Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

35174 Publications

Untersuchung der Hydrodynamik von ovalen Biogasreaktoren mit instrumentierten Strömungsfolgern

Reinecke, S. F.; Jobst, K.; Hampel, U.

Erstmals wurden instrumentierte strömungsfolgende Sensorpartikel mit magnetischer Positionsdetektion in einer Studie der Hydrodynamik von neuartigen, ovalen Biogasreaktoren im Labor- und Technikumsmaßstab eingesetzt. Die Sensorpartikel erfassen autonom die makroskopischen Strömungsvorgänge in den Reaktoren. Die gemessenen Daten der Sensorpartikel liefern vertikale Aufenthaltsprofile und Partikelumlaufzeitverteilungen. Anhand dieser Informationen werden die ovalen Reaktoren hinsichtlich der Durchmischung und der Suspensionseigenschaften bewertet und verglichen.

Keywords: Strömungsfolger; Sensorpartikel; Autonomer Sensor; Biogas; Hydrodynamik

Publ.-Id: 24225

Physical properties of the candidate quantum spin-ice system Pr2Hf2O7

Anand, V. K.; Opherden, L.; Xu, J.; Adroja, D. T.; Islam, A. T. M. N.; Herrmannsdörfer, T.; Hornung, J.; Schönemann, R.; Uhlarz, M.; Walker, H. C.; Casati, N; Lake, B

Physical properties of a pyrohafnate compound Pr2Hf2O7 have been investigated by ac magnetic susceptibility χac(T ), dc magnetic susceptibility χ(T ), isothermal magnetization M(H), and heat-capacity Cp(T )measurements on polycrystalline as well as single-crystal samples combined with high-resolution synchrotron x-ray diffraction (XRD) for structural characterization and inelastic neutron scattering (INS) to determine the crystal-field energy-level scheme and wave functions. Synchrotron XRD data confirm the ordered cubic pyrochlore (Fd¯3m) structure without any noticeable site mixing or oxygen deficiency. No clear evidence of long-range magnetic ordering is observed down to 90 mK, however the χac(T ) evinces slow spin dynamics revealed by a frequency dependent broad peak associated with spin freezing. The INS data reveal the expected five well-defined magnetic excitations due to crystal-field splitting of the J = 4 ground-state multiplet of the Pr3+. The crystal-field parameters and ground-state wave function of Pr3+ have been determined. The Ising anisotropic nature of the magnetic ground state is inferred from the INS as well as χ(T) and M(H) data. Together these properties make Pr2Hf2O7 a candidate compound for quantum spin-ice behavior.

Publ.-Id: 24224

Photo-activated CO releasing molecules

Kubeil, M.; Stephan, H.; Graham, B.; Spiccia, L.

Carbon monoxide has been demonstrated to exhibit several beneficial effects on biological targets (anti-inflammatory, anti-proliferative, anti-apoptotic, anti-oxidative and vasodilatory effects).1 The development of photo-activated CO releasing molecules (photoCORMs) has received considerable attention as a new prodrug approach.2 However, despite the number of photoCORMs reported in the literature, their mechanism of CO release has been little elucidated so far. Herein, we report the synthesis of ruthenium(II)-carbonyl complexes (Figure) functionalized with electron-donating and/or electron-withdrawing bipyridine ligands and investigate the mechanism of CO release (before and after light-activation) using a combination of UV-Vis and FTIR spectroscopy accompanied with a chemometric technique (Multivariate Curve Fitting Analysis).3 The photo-activated CO-release kinetics of the Ru(II)-photoCORMs, as well as the identity of the intermediates and photo-activated products, will be presented. These results have important implications in understanding their chemistry and guiding the design of new photoCORMs.

[1] R. Motterlini, L. E. Otterbein, Nat. Rev. Drug Discov. 2010. 9, 728-743
[2] U. Schatzschneider, British J. Pharmacol. 2014, 172, 1638-1650
[3] C. Bischof, T. Joshi, A. Dimri, L. Spiccia, U. Schatzschneider, Inorg. Chem. 2013, 52, 9297-9308

  • Lecture (Conference)
    8th Asian Biological Inorganic Chemistry Conference (AsBIC8), 04.-09.12.2016, Auckland, New Zealand

Publ.-Id: 24223

In-Situ Analysis and Experiment Regulation at HZDR

Frust, T.; Kelling, J.; Juckeland, G.

A number of experiments at HZDR require in-situ evaluation of the experiment data of the results for automated responses by the experiment control systems. This talk presents two such examples and their current implementations.

  • Invited lecture (Conferences)
    PADC Annual Workshop 2016, 17.-18.10.2016, Jülich, Deutschland

Publ.-Id: 24222

PIConGPU: First Experiences on Minski

Widera, R.; Hübl, A.; Juckeland, G.

PICOnGPU is a highly scalable GPU accelerated particle-in-cell code. This talk presents the first experiences on running this code on IBM Minski (Power8+ with NVIDIA P100 GPUs).

  • Invited lecture (Conferences)
    PADC Annual Workshop 2016, 17.-18.10.2016, Jülich, Deutschland

Publ.-Id: 24221

Luminescence spectra of uranium(VI) – why we observe a spectral shift in cryospectra

Geipel, G.; Stumpf, T.

It is well known, that uranyl carbonates emits at room temperature only phosphorescence with very short lifetimes {Ca2UO2(CO3)3 ~ 50 ns}[1, 2]. The lifetime of UO2(CO3)34+ in aqueous solution at room temperature was determined to be 9.2 ± 0.05 ns. Freezing these solutions results normally in a strong increase of the luminescence lifetime as well as in a strong increase in the measured intensity. This effect is usually explained by the dynamic quench effect of the carbonate ion as well as the dynamic quench effect of the water molecules in the solvation shell. In addition all spectra of the uranyl carbonates show a hypsochromic shift.
The emission of the uranyl ion is assigned to a triplet state. It is also known that the non-complexed uranyl ion has two phosphorescence emitting levels (20500 and 21270 cm-1)[3,4]. The first one is assigned to the direct transition to the lowest vibronic level in the ground state, the second is assigned to the transition of a exited vibronic level to the ground state. The emission peaks at lower wavenumbers correspond to vibronic levels in the ground state and are usually assigned to the transition from the lowest triplet state[5].

We observe for the uranyltricarbonate at room temperature an emission at around 21420 cm-1 and at 20610 cm-1 which are the two emitting levels in this system. From the higher level also the vibronic levels in the ground state were populated. Under cryogenic conditions we observe that the emission from the higher level disappears. This induces a slight blue shift of the spectrum of about 65 cm-1.

Keywords: Uranium; luminescence; spectral shift; cryogenic

  • Poster
    ATAS Workshop, 07.-10.11.2016, Richland, USA

Publ.-Id: 24220

Neuroimaging of intracellular signalling: Development of an 18F-labelled quinoline derivative with high affinity for phosphodiesterase 5.

Wenzel, B.; Liu, J.; Teodoro, R.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Ludwig, F.-A.; Chezal, J. M.; Moreau, E.; Brust, P.; Maisonial-Besset, A.

Objectives: The enzyme cyclic nucleotide phosphodiesterase 5 (PDE5) is involved in receptor-mediated signalling processes by regulation of the intracellular levels of the second messenger cGMP. PDE5 is peripherally located in heart, lungs and smooth muscle cells. Within the CNS it is highly expressed in the cerebellum and hippocampus. There is currently a growing interest in using inhibitors of PDE5 such as Sildenafil (Viagra®) as possible drugs in Alzheimer’s and Huntington’s Disease. Moreover, the effects of PDE5 inhibitors on the growth of different tumour cells are reported. Therefore we aimed to develop a 18F-labelled radioligand for imaging of this enzyme particularly in brain.

Methods: A quinoline scaffold (1) was used as basis for the synthesis of a small library of derivatives with fluoro-containing substituents in position 3, 4 and 8 of the quinoline core. The inhibitory activity of the compounds was determined for the human PDE5A1 and a panel of other PDEs by using an enzyme assay with sildenafil as reference. 18F-labelling of the best candidate ICF24075 was performed on an azetidine ring by using a nosylate precursor (Figure). In vitro autoradiography of [18F]ICF24075 was performed on pig brain slices. In vivo metabolism was investigated in plasma and brain samples of mice 30 min p.i. using micellar chromatography.

Figure: 18F-labelling of [18F]ICF24075

Results: The new ligand ICF24075 showed a good inhibitory activity for PDE5 (IC50 = 5.9 nM) and a high selectivity over other PDEs. 18F-labelling of the secondary carbon atom proceeded only with low labelling yields resulting in RCYs of 1.8 ± 0.3% (decay corr.) of the formulated product. In vitro binding studies demonstrated a specific blockade with sildenafil which was highest in the cerebellum. However, in vivo studies in mice revealed the formation of radiometabolites able to cross the blood-brain barrier.

Conclusions: Due to the presence of radiometabolites in the brain, [18F]ICF24075 is not suitable for specific neuroimaging of PDE5. In particular the unexpected fast metabolic degradation of the 18F-labelled azetidine ring is currently further investigated by in vitro studies to confirm our assumption of N-dealkylation.

Reference: (1) Bi, Y. et al; Bioorg. Med. Chem. Lett. 2004, 14, 1577-1580.

  • Poster
    ISRS 2017 - 22nd International Symposium on Radiopharmaceutical Sciences, 14.05.2017, Dresden, Deutschland
  • Open Access Logo Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 60(2017)S1, 534
    DOI: 10.1002/jlcr.3508

Publ.-Id: 24219

DFT study on the contribution of phonon and electron excitations to the free energy of embedded defect clusters

Posselt, M.; Devaraj, M.

Modeling of nanostructure evolution in solids requires the knowledge of comprehensive data on the properties of point defects and defect clusters. Since most processes occur at elevated temperatures not only the energetics of the defects in the ground state but also their temperature-dependent free energy must be known. The determination of the contribution of phonon and electron excitations to the free binding energy of small embedded defect clusters is illustrated in the case of bcc-Fe. The fundamentals of the first-principles calculation method have been recently described [1]. First of all, the ground state properties of the clusters are determined under zero pressure (ZP) conditions. Second, the phonon contribution to the free energy is calculated within the harmonic approximation using the equilibrium atomic positions determined in the ground state. The application of a quasi-harmonic correction to the ZP-based data does not modify the results significantly. Therefore the obtained data are valid under zero-pressure conditions at higher temperatures than in the framework of the purely harmonic approach. These conditions are usually realized in experiments. Third, the contribution of electron excitations to the defect free energy is calculated. The electron excitations can lead to an additional deviation of the total free energy from the ground state value or can compensate the deviation caused by the phonon contribution. Depending on the examples considered the free binding energy of a defect cluster can differ significantly from the ground state value.
[1] D. Murali, M. Posselt, M. Schiwarth, Phys. Rev. B 92, 064103 (2015).

Keywords: DFT; defect clusters; free energy

  • Lecture (Conference)
    8th Int. Conf. on Multiscale Materials Modeling (MMM 2016), 09.-14.10.2016, Dijon, France

Publ.-Id: 24218

In-magnet measurement setup for proof-of-concept and commissioning of MR integrated proton therapy

Lühr, A.; Gantz, S.; Schellhammer, S.; Zarini, O.; Zeil, K.; Schramm, U.; Hoffmann, A.

There is growing interest to explore the concept of magnetic resonance integrated proton therapy (MRiPT). However, no experimental proof-of-principle has been established so far. The aim of this work was to develop an in-magnet measurement setup that facilitates to investigate the dosimetric feasibility of MRiPT and to develop a commissioning procedure for future MRiPT devices.

Keywords: Proton therapy; MR integrated Radiotherapy; MR guidance; Commissioning; Magnetometry; Proton beam deflection; Pencil beam scanning

  • Contribution to proceedings
    ESTRO 36, 05.05.2017, Wien, Österreich
    Proceedings of ESTRO 36
  • Lecture (Conference)
    ESTRO 36, 05.05.2017, Wien, Österreich

Publ.-Id: 24217

Positron-Annihilation Lifetime Spectroscopy for Materials Science

Wagner, A.

Early experiments on the interaction of positrons (the anti-particles of electrons) with materials revealed a significant sensitivity on the electronic structure. Especially, open-volume defects, such as vacancies, vacancy agglomerates, and dislocations cause attractive electric potentials due to the lack of the repulsive positive potential of the nuclei. With diffusion lengths in the order of 100 nm positrons probe large volumes before getting trapped at positively charged defects which in turn results in a sensitivity of defect concentrations of about 1 in 107 atoms (in metals) . While annihilation lifetimes increase with increasing defect sizes due to reduced local electron densities, one can also infer the momentum-distributions of the annihilation electrons which in turn tell about the chemical compositions in the vicinity of defects. Doppler-broadening spectroscopy and annihilation lifetime spectroscopy have therefore found widespread applications in defect studies in pure metals, alloys, and semiconductors. With increasing defect sizes the formation of the electron-positron bound state – called Positronium (Ps) – becomes possible. While the spin-parallel triplet state has a vacuum annihilation lifetime of 142 ns, this annihilation lifetime gets reduced when the Ps bounces off the walls of porous materials and flipping to the spin-singlet state with 125 ps. In contrast to standard intrusion techniques, porosimetry studies with positrons can be applied for closed porosity as well.
The Helmholtz-Center at Dresden-Rossendorf operates several user beamlines for materials research employing positron annihilation. SPONSOR (Slow POsitroN System Of Rossendorf) uses moderated positrons from 22Na decay which are post-accelerated to energies from 27 eV to 37 keV which are guided magnetically towards the samples under study [1]. The energy dependent range allows performing depth-dependent (coincidence) Doppler-broadening spectroscopy of thin films with thicknesses up to about 1 µm. SPONSOR has been extended by a new installation called AIDA (Apparatus for In-Situ Defect Analysis) which additionally allows temperature-dependent positron annihilation spectroscopy (PAS) from 50 to 1200 K, in-situ ion irradiation and sputtering with noble and reactive gases (up to 5keV ion energy), thin film deposition (Molecular Beam Epitaxy), and four-point probe resistometry. First experiments with this facility on open volume defects in Fe60Al40 alloys have been performed and the results will be presented [2]. Two other user facilities dedicated to positron annihilation lifetime and Doppler-broadening studies in materials research are being operated at a superconducting electron linear accelerator. Hard X-rays from electron-bremsstrahlung generate positrons from pair production. Both installations employ bunched continuous-wave (CW) electron beams with energies between 15 MeV and 30 MeV. The CW-operation results in significantly reduced pile-up effects in the detectors in comparison to normal conducting accelerators. Electron bunch lengths below 10 ps FWHM allows positron annihilation lifetime spectroscopy measurements with high timing resolutions. The bunch repetition rate is adjustable to 26 MHz / 2n, n=0, 1, 2 ... 16 matching wide spans in positron or positronium lifetimes. The GiPS (Gamma-induced Positron Source) generates energetic electron-positron pairs inside the sample under investigation from hard x-rays impinging onto the sample [3]. Therefore, the source is especially suited for materials which are not qualified for vacuum conditions or because they are imposing hazardous conditions or intrinsic radioactivity. Exemplary defect studies on the skyrmoin-lattice compound MnSi [4] will be presented. MePS (the Monoenergetic Positron Source) utilizes positrons with fixed energies ranging from 500 eV to 16 keV[3]. A magnetic beam transport system guides positrons to the samples under investigation. A dedicated chopper/buncher system is used to maintain a high timing resolution for depth-dependent annihilation lifetime studies in thin films. The signal-to-noise ratio is beyond 104 while lifetime resolutions of around 280 ps FWHM have been obtained. Applications of porosimetric studies in low-k dielectrics will be presented. [6].
The MePS facility has partly been funded by the Federal Ministry of Education and Research (BMBF) with the grant PosiAnalyse (05K2013). The initial AIDA system was funded by the Impulse- und Networking fund of the Helmholtz-Association (FKZ VH-VI-442 Memriox). The AIDA facility was funded through the Helmholtz Energy Materials Characterization Platform.

[1] W. Anwand, et al., Defect and Diffusion Forum Vl. 331 25 (2012).
[2] M. O. Liedke, et al., Journal of Applied Physics 117 163908 (2015).
[3] M. Butterling, et al., Nuclear Instruments and Methods in Physics Research B 269, 2623 (2011).
[4] M. Reiner, et al., Scientific Reports 6, 29109 (2016).
[5] M. Jungmann, et al., Journal of Physics: Conference Series 443, 012088 (2013)
[6] A. Uedono, et al., Applied Surface Science 368, 272 (2016).

Keywords: Positron annihilation EPOS MePS GiPS SPONSOR AIDA Memriox ELBE

  • Invited lecture (Conferences)
    2nd International Symposium for Innovative Measurement and Analysis for Structural Materials, Keynote Talk, 27.-29.09.2016, Tsukuba, Japan

Publ.-Id: 24215

Experimental setup to measure magnetic field effects of proton dose distributions: simulation study

Schellhammer, S.; Oborn, B.; Lühr, A.; Gantz, S.; Wohlfahrt, P.; Bussmann, M.; Hoffmann, A.

As a first step towards proof-of-concept for MR-integrated proton therapy, the dose deposited by a slowing down proton pencil beam in tissue-equivalent material is assessed within a realistic magnet assembly. Furthermore, radiation-induced activation and demagnetization effects of the magnet are studied.

The dose distributions of proton pencil beams (energy range 70-180 MeV) passing through a transverse magnetic field of a permanent C-shaped NdFeB dipole magnet (maximum magnetic flux density Bmax = 0.95 T) while being stopped inside a tissue-equivalent slab phantom of PMMA were simulated (Figure 1). The beam was collimated to a diameter of 10 mm. A radiochromic EBT3 film dosimeter was placed centrally between the two phantom slabs parallel to the beam’s central axis. 3D magnetic field data was calculated using finite-element modelling (COMSOL Multiphysics) and experimentally validated using Hall-probe based magnetometry. A Monte Carlo model was designed using the simulation toolkit Geant4.10.2.p02 and validated by reference measurements of depth-dose distributions and beam profiles obtained with Giraffe and Lynx detectors (IBA Dosimetry), respectively. The beam trajectory and lateral deflection were extracted from the film’s planar dose distribution. Demagnetization was assessed by calculating the dose deposited in the magnet elements, and by relating this to radiation hardness data from literature. A worst-case estimate of the radioactivation of the magnet was obtained by taking into account the most common produced mother nuclides and their corresponding daughter nuclides.

The Monte Carlo model showed excellent agreement with the reference measurements (mean absolute range difference: 0.2 mm). The predicted planar dose distribution clearly showed the magnetic field induced beam deflection (Figure 2). The estimated in-plane deflection of the Bragg peak ranged from 0 cm for 70 MeV to 1 cm for 180 MeV in comparison to no magnetic field. No out-of-plane beam deflection was observed. Exposing the film to 2 Gy at the Bragg peak was estimated to cause a mean dose to the magnets of 20 μGy, which is expected to produce negligible magnetic flux loss. The initial activation was estimated to be below 25 kBq.

A first experimental setup capable of measuring the trajectory of a proton pencil beam slowing down in a tissue-equivalent material within a realistic magnetic field has been designed and built. Monte Carlo simulations of the design show that magnetic field induced lateral beam deflections are measurable at the energies studied and radiation-induced magnet damage is expected to be manageable. These results have been validated by irradiation experiments, as reported by Lühr et al. in a separate abstract.

  • Lecture (Conference)
    ESTRO 2017, 05.-09.05.2017, Wien, Österreich

Publ.-Id: 24214

Sites of recurrent disease and prognostic factors in SCLC patients treated with radiochemotherapy

Bütof, R.; Gumina, C.; Valentini, C.; Sommerer, A.; Appold, S.; Zips, D.; Löck, S.; Baumann, M.; Troost, E.

Concurrent radiochemotherapy (RCHT) is the standard treatment in locally advanced small cell lung cancer (SCLC) patients. Due to conflicting results on elective nodal irradiation (ENI) or selective node irradiation (SNI) there is no clear evidence on optimal target volumes. Therefore, the aims of this study were the evaluation of sites of recurrent disease in patients with limited stage SCLC undergoing radiochemotherapy to assess the feasibility and safety of SNI versus ENI and, moreover, the extraction of prognostic factors for loco-regional control, freedom from distant metastases and overall survival.
Material and methods:
A retrospective single-institution study was performed in 54 consecutive patients treated with RCHT. After state-of-the-art staging, all patients underwent three-dimensional conformal radiotherapy to a total dose of 45 Gy in twice-daily fractions of 1.5 Gy starting concurrently with the first or second chemotherapy cycle according to Turrisi et al. [1]. The gross tumour volume (GTV) consisted of the primary tumour and SNI visualized on CT and/or FDG-PET, or confirmed by cytology. The clinical target volume (CTV) was obtained by expanding the GTV, adjusting it for anatomical boundaries, and electively adding the supraclavicular lymph node stations. Thereafter, the CTV was expanded to a planning target volume based on institutional guidelines. Follow-up consisted of a 3-monthly chest x-ray or CT-scan. All sites of loco-regional recurrences were correlated to the initial tumour and dose delivered. The impact of potential prognostic variables on outcome was evaluated using the Cox-regression model.
After a median interval of 11.5 months, 17 patients (31%) relapsed locally or regionally: six within the initial primary tumour volume, five within the initially affected lymph nodes, three metachronously within primary tumour and initially affected lymph nodes, and three both inside and outside of the initial nodal disease. All sites of loco-regional recurrence had received 92%-106% of the prescribed dose. Thirty-seven patients (69%) developed distant metastases (37.8% liver, 35% brain). Among all investigated co-factors only total GTV revealed a significant correlation with patient outcome.
In our study most recurrences occurred in the initial primary tumour or lymph node volume, or distantly. We did not register any case of isolated nodal failure, suggesting the use of selective nodal irradiation, possibly with the addition of supraclavicular irradiation in patients with affected lymph nodes in the upper mediastinum, instead of ENI.
Among all investigated patient- and tumour-related co-factors only total GTV revealed a significant correlation with patient outcome. Further prospective clinical trials are needed for final determination of optimal irradiation fields in SCLC patients.

Keywords: SCLC; locoregional control; distant metastases; overall survival; prognostic factors

Publ.-Id: 24213

Dirac loops in two-dimensional topological material T-graphene

Liu, Y.; Wang, G.; Huang, Q. S.; Guo, L. W.; Chen, X. L.; Zhou, S. Q.

Graphene possesses a peculiar band structure and hence exhibits many fascinating properties from room temperature quantum Hall effect to massless Dirac fermions. With the understanding of graphene, topological materials with the properties similar to or even beyond graphene gradually rise and draw much attention, such as Silicene, Bi2Se3, WTe2 and most recently TaAs. Then a question arises: is it possible for another 2D carbon lattice to exhibit similar properties? If so, what are the determining factors? Here, we demonstrate that a novel two-dimensional carbon allotrope called T-graphene can possess Type-I Dirac points / loops based on the first-principles calculations [1]. T-graphene described by the plane group p4mm (See Fig. 1) can be energetically metastable and dynamically stable. The band structure of T-graphene in Fig. 1 shows the linear dispersion relation at the Fermi level. Two Dirac points are located at asymmetric positions Ξ(0.170, 0.170) between Γ and M and Λ(0, 0.249) between X and Γ, respectively. Furthermore, the linear dispersion relation near the Fermi surface exists in every direction and the cross points form a loop. Such Dirac fermions and a high υF are attributed to crossing π and π* bands and two sublattices. Under certain structure tailoring or straining, the linear dispersion relation is found to be retained. Two type of nanoribbons tailored from T graphene are predicted to have interesting magnetic properties. Besides, two possible routes to obtain T graphene are proposed: carbon deposition on certain metal substrates or electron beam irradiation on the tailored graphene growing on Ni (111). The results provide new insights to search and fabricate two-dimensional topological material.

Keywords: graphene; Dirac fermions; first-principles calculations; 2D materials

  • Poster
    33rd International Conference on the Physics of Semiconductors, 31.07.-05.08.2016, Beijing, China

Publ.-Id: 24212

Ferromagnetism in Silicon Single Crystals with Positively Charged Vacancy Clusters

Liu, Y.; Zhang, X.; Yuan, Q.; Han, J.; Zhou, S.; Song, B.

Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Here, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si. Commercially available p-type Si single crystal wafer is cut into pieces for performing neutron irradiations. The magnetic impurities are ruled out as they can not be detected by secondary ion mass spectroscopy. With positron annihilation lifetime spectroscopy, the positron trapping center corresponding to lifetime 375 ps is assigned to a kind of stable vacancy clusters of hexagonal rings (V6) and its concentration is enhanced by increasing neutron doses. After irradiation, the samples still show strong diamagnetism. The weak ferromagnetic signal in Si after irradiation enhances and then weakens with increasing irradiation doses. The saturation magnetization at room temperature is almost the same as that at 5 K. The X-ray magnetic circular dichroism further provides the direct evidence that Silicon is the origin of this ferromagnetism. Using first-principles calculations, it is found that positively charged V6 brings the spin polarization and the defects have coupling with each other.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors

  • Lecture (Conference)
    APS March Meeting 2016, 14.-18.03.2016, Baltimore, United States of America

Publ.-Id: 24211

Esophageal wall dose-surface maps do not improve the predictive performance of a multivariable NTCP model for acute esophageal toxicity in advanced stage NSCLC patients treated with intensity-modulated (chemo-)radiotherapy

Dankers, F.; Wijsman, R.; Troost, E.; Monshouwer, R.; Bussink, J.; Hoffmann, A.

In our previous work, a multivariable normal-tissue complication probability (NTCP) model for acute esophageal toxicity (AET) Grade ≥2 after highly conformal (chemo-)radiotherapy for non-small cell lung cancer (NSCLC) was developed using clinical parameters and mean esophageal dose (MED). Since the esophagus is a tubular organ, spatial information of the esophageal wall dose distribution may be important in predicting AET. We investigated whether the incorporation of esophageal wall dose-surface data with spatial information improves the predictive power of our NTCP model. For 149 NSCLC patients treated with highly conformal radiation therapy esophageal wall dose-surface histograms (DSHs) and polar dose-surface maps (DSMs) were generated. DSMs were used to generate new DSHs and dose-length-histograms (DLHs) that incorporate spatial information of the dose-surface distribution. Following our previous work, new multivariable NTCP models were developed using histogram derived parameters. Univariate logistic regression analysis showed that these histogram parameters correlated significantly with AET. However, incorporation of esophageal wall dose-surface data with spatial information did not improve the predictive performance of the established multivariable NTCP model based on conventional dose-volume data. For prediction of AET spatial information of the esophageal wall dose distribution is of no added value and it is sufficient to only consider MED as a predictive dosimetric parameter.

Keywords: Non-small cell lung cancer; esophagitis; NTCP; highly conformal radiation therapy; predictive models; dose maps

Publ.-Id: 24210

Targeting cancer with ultrasmall silicon nanoparticles

Licciardello, N.; Zarschler, K.; Singh, G.; Bergmann, R.; Faramus, A.; Ddungu, J. L. Z.; de Cola, L.; Stephan, H.

Renal clearable ultrasmall nanoparticles (sub-10 nm size) have attracted increasing attention for medicinal applications [1, 2]. In this direction, ultrasmall silicon nanoparticles (Si-NPs) are gaining in importance, especially in the imaging of cancer cells [3]. Si-NPs display tuneable photoluminescence, high resistance against photo-bleaching, chemical stability after functionalization and biocompatibility. Covalent modification of the surface with red-emitting dyes for optical imaging, bifunctional chelator agents for radiometals enabling SPECT or PET, and simultaneously targeting vector molecules opens the avenue for the development of new targeted dual imaging agents. In vivo imaging with fast clearing agents possessing numerous surface groups is very attractive. However, defined surface functionalization, especially with suitable targeting molecules, is fairly challenging. Here we report on the surface functionalization of amine-terminated Si-NPs (< 5 nm) with a defined quantity of red-emitting dyes and vector molecules, in order to design targeting optical imaging agents. The modification of these Si-NPs with appropriate chelators for radiometals, such as 64Cu, allows for performing positron emission tomography.

Work financially supported by Helmholtz Virtual Institute “NanoTracking”, Agreement No. VH-VI-421

[1] B. H. Kim, M. J. Hackett, J. Park, T. Hyeon, Chemistry of Materials 2014, 26, 59-71.
[2] K. Zarschler, L. Rocks, N. Licciardello, L. Boselli, E. Polo, K. P. Garcia, L. De Cola, H. Stephan, K. A. Dawson, Nanomedicine: Nanotechnology, Biology and Medicine 2016, 12, 1663-1701.
[3] C. Tu, X. Ma, A. House, S. M. Kauzlarich, A. Y. Louie, ACS Medicinal Chemistry Letters 2011, 2, 285-288.

  • Lecture (Conference)
    8th International Conference on Nanomaterials - Research & Application (Nanocon 2016), 19.-21.10.2016, Brno, Czech Republic

Publ.-Id: 24209

Formation and properties of high-dose nitrogen implanted epitaxially grown Gd2O3 on silicon

Joseph, A.; Tetzlaff, D.; Schmidt, J.; Böttger, R.; Wietler, T. F.; Osten, H. J.

The effects of nitrogen incorporation by high-dose ion implantation in epitaxial Gd2O3 films on Si(111) followed by annealing have been investigated. Nitrogen incorporation is believed to occur by filling the oxygen vacancies or by removing hydroxyl group ions in gadolinium oxide (Gd2O3). The nitrogen content in the oxide layer has been altered by changing the implantation dose. The impact of nitrogen incorporation on Gd-O bonding is studied using X-ray photoelectron spectroscopy. A shift in the Gd and O peak positions indicate the presence of nitrogen in the layer. Raman spectroscopy reveals heavy structural changes. The newly appearing structure is crystalline, but not in agreement with either the known bixbyite (Gd2O3) or rocksalt (GdN) structure. Electron microscopic investigations reveal the formation of cracks and small areas with lower densities or even voids. That structure exhibits similarities with transmission electron microscopy images of gadolinium nitride (GdN) layers. The electronic band gap of Gd2O3 estimated from O1s plasmon energy loss measurements was found to decrease significantly by the incorporation of nitrogen. Reduction in the valence band and conduction band offset is obtained as a function of implantation dose.

Keywords: Band gap; Crystal structure; Gadolinium; X-ray photoelectron spectroscopy; Transmission electron microscopy


Publ.-Id: 24208

Human endothelial cell models in biomaterial research

Hauser, S.; Jung, F.; Pietzsch, J.

Endothelial cell (EC) models have evolved as important tools in biomaterial research due to ubiquitously occurring interactions between implanted materials and the endothelium. However, screening the available literature has revealed a gap between material scientists and physiologists in terms of their understanding of these biomaterial–endothelium interactions and their relative importance. Consequently, EC models are often applied in nonphysiological experimental setups, or too extensive conclusions are drawn from their results. The question arises whether this might be one reason why, among the many potential biomaterials, only a few have found their way into the clinic. In this review, we provide an overview of established EC models and possible selection criteria to enable researchers to determine the most reliable and relevant EC model to use.

Keywords: endothelial cell heterogeneity; vascular grafts; stents; bone regeneration; soft tissue regeneration

Publ.-Id: 24207

Observation of 22Na+-Diffusion in Opalinus Clay using Positron Emission Tomography (GeoPET)

Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Lippmann-Pipke, J.

We applied positron emission tomography (PET) for investigating diffusion of Na-22 in Opalinus clay rock. This enables to derive diffusion parameters on the macroscopic scale of drill cores (diameter 100 mm), and thus to consider effects of anisotropy and heterogeneities. This method is complementary to laboratory measurements with common diffusion cells, which can hardly elucidate such macroscopical spatial effects.
Here, we present the measuring data as motion picture. The underlying PET-data are 20 scans over a period of 143 days after injection of synthetic Opalinus pore water, labelled with Na-22, into an axial blind hole.

Keywords: diffusion; clay rock; heterogeneity; anisotropy; positron emission tomography; PET


Publ.-Id: 24206

Determining femtosecond plasma dynamics via radiation spectra A simulation approach with PIConGPU

Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Schramm, U.; Bussmann, M.

A vital step from simulating complex plasma dynamics and comparing it with experimental measurements or astrophysical observations is predicting observables as e.g. the emitted radiation. This poster focuses on how we compute spectrally and spatially resolved radiation based on Liénard Wiechert potentials in the 3D3V particle-in-cell code PIConGPU. Applications in laser plasma acceleration and astrophysics are given to demonstrate the wide applicability of our synthetic diagnostic method.

Keywords: PIConGPU; radiation; plasma; synthetic diagnostic

  • Poster
    11th Annual PhD Seminar 2016 (HZDR), 17.-19.10.2016, Oberwiesenthal, Deutschland

Publ.-Id: 24205

Hydrophilic Nd3+-Sensitized Upconverting Core-Shell Nanoparticles for Biomedical Applications

Hesse, J.; Sgarzi, M.; Stephan, H.

Currently, there is a widespread interest to use neodymium containing upconverting nanophosphors (UCNPs) for bioimaging applications. The fascination of these nanoparticles derives from their capacity for excitation in the biologically transparent window (650-950 nm), exceptional ability to convert near infrared radiation into visible light (upconversion), which prevents autofluorescence and over-heating effect of biological tissues, capability for deep tissue, and high contrast imaging [1]. Despite the fast progress in lanthanide-doped upconversion nanoparticles, the preparation of ultrasmall, monodisperse and hydrophilic UCNPs that display intense luminescence is still a challenging issue. Only a few examples of ultrasmall and hydrophilic UCNPs have been reported [2-3]. Established strategies for synthesizing UCNPs yield mainly hydrophobic particles[1]. Here, we report the, synthesis and surface modification of sub-10 nm UCNPs with an excitation wavelength of 795 nm, which are composed of a host lattice of crystalline hexagonal phased NaYF4 doped with Nd3+ and Yb3+ as sensitizers, and Er3+, Ho3+ or Tm3+ as emitter ions. Surface passivation by coating with a shell of active and also inert host material is used to enhance the overall upconversion efficiency. We also report the conversion of these into hydrophilic, colloidally-stable, and biocompatible by using mainly ligand exchange strategies and the influence of the coating on the UCNPs’ photophysical properties will also be discussed. Finally, this study will also allow establishing information about biodistribution, pharmacokinetics and formation of protein corona for ultrasmall UCNPs.

Keywords: Upconversion; lanthanide; Sub 10nm particles; surface functionalization; Bio imaging

  • Poster
    6th EuCheMS Chemistry Congress, 11.-15.09.2016, Seville, Spain

Publ.-Id: 24204

Molecular interaction of radio-metals with microorganisms

Raff, J.; Vogel, M.; Schmoock, C.; Günther, A.; Moll, H.; Drobot, B.; Lederer, F.; Li, B.; Foerstendorf, H.; Börnick, H.; Pollmann, K.; Worch, E.; Stumpf, T.

The presentation will give an overview on the radio-ecological work at the Institute of Ressource Ecology and an outlook on planed research activities

Keywords: Microorganisms; bioligands; radionuclides

  • Invited lecture (Conferences)
    Institutsseminar des Instituts für Nukleare Entsorgung, Karlsruher Institut für Technologie, 08.11.2016, Eggenstein-Leopoldshafen, Deutschland

Publ.-Id: 24203

Soft matter nanoparticles based on polyglycerols as efficient multimodal imaging agents for EGF-receptor tumor targeting

Pant, K.; Zarschler, K.; Neuber, C.; Pufe, J.; Pietzsch, J.; Stephan, H.; Haag, R.

Nano-constructs based on macromolecules have become increasingly interesting in the recent years owing to their unique properties like high aqueous stability, biocompatibility etc. in the field of drug delivery, nanomedicine as well as for multi modal imaging. Having multiple modalities on a single carrier molecule obviate the need to administer several compounds with different pharmacokinetics. In this regard, dendritic polyglycerols (dPG) are globular macromolecules with a nano-size (5-20 nm), narrow size distribution (PDI >1.26), high degree of branching and high end group functionalities which makes them amenable to a wide range of chemical modifications.[1] This great versatility allows dendritic polyglycerols to be fine-tuned with respect to various physico-chemical parameters such as particle size, water solubility, surface charge, chemical functionalities, etc, that are relevant for the successful preparation of theranostic systems. Previous studies done on 3H and 64Cu radiolabeled anionic and neutral dPG shows their great potential as platforms for various applications.[2] The presented work here deals with the development of a dendritic polyglycerol derivative as a dual-modal agent for epidermal growth factor receptor (EGFR) specific tumor targeting. In this respect, in a one pot reaction, simultaneously maleimido- bearing fluorescent labels (dye) for in vitro or vivo imaging (cy3/cy7) and macrocyclic chelators for 64Cu (PET tracer) were attached to thiol anchoring groups of the polymeric scaffold. For an EGFR specific targeting, a small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR was attached via a PEG linker. For a controlled purification, an affinity chromatography procedure was used which selectively separates the antibody conjugated multimodal conjugates. This leads to a higher affinity and selectivity of the dual modal conjugates on the tumor cells. 64Cu radiolabeling was done under ambient temperature and physiological pH. Binding and uptake studies were performed using A431 and FaDu cell lines using 64Cu-labeled bioconjugates. Confocal laser scanning microscopy was used to study the receptor-mediated cellular uptake as well as scavenger receptor studies which show a selective affinity of dPG conjugates to the tumor cells. Antibody-dPG multimodal conjugates were injected intravenously to mouse xenografted models for in vivo studies using PET imaging as well as optical imaging which reveal a good tumor targeting of the conjugates. These results reveal an excellent potential of dendritic polyglycerols as multimodal platforms for various biomedical applications.

Keywords: Radiolabeled; nanoparticles; diagnostics; receptor-mediated

  • Lecture (Conference)
    6th European Chemical Society Congress, Seville, Spain, 11.-15.09.2016, English, Spain

Publ.-Id: 24202

In-situ membrane bending setup for strain-dependent scanning transmission x-ray microscopy investigations

Finizio, S.; Wintz, S.; Kirk, E.; Raabe, J.

We present a setup that allows for the in-situ generation of tensile strains by bending x-ray transparent Si3N4 membranes with the application of a pressure difference between the two sides of the membrane, enabling the possibility to employ high resolution space- and time-resolved scanning transmission x-ray microscopy for the investigation of the magneto-elastic coupling.

Keywords: x-ray microscopy; strain; magneto-elastic coupling

Publ.-Id: 24201

Control Of The Magnetization Dynamics In Magnetostrictive Nanostructures Through The Magneto-Elastic Coupling Effect

Finizio, S.; Kirk, E.; Wintz, S.; Raabe, J.

The magneto-elastic (ME) coupling has attracted an increasing interest in the last years, in particular for micro- and nanostructured magnetostrictive materials. The magnetic configuration of these materials can be controlled by mechanical strain (generated e.g. with a piezoelectric substrate), an example of which is the strain induced anisotropy in Ni nanostructures. However, while the quasi-static properties of the ME coupling have been thoroughly investigated, an analysis of the influences of the ME coupling on the magnetization dynamics is still lacking, in part due to the experimental difficulties involved in the use of piezoelectric substrates. Here, we present an alternative path to the use of piezoelectric materials for the investigation of the effect of the ME coupling on magnetization dynamics with time-resolved x-ray magnetic microscopy. With this approach, the magnetostrictive elements are strained by the bending of a thin SiN membrane in-situ, through the generation of a pressure difference between the two sides of the membrane. This is achieved by employing a pressure controlled environmental cell. Using SiN membranes with different geometries, the direction of the applied strain can be tuned, allowing for the generation of a pressure-controlled uniaxial magnetic anisotropy in microstructured Ni elements. Furthermore, this additional ME anisotropy also strongly influences the magnetization dynamics of the Ni structures, thus demonstrating that our approach provides a simple and powerful tool for the analysis of the magnetization dynamics in magnetostrictive elements.

Keywords: magneto-elastic coupling; magnetostriction; magnetization dynamics

  • Lecture (Conference)
    61st Annual Conference on Magnetism and Magnetic Materials, 31.10.-04.11.2016, New Orleans, USA

Publ.-Id: 24200

Neue Ansätze zum Aufspüren und Behandeln von Tumorerkrankungen

Stephan, H.

keine Abstract verfügbar

  • Lecture (others)
    Eingeladener Abendvortrag, 25.10.2016, Zittau, Deutschland

Publ.-Id: 24199

Nuclear and Optical Dual-labelled Imaging Agents

Stephan, H.

For the past decade, nuclear and optical dual-labelled imaging agents have attracted enormous attention 1. Applied to cancer imaging, tumours can be tracked down by nuclear techniques such as SPECT and PET, and subsequently resected using image-guided surgery with the appropriate fluorophores. Moreover, the high spatial resolution of fluorescence imaging permits the elucidation of cell-biological events and thereby gaining a deeper insight into in vitro and in vivo processes. The development of dual imaging probes can be achieved using sophisticated low-molecular compounds that combine moieties for the desired imaging modalities, e.g. dyes for fluorescence optical imaging, and appropriate bifunctional chelator agents (BFCAs) for radiometals enabling SPECT or PET. We have developed BFCAs based on bis(2-pyridylmethyl)-1,4,7-triazacyclononane (DMPTACN) and 3,7-diazabicyclo[3.3.1]nonane (bispidine) that rapidly form stable 64CuII complexes under mild conditions. These BFCAs are well-suited for in vivo application in cancer imaging 2, 3. Since they are also relatively easy to functionalize with multiple modalities, they are ideal chelators for the design of targeted dual-labelled imaging agents (PET, fluorescence imaging) 4, 5.
Here, important features of 64CuII-labelled DMPTACN and bispidine complexes, e.g. stabilities, coordination geometry, ligand exchange kinetics, serum stability, partition coefficients (n-octanol/water), photophysical properties of dye-labelled compounds and biodistribution data will be reported.

1 A. Azhdarinia et al., Mol. Imag. Biol. 2012, 14, 261. 2 S. Juran et al., Bioconjugate Chem. 2009, 20, 347.
3 R. Bergmann et al., Eur. J. Med Chem. 2013, 70, 434. 4 K. Viehweger et al., Bioconjugate Chem. 2014, 25, 1011. 5 H. Stephan et al., Chem. Eur. J. 2014, 20, 17011.

  • Lecture (Conference)
    6th EuCheMS Chemistry Congress, 11.-15.09.2016, Seville, Spain

Publ.-Id: 24198

Implementing High-Order FIR Filters in FPGAs

Födisch, P.; Bryksa, A.; Lange, B.; Enghardt, W.; Kaever, P.

Contemporary field-programmable gate arrays (FPGAs) are predestined for the application of finite impulse response (FIR) filters. Their embedded digital signal processing (DSP) blocks for multiply-accumulate operations enable efficient fixed-point computations, in cases where the filter structure is accurately mapped to the dedicated hardware architecture. This brief presents a generic systolic structure for high-order FIR filters, efficiently exploiting the hardware resources of an FPGA in terms of routability and timing. Although this seems to be an easily implementable task, the synthesizing tools require an adaptation of the straightforward digital filter implementation for an optimal mapping. Using the example of a symmetric FIR filter with 90 taps, we demonstrate the performance of the proposed structure with FPGAs from Xilinx and Altera. The implementation utilizes less than 1% of slice logic and runs at clock frequencies up to 526 MHz. Moreover, an enhancement of the structure ultimately provides an extended dynamic range for the quantized coefficients without the costs of additional slice logic.

Keywords: digital filters; field-programmable gate arrays; FIR filters; fixed-point arithmetic


Publ.-Id: 24197

Digital high-pass filter deconvolution by means of an infinite impulse response filter

Födisch, P.; Wohsmann, J.; Lange, B.; Schönherr, J.; Enghardt, W.; Kaever, P.

In the application of semiconductor detectors, the charge-sensitive amplifier is widely used in front-end electronics. The output signal is shaped by a typical exponential decay. Depending on the feedback network, this type of front-end electronics suffers from the ballistic deficit problem, or an increased rate of pulse pile-ups. Moreover, spectroscopy applications require a correction of the pulse-height, while a shortened pulse-width is desirable for high-throughput applications. For both objectives, digital deconvolution of the exponential decay is convenient. With a general method and the signals of our custom charge-sensitive amplifier for cadmium zinc telluride detectors, we show how the transfer function of an amplifier is adapted to an infinite impulse response (IIR) filter. This paper investigates different design methods for an IIR filter in the discrete-time domain and verifies the obtained filter coefficients with respect to the equivalent continuous-time frequency response. Finally, the exponential decay is shaped to a step-like output signal that is exploited by a forward-looking pulse processing.

Keywords: Cadmium zinc telluride (CdZnTe,CZT) detector; Charge-sensitive amplifier; Digital pulse processing; Digital filter; Deconvolution; Field-programmable gate array (FPGA)


Publ.-Id: 24196

Ferromagnetic resonance of MBE-grown FeRh thin films through the metamagnetic phase transition

Heidarian, A.; Stienen, S.; Semisalova, A.; Hübner, R.; Salamon, S.; Wende, H.; Gallardo, R.; Grenzer, J.; Potzger, K.; Lindner, J.; Bali, R.

A FeRh thin film of 33 nm thickness grown by molecular beam epitaxy (MBE) has been investigated with respect to its temperature dependent magnetic properties by means of ferromagnetic resonance (FMR). Within the ferromagnetic regime, i.e. at temperatures above the antiferromagnetic-to-ferromagnetic phase transition, the resonance field decreases with decreasing temperature reflecting an increasing magnetization. Within the temperature regime of the phase transition, the resonance field behaves non-monotonically, i.e. it suddenly increases with decreasing temperature. The observed asymmetric shape of the FMR absorption line is discussed with respect to a possible small magnetic inhomogeneity of the film coupled to the main ferromagnetic volume of B2 ordered, equiatomic FeRh.

Keywords: FeRh; Ferromagnetic resonance

Publ.-Id: 24195

Charge-sensitive front-end electronics with operational amplifiers for CdZnTe detectors

Födisch, P.; Berthel, M.; Lange, B.; Kirschke, T.; Enghardt, W.; Kaever, P.

Cadmium zinc telluride (CdZnTe, CZT) radiation detectors are suitable for a variety of applications, due to their high spatial resolution and spectroscopic energy performance at room temperature. However, state-of-the-art detector systems require high-performance readout electronics. Though an application-specific integrated circuit (ASIC) is an adequate solution for the readout, requirements of high dynamic range and high throughput are not available in any commercial circuit. Consequently, the present study develops the analog front-end electronics with operational amplifiers for an 8x8 pixelated CZT detector. For this purpose, we modeled an electrical equivalent circuit of the CZT detector with the associated charge-sensitive amplifier (CSA). Based on a detailed network analysis, the circuit design is completed by numerical values for various features such as ballistic deficit, charge-to-voltage gain, rise time, and noise level. A verification of the performance is carried out by synthetic detector signals and a pixel detector. The experimental results with the pixel detector assembly and a 22Na radioactive source emphasize the depth dependence of the measured energy. After pulse processing with depth correction based on the fit of the weighting potential, the energy resolution is 2.2% (FWHM) for the 511 keV photopeak.

Keywords: Analogue electronic circuits; Front-end electronics for detector readout; Gamma detectors (scintillators, CZT, HPG, HgI etc)


Publ.-Id: 24194

Synthesis and Preliminary Biological Evaluation of Indol-3-yl-oxoacetamides as Potent Cannabinoid Receptor Type 2 Ligands

Moldovan, R.-P.; Deuther-Conrad, W.; Horti, A. G.; Brust, P.

A small series of indol-3-yl-oxoacetamides was synthesized starting from the literature known N-(adamantan-1-yl)-2-(5-(furan-2-yl)-1-pentyl-1H-indol-3-yl)-2-oxoacetamide (5) by substituting the 1-pentyl-1H-indole subunit. Our preliminary biological evaluation showed that the fluorinated derivative 8 is a potent and selective CB2 ligand with Ki = 6.2 nM.

Keywords: positron emission tomography; cannabinoid receptor type 2; binding affinity; indole


Publ.-Id: 24193

HASEonGPU—An adaptive, load-balanced MPI/GPU-code for calculating the amplified spontaneous emission in high power laser media

Eckert, C. H. J.; Zenker, E.; Bussmann, M.; Albach, D.

We present an adaptive Monte Carlo algorithm for computing the amplified spontaneous emission (ASE) flux in laser gain media pumped by pulsed lasers. With the design of high power lasers in mind, which require large size gain media, we have developed the open source code HASEonGPU that is capable of utilizing multiple graphic processing units (GPUs). With HASEonGPU, time to solution is reduced to minutes on a medium size GPU cluster of 64 NVIDIA Tesla K20m GPUs and excellent speedup is achieved when scaling to multiple GPUs. Comparison of simulation results to measurements of ASE in Yb3+ : YAG ceramics show perfect agreement.

Keywords: Amplified spontaneous emission; CUDA; GPU cluster; Massively parallel; Monte Carlo integration; High power laser


Publ.-Id: 24191

Extending the truncated Dyson-Schwinger equation to finite temperatures

Dorkin, S. M.; Viebach, M.; Kaptari, L. P.; Kämpfer, B.

In view of the properties of mesons in hot strongly interacting matter the properties of the solutions of the truncated Dyson-Schwinger equation for the quark propagator at finite temperatures within the rainbow-ladder approximation are analysed in some detail. In Euclidean space within the Matsubara imaginary time formalism the quark propagator is not longer a O(4) symmetric function and possesses a discrete spectra of the fourth component of the momentum. This makes the treatment of the Dyson-Schwinger and Bethe-Salpeter equations conceptually different from the vacuum and technically much more involved. The question whether the interaction kernel known from vacuum calculations can be applied at finite temperatures remains still open. We find that, at low temperatures, the model interaction with vacuum parameters provides a reasonable description of the quark propagator, while at temperatures higher than a certain critical value Tc the interaction requires stringent modifications. The general properties of the quark propagator at finite temperatures can be inferred from lattice QCD calculations. We argue that, to achieve a reasonable agreement of the model calculations with that from lattice QCD, the kernel is to be modified in such a way as to screen the infra-red part of the interaction at temperatures larger than Tc. For this, we analyse the solutions of the truncated Dyson-Schwinger equation with existing interaction kernels in a large temperature range with particular attention on high temperatures in order to find hints to an adequate temperature dependence of the interaction kernel to be further implemented in to the Bethe-Salpeter equation for mesons. This will allow to investigate the possible in medium modifications of the meson properties as well as the conditions of quark deconfinement in hot matter.

Publ.-Id: 24190

Interplay of localization and magnetism in (Ga,Mn)As and (In,Mn)As

Yuan, Y.; Sawicki, M.; Dietl, T.; Helm, M.; Zhou, S.

We examine the role of localization on the hole-mediated ferromagnetism in dilute ferromagnetic semiconductors by combining results of electrical and magnetic studies for Mn-implanted GaAs and InAs. In both materials upon increasing the Mn concentration, a change from an insulating (hopping) regime of conductivity to a metallic-like is accompanied by a gradual build-up of a long-range magnetic coupling and a monotonic increase of the Curie temperature. For the least conducting sample no (global) Curie temperature can be identified, although the observed slow dynamics (superparamagnetic-like) confirms the presence of a ferromagnetic coupling acting only over limited (mesoscopic) distances. We tentatively characterize the strength of this local coupling by T*, the largest temperature at which dynamic effects are observable by conventional SQUID magnetometry. Our findings strongly advocate for the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions between diluted spins even on the insulator side of the metal-to-insulator transition. Interestingly, T* at low carrier densities becomes larger in (In,Mn)As compared to (Ga,Mn)As. This constitutes a new experimental support for the suggestion [2] that larger p-d coupling results in higher values of TC only in the regime, where hole localization effects are not crucial.

  • Poster
    ICPS 2016 - 33rd International Conference on the Physics of Semiconductors, 31.07.-05.08.2016, Beijing, China
  • Lecture (Conference)
    PASPS 9th - 9th International Conference on Physics and Applications of Spin Phenomena in Solids, 08.-11.08.2016, Kobe, Japan
  • Lecture (Conference)
    61st Annual Conference on Magnetism and Magnetic Materials, 31.10.-04.11.2016, New Orleans, America

Publ.-Id: 24189

Ferromagnetic Mn-implanted GaP: Microstructures vs. magnetic properties

Yuan, Y.; Hübner, R.; Liu, F.; Sawicki, M.; Gordan, O.; Salvan, G.; Zahn, D. R. T.; Banerjee, D.; Baehtz, C.; Helm, M.; Zhou, S.

We present a systematic investigation on the evolution of microstructure and magnetic properties as a function of the pulsed laser annealing energy in GaMnP prepared by ion implantation and pulsed laser annealing. The sample microstructure was analyzed by high-resolution X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectrometry (RBS), ultraviolet Raman spectroscopy, and extended X-ray absorption fine structure spectroscopy. The presence of X-ray Pendellösung fringes around GaP (004) and RBS channeling prove the epitaxial structure of the GaMnP layer annealed at the optimized laser energy density (0.40 J/cm2). However, a forbidden TO vibrational mode of GaP appears and increases with annealing energy, suggesting the formation of defective domains inside the layer. These domains mainly appear in the sample surface region and extend to almost the whole layer with increasing annealing energy. The reduction of both the Curie temperature and the uniaxial magnetic anisotropy gradually takes place when more defects and the domains appear along the increasing annealing energy density. This fact univocally points to the decisive role of the pulsed laser annealing parameters on the resulting magnetic characteristics in the processed layers, which eventually determine their magnetic (or spintronics) figure of merit.

  • Lecture (Conference)
    ON2016 XI-th International Conference: Ion Implantation and Other Applications of Ions and Electrons, 13.-16.06.2016, Kazimierz Dolny, Poland

Publ.-Id: 24188

Metal pad roll instability in liquid metal batteries

Weber, N.; Beckstein, P.; Galindo, V.; Nore, C.; Herreman, W.; Stefani, F.; Weier, T.

The increasing deployment of renewable energies requires three fundamental changes to the electric grid: more transmission lines, a flexibilisation of the demand and grid scale energy storage. Liquid metal batteries (LMBs) are considered these days as a promising means of stationary energy storage. Built as a stable density stratification of two liquid metals separated by a liquid salt, LMBs have three main advantages: a low price, a long life-time and extremely high current densities. In order to be cheap, LMBs have to be built large. However, battery currents in the order of kilo-amperes may lead to magnetohydrodynamic (MHD) instabilities, which – in the worst case – may short-circuit the thin electrolyte layer. The metal pad roll instability, as known from aluminium reduction cells, is considered as one of the most dangerous phenomena for LMBs. We develop a numerical model, combining fluid- and electrodynamics with the volume-of-fluid method, to simulate this instability in cylindrical LMBs. We explain the instability mechanism similar to that in aluminium reduction cells and give some first results, including growth rates and oscillation periods of the instability.

Keywords: metal pad roll; sloshing; liquid metal battery; OpenFOAM

  • Open Access Logo Magnetohydrodynamics 53(2017)1, 129-140


Publ.-Id: 24187

Chemical stability of BioXmark® following normofractionated and single-fraction proton beam therapy

Troost, E.; Menkel, S.; Enghardt, W.; Hytry, J.; Kunath, D.; Makocki, S.; Hoffmann, A.; Jolck, R.

Use of solid fiducial markers in proton radiation therapy has been approached with care as their presence may cause significant local dose perturbations. Recently, a liquid carbohydrate based fiducial marker (BioXmark®) has been introduced with minimal dose perturbation (relative stopping power = 1.164) and visibility properties suitable for use in image-guided proton therapy (IGPT). The purpose of this work was to investigate the chemical stability of the marker for use in both normofractionated and single fraction proton treatment regimes.

Ten identical custom-made cylindrical polymethylmethacrylate (PMMA) inserts (V = 0.95 mL, douter = 10.0 mm, dinner = 5.0 mm, l = 48 mm) were prepared. BioXmark® markers (150±30 mg) were added to the bottom of the inserts and water (700 μL) was added on top of the markers. The inserts were sealed with a rubber stopper.
A QA dosimetry phantom was modified to accommodate four PMMA inserts simultaneously by inserting these sideway into the proton irradiation field (10 × 10cm) (Figure 1). Four markers (Group A) were irradiated during daily QA for a period of 51 days with 43 fractions ranging from 1.44-1.86 Gy resulting in an accumulated dose of 67.4 Gy. Four other markers (Group B) were irradiated with a single dose of 155.4 Gy and two non-irradiated Control markers were kept on site for the duration of the experiments.
Possible chemical alterations caused by proton irradiation were evaluated by high-performance liquid chromatography (HPLC), electrospray ionization mass spectrometry (ESI-MS),thin-layer chromatography (TLC) and visual inspection of the markers and the aqueous phase above the markers.

No visual alterations between markers from Group A+B and the Control markers were observed. HPLC and TLC analysis of the markers and the aqueous phase above the markers from all three groups did not indicate chemical degradation of the marker materials (Figure 2). This observation was further supported by ESI-MS analysis, which showed identical m/z fragments for all three groups (Figure 2).

The BioXmark®marker showed no chemical degradation after exposure to normofractionated and extremely hypofractionated proton therapy regimes and may serve as a good alternative to solid fiducial markers used for IGPT.

Keywords: BioXmark fiducial marker; proton beam irradiation

Publ.-Id: 24186

E1 and M1 strength functions at low energy

Schwengner, R.; Massarczyk, R.; Bemmerer, D.; Beyer, R.; Junghans, A. R.; Kögler, T.; Rusev, G.; Tonchev, A. P.; Tornow, W.; Wagner, A.

We report on photon-scattering experiments using bremsstrahlung at the γELBE facility of Helmholtz-Zentrum Dresden-Rossendorf and using quasimonoenergetic, polarized γ beams at the HIγS facility of the Triangle Universities Nuclear Laboratory in Durham. To deduce the photoabsorption cross sections at high excitation energy and high level density, unresolved strength in the quasicontinuum of nuclear states has been taken into account. In the analysis of the spectra measured by using bremsstrahlung at γELBE, we perform simulations of statistical γ-ray cascades using the code γDEX to estimate intensities of inelastic transitions to low-lying excited states. Simulated average branching ratios are compared with model-independent branching ratios obtained from spectra measured by using monoenergetic γ beams at HIγS. E1 strength in the energy region of the pygmy dipole resonance is discussed in nuclei around mass 90 and in xenon isotopes. M1 strength in the region of the spin-flip resonance is also considered for xenon isotopes. The dipole strength function of 74Ge deduced from γELBE experiments is compared with the one obtained from experiments at the Oslo Cyclotron Laboratory. The low-energy upbend seen in the Oslo data is interpreted as M1 strength on the basis of shell-model calculations.

Keywords: photonuclear reactions; photon scattering; nuclear resonance fluorescence; photoabsorption cross section; gamma-ray strength function; shell model

  • Invited lecture (Conferences)
    International Conference on Nuclear Data for Science and Technology, 11.-16.09.2016, Brugge, Belgien
  • Open Access Logo European Physical Journal Web of Conferences 146(2017), 05001
    DOI: 10.1051/epjconf/201714605001


Publ.-Id: 24185

Extension of hybrid micro-depletion model for decay heat calculation in DYN3D code

Bilodid, Y.; Fridman, E.; Kotlyar, D.; Shwageraus, E.

Reactor dynamics code DYN3D, stand-alone or in coupling with plant thermo-hydraulic codes such as ATHLET or RELAP, is used to simulate transients and accidents scenarios. The radioactive decay heat generated by nuclear fuel after shutdown plays an important role in a number of accident scenarios. The decay heat model implemented in DYN3D so far is based on the German national standard DIN Norm 25463 (1990) and its applicability is limited to LWR fuel up to 4.1% enrichment.
This work extends the hybrid micro-depletion methodology, recently implemented in DYN3D, to the decay heat calculation by accounting explicitly for the heat contribution from the decay of each nuclide in the fuel. This method does not involve any assumptions about fuel content or operational history and therefore is valid for a wide range of fuel types. Detailed nuclide content of the fuel is calculated by DYN3D in a fuel cycle simulation, taking into account local operational history of each node. Thus, DYN3D is able to accurately calculate the axial decay heat power distribution in each fuel assembly during transients as well as in long term storage.

Keywords: DYN3D; decay heat; microscopic depletion

  • Contribution to proceedings
    26th Symposium of AER on VVER Reactor Physics and Reactor Safety, 10.-14.10.2016, Helsinki, Finland
    Proc. of the 26th Symposium of AER on VVER Reactor Physics and Reactor Safety
  • Lecture (Conference)
    26th Symposium of AER on VVER Reactor Physics and Reactor Safety, 10.-14.10.2016, Helsinki, Finland

Publ.-Id: 24184

Analysis of C/E results of fission rate ratio measurements in several fast lead VENUS-F cores

Kochetkov, A.; Krása, A.; Baeten, P.; Vittiglio, G.; Wagemans, J.; Bécares, V.; Bianchini, G.; Fabrizio, V.; Carta, M.; Firpo, G.; Fridman, E.; Sarotto, M.

During the GUINEVERE FP6 European project (2006-2011), the zero-power VENUS water-moderated reactor was modified into VENUS-F, a mockup of lead cooled fast spectrum system with solid components that can be operated in both critical and subcritical mode.
The Fast Reactor Experiments for hybrid Applications (FREYA) FP7 project was launched in 2011 to support the designs of the MYRRHA Accelerator Driven System (ADS) and the ALFRED Lead Fast Reactor (LFR). Three VENUS-F critical core configurations, simulating the complex MYRRHA core design and one configuration devoted to the LFR ALFRED core conditions were investigated in 2015. The MYRRHA related cores simulated step by step design peculiarities like the BeO reflector and in pile sections. For all of these cores the fuel assemblies were of a simple design consisting of 30 % enriched metallic uranium, lead rodlets to simulate the coolant and Al2O3 rodlets to simulate the oxide fuel.
Fission rate ratios of minor actinides such as Np-237, Am-241 as well as Pu-239, Pu-240, Pu-242 and U-238 to U-235 were measured in these VENUS-F critical assemblies with small fission chambers in specially designed locations, to determine the spectral indices in the different neutron spectrum conditions.
The measurements have been analyzed using advanced computational tools including deterministic and stochastic codes and different nuclear data sets like JEFF-3.1, JEFF-3.2, ENDF/B7.1, ENDF/B6.8, JENDL-4.0 and TENDL-2014. The analysis of the C/E discrepancies will help to improve the nuclear data in the specific energy region of fast neutron reactor spectra.

  • Open Access Logo Contribution to proceedings
    ND2016 - International Conference on Nuclear Data for Science and Technology, 11.-16.09.2016, Bruges, Belgium
    EPJ Web of ConferencesVolume 146, Article number 06007
    DOI: 10.1051/epjconf/201714606007

Publ.-Id: 24183

Contactless inductive flow tomography: recent developments in its application to continuous casting with electromagnetic brakes

Ratajczak, M.; Wondrak, T.; Martin, R.; Stefani, F.; Jacobs, R.

Measuring the velocity in hot and/or aggressive melts is a challenging task. Many applications, like continuous casting of steel, would benefit even from a rough knowledge of the global flow structure of the melt, because the flow structure has a direct impact on the quality of the final product. In continuous casting, electromagnetic brakes (EMBrs) are widely used to influence the flow in the mold, as they are expected to damp undesired flow oscillations that are associated with multiple kinds of defects. Yet, without direct feedback from the mold flow, a tailored process control with EMBrs is hardly possible.
The contactless inductive flow tomography (CIFT) could help to circumvent these problems. The method relies on the induction of a secondary magnetic field if the moving fluid is exposed to a primary magnetic field. From the measurement of the induced magnetic outside the melt, the global flow structure of the melt can be inferred by solving the associated linear inverse problem. A successful application of CIFT to EMBr-influenced mold flows could enable steel producers to cast high quality steel with less rejects. In this paper we will outline the efforts to adapt CIFT to a laboratory liquid-metal mold under the influence of an EMBr.

Keywords: Contactless inductive flow tomography; continuous casting; magnetic field measurement; gradiometric sensor; electromagnetic brake

  • Contribution to proceedings
    WCIPT8 - 8th World Congress on Industrial Process Tomography, 26.-29.09.2016, Foz do Iguacu, Brasilia
  • Lecture (Conference)
    WCIPT8 - 8th World Congress on Industrial Process Tomography,, 26.-29.09.2016, Foz do Iguacu, Brasilia

Publ.-Id: 24182

Performance study of a Mosaic high rate MRPC

Wang, F.; Han, D.; Xie, B.; Wang, Y.; Lyu, P.; Guo, B.; Laktineh, I.; Naumann, L.; Kotte, R.; Dreyer, J.; Garcia, A. L.; Stach, D.; Fan, X.; Akindinov, A.

A prototype of a large mosaic MRPC with low resistive glass for the future upgrade of CMS muon system is presented. This prototype is designed by jointing two pieces of glass together and separating them by fishing lines to prevent sparks. A simulation of the weighting field based on Maxwell shows that the efficiency is higher than 90% in the joint area. In a beam test at HZDR, the prototype achieved ~ 92% detection efficiency and about 60 ps time resolution in the joint area, and ~95% efficiency and 60 ps time resolution in the active area. A rate capability study shows this prototype can withstand 40 kHz/cm2 at least.

Publ.-Id: 24181

Spin caloritronic nano-oscillator

Safranski, C.; Barsukov, I.; Lee, H. K.; Schneider, T.; Jara, A. A.; Smith, A.; Chang, H.; Lenz, K.; Lindner, J.; Tserkovnyak, Y.; Wu, M.; Krivorotov, I. N.

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nanoelectronic devices. Harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here we demonstrate that hermal gradients arising from ohmic heating can be utilized for driving auto-oscillations of magnetization in a ferrimagnetic nanowire via the spin Seebeck effect and for generation of tunable microwave signals. Our work paves the way towards spin caloritronic microwave and magnonic nanodevices.

Keywords: nanooscillator; spincaloritronics; magnetism; spin waves; spin torque

  • Open Access Logo Nature Communications 8(2017), 117
    DOI: 10.1038/s41467-017-00184-5
  • Lecture (Conference)
    Magnonics 2019, 28.07.-01.08.2019, Carovigno, Italien

Publ.-Id: 24180

SIMEX: Simulation of Experiments at Advanced Light Sources

Fortmann-Grote, C.; Andreev, A. A.; Briggs, R.; Bussmann, M.; Buzmakov, A.; Garten, M.; Grund, A.; Huebl, A.; Hauff, S.; Joy, A.; Jurek, Z.; Loh, N. D.; Rüter, T.; Samoylova, L.; Santra, R.; Schneidmiller, E. A.; Sharma, A.; Wing, M.; Yakubov, S.; Yoon, C. H.; Yurkov, M. V.; Ziaja, B.; Mancuso, A. P.

Realistic simulations of experiments at large scale photon facilities, such as optical laser laboratories, synchrotrons, and free electron lasers, are of vital importance for the successful preparation, execution, and analysis of these experiments investigating ever more complex physical systems, e.g. biomolecules, complex materials, and ultra--short lived states of highly excited matter. Traditional photon science modelling takes into account only isolated aspects of an experiment, such as the beam propagation, the photon-matter interaction, or the scattering process, making idealized assumptions about the remaining parts, e.g. the source spectrum, temporal structure and coherence properties of the photon beam, or the detector response. In SIMEX, we have implemented a platform for complete start-to-end simulations, following the radiation from the source, through the beam transport optics to the sample or target under investigation, its interaction with and scattering from the sample, and its registration in a photon detector, including a realistic model of the detector response to the radiation. Data analysis tools can be hooked up to the modelling pipeline easily. This allows researchers and facility operators to simulate their experiments and instruments in real life scenarios, identify promising and unattainable regions of the parameter space and ultimately make better use of valuable beamtime.

  • Contribution to proceedings
    NOBUGS (New Opportunities for Better User Group Software), 17.-19.10.2016, Copenhagen, Denmark

Publ.-Id: 24179

Use of ion irradiation to tune magnetic anisotropy

Osten, J.; Greene, P.; Lenz, K.; Fassbender, J.; Jenkins, C.; Arenholz, E.; Endo, T.; Iwata, N.; Liu, K.

Current challenges in magnetic storage media will be shortly discussed. In detail perpendicular magnetic recording media is addressed. Perpendicular magnetic recording media has the advantage of good data stability but the disadvantage of a high writing field. The writing field is also determined by the anisotropy of the material. To control the anisotropy ion irradiation of Co/Pd multilayers has been investigated. By adjusting the kinetic energy and fluence, the depth and lateral density of the local structural modification are controlled. First-order reversal curve analysis through X-ray magnetic circular dichroism and conventional magnetometry studies shows that the local structural damage weakens the perpendicular anisotropy near the surface, leading to a magnetization tilting towards the in-plane direction. The ion irradiation method is complementary to and may be used in conjunction with, other synthesis approaches to maximize the anisotropy gradient.

Keywords: anisotropy gradient; PMR; ion implantation

  • Invited lecture (Conferences)
    Ion Beams in Materials Engineering and Characterization (IBMEC), 28.09.-01.10.2016, New Dehli, Indien

Publ.-Id: 24178

Incidental dose to cardiac subvolumes does not improve prediction of radiation pneumonitis in Stage 3 NSCLC patients

Wijsman, R.; Dankers, F.; Troost, E.; Hoffmann, A.; Bussink, J.

Purpose: Conflicting results have been reported for the combined effect of heart and lung irradiation on the development of radiation pneumonitis (RP) [1, 2]. The reported studies based on 3D conformal radiotherapy considered the whole heart as an organ-at-risk, thereby not distinguishing between dose to the cardiac ventricles and atria. We assessed whether inclusion of incidental dose to these cardiac subvolumes improved the prediction of Grade ≥3 RP.
Material and methods: We retrospectively assessed 188 consecutive patients with stage III non-small cell lung cancer (NSCLC) having undergone (chemo-)radiotherapy (≥60 Gy) using intensity-modulated radiation therapy (until 2011) or volumetric-modulated arc therapy (starting in 2011). Most patients (n=182) received 66 Gy in 33 (once-daily) fractions to the primary tumour and involved hilar/mediastinal lymph nodes based on FDG-PET/CT. The lungs and heart (ventricles and atria separately in 156 patients that received a contrast enhanced planning CT) were re-contoured to generate accurate dose-volume histogram (DVH) data. RP was assessed using the Radiation Therapy Oncology Group scoring criteria for pulmonary toxicity. Since high multicollinearity was observed between the DVH parameters, those with the highest Spearman correlation coefficient (Rs) were selected for the modelling procedure. Using a bootstrap approach, clinical parameters (such as age, gender, performance, smoking status, forced expiratory volume in 1 second, and cardiac comorbidity, i.e., medical history of myocardial infarction, heart failure, valvular heart disease, cardiac arrhythmias and/or hypertension) and DVH parameters of lungs and heart (assessing atria and ventricles separately and combined) were evaluated for RP prediction.
Results: After a median follow-up of 18.4 months, 26 patients (13.8%) developed RP. Only the median mean lung dose (MLD) differed between groups (15.3 Gy vs 13.7 Gy for the RP and non-RP group, respectively; p=0.004). Most Rs of the lung DVH parameters exceeded those of the heart DVH parameters and only some of the lung DVH parameters were significantly correlated with RP [See Figure 1; highest Rs for MLD (0.21; p<0.01)]. Only cardiac comorbidity was borderline associated with RP (p=0.066) on univariate logistic regression analysis. After bootstrap modelling, heart DVH parameters were seldom included in the model predicting Grade ≥3 RP. The optimal model consisted of: MLD (Odds ratio (OR) 1.28 per Gy increase; p=0.03) and cardiac comorbidity (OR 2.45 in case of cardiac comorbidity; p=0.04). The area under the receiver operator characteristic curve was 0.71, with good calibration of the model.
Conclusion: Incidental dose to the cardiac atria and ventricles did not improve RP risk prediction in our cohort of stage III NSCLC patients as the DVH parameters for lung outperformed those for the heart. The multivariable model containing the variables cardiac comorbidity and MLD is the optimal model for RP prediction in this cohort.
1. Huang, E.X., et al., Heart irradiation as a risk factor for radiation pneumonitis. Acta Oncol, 2011. 50(1): p. 51-60.
2. Tucker, S.L., et al., Is there an impact of heart exposure on the incidence of radiation pneumonitis? Analysis of data from a large clinical cohort. Acta Oncol, 2014. 53(5): p. 590-6.

Publ.-Id: 24176

Shapeable magnetic sensorics

Makarov, D.

The flourishing and eagerness of portable consumer electronics necessitates functional elements to be lightweight, flexible, and even wearable [1,2]. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Such devices fulfill the needs of soft robotics [3], functional medical implants [4] as well as epidermal [5], imperceptible [6] and transient [7] electronics. Key building blocks of navigation and position tracking devices are the magnetic field sensors.
We developed the technology platform allowing us to fabricate high-performance shapeable magnetoelectronics [8] – namely, flexible [9-11], printable [12-14], stretchable [15-17] and even imperceptible [18] magnetosensitive elements. The technology relies on smart combination of thin inorganic functional elements prepared directly on flexible or elastomeric supports. The unique mechanical properties open up new application potentials for smart skins, allowing to equip the recipient with a “sixth sense” providing new experiences in sensing and manipulating the objects of the surrounding us physical as well as digital world [11,18].
Combining large-area printable and flexible electronics paves the way towards commercializing the active intelligent packaging, post cards, books or promotional materials that communicate with the environment and provide the respond to the customer. Realization of this vision requires fabrication of printable electronic components that are flexible and can change their properties in the field of a permanent magnet [13]. For this concept, we fabricated high performance magnetic field sensors relying on the giant magnetoresistive (GMR) effect, which are printed at pre-defined locations on flexible circuitry and remain fully operational over a temperature range from -10°C up to +95°C, well beyond the requirements for consumer electronics [14]. Our work potentially enables commercial use of high performance magneto-sensitive elements in conventional printable electronic industry, which, although highly demanded, had not yet been possible.
In this talk, I will review the recent advances in the field of shapeable magnetic sensorics and emergent applications of this novel technology.

Keywords: Shapeable magnetoelectronics; smart Skins; magnetic field sensors

  • Invited lecture (Conferences)
    Brazilian-German Frontiers of Science & Technology Symposium, 20.-23.09.2016, Campinas, Brazil

Publ.-Id: 24174

Advanced Neutron Dosimetry on VVER-440 Ained to Reactor Equipment Load Evaluation During Life Time Prolongation

Borodkin, P.; Khrennikov, N.; Konheiser, J.; Dzhalandinov, A.; Sidorov, A.; Tsofin, V.; Zaritskiy, S.; Egorov, A.; Kochkin, V.; Erak, D.; Panferov, P.; Makhotin, D.; Teresсhenko, A.

Lifetime of non-restorable reactor equipment (RPV, in- and ex-vessel constructions, reactor support structures) of VVER-440 of first generation may restrict plant-life at whole. Concerning VVER, service life extension has touched the first generation of VVER-440 type reactors. Nowadays, all Russian first generation VVER-440 operated with reduced core by using dummy assemblies except reactor of Unit 4 of Novovoronezh NPP, wich are under operation more than 45 years. In comparison with other power units, the full-core loading scheme of this unit results in the highest neutron fluence accumulated over whole operation period. The analysis of degradation of material property of the equipment under irradiation are urgent in aspect of confirmation of safety of operating VVER units of similar type, and also in connection with an opportunity of further life-time prolongation. Another important aspect of dosimetry research on the Unit 4 of Novovoronezh NPP reactor is the verification and validation of calculational methods used for the prediction of the maximum neutron fluence on the VVER-440 pressure vessel.
Ex-vessel neutron dosimetry at NPP with VVER is used for a purpose of validation of calculations 3D distribution of neutron fluence on the reactor equipment. The reliability of such type validation depends on a quality of measured data and a comprehensive analysis of calculational model. The ex-vessel measurements permit to evaluate real conservatism of RPV neutron fluence evaluation, and, if possible, reduce conservative safety margins. For this purpose special advanced neutron dosimetry research were implemented at Unit 4 of Novovoronezh NPP (NV-4). Neutron activation measurement were performed in ex-vessel positions for different fuel cycles. The measurements of detectors activities also have been performed by different participants.
The purpose of the research was to perform an intercomparison of independent calculational results and comparison with reference data of the full-scale VVER-440 ex-vessel experiment. The paper deals with an analysis of a comparison of results of independent calculations by deterministic and Monte-Carlo codes between themselves and with experimental results. New and improved results of calculations analysed in the paper were run with codes and applied libraries DORT/BUGLE-96, TRAMO/ENDF/B-VII, MCNP/ENDF/B-VII, TORT/BUGLE-96, KATRIN/BGL-440, KATRIN/V7-200N47G. Calculated pure 3D or 3D synthesis multigroup neutron fluence rates in positions of experimental capsules provided by every calculator were used as basic calculational information. Based on the calculated fluence spectra the various reaction rates were computed using the dosimetry cross sections from the library IRDF-2002. The results of intercomparison of different calculation procedures and different experimental techniques give allowance to estimate of the reliable calculational and experimental uncertainties.
This verification of calculated methods provides the reliability of assessment of maximum neutron fluence on reactor equipment accumulated over whole service life period. In addition, with regard to a lifetime extension of Russian VVER-440 type reactors, advices for optimal core loading schemes will be derived. To approve the reliability and/or conservatism of calculation procedures the improved uncertainty-accounted conservative evaluation of RPV radiation loading parameters has been performed. This approach takes into account over- or underestimated C/E ratio and uncertainties of measured and calculated results. Based on such approach the analysis of end-of life-time fluence estimation has been demonstrated in the paper. The paper describes the features of the calculations, compares their results with those of the neutron activation measurements and presents neutron fluence values that were computed.

Keywords: neutron calculation; reactor pressure vessel; neutron fluence monitor; VVER-440

  • Poster
    16th International Symposium on Reactor Dosimetry (ISRD-16), 07.-12.05.2017, Santa Fe, USA
  • Contribution to proceedings
    Sixteenth International Symposium on Reactor Dosimetry (ISRD-16), 07.-12.05.2017, Santa Fe, NM, USA
    Proceedings of the 16th International Symposium on Reactor Dosimetry, West Conshohocken, USA: ASTM International, 978-0-8031-7661-4, 162-174
    DOI: 10.1520/STP160820170088

Publ.-Id: 24173

Update of the code intercomparison and benchmark for muon fluence and absorbed dose induced by a 18 GeV electron beam after massive iron shielding

Müller, S. E.; Fassò, A.; Ferrari, A.; Ferrari, A.; Mokhov, N. V.; Nelson, W. R.; Roesler, S.; Sanami, T.; Striganov, S. I.; Versaci, R.

In 1974, Nelson, Kase, and Svensson published an experimental investigation on muon shielding around SLAC high energy electron accelerators (NIM 120 (1974) 413). They measured muon fluence and absorbed dose induced by 14 and 18 GeV electron beams hitting a copper/water beamdump and attenuated in a thick steel shielding. In their paper, they compared the results with the theoretical models available at that time.

In order to compare their experimental results with present model calculations, we use the modern transport Monte Carlo codes MARS15, FLUKA2011 and GEANT4 to model the experimental setup and run simulations. The results are then compared between the codes, and with the SLAC data. Updated results from this campaign are reported in the presentation.

  • Lecture (Conference)
    SATIF13 - 13th Meeting of the task- force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany
  • Open Access Logo Contribution to proceedings
    SATIF13 - 13th Meeting of the taskforce on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany
    Proceedings of the Thirteenth Meeting of the Working Group for S hielding Aspects of Accelerator, Target and Irradiation Facilities (SATIF-13) Nuclear Science NEA/NSC/R(2018)2 September 2018, 304-314

Publ.-Id: 24172

Transmissionselektronenmikroskopie zur Analyse anodischer Barriereschichten

Hübner, R.; Lämmel, C.; Schneider, M.

Die vorliegende Studie stellt die vielfältigen Möglichkeiten der Transmissionselektronenmikroskopie (TEM) zur Charakterisierung dünner anodischer Barriereschichten vor. Dazu wurden magnetrongesputterte Aluminiumschichten bei unterschiedlichen Pulsfrequenzen oxidiert und mittels TEM analysiert. Unabhängig von den Herstellungsbedingungen sind die Oxidschichten porenfrei und amorph. Die Mikrostruktur des Aluminiums beeinflusst die Oxidschichten nicht. Mittels energiedispersiver Röntgenspektroskopie wurden keine Hinweise auf den Einbau von Elektrolytspezies in die Barriereschichten gefunden.

  • Lecture (Conference)
    Anodisieren - Oxidschichten von hart bis smart, 24.-25.11.2016, Dresden, Deutschland

Publ.-Id: 24170

X-ray microtomography of Taylor bubbles with mass transfer and surfactants in capillary two-phase flow

Boden, S.; Haghnegahdar, M.; Hampel, U.

Development and application of techniques to measure local properties of dynamic flows is in the focus of the work of the Institute of Fluid Dynamics at HZDR and of the AREVA Endowed Chair of Imaging Techniques in Energy and Process Engineering at TU Dresden. In this paper we report on the application of enhanced X-ray microradiography and microtomography techniques to measure Taylor bubble shapes in micro- and milli-channels. Further, experiments to inves-tigate the mass transport and the influence of surfactants were conducted. The re-sulting flow structural data will foster meso- and microscalic numerical flow mod-el development for small channel multiphase flow.

  • Book chapter
    in: Advances in Mathematical Fluid Mechanics, Basel: Springer, 2017, 978-3-319-56601-6, 589-608
    DOI: 10.1007/978-3-319-56602-3

Publ.-Id: 24169

Advanced MRI for assessment of toxicity after photon and proton based radiation therapy in primary brain tumors.

Raschke, F.; Wesemann, T.; Petr, J.; Wahl, H.; Werner, A.; van den Hoff, J.; Krex, D.; Krause, M.; Linn, J.; Troost, E.

In brain tumors, proton beam radiotherapy (RTx) reduces the radiation dose to healthy brain tissue outside the planning target volume compared to conventional photon based RTx. However, there is still a lack of prospective studies investigating the objective (i.e., surrogate imaging marker) and subjective (i.e., patient questionnaires) effects of photon vs. proton beam RTx for brain tumor patients. In this prospective study, primary brain tumor patients undergoing either photon- or proton-beam (chemo)RTx are being scanned using an advanced MRI protocol at 3T before RTx and at 3-monthly intervals thereafter. The MR protocol comprises conventional anatomical imaging (FLAIR, T1w, T2w, DWI) and state of the art MR sequences including quantitative T1, T2, T2* and Proton Density (PD) imaging (Figure 1), Diffusion Tensor Imaging, 2D MR spectroscopic imaging as well as ASL, T1* and T2* perfusion imaging.

In this NCT granted project, we will investigate qualitative and quantitative MR changes after photon and proton RTx in tumor tissue and surrounding normal appearing brain and correlate the results to the radiation dose fields as well as neurocognitive function and quality of life of the patients. The primary goal is to establish a rational for proton beam therapy in primary brain tumor patients with a long life expectancy and thus at risk of developing radiation sequelae (e.g., neurocognitive impairment, acute and late toxicity after RTx). Secondary goal is the combined analysis of the advanced multimodal MR data to identify infiltrative tumor tissue not visible on conventional MRI and predict local tumor control.

Keywords: brain tumors; proton; MRI

  • Poster
    NCT Retreat, 28.-29.11.2016, Heidelberg, Deutschland

Publ.-Id: 24168

Radiolabelled polymeric materials for imaging and treatment of cancer: Quo Vadis?

Pant, K.; Sedláček, O.; Nadar, R. A.; Hrubý, M.; Stephan, H.

Owing to their tunable blood circulation time and suitable plasma stability, polymer-based nanomaterials hold a great potential for designing and utilising multifunctional nanocarriers for efficient cancer imaging and effective treatment of cancer. When tagged with appropriate radionuclides, they may allow for specific detection (diagnosis) as well as the destruction of tumours (therapy) or even customization of materials, aiming to both diagnosis and therapy (theranostic approach). This review provides an overview of recent developments of radiolabelled polymeric nanomaterials (natural and synthetic polymers) for molecular imaging of cancer, specifically, applying nuclear techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Different approaches to radiolabel polymers are evaluated from the methodical radiochemical point of view. This includes new bifunctional chelating agents (BFCAs) for radiometals as well as novel labelling methods. Special emphasis is given to eligible strategies employed to evade the mononuclear phagocytic system (MPS) in view of efficient targeting. The discussion encompasses promising strategies currently employed as well as emerging possibilities in radionuclide-based cancer therapy. Key issues involved in the clinical translation of radiolabelled polymers and future scopes of this intriguing research field are also discussed.

Keywords: polymers; cancer; radiodiagnosis; radiotherapy; targeting; nuclear medicine; theranostics


Publ.-Id: 24167

Modification of semiconductor or metal nanoparticle lattices in amorphous alumina by MeV heavy ions

Bogdanovic Radovic, I.; Buljan, M.; Karlušić, M.; Jerčinović, M.; Dražič, G.; Bernstorff, S.; Boettger, R.

In the present work we investigate effects ofMeVheavy ions (from 0.4 MeVXe to 15 MeVSi) on regularly ordered nanoparticle (NP) lattices embedded in amorphous alumina matrix. These nanostructures were produced by self-assembling growth using magnetron-sputtering deposition. From grazing incidence small-angle x-ray scattering measurements we have found that the usedMeV heavy ions do not change the NPsizes, shapes or distances among them. However, ions cause a tilt of the entire NP lattice in the direction parallel to the surface. The tilt angle depends on the incident ion energy, type and the applied fluence and a nearly linear increase of the tilt angle with the ion fluence and irradiation angle was found. This way,MeV heavy ion irradiation can be used to design custom-made NPlattices. In addition, grazing incidence small-angle x-ray scattering can be effectively used as a method for the determination of material redistribution/shift caused by the ion hammering effect. For the first time, the deformation yield in amorphous alumina was determined for irradiation performed at the room temperature.

Keywords: nanoparticles; MeV heavy ions; ion hammering; amorphous alumina; GISAXS

Publ.-Id: 24166

Ano-rectal wall dose-surface maps localise the dosimetric benefit of hydrogel rectum spacers in prostate cancer radiotherapy

Vanneste, B.; Buettner, F.; Pinkawa, M.; Lambin, P.; Hoffmann, A.

Background and Purpose
To evaluate spatial differences in dose distributions of the ano-rectal wall (ARW) using dose-surface maps (DSM) between prostate cancer patients receiving intensity-modulated radiation therapy with and without implantable rectum spacer (IMRT+IRS; IMRT-IRS, respectively), and to correlate this with late gastro-intestinal (GI) toxicities using validated spatial and non-spatial normal-tissue complication probability (NTCP) models.

Materials and Methods
For 26 patients DSMs of the ARW were generated. From the DSMs various shape-based dose measures were calculated at different dose levels: lateral extent, longitudinal extent, and eccentricity. The contiguity of the ARW dose distribution was assessed by the contiguous-DSH (cDSH). Predicted complication rates between IMRT+IRS and IMRT-IRS plans were assessed using a spatial NTCP model and compared against a non-spatial NTCP model.

Lateral extent, longitudinal extent and cDSH were significantly lower in IMRT+IRS than for IMRT-IRS at high-dose levels. Largest significant differences were observed for cDSH at dose levels >50Gy, followed by lateral extent at doses >57Gy, and longitudinal extent. Significant decreases (p = 0.01) in median rectal and anal NTCPs were predicted when using an IRS.

Local-dose effects are predicted to significantly reduce by an IRS. Differences in predicted GI toxicity rates exist between spatial and non-spatial NTCP models.

Keywords: Prostate cancer; Radiotherapy; Rectum spacer; Dose-surface maps

Publ.-Id: 24165

Magnetization dynamics of a single Fe-filled carbon nanotube detected by ferromagnetic resonance

Lenz, K.; Narkowicz, R.; Reiche, C. F.; Kákay, A.; Mühl, T.; Büchner, B.; Suter, D.; Lindner, J.; Fassbender, J.

Designing future spintronic devices or entities requires the knowledge of their static and dynamic properties. However, the precise magnetic characterization of a single nanostructure like a nanowire or dot, e.g. by ferromagnetic resonance, is still an experimental challenge.
Broadband ferromagnetic resonance (FMR) or cavity-based FMR usually lack the necessary sensitivity to measure single micron-sized or smaller structures. Measurements of arrays of such elements often might be no alternative due to inhomogeneity either.
Here we show that microresonator FMR [1] can overcome these limitations. By decreasing the resonator size the filling factor is increased, therefore boosting the FMR sensitivity by several orders of magnitude.
This allows for measuring even a single Fe-filled carbon nanotube (Fe-CNT) [2]. The Fe-filling inside the CNT has a diameter of 42 nm with an initial length of several micrometers (see Fig. 1). In order to understand the origin of the various resonance peaks, a focused ion beam was used to shorten little-by-little the length of the Fe-CNT after each FMR measurement.
Furthermore, angle-dependent FMR measurements were performed to extract the anisotropy contributions (like shape and magnetocrystalline anisotropy). In addition, the measured narrow linewidth suggests that the Fe-filling is a well ordered crystal, as confirmed by transmission electron microscopy. Therefore, besides the magnetic characterization of a single nanostructure, the microresonator FMR can also provide ‘indirectly’ information about the crystalline structure.

Keywords: ferromagnetic resonance; magnetization; nanostructures; microresonator; microwaves; carbon nanotubes; magnetism

  • Invited lecture (Conferences)
    5th International Conference on Microwave Magnetics, 05.-08.06.2016, Tuscaloosa, USA
  • Lecture (Conference)
    DPG Frühjahrstagung der SKM, Dresden, 19.-24.03.2017, Dresden, Deutschland
  • Invited lecture (Conferences)
    Intermag Europe 2017, IEEE International Magnetics Conference, 24.-28.04.2017, Dublin, Irland

Publ.-Id: 24164

The role of the internal demagnetizing field for the dynamics of a magnonic crystal

Langer, M.; Röder, F.; Gallardo, R. A.; Schneider, T.; Stienen, S.; Gatel, C.; Hübner, R.; Bischoff, L.; Lenz, K.; Lindner, J.; Landeros, P.; Fassbender, J.

Magnonic crystals with locally alternating properties and specific periodicities exhibit interesting effects, such as a multitude of different spin-wave states with adjustable band gaps. This work aims for demonstrating and understanding the key role, which local demagnetizing fields play in such systems. In order to get direct access to this matter, the spin-dynamics of a magnonic crystal were reconstructed from ‘bottom-up’, i.e. the structural shape as well as the internal field landscape of the structure were experimentally reconstructed on the nanoscale using electron holography. Subsequently, both properties were utilized to perform dynamic response calculations. The simulations yield the frequency-field dependence as well as the angular dependence of spin waves in a magnonic crystal and reveal the governing role of the internal field landscape around the backward-volume geometry. Connecting the internal field landscape with the individual spin-wave mode localization, a comprehensive model is presented describing the complex angle-dependent spin-wave behavior around 360◦ rotation of an in-plane external field. A significant spin-wave propagation is reported for a broad angular range around the Damon-Eshbach geometry.

Keywords: magnonic crystal; electron holography; magnetic nanostructure; demagnetizing field; magnetization dynamics; ferromagnetic resonance; micromagnetic simulation


Publ.-Id: 24163

Melanoma targeting with [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analogs: Effects of cyclization on the radiopharmaceutical properties

Carta, D.; Salvarese, N.; Morellato, N.; Gao, F.; Sihver, W.; Pietzsch, H.-J.; Biondi, B.; Ruzza, P.; Refosco, F.; Carpanese, D.; Rosato, A.; Bolzati, C.

The purpose of this study was to evaluate the effect of cyclization on the biological profile of a [99mTc(N)(PNP3)]-labeled α-melanocyte stimulating hormone peptide analog. A lactam bridgecyclized H-Cys-Ahx-Ala3-c[Lys4-Glu-His-D-Phe-Arg-Trp-Glu10]-Arg11-Pro-Val-NH2 (NAP―NS2) and the corresponding linear H-Cys-Ahx-Ala-Nle-Asp-His-D-Phe-Arg-Trp-Gly-NH2 (NAP―NS1) peptide were synthetized, characterized by ESI-MS spectroscopy and their melanocortin-1 receptor (MC1R) binding affinity was determined in B16/F10 melanoma cells. The consistent [99mTc(N)(PNP3)]-labeled compounds were readily obtained in high specific activity and their stability and biological properties were assessed. As an example, the chemical identity of [99mTc(N)(NAP–NS1)(PNP3)]+ was confirmed by carrier added experiments supported by radio/UV HPLC analysis combined with ESI(+)-MS. Compared with the linear peptide, cyclization negatively affected the biological properties of NAP–NS2 peptide by reducing its binding affinity for MC1R and by decreasing the overall excretion rate of the corresponding [99mTc(N)(PNP3)]-labeled peptide from the body as well as its in vivo stability. [99mTc(N)(NAP–NS1)(PNP3)]+ was evaluated for its potential as melanoma imaging probe in murine melanoma model. Data from in vitro and in vivo studies on B16/F10 melanoma model of [99mTc(N)(NAP–NS1)(PNP3)]+ clearly evidenced that the radiolabeled linear peptide keeps its biological properties up on the conjugation to the [99mTc(N)(PNP3)]-building block. The progressive increase of the tumor-to-nontarget ratios over the time indicate a quite stable interaction between the radiocomplex and the MC1R.

Keywords: Tc-99m; alpha-MSH; melanoma; MC1R; peptides; SPECT; Imaging

Publ.-Id: 24162

Radiobiological evaluation of established Glioblastoma multiforme cell lines as preclinical models in mice

Jakob, A.; Linge, A.; Löck, S.; Thames, H. D.; Baumann, M.; Krause, M.; von Neubeck, C.

Less than 5 % of the patients diagnosed with the brain tumor Glioblastome multiforme (GBM) survive more than three years despite an intense therapy of surgery, radiation and application of the chemotherapeutic drug temozolomide (TMZ). The poor outcome underlines a need for the development of new treatment strategies which depends on the availability of suitable preclinical models. Here, we present results of the establishment and characterization of GBM models for the use in radiobiological research.
Basic in vitro investigations on the 5 GBM cell lines HGL21, LN-229, A7, U-251 MG and U-87 MG demonstrated radioresistance. The surviving fractions at a dose of 2 Gy X-rays ranged from 55 % (U-87 MG) to 85 % (A7). Administration of combined treatment with TMZ changed the cell survival in accordance to the methylation status of the MGMT promotor. Highly methylated cell lines LN-229, U-251 MG and U-87 MG showed the strongest response to TMZ.
Subcutaneous engraftment in nude mice further confirmed an aggressive character of the models.
High take rates for all cell lines were determined by means of the limiting dilution assay. Take doses 50 % , which indicate the cell number necessary to induce tumors in half of the animals, are in the range of 22 (HGL-21) to 187 (U-87 MG) cells reflecting a high content of stem-like cells. In contrast, extensive tumor control dose experiments of single dose treatment under hypoxic or ambient blood flow with or without combination with TMZ did not confirm the radioresistant phenotype. The tumor control doses 50 % (TCD50) ranked between 30 - 40 Gy under hypoxic conditions with the exception of U-87 MG (58 Gy). Additional treatment with TMZ decreased the TCD50 dramatically in 3 (LN-229, A7, U-87 MG) out of 4 models to values below 25 Gy.
Although the models partly mimic the clinical GBM characteristics, the radioresistance measured in vitro does not translate to the in vivo situation. As the models should mirror the clinical situation closely, their suitability for preclinical studies remains questionable.

  • Lecture (Conference)
    Young Scientist Forum 2016, 24.11.2016, Poznan, Poland, Poland

Publ.-Id: 24161

Efficient simulation of stationary multivariate Gaussian random fields with given cross-covariance

Teichmann, J.; van den Boogaart, K. G.

The present paper introduces a new approach to simulate any stationary multivariate Gaussian random field whose cross-covariances are predefined continuous and integrable functions. Such a field is given by convolution of a vector of univariate random fields and a functional matrix which is derived by Cholesky decomposition of the Fourier transform of the predefined cross-covariance matrix.

In contrast to common methods no restrictive model for the cross-covariance is needed, it is stationary and can also be reduced to the isotropic case. The computational effort is very low since fast Fourier transform can be used for simulation. As will be shown the algorithm is computationally faster than a recently published spectral turning bands model. The applicability is demonstrated using a common numerical example with varied spatial correlation structure.

The model was developed to support simulation algorithms for mineral microstructures in geoscience.

Keywords: image processing; convolution; cross-covariance; Cholesky decomposition; Fourier transformation

Publ.-Id: 24160

Probing high-intensity laser-matter interaction at the Helmholtz International Beamline for Extreme Fields at the European XFEL

Schramm, U.

Talk on Probing high-intensity laser-matter interaction at the Helmholtz International Beamline for Extreme Fields at the European XFEL

Keywords: Relativistic Laser Plasma; HIBEF

  • Invited lecture (Conferences)
    PWSC 8th Petawatt Scientific Committee and ICUIL 2016, 10.-16.09.2016, Montebello, Canada

Publ.-Id: 24159

Numerical Modelling of a Direct Contact Condensation Experiment using the AIAD Framework

Höhne, T.; Gasiunas, S.; Šeporaitis, M.

The Lithuanian Energy Institute (LEI) test case deals with direct contact condensation (DCC) in the two-phase stratified steam-water flow. The main goal of CFD simulations of these experiments is to compute new models of heat and mass transport from saturated vapour to liquid over a free surface and the temperature profiles across the liquid flow in a channel. Condensation occurs mainly on free surfaces for instance at PTS scenarios. The knowledge of the accurate coolant temperature is important for nuclear safety assessment.
Three different direct contact condensation models for the heat transfer within the AIAD framework at the free surface were formulated and tested. The AIAD model describes a consistent set of model correlations for the interfacial area density, the drag, the non-resolved disturbances of a free surface and the turbulence damping the interface. The calculated surface temperature profiles agree well with the experiment. Further model development should focus on “CFD grade” experimental data and direct numerical simulations.

Keywords: CFD; CMFD; horizontal flow; PTS; PWR; AIAD; DCC; two-phase flow; two fluid flow

Publ.-Id: 24157

Numerical Modelling of a Direct Contact Condensation Experiment

Höhne, T.; Gasiunas, S.; Šeporaitis, M.

The Lithuanian Energy Institute (LEI) test case deals with direct contact condensation (DCC) in the two-phase stratified steam-water flow. The main goal of CFD simulations of these experiments is to compute new models of heat and mass transport from saturated vapour to liquid over a free surface and the temperature profiles across the liquid flow in a channel. Condensation occurs mainly on free surfaces for instance at PTS scenarios. The knowledge of the accurate coolant temperature is important for nuclear safety assessment.
Three different direct contact condensation models for the heat transfer within the AIAD framework at the free surface were formulated and tested. The AIAD model describes a consistent set of model correlations for the interfacial area density, the drag, the non-resolved disturbances of a free surface and the turbulence damping the interface. The calculated surface temperature profiles agree well with the experiment. Further model development should focus on “CFD grade” experimental data and direct numerical simulations.

Keywords: CFD; CMFD; horizontal flow; PTS; PWR; AIAD; DCC; two-phase flow; two fluid flow

  • Contribution to proceedings
    2nd World Congress on Momentum, Heat and Mass Transfer (MHMT’17), 07.-08.04.2017, Barcelona, Spanien
  • Lecture (Conference)
    2nd World Congress on Momentum, Heat and Mass Transfer (MHMT’17), 07.-08.04.2017, Barcelona, Spanien

Publ.-Id: 24156

Nano patterns self-aligned to Ga dimer rows on GaAs surfaces

Engler, M.; Škereň, T.; Facsko, S.

Ion beam irradiation of semiconductors is a method to produce regular periodic nanoscale patterns self-organized on wafer scale. At low temperatures, the surface of semiconductors is typically amorphized by the ion beam. Above a material dependent dynamic recrystallization temperature however, the surface remains crystalline and ion beam irradiation produces regular arrays of faceted ripples on III-V semiconductors. This provides a powerful single-step technique for the production of nanostructures on a large area. On (001) surfaces these ripples are parallel to the [1-10] direction without any external anisotropy. The origin of this self-alignment was not fully understood until now. A simple experiment exposing the front side and back side of a GaAs(001) wafer to the ion beam clarifies its origin and proves that the ripples align to the Ga dimer rows. As the direction of Ga dimer rows rotates by 90°on the back side, the orientation of the ripples also rotates by 90° to [110]. We discuss the experimental results in view of a model where the pattern formation is driven by creation of vacancies and ad-atoms by the ion beam and their diffusion, which is linked to the direction of dimers on the surface.

Keywords: ion beam patterning; nano patterning; GaAs; AFM; ion irradiation

Publ.-Id: 24155

Valuation of Uncertainty in Geometallurgical Process Optimisation

van den Boogaart, K. G.; Tolosana Delgado, R.

Geometallurgical parameters such as block models and process response models always come with a certain (geo-)statistical uncertainty. Geometallurgical optimisation often treats these model values as if they were certain. With easy to understand model examples we demonstrate the economic effect of ignoring the uncertainty. Our stochastic optimisation method, taking it into account, uniformly outperforms the best deterministic approach, often substantially. As the method is fully aware of the underlying model uncertainty, it can quantify the value of certainty and information and thus assign economic values to geometallurgical exploration and geometallurgical processing testwork. In this way the geometallurgist can objectively justify detailed exploration and processing experiments, by computing the effect on the expected NPV upfront.

Keywords: Geometallurgy; Uncertainty; Geostatistics

  • Lecture (Conference)
    Process Mineralogy 2017, 20.-22.03.2017, Cape Town, South Africa
  • Open Access Logo Contribution to proceedings
    Process Mineralogy 2017, 20.-22.03.2017, Cape Town, Sourth Africa

Publ.-Id: 24154

Temperature-Dependent Charge Transport through Individually Contacted DNA Origami-Based Au Nanowires

Teschome, B.; Facsko, S.; Schönherr, T.; Kerbusch, J.; Keller, A.; Erbe, A.

DNA origami nanostructures have been used extensively as scaffolds for numerous applications such as for organizing both organic and inorganic nanomaterials, studying single molecule reactions, and fabricating photonic devices. Yet, little has been done toward the integration of DNA origami nanostructures into nanoelectronic devices. Among other challenges, the technical difficulties in producing well-defined electrical contacts between macroscopic electrodes and individual DNA origami-based nanodevices represent a serious bottleneck that hinders the thorough characterization of such devices. Therefore, in this work, we have developed a method to electrically contact individual DNA origami-based metallic nanowires using electron beam lithography. We then characterize the charge transport of such nanowires in the temperature range from room temperature down to 4.2 K. The room temperature charge transport measurements exhibit ohmic behavior, whereas at lower temperatures, multiple charge transport mechanisms such as tunneling and thermally assisted transport start to dominate. Our results confirm that charge transport along metallized DNA origami nanostructures may deviate from pure metallic behavior due to several factors including partial metallization, seed inhomogeneities, impurities, and weak electronic coupling among AuNPs. Besides, this study further elucidates the importance of variable temperature measurements for determining the dominant charge transport mechanisms for conductive nanostructures made by self-assembly approaches.

Keywords: DNA origami; gold nanoparticles; metallization; electrical contacting; charge transport


Publ.-Id: 24153

Iron pnictide thin films: Synthesis and physics

Haindl, S.; Kidszun, M.; Kampert, E.

Superconducting thin films play a prominent role in applications of superconductivity and provide an essential source for studying physical phenomena. Here, we summarize the activities for iron pnictide thin films with a focus on the German Special Priority Programme from 2009 until today. The quick availability of such films after the discovery of superconductivity in the iron-based superconductors enabled a number of experiments. After a general introduction and a brief historical overview we focus on film synthesis of iron pnictides by a two-step method and by pulsed laser deposition, the assessment of their application potential, the upper critical fields in iron oxypnictides of F-doped LaOFeAs and F-doped Sm1-xLaxOFeAs and on superconductivity in Fe/BaFe2As2 heterostructures.

Publ.-Id: 24152

Direct numerical simulation of an arbitrarily shaped particle at a fluidic interface

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

A consistent formulation is presented for the direct numerical simulation of an arbitrarily shaped colloidal particle at a deformable fluidic interface. The rigid colloidal particle is decomposed into a collection of solid spherical beads and the three-phase boundaries are replaced with smoothly spreading interfaces. The major merit of the present formulation lies in the ease, with which the geometrical decomposition of the colloidal particle is implemented, yet allowing the dynamic simulation of intricate three-dimensional colloidal shapes in a binary fluid. The dynamics of a rod-like, of a plate-like, and of a ring-like particle are presently tested. It is found that plate-like particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force. Using the Bond number, i.e. the ratio of the gravitational force to the reference capillary force, a spherical particle with equal affinity for the two fluids breaks away from a fluidic interface at the critical value Bo = 0.75. This value is in line with our numerical experiments. It is here shown that a plate and a ring of equivalent masses detach at greater critical Bond numbers approximately equal to Bo = 1.3. Results of this study will find applications in the stabilisation of emulsions by colloids and in the recovery of colloidal particles by rising bubbles.


Publ.-Id: 24151

In situ bow change of Al-alloy MEMS micromirrors during 248-nm laser irradiation

Mai, A.; Bunce, C.; Hübner, R.; Pahner, D.; Dauderstädt, U.

Micromirror based spatial light modulators (SLMs) developed by the Fraunhofer Institute for Photonic Microsystems are well established in microlithography applications. Serving, e.g., as reflective, programmable photomasks in deep-UV mask writers, they enable highly flexible pattern generation. During operation, the micromirror bow significantly impacts contrast and the resolvable feature size of generated patterns. In some situations, MEMS micromirrors tend to change their bow during laser irradiation. A test regime including a characterization unit for the in situ analysis of MEMS micromirror topology has been developed to measure the bow change under various irradiation conditions. Experiments in which SLMs were irradiated by a 1-kHz, 248-nm pulse laser revealed that mirror bowing can occur in both directions (concave and convex). The bowing direction is dependent upon the applied irradiation parameters such as pulse-energy density, pulse number, and the deposited energy. Sustained irradiation at energy densities exceeding a certain limit can potentially become a limiting factor for the resolvable feature sizes of the patterns generated and, therefore, for the usable SLM lifespan.

Keywords: spatial light modulator; micromirror array; micro-(opto)-electro-mechanical-system device; laser; UV; in situ

Publ.-Id: 24150

Generation of high charge electron beams by ionization injection

Couperus, J. P.; Köhler, A.; Zarini, O.; Krämer, J.; Pausch, R.; Debus, A.; Hübl, A.; Garten, M.; Bussmann, M.; Irman, A.; Schramm, U.

One of the most challenging aspects in Laser wakefield acceleration (LWFA) is controlled injection of electrons into the correct phase of the accelerating field. In the ionization injection scheme this is addressed by adding a small fraction of high Z gas to the accelerating medium. Electrons in the K-shell possess a high ionization threshold which is only reached around the laser maximum, close to the center of the propagation axis. Compared to wave-breaking injection, ionization injection requires relatively low laser intensities and plasma densities, allowing us to drive the wakefield in a more stable way.
We present an extensive experimental parameter study, showing the influence of Nitrogen doping concentration on beam parameters: energy spread, charge & repeatability. We discuss the influence of laser energy and plasma density on maximum reachable energy and conversion efficiency.
We show a regime where our laser system (2.5J on target, 30 fs) generates stable electron beams (252 MeV, +/- 9% shot-to-shot) with narrow bandwidth (36 MeV +/- 11MeV FWHM) and high charge (292 pC +/- 59 pC within 1/e2) electron beams, while retaining a low background.

Keywords: Laser wakefield acceleration; LWFA

  • Poster
    Advanced Accelerator Concepts Workshop (AAC 2016), 02.08.2016, National Harbor, Maryland, USA
  • Lecture (Conference)
    Novel Accelerators Workshop 2016, 24.10.2016, Paris, France

Publ.-Id: 24149

High temperature stable TCOs as selective transmitter for solar thermal applications

Lungwitz, F.; Schumann, E.; Guillen, E.; Escobar-Galindo, R.; Gemming, S.; Krause, M.

Materials used in the receiver tubes of a solar thermal power plant must exhibit several properties, e.g. high temperature stability, high absorption in the solar region and low thermal emittance. Nowadays, temperatures of up to 450°C and up to 550°C are reached using parabolic trough arrays and solar tower absorbers, respectively, whereas temperatures up to 800°C or higher could be reached if the receiver materials were stable enough. Previous R&D approaches for high temperature solar receiver materials include multilayer coatings deposited by PVD or sol-gel techniques. Here, a new concept for solar-selective coating is presented. A transparent conductive oxide (TCO) is deposited as a solar selective transmitter on a black body absorber to implement both, high absorption (from the black body) in the ultraviolet, visible and near infrared spectral range (300 nm – 2500 nm) as well as high reflectivity (from the TCO) in the infrared (> 2500 nm) in a relative simple material design. Therefore SnO2:Ta and TiO2:Ta thin films are reactively magnetron co-sputtered from tantalum doped and undoped metal targets at high temperatures (400°C - 700°C). By changing dopant concentration, oxygen flux, process pressure and deposition temperature the optical properties of these films can be tailored to meet the requirements of a solar selective transmitter coating. It is also shown that the electrical properties of the TCO, namely charge carrier concentration and mobility, determine the optical behavior. The correlation between structural, optical, and electrical properties is analyzed by Raman Spectroscopy and Spectroscopic Ellipsometry (SE) both at room- and especially (in situ) at hightemperatures simulating the conditions where the functional coating is supposed to operate. Additionally, Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction (XRD), UV-VIS spectrometry, and Hall Effect measurements are performed. Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.

Keywords: solar thermal; transparent conductive oxide

  • Lecture (Conference)
    15th International Conference on Plasma Surface Engineering, 14.09.2016, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 24146

Source term and shielding calculations for the installation of a new cyclotron for medical applications at HZDR

Konheiser, J.; Ferrari, A.; Müller, S. E.; Naumann, B.

In the presentation results for source term and shielding calculations for the installation of a new cyclotron at the Helmholtz-Zentrum Dresden-Rossendorf are given. This cyclotron will be used to produce radioisotopes for medical applications. The source terms for a proton beam hitting an18O-enriched water target were calculated with MCNP6 and FLUKA, and compared to source terms used in the literature for exclusive18O(p,n)18F production. It was found that the additional channels which are present during the cyclotron operation may not be neglected. In addition, a significant contribution from gamma-radiation produced by the proton beam in the water target was taken into account. Based on the results from the Monte Carlo simulations, theestimated dose rates in public areas around the cyclotron building are significantly below the allowed limits provided by the legal authorities.
To validate the radiation fields obtained in the simulations, an experimental program has been started using activation samples originally used in reactor dosimetry. These samples are placed at well defined positions in the radiation field, and after irradiation are analyzed for residual activation. The results can then be compared to the simulated results. We will present the status of this program.

Keywords: cycloton; 18F production; neutron source; dose rates; activation measurement

  • Poster
    SATIF-13 - 13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany
  • Contribution to proceedings
    SATIF-13 - 13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities, 10.-12.10.2016, Dresden, Germany
    Shielding Aspects of Accelerator, Target and Irradiation Facilities (SATIF),Nuclear Science NEA/NSC/R(2018)2, Wien/Paris: OECD-NEA

Publ.-Id: 24145

In-Depth Performance Analysis for OpenACC/CUDA/OpenCL Applications with Score-P and Vampir

Juckeland, G.; Henschel, R.

Participants will work with Score-P/Vampir to learn how to dive into the execution properties of CUDA and OpenACC applications. We'll show how to use Score-P to generate a trace file and how to study it with Vampir. Additionally, we'll use the newly established OpenACC tools interface to also present how OpenACC applications can be studied for performance bottlenecks. This lab utilizes GPU resources in the cloud, you are required to bring your own laptop.

Keywords: Score-P; Vampir; Tracing; Performance-Analysis

  • Lecture (Conference)
    GTC Europe 2016, 28.-29.09.2016, Amsterdam, Nederland

Publ.-Id: 24143

Introduction into Raman spectroscopy

Krause, M.

Fundamentals and new developments in Raman spectroscopy

  • Invited lecture (Conferences)
    Friends2-Workshop: Advanced coating and characterization techniques, 19.-20.09.2016, Dresden-Rossendorf, Deutschland

Publ.-Id: 24142

Comparative study of the deposition of highly reflectant metal thin films by ionized PVD techniques

Rincón Llorente, G.; Guillén Rodríguez, E.; Schumann, E.; Heras Pérez, I.; Mesko, M.; Munnik, F.; Krause, M.; Escobar Galindo, R.

The degree of ionization during Physical Vapor Deposition (PVD) plays a critical role on the final surface quality of the deposited coatings. In this work a comparative study of metal thin films (Al, Cu, Ag) deposited by conventional DC-Magnetron Sputtering (DCMS) and highly ionized techniques such as Filtered Cathodic Vacuum Arc (FCVA) and high power impulse magnetron sputtering (HiPIMS) was performed. The final scope of the study is aimed to optimize the deposition parameters to achieve higher specular reflectance as this have a critical influence in the yield of solar plants based on concentrated solar power. In this regard, the optical constants of the deposited films were modeled departing from ellipsometry data. A comparison of the experimental reflectance with that obtained after optical simulation was also carried out. The achieved optical performance of the films was further compared to the structural properties resulting from different deposition techniques. Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA)was applied to explore the potential oxidation of the films during deposition. Surface morphological changes were explored by Scanning Electron Microscopy (SEM). In addition, Atomic Force Microscopy (AFM) measurements at different deposition times allowed exploring the dynamics of the growth mechanism of the films.

Keywords: PVD techniques; Optical properties; Simulation; RBS; AFM

  • Lecture (Conference)
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 24140

Impurity suppression in sputtered metallic thin films using HiPIMS

Mesko, M.; Munnik, F.; Heller, R.; Grenzer, J.; Hübner, R.; Halanda, J.; Gemming, S.; Krause, M.

Composition and microstructure of thin films deposited by PVD are often influenced by the presence of residual gas. Therefore, it would be desirable to enable thin film growth without residuals incorporation. Strategies to avoid impurities incorporation are substrate heating, applying substrate bias, and reduction of base pressure to ultra-high vacuum (UHV) conditions. Industrial demand for low temperature and low cost processes often precludes these approaches. More recently, a very important question has been raised regarding high power impulse magnetron sputtering (HiPIMS) to form pure metallic films at low deposition rates and high values of base pressure in the deposition chamber [1].

In this study, HiPIMS was applied for room-temperature deposition of pure metallic thin films of Al, Ti, and Cu. These metals are distinguished by their oxygen affinities and melting temperatures. Deposition of carbon top layers was used to differentiate between residual gas and post-deposition contamination. Elastic recoil detection analysis (ERDA) revealed that HiPIMS produces bulk-impurity-free metallic thin films. The growth of such high-purity metallic thin films can be partly explained by gas rarefaction and the self-cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. Proposed deposition mechanism will be explained in sufficient detail. The compositional effects are correlated with differences in the film microstructure revealed by SEM, XRD, and TEM analyses.

[1] P. Pokorný et al., Plasma Processes Polym. 12, 416 (2015)

Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged. This work was also funded by the ERDF, Project CAMBO, ITMS: 2622022079, and by Slovak grant agency VEGA, project no. 1/0503/15

Keywords: HiPIMS; Room temperature PVD; High-purity metallic films; ERDA

  • Poster
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 24139

In situ RBS, Raman, and ellipsometry studies of layered material systems at elevated temperatures

Wenisch, R.; Heras, I.; Lungwitz, F.; Janke, D.; Guillén, E.; Heller, R.; Gemming, S.; Escobar Galindo, R.; Krause, M.

The detailed knowledge of composition and structure is essential for the understanding of processes and properties of functional materials at elevated temperatures. To ensure materials functionality under in operando conditions, new concepts for analysis and process monitoring are necessary. In this contribution, selected layered material systems were studied in situ at temperatures up to 830°C by Rutherford backscattering (RBS), Raman spectroscopy, and ellipsometry within a cluster tool. Metal induced crystallization (MIC) is a promising technique for hydrogen-free synthesis of two-dimensional materials. Here, Si/Ag bilayers are studied as model system. The Si/Ag layer stacks are annealed at temperatures of 380 to 700°C. simultaneously, depth profiles of the elements are investigated by RBS revealing the diffusion kinetics. The changes in the phase structure and the degree of crystallinity are analyzed by Raman spectroscopy. Both the quick initial nucleation and ensuing growth processes are investigated. MIC is observed for all temperatures under study, while layer exchange occurs only for optimized process conditions.
As an example for high-temperature functional coatings, AlTiOxN1-x thin films were investigated in order to understand the influence of the oxygen to nitrogen ratio on the optical properties and their failure mechanisms at high temperatures. Ellipsometry and RBS results showed the influence of the initial oxygen content in the sample, inward diffusion of oxygen into the coating, and the high temperature stability of AlTiOxN1-x thin films. The low emittance of AlTiOxN1-x, allowed performing in situ RBS analysis at temperature up to 830°C for the first time.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the
HGF via the W3 program (S.G.) is gratefully acknowledged.

Keywords: cluster tool; in situ analysis; RBS; Raman

  • Lecture (Conference)
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 24136

The role of Ga droplets in the epitaxy of GaAs nanowires on Si substrates

Dimakis, E.

The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si substrates, as well as the droplet-confined alternate pulsed epitaxy of GaAs nanowires, are discussed.

  • Invited lecture (Conferences)
    FemtoTera Workshop, 29.09.2016, Óbuda University, Budapest, Hungary

Publ.-Id: 24135

Growth and applications of III-V nanowires on Si substrates

Dimakis, E.

III-V semiconductor nanowires have been a subject of intense research over the last 10 years and a plethora of exciting nanoscale phenomena has been unveiled. The peculiar strain relaxation mechanisms in nanowire heterostructures offer the possibility to integrate epitaxially materials with large mismatch of lattice parameters and thermal expansion coefficients. Thus, one can tailor the (opto)electronic properties of nanowire heterostructures using an extended palette of materials compared to traditional thin-film heterostructures. Furthermore, the epitaxial growth of III-V nanowires on lattice mismatched Si substrates is of great interest, because the two complementary technologies can thus be integrated on single multifunctional chips combining the superior electronic and optoelectronic properties of the former with the mature CMOS technology of the latter.
This seminar will be focusing on III-As nanowires grown on Si(111) substrates by molecular beam epitaxy. Starting from the basic description of the vapor-liquid-solid growth of GaAs nanowires and the self-induced growth of InAs nanowires [1,2], the problem of structural polytypism and its effect on the nanowire optoelectronic and electrical properties will be discussed [3,4] and, finally, the droplet-confined alternate pulsed epitaxy will be proposed as a unique growth mode that offers compatibility with the Si-CMOS processing standards [5]. Finally, the growth and the structural properties of coaxial multishell (In,Al,Ga)As/GaAs nanowires will be presented, and their application in light emitting diodes or modulation doped heterostructures will be discussed [6].

[1] E. Dimakis, J. Lähnemann, U. Jahn, S. Breuer, M. Hilse, L. Geelhaar, and H. Riechert, Cryst. Growth Des. 2011, 11, 4001–4008
[2] A. Biermanns, E. Dimakis, A. Davydok, T. Sasaki, L. Geelhaar, M. Takahasi, and U. Pietsch, Nano Lett. 2014, 14, 6878−6883
[3] P. Schroth, M. Köhl, and J.-W. Hornung, E. Dimakis, C. Somaschini, L. Geelhaar, A. Biermanns, S. Bauer, S. Lazarev, U. Pietsch, T. Baumbach, Phys. Rev. Lett. 2015, 114, 055504
[4] G. Bussone, H. Schäfer-Eberwein, E. Dimakis, A. Biermanns, D. Carbone, A. Tahraoui, L. Geelhaar, P. Haring Bolívar, T. U. Schülli, and U. Pietsch, Nano Lett. 2015, 15, 981−989
[5] L. Balaghi, T. Tauchnitz, R. Hübner, L. Bischoff, H. Schneider, M. Helm, and E. Dimakis, Nano Lett. 2016, 16, 4032−4039
[6] E. Dimakis, U. Jahn, M. Ramsteiner, A. Tahraoui, J. Grandal, X. Kong, O. Marquardt, A. Trampert, H. Riechert, and L. Geelhaar, Nano Lett. 2014, 14, 2604−2609

  • Invited lecture (Conferences)
    Seminar, ANKA - Karlsruhe Institute of Technology (KIT), 15.09.2016, Eggenstein-Leopoldshafen, Germany

Publ.-Id: 24134

Growth and applications of III-V nanowires on Si substrates

Dimakis, E.

III-V semiconductor nanowires have been a subject of intense research over the last 10 years and a plethora of exciting nanoscale phenomena has been unveiled. The peculiar strain relaxation mechanisms in nanowire heterostructures offer the possibility to integrate epitaxially materials with large mismatch of lattice parameters and thermal expansion coefficients. Thus, one can tailor the (opto)electronic properties of nanowire heterostructures using an extended palette of materials compared to traditional thin-film heterostructures. Furthermore, the epitaxial growth of III-V nanowires on lattice mismatched Si substrates is of great interest, because the two complementary technologies can thus be integrated on single multifunctional chips combining the superior electronic and optoelectronic properties of the former with the mature CMOS technology of the latter.
This seminar will be focusing on III-As nanowires grown on Si(111) substrates by molecular beam epitaxy. Starting from the basic description of the vapor-liquid-solid (self-induced) growth of GaAs (InAs) nanowires [1,2], the problem of structural polytypism and its effect on the nanowire optoelectronic and electrical properties will be discussed [3,4] and, finally, the droplet-confined alternate pulsed epitaxy will be proposed as a unique growth mode that offers compatibility with the Si-CMOS processing standards [5]. Finally, the growth and the structural properties of coaxial multishell (In,Al,Ga)As/GaAs nanowires will be discussed, and their application in light emitting diodes or modulation doped heterostructures will be demonstrated [6].

[1] E. Dimakis, J. Lähnemann, U. Jahn, S. Breuer, M. Hilse, L. Geelhaar, and H. Riechert, Cryst. Growth Des. 2011, 11, 4001–4008
[2] A. Biermanns, E. Dimakis, A. Davydok, T. Sasaki, L. Geelhaar, M. Takahasi, and U. Pietsch, Nano Lett. 2014, 14, 6878−6883
[3] P. Schroth, M. Köhl, and J.-W. Hornung, E. Dimakis, C. Somaschini, L. Geelhaar, A. Biermanns, S. Bauer, S. Lazarev, U. Pietsch, T. Baumbach, Phys. Rev. Lett. 2015, 114, 055504
[4] G. Bussone, H. Schäfer-Eberwein, E. Dimakis, A. Biermanns, D. Carbone, A. Tahraoui, L. Geelhaar, P. Haring Bolívar, T. U. Schülli, and U. Pietsch, Nano Lett. 2015, 15, 981−989
[5] L. Balaghi, T. Tauchnitz, R. Hübner, L. Bischoff, H. Schneider, M. Helm, and E. Dimakis, Nano Lett. 2016, 16, 4032−4039
[6] E. Dimakis, U. Jahn, M. Ramsteiner, A. Tahraoui, J. Grandal, X. Kong, O. Marquardt, A. Trampert, H. Riechert, and L. Geelhaar, Nano Lett. 2014, 14, 2604−2609

  • Invited lecture (Conferences)
    Seminar, Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (FORTH), 05.08.2016, Heraklion, Greece

Publ.-Id: 24133

Droplet-confined alternate pulsed epitaxy of GaAs nanowires on Si substrates: meeting the typical MBE standards

Tauchnitz, T.; Balaghi, L.; Bischoff, L.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.

We introduce a growth scheme with alternate Ga and As4 pulses for the self-catalyzed growth of free-standing GaAs nanowires on Si(111) substrates. Unlike the conventional growth mode, our scheme offers a wide growth temperature window (450 – 600 °C), low growth rates (down to 1-2 monolayers per As4 pulse), and the ability for defect-free and abrupt growth interruptions, meeting the typical MBE standards. We demonstrate the possibility to grow defect-free zinc blende nanowires in the whole temperature window and to probe the growth dynamics in specially designed experiments.

Keywords: nanowire; self-catalyzed; alternate pulsed epitaxy; GaAs; Si substrate

  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy (MBE 2016), 04.09.2016, Montpellier, France

Publ.-Id: 24130

Exciton recombination at crystal-phase quantum rings in GaAs/InxGa1−xAs core/multishell nanowires

Corfdir, P.; Lewis, R. B.; Marquardt, O.; Küpers, H.; Grandal, J.; Dimakis, E.; Trampert, A.; Geelhaar, L.; Brandt, O.; Phillips, R. T.

We study the optical properties of coaxial GaAs/InxGa1-xAs core/multishell nanowires with x between 0.2 and 0.4 at 10K. The evolution of the photoluminescence energy of the InxGa1-xAs quantum well shell with x and shell thickness agrees with the result of 8-band k.p calculations, demonstrating that the shell growth is pseudomorphic. At low excitation power, the photoluminescence from the shell is dominated by the recombination of exciton states deeply localized within the shell. We show that these states are associated with crystal-phase quantum rings that form at polytype segments of the InxGa1-xAs quantum well shell.

Publ.-Id: 24129

Functional behavior of the anomalous magnetic relaxation observed in melt-textured YBa2Cu3O7- δ samples showing the paramagnetic Meissner effect

Dias, F. T.; Vieira, V. N.; Garcia, E. L.; Wolff-Fabris, F.; Kampert, E.; Gouvea, C. P.; Schaf, J.; Obrados, X.; Puig, T.; Roa, J. J.

We have studied the functional behavior of the field-cooled (FC) magnetic relaxation observed in melt- textured YBa2Cu3O7- δ(Y123) samples with 30 wt% of Y2Ba1Cu1O5 (Y211) phase, in order to investigate anomalous paramagnetic moments observed during the experiments. FC magnetic relaxation experiments were performed under controlled conditions, such as cooling rate and temperature. Magnetic fields up to 5T were applied parallel to the ab plane and along the c-axis. Our results are associated with the para-magnetic Meissner effect (PME), characterized by positive moments during FC experiments, and related to the magnetic flux compression into the samples. After different attempts our experimental data could be adequately fitted by an exponential decay function with different relaxation times. We discuss our results suggesting the existence of different and preferential flux dynamics governing the anomalous FC paramagnetic relaxation in different time intervals. This work is one of the first attempts to interpret this controversial effect in a simple analysis of the pinning mechanisms and flux dynamics acting during the time evolution of the magnetic moment. However, the results may be useful to develop models to explain this interesting and still misunderstood feature of the paramagnetic Meissner effect.

Publ.-Id: 24128

Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs2CuCl4

Cong, P. T.; Postulka, L.; Wolf, B.; van Well, N.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M.

Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 in magnetic fields along the a axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at TN. Isothermal measurements at T < TN of the sound attenuation a reveal two closely spaced features of different characters on approaching the material’s quantum-critical point (QCP) at Bs = 8.5 T for B II a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature TN(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material’s spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/kB = 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.

Publ.-Id: 24127

A monomeric copper-phosphoramide complex: Synthesis, structure, and electronic properties

Henriques, M. S.; Gorbunov, D. I.; Ponomaryov, A. N.; Saneei, A.; Pourayoubi, M.; Dusek, M.; Zvyagin, S.; Uhlarz, M.; Wosnitza, J.

We report on a novel phosphoramide complex with formula Cu(NO3)2([C5H10N]3PO)2. This complex is the first example of a copper monomeric phosphoric triamide having an octahedral Cu[O]6 coordination environment. Cu(NO3)2([C5H10N]3PO)2 crystallizes in the monoclinic space group P21/n with the Cu atom located at an inversion center, as determined by single-crystal X-ray diffraction. Magnetic measurements along the principal crystallographic directions of the single crystal indicate that the complex is a paramagnet with very low magnetic anisotropy. Electron paramagnetic resonance spectra reveal the presence of two Cu2+ sites and make it possible to extract the hyperfine coupling.

Publ.-Id: 24126

Evaluation of E-Waste Processing through Secondary Copper Smelting

Rhamdhani, M. A.; Ghodrat, M.; Brooks, G.; Masood, S.; Corder, G.; Haque, N.; Reuter, M. A.

Wastes of electronics and electrical equipment (WEEE) or simply e-wastes contain many valuable elements that include base metals (Cu, Fe, Pb, Al), precious metals (Au, Ag, Pt, Pd), other metals (Sn, Se, Te, Ta, Co, In, Ru, etc); as well as hazardous elements. Sustainable extraction of the valuable elements from e-waste is challenging due to the complexities of the materials and associated processing routes. There have been a number of processing and extraction techniques developed at laboratory level and few are implemented in industrial practices [1]. The processes implemented at industrial scale are mainly based on an improved combination of traditional extractive metallurgy processes (for example a combined pyrometallurgy, hydrometallurgy and electrometallurgy processes). Although practiced at industry scale, these processes and processing routes are far from optimised. Development of new technologies and/or improvement of the existing practices are still needed. Some of the barriers for improvement include: lack of fundamental knowledge (behaviour of all of these elements, which are governed by their solution thermodynamics); limited sound technoeconomic analyses; as well as limited understanding on the environmental impact of the different processing routes.

Keywords: E-Waste; E-Waste processing; WEEE recycling; precious metals; secondary copper

  • Lecture (Conference)
    8th Annual High Temperature Processing Symposium 2016, 01.-02.02.2016, Melbourne, Australien


Publ.-Id: 24125

Recycling Indices Visualizing the Performance of the Circular Economy

Reuter, M. A.; van Schaik, A.

The EU has adopted an ambitious Circular Economy (CE) package. This action plan aims to "close" the loop of product lifecycles through improved product design, improved collection, recycling, remanufacture and re-use. Through this the EU envisages to bring benefits both environmentally as well as economically. Recycling forms the heart of the CE system; metal and material recycling and metallurgical processing are key enablers. Maximizing the recovery of materials from End-of-Life (EoL) products, while simultaneously lowering the environmental footprint, is a vital outcome. Therefore, designing greener products while also optimizing organisational and technology infrastructures of industrial recycling processing flow sheets are vital. This enables the maximal recovery of materials and also especially strategic elements from EoL products, requiring a deep understanding of the fundamental opportunities and limits and the dynamics of the evolving and agile system. In order to inform the consumer, this paper presents the developed Recycling Index (RI) (analogous to the EU Energy Labels) that includes a new Material-RI.These are based on simulation models that have their roots in minerals and metallurgical processing. It builds on previous work by the authors that visualises and communicate the recycling performance of a product as well as of the individual materials in a clear, easy and transparent manner. It will help to empower the consumer to make informed purchasing decisions. Furthermore, RIs are essential for communicating greener design and efforts to improve resource efficiency by producers and state-of-the art recycling and (metallurgical) processing technology by industry. The RI is an excellent tool to provide insight into possibilities and improvements as well as barriers and limits for CE to policy makers and to close the missing links in the CE.

Keywords: Recycling; Design for Recycling; Recycling Index; Simulation; Calculation methods for recycling rates; Circular Economy

  • World of Metallurgy - Erzmetall 69(2016)4, 201-216


Publ.-Id: 24124

Strategic metal recycling: adaptive metallurgical processing infrastructure and technology are essential for a Circular Economy

Reuter, M. A.; van Schaik, A.

Recycling forms the heart of the Circular Economy (CE) system. Ultimately all products will have to be recycled at their End-of-Life (EoL). Maximizing the recovery of materials and also especially strategic elements from EoL products requires a deep understanding of the fundamental limits and the dynamics of the evolving system, thus an adaptive processing and metallurgical infrastructure is critical to recover all metals and materials. Paramount is the quantification of the “mineralogy”, the complex and interlinked composition of products, to trace and quantify specifically all the losses of materials, metals, alloys, etc. due to thermodynamic and other non-linear interactions. We named this product centric recycling. The recycling potential and performance must be quantified and demonstrated for products, collection systems, waste separation and recovery technologies, and material supply. Emphasis is also placed on informing the consumer through iRE i.e. informing Resource Efficiency in an easy-to-understand way. System Integrated Metal Processing (SIMP) using big-data, multi-sensors, simulation models, metallurgy, etc. links all stakeholders through Circular Economy Engineering (CEE), an important enabler to maximize Resource Efficiency and thus iRE.

Keywords: EoL; CE; CEE

  • Annales des Mines - Responsiabilité & Environnement (2016)82, 62-66


Publ.-Id: 24123

Gold - A Key Enabler of a Circular Economy: Recycling of Waste Electric and Electronic Equipment

Reuter, M. A.; van Schaik, A.

Metals are an essential and critical component of today's society: a moment's reflection on their ubiquitous presence in virtually all energy and material production processes is sufficient to confirm this. Metals play a key role in enabling sustainability through various high-tech applications in society. However, the resources of our planet are limited, as is the strain to which we can subject it in terms of emissions, pollution, and disposal of waste. For these reasons, finding ways to lower the environmental footprint of our collective existence and therefore lowering greenhouse gas and other emissions is a vital priority. The principal theme of this contribution is the maximization of resource efficiency as well as enabling a circular economy (CE) through the recycling of waste electric and electronic equipment, with a focus on precious metals (PMs) (incorporating gold, silver, and the platinum group metals [PGMs]) and the base-metal industry that enables their recycling. The detailed and deep knowledge that is required to systemically fully understand resource efficiency in the context of a CE are discussed and the concepts of design for resource efficiency and design for recycling elaborated on. Specifically, the understanding of product-centric recycling is highlighted, setting it apart from the usual material-centric recycling approaches. The latter focus more on bulk materials and therefore inherently limit the maximal recovery of technologically critical elements in particular, as well as PMs and PGMs. The base metals – principally, copper, cobalt, lead, nickel, tin, and zinc – all play a crucial part in the present society. Increasingly, these are linked in concert to form the crucial carrier metals for the sustainable CE society termed the “web of metals” and “web of products” or, in a more modern paradigm, system integrated metal production–in other words, the process metallurgical Internet of things. This chapter also examines the special and crucial role base metals have in acting as enablers in any recycling efforts, as they also play a key role during recycling, such as copper and lead being the solvent of gold and other PMs and PGMs and release them during refining. Above all, the PMs are key economic enablers for the economic viability of recycling as well as the metallurgical infrastructure (system integrated metal production/Internet of things) that makes it possible to recover PMs and PGMs and their other associated elements.

Keywords: Critical metals; Design for recycling; Furnace technology; Gold; Hydrometallurgy; Internet-of-things; Precious metals; Process metallurgy; Pyrometallurgy; Recycling; System integrated Metal production; WEEE


Publ.-Id: 24122

Digitalizing the Circular Economy: Circular Economy Engineering Defined by the Metallurgical Internet of Things

Reuter, M. A.

Metallurgy is a key enabler of a circular economy (CE), its digitalization the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of me tallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT.

Keywords: digitalization the metallurgical Internet of Things (m-IoT)


Publ.-Id: 24121

Fast neutron-induced fission at the time-of-flight facility nELBE

Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S.

The fast neutron-induced fission cross section of Pu(242) was determined the range of 0.5 MeV and in 10 MeV relative to U(235)(n,f) at the neutron time-of-flight facility nELBE. Using the high spontaneous fission rate of Pu(242) to determine the number of target atoms makes the cross section independent from the detection. Sophisticated neutron transport simulations with Geant 4 and MCNP 6 are used to correct the neutron scattering. The determined relative cross section is in good agreement with current experimental and evaluated data sets.

Keywords: neutron-induced fission cross section; neutron scattering corrections; fast neutrons; nELBE

  • Lecture (Conference)
    ND2016 - International Conference on NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, 11.-16.09.2016, Bruges, Belgien
  • Open Access Logo Contribution to proceedings
    ND 2016 - International Conference on NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, 11.-16.09.2016, Bruges, Belgien
    EPJ Web of Conferences, Les Ulis Cedex A
    DOI: 10.1051/epjconf/201714611023

Publ.-Id: 24120

Temperature Quenching in LAB based liquid scintillator

Sörensen, A.; Junghans, A. R.; Kögler, T.; Wagner, A.; Zuber, K.

This work investigated the effect of temperature changes on the light output of LAB based liquid scintillator in a range from -5°C to 30°C with a-particles and electrons in a small scale setup. Assuming a linear behaviour, a combined negative temperature coefficient of (-0.29+-0.01) % / °C is found. Considering hints for a particle type dependency, electrons show (-0.17+-0.02) % / °C, whereas the temperature dependency seems stronger for a-particles, with (-0.35+-0.03) % / °C. A pulse shape analysis shows increased strength of a slow decay component at lower temperatures, pointing to reduced non-radiative triplet state de-excitations at lower temperatures.

Keywords: lineare Alcyl benzene; temperature quenching

Publ.-Id: 24119

Plutonium interaction studies with the Mont Terri Opalinus Clay isolate Sporomusa sp. MT-2.99: changes in the plutonium speciation by solvent extractions.

Moll, H.; Cherkouk, A.; Bok, F.; Bernhard, G.

Since plutonium could be released from nuclear waste disposal sites, the exploration of the complex interaction processes between plutonium and bacteria is necessary for an improved understanding of the fate of plutonium in the vicinity of such a nuclear waste disposal site. In this basic study the interaction of plutonium with cells of the bacterium, Sporomusa sp. MT-2.99, isolated from Mont Terri Opalinus Clay, was investigated anaerobically (in 0.1 M NaClO4) with or without adding Na-pyruvate as an electron donor. The cells displayed a strong pH dependent affinity for Pu. In the absence of Na-pyruvate a strong enrichment of stable Pu(V) in the supernatants was discovered, whereas Pu(IV)-polymers dominated the Pu oxidation state distribution on the biomass at pH 6.1. A pH-dependent enrichment of the lower Pu oxidation states (e.g. Pu(III) at pH 6.1 which is considered to be more mobile than Pu(IV) formed at pH 4) was observed in the presence of up to 10 mM Na-pyruvate. In all cases, the presence of bacterial cells enhanced removal of Pu from solution and accelerated Pu interaction reactions, e.g. biosorption and bioreduction.

Keywords: plutonium; bacteria; Sporomusa sp; biosorption; bioreduction; solvent extractions


Publ.-Id: 24118

The case of a rough potential energy surface: Discrepancies between results of NEB and MD calculations

Posselt, M.

Vacancy migration is studied in a silicon crystal with atomic interactions described by the Kumagai potential [1]. The basic functional form of this potential is very similar to the Tersoff potential. The main improvements concern the values of the elastic constants and the melting temperature. However, the potential energy surface is as rough as in the case of the Tersoff potential. In the ground state the vacancy has the “normal” tetrahedral configuration. The migration in the rugged potential energy landscape leads to peculiarities. Extensive Molecular Dynamics (MD) calculations show that the atomic mechanism of the migration process depends on temperature. The vacancy migration energy changes at about 1000 K: At lower and higher temperatures it is about 0.71 and 0.41 eV, respectively. Investigations on the dominating defect structure show that below about 1000 K the tetrahedral vacancy prevails whereas at higher temperature a modified version of the tetrahedral vacancy, the split vacancy and other configurations become dominant.
Applying the Nudged Elastic Band (NEB) method to the potential energy surface in the ground state, the transition between neighboring tetrahedral vacancy structures was studied. A number of intermediate metastable states were found, amongst them the modified version of the tetrahedral vacancy and the split vacancy. The maximum barrier for the migration between one ground state configuration to another is about 0.9 eV, whereas a barrier of about 0.3 eV is found for the transition from the split to the modified tetrahedral structure. Comparing with the results of MD simulations one may assume that in the high temperature range the vacancy moves mainly between high-energy configurations such as the split and the modified tetrahedral structure. The reason why the vacancy is not very often found in the ground state is not completely clear. Obviously, the free energy landscape at elevated temperature differs strongly from the ground-state energy landscape. Vibrational degrees of freedom may lead to the narrowing of the path to the tetrahedral state while the path between the high energy states may become much broader.
[1] T. Kumagai et al., Comput. Mater. Sci. 39, 457 (2007)

Keywords: molecular dynamics; nudged elastic band method; potential energy surface

  • Poster
    Int. Focus Workshop on Bridging-Time Scale Techniques and their Application in Atomistic Computational Science, 12.-15.09.2016, Dresden, Germany

Publ.-Id: 24117

Local Scale-Invariance of the 2+1 dimensional Kardar-Parisi-Zhang model

Kelling, J.; Ódor, G.; Gemming, S.

Local Scale-Invariance theory is tested by extensive dynamical simulations of the driven dimer lattice gas model, describing the surface growth of the 2+1 dimensional Kardar–Parisi–Zhang surfaces. Very precise measurements of the universal autoresponse function enabled us to perform nonlinear fitting with the scaling forms, suggested by local scale-invariance (LSI). While the simple LSI ansatz does not seem to work, forms based on logarithmic extension of LSI provide satisfactory description of the full (measured) time evolution of the autoresponse function.

Keywords: Kardar-Parisi-Zhang; Local Scale-Invariance; Monte-Carlo; GPU

Related publications


Publ.-Id: 24116

Inter-sublevel dynamics in single InAs/GaAs quantum dots probed by strong terahertz excitation

Stephan, D. R.

In this thesis, the response of single self-assembled quantum dots to strong terahertz pulses is investigated by measuring the emitted photoluminescence spectrally as well as in a time-resolved manner, revealing the dynamics of the system. Experimentally, this is realized by combining the micro-photoluminescence technique with illumination from a free-electron laser, which provides intense, tunable narrow-band terahertz pulses. The photoluminescence is triggered by spectrally tunable near-infrared illumination with a synchronized, mode-locked titanium sapphire laser. The measured transients are evaluated with a rate-equation model, taking into account the precise detector response. These measurements reveal three distinct effects, which appear or are obscured depending on the excitation conditions. Firstly, the conduction band inter-sublevel s-p transition is excited by the THz pulses. However, for strong terahertz intensities, a loss of photoluminescence is observed, which can lead to total depletion at very high intensities. This is attributed to the transfer of charge carriers into the wetting layer. Thirdly, for certain near-infrared energies, the opposite behavior is observed, in which the terahertz pulse causes an increase of photoluminescence. The cause of this effect is the release of previously trapped charge carriers, which is also visible in the photoluminescence spectrum. The source of the additional charge carriers is unambiguously identified as the wetting layer. The obtained data is compared to previous studies, and an overview of the relevant theory is presented. In addition, a description of the custom built experimental setup is given.

Keywords: InAs/GaAs semiconductor quantum dot; time-resolved photoluminescence; micro-photoluminescence; free-electron laser; terahertz excitation; carrier dynamics

  • Book (Authorship)
    München: Verlag Dr. Hut, 2016
    122 Seiten

Publ.-Id: 24115

Nodal recurrence after stereotactic body radiotherapy for early stage non-small cell lung cancer: incidence and proposed risk factors

Wink, K. C. J.; van Baardwijk, A.; Troost, E. G. C.; de Ruysscher, D.

Stereotactic body radiotherapy (SBRT) is an alternative to surgery for patients with early stage non-small cell lung cancer (NSCLC) who are inoperable due to comorbid disease or who refuse surgery. SBRT results in an excellent local control rate of more than 90%, which is comparable to surgery, while short and long-term overall toxicity is low. Surgically treated patients are often more extensively staged pre-operatively, e.g. with EBUS, and undergo intra-operative lymph node dissection or sampling. Occult nodal metastases (ONM) detected by lymph node dissection have been shown to increase the incidence of regional recurrence (RR) after surgery, which is associated with poor outcome. In patients undergoing SBRT, however, definite pathological nodal staging is lacking. Therefore, other ways to identify patients at high risk for ONM and RR might be thought for.
The aim of this systematic review is to summarize the incidence of and risk factors for RR after SBRT and compare these to those after surgery.

Keywords: SBRT; SABR; NSCLC; regional recurrence; lymph node; early stage

Publ.-Id: 24114

Cyclotron resonance and photoluminescence studies of dilute GaAsN in magnetic fields up to 62 Tesla

Eßer, F.

In this thesis, we investigate optical and electrical properties of dilute nitride semiconductors GaAsN in pulsed magnetic fields up to 62 T. For the most part, the experiments are performed at the Dresden High Magnetic Field Laboratory (HLD).
In the first part of this thesis, the electron effective mass of GaAsN is determined with a direct method for the first time. Cyclotron resonance (CR) absorption spectroscopy is performed in Si-doped GaAsN epilayers with a nitrogen content up to 0.2%. For the CR absorption study, we use the combination of the free-electron laser FELBE and pulsed magnetic fields at the HLD, both located at the Helmholtz-Zentrum Dresden-Rossendorf. A slight increase of the CR electron effective mass with N content is obtained. This result is in excellent agreement with calculations based on the band anticrossing model and the empirical tight-binding method. We also find an increase of the band nonparabolicity with increasing N concentration in agreement with our calculations of the energy dependent momentum effective mass.
In the second part of this thesis, the photoluminescence (PL) characteristics of intrinsic GaAsN and n-doped GaAsN:Si is studied. The PL of intrinsic and very dilute GaAsN is characterized by both GaAs-related transitions and N-induced features. These distinct peaks merge into a broad spectral band of localized excitons (LEs) when the N content is increased. This so-called LE-band exhibits a partially delocalized character because of overlapping exciton wave functions and an efficient interexcitonic population transfer. Merged spectra dominate the PL of all Si-doped GaAsN samples. They have contributions of free and localized excitons and are consequently blue-shifted with respect to LE-bands of intrinsic GaAsN. The highly merged PL profiles of GaAsN:Si are studied systematically for the first time with temperature-dependent time-resolved PL. The PL decay is predominantly monoexponential and has a strong energy dispersion. In comparison to formerly reported values of intrinsic GaAsN epilayers, the determined decay times of GaAsN:Si are reduced by a factor of 10 because of enhanced Shockley-Read-Hall and possibly Auger recombinations.
In the third part of this thesis, intrinsic and Si-doped GaAsN are investigated with magneto-PL in fields up to 62 T. A magneto-PL setup for pulsed magnetic fields of the HLD was built for this purpose. The blue-shift of LE-bands is studied in high magnetic fields in order to investigate its delocalized character. The blue-shift is diminished in intrinsic GaAsN at higher temperatures, which indicates that the interexcitonic population transfer is only active below a critical temperature 20 K < T < 50 K. A similar increase of the temperature has no significant impact on the partially delocalized character of the merged spectral band of GaAsN:Si. We conclude that the interexcitonic transfer of Si-doped GaAsN is more complex than in undoped GaAsN. In order to determine reduced masses of undoped GaAsN and GaAs:Si, the field-induced shift of the free exciton transition is studied in the high-field limit. We find an excellent agreement of GaAs:Si with a formerly published value of intrinsic GaAs which was determined with the same method. In both cases, the reduced mass values are enhanced by 20% in comparison to the accepted reduced mass values of GaAs. The determined GaAsN masses are 1.5 times larger than in GaAs:Si and match the rising trend of formerly reported electron effective masses of GaAsN.

Keywords: dilute nitride; recombination dynamics; effective mass; pulsed magnetic fields; magneto-photoluminescence

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-072 2016
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 24113

Rohstoffe für die Energieversorgung der Zukunft

Angerer, G.; Buchholz, P.; Gutzmer, J.; Hagelten, C.; Herzig, P.; Little, R.; Trauer, R. K.; Welker, F.-W.

  • Book (Authorship)
    München: Acatech, 2016
    198 Seiten

Publ.-Id: 24112

Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203] [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275] [276] [277] [278] [279] [280] [281] [282] [283] [284] [285] [286] [287] [288] [289] [290] [291] [292] [293]