Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The generic strategy of core physics codes benchmarking which has been elaborated within the European NURESIM code platform development was applied to benchmarking of the 3D neutron kinetics code DYN3D for applications to VVER-type reactors. Numerical and experimental benchmark problems were considered for code verification and validation.
Mathematical problems with given cross sections are used for the verification of the mathematical methods applied e.g. in nodal codes against finite difference solutions.
After minimisation of numerical errors, modelling errors have to be considered. Diffusion approximation and homogenisation error are due to simplified physical approaches and can be estimated by comparing diffusion solutions with more accurate Monte Carlo or deterministic transport solutions.
A series of 2D whole core benchmarks for different core loadings and operational conditions for VVER-1000 reactors was defined for this purpose. Reference transport solutions were calculated by the MARIKO and APOLLO codes based on Method of Characteristics. Homogenised two-group and few-group diffusion parameters were derived from the reference solutions and used as cross section data for the nodal diffusion code DYN3D. The DYN3D solutions were compared to the reference solution. It was shown that the homogenisation error can be significantly reduced, if Assembly Discontinuity Factors (ADF) and Reference Discontinuity Factors (RDF) which are obtained from the transport solution by applying equivalence theory are used.
A study using the multi-group version of DYN3D has shown that increasing the number of groups in the considered cases has only a small effect in comparison with homogenisation error.
Experimental problems are used for code validation. Experimental data for VVER reactors, which were used for the benchmarking of the DYN3D code within NURESIM, are power distribution measurements at the full-size (VVER-1000) experimental facility V-1000, which have been well documented within the EC project VALCO, and kinetic experiments at the LR-0 zero power reactor in NRI Řež.
The code DYN3D has proved to be an effective tool for steady-state and kinetics core calculations. The high accuracy of the code is based on the advanced nodal method “HEXNEM2”, multi-group approach, applying discontinuity factors, and intra-nodal flux reconstruction.

A (001) SrTiO3 wafer has been investigated in situ at room temperature under application of a static electric field of varying polarity by the fluorescence X-ray Absorption Near Edge Structure (XANES) analysis at the Sr-K and Ti-K absorption edges. The XANES spectra show a clear shift of the Ti-K absorption edge energy. The shift is attributed to a change of the Ti valence state in a volume invoked by diffusion of the oxygen ions and vacancies. No shift was observed for the Sr-K absorption edge energy. Theoretical calculations support these findings.

In this study the consequences of the discretization effect is investigated for the full calculation chain starting with the steady state calculation continuing with the burnup calculations and finishing with the evaluation of the safety coefficients. The investigation is based on Mixed Oxide (MOX) Fuel with reactor grade Plutonium. Detailed evaluation of the convergence behavior, the influence of the discretization on the neutron spectrum and the isotopic composition during burnup is given. Finally the influence on the few group cross section preparation and an estimation of the influence of discretization on the safety coefficients is shown.

This work presents a improved onset for the analysis of experiments by the development of an analytical approximation solution for a space-time dependent P1 neutron transport problem in a one dimensional system consisting of homogenized medium with a central external source with Green's functions. The delayed neutron production is implemented in two additional time scales with the multiple scale expansion method. The approximation solutions are developed for the switch off of the source. First applications are shown for the analysis of the YALINA Booster experiment.

The ATWS transient “Loss of main feed water supply” in a generic four-loop PWR at the nominal power of 3750 MW was analyzed using the coupled code system DYN3D/ATHLET. A variation of the MOX-fuel-assembly portion in the core has an effect on the reactivity coefficients of the fuel temperature and the moderator density. These two parameters mainly influence the behaviour of the coolant pressure, which is safety-relevant. It has been demonstrated that the pressure maximum decreases with an increasing portion of MOX. For all core loadings considered, both primary-circuit mechanical integrity and sufficient core cooling are guaranteed.

Wird die an öffentlich finanzierten außeruniversitären Forschungseinrichtungen zunehmend wichtiger werdende Programmbudgetierung durch eine leistungsbezogene Budgetierung ergänzt, kann die durch das Neue Steuerungsmodell geforderte Wirkungsorientierung der Ressourcenallokation forciert werden. Darüber hinaus ermöglicht die Übernahme von Kriterien der externen Evaluierung in die budgetierungsrelevanten Leistungsindikatoren eine Verknüpfung zwischen externen Anforderungen der Träger der Einrichtungen und internen Leistungsanreizen. Mit dem vorliegenden Beitrag wird eine Evaluationskonzeption vorgestellt, mit welcher das leistungsbezogene Budgetierungsmodell einer öffentlich finanzierten außeruniversitären Forschungseinrichtung bewertet sowie verbessert werden kann.

Hydrogen (H) incorporation into AlGaN/GaN heterostructures used in high electron mobility transistors, grown by different methods, is studied by high-resolution depth profiling. Samples grown on sapphire and Si(1 1 1) substrates by molecular-beam epitaxy and metal–organic vapour phase epitaxy; involving H-free and H-containing precursors, were analysed to evaluate the eventual incorporation of H into the wafer. The amount of H was measured by means of nuclear reaction analysis (NRA) using the ¹H(¹⁵N,αγ )¹²C reaction up to a depth of ∼110 nm into the heterostructures. Interestingly, the H profiles are similar in all the samples analysed, with an increasing H content towards the surface and a negligible H incorporation into the GaN layer (0.24 ± 0.08 at%) or at the AlGaN/GaN interface. Therefore, NRA shows that H uptake is not related to the growth process or technique employed and that H contamination may be due to external sources after growth. The eventual correlation between topographical defects on the AlGaN surface and the H concentration are also discussed. (Some figures in this article are in colour only in the electronic version)

In nuclear reactor safety the mixing of borated and deborated water is a critical issue that needs investigation, assessment and prediction. Such mixing is buoyancy driven and numerical codes must correctly model momentum transfer between components of different density. To assess and develop CFD models for buoyancy driven mixing we set up a simple vertical mixing test facility (VeMix) and equipped it with a newly developed planar electrical imaging sensor. This imaging sensor acquires conductivity images of the liquid at the rear channel wall with a speed of 2,500 frames per second. By adding NaCl tracer to the denser component we were able to visualize the mixing process in high spatial and temporal detail. Furthermore, an image processing algorithm based on the optical flow concept was implemented and tested which allows the measurement of flow pattern velocities. Selected experiments at different Richardson numbers were run with two components of different density (pure water and glucose-water mixture) simulating borated and deborated water in a light water reactor scenario. These experiments were compared to CFD calculations using standard turbulence models. Good agreement between experimental data and first CFD simulations was found.

One of the major elements in tritium processing systems is hydrogen isotopes identification and separation. Work with multiple hydrogen isotopes at the is often accompanied by isotopic mixing. Maintaining isotopic purity of tritium is one of the major tasks in new generation Texas Neutrino Mass Experiment (NEXTEX). We developed unique Raman Spectrometer capable of detecting hydrogen isotopes T2, HT, H2, D2, TD and H2 at pressures near 10 Pa with signal-to-noise ratio better than 2 during minutes long observations. This spectrometer is capable of distinguishing traces of numerous isotopomers at partial concentration as low as 1:4000 and can be also used as a medical diagnostic tool. Additionally I will discuss some aspect of our Coherent Raman Spectrometer and its ability to measure molecular kinetics in low temperatures plasmas.

Ultra-sensitive in-beam γ-ray spectroscopy studies for nuclear astrophysics are performed at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator, deep underground in Italy's Gran Sasso laboratory. By virtue of a specially constructed passive shield, the laboratory γ-ray background for Eγ < 3 MeV at LUNA has been reduced to levels comparable to those experienced in dedicated offline underground γ-counting setups. The γ-ray background induced by
an incident α-beam has been studied. The data are used to evaluate the feasibility of sensitive inbeam experiments at LUNA and, by extension, at similar proposed facilities.

The complete failure of the reactor scram system upon request during an operational transient is called anticipated transient without scram (ATWS). According to the German regulatory guidelines, postulated ATWS events have to be analyzed with regard to their consequences on the safety of nuclear power plants.
Since the course of ATWS transients is determined by a strong interaction of the neutron kinetics with the thermal hydraulics of the system, coupled 3D neutron kinetic/thermal hydraulic code systems are adequate tools for the analysis of such transients. The coupled code system DYN3D/ATHLET developed at FZD is applied to the analysis of an ATWS transient. The objective of the present work is to perform a best-estimate analysis with consequent use of a 3D neutron kinetic code (DYN3D) in combination with an advanced thermal hydraulic system code (ATHLET) together with a quantification of differences in the course and the results of transients, which arise from the uncertainties of thermal hydraulic and neutron-physical conditions.
Typically, the complete failure of the main feed water supply is assumed to be the bounding ATWS event with regard to the maximum primary coolant pressure, which can be reached during the transient. The limitation of the coolant pressure is a pre-condition for the integrity of the primary circuit. The situation is aggravated if the main coolant pumps remain in operation.
For this particular transient, the influence of different thermal hydraulic and neutron-physical conditions on the course of the transient was analyzed.
In a number of code runs all systems which have an influence on the course of the transient were varied. These are the auxiliary boration system and the auxiliary feed water supply. Further, the influence of the modeling of the pressurizer safety and relief valves as well as the steam bypass system on the secondary side was assessed. The variation of the pressurizer relief and safety valve behavior has the biggest influence on the primary circuit coolant pressure.
In the second part, two different core loading patterns were generated for the analyses by varying the number of MOX (mixed oxide) fuel assemblies (FA) in the core. The basic core loading contains 64 MOX FA. All these MOX FA were replaced by standard uranium oxide FA. The presence of MOX in the core has a remarkable influence on the reactivity coefficients of the fuel temperature and the moderator density. These two parameters mainly influence the behavior of the coolant pressure in the first part of the transient. It has been demonstrated that the pressure maximum decreases with growing MOX portion in the core.
The maximum pressure determined in the calculations with variation of system and neutron-physical boundary conditions does not reach the allowed limit for the primary circuit.

Electromagnetic dipole absorption cross-sections of transitional nuclei with large-amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of Instantaneous Shape Sampling, which is based on the slow shape dynamics as compared to the dipole vibrations. The dipole strength is calculated by means of RPA for the instantaneous shapes, the probability of which is obtained by means of IBA-1. Very good agreement with the experimental absorption cross sections near the nucleon emission threshold is obtained. The dipole strength in this energy region is controlled by the Landau fragmentation.

Hadron masses; If we would have a theory; Modelling, parametrizing, guessing

eta, eta' meson production in NN collisions

Chiral Symmetry and Medium-Modifications of Hadrons

Der Vortrag soll Schülern einen Einblick in die Arbeit eines Naturwissenschaftlers geben und Ihnen helfen, sich für Ihr anstehendes Studium zu orientieren.

The Creation and Manipulation of Particle Beams using Lasers opens new Paths towards compact, ultrabright Radiation Sources. With the advent of high-intensity, ultrashort Laser Sources it has become possible to accelerate Electrons and Ions with table top Laser Systems in the Laboratory. Moreover, Lasers can be used to cool Ion Beams to millikelvin Temperatures. In my talk I will focus on the Study of Laser-Matter Interaction by realistic large-scale Particle Simulations which can give insight into the complex Plasma Phenomena leading to the Creation of ultrabrilliant Particle Beams. I will introduce the numerical Methods used in these Computer Experiments and draw the Connection towards recent and future Experiments planned at FZD and GSI.

In diesem Vortrag werden die Prinzipien der Laserteilchenbeschleunigung sowie wichtige Anwendungen der dabei erzeugten Teilchenstrahlen vorgestellt.

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.

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 .

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.

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.

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.

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.

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)

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.

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.

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.

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 MnO_1.94) in the Mn–InAs-RTA epitaxial layers which might be the origin of the room-temperature ferromagneticlike response observed.

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.

Gamma-induced positron generation has been performed using the superconducting electron accelerator ELBE at the Research Center Dresden-Rossendorf.

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

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).

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.

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.

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.

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.

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.

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.

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.

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.

In this talk we present the scientific program of the Laser Particle Acceleration Group and the status of the DRACO laser system.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

A short review on Flash Lamp Annealing

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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)

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.

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.

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.

Report on the activities in the field of ion beam modification of magnetic materials.

kein Abstract vorhanden

kein Abstract vorhanden

kein Abstract vorhanden

kein Abstract vorhanden

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.

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.

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.

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.