of power distribution deformation from one fuel element to another in transient calculations with use of spatial kinetics model. In calculation of reactivity accidents, its application makes it possible to avoid the additional conservatism derived from nodal calculation of power distributions. The resulting description of distribution behavior is expected to be used in thermal and mechanical calculation of fuel assemblies in transients.
The reconstructed power distributions will be used to calculate power densities in all fuel elements in the reactor core with use of BIPR-8 calculation code [1]. Verification calculations have been carried out by comparing the data of element-by-element power distribution in one cassette calculated with use of PERMAK [2] and BIPR-8 codes to test the method used and a new nodule of BIPR-8 where the method is implemented.
  • Contribution to proceedings
    22nd Symposium of Atomic Energy Research (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic
    Proceedings of the 22nd AER Symposium, Budapest: MTA Energoatom, 9789635086276, 177-191

Publ.-Id: 18323 - Permalink


The first comparison of the seventh AER Dynamic Benchmark problem results obtained by RELAP5-3D and DYN3D/ATHLET computing codes
Bencik, M.; Hadek, J.; Kozmenkov, Y.; Kliem, S.;
The paper gives the first comparison of the 7th three-dimensional AER dynamic benchmark calculation results received with the codes RELAP5-3D (ÚJV) and DYN3D/ATHLET (HZDR). This benchmark was defined by A. Kotsarev, M. Lizorkin and R. Petrin at the 20th AER Symposium in Hanassari (Finland). It is focused on investigation of transient behavior in a VVER-440 nuclear power plant. Its initiating event is the opening of the main isolation valve and re-connection of the loop with its main circulation pump in operation. A water slug with lower temperature of 100 K enters the core which leads to a reactor power excursion. The activation of the reactor scram is caused by the corresponding power level signal. As a result of the scram, the turbines are turned-off by closure of the turbine isolation valves. All main circulation pumps remain in operation. Each participant had to use its own developed input plant data deck and parameterized library of macroscopic cross sections. The VVER-440/213 plant is at the end of the first fuel cycle and in hot full power conditions. The initial reactor power tuning and burnup calculations were performed with the code DYN3D by both participants. The first part of paper contains a brief description of RELAP5-3D and DYN3D/ATHLET system codes, their NPP input decks and reactor core models. The second part shows the comparison of important global and local time dependent parameters. The trends of main calculated parameters are very close. The calculated nuclear and thermal-hydraulic phenomena like reactor power, cold leg mass flow rates, cold and hot leg coolant temperatures, upper plenum pressure, pressurizer water level and steam generator powers agree quite well.
  • Contribution to proceedings
    22nd Symposium of Atomic Energy Research (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic
    Proceedings of the 22nd AER Symposium, Budapest: MTA Energoatom, 9789635086276, 653-675

Publ.-Id: 18322 - Permalink


Spectroscopic Ellipsometry Studies of nc-Si/a-Si and nc-Si/SiOx Systems: Optical Characterization of Crystallization
Nogay, G.; İlday, S.; Turan, R.; Heinig, K.-H.; Friedrich, D.;
Third generation solar cells are expected to utilize the quantum size effect occurring in the semiconductor quantum dots fabricated in an appropriate matrix. A promising and well-studied material system is the Si nanocrystals fabricated in an oxide matrix such as SiO2. In spite of extensive research efforts on this material system, a successful device realization has not been possible due to the difficulties in the device fabrication and the electronic transport in the dielectric matrix that forms an insulating medium for the charge transport. In order to overcome the problems related to the electronic transport while not losing the quantum size effect, the use of a sponge-like nanostructure has recently been proposed. Si nanosponge is composed of tiny interconnected Si nanostructures embedded in an oxide matrix. These nanostructures form an interconnected quantum structure where the charge transport does not require the tunneling current which needs well positioned quantum dots. The band gap of the material can still be engineered by process parameters for tandem solar cell fabrication. Sinanosponge is then a promising candidate for the fabrication of third generation photovoltaic (PV) solar cells. In this work, Si-nanosponge structures were fabricated successfully in a SiOx matrix in a wide range of x values (0 Keywords: phase separation, SiO, silicon, Raman, Ellipsometry, PV cell
  • Lecture (Conference)
    Solar Electricity Conference & Exhibition (SOLARTR-2), 07.-09.11.2012, Antalya, Turkey

Publ.-Id: 18321 - Permalink


Overcoming challenges to the formation of high-quality polycrystalline TiO2:Ta transparent conducting films by magnetron sputtering
Neubert, M.; Cornelius, S.; Fiedler, J.; Gebel, T.; Liepack, H.; Kolitsch, A.; Vinnichenko, M.;
The work is focused on understanding the physical processes responsible for the modification of the structure, electrical and optical properties of polycrystalline TiO2:Ta films formed by annealing of initially amorphous films grown by DC magnetron sputtering of electrically conductive ceramic targets. It is shown that fine tuning of the oxygen content during deposition of amorphous TiO2:Ta films is critical to achieving low resistivity and high optical transmittance after annealing. Increasing the total pressure during magnetron sputter deposition is shown to decrease the sensitivity of the annealed films to the oxygen flow variation during deposition of the initially amorphous layers. Polycrystalline anatase TiO2:Ta films of low electrical resistivity (ρH=1.5×10-3 Ω cm), high free electron mobility (µH=8cm²/Vs) and low extinction (k550nm=0.006) are obtained in this way at a total pressure of 2 Pa. The dependence of the polycrystalline film electrical properties on the oxygen content is discussed in terms of Ta dopant electrical activation/deactivation taking into account the formation of compensating defects at different oxygen pressures. The temperature-dependent transport of the polycrystalline anatase TiO2:Ta films is investigated showing the dominant role of the optical phonon scattering in the case of films with an optimum Ti/O ratio.
Keywords: TCO, transparent, conductive, oxide, TiO2, titania, tantalum, polycrystalline, sputter, annealing

Publ.-Id: 18320 - Permalink


The German-Turkish project RainbowEnergy: A Si-based nanocomposite absorber for thin film PV cells
Heinig, K.-H.; Aydinli, A.; Turan, R.; Hauschild, D.;
Si-based thin film PV cells suffer from a rather low efficiency. This leads to a relative small market share, although their module prices are comparably low. RainbowEnergy aims at a novel nanostructured Si-based thin film PV cell absorber, which increases the efficiency substantially without increasing the module costs. Large-scale patterning by spontaneous self-structuring during spinodal decomposition of metastable SiO is a
promising synthesis process of nanostructured Si absorbers for 3rd generation thin-film solar cells. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP, several seconds), very Rapid Thermal Processing (vRTP, dwell time tens of msec), and laser annealing. If after phase separation SiOx --> 0.5SiO2 + (1-0.5x)Si the volume fraction of Si exceeds ~30%, then Si forms a percolated nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on kinetic Monte-Carlo. As the wire diameters coarsens with time of heat treatment like d~t1/3, and because the Si bandgap opens for nmstructures by quantum confinement, a band gap engineering for PV cell optimization becomes feasible. It will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way with industrial partners
Keywords: solar cells, nanocomposite, silicon, thin film, laser annealing, kinetic Monte Carlo simulations
  • Invited lecture (Conferences)
    Solar Electricity Conference & Exhibition (SOLARTR-2), 07.-09.11.2012, Antalya, Turkey

Publ.-Id: 18319 - Permalink


Development of recombinant receptor tyrosine kinase ligands for diagnostics and therapy of tumors based on radionuclides
Pietzsch, D.; Mosch, B.; Pietzsch, J.;
Introduction
Several receptor tyrosine kinases, like the epidermal growth factor receptor (EGFR) play a critical role in tumors and, therefore, are promising targets for tumor imaging and tumor therapy. The present work aims at development of novel recombinant EGF analogs as potential radioligands or receptor-targeted components for functionalization of nanoparticles. This approach uses selective alteration of protein structure by unnatural amino acids, which amenables the protein for both radiolabeling and functionalization by the Click-chemistry.

Material and methods
The structural alteration of the recombinant protein is possible by supplementation based incorporation, because E. coli tRNA can not differ between methionine and azidohomoalanine. So these two amino acids can be exchanged during protein biosynthesis. Therefore, azidohomolalanine was added into methionine-free medium during cultivation of transformed bacteria. Vectors with both GST-tag and His-tag and corresponding methods for purification were tested and first experiments for the Click reaction of the structurally modified protein with biotinylated alkynes, fluorescence dye-labeled and 18F labeled alkynes were realised.

Results and conclusion
The purification of the GST fusion protein only resulted in the unmodified protein, but not in the azido-functionalised protein. Subsequently, native purification of a His-tagged EGF was established and the incorporation of azides into the target protein could be demonstrated by Click reaction with an alkyne. Ongoing work focuses on optimization of this approach. Afterwards, the purified and labeled proteins will be tested concerning their pharmacological properties as potential radioligands or targeted components of functionalized nanoparticles.
  • Lecture (Conference)
    Sixth Berder meeting "Nanomedicine in Oncology", 26.-29.09.2012, Berder Island, France
  • Contribution to proceedings
    Sixth Berder meeting "Nanomedicine in Oncology", 26.-29.09.2012, Berder Island, France
    Proceedings of Sixth Berder meeting "Nanomedicine in Oncology", Paris, 12-13

Publ.-Id: 18318 - Permalink


Experimental hypoxia does not influence gene expression and protein synthesis of Eph receptors and ephrin ligands in human melanoma cells in vitro.
Reissenweber, B.; Mosch, B.; Pietzsch, J.;
Eph receptor tyrosine kinases and their ephrin ligands are supposed to play important roles in melanoma progression and metastasis. Moreover, hypoxia is known to contribute to melanoma metastasis. In this study, the influence of experimental hypoxia on expression and synthesis of EphA2 and EphB4, and their corresponding ligands ephrinA1, ephrinA5, and ephrinB2 was systematically studied in four human melanoma cell lines in vitro. Melanoma cell monolayer and spheroid cultures were used as both extrinsic and intrinsic hypoxia models. Hypoxic conditions were confirmed by analyzing HIF-1α/-2α expression, VEGF expression, and cellular uptake of [18F]fluoromisonidazol. In normoxia, EphA2, EphB4, ephrinA1, ephrinA5, and ephrinB2 expression was detectable in all cell lines with varying extent. Considerable protein synthesis of EphA2 was detected in all cell lines. However, no effect of experimental hypoxia on both Eph/ephrin expression and protein synthesis was observed. This contributes critically to debating the hypothesis that hypoxia regulates the Eph/ephrin system in melanoma.

Publ.-Id: 18317 - Permalink


Si nanowire networks embedded in SiO2 formed by spinodal decomposition of SiO – a novel absorber material for 3rd generation solar cells
Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Liedke, B.; Kelling, J.; Friedrich, D.; Hauschild, D.; Stegemann, K.-H.; Keles, U.; Bulutay, C.; Aydinli, A.;
Large-scale patterning by spontaneous self-structuring during spinodal decomposition of metastable SiO is a very promising synthesis process of novel nanostructured Si absorbers for 3rd generation thin-film solar cells [1]. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP, several seconds) and very Rapid Thermal Processing (vRTP, dwell time tens of msec). When the volume fraction of Si exceeds ~30% after the phase separation SiOx-->0.5SiO2+(1-0.5x)Si, then Si forms a nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on bit-coded kinetic Monte-Carlo. There is a considerable Si band gap widening due to quantum confinement in the nanowire network. As the wire diameter coarsens with time of heat treatment like d~t0.33, the band gap of the Si nanosponge can be optimized for solar cell application. Using an atomistic pseudopotential method, the band gap of sponges have been studied. Finally it will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way by industrial partners.
Keywords: solar cells, nanocomposite, silicon, nanowire, band gap, laser annealing, sputter deposition, kinetic Monte Carlo simulations
  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2012, Symp. Y, 14.-18.05.2012, Srasbourg, France

Publ.-Id: 18316 - Permalink


Ion-beam synthesis of magnetic semiconductors
Potzger, K.;
This review focuses on current research on the topic of ion beam based approaches for the fabrication of magnetic semiconductors. Among them, classic semiconductors such as Si, Ge, GaAs as well as solid–gas compounds such as ZnO or GaN doped with transition metals are currently in the focus of research. Those are considered to be basic materials for future spintronics devices. In the review also possible pitfalls leading to misinterpretation of the data obtained will be discussed.
Keywords: Ion implantation, Diluted magnetic semiconductors

Publ.-Id: 18315 - Permalink


Kinetic Monte Carlo Simulations at Spatiotemporal Scales of Experiments
Heinig, K.-H.;
In comparison with MD, the kinetic Monte Carlo (kMC) method allows the treatment of much larger systems for much longer time periods on the atomistic level. Implementing the kMC method as a stochastic probabilistic cellular automaton according to the definition of Steven Wolfram, the simulations can be performed with many-body potentials projected onto a lattice, and a bit-coding makes the calculations extremely fast. Additionally, by Massively Parallel Programming (MPP) using NVIDIA graphic cards with CUDA programming, we accelerated kMC simulations by almost two orders of magnitude. Other than for finite element and MD codes, MPP cannot be straightforward implemented for the stochastic probabilistic Markov chain of kMC. We have extended the recently by Tobias Preis developed MPP method (Ising model with spin-flip kinetics) to much more complex conservative cellular automata with Kawasaki exchanges. Based on these methodological developments, we present large-scale simulations on the self-organization of surface nanopatterns under ion irradiation and on the scaling behavior of nanosponge formation.
Keywords: kinetic Monte Carlo simulations, program code development, massive parallel programming, CUDA, scaling phenomena
  • Invited lecture (Conferences)
    International Workshop on "Beyond Molecular Dynamics: Long Time Atomic-Scale Simulations", 26.03.2012, Dresden, Germany

Publ.-Id: 18314 - Permalink


Inactivation of HNSCC Cells by 90Y-Labeled Cetuximab Strictly Depends on the Number of Induced DNA Double-Strand Breaks
Saker, J.; Kriegs, M.; Zenker, M.; Heldt, J.-M.; Eke, I.; Pietzsch, H.-J.; Grénman, R.; Cordes, N.; Petersen, C.; Baumann, M.; Steinbach, J.; Dikomey, E.; Kasten-Pisula, U.;
Radioimmunotherapy is considered to have great potential for efficient and highly specific treatment of tumors. The aim of this study was to determine the efficacy of radioimmunotherapy when using 90Y-labeled cetuximab and to determine to what degree induction and repair of DNA double-strand breaks (DSBs) are decisive for this approach.
Methods: This study was performed with 9 cell lines of squamous cell carcinoma of the head and neck (HNSCC) differing strongly in epidermal growth factor receptor (EGFR) expression. The radionuclide 90Y was coupled by the chelator trans-cyclohexyl-diethylene-triaminepentaacetic acid (CHX-A"-DTPA)/linker construct to the EGFR-directed antibody cetuximab to yield 90Y-Y-CHX-A"-DTPA-cetuximab with a specific activity of approximately 1.2 GBq/mg. EGFR expression was determined by immunofluorescence and Western blotting, cetuximab binding by fluorescence-activated cell sorter analysis, the number of DSBs by immunofluorescence staining Gamma-H2AX/53BP1-positive repair foci, and cell survival by colony formation.
Results: For the 9 HNSCC cell lines, cetuximab binding correlated with the amount of EGFR present in the cell membrane (r2 = 0.967, P < 0.001). When cells were exposed to 90Y-Y-CHX-A"-DTPA-cetuximab, the number of induced DSBs increased linearly with time (r2 = 0.968, P 5 0.016). This number was found to correlate with the amount of membranous EGFR (r2 = 0.877, P = 0.006). Most DSBs were repaired during incubation at 37C, but the small number of remaining DSBs still correlated with the amount of membranous EGFR (24 h: r2 = 0.977, P < 0.001; 48 h: r2 = 0.947, P < 0.001). Exposure to 90Y-Y-CHX-A"-DTPA-cetuximab also resulted in efficient cell killing, whereby the extent of cell killing correlated strongly with the respective number of remaining DSBs (r2 = 0.989, P < 0.001) and with the amount of membranous EGFR (r2 = 0.967, P < 0.001). No cell killing was observed for UTSCC15 cells with low EGFR expression, in contrast to the strong reduction of 86% measured for UTSCC14 cells showing a strong overexpression of EGFR.
Conclusion: 90Y-YCHX-A"-DTPA-cetuximab affected cell survival through the induction of DSBs. This treatment was especially efficient for HNSCC cells strongly overexpressing EGFR, whereas no effect was seen for cells with low levels of EGFR expression. Therefore, EGFR-directed radioimmunotherapy using 90Y-YCHX-A"-DTPA-cetuximab appears to be a powerful tool that can be used to inactivate tumors with strong EGFR overexpression, which are often characterized by a pronounced radioresistance.
Keywords: targeted radioimmunotherapy; EGFR; 90Y-Y-CHXA"-DTPA-cetuximab; double-strand breaks; cell inactivation

Publ.-Id: 18313 - Permalink


Structured electrodeposition in magnetic gradient fields
Uhlemann, M.; Tschulik, K.; Gebert, A.; Mutschke, G.; Fröhlich, J.; Bund, A.; Yang, X.; Eckert, K.;
Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.
Keywords: Electrochemistry, Electrolysis, Magnetohydrodynamics, Metal deposition, Magnetic fields, Magnetic forces, Electrolyte convection

Publ.-Id: 18312 - Permalink


3D Neutronic and Thermal-Hydraulic Analysis of High Conversion Th-U233 PWR core
Baldova, D.; Fridman, E.;
This paper presents the development of a high conversion Th-U233 fuel cycle that is considered for current generation of Pressurized Water Reactors (PWRs). The proposed core design consists of 193 typical 17x17 PWR fuel assemblies. Each fuel assembly is subdivided into two regions designated as seed and blanket. The central seed region, which has high U233 content, serves as a neutron supplier for the peripheral blanket region. The blanket region, which consists mostly of Th232, acts as a U233 breeder. The pins dimensions and U233 content in each region were optimized to achieve maximal fissile inventory ratio (FIR) at discharge, taking into account the target fuel cycle length of 12 months and 3-batch reloading scheme. In this study, 3D core model of a high conversion Th-U233 PWR core is developed and analyzed in order to assess the fuel cycle performance and evaluate maximum achievable power density level of the proposed design.
Keywords: Th-U233 fuel cycle, fissile inventory ratio (FIR), thermal-hydraulic analysis
  • Lecture (Conference)
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
  • Open Access LogoContribution to proceedings
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea

Publ.-Id: 18311 - Permalink


Atomistic simulations of Au-silica nanocomposite film growth
Khan, S. A.; Heinig, K.-H.; Avasthi, D. K.;
The growth of Au-silica nanocomposite film is simulated in the framework of kinetic three dimensional lattice Monte Carlo simulations considering the basic phenomena in the deposition process. In case of co-sputter deposition, the growth kinetics of nanoparticles has been studied taking into consideration the effect of the energetic sputtered species reaching the surface of the film during deposition. Formation of Au nanorod like structures are predicted under certain growth conditions particularly when surface diffusion assisted phase separation plays the dominant role and bulk kinetics is frozen. The observed dependence of the Au nanoparticle size on Au/silica ratio is in agreement with the experimental results.
Keywords: Nanocomposite, sputter deposition, Au-silica, kinetic Monte-Carlo simulations

Publ.-Id: 18310 - Permalink


High conversion Th-U233 fuel cycle for current generation of PWRs
Baldova, D.; Fridman, E.;
This paper assesses the basic possibility of achieving a high conversion Th-233U fuel cycle that can be used for the current generation of Pressurized Water Reactors. The main fuel assembly design, describe in this paper, follows the RTF SBU design. A 17 x 17 heterogeneous PWR fuel assembly, which can ensure high conversion, was considered. Such heterogeneous fuel assembly geometry consists of central 233U based seed region and a large 232Th based blanket region. The fuel pins in the seed region has a standard PWR pins dimensions. However, the fuel pins in the blanket region was enlarged in order to reduce the moderation to fuel ratio and facilitated the resonance neutron absorption in blanket. This paper describes the 2D neutronics analysis of the proposed fuel assembly. The main analysis was performed with the deterministic lattice transport code HELIOS. The obtained results were conformed using the continuous-energy Monte-Carlo code Serpent. The fuel cycle length was evaluated by applying Non-Linear Reactivity Model to the results of fuel assembly burnup calculations. The 233U content was adjusted to achieve fuel cycle length of 18 months and maximum fissile inventory ratio (FIR). The results of the analysis have been shown that for the heterogeneous seed-blanket (SB) fuel assembly, a FIR of about 0.94 can be achieved.
Keywords: High Conversion Fuel Cycle, Fissile Inventory Ratio, Seed-blanket fuel assembly
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland
  • Open Access LogoContribution to proceedings
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland
    Proceedings Jahrestagung Kerntechnik

Publ.-Id: 18309 - Permalink


Vortrag zur Mitgliederversammlung der DGVC 2012
Härting, H.-U.;
Im ersten Teil des Beitrags wird eine kurze Vorstellung des HZDR gegeben. Es wird weiterhin auf die Arbeit des Instituts für Fluiddynamik eingegangen,
mit den Schwerpunkten auf der Abteilung für Experimentelle Thermofluiddynamik sowie der Mitarbeit von Studenten an aktuellen Forschungsthemen.
Im zweiten Teil des Beitrags wird das Forschungsvorhaben „Geneigt rotierender Festbettreaktor“ vorgestellt sowie Hintergründe und Zwischenergebnisse
präsentiert.
Keywords: HZDR, Institut für Fluiddynamik, Geneigt rotierender Festbettreaktor
  • Lecture (others)
    Mitgliederversammlung Dresdner Gesellschaft für Verfahrenstechnik und Chemieingenieurwesen e.V. 2012, 22.06.2012, Dresden, Deutschland

Publ.-Id: 18308 - Permalink


Plasmon resonance tuning in Ag nanoparticles arrays grown on ripple patterned templates
Ranjan, M.; Facsko, S.; Fritzsche, M.; Mukherjee, S.;
A bottom-up approach to grow highly ordered self-assembled silver nanoparticles arrays on ripple patterns produced by low energy ion irradiation is reported. The advantage of this approach over other self-assembling or lithographic methods is the flexibility to tune the array periodicity down to 20 nm with inter-particle gaps as low as 5 nm along the ripples. The silver nanoparticle arrays grown on these rippled surfaces are optically anisotropic, i.e. they exhibit a direction dependent shift in their localised surface plasmon resonance. The reason for the observed anisotropy is a direction dependent plasmonic field coupling. In this way the capability to tune the plasmon resonance by varying the ripple wavelength is demonstrated.
Keywords: Ag nanoparticles, plasmonic properties, ion induced ripple paterns

Publ.-Id: 18307 - Permalink


X-ray absorption near-edge structure of hexagonal ternary phases in sputter-deposited TiAlN films
Gago, R.; Soldera, F.; Hübner, R.; Lehmann, J.; Munnik, F.; Vázquez, L.; Redondo-Cubero, A.; Endrino, J. L.;
Titanium aluminium nitride (TiAlN) coatings have been grown by reactive (Ar/N2) direct-current magnetron sputtering from a Ti50Al50 compound target. The film composition has been quantified by ion beam analysis showing the formation of Al-rich nitrides (Ti/Al~0.3), with stoichiometric films for N2 contents in the gas mixture equal or above ~25%. The surface morphology of the films has been imaged by atomic force microscopy, showing very smooth surfaces with roughness values below 2 nm. X-ray and electron diffraction patterns reveal that the films are nanocrystalline with a wurzite (w) structure of lattice parameters larger (~2.5%) than those for w-AlN. The lattice expansion correlates with the Ti/Al ratio in stoichiometric films, which suggests the incorporation of Ti into w-AlN. The atomic environments around Ti, Al and N sites have been extracted from the X-ray absorption near-edge structure (XANES) around Ti2p, Al1s and N1s edges, respectively. The analysis of the XANES spectral lineshape and comparison with reported theoretical calculations confirm the formation of a ternary hexagonal phase.
Keywords: nitride materials; vapour deposition; atomic scale structure; NEXAFS/XANES

Publ.-Id: 18306 - Permalink


Pipetting Nanowires: In Situ Visualization of Solid-State Nanowire-to-Nanoparticle Transformation Driven by Surface Diffusion-Mediated Capillarity
Toimil-Molares, M. E.; Röntzsch, L.; Sigle, W.; Heinig, K.-H.; Trautmann, C.; Neumann, R.;
The most interesting applications of nanotubes include their use as storage media for atoms and small molecules, as nanoscale capsules for chemical reactions, and as nanopipettes for material delivery. The geometrical transformation of metallic copper nanowires, confined in graphitic coating, into crystalline nanoparticles of up to tenfold increased diameter is reported. In situ transmission electron microscopy images at 500 °C, recorded as movies, provide an exceptional real-time visualization of Cu draining out of the carbon coating. The solid content of the carbon tube is effectively evacuated over micrometer distances towards the open end, transforming each nanowire into a single monocrystalline, facetted Cu particle. Kinetic Monte Carlo simulations propose that this dramatic morphological transformation is driven by surface diffusion of Cu atoms along the wire/tube interface, thus minimizing the total free energy of the system.
Keywords: Nanowires, Capillarity, Swift Heavy Ions, kinetic Monte Carlo Simulations, Carbon Nanotubes, TEM

Publ.-Id: 18305 - Permalink


The LIMMCAST Program at HZDR: Modelling of Fluid Flow and Transport Phenomena in the Continuous Casting Process
Gerbeth, G.; Eckert, S.; Stefani, F.; Timmel, K.; Wondrak, T.;
Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications.We present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-up Mini-LIMMCAST will be presented, which works with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. First results from LIMMCAST and Mini-LIMMCAST will be presented covering the following phenomena: fully contactless electromagnetic tomography of the flow in the mould, flow monitoring by a multitude of ultrasonic sensors, and analysis of the flow in the mould under the influence of an electromagnetic brake: intensification of the flow turbulence contrary to the expected flow damping, injection of argon bubbles through the stopper rod: occurrence of pressure oscillations.
Keywords: Continuous casting, liquid metal model, mould flow, flow measurements, two-phase flow, magnetic flow tomography, ultrasound Dopplermethod
  • Journal of Iron and Steel Research International 19(2012)Suppl.1-1, 1-8
  • Invited lecture (Conferences)
    7th International Conference on Electromagnetic Processing of Materials (EPM2012), 22.-26.10.2012, Peking, China

Publ.-Id: 18304 - Permalink


Two-Magnon Excitations: From Periodical Perturbations to Magnonic Crystals
Lenz, K.;
Two-magnon scattering is a well-known effect e.g.\ in ferromagnetic resonance experiments leading to a linewidth broadening. Available theory so far was based on random defects acting as a dipolar scattering potential. Recently it was shown by Landeros and Mills [1] that this theory can be extended to handle two-magnon scattering in \emph{periodically} perturbed films, which can be easily created by lithographical patterning. These perturbed films are the intermediate step towards full magnonic crystals.
The extended model allows for analytically calculating the response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments as I will show. A striking feature e.g.\ is the mode splitting due to the two-magnon scattering which opens magnonic band gaps. This splitting can be tailored by the geometric and magnetic sample parameters.

This work was supported by the DFG grants FA 314/6-1, FA314/3-2.
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18303 - Permalink


Frequency and field control of the magnetic relaxation in 2D magnonic crystals
Lenz, K.; Körner, M.; Gallardo, R.; Landeros, P.; Facsko, S.; Lindner, J.; Fassbender, J.ORC
We present a method of changing the magnetic damping by more than 500% in 2D magnonic crystals. These magnonic crystals have been prepared either by direct nanopatterning of the magnetic layer using electron beam lithography or by nanostructuring the substrates prior to deposition by ion beam erosion.
It was shown theoretically that magnetic defect structures lead to an increased magnetic damping due to two-magnon scattering [1]. This two-magnon scattering contribution to the magnetic relaxation can be easily determined e.g. from frequency dependent ferromagnetic resonance measurements (FMR) [2]. It is characterized by a non-linear but monotonous increase of the resonance linewidth with excitation frequency. Recent extension of this theory to films with a periodic defect structure, like 2D magnonic crystals, shows that the two-magnon scattering increases the damping only at certain frequencies related to the structural dimensions [3].
This in turn means that by slightly changing the excitation frequency by a few GHz two-magnon scattering enhanced damping can be switched on and off in addition to the intrinsic Gilbert damping that is always present. The frequency where this happens can be preselected by the periodicity of the magnonic crystal [3,4]. Moreover, it is possible to control the damping by the direction of the in-plane magnetic field. For application in spintronic devices it could be very interesting to have a selectively higher or lower damping at certain frequencies. In conventional materials only a monotonous increase of damping with frequency is achievable.
This work was supported by the DFG grant FA 314/6-1.
  • Lecture (Conference)
    12th Joint MMM-Intermag Conference, 14.-18.01.2013, Chicago, USA

Publ.-Id: 18302 - Permalink


Ion implantation techniques for silicon based photovoltaics and light emitters
Lipp Bregolin, F.; Sias, U. S.; Behar, M.; Prucnal, S.; Rebohle, L.; Skorupa, W.;
The broad adoption of ecologically friendly and cost-effective renewable energy sources and the continuous advances of the information technology industry are two of the most relevant topics in the current needs of our modern society.
The ion implantation techniques are very powerful tools and will continue to play an important part in the achievement of such goals.
In the present work, two main issues will be addressed. The first one covers the continuous search for efficient and durable silicon based light emitters for fully integrated silicon photonics. The second is the use of new processing techniques for solar cell technologies, where cost reduction is the everlasting ambition.
The light emitters made by hot ion implantation show strong enhancement of the photoluminescence intensities in comparison with the ones implanted at room temperature. In the case of photovoltaics, the plasma immersion ion implantation combined with millisecond flash lamp annealing of Solar-grade mc-Si are used for texturization and dopant activation. This approach shows very encouraging results for the fabrication of the emitter at a low thermal budget, decreasing the overall production costs.
By correlating the results of a number of experimental techniques, a qualitative explanation for the influence of the ion implantation and further fabrication parameters on the characteristics of each system is presented.
Keywords: ion implantation, light emitter, photoluminescence, electroluminescence, silicon photonics, photovoltaics, solar cells
  • Invited lecture (Conferences)
    ION 2012 - Ion implantation and other applications of ions and electrons, 25.-28.06.2012, Kazimierz Dolny, Poland,, Polska

Publ.-Id: 18301 - Permalink


Comments on “Comparative Study With New Accuracy Metrics for Target Volume Contouring in PET Image Guided Radiation Therapy”
van den Hoff, J.; Hofheinz, F.;
Phantom measurements with glass inserts in a hot background are still used frequently for calibration and performance assessment of volume delineation algorithms in PET. Taking as an example the recent paper by Shepherd et al.: Comparative Study with New Accuracy Metrics for Target Volume Contouring in PET Image Guided Radiation Therapy (IEEE Trans Med Imaging. 2012 Jun 4. [Epub ahead of print]), we demonstrate that this is not a valid approach due to the discontinuity introduced in the background by the cold walls of the glass inserts. We, moreover, emphasize that in order to define a sensible ground truth for performance assessment of contouring algorithms in patient data it is necessary to average over a sizable number of experienced observers and lesions in order to compensate for the substantial inter-observer variability.

Publ.-Id: 18300 - Permalink


Investigation of resistive switching in YMnO3 thin films grown by PLD technique.
Bogusz, A.;
Multiferroic materials are promising candidates for creation of a new generation of memory devices. This work investigates electrical properties of YMnO3 thin films, reported as resistive switching material. Thin YMnO3 films (<200 nm) were grown by pulsed laser deposition on Si substrates with Pt bottom electrode at 800°C and varying partial pressure of oxygen. Characterization of as-grown samples by X-ray diffraction and scanning electron microscopy was followed by determination of electrical properties of films in metal-insulator-metal (MIM) configuration. Results indicate the unipolar resistive switching of all of YMnO3 films with high resistance ratio (>10000) of high over low resistance state. Switching mechanism is ascribed to the structural transitions within the film upon applied current.
  • Lecture (others)
    Topical problems in theoretical physics, 28.11.2012, Chemnitz, Germany

Publ.-Id: 18299 - Permalink


Epitaxial growth of SrTiO3 (0 0 1) films on multilayer buffered GaN (0 0 0 2) by pulsed laser deposition
Luo, W. B.; Jing, J.; Shuai, Y.; Zhu, J.; Zhang, W. L.; Zhou, S.; Gemming, S.; Du, N.; Schmidt, H.;
SrTiO3 films were grown on CeO2/YSZ/TiO2 multilayer buffered GaN/Al2O3 (0 0 0 1) substrates with and without the YBa2Cu3 O7−x (YBCO) bridge layer by pulsed laser deposition (PLD). The deposition process of the buffer layers was in situ monitored by reflection high-energy electron diffraction. The crystallographical orientation of the heterostructure was studied by x-ray diffraction (XRD). With the introduction of the YBCO (0 0 1) layer, the STO (0 0 1) film was epitaxially grown on the GaN substrate. There were three sets of inplane domains separated from each other by 30° in both STO and YBCO buffer layers. The epitaxial relationship was STO (0 0 2)[1 1 0]∥YBCO(0 0 1)[1 1 0]∥CeO2(0 0 2)[0 1 0]∥YSZ (0 0 2)[0 1 0]∥GaN(0 0 0 1)[1 1 -2 0] according to XRD results. By comparing the orientation of STO grown on GaN with and without the YBCO top buffer layer, the surface chemical bonding was found to be a very important factor in determining the orientation relationship of STO.

Publ.-Id: 18298 - Permalink


Study of Neutron Induced Defects in Ceramics using the GiPS Facility
May-Tal Beck, S.; Butterling, M.; Anwand, W.; Beck, A.; Wagner, A.; Brauer, G.; Israelashvili, I.; Hen, O.;
There has been an increased interest in defects within structural materials motivated by future fission and fusion reactor needs. While reactor steels are extensively studied, much more research effort is needed in order to understand radiation damage in ceramic materials and its effect on their macroscopic characteristics (1).
Sapphire – the single crystal of Al2O3, is a candidate material to serve in diagnostic systems for burning plasma experiments (2), due to its transparency to a wide range of wavelengths (200-5000 nm), high melting temperature (~2300K) and hardness close to that of a diamond. Its optical and electronic properties are expected to be affected by the harsh radiation environment.
The family of ceramics that contains Boron is another interesting group of materials for the nuclear industry, mainly due to high cross sections for thermal neutron capture in Boron, which produce helium inside the material. The much higher neutron flux expected in future reactors can cause swelling of materials and macroscopic cracks formation. Helium is also considered to be one of the most interesting challenges for fusion reactors, due to alpha particles production in the D-T reaction. Materials that will be used as first wall, matrices for Li, or coating materials, will suffer from high radiation damage.
The sensitivity of Positron Annihilation Spectroscopy (PAS) methods to point defects makes them perfect tools to study radiation damage in its first stages of creation.
Especially, Positron Annihilation Lifetime Spectroscopy (PALS) is sensitive to size and concentration of the point defects and Coincidence Doppler Broadening (CDB) can probe changes in defect characteristics as well as in electron momenta in the lattice We present first results of Sapphire and Boron Carbide (B4C) samples investigated at the Gamma Induced Positron Spectroscopy (GiPS) facility at the HZDR (3). Unirradiated Sapphire and B4C samples were measured, as well as neutron irradiated samples, to a fluence of 6x10E18 n/cm2 and ~10E15 n/cm2 for the Sapphire and B4C samples, respectively. In the GiPS facility, four pairs of detectors, each consisting of BaF2 and HPGe detectors, allow to measure PALS, DB and to use the correlated information to measure also CDB and Age-Momentum Correlation (AMOC). Results from these measurements will be discussed.
References
[1] Workshop on Advanced Computational Materials Science: Application to Fusion and Generation IV Fission Reactors, Washington, D.C. 31 March – 2 April 2004.
[2] D.M. Duffy, Phil. Trans. R. Soc. A 368 (2010) 3315-3328.
[3] M. Butterling et al., Phys. Status Solidi A 207 (2010) 334-337.
Keywords: neutron induced defects, ceramics, gamma-radiation induced positron spectroscopy
  • Poster
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012076
    DOI: 10.1088/1742-6596/443/1/012076

Publ.-Id: 18297 - Permalink


Vacancy-induced hardening in Fe-Al alloys
Lukac, F.; Cizek, J.; Prochazka, I.; Jiraskova, Y.; Janickovic, D.; Anwand, W.; Brauer, G.;
Iron aluminides are perspective materials for high temperature structural applications due to a high mechanical strength and excellent corrosion resistance. Hardness of Fe-Al alloys shows non-trivial dependence on chemical composition and thermal treatment of samples and cannot be fully explained by consideration of intermetallic phases formed according to the equilibrium phase diagram of Fe-Al system. Hardening caused by quenched-in non-equilibrium vacancies was proposed to explain rise of hardness in quenched Fe-Al alloys [1].
In the present work the concentration of quenched-in vacancies in Fe-Al alloys with various Al content cAl ranging from 18 to 49 at.-% was determined by means of two techniques of positron annihilation spectroscopy (PAS): (i) positron lifetime spectroscopy was employed for investigation of samples with vacancy concentration less than 2 x 10-4 at.-1 representing a limit for saturated positron trapping; (ii) in samples containing more vacancies than 2 x 10-4 at.-1, the vacancy concentration was determined using back-diffusion measurement of monoenergetic slow positrons. It has been demonstrated that both these methods give mutually consistent results [2].
Non-equilibrium vacancies were detected in all alloys studied after quenching from 1000°C. The concentration of quenched-in vacancies strongly increases with increasing Al content from 10-5 at.-1 in the alloy with cAl = 18 at.-% up to 10-1 at.-1 in the alloy with cAl = 49 at.-%. Comparison of the vacancy concentration and the Vickers microhardness measured on quenched samples revealed that hardness indeed increases with increasing concentration of quenched-in vacancies. In alloys with cAl > 30 at.-% the concentration of quenched-in vacancies exceeds 10-4 at.-1 and the hardness was found to be proportional to square root of the vacancy concentration in agreement with solution hardening model proposed by Chang et al. [1]. Subsequent annealing of samples at 520 °C causes recovery of quenched-in vacancies. This is accompanied by a drop of microhardness, but only in alloys where the initial concentration of quenched-in vacancies was least 10-4 at.-1. Hence, vacancies have a measurable effect on hardness of Fe-Al alloys when their concentration becomes 10-4 at.-1 or higher.
References
[1] Y. A. Chang et al., Intermetallics 1, 107 (1993).
[2] J. Čížek et al., Physica B (2012) doi:10.1016/j.physb.2011.12.122.
Keywords: Fe-Al alloys, vacancy-induced hardening, positron annihilation spectroscopy
  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012025
    DOI: 10.1088/1742-6596/443/1/012025

Publ.-Id: 18296 - Permalink


Flash lamp annealing of Tungsten surfaces marks a new way to optimized slow positron yields
Anwand, W.; Butterling, M.; Johnson, J. M.; Reuther, H.; Wagner, A.; Skorupa, W.; Brauer, G.;
Tungsten is often used as a positron moderator in mono-energetic positron beams [1] with 22Na positron sources. Therefore, mono-crystalline W foils with a thickness of about 2 μm are commonly used. The efficiency of such tungsten moderators strongly depends on the heat treatment of the tungsten foils. Currently, the annealing of such thin foils is mostly done at temperatures of about 2000 oC under vacuum conditions with a considerable difficulty. For this reason, a new method was sought to quickly anneal W foils to produce manageable, low-cost moderators with a high efficiency suitable for mono-energetic positron beams.
Flash lamp annealing (FLA) offers a chance for the optimization of the moderator properties. With FLA, the surface of a W foil can be heated above the melting point (3422ºC) in 1 to 3 ms without melting the whole volume. The heat treatment was carried out in an Ar flow. In this way, a surface cleaning and a considerably longer positron diffusion length could be reached.
Conventional poly-crystalline W foils with a thickness of 9 μm + 25% and heat treated by FLA were characterized by Auger electron spectroscopy, scanning electron microscopy and slow positron implantation spectroscopy and then tested as positron moderators. First promising results obtained with these W foils will be presented and it will be shown that this technique is applicable to tungsten meshes too.
References
[1] P.G. Coleman, Positron Beams and their applications, World Scientific Publishing, Singapore, 2000
Keywords: Tungsten foils, positron moderation, Flash Lamp Annealing
  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012072
    DOI: 10.1088/1742-6596/443/1/012072

Publ.-Id: 18295 - Permalink


Defect studies of ZnO films prepared by pulsed laser deposition on various substrates
Melikhova, O.; Cizek, J.; Kuzel, R.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Connolly, J.; Mccarthy, E.; Krishnamurthy, S.; Mosnier, J.-P.;
The quality of ZnO thin films was characterized in this work by slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD). The ZnO films were grown by pulsed laser deposition (PLD) on three different substrates: sapphire (0001) single crystal, MgO (100) single crystal and amorphous fused silica (FS). Films deposited on all substrates exhibit wurtzite ZnO structure and are characterized by an average crystallite size 20 - 100 nm.
Microstructure of ZnO films is strongly influenced by substrate. XRD investigations revealed that ZnO films deposited on sapphire (0001) and MgO (100) single crystalline substrates exhibit local epitaxy, i.e. a well-defined relation between film crystallites and the substrate. On the other hand, the film deposited on FS substrate exhibits (0002) fiber texture with random lateral orientation of crystallites in the plane of substrate. The films deposited on single crystalline substrates exhibit narrow XRD (0002) rocking curves with the half-widths (FWHM) of 1.3° and 1.2° for the film deposited on sapphire (0001) and MgO (100) substrate, respectively. On the other hand, the film deposited on amorphous FS substrate exhibits significantly wider XRD (0002) rocking curve having half width of 10°. Hence, the mosaic spread of planes is relatively small for the films grown on single crystalline substrates while it is substantial for the film grown on amorphous FS substrate. The half width of the XRD rocking curve is often used as a measure of quality of epitaxial thin films. However, half width of the rocking curve is a measure of the perfection of the structural relationship but is not directly correlated with the density of defects in the film. SPIS investigations revealed that ZnO films deposited on MgO and sapphire single crystalline substrates exhibit significantly higher density of defects than the film deposited on amorphous FS substrate despite the fact that half width of rocking curve exhibits opposite behaviour. In ZnO film deposited on the amorphous FS substrate the mismatch between atomic positions in the substrate and in the film is to some extend compensated for by many differing orientations (tilting) of the ZnO crystallites. As a consequence, the density of misfit dislocations in ZnO crystallites is relatively low and positrons are trapped predominantly at open volume misfit defects at the interfaces between the crystallites. On the other hand, ZnO films deposited on MgO and sapphire single crystalline substrates exhibit local epitaxy. In these cases, the lattice mismatch between the film and the substrate is accumulated mainly by misfit dislocations.
Keywords: ZnO films, pulsed laser deposition, X-ray diffraction, slow positron implantation spectroscopy, structure, defects
  • Poster
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012018
    DOI: 10.1088/1742-6596/443/1/012018

Publ.-Id: 18294 - Permalink


PGB pair production at LHC and ILC as a probe of the topcolor-assisted technicolor models
Liu, G.; Zhang, H.; Zhou, P.;
The topcolor-assisted technicolor (TC2) model predicts some light pseudo goldstone bosons (PGBs), which may be accessible at the LHC or ILC. In this work we study the pair productions of the charged or neutral PGBs at the LHC and ILC. For the productions at the LHC we consider the processes proceeding through gluon-gluon fusion and quark-antiquark annihilation, while for the productions at the ILC we consider both the electron-positron collision and the photon-photon collision. We find that in a large part of parameter space the production cross sections at both colliders can be quite large compared with the low standard model backgrounds. Therefore, in future experiments these productions may be detectable and allow for probing TC2 model.

Publ.-Id: 18293 - Permalink


First experiments with the MePS
Jungmann, M.; Krause-Rehberg, R.; Anwand, W.; Butterling, M.; Wagner, A.; Cowan, T. E.;
The MePS system (Mono-energetic Positron Spectroscopy) is located in the Helmholtz Center Dresden-Rossendorf (HZDR) [1]. It is one of the installations at ELBE (Electron Linac for beams with high Brilliance and low Emittance) which supplies a 40-MeV electron beam [2]. MePS makes use of the excellent time structure of the primary electron beam of ELBE (repetition frequency up to 26 MHz; bunch length < 5ps) to produce a pulsed, intense slow-positron positron beam to allow positron lifetime spectroscopy.
In autumn 2011 the system was completed and tested. A new moderator was successfully installed (tungsten meshes on a tungsten foil). Moreover, the accelerator stage together with a sample chamber was added. At a rather low primary electron beam current of 48 μA (maximum current: 1 mA) a count rate of 9400 cps was obtained in a BaF2/PMT detector close to the sample. In order to avoid spurious signals which are in other systems often obtained by positrons being reflected from the sample surface, a bended tube (45°) was added between accelerator and sample chamber. Although up to now no chopper stage is in use, the signal to background ratio is 104. However, a chopper will be used in the future to improve this ratio and the time resolution which is now only about 500 ps.
The MePS system has been used to study the pore system of a series of low-k dielectric layers
References
[1] http://positron.physik.uni-halle.de/EPOS/
[2] www.HZDR.de/db/Cms?pNid=145.
Keywords: Mono-energetic Positron Spectroscopy, intense positron source, electron linac
  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access LogoJournal of Physics: Conference Series 443(2013), 012088
    DOI: 10.1088/1742-6596/443/1/012088

Publ.-Id: 18292 - Permalink


PET measurements of liquid aerosol deposition in pebble beds
Barth, T.; Ludwig, M.; Kulenkampff, J.; Gründig, M.; Hampel, U.; Lippmann-Pipke, J.; Bieberle, A.;
The deposition and resuspension behavior of carbonaceous dust in the primary circuit of a High Temperature Reactor (HTR) is a tremendous safety issue for the assessment of Design Basis Accidents. In this work the deposition of 18F labeled monodisperse aerosol particles in a pebble bed is recorded by means of Positron Emission Tomography (PET) in order to explore the particle behavior in this geometry. Our feasibility study gives first insights into the temporal and a fully 3D spatial distribution of the particle deposits in a pebble bed obtained by PET.
An air driven small scale test facility is used for the generation of a particle laden turbulent flow field through a model pebble bed. Its Reynolds numbers cover the range typically found in a HTR pebble bed. The results of total pressure drop measurements over the pebble bed with respect to Reynolds number show relatively good agreement to literature which assumes the correct fluid mechanic downscaling of the facility.
A condensational aerosol generator was charged with KF condensation nuclei labeled with 18F. The aerosols are made of DEHS and are injected far upstream from the pebble bed. Concentration measurements upstream and downstream of the pebble bed were performed by means of isokinetic sampling and a condensational particle counter. The results agree with typical deposition curves related to turbulent and inertia driven particle deposition.
A small portion of the initially applied activity was detected in the field of view of the scanner. The longitudinal, slice-wise activity distribution shows an exponential digression of deposited particles in downstream direction. In a deposition experiment in the inertia impact regime, PET image quality allows to conclude that the deposited particles are located in the vicinity of the upstream located stagnation points
Keywords: high temperature reactor, pebble bed, particle deposition, positron emission tomography
  • Contribution to proceedings
    6th International Topical Meeting on High Temperature Reactor Technology, 28.10.-01.11.2012, Tokyo, Japan

Publ.-Id: 18291 - Permalink


Periodic Nanoscale Patterns Induced by Ion Irradiation: Ripples, Dots, and Holes
Facsko, S.;
The morphology of surfaces after irradiation with low en- ergy ions (E < 50 keV) exhibits a variety of character- istics depending on the ion beam parameters and the ma- terial properties. Surfaces exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns. The structure size of these patterns is in the range of 10 to 100 nm and occasionally a high degree of ordering is achieved. Therefore, they have attracted interest recently as templates for nanostructured thin films or for structuring films by an erosive process [1].
On materials which turn amorphous during ion irradiation the formation of periodic patterns relies on at least two inter- playing processes: surface roughening due to local variation of erosion rate and smoothing via diffusional processes. In addition, atomic relocations on the surface and in the bulk resulting from the collision cascade have been identified as equally important. Therefore, the surface morphology de- pends on the details of the energy deposition by the incom- ing ion beam and on the details of surface and bulk diffu- sion. At the atomic level sputtering, the creation of surface and bulk defects, and the influence of the ion beam on sur- face diffusion processes play a decisive role for the mor- phology evolution.
surface normal and at room temperature produces ripple patterns oriented perpendicular to the ion beam direction. Higher incidence angles can lead to ripple patterns oriented parallel to the ion beam direction. Normally, coarsening of the ripple pattern with ion fluence is observed. In addition, the order increases with fluence up to 1 × 1018 cm−2 .
At normal incidence or for incidence angles smaller than 50◦ smoothing dominates on elemental materials. However, additional surface instabilities can exist due to the presence of a second atomic species on the surface. Hexagonally or- dered dot or hole patterns are thus observed at normal ion incidence on compound materials, like III-V semiconduc- tors, or on Si and Ge surfaces with concurrent deposition or implantation of foreign atoms [2, 3].
Keywords: ion induced nanopatterns, Ge nanostructures
  • Lecture (Conference)
    19th International Workshop on Inelastic Ion-Surface Collisions (IISC-19), 16.-21.09.2012, Frauenchiemsee, Deutschland

Publ.-Id: 18290 - Permalink


Ion Induced Patterns on Crystalline Ge Surfaces
Facsko, S.; Ou, X.; Mücklich, A.;
Low energy ion irradiations of surfaces can induce the formation of patterns with periodicities in the range of tens to hundreds of nanometers. These patterns have been used as templates for growing thin films with interesting anisotropic properties resulting from the modulation of their interface and surface [1].
At off-normal angle of incidence between around 55° and 70° and at room temperature ripple patterns oriented perpendicular to the ion beam direction are observed. At normal incidence or for incidence angles smaller than 55° smoothing dominates on elemental materials, like Si and Ge. However, additional surface instabilities can exist due to the presence of a second atomic species on the surface. Furthermore, on crystalline surfaces anisotropic diffusion or kinetic restrictions can also lead to additional instabilities.
We studied ion induced pattern formation on Ge surfaces with 1 keV Ar+ at elevated temperature. In contrast to irradiations at room temperature we found pattern formation even at normal ion incidence. Similar to the case of ion irradiated crystalline metal surfaces a new instability appears at higher temperature due to the Ehrlich-Schwoebel barrier [2]. Depending on the surface orientation checkerboard or isotropic hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface are observed (see Fig. 1a, b).
Keywords: ion induced nanopatterning, Ge nanostructures
  • Poster
    25th International Conference on Atomic Collisions in Solids (ICACS 25), 21.-25.10.2012, Kyoto, Japan

Publ.-Id: 18289 - Permalink


Ion irradiation of Ge: from sponge-like structure to periodic pattern formation
Facsko, S.; Fritzsche, M.; Ou, X.; Böttger, R.; Bischoff, L.;
Ion irradiation of materials can lead to swelling and the formation of sponge like structures. Especially Ge is susceptible to ion induced swelling for ions with energies in the range of 10 keV to 100 MeV. At lower ion energy, however, surface nanopattern can be produced by ion irradiation. These structures show periodicities in the range of a few tenths to hundreds of nanometers and are promising templates for producing nanostructured thin films. Periodic ripple patterns are observed frequently for ion irradiation at incidence angles greater than 55° to the surface normal. At normal incidence dot or hole patterns with hexagonal symmetry are observed only under special irradiation conditions.
We studied the formation of hexagonally arranged hole patterns on Ge(001) surfaces induced by irradiation with a scanned focused Ga+ ion beam (FIB) at normal incidence. Hole patterns with characteristic length of about 50 nm are observed in a narrow energy range of 4 - 6 keV (Fig. 1a). These patterns are independent of ion flux in a range of several orders of magnitude. In addition, the patterns induced by FIB irradiations were compared to broad beam Ga+ irradiations at the same ion energy. No differences were found demonstrating that FIB irradiations with a large overlap of the scanned beam are identical to conventional broad beam irradiations. Using heavy ions, like Bi dimers and trimers, in a mass separated FIB regular hexagonally ordered dot patterns are formed instead at normal incidence (Fig. 1b).
Furthermore, ion induced pattern formation on Ge surfaces with 1 keV Ar+ at normal incidence and higher temperature was studied. Similar to the case of ion irradiated crystalline metal surfaces on the crystalline Ge surface a new instability appears at higher temperature due to the Ehrlich-Schwoebel barrier. In this case, we observe regular checkerboard or hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface (see Fig. 1c).
Keywords: ion induced nanopatterning, Ge nanostructures
  • Invited lecture (Conferences)
    18th International Conference on Ion Beam Modification of Materials (IBMM-18), 02.-07.09.2012, Qingdao, China

Publ.-Id: 18288 - Permalink


Anisotropic surface enhanced Raman scattering in nanoparticle and nanowire arrays
Ranjan, M.; Facsko, S.;
Silver nanoparticles and nanowires self-aligned on pre-patterned rippled substrate are presented as active surface enhanced Raman scattering (SERS) substrates. The reported inter-particle gap of 5 nm and array periodicity of 35 nm are much lower than current lithographic limits. The observed anisotropy in SERS and surface plasmon resonance in such arrays is attributed to different plasmonic field enhancement along and across the chains of nanoparticles not due to shape anisotropy. For nanoparticle arrays higher SERS intensity is found along the particle chain, but for nanowire arrays higher SERS intensity is found for excitation across the wires. Higher intensity across nanowire arrays supports the argument that the SERS phenomenon is due to electromagnetic field enhancement (hot-junctions) caused by localized surface plasmon resonance across the nanowires having a 35 nm gap. The effect of inter-particle gap, ordering, and aspect ratio on field enhancement is demonstrated. Higher SERS intensity is observed in aligned elongated nanoparticles compared to aligned spherical, non-ordered nanoparticles, or aligned nanowires. Aligned silver scattering more strongly than aligned gold nanowires.
Keywords: Ag nanoparticles, ion induced ripple paterns, surface enhanced plasmon resonance

Publ.-Id: 18287 - Permalink


The Helmholtz beamline at the European XFEL - Ultra-bright, ultra-fast, and coherent hard X-ray pulses for laser plasma science
Schramm, U.; Cowan, T.;
Status of the Helmholtz beamline project at the European XFEL: Ultra-bright, ultra-fast, and coherent hard X-ray pulses for laser plasma science
  • Invited lecture (Conferences)
    33rd International Workshop on Physics of High Energy Denisty in Matter, 13.-16.01.2013, Hirschegg, Österreich

Publ.-Id: 18286 - Permalink


Neutron shielding studies on an advanced molten salt fast reactor design
Merk, B.; Konheiser, J.;
The molten salt reactor technology has gained some new interest, but the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes more challenging than in historic concepts. One very interesting and innovative result of the EVOL project is the fluid flow optimized design of the inner reactor vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all internal structures. Based on this new geometry a model for neutron physics calculation is presented. The major steps are: the modeling of the curved geometry in the unstructured mesh neutron transport code HELIOS and the determination of the real neutron lfux and power distribution for this new geometry. The developed model is then used for the determination of the neutron fluences in the inner and outer wall of the system and for developing an optimized shielding strategy for the molten salt fast reactor to keep the fluence in the safety related outer vessel below the limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system will be comparable to a sodium cooled fast reactor.
Keywords: molten salt reactor; molten salt; fast reactor; nuclear power; nuclear reactor; advanced shielding; neutron transport; HELIOS

Publ.-Id: 18285 - Permalink


On the major DYN3D developments for fast reactor design and transient analysis
Merk, B.; Kliem, S.;
Due to the French project ASTRID [1], the European CP-ESFR [2] project, and the MYRRHA/FASTEF project [3], the research work on fast reactors has got a new push in Europe. Additionally to this European projects a strong project is growing in Russia based on the lead cooled fast reactor design BREST [4]. Following this trend, the Institute of Resource Ecology at the Helmholtz-Zentrum Dresden-Rossendorf has decided to start several projects dedicated to fast reactor technology [5], among them the extension of the well validated LWR core simulator DYN3D.
The new developments, first validation results, and the next strategic steps for the adaption of the code for the improved simulation of fast reactor cores are presented.
Keywords: DYN3D, fast reactors, fast reactor design, fast reactor safety
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland
    Jahrestagung Kerntechnik 2013
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland

Publ.-Id: 18284 - Permalink


Fine distributed moderating material to the enhance feedback effects in LBE cooled fast reactors
Merk, B.;
Problem of small feedback effects in fast reactors and some onsets to enhance the negative feedback effects have been discussed last year in an IAEA meeting in Vienna [[1]]. Small negative feedback effects are a common problem in all fast reactors. Especially in lead and lead bismuth eutectic (LBE) cooled reactors this problem is evident, due to the hard neutron spectrum. This hard neutron spectrum is caused by the very weak moderation effect in the heavy coolant even compared to sodium and appears due to the significantly higher atomic mass of lead.
A side view to the community of sodium cooled reactors (SFR) indicates a possible solution for the enhancement of one important negative feedback effect, the fuel temperature effect. The use of moderating material to improve the fuel temperature effect and the sodium void reactivity has already been discussed and investigated in detail for SFR with metallic fuel [[2]]. The concept of zirconium-hydride (ZrH) pins in reactors with metallic fuel has even been investigated before in several publications [[3]], [[4]], [[5]], [[6]]. A first test was already published for the use of ZrH in MOX fuelled, but steam cooled fast reactors [[7]]. In the last time, a new proposal has been analyzed. The negative feedback effects in a sodium cooled fast reactor are significantly enhanced by the introduction of fine distributed moderating material. The absolute value of the fuel temperature effect is significantly increased in combination with a decrease of the positive coolant effect by adding fine distributed moderating material, either in a layer inside the cladding or in the wire wrapper. The study has been focused in the first step on the choice of the ideal moderating material [[8]], [[9]] and in a second step on the optimization of the placing of the zirconium hydride to limit the influence on power distribution and burnup [[10]], [[11]].
The thermal stability of the hydrogen bearing compound is of paramount importance for the use of moderating material in a heavy liquid metal cooled fast reactor (HLMR) where significantly higher temperatures can be accepted during transients than in a SFR. Possible hydrogen bearing materials have already been discussed in a textbook on metal hydrides [[12]] and the effects in SFR has already been analyzed and published [13].
In this work it is demonstrated, that the concept of enhanced feedback coefficients is transferable to LBE cooled fast reactors. The demonstration is based on the fuel assembly design of the CDT project. The effect of the moderating material on the neutron spectrum, on the kinf, and on the fuel temperature feedback and the coolant feedback is shown, discussed and compared to SFRs.
Keywords: fast reactor, moderating material , fast reactor core design, Yttrium hydride, zirconium hydride, liquid metal cooled reactor, lead
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland
    Jahrestagung Kerntechnik 2013
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland

Publ.-Id: 18283 - Permalink


Polarization of a stored beam by spin-filtering
Augustyniak, W.; Barion, L.; Barsov, S.; Bechstedt, U.; Benati, P.; Bertelli, S.; Carassiti, V.; Chiladze, D.; Ciullo, G.; Contalbrigo, M.; Dalpiaz, P.; Dymov, S.; Engels, R.; Erwen, W.; Fiorini, M.; Gaisserde, M.; Gebel, R.; Goslaswski, P.; Grigoriev, K.; Guidoboni, G.; Kacharava, A.; Khoukaz, A.; Kulikov, A.; Kleines, H.; Langenberg, G.; Lehrach, A.; Lenisa, P.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Marianski, B.; Martin, S.; Mchedlishvili, D.; Merzliakov, S.; Meshkov, I.; Meyer, H.; Mielke, M.; Mikirtychiants, M.; Mikirtychiants, S.; Nass, A.; Nekipelov, M.; Nikolaev, N.; Nioradze, M.; Oellers, D.; Papenbrock, M.; Pappalardo, L.; Pesce, A.; Polyanskiy, A.; Prasuhn, D.; Rathmann, F.; Sarkadi, J.; Smirnov, A.; Seyfarth, H.; Shmakova, V.; Statera, M.; Steffens, E.; Stein, H.; Stockhorst, H.; Straatman, H.; Stroher, H.; Tabidze, M.; Tagliente, G.; Thorngren-Engblom, R.; Trusov, S.; Trzcinski, A.; Valdau, Y.; Vasiliev, A.; von Wurtemberg, K.; Weidemann, C.; Wustner, P.; Zupranski, P.;
The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons. (C) 2012 Elsevier B.V. All rights reserved.

Publ.-Id: 18282 - Permalink


Optical study of superconducting Ga-rich layers in silicon
Fischer, T.; Pronin, A. V.; Skrotzki, R.; Herrmannsdörfer, T.; Wosnitza, J.; Fiedler, J.; Heera, V.; Helm, M.; Schachinger, E.;
We performed phase-sensitive terahertz (0.12–1.2 THz) transmission measurements of Ga-enriched layers in silicon. Below the superconducting transition T c middle = 6.7 K we find clear signatures of the formation of a superconducting condensate and of the opening of an energy gap in the optical spectra. The London penetration depth λ(T ) and the condensate density ns = λ2(0)/λ2(T ) as functions of temperature demonstrate behavior typical for conventional superconductors with λ(0) = 1.8 μm. The terahertz spectra can be well described within the framework of Eliashberg theory with strong electron-phonon coupling: the zero-temperature energy gap is 2Δ(0) = 2.64 meV and 2Δ(0)/kBTc = 4.6, consistent with the amorphous state of Ga. At temperatures just above Tc, the optical spectra demonstrate Drude behavior.

Publ.-Id: 18281 - Permalink


Thermodynamic properties of CoCr2O4: specific heat and magnetic entropy
Uhlarz, M.; Pronin, A. V.; Wosnitza, J.; Prokhorov, A. S.; Bush, A. A.;
We present the temperature dependence of the specific heat of CoCr2O4 between 2.08 K and 306 K in zero magnetic field. The lattice component can be described by the Komada–Westrum model with a characteristic temperature ΘKW = 541 K. The entropy of the magnetic component amounts to 33.51 J mol-1 K-1 at T = 298.15 K, in good agreement with the magnetic entropy of Co2+ and Cr3+ ions with completely quenched orbital moments. We compare our results with data available in literature.

Publ.-Id: 18280 - Permalink


Γ3-Type Lattice Instability and the Hidden Order of URu2Si2
Yanagisawa, T.; Mombetsu, S.; Hidaka, H.; Amitsuka, H.; Akatsu, M.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Huang, K.; Maple, M. B.;
We have performed ultrasonic measurements on single-crystalline URu2Si2 with pulsed magnetic fields, in order to check for possible lattice instabilities due to the hybridized state and the hidden-order state of this compound. The elastic constant (C11 - C12)/2, which is associated with a response to the Γ3-type symmetry-breaking (orthorhombic) strain field, shows a three-step increase at H ≥ 35 T for H || c at low temperatures, where successive meta-magnetic transitions are observed in the magnetization. We discovered a new fact that the absolute change of the softening of (C11 - C12)/2 in the temperature dependence is quantitatively recovered at the suppression of hybridized-electronic state and the hidden order in high-magnetic field for H || c associated with the successive transitions. The present results suggest that the Γ3-type lattice instability, is related to both the emergence of the hybridized electronic state and the hidden-order parameter of URu2Si2. On the other hand, magnetic fields H || [100] and [110] enhance the softening of (C11 - C12)/2 in the hidden order phase, while no step-like anomaly is observed up to 68.7 T. We discuss the limitation of the localized-electron picture for describing these features of URu2Si2 by examination of a crystalline electric field model in terms of mean-field theory.

Publ.-Id: 18279 - Permalink


Particle deposition study in a horizontal turbulent duct flow using optical microscopy and particle size spectrometry
Barth, T.; Lecrivain, G.; Hampel, U.;
A new technique based on optical microscopy and particle size spectrometry is here presented to investigate deposition of aerosol particles. Micron-sized monodisperse liquid particles were injected in a horizontal duct flow. The turbulent flow field was recorded using Particle Image Velocimetry. The airborne particle size and number concentration was determined by isokinetic sampling in combination with an Aerodynamic Particle Sizer (APS). The surface deposited particles were counted by means of optical microscopy, which was found to be a robust and simple recording method. The particle deposition velocity was directly determined out of the number of deposited particles detected by the microscope and the airborne particle number concentration recorded by the APS. The present results show good agreement with similar studies and prove the potential of optical microscopy for the detection of wall deposited particles in comparison to the more complex and expensive methods such as fluorescence based wet chemistry or neutron activation techniques.
Keywords: Particle deposition, turbulent flow, optical microscopy, aerodynamic particle sizer, particle image velocimetry

Publ.-Id: 18278 - Permalink


Spectroscopic study of americium(III) complexes with nitrogen containing organic model ligands
Raditzky, B.; Sachs, S.; Schmeide, K.; Barkleit, A.; Geipel, G.; Bernhard, G.;
For the first time, the complexation of Am(III) with low molecular weight nitrogen containing aromatic model ligands, representing structural building blocks of humic acid, has been investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The complex formation with anthranilic acid and picolinic acid was studied at pH 3.8 and 6.0 at an ionic strength of 0.1 M (NaClO4) and room temperature. At pH 3.8, where both investigated ligands occur as zwitterionic species, a 1:1 Am(III) picolinate complex is formed with a stability constant of log β11 = 3.81 ± 0.44. The Am(III) complexation with anthranilic acid in its zwitterionic form seems to be hindered, due to electrostatic repulsion between the protonated amino group and the metal ion. With both ligands, Am(III) complexes could be identified at pH 6.0, where the fully deprotonated species of anthranilic acid and picolinic acid occur. Under the given experimental conditions, a 1:1 Am(III) anthranilate complex with log β11 = 3.70 ± 0.11 is formed. For the Am(III) picolinate system 1:1 and 1:2 complexes with log β11 = 3.83 ± 0.22 and log β12 = 7.34 ± 0.04, respectively, were identified. For comparison, the complex formation of Am(III) was also studied with phthalic acid as an example for the interaction of Am(III) with carboxylic groups.
Keywords: americium(III), complexation, nitrogen containing model ligands, anthranilic acid, picolinic acid, phthalic acid, UV-Vis, TRLFS

Publ.-Id: 18277 - Permalink


Semiconductor nanocrystals embedded in high-k matarials
Brenner, F.; Haas, S.; Schneider, F.; Klemm, V.; Schreiber, G.; von Borany, J.; Heitmann, J.;
The combination of high-k materials and nanocrystalline semiconductors leads to remarkable properties for various applications. The phase separation of ZrGeO and ZrSiO films in superlattice geometries were investigated. In case of the Si containing films, round-shaped clusters within a crystalline ZrO2 matrix have been observed after annealing at 1000 °C.
The appearance of nanocrystalline Si could not be shown, whereas amorphous clusters within the crystalline ZrO2 matrix were formed. For the Ge containing films, the formation of Ge nanocrystals was observed after annealing at 650 °C. In both material systems the ZrO2 matrix crystallized in the tetragonal phase.
Keywords: nanocrystals, high-k materials, multilayers
  • Invited lecture (Conferences)
    221st Meeting of Electrochemical Society, Symposium Advanced Nanomaterials and Processing, 06.-10.05.2012, Seattle, USA

Publ.-Id: 18276 - Permalink


Corrosion behaviour of Ti-48Al-2Nb-2Cr alloys
Pelic, B.; Rafaja, D.; Masset, P. J.; Seifert, H. J.; Bortolotto, L.; Schütze, M.; Wolf, G.; Loeh, I.;
γ-TiAl intermetallics are attractive materials for high-temperature structural applications in the aerospace and automobile industries. However, they show environmental embrittlement at elevated temperatures that is mainly related to their low high-temperature corrosion resistance. One way how to improve the high-temperature corrosion resistance is the deposition of protective coatings on the surface of the base material. In this study, samples of a Ti-Al alloy with the chemical composition Ti-48Al-2Cr-2Nb (at.%) were covered by physically vapour deposited (PVD), by metalorganic chemically vapour deposited (MOCVD) and by high-velocity oxy-fuel (HVOF) sprayed coatings. All coatings were based on the Ti-Al alloys and contained different amounts of alloying elements. The corrosion experiments were performed in molten salts containing 75 wt.% Na2SO4 and 25 wt.% NaCl at 850ºC up to 336 h. Both, PVD and CVD protected coatings reduced the changes in the mass of the samples over the corrosion time. Still, the formation of TiO2 could not be avoided, as it was confirmed by glancing-angle X-ray diffraction experiments.
Keywords: TiAl alloys, coatings, CVD, PVD, HVOF, high temperature oxidation/corrosion

Publ.-Id: 18275 - Permalink


Helmholtz Institut Freiberg für Ressourcentechnologie stellt sich vor: Spurenelemente für eine gesunde Wirtschaft
Birtel, S.;
Präsentation über die Arbeitsfelder und Struktur des HIF vor allem Bewerbungsmöglichkeiten für Studenten, insbesondere Ingenieure, Geowissenschaftler
Keywords: Jobmöglichkeiten, Ingenieure, Geowissenschaftler
  • Lecture (others)
    ORTE Freiberg, 10.01.2013, Freiberg, Deutschland

Publ.-Id: 18274 - Permalink


Nanopattering on crystal Ge surfaces
Ou, X.; Grenzer, J.; Facsko, S.;
In contrast to the nanopattering on amorphous semiconductor surfaces by ion irradiation, nanostructures on crystal Ge surfaces are created by irradiation under the temperatures above the recrystallization temperature. The temperature, fluence and orientation dependence on the nanopattens formation are demonstrated in this talk.
Keywords: irradiation, nanopattern, crystal Ge surface
  • Lecture (others)
    Forschergruppe 845 project workshop, 07.-08.11.2012, Dresden, Germany

Publ.-Id: 18273 - Permalink


Nano structure induced by ion beam sputtering
Ou, X.; Grenzer, J.; Facsko, S.;
Horizontal silicon nanowires arrays on insulator fabricated by ion irradiation and Nano-dot and nano-hole pattern on Si generated by metal incorporation during the ion beam sputtering
Keywords: irradiation, nanopatterning
  • Lecture (others)
    Forschergruppe 845 project workshop, 07.-08.02.2012, Kaiserslautern, Germany

Publ.-Id: 18272 - Permalink


Crystallization of the high-dose hydrogen ion implanted silicon-on-insulator layers under millisecond pulse annealing
in Russian
Tyschenko, I. E.; Volodin, V. A.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.;
Crystallization of the silicon-on-insulator films implanted with high dose of hydrogen ions was investigated under pulse millisecond annealing. Three-phase structure, consisted of the silicon nanocrystals, amorphous silicon, and hydrogen bubbles, was observed from the as-implanted samples. It was shown that the nanocrystal structure of the films is remained under pulse annealing up to 1000◦C. As pulse annealing temperature was increased, the nanocrystal diameter incrased from 2 to 5 nm, and the naoncrystal fraction rose to 70%. From the analysis of the crystalline-phase growth activation energy, it was speculated about the atomic hydrogen diffusion as limiting factor of the crystallization of the highly-hydrogenated ( 50 at%) silicon films.
Keywords: Crystallisation, SOI, hydrogen, pulse annealing
  • Fizika i Tekhnika Poluprovodnikov 47(2013)5, 591-596

Publ.-Id: 18270 - Permalink


Basic structures of integrated photonic circuits for smart biosensor applications
Germer, S.; Rebohle, L.; Skorupa, W.; Helm, M.;
Integrated optics concerns mainly the generation, guiding, and detection of light. Especially biosensing needs systems that incorporate electrical, electronic, and photonic devices for the detection of harmful substances, like synthetic oestrogens or plasticizers. We present here recent developments in the integration of our Si-based light emitter into a photonic circuit for a planar optical waveguide-based biodetection system.
Keywords: biosensor, waveguide, silanization, organosilane, photonic crystals
  • Poster
    DOKDOK 2012, 07.-11.10.2012, Oppurg, Deutschland
  • Lecture (Conference)
    Optics & Optoelectronics, 15.-18.04.2013, Prag, Tschechien
  • Contribution to proceedings
    Optics&Optoelectronics, 15.-18.04.2013, Prag, Tschechien
    Optical Sensors 2013; Sprocceings of SPIE Vol 8774, 87740P
    DOI: 10.1117/12.2014920

Publ.-Id: 18269 - Permalink


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