Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The heart of the radiation source ELBE at the Forschungszentrum Dresden-Rossendorf (FZD) is a 40-MeV LINAC with an average current of 1 mA. Due to its superconducting technology, the time structure is different from conventional LINACs. Electron bunches as short as 2 ps with a 26 MHz repetition rate can be used in continuous operation (cw) mode. This is an ideal host for an intense positron source. After organizing SLOPOS-9 in Rossendorf, it was decided to add EPOS (ELBE Positron Source) to the existing experiments at ELBE. EPOS consists of two LINAC-based setups, Gamma-induced Positron Spectroscopy (GiPS) and Monoenergetic Positron Spectroscopy (MePS). The GiPS setup, where positrons are produced inside the whole sample volume by pair production using a pulsed gamma beam, is unique so far. Here, bulky samples such as coarse powders, dispersions, but also liquids or whole devices of non-destructive testing can be investigated by all positron techniques important for materials science (lifetime spectroscopy, age-momentum correlation, and coincidence Doppler broadening spectroscopy). The same techniques will be applied at the MePS setup, where slow, mono-energetic positrons will be generated by moderation to study near-surface layers. This system is still under construction. The EPOS system will be completed by two conventional setups, a continuous slow positron beam and a positron lifetime/ Doppler spectrometer, both operated by 22Na sources.

Current practice of Pu recycling in existing LWRs in the form of U-Pu mixed oxide fuel (MOX) is not efficient due to continuous Pu production from U-238. The use of Th-Pu mixed oxide (TOX) fuel will considerably improve Pu consumption rates because virtually no new Pu is generated from thorium. In this study, the feasibility of Pu recycling in a typical pressurized water reactor (PWR) fully loaded with TOX fuel is investigated.
Detailed 3-dimensional 100% TOX and 100% MOX PWR core designs are developed. The full MOX core is considered for comparison purposes. The design stages included determination of Pu loading required to achieve 18-month fuel cycle assuming three-batch fuel management scheme, selection of poison materials, development of the core loading pattern, optimization of burnable poison loadings, evaluation of critical boron concentration requirements, estimation of reactivity coefficients, core kinetic parameters, and shutdown margin.
The performance of the MOX and TOX cores under steady-state condition and during selected reactivity initiated accidents (RIA) is compared with that of the actual uranium oxide (UOX) PWR core.
Part I of this paper describes the full TOX and MOX PWR core designs and reports the results of steady state analysis. The TOX core requires a slightly higher initial Pu loading than the MOX core to achieve the target fuel cycle length. However, the TOX core exhibit superior Pu incineration capabilities.
The significantly degraded worth of control materials in Pu cores is partially addressed by the use of enriched soluble boron and B4C as a control rod absorbing material. Wet annular burnable absorber (WABA) rods are used to flatten radial power distribution. The temperature reactivity coefficients of the TOX core were found to be always negative. The TOX core has a slightly reduced, as compared to UOX core, but still sufficient shutdown margin.
In the TOX core βeff is smaller by about a factor of two in comparison to the UOX core and even lower than that of the MOX core. The combination of small βeff and reduce control materials worth may potentially deteriorate the performance under RIA conditions and requires an additional examination. The behavior of the considered cores during the most limiting RIAs, such as rod ejection, main steam line break, and boron dilution, is further investigated and reported in Part II of the paper.

Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. The ideal candidate for it is the superconducting RF photogun (SRF gun) which can be easily operated in CW like a DC photogun and may reach the beam quality of a normal conducting RF photogun. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high-average power into the gun and finally the risk of beam excitation of higher order cavity modes. At the FZ Dresden-Rossendorf a SRF gun has been developed and installed at the ELBE superconducting linac. The SRF gun is designed for an average current of 1 mA and an maximum electron energy of 9 MeV. The 1.3 GHz cavity consists of three full cells with TESLA geometry, a specially designed half-cell where the photocathode is placed. The photocathode with a Cs2Te photoemission layer is normal-conducting and cooled by liquid nitrogen. In the talk an overview of the technical concept, the RF properties, the photo cathode development, and beam parameter measurements will be given.

A room-temperature reaction between [Re₆S₈(OH)₆]⁴⁻ and acetic acid in an aqueous solution resulted in the substitution of all terminal hydroxo groups by acetate ligands, affording a new hexanuclear anionic rhenium cluster complex [Re₆S₈(CH₃COO)₆]⁴⁻. The complex was isolated as a potassium salt with the composition of K₄[Re₆S₈(CH₃COO)₆]·8H₂O (1) and characterized by X-ray single-crystal diffraction and elemental analyses, IR, ¹H NMR, UV–Vis, and luminescence spectroscopies.

We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles > 10° degrees, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180° degrees) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.

A sophisticated coligand strategy is presented for peptide-derived radioconjugates based on ^99mTc '4 + 1' mixed-ligand complexes. The new pharmacologically active coligands are assessed for ^99mTc-labeling of the RGD-peptide cyclo(Arg-Gly-Asp-D-Tyr-Lys) which is an established vehicle to target a_vß₃ integrins playing a crucial part in tumor pathogenesis.
Complexes of the general formula [^99mTc(NS₃R)X] were synthesized and evaluated, in which Tc(III) is coordinated by NS₃R, a derivative of the tetradentate chelator 2,2´,2´´-nitrilotriethanethiol (NS₃), and by X, a monodentate binding isocyanide bearing the biomolecule. The novel tetradentate chelators (NS₃R = NS₃crown, NS₃en, NS₃(COOH)₃) constitute NS₃ with a crown ether, an amine or a tricarboxylic acid as pharmacological modifiers. The isocyanides (X = L2-RGD, L2-Lys) contained the linker isocyanobutanoic acid (L2) coupled to N⁶-Lys of the RGD-peptide and additionally to a single Lys.
The lipophilicity (distribution coefficient log D_O/W, pH = 7.4) of the RGD-containing radiotracers decreased in the order of the coligands NS₃crown (-1.7 +/- 0.1), NS₃en (-2.7 +/- 0.1) and NS₃(COOH)₃ (-3.3 +/- 0.1). In the same order of the coligands, the biodistribution of the series [^99mTc(NS₃R)(L2-RGD)] in normal rats showed a decrease of hepatobiliary and an increase of urinary excretion.
The ratio of specifically to unspecifically uptaken activity (sum of surface bound and internalized activity) in a_vß₃ integrin-expressing M21 cells was in the range of approximately 4-5 and comparable for all [^99mTc(NS₃R)(L2-RGD)] tracers. The biodistribution of [^99mTc(NS₃en)(L2-RGD)] in v/v mice bearing M21 and M21L (control) tumor xenografts exhibited a specific tumor uptake with a low target-background ratio.
The metabolic stability of the [^99mTc(NS₃R)(L2-RGD)] tracers in normal rats was high, since 75-87% of the radioactivity in the plasma extract was assigned to the injected radiotracers 60 min after intravenous
application in a rat. The hypothetical metabolites [^99mTc(NS₃R)(L2-Lys)] were not found.
These results demonstrate a considerable improvement of in vivo properties of ^99mTc '4 + 1' peptide conjugates and open up the possibility of applying the labeling approach for further radiodiagnostic peptides.

The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces.
Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes.
For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3^-, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system.
The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered.
A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important.
A significant different surface complexation is observed for Al2O3. The formation of innerspheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested.
The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces.
In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2 ^+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes.
The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.

The self-organisation of periodic pattern on (001)Ge by bombardment with different heavy ion species (Bi+, Bi++, Bi2+, Bi3+, Bi3++) obtained from a liquid metal ion source in a mass separating 30 kV FIB system was studied. Aspect ratios exceeding values reported so far for elemental semiconductors substantially were found after cluster irradiation. An excellent regular self-ordering of dot (40 nm in height, interdistance of ~50 nm) and ripple pattern was achieved. Despite of high ion fluence, Raman measurements prove a crystalline surface layer. This result deviates drastically from monomer irradiation, where similar to former ion irradiation of Ge a spongy amorphous surface layer is formed. For the transition from the usual behaviour to the unexpected pronounced pattern formation a threshold of the energy density deposited by the collision cascade was identified: If the deposited energy density exceeds the melting threshold, dot or ripple pattern appear. In our model we assume that the ion-impact-induced deposition of energy per volume (estimated by SRIM) must exceed the energy needed for melting. Thus, Bi segregation during re-solidification of the melted pool and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.

Hauszeitung des FZD

The effect of rare-earth clustering in dielectric media on the electroluminescence (EL) intensity, the charge trapping and the EL quenching was investigated using the example of Tb and Eu-implanted SiO₂ layers. It was shown that the increase in the REO_X cluster size induced by an increase in the furnace annealing temperature resulted in an increase in the concentration of electron traps with capture cross sections from 2 x 10^-15 to 2 x 10^-18 cm². This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO₂ matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE³⁺ ions. For the main EL lines of Tb³⁺ and Eu³⁺ ions the relation of the EL quenching to negative and positive charge generation in the SiO₂ was considered. It was demonstrated that in case of REO_X nanoclusters with small sizes (up to 5 nm) the E!
L quenching process can mainly be explained by a defect shell model which suggests the formation of negatively charged defect shells around the nanoclusters leading to a Coulomb repulsion of hot electrons and a suppression of the RE³⁺ excitation. At high levels of the injected charge (more than 2 x 10²⁰ e/cm²) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO₂ at a distance beyond the tunneling distance from the SiO₂-Si interface. In case of Eu-implanted SiO₂ the quenching of the main EL line of Eu³⁺ is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu³⁺ line is proposed. (C) 2010 American Institute of Physics.

In many technological processes involving liquid metals or semiconductor melts the velocity fields cannot be measured due to the lack of commercial measuring techniques for opaque melts. We present two measuring techniques which have proven recently as providing reliable velocity measurements in liquid metals, at least in the temperature range up to about 700°C: the ultrasonic Doppler Velocimetry (UDV) and the contactless inductive flow tomography (CIFT). UDV is capable of delivering velocity profiles along the ultrasonic beam with a time-resolution of about 20 Hz. CIFT is based on the flow-induced modification of some externally applied magnetic field, which is measured by some array of magnetic field sensors outside of the melt. We present measurements with both techniques at the small-scale liquid metal model Mini-LIMMCAST of the continuous steel casting process. Both measuring methods give consistent results for the jets evolving from the nozzle outlets.

The standard model of rare-earth magnetism assumes that magnetic anisotropy is mainly caused by single-ion effects. The importance of two-ion anisotropy is still disputed. For a number of materials this two-ion anisotropy is in the same order of magnitude and strongly influences the magnetic properties. Single crystalline Tb₅Ge₃ has a high moment and low symmetry and, because of this, a large anisotropy is expected. In the present study the influence of the two-ion interaction was investigated. Magnetization and magnetostriction were measured in high magnetic fields up to 60 T. The magnetic phase diagram constructed for the main crystallographic directions shows antiferromagnetism in zero field and a number of magnetic phases at higher fields. The exchange interaction was evaluated based on a model calculation of these phase diagrams. We conclude that a huge anisotropy in the two-ion interaction is present, which overwhelms the single-ion effects.

Mn doped Ge (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior is entirely different from the GaAs:Mn system [1], the prototype of a ferromagnetic semiconductor.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic Ge substrates, at 350 °C (resulting in Mn5Ge3 clusters) and -40 °C (without precipitates) [1-4]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, flash lamp and pulsed laser annealing (PLA) has been applied. We obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [1]; (2) nanocrystalline Mn5Ge3 embedded inside the Ge matrix [2]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [3]. Indeed all samples show p-type conductivity with a hole concentration ranging from 1018 to 1020 cm³. The highest concentrations above 1020 cm³ can only be achieved by PLA. In the sample with the largest hole concentration of 2.1×1020 cm³, we observed a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K [3, 4]. We argue that the hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn [4]. In addition to the compatibility to Si technology, ion implantation followed by PLA is an established scalable chip technology and may have a significant industry impact.

[1] S. Zhou et al., APL, 95, 172103 (2009).
[2] S. Zhou et al., APL, 95, 192505 (2009).
[3] S. Zhou et al., PRB 81, 165204 (2010).
[4] S. Zhou et al., APL, in press (2010).

Manganese doped Germanium (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. In recent years, Ge:Mn thin layers as well as nanostructures have been fabricated, mostly by LT-MBE, and analyzed [1-4]. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior (magnetoresistance: MR, anomalous Hall effect: AHE) is entirely different from the GaAs:Mn system, the prototype of a ferromagnetic semiconductor. For instance, the previously reported AHE in Ge:Mn (i) was observed at temperatures above 10 K, (ii) but exhibited no hysteresis, and (iii) changed the sign of its slope. This behavior has been ascribed to Mn-diluted Ge [2, 4], Mn-rich spinodal decomposed phases [3] and MnGe precipitates [5], respectively. We argue that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 10¹⁹ cm^-3.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic, n-type Ge substrates, at 350 °C (resulting in Mn5Ge3 clusters) and -40 °C (without precipitates) [6-8]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, several annealing procedures have been applied, namely ms flash lamp annealing and nsec pulsed laser annealing with various optical fluences. By this systematic preparation, we obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [6]; (2) nanocrystalline Mn5Ge3 embedded inside the Ge matrix [7]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [8]. Indeed all samples show p-type conductivity with a hole concentration ranging from 10¹⁸ to 10²⁰ cm^-3. The highest concentrations above 1020 cm^-3 can only be achieved with the help of pulsed laser annealing. A careful characterization of structure, magnetic and transport properties, leads us to the following conclusions.

(1) From 20 to 10 K the resistance of samples with a hole concentration of >10¹⁸ cm^-3 increases in an activated manner with an activation energy of 4 meV, but below 10 K it saturates, i.e. the sample behaves metallic.
(2) We evoke the consideration of a two-band-like conduction in Ge:Mn. Above 10 K another conducting channel with different mobility is active, resulting in the drop of resistivity and the anomalous Hall resistance. The latter can be well described over a wide of parameters by considering two types of carriers with different mobility and population (see Ref. 6).
(3) In the sample with the largest hole concentration of 2×10²⁰ cm^-3, we observed, for the first time to our knowledge, a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K. This is our key result, shown in Fig. 1, and is a strong evidence for carrier-mediated ferromagnetism. Note however that considering mere magnetization data, ferromagnetism remains present up to >100 K.

In summary, we present the magnetic and magnetotransport properties of a series of Ge:Mn samples with hole concentrations ranging from 10¹⁸ to 2x10²⁰ cm^-3. The hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn, similar as is known for GaAs:Mn. A high-concentration co-doping with a shallow acceptor may allow to increase the hole concentration further, possibly resulting in a dramatically increased Curie temperature. In addition to the compatibility to Si technology, ion implantation followed by pulsed laser annealing is an established scalable chip technology and therefore may have a significant industry impact.

References:

[1] Y. D. Park et al., Science 295, 651 (2002).
[2] F. Tsui et al., Phys. Rev. Lett. 91, 177203 (2003).
[3] M. Jamet et al., Nature Mater. 5, 653 (2006).
[4] C. Zeng, et al., Phys. Rev. Lett. 100, 066101 (2008).
[5] O. Riss, et al., Phys. Rev. B 79, 241202(R) (2009).
[6] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009).
[7] S. Zhou et al., Appl. Phys. Lett. 95, 192505 (2009).
[8] S. Zhou et al., Phys. Rev. B (2010), submitted.

The III-V compound GaMnAs is considered as being the prototype diluted ferromagnetic semiconductor (FMS), exhibiting negative magnetoresistance (MR) and anomalous Hall effect (AHE) related to carrier-mediated ferromagnetism. However, it would be very desirable to have a group-IV FMS, being compatible with silicon technology. In particular manganese-doped germanium prepared using low-temperature molecular beam epitaxy (LT-MBE) has proven to be a very promising material [1]. Still, no direct correspondence between transport and magnetization data has been reported yet to date. The reported MR and AHE in Ge:Mn are likely caused by (super)paramagnetic Mn ions or precipitates or by two-band-like conduction [2]. We believe that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 10¹⁹ cm^-3, which indicates the possible unsuitability of LT-MBE to achieve a large hole concentration in Ge:Mn.

In this contribution, we show that the hole concentration can be increased by two orders of magnitude, from 10¹⁸ to 10²⁰ cm^-3, through Mn-ion implantation into Ge followed by pulsed laser annealing [3]. In Mn-doped Ge with a hole-concentration of around 2.1×10²⁰ cm^-3, we observe that the longitudinal (Fig. 1c) and the Hall (Fig. 1b) resistance exhibit the same hysteresis as the magnetization (Fig. 1a) at temperatures below 10 K. This hysteresis in magneto-transport is usually considered as a direct evidence of carrier-mediated ferromagnetism. In sharp contrast to this, such effects are absent in Mn-doped Ge with a smaller hole-concentration. Below 10 K, the resistance of Ge:Mn films is nearly constant, i.e., quasi metallic, while from 10 to 20 K it decreases steeply with an activation energy of 4 meV. The magnetic and magneto-transport properties can be qualitatively well explained within a picture of dopant segregation and the formation of bound magnetic polarons. We will present a comprehensive correlation between the magnetic, transport and structural properties of Ge:Mn samples with different hole concentrations, as well as a comparison with literature. Note that ion implantation followed by pulsed laser annealing is an established scalable chip technology and may have a significant industry impact.

[1] Y. D. Park et al., Science 295, 651 (2002); M. Jamet et al., Nature Mater. 5, 653 (2006).
[2] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009); Appl. Phys. Lett. 95, 192505 (2009).
[3] S. Zhou et al., Phys. Rev. B (2010), submitted.

Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr-precipitates in neutron irradiated Fe-12.5at%Cr alloy at the irradiation doses up to 12 dpa, fluence about 140 ndpa/s and T=300 C. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data [1,2] on the defect structure of this material irradiated at the doses of 0.6 and 1.5 dpa are used to calibrate the model. It was found the saturation behaviour of free vacancy and free SIA concentrations, number density of SIAC and Cr-precipitates volume fraction for neutron expose great than 0.006 dpa; strong peak of SIAC with the average diameter about 0.5 nm and presence of VC with radius less 0.5 nm.

We describe a two-step synthesis of pure multiwall MoS₂ nanotubes with a high degree of homogeneity in size. The Mo₆S₄I₆ nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H₂S/H₂ mixture leads to the MoS₂ nanotubes still grouped in hedgehog-like morphology. The described method enables a large scale production of MoS₂ nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo₆S₄I₆ nanowires and the MoS₂ nanotubes. The unit cell parameters of the Mo₆S₄I₆ phase are proposed. Blue shift in optical absorbance and metallic behaviour of MoS₂ nanotubes in two-probe measurement are explained by a high defect concentration.

We report on the generation of proton pulses with maximum energies exceeding 15MeV bymeans of the irradiation of few micron thick metal foils by ultrashort (30 fs) laser pulses at a power level of 100 TW. In contrast to the well known situation for longer laser pulses, here, a near linear scaling of the maximum proton energy with laser power can be found. Aiming for radiobiological applications the long and short term stability of the laser plasma accelerator as well as a compact energy selection and dosimetry system is presented. The first irradiation of in vitro tumour cells showing dose dependent biological damage is demonstrated paving the way for systematic radiobiological studies.

Die Strömung in der Metallschmelze hat einen wesentlichen Einfluss auf die Produktqualität beim Stranggießen. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Optimierung dieser Strömung basierte bisher vor allem auf numerischen Simulationen und Modellexperimenten mit Wasser. Obwohl die Strömungsuntersuchungen an diesen Wassermodellen signifikante Erkenntnisgewinne über die Strömung und die optimale Auslegung z. B. des Tauchrohrs oder der Eintauchtiefe des Tauchrohrs gebracht haben, stoßen diese Modelle für eine Reihe von Fragestellungen an ihre physikalischen Grenzen, da Flüssigmetalle z. B. sehr hohe Oberflächenspannungen und sehr kleine Prandtl-Zahl besitzen, und Wasser offensichtlich für Untersuchungen des Einflusses von Magnetfeldern völlig ungeeignet ist.
In den vergangenen Jahren wurden am Forschungszentrum Dresden-Rossendorf experimentelle Versuchsanlagen mit niedrig schmelzenden Legierungen für die physikalische Modellierung des Stranggussprozesses aufgebaut. Ziel ist die systematische Untersuchung der Flüssigmetallströmungen und Transportprozesse in Verteiler, Tauchrohr und Kokille. Dabei steht insbesondere die Wirkung elektromagnetischer Felder, wie sie in Form von elektromagnetischen Bremsen oder Rührern bereits im industriellen Einsatz sind, im Mittelpunkt. Außerdem bieten die Versuchsanlagen gute Bedingungen für die Erprobung neuer Messtechniken und Anlagenkomponenten. Die Versuchsanlage „CONCAST-LMM“ (Continuous Casting Liquid Metal Model) ist 2009 fertig gestellt worden und arbeitet mit einer Sn60Bi40-Legierung als Modellfluid im Temperaturbereich von 200°C bis 400°C. Ein kleineres Modell mit der eutektischen GaInSn-Legierung wird bei Raumtemperatur betrieben. Die Strömungseigenschaften werden mit Hilfe lokaler Sonden sowie modernen Ultraschall und elektromagnetischen Methoden vermessen.
Im Rahmen dieses Beitrages werden Strömungsmessungen in einer einphasigen Flüssigmetallströmung in der Kokille unter Einwirkung eines statischen Magnetfeldes vorgestellt und mit entsprechenden numerischen Simulationen verglichen. Es zeigt sich, dass das Magnetfeld den aus dem Tauchrohr in die Kokille austretenden Jet ablenkt und lokale Rezirkulationsgebiete verstärkt. Die bremsende Wirkung des Magnetfeldes stellt sich als äußerst komplex dar. Eine gleichmäßige Reduktion der Strömungsgeschwindigkeit im gesamten Volumen wird nicht beobachtet.

Near equiatomic and Ti-rich Ni–Ti polycrystalline films have been deposited by magnetron co-sputtering using a chamber installed at a synchrotron radiation beamline. The in situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during film processing.
The depositions on a 140 nm amorphous SiO2 buffer layer heated at 520°C (without applying bias voltage, Vb, to the substrate) led to a preferential growth of <100> oriented grains of the Ni–Ti B2 phase from the beginning of film growth until the end of the deposition.
Films exhibiting a preferential growthof <110> oriented grains of the Ni–Ti B2 phase from the beginning of the deposition were obtained (without and with a Vb of - 45 V) by using a TiN coating with a topmost layer formed by <111> oriented grains. Those trends have been observed for the growth of near equiatomic (~50.0 at.% Ti–Ni) and Ti-rich (~50.8 at.% Ti–Ni) Ni–Ti films.
Additionally, an ion gun had been commissioned, which allows ion bombardment during sputter deposition or post-deposition ion irradiation. In this first series of experiments, a Ni–Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e., avoiding surface oxide formation), thus modifying deliberately the microstructure of the film locally.

This workshop focus on the electrical characterization of vertical and horizontal Si nanowires.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface
potential. Since KPFM was developed in 1991 the measured KPFM signal was attributed to the contact potential difference (CPD) between conductive probe and sample. We show that the CPD is not suitable to describe the measured Kelvin bias in semiconductors quantitatively and introduce a unique KPFM model [1] which successfully correlates the measured Kelvin bias with the difference between Fermi energy and respective band edge. Quantitative dopant profiling is demonstrated on cross-sectionally prepared Si epilayer structures and on a Si dynamic random access memory cell.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80 (2009) 085305.

Arsenic-doped ZnMgO films were fabricated on SiO₂ by the radio frequency magnetron sputtering technique at different substrate temperatures during growth. The yielded films were characterized by room temperature Hall measurement, x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, secondary ion mass spectroscopy, nuclear reaction analysis and low-temperature photoluminescence. As-doped samples grown at low substrate temperature (350 degrees C) were n-type conducting (n similar to 10¹⁸ cm^-3), with evidence showing that the hydrogen impurity was an important shallow donor associated with the observed n-type conduction. Conversion of n-type to p-type conduction being observed at the substrate temperature of similar to 400 degrees C was associated with the formation of the As_Zn(V_Zn)₂ shallow acceptor complex and the drastic reduction of the hydrogen content.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to locally doped semiconductors. Quantitative dopant profiling by means of KPFM is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions [2].
In addition, the frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer on top [3]. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

Failure analysis and optimization of nanoelectronic devices demand knowledge of their electrical properties. Especially, quantitative profiling of dopant concentrations is essential for process and device engineering in semiconductor industry. The most straightforward nanometrology technique is the Kelvin probe force microscopy (KPFM) where electrostatic forces are detected.
Quantitative dopant profiling by means of KPFM measurements is successfully shown on a conventional static random access memory (SRAM) cell and on
cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different pulsed laser annealed Mn-implanted Ge samples by revealing a strong variation of the Fermi level position on the micrometer scale in dependence on
the annealing conditions after Mn implantation [2].
In addition, the frequency dependence of the KPFM bias is discussed. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, the frequency dependence is samplespecific and KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor are
probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm,
and H. Schmidt, Phys. Rev. B 81 (2010), 165204.

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to locally doped semiconductors. Quantitative dopant profiling by means of KPFM is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions [2].
In addition, the frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer on top [3]. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).

A combined experimental and theoretical study is presented revealing the influence of metal-molecule coupling on electronic transport through single-molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current-voltage characteristics to a single-level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal-molecule coupling. The values found for these parameters are rationalized with the help of density-functional-theory-based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.

The behavior of particles driven through a narrow constriction is investigated in experiment and simulation. The system of particles adapts to the confining potentials and the interaction energies by a self-consistent arrangement of the particles. It results in the formation of layers throughout the channel and of a density gradient along the channel. The particles accommodate to the density gradient by reducing the number of layers one by one when it is energetically favorable. The position of the layer reduction zone fluctuates with time while the particles continuously pass this zone. The flow behavior of the particles is studied in detail. The velocities of the particles and their diffusion behavior reflect the influence of the self-organized order of the system.

The mechanically controllable break junction technique is used to study charge transport through suspended DNA molecules. The current-voltage (I-V) characteristics in an aqueous solution display series of negative differential resistance (NDR) and hysteresis behavior. Under high-vacuum conditions, the peak positions of NDR shift to lower voltage, and the amplitude is reduced dramatically. The observed NDR behavior is consistent with the polarization mechanism in DNA molecular junctions, which demonstrates a change in the coupling of the molecular level to a polaron mode under different environment.

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Talk on the status of laser proton acceleration and online dosimetry with respect to radiobiological applications.

In this article, dispersed flow of viscous oil and water is investigated. The experimental work was performed in a 26.2-mm-i.d. 12-m-long horizontal glass pipe using water and oil (viscosity of 100 mPa.s and density of 860 kg/m³) as test fluids. High-speed video recording and a new wire mesh sensor based on capacitance (permittivity) measurements were used to characterize the flow. Furthermore, holdup data were obtained using quick-closing-valves technique (QCV). An interesting finding was the oil-water slip ratio greater than one for dispersed flow at high Reynolds number. Chordal phase fraction distribution diagrams and images of the holdup distribution over the pipe cross-section obtained via wire-mesh sensor indicated a significant amount of water near to the pipe wall for the three different dispersed flow patterns identified in this study: Oil-in-water Homogeneous Dispersion (o/w H), Oil-in-water Non-homogeneous Dispersion (o/w NH) and Dual continuous (Do/w & Dw/o). The phase slip might be explained by the existence of a water film surrounding the homogeneous mixture of oil in water in a hidrofilic-oilfobic pipe.

Marangoni convection is involved in many technological processes. The substances of industrial interest are often governed by diffusive heat transport and their physical modelling is limited with respect to the Prandtl number Pr. The present paper addresses this deficiency. Studies were made on molten salts having Pr values in an intermediate range well below that of the typically employed organics. Since some of the selected species have a relatively high melting point, a high-temperature facility which allows studying thermocapillary convection at temperatures in excess of 1000°C was built. The results presented here were obtained in a cylindrical geometry, although the equipment that was built is not restricted to this configuration because of its modular construction. Modelled after some applications, the fluid was heated centrically on top. The bulk was embedded in a large thermostatically controlled reservoir so as to establish the lower ambient reference temperature. A characteristic size of the experimental cell was chosen such that, on the one hand, the dynamic Bond number Bo did not become too high; on the other hand, the liquid had to have a certain depth to allow particle image velocimetry. The complicated balance between body forces and thermocapillary forces in the case of intermediate Bo was found to result in a distinct local separation into a bulk motion governed by natural convection with a recirculating Marangoni flow on top. In contrast to low viscosity organics, the vapour pressure of which increases considerably with decreasing Pr, high values of the Marangoni number can be reached. Comparisons of the topology of Marangoni vortices between molten salts with 2.3 <= Pr <= 6.4 and a silicone oil with Pr typically one order of magnitude higher suggest that the regime of non-negligible heat diffusion is entered.

This contribution aims at introducing a new multiscale, multicomponent CFD/CMFD approach for the simulation of thermal-hydraulics flows evolving in complex component-scale configurations. In this novel approach, the flow system could involve one or two fluids, convective and conductive heat transfer in solids, and phase-change heat transfer. This is made possible thanks to the Immersed Surfaces Technology (IST), a methods inspired from Interface Tracking techniques for two-phase flow, whereby solid bodies contained in the system are defined using a solid level set function to describe their surfaces, transcending conventional unstructured and body-fitted grids (BFC). In a typical two-phase flow, material properties of the fluids and the solid are segregated based on the gas-liquid and solid Level-Set functions. The technique helps solve conjugate heat transfer problems without resorting to explicit jump conditions. Selected validation test-cases are presented here. The main application includes steady and transient solutions of the boron dilution in the ROCOM test case.

Systematic evolution of the 400 nm electroluminescence (EL) with increasing flash lamp annealing (FLA) temperature from 800 to 1100 °C in an Er-doped Ge-rich metal-oxide semiconductor structure is presented. No significant change in the 1535 nm Er EL is observed with increasing FLA temperature. Enhancement of the 400 nm EL decay time with rising FLA temperature is found to be associated with recrystallization of the damaged Ge clusters in the absence of Ge outdiffusion. The 400 nm EL quenching with continuous charge injection process is also discussed within the device operation time.

The investigation of the correlations between magnetic and lattice degrees of freedom provides a better understanding of the underlying physics of frustrated and low-dimensional spin systems. Ultrasound experiments are proven to be a powerful tool to probe the spin-lattice interactions and lattice instabilities. Here, we will present some recent outcome of our ultrasound studies performed at high magnetic fields. We report results of our investigations of the frustrated spin system CdCr₂O₄ [1]. This material shows a wide magnetization plateau, from 28 to 58 T, at one half of the full moment of S = 3/2 Cr³⁺. We further present results for the low-dimensional quantum antiferromagnets Cs₂CuCl₄ [2] and NiCl₂-4SC(NH₂)₂ [3]. The spin-strain coupling is discussed in frame of the exchange-striction mechanism.

Recently, the new skutterudite superconductor PrPt₄Ge₁₂ with the comparably high transition temperature of T_c = 7.9 K was discovered [1]. First experiments gave evidence for strong coupling and hint at point-like nodes of the order parameter [2]. The Sommerfeld coefficient is rather low and indicates that PrPt₄Ge₁₂ is not a heavy-fermion superconductor. Here, we present results of a de Haas-van Alphen (dHvA) study performed on a high-quality single crystal. Several dHvA frequencies could be resolved over a broad angular range. The small band-resolved effective masses (less than half the free-electron mass) confirm the non-heavy-fermion character of the electron system. To get insight into the nature of the mass renormalization, the experimental data are compared with state-of-the-art band-structure calculations

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Vanadium doped ZnO thin films (Zn1−xVxO, where x=0.05 or x=0.13) were grown on c-cut sapphire substrates using pulsed laser deposition technique. Their structure and magnetic properties were examined in relation to the doping concentration. All deposited films were highly oriented along the c-axis and exhibited ferromagnetic behavior with a Curie temperature up to 300 K. The crystal structure was found to be better for layers with lower vanadium concentration. The films had a porous fine-grained microstructure and a column-like character as the V concentration was reduced. A weak dependence of magnetization on temperature was observed. The saturation magnetization was found to be strongly dependent on the crystal structure, grain size and V-ion concentration.

We report on high-field magnetization, specific-heat and electron spin resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz)₂(HF₂)]PF₆. The frequency-field diagram of ESR modes below T_N \approx 4.38 K is described in the frame of the mean-field theory. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the inter/intra-plane exchange-interaction ratio, J'/J = 1/16. It is argued that despite of onset of 3D long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations.

In this paper detailed studies on modification of structural and magnetic properties of Ni-doped hafnium oxide (HfO2) thin films are reported. We used 200 keV Ni beam for doping of Ni. For homogeneous dispersion and activation of doped Ni ions, 120 MeV Ni swift heavy ions (SHI) irradiation was used. This unique combination of Ni doping by ion beam and dispersing and activating by Ni SHI irradiation of HfO2 films is reported for the first time. The origin of ferromagnetism in the Ni-doped HfO2 thin films is investigated. We demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization versus temperature data. Rutherford backscattering data are used to establish that Ni ions are implanted in the HfO2 matrix at the predicted location. Dispersion of implanted Ni and lattice defects such as oxygen vacancies are attributed to be the main source of ferromagnetism.

Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Using THz-range FEL- and BWO-based electron spin resonance (ESR) spectroscopy techniques, the frequency-field dependence of magnetic excitations in the hexagonal multiferroic YMnO₃ in the antiferromagnetically (AFM) ordered phase has been studied. A slope of the frequency-field dependences of AFM resonance modes, ~ 0.5 cm⁻¹/T, is explaned in terms of the triangular AFM model. A gap in the excitation spectrum, ~ 42 cm−1, was observed directly. A fine structure of AFM resonance absorption observed by as is a clear signature of a finite interaction between the neighboring Mn³⁺ layers. The interplane exchange interactions constants, J₁ = -510 mK and J₂ = -350 mK, have been estimated.

Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H shell burning. In particular, the strengths of low-energy resonances with E < 200 keV in 25Mg(p,gamma)26Al determine the production of 26Al and a precise knowledge of these nuclear data is highly desirable. Absolute measurements at such low-energies are often very difficult and hampered by gamma-ray background as well as changing target stoichiometry during the measurements. The latter problem can be partly avoided using higher energy resonances of the same reaction as a normalization reference. Hence the parameters of suitable resonances have to be studied with adequate precision. In the present work we report on new measurements of the resonance strengths omega_gamma of the E = 214, 304, and 326 keV resonances in the reactions 24Mg(p,gamma)25Al, 25Mg(p,gamma)26Al, and 26Mg(p,gamma)27Al, respectively. These studies were performed at the LUNA facility in the Gran Sasso underground laboratory using multiple experimental techniques and provided results with a higher accuracy than previously achieved.

We have investigated low-temperature elastic properties of PrMg₃ with a non-Kramers Gamma₃ doublet ground state using ultrasonic measurements. Although the Gamma₃ doublet possesses electric quadrupoles O_u and O_v with Gamma₃-symmetry and magnetic octupole T_xyz with Gamma₂, PrMg₃ reveals no sign of symmetry breaking long-range ordering down to 20 mK. [1] The elastic constant of (C₁₁-C₁₂)/2 in PrMg₃ exhibits remarkable softening below 8 K, which is well described in terms of a Curie-type quadrupole susceptibility for the Gamma₃ doublet. An appreciable upturn in (C₁₁-C₁₂)/2 below 800 mK in PrMg₃ may indicate an transition into an exotic ground state due to the quadrupole Kondo state being screened by conduction electrons. Frequency dependence in (C₁₁-C₁₂)/2 and its attenuation coefficients at low temperature in PrMg₃ suggests quadrupole fluctuations possessing a characteristic relaxation time tau = tau₀exp(E/kT) with tau₀ = 6x10^-11 sec and an activation energy E = 410 mK. The low-temperature behavior in (C₁₁-C₁₂)/2 of PrMg3 under magnetic fields is also presented.

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The nuclear data needs for underground accelerators will be reviewed, with a focus on the present and future LUNA program.

The 14N(p,g)15O reaction is the bottleneck of the carbon-nitrogen-oxygen (CNO) cycle, thus determining its speed. The precise knowledge of its cross section is necessary to address the recently discovered discrepancy for elemental abundances in the standard solar model, the so-called solar abundance problem. Several experimental efforts are underway to improve the precision, among them lifetime measurements of excited states in the 15O compound nucleus. The seminar talk will report on a different approach, namely a direct cross section measurement at comparatively high energy, 0.5-1.5 MeV, recently performed at the Dresden Tandetron.

The linear stability of magnetohydrodynamic Taylor-Couette flows in axially unbounded cylinders is considered for magnetic Prandtl number unity. Magnetic background fields varying from purely axial to purely azimuthal are imposed, with a general helical field parametrized by beta=B-phi/B-z. We map out the transition from the standard magnetorotational instability (MRI) for beta=0 to the nonaxisymmetric azimuthal magnetorotational instability for beta ->infinity. For finite beta, positive and negative wave numbers m, corresponding to right and left spirals, are no longer degenerate. For the nonaxisymmetric modes, the most unstable mode spirals in the opposite direction to the background field. The standard (beta=0) MRI is axisymmetric for weak fields (including the instability with the lowest Reynolds number) but is nonaxisymmetric for stronger fields. If the azimuthal field is due in part to an axial current flowing through the fluid itself (and not just along the central ax! is), then it is also unstable to the nonaxisymmetric Tayler instability which is most effective without rotation. For purely toroidal fields the solutions for m=+/- 1 are identical so that in this case no preferred helicity results. For large beta the wave number m=-1 is preferred, whereas for beta less than or similar to 1 the mode with m=-2 is most unstable. The most unstable modes always spiral in the same direction as the background field. For background fields with positive and not too large beta the kinetic helicity of the fluctuations proves to be negative for all the magnetic instabilities considered.

Purpose: Before the novel technology of laser-based particle acceleration can be used for clinical applications, several requirements have to be fulfilled. These are the supply of stable and reliable particle beams with reproducible properties, sufficient particle intensity and useable energy spectra. Additionally, a precise dose delivery in an appropriate time and the exposure of a desired irradiation field are needed. Beside these demands, consequences on dosimetry as well as on the radiobiological effect have to be investigated for ultra-short pulsed laser-accelerated particle beams. Method andMaterials: The joint project onCOOPtics, an interdisciplinary and multicenter institution focusing on the development of a laser particle accelerator for radiation oncology, is introduced. The worldwide first systematic in vitro irradiations with laser-accelerated electrons performed with the JeTi laser system will be presented focusing on the experimental setup, practical experiences and on dosimetric and radiobiological results. In a next step, cell irradiation experiments with laser-accelerated protons have been prepared. Therefore, a dedicated dosimetric system was developed. It is integrated into a device that can be installed at different laser and conventional accelerators and serves also as cell or animal irradiation device. Results: A laser accelerator was successfully optimized for systematic radiobiological experiments performed over 3 months. No significant differences between laser-accelerated and conventional 6 MeV electron beams were found. An integrated dosimetry and cell irradiation device for systematic in vitro and in vivo experiments with laser-accelerated protons was developed, characterized, calibrated and successfully tested with both continuous and pulsed proton beams. Cell irradiations with protons have been started. Conclusion: Laser accelerators can be used for radiobiological experiments, meeting all necessary requirements like homogeneity, stability and precise dose delivery. Nevertheless, before fulfilling the much higher requirements for clinical application, several improvements concerning i.e. proton energy, spectral shaping and patient safety are necessary. Supported by BMBF (03ZIK445).

Self-organization at the nanoscale is a key issue in modern material science as it promises a potential route to commercially scalable production of functional nanomaterials. Here we present the growth-structure study of self-organized layered arrays of carbon encapsulated Ni nanoparticles grown by means of pulsed filtered cathodic vacuum arc deposition. Influence of the oblique ion incidence and Ni content on the film morphology is investigated. The film morphology has been determined by transmission electron microscopy (TEM) and grazing incidence small angle x-ray scattering (GISAXS) while C/Ni ratio was determined by means of nuclear reaction analysis. The C:Ni films with the Ni content in the range of ~6-50 at.% are considered. The results show that for the perpendicular incoming depositing ion incidence the C:Ni film structure consists of alternating self-organized nickel carbide and carbon layer oriented parallel to the film surface. However, for the oblique ion incidence the layered structure tilts in relation to the surface. The tilting angle and periodicity strongly depends on the deposition angle as well as on the Ni content. Combined TEM and GISAXS analysis shows that the film cross-sections can be described by two density modulation waves advancing with the growing film surface – one towards the incoming ions, another one with the weaker amplitude moving in roughly perpendicular direction. The results are discussed on the basis of the interplay between thermodynamically driven phase separation and energetic ion induced ballistic effects. Such structures show significant anisotropy which can be considered for tribological, optical, magnetic or magnetotransport applications.

(i)PVD growth of carbon-transition metal nanocomposites: from energetic condensation to periodic precipitation patterns

The recently claimed observations of non-negligible amounts of 6Li in old halo stars have renewed interest in the Big-Bang Nucleosynthesis (BBN) of 6Li. One important ingredient in the predicted BBN abundance of 6Li is the low-energy D(alpha,gamma)6Li cross section. Up to now, the only available experimental result for this cross section showed an almost constant astrophysical S-factor below 400 keV, contrary to theoretical expectations. We report on a new measurement of the D(alpha,gamma)6Li reaction using the break-up of 6Li at 150 A MeV. Even though we cannot separate experimentally the Coulomb contribution from the nuclear one, we nd clear evidence for Coulomb-nuclear interference by analyzing the scattering-angular distributions. This is in-line with our theoretical description which indicates a drop of the S24-factor at low energies as predicted also by most other models. Consequently, we find even lower upper limits for the calculated primordial 6Li abundance than before.

The so called “double-heterogeneity”, characterizing High Temperature Gas cooled Reactors (HTGR) block type fuel elements, presents a challenge for existing deterministic lattice codes that were originally developed for LWR applications. A large number of TRISO particles randomly dispersed in the fuel compact introduces an additional complexity into the modeling. The Monte Carlo (MC) based codes, which are capable of simulating complex geometries of HTGR fuel elements, are mainly used for the reference calculations. The use of MC codes as production tools for a few-group cross section generation for 3D nodal codes is still very limited due to the high computational costs.
Recently a new few-group cross section generation methodology for a full core analysis of HTGRs was proposed. This methodology is based on homogenization approach called Reactivity equivalent Physical Transformation (RPT). The RPT methodology combines high spatial resolution of MC codes with superior computational speed of deterministic lattice codes. At the first stage, a MC code is used to simulate an HTGR fuel element with explicitly described TRISO particles at the beginning of life (BOL) and at the nominal operational conditions. At the second stage the TRISO particles are homogenized with the fuel compact graphite to get rid of double-heterogeneity problem. It is well known that a simple volume-weighted homogenization of TRISO particles in the graphite matrix results in the underestimation of the self-shielding effect. However, according to the RPT approach, TRISO particles are homogenized in a smaller central volume rather than in entire fuel compact. The volume of the smeared region is adjusted in such way that k-inf of homogenized geometry matches that of the reference heterogeneous one obtained from MC reference calculations. Since the radius of the smeared zone was determined at the beginning of life (BOL) it is kept constant and is used for depletion and branch-off calculations by lattice codes.
The main disadvantage of the RPT approach is the fact that TRISO particles are smeared together with the compact graphite and constitute one homogeneous material. Keeping in mind that the fuel and graphite temperatures may significantly vary during the reactor operation, these temperatures should be decoupled during a few-group cross section generation. However in the majority of lattice codes temperatures are assigned to the regions (e.c. HELIOS code) or to the homogeneous materials (e.c. CASMO code) rather than to particular nuclides like in the MC codes. In order to overcome this disadvantage the RPT methodology has been modified in a way that only TRISO particles are smeared in the central compact region while all compact graphite is concentrated in the remained outer compact region. This modification allows assigning different temperatures to the fuel and as well as to the compact matrix graphite.
The main objective of this study is to verify the modified RPT methodology. A set of depletion calculations of a prismatic block-type HTGR fuel lattice of fuel and coolant channels was performed. Two models of prismatic fuel assembly are considered: 1) 3D model with explicitly described TRISO particles; 2) 2D model, in which TRISO particles are homogenized using the modified RPT approach. 3D calculations are performed with MCNP based depletion code BGCore. 2D calculations are carried out with BGCore code and deterministic lattice code HELIOS 1.9. The comparison between 3D and 2D results is reported. Conclusions regarding validity of modified RPT approach are drawn.

DYN3D is an advanced nodal code for the three-dimensional steady-state and transient analysis of LWR cores with quadratic and hexagonal fuel assemblies. Although a new version of DYN3D for the simulation of block type High Temperature Gas cooled Reactors (HTGR) is currently under development, the main objective of this work is to demonstrate the applicability of the standard DYN3D version for the steady-state analysis of HTGR core. A preliminary reactor physic analysis procedure in which few group cross section sets are generated using HELIOS 1.9 transport lattice code and full core calculations are performed by DYN3D will be established. The Reactivity equivalent Physical Transformation (RPT) approach will be applied in order to eliminate the double-heterogeneity of HTGR fuel elements in HELIOS calculations. The full core analysis of the reference simplified HTGR core will be performed with DYN3D using macroscopic nodal cross sections provided by HELIOS. At this stage thermo-hydraulic feedback is not considered. The results of DYN3D calculations such as neutron multiplication factor, radial and axial power distribution, will be compared with those obtained from reference full core MCNP simulation.

Die Verwendung von Th-basierten Brennstoffkreisläufen als Alternative zum U-Brennstoffkreislauf wurde ausgiebig in den Anfangsjahren der Kernenergienutzung zwischen Mitte der 1950er und Mitte der 1970er Jahre erforscht. Obwohl der Nachweis zur Nutzung von Th in einer Reihe von thermischen und schnellen Systemen erbracht wurde, ist es nicht zur kommerziellen Anwendung von Th-Brennstoffen gekommen, bis das Interesse an Th-Brennstoffkreisläufen in den 1980er Jahren schließlich einschlief, vor allem wegen der großen Uranreserven und der Furcht vor nuklearer Proliferation. Die neuerliche Wiederbelebung des Interesses an Th-Kreisläufen, insbesondere in kommerziell betriebenen Druckwasserreaktoren (DWR), ist in erster Linie auf ihr Potential zur Lösung von Proliferationsrisiken, bei der Schonung natürlicher Uranvorkommen und bei der Entsorgungsproblematik im konventionellen Urankreislauf zurückzuführen. Der vorliegende Artikel gibt eine Übersicht über einige der neuesten Studien, die sich mit Implementierungsszenarien und den zu erwartenden Vor- und Nachteilen von Th-basierten Brennstoffen in der aktuellen DWR-Generation auseinandersetzen.

The synthesis of transparent conductive oxides (TCO) with high transmittance in the near infrared (IR) spectral range is a key requirement for increasing the power conversion efficiency in thin film solar cells. As the absorption at energies close to the Si band gap (1.1 eV) is caused by the free electron plasma it is necessary to maximize their mobility at moderate densities (~5x10²⁰ cm^-3) in order to simultaneously reach low resistivities of ~2x10^-4 Ohm*cm and improve the IR transmittance.
Therefore a reactive magnetron sputtering method using metallic Zn/Al alloy targets was developed to achieve high carrier mobilities (~45 cm²/Vs) in ZnO:Al thin films. The influence of growth temperature, oxygen partial pressure and target Al concentration on the electrical film properties has been investigated systematically by Hall effect measurements.
Additionally XRD, X-TEM, AFM, ERDA, RBS and spectroscopic ellipsometry were employed to reveal film structure, composition and optical properties. The experimentally observed limit of mobility in polycrystalline ZnO:Al is discussed in terms of ionized impurity scattering and clustering as well as grain boundary limited transport.

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The magnetoconductance of an open carbon nanotube (CNT)-quantum wire was measured in pulsed magnetic fields. At low temperatures, we find a peculiar split magnetoconductance peak close to the chargeneutrality point. Our analysis of the data reveals that this splitting is intimately connected to the spin-orbit interaction and the tube chirality. Band-structure calculations suggest that the current in the peak regions is highly spin polarized, which calls for application in future CNT-based spintronic devices.

Low-energy magnetic excitations in the S= 1/2 chain compound [(C₆H₉N₂)CuCl₃]CuCl₃ [known as (6MAP)CuCl₃] are probed by means of tunable-frequency electron spin resonance. Two modes with asymmetric (with respect to the hnu =gµ_BB line) frequency-field dependences are resolved, illuminating the striking incompatibility with a simple uniform S= 1/2 Heisenberg chain model. The unusual ESR spectrum is explained in terms of the recently developed theory for S= 1/2 chains, suggesting the important role of next-nearest-neighbor interactions in this compound. Our conclusion is supported by model calculations for the magnetic susceptibility of (6MAP)CuCl₃, revealing a good qualitative agreement with experiment

Reactive pulsed magnetron sputtering (RPMS) is employed to grow Al-doped ZnO (AZO) films on fused silica and epitaxially on Al2O3(001). The RPMS process window for obtaining highly transparent and conductive AZO with high mobility and the influence of process parameters such as oxygen partial pressure and substrate temperature are discussed. It is shown that the optimum electrical properties depend stronly on the Al concentration of the sputtering target and that mobility on fused silica is limited to about 45 cm²/Vs. The relations between depostion conditions and film microstructure, stochiometry and electrical properties are investigated, pointing to an enrichment of Al with increasing substrate temperature leading to a deterioration of crystalline structure and carrier mobility.
Finally the observed limitations of electrical properties are categorized and discussed in terms of ionized impurity scattering and grain boundary limited transport.

In this paper we consider various issues of design, fabrication, and performance of non-destructive pulsed magnets at the Dresden High Magnetic Field Laboratory. Currently, a variety of pulsed magnets are in operation in the laboratory. A 70 T/8.5 MJ magnet, having a 24 mm bore and generating field pulses of about 150 ms duration serves as a workhorse for external users and for in-house research. Smaller 60–65 T/1.5 MJ magnets with a bore of 20 mm and pulse duration of 25 ms have been proven to be very reliable in operation. In addition, a new 90 T/9MJdual-coil magnet has recently achieved 87.2 T in a 20 mm bore. A 60 T/43 MJ longpulse magnet is currently tested. Questions of magnet longevity, coil monitoring, as well as magnetic-field measurements are addressed. Further magnet-technology developments and the route to 100 T are discussed.

Results of ac-susceptibility, specific-heat, magnetization, and electron-spin-resonance studies of a [Gd₂(fum)₃(H₂O)₄]·3H₂O (fum=fumarate, C₄H₂O₄) powder samples are reported. The results of these measurements enabled us to identify the studied compound as a three-dimensional S = 7/2 Heisenberg magnet with T_N = 0.19 K and dominant crystal-field anisotropy. The susceptibility studies conducted at audio frequencies and temperatures from 2 to 30 K revealed that the application of static magnetic fields induces a slow spin relaxation. The relaxation is not associated with an anisotropy energy barrier and is explicable assuming resonant phonon trapping. The magnetic field dependence of the relaxation time is consistent with the proposed scenario and suggests that a strong spin-lattice interaction may be the mechanism governing the relaxation properties in the studied system

An overview of the activity on metal oxides grown by reactive pulsed magnetron sputtering (RPMS) is presented, including high refractive index materials (Nb2O5) and transparent conductive oxides (Sn-doped In2O3 and Al-doped ZnO). For Nb2O5 the influence of process parameters such as plasma density and substrate temperature on optical properties, their thermal stability and film microstructure are discussed. In case of Sn-doped In2O3 (ITO) it is shown that by isothermal or electric current annealing amorphous films crystallize at different activation energies and that the resistivity decreases in two steps ascribed to relaxation and Sn donor activation. Finally it is shown that by RPMS films of Al-doped ZnO (AZO) with high mobility (45 cm²/Vs) can be obtained. The existence and dependence of an optimum substrate temperature for maximum mobility is discussed. Furthermore it is shown that in polycrystalline AZO the carrier mobility is limited by a combination of ionized impurity scattering and grain boundary limited transport depending on the carrier concentration. These effects are also influenced by the Al concentration in the sputtering target.

The transverse acoustic wave propagating along the [100] axis of the cubic Tb₃Ga₅O₁₂ (acoustic c₄₄ mode) is doubly degenerate. A magnetic field applied in the direction of propagation lifts this degeneracy and leads to the rotation of the polarization vector - the magnetoacoustic Faraday rotation. Here, we report on the observation and analysis of the magnetoacoustic Faraday effect in Tb₃Ga₅O₁₂ in static and pulsed magnetic fields. We present also a theoretical model based on magnetoelastic coupling of 4f electrons to both, acoustic and optical phonons and an effective coupling between them. This model explains the observed linear frequency dependence of the Faraday rotation angle.

Increasing the power conversion efficiency of modern thin film solar cells based on absorbers like silicon (Eg=1.11 eV), CuIn_xGa_(1-x)Se_2 (Eg=1.0-1.5 eV) and CdTe (Eg=1.44 eV) is one of the major goals of research devoted to photovoltaics. These cells rely on transparent electrodes made of transparent conductive oxides (TCO) whose high transmittance and low resistivity result in a high short circuit current and fill factor enabling high cell efficiency.

In TCOs absorption in the near infrared (NIR) and visible spectral region is caused by the free electrons and is influenced by their density and mobility inside the host lattice. Due to this inter-relation of optical and electrical properties TCOs with highest carrier mobility at moderate electron densities (~5x10²⁰ cm^-3) are required to simultaneously reach low resistivities and high NIR transmittance. Furthermore the deposition process used should be cost effective and scalable to large area substrates.

Therefore a reactive magnetron sputtering method using metallic Zn/Al alloy targets was developed to achieve high carrier mobilities (µ~45 cm²/Vs) in ZnO:Al (AZO) thin films [1], which is comparable to values achieved with other methods like RF magnetron sputtering or pulsed laser deposition.
Mass spectrometry and high accuracy capacitive pressure sensing together with a variation of the magnetron discharge parameters allowed for a fine control of oxygen partial pressure (p_O2). The dependence of the films electrical properties on the substrate temperature (T_S), the Al content in the sputter targets and p_O2 have been investigated systematically by Hall-effect measurements. Spectroscopic ellipsometry was used to determine film thickness and optical properties. The film structure, morphology and elemental composition was analysed by various methods including AFM, XRD, X-TEM, ERDA and RBS. Analysis of the film composition together with Hall-effect data was used to estimate Al donor activation.

Results show that there are optimum values of T_S and p_O2 at which films with resistivities down to ~2.3x10^-4 Ohm*cm and free electron densities of ~6.0x10²⁰ cm^-3 were achieved. A shift of these optimum growth parameters and the resulting film properties with the target Al content has been detected. The observed limit of mobility in polycrystalline AZO is discussed in terms of ionized impurity scattering and clustering as well as grain boundary limited transport.
Recent investigations of Al concentration in the films and local bonding structure, revealed by XANES seem to explain the well known deterioration of resistivity in AZO at elevated substrate temperatures or after annealing.

Radionuclides represent a serious health risk to humans in case of incorporation. To get a first insight into the transport and metabolism of trivalent actinides in the human organism, we investigated the in vitro speciation of curium(III) in human urine samples using fluorescence spectroscopy. Since in speciation studies trivalent lanthanides are often used as analogs for trivalent actinides, we probed the suitability of this theory by investigating the speciation of europium(III) in human urine, too. Comparison with reference spectra of both heavy metals in model urine and of their complexes with single organic urine constituents then allowed for the determination of the dominant species. Furthermore the chemical composition of all urine samples was analyzed and the parameters affecting the metals’ speciation were determined. Surprisingly the chemical composition of the natural urine samples does not seem to have a great influence on the dominant species. Instead the pH was found to be the most important parameter. For both, the actinide and the lanthanide, two analog species were identified in dependence on the pH: In samples with slight acidic pH a curium(III) and europium(III) citrate complex dominates, respectively, while in samples with near neutral pH a ternary complex with phosphate and citrate as ligands is formed in each case. Comparison with thermodynamic modeling yields some discrepancies especially at higher pH which is due to a lack of data for the ternary species of both heavy metals.

We investigated the immobilization of the estrogen receptors hER_α on the silanized SiO₂ surfaces for biosensor applications. The conjugation of the estrogen receptor hER_α to the quantum dot dye QD655 was achieved. In order to obtain an optimal immobilization of the estrogen receptor hER_α on the functionalized SiO₂ surface, the bioconjugate hER_α-QD655 (Rcpt-qd655) solution was prepared with higher a molarity ratio of 10 to 20 between the QDs and the receptors. A blue laser with an excitation wavelength of 405 nm was used for photoluminescence spectroscopy (PL) investigations to monitor the bioconjugate Rcpt-qd655 immobilization on the silanized SiO₂ surfaces with three different functional groups namely -NH₂, -COO^- and -SH. Several wash processes were applied to remove the excess receptors from the surface after the immobilization. A Fourier transform infrared spectroscopy (FTIR) was used to control the biofilm background after each wash of the receptor coated surface which allows the optimization of the immobilization protocol. In order to test its stability the Quartz crystal microbalance (QCM) was employed and the receptor density was calculated.
Finally the optimal biolayer (silane film+ hER_α receptor) was tested for measurements of 17 ß-estradiol (E2) concentration of 1µM in waterish solution. The measurement concept outlined in [L. Rebohle et al., Vacuum 83 (2009) 24-28] was applied. The whole system was investigated by PL, which exhibits two color signals, namely from the receptor and the detected E2 molecules.

The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterisation. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I), irradiated and recovery annealed (IA) and irradiated, recovery annealed and re-irradiated (IAI). The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations.
In a first step the trepans taken from the RPV Greifswald Unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the Master Curve approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behaviour. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on sub size Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens. The evaluated Charpy-V TT41J shows a better accordance with the irradiation fluence along the wall thickness than the Master Curve reference temperature T0.
The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. T0 increases from -120°C at the inner surface to -104°C at a distance of 33 mm from it and again to -115°C at the outer RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The re-embrittlement during 2 campaigns operation can be assumed to be low for the weld and base metal.

The reliability and predictability of classical molecular dynamics simulations is based on the precision of the interatomic potential used. Because Si has such a great technological importance there is a clear need for more accurate potentials. Recently, a new bond-order potential has been developed [1] by modifying the well-known analytical form given by Tersoff. It has been shown that this potential can reproduce many structural and thermodynamic properties of diamond-structure Si, such as the elastic constants and the melting characteristics, and it is able to determine the cohesive energy and the lattice constants of other solid phases reasonably well [1,2]. Furthermore, the potential yields rather correct data on structure and thermodynamics of liquid and amorphous Si. [2].
In the present work the new bond-order potential is applied to investigate point defect energetics and kinetics as well as solid phase epitaxial recrystallization of amorphous Si. The structure and the formation energy of the most stable configurations of vacancies and self-interstitials are determined. The migration of point defects is simulated and the characteristic migration pathways are identified. A more comprehensive study on preparation and properties of amorphous Si than in [2] is performed, and the results are compared with available experimental data. Solid phase epitaxial recrystallization is simulated at different temperatures and the recrystallization rate is determined. The results on point defect properties and solid phase epitaxial recrystallization are compared with those obtained by the Stillinger-Weber and the Tersoff potential as well as with experimental data and results of first principle calculations. Finally, a comparison is made with available results determined by two other bond-order potentials which have been recently developed [3-6].

[1] T. Kumagai, S. Izumi, S. Hara, S. Sakai, Comput. Mater. Sci. 39 (2007) 457.
[2] P. K. Schelling, Comput. Mater. Sci. 44 (2008) 274.
[3] B. A. Gillespie, X. W. Zhou, D. A. Murdick, H. N. G. Wadley, R. Drautz, D. G. Pettifor, Phys. Rev. B 75
(2007) 155207.
[4] B. A. Gillespie, H. N. G. Wadley, J. Crystal Growth 311 (2009) 3195.
[5] J. D.Schall, G. Gao, J. A. Harrison, Phys. Rev. B 77 (2008) 115209.
[6] B.-J. Lee, CALPHAD 31 (2007) 95.

I will describe the basic properties of intersubband transitions in quantum wells, partly along the lines of the now ten-years-old review paper [1]. I will proceed from the very basic to the discussion of some more specific systems, like superlattices or transitions within the valence band, and to some recently discovered, rather subtle effects.
An interesting interplay is found with transitions between shallow impurity states, which becomes particularly striking in superlattices and coupled quantum wells [2]. Based on a calculation that treats the heterostructure potential and the random-impurity potential on the same footing [3], we can successfully explain or re-interpret some old, hitherto poorly understood data (see Fig. 1).
Another subtle effect emerges, if intersubband spectra are recorded using time-domain terahertz spectroscopy, i.e. fully resolving the phase of the electric field. We show that transmission and absorption spectra are not equivalent, and whereas the absorption line has a standard Lorentzian shape, the transmission spectrum exhibits a Fano-type lineshape (see Fig. 2). This has been explained with the influence of the so-called ponderomotive current [4].
Most of the more recent experimental work discussed here was performed mainly by Dominik Stehr and Martin Wagner (both FZD), most of the samples used were provided by Gottfried Strasser (TU Vienna) and his group, and for part of this work the collaboration with the theory group of Univ. Marburg (D. Golde, M. Kira, S. W. Koch) was indispensable.
[1] M. Helm, “The basic physics of intersubband transitions”, in “Semiconductors and Semimetals”, Vol. 62, p. 1-99 (2000).
[2] D. Stehr, C. Metzner, M. Helm, T. Roch, and G. Strasser, “Resonant impurity bands in semiconductor superlattices”, Phys. Rev. Lett. 95, 257401 (2005).
[3] D. Stehr, M. Helm, C. Metzner, and M. C. Wanke, “Microscopic theory of impurity states in coupled quantum wells and superlattices”, Phys. Rev. B 74, 085311 (2006).
[4] D. Golde, M. Wagner, D. Stehr, H. Schneider, M. Helm, A.M. Andrews, T. Roch, G. Strasser, M. Kira, and S.W. Koch: “Fano signatures in the intersubband terahertz response of optically excited semiconductor quantum wells”, Phys. Rev. Lett. 102, 127403 (2009).

We report the investigation of two nonlinear optical phenomena which are related to intra-excitonic transitions in semiconductor quantum wells and thus occur in the THz range. This is, on one hand, the generation of THz sidebands of near-band gap radiation, a perturbative process, and on the other hand, the AC Stark effect manifested by the Autler-Townes splitting as a non-perturbative effect. Both phenomena are induced by the strong THz field of the Dresden THz free-electron laser.

The discovery of superconductivity in heavily boron-doped diamond [1] has demonstrated that group-IV semiconductors can become superconducting upon carrier doping even at ambient conditions. Meanwhile superconductivity has been found in further heavily doped group-IV semiconductors such as Si and SiC [2]. Compared to these semiconductors, Ge seems to be less promising for realizing superconductivity as was based upon estimates of the electron-phonon coupling strength [3]. The challenge is to achieve extremely high hole concentrations which are commonly limited by the equilibrium solid solubility of the acceptor. Nevertheless, we succeeded in making Ge superconducting as recently reported [4]. A nonequilibrium doping process consisting of 100 keV Ga+-ion implantation with a fluence of 21016cm-2 and subsequent 3 ms flash-lamp annealing (FLA) enabled hole concentrations as high as 1.41021 cm-2. The superconducting state was observed in a thin (~60 nm) Ge layer with a maximum Ga content of about 8 at.% at critical temperatures below 0.5 K. From the measured critical parameters it follows that Ga-doped Ge is a type-II superconductor with a large Ginzburg-Landau parameter (>103).
The structure as well as the superconducting properties of the Ga-doped Ge layers depend sensitively on the preparation conditions as shown in Fig. 1. In search for higher transition temperatures, implantation and annealing conditions were varied in a more comprehensive study. Critical temperatures above 1 K were obtained for samples either implanted with 41016 cm-2 and flash-lamp annealed at 52 Jcm-2 or implanted with 21016 cm-2 and subjected to rapid thermal annealing (RTA) at 910°C for 60 s (Fig. 2). Critical magnetic fields perpendicular and parallel to the Ge:Ga plane up to about 0.3 and 1 T, respectively, were observed. Thus superconductivity in thin Ge:Ge layers is a robust effect and could be utilized in superconducting quantum devices.

[1] E. A. Ekimov, V. A. Sidorov, E. D. Bauer, et al., Nature 428, 542 (2004)
[2] K. Iakoubovskii, Physica C 469, 675 (2009)
[3] L. Boeri, J. Kortus, O. K. Anderson, J. Phys. Chem. Solids 67, 552 (2006)
[4] T. Herrmannsdörfer, V. Heera, O. Ignatchik, et al., Phys. Rev. Lett. 102, 217003 (2009)

FTIR spectroscopy has become an important non-destructive tool in gathering structural information of biological macromolecules at atomic resolution and under functional conditions. Modern instrumentation allows recording high resolution IR spectra of biomolecules in liquids, thin films, and adsorbed monolayers without chemical modification. The time-course of structural changes of biomolecules can be followed easily down to ~20 ms time resolution with rapidly scanning interferometers. If such reactions are highly reproducible, molecular mechanisms can be studied at a time resolution down to ns by step scan interferometers. Despite the advanced user-friendliness in operating modern FTIR spectrometers, the use of the adequate detector type, the correct adjustment of the signal to noise ratio, the setting of optical and electronic filters to physically restrict the band width and the corresponding choice of the interferometer scanning speed are crucial parameters in the hand of the user. Their prudential use is essential for gaining high quality spectra by proper signal averaging procedures in static as well as time-resolved experiments and for avoiding spectral artefacts inherent to improper sampling of both the optical path and the intensity of the IR interferogram.

Over the past decade, molecular imaging has revolutionized medical diagnostics especially the detection of cancer. Among this new frontier, positron emission tomography (PET) allows early diagnoses, efficient monitoring of therapeutic treatment, and quantitative imaging of cancer. One of the most attractive positron-emitting radionuclide is ⁶⁴Cu, which is meanwhile readily available in high specific activity from small cyclotrons. ⁶⁴Cu-labeled peptides represent very interesting vector molecules for certain entities of cancer.

Figure 1: Bifunctional chelating agents (BFCAs) for stable binding of copper radionuclides (arrows show the position of BFCAs for the linkage to peptides)

Pyridine-containing macrocyclic amine ligands I, bispidine II and cyclam tetrapropionic acid III derivatives (Fig. 1), which simultaneously allow the coupling to peptides, have been developed for the stable fixation of copper radionuclides.^[1-3] Corresponding bioconjugates with bombesin as well as neurotensin form rapidly very stable radiocopper complexes which permit clear visualization of tumor tissue in small animal PET studies.

Literature:

[1] G. Gasser, L. Tjioe, B. Graham, M.J. Belousoff, S. Juran, M. Walther, J.-U. Künstler, R. Bergmann, H. Stephan, L. Spiccia, Bioconjugate Chem. 2008, 19, 719-730. [2] S. Juran, M. Walther, H. Stephan, R. Bergmann, L. Steinbach, W. Kraus, F. Emmerling, P.Comba, Bioconjugate Chem. 2009, 20, 347-59. [3] A. Röhrich, R. Bergmann, A. Kretzschmann, S. Noll, J. Steinbach, J. Pietzsch, H. Stephan, 2010, submitted.

The extreme versatility of dendrimers makes them attractive for drug delivery applications. In this perspective, binding of potential drug molecules non-covalently at the interior of dendritic hosts seems to be the most appropriated strategy. We have established glycodendrimers with dense maltose shell which may be utilized to encapsulate nanometer sized guest molecules. ^[1] This is of particular interest since it has been shown that polynuclear cluster compounds have antitumoral as well as antiviral properties. ^[2]

The encapsulation and release of an anionic rhenium cluster complex [Re₆S₈(OH)₆]^{4- [3]} in biocompatible maltose-decorated dendrimers (generation 4 and 5) have been studied in detail applying different physico-chemical methods, e.g. UV/vis, time-resolved laser-induced fluorescence spectroscopy, laser induced liquid bead ion desorption mass spectrometry and dynamic light scattering measurements. On average, 4 – 5 cluster anions can be captured in the interior of sugar-coated dendrimers, and a slow release of cluster complexes was observed under physiological conditions.

The encapsulation and release properties of maltose-decorated nanocarriers imply the possibility for the development of the next generation dendritic hosts with targeting moieties.

Literature:

[1] B. Klajnert et al., Chem. Eur. J. 2008, 14, 7030. [2] J. T. Rhule et al., Chem. Rev. 1998, 98, 327. [3] K. A. Brylev et al., Inorg. Chem. 2007, 46, 7414.

Since their discovery in 1991, Peptide Nucleic Acids (PNAs) have been used in molecular biology, mainly for detecting single base mismatches in oligonucleotide sequences. [1] Due to their non natural pseudo-peptide backbone, which replaces the phosphate-ribose backbone of natural DNA, PNAs are stable against enzymatic degradation. Furthermore, as they form very stable hybrids with both DNA and RNA, PNAs have also been thought to be useful for antisense and antigene therapies. Nuclear medicine is another field of research where PNAs have been used, as, for example, possible agents in the so-called “pretargeting approach”.[2] In this context, we are interested in the radiolabeling of PNA strands with therapeutically relevant nuclides, e.g. ¹⁸⁸Re. En route to explore the wide potential of this “pretargeting using PNA” principle, we prepared a new azido derivative of 2,2´-dipicolylamine, namely 2-azido-N,N-bis((pyridin-2-yl)methyl)ethanamine (Dpa-N₃). It was demonstrated that Dpa-N₃ could be efficiently labeled with both [Re(CO)₃(H₂O)₃]Br and [^99mTc(H₂O)₃(CO)₃]⁺ to give [Re(CO)₃(Dpa-N₃)]Br and [^99mTc(CO)₃(Dpa-N₃)]⁺, respectively. Furthermore, Dpa-N₃ was successfully coupled to a PNA oligomer. Subsequent labeling of Dpa-PNA with [^99mTc(H₂O)₃(CO)₃]⁺ afforded [^99mTc(CO)₃Dpa-PNA] in radiochemical yields > 90% (Figure 1). Biodistribution studies of [^99mTc(CO)₃Dpa-PNA] in Wistar rats showed a very fast blood clearance and modest accumulation in the kidneys. There was no significant activity in the thyroid and the stomach, demonstrating a high in vivo stability of the ^99mTc-labeled Dpa-PNA conjugate.

[1] P. E. Nielsen, M. Egholm, R. H. Berg, O. Buchhardt, Science, 1991, 254, 1497
[2] G. Mardirossian, K. Lei, M. Rusckowski, F. Chang, T. Qu, M. Egholm, D.J. Hnatowich, J Nucl Med, 1997, 38, 907
[3] G. Gasser, K. Jäger, M. Zenker, R.Bergmann, J. Steinbach, H. Stephan, N. Metzler-Nolte, 2010, submitted.

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A new macrocyclic ligand, 2-[4,7-bis(2-pyridylmethyl)-1,4,7-triazacyclononan-1-yl]acetic acid (1), binds copper strongly and the resulting radiocopper(II)-ligand complex exhibits high in vivo stability. The pendant carboxylic group enables this derivative to be conjugated to the N-terminal amino acid residues of peptides. Exploiting this, two stabilized bombesin derivatives have been coupled to 1 and radiolabeled with the positron emitter copper-64.
In vitro binding characteristics of the [64Cu]CuII-labeled bombesin conjugates in gastrinreleasing peptide receptor (GRPR) overexpressing prostate cancer (PC-3) cells have been evaluated. Biodistribution studies performed in Wistar rats indicate a specific uptake in the GRPR-rich pancreas and rapid renal elimination. Small animal PET imaging studies confirmed a high extent of tumor accumulation in NMRI nu/nu mice bearing the human prostate tumor PC-3. Incorporation of one additional glutamic acid residue within the spacer between bombesin and the radiolabeled complex leads to a higher tumor-to-muscle uptake ratio.

Three new bifunctional chelating agents (BFCAs) I – III have been prepared. These ligands can be efficiently radiolabeled with ⁶⁴Cu^II under mild conditions. The carboxylate and alcohol substituents allow to introduce appropriate biomolecules, e.g. peptides such as bombesin and neurotensin by amide coupling. The new BFCAs were found to be hydrophilic and therefore are attractive candidates for developing new copper(II)-based radiopharmaceuticals.

1,4,8,11-Tetraazacyclotetradecane (cyclam) derivatives with one to four appending dipeptide residues (Arg-Tyr) have been synthesized. Kinetics of complex formation with copper(II) was investigated by UV/vis spectroscopy to show a deceleration with increasing substitution degree of the cyclam core. Radiolabeling experiments with ⁶⁴Cu^II on the peptide tetramer 5 revealed a smooth and efficient complexation. Challenge studies of ⁶⁴Cu5 in the presence of cyclam as competing ligand prove the high kinetic inertness of the radiocopper(II) complex formed with 5.

The three bispidine-derived ligands L1 - L3 (bispidine = 3,7-diazabicyclo[3.3.1]-nonane) have been labeled with ⁶⁴Cu, and the radioactive copper(II) complexes have been investigated for potential radiopharmaceutical applications. The thermodynamic stability of copper(II) complexes with the 2^nd generation bispidines L2 and L3 is significantly higher than with L1 as a 1^st generation bispidine. Despite this, labeling kinetics and challenge experiments indicate that L1 has advantages as a ligand for radiocopper(II) applications over the new ligands L2 and L3. The copper(II) complexes of all three bispidine ligands were found to be rather hydrophilic (log D_o/w at pH = 7.4: ⁶⁴Cu-L1 = -2.88, ⁶⁴Cu-L2 = -1.45, ⁶⁴Cu-L3 = -1.94). In vitro experiments with rat plasma give evidence that the ⁶⁴Cu complexes of L1 – L3 are very stable.

Eph receptors and their ephrin ligands were identified in the late 1980's. Subsequently, they were linked to different physiological and pathophysiological processes like embryonic development, angiogenesis, and tumorigenesis. In this regard, recent work focused on the distribution and effects of Eph receptors and ephrins on tumor cells and tumor microenvironment. The purpose of this review is to outline the role of these molecules in physiological angiogenesis and pathophysiological tumor angiogenesis. Furthermore, novel therapeutical approaches are discussed as Eph receptors and ephrins represent attractive targets for antiangiogenic therapy.

Removal of phenol under iron-carbon (Fe-C) microelectrolysis was enhanced by O2-microbubble. The removal rate (R0) of phenol reached 65% in 2 h. O2 bubbling plays a critical role, as compared to the air and N2 bubbling, in which only 9.5% and 4% of phenol is removed in 2 h, respectively. It shows that more dissolved oxygen in water is favorable for the oxidation process. Phenol removal is effective at lower temperature or/and higher dissolution pressure also confirms the role of dissolved oxygen. In the microbubble-assisted microelectrolysis system, O2, Fe-C pellets, and H2SO4 are the necessary conditions for the oxidation of phenol. The conversion of phenol follows the kinetics of the pseudo-first order, polynomially increases with the increasing amount of Fe-C pellets or/and sulfuric acid. Catechol, hydroquinone, and low molecular carboxylic acids are the major products.

Aim.
Labeling of specific monoclonal antibodies or their fragments with suitable radionuclides can be utilized for diagnosis of autoimmune disorders or in preclinical research for elucidation of the role of specific cell types in underlying disease pathophysiology. In contrast to other radionuclides, ⁸⁹Zr as a marker for positron emission tomography (PET) and protocols for ⁸⁹Zr production so far have found relatively little interest despite the many advantages of this radionuclide.
Methods.
We examined the production, separation, and characterization of ⁸⁹Zr, including supplementation of a commercial Cyclone^® 18/9 with a self-made Solid Target System (STS) and the construction of a re-usable target holder. Optimized conditions to reduce undesired long-lived side products were specified. Obtained [⁸⁹Zr]Zr-oxalate was used for labeling of anti-B cell antibodies with desferrioxamine-p-SCN as a bifunctional chelator. ⁸⁹Zr-labeled antibodies were injected in DBA/1 mice to examine usability for detection of B cells in vivo by PET.
Results.
The improved conditions yielded ⁸⁹Zr of high purity with smaller amounts of long living ⁸⁸Zr isotope compared to other methods. The antibody labeling procedure yielded crude mixtures containing non-chelated metal, which were separated using desalting columns. Analytical radio-HPLC and TLC revealed ⁸⁹Zr-labeled antibodies of sufficient purity. PET measurements showed binding of ⁸⁹Zr-labeled anti-B cell antibodies in tissues with high frequencies of B cells, i.e. in spleen and lymph nodes.
Conclusion.
Labeling of antibodies directed to specific cell types with ⁸⁹Zr according to our protocol turned out to be an effective tool for in vivo visualization and tracking of cells in mice by immuno-PET.

Cyclin-dependent kinases 4 and 6 (Cdk4/6) are important components of cell cycle activation and control in early G₁ phase. Both enzymes and their regulators, e.g., cyclins, play critical roles in embryogenesis, homeostasis, and cancerogenesis. Cdk4/6 are attractive targets for cancer treatment. Recently, numerous selective small molecule inhibitors of Cdk4/6 have been developed. The potential of Cdk4/6 inhibitors, particularly, pyrido[2,3-d]pyrimidine derivatives, as both anti-cancer drugs and ¹²⁴I- and ¹⁸F-radiolabeled tracers for cancer imaging using positron emission tomography is discussed.

In the present contribution, high-resolution positron lifetime and coincidence Doppler broadening spectroscopies are used to characterize defects in Fe76Al24 and Fe72Al28 alloys. In order to facilitate defect identification, we also perform a theoretical study of basic vacancy-like defects in three phases of the Fe–Al system: ordered, short-range ordered, and disordered. Positron characteristics, like positron lifetime, positron binding energy to defects, high-momentum parts of Doppler broadening curves and specific trapping rates, are calculated for various defect configurations. The results are discussed in the context of experimental data obtained here and available in literature.

The exchange of solvent and anions from [⁸⁹Zr]Zr-oxalate in oxalic acid to [⁸⁹Zr]ZrCl₄ in HCl is a crucial step in the production of ⁸⁹Zr. A fast and reproducible method using cation instead of anion exchange resin giving a recovery of 98.5 ± 1.1% is described here. Obtained ⁸⁹Zr was used for labeling a monoclonal antibody directed against CD4⁺ T helper cells.