Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

35836 Publications

Ab initio wave function-based methods for excited states in solids: Correlation corrections to the band structure of ionic oxides

Hozoi, L.; Birkenheuer, U.; Fulde, P.; Mitrushchenkov, A.; Stoll, H.

Ab initio wave function-based methods are applied to the study of electron correlation effects on the band structure of oxide systems. We choose MgO as a prototype closed-shell ionic oxide. Our analysis is based on a local Hamiltonian approach and performed on finite fragments cut from the infinite solid. Localized Wannier functions and embedding potentials are obtained from prior periodic Hartree-Fock (HF) calculations. We investigate the role of various electron correlation effects in reducing the HF band gap and modifying the bandwidths. On-site and nearest-neighbor charge relaxation as well as long-range polarization effects are calculated. Whereas correlation effects are essential for computing accurate band gaps, we found that they produce smaller changes on the HF bandwidths, at least for this material. Surprisingly, a broadening effect is obtained for the O 2p valence bands. The ab initio data are in good agreement with the energy gap and bandwidth derived from thermoreflectance and x-ray photoemission experiments. The results show that the wave function-based approach applied here allows for well controlled approximations and a transparent identification of the microscopic processes which determine the electronic band structure.

Keywords: electronic structure; quantum chemistry; electron correlation; local correlation methods; frozen local hole approximation; ionic systems; MgO; band structure; quasi particles; band gap

Publ.-Id: 10692

Intersubband relaxation dynamics in single and double quantum wells based on strained InGaAs/AlAs/AlAsSb

Villas-Boas Grimm, C.; Priegnitz, M.; Winnerl, S.; Schneider, H.; Helm, M.

Intersubband relaxation dynamics in single and coupled double quantum well (QW) structures based on strained InGaAs/AlAs/AlAsSb are studied by femtosecond pump probe spectroscopy at wavelengths around 2 um. For single QWs the transient transmission was observed to decay exponentially with a time constant of 2 ps, showing that side valleys have negligible influence on the intersubband relaxation dynamics for strained InGaAs QWs. For double QWs, the pump-probe signal at the intersubband energy involving the two electronic levels located at the wider QW exhibits an induced absorption component attributed to the population of the second subband (associated with the narrow QW) by hot-electrons.

Keywords: Intersubband relaxation; InGaAs/AlAs/AlAsSb; single quatum well; double quatum well

Publ.-Id: 10691

Ion-induced ripple structures on silicon, x-ray measurements and TEM

Hanisch, A.; Grenzer, J.; Facsko, S.; Biermanns, A.; Pietsch, U.; Metzger, T. H.; Carbone, G.

Ion-induced ripple structures on silicon, x-ray measurements and TEM The formation of periodic surface structures varying from several nanometers to a few micrometers caused by ion-beam sputter erosion processes on semiconductor surfaces has attracted significant interest for the fabrication of laterally structured materials on a nanoscale.
We started systematic investigations of the rippled surface produced by Xe irradiation applying AFM. The subsurface structure has been identified by both TEM and depth resolved X-ray scattering methods such as GID. Furthermore the crystal structure of semiconductor surfaces should also kept clearly in mind. There is a strong evidence that the formation of ripples via ion beam erosion depends on preferred crystallographic directions of the silicon lattice.

Keywords: ion beam errosion; X-ray measurements

  • Poster
    7th Autumn School on X-ray scattering from surfaces and thin layers, 04.-06.10.2007, Smolenice, Slovakia

Publ.-Id: 10690

Beam dynamics studies for a 3½ cell superconducting RF photo injector operating at low and high bunch charge

Staufenbiel, F.; Janssen, D.; Kamps, T.; Lehnert, U.; Lipka, D.; Michel, P.; Teichert, J.; Xiang, R.

This paper presents the results of electron beam tracking simulations with the ASTRA code for the 3½ cell superconducting RF gun at the Forschungszentrum Dresden-Rossendorf. The SRF gun will improve the quality of the electron beam parameters for the ELBE superconducting electron linear accelerator. The ELBE electron accelerator is a general purpose facility for secondary radiation production. The facility produces x-rays, gamma-rays, neutrons, positrons and IR FEL radiation. The SRF gun will run in two operation modes with different repetition rates and bunch charges of the pulsed electron beam. The commonly used ELBE mode will operate with electron bunches with 13 MHz repetition rate and a bunch charge of about 77 pC with a maximal average current of 1 mA. The high charge mode with 500 kHz repetition rate and a bunch charge up to 1 nC will be used to generate neutrons by inducing nuclear reactions. For the future BESSY Soft X-ray FEL a bunch charge of about 2.5 nC is required. For these operation modes of the SRF gun preferential operation parameters are determined by the results of beam dynamics studies.

Publ.-Id: 10689

Nanostrukturen - Neue Konzepte und Verfahren für die Photovoltaik

von Borany, J.

Der Beitrag gibt einen kurzen Überblick über neue technologische und konzeptionelle Entwicklungen auf dem Gebiet der Si-Photovoltaik.
Im Mittelpunkt stehen dabei Beiträge des FZD zur Entwicklung transparenter leitfähiger Oxide sowie Nanocluster-Strukturen (Halbleiter, Metalle), deren Quanteneffekte bzw. Lichtstreuung innovative Ansätze für Hocheffizienz-Solarzellen ermöglichen.

Keywords: photovoltaics; transperent conductive oxide; nanoclusters

  • Lecture (others)
    Gründerimpuls-Veranstaltung "Nanotechnologie", 10.10.2007, Dresden, Germany

Publ.-Id: 10688

Flux dependene of cluster formation in neutron irradiated weld material

Ulbricht, A.; Bergner, F.; Hein, H.; Kammel, M.

A flux effect on the formation of irradiation-induced clusters in reactor presure vessel (RPV) steels and weld materials is usually assumed. However, it is not easy to quantify this effect because changes of neutron flux are frequently mixed with changes of fluence. This investigation is focused on the influence of neutron flux on the formation of irradiation-induced clusters at a fixed fluence. Small-angle neutron scattering experiments were performed for a neutron irradiated RPV weld material containing 0.22wt% Cu. Clearly distinguishable scattering curves were observed for the irradiated conditions. Data analysis shows that the peak radius of the cluster size distribution of the material irradiated at higher neutron flux of 2.1x10E12 cm^-2s^-1 (E > 1 MeV) is 0.85 nm and the peak radius for the material irradiated at a 35 times lower flux is 1.60 nm. The cluster volume fraction was found to be independent of flux. The effect of flux on the cluster size is surprisingly strong and indicates that cluster growth must have occurred during the low flux irradiation.

Keywords: SANS; RPV steel; weld; irradiation-induced clusters; flux effect

  • Poster
    4th European Conference on Neutron Scattering, 25.-29.06.2007, Lund, Sweden
  • Contribution to proceedings
    4th European Conference on Neutron Scattering, 25.-29.06.2007, Lund, Sweden
    Poster Presentations 4th European Conference on Neutron Scattering, Lund: Media-Tryck, 434-434
  • Contribution to external collection
    U. Stahnke, A. Brandt, H. A. Graf: BENSC Experimental Reports 2007, Berlin: Hahn-Meitner-Institut, HMI-B617, 2008, ISSN 0936-0891, 210-210

Publ.-Id: 10687

s-d exchange interaction induced magnetoresistance in magnetic ZnO

Xu, Q.; Hartmann, L.; Schmidt, H.; Hochmuth, H.; Lorenz, M.; Spemann, D.; Grundmann, M.

The magnetoresistance (MR) effect in Co-doped ZnO films prepared by pulsed laser deposition on a-plane sapphire substrates with electron concentration at 5 K ranging from 8.3×10^(17) cm^(−3) to 9.9×10^(19) cm^(−3) has been studied experimentally and theoretically. A large positive MR of 124% has been observed in the film with the lowest electron concentration of 8.3×10^(17) cm^(−3), while only a negative MR of −1.9% was observed in the film with an electron concentration of 9.9×10^(19) cm^(−3) at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin splitting of the conduction band. The negative MR is attributed to the magnetic field suppressed weak localization. The presented modeling of superimposed positive and negative MR well agrees with the experimentally observed MR and hints at the physical origin of MR in Co-doped ZnO.

Keywords: 75.50.Pp; 75.47.De; 75.30.Et; 73.20.Fz

  • Physical Review B 76(2007), 134417

Publ.-Id: 10686

HF-Modulationsspektroskopie zur Bestimmung optischer Parameter in trüben Medien

Schleicher, E.; Da Silva, M. J.; Paul, S.; Hampel, U.

Die ortsaufgelöste HF-Modulationspektroskopie ist eine Methode zur Quantifizierung optischer Parameter wie Absorption und Streuung von trüben Medien. Sie findet sowohl in der medizinischen Diagnostik zur Bestimmung der Blutsauerstoffsättigung im Kapillarbett als auch in technischen Prozessen beispielsweise zur Trübungs- oder Fettgehaltsmessung Anwendung. Das in diesem Beitrag vorgestellte Messsystem arbeitet auf Basis der homodynen Demodulation und eröffnet auf Grund der faseroptischen Ankopplung ein breites Einsatzgebiet. Erste vielversprechende Ergebnisse werden vorgestellt.

Keywords: NIR-spectroscopy; laser diagnostics; optical properties; turbid media; RF-modulation spectroscopy

  • Contribution to proceedings
    8. Dresdner Sensor-Symposium, 10.-12.12.2007, Dresden, Germany
    Dresdner Beiträge zur Sensorik, Band 29, Dresden: TUDpress, Verlag der Wissenschaft GmbH, ISBN-13: 978-3-940046-45-1, 79-82
  • Lecture (Conference)
    8. Dresdner Sensor-Symposium, 11.12.2007, Dresden, Germany

Publ.-Id: 10685

Phase change in Fe implanted rutile TiO2 after thermal treatment

Talut, G.; Reuther, H.; Zhou, S.; Potzger, K.

Diluted magnetic semiconductors (DMS) are materials which simultaneously exhibit ferromagnetic and semi-conducting properties by substitution of transition metal atoms onto cation sites. Recently, transition metal doped TiO2 has been reported to be ferromagnetic above room temperature. It was found that nanoscaled precipitates can substantially contribute to the ferromagnetic properties.
In this study, commercial rutile TiO2(110) single crystals were implanted with 180 keV 57Fe ions at 623 K with fluences between 1x10^16 and 4x10^16 cm^-2 and subsequently annealed at temperatures up to 1073 K. The maximum Fe concentration at projected range Rp = 89 nm was about 5 %.
Virgin, implanted and post-annealed samples were investigated using conversion electron Mößbauer spectroscopy, channeling Rutherford backscattering spectrometry (C-RBS), synchrotron-XRD, and super-conducting quantum interference device (SQUID) magnetometry.
Crystalline, imperfect bcc-Fe and FeO-TiO2 composites (or solid solution) were detected in the sample implanted with 4x10^16 cm^-2 already in the as-implanted state. Besides secondary phases a small fraction of Fe^2+ is observed in the as-implanted and at 923 K annealed sample and can be ascribed to Fe substituting Ti sites.
During annealing at 923 K, both phases grow in grain size, while the amount of FeO-TiO^2 is drastically increased, accompanied by a change of the Fe site location. After annealing at 1073 K, FeO-TiO2 composites are the predominated precipitates at the cost of metallic Fe. Both, bcc-Fe and FeO-TiO2 composites are textured.
According to the CEMS and SQUID measurements the origin of ferromagnetism is attributed to bcc-Fe-clusters. The oxidization of metallic Fe with increasing annealing temperature results in the decrease of the saturation moment .

Keywords: DMS; Fe; rutile

  • Poster
    International Conference on the Applications of the Mössbauer Effect, 14.-19.10.2007, Kanpur, India

Publ.-Id: 10678

Photovoltaics related research activities at the Forschungszentrum Dresden-Rossendorf

von Borany, J.; Gerbeth, G.; Rogozin, A.; Shevchenko, N.; Schmidt, B.

A summary is given on photovoltaics related research activities at FZD.

  • Poster
    WE-Heraeus-Seminar "Photonmanagement in Solar cells", 28.10.-01.11.2007, Bad Honnef, Germany

Publ.-Id: 10677

Materials Research Using Ion Beams at the Dresden Ion Beam Centre

Möller, W.

The Ion Beam Centre at Forschungszentrum Dresden-Rossendorf (FZD) is nearly exclusively dedicated to Materials Research. Three electrostatic accelerators (1.8 MV single-ended, 3 MV Tandetron, 5 MV tandem) and three ion implanters (40 kV, 200 kV, 500 kV) are available which provide multispecies irradiation possibilities for surface analysis and modification. Users are offered the full spectrum of high-energy analytical methods including Rutherford Backscattering (RBS), Elastic Recoil Detection Analysis (ERDA), Nuclear Reaction Analysis (NRA), and Proton Induced X-ray Emission (PIXE). Special equipment provides an external beam for RBS and PIXE, a microbeam setup which allows ERD and RBS/channeling analyses, RBS and ERDA depth profiling with ultrahigh depth resolution, as well as real-time in-situ analysis during surface processing.
The Centre delivers about half of its capacities to external users from research and industry. Researchers from other European States are funded by the European Commission for Transnational Access to the laboratory.
The short lecture will display the general features of the Centre and address a few selected applications. The prominent role of ion beam applications to materials research will be discussed.

  • Lecture (Conference)
    Workshop on Small-Scale Accelerator Facilities, 08.09.2007, Aghios Nikolaos, Greece

Publ.-Id: 10676

Puzzling Energy and Angle Distributions of Atoms Ejected during Reactive Magnetron Sputtering: Effects of Target Texture?

Möller, W.; Güttler, D.; Cornelius, S.

During reactive magnetron sputtering of TiN in an Ar/N2 gas mixture, energy and angle distributions of sputtered Ti neutrals have been measured using a HIDEN EQP energy-resolving mass spectrometer. Both kind of distributions show features which are not consistent with the expectations from standard collisional sputtering theory being valid for a random structure of the target. Distributions of the energy E have been obtained from both metallic and poisoned areas of the target. As expected from the Thompson distribution, f(E) ~ E/(E+Us)^3, they peak at half of the surface binding energies Us, but are significantly narrower than predicted. The distributions of the emission angle (with respect to the surface normal) exhibit pronounced maxima tilted by ~40° from the target normal, thus strongly deviating from the expected cosine behaviour, f(alpha) ~ cos(alpha).
Any experimental artifacts can be excluded which might result in the above observations. As the only reasonable explanation we propose potential effects of texture, which might be originally present at the target surface or develop during ion bombardment. For the angular distributions, this is in qualitative accordance with sputter ejection patterns from crystals at keV incident energy as reported in literature. Corresponding collisional computer simulations for the present conditions are in preparation, as are detailed structural diagnostics of the target surface.

  • Lecture (Conference)
    Symposium on Reactive Sputter Deposition, 06.-07.12.2007, Leoben, Austria

Publ.-Id: 10675

Mechanismen und Modellierung der Targetvergiftung beim reaktiven Magnetron- Sputtern

Möller, W.; Güttler, D.; Abendroth, B.; Grötzschel, R.

Ein globales Modell eines Ar/N2-Magnetron-Plasmas wird mit einer dynamischen kollisionären Computersimulation der Plasma-Oberflächen-Wechselwirkung (TRIDYN) kombiniert, um die Verbindungs-Bildung an der Oberfläche eines Ti-Sputtertargets (die sog. Target-Vergiftung) zu modellieren. Der Beschuss mit energetischen Ionen und die damit verbundene Implantation von Reaktivgas-Atomen resultiert in einer modifizierten Oberflächenschicht, deren Dicke die einer Monolage weit übersteigt. Bei steigendem Reaktivgas-Partialdruck bleibt diese Dicke etwa konstant, während die Stickstoff-Konzentration bis zur stöchiometrischen Sättigung ansteigt. Wesentliche Mechanismen sind die direkte Implantation der Reaktivgasionen und die Rückstoßimplantation adsorbierter Reaktivgasatome durch Inertionen-Beschuss.
Experimentell wurde das Stickstoffinventar in der Target-Oberfläche eines unbalancierten 2''-Magnetrons in verschiedenen Ar/N2-Gasmischungen und bei einem Totaldruck von ca. 0.3 Pa in einer Echtzeit-in-situ-Anordnung mit Hilfe der 14N(d,)12C-Kernreaktion vermessen. Das gemessene Sättigungsinventar stimmt mit den Ergebnissen der Modellierung sehr gut überein. Aus dem Vergleich der Abhängigkeiten vom Reaktivgas-Partialdruck kann geschlossen werden, dass (i) die Ionenimplantation allein die Resultate nicht zu beschreiben vermag und dass (ii) die Adsorption und nachfolgende Rückstoß-Implantation von Reaktivgas-Molekülen einen bedeutenden Beitrag liefert, während Reaktivgas-Radikale aus dem Plasma eine eher vernachlässigbare Rolle spielen.
Es wird weiterhin bei ausreichend niedrigem Stickstoff-Partialdruck eine signifikante laterale Variation des Stickstoff-Inventars über die Targetoberfläche beobachtet, die sich durch den gegenüber dem Neutralgasfluss deutlich erhöhten Ionenfluss in der race-track-Region des Magnetrons und die daraus resultierende Verschiebung der Depositions/Erosions-Balance erklärt.

  • Lecture (Conference)
    13. Fachtagung Plasmatechnologie, 06.03.2007, Bochum, Germany

Publ.-Id: 10674

Nanostructures by Ion-Driven Self-Organisation

Möller, W.

No abstract available

  • Lecture (others)
    Materials Modelling Seminar, 24.10.2007, Loughborough, United Kingdom

Publ.-Id: 10673

Nanostrukturen durch Ionen-getriebene Selbstorganisation

Möller, W.

No abstract available

  • Lecture (others)
    Physikalisches Kolloquium, 22.10.07, Bochum, Germany

Publ.-Id: 10672

Plasma-Target Interaction in Reactive Magnetron Sputtering

Möller, W.

No abstract available

  • Invited lecture (Conferences)
    Master Class: Physics and Technology of Plasma-Enhanced CVD Methods, 06.-13.10.2007, Bad Honnef, Germany

Publ.-Id: 10670

Target Poisoning during Reactive Magnetron Sputtering

Möller, W.

No abstract available

  • Invited lecture (Conferences)
    VEIT 2007 - 15th International Summer School on Vacuum, Electron, and Ion Technologies, 19.09.07, Sozopol, Bulgaria

Publ.-Id: 10669

The influence of non-uniform target poisoning on the energy distributions of atoms sputtered in a reactive DC magnetron discharge

Güttler, D.; Möller, W.

The lateral variation of the energy distributions of sputtered Ti atoms has been investigated by energy resolved mass spectrometry during reactive DC magnetron sputter deposition of TiN from a Ti target in an argon/nitrogen gas mixture. The mass spectrometer was placed at substrate position and scanned across the target surface of a two inch planar circular magnetron. The energy distribution of sputtered particles is influenced by their origin, showing significant differences between the center and the erosion zone of the target. The results are interpreted in terms of laterally different states of target poisoning, which results in a variation of the surface binding energy. The reactive gas target coverage as derived from the sputtered energy distributions is in reasonable agreement with predictions from model calculations.

Keywords: magnetron; reactive sputtering; target poisoning; energy distribution; modeling; surface binding energy

  • Plasma Sources Science & Technology 17(2008), 025016

Publ.-Id: 10668

Memory and luminescence properties of Si nanocrystals fabricated by ion beam mixing

Beyer, V.; Heinig, K.-H.; Schmidt, B.; Stegemann, K.-H.; Dimitrakis, P.

Ion irradiation induced interface mixing was used to generate silicon nanocrystals at the SiO2-Si interface of metal-oxide-semiconductor (MOS) structures aiming at electronic memory applications, photoluminescence as well as electroluminescence. No particular processing issues have
been encountered during integration of this technique in standard submicronic C-MOS technology. The memory properties of the fabricated structures as a function of the Si+-irradiation dose as well as annealing temperature and time have been examined through electrical measurements of capacitors and transistors. Low-voltage operating devices that can endure more than 10^6 programming/erasing cycles have been successfully achieved. While excellent device uniformity and reproducibility have been observed over 6-inch wafers, more research is still required to improve charge retention. The photoluminescence of the ion irradiated MOS structure gives a profile in the red region which is typical for Si nanocrystals. Preliminary results about the electroluminescence caused by an applied ac voltage will be reported too.

Keywords: ion irradiation; interface mixing; photoluminescence; electroluminescence; memory; Si NC; nanocrystals; MOS

  • Lecture (Conference)
    SEMINANO'07 - 3rd International Workshop on Semiconductor Nanostructures, 13.-16.06.2007, Bad Honnef, Germany

Publ.-Id: 10667

Reactivation of damaged rare earth luminescence centers in ion-implanted Metal-Oxide-Silicon light emitting devices

Prucnal, S.; Rebohle, L.; Nazarov, A. N.; Skorupa, W.

Charge trapping and quenching of the electroluminescence (EL) in SiO2 layers implanted by Ge and rare earth (RE) ions during hot electron injection were investigated. In case of the SiO2:Ge layer the EL quenching is caused by the transformation of the luminescent defects (≡Ge-Si≡ or ≡Ge-Ge≡) to optically not active centers during hot electron excitation, whereas the EL from rare earth centers is quenched due to the electron trapping by RE-centers or their surrounding but not due to their optical deactivation. Therefore, the flash lamp post-injection annealing releasing trapped electrons reactivates RE centers and increases the operating time of Metal-Oxide-Silicon light emitting devices (MOSLEDs).

Keywords: charge trapping; rare earth; luminescence centers; MOSLED; FLA

  • Applied Physics B 91(2008)1, 123-126

Publ.-Id: 10666

Investigation of the temperature degradation and re-activation of the luminescent centres in rare earth implanted SiO2 layers

Prucnal, S.; Rebohle, L.; Skorupa, W.

The temperature quenching mechanisms of the electroluminescence (EL) and the reactivation of the rare earth luminescent centres by the flash lamp annealing (FLA) made after hot electron injection into the SiO2 layer implanted by Tb and Gd was investigated. An increase of the temperature from room temperature up to 150oC reduces the gate voltage of about 3 V and increases the rate of the EL quenching process and the degradation of the Metal-Oxide-Silicon Light Emitting Diode (MOSLED) structure by a of factor of three. On the other hand, the post-injection FLA reactivates the RE centres switched off by electrons trapped around them during hot electron impact excitation, increasing the operating time of the MOSLEDs devices.

Keywords: electroluminescence; rare earth; temperature quenching; silicon dioxide

  • Solid State Phenomena 131-133(2008), 595-600

Publ.-Id: 10665

Energy transfer from Gd to Er atoms in SiO2(GdEr)-MOSLEDs produced by ion implantation

Prucnal, S.; Sun, J. M.; Skorupa, W.; Rebohle, L.

The excitation mechanism of electroluminescence (EL) of erbium ions co-implanted with gadolinium into the SiO2 layer of light emitting MOS devices (MOSLED) was investigated. Er ions were implanted into the SiO2 layer with a concentration of 2%, subsequently implanted by gadolinium ions with concentrations of 0.5, 1.5 and 3%. The Er implanted SiO2 exhibits the typical peak at 1540 nm and weak luminescence in the green and blue region. Two green peaks correspond to the radiative transitions from the 2H11/2 and 4S3/2 energy levels to the 4I15/2 ground state and blue peaks to those from the 2H9/2 and 4F5/2 to the 4I15/2. Silicon dioxide containing erbium co-implanted with Gd exhibits two different excitation mechanisms: direct Er3+ ion excitation by the hot electrons and the energy transfer from the 6PJ energy level of Gd to the 4f energy states of Er3+ leading to an increase of the EL of Er in the visible region. The additional implantation of Gd has no influence on the infrared luminescence at 1540 nm.

Keywords: rare earth; electroluminescence; energy transfer; MOSLED

Publ.-Id: 10663

Fourfold increase of the ultraviolet (314 nm) electroluminescence from SiO2:Gd layers by fluorine co-implantation and flash lamp annealing

Prucnal, S.; Sun, J. M.; Rebohle, L.; Skorupa, W.

Efficient ultraviolet electroluminescence (UVEL) is obtained from Metal-Oxide-Silicon (MOS) structures with the SiO2 :Gd/F active layers prepared by flash-lamp annealing and Gd and F co-implantation. We observed a doubling of both the UVEL intensity and the defect related luminescence by increasing the fluorine concentration. This is due to suppression of the hot electron scattering on the donor-type level of the E’-center which number is reduced by the fluorine and increasing the optical active Gd3+ centres by Gd-F3 molecule formation. Also, fluorine co-implantation has no influence on the operating time of the MOS diode. Additionally, the flash lamp annealing doubled the ultraviolet electroluminescence from SiO2 layers implanted by gadolinium alone or in combination with fluorine. This is related to the suppression of cluster formation of rare earth atoms occurring during conventional annealing methods.

Keywords: rare earth; electroluminescence; MOSLED

  • Applied Physics Letters 91(2007), 181107

Publ.-Id: 10662

Wächter im Rohr

Vogel, M.

Neuer Sensor erfasst Strömungsmuster elektrisch neutraler Fluide

Keywords: wire-mesh sensor; non-conducting fluids

  • Physik Journal 6(2007)10, 14-15

Publ.-Id: 10661

Leistungsstarke Emitter und einfach handhabbare Detektoren für die Terahertz-Time-Domain-Spektroskopie

Dreyhaupt, A.; Peter, F.; Winnerl, S.; Nitsche, S.; Wagner, M.; Schneider, H.; Helm, M.; Köhler, K.

Skalierbare Antennenstrukturen basierend auf photoleitenden GaAs-Substraten eignen sich hervorra-gend zur Erzeugung und Detektion von gepulster THz-Strahlung. Als Emitter liefern diese Elemente intensivere THz-Strahlung verglichen mit gängigen Emittern, wenn die Anregung mit einem typischen Titan-Saphir-Laser-Oszillator-System erfolgt. Für die Detektoren werden Substrate mit unterschiedli-chen Ladungsträger-Lebensdauern verglichen. Die Detektoren sind sehr flexibel bezüglich der Fokus-sierung sowohl des Terahertz- wie des nahinfraroten Abfragestrahls. Experimente zur Terahertz-Time-Domain-Spektroskopie (THz-TDS) an Papierschichten und Schokoladenpralinen dienen als Beispiel für die Stärke dieser Technik.

Keywords: Terahertz; photoleitend; Time-Domain-Spektroskopie

  • Technisches Messen 75(2008), 3-13

Publ.-Id: 10660

Fluorine-18 radiolabeled S100/calgranulins as potential probes for characterization of receptor of advanced glycation endproducts (RAGE) by positron emission tomography (PET) in vivo

Pietzsch, J.; Hoppmann, S.; Richter, S.; Haase, C.

kein Abstract verfügbar

  • Poster
    14th Congress of Calcium Binding Proteins and Calcium Function in Health and Disease, 16.-21.10.2007, La Palma, Spain
  • Open Access Logo Abstract in refereed journal
    Calcium Binding Proteins 2(2007), 80

Publ.-Id: 10659

Synthesis, Copper(II) Complexation, 64Cu-Labeling and Bioconjugation of a New Bis(2-pyridylmethyl) Derivative of 1,4,7-Triazacyclononane

Gasser, G.; Tjioe, L.; Graham, B.; Belousoff, M. J.; Juran, S.; Walther, M.; Künstler, J.-U.; Bergmann, R.; Stephan, H.; Spiccia, L.

A new ligand derivative of 1,4,7-triazacyclononane (TACN), 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (6), has been synthesized and its complexation behavior towards Cu2+ ions investigated. The ligand 6 has been characterized by spectroscopic methods and a molecular structure of a corresponding Cu(II) complex has been elucidated by single crystal X-ray analysis. The suitability of 6 for conjugation to peptide substrates has been shown by amide coupling of 6 to the stabilized derivative of bombesin (BN), βAla-βAla-[Cha13, Nle14]BN(7-14), to give the conjugate 8. The free ligand 6 and the bioconjugate 8 were labeled with 64Cu2+ and the resulting complexes, 64Cu . 6 and 64Cu . 8, were found to be stable in the presence of a large excess of a competing ligand (cyclam) or the copper-seeking superoxide dismutase (SOD), as well as in rat plasma.
Biodistribution studies of 64Cu . 8 in Wistar rats showed a high activity uptake into the pancreas (5.76 ± 0.25 SUV, 5 min p.i.; 3.93 ± 0.25 SUV, 1 h p.i.), which is the organ with high levels of gastrin-releasing peptide receptor (GRPR). This receptor is over-expressed in a large number of breast and prostate carcinomas. The novel 64Cu . 6 complex had a dominating influence on the non-specific activity biodistribution of its BN conjugate, since the distribution data of 64Cu . 6 are similar to 64Cu . 8. The 64Cu complexes exhibited a low activity accumulation in the liver tissue and an extensive renal clearance, which was distinctively different to the biodistribution of 64CuCl2, suggesting that 64Cu . 6 does not undergo significant demetalation, but rather exhibits high in vivo stability.

  • Bioconjugate Chemistry 19(2008)3, 719-730

Publ.-Id: 10658

The IR-Beam Transport System from the ELBE-FELs to the User Labs

Seidel, W.; Grosse, E.; Justus, M.; Leege, K.-W.; Proehl, D.; Schlenk, R.; Winter, A.; Wohlfarth, D.; Wuensch, R.

In the Forschungszentrum Dresden-Rossendorf, two free-electron lasers (FELs) have been put into operation. They produce laser light in the medium and the far infrared wavelength range (4-150 ìm). The IR ligh is transported to several laboratories in the same building and to the adjacent building of the High Magnetic Field Laboratory as well, where the experimental setups are up to 70maway from the FELs. Constructional peculiarities, the large wavelength range, the high average power in cw regime, and the beam property requirements of the users pose a challenge to the beam line design. The transport system includes vacuum pipes, diagnostic elements, plane and toroidal gold-covered copper mirrors, and exit windows. The designed transport system produces a beam waist at selected spots in each laboratory representing a magnified image of the outcoupling hole. Spot size and position are independent of the wavelength.

  • Poster
    29th International Free Electron Laser Conference FEL 2007, 26.-31.08.2007, Novosibirsk, Russia
  • Contribution to proceedings
    29th International Free Electron Laser Conference FEL 2007, 26.-31.08.2007, Novosibirsk, Russia
    Proceedings of FEL 2007

Publ.-Id: 10657

In vivo catabolism of glycated and glycoxidized LDL: a comparative study with LDL modified in vitro or LDL isolated from prediabetic and diabetic patients

Pietzsch, J.; Haase, C.; Hoppmann, S.; Richter, S.; Graessler, J.; Kopprasch, S.; Julius, U.

kein Abstract verfügbar

  • Abstract in refereed journal
    Diabetologia 50(2007)Suppl. 1, 485
    DOI: 10.1007/s00125-007-0809-7
  • Poster
    43rd Annual Meeting of the European Association for the Study of Diabetes (EASD), 16.-21.09.2007, Amsterdam, Niederlande

Publ.-Id: 10656

Expression, purification and fluorine-18 radiolabeling of recombinant S100 proteins - potential probes for molecular imaging of receptor for advanced glycation endproducts (RAGE) in vivo

Hoppmann, S.; Haase, C.; Richter, S.; Pietzsch, J.

Data concerning the pathophysiological role of the interaction of circulating S100 proteins, a multigenic family of Ca2+-modulated proteins, with the receptor for advanced glycation endproducts (RAGE) in cardiovascular diseases, inflammatory processes, and tumorigenesis in vivo are scarce. One reason is the shortage of suitable radiotracer methods. We report a novel methodology using recombinant human S100A1, S100B, and S100A12 as potential probes for molecular imaging of this interaction. Therefore, human S100 proteins were cloned as GST fusion proteins in the bacterial expression vector pGEX-6P-1 and expressed in E. coli strain BL21. Purified recombinant human S100 proteins were radiolabeled with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). The radiolabeled recombinant S100 proteins (18F-S100) were used in biodistribution experiments and small animal positron emission tomography (PET) studies in rats. The tissue-specific distribution of 18F-S100 proteins in vivo correlated well with the anatomical localization of RAGE, e.g., in lungs and in the vascular system. These findings indicate circulating S100A1, S100B, and S100A12 proteins to be ligands for RAGE in rats in vivo. The approach allows the use of small animal PET and provides novel probes to delineate functional expression of RAGE under normal and pathophysiological conditions in rodent models of disease.

Publ.-Id: 10654

Glycoxidation of low-density lipoprotein in impaired glucose tolerance: implications for the pathogenesis of diabetic vascular disease

Kopprasch, S.; Graessler, J.; Bornstein, S. R.; Pietzsch, J.

Atherosclerosis, a major vascular complication of type 2 diabetes mellitus (DM2), is a chronic inflammatory disease with increased glycoxidative stress in response to cellular and systemic glucose overload and lipid retention in the vessel wall. Glycoxidative modification of low density lipoprotein (LDL) is considered as a major causative factor of accelerated atherosclerosis in diabetic patients. Since atherogenesis starts before DM2 is diagnosed, this review will focus on the nature and extent of glycoxidative changes of LDL in subjects with impaired glucose tolerance (IGT). We review the evidence for the enhanced atherogenicity of LDL from IGT subjects including their contribution to the conversion of macrophages into a proatherogenic phenotype.

  • Vascular Disease Prevention 5(2008), 24-28

Publ.-Id: 10653

Magnetic field effects on electrochemical metal depositions

Bund, A.; Ispas, A.; Mutschke, G.

This paper will discuss recent experimental and numerical results from the authors' labs on the effects of moderate magnetic (B) fields in electrochemical reactions. The probably best understood effect of B fields during electrochemical reactions is the magnetohydrodynamic (MHD) effect. In the majority of cases it manifests itself in increased mass transport rates which are a direct consequence of Lorentz forces in the bulk of the electrolyte [1]. Of course, enhanced mass transport can directly affect the electro­crystallization and the structure of a growing metal layer. The partial currents for the nucleation of Nickel and Nickel-Iron alloys in magnetic fields were determined using an in-situ micro-gravimetric technique. They will be discussed on the basis of recent nucleation models [2].
A careful analysis of the governing equations shows that MHD problems must be treated in 3D geometry. We will discuss digital simulations of MHD flows during copper electrolysis. In most cases there is a complex interplay of natural and magnetically driven convection (see Fig. 1).
Acknowledgments: This work was supported by the German Science Foundation within the frame work of the collaborative research center 609 "Electromagnetic flow control in metallurgy, crystal growth and electrochemistry"
1) T. Weier, K. Eckert, S. Muehlenhoff, C. Cierpka, A. Bund, M. Uhlemann, Electrochem. Commun., 9 (2007) 2479.
2) L. Heerman, A. Tarallo, J. Electroanal. Chem. 470 (1999) 70.

Keywords: electrochemical deposition; metal deposition; magnetic field; magnetohydrodynamic effect; numerical simulation

  • Invited lecture (Conferences)
    International Conference on Magneto-Science (ICMS2007), 11.-15.11.2007, Hiroshima, Japan
  • Open Access Logo Science and Technology of Advanced Materials 9(2008), 024208

Publ.-Id: 10652

Effect of elevated temperature on optical properties of Al-doped polycrystalline ZnO films

Vinnichenko, M.; Rogozin, A.; Kolitsch, A.; Möller, W.

Al doping of ZnO thin films by ion implantation and subsequent annealing was tested. A combination of Drude term with Tanguy oscillator (excitonic effects) is shown to be an appropriate parameterization of dielectric function of highly doped ZnO. The free electron density values obtained by spectroscopic ellipsometry analysis are in good agreement with those determined by Hall effect measurements.

Keywords: spectroscopic ellipsometry; transparent conductive oxides; Al-doped ZnO; reactive magnetron sputtering

  • Lecture (Conference)
    Woollam-Ellipsometrie-Seminar, 24.10.2007, Darmstadt, Germany

Publ.-Id: 10651

Factors influencing the formation of small dense low-density lipoprotein particles in dependence on the presence of the metabolic syndrome and on the degree of glucose intolerance

Julius, U.; Dittrich, M.; Pietzsch, J.

Small dense low-density lipoprotein (LDL) particles are known to be especially atherogenic. Several mechanisms are involved in this atherogenicity.

We wanted to look for the presence of small dense LDL particles depending on gender, metabolic syndrome (MS) and different degrees of glucose intolerance. Moreover, we looked for anthropometric factors and factors of lipid and carbohydrate metabolism that are associated with changes in the LDL size.

We studied 752 persons (330 males, 422 females; age 40 ± 17 years). LDL particle size was estimated with polyacrylamide gel electrophoresis. Males had smaller LDL particles than females. Probands with the MS had smaller LDL particles than those without this syndrome. With rising plasma triglyceride (TG) levels more small dense LDL particles were seen. The highest proportion of these small dense LDL particles was observed in the subgroup of type 2 diabetic patients. In the whole material, the mean LDL diameter was correlated negatively with plasma TG and very low-density lipoprotein components (TG, cholesterol and proteins) and positively with high-density lipoprotein cholesterol. In a linear stepwise regression analysis different significant factors influencing the LDL size were found in the whole population, in normoglycaemic probands, in persons with impaired glucose tolerance, in type 2 diabetic patients and in type 2 diabetic patients injecting insulin.

Our data point to different mechanisms of the formation of small dense LDL particles in dependence on the degree of glucose intolerance. Moreover, the target values for plasma TG should be set lower.

Publ.-Id: 10650

Uranium species formed by monocellular algae - EXAFS investigations at 30 K -

Günther, A.; Roßberg, A.

Bestimmung von U-P Koordinationen in U(VI) - Algen Komplexen bei pH 5 und pH 6

  • Lecture (others)
    ROBL - Radiochemie Workshop, 19.12.2006, Rossendorf, Germany

Publ.-Id: 10649

Structural and mechanical characterization of BCxNy thin films deposited by pulsed reactive magnetron sputtering

Krause, M.; Bedel, L.; Taupeau, A.; Kreissig, U.; Munnik, F.; Abrasonis, G.; Kolitsch, A.; Radnoczi, G.; Zsolt, C.; Vanhulsel, A.

BCxNy thin films deposited at 250°C by pulsed reactive magnetron sputtering of a B4C target in an Ar/N2 plasma were studied by elastic recoil detection analysis, FTIR, Raman, and photoelectron spectroscopy, electron microscopy, and nanoindentation. In the concentration range of 6 % to 100 % N2 in the sputter plasma the segregation into nanocrystalline hexagonal boron nitride and amorphous sp2 carbon is the dominant process during the film growth. The stoichiometric ratio and structural details of the major phases depend on the N2 concentration in the plasma and have significant influence on the Young’s modulus and the elastic recovery of the BCxNy thin films.

Keywords: BCxNy; thin films; magnetron sputtering; spectroscopy; structural properties; mechanical properties

Publ.-Id: 10647

Comparison of in-beam and off-beam PET experiments at hard photons

Möckel, D.; Kluge, T.; Pawelke, J.; Enghardt, W.

In-beam positron emission tomography (in-beam PET) is a valuable in situ method for quality assurance in radiation therapy. It is well investigated for therapy with carbon ions and has been successfully clinically implemented at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. The extension of this efficient technique to other radiation treatment modalities may be worthwhile. For protons and 3-He the feasibility has already been investigated. Furthermore, it seems possible for the case of radiotherapy with high-energy photons, since positron emitters are generated by photons with energies above ~20 MeV due to (gamma, n) reactions (predominantly 11-C and 15-O in tissue).
In this regard, promising conclusions have been obtained by Geant4 simulations as well as by off-beam PET experiments using a conventional PET scanner. However, in the case of off-beam PET the time delay between irradiation and measurement causes a decrease of the number of positron emitters resulting in reduced counting statistics. At worst short-lived isotopes cannot be detected. Thus, a small double head PET camera consisting of two BGO block detectors was built up at the irradiation site to measure the generated beta+ activity distribution simultaneously to the irradiation. The relation between deposited dose and beta+ activity density was quantified. The obtained results are presented and compared to that of off-beam PET experiments. Higher activities as well as an improved contrast between materials of different stoichiometry is achieved by measuring in-beam showing the advantage of in-beam PET over off-beam PET. Thus, the application of in-beam PET at radiation therapy with high-energy photons can be useful for quality assurance, comprising monitoring of dose delivery, patient positioning and tumour response.

  • Lecture (Conference)
    2007 Nuclear Science Symposium and Medical Imaging Conference, 27.10.-03.11.2007, Honolulu, Hawaii, USA
  • Contribution to proceedings
    2007 Nuclear Science Symposium and Medical Imaging Conference, 27.10.-03.11.2007, Honolulu, Hawaii, USA, 1-4244-0923-3

Publ.-Id: 10646

Immobilization of selenium on Fe3O4 and Fe/FeC3 ultrasmall particles

López De Arroyabe Loyo, R.; Nikitenko, S.; Scheinost, A.; Simonoff, M.

Magnetic nanoparticles, NPs, have a number of features that make them ideally suited for the removal of toxic elements from liquid waste: high surface-area-to-volume ratio, high reactivity, easy dispersability, and simple recovery of the particles from solution using an external magnetic field. In this paper we studied the sorption of selenite ions onto Fe3O4 and Fe/Fe3C NPs in the aqueous solutions under anoxic conditions. The results show that Se(IV) sorption is extremely rapid : the equilibrium is reached in approximately 10 and 30 min for Fe3O4 and Fe/Fe3C NPs respectively at pH= 4.9÷5.1 in the solutions of 0.1M NaCl. The distribution coefficients are also very high for both kinds of NPs (Kd> 3000). Increasing pH to 10.3 or adsorption of organic ligands, like L-Lysine or dodecanoate, cause the decrease in Kd values. However, even in these cases Kd values exceed 150. Magnetic NPs loaded with selenium can be easily and completely removed from solution with 0.4T permanent magnet. XAS study revealed the absence of Se(IV) reduction during the sorption onto Fe3O4 NPs in the pH range of 4.8-8.0. By contrast, the removal of selenite ions with Fe/Fe3C NPs in anaerobic conditions occurs via Se(IV) reduction to Se(-II) followed by formation of iron selenide at the particles surface. Thus, the Fe/Fe3C NPs are superior to Fe3O4 NPs due to their ability to immobilize rapidly selenium via reductive mechanism. Presumably these particles could be also effective for the removal of other contaminants such as hexavalent chromium, actinides, technetium, and toxic organic compounds.

  • Environmental Science & Technology 42(2008)7, 2451-2456

Publ.-Id: 10645

Numerical and experimental study of a two-phase cylindrical stirrer

Pedchenko, A.; Bojarevics, A.; Priede, J.; Gerbeth, G.; Hermann, R.

A two-phase inductive stirrer represents a modification of a standard induction heater with the goal to change the flow structure in the melt qualitatively. It consists of a secondary induction coil without a direct connection to a power supply, but an own electrical circuit in order to create a phase shift to the primary current. The electric current in this secondary circuit is solely induced by the current in the primary circuit. This kind of magnetic field tailoring allows to arrange the flow in the molten zone as desired. For instance, the usual double vortex structure of an induction heater can easily be changed to a single torus. The resulting flow direction at the zone surface is from the primary to the secondary coil.
We present results of numerical simulations for the flow and the temperature distribution in the molten zone. In addition, model experiments using the GaInSn melt have been performed with direct measurements of the melt velocity and corresponding comparison to numerics.

  • Lecture (Conference)
    3rd Sino-German Workshop on Electromagnetic Processing of Materials, 15.-19.10.2007, Shanghai, China

Publ.-Id: 10644

An alternating magnetic field driven flow in a spinning cylindrical container

Shatrov, V.; Gerbeth, G.; Hermann, R.

The paper presents a numerical analysis of the free surface liquid metal flow driven by an alternating (ac) magnetic field in a spinning cylindrical container. The axisymmetric flow structure is analyzed for various values of the magnetohydrodynamic interaction parameter and Ekman numbers. The governing hydrodynamic equations are solved by a spectral collocation method, and the alternating magnetic field distribution is found by a boundary-integral method. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface. It is found that the container rotation may reduce the meridional flow significantly.

  • Journal of Fluids Engineering - Transactions of the ASME 130(2008), 071201

Publ.-Id: 10643

Measurement of 25Mg(p,gamma)26Al resonance strengths via gamma spectrometry

Formicola, A.; Best, A.; Imbriani, G.; Junker, M.; Bemmerer, D.; Bonetti, R.; Broggini, C.; Caciolli, A.; Confortola, F.; Corvisiero, P.; Costantini, H.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gyürky, G.; Gustavino, C.; Lemut, A.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.

The COMPTEL instrument performed the first mapping of the 1.809 MeV photons in the Galaxy, triggering considerable interest in determing the sources of interstellar 26Al. The predicted 26Al is too low compared to the observation, for a better understanding more accurate rates for the 25Mg(p,gamma)26Al reaction are required. The 25Mg(p,gamma)26Al reaction has been investigated at the resonances at Er= 745; 418; 374; 304 keV at Ruhr-Universität Bochum using a Tandem accelerator and a 4pi NaI detector. In addition the resonance at Er = 189 keV has been measured deep underground laboratory at Laboratori Nazionali del Gran Sasso, exploiting the strong suppression of cosmic background. This low resonance has been studied with the 400 kV LUNA accelerator and a HPGe detector. The preliminary results of the resonance strengths will be reported.

Keywords: Nuclear Astrophysics; Experiment; LUNA; Resonance strengths

Publ.-Id: 10642

Solitary excitations in quantum sine-Gordon spin chains

Zvyagin, S.

The sine-Gordon equation is one of the most famous “soliton” equations, relevant to an extremely broad class of physical phenomena. On the quantum level the sine-Gordon model is one of the paradigms of the quantum field theory. One of the most prominent examples of the sine-Gordon quantum systems is a S=1/2 antiferromagnetic chain perturbated by an alternating g-tensor and/or the Dzyaloshinskii-Moriya interaction. Interestingly, in the presence of such interactions, application of a uniform external field H, in addition to incommensurate soft modes, induces opening of an energy gap, Δ ~ H2/3. Most importantly, the sine-Gordon equation is exactly solvable. The spectrum of the quantum sine-Gordon spin chain has been predicted to consist of a soliton, antisoliton and their bound sates, called “breathers”.
Here, we report a detailed study of the magnetic excitation spectrum in copper pyrimidine dinitrate (Cu-PM), which has been recently identified as an S=1/2 antiferromagnetic chain with a field-induced spin gap, and is probably the best realization of the quantum sine-Gordon spin chain model known to date. By employing high-field high-resolution tunable-frequency submillimeter wave electron spin resonance (ESR) spectroscopy, the field-induced gap has been observed directly; ten excitation modes were resolved in the low-temperature spectrum, and their frequency-field diagram was systematically studied in magnetic fields up to 25 T. Signatures of three breather branches and a soliton, as well as those of several multi-particle excitation modes were identified. In addition, we report temperature and field measurements of the ESR spectrum, allowing us to test a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)]. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of spin-1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment in both cases is obtained.

  • Invited lecture (Conferences)
    Universität Kobe, 15.01.2007, Kobe, Japan

Publ.-Id: 10641

Micro-crystalline inclusions analysis by PIXE/RBS

Strivay, D.; Ramboz, C.; Gallien, J.-P.; Grambole, D.; Sauvage, T.

A characteristic feature of the nuclear microprobe using a 3 MeV proton beam is the long range of particles (around 70 micrometers in light matrices). The PIXE method, with EDS analysis and using the multilayer approach for treating the X-ray spectrum allows the chemistry of an intracrystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (Z and e, respectively) are known (the depth of the inclusion floor is Z+e). The parameter Z of an inclusion in a mineral can be measured with a precision of around 1 micrometer using a motorized microscope. However, this value may significantly depart from Z if the analyzed inclusion has a complex shape. The parameter e can hardly be measured optically. By using combined RBS and PIXE measurements, it is possible to obtain the geometrical information needed for quantitative elemental analysis. This paper will present measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE-RBS will be presented.

  • Poster
    9th European Conference on Accelerators in Applied Research and Technology, 03.-07.09.2007, Florence, Italy
  • Nuclear Instruments and Methods in Physics Research B 266(2008), 2375-2378
    DOI: 10.1016/j.nimb.2008.03.068

Publ.-Id: 10640

Crystallographically oriented Co and Ni nanocrystals inside ZnO formed by ion implantation and post-annealing

Zhou, S.; Potzger, K.; von Borany, J.; Grötzschel, R.; Skorupa, W.; Helm, M.; Fassbender, J.

In the last decade, transition metal doped ZnO has been intensively investigated as a route to room temperature diluted magnetic semiconductors (DMS). However the origin for the reported ferromagnetism in ZnO based DMS remains questionable. Possible options are diluted magnetic semiconductors, spinodal decomposition or secondary phases. In order to clarify this question, we have performed a thorough characterization of the structural and magnetic properties of Co and Ni implanted ZnO single crystals. Our measurements reveal that Co or Ni nanocrystals (NCs) are the major contribution of the measured ferromagnetism. Already in the as-implanted samples, Co or Ni NCs have formed, and they exhibit superparamagnetic properties. The Co or Ni NCs are crystallographically oriented with respect to the ZnO matrix. Their magnetic properties, e.g. the anisotropy and the superparamagnetic blocking temperature can be tuned by annealing.
We discuss the magnetic anisotropy of Ni NCs embedded in ZnO concerning the strain anisotropy.

Keywords: ZnO; Ion implantation; Magnetic nanocrystals

Publ.-Id: 10639

Fe implanted ZnO: magnetic precipitates versus dilution

Zhou, S.; Potzger, K.; Talut, G.; Reuther, H.; von Borany, J.; Grötzschel, R.; Skorupa, W.; Helm, M.; Fassbender, J.; Volbers, N.; Lorenz, M.; Herrmannsdörfer, T.

Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors argue that the observed ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition rather than from carrier mediated magnetic impurities, as required for a diluted magnetic semiconductor. In the present paper we answer this question for Fe-implanted ZnO single crystals comprehensively. Different implantation fluences, temperatures and post-implantation annealing temperatures have been chosen in order to evaluate the structural and magnetic properties over a wide range of parameters. Three different regimes with respect to Fe concentration and process temperature are found: 1) Disperse Fe^{2+} and Fe^{3+} at low Fe concentrations and low processing temperatures, 2) FeZn_2O_4 at very high processing temperatures and 3) an intermediate regime with a co-existence of metallic Fe (Fe^0) and ionic Fe (Fe^{2+} and Fe^{3+}). Ferromagnetism is only observed in the latter two cases, where inverted spinel ZnFe_2O_4 and \alpha-Fe nanocrystals are the origin of the observed ferromagnetic behavior, respectively. The ionic Fe in the last case could contribute to a carrier mediated coupling. However, the separation between Fe ions is too large to couple ferromagnetically due to the lack of p-type carrier. For comparison investigations of Fe-implanted epitaxial ZnO thin films are presented.

Keywords: ZnO; Fe; Implantation; Magnetism

  • Journal of Applied Physics 103(2008)2, 023902

Publ.-Id: 10638

Using X-ray diffraction to identify precipitates in transition metal doped semiconductors

Zhou, S.; Potzger, K.; Talut, G.; von Borany, J.; Skorupa, W.; Helm, M.; Fassbender, J.

In the past decade, room temperature ferromagnetism was often observed in transition metal doped semiconductors, which were claimed as diluted magnetic semiconductors (DMS). Nowadays intensive activities are devoted to clarify weather the observed ferromagnetism stems from carrier mediated magnetic impurities, ferromagnetic precipitates or spinodal decomposition. In this paper, we have correlated the structural and magnetic properties of transition metal doped ZnO, TiO2 and Si, prepared by ion implantation. Crystalline precipitates, i.e. transition metal (Co, Ni) and Mn-silicide nanocrystals, are responsible for the magnetism. Additionally due to their orientation nature with respect to the host, these nanocrystals in some cases are not detectable by conventional x-ray diffraction (XRD). This nature results in the pitfall of using XRD to exclude magnetic precipitates in DMS materials.

Keywords: X-ray diffraction; Nanocrystals; Magnetic semiconductors

  • Journal of Applied Physics 103(2008), 07D530
    DOI: 10.1063/1.2828710
  • Lecture (Conference)
    52nd Conference on Magnetism and Magnetic Materials and Intermag Conference, 05.-09.11.2007, Tampa, United States
  • Lecture (Conference)
    DPG Spring Meeting 2008, 24.-29.02.2008, Berlin, Germany

Publ.-Id: 10637

Ab-initio calculation of Exchange Interactions in YMnO3

Novak, P.; Chaplygin, I.; Seifert, G.; Gemming, S.; Laskowski, R.

Hexagonal manganites with the composition RMnO3 undergo several magnetic phase transitions due to frustration effects between the manganese centres, which are located on a triangular lattice. Additional local magnetic moments of the metal R give rise to a rich variety of different magnetic phases, especially in the low-temperature region. In the parent compound YMnO3 only the manganese centres can be magnetic, thus it allows the investigation of the Mn-Mn coupling strength. All-electron density-functional calculations are carried out for several relative spin arrangements of nearest and next nearest neighbouring Mn sites; the standard spin-polarised LSDA and an extension to non-collinear magnetism are employed. In order to extract the coupling constants a Heisenberg model is fitted to the total energy differences between the investigated structures.

Keywords: manganites; multiferroics; magnetism; density functional theory; non-collinear; spin spiral

  • Lecture (Conference)
    ICMAT07, 01.-06.07.2007, Singapore, Singapore

Publ.-Id: 10636

Finite-element simulation and performance of pulsed magnets

Skourski, Y.; Herrmannsdörfer, T.; Sytcheva, A.; Wosnitza, J.; Wustmann, B.; Zherlitsyn, S.

es hat kein Abstract vorgelegen

  • Poster
    MT-20 - 20th Biennial Conference on Magnet Technology, 27.-31.08.2007, Philadelphia, USA

Publ.-Id: 10635

Evidence for an FFLO state in the organic superconductor k-(BEDT-TTF)2Cu(NCS)2

Wosnitza, J.

es hat kein Abstract vorgelegen

  • Lecture (Conference)
    ISCOM 2007 - 7th International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets, 24.-29.09.2007, Peniscola, Spain

Publ.-Id: 10634

Measurement techniques for liquid metal flows

Cramer, A.; Eckert, S.; Gerbeth, G.

Commerical Measuring Techniques for Liquid Metal Flows (MTLMF) are hardly available. The reason for this deficiency has to be sought in the properties of the metallic melts (opaqueness, heat capacity), high temperatures, chemical reactivity, interfacial effects, and sensitivity to electromagnetic noise. Therefore, embodyments of MTLMF are primarily to be found on a laboratory scale.

Velocity measuring techniques may be distinguished using the influence they exert on the flow as a criterion. The local probes, e.g. electric potential probes and mechano-optical sensors, are invasive. Ultrasonic methods, the most prominent member of which is Ultrasonic Doppler Velocimetry (UDV), may on the one hand not be termed invasive - but on the other hand still need contact. Examples of contact-less techniques are the inductive methods (inductive flowmeters, Contact-less Inductive Flow Tomography (CIFT)) and X-ray radiography.

Leaving aside local probes and X-ray techniques, the present lecture reports on the state of the art of UDV and CIFT. Exemplary investigations in our lab are discussed, showing limitations and future challenges of both these non-invasive MTLMFs.

  • Lecture (others)
    AMPERE meeting, 10.-11.07.2007, Paris, France

Publ.-Id: 10633

Tollmien-Schlichting wave damping by a streamwise oscillating Lorentz force

Albrecht, T.; Metzkes, H.; Grundmann, R.; Mutschke, G.; Gerbeth, G.

We present 2-D and 3-D Direct numerical Simulations of Tollmien-Schlichting (TS) wave superposition in a flat plate boundary layer, where the initial TS wave is intended to be canceled out by a second wave of opposite phase.

  • Magnetohydrodynamics 44(2008)3, 205-222

Publ.-Id: 10632

European research on thermal hydraulics for heavy liquid metal ADS applications

Roelofs, F.; Class, A.; Jeanmart, H.; Ciampichetti, A.; Gerbeth, G.; Fazio, C.

The objective of the European 6th framework project EUROTRANS, sponsored by the European Commission, is to demonstrate the technical feasibility of transmutation of high level nuclear waste using Accelerator Driven Systems (ADS). Within this objective the design of a European experimental ADS (XT-ADS) should demonstrate the technical feasibilities to transmute a sizeable amount of waste and to operate an ADS safely. The XT-ADS will be a subcritical reactor system having liquid lead-bismuth eutectic (LBE) as coolant. This liquid LBE is also intended to serve as target material for the spallation reaction which forms a crucial part to the subcritical reactor core. Since LBE is used as core coolant and spallation material, knowledge of the thermal hydraulic behaviour of LBE is essential.

  • Lecture (Conference)
    ENC 2007 - European Nuclear Conference, 16.-19.09.2007, Brussels, Belgium

Publ.-Id: 10631

Effect of electromagnetic stirring on microstructure evolution and mechanical properties of peritectic Ti-Al alloy

Biswas, K.; Hermann, R.; Gerbeth, G.; Priede, J.

The effects of strong melt convection on microstructure evolution and resulting mechanical properties of Ti45Al55 peritectic alloys has been investigated. The samples are subjected to both conventional induction melting as well as enhanced melt stirring by applying an external magnetic field using a specially designed floating zone arrangement. The stirred samples show a significant improvement of the plastic deformability compared to the conventionally melted samples. Additionally, the fracture surface of the stirred samples exhibits more deformation. A strong change in the morphology of properitectic phase from dendritic to spherical together with an increase in the properitectic phase fraction was observed in the stirred samples. The possible reason of the change in morphology is explained as a result of spherical growth under forced convection. Compositional line-scan shows that the Al-depletion layer near the interface of (a2+g) colonies and g matrix reduces in the stirred samples due to the enhanced mass transfer under the effect of strong stirring.

  • Lecture (Conference)
    5th Decennial International Conference on Solidification Processing - SP07, 23.-25.07.2007, Sheffield, United Kingdom

Publ.-Id: 10630

Absolute versus convective helical magnetorotational instability in a Taylor-Couette flow

Priede, J.; Gerbeth, G.

We analyze numerically the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number (Pm=0). The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small amplitude perturbations.

  • Lecture (Conference)
    MHD Laboratory Experiments for Geophysics and Astrophysics, 01.-03.10.2007, Catania, Italy

Publ.-Id: 10629

Microsegregation in liquid Pb-based eutectics

Plevachuk, Y.; Sklyarchuk, V.; Yakymovych, A.; Gerbeth, G.; Eckert, S.

The temperature dependence of electrical conductivity, thermoelectric power and viscosity of Pb-based eutectic and near eutectic systems were studied. An anomalous behavior of the physical properties in the liquid binary Pb-Sn, Pb-Bi, Pb-Mg and ternary Pb-Bi-Sn melts has been revealed well above the liquidus. The temperature range of the anomalies reaches hundreds degrees and depends on the sample composition. The results obtained are interpreted in the context of the assumption that microsegregation areas formed by micro and nanoclusters exist in the eutectic and near eutectic systems.

  • Lecture (Conference)
    4th International Workshop on Functional and Nanostructured Materials, 01.-06.09.2007, Gdansk, Poland
  • Journal of Non-Crystalline Solids 354(2008), 4443-4447
    DOI: in press

Publ.-Id: 10628

Melting-solidification process in Pb-Bi melts

Sklyarchuk, V.; Plevachuk, Y.; Gerbeth, G.; Eckert, S.

Electrical conductivity, s(T), and thermoelectric power, S(T), of liquid Pb-Bi alloys of eutectic and near eutectic compositions were investigated in the “melting-solidification” temperature region. The revealed discrepancies between the heating and cooling s(T) and S(T) curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheterogeneous structure of the Pb-Bi melts. A solidification mechanism is proposed.

  • Lecture (Conference)
    XIII International Seminar on Physics and Chemistry of Solids, 10.-13.06.2007, Ustron, Poland

Publ.-Id: 10627

Atomic layer deposition of Iridium Oxide thin films from Ir(acac)3 and Ozone

Hämäläinen, J.; Kemell, M.; Munnik, F.; Kreissig, U.; Ritala, M.; Leskelä, M.

Iridium oxide thin films were grown with atomic layer deposition (ALD) from Ir(acac)3 and ozone between 165 and 200 °C. The films were successfully deposited on soda lime glass, silicon substrate with native oxide and Al2O3 adhesion layer. Saturation of the growth rate with respect to both precursors was verified and the film thickness depended linearly on the number of deposition cycles applied. The iridium oxide films had low impurity contents and good adhesion to all tested surfaces. IrO2 film deposited at 185 °C had homogeneous depth profile and contained 3.5 at. % hydrogen and less than 0.5 at. % carbon impurities. Resistivities of about 40 nm thick IrO2 films varied between 170 and 200 μΩcm. The films deposited above 200 °C were metallic iridium. All the films deposited were crystalline according to X-ray diffraction patterns.

Keywords: atomic layer deposition; ALD; iridium oxide; IrO2; conductive oxide; thin film

Publ.-Id: 10626

The new facilities and research at HLD

Wosnitza, J.

Abstrakt hat nicht vorgelegen

  • Invited lecture (Conferences)
    EuroMagNET, 22.-23.10.2007, Nijmegen, Niederlande

Publ.-Id: 10625

Positron annihilation study of hydrogen trapping at open-volume defects: comparison of nanocrystalline and epitaxial Nb thin films

Cizek, J.; Prochazka, I.; Danis, S.; Melikhova, O.; Vlach, M.; Zaludova, N.; Brauer, G.; Anwand, W.; Mücklich, A.; Gemma, R.; Nikitin, E.; Kirchheim, R.; Pundt, A.

H interaction with defects in thin Nb films was investigated in this work. Thin Nb films were prepared by the cold cathode beam sputtering. First, microstructure of the as deposited films was characterized. The films sputtered at room temperature exhibit nanocrystalline grains, while those sputtered at high temperature (T = 850 ◦C) are epitaxial. Subsequently, the films were step-by-step electrochemically charged with H. Development of microstructure and evolution of defect structure with increasing H concentration was investigated by slow positron implantation spectroscopy combined with X-ray diffraction. It was found that H is trapped at open-volume defects in the thin films of both kinds. The nanocrystalline films exhibit significantly extended H solubility in the alpha-phase. Formation of the hydride-phase (Nb-H) at higher H concentrations leads to introduction of new defects. These are most probably dislocation loops that are emitted by growing hydride-phase particles.

  • Journal of Alloys and Compounds 446-447(2007), 484-488

Publ.-Id: 10624

Hydrogen-induced defects in niobium

Cizek, J.; Prochazka, I.; Danis, S.; Cieslar, M.; Brauer, G.; Anwand, W.; Kirchheim, R.; Pundt, A.

The introduction of new defects due to H-loading of Nb, their population as a function of the H concentration, and the mechanism of their formation are investigated by positron annihilation spectroscopy (PAS). In addition, X-ray diffraction (XRD), and transmission electron microscopy (TEM) are applied. Furthermore, the results obtained by the experimental techniques are compared with theoretical calculations of energetic stability and positron characteristics of various defect-H configurations. It is found that vacancies surrounded by H atoms are introduced into the specimens by H-loading. The density of these vacancy-H complexes increases with increasing concentration of H in the specimens. The H-induced vacancies are formed even in the alpha-phase field, when the metal–H system is a single phase solid solution. The stability of the H-induced defects and the
mechanism of their formation are discussed.

  • Journal of Alloys and Compounds 446-447(2007), 479-483

Publ.-Id: 10623

Pressure dependence of the electronic properties of the quasi-two-dimensional organic superconductor beta"-(ET)2SF5CH2CF2SO3

Hagel, J.; Ignatchik, O.; Wosnitza, J.; Pfleiderer, C.; Schlueter, J. A.; Davis, H.; Winter, R.; Gard, G. L.

We report on pressure-dependent superconducting and transport properties of the quasi-two-dimensional organic superconductor b"-(ET)2SF5CH2CF2SO3. With increasing pressure both the superconducting transition temperature, Tc, as well as the effective mass, mc, decrease monotonously. By assuming a direct relationship between mc and the superconducting coupling parameter λ, the pressure dependence of Tc can be well described by the modified McMillan equation. For all pressures in the metallic state the resistance follows q = q0 + AT2 at low temperatures. The coefficient A, however, is found to be not proportional to m2 c as expected for a purely electronic origin of the T2 behavior.

  • Physica C 460-462(2007), 639-640

Publ.-Id: 10622

Effect of the Ru content on the phase equilibria in the RuSr2GdCu2O8 synthesis

Casini, E.; Papageorgiou, T. P.; Herrmannsdoerfer, T.; Wosnitza, J.; Braun, H. F.

In this study we report the synthesis and characterization of four samples prepared with a nominal RuSr2GdCu2O8 starting composition following a two-step procedure, involving the Sr2GdRuO6 compound as precursor, in a controlled atmosphere. A chemicalvapour-transport process in an open system is used to control the Ru content in these samples during the annealing cycle. We observe that high Ru-oxides mass transport results in a change of the phases in equilibrium at the RuSr2GdCu2O8 composition and a multiphase product is obtained. Rietveld refinement analysis and SEM-EDX studies are carried out in order to estimate the Ru content in the asprepared RuGd1212.

  • Physica C 460-462(2007), 401-402

Publ.-Id: 10621

Capacitance sheds light on complex flows

Swarup, B.

Engineers could soon have a much better idea of what is going on inside pipelines and industrial reactors thanks to a new flow sensor developed by scientists in Germany. The device is able to distinguish between different substances in a flowing mixture and it could help solve tricky flow problems such as how to move unruly mixtures of oil, gas and water from deep undersea wells to the surface.

Keywords: capacitance wire mesh sensor; multiphase flow measurement

Publ.-Id: 10620

Physikalische Modellierung von Strömungen für Kristallzüchtungen

Gerbeth, G.; Grants, I.; Galindo, V.

Physikalische Modellierung von Strömungen für Kristallzüchtungen

  • Lecture (Conference)
    Magnetfelder in der Kristallzüchtung - offenes Statusseminar des Projektes KristMAG, 18.-20.06.2007, Berlin, Germany

Publ.-Id: 10619

Qualitative and quantitative analysis of selected liquid flow texture scenario in trickle bed reactors using high resolution gamma ray tomography

Schubert, M.; Hampel, U.; Hessel, G.; Lange, R.; Zippe, C.

Trickle bed reactor performance and safety may suffer from radial and axial liquid maldistribution and thus from non-uniform utilization of the catalyst packing. Therefore, experimental analysis and fluid dynamic simulation of liquid-gas flow in trickle bed reactors is an important topic in chemical engineering. In the presented study for the first time a truly high-resolution gamma ray tomography technique was applied to the quantitative analysis of the liquid flow texture in a laboratory cold flow trickle bed reactor of 90 mm diameter. The objective of this study was the comparative analysis of the liquid flow dynamics for two different initial liquid distributions and two different types of reactor configurations. Thus, the hydrodynamic behavior of a glass bead packing was compared to a porous Al2O3 catalyst particle packing using inlet flow from a commercial spray nozzle (uniform initial liquid distribution) and inlet flow from a central point source (strongly non-uniform initial liquid distribution), respectively. The column was operated in downflow mode at a gas flow rate of 180 L/h and at liquid flow rates of 15 L/h and 25 L/h.

Keywords: Gamma ray tomography; Multiphase flow; Trickle bed; Liquid saturation; Liquid distribution; Liquid spreading

  • Contribution to proceedings
    8th International Conferences on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS8), 16.-19.12.2007, Delhi, India
  • Poster
    8th International Conferences on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering (GLS8), 16.-19.12.2007, Delhi, India

Publ.-Id: 10618

On magnetohydrodynamic drag reduction and flow control behind a body

Gerbeth, G.; Shatrov, V.

In the first part we present results of direct numerical simulations on turbulent channel flow drag reduction using electromagnetic forces. The Lorentz force is created by the interaction of a permanent magnetic field and an electric current from electrodes placed on the bottom wall surface. We consider the two cases of a spanwise oscillating force and a streamwise steady force. In the second part the flow behind an electromagnetically self-moved sphere is considered for which a drag reduction is found. Results on the linear and nonlinear flow stability will be provided.

Keywords: magnetohydrodynamic drag reduction; efficiency

  • Lecture (Conference)
    6th International Congress on Andustrial and Applied Mathematics (ICIAM 07), 16.-20.07.2007, Zurich, Switzerland

Publ.-Id: 10617

Liquid flow texture analysis in trickle bed reactors using high resolution gamma ray tomography

Schubert, M.; Hampel, U.; Hessel, G.; Lange, R.; Zippe, C.

Trickle bed reactor performance and safety may suffer from radial and axial liquid maldistribution and thus from non-uniform utilization of the catalyst packing. Therefore, experimental analysis and fluid dynamic simulation of liquid-gas flow in trickle bed reactors is an important topic in chemical engineering. In the presented study for the first time a truly high-resolution gamma ray tomography technique was applied to the quantitative analysis of the liquid flow texture in a laboratory cold flow trickle bed reactor of 90 mm diameter. The objective of this study was the comparative analysis of the liquid flow dynamics for two different initial liquid distributions and two different types of reactor configurations. Thus, the hydrodynamic behavior of a glass bead packing was compared to a porous Al2O3 catalyst particle packing using inlet flow from a commercial spray nozzle (uniform initial liquid distribution) and inlet flow from a central point source (strongly non-uniform initial liquid distribution), respectively. The column was operated in downflow mode at a gas flow rate of 180 L/h and at liquid flow rates of 15 L/h and 25 L/h.

Keywords: Gamma ray tomography; Multiphase flow; Trickle bed; Liquid saturation; Liquid distribution; Liquid spreading

Publ.-Id: 10616

MFZ Intermetallischer Verbindungen

Behr, G.; Hermann, R.; Löser, W.; Priede, J.; Gerbeth, G.

  • Lecture (Conference)
    Magnetfelder in der Kristallzüchtung - Offenes Statusseminar des Projektes KRISTMAG, 18.-20.06.2007, Berlin, Germany

Publ.-Id: 10615

VGF-Kristallzüchtung mit externen Magnetfeldern

Lantzsch, R.; Galindo, V.; Grants, I.; Pätzold, O.; Gerbeth, G.; Stelter, M.

  • Lecture (Conference)
    Magnetfelder in der Kristallzüchtung - Offenes Statusseminar des Projektes KRISTMAG, 18.-20.06.2007, Berlin, Germany

Publ.-Id: 10614

Competition between damage buildup and dynamic annealing in ion implantation into Ge

Posselt, M.; Bischoff, L.; Grambole, D.; Herrmann, F.

In order to investigate the effect of ion flux and irradiation temperature on defect evolution in germanium during the process of ion implantation, a focused ion beam system is used. Channeling implantation of Ga ions is performed at two very different ion fluxes (1012 and 1019 cm-2 s-1), at two temperatures (room temperature and 250 0C), and at five different fluences, ranging from 5x1012 to 5x1014 cm-2. The depth distributions of Ga and the implantation damage are determined by SIMS and micro-RBS/C, respectively. The fluence dependence of the measured range profiles and of the implantation damage is strongly influenced by the ion flux and the implantation temperature. These results are explained by the competition between damage buildup and dynamic annealing during the ion bombardment. For the two implantation temperatures considered, the time scale for intracascade defect relaxation can be estimated. At 250 °C, the maximum lifetime of the defects is less than 10 s. On the other hand, at room temperature no significant annealing is found within the first 10 s after ion impact. The measured Ga depth profiles can be reproduced by atomistic computer simulations using a phenomenological model to describe the probability that an implanted ion collides with a target atom of a damaged region. This probability depends on the total nuclear energy deposition per target atom and on two empirical parameters [1].
[1] M. Posselt, L. Bischoff, D. Grambole, F. Herrmann, Appl. Phys. Lett. 89 (2006) 151918

Keywords: germanium; ion implantation; damage; dynamic annealing

  • Poster
    GADEST 2007 - 12th International Autumn Meeting Gettering and Defect Engineering in Semiconductor Technology, 14.-19.10.2007, Erice, Sicily, Italy

Publ.-Id: 10613

Dependence of the correlation factor for self-diffusion by vacancies and self-interstitials on the migration mechanism: an atomistic study

Posselt, M.

Self-diffusion in Si is determined by the concentration and the mobility of both vacancies and self-interstitials. The self-diffusion coefficient is usually given by Dsd = fV CV DV + fI CI DI, where CV and CI are the relative concentrations of vacancies and self-interstitials, respectively; DV and DI denote the diffusivities. The quantities fV and fI describe the correlation between the migration of Si atoms and the migration of vacancies and self-interstitials; fV and fI are therefore called correlation factors. The statistical theory of diffusion [1,2] allows the determination of these factors if certain atomic mechanisms for vacancy and self-interstitial migration are assumed. On the other hand, the self-diffusion coefficient per point defect as well as the point defect diffusivity can be calculated by molecular dynamics (MD) simulations. The ratio of both quantities yields the correlation factors fV and fI. In this manner, they can be determined without any assumption about the atomic migration mechanisms.
In the present work, point defect migration and the related atomic mobility are investigated by MD simulations using the interatomic potentials of Stillinger-Weber and Tersoff. It is shown that the value of fV = 0.5 obtained by MD simulations is identical with that determined by the statistical diffusion theory, since the simple atomic mechanism assumed in this theory is also found by the simulations. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. MD simulations with the Stillinger-Weber potential show, that the self-interstitial migration is dominated by the dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor fI are different, namely 0.56 and 0.73 for the dumbbell and the interstitialcy mechanism, respectively. The latter value corresponds to that obtained by the statistical theory [2] which assumes an interstitialcy mechanism. However, results of recent investigations on intrinsic point defects in silicon using a unified view from crystal growth, wafer processing and metal diffusion [3], and on dopant and defect diffusion [4] demonstrate, that in the framework of state-of-the-art modeling a reasonable interpretation of experimental data can be only given by assuming fI = 0.5…0.6. The comparison with results of the present atomistic study leads to the conclusion that self-interstitial migration in Si should mainly occur via the dumbbell mechanism.
[1] K. Compaan, Y. Haven, Trans. Faraday Soc. 52 (1956) 786
[2] K. Compaan, Y. Haven, Trans. Faraday Soc. 54 (1958) 1498
[4] V.V. Voronkov, R. J. Falster, Solid State Phenomena 108-109 (2005) 1
[3] H.Bracht, Physica B 376-377 (2006) 11

Keywords: silicon; diffusion; point defects; atomistic simulation

  • Poster
    GADEST 2007 - 12th International Autumn Meeting Gettering and Defect Engineering in Semiconductor Technology, 14.-19.10.2007, Erice, Sicily, Italy

Publ.-Id: 10612

Direct numerical computation of the lift force acting on single bubbles

Bothe, D.; Schmidtke, M.; Warnecke, H.-J.

Bubbles in shear flows experience a lift force, causing them to migrate sideward while they are rising. This lateral migration is also observed in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force – expressed by the lift force coefficient CL – for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. The pressure and the velocity fields near the interface are investigated and the contribution of dynamic pressure and the circulation of the lift force are discussed.

Keywords: rise of bubbles; lift coefficient; Volume of Fluid method; shear flow

  • Contribution to proceedings
    6th International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany
  • Lecture (Conference)
    6th International Conference on Multiphase Flow, ICMF 2007, 09.-13.07.2007, Leipzig, Germany

Publ.-Id: 10611

Radiopharmaceutical Tools for Molecular Imaging and Therapy of Tumors

Juran, S.

kein Abstract verfügbar

  • Lecture (others)
    Institutskolloquium, Monash-University, School of Chemistry, 26.10.2007, Melbourne, Australia

Publ.-Id: 10610

Erweiterung des ATHLET – Datensatzes des KKK um das 4 – Quadranten – Modell des Rückströmraumes und Ergebnisse der Simulation der Transiente vom 28.06.2007

Laczkó, G.; Kliem, S.; Rohde, U.

Die in diesem Bericht dokumentierten Ergebnisse sind vertraulich.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2007
    40 Seiten
    ISSN: 1437-322X

Publ.-Id: 10609

Vertical gradient freeze growth with external magnetic fields

Lantzsch, R.; Grants, I.; Pätzold, O.; Stelter, M.; Gerbeth, G.

The Vertical Gradient Freeze (VGF) method is an important technique for the growth of bulk semiconductors from the melt. The structural and electrical properties of the crystals depend on the melt flow which can be influenced by external magnetic fields. By applying an AC field, the flow can be tailored to improve the quality of the crystals and the yield of the growth process. The induced melt flow, however, tends to be time-dependent which might be avoided by combining the AC field with a DC field.

Keywords: Vertical Gradient Freeze crystal growth with external magnetic fields

  • Lecture (Conference)
    The 15th International Conference on Crystal Growth, 11.-17.08.2007, Salt Lake City, Utah, USA
  • Journal of Crystal Growth 310(2008)7-9, 1518-1522

Publ.-Id: 10608

Tailored magnetic fields in the melt extraction of metallic filaments

Cramer, A.; Galindo, V.; Gerbeth, G.; Priede, J.; Bojareviecs, A.; Gelfgat, Y.; Andersen, O.; Kostmann, C.; Stephani, G.

Melt extraction is a near-net-shape casting process in which a swiftly rotating disc draws filaments out of a melt. The melt solidifies at the V-shaped circumferential edge upon first contact, and the layer grows while the disc moves further through the liquid pool. A disc may be equipped with several edges to increase the performance. Further, the perimeter may be notched to produce fibres having a certain length. During rapid cooling, the filament shrinks and is finally flung away by centrifugal force. Two different methods were developed in the seventies and established on industrial scale. Nonetheless, both still show their specific inadequacy. The extraction out of a crucible is characterised by a relatively large surface allowing multi-edge and thus efficient operation. Usually, the melt contained in a refractory is lifted slowly toward the disc. Induction heating and shear stress supplied by the disc lead to turbulent melt motion, which limits the process with respect to extraction velocity and, in turn, to relatively thick fibres. It is possible to extract ultra-fine filaments from a pending drop. That needs melting of a rod at its tip, which is usually accomplished by an oxygen-acetylene torch. Though the confined volume and capillary forces due to a small radius of curvature permit high extraction velocity, the productivity suffers from the fact that only one edge can be used.
Damping of velocity fluctuations may be realised by a static magnetic field. Concerning the crucible extraction, extended series measurements showed that globally applying such a magnetic brake has two effects:
(i) it is possible to achieve higher extraction speed, but
(ii) the fibre diameter is barely affected. High speed video recordings revealed that extraction takes place only during duty cycles. Instead of producing thinner fibres, as has to be expected from higher circumferential speed in case of continuous extraction due to conservation of mass, the damping also reduces the mean velocity, and in turn the mass transport onto the disc; the globally applied magnetic brake influences the length of the duty cycle. Here, the tailored magnetic solution is a concentration of magnetic flux density to the small meniscus region of the extraction zone by means of ferromagnetic parts. This local stabilisation significantly reduces the fibre diameter. Poor efficiency of the pending drop technique can be overcome with extraction from a molten edge. The problem to be solved is melting the sheet directly at its edge. Owing to geometric restrictions, electromagnetic heating with a long inductor having two opposing branches would either release most of the heat at a certain distance from the edge, or in the disc. Passing the current in the same direction through the branches in combination with optimisation with respect to the skin effect allows moving the area of heat impingement almost entirely outside the inductor toward the edge of the jutting through sheet. In two experiments, a platinum sheet was molten directly at its edge and very thin tin fibres were produced.

  • Poster
    LMPC 2007 International Symposium on Liquid Metal Processing and Casting, 02.-05.09.2007, Nancy, France
  • Contribution to proceedings
    LMPC 2007 International Symposium on Liquid Metal Processing and Casting, 02.-05.09.2007, Nancy, France
    Tailored magnetic fields in the melt extraction of metallic filaments, 305-311
  • Metallurgical and Materials Transactions B 40(2009), 337-344

Publ.-Id: 10607

Ion beam synthesis and charge storage behavior of Au nanocrystals in thin SiO2 layers

Beyer, V.; Eichhorn, F.; von Borany, J.; Mücklich, A.; Müller, T.

Au nanocrystals (NCs) were synthesized in a thin SiO2 layer by ion implantation and annealing in a tight distribution close to the Si/SiO2 interface. Between the NCs and the Si substrate a thin tunneling oxide forms self-organized during annealing totally depleted from Au NCs. Memory behavior is demonstrated by electron charging and discharging on metal-oxide-semiconductor capacitors. Lenticular liquid Au:Si droplets nucleate at the Si/SiO2 interface from silicon regions supersaturated by Au close to the oxide. Au NCs embedded in SiO2 above these droplets are stabilized during annealing due to a modified detailed balance of Au atom detachment and attachment. Capacitance-voltage and spreading resistance measurements reveal the impact of the Au contamination in the Si substrate. Structure and distribution of Au droplets and NCs are characterized by x-ray diffraction and transmission electron microscopy .

Keywords: ion beam synthesis; nanocrystals; memory; Au

  • Journal of Applied Physics 104(2008), 024512

Publ.-Id: 10606

Multicenter standardized FDG-PET diagnosis of mild cognitive impairment, Alzheimer's disease and other dementias

Mosconi, L.; Tsui, W. H.; Herholz, K.; Pupi, A.; Drzezga, A.; Lucignani, G.; Reimann, E. M.; Holthoff, V.; Kalbe, E.; Sorbi, S.; Diehl-Schmid, J.; Perneczky, R.; Clerici, F.; Caselli, R.; Beuthien-Baumann, B.; Kurz, A.; Minoshima, S.; de Leon, M. J.

This multicenter study examined F-18-FDG PET measures in the differential diagnosis of Alzheimer's disease (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB) from normal aging and from each other and the relation of disease-specific patterns to mild cognitive impairment (MCI). Methods: We examined the F-18-FDG PET scans of 548 subjects, including 110 healthy elderly individuals ("normals" or NLs), 114 MCI, 199 AD, 98 FTD, and 27 DLB patients, collected at 7 participating centers. Individual PET scans were Z scored using automated voxel-based comparison with generation of disease-specific patterns of cortical and hippocampal F-18-FDG uptake that were then applied to characterize MCI. Results: Standardized disease-specific PET patterns were developed that correctly classified 95% AD, 92% DLB, 94% FTD, and 94% NIL. MCI patients showed primarily posterior cingulate cortex and hippocampal hypometabolism (81%), whereas neocortical abnormalities varied accordi!
ng to neuropsychological profiles. An AD PET pattern was observed in 79% MCI with deficits in multiple cognitive domains and 31% amnesic MCI. F-18-FDG PET heterogeneity in MCI with non-memory deficits ranged from absent hypometabolism to FTD and DLB PET patterns. Conclusion: Standardized automated analysis of F-18-FDG PET scans may provide an objective and sensitive support to the clinical diagnosis in early dementia. Key Words: F-18-FDG PET; Alzheimer's disease; frontotemporal dementia; Lewy body dementia; mild cognitive impairment; normal aging; hippocampus.

  • Journal of Nuclear Medicine 49(2008)3, 390-398

Publ.-Id: 10605

Low-lying dipole strength and nuclear deformation

Frauendorf, S.

Low-lying dipole strength and nuclear deformation

  • Lecture (Conference)
    ECT* Trento Workshop On Exotic Modes Of Excitation: From Nuclear Structure to Astrophysics, 07.-11.10.2007, Trento, Italy

Publ.-Id: 10604

Tidal Waves and Boson Condensation in Transitional Nuclei

Frauendorf, S.

Tidal Waves and Boson Condensation in Transitional Nuclei

  • Lecture (Conference)
    Seminar INFN Legnaro, 07.10.2007, Legnaro, Italy

Publ.-Id: 10603

Evolution of vortex structures in an electromagnetically excited separated flow

Cierpka, C.; Weier, T.; Gerbeth, G.

For the present study time periodic wall parallel Lorentz forces have been used to excite the separated flow on the suction side of an inclined flat plate. Experiments for a Reynolds number of 10^4 and an angle of attack of a = 13° are reported. The controlled flow is characterised by a small number of relatively large scale vortices, which are related to the control mechanism. The influence of the main parameters, i.e. the excitation frequency, amplitude and wave form on the suction side flow structures was investigated by analysing time resolved particle image velocimetry (TR–PIV) measurements using continuous wavelet analysis for vortex detection and characterisation. Statistical analysis of the coherent structures of the flow was performed on a large amount of data samples.

Publ.-Id: 10602

GeV-scale electron acceleration in a gas-filled capillary discharge waveguide

Karsch, S.; Osterhoff, J.; Popp, A.; Rowlands-Rees, T. P.; Major, Z.; Fuchs, M.; Marx, B.; Hörlein, R.; Schmid, K.; Veisz, L.; Becker, S.; Schramm, U.; Hidding, B.; Pretzler, G.; Habs, D.; Grüner, F.; Hooker, S. M.; Krausz, F.

We report experimental results on laser-driven electron acceleration with low divergence. The electron beam was generated by focussing 750-mJ, 42-fs laser pulses into a gas-filled capillary discharge waveguide at electron densities in the range between 1018 cm−3 and 1019 cm−3. Quasi-monoenergetic electron bunches with energies as high as 500 MeV have been detected, with features reaching up to 1 GeV, albeit with large shot-to-shot fluctuations. A more stable regime with higher bunch charge (20-45 pC) and less energy (200-300 MeV) could also be observed. The beam divergence and the pointing stability are around or below 1 mrad and 8 mrad, respectively. These findings are consistent with self-injection of electrons into a breaking plasma wave.

Keywords: PACS: 41.75.Jv; 42.65.Jx; 52.38.Kd


Publ.-Id: 10601

Underground facilities for nuclear astrophysics

Bemmerer, D.

Recent progress in astronomy, in many cases by satellite-based observatories, has led to much more precise astronomical data. Nuclear data with matching precision are necessary for a proper understanding of astronomical scenarios such as the big bang, stable and explosive stellar burning. In the case of nuclear reaction cross sections, precision data require measurements directly at Gamow peak energies, where the absolute value of the cross section is very low. In the present lecture, underground facilities for nuclear astrophysics are reviewed with a focus on providing cross section data. For activation studies, shallow and deep underground laboratories have been employed. Exemplary results from the Felsenkeller Dresden/Germany shallow underground laboratory and the Gran Sasso/Italy deep underground facility are shown and discussed. For in-beam gamma-spectroscopy studies, so far only the LUNA facility at Gran Sasso is available. The salient features of LUNA and some recent results are shown. The lecture ends with an outlook on currently proposed new underground accelerators in Italy, the United States, the United Kingdom and Romania.

Keywords: nuclear astrophysics; underground accelerator; activation; in-beam gamma-spectroscopy; LUNA; nucleosynthesis

  • Invited lecture (Conferences)
    Fourth European Summer School on Experimental Nuclear Astrophysics, 26.09.-03.10.2007, Santa Tecla, Italy

Publ.-Id: 10600

From conventional to unconventional superconductivity

Wosnitza, J.

hat nicht vorgelegen

  • Invited lecture (Conferences)
    International School "Magnetic Fields for Science", 27.08.-08.09.2007, Cargèse, France
  • Lecture (Conference)
    International Summer School: Symmetries and Phase Transitions - from Crystals and Superconductors to the Higgs particle and the Cosmos, 29.08.-02.09.2016, Dresden, Deutschland

Publ.-Id: 10599

de Haas-van Alphen investigations on the nonmagnetic superconductors LuNi2B2C and YNi2B2C

Bergk, B.; Ignatchik, O.; Bartkowiak, M.; Petzold, V.; Rosner, H.; Canfield, P. C.; Behr, G.; Sheikin, I.; Perenboom, J.; Wosnitza, J.

We present de Haas-van Alphen (dHvA) investigations on the nonmagnetic borocarbide
superconductors LuNi2B2C and YNi2B2C. The measurements were carried out by use of a cantilevertorque method on a rotator set up in high magnetic fields up to 32 T and at low temperatures down to 50 mK. From the normal-state oscillations we determine the electronic band structure of the material. From comparison with full-potential local-orbital calculations we assigned the measured dHvA frequencies to the different bands identified the expected spherical, cubic and ‘cushion’-like closed Fermi surfaces. Additionally, we found frequencies that probably belong to a complicated multipleconnected Fermi-surface sheet. Further, we performed temperature-dependent measurements that allowed the extraction of the effective band masses of the different Fermi-surface sheets. We find mass enhancements in comparison to the calculated values that are due to electron-phonon coupling.
Finally, we are able to determine the angular dependences of the electron-phonon coupling for the different Fermi-surface sheets.
Below the upper critical field, Bc2, an additional damping of the oscillation amplitude appears. This decrease might be related to the increase of the superconducting gap parameter which could be calculated from quantitative measurements of this effect. However, the analysis is hampered by additional influences originating form changes in the flux-line lattice that appear close to the superconducting phase transition. Therefore, we compare two differently grown crystals. The one grown by a zone-melting method shows a rather abrupt vanishing of the oscillation amplitude in the superconducting state. In contrast, for the flux-grown crystals we observe a smooth damping
combined with a broad phase transition.

  • Lecture (Conference)
    International School "Magnetic Fields for Science", 27.08.-08.09.2007, Cargèse, France

Publ.-Id: 10598

Simulating the stopping dynamics of highly charged ions in an ultra-cold, strongly coupled plasma

Bussmann, M.; Schramm, U.; Habs, D.

We introduce a method for stopping highly charged ions (HCIs) in a laser-cooled one-component plasma (OCP) of 24Mg+ ions and present results on stopping times derived from realistic molecular dynamics simulations of the complete stopping process. This stopping scheme can provide ultra-cold highly charged ions for future in-trap precision mass measurements. The choice of an ultra-cold ion plasma as a stopping medium is governed by the almost negligible charge exchange of the HCI with the laser-cooled ions and the very low temperatures which can be reached. In our analysis we focus on the stability and fast recooling of the plasma – two features essential for the experimental realization of this stopping scheme.

Keywords: 02.70.Ns; 34.50.Bw; 32.80.Pj; 21.10.Dr; 52.27.Gr; 52.27.Jt; Stopping; Highly charged ions; Laser cooling; Plasma; Strong coupling; Molecular dynamics simulation

Publ.-Id: 10597

High-magnetic-field studies of the new spin-1 Haldane-chain material NENB

Ozerov, M.; Cizmar, E.; Zvyagin, S. A.; Wosnitza, J.

Antiferromagnetic quantum spin-1 chains have been the subject of intensive theoretical and
experimental studies, fostered especially by the Haldane conjecture (F.D.M. Haldane, Phys. Lett. 93A
(1983) 464). In this work we report results of high-magnetic-field studies of the new spin-1 chain
material Ni[C2H8N2](2)NO2BF4 (NENB). The magnetic susceptibility, low-temperature magnetization
and high-field electron spin resonance (ESR) studies unambiguously indicate that NENB is a Haldanechain
material. Two critical fields were revealed by high-field (up to 15 T) magnetization
measurements indicating a field-induced collapse of the spin-singlet ground state and a finite
anisotropy of the g-factor in fields applied parallel and perpendicular to the chain direction. The spin
gap has been measured directly by means of the high-field ESR, revealing Δ = 17.4 K.

  • Lecture (Conference)
    International School "Magnetic Fields for Science", 27.08.-08.09.2007, Cargèse, France

Publ.-Id: 10596

Investigations to the synthesis of n.c.a. [18F]FClO3 as electrophilic fluorinating agent

Hiller, A.; Fischer, C.; Jordanova, A.; Patt, J. T.; Steinbach, J.

An approach to synthesize the electrophilic fluorinating agent no-carrier-added (n.c.a.) [18F]perchloryl fluoride ([18F]FClO3) in superacidic media in the presence of KClO4 or anhydrous perchloric acid starting from [18F]fluoride was demonstrated in this study. However, the radiochemical yields were low (1–6%) and poorly reproducible. Fluorosulphonic acid proved to be an essential intermediate as revealed by non-radioactive experiments. A key problem in the preparation of [18F]FClO3 is the assumed kinetic inhibition due to the unfavourable stoichiometric ratio of the ClO4 moiety to [18F]HSO3F.

Keywords: Fluorine-18; Perchloryl fluoride; Electrophilic fluorination; No carrier added

Publ.-Id: 10595

Preparing a laser cooled plasma for stopping highly charged ions

Bussmann, M.; Schramm, U.; Habs, D.

We present a new cooling scheme for the preparation of highly charged ions for future in-trap precision experiments. A plasma of laser cooled 24Mg+ ions trapped in a 3D harmonic confinement potential is used as a stopping medium for the highly charged ions. We focus on the dynamic evolution of the plasma, determining suitable cooling conditions for fast recooling of the 24Mg+ ions. The results of a realistic parallel simulation of the complete stopping process presented here indicate that a small, constant detuning of the laser frequency is sufficient for subsequent recooling of the plasma, thus maintaining the stability of the plasma.

Keywords: 02.70.Ns Molecular dynamics and particle methods; 32.80.Pj Optical cooling of atoms; trapping; 34.50.Bw Energy loss and stopping power; 52.27.Gr Strongly-coupled plasmas

Publ.-Id: 10594

Tracerkinetische Grundlagen von Perfusionsmessungen mit diffusiblen Tracern in der PET

van den Hoff, J.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Dresdner Expertengespraeche im OncoRay: Durchblutung in Tumoren, 04.10.2007, Dresden, Germany

Publ.-Id: 10593

Correlations between MRS alterations and cerebral ammonia and glucose metabolism in citthotic patients with and without hepatic encephalopathy

Weissenborn, K.; Ahl, B.; Fischer-Wasels, D.; van den Hoff, J.; Hecker, H.; Burchert, W.; Köstler, H.

Hepatic encephalopathy (HE) is considered to be mainly due to increased ammonia metabolism of the brain. If this hypothesis is true, cerebral glucose utilisation, which is considered to represent brain function, should be closely related to cerebral ammonia metabolism. The aim of the present study was to analyse if cerebral ammonia and glucose metabolism in cirrhotic patients with early grades of HE are as closely related as could be expected from current hypotheses on HE.

13N-ammonia- and 18F-fluorodesoxyglucose (FDG) - PET, magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were performed in 21 cirrhotic patients with grade 0 -1 HE. Quantitative values of cerebral ammonia uptake and retention rate and glucose utilisation were derived for several regions of interest and were correlated to the MRS data of the basal ganglia, the white matter and the frontal cortex.

A significant correlation between plasma ammonia levels and cerebral ammonia metabolism, respectively, and MRS alterations could be shown only for the white matter. In contrast, the MRS alterations in all three regions studied were significantly correlated with the glucose utilisation of several brain regions. Cerebral ammonia and glucose metabolism were not correlated.

Increase of cerebral ammonia metabolism is an important but not the exclusive causal factor for the development of hepatic encephalopathy.

  • Journal of Gastroenterology and Hepatology 56(2007)12, 1736-1742

Publ.-Id: 10591

Determination of the superconducting gap of LuNi2B2C

Bergk, B.; Ignatchik, O.; Bianchi, A. D.; Jäckel, M.; Wosnitza, J.; Perenboom, J.; Canfield, P. C.

We present de Haas–van Alphen (dHvA) measurements of the nonmagnetic borocarbide LuNi2B2C. In the superconducting state below the upper critical field, Bc2, the dHvA signal shows an additional damping. For some field orientations we observe a very strong damping close to Bc2 and only a very weak effect at lower fields in the superconducting state. We discuss the origin of the different dampings and their relation to the superconducting gap.

  • Physica C 460-462(2007), 630-631

Publ.-Id: 10590

Structural phase transition in two-dimensional tetramer-cuprate Na5RbCu4(AsO4)(4)Cl-2

Gnezdilov, V.; Bedarev, V.; Gnatchenko, S.; Pashchenko, M.; Pashkevich, Y.; Lemmens, P.; Zvyagin, S.; Mo, X.; Queen, W.; Hwu, S.

Raman scattering and optical birefringence are used in to investigate a low-temperature phase transition in a single crystal of the two-dimensional Na5RbCu4(AsO4)(4)Cl-2. Phonon anomalies point to a first-order nature of the transition. The observed transition is most probably related to an order-disorder transition of the Rb ion positions along the z axis within the ionic framework of mixed alkali metal chloride lattices.

  • Low Temperature Physics 33(2007), 684-687

Publ.-Id: 10589

Adhesion of PBO fiber in epoxy composites

Mäder, E.; Melcher, S.; Liu, J. W.; Gao, S. L.; Bianchi, A. D.; Zherlitsyn, S.; Wosnitza, J.

A composite of poly p-phenylene-2,6-benzobisoxazole (PBO) fiber and epoxy resin has excellent electrical insulation properties. However, it is a challenging issue to improve its mechanical properties because of poor adhesion between PBO fiber and matrix. The relatively smooth and chemically inactive surface of PBO fiber prevent efficient chemical bonding in the composite interface. Here, we report the surface modification of PBO fibers by UV irradiation, O-2 and NH3 plasma, as well as acidic treatments. We found that the surface free energy and roughness are increased for both sized and extracted fibers after plasma treatments together with maleic anhydride grafting. The sized fiber shows marginal improvement in adhesion strength and no change in fiber tensile strength because of the barrier effect of the finish. For the extracted fiber, however, the tensile strength of the fiber is sensitive to surface treatment conditions and considerable strength reduction occurred, parti! cularly for cases of acidic treatments and UV irradiation. This is because that the treatments increase the surface roughness and introduce more surface flaws. The extracted fiber surface has no adequate wetting and functional groups, which in turn results in coarse interface structures and causes reduction or no apparent variation of the adhesion strength. The fracture surfaces after single fiber pull-out tests exhibit adhesive interfacial failure along the fiber surface, which is further confirmed by similar adhesion strength and interlaminar shear strength values when the fiber was embedded in various epoxy resins with different temperature behavior.

  • Journal of Materials Science 42(2007), 8047-8052

Publ.-Id: 10588

Endotaxial growth of InSb nanocrystals on the bonding interface of silicon-oninsulator structure

Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

Endotoxial growth of InSb nanocrystals

Keywords: nanocrystals; InSb; SOI

  • Lecture (Conference)
    Third International Conference "Micro&Nano2007" on Micro- Nanoelectronics, Nanotechnology and MEMs, 18.-21.11.2007, Athen, Greece

Publ.-Id: 10587

The properties of the nanometer thick Si/Ge films-on-insulator produced by Ge+ ion implantation and subsequent hydrogen transfer

Tyschenko, I. E.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

RBS investigations on Ge+ implanted silicon films on insulators

Keywords: Si/Ge films; implantation; RBS

  • Lecture (Conference)
    3rd International Conference "Micro&Nano2007" on Micro- Nanoelectronics, Nanotechnology and MEMs, 18.-21.11.2007, Athen, Greece

Publ.-Id: 10586

Measurements of non-Gaussian noise in quantum wells

Ben Simon, A.; Paltiel, Y.; Jung, G.; Berger, V.; Schneider, H.

Gaussian generation-recombination is known to be a dominant mechanism of current noise in quantum well systems biased by electric field normal to the layers. We have found pronouncedly non-Gaussian excess current noise in n-type and p-type multiple quantum wells. The non-Gaussian noise has been attributed to metastable spatial configurations of electric field. The metastability is likely originating from negative differential conductance caused by intervalley scattering in n-type wells and heavy and light holes tunneling in p-type wells. At a constant bias the quantum well system randomly switches between a high resistivity state with low current flow and low resistive state with high current flow. The non-Gaussianity of the noise is more pronounced in p-type wells where the time traces of current fluctuations resemble closely two-level random telegraph signal which has not been straightforwardly observed in n-type wells. The non-Gaussian character of the noise in n-type systems has been revealed by measurements of nonzero skewness of the amplitude distributions. The difference between noise properties of n- and p-type systems has been attributed to small capture probability of electrons in n-type wells, as opposed to very high capture probability of holes in p-type wells. As a consequence the noise of any p-type multi-well system is dominated by fluctuations of a single while in the n-type the noise appears as a superposition of many fluctuators associated with individual wells.

Keywords: generation-recombination noise; random telegraph noise; skewness; GaAs/AlGaAs; quantum well

Publ.-Id: 10585

The influence of the implantation sequence on the (SiC)1-x (AlN)x formation

Pezoldt, J.; Rybin, P. V.; Kulikov, D. V.; Trushin, Y. V.; Yankov, R. A.; Voelskow, M.; Kreissig, U.

The influence of the implantation sequence on the defect and implant distribution during (SiC)1-x (AlN)x formation was studied by Rutherford backscattering spectrometry/ion channelling (RBS/C) and elastic recoil detection. It is shown that the implantation sequence aluminum followed by nitrogen lead to an improved crystallinity compared to the reverse implantation sequence for implantation temperatures above 400o C. The results obtained are discussed in relation to the defects distributions calculated by using a developed model which includes the effect of stress self-consistently.

Keywords: Ion implantation; RBS; ERD; defect distribution

  • Nuclear Instruments and Methods in Physics Research B 166/167(2000)1-4, 758-763

Publ.-Id: 10584

Verfahren zur Kontrolle von Bestrahlungen an Bestrahlungseinrichtungen mit in-beam Positronenemissionstomographen

Crespo, P.; Heidel, K.; Enghardt, W.; Fiedler, F.

Aufgabe der Erfindung ist es, eine wirkliche Echtzeit-Beobachtung der laufenden Bestrahlung weitgehend verzerrungsfrei zu ermöglichen. Außerdem soll mit dem Verfahren eine Korrektur der physiologischen Prozesse möglich werden.
Die Erfindung beinhaltet, dass die Flugzeitdifferenz der Annihilationsquanten gemessen wird und deren Korrelation mit der Mikro- und/oder Makrostruktur des Strahls und den Ortskoordinaten kombiniert und in ein Echtzeitdatenerfassungssystem eingespeist wird und dass in Echtzeit eine bildliche Darstellung der ß+-Aktivität, die im Patienten erzeugt wird, sowie eine off-line-Korrektur der Abbildungsfehler auf Grund physiologischer Prozesse erfolgt.

  • Patent
    WO 2007 / 087790 A1
  • Patent
    DE 10 2006 004 687 A1

Publ.-Id: 10583

P0605 - Anordnung zur zweidimensionalen Messung von verschiedenen Komponenten im Querschnitt einer Mehrphasenströmung

Da Silva, M. J.; Hampel, U.; Schleicher, E.; Prasser, H.-M.

Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur schnellen Messung der Phasen- oder der Komponentenverteilung in einem Strömungsquerschnitt für Stoffgemische auch nichtleitender Art auf Basis einer Messung der komplexen elektrischen Admittanz anzugeben.
Die Erfindung beinhaltet im Wesentlichen, dass

  • den Sendeelektroden (3a) der Anregungsebene mindestens ein Sinusgenerator (5) vorgeschaltet ist, der die Sendeelektroden (3a) mit einer Wechselspannung beaufschlagt,
  • den Empfängerelektroden (3b) Strom-Spannungswandler (7) nachgeschaltet sind, die den von mindestens einer Anregungselektrode (3a) durch das Medium zu den Empfängerelektroden (3b) fließenden Wechselstrom verstärken und in ein Spannungssignal umwandeln,
  • den Strom-Spannungswandler (7) Filtergruppen (10, 11, 16) und Vektorvoltmeter (8) nachgeschaltet sind, mit denen das komplexe Signalverhältnis Ua/Ue messtechnisch erfasst wird.
  • Patent
    DE 10 2006 019 178 A1
  • Patent
    DE 10 2006 019 178 B4 - 02 Apr 2009
  • Patent
    US 7940038 B2 - 10.05.2011

Publ.-Id: 10582

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