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33403 Publications

Kompakte Laserbeschleuniger und ihre Anwendungen

Bussmann, M.
In diesem Vortrag werden die Prinzipien der Laserteilchenbeschleunigung sowie wichtige Anwendungen der dabei erzeugten Teilchenstrahlen vorgestellt.
Keywords: laser, particle, acceleration
  • Lecture (others)
    FZD-Vortrag für Besucher des Abendgymnasiums Bautzen, 08.07.2008, Dresden Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12239
Publ.-Id: 12239


Thermal and Chemical Freeze-out in Spectator Fragmentation

Trautmann, W.; Bassini, R.; Begemann-Blaich, M.; Ferrero, A.; Fritz, S.; Gaff-Ejakov, S. J.; Groß, C.; Imme, G.; Iori, I.; Kleinevoß, U.; Kunde, G. J.; Kunze, W. D.; Le Fevre, A.; Lindenstruth, V.; Lukasik, J.; Lynen, U.; Maddalena, V.; Mahi, M.; Möhlenkamp, T.; Moroni, A.; Müller, W. F. J.; Nociforo, C.; Ocker, B.; Odeh, T.; Orth, H.; Petruzzelli, F.; Pochodzalla, J.; Raciti, G.; Riccobene, G.; Romano, F. P.; Rubehn, T.; Saija, A.; Sann, H.; Schnittker, M.; Schüttauf, A.; Schwarz, C.; Seidel, W.; Serfling, V.; Sfienti, C.; Trzcinski, A.; Tucholski, A.; Verde, G.; Wörner, A.; Hongfei, X.; Zwieglinski, B.
Isotope temperatures from double ratios of hydrogen, helium, lithium, beryllium, and carbon isotopic yields, and excited-state temperatures from yield ratios of particle-unstable resonances in 4He, 5Li, and 8Be, were determined for spectator fragmentation, following collisions of 197Au with targets ranging from C to Au at incident energies of 600 and 1000 MeV per nucleon. A deviation of the isotopic from the excited-state temperatures is observed which coincides with the transition from residue formation to multi-fragment production, suggesting a chemical freeze-out prior to thermal freeze-out in bulk disintegrations.
  • Physical Review C 76(2007), 064606

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Permalink: https://www.hzdr.de/publications/Publ-12238
Publ.-Id: 12238


Nuclear Astrophysics with real photons at ELBE

Nair, C.; Junghans, A. R.; Erhard, M.; Bemmerer, D.; Beyer, R.; Grosse, E.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Schwengner, R.; Wagner, A.
The neutron deficient p-nuclei thought to be produced in explosive stellar environments through chains of photodisintegration reactions on heavy seed nuclei. The modelling of the nucleosynthesis for the p-nuclei is mainly based on statistical model calculations and the knowledge of the experimental cross sections for the prediction of the p-nuclei abundances is of crucial importance. To forward in this direction we have started and experimental program at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf . Photodisintegration measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed via photoactivation technique with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. In particular the (gamma,alpha) reactions of the mentioned nuclei were studied for the first time at different endpoint energies above and close to the threshold. The activation yields from all measurements are compared with calculations using cross sections from recent Hauser-Feshbach models .
Keywords: p-nuclei, photoactivation, bremsstrahlung
  • Invited lecture (Conferences)
    Seminar at the National Superconducting Cyclotron Laboratory, Michigan State University as a JINA (Joint Institute of Nuclear Astrophysics) visitor, 04.08.2008, Michigan, United States of America

Permalink: https://www.hzdr.de/publications/Publ-12237
Publ.-Id: 12237


Photoactivation studies on astrophysically relevant nuclei: measuring techniques for activated samples

Nair, C.; Junghans, A. R.; Erhard, M.; Bemmerer, D.; Degering, D.; Beyer, R.; Grosse, E.; Koehler, M.; Klug, J.; Kosev, K.; Rusev, G.; Schilling, K. D.; Wagner, A.; Schwengner, R.
For studying the neutron deficient p-nuclei experimentally, we have started and experimental program at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf . Photodisintegration measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed via photoactivation technique with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. In particular the (gamma,alpha) reactions of the mentioned nuclei were studied for the first time at different endpoint energies above and close to the threshold. The activation yields from all measurements are compared with calculations using cross sections from recent Hauser-Feshbach models. The radioactive decay of irradiated targets with very low counting statistics was studied at the low-background underground laboratory "Felsenkeller" in Dresden.
Keywords: photoactivation, p-nuclei, underground laboratory 'felsenkeller'
  • Poster
    IEEE Nuclear Science Symposium, 20.-24.10.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12236
Publ.-Id: 12236


Experimental and numerical investigations of natural circulation phenomena in passive safety systems for decay heat removal in large pools

Krepper, E.; Beyer, M.
Modern concepts of nuclear power reactor systems are equipped with passive systems for decay heat removal. Examples are the pool of the emergency condenser (BWR-1000) or the pool of the ESBWR. These systems operate without active influence from outside. The questions arise: How reliable are the based physical mechanisms? Are they understood completely? Are actual models able to describe the phenomena?
In different passive systems the energy is transferred by natural circulation into large pools which are considered as infinite heat sink. The paper deals with experiments and with CFD simulations to investigate the capability of actual CFD codes to describe these phenomena. In the FZ Dresden-Rossendorf at the facility TOPFLOW heating up tests of an emergency condenser were performed. During these tests also the temperature courses on the secondary side of the pool were recorded. The data recording comprises periods starting from single phase liquid until steam on the secondary pool side was found. During these experiments temperature stratification phenomena were observed, which were found in earlier small scale tests. In the paper also these small scale experiments are described. A detailed CFD analysis of these experiments was performed. An explanation of the observed phenomena on the basis of the small scale tests and the CFD simulations is presented.
Keywords: Passive safety systems, Experiments, CFD, natural circulation
  • Contribution to proceedings
    17th International Conference on Nuclear Engineering, ICONE-17, 12.-16.07.2009, Brussels, Belgium
  • Lecture (Conference)
    17th International Conference on Nuclear Engineering, ICONE-17, 12.-16.07.2009, Brussels, Belgium
  • Nuclear Engineering and Design 240(2010), 3170-3177
    DOI: 10.1016/j.nucengdes.2010.05.050

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Permalink: https://www.hzdr.de/publications/Publ-12235
Publ.-Id: 12235


Surfing the plasma wake - particle acceleration with laser light

Schramm, U.
Modern short-pulse high-power lasers can, for a few optical cycles, generate electrical field strengths strong enough to accelerate electrons to relativistic energies. Rectifying these fields by means of a laser plasma can lead to acceleration gradients that exceed conventional rf-based technology by many orders of magnitude. Recent results in this field will be discussed as well as potential applications of laser accelerated particle pulses.
Keywords: laser plasma acceleration
  • Invited lecture (Conferences)
    Tata Institute of Fundamental Research, Institute Seminar, 12.1.2009, Mumbai, India
  • Invited lecture (Conferences)
    Institute of plasma research, Seminar, 13.1.2009, Ahmenabad, India

Permalink: https://www.hzdr.de/publications/Publ-12234
Publ.-Id: 12234


Prospects of high intensity laser driven radiation sources

Schramm, U.
Recent development in table-top high-power lasers of the 100 Terawatt class combined with an improved understanding of relativistic laser matter interaction now allows for the discussion of applications of laser accelerated particle beams and secondary radiation sources. In this presentation, an introduction covering the underlying mechanisms will be given followed by a presentation of the novel combined laser-accelerator facility at FZD and its goals as, e.g., laser driven proton oncology.
Keywords: laser particle acceleration, secondary sources
  • Invited lecture (Conferences)
    Eighth DAE-BRNS National Laser Symposium (NLS-08), 07.-10.1.2009, Delhi, India
  • Invited lecture (Conferences)
    Lecture Laser and Neutron Physics Section of BARC, 14.1.2009, Mumbai, India

Permalink: https://www.hzdr.de/publications/Publ-12233
Publ.-Id: 12233


Structural investigations of ZnO thin films grown by reactive pulsed magnetron sputtering at different substrate temperatures

Redondo-Cubero, A.; Vinnichenko, M.; Krause, M.; Gago, R.
Zinc oxide (ZnO) is a promising material for electronic and optical applications [1]. As in the case of other wide bandgap compounds (i.e. GaN) grown in heteroepitaxy conditions, the final electrical properties of the film are affected by its crystal quality. Rutherford backscattering spectrometry (RBS) in channeling mode (RBS/C) is a well proved method to obtain this physical information in such structures, with the additional advantage of in-depth information [2]. In this work, we report RBS/C and Raman characterization of ZnO thin films grown onto (0001) oriented sapphire [3] by reactive pulsed magnetron sputtering at substrate temperatures (Ts) spanning from 22ºC to 550ºC .
Random and RBS/C measurements were performed along the and axes of the wurtzite lattice (P63mc) of ZnO [1] with a 3.035 MeV He+ beam. The sample position was controlled by a 3-axis goniometer. The micro-Raman spectra were collected at an excitation wavelength of 532 nm. The influence of substrate temperature onto low- and high-frequency E2 modes of the resulting film was monitored. The low-frequency E2 mode is associated with the vibration of the heavy Zn sublattice, while the high-frequency E2 mode involves only the oxygen atoms.
Stoichiometry of the oxide layer was determined from the random RBS spectra, which showed a constant composition except for an O-rich interface (associated with Zn in-diffusion). RBS/C angular scans along the axis revealed a progressive enhancement of crystal quality of wurtzite ZnO with substrate temperature, with a <0001> textured growth even for low substrate temperatures (100ºC). The film crystallinity is greatly increased for substrate temperatures above 400ºC, a behaviour also confirmed by Raman measurements. The latter shows significant decrease of the line width which in the case of low-frequency E2 mode at Ts>400 °C approaches and even becomes smaller than the values of reference single crystal sample. Also, the Raman peak positions do not change for the films grown at temperatures above 400°C. Further RBS/C analysis along the oblique axis was carried out to determine the possible influence of strain. The angular scan showed no-shift among different ZnO depths, revealing a non-strained film under the technique limits. From these measurements, it can be concluded that epitaxial ZnO films can be grown by pulsed reactive magnetron sputtering without appreciable strain on sapphire substrates at Ts ~550ºC.

References:
1. Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Dogan, V. Avrutin, S.-J. Cho, and H. Morkoc, J. Appl. Phys. 98, 041301 (2005).
2. L.C. Feldman, J.W. Mayer and S.T. Picraux, Material analysis by ion channeling, NY, Academic Press (1982).
3. M. Vinnichenko, N. Shevchenko, A. Rogozin, R. Grötzschel, A. Mücklich, A. Kolitsch and W. Möller, J. Appl. Phys. 102, 113505 (2007)
Keywords: ZnO, epitaxial growth, reactive pulsed magnetron sputtering
  • Poster
    Charged and neutral particles channeling phenomena (Channeling 2008), 25.10.-01.11.2008, Erice, Italy

Permalink: https://www.hzdr.de/publications/Publ-12232
Publ.-Id: 12232


Experiments on nuclear rotation

Schwengner, R. Keywords: Nuclear structure, gamma-ray spectroscopy, collective rotation, magnetic rotation, cranking model, shell model
  • Lecture (others)
    Institutsseminar des Instituts für Strahlenphysik, 20.08.2008, Dresden-Rossendorf, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12231
Publ.-Id: 12231


Flavonoids – organic compounds with strong interactions towards uranium

Geipel, G.; Viehweger, K.; Bernhard, G.
Flavonoids belong to a class of secondary plant metabolites. They are most commonly known for their antioxidant activity. Next to chlorophyll flavonoids are the most important group of visible plant pigments.
We studied by use of spectrophotometric techniques the interaction of several flavonoids with uranium. The change in the spectral properties of the flavonoids was used to determine the stability constants. Spectra were evaluated with the factor analysis program Specfit. All spectra of flavonoids show strong change with increasing uranium concentration at constant pH. Stability constants were derived for quercetin, hesperetin, hesperidin, the aglycon of hesperetin. Hesperetin was obtained by hydrolytic splitting of the glycoside hesperidin.
The overall structure Isosbestic points in the absorption spectra indicate a clear interaction between the flavonoids and uranium(VI).
The most strong interaction was found for quercetin. The derived stability constant was assigned to be log β131 = 41.4 ± 0.4 at an ionic strength of 0.1 M for the reaction

UO22+ + C15H5O75- + 3 H+ → UO2C15H8O7 (1)

Hesperidin and hesperetin show much lower stability constants. For example the stability constant for the hesperetin complex at 0.1 M ionic strength was determined to be log β121 = 31.0 ± 0.6.
We assume that the complex formation occur by a ring formation, whereas quercitin forms a 6-membered ring between a phenolic group and the ketone oxygen in the benzopyran-4-one ring whereas hesperidin and hesperetin form 5-membered rings.
Keywords: Uranium, Flavonoids
  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-12230
Publ.-Id: 12230


An U accumulating plant – a suitable tool for remediation?

Viehweger, K.; Geipel, G.; Bernhard, G.
Abstract. Large areas were disturbed in the southern “Erzgebirge”, Germany, due to former uranium mining activities. Great efforts were done for the remediation and restoration during the last decade. Nevertheless there are some small areas, which are not yet rehabilitated and therefore possess exalted uranium soil contents.
The first step was the evaluation of different former U mining sites. Reconstructed areas contain considerable less amounts of U compared with a leaved stock pile near Johanngeorgenstadt. To get more reliable data on the bioavailability of U in this distinct soil, a sequential chemical soil fractionation procedure was accomplished. The bioavailable U were recovered from the first 3 extraction steps (~ 30 mg*Kg-1).
Fortunately we could identify the well known heavy metal hyperaccumulator Arabidopsis halleri (also known as Cardaminopsis halleri) in this U contaminated area. A basic tool for the characterisation of metal mobility within the soil-plant system is the soil-to-plant transfer factor or accumulation factor. Arabidopsis plants growing on the mining dump achieved accumulation factors around 2.6 for roots and 1.1 for shoots, respectively.
To get more insight in mechanisms underlying plant U uptake and accumulation, a hydroponic grow system under laboratory conditions was developed. The accumulation factors in this system were around 1670 for roots and 625 for shoots. It is obvious that U is clear more bioavailable for plants in hydroponic solution than in the soil from the former mining side.
Despite this enormous U accumulation it is mandatory to evaluate the U tolerance and toxicity under hydroponic conditions. The classical root-elongation test was used for estimation of the tolerance index (TI). Plants growing permanent with U could increase their TI within 7 weeks. Nevertheless U had a negative impact on the plant fitness indicated by a significant decrease of chlorophyll a/b ratio during the growth period. Additionally, spectroscopic measurements of leaves and chlorophyll extracts revealed some disturbances of chlorophyll biosynthesis and proper function of photosystem I, respectively.
We could identify a U accumulating plant, which is able to take up enormous amounts of U in hydroponic solution. To make this plant suitable for remediation processes it is crucial getting a deeper insight in uptake, sequestration and U tolerance pathways. The described hydroponic system could be useful tool for this purpose.
Keywords: Plants, uranium
  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-12229
Publ.-Id: 12229


Dipole strength in 89Y and 90Zr up to the neutron-separation energy

Schwengner, R. Keywords: Nuclear structure, nuclear spectroscopy, photon scattering, gamma-ray strength functions, photoabsorption cross section, random-phase approximation
  • Lecture (Conference)
    DPG Frühjahrstagung, 10.-14.03.2008, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-12228
Publ.-Id: 12228


Strength-function measurements

Schwengner, R. Keywords: Nuclear structure, gamma-ray spectroscopy, photon scattering, strength functions, absorption cross sections, random-phase approximation
  • Lecture (Conference)
    Workshop on Modern Methods Using Fast Neutrons for Research Related to the Transmutation of Nuclear Waste, 13.-15.02.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12227
Publ.-Id: 12227


NeuLAND MRPC Prototype construction and testing at Electron Linear Accelerator (ELBE)

Bemmerer, D.; Yakorev, D.; Stach, D.; Wagner, A.
Different prototypes of Multigap resistive plate chamber detector (MRPC) for the future NeuLAND detector were built and tested at the ELBE electron beam in FZD. Results and future plans are discussed.
Keywords: MRPC, RPC, Multigap resistive plate chamber, Resistive plate chamber, NeuLAND, FAIR, gas chamber, ELBE
  • Lecture (Conference)
    NeuLAND Working Group Meeting, 24.-26.09.2008, Sinaia, Romania

Permalink: https://www.hzdr.de/publications/Publ-12226
Publ.-Id: 12226


Room-temperature ferromagneticlike behavior in Mn-implanted and postannealed InAs layers deposited by Molecular Beam Epitaxy

González-Arrabal, R.; González, Y.; González, L.; García-Hernández, M.; Munnik, F.; Martín-González, M. S.
We report on the magnetic and structural properties of Ar- and Mn-implanted InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and the effect of Rapid Thermal Annealing (RTA) for 30 s at 750 °C. Channelling Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are subsbtitutional in the In site of the InAs lattice, like in a diluted magnetic semiconductor (DMS). All of these samples show diamagnetic behavior. However, after RTA treatment the Mn–InAs films exhibit room-temperature magnetism. According to PIXE measurements the Mn atoms are no longer substitutional. When the same set of experiments was performed with Ar as implantation ion, all of the layers present diamagnetism without exception. This indicates that the appearance of room-temperature ferromagneticlike behavior in the Mn–InAs-RTA layer is not related to lattice disorder produced during implantation but to a Mn reaction produced after a short thermal treatment. X-ray diffraction patterns and Rutherford backscattering measurements evidence the segregation of an oxygen-deficient MnO2 phase (nominally MnO1.94) in the Mn–InAs-RTA epitaxial layers which might be the origin of the room-temperature ferromagneticlike response observed.
Keywords: DMS, InMnAs, room temperature magnetism, PIXE, implantation, III-V semiconductors

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Permalink: https://www.hzdr.de/publications/Publ-12225
Publ.-Id: 12225


Fast Digitizing and Digital Signal Processing of Detector Signals

Hannaske, R.
A fast-digitizer data acquisition system recently installed at the neutron time-of-flight experiment nELBE, which is located at the superconducting electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf, is tested with two different detector types. Preamplifier signals from a high-purity germanium detector are digitized, stored and finally processed. For a precise determination of the energy of the detected radiation, the moving-window deconvolution algorithm is used to compensate the ballistic deficit and different shaping algorithms are applied. The energy resolution is determined in an experiment with γ-rays from a 22Na source and is compared to the energy resolution achieved with analogously processed signals. On the other hand, signals from the photomultipliers of barium fluoride and plastic scintillation detectors are digitized. These signals have risetimes of a few nanoseconds only. The moment of interaction of the radiation with the detector is determined by methods of digital signal processing. Therefore, different timing algorithms are implemented and tested with data from an experiment at nELBE. The time resolutions achieved with these algorithms are compared to each other as well as to reference values coming from analog signal processing. In addition to these experiments, some properties of the digitizing hardware are measured and a program for the analysis of stored, digitized data is developed. The analysis of the signals shows that the energy resolution achieved with the 10-bit digitizer system used here is not competitive to a 14-bit peak-sensing ADC, although the ballistic deficit can be fully corrected. However, digital methods give better result in sub-ns timing than analog signal processing.
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-510 2009
  • Poster
    Graduate Students Seminars, 27.-29.08.2008, Limbach-Oberfrohna, Deutschland
  • Lecture (others)
    IKTP Institutsseminar, 20.11.2008, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-12224
Publ.-Id: 12224


Progress of the EPOS project: Gamma-Induced Positron Spectroscopy (GiPS)

Krause-Rehberg, R.; Anwand, W.; Brauer, G.; Butterling, M.; Cowan, T.; Jungmann, M.; Krille, A.; Schwengner, R.; Wagner, A.
Gamma-induced positron generation has been performed using the superconducting electron accelerator ELBE at the Research Center Dresden-Rossendorf.
  • Contribution to proceedings
    The XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India
    Progress of the EPOS Project: Gamma-Induced Positron Spectroscopy (GiPS)
  • Lecture (Conference)
    The XVth International Conference on Positron Annihilation (ICPA-15), 18.-23.01.2009, Kolkata, India
  • Physica Status Solidi (C) 6(2009)11, 2451-2455
    DOI: 10.1002/pssc.200982076

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Permalink: https://www.hzdr.de/publications/Publ-12223
Publ.-Id: 12223


Structural and electrochemical studies on uranyl(VI) complex with pentadentate Schiff base ligand: A guide to stable uranyl(V)

Takao, K.; Kato, M.; Takao, S.; Nagasawa, A.; Scheinost, A. C.; Bernhard, G.; Hennig, C.; Ikeda, Y.
Uranium(V) is normally instable in solution because of its disproportionation. On the other hand, U(V) has one unpaired electron in the 5f orbital, i.e., 5f1 configuration., and hence chemistry of U(V) is essential for the systematic understanding of actinide chemistry. Previously, we studied electrochemical behavior of U(VI) complexes in non-aqueous solvents, and obtained insight that multidentate ligands may stabilize U(V).1 From this point of view, we have found that two stable U(V) complexes [UVO2(salophen)DMSO]– (salophen = N,N’-disalicylidene-o-phenylenediaminate) and [UVO2(dbm)2DMSO]– (dbm = dibenzoylmethanate) are stable in DMSO.1-4 However, dissociation of a unidentate ligand (L) such as DMSO in [UVO2(salophen)L]– was also observed at lower L concentration. This prevents preparation and observation of a “pure” U(V) complex. On the basis of this knowledge, we obtained a hint that it is better to exclude L from a U(V) complex for its stability. Normally, U(VI) (UO22+) has 3–6 coordination sites in its equatorial plane, and probably most prefers 5 even in a bulky ligand.5 In this study, we selected N,N’-disalicylidenediethylenetriaminate (saldien2–)6 as a pentadentate ligand to satisfy this request. The U(VI) complex with saldien2– was characterized by single crystal X-ray analysis and X-ray absorption fine structure (XAFS) spectroscopy, and its electrochemical behavior in DMSO and N,N-dimethylformamide (DMF) was studied.
The obtained U(VI)-saldien2– complex recrystallized from DMSO was identified as orthorhombic UVIO2(saldien)•DMSO by single crystal X-ray analysis (Fig. 1). It should be noted that all coordination sites in the equatorial plane of UO22+ are occupied by saldien2–, and that any unidentate ligands are excluded as desired. A DMF solution of UVIO2(saldien) shows k3-weighted U LIII-edge EXAFS spectrum similar to that in solid state, indicating that the structure of UVIO2(saldien) remains even in the solution. This is supported by structural parameters from EXAFS curve fit.
Redox behavior of UVIO2(saldien) in DMSO and DMF was studied by using cyclic voltammetry. As a result, quasi-reversible redox waves were observed around E°’ = –1.582 ± 0.005 V vs. Fc/Fc+ (Ep = 0.080–0.170 V at v = 0.010–0.500 V•s–1) in DMSO and E°’ = –1.632 ± 0.003 V vs. Fc/Fc+ (Ep = 0.076–0.141 V at v = 0.010–0.500 V•s–1) in DMF. UV-Vis-NIR absorption spectral changes with the electrochemical reduction of UVIO2(saldien) were recorded using the spectroelectrochemical technique.1,4 The result of the DMSO solution is shown in Fig. 2. From the absorbance change, the electron stoichiometry in the reduction of UVIO2(saldien) was determined as 0.92 in DMSO and 0.82 in DMF using the Nernstian relationship. This quantity close to unity reveals that the following reaction occurs in both solutions.

UVIO2(saldien) + e– = [UVO2(saldien)]–

As we expected, it was found that UVIO2(saldien) without unidentate ligands results in the stable U(V) complex, [UVO2(saldien)]–, in DMSO and DMF. This U(V) species also shows the characteristic absorption bands of U(V) at 620, 700, 830, 1390, and 1890 nm as well as other U(V) species, [UVO2(salophen)DMSO]– and [UVO2(dbm)2DMSO]–.1,4
Keywords: U(V), Structure, Stability, Electrochemistry, Absorption Spectrum
  • Lecture (Conference)
    ACTINIDES 2009, 12.-17.07.2009, San Francisco, USA

Permalink: https://www.hzdr.de/publications/Publ-12222
Publ.-Id: 12222


X-ray absorption fine structures of uranyl(V) complexes in non-aqueous solutions

Takao, K.; Tsushima, S.; Takao, S.; Scheinost, A. C.; Bernhard, G.; Ikeda, Y.; Hennig, C.
Actinide elements at oxidation states +5 and +6 exist as actinyl ions (AnO2n+, An = U, Np, Pu, Am) with typical trans-dioxo arrangement. Among them U(V) is quite instable due to the disproportionation. Recently, U(V) attracts special interest, because this field of actinides has been little explored despite its importance in the nuclear engineering. Especially, the U(V) solution chemistry is quite important in nuclear fuel reprocessing and environmental risks with long-term storage of radioactive waste. Structure of U(V) species is one of the essential parts of its chemistry. Actually, several crystal structures of U(V) compounds were reported previously. On the other hand, structure of U(V) species in solutions are not investigated so far except for EXAFS studies of UVO2(CO3)35– in an aqueous system.1,2 In this study, we report the structure determination of two U(V) complexes, [UVO2(salophen)DMSO]– (1V, salophen = N,N’-disalicylidene-o-phenylenediaminate) and [UVO2(dbm)2DMSO]– (2V, dbm = dibenzoylmethanate), in DMSO.3-6
The k3-weighted EXAFS spectra of 1V, 1VI, 2V, and 2VI and their Fourier transforms (FTs) are shown in Fig. 1. The structures of these U(V) and U(VI) complexes in DMSO solutions were determined by the EXAFS curve fits on the basis of the molecular structures of 1VI and 2VI from single crystal X-ray analyses.5,6 The best fit curve for each EXAFS spectrum and FTs are also displayed in Fig. 1. As a result, the interatomic distances between U and axial O (Oax) were determined as 1.84 Å for 1V and 1.85 Å for 2V, which are comparable with other U(V) complexes in crystal structures. On the other hand, the U–Oax distances of 1VI and 2VI are evaluated 1.80 and 1.78 Å, respectively. The lengthening of the U–Oax distance of 0.04–0.07 Å with the reduction of U(VI) to U(V) corroborates our previous estimation from IR spectra for 1V/1VI and 2V/2VI couples.4,5 The interatomic distances between U and coordinating atoms of salophen2– and dbm– are also lengthened 0.04–0.14 Å with the reduction from U(VI) to U(V). It should be noted that a long interatomic distance between U and O of DMSO (U–ODMSO; ca. 2.90 Å) was found in both 1V and 2V. Although these U–ODMSO distances seem unusual, those are still shorter than the sum of van der Waals radii of U and O (1.86 + 1.52 = 3.38 Å),9 indicating that such a long U–ODMSO interaction is still possible. The long U–ODMSO distance implies the very weak coordination of DMSO to U(V) in 1V and 2V. Actually, we previously observed that 1V may release DMSO at lower DMSO concentration.1 The week coordination of the unidentate ligand (L) such as DMSO might be a reason why U(V) solvates (UVO2(L)5+) is instable even in L,10,11 and provides an insight that strong multidentate ligand is required for stabilization of U(V).
Keywords: XAFS, U(V), Solution Chemistry, Structure, Stability
  • Lecture (Conference)
    Actinides 2009, 12.-17.07.2009, San Francisco, USA
  • Inorganic Chemistry 48(2009)20, 9602-9604

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Permalink: https://www.hzdr.de/publications/Publ-12221
Publ.-Id: 12221


The time-of-flight setup for inelastic scattering measurements at nELBE

Beyer, R.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Matic, A.; Nolte, R.; Schilling, K.-D.; Schwengner, R.; Wagner, A.
At the nELBE facility at Forschungszentrum Dresden-Rossendorf fast neutrons with kinetic energies of 0.1 to 10 MeV will be used to deliver nuclear data on neutron induced reactions.
First experiments on neutron scattering on Fe-56 were performed using a double time-of-flight setup. This setup is based on proton recoil detectors and an array of 42 Barium-Flouride crystals. Emitted photons and neutrons are detected in coincidence to determine the inelastic neutron scattering cross section.
Keywords: nELBE, inelastic neutron scattering, double time-of-flight
  • Lecture (Conference)
    EFNUDAT progress and general assembly meeting, 01.-03.10.2008, Uppsala, Sverige

Permalink: https://www.hzdr.de/publications/Publ-12220
Publ.-Id: 12220


Transmutation with fast neutrons

Beyer, R.
Nuclear Transmutation is one way to reduce the amount nuclear waste that has to be disposed for hundred thousands of years. The idea is to convert long lived isotopes in to short lived ones by nuclear interaction with fast neutrons. This procedure will take place in future types of nuclear facilities, like generation IV reactors or accelerator driven systems. At the neutron time-of-flight setup nELBE at Forschungszentrum Dresden-Rossendorf experiments will be performed to obtain neutron induced reaction cross sections which are necessary to develop and construct such facilities.
Keywords: nuclear transmutation, nELBE, neutron time-of-flight
  • Lecture (others)
    3rd FZD Graduate Students Seminar, 27.-29.08.2008, Limbach-Oberfrohna, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12219
Publ.-Id: 12219


Experimental investigation of the residues produced in the 136Xe+Pb and 124Xe+Pb fragmentation reactions at 1A GeV

Henzlova, D.; Schmidt, K. H.; Ricciardi, M. V.; Kelic, A.; Henzl, V.; Napolitani, P.; Audouin, L.; Benlliure, J.; Boudard, A.; Casarejos, E.; Ducret, J. E.; Enqvist, T.; Heinz, A.; Junghans, A. R.; Jurado, B.; Krasa, A.; Kurtukian, T.; Leray, S.; Ordonez, M. F.; Pereira, J.; Pleskac, R.; Rejmund, F.; Schmitt, C.; Stephan, C.; Tassan-Got, L.; Villagrasa, C.; Volant, C.; Wagner, A.; Yordanov, O.
The nuclide cross sections and longitudinal velocity distributions of residues produced in the reactions of 136Xe and 124Xe at 1A GeV in a lead target were measured at the high-resolution magnetic spectrometer, the fragment separator (FRS) of GSI. The data cover a broad range of isotopes of the elements between Z=3 and Z=56 for 136Xe and between Z=5 and Z=55 for 124Xe, reaching down to cross sections of a few microbarns. The velocity distributions exhibit a Gaussian shape for masses above A=20, while more complex behavior is observed for lighter masses. The isotopic distributions for both reactions preserve a memory on the projectile N/Z ratio over the whole residue mass range.
Keywords: cross section residue high-resolution magnetic spectrometer fragment separator FRS GSI

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Permalink: https://www.hzdr.de/publications/Publ-12218
Publ.-Id: 12218


Ultra-low-energy ion-beam-synthesis of Ge nanocrystals in thin ALD Al2O3 layers for memory applications

Dimitrakis, P.; Mouti, A.; Bonafos, C.; Schamm, S.; Ben Assayag, G.; Ioannou, V.; Schmidt, B.; Becker, J.; Normand, P.
Structural and electrical properties of ALD-grown 5 and 7 nm-thick Al2O3 layers before and after implantation of Ge ions (1 keV, 0.5–1 x 1016 cm-2) and thermal annealing at temperatures in the 700–1050°C range are reported. Transmission Electron Microscopy reveals the development of a 1 nm-thick SiO2-rich layer at the Al2O3/Si substrate interface as well as the formation of Ge nanocrystals with a mean diameter of ca. 5 nm inside the implanted Al2O3 layers after annealing at 800 °C for 20 min. Electrical measurements performed on metal–insulator–semiconductor capacitors using Ge-implanted and annealed Al2O3 layers reveal charge storage at low-electric fields mainly due to location of the Ge nanocrystals at a tunnelling distance from the substrate and their spatial dispersion inside the Al2O3 layers.
Keywords: Ion implantation, Ge nanocrystals, nanocrystal memory
  • Lecture (Conference)
    16th biannual conference of Insulating Films on Semiconductors, 29.06.-01.07.2009, Cambridge, United Kingdom
  • Microelectronic Engineering 86(2009), 1838-1841
    DOI: 10.1016/j.mee.2009.03.074

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Permalink: https://www.hzdr.de/publications/Publ-12217
Publ.-Id: 12217


Prospects of Laser Cooling of Ion Beams at CSR

Bussmann, M.
This talk focuses on the prospects of laser cooling of ion beams at the storage rings CSRe and CSRm located at the Institute of Modern Physics in Lanzhou, China.
Keywords: laser cooling, ion beams, relativistic energies, storage ring, CSR, CSRe, CSRm
  • Invited lecture (Conferences)
    Seminar of the Institute of Modern Physics, CAS, 19.11.2008, Lanzhou, China

Permalink: https://www.hzdr.de/publications/Publ-12216
Publ.-Id: 12216


Laser Cooling of Ion Beams at PALLAS and ESR

Bussmann, M.
Recent experiments at the ESR storage ring at GSI have shown that it is possible to cool relativistics ions beams using table top laser systems. We present results from these experiments including precision laser spectroscopy measurements of the 2S1/2-2P1/2 and 2S1/2-2P3/2 transition in C3+. We compare the prospects of future laser cooling experiments at GSI and FAIR with experiments on crystalline ion beams caried out at the table top storage ring PALLAS.
Keywords: laser, laser cooling, ion beam, storage ring, PALLAS, ESR, GSI, C3+, laser spectroscopy, VUV, x-ray
  • Invited lecture (Conferences)
    Seminar of the Institute of Modern Physics, CAS, 18.11.2008, Lanzhou, China

Permalink: https://www.hzdr.de/publications/Publ-12215
Publ.-Id: 12215


Laser Cooling of Ions in Traps and Storage Rings

Bussmann, M.
Laser Cooling of Ions is an established technique for providing ultracold ions for precision experiments in traps. In this talk I will present the prospects of laser cooling of ion beams in storage rings, showing both the similarities and differences of this new cooling scheme compared to traditional in-trap laser cooling.
Keywords: laser cooling, ion beam, PALLAS, Paul trap, storage ring, ion, laser
  • Invited lecture (Conferences)
    Seminar of the Institute for Modern Physics, CAS, 17.11.2008, Lanzhou, China

Permalink: https://www.hzdr.de/publications/Publ-12214
Publ.-Id: 12214


Cooling of Ions

Bussmann, M.
Measuring the properties of heavy ions with high accuracy demands precise control of their
motional degrees of freedom in an isolated environment. Such a situation can be achieved by
combining modern cooling techniques with new means to trap and store the ions of interest. The first lecture will provide an overview of current state-of-the-art techniques to trap and store ions, including a comparison of the ion dynamics in the two most common types of ion traps, Penning and Paul traps, with the ion dynamics in storage rings.
This overview will be followed by an introduction to some widely used cooling techniques, focusing on sympathetic cooling and laser cooling. Based on this introduction the second lecture will give inside to current high accuracy experiments with ions in traps and storage rings with emphasis on sympathetic cooling of highly charged ions and laser cooling of ion beams. I will conclude with an outlook on future high accuracy measurements of heavy, unstable nuclei and accurate laser X-ray spectroscopy of Li-like and Na-like electronic transitions in heavy ions at future storage ring facilities.
Keywords: laser cooling, Paul trap, Penning trap, storage ring, ion beam, crystalline ion beam, phase transition, laser spectroscopy, x-ray, VUV
  • Invited lecture (Conferences)
    International WE-Heraeus Summer School: Atomic Properties of the Heaviest Elements, 24.08.-06.09.2008, Wittenberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12213
Publ.-Id: 12213


Laseraktivitäten am FZD in Rossendorf

Bussmann, M.
In this talk we present the scientific program of the Laser Particle Acceleration Group and the status of the DRACO laser system.
Keywords: laser, particle acceleration, ion beam, electron beam, DRACO
  • Invited lecture (Conferences)
    Gruppenseminar des Lehrstuhls für Experimentelle Kernphysik der Ludwig-Maximilians-Universität München, 16.05.2008, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12212
Publ.-Id: 12212


Laser-Cooling of Ion Beams at Relativistic Energies

Bussmann, M.
Recent Experiments at the Experimental Storage Ring at GSI have seen the successful application of laser cooling of bunched C3+ ion beams at relativistic energies of 122 MeV per nucleon. Major results of these experiments include the attainment of space-charge dominated beams, evidence for collective ion motion, three-dimensional cold beams and precision laser spectroscopy in the deep UV spectral range. The talk will review these results, showing that measurements of important beam properties such as momentum spread and bunch length are currently limited by the beam diagnostics available. Several solutions to better resolve the beam momentum spread will be presented, which can be easily included in future experiments. These experimental efforts are supplemented by extensive computer simulations of laser-cooled bunched ion beams which can provide insight into the ion-dynamics on the single-particle level. The talk will conclude with an outlook to the exciting possibilities for laser cooling of ion beams at FAIR.
Keywords: laser cooling, ion beam, crystalline beam, FAIR, ESR, GSI, laser spectroscopy, VUV, X-ray
  • Invited lecture (Conferences)
    Atomphysik-Seminar, 14.05.2008, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12211
Publ.-Id: 12211


Commissioning of the double Penning trap system MLLTRAP

Kolhinen, V. S.; Bussmann, M.; Gartzke, E.; Habs, D.; Neumayr, J. B.; Schürmann, C.; Szerypo, J.; Thirolf, P. G.
A cylindrical double Penning trap system has been installed and commissioned at the Maier-Leibnitz-Laboratory (MLL) in Garching. This trap system has been designed to isobarically purify low-energy ion beams and perform highly accurate mass measurements. Technical details of the device and the first results of the commissioning measurements will be presented. The mass resolving power achieved in the first trap for 119Rb ions is R=139(2)×103, while a relative mass uncertainty of δm/m=2.9×10−8 was reached with the second trap (no analysis of systematic uncertainties included) when using 87Rb as a reference ion for 85Rb.
Keywords: Penning trap; Mass measurement; Mass separation; Buffer gas cooling

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Permalink: https://www.hzdr.de/publications/Publ-12210
Publ.-Id: 12210


Criteria for system solution in Particle Therapy Positron Emission Tomography

Shakirin, G.
Image processing in Particle Therapy Positron Emission Tomography (PT-PET) differs significantly from one in conventional nuclear medicine PET. The evaluation of dose delivery in particle therapy requires specific tasks to be solved during the analysis of the PT-PET images. Therefore, dedicated image quality criteria have been developed for PT-PET. These criteria together with a 3D configuration tool allow to construct an optimum PT-PET system for a given particle therapy facility and PET components supplier.
Keywords: in-beam PET, radiation therapy
  • Invited lecture (Conferences)
    Conference on Clinical and Experimental Research in Radiation Oncology (CERRO), 17.-24.01.2009, Les Menuires, France

Permalink: https://www.hzdr.de/publications/Publ-12209
Publ.-Id: 12209


Ion Bombardment of Solids - unified simulation of damage formation and thermally activated relaxation

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.
Till now, damage formation and thermally activated relaxation are calculated by different atomistic methods like Binary Collision Approximation (BCA, TRIM code) and kinetic Monte Carlo (kMC), respectively. However, frequently damage formation and relaxation happens simultaneously. Molecular Dynamics (MD), which treats both processes, can not describe them on experimental spatiotemporal scales due to insufficient computer power. Here, an unified TRIM-kMC simulation method will be presented and applied to ion-induced nanopatterning of surfaces as well as mixing and phase separation of intermetallic compounds.
Keywords: ion implantation, TRIM, Kinetic Monte-Carlo, unified description, nanopatterninig, interface mixing, phase separation
  • Lecture (others)
    Seminar at MFA of KFKI of Budapest, 11.11.2008, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-12208
Publ.-Id: 12208


Simulation of defects and composition after irradiation of ultrathin Pt/Co/Pt film with Ga+

Liedke, B.; Facsko, S.; Fassbender, J.ORC; Jaworowicz, J.; Ferre, J.; Maziewski, A.; Vernier, N.; Möller, W.
Spin reorientation transition from in-plane to out-of-plane state has been observed experimentally in Pt/tCo/Pt film (tCo=3nm) after ion irradiation with 30 keV Ga+ [1]. Theoretical studies of the collision intermixing and defects creation processes of irradiated are presented. By means of TRIDYN simulations the dependence of composition and sputtering yield on ion fluence in the range of 1014 to 5 · 1016 ions/cm2 is elucidated. Simulations show that ion fluence plays non-neglectable role in case of erosion and intermixing of the interface (which likely gives a certain strain to the system), which give rise to the new phenomena, the so-called swelling effect. On the other hand the swelling effect can relax the strain in the film and give rise to an increase of the magnetic anisotropy. However, the strain relaxation can be strongly non-uniform on the full square area providing a mixture of patches with in-plane or out-of-plane anisotropy. The presence of relatively large and quasi-uniform perpendicular anisotropy partially comes from peculiar strain states at the interface. Simulated compositions are compared with experimentally observed irradiation induced phenomena.
Keywords: TRIDYN, implantation, Monte-Carlo simulation, intermixing, swelling
  • Poster
    PHYSICS OF MAGNETISM 2008, 24.-27.06.2008, Poznan, Poland

Permalink: https://www.hzdr.de/publications/Publ-12206
Publ.-Id: 12206


Fluorescence properties of a uranyl(V)-carbonate species [U(V)O2(CO3)3]5− at low temperature

Großmann, K.; Arnold, T.; Ikeda, A.; Steudtner, R.; Geipel, G.; Bernhard, G.
Fluorescence properties of a uranyl(V)-carbonate species in solution are reported for the first time. The fluorescence characteristics of the stable aqueous uranyl(V)-carbonate complex [U(V)O2(CO3)3]5− was determined in a frozen solution (T = 153 K) of 0.5mM uranium and 1.5M Na2CO3 at pH 11.8 by time resolved laser-induced fluorescence spectroscopy (TRLFS). Two different wavelengths of 255nm and 408 nm, respectivelywere used to independently of each other excite the uranyl(V)-carbonate species. The resulting U(V) fluorescence emission bandswere detected between 380nmand 440 nm, with a maxima at 404.7nm (excitation with 255 nm) and 413.3nm (excitation with 408 nm), respectively. It was found that by using an excitation wavelength of 255nm the corresponding extinction coefficient was much higher and the fluorescence spectrum better structured than the ones excited at 408 nm. The fluorescence lifetime of the uranyl(V)-carbonate species was determined at 153K as 120s. TRLFS investigations at room temperature, however, showed no fluorescence signal at all.
Keywords: U(V) Uranyl(V)-carbonate Fluorescence Laser fluorescence spectroscopy

Permalink: https://www.hzdr.de/publications/Publ-12205
Publ.-Id: 12205


Boltwoodite [K(UO2)(SiO3OH)(H2O)1.5] and Compreignacite K2[(UO2)3O2(OH)3]2 • 7 H2O Characterized by Laser Fluorescence Spectroscopy

Arnold, T.; Baumann, N.
Synthetically prepared boltwoodite and compreignacite were characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS). The obtained TRLFS emission spectra of both synthesized uranium minerals differ from each other in their positions of the vibronic peak maxima and in their fluorescence lifetimes. Also, the shapes of the spectra and their respective intensities are different. The TRLFS–spectrum of boltwoodite showed well-resolved sharp vibronic peaks at 485.1, 501.5, 521.2, 543.0, 567.4, and 591.4 nm with deep notches between them and compreignacite is characterized by two broad peaks with various shoulders. Here five emission bands were identified at 500.7, 516.1, 532.4, 554.3, and 579.6 nm. The shape of the TRLFS spectra of compreignacite is typical for uranium in a hydroxide coordination environment. For both minerals two fluorescence lifetimes were extracted. The two species of boltwoodite and compreignacite, respectively, showed the same positions of the peak maxima showing that the coordination environments are similar, but differ in the chemistry and number of possible quenchers, e.g. water molecules and hydroxide groups. For boltwoodite fluorescence lifetimes of 382 and 2130 ns, and for compreignacite shorter ones of 202 and 914 ns, respectively, were determined. The spectroscopic signatures of the two uranyl minerals reported here could be useful for identifying uranyl(VI) mineral species as colloids, as thin coatings on minerals, as minor component in soils, or as alteration products of nuclear waste.
Keywords: Boltwoodite, Compreignacite, Uranium(VI), Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS)

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Permalink: https://www.hzdr.de/publications/Publ-12204
Publ.-Id: 12204


Precision measurements of the reconstructed image resolution for different PET and PET/CT scanners with the NEMA phantom.

Mix, M.; Weber, W. A.; van den Hoff, J.
Objectives:
For multicenter PET studies robust techniques are required to measure the reconstructed image resolution of different PET systems. The aim of this study was to determine the reconstructed image resolution (RIR) using a NEMA phantom as a function of count statistics and image contrast.

Methods:
Measurements with the NEMA whole-body (WB) phantom at 7 scanner systems at different signal-to-noise levels and different target to background (T/BG) ratios were analyzed. Images were reconstructed iteratively using the default scanner WB reconstruction protocol. For each sphere, the image data were transformed to spherical coordinates relative to the center of the respective sphere yielding radial profiles. The RIR was then determined by fitting the convolution of a Gaussian point spread function with the object function (sphere+wall+BG) to these profiles.

Results:
With the presented procedure the RIR can be determined easily with a high statistical accuracy (average accuracy in 593 spheres 2.8+/-0.1%). For all scanners the RIR was distinctly lower than the scanner resolution according to NEMA. Image resolution was independent from counting statistic but deteriorated with decreasing target to BG (T/BG) ratios. The average resolution degradation in relation to the background free case was ~30% for a 6:1 T/BG ratio, over 50% for 3:1 and ~80% for 1.5:1. The degradation of RIR with decreasing contrast differed between the studied scanners.

Conclusions:
The presented algorithm is a robust approach for precise measuring reconstructed image resolution (RIR). The marked contrast ratio dependence of the RIR should be considered for quantitative PET studies in a multicenter setting.
  • Lecture (Conference)
    SNM 56th Annual Meeting, 13.-17.06.2009, Toronto, Canada

Permalink: https://www.hzdr.de/publications/Publ-12203
Publ.-Id: 12203


Diffusion suppression etc. during electrical activation in implanted Ge and Si-SOI

Skorupa, W.
Recent results on diffusion suppression, electrical activation and related problems in implanted Ge and Si-SOI were reported. A prospect regarding millisecond thermal processing of high k dielectrics was given.
  • Invited lecture (Conferences)
    24. Nutzertreffen Kurzzeittemperung, 23.10.2008, Dortmund, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12202
Publ.-Id: 12202


Rare Earth Ion Beam Processing for Silicon Photonics

Skorupa, W.; Rebohle, L.; Prucnal, S.; Cherkouk, C.; Helm, M.
Combining silicon-based electronic circuits with optoelectronic functionality is one of the key challenges for the future semiconductor technology. Such work must not only be devoted to the “telecommunication” wavelength of 1.54 µm because there are much more applications requiring light sources from the UV to IR wavelength range. In our work we employed ion beam processing to embed different rare earth (RE) luminescent centers (Gd, Ce, Tm, Tb, Eu, Er) into the silicon dioxide layer of purpose-designed Metal-Oxide-Silicon-based Light Emitting Devices (MOSLEDs) with advanced electrical performance. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. Several developments for improving the device stability will be proposed related to charge compensation and the elimination of defects in SiO2. The electrical and electroluminescence properties of these devices are discussed and evaluated in respect of possible applications for biosensing applications. As an example our recent effort to detect estrogens in drinking water will be discussed.
  • Invited lecture (Conferences)
    2008 MRS Fall Meeting, Symposium D: Rare-Earth Doping of Advanced Materials for Photonic Applications, 01.-05.12.2008, Boston MA, USA

Permalink: https://www.hzdr.de/publications/Publ-12201
Publ.-Id: 12201


Casting experiments and materials studies for restoring lead pipes in historical organs

Skorupa, W.; Rossner, M.; Werner, H.; Eule, A.-C.; Schucknecht, T.; Rafaja, D.; Hausmann, U.; Wegscheider, K.
We will report on a new casting technique basing on old recipes from the 17. and 18. century to produce new pipes approaching the quality of the old ones. Materials studies of old and new metal probes were performed by metallography and other methods. Different casting variants as well as the influence of hammering the casted metal plates onto the microstructure were investigated. In the course of these studies special consideration was devoted to the restoration projects at Borgentreich/Westfalen (Eule) and Stralsund/Vorpommern (Wegscheider).
  • Invited lecture (Conferences)
    25. Congress of the International Society of Organbuilders (ISO), 21.-26.09.2008, Danzig-Stralsund, Polen-Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12200
Publ.-Id: 12200


A short review on Flash Lamp Annealing

Skorupa, W.
A short review on Flash Lamp Annealing
  • Invited lecture (Conferences)
    Industrie-Projekttreffen mit BASF und Zentrum für Sonnenenergie-& Wasserstoff-Forschung Baden-Württemberg (ZSW), 18.11.2008, Stuttgart, Germany

Permalink: https://www.hzdr.de/publications/Publ-12199
Publ.-Id: 12199


Old Physics for Modern Nanotechnologies - Studies of Nano-Scale Ordering by Simulations and Experiments

Heinig, K.-H.
Shaping and ordering of nanostructures is mandatory for many applications. However, top-down approaches like electron lithography have their limits and are expensive. Here, we present some bottom-up approaches like self-ordering and alignment at interfaces, which are driven by well-known thermodynamic processes like phase separation and surface energy minimization. The reaction pathways are studied by atomistic computer simulations and verified by experiments. The relevance for some applications, e.g. FLASH memories and Si-based light emitters, will be demonstrated.
Keywords: nanostructure formation, nanostructure shaping, ion irradiation, self-organisation, kinetic Monte Carlo simulation
  • Invited lecture (Conferences)
    Fizikai és Anyagtudományi Kutatóintézet Tanácstermében, 21.05.2008, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-12198
Publ.-Id: 12198


Spontaneous formation of regular nanopattern on surfaces during thin film deposion and ion beam erosion

Heinig, K.-H.
Ion erosion of surface results under specific conditions to formation of dot-like or ripple-like nanopattern. These self-organized nanopattern are promising for different nanotechnologies. The presentation gives an overview of experimental techniques and results as well theoretical models and simulation work.
Keywords: ion erosion, nanopattern, experiments, theory, kinteic Monte Carlo simulations
  • Invited lecture (Conferences)
    Winter School on Nanoelectronic and Nanophotonics, 19.-25.01.2009, Ankara, Turkey

Permalink: https://www.hzdr.de/publications/Publ-12197
Publ.-Id: 12197


Formation of nanodots, nanowires, wormholes etc. driven by capillary forces-reaction pathways predicted by atomistic simulations.

Heinig, K.-H.
The use of ion irradiation methods for bulk nanostructure formation will be presented. The focus will be on the help of cappilary forces to find controllable reaction pathways for nanostructure formation. These pathways are demonstrated by kinetic Monte Carlo simulations
Keywords: nanostructure formation, ion implantation, nanodots, nanowires, kinetic Monte Carlo simulation
  • Invited lecture (Conferences)
    Winter School on Nanoelectronic and Nanophotonics, 19.-25.01.2009, Ankara, Turkey

Permalink: https://www.hzdr.de/publications/Publ-12196
Publ.-Id: 12196


Fundamentals of Ion Beam Synthesis of Nanostructures

Heinig, K.-H.
Fundamentals of ion-beam-solid-interactions will be presented. An overview over ion implantation techniques will be given. Range profile calculations, defect creation processes as well as annealing method will be treated. Finally, methods of ion beam synthesis based on phase separation of implanted species will be discussed.
Keywords: ion implantation, ion beam synthesis, kinetic Monte Carlo simulation, TRIM, lecture
  • Invited lecture (Conferences)
    Winter School on Nanoelectronic and Nanophotonics, 19.-25.01.2009, Ankara, Turkey

Permalink: https://www.hzdr.de/publications/Publ-12195
Publ.-Id: 12195


Novel LEFET with two self-aligned Si nanocrystal layers

Heinig, K.-H.; Beyer, V.; Schmidt, B.; Stegemann, K.-H.
A light emitting feld-effect transistor (LEFET) which is based on self-aligned silicon nanocrystal delta-layers in the gate oxide of a nMOSFET device with an active gate area of 20x20 µm2 is demonstrated. Two layers of Si NCs were prepared in the gate oxide close to both Si/SiO2 interfaces by ion irradiation through the 50 nm poly-Si/15 nm SiO2/(001)Si substrate LEFET stack and subsequent annealing. An AC voltage was applied to the gate in order to inject charges of both polarities in the Si NCs. AC voltage and frequency dependent electroluminescence spectra were recorded as a function of the annealing conditions.
Keywords: nanotechnology, ion irradiation, electroluminescence, field effect transistor, modelling, kinetic Monte Carlo simulation
  • Invited lecture (Conferences)
    Workshop on Nanoelectronics and Nanophotoniocs, 26.-28.01.2009, Ankara, Turkey

Permalink: https://www.hzdr.de/publications/Publ-12194
Publ.-Id: 12194


Mapping of two-plus-one-dimensional KPZ growth onto driven lattice gas model of dimers

Ódor, G.; Liedke, B.; Heinig, K.-H.
We show that a 2+1 dimensional discrete surface growth model exhibiting KPZ class scaling can be mapped onto a two dimensional conserved lattice gas model of directed dimers. In case of KPZ height anisotropy the dimers follow driven diffusive motion. We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class. This opens up the possibility of analyzing growth models via reaction-diffusion models, which allow much more efficient computer simulations.
Keywords: KPZ class scaling, lattice gas model, Monte Carlo simulation
  • Poster
    International Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12193
Publ.-Id: 12193


Swift-heavy-ion-induced shaping of spherical nanoparticles into disks and rods

Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev, C.
The swift heavy ion induced deformation of SiO2 and metal nanoparticles were studied intensively in the last years. Recently, we reported on ion beam shaping of Ge nanospheres [1]. Surprisingly, Ge nanospheres in silica form oblate ellipsoids, what is opposite to prolate ellipsoids found for metal spheres.
This presentation reports on the experimental features of the shaping of Ge nanospheres and our theoretical search for the shaping mechanism(s). A stack of alternating Ge and SiO2 layers was sputtered on an oxidized Si wafer. The Ge layer thickness varied from 2.5 to 7.5 nm with 100 nm SiO2 in-between. Heating this layer stack to 950 °C for 300 s transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 10 to 40 nm. After irradiation with (1-10)x1014 I7+cm-2 at 38 MeV, cross-section TEM images of as-prepared and irradiated samples showed that the largest Ge nanospheres kept spherical, whereas medium-size Ge spheres became oblates, and smaller ones shaped diamond-like. The different shaping of metal and semiconducting spheres is explained by their differences in thermodynamic properties.
Keywords: swift heavy ions, irradiation, nanostructure, shaping, modelling, simulation
  • Lecture (Conference)
    16th International conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12192
Publ.-Id: 12192


Surface modification using Binary Collision Approximation and 3D Lattice Kinetic Monte Carlo simulation

Liedke, B.; Facsko, S.; Heinig, K.-H.; Möller, W.
Periodic pattern formation during low energetic ion-beam bombardment has been observed for many different surfaces. Two different kinds of approaches have been used to explain and simulate the pattern formation and evolution in time: (i) continuum theories, which are based on the Bradley and Harper model, and (ii) Kinetic Monte Carlo method (KMC) for surface diffusion coupled with Sigmund’s theory to incorporate sputtering. Both of them have been developed in terms of surface processes induced by ion sputtering, although without including microscopic effects, i.e. defect creation and diffusion of vacancies in the bulk.
We present a new approach using Binary Collision Approximation for simulating collision cascades during ion bombardment coupled with 3D Lattice KMC Ising model, to simulate surface and bulk diffusion of defects and vacancies. The combination of these two models gives an advantage on the simple Gaussian approximation of the deposited energy proposed by Sigmund, because it includes detailed collision cascades into the discrete lattice system. In addition, information about the relation between atomistic features, i.e. vacancies and defects creation and annihilation, sputtering yield distribution, bulk and surface diffusion, and pattern formation is obtained. We will present the time evolution of surface morphology for different initial system parameters and compare it with continuum theories. Moreover, the influence of substrate temperature on the pattern evolution is studied.
Keywords: ion irradiation, collision cascade, binary collision approximation, kinetic Monte Carlo, surface pattern, nanostructure
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12191
Publ.-Id: 12191


Surface patterning by ion erosion – atomistic computer simulations

Heinig, K.-H.; Numazawa, S.
Surface ripple formation by low-energy ion erosion is a far-from-equilibrium process for which standard thermodynamics have to be put into question. Thus, an effective negative surface tension can be found under low-energy ion irradiation of surfaces [1] and ion beam mixing of interfaces [2]. This negative surface tension tends to increase the surface by inverse Ostwald ripening or surface patterning [2]. Here, for very low energy ion irradiation of surfaces patterning is predicted to evolve even without sputtering, resulting solely from defect creation and annihilation kinetics. Self-organisation of surface pattern by irradiation with ions in the region of keV-energies is strongly affected by sputtering, but even in that case far-from-equilibrium surface defect kinetic can play a major role. This will be underlined by a theoretical study of the temperature-dependent ripple formation found recently on Ag(110) [3]. In agreement with the experiment, kinetic Monte-Carlo calculations show that under ion irradiation at low temperatures (111) facets become unstable, resulting in a ripple rotation from (111) facets to (100) facets.
Keywords: ion erosion, surface pattern, nanostructure, modelling, kinetic Monte Carlo
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12190
Publ.-Id: 12190


Nanocomposite Au-SiO2 thin film deposition by co-sputtering: comparison of experiments with atomistic simulations

Khan, S.; Heinig, K.-H.; Avasthi, D.
Fast atom beam co-sputtering has been found to be an excellent technique for producing metal nanoclusters in variety of matrices without the need of any post-deposition annealing. The films thus prepared show homogeneous distribution of nanoclusters having rather narrow size distributions. The average size of these embedded nanoclusters can be effectively controlled by varying the ratio of sputtered metal and matrix species. In this contribution, we present results from the computer simulation of the deposition process to investigate the structural evolution and growth of Au nanoclusters embedded in silica matrix during co-sputtering. A three dimensional kinetic Monte Carlo technique has been used here to study the growth kinetics of nanoparticles taking into consideration the effect of the energetic sputtered species reaching the surface of the film during deposition. Nucleation and subsequent growth of Au nanoclusters has been simulated under different deposition conditions. As a result, the simulation has been shown to be useful for deposition parameters optimization in the process of nanocomposite thin film growth by fast atom beam co-sputtering.
Keywords: layer deposition, co-sputtering, nanostructure, kinetic Monte Carlo
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12189
Publ.-Id: 12189


Facetting Morphology of Crystallites under Ion Irradiation – a 3D Kinetic Lattice Monte Carlo Study

Heinig, K.-H.; Röntzsch, L.
The orientation-dependent surface energies of crystal facets determine the shape of crystallites via Wulff’s theorem. Thus, in the framework of a nearest neighbor Ising model, the equilibrium shape of a fcc crystallite is a truncated octahedron. This crystallite shape is found frequently, e.g. for A-type CoSi2 crystallites embedded in silicon.
In this contribution we show that crystallites change their shape under intense ion irradiation. A first indication for a crystallite shape change under ion irradiation was reported several years ago [1]. In a Monte Carlo simulation the continuing vacancy production transformed the equilibrium fcc crystallite shape of a truncated octahedron into the steady-state shape of a cube. Here we present a systematic study of ion-irradiation-induced crystallite shape changes for different crystal structures and different irradiation intensities and temperatures. For the first time, an explanation of the shape changes based on the surface defect kinetics will be given: Whereas in thermodynamics the equilibrium concentration of surface defects is determined by energetics (“detailed balance”), under ion irradiation its steady-state value is controlled by the geometry of atomic displacements. Consequently, facets with a high atomic area density become unstable. It will be shown that this facet instability might be the reason for temperature dependent pattern formation on metal surfaces under ion erosion [2].
[1] P. Bellon, Phys. Rev. Letters 81, 4176 (1998).
[2] U. Valbusa et al., J. Phys.: Condens. Matter 14, 8153 (2002).
Keywords: ion irradiation, surface energy, crystal shape, kinetic Monte Carlo
  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM 08), 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12188
Publ.-Id: 12188


Mapping of 2 + 1 dimensional KPZ growth onto driven lattice gas model of dimers

Odor, G.; Liedke, B.; Heinig, K.-H.
We show that a 2+1 dimensional discrete surface growth model exhibiting KPZ class scaling can be mapped onto a two dimensional conserved lattice gas model of directed dimers. In case of KPZ height anisotropy the dimers follow driven diffusive motion. We confirm by numerical simulations that the scaling exponents of the dimer model are in agreement with those of the 2+1 dimensional KPZ class. This opens up the possibility of analyzing growth models via reaction-diffusion models, which allow much more efficient computer simulations.
Keywords: crystal growth, KPZ equation, Edward-Wilkinson equation, scaling behavior, Monte-Carlo simulation

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Permalink: https://www.hzdr.de/publications/Publ-12187
Publ.-Id: 12187


Ion mass dependence of irradiation-induced local creation of ferromagnetism in Fe60Al40 alloys

Fassbender, J.ORC; Liedke, M. O.; Strache, T.; Moeller, W.; Menendez, E.; Sort, J.; Rao, K. V.; Deevi, S. C.; Nogues, J.
Ion irradiation of Fe60Al40 alloys results in the phase transformation from the paramagnetic, chemically ordered B2 phase to the ferromagnetic, chemically disordered A2 phase. The magnetic phase transformation is related to the number of displacements per atom (dpa) during the irradiation. For heavy ions (Ar+, Kr+, and Xe+), a universal curve is observed with a steep increase in the fraction of the ferromagnetic phase that reaches saturation, i.e., a complete phase transformation, at about 0.5 dpa. This proves the purely ballistic nature of the disordering process. If light ions are used (He+ and Ne+), a pronounced deviation from the universal curve is observed. This is attributed to bulk vacancy diffusion from the dilute collision cascades, which leads to a partial recovery of the thermodynamically favored B2 phase. Comparing different noble gas ion irradiation experiments allows us to assess the corresponding counteracting contributions. In addition, the potential to create local ferromagnetic areas embedded in a paramagnetic matrix is demonstrated.
  • Physical Review B 77(2008), 174430

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Permalink: https://www.hzdr.de/publications/Publ-12186
Publ.-Id: 12186


Application of self-actuated 32 cantilever array in atomic force surface measurements

Gotszalk, T.; Zawierucha, P.; Woszczyna, M.; Zielony, M.; Ivanov, T.; Ivanova, K.; Volland, B. E.; Sarov, Y.; Persaud, A.; Dontzov, D.; Schmidt, B.; Nikolov, N.; Kostic, I.; Engl, W.; Sulzbach, T.; Mielczarski, J.; Kolb, S.; Pedreau, R.; Huq, S. E.; Edinger, K.; Fortagne, O.; Blom, H. O.; Rangelow, I. W.
Main industry requirement for applying scanning probe microscopy in surface measurements is the high
scan speed, which allow the microelectronics producers to obtain the information about the technological
process quality in-situ on the semiconductor wafer. Common single topography measurement consume few
minutes for scanning area about 100 μm2 because of limited cantilever dynamic properties. To overcome
this problem one may utilize the cantilever with resonance frequency above 1 MHz but in this case,
cantilever suffer from wear and it requires complicated, large bandwidth measurement system. Different
approach to high speed topography measurement is to apply massive array of cantilevers, where the
surface topography image is taken simultaneously from every probe.
In the contribution present the application of the one dimensional VLSI NEMS-chip (Very Large Scale
Integrated Nano Electro Mechanical System) incorporating 32 proximal probes for high speed atomic force
microscopy measurements will be presented. Each array cantilever integrates a thermal deflection actuator, a
piezoresistor acting as a deflection detector and a microtip with radius of 10 nm.
Keywords: NEMS, proximal AFM probe array, piezoresistive deflection sensing, thermal deflection actuation
  • Poster
    34th Micro and Nano Engineering Conference MNE08, 15.-18.09.2008, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-12183
Publ.-Id: 12183


Acceleration of irradiation hardening of low-copper reactor pressure vessel steel observed by means of SANS and tensile testing

Bergner, F.; Ulbricht, A.; Viehrig, H.-W.
Neutron irradiation of low-copper reactor pressure vessel steels containing manganese and nickel gives rise to microstructural changes and a deterioration of mechanical properties apparently progressing slower than in steels containing more than or about 0.1 wt% Cu. An acceleration of this process after accumulation of a threshold fluence caused by so-called late blooming phases is a matter of debate. We report results of small angle neutron scattering (SANS) experiments and tensile tests for two low-Cu model RPV steels irradiated at 255°C. Motivation for the use of the integrated magnetic scattering as a microstructural parameter combining the volume fraction and magnetic contrast of nanometre-sized irradiation-induced features is given. The results indicate one of the rare cases of acceleration of both the change of a microstructural parameter and the yield stress increase. The issues of the nature of the irradiation-induced features, the role of phosphorus, and the observed strong correlation of integrated magnetic scattering and yield stress increase are addressed.
Keywords: neutron irradiation; SANS; tensile testing; pressure vessel steel

Permalink: https://www.hzdr.de/publications/Publ-12182
Publ.-Id: 12182


Investgation of crosstalk in cantilever arrays

Frank, A.; Zöllner, J.-P.; Sarov, Y.; Ivanov, T.; Klett, S.; Gotszalk, T.; Zielony, M.; Zawierucha, P.; Schmidt, B.; Zier, M.; Nikolov, N.; Engl, W.; Sulzbach, T.; Langlotz, E.; Dontsov, D.; Schott, W.; Rangelow, I. W.
In this paper a macro model of a cantilever for mixed domain simulation only with SPICE is presented. Based on lumped elements of equivalent circuits a model is developed, which realizes a coupled electro-thermal-mechanical simulation including crosstalk effects. Capacitive crosstalk through the substrate are evaluated and modelled with SPICE. This is verified with measurement and helps to solve the crosstalk effect.
Keywords: Cantilever array, SPICE simulation, MEMS modeling
  • Lecture (Conference)
    EUROSENSORS XXII, 07.-10.09.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12181
Publ.-Id: 12181


Fabrication of ultra-shallow p-n junctions by ion beam processing

Zier, M.
Ultra-shallow p-n junctions in silicon play an important role in semiconductor industry, for example as source-drain extensions in highly integrated MOSFETs. The present talk shows their application as piezo-resistive bending sensors in massively parallel AFM arrays.
Difficulties in fabrication of ultra-shallow p-n junctions will be discussed and potential solutions will be given. To obtain ultra-shallow junctions several methods can be employed: pre-amorphisation, low energy ion implantation or the formation of a region with an enhanced vacancy concentration near the sample surface by high energy Si implantation. The activation of the dopant can be accomplished either by rapid thermal annealing or flash lamp annealing. Finally, the characterisation of the ultra-shallow doped layers using electrical and SIMS measurements will be shown.
Keywords: ion beam modification ion implantation ultra-shallow junction
  • Lecture (others)
    Materials Science Seminar, 29.04.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12180
Publ.-Id: 12180


Fabrication of ultra-shallow p-n junctions in Si using fast and ultra-fast annealing

Zier, M.; Schmidt, B.
Ultra-shallow p-n junctions in silicon play an important role in the semiconductor industry, for example as source-drain extensions in highly integrated MOSFETs or in this case as piezo-resistive bending sensors for application in massively parallel AFM arrays.
To obtain ultra-shallow junctions several methods of fabrication have been employed: low energy ion implantation and vacancy enhancement near the sample surface by using high energy Si+ implantation followed by in-diffusion of boron from a solid source. The activation of the dopant was accomplished either by rapid thermal annealing or flash lamp annealing.
I-V measurements of the diode formed by the p-n junction show excellent diode behaviour of the p-doped layers, indicating that all employed fabrication methods result in real p-n junctions. The concentration depth profile of boron in the samples have been measured by SIMS, using O2- ions of 1500 and 500eV to minimise distortion of the depth profile due to the ion bombardment. Finally, measured sheet resistances of the p-doped layers obtained from dedicated test structures are compared against each other.
Keywords: ion implantation ultra-shallow junction RTA FLA
  • Poster
    16th International Conference on Ion Beam Modification of Materials 2008, 31.08.-05.09.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12179
Publ.-Id: 12179


[18F]FETA PET - A new method for hot spot imaging of the ischemic penumbra in acute stroke

Barthel, H.; Großmann, U.; Zeisig, V.; Patt, M.; Wagner, D.; Patt, J.; Kluge, M.; Franke, H.; Sorger, D.; Luthardt, J.; Nitzsche, B.; Dreyer, A.; Brust, P.; Steinbach, J.; Boltze, J.; Emmrich, F.; Sabri, O.
Objectives:
In acute ischemic stroke, an imaging method to directly visualize the ischemic penumbra - the salvageable part of the affected brain - in positive image contrast would potentially improve therapy stratification and monitoring. This study aimed to test [18F] fluoroetanidazole ([18F]FETA), a second-generation radiolabeled 2-nitroimidazole, for the first time with respect to its suitability to image brain hypoxia with positron emission tomography (PET).

Methods:
Primary embryonal corticoencephalic cells (Wistar rats) and necortical brain slices (Sprague Dawley rats) were ex vivo exposed to nitrogen or air. The cells and brain slices were incubated with 5MBq [18F]FETA up to 120min, respectively. The activities of three nitroreductases - enzymes which mediate the intracellular [18F]FETA accumulation - were determined in the corticoencephalic cells. Further, organ distribution was determined in Sprague
Dawley rats up to 2h after i.v. injection of 20MBq [18F]FETA, and ex vivo brain autoradiography was performed up to 24h after permanent middle cerebral artery occlusion (pMCAO). Target-to background image contrast of [18F]FETA autoradiograms at 3h after pMCAO was compared with that of corresponding [18F]fluoromisonidazole ([18F]FMISO) autoradiograms. At 24h after pMCAO, animals were additionally i.v. injected with 1MBq [14C]iodoantipyrine to determine the local cerebral blood flow (lCBF). Nissl staining of brain slices as well as stroke-specific MRI were carried out at 24h after pMCAO to confirm the existence and localization of ischemic brain tissue damage.

Results:
In vitro, the oxygen concentration in the cell suspension was < 1 mm Hg and ~70 mm Hg under nitrogen and air, respectively. The normoxic [18F]FETA uptake by the cells and the brain slices was low and constant over time (0.3±0.08 %ID.mio cells-1 and 0.04±0.01 %ID.g tissue-1). In contrast, under hypoxia a time-dependent linear increase of the [18F]FETA uptake was found which was 2.0- and 2.5-fold by the cells and 2.0- and 2.4-fold by the brain slices at 60min and 120min (p< 0.05), respectively. The analyses of nitroreductases activities showed that cell oxygenation does not affect the enzyme activities. The biodistribution studies revealed fast blood clearance, a rapid urinary excretion and a constantly low uptake in unaffected brain tissue (0.1±0.02 %ID.g-1). Ex vivo brain autoradiography in the pMCAO rats showed a relevant time-dependent [18F]FETA uptake in ipsilateral brain regions which reached maximum target-to background ratios of 3.3±0.2 at 3h. The corresponding [18F]FMISO uptake ratios were only 1.5±0.3 (p< 0.05). Furthermore, at 24h after pMCAO the lCBF was reduced in the infarction core (as determined by Nissl staining and MRI) and surrounding brain areas by 25% and 10%, respectively.

Conclusions:
These results demonstrate that [18F]FETA has a better potential than [18F]FMIS to serve as a brain hypoxia marker. Further testing of this promising new stroke PET marker is warranted. First results employing a new sheep stroke model developed recently by our group [1] are encouraging.

References:
[1] Boltze et al., J Cereb Blood F Metab 2008

First and second author contributed equally to this study

This research was supported by the Translational Centre for Regenerative Medicine Leipzig/BMBF (PtJ-Bio 0313909)
  • Lecture (Conference)
    XXIVth International Symposium on Cerebral Blood Flow, Metabolism and Function and the IXth International Conference on Quantification of Brain Function with PET, 29.06.-03.07.2009, Chicago, USA
  • Abstract in refereed journal
    Journal of Cerebral Blood Flow and Metabolism 29(2009)Suppl. 1, S42-S43

Permalink: https://www.hzdr.de/publications/Publ-12178
Publ.-Id: 12178


Scanning proximal probes for parallel imaging and lithography

Ivanova, K.; Sarov, Y.; Ivanov, T.; Frank, A.; Zöllner, J.; Bitterlich, C.; Wenzel, U.; Volland, B. E.; Klett, S.; Rangelowa, I. W.; Zawierucha, P.; Zielony, M.; Gotszalk, T.; Dontzov, D.; Schott, W.; Nikolov, N.; Zier, M.; Schmidt, B.; Engl, W.; Sulzbach, T.; Kostic, I.
Scanning proximity probes are uniquely powerful tools for analysis, manipulation, and bottom-up synthesis. A massively parallel cantilever-probe platform is demonstrated. 128 self-sensing and self-actuated proximal probes are discussed. Readout based on piezoresistive sensors and bending control based on bimorph dc/ac actuations are described in detail.
Keywords: Scanning proximity probes, piezoresistive sensing, bimorph actuations, parallel cantilever-probe platform
  • Journal of Vacuum Science & Technology B 26(2008)6, 2367-2373
    DOI: 10.1116/1.2990789

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Permalink: https://www.hzdr.de/publications/Publ-12177
Publ.-Id: 12177


Shaping of nanospheres into disks and rods with swift heavy ions

Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev, C.
The swift heavy ion induced deformation of SiO2 and metal nanoparticles were studied intensively in the last years. Recently, we reported on ion beam shaping of Ge nanospheres. Surprisingly, Ge nanospheres in silica form oblate ellipsoids, what is opposite to prolate ellipsoids found for metal spheres.
This presentation reports on the experimental features of the shaping of Ge nanospheres and our theoretical search for the shaping mechanism(s). A stack of alternating Ge and SiO2 layers was sputtered on an oxidized Si wafer. The Ge layer thickness varied from 2.5 to 7.5 nm with 100 nm SiO2 in-between. Heating this layer stack to 950 °C for 300 s transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 10 to 40 nm. After irradiation with (1-10)x1014 I7+cm-2 at 38 MeV, cross-section TEM images of as-prepared and irradiated samples showed that the largest Ge nanospheres kept spherical, whereas medium-size Ge spheres became oblates, and smaller ones shaped diamond-like. The different shaping of metal and semiconducting spheres is explained by their differences in thermodynamic properties.
Keywords: Ge nanoparticles, ion beam shaping
  • Lecture (Conference)
    Workshop "Ionenstrahlphysik und Nanotechnologie", 11.-12.04.2008, Darmstadt-Wixhausen, Germany

Permalink: https://www.hzdr.de/publications/Publ-12176
Publ.-Id: 12176


Electroluminescence in silicon nanocrystals fabricated by ion beam mixing and annealing of gate oxide/silicon interfaces

Schmidt, B.; Heinig, K.-H.; Beyer, V.; Stegemann, K.-H.
A light emitting field-effect transistor (LEFET) which is based on silicon nanocrystals in the gate oxide is demonstrated. The Si nanocrystals in the gate oxide were optimized for a multi-dot floating-gate nonvolatile memory operation [1]. For this aim, ion irradiation through the MOSFET stack of 50 nm poly-Si/15 nm SiO2/Si substrate was performed with 50 keV Si+ ions. The ion beam mixing of the upper poly-Si/SiO2 interface and the lower SiO2/(001)Si interface leads to Si excess in the gate oxide. Subsequent rapid thermal annealing reforms sharp interfaces and separates the excess Si from SiO2. Adjacent to the recovered interfaces, 3-4 nm thick SiO2 zones denuded completely of excess Si have been found, whereas the more distant tails of excess Si form well-aligned narrow layers of nanocrystals with 2-3 nm diameter. LEFETs with an active gate area of 20x20 µm2 were fabricated as nMOSFET devices in a standard 0.6 µm CMOS process line. An AC voltage was applied to the gate in order to inject charges of both polarities into the lower and upper Si nanocrystal layer from the channel and the poly-Si gate of the transistor, respectively. AC voltage and frequency dependent electroluminescence spectra were recorded in the wavelength region of 400-1000 nm as a function of the annealing conditions. The performance of the LEFETs and further possibilities of optimization of efficient light emission will be discussed.
[1] B. Schmidt, et al. Nucl. Instr. and Meth. B 242 (2006) 146.
Keywords: Silicon nanocrystals, electroluminescence, light emitting field-effect transistor
  • Lecture (Conference)
    E-MRS Spring Meeting, 26.-30.05.2008, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-12175
Publ.-Id: 12175


Nanomagnets - created and tailored by ions

Fassbender, J.ORC
Report on the activities in the field of ion beam modification of magnetic materials.
Keywords: magnetism, ion irradiation, focused ion beam, binary alloys, nanostructures
  • Invited lecture (Conferences)
    Physik von Nanostrukturen, 19.12.2008, Dresden, Deutschland
  • Lecture (Conference)
    International Seminar and Workshop on Magnonics: From Fundamentals to Applications, 02.-07.08.2009, Dresden, Deutschland
  • Lecture (others)
    Forschungsseminar, 13.05.2009, Berlin, Deutschland
  • Invited lecture (Conferences)
    Kolloquiumsvortrag Universität Paderborn, 02.07.2009, Paderborn, Deutschland
  • Lecture (others)
    SFB 668 - Kolloquium Magnetismus vom Einzelatom zur Nanostruktur, 16.06.2009, Hamburg, Deutschland
  • Invited lecture (Conferences)
    Nanoscale Modification of Surfaces and Thin Films, 30.08.-03.09.2009, Rathen, Deutschland
  • Invited lecture (Conferences)
    Kolloquium, Institute of Physics, 21.02.2014, Bhupaneshwar, Indien
  • Invited lecture (Conferences)
    Kolloquium, Universität Kiel, 27.01.2014, Kiel, Deutschland
  • Invited lecture (Conferences)
    Kolloquium Institute of Physics, Polish Academy of Sciences, 07.10.2014, Warschau, Polen
  • Invited lecture (Conferences)
    Eigth International Meeting on Recent Developments in the Study of Radiation Effects in Matter, 20.-23.09.2015, Kerteminde, Dänemark
  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 13.10.2015, Leipzig, Deutschland
  • Invited lecture (Conferences)
    Colloquium, 17.05.2016, Krakow, Polen
  • Invited lecture (Conferences)
    Kolloquium, 07.07.2016, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12174
Publ.-Id: 12174


Fundamentals and Modelling of Reactive Magnetron Sputtering

Moeller, W.
kein Abstract vorhanden
  • Invited lecture (Conferences)
    Tutorial "Fundamentals and Trends of Plasma Surface Processing", 14.09.2008, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-12173
Publ.-Id: 12173


Reactive Magnetron Sputtering of Nitrides and Oxides: Understanding the Process and Optimizing the Film Quality

Moeller, W.
kein Abstract vorhanden
  • Invited lecture (Conferences)
    Plasmas, Surfaces, and Thin Films, 11.06.2008, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-12172
Publ.-Id: 12172


Nanostructures by Ion-Driven Self-Organisation: Can Ions Induce Order?

Moeller, W.
kein Abstract vorhanden
  • Lecture (others)
    VERA-Seminar, 05.06.2008, Wien, Austria

Permalink: https://www.hzdr.de/publications/Publ-12171
Publ.-Id: 12171


Nanostructures by Ion-Driven Self-Organisation

Moeller, W.
kein Abstract vorhanden
  • Lecture (others)
    Kolloquium des Max-Planck-Institutes für Plasmaphysik, 18.04.2008, Garching/ Muenchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-12170
Publ.-Id: 12170


Forschung und Entwicklung für die Verfahrenstechnik

Kryk, H.
In einem Übersichtsvortrag werden die Aktivitäten des Institutes für Sicherheitsforschung auf den Gebieten der Verfahrens-, Prozess- und Messtechnik vorgestellt. Dies umfasst sowohl die Arbeiten zur Prozessaufklärung und Reaktionskalorimetrie zur Erhöhung der Sicherheit und Effektivität chemischer Prozesse als auch die Entwicklung und Anwendung von Spezialmesstechnik zur Untersuchung von Mehrphasenströmungen in verfahrenstechnischen Apparaten und Anlagen einschließlich der Modellierung und Simulation unter Nutzung von CFD-Methoden.
Einen Schwerpunkt der Präsentation bilden die Möglichkeiten und Perspektiven des Einsatzes von Praktikanten, Diplomanden und Doktoranden chemisch-technischer Studienrichtungen am Institut für Sicherheitsforschung des FZD.
  • Lecture (others)
    Hochschul-Informationstag, 10.01.2008, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12169
Publ.-Id: 12169


A rotating cell for in situ Raman spectroelectrochemical studies of photosensitive redox systems

Kavan, L.; Janda, P.; Krause, M.; Ziegs, F.; Dunsch, L.
A recently developed rotating spectroelectrochemical cell for in situ Raman spectroscopic studies of photoreactive compounds without marked decomposition of the sample is presented. Photochemically unstable compounds like fullerenes are difficult to be studied under stationary conditions by in situ spectroelectrochemistry using laser excitation as in Raman spectroscopy. Therefore, a rotating spectroelectrochemical was developed to avoid these difficulties. The cell can be used for any type of a planar electrode and of electrode materials in contact with aqueous or non-aqueous solutions as well as ionic liquids under appropriate laser power and accumulation times. The innovative advantage consists in the precession movement of the spectroelectrochemical cell with an eccentric drive. This precession movement allows a fixed electrical connection to be applied for interfacing the electrochemical cell to a potentiostat. Hence, any electrical imperfections and noise, which would be produced by sliding contacts, are removed. Further advantage of the rotating cell is a dramatic decrease of the thermal load of the electrochemical system. The size of the spectroelectrochemical cell is variable and dependent on the thickness of the cuvettes used ranging up to ca. 10 mm. The larger measuring area causes a higher sensitivity in the spectroscopic studies using this cell. The as constructed spectroelectrochemical cell is easy to be handled. The application of the cell is demonstrated for ordered fullerene C60 layers and the spectroelectrochemical behavior of nanostructured fullerenes. Here the charge transfer at highly ordered fullerene C60 films was studied by in situ Raman spectroelectrochemistry under appropriate laser power and accumulation time without marked photodecomposition of the sample.
Keywords: spectroelectrochemistry, Raman spectroelectrochemical cell, in situ measurements, fullerenes, fullerene layers
  • Analytical Chemistry 81(2009), 2017-2021

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Permalink: https://www.hzdr.de/publications/Publ-12168
Publ.-Id: 12168


An anisotropic Heisenberg model on the trigonal lattice for multiferroic oxides

Kunze, T.; Gemming, S.; Olbrich, C.; Chaplygin, I.; Schmidt, P.; Schreiber, M.
Hexagonal manganites are oxides, in which structural, electronic, and magnetic degrees of freedom are coupled in a complex manner. Therefore, such materials have the potential for novel, nanoscale sensing and switching applications. Manganites are composed of dense-packed hexagonal manganese oxide layers with strong in-plane and weak interlayer coupling, thus the possible spin configurations may be studied with the help of a two-dimensional model Hamiltonian. For this purpose a two-dimensionally periodic trigonal spin system is qualitatively studied with the help of an extended multiparameter Heisenberg model. The temperature dependence of the magnetisation is investigated with the help of a Metropolis-Monte-Carlo algorithm as a function of the anisotropy term and of an external magnetic field. Thermodynamic quantities such as the total energy, the heat capacity and the magnetization are determined by statistical evaluation.
  • Poster
    DPG Frühjahrstagung, 25.-29.02.2008, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12167
Publ.-Id: 12167


Nanoschreiben mit fokussierten Ionen

Bischoff, L.
Fokussierte Ionenstrahlsysteme (FIB) sind ein modernes Werkzeug für die Strukturerzeugung sowie deren Analyse im µm bis in den nm- Bereich hinein. Ein Ionenstrahl, der aus einer Flüssigmetall-Ionenquelle (Liquid Metal Ion Source - LMIS) kommt wird mittels einer Ionenpotik beschleunigt und in einen Spot von bis zu wenigen nm fokussiert und dann Computergesteuert über die Probe geführt. Eine Auflösung von kleiner 10 nm bei Stromdichten von mehr als 10 Acm-2 können erreicht werden.
Der Einsatz von FIB Systemen ist spezialisiert auf die Präparation von Proben in der Analytik der Halbleiterindustrie sowie der nm - Strukturerzeugung in der Forschung. Die pixelweise Abarbeitung des Ionenstrahlschreibens ist für eine Massenproduktion nicht geeignet aber umso mehr für die Erzeugung von Prototypen neuer Bauelemente. Besonders effektiv ist die Kopplung des FIB mit einem Rasterelektronenmikroskop zu einem Zweistrahlsystem. Die Erweiterung auf neue Ionenarten durch den Einsatz spezieller Legierungen in der Ionenquelle eröffnet ein breites Spektrum neuer Anwendungsfelder.
Ausgewählte Applikationen aus dem FZD werden demonstriert und erläutert.
Keywords: Fokussierte Ionenstrahlsysteme; Strukturerzeugung; Analyse; nm- Bereich; Anwendungen
  • Lecture (others)
    Lange Nacht der Wissenschaften Dresden, 04.07.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12166
Publ.-Id: 12166


Application of mass-separated focused ion beams

Bischoff, L.; Akhmadaliev, C.; Pilz, W.; Schmidt, B.
During the last decades, focused ion beams (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance within the nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning from the µm- to the nm-range without any lithographic steps using Gallium and also other ion species which are of increasing interest. An introduction in design and operation of mass separated FIB systems, equipped with alloy liquid metal ion sources and the development and characterization of suited alloy liquid metal ion sources is given and their preparation and characterisation is discussed.
Keywords: focused ion beams;alloy liquid metal ion source;preparation;characterisation
  • Lecture (others)
    Seminar at Carl Zeiss NTS, 07.05.2008, Oberkochen, Germany

Permalink: https://www.hzdr.de/publications/Publ-12165
Publ.-Id: 12165


Application of Focused Ion Beams

Bischoff, L.
During the last decades, focused ion beams (FIB) became a very useful and versatile tool in microelectronics industry, as well as in the field of basic and applied research and derived an exceedingly importance within the nanotechnology. For special purposes like ion milling, ion beam writing for doping or patterning from the µm- to the nm-range without any lithographic steps using Gallium and also other ion species which are of increasing interest. An introduction in design and operation of mass separated FIB systems, equipped with alloy liquid metal ion sources and the development and characterization of suited ion sources is given.
Examples, like ion beam synthesis of CoSi2 nano-structures, sputtering investigations and applications, the formation of ripples under FIB irradiation or the fabrication of NEMS structures on SOI substrates should demonstrate the manifold utilization of the microbeam technology.
Finally an outlook to prospective work with FIB in FZD is presented.
Keywords: focused ion beam; nanotechnology; liquid metal ion source
  • Lecture (others)
    Seminar Materials Science at FZD, 28.10.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12164
Publ.-Id: 12164


Si+ implantation induced photoluminescence enhancement in PMMA

Tsvetkova, T.; Balabanov, S.; Avramov, L.; Borisova, E.; Bischoff, L.
Si+ ion implantation effects on the photoluminescence (PL) properties of polymethyl-methacrylate (PMMA) have been studied. Low-energy ion implantation (E=30÷50 keV) was carried out over a range of different ion doses (D=1013÷1017 cm-2). The observed effect of PL enhancement (PLE) is essentially dependent on the ion dose. For certain doses, the overall amplitude of the PL emission has a several times (~ 5 times) increase. Electron microscopy results and surface elemental analysis reveal implanted Si atoms clustering which could be related to the observed PLE effects.
Keywords: ion implanted polymers; polymethyl-methacrylate; photoluminescence
  • Przeglad elektrotechniczny 84(2008)3, 72-74

Permalink: https://www.hzdr.de/publications/Publ-12162
Publ.-Id: 12162


Ultrasound Doppler array used for vortex investigations in liquid metals

Franke, S.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.
An Ultrasound Doppler system for measuring the flow velocity field of magnetically-driven metal is introduced: Two orthogonally arranged sensor line arrays facilitate a two-dimensional measurement of two velocity components (2d/2c) in an area of 70 x 70 mm2. First measurement results of liquid metal flows driven by a rotating magnetic field are presented.
Keywords: Ultrasound Doppler method, sensor array, liquid metal, rotating magnetic field
  • Lecture (Conference)
    Sensor 2009, 26.-28.05.2009, Nürnberg, Germany

Permalink: https://www.hzdr.de/publications/Publ-12161
Publ.-Id: 12161


NEMS structures on SOI by writing FIB implantation and subsequent anisotropic wet chemical etching

Bischoff, L.; Schmidt, B.; Lange, H.
The further miniaturization of silicon nanomechanical structures in combination with the highly developed microelectronic technology at the micro- and nanometer level will lead to a new generation of nano-electro-mechanical systems (NEMS). A modern technique to fabricate such three-dimensional structures is the combination of high-concentration p-type doping of silicon by high resolution writing implantation using a focused ion beam (FIB) and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale thickness and width have been fabricated using 30 keV Ga+ ion implantation and subsequent anisotropic etching in KOH/H2O solution on Silicon-On-Insulator (SOI) substrates. Design and fabrication considerations to achieve freestanding Si structures, like nanowires and -bridges are discussed and some typical structures are shown. Electrical measurements are demonstrated which reveal a broad spectrum in the field of sensor applications.
Keywords: nano-electro-mechanical systems; focused ion beam; anisotropic etching;sensor applications
  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, 11.-12.04.2008, Darmstadt, Germany

Permalink: https://www.hzdr.de/publications/Publ-12160
Publ.-Id: 12160


Comparative study of gas-oil and gas-water two-phase flow in a vertical pipe

Szalinski, L.; Da Silva, M. J.; Thiele, S.; Beyer, M.; Lucas, D.; Hampel, U.; Hernandez Perez, V.; Abdulkareem, L. A.; Azzopardi, B. J.
A wire-mesh sensor has been employed in a vertical pipe of 67 mm diameter and 6 m length to investigate two-phase flows of two different two-phase mixtures. Conductivity-based measuring electronics was used to measure water-air flow and permittivity-based one for silicone oil-air flow. This experimental setup enables a direct comparison of both two-phase flow systems. Thus, wire-mesh sensor data of both gas-liquid systems were analysed with regard to radial gas volume fraction profiles and bubble size distributions. Furthermore wire-mesh sensor images were evaluated to determine the occurring flow pattern. A flow pattern map was created which contains all experimental measurement points denoted with observed flow pattern.
Keywords: gas-liquid flow, flow visualization, wire-mesh sensor, capacitance, permittivity, conductivity
  • Contribution to proceedings
    3rd International Workshop on Process Tomography, 17.-19.04.2009, Tokyo, Japan
    Proceedings of 3rd International Workshop on Process Tomography
  • Lecture (Conference)
    3rd International Workshop on Process Tomography (IWPT-3), 17.-19.04.2009, Tokyo, Japan
  • Chemical Engineering Science 65(2010)12, 3836-3848
    DOI: 10.1016/j.ces.2010.03.024

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Permalink: https://www.hzdr.de/publications/Publ-12159
Publ.-Id: 12159


Nano-Structures made by Swift Heavy Ions

Bolse, W.; Paulus, H.; Bolse, T.; Bischoff, L.
Recently we have discovered that the irradiation of thin oxide films with swift heavy ions (SHI) at small incident angles results in an instability of the film against periodic cracking and subsequent reorganisation on a sub-micron level due to ion hammering. Varying the conditions during irradiation (ion species, rotating the target) we were able to generate a wide range of nano-structures and patterns, the most interesting of which was an array of NiO-nanopillars with a diameter of the order of 100 nm and a height of about 2000 nm. Unfortunately, the arrangement of these nanotowers was not regular. [1] To overcome this problem, we have prestructured the films by means of a focused ion beam with an array of perpendicular cuts of about 100 nm width and 1000 nm distance. In fact, the subsequent irradiation with SHI under grazing incidence and permanent target rotation results in an ordered array of the NiO nanotowers. To our surprise, the same treatment of TiO-films lead to an ordered pattern of holes.
[1] W. Bolse, T. Bolse, C. Dais, D. Etissa-Debissa, A. Elsanousi, A. Feyh, M. Kalafat, H. Paulus, Surf. Coat. Technol. 200 (2005) 1430
Keywords: swift heavy ions; nano-structures; prestructured; focused ion beam; TiO-film
  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-12158
Publ.-Id: 12158


Spin-state transition and spin-polaron physics in cobalt oxide perovskites: ab initio approach based on quantum chemical methods

Hozoi, L.; Birkenheuer, U.; Stoll, H.; Fulde, P.
A fully ab initio scheme based on quantum chemical wavefunction methods is used to investigate the correlated multiorbital electronic structure of a 3d-metal compound, LaCoO3. The strong short-range electron correlations, involving both Co and O orbitals, are treated by multireference techniques. The use of effective parameters like the Hubbard U and interorbital U′, J terms and the problems associated with their explicit calculation are avoided with this approach. We provide new insight into the spin-state transition at about 90 K and the nature of charge carriers in the doped material. Our results indicate the formation of a t2g4eg2 high-spin state in LaCoO3 for T > 90K. Additionally, we explain the paramagnetic phase in the low-temperature lightly doped compound through the formation of Zhang-Rice-like O hole states and ferromagnetic clusters.
Keywords: heavy fermions, electron correlation, local correlation methods, high-Tc superconductors

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Permalink: https://www.hzdr.de/publications/Publ-12157
Publ.-Id: 12157


Ultrasound Doppler array system for flow field investigations in liquid metals

Franke, S.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.
An Ultrasound Doppler system for measuring the flow velocity field of magnetically-driven metal is introduced: Two orthogonally arranged sensor line arrays facilitate a two-dimensional measurement of two velocity components (2d/2c) in an area of 70 x 70 mm2. First measurement results of liquid metal flows driven by a rotating magnetic field are presented.
Keywords: Ultrasound Doppler method, sensor array, liquid metal, rotating magnetic field
  • Flow Measurement and Instrumentation 21(2010)3, 402-409

Permalink: https://www.hzdr.de/publications/Publ-12156
Publ.-Id: 12156


Application of rate theory modeling to cluster evolution in binary Fe-Cu alloys

Birkenheuer, U.; Bergner, F.; Ulbricht, A.; Gokhman, A.; Almazouzi, A.
A rate theory model for the simulation of the irradiation-induced time-evolution of Cu-rich precipitates in Fe-Cu model alloys is presented which takes into account that precipitate clusters are mixed Cu-vacancy aggregates by explicitly allowing the defect clusters to absorb vacancies. The resulting Vacancy-Coupled Copper Clustering (V3C) model is calibrated on a series of SANS experiments on two different Fe-Cu model alloys neutron-irradiated at four different doses. Quantitative agreement with the SANS experiments could be achieved by introducing a dependence of the Fe-Cu interface energy on the amount of vacancies in the mixed precipitate clusters. This energy is a function of the weight-percentage of Cu in the iron matrix. An analytic expression for this dependence is suggested.
Keywords: rate theory, percipitation, Fe-Cu model alloys, SANS experiments, neutron irradiation, irradiation damage, ageing of steels
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-501 Dezember 2008, 70-76

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Permalink: https://www.hzdr.de/publications/Publ-12155
Publ.-Id: 12155


Fabrication of light-emitting Si quantum dots by pulsed annealing of Si-rich SiO2 layers

Kachurin, G. A.; Yankov, R. A.; Cherkova, S. G.; Marin, D. V.
Thin Si-rich SiO2 layers have been prepared by implantation of 100 to 190 keV Si ions in thermally grown oxide films. The ion doses provided the excess Si concentration of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments to form light-emitting Si quantum dots. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using a spectroscopy of PL excited at room temperature by a nitrogen laser (λ = 337 nm). The excess Si atoms in SiO2 are not free to migrate, but are rather incorporated into the oxide network. The fabrication of Si-ncs necessitates segregation of the Si atoms, availability of sinks to which these atoms may diffuse, availability of Si-phase nucleation centers, growth of the incipient nanoprecipitates, their crystallization, and, finally, the Ostwald ripening Due to the high temperatures resulting from intense light pulses, the different stages in the formation of light-emitting Si quantum dots may occur quite rapidly. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si in the SiO2 atomic network and the formation of quantum dots that luminesce in the visible portion of the spectrum (400-600 nm). For laser pulse duration of 20 ns no formation of nanocrystals occurs, which is evidently associated with the insufficient growth time. However, if one creates in advance amorphous Si precipitates of the right size, it is possible to form quantum-size Si nanocrystals by pulsed laser processing. This process occurs most likely via melting rather than in a solid phase, favored by the release of latent heat and the reduction in temperature of melting of the nanoparticles. Photoluminescence band near 800 nm, typical to quantum-size Si nanocrystals, was found after laser annealing. Formation of the luminesing Si nanocrystals in Si-rich SiO2 layers is feasible under the influence of intense light pulses of 20 ms and 1 s duration. In this case the SiO2 layer has not been heated above the Si melting point. Comparison of the nanocrystals formation rate and the estimates of the diffusion-limited growth yields diffusivity of the excess Si in SiO2 that are substantially larger than the values obtained in experiments using stationary annealing. The discrepancies may be explained by the existence of a transient mechanism of rapid growth at the very beginning of the pulsed annealing.
  • Poster
    15th International Conference on Semiconductor Dots, 11.-16.05.2008, Gyeongju, Korea

Permalink: https://www.hzdr.de/publications/Publ-12153
Publ.-Id: 12153


Pulsed annealing creation of light-emitting Si nanostructures in SiO2 layers implanted with Si ions

Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Implantation of 100-190 keV Si ions in thin SiO2 layers followed by intense light pulse annealing was used to form Si quantum dots. The ion doses provided the excess Si concentrations of ~10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation anneals. The pulse durations were 20ns, 20ms and 1s, respectively. Studies were carried out using photoluminescence excited at 20 oC by a N2 laser. Treatments for 20ns are already sufficient for the segregation of Si and formation of low-dimensional clusters, emitting light in the visible range (400-600 nm). For 20ns pulses no formation of Si-ncs occurs, which is associated with the lack of annealing time. However, if one creates in advance amorphous Si nanoprecipitates, it is possible to form Si-ncs by laser pulses. The crystallization occurs most likely via melting. Formation of the Si-ncs is feasible under the 20ms and 1s light pulses. In this case the temperatures never exceeded Si melting point. Comparison of the Si-ncs formation rate and the estimates of the expected diffusion-limited grain growth yields diffusivity of Si in SiO2 that is much higher, than the values obtained for stationary annealing. Possible mechanism of Si-ncs formation is discussed.
  • Lecture (Conference)
    9th International Conference on Applications of Nuclear Techniques, 08.-14.06.2008, Crete, Greece

Permalink: https://www.hzdr.de/publications/Publ-12152
Publ.-Id: 12152


Luminescing quantum-size Si nanostructures formed in Si rich SiO2 by intense light pulses

Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Implantation of Si ions in thin thermally grown SiO2 layers followed by intense light pulse annealing was used to form light-emitting Si nanostructures. The ion doses provided the excess Si concentration of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using a spectroscopy of PL excited at room temperature by a nitrogen laser (λ = 337 nm). Due to the high temperatures resulting from intense light pulses, the different stages in the formation of light-emitting Si nanostructures may occur quite rapidly. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si in the SiO2 atomic network and the formation of clusters that luminesce in the visible portion of the spectrum (400-600 nm). For laser pulse duration of 20 ns no formation of nanocrystals occurs, which is evidently associated with the insufficient growth time. However, if one creates in advance amorphous Si precipitates of the right size, it is possible to form quantum-size Si nanocrystals by pulsed laser processing. This process occurs most likely via melting rather than in a solid phase, favored by the release of latent heat and the reduction in temperature of melting of the nanoparticles. Photoluminescence band near 800 nm, typical to quantum-size Si nanocrystals, was found after laser annealing. Formation of the luminesing Si nanocrystals in Si-rich SiO2 layers is feasible under the influence of intense light pulses of 20 ms and 1 s duration. In this case the SiO2 layer has not been heated above the Si melting point. Comparison of the nanocrystals formation rate and the estimates of the diffusion-limited growth yields diffusivity of the excess Si in SiO2 that are substantially larger than the values obtained in experiments using stationary annealing. The discrepancies may be explained by the existence of a transient mechanism of rapid growth at the very beginning of the pulsed annealing.
  • Poster
    The 15th International Conference on Luminescence and Optical Spectroscopy of Condensed Matter (ICL'08), 07.-11.07.2008, Lyon, France

Permalink: https://www.hzdr.de/publications/Publ-12151
Publ.-Id: 12151


Light-emitting Si nanostructures formed in Si-rich SiO2 by pulsed annealing

Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Formation of Si-nanocrystals hase been achieved under the influence of intense light pulses of 20 ms and 1 s duration. In this case the Si surface has not been observed to melt, and therefore the SiO2 layer has not been heated above 1400 °C. Comparison of the Si-nc formation rate and the estimates of the diffusion-limited growth yields diffusivity of the excess Si in SiO2 that are substantially larger than the values obtained in experiments using stationary annealing. The discrepancies have been explained by the occurrence of a transient mechanism of rapid growth at the start of the pulsed annealing.
  • Poster
    16th Annual International Conference on Composites/Nano Engineering (ICCE-16), 20.-26.06.2008, Kunming (City of Eternal Spring), China

Permalink: https://www.hzdr.de/publications/Publ-12150
Publ.-Id: 12150


Light-emitting Si nanostructures formed in Si implanted SiO2 layers by pulsed anneals

Kachurin, G. A.; Cherkova, S. G.; Marin, D. V.; Yankov, R. A.
Thin thermally grown SiO2 layers were implanted with 100 to 190 keV Si ions. The ion doses provided the excess Si concentration of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments to analyze their possibilities to synthesize the light-emitting Si nanocrystals (Si-ncs) and therewith the mechanism of Si-ncs formation . The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using the photoluminescence spectroscopy, excited at 20 oC by a nitrogen laser (λ = 337 nm). The formation of Si-ncs necessitates segregation of the Si atoms from the oxide network, availability of sinks to which these atoms may diffuse, availability of Si-phase nucleation centers, growth of the incipient nanoprecipitates, and, finally, their crystallization. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si and for formation of nanostructures that luminesce in the visible range (400-600 nm). For laser pulse duration of 20 ns no formation of Si-ncs occurs. However, if one creates in advance amorphous Si nanoprecipitates, it is possible to form the luminescing Si-ncs by the 20-ns pulses. This process occurs most likely via melting, favored by the release of the latent heat. Formation of the luminescing Si-ncs is feasible under the 20-ms and 1-s light pulses. In these cases the SiO2 layer has not been heated above the Si melting point. Comparison of the Si-ncs formation rate with their conjectural diffusion-limited growth suggests the existence of a transient non-diffusional mechanism at the beginning of the pulsed annealing.
  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-12149
Publ.-Id: 12149


Light-emitting Si quantum dots formed by pulsed annealing

Kachurin, G. A.; Cherkova, S. G.; Yankov, R. A.; Marin, D. V.
Pulsed anneals are of high practical importance as they enable one to perform heat treatment locally while affecting insignificantly the adjacent regions. This is particularly advantageous for the processing of low dimensional devices. The ongoing drive for smaller devices coupled with the discovery of strong luminescence from quantum-sized Si nanocrystals (Si-ncs) has spurred extensive research into the processes of their fabrication. Nowadays a decomposition of supersaturated solid solution of Si in SiO2 layers is mostly employed for this purpose. The fabrication of Si-ncs necessitates segregation of the Si atoms, availability of sinks to which these atoms may diffuse, availability of Si-phase nucleation centers, growth of the incipient clusters, and subsequent crystallization. Our work is an attempt to address the dependence of the light-emitting Si nanostructure formation on the length of the annealing light pulses. Implantation of Si ions in thin thermally grown SiO2 layers followed by intense light pulse annealing was used to form Si quantum dots. The ion doses provided the excess Si concentrations of about 10-15%. KrF excimer laser pulses, flash lamp annealing and rapid thermal annealing were used for the post-implantation heat treatments. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Studies were carried out using photoluminescence excited at 20 °C by a N2 laser (λ = 337 nm). Due to the high temperatures resulting from intense light pulses, the different stages in the formation of light-emitting Si nanostructures may occur quite rapidly. Treatment for times as short as 20 ns is already sufficient for the segregation of the excess Si and the formation of low dimensional clusters that emit light in the visible range (400-600 nm). For 20 ns laser pulses of no formation of Si-ncs occurs, which is evidently associated with the insufficient growth time. However, if one creates in advance amorphous Si nanoprecipitates, it is possible to form Si-ncs by pulsed laser processing. The crystallization occurs most likely via melting rather than in a solid phase, favored by the release of latent heat and the reduction in temperature of melting of the low dimensional particles. Formation of the luminescing Si-ncs is feasible under the 20 ms and 1 s intense light pulses. In this case the temperatures never exceeded Si melting point. Comparison of the Si-ncs formation rate and the estimates of the expected diffusion-limited grain growth yields diffusivity of the excess Si in SiO2 that are several orders larger, than the values obtained in experiments using stationary annealing. Possible mechanism of Si-ncs formation is discussed.
  • Poster
    Workshop on Recent Advances of Low Dimensional Structures and Devices (WRA-LDSD), 07.-09.04.2008, Nottingham, UK

Permalink: https://www.hzdr.de/publications/Publ-12148
Publ.-Id: 12148


Radiosynthesis and radiopharmacological evaluation of [N-methyl-11C]Org 34850 as a glucocorticoid receptor (GR)-binding radiotracer

Wüst, F.; Knieß, T.; Henry, B.; Peeters, B. W. M. M.; Wiegerinck, P. H. G.; Pietzsch, J.; Bergmann, R.
The radiosynthesis of [N-methyl-11C]Org 34850 as a potential brain glucocorticoid receptor (GR)-binding radiotracer is described. The radiosynthesis was accomplished via N-methylation of the corresponding desmethyl precursor with [11C]methyl triflate in a remotely controlled synthesis module to give the desired compound in a radiochemical yield of 23+/-5% (decay-corrected, based upon [11C]CO2) at a specific activity of 47+/-12 GBq/mmol (n ¼ 15) at the end-of-synthesis (EOS). The radiochemical purity after semi-preparative HPLC purification exceeded 95%. The total synthesis time was 35–40 min after end-of-bombardment (EOB).

The radiotracer is rapidly metabolized in rat plasma leading to the formation of two more hydrophilic metabolites as the major metabolites. Radiopharmacological evaluation involving biodistribution and small animal PET imaging in normal Wistar rats showed that the compound [N-methyl-11C]Org 34850 is not able to sufficiently penetrate the blood–brain barrier. Therefore, compound [N-methyl-11C]Org 34850 seems not to be a suitable PET radiotracer for imaging rat brain GRs. However, involvement of Pgp or species differences requires further clarification to establish whether the radiotracer [N-methyl-11C]Org 34850 may still represent a suitable candidate for imaging GRs in humans.
Keywords: [N-methyl-11C]Org 34850; Glucocorticoid receptor; Positron emission tomography (PET)

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Permalink: https://www.hzdr.de/publications/Publ-12146
Publ.-Id: 12146


Messtechnik für Mehrphasenströmungen - Sensoren, Systeme und Anwendungen

Schleicher, E.; Da Silva, M. J.; Fischer, F.; Bieberle, A.; Bieberle, M.; Hampel, U.
Die Untersuchung von Mehrphasenströmungen ist für viele Forschungs- und Industriebereiche von großer Bedeutung. Im Bereich der Verfahrenstechnik und Kernenergietechnik bestimmen beispielsweise das Verhalten und die Struktur von Gasblasen maßgeblich Effizienz und Sicherheit von Prozessen in Rohrsystemen, Behälter oder Reaktoren. Angesichts dieses breiten Anwendungsspektrums sind in der Vergangenheit verschiedene Messmethoden und Systeme entwickelt worden, um die Untersuchung von Mehrphasenströmungen zu ermöglichen, bestimmte Phänomene sichtbar zu machen und um numerische Strömungsmodelle s. g. CFD-Codes (computational fluid dynamics) zu validieren. Am Institut für Sicherheitsforschung des Forschungszentrums Dresden-Rossendorf wurden beispielsweise auf elektrischer Leifähigkeit sowie Kapazität basierende Systeme wie Nadelsonden und Gittersensoren entwickelt, die in Zweiphasenströmungen den Gasgehalt und die Phasenverteilung mit sehr hohen räumlichen und zeitlichen Auflösungen erfassen können. Darüber hinaus werden verstärkt auch nicht-invasive tomographische Verfahren wie die Gamma-CT und die ultraschnelle Röntgen-CT beforscht. Letztere ist in der Lage bis zu 7000 tomographische Schnittbilder pro Sekunde mit einer Ortsauflösung von bis zu 1 mm zu erzeugen.
Keywords: flow measurement, two-phase flow, Ultra fast X-ray CT, multi phase flow measurement, flow visualization, capacitance measurement, high resolution gamma ray tomography, void fraction determination, wire mesh sensor
  • Invited lecture (Conferences)
    Institutskolloquium, 25.11.2008, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12145
Publ.-Id: 12145


The Naimark dilated PT-symmetric brachistochrone

Günther, U.; Samsonov, B.
The quantum mechanical brachistochrone system with PT-symmetric Hamiltonian is Naimark dilated and reinterpreted as subsystem of a Hermitian system in a higher-dimensional Hilbert space. This opens a way to a direct experimental implementation of the recently hypothesized PT-symmetric ultra-fast (wormhole-like) brachistochrone regime of [C. M. Bender et al, Phys. Rev. Lett. 98, 040403 (2007)] in an entangled two-spin system. The talk is mainly based on Phys. Rev. Lett. 101, 230404 (2008).
Keywords: quantum brachistochrone, quantum computing, PT quantum mechanics, strongly non-Hermitian regime, exceptional point, Anandan-Aharonov lower bound, ultra-fast evolution, POVM, Naimark dilation, Naimark extension, entangled state, two-qubit system, wormhole
  • Lecture (Conference)
    QTRF5 - Quantum Theory: Reconsideration of Foundations, 5, 14.-19.06.2009, Vaxjo, Sweden

Permalink: https://www.hzdr.de/publications/Publ-12144
Publ.-Id: 12144


Photochemical reduction of UO22+ in the presence of alcohol studied by DFT calculations

Tsushima, S.
A well-known photochemical process of UVIO22+ reduction to UVO2+ in the presence of alcohols was studied by density functional theory (DFT) calculations. It was found that the first process which takes place is a photoexcitation of the ground-state UO22+ to the triplet excited state (*UO22+) followed by a significant shortening of the *UO22+-to-alcohol Oax-H distance. A charge transfer from *UO22+ to alcohol and hydrogen abstraction takes place in the following step. Consequently, UVIO22+ gets reduced to UVO(OH)2+. The photochemical byproduct RC·HOH acts further as a reducing agent toward UO22+ to yield UO2+ and RCHO (aldehyde). Only a combination of these two reactions can explain a high quantum yield of this reaction. In the absence of alcohol, the lowest-lying triplet state exhibits a different character, and photoreduction is unlikely to take place via the same mechanism. The present results agree well with recent experimental finding [J. Am. Chem. Soc. 2006, 128, 14024] and supports the idea that the Oax-H linkage between UO22+ and the solvent molecule is the key to the photochemical reduction process.
  • Inorganic Chemistry 48(2009)11, 4856-4862
  • Lecture (Conference)
    ROBL-Radiochemie Workshop, 18.12.2008, Dresden, Germany

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Permalink: https://www.hzdr.de/publications/Publ-12143
Publ.-Id: 12143


Anisotropic scaling of ripple morphologies on high-fluence sputtered silicon

Keller, A.; Cuerno, R.; Facsko, S.; Möller, W.
The evolution of Si(100) surfaces has been studied during oblique high-fluence ion sputtering by means of atomic force microscopy. The observed surface morphology is dominated by nanoscale ripples and kinetic roughening at small and large lateral scales, respectively. The large-scale morphology exhibits anisotropic scaling at high fluences with different roughness exponents an = 0.76 ± 0.04 and ap = 0.41 ± 0.04 in the directions normal and parallel to the incident ion beam, respectively. Comparison with the predictions of single field and two-field ("hydrodynamic") models of ion erosion suggests the relevance of nonlinearities that are not considered in the simpler anisotropic Kuramoto-Sivashinsky equation.

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Permalink: https://www.hzdr.de/publications/Publ-12142
Publ.-Id: 12142


Sorption databases for increasing confidence in performance assessment

Richter, A.; Brendler, V.; Nebelung, C.; Payne, T.; Brasser, T.
World-wide activities focus on the remediation of radioactively contaminated sites. One common aim is to deliver a more profound chemical base for risk assessment, namely all those physico-chemical phenomena governing the contamination plume development in time and space. Coupled transport codes able to tackle this challenge have to simplify the resulting very complex reaction pattern. To do so in an adequate way requires extending the knowledge about retardation and mobilisation phenomena and the underlying basic processes and interactions (e.g. physisorption, chemisorption, surface precipitation).
Interactions at the solid-liquid interface can be described by two complementary approaches, the empirical Kd concept and the mechanistic Surface Complexation Models (SCM).
Kd’s are used by most reactive transport and risk assessment codes due to the straightforward numerics involved. In addition, the Kd concept is often the only feasible option for complex solid phases. However, the Kd concept is a rather simplistic approach. Many very different basic physico-chemical phenomena are contained in just one conditional parameter. Therefore, extrapolating Kd values may yield very large uncertainties.
SCM allows for the partitioning of retardation into the most important underlying physico-chemical processes. Parameters are site-independent and applicable despite large variations in geochemical conditions. This presents a high potential to increase confidence in safety analysis and risk assessment studies (performance assessment). The mechanistic description of sorption processes with SCM allows a thermodynamically consistent calculation of the species distribution between liquid and solid phase combined with more reliable inter- and extrapolations. However, this requires that all mineral constituents of the solid phase are characterized. Another issue is the large number of required parameters combined with time-consuming iterations.
Addressing both approaches, we present two sorption databases, developed mainly by or under participation of the Forschungszentrum Dresden-Rossendorf (FZD). Both databases are implemented as relational databases, assist identification of critical data gaps and the evaluation of existing parameter sets, provide web based data search and analyses and permit the comparison of SCM predictions with Kd values.
RES³T (Rossendorf Expert System for Surface and Sorption Thermodynamics) is a digitized thermodynamic sorption database (see www.fzd.de/db/RES3T.login) and free of charge. It is mineral-specific and can therefore also be used for additive models of more complex solid phases.
ISDA (Integrated Sorption Database System) connects SCM with the Kd concept but focuses on conventional Kd. The integrated datasets are accessible through a unified user interface.
An application case, Kd values in Performance Assessment, is given.
Keywords: RES3T, ISDA, database, sorption, surface complexation, KD, prediction
  • Lecture (Conference)
    ICEM'09 - 12th International Conference on Environmental Remediation and Radioactive Waste Management, 11.-15.10.2009, Liverpool, United Kingdom
  • Contribution to proceedings
    ICEM 2009, 11.-15.10.2009, Liverpool, United Kingdom
    Proceedings of the 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management, ICEM2009-16053

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Permalink: https://www.hzdr.de/publications/Publ-12141
Publ.-Id: 12141


Sizing of safety valves using ANSYS CFX-Flo

Moncalvo, L.; Friedel, B.; Jörgensen, T.; Höhne, T.
This work discusses the effect of the degree of fineness of the flow volume discretization and that of the turbulence model on the accuracy of reproduction of air mass flow rates in two safety valves using the CFD software ANSYS Flo. Calculations show that the degree of fineness of the discretization is the decisive factor
affecting the exactness of the calculations and that the best reproduction is achieved with grids where at least two cells are built on the smallest edge. The selection of the turbulence model has by far in comparison a lower impact; however, the best accuracy is obtained using the standard k-x model and the SST modification of Menter.
Keywords: CFD, Safety valves

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Publ.-Id: 12140


Site-selective determination of coordination symmetries by anisotropic anomalous X-ray scattering

Zschornak, M.; Leisegang, T.; Stöcker, H.; Weißbach, T.; Gemming, S.; Meyer, D. C.

Based on an experiment of Kirfel and Petcov on rutile (136) P42/mnm, which verified anisotropic anomalous scattering (AAS) by measuring ‘Forbidden Reflection near Edge Diffraction’ (FRED), we aimed to extend the results with allowed reflections to extract more tensor symmetries of the Ti scattering factor tensor f ij by fitting the model of AAS to the experimental data. Results from DFT calculations will also be presented. Furthermore we intended to study possible restrictions for atomic site occupation of unknown structures in an identified space group due to these local symmetry relations exemplary for this model structure.

Experiments were carried out at DESY/HASYLAB BL C using a Si (111) double crystal monochromator tuned to an energy of 4985eV. An automated optimization and Y-scan routine for a sample setup with rotating degree of freedom assured AAS measurements at the reflection maxima. The rutile samples investigated were 10x10x1mm3 wafers in (001), (110) and (111) orientation and Y-scans were measured for the reflections 001, 220, 110 and 111.

Ti occupies Wyckoff site 2a, its tensor symmetry must follow the local symmetry m.mm leaving 3 complex elements f 11, f 12, f 33. Simulations showed dependencies: 001 to f 12, 220 to f 11- f 33, 110 to f 11- f 33, 111 to f 12. For the 001 reflection intensity real and imaginary part correlate, but the 111 intensity displays asymmetric influence so the ambiguity is separable.

The measured data show clear evidence of AAS and the 001 FRED and 111 intensities could be fitted:

f ’ Ti d ’ 12 = -5.44 * 0.5(8)

f ” Ti d ” 12 = 3.98 * 1.4(2)

Since f 13 and f 23 were refined to zero, the positioning of Ti in the unit cell would by inverse symmetry arguments only be consistent with respect to site symmetry on Wyckoff sites a, b, e, f, g (out of k ).

Keywords: Anisotropic Anomalous X-Ray Scattering, Resonant X-Ray Scattering, Forbidden Reflection near Edge Diffraction
  • Poster
    XXI Congress and General Assembly of the International Union of Crystallography, 23.-31.08.2008, Osaka, Japan

Permalink: https://www.hzdr.de/publications/Publ-12139
Publ.-Id: 12139


Anisotropic Anomalous Scattering in Rutile TiO2

Zschornak, M.; Leisegang, T.; Gutmann, E.; Stöcker, H.; Meyer, D. C.

Based on an experiment of A. Kirfel and A. Petcov on rutile TiO2, space group (136) P42 mnm in 1989 [1], which verified the anisotropic anomalous scattering (AAS) in rutile through measuring ‘Forbidden Reflection near Edge Diffraction’ (FRED) intensity at the 100 and 001 forbidden reflections just above the Ti-K absorption edge, we aimed to extend the results by measuring AAS not only for forbidden but also for allowed reflections, to find effects of anisotropy also in this case and to fit the model of anisotropic scattering [2] to the experimental data.

Experiments were carried out at DESY/HASYLAB beamline C1 (CEMO) using a (111) double crystal monochromator at the Ti resonance energy E = 4985 eV. An automated optimization and Y-scan routine called ‘Peak-Optimized-Psi-Scan (POPS)’ which we programmed with LabView for a sample setup with rotating degree of freedom was tested for the first time for synchrotron conditions.

The rutile samples investigated were three 10 x 10 x 1 mm3 wafers synthesized by Crystec GmbH in (001), (110) and (111) orientation and Y-scans were measured for the reflections 001, 220, 110 and 111, respectively. Since the Ti in rutile occupies Wyckoff site 2a, its tensor symmetry must follow the local symmetry m.mm leaving 3 independent complex elements for the symmetric scattering tensor, f 11, f 12 and f 33. Calculations and simulations with the developed ‘TensorScattering’ code (Fig. 1) showed following dependencies: 001 to f 12, 220 to f 11- f 33, 110 to f 11- f 33 and 111 to f 12. For the 001 reflection intensity the real and imaginary parts correlate, but the 111 intensity shows asymmetric influence so that the ambiguity should be separable.

The measured data show clear evidence of AAS and the 001 FRED and 111 reflection intensities could be fitted quite reasonably within the model. They were fitted simultaneously because both only depend on f 12, since the 111 is also forbidden within the Ti partial structure and the isotropic flat contribution is caused only by the oxygen partial structure. Within the fit the isotropic part of the 111 reflection intensity locks the constant and the asymmetry detangles f ’ 12 and f ” 12. They were evaluated due to refinement as:

f ’ 12 = f ’ Ti(E=4985eV) * d ’ 12 = -5.44 el * 0.58(2)

f ” 12 = f ” Ti(E=4985eV) * d ” 12 = 3.98 el * 1.42(0)

References

[1] A. Kirfel, A. Petcov, Anisotropy of anomalous dispersion. II. FRED (Forbidden Reflection near Edge Diffraction) in Rutile, TiO2, HASYLAB/DESY Jahresbericht (1989) 385-386.

[2] A. Kirfel, W. Morgenroth, Anisotropy of anomalous scattering in X-ray diffraction. III. `Forbidden' axial reflections in space groups up to orthorhombic symmetry, Acta Crystallogr. A 49 (1993) 35-45.

Keywords: Anisotropic Resonant X-Ray Scattering, Anisotropic Anomalous X-Ray Scattering, Forbidden Reflection near Edge Diffraction
  • Poster
    16. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 03.-06.03.2008, Erlangen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-12138
Publ.-Id: 12138


Study of omega-meson production in pp collisions at ANKE

Barsov, S.; Buscher, M.; Hartmann, M.; Hejny, V.; Kacharava, A.; Keshelashvili, I.; Khoukaz, A.; Koptev, V.; Kulessa, P.; Kulikov, A.; Lehmann, I.; Leontyev, V.; Macharashvili, G.; Maeda, Y.; Mersmann, T.; Merzliakov, S.; Mikirtytchyants, S.; Mussgiller, A.; Oellers, D.; Ohm, H.; Rathmann, F.; Schleichert, R.; Seyfarth, H.; Stroher, H.; Trusov, S.; Valdau, Y.; Wustner, P.; Yaschenko, S.; Wilkin, C.
The production of omega-mesons in the pp --> pp omega reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92 MeV by detecting the two final protons and reconstructing their missing mass. The large physical background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross-sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the phi-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the phi/omega production ratio.

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Permalink: https://www.hzdr.de/publications/Publ-12137
Publ.-Id: 12137


Prediabetic and diabetic in vivo modification of circulating low density lipoprotein attenuates its stimulatory effect on adrenal mineralocorticoid secretion

Kopprasch, S.; Pietzsch, J.; Ansurudeen, I.; Graessler, J.; Krug, A. W.; Erhart-Bornstein, M.; Bornstein, S. R.
Modification of low-density lipoprotein (LDL) and abnormal aldosterone and cortisol metabolism have been implicated in the pathogenesis of type 2 diabetes (DM2) and diabetic vascular disease. Since LDL serves as a major cholesterol source for adrenal steroidogenesis, we investigated whether LDL modification in prediabetic and diabetic subjects influences adrenocortical aldosterone and cortisol release. LDL was isolated from 30 subjects with normal glucose tolerance (NGT-LDL), 30 subjects with impaired glucose tolerance (IGT-LDL), and 26 patients with DM2 (DM2-LDL). Oxidation and glycoxidation characteristics of LDL apolipoprotein B100 of each individual was assessed by gas chromatography-mass spectrometry analysis. Human adrenocortical cells (NCI-H295R) were incubated for 24 h with 100 microg/ml LDL and after removal of supernatants stimulated for a further 24 h with angiotensin II (AngII). In supernatants, aldosterone and cortisol secretion was measured. IGT-LDL and DM2-LDL were substantially more modified than NGT-LDL. Each of the five measured oxidation/glycoxidation markers was significantly positively associated with glycemic control, measured as HbA(1c). LDL from all subjects stimulated both the basal and AngII-induced aldosterone and cortisol release from adrenocortical cells. However, hormone secretion was significantly inversely related to the degree of LDL oxidation/glycoxidation. We conclude that LDL modifications in IGT and DM2 subjects may have significant clinical benefits by counteracting prediabetic and diabetic overactivity of the renin-angiotensin-aldosterone system and enhanced cortisol generation.

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Publ.-Id: 12136


Resonant two-photon transitions, quadratic detection, and photocurrent autocorrelation using multiple quantum wells

Schneider, H.; Liu, H. C.; Winnerl, S.; Drachenko, O.; Helm, M.; Walther, M.; Faist, J.
We report on two-photon detection based on quantum well intersubband nonlinear absorption. Three equidistant subbands, two of which are bound in the quantum well, and the third one in the continuum, result in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors [1]. This device is very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL). Using these detectors as a quadratic autocorrelator for mid-infrared pulses, temporal resolution is only limited by the sub-ps intrinsic time constants of the intersubband transitions, namely the intersubband relaxation time and the phase relaxation time. We have investigated the performance of devices operating at various wavelengths from the mid-infrared to the Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, device operation at shorter wavelengths around 5.5 µm is still possible at room temperature, which is crucial for applications in practical systems.
[1] H. Schneider, T. Maier, H. C. Liu, M. Walther, and P. Koidl, Optics Lett. 30, 287 (2005).
Keywords: intersubband transition, two-photon absorption, quantum well infrared photodetector, autocorrelation, free-electron laser
  • Invited lecture (Conferences)
    SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA

Permalink: https://www.hzdr.de/publications/Publ-12135
Publ.-Id: 12135


Two-photon photocurrent spectroscopy of quantum well intersubband relaxation and dephasing

Schneider, H.; Liu, H. C.; Maier, T.; Walther, M.
We have studied electron intersubband relaxation and dephasing in n-type InGaAs/AlGaAs quantum wells by femtosecond two-photon photocurrent spectroscopy using mid-infrared pulses of 165 fs duration. The approach enables us to determine systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes [1]. By varying the excitation energy, we also tuned the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state [2]. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.
[1] H. Schneider, T. Maier, M. Walther, H. C. Liu, Appl. Phys. Lett. 91, 191116 (2007).
[2] H. Schneider, T. Maier, H. C. Liu, M. Walther, Opt. Express 16, 1523 (2008).
Keywords: intersubband transition, two-photon absorption, quantum well infrared photodetector, phase relaxation, autocorrelation
  • Invited lecture (Conferences)
    SPIE Photonics West, 24.-29.01.2009, San Jose, CA, USA

Permalink: https://www.hzdr.de/publications/Publ-12134
Publ.-Id: 12134


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