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39291 Publications

Subspace Multinomial Logistic Regression Ensemble for Classification of Hyperspectral Images

Khodadadzadeh, M.; Ghamisi, P.; Contreras, C.; Gloaguen, R.

Exploiting multiple complementary classifiers in an ensemble framework has shown to be effective for improving hyperspectral image classification results, especially when the training samples are limited. With a different principle and based on this assumption that hyperspectal feature vectors effectively lie in a low-dimensional subspace, the subspace-based techniques have shown great classification performance. In this work, we propose a new ensemble method for accurate classification of hyperspectral images, which exploits the concept of subspace projection. For this purpose, we extend the subspace multinomial logistic regression classifier (MLRsub) to learn from multiple random subspaces for each class. More specifically, we impose diversity in constructing MLRsub by randomly selecting bootstrap samples from the training set and subsets of the original hyperspectral feature space, which leads to generate different class subspace features. Experimental results, conducted on two real hyperspectral data sets, indicate that the proposed method provides significant classification results in comparison with other state-of-the-art approaches.

Keywords: Hyperspectral images; classification; ensemble-based approaches; subspace multinomial logistic regression; remote sensing

  • Contribution to proceedings
    IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 22.-27.07.2018, Valencia, Spain

Publ.-Id: 28612

Tuning of electrocatalytic properties of MoS2 by chalcogenide ion implantation

Luxa, J.; Mazánek, V.; Mackova, A.; Malinsky, P.; Akhmadaliev, S.; Sofer, Z.

MoS2 is one of the most explored and promising material for electrocatalytic water splitting by hydrogen evolution reaction (HER). However, in its bulk form, MoS2 possesses only poor activity towards HER. Therefore, appropriate treatment has to be employed to tune its catalytic properties. In this study, we report the influence of ion bombardment (S, Se and Te ions) with medium ion energy (400 keV) and various ion fluences (1 × 1014–1 × 1016 ions/cm2) on the electrocatalytic properties of bulk MoS2 crystals. Our results showed that upon irradiation, sulfur vacancies were created. Upon exposure to ambient atmosphere, sulfur vacancies were partially replaced by oxygen, which led to surface oxidation. Nevertheless, samples irradiated using the higher range of ion fluences have generally showed enhanced catalytic HER performance in comparison with untreated MoS2 crystals. Furthermore, we have also demonstrated that ion irradiation/implantation can serve as a tool for doping of MoS2 crystals with Se and Te which can also influence the HER performance. The reported results demonstrate that ion beam irradiation can be used for doping as well as creation of sulfur vacancies in bulk MoS2 crystals which is fundamental for the HER performance.

Keywords: Electrocatalysis; Hydrogen evolution reaction; Ion implantation; MoS2

Related publications

Publ.-Id: 28611

Probing plutonium dioxide nanoparticles with various synchrotron methods

Gerber, E.; Romanchuk, A.; Pidchenko, I.; Hennig, C.; Trigub, A.; Weiss, S.; Scheinost, A.; Rossberg, A.; Kalmykov, S.; Kvashnina, K.

Plutonium is one of the most complicated element among actinides. It can exist in four different oxidation states (III, IV, V, VI) under environmental conditions. Due to the small value of standard electrode potentials among these linked oxidation states plutonium can change its oxidation state easily. Moreover, plutonium may exist in several oxidation states simultaneously, which makes its chemistry even more complex.
It was previously shown that plutonium migrates in colloidal form in the subsurface environment with the distance of several kilometers. It turned out that so called “colloidal Pu(IV) polymers” are in fact aggregates of PuO2 nanoparticles with diameters ~ 2 nm. However, the certain structure and stoichiometry of these colloids, as well as presence of other oxidation states but Pu(IV) is still debated.

This contribution will show results of plutonium oxide nanoparticle studies at the large-scale facility – The European Synchrotron (ESRF) by complementary methods that used X-rays in different regimes to probe the Pu oxide nanoparticles. Samples were prepared by rapid chemical precipitation using precursors in the different oxidation states (Pu(III), Pu(IV), Pu(V) and Pu(VI)). These precursors were obtained by chemical reduction or oxidation of Pu stock solution. The obtained nanoparticles were characterized at the different beamlines at the ESRF. It gives the opportunity to study our samples with various techniques: X-ray diffraction (XRD), pair distribution function analysis (PDF), and several types of spectroscopies: high energy resolution fluorescence detection (HERFD) at L3 and M5-edges, X-ray emission spectroscopy (XES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The applying multifold synchrotron methods benefits to discover features, which may be unclear or even indistinguishable, these approach is also crucial to confirm results, obtained with individual methods.
It was found that small (2 nm) nanoparticles are formed from the Pu(III), Pu(IV), Pu(V) aqueous solutions, with the crystal structure close to PuO2, without any other Pu-O contributions or oxidation states of Pu except Pu(IV).

Related publications

  • Lecture (Conference)
    RAD 2019 Conference, 10.-14.06.2019, Herceg Novi, Montenegro

Publ.-Id: 28610

Subspace clustering algorithms for mineral mapping

Khodadadzadeh, M.; Contreras, C.; Tusa, L.; Gloaguen, R.

The application of drill core hyperspectral data in exploration campaigns is receiving great interest to obtain a general overview of a mineral deposit. However, the main approach to the investigation of such data is by visual interpretation, which is subjective and time-consuming. To address this issue, recently, the use of machine learning techniques is proposed for the analysis of this data. For drill core samples that for which only very little prior knowledge is often available, applying classification algorithms which are supervised learning methods is very challenging. In this paper, we suggest to use clustering (unsupervised) methods for mineral mapping, which are similar to classification but no predefined class labels are needed. To handle mapping of the very highly mixed pixels in drill core hyperspectral data, we propose to use advanced subspace clustering methods, in which pixels are assumed to lie in a union of low-dimensional subspaces. We conduct a comparative study and evaluate the performance of two well-known subspace clustering methods, i.e., sparse subspace clustering (SSC) and low-rank representation (LRR). For the experiments, we acquired VNIR-SWIR hyperspectral data and applied scanning electron microscopy based Mineral Liberation Analysis (MLA) for two drill core samples. MLA is a high-resolution imaging technique that allows detailed mineral characterization. We use the high-resolution MLA image as a reference to analyze the clustering results. Qualitative analysis of the obtained clustering maps indicates that the subspace clustering methods can accurately map the available minerals in the drill core hyperspectral data, especially in comparison to the traditional k-means clustering method.

Keywords: Mineral mapping; drill core; hyperspectral data; subspace clustering; remote sensing

  • Contribution to proceedings
    SPIE Image and Signal Processing for Remote Sensing XXIV, 10.-13.09.2018, Berlin, Germany

Publ.-Id: 28609

High-precision image-guided proton irradiation of mouse brain sub-volumes

Suckert, T.; Müller, J.; Beyreuther, E.; Bütof, R.; Dietrich, A.; Gotz, M.; Haase, R.; Schürer, M.; Tillner, F.; Krause, M.; Lühr, A.; von Neubeck, C.


Proton radiotherapy offers the potential to reduce normal tissue toxicity. However, clinical safety margins, range uncertainties and varying relative biological effectiveness (RBE) may result in a critical dose in tumor-surrounding normal tissue. To assess potential adverse effects in preclinical studies, we established stereotactic proton mouse brain irradiation and a cell-based analysis of radiation damage repair.
Material and methods:
A setup to shape a proton beam with 7 mm range in water and 3 mm in diameter was built and dosimetrically characterized. Cone-beam computed tomography (CBCT) and orthogonal X-ray imaging were used to delineate the right hippocampus (target) and to position the mice, respectively. For two mouse strains (C57BL/6 and C3H), brains were irradiated with 4 Gy or 8 Gy and excised after 30 min or 3 h. Brain sections (3 µm) were cut every 100 µm and DNA double-strand break (DSB) repair kinetics was visualized by staining for cell nuclei and H2AX. Imaged sections were analyzed with an automated and validated processing pipeline to provide a quantitative, spatially-resolved damage indicator.
Twenty mice underwent the treatment workflow including imaging, target delineation, positioning, and irradiation. The analyzed DNA damage pattern clearly visualized the radiation effect and could be mapped onto the measured dose distribution. For all evaluated C3H mice, the proton beam hit the right hippocampus and stopped in the brain. Damage pattern became spatially more extended and diffuse for 8 Gy and 3 h after irradiation, respectively. C57BL/6 mice showed comparable damage distributions, however, with larger spatial variation of the beam alignment relative to the hippocampus.
We established and biologically validated stereotactic proton irradiation of mouse brains. The clinically-oriented workflow facilitates (back-) translational studies. Geometric accuracy and cell-based assessment enable a biologically and spatially resolved analysis of radiation response and RBE.

Keywords: Relative biological effectiveness (RBE); H2AX; particle therapy; small animal irradiation; normal tissue toxicity

Publ.-Id: 28608

Tonic signaling and its effects on lymphopoiesis of CAR-armed hematopoietic stem and progenitor cells

Albert, S.; Koristka, S.; Gerbaulet, A.; Cartellieri, M.; Arndt, C.; Feldmann, A.; Berndt, N.; Loureiro, L.; von Bonin, M.; Ehninger, G.; Eugster, A.; Bonifacio, E.; Bornhäuser, M.; Bachmann, M.; Ehninger, A.

Long-term survival of adoptively transferred chimeric antigen receptor (CAR) T cells is often limited. Transplantation of hematopoietic stem cells (HSCs) transduced to express CARs could help to overcome this problem as CAR-armed HSCs can continuously deliver CAR+ multi-cell lineages (e.g. T cells, NK cells). In dependence on the CAR construct a variable extent of tonic signaling in CAR T cells was reported, thus, effects of CAR-mediated tonic signaling on the hematopoiesis of CAR-armed HSCs is unclear. To assess effects of tonic signaling two CAR constructs were established and analyzed: (i) A signaling CAR inducing a solid antigen-independent tonic signaling termed CAR-28/, and (ii) a non-stimulating control CAR construct lacking intracellular signaling domains termed CAR-Stop. Bone marrow (BM) cells from immunocompetent mice were isolated, purified for HSC-containing Lin-cKit+ (LK) cells or the LK Sca-1+ subpopulation (Lin Sca 1+cKit+, LSK) and transduced with both CAR constructs. Subsequently, modified BM cells were transferred into irradiated mice where they successfully engrafted and differentiated into hematopoietic progenitors. HSCs expressing the CAR-Stop sustained normal hematopoiesis. In contrast, expression of the CAR-28/ led to elimination of mature CAR+ T and B cells suggesting that the CAR-mediated tonic signaling mimics autorecognition via the newly recombined immune receptors in the developing lymphocytes.

Keywords: Chimeric antigen receptors; tonic signaling; HSC transplantation; hematopoiesis; HSC engraftment; immunotherapy; adaptive immune system

Publ.-Id: 28607

Multidimensional fluid mixing capabilities of ATHLET 3.1A during an overcooling transient in a generic PWR KONVOI

Diaz Pescador, E.

In the presented work, a simulation of a 10% main steam line break (MSLB) in steam generator (SG) 1 in a generic German PWR KONVOI model is carried out and investigated by means of the system code ATHLET 3.1A. The accident analysis is focused first, on a thermal-hydraulic transient characterization, in order to subsequently study the multidimensional fluid mixing in the reactor pressure vessel (RPV), and further verification against suitable experimental data. With this aim, in the ATHLET simulation, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions from the test PKL G3.1. The obtained results show an increase in the heat removal through the U-tubes of SG 1during boil-off, giving rise to an asymmetric overcooling in the reactor coolant system. At the arrival of the overcooled water to the RPV, the cold water stream mixes with the ambient coolant in the downcomer and eventually spreads across the whole region. In the core region, the overcooled water propagates from the periphery towards the core centre. The obtained behavior is in good agreement with the experimental results from the ROCOM and PKL test facilities.

  • Poster
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Germany

Publ.-Id: 28606

Integration of drone-borne hyperspectral and geomagnetic data. A combined approach in geologic remote sensing. A test from the Siilinjärvi carbonatite, Finland.

Jackisch, R.; Zimmermann, R.; Lorenz, S.; Saartenoja, A.; Pirttijärvi, M.; Heincke, B.; Gloaguen, R.

The worlds need for critical materials sees a surge since the last two decades. Most of Europe’s larger mineral deposits have been discovered and exploited by now. A rising need to include formerly unattractive or inaccessible prospects is apparent. Here, using drones for detailed prospecting of small areas comes in handy. Drones have the advantage of being cost-efficient, easily deployable and having a short turn-around time for high resolution data.
With this study, we introduce a novelty approach for non-invasive mineral exploration based on the integration of remote sensing applications. In particular, we combine the advantage of light-weight drone technology with a snapshot hyperspectral camera and a magnetometer. The platform delivers specified, integrated measurements of spectrometric high-resolution surface images fused with data of the earth’s magnetic field. This allows us to identify surficial rock exposures and the estimation of the subsurface proportions of the aforesaid target.
The sensor system is attached to an octocopter platform with a flight endurance of around 30 minutes. A fixed-wing drone is used to acquire magnetic data of the same target with a larger area. The combined data is processed through a framework of correction software and projected on digital elevation models (DEMs) from the target area. The DEMs are acquired via Structure-from-Motion Multi-View Stereo photogrammetry. Hyperspectral data is corrected for topographic effects and automatically georeferenced using the MEPHYSTo toolbox. Magnetic data is calibrated for orientation effects and corrected for diurnal and external induced field fluctuations via base station recordings. We validate the measurements with a field-tested assembly of different techniques, e.g., mineralogical and geochemical analysis, in-situ ground spectroscopy and geomagnetic readings.
The results are promising and we demonstrate that drone-based exploration becomes more affordable, intuitive and accessible to the mining sector and the geoscientific community.

Keywords: UAS; UAV; remote sensing; mineral exploration; hyperspectral; geomagnetic; fluxgate

Publ.-Id: 28605

Investigations on the thermal-hydraulic behavior of a generic PWR KONVOI during a 1% cold leg small-break loss of coolant accident using the system code ATHLET

Diaz Pescador, E.; Schäfer, F.; Wilhelm, P.; Kliem, S.

In the presented paper, a simulation of a small-break loss of coolant accident (SBLOCA) with a 1% break in the cold leg 1 in a generic German PWR KONVOI model is carried out and investigated by means of the thermal-hydraulic system code ATHLET 3.1A. The accident analysis is focused first on a thermal-hydraulic characterization of the SBLOCA, and a subsequent qualitative comparison with the test PKL H1.1. With this aim, in the simulation with ATHLET 3.1A, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions of the test PKL H1.1.
The test PKL H1.1 reproduces a SBLOCA superposed by additional system failures, such as unavailability of the high-pressure safety injection and the automatic secondary-side cool-down. The test was conducted in the framework of the OECD/PKL3 project in the large-scale test facility PKL (“Primärkreislauf”), operated by Framatome Germany, as a counterpart test of LSTF/ROSA SB-CL-32.
The second part of the paper is devoted to the study of the boron dilution into the steam generators, and the subsequent transport and fluid mixing phenomena in the reactor pressure vessel. The results in the simulation, show how the implementation of a 200 K/h cool-down through the steam generators, initiated at a peak cladding temperature (PCT) of 500°C, is able to eventually achieve a long-term safe stable condition, due to the injection of cold water, first from the hydro-accumulators at a pressure of 26 bar, and then the actuation of the low pressure safety injection at a pressure of 10 bar.
This outcome is also observed in the test H1.1. Nevertheless, unlike the results obtained in the test, the implementation of the 200 K/h cool-down during the SBLOCA in the simulation cannot avoid core damage, fact strongly influenced by the initial pressure differences between the KONVOI model and the PKL test facility, being the latter limited by design constraints to a maximum pressure of 50 bar.

Keywords: KONVOI; small-break loss of coolant accident; cool-down procedure; emergency core cooling systems; ATHLET 3.1A

  • Lecture (Conference)
    ICONE 27. 27th International Conference on Nuclear Engineering, 19.-24.05.2019, Ibaraki, Japan
  • Contribution to proceedings
    ICONE 27. 27th International Conference on Nuclear Engineering, 19.-24.05.2019, Ibaraki, Japan, Mechanical Engineering Journal (JSME): The Japan Society of Mechanical Engineers

Publ.-Id: 28604

Atomistic Simulations to Design a Room-Temperature Single Electron Transistor

Prüfer, T.; Möller, W.; von Borany, J.; Heinig, K. H.

For future low power-consumption nanoelectronics, a room-temperature single-electron transistor may be configured by placing a small (few nm diam.) Si nanodot in a thin (<10 nm) SiO2 interlayer in Si. This can be achieved by ion-irradiation induced interface mixing, which turns the oxide layer into metastable SiOx, and subsequent high-temperature thermal decomposition which leaves, for a sufficiently small mixed volume, a single Si nanodot in the SiO2 layer. Corresponding ion mixing simulations have been performed using the binary collision approximation (BCA)[1], followed by kinetic Monte-Carlo (KMC) simulations[2] of the decomposition process, with good qualitative agreement with the structures observed in related experiments. Quantitatively, however, the BCA simulation appears to overestimate the mixing effect. This is attributed to the neglect of the positive entropy of mixing of the Si-SiO2 system, i.e. the immiscibility counteracts the collisional mixing by “up-hill diffusion” [3]. Consequently, intermitting KMC diffusion steps have been introduced into the BCA mixing simulation, resulting in an excellent predictive power for the irradiation step of the production process. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

  • [1] W. Möller et al., NIM B, 322, 23–33
  • [2] M. Strobel et al., PRB 64, 245422
  • [3] B. Liedke et al., NIM B 316 (2013) 56–61

Related publications

  • Lecture (Conference)
    E-MRS 2018 Fall Meeting, 17.-21.09.2018, Warschau, Polen

Publ.-Id: 28603

Si Quantum Dots for Single Electron Transistor: Synthesis, Characterization and Theoretical Comparison

Prüfer, T.; Wolf, D.; Engelmann, H.-J.; Hübner, R.; Bischoff, L.; Hlawacek, G.; Heinig, K.-H.; Facsko, S.; Xu, X.; von Borany, J.

The appearance of quantum effects makes nanoparticles (NPs) more and more important in semiconductor physics and especially in nanoelectronics. One very promising application is the single electron transistor (SET). Common field effect transistors (FET) could be outperformed by SETs in many applications because of their ultra-low power consumption (~100 times). Important for the fabrication of SETs operating at room temperature is the control of position and size of nano dots (<5nm). Our CMOS-compatible approach to manufacture SETs follows a two-step synthesis of NPs: (i) Producing tiny SiOx volumes by ion beam irradiation of ultrathin buried SiO2 layers (<10nm) and (ii) self-organizing single Si nanodots by phase separation during thermal treatment.
Energy-filtered transmission electron microscopy (EFTEM) is an advanced technique for the structural analysis of Si NPs in buried SiO2 layers. Although the NPs in the SiO2 layer superimpose in 2-dimentional projections from cross-sectional TEM samples, we managed to characterize the density and size distribution of the formed nanoclusters using the knowledge of the electron mean free path length to convert the Si-plasmon-loss filtered TEM image into a Si-thickness map. Here we will present the characterization and a comparison with theory to show a significant overestimation of the mixing effect by BCA simulation. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072.

Related publications

  • Lecture (Conference)
    European Materials Research Society Fall Meeting, 17.-21.09.2018, Warschau, Polen

Publ.-Id: 28602

A sizeable change in the electronic properties of GaAs via strain engineering in lattice-mismatched core/shell nanowires

Schneider, H.; Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Helm, M.; Dimakis, E.

III-V compound semiconductors have fueled many breakthroughs in physics and technology owing to their direct band gap and high electron mobility. It has also been very important that these fundamental properties can be tailored in ternary or quaternary alloys by selecting the chemical composition appropriately. Here we explore the great possibilities for strain engineering in core/shell nanowires as an alternative route to tailor the properties of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InₓGa₁₋ₓAs or GaAs/InₓAl₁₋ₓAs core/shell nanowires can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic properties. Core/shell nanowires were grown in the self-catalyzed mode on SiOₓ/Si(111) substrates by molecular beam epitaxy. Strain analysis was performed using synchrotron X-ray diffraction and Raman scattering spectroscopy, and showed that for a thin enough core, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness, we obtain a heavily tensile-strained core and an almost strain-free shell. The tensile strain of the core exhibits a predominantly-hydrostatic character and causes the reduction of the GaAs band gap energy in accordance with our theoretical predictions using deformation-potential theory and first-principle calculations. For 7 % of strain (x = 0.54), the band gap energy was reduced to 0.87 eV at 300 K, i.e. a remarkable reduction of 40 %. Signatures of valence-band splitting were also identified in polarization-resolved photoluminescence measurements, as a result of the strain anisotropy in GaAs. Presuming a reduced effective mass of electrons in the tensile-strained core of GaAs/InₓAl₁₋ₓAs nanowires (core diameter = 22 nm, x = 0.39 - 0.49), the corresponding electron mobility was measured by time-domain terahertz spectroscopy to be in the range of 4000 cm²/V·s at 300 K. These values are the highest reported, even in comparison to GaAs/AlₓGa₁₋ₓAs nanowires with double the core thickness. Our results demonstrate that strained GaAs in core/shell nanowires can resemble the electronic properties of InₓGa₁₋ₓAs, surmounting issues with phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the device performance.

Keywords: core/shell III-V semiconductor nanowires; molecular eam epitaxy; MBE; strain; effective mass

Related publications

  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Publ.-Id: 28601

Squeezing information about ThO2 nanoparticles’ size and shape from high resolution XANES

Amidani, L.; Rossberg, A.; Romanchuk, A.; Plakhova, T.; Kvashnina, K.

Extracting information on the size and shape of very small nanoparticles (NPs) is not a trivial task and it is fundamental to push the analysis of the available techniques to extract as much in-formation as possible from the available data. In this perspective we present a detailed modelling of Th L3 edge high resolution XANES collected on ThO2 NPs showing how the size and shape of the NP impacts the spectral shape.
Nanoparticles of ThO2 with average size between 2 and 35 nm were synthesized by chemical precipitation and measured at Th L3 edge with High-Energy Resolution Fluorescence Detected (HERFD) XANES. The HERFD-XANES spectrum of NPs with diameter above 2.5 nm are all very similar, while for NPs below 2.5 nm the first post edge feature is missing. In order to un-derstand what this absence could be correlated to, we performed a series of simulations with the FDMNES code on particles of different shape and with size close to 2 – 2.5 nm. We considered three possible shapes and cut the structures from ThO2 bulk. As a first approximation we did not consider disorder at the surface, but only the effects induced by size and shape. After cutting the NPs from the bulk, the symmetry of the crystal is lowered and different Th atoms have different local environment. We set the cutoff radius of our simulations to 6 Å and identified the groups of equivalent Th atoms by comparing the local environment of each Th up to 6 Å. To fully characterize the XANES of the NP under study, a separate simulation per equivalent Th atom was performed with the FDMNES code.
By comparing the simulations of Th atoms at the surface and inside the NP it clearly emerges that the first post edge feature is particularly sensitive to the number of Th second nearest neigh-bors. The spectrum of a specific shape is given by the weighted average of all the different Th in the NP. Considering that the shape determines how many Th with a specific local environment will be present, each shape results in a different final spectrum. By comparing the data and the simulations we suggest that the ThO2 NP with diameter below 2.5 nm have octahedral shape.

Related publications

  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28600

Mineral mapping of drill core hyperspectral data with extreme learning machines

Contreras, C.; Khodadadzadeh, M.; Ghamisi, P.; Gloaguen, R.

Hyperspectral scanners are increasingly being used in the mining industry as a non-destructive and non-invasive technique to efficiently map minerals in drill core samples. Hyperspectral data allows the characterization of different mineral assemblages, structural features and alteration patterns based on reflectance spectrum profiles. Traditional methods to analysis drill core hyperspectral data include the use of reference spectral libraries by visual analysis or a well established software. However, although these approaches produce good results, they are time-consuming and prone to errors. Therefore, in this paper, we take advantage of the latest and advanced machine learning techniques proposed in different scientific fields and explore the use of extreme learning machines (ELM) to map minerals in drill core hyperspectral data. This is a supervised technique that provides fast and automatic means to characterize hyperspectral data. To be able to implement this technique, a reference map was generated from the drill core hyperspectral data. The obtained results indicate that ELM can successfully map minerals in drill core hyperspectral data producing better quantitative and qualitative results than a typical RF classifier.

Keywords: Drill cores; hyperspectral data; mineral mapping; extreme learning machine; random forest

  • Open Access Logo Contribution to proceedings
    2019 IEEE International Geoscience and Remote Sensing Symposium., 28.07.-02.08.2019, Yokohama, Japan
    IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium


Publ.-Id: 28599

The Structural and Compositional Changes of Graphene Oxide Induced by Irradiation With 500 keV Helium and Gallium Ions

Malinsky, P.; Macková, A.; Florianová, M.; Cutroneo, M.; Hnatowicz, V.; Bohácová, M.; Szokölová, K.; Böttger, R.; Sofer, Z.

Structural and compositional modification of 2D materials as graphene or graphene oxide (GO) are topical objects of nowadays due to their many technological applications. Ion irradiation of graphene based materials, as a method for improvement of their surface properties started recently. Ion mass, energy, and fluence are crucial for forming of GO electrical, optical, and mechanical properties. In this work, the GO films are irradiated with 500 keV He and Ga ions to different fluences. The ions with different masses and electronic/nuclear stopping power ratios, are chosen with the aim to examine mechanisms of radiation defect creation. The elemental composition of the GO is investigated using Rutherford back-scattering (RBS) and elastic recoil detection analysis (ERDA) techniques. The structural and chemical changes are characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy and the electrical properties are determined by two-point method. The RBS and ERDA analyses indicate deoxygenation and dehydrogenation of the irradiated GO surface. The thickness and the degree of O and H depletion depend on the ion mass. XPS and Raman spectroscopy show removal of oxygen functionalities and structural modifications leading to a decrease in the surface resistivity.

Keywords: graphene oxide; ion Irradiation; Helium; Gallium; structure; composition

Related publications

Publ.-Id: 28598

A Machine Learning Technique for Drill Core Hyperspectral Data analysis

Contreras, C.; Khodadadzadeh, M.; Tusa, L.; Ghamisi, P.; Gloaguen, R.

Hyperspectral data are increasingly being used to map minerals in drill core samples allowing a non-invasive and non-destructive characterization of the mineral assemblages, and therefore, the mineralogical composition of a system, its variability, and structural features. The analysis of drill core hyperspectral data is traditionally carried out by a visual interpretation of the spectra and a comparison with reference libraries using spectral similarity measures. Although this approach produces good results it is time-consuming and subjective. In this work, we introduce, for the first time, an innovative automatic mineral mapping technique for drill core hyperspectral data by using a machine learning approach. More specifically, we propose to exploit detailed information coming from the Scanning Electron Microscopy (SEM)-based Mineral Liberation Analysis (MLA) to train a supervised classifier. For the extraction of input features, a traditional technique is explored, i.e., Principal Component Analysis (PCA). For the classification step, we suggest to use Random Forest (RF) because of its significant performance when there are few training samples available. Experimental results conducted on a VNIR-SWIR drill core hyperspectral dataset, show accurate classification results.

Keywords: Drill core hyperspectral data; Mineral Liberation Analysis; Random Forest; mineral mapping

Publ.-Id: 28597

Comparison of pancreatic respiratory motion management with three abdominal corsets for particle radiation therapy

Dolde, K.; Schneider, S.; Stefanowicz, S.; Alimusaj, M.; Flügel, B.; Saito, N.; Troost, E. G. C.; Pfaffenberger, A.; Hoffmann, A. L.

Background and Purpose: Abdominal organ motion seriously compromises the targeting accuracy for particle therapy in patients with pancreatic adenocarcinoma. This study compares three different abdominal corsets regarding their ability to reduce pancreatic motion and their potential usability in particle therapy.

Materials and Methods: A patient-individualized polyurethane (PU), a semi-individualized polyethylene (PE), and a patient-individualized 3D-scan based polyethylene (3DPE) corset were manufactured for one healthy volunteer. Time-resolved volumetric magnetic resonance imaging (4D-MRI) and single-slice 2D cine-MRI scans were acquired on two consecutive days to compare free-breathing motion patterns with and without corsets. The corset material properties, such as thickness variance, material homogeneity in Hounsfield units (HU) on CT scans, and manufacturing features were compared. The water equivalent ratio (WER) of corset material samples was measured using a multi-layer ionization chamber for proton energies of 150 MeV and 200 MeV.

Results: All corsets reduced the pancreatic motion on average by 9.6 mm in inferior-superior and by 3.2 mm in anterior-posterior direction. With corset, the breathing frequency was approximately doubled and the day-to-day motion variations were reduced. The WER measurements showed an average value of 0.993 and 0.956 for the PE and 3DPE corset, respectively, and of 0.298 for the PU corset. The PE and 3DPE corsets showed a constant thickness of 2.8 ± 0.2 mm and 3.8 ± 0.2 mm, respectively and a homogeneous material composition with a standard deviation (SD) of 31 HU and 32 HU, respectively. The PU corset showed a variable thickness of 4.2−25.6 mm and a heterogeneous structure with air inclusions with an SD of 113 HU.

Conclusion: Abdominal corsets are effective devices to reduce pancreatic motion. For particle therapy, PE-based corsets are preferred over PU-based corset due to their material homogeneity and constant thickness.

Keywords: Motion management; pancreatic cancer; abdominal corset; image-guided radiotherapy; 4DMRI; particle therapy

Publ.-Id: 28596

Non-classical Liquid Metal Ion Sources for advanced FIB nano-patterning

Mazarov, P.; Bischoff, L.; Pilz, W.; Klingner, N.; Nadzeyka, A.; Stodolka, J.; Gierak, J.

Focused Ion Beam (FIB) processing has been developed into a well-established and still promising technique for direct patterning and proto-typing on the nm scale. Exploring the Liquid Metal Alloy Ion Sources (LMAIS) potential represents a promising alternative to expand the global FIB application fields. Especially, Ion Beam Lithography (IBL) as direct, resistless and three-dimensional patterning enables a simultaneous in-situ process control by cross-sectioning and inspection. Thanks to this, nearly half of the elements of the periodic table are made available in the FIB technology as a result of continuous research in this area during the last forty years. Key features of a LMAIS are long life-time, high brightness and stable ion current. Recent developments could make these sources to an alternative technology feasible for nano-patterning challenges, e.g. to tune electrical, optical, magnetic or mechanical properties.

In this contribution the operation principle, the preparation and testing process as well as prospective domains for modern FIB applications will be presented. As an example we will introduce a Ga35Bi60Li5 LMAIS in detail. It enables high resolution imaging with light Li ions and sample modification with Ga or heavy polyatomic Bi clusters, all coming from one ion source.

L. Bischoff, P. Mazarov, L. Bruchhaus, and J. Gierak, Appl. Phys. Rev. 3, 021101 (2016).

Related publications

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 31.03.-05.04.2019, Regensburg, Germany

Publ.-Id: 28594

The race against time: TOF-SIMS in the HIM

Klingner, N.; Heller, R.; Hlawacek, G.

The helium ion microscope (HIM), well known for its high-resolution imaging and nanofabrication performance, suffered from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. Recently, a magnetic sector and a time-of-flight secondary ion mass spectrometer (TOF-SIMS) have been developed that can be retrofitted to existing microscopes [1,2]. We report on our time-of-flight setup using a straight secondary ion extraction optics that has been designed and optimized for highest transmission. The high efficiency is the most crucial parameter to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. As a major advantage the time-of-flight approach inherently can measure all masses in parallel and thus provides the complete picture of the sample composition. The TOF-SIMS is a versatile add-on that helps the user to get previously unknown details about his samples and is therefore beneficial for many applications. At the end we will also give an outlook on future developments.

[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018). Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.

Related publications

  • Lecture (Conference)
    Advances in Gas-Ion Microscopy - The Second International Meeting of The PicoFIB Network, 13.02.2019, London, Großbritanien

Publ.-Id: 28593

A Time-of-Flight Secondary Ion Mass Spectrometer Add-on for the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Facsko, S.

In a Helium Ion Microscopes (HIM) a Gas Field Ion Source (GFIS) is used to create a Helium or Neon ion beam with a diameter smaller than 0.5 nm and 1.8 nm, respectively. The method is well known for its high resolution imaging and nano-fabrication capabilities which it is able to provide not only for conducting but also insulating samples without the need for a conductive coating.

However, the existing HIM tools suffered from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. Recently, we designed, implemented and reported on the first time-of-flight secondary ion mass spectrometry (TOF-SIMS) add-on that can be retrofitted to existing microscopes [1,2,3].

After a brief introduction to the HIM, I will focus on the new time-of-flight setup. It is based on fast blanking electronics that chop the primary beam into pulses with a minimal length of 20 ns. In combination with a MCP based stop detector this enables TOF backscattering spectrometry with 54 nm lateral resolution [1,2] - the world record for spatially resolved backscattering spectrometry. In order to extend the TOF setup for SIMS an ion optic has been designed and optimized for high transmission by ion transport simulations and an evolutionary algorithm. The high transmission is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering.

The setup can obtain SIMS data from a region of interest or can be used in imaging mode to obtain elemental line profiles and maps of the surface. For m/q ≤ 80 u a m/∆m > 200 has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g. C, N). The lateral resolution has been evaluated to 8 nm using the knife edge method and a 75%/25%. The results will be compared to the theoretical achievable lateral resolution and the limiting experimental and physical constraints of this approach will be reviewed.


[1] Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Notte, J. A.; Huang, J. and Facsko, S. (2016). Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry, Ultramicroscopy 162 : 91-97.
[2] Heller, R.; Klingner, N.; Hlawacek, G. (2016). Backscattering Spectrometry in the Helium Ion Microscope: Imaging Elemental Compositions on the nm Scale. In: Hlawacek, G. & Gölzhäuser, A. (Ed.), Helium Ion Microsc., Springer International.
[3] Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S. and von Borany, J.; (2018) Time-of-flight secondary ion mass spectrometry in the helium ion microscope, submitted.

Related publications

  • Lecture (Conference)
    SIMS Europe 2018, 16.-18.09.2018, Münster, Germany

Publ.-Id: 28592

Compositional analysis and in-situ experiments in the HIM

Klingner, N.; Heller, R.; Hlawacek, G.; von Borany, J.; Serralta, E.; Facsko, S.

The HIM is well known for its imaging with spot sizes below 0.5 nm, its nano-fabrication capabilities, the small energy spread of less than 1 eV and the extremely high brightness. However, it still suffers from the lack of instruments for in-situ studies as well as capabilities for a well integrated material analysis. In the first part a plug and socket system for sample holders will be shown with up to six freely customizable high-voltage electrical connections Additionally time-of flight spectrometry has been implemented for compositional analysis [1]. New results, drawbacks and derive conclusions for the practical use of time-of-flight SIMS will be presented [2]. Our setup delivers a mass resolution delta m < 0.3 u (for m/q < 80 u) and a lateral resolution of 8 nm.

[1] N. Klingner, R. Heller, G. Hlawacek, J. von Borany, J.A. Notte, J. Huang, S. Facsko. Ultramicroscopy 162 (2016), pp 91-97
[2] N. Klingner, R. Heller, G. Hlawacek, S. Facsko, J. von Borany (2018), submitted

Related publications

  • Lecture (Conference)
    2nd international HeFIB conference on Helium and emerging Focused Ion Beams, 11.-13.06.2018, Dresden, Germany

Publ.-Id: 28591

High Resolution in 3 dimensions – TOF-SIMS in the Helium Ion Microscope

Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.

Ongoing miniaturization in semiconductor industry, nanotechnology and life science requirement further improvements for high-resolution imaging, fabrication and analysis of the produced nanostructures. Continuously shrinking object dimensions lead to an enhanced demand on spatial resolution and surface sensitivity of modern analysis techniques. Secondary ion mass spectrometry (SIMS), as one of the most powerful techniques for surface analysis, performed on the nanometer scale may comply with this demands. The direct determination of the sputtered ions mass provides elemental and molecular information and even allows to measure isotope concentrations.

During the last decades, primary ion species used in SIMS have been optimized in terms of best ionization probabilities and less molecular fragmentation. Thereby, highest mass-resolution has been one of the biggest design goals in the development of new SIMS spectrometers. In contrast to former developments, our approach aims for ultimate lateral resolution.

In recent years helium ion microscopy has been developed as a valuable tool for nanofabrication and high-resolution imaging. Helium ion microscopy (HIM) utilizes a gas field ion source to form a helium or neon ion beam with a diameter of less than 0.5 nm and 1.8 nm, respectively. This is not only possible for conducting but also for insulating samples without the need for a conductive coating. However, the existing tools suffer from the lack of a well integrated analytic method that can enrich the highly detailed morphological images with materials contrast. While the technology is relatively young several efforts have been made to add such an analytic capability. Past and ongoing activities of various labs for in situ analysis will be summarized.

Recently, we implemented time-of-flight (TOF) spectrometry to measure the energy of backscattered particles, the mass of sputtered ions [1, 2]. In future activities we intent to determine the energy loss of transmitted particles as well. Based on the findings obtained with this first approachof integrating a TOF SIMS setup, a dedicated extraction optics for secondary ions has been designed and tested (see figure 1).

The focus of this presentation will be on the technical realization of the significantly improved setup. The setup can be operated in spot mode to obtain local mass spectra or in imaging mode to obtain element maps of the specimen surface (see figure 2).

New results, drawbacks and derived conclusions for the practical use of this promising technique will be presented [4]. Similarities and differences to the also recently developed system using a sophisticated magnetic sector field analyzer will be shown [5]. We will reveal that SIMS can be performed with unprecedented lateral resolutions.

First experiments revealed a very high relative transmission which is crucial to collect enough signal from nanoparticles prior to their complete removal by ion sputtering. For m / q <= 80 u a mass resolution of delta m <= 0.3 u has been achieved. This is sufficient for many life science applications that rely on the isotope identification of light elements (e.g.: C, N). The lateral resolution of 8 nm has been evaluated using the knife edge method and a 75 % / 25 % criterion and represents a world record for spatially resolved secondary ion mass spectrometry.

The results will be compared to the theoretical limit of achievable lateral and depth resolution and the experimental and physical constraints of this approach will be reviewed.

Related publications

  • Invited lecture (Conferences)
    HRDP 9 - 9th International Workshop on High-Resolution Depth Profiling, 25.-29.06.2018, Uppsala, Sweden

Publ.-Id: 28590

Application of a new model for bubble-induced turbulence to bubbly flows in containers and vertical pipes

Liao, Y.; Ma, T.; Krepper, E.; Lucas, D.; Fröhlich, J.

The present paper extends the baseline model for the CFD-simulation of turbulent poly-disperse bubbly flows in the Euler-Euler framework by improving the modelling of bubble-induced turbulence. The closure terms in the transport equations of the k-ω SST model are revisited and replaced with a new model recently proposed by Ma et al. (Ma et al., Physical Review Fluids 2, 034301, 2017) which is based on an analysis of the turbulent kinetic energy budget obtained from direct numerical simulation data. Detailed validation results for various flow configurations with a wide range of gas and liquid volumetric fluxes are presented. In case of vertical pipe flow significant improvements in the predicted gas volume fraction and velocity profiles are obtained, especially in high gas volume fraction cases where bubble-induced turbulence is dominant. Simulations of other configurations, such as uniform and non-uniform bubble columns, show that the new model results in an also for these cases overall improvement. Therefore, the baseline model is now updated to include the new model for bubble-induced turbulence.

Keywords: Bubbly flow; Bubble-induced turbulence; Euler-Euler modelling; Baseline model


Publ.-Id: 28589

Verification of ATHLET against TRACE on Superphenix start-up tests

Di Nora, V. A.; Fridman, E.; Mikityuk, K.

The thermal-hydraulics (TH) code ATHLET has been upgraded to be capable of sodium flow modeling. Its new extension is under verification and validation phase. The presented study aimed to demonstrate ATHLET capability in Sodium-cooled Fast Reactor (SFR) transient predictions, through the comparison against TRACE TH code, this last being more established and tested for SFR applications. Calculations were performed on a set of start-up tests on Superphénix (SPX) SFR, and compared with TRACE results, which were used as a reference. It has been shown that given a specific set of reactivity coefficients, ATHLET and TRACE give consistent and close results.

Keywords: Superphénix start-up tests; Benchmarking ATHLET against TRACE; ATHLET for SFRs

  • Lecture (others)
    Workshop of Doctoral Candidates (PhD student seminar), 13.12.2018, Zittau, Deutschland

Publ.-Id: 28588

Time-lapse imaging of particle invasion and deposition in porous media using in situ X-ray radiography

Da Assuncao Godinho, J. R.; Chellappah, K.; Collins, I.; Ng, P.; Smith, M.; Withers, P. J.

This paper introduces time-lapse radiography as an in situ technique to image and quantify changes in the internal structure of a porous medium with sub-second temporal resolution. To demonstrate the technique’s potential, an experiment was performed using a model system involving flow of a suspension containing ground marble particles through a porous bed of compacted glass beads housed within a pressurized flow rig. During the experiment, particle deposition occurred both within the internal porous structure and on its surface (forming a filter cake). The volume of particles deposited was derived from changes in the grey scale of the radiographs. At the initial stages of the experiment, the volume of particles deposited internally was seen to increase linearly with time. The subsequent growth and compaction of an external filter cake decreased the rate of internal particle deposition. The filter cake’s structure was observed to fail owing to increasing stress at higher pressures. The demonstrative experiment illustrates the potential of time-lapse radiography as a new tool to elucidate mechanisms underpinning formation damage, and to optimize drilling fluids and enhanced oil recovery (EOR). A critical assessment of the technique’s advantages and limitations to characterise particulate behaviour within porous media is included.

Keywords: Permeability; formation damage; fines migration; filter cake; EOR; computed tomography

Publ.-Id: 28586

Bubble Generation by Micro-Orifices with Application on Activated Sludge Wastewater Treatment

Mohseni, E.; Herrmann-Heber, R.; Reinecke, S. F.; Hampel, U.

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 30 µm to 200 µm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with rubber membrane diffusers bubbles generated from the micro-orifices transfer up to 82% more oxygen content into the continuous phase at up to 75% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency. Therefore, we also expect an improvement in the oxygen transfer coefficient KLa and standard oxygen transfer efficiency SOTE compared to commercial rubber membrane diffusers.

Keywords: Bubble Generation; Micro-orifices; Aeration; Biological Wastewater Treatment; Rubber Membrane Diffusers; Oxygen Transfer


Publ.-Id: 28585

Ion-induced surface patterning and its application in nanofabrication via templated growth

Erb, D.; Malsch, G.; de Schultz, R.; Facsko, S.

Low-energy ion irradiation of surfaces can lead to nanoscale pattern formation with a wide variety of morphologies, resulting from a number of interacting ballistic and diffusive mechanisms which govern the mass redistribution under ion irradiation. The choice of process parameters such as sample temperature or ion incidence angle determines the relative influence of these mechanisms and thereby the pattern morphology.
After briefly outlining the patterning mechanisms and discussing the resulting morphologies on semiconductor surfaces, we present our approaches at templated nanostructure growth based on these ion-induced surface patterns. They include epitaxial nanowires via geometric shading, long-range chemical ordering in diblock-copolymer thin films, and engineering of magnetic anisotropy in topographically modulated thin films.
The required technologies of low-energy ion irradiation, polymer chemistry, and physical vapor deposition are well-established and can readily be implemented at industrially relevant scales. Thus, nanostructured materials fabricated in such bottom-up manner have the potential to make substantial contributions to solving our society’s present challenges: They can increase the sensitivity of diagnostical tools in medicine, lead to novel information technology, or enhance the efficiency of energy harvesting from renewable sources.

Related publications

  • Poster
    SNI2018 - Conference for Research with Synchrotron Radiation, Neutrons and Ion Beams at Large Facilities, 17.-19.09.2018, Garching, Deutschland

Publ.-Id: 28584

Nanostructure arrays via templated growth

Erb, D.; Schlage, K.; Röhlsberger, R.; Facsko, S.

Nanostructured materials have the potential to make substantial contributions to solving our society’s present challenges, e.g. in the fields of medicine, information technology, or energy harvesting from renewable sources. The possibility to fabricate them at industrially relevant scales will maximize the impact of such materials.
We present bottom-up nanopatterning approaches which promise easy implementation and scale-up by combining well-established techniques and effects:
(a) spontaneous nanopatterning of crystalline surfaces upon heating,
(b) suface nanopatterning induced by low-energy ion irradiation,
(c) diblock copolymer self-assembly
(d) physical vapor deposition with selective wetting,
(e) physical vapor deposition with geometrical sha-ding.
Combinations of these techniques and effects can result in highly regular nanostructure arrays of various morphologies and are applicable to a wide range of materials. The versatility of these approaches enables creative research and may lead to beneficial applications in diverse fields, ranging from optics and magnetism to catalysis.

Related publications

  • Invited lecture (Conferences)
    NAP2018 - 8th International Conference on Nanomaterials: Applications & Properties, 09.-14.09.2018, Zatoka, Ukrajina

Publ.-Id: 28583

Surface nanopatterning induced by low-energy ion irradiation: Experimental investigations of non-equilibrium pattern formation

Erb, D.; de Schultz, R.; Malsch, G.; Facsko, S.

Irradiating a surface with low-energy ions of about 100 to 1000 eV activates a number of different processes: the surface is eroded by sputtering; the ion impacts create vacancies and ad-atoms; mass redistribution of the mobile species proceeds via both diffusive and ballistic effects; anisotropies in mass redistribution can be induced both by the ion beam and the structure of the surface on the atomic scale. Some mechanisms destabilize the surface height while others lead to surface smoothing. The simultaneous presence of such counteracting effects can result in the formation of periodic nanoscale surface patterns. Depending on factors such as temperature, ion energy, or the incidence orientation of the ion beam, the individual surface processes are enhanced or suppressed, yielding different pattern morphologies. The fact that the patterning can be influenced by various readily accessible external parameters offers a way toward deeper understanding of the underlying processes and their interactions. Furthermore, it enables large-scale production of novel templates for bottom-up fabrication of nanostructures or nanostructured materials for future applications in diverse fields, ranging from optics and magnetism to catalysis.
We discuss our experimental studies of ion-induced pattern formation on different semiconductor surfaces in dependence of external process parameters and with regard to temporal evolution, pattern symmetry and morphology, and patterning defects. Further, we present our approaches to employing these patterned surfaces for nanostructure fabrication, especially by means of physical vapor deposition.

Related publications

  • Lecture (Conference)
    CAARI 2018 - 25th Conference on Application of Accelerators in Research and Industry, 12.-17.08.2018, Grapevine, USA

Publ.-Id: 28582

Morphology, density, and temporal evolution of topological defects in reverse epitaxy

Erb, D.; Malsch, G.; Facsko, S.

Low-energy ion-irradiation of semiconductors above their recrystallization temperature has been shown to induce regular nanoscale patterning of the crystalline surface. The mechanism is called reverse epitaxy in analogy to epitaxy in growth: ion-induced mobile vacancies and ad-atoms on the crystalline surface encounter the Ehrlich-Schwoebel energy barrier for crossing terrace steps and exhibit preferential diffusion along specific in-plane directions. This can lead to the formation of well-defined faceted surface structures with morphologies strongly dependent on crystalline structure and surface orientation. For instance, GaAs(001) and InAs(001) develop periodic ripple structures with a saw tooth profile.
We have studied the topological defects in ion-induced patterns on GaAs(001) and InAs(001), i.e. ripple junctions, and present results from both experiments and simulations on the following aspects:

  • defect morphology and the influence of polar and azimuthal ion incidence angles thereon
  • dependence of the defect density on sample temperature and ion energy
  • temporal evolution of the defect density
  • defect motion and annihilation processes
We find strong dependencies on the easily controllable external process parameters, which is crucial information when preparing ion-induced surface patterns for specific applications.

Related publications

  • Poster
    Ion Beam Workshop 2018 - MAT Science Week, 24.04.2018, Darmstadt, Deutschland

Publ.-Id: 28581

A route to epitaxial growth of periodic metal nanostructure arrays

Erb, D.; Malsch, G.; Hübner, R.; Lenz, K.; Lindner, J.; Facsko, S.; Helm, M.; Fassbender, J.

Epitaxial thin film growth on planar substrate surfaces is well-established for many materials. We present a novel bottom-up approach showing that it can also be feasible to grow nanostructures in an oriented manner on nanopatterned crystalline surfaces. Produced by a scalable procedure on large surface areas, such nanostructure arrays may find diverse applications in research and technology, e.g. in the fields of magnetism or catalysis.
On semiconductor substrates, nanoscale surface patterns with well-defined lateral periodicity form under low-energy ion irradiation via non-equilibrium self-assembly of vacancies and ad-atoms [1]. For appropriate process temperatures, the crystallinity of the substrate is retained during ion irradiation. When a material is then deposited onto the substrate by PVD under non-normal incidence, shadowing effects give rise to the formation of separated nanostructures [2], while a suitable lattice matching can induce epitaxial growth.
In this contribution, we outline the patterning and growth procedure. As an example, we will present periodic Fe/Au nanostructure arrays and discuss their strongly anisotropic optical and magnetic properties.

[1] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender,
S. Facsko, Nanoscale 7, 18928 (2015)
[2] Q. Jia, X. Ou, M. Langer, B. Schreiber, J. Grenzer, P. F. Siles, R. D. Rodriguez,
K. Huang, Y. Yuan, A. Heidarian, R. Hübner, T. You, W. Yu, K. Lenz, J. Lindner,
X. Wang, and S. Facsko, Nano Research 15, 1 (2017)

Related publications

  • Poster
    DPG Frühjahrstagung 2018 - Sektion Kondensierte Materie, 11.03.2018, Berlin, Deutschland

Publ.-Id: 28580

Ion-induced nanopatterning of crystalline surfaces for applications in bottom-up nanostructure fabrication

Erb, D.; Hübner, R.; Malsch, G.; de Schultz, R.; Grenzer, J.; Lenz, K.; Lindner, J.; Facsko, S.

Nanostructured materials will be key components in future technological solutions of our society’s present challenges: They can enhance the efficiency of energy harvesting from renewable sources, increase the sensitivity of diagnostical tools in medicine, or enable novel information technology. For making substantial contributions to these fields by applying nanostructured materials, we must be able to fabricate them easily and reproducibly on industrially relevant scales. This can be achieved by the bottom-up approach of templated growth on substrates nanopatterned by ion irradiation: The required technologies of low-energy ion irradiation, polymer chemistry, and physical vapor deposition are well-established.
In this contribution, we outline the mechanism of self-assembly of vacancies and adatoms on crystalline semiconductor surfaces induced by low-energy ion irradiation [1,2]: At temperatures above the material’s recrystallization temperature, the substrate crystallinity is retained. Thus, diffusion of vacancies and adatoms on the surface is highly anisotropic, which leads to the formation of surface nanopatterns reflecting the crystal symmetry of the substrate material. The various resulting pattern morphologies and the influence of external process parameters will be presented. We hope to initiate discussion and collaboration by highlighting potential applications based on these ion-induced nanopatterns, such as growing epitaxial nanowire arrays by shadowing effects at oblique incidence deposition, or inducing long-range order in copolymer thin films to fabricate chemically nanopatterned templates for nanostructure growth [3].

We thank K. Potzger and A. Henschke (HZDR) for their support in MBE for templated nanowire growth.

[1] X. Ou et al., Nanoscale 7, 18928 (2015)
[2] Q. Jia et al., Nano Research 15, 1 (2017)
[3] D. Erb et al., Science Advances 1, e1500751 (2015)

Related publications

  • Lecture (Conference)
    SHIM-ICACS 2018 - 10th InternationaL Symposium on Swift Heavy Ions in Matter & 28th International Conference on Atomic Collisions in Solids, 01.-06.07.2018, Caen, France

Publ.-Id: 28579

Ex situ n+ doping of GeSn alloys via non-equilibrium processing

Prucnal, S.; Berencén, Y.; Wang, M.; Rebohle, L.; Böttger, R.; Fischer, I. A.; Augel, L.; Oehme, M.; Schulze, J.; Voelskow, M.; Helm, M.; Skorupa, W.; Zhou, S.

Full integration of Ge-based alloys like GeSn with complementary-metal-oxide-semiconductor technology would require the fabrication of p- and n-type doped regions for both planar and tri-dimensional device architectures which is challenging using in situ doping techniques. In this work, we report on the influence of ex situ doping on the structural, electrical and optical properties of GeSn alloys. n-type doping is realized by P implantation into GeSn alloy layers grown by molecular beam epitaxy (MBE) followed by flash lamp annealing. We show that effective carrier concentration of up to 1 × 10^19 cm−3 can be achieved without affecting the Sn distribution. Sn segregation at the surface accompanied with an Sn diffusion towards the crystalline/amorphous GeSn interface is found at P fluences higher than 3 × 10^15 cm−2 and electron concentration of about 4 × 10^19 cm−3. The optical and structural properties of ion-implanted GeSn layers are comparable with the in situ doped MBE grown layers.

Keywords: Ge; GeSn; MBE; n-type doping; flash lamp annealing; ion implantation

Related publications


Publ.-Id: 28578

Structural and electrical properties of Se-hyperdoped Si via ion implantation and flash lamp annealing

Liu, F.; Prucnal, S.; Yuan, Y.; Heller, R.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

We report on the hyperdoping of silicon with selenium obtained by ion implantation followed by flash lamp annealing. It is shown that the degree of crystalline lattice recovery of the implanted layers and the Se substitutional fraction depend on the pulse duration and energy density of the flash. While the annealing at low energy densities leads to an incomplete recrystallization, annealing at high energy densities results in a decrease of the substitutional fraction of impurities. The electrical properties of the implanted layers are well-correlated with the structural properties resulting from different annealing processing.

Keywords: Silicon; hyperdoping; Se; flash lamp annealing; ion implantation

Related publications

Publ.-Id: 28577

Prophylactic cranial irradiation in stage IV small cell lung cancer: 5 Selection of patients amongst European IASLC and ESTRO experts

Putora, P. M.; Glatzer, M.; Belderbos, J.; Besse, B.; Blackhall, F.; Califano, R.; Cappuzzo, F.; de Marinis, F.; Dziadziuszko, R.; Felip, E.; Faivre-Finn, C.; Früh, M.; Garrido, P.; Le Pechoux, C.; Mcdonald, F.; Nestle, U.; Novello, S.; O‘Brien, M.; Paz Ares, L.; Peeters, S.; Pöttgen, C.; Ramella, S.; Reck, M.; Slotman, B.; Troost, E. G. C.; Houtte, P. V.; Westeel, V.; Widder, J.; Mornex, F.; de Ruysscher, D.

Background: Due to conflicting results between major trials the role of prophylactic cranial irradiation (PCI) in stage IV small cell lung cancer (SCLC) is controversial. Methods: We obtained a list of 13 European experts from both the European Society for Therapeutic Radiation Oncology (ESTRO) and the International Association for the Study of Lung Cancer (IASLC). The strategies in decision making for PCI in stage IV SCLC were collected. Decision trees were created representing these strategies. Analysis of consensus was performed with the objective consensus methodol-ogy.
Results: The factors associated with the recommendation for the use of PCI included the fitness of the patient, young age and good response to chemotherapy. PCI was recommended by the majority of experts for non-elderly fit patients who had at least a partial response (PR) to chemotherapy (for complete remission (CR): 85% of radiation oncologists and 69% of medical oncologists, for partial remission: 85% of radiation oncol- ogists and 54% of medical oncologists). For patients with stable disease after chemotherapy, PCI was rec- ommended by 6 out of 13 (46%) radiation oncologists and only 3 out of 13 medical oncologists (23%). For elderly fit patients with CR, a majority recommended PCI (62%) and no consensus was reached for patients with PR. Conclusion: European radiation and medical oncologists specializing in lung cancer recommend PCI in selected patients and restrict its use primarily to fit, non-elderly patients who responded to chemotherapy.

Keywords: Small cell lung cancer; PCI; Stage IV; Expert opinion; ESTRO; IASLC

Publ.-Id: 28576

Oxygen Exchange Kinetics of SrTiO3 Single Crystals: A Non-Destructive, Quantitative Method

Stoeber, M.; Cherkouk, C.; Leisegang, T.; Schelter, M.; Zosel, J.; Walter, J.; Hanzig, J.; Zschornak, M.; Prucnal, S.; Boettger, R.; Meyer, D. C.

The time-resolved oxygen exchange rate of strontium titanate (SrTiO3) single crystals is studied by means of oxygen solid electrolyte coulometry (OSEC) and compared to model calculations. Experiments are performed on pure, ion implanted (Ni, Ag, O and N ions) and partially covered crystals with silver layer. In this work, a theoretical model is used, which is based on defect chemistry under equilibrium conditions. It is applied as a fit in order to determine the effective rate constants and activation energy of the oxygen exchange reaction on the crystal surface. OSEC is used for the first time to characterize kinetic parameters of oxygen exchange on single crystalline surfaces. Transmission electron microscopy and sputter X-ray photoelectron spectroscopy are performed to determine structural and chemical changes after ion implantation.

Keywords: strontium titanate; ion implantation; oxygen exchange reaction; X-ray photoelectron spectroscopy

Related publications

Publ.-Id: 28575

Ion Beam Modification of ZnO Epilayers: Sequential Processing

Turos, A.; Ratajczak, R.; Mieszczynski, C.; Jozwik, P.; Stonert, A.; Prucnal, S.; Heller, R.; Skorupa, W.; von Borany, J.; Guziewicz, E.

Defect agglomeration in ion-implanted compound semiconductors produces lattice stress eventually causing plastic deformation at sufficiently high fluence. Consequently, a dislocations tangle is formed which can hardly be completely removed by thermal annealing. To solve this problem, a new method of sequential processing has been developed consisting of low fluence ion implantation followed by subsequent annealing. The procedure can be then repeated until the required impurity concentration has been reached without producing excessive damage. Epitaxial ZnO layers are grown using the atomic layer deposition (ALD) technique. Structural changes in ZnO epilayers due to Yb-ion implantation and subsequent annealing are analyzed by Rutherford backscattering/channeling (RBS/c) and photoluminescence (PL). Correlation between defect transformations and PL efficiency is determined. Increased Yb-atom optical activation upon sequential processing as compared to the standard single-step annealing is observed.

Keywords: ZnO; ALD; Defects; ion implantation; RBS

Related publications


Publ.-Id: 28574

Fractionwise verification of delivered proton dose to prostate cancer patients based on daily in-room CT imaging

Stützer, K.; Valentini, C.; Agolli, L.; Hölscher, T.; Thiele, J.; Dutz, A.; Löck, S.; Krause, M.; Baumann, M.; Richter, C.

Purpose: Retrospective proton dose calculation based on a unique dataset of daily CT images to confirm our prostate patient positioning and immobilization protocol for counterbalancing interfractional motion.
Material/Methods: For 12 prostate cancer patients treated to 74GyE with double-scattered lateral or anterior oblique proton fields, daily (27-37, median 32) in-room control CTs (cCT) were acquired. Patient preparation includes a drink protocol, water-filled endorectal balloon insertion, bony anatomy alignment by orthogonal X-Ray imaging, and CT-based verification of prostate location via implanted fiducial marker positions. Fraction doses were calculated on all manually delineated cCTs and accumulated on the planning CT by a deformable image registration (DIR) in RayStation 5.99. DVH parameters of iCTVs, bladder, rectum, femoral heads, bladder and rectal wall were analyzed fractionwise prior and after DIR and values from the cumulated and planned dose distributions were compared.
Results: Fig.1 shows the fractionwise assessed DVH parameters for one patient. 275 fraction doses were analyzed in total without finding trends for improving or worsening DVH parameters over treatment time. Intended target coverage, D98%(iCTV)>95%, was missed in 29 cCTs (10.5%) due to suboptimal bladder filling, endorectal balloon position or delineation variation. No overdosage was observed (D2%(iCTV)<105%). DIR led partly to notable changes of DVH parameters (Fig.1). No alarming differences exist between planned and cumulated doses (Fig.2), but significant changes (p<0.05, Wilcoxon signed rank test) were found for D2%(iCTV), V75%(bladder) and V30Gy(bladder wall).
Conclusion: Despite some suspicious fractions, the total delivered doses to prostate cancer patients are accurate with the applied positioning and immobilization protocol.

  • Lecture (Conference)
    58th annual conference of the particle therapy co-operative group, 10.-15.06.2019, Manchester, United Kingdom

Publ.-Id: 28573

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

Yuan, Y.; Xu, C.; Hübner, R.; Jakiela, R.; Böttger, R.; Helm, M.; Sawicki, M.; Dietl, T.; Zhou, S.

Ion implantation of Mn combined with pulsed laser melting is employed to obtain two representative compounds of dilute ferromagnetic semiconductors (DFSs): Ga1−xMnxAs and In1−xMnxAs. In contrast to films deposited by the widely used molecular beam epitaxy, neither Mn interstitials nor As antisites are present in samples prepared by the method employed here. Under these conditions the influence of localization on the hole-mediated ferromagnetism is examined in two DFSs with a differing strength of p-d coupling. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1−xMnxAs compared to Ga1−xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Furthermore, the findings support strongly 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 even on the insulator side of the metal-insulator transition.

Keywords: electronic-structure; magnetotransport properties; curie-temperature; coulomb gap; (ga,mn)as; ga1-xmnxas; semiconductors; ferromagnetism

Related publications

  • Poster
    DPG-Jahrestagung und DPG-Frühjahrstagung, 13.03.2018, Berlin, Deutschland

Publ.-Id: 28572

Luminescence in the Visible Region from Annealed Thin ALD-ZnO Films Implanted with Different Rare Earth Ions

Ratajczak, R.; Guziewicz, E.; Prucnal, S.; Łuka, G.; Böttger, R.; Heller, R.; Mieszczynski, C.; Wozniak, W.; Turos, A.

Epitaxial ZnO thin films grown by atomic layer deposition on GaN/Al2O3 substrates are implanted with Yb, Dy, and Pr ions to a fluence of 5e14 atcm-2 and subsequently anneals at 800 C using a rapid thermal annealing (RTA) system. Structural properties of implanted and annealed ZnO films and the optical response are evaluated by channeling Rutherford backscattering (RBS/c) and photoluminescence spectroscopy (PL), respectively. RTA leads to a partial removal of the post-implantation defects with simultaneous native defects transformation and optical activation of RE ions. It is found that two groups of defects: defects formed during implantation process and native defects, play an important role in the luminescence in the visible region. The room temperature PL spectra obtained from annealed ZnO:RE films do not show sharp PL lines from transitions within the RE 4f shell, but show near band gap emission and defect related emission, which energy emission is controlled by the RE atoms. It suggests a presence of RE-related complexes that are formed during hightemperature annealing in oxygen atmosphere. The excitonic and defect emission modified by RE ions create an optical response of the system resulting in a specific color of the emitted light.

Keywords: ZnO; flash lamp annealing; PL; ion implantation; rare earth

Related publications


Publ.-Id: 28571

Strain and Band-Gap Engineering in Ge-Sn Alloys via P Doping

Prucnal, S.; Berencén, Y.; Wang, M.; Grenzer, J.; Voelskow, M.; Hübner, R.; Yamamoto, Y.; Scheit, A.; Bärwolf, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Żuk, J.; Turek, M.; Droździel, A.; Pyszniak, K.; Kudrawiec, R.; Polak, M. P.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge−Sn alloys. The heavily doped n-type Ge−Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge−Sn layers and to modify the lattice parameter of P-doped Ge−Sn alloys. The strain engineering in heavily-P-doped Ge−Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge−Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1 × 10^20 cm the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology.

Keywords: Ge; GeSn; n-type doping; ion implantation; x-ray diffraction; Raman spectroscopy; strain

Related publications


Publ.-Id: 28570

Advanced doping of Ge and GeSn

Prucnal, S.; Berencén, Y.; Hübner, R.; Böttger, R.; Rebohle, L.; Skorupa, W.; Wang, M.; Helm, M.; Zhou, S.

One of the main obstacles towards wide application of Ge in nanoelectronics is the indirect band gap of Ge and the lack of an efficient doping method with well controlled junction depth. Heavily n-type doped Ge becomes a quasi-direct bandgap semiconductor [1] which makes it very attractive for modern optoelectronics but n-type Ge doped above 5×10^19 cm-3 is metastable and thus difficult to be achieved [2]. In contrast to Ge, the GeSn alloy with direct band gap is the most promising semiconductor material for light emitters integrated with CMOS technology [3]. Here an overview of different doping techniques of Ge and fabrication methods to form GeSn will be presented. Special attention will be focused on the use of ion implantation followed by flash-lamp (FLA) annealing for the fabrication of heavily doped n-type Ge and GeSn with direct band gap [4]. In contrast to conventional annealing procedures, rear-side FLA leads to full recrystallization of Ge and GeSn, and simultaneously the Sn segregation and diffusion of n-type dopants are supressed. The maximum electron concentration is well above 10^20 cm-3 both in Ge and in GeSn with Sn concentration up to 6%. Due to the ultra-high n-type doping, Ge becomes a quasi-direct band gap semiconductor showing room-temperature photoluminescence from G-HH transitions [4]. The recrystallization mechanism and the dopant distribution in Ge and GeSn alloy synthesized by ion implantation during rear-side FLA are discussed in detail.
Moreover, we report on the strong mid-IR plasmon absorption in heavily n-type doped Ge and GeSn thin films in the wavelength range from 3000 nm to 10 000 nm.

[1] R. E. Camacho-Aguilera et al., Optics Express 20, 11316-11320 (2012)
[2] S. Prucnal et al., Sci. Rep. 6, 27643 (2016).
[3] S. Wirths et al., Nat. Photon., 9, 88–92 (2015)
[4] S. Prucnal et al., Semicond. Sci. Technol. 32, 115006 (2017).

Keywords: Ge; GeSn; ion implantation; flash lamp annealing; n-type doping

Related publications

  • Lecture (Conference)
    34th International Conference on the Physics of Semiconductors, 29.07.-03.08.2018, Montpellier, France

Publ.-Id: 28569

Robust intensity-modulated proton therapy with dose-escalated simultaneous integrated boost reduces the low-dose to surrounding tissues in pancreatic cancer patients

Stefanowicz, S.; Zschaeck, S.; Troost, E. G. C.

This in-silico study on simultaneous integrated boost dose-escalation in non-metastatic pancreatic cancer patients dosimetrically compared robust multi-field optimized intensity-modulated proton therapy (IMPT) with volumetric modulated arc therapy (VMAT).

Material and Methods
For five patients, both treatment plans were optimized on free-breathing CTs using RayStation. For VMAT, at least 95% of the prescribed doses of 66Gy and 51Gy to the boost (GTV) and PTV (CTV+5mm), respectively, were to cover 95% of the targets. For IMPT, robust optimization with a setup uncertainty of 5mm and a density uncertainty of 3.5% was applied to the GTV and CTV, with the aforementioned dose levels (RBE) again covering 95% of the targets. The OAR dose constraints adhered to local guidelines and QUANTEC.

All treatment plans reached the prescribed doses to the targets. Doses to the bowel, stomach and/or liver exceeded at least one constraint in all treatment plans, since those OARs were next to or within the targets. While VMAT reduced the median V50Gy of the stomach, doses to the remaining gastrointestinal organs, e.g. liver and kidneys, were lower for IMPT (Fig. 1). Overall, IMPT deposited less low dose outside the CTV (Fig. 2, median integral V20Gy: 1483.4ccm vs. 756.2ccm).

Disregarding inter- and intra-fractional organ motion, dose escalation with IMPT and VMAT is possible. IMPT reduced the dose to surrounding normal tissues, except for OARs overlapping with the target volume, in which the dose was higher due to the robust optimization approach. Additional patients will be included in this study.

  • Poster
    PTCOG 58, 10.-15.06.2019, Manchaster, UK

Publ.-Id: 28568

Abnormal lattice location and electrical activation in chalcogen-hyperdoped Si

Wang, M.; Prucnal, S.; Debernardi, A.; Heller, R.; Yuan, Y.; Xu, C.; Berencén, Y.; Böttger, R.; Rebohle, L.; Skorupa, W.; Helm, M.; Zhou, S.

Hyperdoping has emerged as a promising method for designing semiconductors with unique physical properties. In general, these properties are primarily determined by the lattice location of the impurity atoms in the host material. In this contribution, the lattice location of implanted chalcogens in Si was experimentally determined by means of Rutherford backscattering/channeling (RBS/C). The implication on the electrical activation of chalcogens in Si will be discussed with respect to the Hall effect results. The obtained carrier concentration and the RBS angular scans across the <100> and <110> axis reveal that the electrically active/inactive concentration of Te correlates with the concentration of substitutional/interstitial site Te atoms. Surprisingly, contrary to the general belief, we find that the interstitial fraction decreases with increasing impurity concentration. This abnormal dependence of lattice location and electrical activation on impurity concentration suggests that the formation energy for the substitutional Te or Te-Te dimers in Si is lower than for the interstitial Te. This assumption is theoretically verified by the first-principles calculations.

Related publications

  • Lecture (Conference)
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 28.06.2018, San Antonio, USA

Publ.-Id: 28567

Extended infrared photoresponse in room-temperature Si hyperdoped with Te

Wang, M.; Berencén, Y.; Prucnal, S.; García-Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.

Presently, room-temperature infrared sub-band-gap photoresponse in Si is of great interest for the development of on-chip complementary-metal-oxide-semiconductor (CMOS)-compatible photonic platforms [1]. One of the most promising approaches to further extend the photoresponse of Si to the mid- and far-infrared (MIR/FIR) ranges consists of introducing deep-level dopants into the Si band gap at concentrations in excess of the solid solubility limit [2]. In this work, we demonstrate strong room-temperature sub-band-gap photoresponse of photodiodes based on Si hyperdoped with tellurium [3]. A CMOS-compatible approach of combining ion implantation with pulsed laser melting was applied to synthesize single-crystalline and epitaxial Te-hyperdoped Si layers with a Te concentration five orders of magnitude above the solid solubility limit. Driven by increasing Te concentration, both the insulator-to-metal transition and a band-gap renormalization are observed. The sub-band optical absorptance in the resulting Te-hyperdoped Si layers is found to increase monotonically with increasing Te concentration and extends well into the MIR/FIR ranges (1.4 to 25 μm). Importantly, the MIR/FIR optoelectronic response from Te-hyperdoped Si photodiodes is demonstrated to be related with known Te deep-energy levels into the Si band-gap. This work contributes to pave the way towards establishing a Si-based broadband infrared photonic system operating at room temperature.

Related publications

  • Lecture (Conference)
    ION 2018 - XII-th International Conference on Ion Implantation and other Applications of Ions and Electrons, 19.06.2018, Kazimierz Dolny, Poland
  • Poster
    IBMM-2018 - The 23rd International Conference on Ion Beam Analysis, 25.06.2018, San Antonio, USA
  • Poster
    ICPS-2018 - 34th International Conference on the Physics of Semiconductors, 30.07.2018, Montpellier, France

Publ.-Id: 28566

Towards room-temperature extended infrared Si-based photoresponse: A case study of Te-hyperdoped Si

Wang, M.; Berencén, Y.; García Hemme, E.; Hübner, R.; Yuan, Y.; Xu, C.; Rebohle, L.; Böttger, R.; Heller, R.; Schneider, H.; Skorupa, W.; Helm, M.; Zhou, S.

Presently,room-temperature broadband Si-based photodetectors are required for Si photonic systems.Here,we demonstrate roomtemperature sub-band gap photoresponse of photodiodes based on Si hyperdoped with Te.The epitaxially recrystallized Te-hyperdoped Si layers are developed by ion implantation combined with pulsed laser melting and incorporate Te concentrations beyond the solid solubility limit.An insulator-to-metal transition driven by increasing Te concentration accompanied with a band gap renormalization is observed.The optical absorptance is found to increase monotonically with increasing Te concentration and extends well into the mid- and far- infrared regions.This work contributes to establish room temperature Si-based broadband infrared photonic system.

Related publications

  • Lecture (Conference)
    DPG-Frühjahrstagung 2018, 12.03.2018, Berlin, Germany

Publ.-Id: 28565

Mid- to far-infrared localized surface plasmon resonance in chalcogen-hyperdoped Si

Wang, M.; Prucnal, S.; Berencén, Y.; Rebohle, L.; Schönherr, T.; Yuan, Y.; Xu, C.; Khan, M. B.; Böttger, R.; Skorupa, W.; Helm, M.; Zhou, S.

Mid-infrared plasmonic sensing allows the direct targeting of molecules relevance in the so-called “vibrational fingerprint region”. Presently, heavily doped semiconductors exhibiting the potential to replace and outperform metals in the mid- infrared frequency range to revolutionize plasmonic devices. In this work, we demonstrate the occurrence of localized surface plasmon resonances (LSPR) in Te heavily-doped Si layers developed by ion implantation combined with flash lamp annealing. We fabricate micrometer-sized antennas out of the Te-hyperdoped Si layers by electron-beam lithography and reactive ion etching processes. The optical response characterized by Fourier-transform infrared (FTIR) spectroscopy demonstrates the enhancement of localized plasmon resonances in antennas, from mid- to far- infrared frequency range. Our results set a new path toward integration of plasmonic sensors with the one-chip CMOS platform.

Related publications

  • Poster
    DPG-Frühjahrstagung 2018, 14.03.2018, Berlin, Germany

Publ.-Id: 28564

Towards a Vertical Nanopillar-Based Single Electron Transistor – A High-Temperature Ion Beam Irradiation Approach

Xu, X.; Heinig, K.; Möller, W.; Gharbi, A.; Tiron, R.; Engelmann, H.; Bischoff, L.; Prüfer, T.; Hübner, R.; Facsko, S.; Hlawacek, G.; von Borany, J.

We propose an ion irradiation based method to fabricate a single Si nanocrystal embedded in a Si(001)/SiO2/Si nanopillar layer stack as a prerequisite for manufacturing a CMOS-compatible, room-temperature Si single electron transistor. After either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) irradiation of the nanopillars (with diameter of 35 nm and height of 70 nm) at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the program TRI3DYN. We assume that it is the result from the ion beam induced amophisation of Si accompanied by the ion hammering effect. The amorphous nano-structure behaves viscously and the surface capillary force dictates the final shape. To confirm such a theory, ion irradiation at elevated temperatures (up to 672 K) has been performed and no plastic deformation was observed under these conditions. Bright-field transmission electron microscopy micrographs confirmed the crystallinity of the substrate and nanopillars after HT-irradiation.
When a semiconductor material such as silicon is heated above its amorphisation critical temperature during ion irradiation, it stays crystalline due to an interplay between ion damage and dynamic annealing process. Viscous flow does not occur for the crystalline nano-structures and the shape remains intact. This effect has been observed previously mainly for swift heavy ions and energies higher than 100 keV. Such high-temperature irradiation, when carried out on a nanopillar with Si/SiO2/Si layer stack, would induce ion beam mixing without suffering from the plastic deformation of the nanostructure. Due to a limited mixing volume, single Si-NCs would form in a subsequent rapid thermal annealing process via Oswald ripening and serve as a basic structure of a gate-all-around single electron transistor device.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

Related publications

  • Lecture (Conference)
    2018 MRS Fall Meeting & Exhibit, 25.11.2018, Boston, USA

Publ.-Id: 28563

Synthesis and characterization of transition-metal germanides

Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Helm, M.; Zhou, S.; Prucnal, S.

Si was sufficient to fulfil the requirements of microelectronic industry for more than five decades. Further progress based on the miniaturisation of transistors is challenging. Therefore new materials and concepts are considered for the next generation of nanoelectronics. In this work, we present the formation of transition-metal germanides epitaxially grown on Ge wafer. Those materials have great promise for both the ohmic contacts to n-type Ge with extremely low specific contact resistivity and spintronics. The transition-metal germanides are synthesized by metal sputtering on Ge followed by millisecond range flash lamp annealing which is suitable for larger-area fabrication and compatible with CMOS technology. On one hand, orthorhombic NiGe whose contact resistivity is only around 1.2×10-6 Ω cm2, is beneficial for achieving high-performance Ge-based nano-electronic devices. On the other hand, cubic FeGe with B20 phase is a Skyrmion-carrier material attractive for spintronics. In summary, the epitaxial transition-metal germanides materials can be obtained by a novel epitaxial approach which provides insight to their technological usage.

Keywords: transition-metal germanides; spintronics

Related publications

  • Poster
    2018 DPG Spring Meeting Berlin, 12.03.2018, Berlin, Germany

Publ.-Id: 28562

Ultra-fast solid phase epitaxy of Mn5Ge3 on (001) Ge substrate

Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Xu, C.; Grenzer, J.; Helm, M.; Zhou, S.; Prucnal, S.

In the present work, we report on epitaxial growth of ferromagnetic Mn5Ge3 thin films on (001) Ge substrates induced by Mn in-diffusion during non-equilibrium flash lamp annealing for 20 ms. The ferromagnetic Mn5Ge3/Ge samples with very sharp interface between the Mn5Ge3 layer and the Ge substrate can be used to fabricate spintronic devices. Temperature-dependent magnetization reveals a Curie temperature of 282 K which can be tuned much above room temperature by strain engineering and/or co-doping with C. The microstructural properties of the fabricated films were investigated by X-ray diffraction, cross-sectional TEM and Rutherford backscattering spectrometry. Both used material and technology are highly compatible with complementary metal-oxide-semiconductor (CMOS) technology and can be used for spintronics.

Keywords: Epitaxial growth; ferromagnetic; flash lamp annealing

Related publications

  • Poster
    2018 EMRS Spring Meeting Strasbourg, 18.06.2018, Strasbourg, France

Publ.-Id: 28561

Challenges of the Circular Economy: A Material, Metallurgical, and Product Design Perspective

Reuter, M.; van Schaik, A.; Gutzmer, J.; Bartie, N.; Abadías-Llamas, A.

Circular economy’s (CE) noble aims maximize resource efficiency (RE) by among others extending product life cycles and using wastes as resources. Modern society’s vast and increasing amounts of waste and consumer goods, their complexity and functional material combinations is challenging the viability of the CE in spite of various alternative business models promising otherwise. The metallurgical processing of CE enabling technologies requires in the end a sophisticated and agile metallurgical infrastructure. The challenges of reaching a CE will among others be highlighted in terms thermodynamics, transfer processes, technology platforms, digitalization of the processes of the CE stakeholders, design for recycling (DfR) based on a product (mineral)-centric approach, challenging material centric considerations. Integrating product centric considerations into the water, energy, transport, heavy industry, and other smart grid systems will maximize the RE of future smart sustainable cities, providing the fundamental detail for realizing and innovating the United Nation’s Sustainability Development Goals.

Keywords: Circular economy; Process metallurgy; Thermoeconomics; Exergy; Design for Recycling


Publ.-Id: 28559

The Geo-metallurgy of the circular economy: Fairphone

Reuter, M. A.

tools - HSC Sim & GaBi LCA
Particle description of recycling systems inclusive of exergy & energy
Analysis of systems: Rock, residue, recyclate to refined metal
Copper production system: Irreversibility analysis of system & Footprint of complete system
Bill-of-Materials & Full Material Declaration linked to metallurgy, alloy and materials production

Keywords: HSC Sim; GaBi LCA; recycling systems; exergy; energy; Recycling

  • Invited lecture (Conferences)
    International Mineral Processing Congress, 17.-21.09.2018, Moskau, Russland

Publ.-Id: 28558

Thermodynamic evaluation using the law of mass action under consideration of the activity coefficients in the system NdCl3-HCl (or NaOH)-H2O-DEHPA-kerosene

Scharf, C.; Ditze, A.

For the recovery of neodymium, an important rare earth metal, solvent extraction using DEHPA as extractant is a possible process for winning and recycling. A preceding study by the authors has provided extensive experimental data of the system neodymium-chloride-hydrochloric acid (or sodium hydroxide)-water-di-(2-ethylhexyl)phosphoric acid (DEHPA)-kerosene. It was found that the description of the reaction Nd3+ + 3 (DEHPA)2 <=> Nd(DEHP·DEHPA)3 + 3 H+ by an ideal mass action law is only partly satisfactory. This article investigates the contribution of several parameters to non-ideality. On this basis, expressions for activity coefficients of neodymium in the aqueous phase as well as DEHPA and neodymium in the organic phase are derived. The resulting equations are shown to represent the system with considerably better accuracy than previously possible.

Keywords: thermodynamic evaluation; solvent extraction; neodymium; DEHPA

Publ.-Id: 28557

CIRCULAR ECONOMY STRATEGIES - Responsible Business Practices // Process Model Based Footprints Using HSC Chemistry Software

Reuter, M. A.; Roine, A.

SusCritMat aims to educate people from Master’s student level up, both in industry and academia about important aspects of Sustainable critical raw materials. In a novel concept, it introduces courses on these complex and interdisciplinary topics in a modula structure, adaptable to a variety of different formats and accessible to both students and managers in industry. These courses will develop new skills which will help participants to better understand the impact and role of critical raw materials in the whole value chain; enabling them to identify and mitigate risks. Understanding the bigger picture and the interconnected nature of global business and society is increasingly necessary to and valued by industry. SusCritMat is an EU-funded project that brings together the technical and pedagogical expertise of leading educational institutions and business partners. It uses and creates teaching materials which can be combined into different course formats. Multi-media education materials will be made available to participants of summer and winter schools so that they can work with state-of-the-art techniques and data.

Keywords: Circular Economy; resource efficiency; sustainability; Digitalization; Simulation

  • Lecture (others)
    SusCritMat Autumn School for Professionals 2018, 24.-26.10.2018, Delft, Niederlande

Publ.-Id: 28556

Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

Schramm, A.; Bock, B.; Schmidt, A.; Zienert, T.; Ditze, A.; Scharf, C.; Aneziris, C. G.

To investigate possible reactions between differently coated carbon-bonded alumina filters and an AZ91 magnesium alloy melt, immersion tests were carried out. Uncoated as well as MgAl2O4-, Al2O3-, nano- (carbon nano tubes/alumina nano sheets) and MgO-C-coated filters were tested. Thermodynamic calculations showed that only magnesia (MgO) and carbon are stable against molten magnesium; alumina (Al2O3) and spinel (MgAl2O4) will be reduced under the formation of magnesia. Optical and scanning electron microscopy as well as EDX analysis were performed near and at the filter-magnesium alloy-interface of the cooled and sectioned filter samples after their immersion into the AZ91 melt. The results of the thermodynamic calculations were confirmed by the experiments. The MgO-C-coated filter was the only one that did not show an in situ-formed layer on its surface after being in contact with the magnesium alloy melt. The alumina- or spinel-containing filter surfaces displayed platelet-like in situ layers after their contact with the molten AZ91. The results of the EDX analysis of these layers suggest their composition of MgO, since notable respective Mg and O contents were detected, as predicted by the calculations.

Keywords: Ceramic Foam Filter; Interfaces; Al2O3; MgO

Publ.-Id: 28555

Semi-Solid remelting of Magnesium-Chips

Ohmann, S.; Ditze, A.; Scharf, C.

Compact and loose magnesium chips were processed by means of remelting. The remelting was successfully performed using the new method of semi-solid melting, without the addition of flux, at temperatures between 580°C and 600°C. In this temperature range, the exothermic reaction between magnesium and the oxygen present in the surrounding atmosphere is avoided; in addition, the oxygen layer of the chips is stripped off by the particles of the semi-solid melt. Results show that more than 95% of the magnesium chips can be recovered as metal. Experiments were performed on different scales to obtain production parameters for the recycling process. Larger particle sizes of magnesium chips can be remelted faster than smaller ones. The ability to remelt at temperatures in the semi-solid region of alloys demonstrates the possibility of recovering virtually all of the metal from the chips.

Publ.-Id: 28554

System integration, Environmental impact and Business models

Reuter, M. A.

Determine economic feasibility (OPEX and CAPEX) for industrial scale pretreatment based on different energy sources and their integration with existing industrial production of Mn-alloys for different cases;
Prepare a business plan for implementation of pretreatment technology at the project partners;
Prepare a strategy for future exploitation of the developed technology outside the project consortium and identify how this will reduce CO2 emissions also by including the embodied energy of the system;
Assess environmental impact on manganese alloy production, especially effect on CO2 emission and energy consumption of industrial scale pretreatment in separate unit integrated with existing industrial Mn-alloy production. This will be estimated by linking system simulation with environmental footprint using LCA and Life Cycle Cost analysis tools; and
Maximize the resource efficiency of manganese production by optimising the processing and the infrastructure of the system of technologies. This will be based on applied scales for mass flows and production processes. Both energy and exergy efficiency will be maximized.

Keywords: energy efficiency; exergy efficiency; resource efficiency

  • Lecture (others)
    PreMa Project Meeting, 22.-23.10.2018, Trondheim, Norwegen
  • Lecture (others)
    PreMa Projekt Meeting, 13.-14.11.2019, Oberursel, Deutschland

Publ.-Id: 28553

Multi-source hyperspectral imaging of carbonatite-hosted REE-Nb-Ta mineralization at Marinkas Quellen, Namibia

Booysen, R.; Zimmermann, R.; Lorenz, S.; Gloaguen, R.; Nex, P. A. M.

The demand for mineral and metalliferous resources needs to match the continued global rise in population and global economic growth. Rare Earth Elements (REEs), Niobium (Nb) and Tantalum (Ta) are such deposits in high demand. This global rise makes it difficult to meet the growing demand using only the currently available resources, such as recycled REEs and known REE deposits. Although the concept of a purely circular economy is very attractive through the use of recyclable REE-Nb-Ta, this model is not completely sustainable due to the increased energy needed to bolster such a model. Therefore, a renewed focus on the exploration of REE-Nb-Ta deposits is imperative to ensure the future development of this commodity.
Traditional exploration techniques are mainly based on extensive field work supported by geophysical surveying. Restrictions such as field accessibility, financial status, area size and climate can hinder these traditional exploration techniques. Hence, we suggest to increase the use of multi-source and multi-scale hyperspectral remote sensing in order to decrease conventional restrictions in the exploration of minerals through the use of aerial and ground-based methods. The multi-scale, multi-source approach will consist of a downscaling procedure, moving from low spatial resolution to high spatial resolution. Firstly, satellite data (Sentinel-2) will be used to identify the study area, then hyperspectral airborne data (HyMap) will be used to refine the area of interest. Subsequently, a snapshot hyperspectral camera will be attached to a UAV to acquire drone-borne data for the investigation of the deposit in more detail. We further argue that the addition of drone-borne hyperspectral data can also vastly improve the accuracy of field mapping in future mineral exploration. Drone-borne measurements can supplement and direct geological observation immediately in the field and therefore allow better integration with in-situ ground investigations. In particular, in inaccessible and remote areas with little infra-structure, such systems are an excellent reconnaissance tool because it allows a systematic, dense and completely non-invasive surveying, which is often not possible using ground-based techniques. Additionally, spectral and spatial information will be integrated by combining drone-borne hyperspectral and Light Detection And Raging (LiDAR) data to provide more accurate classification results.
Ultimately, the corrected drone-borne data provide information on the spectral signatures of outcropping lithologies to the exploration teams. This is achieved by using end-member modelling and classification techniques such as non-linear machine learning algorithms, e.g., Neural Networks and decision tree based methods. The drone based data are integrated in a comprehensive workflow including in-situ acquisitions and results in an hypercloud. The validation of the resulting digital outcrop is performed via field spectroscopy, portable XRF and representative geochemical whole-rock analysis.
The area of interest for this study is the massive carbonatite intrusion at Marinkas Quellen, Namibia. The location is in a remote environment and characterized by difficult terrains and a complete carbonatite suite (e.g. calsio-, ferro- and magnesio-carbonatites). The first two factors would normally impede or restrict traditional field surveying. Preliminary results indicate that drone-borne surveying has a very high potential to directly detect REE-concentrations and indicator minerals for Nb and Ta, in fundamentally lowering the acquisition costs and increasing the information potential of data captured in the field.

Keywords: REEs; Multis-source; Hyperspectral; Exploration; Marinkas Quellen

  • Poster
    WHISPERS - Hyperspectral Image and Signal Processing Workshop, 23.-26.09.2018, Amsterdam, The Netherlands

Publ.-Id: 28552

Experimental study of the natural convection heat transfer performance for finned oval tubes at different tube tilt angles

Unger, S.; Beyer, M.; Thiele, J.; Hampel, U.

The natural convection heat transfer of finned oval tubes was studied for different tube tilt angles (0° to 40°), fin spacing (6 mm to 16 mm) and Rayleigh numbers (11000 to 130000). Fin efficiency was determined by temperature measurements along the fin surface and temperature gradient calculations. Nusselt number and volumetric heat flux density were chosen as assessment parameters for the thermal performance. A comparison of the experimental data with correlations from literature was made and good agreement was found. Furthermore, the uncertainty by the measurements was evaluated. In the horizontal tube orientation (0°) the Nusselt number increases with fin spacing, however the fin efficiency and the volumetric heat flux density reduce. The tilt angle of the longitudinal tube axis was found to have an essential impact on the thermal performance, in particular when the fin spacing is high. For the higher fin spacing values the horizontal orientation gives highest Nusselt number and volumetric heat flux density. At tube tilt angle of 40° the thermal performance becomes lowest for all fin spacing values. When the fin spacing is low, the effect of tube tilt angle is minor. From the experimental results correlations between Nusselt number, Rayleigh number, fin spacing and tube tilt angle are proposed to assist the future design of heat exchanger with tilted finned oval tubes.

Keywords: Finned oval tubes; Natural convection; Heat transfer; Tube tilt angle; Heat transfer correlation

Publ.-Id: 28551

Stoffkreislauf der Metalle – von der Gewinnung bis zum Recycling

Reuter, M. A.; Stelter, M.

In der heutigen Zeit bestimmen Metalle unser tägliches Leben. Im Bereich der Mobilität – sei es beim Auto mit Verbrennungsmotor oder bei Elektrofahrzeugen – sind immer Metalle die wesentlichen Bestandteile, ohne die unsere Welt nicht funktionieren würde. Im Bereich der Kommunikation, der Unterhaltungselektronik, aber auch in der Medizin sind sie ebenfalls unverzichtbar. Ihre herausragenden Eigenschaften – wie Härte, Duktilität, Umformbarkeit, Korrosionsbeständigkeit – machen sie zu idealen Werkstoffen für fast alle Anwendungen. Besonders zeichnet sie aber die Recyclingfähigkeit aus, denn Metalle können prinzipiell zu 100 % nach ihrer Nutzung zurückgewonnen werden.
Dass wir dies bisher nur eingeschränkt tun, hat verschiedene Ursachen. In der Arbeitsgruppe sollen die Aspekte der Kreislaufwirtschaft beleuchtet werden. So werden technologische Möglichkeiten und Grenzen in Beziehung zu den ökonomischen Bezügen gestellt. Gibt es eine optimale Kreislaufführung und, wenn ja, wie sieht sie aus? Welche Faktoren beeinflussen die dafür notwendigen unangewandten Prozesse? Ist es sinnvoll, in jedem Fall zu versuchen, eine Recyclingrate von 100 % zu erreichen? Und ist dies überhaupt möglich?
Eine differenzierte Betrachtung bezüglich unterschiedlicher Stoffgruppen ist dabei erforderlich. Eine weiter in die Details eindringende Betrachtung soll am Beispiel der Metalle den Teilnehmenden der Arbeitsgruppe Chancen und Risiken der Stoffkreislaufführung vermitteln. In Gesprächsrunden und Diskussionen sollen die Vor- und Nachteile von technologischen Prozessen herausgearbeitet und deren Nutzen für die Kreislaufführung der Werkstoffe bewertet werden.

Keywords: Recyclingfähigkeit; Metalle; optimale Kreislaufführung

  • Lecture (others)
    Workshop - Sommerakademie der Studienstiftung, 19.-30.08.2018, St. Johann, Italien

Publ.-Id: 28550

Circular Economy engineering - Recycling 4.0 - Challenges of the circular economy

Reuter, M. A.

The last hundred years have brought an unprecedented increase in natural resource use. This trend is likely to continue in the coming decades. Global resource use is expected to double by 2030. For Europe, these developments raise major concerns . Europe's economy depends on an uninterrupted flow of natural resources , metals, minerals, energy carriers and other raw materials , with imports providing a substantial proportion of these materials in many cases. Increasingly, this dependence will be a source of vulnerability, as growing global competition for natural resources has contributed to marked increases in price levels and volatility. Uncertain and unstable prices disrupt the industrial sectors that are dependent on these resources. At the same time, rapid increases in extraction and exploitation of natural resources are having a wide range of negative environmental impacts, particularly in Europe. Air, water and soil pollution, acidification of ecosystems, biodiversity loss, climate change and waste generation put economic and social well-being at risk. Creating a circular economy in Europe can help to address many of these challenges, and further improve the efficiency of resource use. It will have obvious economic benefits, reducing costs and risks while enhancing competitiveness. European leadership in the transition to a circular economy also offers opportunities securing first-mover advantages in the global economy.

The conference will address the issues impacting the transition from the linear take-make-consume-dispose economic model that currently dominates to a circular model that represents a fundamental alternative and explore the huge challenges and business opportunities in a circular economy. The conference will include presentations and panel discussions featuring renowned researchers within circular economy and leading Polish businesses presenting relevant projects and views on why and how the circular economy is introduced in their factories. It will bring together industry leaders, authorities and city planners, technology providers, business consultants, researchers and inventors, all with the common goal of driving innovation in new materials and better, more economic products and services and securing first-mover advantages in the global economy.

Recycling 4.0: digitalizing the system
Recycling 4.0: physics of separation
Recycling 4.0: industrial applications
Recycling 4.0 digital platforms

Keywords: Recycling 4.0

  • Invited lecture (Conferences)
    European Technology Forum 2018 / From Waste to Resources, 26.-27.09.2018, Katowice, Polen
  • Invited lecture (Conferences)
    THM-Kolloquim, 08.10.2018, Freiberg, Deutschland

Publ.-Id: 28549

SOCRATES 3nd Network-Wide Event

Reuter, M. A.

What have we done so far?
Current Status of SOCRATES projects
Communication, Dissemination and Exploitation progress
What are we going to do? Our contribution to SOCRATES

Keywords: SOCRATES; Copper production process; HSC Sim

  • Lecture (others)
    SOCRATES 3nd Network-Wide Event, 13.-16.02.2018, Bonn, Deutschland

Publ.-Id: 28548

Numerical Studies of Normal Conducting Deflecting Cavity Designs for the ELBE Accelerator

Hallilingaiah, T. G.; van Rienen, U.; Arnold, A.; Lehnert, U.; Michel, P.

Currently, in the electron linac ELBE there is a single beam line. Therefore, at any given time only single user can use the beam. Moreover, as different user experiments require distinct beam intensity settings, not all the experiments fully utilize the 13 MHz CW beam capability of the facility. To utilize the full beam capacity, multiple beam lines can be established by using an array of transverse deflecting structures. For that, an RF cavity was the design choice due to its inherent advantages with respect to repeatability of the kick voltage amplitude and phase, and the possibility of CW operation in the MHz range. Potential design candidates are the CEBAF RF separator, the three proposed crab cavities for the HL-LHC upgrade project, and a novel NC deflecting cavity design. In this comparative study, the figures of merit of the cavities are computed from electromagnetic field simulations for a transverse voltage of 300 kV. This comparative study supported our selection of the deflecting cavity design for ELBE.

Keywords: normal conducting; RF cavity; RF kicker; beam spreader

Related publications

  • Open Access Logo Contribution to proceedings
    9th International Particle Accelerator Conference, 29.04.-04.05.2018, Vancouver, British Columbia,, Canada
    Proceedings of the 9th International Particle Accelerator Conference: JACoW, ISBN 978-3-95450-184-7, 3824-3827
    DOI: 10.18429/JACoW-IPAC2018-THPAL074


Publ.-Id: 28547

Sub-threshold production of K0s mesons and Λ hyperons in Au(1.23A GeV)+Au

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.; Leifels, Y.

We present first data on sub-threshold production of K0 s mesons and Λ hyperons in Au+Au collisions at √sNN = 2.4 GeV. We observe an universal scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their part> scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable χ2 values.


Publ.-Id: 28546

Mixed-valent neptunium oligomer complexes based on cation-cation interactions

Schöne, S.; März, J.; Stumpf, T.; Ikeda-Ohno, A.

Mixed-valent tri- and tetranuclear complexes of neptunium, [{NpIVCl4}{NpVO2Cl(THF)3}2]·THF and [{NpIVCl3}{NpVO2(μ2-Cl)(THF)2}3{μ3-Cl}] (THF = tetrahydrofuran), were synthesised and characterised. Both the complexes are formed via the cation-cation interactions between the Np(IV) centre and the axial oxygens of the neptunyl(V) unit (i.e. transdioxo NpO2+ cation), demonstrating the potential of cation-cation interactions for further exploring the oligomer/cluster chemistry of actinides.

Keywords: actinides; neptunium; mixed-valence; oligomers; polymers; coordination; structure characterisation; cation-cation interactions


Publ.-Id: 28545

Strong absorption of hadrons with hidden and open strangeness in nuclear matter

Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Chernenko, S.; Chlad, L.; Chudoba, P.; Ciepal, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kornas, F.; Kotte, R.; Kubos, J.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Linev, S.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Malige, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowsk, K.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Prozorov, A. P.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Smyrski, J.; Spataro, S.; Spies, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Ungethüm, C.; Vazquez Doce, O.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.

We present the first observation of K- and φabsorption within nuclear matter by means of π- -induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K-/K+)W / (K-/K+)C is found to be 0.319 \pm 0.009(stat)+0.014-0.012 (syst) indicating a larger absorption of K- in heavier targets as compared to lighter ones. The measured φ/K- ratios in π-+C and π^- +W reactions within the HADES acceptance are found to be equal to 0.55±0.03(stat)+0.06−0.07 (syst) and to 0.63±0.05(stat)−0.11+0.11 (syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the φmeson in nuclear medium is strongly coupled to the K- dynamics. The large difference in the φ production off C and W nuclei is discussed in terms of a strong \phiN in-medium coupling.


Publ.-Id: 28544

Observation of multiple magnetic phases and complex nanostructures in Co implanted amorphous carbon films

Suschke, K.; Gupta, P.; Williams, G. V. M.; Hübner, R.; Markwitz, A.; Kennedy, J.

Room temperature implantation of 30 keV Co ions into an amorphous carbon film with a high fluence of 1.2×1017 Co/cm2 results in formation of magnetic nanostructures displaying multiple magnetic phases. Cross-sectional TEM images show formation of Co containing nanoparticles at the surface and near-surface regions of the implanted films. EDXS measurements suggest the nanoparticles to be composed primarily of Co and O at the surface and Co and C in deeper regions. These nanoparticles with differing compositions were observed to be segregated by a thin layer devoid of Co. Magnetic measurements reveal the presence of superparamagnetic behavior from small CoxC nanoclusters with a blocking temperature of 5 K. There is a small fraction of larger CoxC nanoclusters that show magnetic hysteresis even at room temperature. The saturation magnetic moment is as high as 0.51 μB/Co at 2 K and 0.32 μB/Co at room temperature. Spin-disorder is seen with a range of spin glass temperatures below ∼70 K. Our high fluence Co implantation into amorphous carbon has resulted in the formation of complex magnetic nanostructures composed of cobalt, oxygen, and carbon. These nanostructures give rise to multiple magnetic phases such as superparamagnetism, spin glass, ferromagnetism, and possibly antiferromagnetism.

Keywords: a-C; DLC; Ion implantation; Superparamagnetic; Magnetization; Cobalt oxide; Cobalt carbide

Related publications

  • Journal of Physics and Chemistry of Solids 127(2019), 158-163

Publ.-Id: 28543

On a spectral problem in magnetohydrodynamics and its relevance for the geodynamo

Stefani, F.; Tretter, C.

One of the most remarkable features of the geodynamo is the irregular occurrence of magnetic field reversals. Starting with the operator theoretical treatment of a non-selfadjoint dynamo operator, we elaborate a dynamical picture of those reversals which relies on the existence of exceptional spectral points.

Keywords: geodynamo; magnetohydrodynamics


Publ.-Id: 28542

Laser Plasma Based Accelerators for Radiobiological Applications - From Research Field MATTER to HEALTH

Metzkes-Ng, J.; Levy, Dan

Laser Plasma Based Accelerators for Radiobiological Applications - From Research Field MATTER to HEALTH

  • Invited lecture (Conferences)
    Festive Symposium on the occasion of the inaugruation of the Helmholtz Tel Aviv Office, 22.10.2018, Tel Aviv, Israel

Publ.-Id: 28541

Response of the QED(2) Vacuum to a Quench: Long-term Oscillations of the Electric Field and the Pair Creation Rate

Otto, A.; Graeveling, D.; Kämpfer, B.

We consider -- within QED(2) -- the backreaction to the Schwinger pair creation in a time dependent, spatially homogeneous electric field. Our focus is the depletion of the external field as a quench and the subsequent long-term evolution of the resulting electric field. Our numerical solutions of the self consistent, fully backreacted dynamical equations exhibit a self-sustaining oscillation of both the electric field and the pair number depending on the coupling strength.


Publ.-Id: 28540

Probing Interlayer Excitons in a Vertical van der Waals p-n Junction using Scanning Probe Microscopy Technique

Rahaman, M.; Wagner, C.; Mukherjee, A.; Lopez-Rivera, A.; Gemming, S.; Zahn, D. R. T.

Two dimensional (2D) semiconductors feature exceptional optoelectronic properties controlled by strong confinement in one dimension. In this contribution, we studied interlayer excitons in a vertical p-n junction made of bilayer n-type MoS2 and few layers p-type GaSe using current sensing atomic force microscopy (CSAFM). The p-n interface is prepared by mechanical exfoliation onto highly ordered pyrolytic graphite (HOPG). Thus the heterostructure creates an ideal layered system with HOPG serving as the bottom contact for the electrical characterization. Home-built Au tips are used as the top contact in CSAFM mode. During the basic diode characterization, the p-n interface shows strong rectification behavior with a rectification ratio of 104 at ±1 V. The I-V characteristics reveal pronounced photovoltaic effects with a fill factor of 0.55 by excitation below the band gap. This phenomenon can be explained by means of the dissociation of interlayer excitons at the interface. The possibility of the interlayer exciton formation is indicated by density functional theory (DFT) calculations on this heterostructure: the valence band of GaSe and the conduction band of MoS2 contribute to an excitonic state at an energy of about 1.5 eV. The proof of such excitonic transition is provided by photoluminescence measurement at the p-n interface. Finally, photocurrent mapping at the interface under 785 nm excitation provides evidence of efficient extraction of such excitons. Our results demonstrate two dimensional device for future optoelectronics and light harvesting assisted by interlayer excitons in van der Waals heterostructure.

Keywords: van der Waals heterojunction; interlayer exciton; MoS2; GaSe; p-n junction; optoelectronics; density functional theory

Publ.-Id: 28539

Damage formation and Er structural incorporation in m-plane and a-plane ZnO

Macková, A.; Malinský, P.; Jagerová, A.; Mikšová, R.; Nekvindová, P.; Cajzl, J.; Rinkevičiūtė, E.; Akhmadaliev, S.

The various crystallographic orientations in semiconductors as ZnO exhibit different resistivity under the ion beam irradiation/implantation. Study of the various crystallographic orientations is mandatory for nano-structured semiconductor system development. This paper reports on the implantation damage build-up, structural modification and Er dopant position in a-plane and m-plane ZnO implanted with Er+ 400 keV ions at the ion fluences 5 × 1014, 2.5 × 1015, 5 × 1015 cm-2 and subsequently annealed at 600 °C in O2 atmosphere using Rutherford Back-Scattering spectrometry (RBS) in channelling mode as well as using Raman spectroscopy. Strongly suppressed surface damage formation was observed in both crystallographic orientations compared to the deep damage growth with the increased ion implantation fluence. More progressive damage accumulation appeared in m-plane ZnO compared to a-plane ZnO. Simultaneously, the strong Er out-diffusion depth profile in m-plane ZnO accompanied by the damage accumulation at the surface was observed after the annealing. Contrary, the surface recovery accompanied by Er concentration depth profiles keeping a normal distribution with a small maximum shift to the surface was observed in a-plane ZnO. Different structure recovery and Er behaviour was evidenced in a-plane and m-plane ZnO by RBS-C, moreover Raman spectroscopy proved a lower damage at higher ion fluences introduced in a-plane ZnO compared to m-plane. The structure modifications were discussed in connection with a damage accumulation and Er concentration depth profile shape in various ZnO crystallographic orientations in as-implanted and as-annealed samples.

Keywords: a-Plane and m-plane ZnO doped; Damage accumulation asymmetry; Er ion implantation in ZnO; RBS channelling; Damage depth profiling

Related publications

Publ.-Id: 28538

Defects in hydrogen implanted SiC

Zhang, X.; Li, Q.; Wang, M.; Zhang, Z.; Akhmadaliev, S.; Zhou, S.; Wu, Y.; Guo, B.

SiC is a widely used wide-bandgap semiconductor. Ion implantation is often employed in SiC for doping, defect engineering and transferring of SiC thin films on different substrates. To transfer SiC or to get freestanding thin SiC films by "smart-cut" [Appl. Phys. Lett. 112 (2018) 192102], a large fluence of hydrogen (proton) ion implantation will be applied. Here, we show the structure and defect properties in 6H-SiC single crystals after hydrogen implantation up to a fluence of 5 x 1016 cm-2 at different energies of ions. We present the characterization by Rutherford Backscattering/Channeling spectrometry, Raman spectroscopy and electron spin resonance. Upon H+ ion implantation, point defects are mainly created and cause the lattice vibration softening. Our analysis also suggests that H+ ion implantation induces less lattice disorder than heavy ions at fluences producing the same number of displacements per atom. We also discuss the possible nature of the point defects and their influence on the electrical properties.

Keywords: SiC; Defects; Ion implantation; Raman-Spectroscopy; Damage formation; Ion; Surface; Neutron

Related publications

Publ.-Id: 28537

Thermocapillary convection during hydrogen evolution at microelectrodes

Massing, J.; Mutschke, G.; Baczyzmalski, D.; Hossain, S. S.; Yang, X.; Eckert, K.; Cierpka, C.

The origin of strong electrolyte flow during water electrolysis is investigated, that arises at the interface between electrolyte and hydrogen bubbles evolving at microelectrodes. This Marangoni convection was unveiled only recently (Yang et al., PCCP, 2018, [1]) and is supposed to be driven by shear stress at the gas-liquid interface caused by thermal and concentration gradients. The present work firstly allows a quantification of the thermocapillary effect and discusses further contributions to the Marangoni convection which may arise also from the electrocapillary effect. Hydrogen gas bubbles were electrolytically generated at a horizontal Pt microelectrode in a 1MH2SO4 solution. Simultaneous measurements of the velocity and the temperature field of the electrolyte close to the bubble interface were performed by means of particle tracking velocimetry and luminescent lifetime imaging. Additionally, corresponding numerical simulations of the temperature distribution in the cell and the electrolyte flow resulting from thermocapillary stress only were performed. The results confirm significant Ohmic heating near the micro-electrode and a strong flow driven along the interface away from the microelectrode. The results further show an excellent match between simulation and experiment for both the velocity and the temperature field within the wedge-like electrolyte volume at the bubble foot close to the electrode, thus indicating the thermocapillary effect as the major driving mechanism of the convection. Further away from the microelectrode, but still below the bubble equator, however, quantitative differences between experiment and simulation appear in the velocity field, whereas the temperature gradient still matches well. Thus, additional effects must act on the interface, which are not yet included in the present simulation. The detailed discussion tends to rule out solution-based effects, generally referred to as solutal effects, whereas electrocapillary effects are likely to play a role. Finally, the thermocapillary effect is found to exert a force on the bubble which is retarding its departure from the electrode.

Keywords: Water electrolysis; Thermocapillary convection; Microbubbles; Fluorescence lifetime imaging; Numerical simulation; Hydrogen evolution


Publ.-Id: 28536

Messung der Marangoniströmung an elektrochemisch erzeugten Wasserstoffblasen

Massing, J.; Baczyzmalski, D.; Yang, X.; Mutschke, G.; Eckert, K.; Cierpka, C.

Bei der Wasserstoffelektrolyse kann es aufgrund von Gradienten in der Konzentration und der Temperatur zu Gradienten in der Oberflächenspannung an der Phasengrenzfläche der Wasserstoffblase kommen. Die dadurch angetriebene Marangoniströmung konnte erstmals an einer Mikroelektrode für verschiedene Potentiale gemessen werden. Die Strömungsgeschwindigkeit korreliert eindeutig mit dem elektrischen Strom. Für die vorgestellte Untersuchung werden sowohl der Einfluss des Konzentrationsgradienten als auch der Einfluss des Temperaturgradienten diskutiert und eine Größenordnungsabschätzung zur Beschreibung des Phänomens durchgeführt. Erste Ergebnisse zu Temperaturmessungen auf der Basis von temperatursensitiven Partikeln an der Wasserstoffblase ergänzen die in der Größenordnungsabschätzung gemachten Annahmen und zeigen die lokale Erwärmung am Blasenfuß.

Keywords: Elektrolyse; Gasentwicklung; Wasserstoff; Mikroelektrode; PIV; Temperaturmessung

  • Lecture (Conference)
    26. Fachtagung "Experimentelle Strömungsmechanik", 04.-06.09.2018, Rostock, Deutschland

Publ.-Id: 28535

Longitudinal modulation of electron-cooled C-12(6+) and O-16(8+) ion beams at heavy ion storage ring CSRe

Wang, H.; Wen, W.; Huang, Z.; Zhang, D.; Hai, B.; Bussmann, M.; Winters, D.; Zhao, D.; Zhu, X.; Li, J.; Li, X.; Mao, L.; Mao, R.; Zhao, T.; Yin, D.; Wu, J.; Yang, J.; Yuan, Y.; Ma, X.

The longitudinal dynamics of electron-cooled and radio-frequency (RF)-bunched C-12(6+) and O-16(8+) ion beams have been investigated at a heavy-ion experimental cooler storage ring CSRe. An rf-buncher was employed to longitudinally modulate the ion beams. A new resonant Schottky pick-up was applied to monitor the intensities and longitudinal dynamics of stored and electron-cooled ion beams. Using electron-cooling, the separated Schottky noise signals of the C-12(6+) and O-16(8+) ions were clearly observed in the Schottky spectrum. The storage times and the particle numbers of both ion beams were measured by Schottky noise, which demonstrated the ability to perform Schottky mass spectrometry measurements and also the measurement of highly charged ions at the CSRe. In addition, an enhancement of the Schottky noise signals was observed for rf-bunched ion beams, which could be used to diagnose the intensity ion beams at storage rings. Finally, a broadly longitudinal manipulation of the ion beams by scanning the bunching frequency was realized. The investigation of electron-ion recombination experiment at ultra-low collision energies by scanning the bunching frequency of the ion beams at the storage ring CSRe is proposed.

Keywords: electron cooloing; schottky; ion beam

Related publications

Publ.-Id: 28534

Coatings in harsh space environment

Pelizzo, M. G.; Corso, A. J.; Tessarolo, E.; Böttger, R.; Hübner, R.

In recent years, the study of space agent effects on optical coatings has become priority in view of future selected missions which will explore increasingly hostile environments. The impact on the morphology, on the structure and on the performance of coatings and materials due to ion and electron irradiation has been studied through various investigative techniques [1,2]. The irradiation sessions have been carried out at accelerators adopting different experimental regimes to reproduce space conditions in laboratory. A predictive model of the optical performance based on of the damage induced by protons and alpha particles has been developed [3]. Changes in the reflectance and transmittance properties have been attributed to density and refraction index variations due to implantation of low energetic particles. Bubble formation has been observed in metals, while delamination occurs when particles accumulated at interfaces, such as those in metal-protected thin films. Blistering of top layers has been observed in oxide-protected metal coatings (Fig.1). Impact on the performance of the coatings in various spectral ranges including extreme ultraviolet is discussed.
[1] Pelizzo, M.; Corso, A.J.; Zuppella, P.; Windt, D.L.; Mattei, G.; Nicolosi P., Stability of extreme ultraviolet multilayer coatings to low energy proton bombardment. Opt. Express 2011, 19, 14838-14844.
[2] Zuccon, S.; Napolitani, E.; Tessarolo, E.; Zuppella, P.; Corso, A.J.; Gerlin, F.; Nardello, M.; Pelizzo, M.G. Effects of helium ion bombardment on metallic gold and iridium thin films. Opt. Mat. Express 2015, 5(1), 176–187.
[3] M.G. Pelizzo, A.J. Corso1, E. Tessarolo, R. Böttger, R. Hübner, E. Napolitani, M. Bazzan, M. Rancan, L. Armelao, W. Jark, D. Eichert, A. Martucci, Morphological and functional modifications of optical thin films for space applications irradiated with low-energy helium ions, paper in preparation, 2018.

Related publications

  • Lecture (Conference)
    Physics of X-Ray and Neutron Multilayer Structures, PXRNMS 2018, 07.-09.11.2018, Palaiseau, France

Publ.-Id: 28533

Effect of Ni-Ion Implantation into TiO2 Thin Films for Improving Resistive Switching Properties

Das, D.; Barman, A.; Bhowmick, S.; Phase, D. M.; Rajput, P.; Jha, S. N.; Kanjilal, D.; Hübner, R.; Kanjilal, A.

The expedition for non-volatile memories (NVM) is still on, owing to the rapid convergence of current memory technologies to their physical limits [1]. In recent years, TiO2 thin film-based Resistive Random Access Memory (RRAM) devices have shown great promise to the future NVM technology due to their low cost, easy fabrication, scalability, and higher operation speed [1-2]. Switching from a low-resistance state (LRS) to the high-resistance state (HRS) is quite debatable [2]. However recent studies [3-4] suggest controlled defect (oxygen vacancy, OV) engineering by ion implantation may significantly improve the switching performance. In this respect, controlled incorporation of foreign elements in the host (TiO2 films) by ion beam implantation would be advantageous for OV formation.Results obtained for 35 keV Ni-doped TiO2 thin films will be presented here, emphasizing the enhancement of the LRS to HRS ratio for improving the resistive switching properties. The formation of graded Ni layer, regions will be addressed by detailed transmission electron microscopy studies. Whereas the extended X-ray absorption fine structure (EXAFS) measurements will show an increase in white light intensity at the Ni-K edge along with the change in pre-edge feature (compared to metallic Ni), indicating the interaction of Ni ions with the host matrix. Further, Ni-doping induced evolution of Ti3+ state will be demonstrated by X-ray photo electron spectroscopy, supporting the development of OV. Following the fabrication of Au/Ni-TiO2/Pt RRAM devices, charge transport mechanism will finally be explained on the basis of different conduction mechanisms.
[1] Yang, J. J., Pickett, M. D., Li, X., Ohlberg, D. A., Stewart, D. R., & Williams, R. S. (2008) , Nature Nanotech. 3(7), 429.
[2] Lee, M. H., Kim, K. M., Kim, G. H., Seok, J. Y., Song, S. J., Yoon, J. H., & Hwang, C. S. (2010), Applied Physics Letters, 96(15), 152909.
[3] Pan, X., Shuai, Y., Wu, C., Luo, W., Sun, X., Zeng, H & Zhang, W. (2016), Applied Physics Letters, 108(3), 032904.
[4] Wylezich, H., Mähne, H., Heinrich, A., Slesazeck, S., Rensberg, J., Ronning & Mikolajick, T. (2015). Journal of Vacuum Science & Technology B, 33(1), 01A105.

Related publications

  • Poster
    5th International Conference on Ion Beams in Materials Engineering and Characterizations, IBMEC 2018, 09.-12.10.2018, New Delhi, India

Publ.-Id: 28532

Developing nanocrystalline thin film based radiation dosimeter

Pal, S.; Bhowmick, S.; Das, D.; Khan, S. A.; Kanjilal, D.; Hübner, R.; Kanjilal, A.

Radiation dosimetry is an important field of research due to its potential in various applications like food safety, personal dosimetry, environmental monitoring, radiation therapy, etc [1]. In general, most radiation dosimetric studies are related with electromagnetic radiation (γ radiation, UV radiation, etc.). However, the increased use of hadron therapy (radiation therapy using charged particles) in cancer and tumor treatment demands inclusion of ion beam dosimetry study for radiation dosimetry [2]. In this regard, it is a need to develop novel dosimeters with thin films for online monitoring of the radiation dose delivered to patient. In contrast to powder sample based dosimeter, here very less material will be required demanding very high sensitive phosphors. Aluminium oxide (Al2O3) (specially, carbon doped) can be a good choice due to its very high thermoluminescence (TL) sensitivity [2]. Moreover, this material is considered to be the best material for optically stimulated luminescence (OSL), a suitable radiation dosimetric technique for online monitoring. Regarding thin films, choice of substrate is always a matter of interest. Here, a comprehensive radiation dosimetric study of as-grown and annealed Al2O3 deposited on different substrates (i.e. silicon, Al foil, kapton tape, etc) by using RF magnetron sputtering and anodized porous Al2O3 will be presented. The variation in radiation response will be discussed in the light of detailed structural and optical properties analysis of the said thin films [3].
1. Thermoluminescence of solids, SWS Mckeever, Cambridge university press, 1988.
2. G. O. Sawakuchi et al. J. Appl. Phys. 104 (2008) 124903.
3. W. L. Xu et al. Appl. Phys. Lett. 85 (2004) 4364.

Related publications

  • Lecture (Conference)
    International Conference on Current Trends in Materials Science and Engineering, CTMSE 2018, 19.-20.01.2018, Kolkata, India

Publ.-Id: 28531

Study of thermoluminescence property of C+ ion doped anodized alumina

Bhowmick, S.; Das, D.; Asirvatham, J.; Khan, S. A.; Sen, D.; Hübner, R.; Kanjilal, D.; Kanjilal, A.

The application of thermoluminescence (TL) has created immense interest due to their potential to determine radiation doses for food-safety, radiation therapy, personal dosimetry, environmental monitoring, etc. However, the performance of a phosphor relies on thermally stimulated light emission from luminescent centres created during the exposure to an ionizing radiation. Aluminum oxide (Al2O3) is one of the promising materials for dosimetry. Although this material was forgotten for a long time due to its low sensibility compared with that of TLD-100, it recently regained interest owing to the development of anion defects in Al2O3:C single crystals. It was reported to be highly sensitive, even more than TLD-100, though conventional crystal growth technique requires high temperature in the presence of a high tumbling atmosphere. Nevertheless, the TL sensitivity of crystalline Al2O3 can be enhanced by doping with carbon, but this is only good for low dose radiation monitoring (typically 0.1-100 Gy). Interestingly, a prominent TL sensitivity can be achieved from nanocrystals with increasing surface-to-volume ratio because of increasing surface states. Therefore, judicial use of Al2O3 nanocrystallites will give a fertile ground for offline dose monitoring. The nanotrenches of anodized alumina in this respect can also give additional path for improving efficiency, which can be enhanced further by controlled introduction of C in Al2O3 matrix. Since ion beam implantation is known to be a powerful method because of its ability to control over distribution of dopants and residual defects, it is therefore important to understand the impact of C+ ions in controlling the formation of traps in anodized alumina and also to explore its suitability for ion beam dosimetry by following the TL glow curves with increasing fluence (i.e. ions/cm2).
To execute this plan, after optimizing the porosity, the penetration depth of C+ ions in Al2O3 layers have been calculated by SRIM. Typical porous structure in the present set of samples is shown in Figs. 1 and 2. Based on this understanding, the anodized alumina has been exposed to 50 keV C+ ions in the fluence range of 2.33×1015 to 1.3×1016 ions/cm2. Following the initial structural analysis by XRD, TL response of the ion irradiated samples was characterized, showing a systematic rise in intensity with increasing fluence (Figure 3). For understanding of the underlying process, the anodized alumina before and after irradiation have now been studied by various techniques, like SEM, TEM, XRD, RBS, and XPS.

Related publications

  • Open Access Logo Contribution to external collection
    in: IUAC Annual Report 2016-2017, New Delhi: Inter University Accelerator Centre, 2018, 148-149

Publ.-Id: 28530

Understanding the role of carbon in active trap centre formation in porous alumina

Bhowmick, S.; Pal, S.; Das, D.; Khan, S. A.; Gupta, M.; Barman, S. R.; Kanjilal, D.; Hübner, R.; Kanjilal, A.

In recent days, carbon doped alumina (Al2O3:C) are gaining immense interest as a potential radiation dosimetric material due to very high thermoluminescence (TL) sensitivity [1]. Despite of some theoretical predictions [2, 3] as well as experimental results, exact role of carbon in forming active trap centres in alumina matrix is still not conclusive, and thus it requires further investigation. Here we report a detailed study of porous alumina in a systematic way by various complementary techniques, such as HAADF-STEM, EDS mapping, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) before and after carbon doping. For that, ion beam implantation technique has been employed due to controlled incorporation of carbon in selective areas of Al2O3. Further, the anodized alumina with a porous structure is expected to play a crucial role due to high surface-to-volume ratio. Amorphous porous alumina has been synthesized electrochemically [4] where the porous structure have been confirmed by SEM and TEM. The amorphous nature is also consistent with the GIXRD results. The corresponding elemental mapping suggests the carbon penetration depth in the amorphous Al2O3 matrix. Detailed XAS and depth dependent XPS studies reveal possible role of carbon atoms in Al2O3 as active trap centres, and so the TL response. The observed results are in good agreement with the recent theoretical works, and therefore will be helpful for further improvement of dosimetric sensing.
1. G. O. Sawakuchi et al. J. Appl. Phys. 104 (2008) 124903
2. H. D. Tailor et al. J. Vac. Sci. & Technol. A 33 (2015) 01A120
3. L. Ao et al. J. Appl. Phys. 122 (2017) 025702
4. H. Masuda et al. Science 268 (1995) 1466

Related publications

  • Poster
    International Conference on Current Trends in Materials Science and Engineering, CTMSE 2018, 19.-20.01.2018, Kolkata, India

Publ.-Id: 28529

Carbon Nanotubes – A Route Towards Space Application

Abbe, E.; Renger, T.; Sznajder, M.; Klemmed, B.; Starruß, E.; Hübner, R.; Schüler, T.; Bärtling, Y.; Muchow, B.; Tajmar, M.; Schmiel, T.

Over the last years, Carbon Nanotubes (CNTs) drew interdisciplinary attention. Regarding space technologies, a variety of potential applications were proposed and pre-investigated, e.g. electro-static discharge (ESD) coatings, electromagnetic interference (EMI) shields or high-strength materials for structural applications. However, no complex data regarding the behaviour and degradation process of CNTs under space environment have been collected so far and only a limited number of real space experiments and applications of CNTs exists nowadays. Therefore, it is necessary to investigate the influence on these new materials in space environment and to revaluate the application potential of CNTs in space technologies.
To this end, the Carbon Nanotubes – Resistance Experiment (CiREX) was developed. CiREX is a small and compact experiment, which is designed for small satellites like Cubesats. These satellites are a class of nanosatellites with a standardised size and form. CiREX was developed for SOMP2 (Student Oxygen Measurement Project 2) wich is a double unit Cubesat. The design and construction was performed by master and PhD students at the Technische Univeristät Dresden.
CiREX is the first in-situ space material experiment for CNTs. Multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) show extraordinarily properties. As a result of the nearly one-dimensional structure, the electrical transport is ballistic which only applies within the tubes. In CNT networks, the contacts between the tubes become more effective and therefore electrical resistance increases. Consequently, the ohmic behaviour of CNT networks is strongly influenced by adsorbed ions and molecules, the defect structure, the contact resistance of the network and thermal modifications. The influence of these effects were considered during the design process of CiREX. Accordingly, this experiment measures the electrical resistance of CNT networks under the harsh space environment. Its design, electrical measurement and the satellites interfaces will be discussed in detail.
To evaluate the data obtained from CiREX, ground validation tests are mandatory. As part of a test series the behaviour of CNTs under solar light were examined. SWNTs, MWNTs and multi-walled carbon nanotubes/resin composite (ME) were exposed to a solar light simulator. Furthermore, we have measured the resistance of the samples during the irradiation. After the exposure, the defect density and surface structure of the tubes were investigated with Raman scattering and scanning electron microscope. The results show a clear indication that solar light can influence the electrical behaviour and the tubes structure.

Related publications

  • Poster
    14th International Symposium on Materials in the Space Environment, ISMSE 14th, 01.-05.10.2018, Biarritz, France

Publ.-Id: 28528

Towards anatase promotion in Cr (co-)doped TiO2 sputtered films

Gago, R.; Prucnal, S.; Hübner, R.; Jiménez, I.; Javier Palomares, F.

Many applications of TiO2 partially rely on its good performance as solvent for impurities [1]. In particular, metal (cation) dopants can functionalize or enhance TiO2 as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. Special attention has been devoted to TiO2 photoactivity where doping has been extensively studied towards band-gap narrowing to achieve visible-light (VISL) response [2]. Metal doping (Cr,Mo,V…) can increase VISL absorption but introduces severe structural distortions that additionally result in carrier recombination centers [4]. Our research seeks for processing routes to improve the structural quality of Cr (co-)doped films produced by magnetron sputtering with emphasis in phase selectivity. Namely, the promotion of anatase is preferred due to the superior photoactivity of this phase or phase mixtures with high anatase content [5]. Recently [6], we have reported the impact of non-contact flash-lamp annealing (FLA) on monolithic TiO2(:Cr) films. By tuning the energy flux, FLA yields customized TiO2 phases but, in doped structures, phase formation only takes place for low Cr contents (< 5 at.%) and the rutile structure is mostly favored. On the contrary, modulated film architecture has shown promising results for anatase growth [7]. In this paper, such scheme, in conjunction with FLA, is explored in detail to optimize the film structural quality and growth design.
REFs: [1] Sacerdoti et al., J. Solid State Chem. 177, 1781 (2004); [2] Henderson, Surf. Sci. Rep. 66, 185 (2011); [3] Matsumoto et al. Science 291, 854 (2001); [4] Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [5] Scanlon et al., Nat. Mater. 12, 798 (2013); [6] R. Gago, S. Prucnal et al., J. Alloys & Compounds 729 (2017) 438; [7] R. Gago, S. Prucnal et al., to be submitted.

Keywords: TiO2; magnetron sputtering; flash-lamp-annealing; photocatalysis

Related publications

  • Lecture (Conference)
    16th International Conference on Plasma Surface Engineering, PSE 2018, 17.-21.09.2018, Garmisch-Partenkirchen, Germany

Publ.-Id: 28527

Unraveling energy loss processes of low energy heavy ions in 2D materials

Wilhelm, R. A.; Grande, P. L.

Structuring of 2D materials and their heterostructures with ion beams is a challenging task, because typically low ion energies are needed to avoid damage to a substrate. In addition, at the very first monolayers of a material, ions are not yet in charge equilibrium, i.e. they may either charge up or neutralize depending on their velocity. The change in electronic structure of the ion during scattering affects the energy, which can be transferred to the recoil and therefore the energy available for defect formation. In order to make reliable use of ion beams for defect engineering of 2D materials, we present here a new model for charge state and charge exchange dependent kinetic energy transfer. Our model can be applied to all ion species, ion charge states, and energies. It is especially powerful for predicting charge state dependent stopping of slow highly charged ions.

Keywords: Ions; Stopping; 2D Materials; Highly Charged Ions

Related publications

  • Open Access Logo Communications Physics 2(2019)1, 89
    DOI: 10.1038/s42005-019-0188-7
    Cited 24 times in Scopus
  • Lecture (Conference)
    Frühjahrestagung der Deutschen Physikalischen Gesellschaft, Sektion Festkörperphysik, 31.03.-05.04.2019, Regensburg, Deutschland
  • Poster
    European Conference on Atoms, Molecules, and Photons (ECAMP), 07.-12.04.2019, Florenz, Italien
  • Poster
    Electron, Photon, and Ion Collisions on Molecular & Atomic Nanostructures (EPIC-MAN), 22.07.2019, Caen, Frankreich

Publ.-Id: 28526

A radiation response model to assess clinical RBE variability in proton therapy

Eulitz, J.; Lutz, B.; Wohlfahrt, P.; Dutz, A.; Enghardt, W.; Krause, M.; Troost, E. G. C.; Lühr, A.

Currently, the clinical implementation of a variable relative biological effectiveness (RBE) in proton therapy is controversially discussed. First clinical evidence indicated a variable RBE for brain irradiation, which needs to be substantiated. For assessing clinical RBE variability, we established a normal tissue response model and applied it to follow-up magnetic resonance (MR) images.

Four glioma patients (grade II-III) showing late morphological T1-weighted contrast-enhanced (T1w-CE) MR image changes and suspicious necrosis were considered. All were treated with passive scattering at the UniversityProtonTherapyDresden (UPTD). Dose, and linear energy transfer (LET) were calculated with a TOPAS-based Monte-Carlo (MC) simulation framework dosimetrically validated for UPTD. To establish radiation response, logistic regression models based on dose and / or LET were trained on T1w-CE MR voxels classified as change (1) or no change (0). Model performance was assessed by the area under the curve (AUC) performing leave-one-out cross validation.

Correlating image changes with dose and LET resulted in high predictive power (AUC=0.87). TD50 values (dose at which 50% of patient voxels show toxicity) decreased linearly with LET (intercept and slope of 88.9 Gy and -10.9 Gy/(keV/μm), respectively). Models considering either dose or LET performed only moderately (AUC of 0.68 and 0.64, respectively). LET averaging method (dose-averaged or track-averaged) had no impact on model performance.

Only the model based on dose and LET led to high predictive power for late MR image changes, suggesting a variable radiation response and, hence, non-constant RBE. This study enables and encourages in-depth assessment of clinical RBE variability in proton therapy.

Keywords: Proton Therapy; Clinical RBE; Monte-Carlo; Passive Scattering

  • Lecture (Conference)
    58th annual conference of the particle therapy co-operative group (PTCOG), 10.-15.06.2019, Manchester, England

Publ.-Id: 28525

From curvilinear magnetism to shapeable magnetoelectronics

Makarov, D.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films and nanowires where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system [1,2]. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics [3] for automotive but also virtual and augmented reality appliances [4,5]. The balance between the fundamental and applied inputs stimulates even further the development of new theoretical methods and novel fabrication/characterization techniques [6-8].

[1] R. Streubel et al., Magnetism in curved geometries. J. Phys. D: Appl. Phys. (Review) 49, 363001 (2016).
[2] D. Sander et al., The 2017 magnetism roadmap. J. Phys. D: Appl. Phys. (Review) 50, 363001 (2017).
[3] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Review) 3, 011101 (2016).
[4] G. S. Cañón Bermúdez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
[5] G. S. Cañón Bermúdez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[6] R. Streubel et al., Retrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies. Nature Communications 6, 7612 (2015).
[7] T. Kosub et al., All-electric access to the magnetic-field-invariant magnetization of antiferromagnets. Phys. Rev. Lett. 115, 097201 (2015).
[8] T. Kosub et al., Purely antiferromagnetic magnetoelectric random access memory. Nature Communications 8, 13985 (2017).

Keywords: magnetic field sensors; flexible electronics; curvature effects in magnetism

Related publications

  • Invited lecture (Conferences)
    Invited talk at the NC State University, 16.01.2019, Raleigh, USA

Publ.-Id: 28524

Simulation challenges for the community in complex LPA designs at the example of hybrid LWFA - PWFA

Debus, A.; Pausch, R.; Steiniger, K.; Garten, M.; Rudat, S.; Hübl, A.; Widera, R.; Couperus Cabadağ, J. P.; Kurz, T.; Schöbel, S.; Köhler, A.; Zarini, O.; Heinemann, T.; de La Ossa, A.; Irman, A.; Schramm, U.; Bussmann, M.

Increasingly complex experimental LPA designs, such as current hybrid LWFA-PWFA experiments integrate different physics regimes (LPA, e- beam tracking, gas dynamics, etc...) require simulations at multiple scales (more physics, more data). Working in mixed teams of experimentalists and theoreticians with specialists from different affiliations requires tighter interfacing of different codes with experimental data analysis.

Key challenges for laser-plasma accelerator simulations are
* Predictive start-to-end simulations, while retaining the ability to understand and optimize sub-systems.
* Common interfacing standards (OpenPMD -- exchange particle and mesh based data from scientific simulations and experiments)
* Tolerance analysis (Analyse the impact of variations in initial conditions and accelerator design).
* Synthetic Diagnostics (Experimental diagnostics modeled in-situ at simulation time)
* Simulation as-a-service (Within some predefined range of simulation scenarios, running additional simulation for some LPA design is made easy for non-specialists.)

Keywords: PIConGPU; synthetic diagnostics; simulation-as-a-service; tolerance analysis; parameter scans; OpenPMD; predictive start-to-end simulations; GUI

  • Lecture (Conference)
    EuPRAXIA Yearly Meeting, 19.-22.11.2018, Frascati, Italy

Publ.-Id: 28523

From LWFA bunch durations to bunch profile and micro-structure: Longitudinal electron bunch diagnostics for LWFA based on broadband, spectral CTR measurements at single-shot

Debus, A.; Zarini, O.; Laberge, M.; Couperus Cabadağ, J. P.; Koehler, A.; Kurz, T.; Schoebel, S.; Kraemer, J.; Hannasch, A.; Zgadzaj, R.; Bussmann, M.; Downer, M.; Schramm, U.; Irman, A.

Laser-wakefield accelerators (LWFA) feature electron bunch durations on a scale of a few fs. Precise knowledge of the longitudinal profile of such ultra-short electron bunches is essential for the design of future table-top X-ray light sources. The resolution limit, as well as the limited reproducibility of electron bunches, pose big challenges for LWFA beam diagnostics.

Spectral measurements of broadband transition radiation from LWFA electron bunches passing through a metal foil are especially promising for analyzing ultrashort longitudinal bunch characteristics ranging from of tens of fs down to sub-fs.

Our broadband, single-shot spectrometer combines the TR spectrum in UV/VIS (200-1000nm), NIR (0.9-1.7μm) and mid-IR (1.6-12μm). A complete characterization and calibration of the spectrometer has been done with regard to wavelengths, relative spectral sensitivities and absolute photometric sensitivity. Our spectrometer is able to characterize electron bunches with charges as low as 1 pC and resolve time-scales from 0.7 to 40 fs.

We present results from recent measurement campaign by analyzing transition radiation spectra produced by nC class LWFA electron bunches using ionization-injection, while complementary data on the transverse bunch profile is provided by simultaneously imaging the CTR in the far- and near-field.

We discuss the data analysis from detection to profile reconstruction with error analysis and show electron bunch profiles as determined from experimental density scan measurements.

Keywords: broadband spectrometer; single-shot bunch length measurement; coherent transition radiation; absolute calibration; electron bunch duration; longitudinal profile; absolute calibration; UV; VIS; NIR; MIR

  • Lecture (Conference)
    Advanced Accelerator Concepts (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Publ.-Id: 28522

Traveling-Wave Electron Acceleration: Laser-plasma acceleration without limits from dephasing and pump-depletion

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

We show how to simultaneously eliminate both dephasing and depletion constraints of laser-plasma accelerators. For this we introduce the Traveling-wave electron accelerator (TWEAC) approach, in which the wakefield driver is not provided by a single laser pulse, but instead by a region of overlap of two obliquely incident, ultrashort laser pulses with tilted pulse-fronts in the line foci of two cylindrical mirrors, aligned to coincide with the trajectory of subsequently accelerated electrons. Such a geometry of laterally coupling the laser into a plasma allows for the region of overlap to move with the vacuum speed of light, while its field is continuously being replenished by the successive parts of the laser pulse. Supported by 3D particle-in-cell simulations, we show that this results in quasi-stationary acceleration conditions for an electron bunch along the total acceleration length, which allows to break both the dephasing and depletion limit of LWFA.

Particularly, and in contrast to LWFA and PWFA, a single TWEAC-stage can arbitrarily be extended in length to higher electron energies without changing the underlying acceleration mechanism. Additionally, the TWEAC geometry greatly facilitates reducing beam transport distances between the laser-plasma accelerator and subsequent insertion devices, such as undulators, plasma lenses or colliding laser pulses, to below millimeters. After analyzing stability of acceleration and possible limits of the scheme, we present energy scaling laws for both laser as well as electrons and detail experimental design considerations.

In the future, we expect the new TWEAC technique to greatly reduce the need for staging in order to attain higher electron energies beyond 10GeV, possibly reaching for the energy frontier of high-energy physics. For lower GeV-scale electron energies, TWEAC at high plasma densities and 10TW-class laser systems could enable compact accelerators at kHz-repetition rates.

Keywords: Laser-produced plasmas; Plasma-based accelerators; Laser-wakefield acceleration; Traveling-wave electron acceleration; TWEAC

  • Lecture (Conference)
    Advanced Accelerator Concepts 2018 (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Publ.-Id: 28521

Advancing predictive capabilties of LWFA simulations using PIConGPU: From improved modeling to novel measurement methods via synthetic radiation diagnostics

Debus, A.; Pausch, R.; Steiniger, K.; Widera, R.; Huebl, A.; Garten, M.; Irman, A.; Couperus Cabadağ, J.; Zarini, O.; Koehler, A.; Schramm, U.; Bussmann, M.

In a close interplay between particle-in-cell simulations and experimental measurements, we present new insights into the modeling of laser wakefield accelerators and discuss the arising challenges for laboratory diagnostics. These challenges were tackled by developing new methods for determining key parameters of the experiment by studying synthetic radiation diagnostics predicted by simulations.

The combination of an unprecedented experimental campaign studying the parameter dependence of beam loading during LWFA and an accompanying, extensive simulation campaign using the 3D3V particle-in-cell code PIConGPU made it possible to provide unique feedback between experiment and theory. This poster shows the step-by-step improvements through this interplay from the simulation perspective. Quantitatively more accurate methods such as the use of Gauss-Laguerre modes or a variety of ionization models are presented as well as more performant computational procedures.

Only through these improvements it was possible to reproduce the dynamics from the experiment and gain a deeper insight into the self-truncated ionization injection regime.

Moreover, this interplay also revealed the limits of current laboratory diagnostics. Synthetic in-situ radiation diagnostics in PIConGPU spurred the development of new diagnostic methods for experiments. For example, the shift in laser focus position due to self-focusing in the plasma can now be quantified by spectral radiation signatures. Applying these new methods will enable an even more accurate understanding of laser plasma dynamics in experiments in the near future.

Keywords: radiation; LWFA; particle-in-cell; PIConGPU; synthetic diagnostics

  • Poster
    Advanced Accelerator Concepts 2018 (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Publ.-Id: 28520

Transverse electron beam dynamics in the beam loaded regime

Koehler, A.; Pausch, R.; Couperus Cabadağ, J. P.; Zarini, O.; Krämer, J.; Kurz, T.; Debus, A.; Bussmann, M.; Schramm, U.; Irman, A.

GeV electrons show the extraordinary advances of laser-wakefield acceleration (LWFA). Optimized beam parameters will enable drivers for compact secondary radiation sources. One essential key is a high quality electron bunch with low energy spread, small divergence and spot size. In this paper, the impact of beam loading on the transverse electron dynamic is systematically studied by investigating betatron radiation and electron beam divergence. The deployed LWFA setup yields reproducibly injected charges up to 0.5 nC and small energy spreads. The recorded betatron radiation reveals that the beam amplitude at the accelerator exit stays around one micron.

Keywords: LWFA; laser-wakefield acceleration; betatron source; beam loading; electron beam dynamics; laser-plasma interactions; x-ray

  • Lecture (Conference)
    16th International Conference on X-Ray Lasers (ICXRL), 07.-12.10.2018, Prag, Tschechische Republik

Publ.-Id: 28519

Compact X-ray sources by Traveling-Wave Thomson scattering and All-Optical FELs

Debus, A.; Steiniger, K.; Pausch, R.; Huebl, A.; Widera, R.; Siebold, M.; Loeser, M.; Albach, D.; Roeser, F.; Cowan, T.; Schramm, U.; Bussmann, M.

Compact synchrotron and SASE-FEL sources in the hard X-ray range require both compact electron accelerators and undulators. Traveling-Wave Thomson-Scattering (TWTS) provides an all-optical undulator with hundreds to thousands of undulator periods from high-power, pulse-front tilted lasers pulses. These allow to realize optical free-electron lasers (OFELs) with state-of-the-art technology in electron accelerators and laser systems.

We provide an overview on the applications that become possible with TWTS -- bright Thomson sources with high photon-yields, all-optical FELs and a novel class of laser-plasma accelerators not limited by dephasing and pump depletion. We outline both experimental and computational challenges and present recent results.

Keywords: Laser-produced plasmas; Plasma-based accelerators; Laser-wakefield acceleration; Traveling-wave electron acceleration; TWEAC

  • Lecture (Conference)
    16th International Conference on X-Ray Lasers (ICXRL), 07.-12.10.2018, Prag, Tschechische Republik

Publ.-Id: 28518

Off-harmonic optical probing of high intensity laser-matter interaction with a stand-alone probe laser system

Bernert, C.; Kraft, S.; Loeser, M.; Metzkes-Ng, J.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Siebold, M.; Zeil, K.; Ziegler, T.; Schramm, U.

The development of high-intensity short-pulse lasers in the petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets to generate proton beams with multiple 10 MeV energy per nucleon. The optimization of the acceleration process calls for a comprehensive exploration of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly well suited in the case of cryogenic hydrogen jet targets [1]. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronizable probe laser system for off-harmonic probing at the DRACO laser at the Helmholtz-Zentrum Dresden – Rossendorf showed promising performance [2]. Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator (Light Conversion) operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating (Optigrate Corp) is used as a hybrid stretcher and compressor unit. The subsequent diode pumped regenerative Yb:CaF2 laser amplifier includes a spectral shaping element and chirped mirrors for GDD compensation. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ and thus extends the recent developments [3] into the sub 200 fs region. Additionally, we present recent experimental results deploying the upgraded probe laser system and its harmonics in an experiment dedicated to laser-proton acceleration from a renewable cryogenic hydrogen jet at the DRACO laser.

  • Lecture (Conference)
    ICUIL 2018, 09.-14.09.2018, Lindau, Deutschand

Publ.-Id: 28517

Probing of laser-plasma experiments at DRACO with a stand-alone probe laser system

Bernert, C.; Brack, F.-E.; Kraft, S.; Kroll, F.; Löser, M.; Metzkes-Ng, J.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Siebold, M.; Zeil, K.; Ziegler, T.; Schramm, U.

In the last decade the investigation of laser-driven plasmas has gained great importance for the development of compact ion accelerator schemes with the efficient generation of multiple 10 MeV proton beams from TNSA experiments with PW laser systems like the Dresden laser acceleration source (DRACO) at the Helmholtz-Zentrum Dresden - Rossendorf. The exploration of the plasma dynamics and its microscopic parameters is crucial for the optimization of the acceleration process. Optical probing is one technique to investigate the temporal plasma evolution and complements numerical particle-in-cell simulations of the underlying physics. However, strong plasma self-emission at the driver lasers wavelength and its harmonics often masks the laser plasma interaction region and thus complicates the data analysis.
Here, we present the implementation of a stand-alone probe laser system, which is temporally synchronized to the DRACO laser. The probe laser system consisting of a seed laser and one regenerative amplifier is based on Yb:YAG and thus provides a fundamental wavelength of 1030 nm, which is different from the wavelength of the DRACO driver laser (800 nm) and its harmonics. We present the advantages of this probing approach, which was tested during an experimental campaign with wire targets of different materials and diameters in the µm range, and give an inside on the current challenges and developments of the probing system.

  • Lecture (Conference)
    DPG Frühjahrstagung Würzburg, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 28516

Froth properties and ist effect on lab-scale flotation of carbonaceous sedimentary apatite ore

Hoang, D. H.; Kupka, N.; Peuker, U. A.; Rudolph, M.

The froth ability, froth stability and the froth structure are strong influences in flotation process i.e. on
water recovery, bubble size, entrainment of gangue particle, flotation rate constants, grade and recovery. The labscale
flotation of rich apatite ore with a high mass pull leads to significant changes in pulp and froth properties over
time. The froth stability decreases with increasing the flotation time. These changes can be related to different solid contents, reagent concentration, froth heights and bubble size distributions. This study presents the results from froth studies and discussions on the particle size of fully liberated silicates and degree of entrainment based on automated mineralogy size-by-size analysis. The change of entrainment in a rich apatite ore batch flotation with time will describe more precisely by measuring froth properties using a Dynamic Foam Analyzer. It is concluded that the degree of entrainment is not only dependent on particle size but also the pulp density due to its effect on particle settling and also froth properties in varying resistance to particle drainage. Furthermore, entrainment models are applied to predict the effect of size, flotation time on entrainment.

Keywords: Froth properties; apatite flotation; Entrainment; automated mineralogy

  • Contribution to proceedings
    29th International Mineral Processing Congress, IMPC 2018, 17.-21.09.2018, Moscow, Russia
    Conference Proceeding: Canadian Institute of Mining, Metallurgy and Petro, 978-703022711-9, 1748-1757

Publ.-Id: 28515

Froth properties and entrainment in lab-scale flotation: A case of carbonaceous sedimentary phosphate ore

Hoang, D. H.; Heitkam, S.; Kupka, N.; Hassanzadeh, A.; Peuker, U. A.; Rudolph, M.

In flotation, the froth characteristics strongly influence the separation process as they are linked to water recovery, bubble size, entrainment of gangue particles, flotation rate constants and finally grade and recovery. In the case of a high-grade apatite ore with a high mass pull in lab-scale flotation, significant changes in pulp and froth properties occur, such that the froth stability decreases with increasing flotation time. These changes can be related to different particle and reagent concentrations. We describe the change of entrainment in a rich apatite ore batch flotation with time more precisely by measuring froth properties using a Dynamic Froth Analyzer (DFA). It is concluded that the degree of entrainment is not only dependent on particle size but also the pulp density due to its effect on particle settling and also froth properties in varying resistance to drainage. Through a combination of time-resolved dynamic froth analysis and automated mineralogy, we identify the dynamic effects governing in the froth and compare the entrainment results with existing models. Furthermore, our analyses offer novel support for the extension of the common understanding of the entrainment phenomena.

Keywords: Froth flotation; froth stability; apatite; entrainment; automated mineralogy; dynamic froth analysis (DFA)


Publ.-Id: 28514

Importance of understanding structure-property relationships in Feldspar for Radiofluorescence dating

Sharma, S. K.; Fuchs, M.; Heitmann, J.; Gloaguen, R.

Feldspar is a common mineral that has been used efficiently for the past few decades for luminescence dating. The process of separation of Feldspar from rock mineral is a time consuming process, and requires an expertise with different chemical processes. The luminescence properties in Feldspar are controlled by the presence/absence of defect in the host lattice. In the present talk, i will discuss about the different defects, luminescence properties, and their dependence on the crystal structure of Feldspar. The work is carried out on three different samples, currently being used for radio-fluorescence dating.

Keywords: Feldspar; optical properties; luminescence dating; ESR

  • Invited lecture (Conferences)
    3rd IR-RF Workshop 2018, 26.-28.02.2018, Leipzig, Germany

Publ.-Id: 28513

Gewinnung und Anreicherung von Molybdän aus niedrig konzentrierten sulfatischen Lösungen mittels Solventextraktion

Helbig, T.; Scharf, C.

Der sogenannte Theisenschlamm, ein Haldenmaterial der einstigen Kupferschieferverhüttung in der Region Mansfeld, besitzt neben den Hauptkomponenten Zink und Blei, auch geringe Konzentrationen von z. B. Molybdän, Rhenium und Germanium. Im r⁴-Projekt „Theisenschlamm“ erfolgt im ersten Schritt die Laugung dieses Materials, wobei Lösungen mit ca. 20 mg/L Molybdän erhalten werden. Zur anschließenden elementselektiven Weiterverarbeitung der Laugungslösung wird u. a. die Solventextraktion untersucht. Für die selektive Gewinnung von Molybdän wurden Organophosphorsäure- sowie Oximverbindungen verglichen und Cyanex 272 als vielversprechendstes Extraktionsmittel ausgewählt. Weiterführende Untersuchungen werden in einer kontinuierlichen Mixer-Settler-Anlage (MEAB MSU-0,5) durchgeführt. Die Einflüsse verschiedener Parameter, wie z. B. die Rückführung der Organik und die Volumenströme der beiden Phasen, auf die selektive Molybdän-Extraktion und Anreicherung sowie die Möglichkeit des Scrubbings und Strippens der organischen Phase werden vorgestellt.

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Extraktion & Rohstoffe, 12.-13.03.2018, Frankfurt am Main, Deutschland

Publ.-Id: 28512

Laser-driven radiobiology experiments at Draco Petawatt

Brack, F.-E.; Kroll, F.; Metzkes, J.; Obst, L.; Kraft, S.; Schlenvoigt, H.-P.; Gaus, L.; Beyreuther, E.; Karsch, L.; Pawelke, J.; Zeil, K.; Schramm, U.

Summary of the current status and carried out experiments of Laser-driven radiobiology experiments at Draco Petawatt

  • Lecture (Conference)
    LIGHT Meeting, 19.-20.04.2018, Darmstadt, Deutschland

Publ.-Id: 28511

Laser-Based Particle Accelerators at HZDR - Ions

Brack, F.-E.; Kroll, F.; Metzkes, J.; Obst, L.; Kraft, S.; Schlenvoigt, H.-P.; Gaus, L.; Ziegler, T.; Rehwald, M.; Zeil, K.; Schramm, U.

Summary of the current status and carried out experiments of Laser-driven ion experiments at Draco

  • Lecture (Conference)
    Matter and Technology Student Retreat, 11.06.2018, Berlin, Deutschland

Publ.-Id: 28510

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